Note: Descriptions are shown in the official language in which they were submitted.
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HANDOVER MECHANISM IN CELLULAR NETWORKS
FIELD
[0001] This disclosure relates to handover procedures in cellular
wireless
networks, and more particularly, in heterogeneous networks.
BACKGROUND
[0002] Wireless communication systems can include a network of one or
more
base stations to communicate with one or more user equipment (UE) such as
fixed and
mobile wireless communication devices, mobile phones, or laptop computers with
wireless communication cards. Base stations are spatially distributed to
provide radio
coverage in a geographic service area that is divided into cells. A UE that is
located
within a base station's cell of coverage area is generally registered with the
base
station. The UE and the base station communicate with each other via radio
signal. The
base station is called the serving base station of the UE and the cell
associated with the
base station is called the serving cell of the UE.
[0003] In some wireless networks, cells of different coverage sizes may be
deployed to improve cell coverage or to offload traffic. For example, in an
Evolved
Universal Terrestrial Radio Access Network (E-UTRAN), small cells (e.g., pico
cells,
relay cells, or femto cells) may be deployed with overlaid macro cells. A
network
including large cells (e.g., macro cells) as well as small cells (e.g., pico
cells, relay
cells, femto cells) may be referred to as a heterogeneous network. A UE in the
heterogeneous network may move in a large geographical area which may trigger
a
handover procedure and result in changing of the UE's serving cells.
BRIEF DESCRIPTION OF DRAWINGS
[0004] For a more complete understanding of this disclosure, reference
is now
made to the following brief description of the drawings, taken in connection
with the
accompanying drawings and detailed description, wherein like reference
numerals
represent like parts.
[0005] FIG. 1 is a schematic representation of an example
heterogeneous
wireless communications network.
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[0006] FIG. 2 is a schematic block diagram illustrating various layers
of access
nodes and user equipment in a wireless communication network.
[0007] FIG. 3 is a schematic block diagram illustrating an access node
device.
[0008] FIG. 4 is a schematic block diagram illustrating a user
equipment
device.
[0009] FIG. 5 is a schematic presentation of an example deployment of
a
heterogeneous network.
[0010] FIG. 6a is a schematic state diagram illustrating a handover
mechanism
involving an intermediate handover (IHO) state.
[0011] FIG. 6b is a schematic flow chart illustrating a method may be
performed by a serving cell for IHO candidate cell selection.
[0012] FIG. 7 is a schematic illustrating an example deployment of a
heterogeneous network.
[0013] FIGS. 8a-b are schematic block diagrams illustrating example
user plane
protocol stacks.
[0014] FIGS. 9a-b are schematic block diagrams illustrating example
control
plane protocol stacks.
[0015] FIG. 10 is a schematic flow diagram illustrating an example
handover
procedure with an IHO state.
[0016] FIGS. 1 1 a-c are schematic flow diagrams illustrating example IHO
anchor transfer procedures.
[0017] FIGS. 12-13 are schematic flow diagrams illustrating example
handover
procedures with an IHO state.
DETAILED DESCRIPTION
[0018] The present disclosure is directed to systems, methods, and
apparatuses
for handover in wireless communications networks, especially in heterogeneous
wireless communication networks. Heterogeneous networks may include cells of
various coverage sizes resulting at least in part from different transmission
power levels
of base stations, e.g., macro cell, femto cell, pico cell, relay cell, etc. As
the UE moves
across cell boundaries, a handover procedure may be performed to ensure that
the UE is
connected or camped on a serving cell with good coverage for the UE.
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[0019] Since the heterogeneous network may contain various types of
cells,
there may be overlaps between coverage areas of multiple cells, especially in
unplanned clustered cell deployments where a large number of small cells may
be
situated within a macro cell's coverage area. When a UE traverses between
adjacent
cells with overlapped coverage area, there might be multiple handovers. The UE
may
only stay with one cell for a short time before it switches to another cell.
Frequently
switching a UE among multiple cells may incur significant signalling overhead,
delay,
data interruptions, and/or quality of service (QoS) degradation.
[0020] To improve the QoS, an intermediate handover (IHO) state can be
introduced to reduce unnecessary and unwanted handovers. The UE may be in the
IHO
state before it is handed over to a target cell completely. During the IHO
state, the UE
can be connected to the serving cell as well as one or more neighbouring
cells. The
neighbouring cells that are connected to the UE during the IHO state are
referred to as
IHO candidate cells. One cell that actively transmits data to the UE is
referred to as the
Anchor cell. The IHO state can be transparent to the core network. Therefore,
the IHO
state can also be referred to as a network agnostic mobility management (NA-
MM)
state.
[0021] Certain protocol and signaling changes can be made to
incorporate the
IHO state in handover procedures.
[0022] Certain aspects of the disclosure pertain to a method performed at a
first
base station of a wireless communications network. The first base station can
receive
an indication that a user equipment (UE) is receiving coverage signal from a
second
base station. The information destined for the UE can be forwarded to the
second base
station. A communications link can be maintained with the UE after
transmitting the
data packet to the second base station.
[0023] In certain implementations, the indication is a quality of
service
indicator.
[0024] In certain implementations, the coverage signal includes one or
more of:
a reference signal, a system information broadcast signal, or a data
transmission signal
transmitted by a base station.
[0025] Certain aspects of the implementations may also include
receiving a data
packet destined to the Evolved Packet Core (EPC) from the second base station
and
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maintaining a communications link with the UE after receiving the data packet
from the
second base station.
[0026] In certain implementations, forwarding the data packet may also
include
receiving the data packet from the second base station. The data packet can be
-- decrypted to form Packet Data Convergence Protocol (PDCP) Service Data Unit
(SDU). The encrypted data packet can be forwarded to the EPC.
[0027] In certain implementations, receiving the data packet destined
for the
EPC from the second base station is performed across an X2 interface.
[0028] In certain implementations, receiving the data packet destined
for the
-- EPC from the second base station is performed across an Si interface.
[0029] In certain implementations, maintaining the communication link
with
the UE includes maintaining RRC_connected state with the UE.
[0030] In certain implementations, maintaining the RRC_connected state
with
the UE includes reserving the C-RNTI assigned for the UE.
[0031] In certain implementations, forwarding the data packet may also
include
receiving the data packet from the EPC. The data packet can be encrypted to
form
PDCP PDU. The encrypted data packet can be forwarded to the second base
station.
[0032] In certain implementations, forwarding the data packet destined
for the
UE to the second base station is performed across an X2 interface.
[0033] In certain implementations, forwarding the data packet destined for
the
UE to the second base station is performed across an Si interface.
[0034] In certain implementations, maintaining the communication link
with
the UE includes maintaining RRC_connected state with the UE.
[0035] In certain implementations, maintaining the RRC_connected state
with
-- the UE includes reserving the C-RNTI assigned for the UE.
[0036] Certain aspects of the implementations may also include
receiving an
indication that the coverage signal from the second base station is stronger
than a
coverage signal from the first base station. Control of communications for the
UE can
be handed to the second base station. The communications link with the UE can
be
terminated.
[0037] In certain implementations, the indication is a quality of
service
indicator.
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[0038] Certain aspects of the implementations are directed to systems,
apparatuses, and methods performed at a first base station of a wireless
communications network. A request for an intermediate handover (IHO) can be
received from a second base station. The request to perform the IHO can be
accepted,
wherein the first station acting as an IHO candidate base station. A data
packet
destined for a UE can be received from the second base station. transmitting
the
received data packet to the UE. A communications link with the UE can be
maintained
after receiving the data packet from the second base station.
[0039] In certain implementations, transmitting the data packet to the
UE may
also include receiving a data packet from the second base station to form the
PDCP
PDU. The encrypted data packet (PDCP PDU) can be forwarded to the UE.
[0040] In certain implementations, maintaining the communication link
with
the UE includes maintaining RRC_connected state with the UE.
[0041] In certain implementations, maintaining the RRC_connected state
with
the UE includes reserving the C-RNTI assigned for the UE.
[0042] Certain implementations may also include receiving an
indication that
the coverage signal from second base station is stronger than a coverage
signal from the
first base station. The second base station and the UE can be informed about
the
indication. The communications link with the UE can be terminated.
[0043] In certain implementations, the indication is a quality of service
indicator.
[0044] In certain implementations, receiving the data packet destined
for the
UE from the second base station is performed across an X2 interface.
[0045] In certain implementations, receiving the data packet destined
for the
UE from the second base station is performed across an Si interface.
[0046] Certain aspects are directed to systems, apparatuses, and
methods
performed at a first base station of a wireless communications network. A data
packet
can be received from a UE. A data packet destined for the EPC can be forwarded
to a
second base station. A communications link can be maintained with the UE after
transmitting the data packet to the second base station.
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[0047] In certain implementations, forwarding the data packet can
include
receiving the PDCP PDU from the UE and forwarding the PDCP PDU to the
second base station.
[0048] In certain implementations, forwarding the data packet destined
for the
EPC to the second base station is performed across an X2 interface.
[0049] In certain implementations, forwarding the data packet destined
for the
EPC to the second base station is performed across an Si interface.
[0050] In certain implementations, maintaining the communication link
with
the UE includes maintaining RRC_connected state with the UE.
[0051] In certain implementations, maintaining the RRC_connected state with
the UE includes reserving the C-RNTI assigned for the UE.
[0052] Certain implementations can also include a serving base station
configured to receive an indication that a user equipment (UE) is receiving
coverage
signal from a second base station. The serving base station can transmit a
data packet
destined for the UE to the second base station and maintain a communications
link with
the UE after transmitting the data packet to the second base station.
[0053] A neighboring base station can be configured to receive the
data packet
from the serving base station and transmit the data packet to the UE.
[0054] In certain implementations, the serving base station transmits
the data
packet to the neighboring base station across an X2 interface.
[0055] In certain implementations, the serving base station transmits
the data
packet to the neighboring base station across an Si interface.
[0056] In certain implementations, the system is configured to
allocate a cell
radio network temporary identifier (C-RNTI) to the neighboring base station.
[0057] In certain implementations, the neighboring base station is
configured to
determine that the UE has a C-RNTI that matches the C-RNTI of the neighboring
base
station.
[0058] In certain implementations, the system is configured to assign
a new C-
RNTI to the neighboring base station.
[0059] Certain implementations are directed to systems, apparatuses, and
methods performed at a serving base station of a wireless communications
network, the
base station in communication with a user equipment (UE). A measurement report
can
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be received from the UE, the measurement report indicating a quality of
service for the
source base station and one or more neighboring base stations. An X2AP
handover
request message can be transmitted to at least a subset of the one or more
neighboring
base stations, the X2AP handover request message indicating an intermediate
handover
(IHO) state. A handover request acknowledgement message can be received from
the
at least a subset of the one or more neighboring base stations, the handover
request
acknowledgement message including a radio resource control (RRC)
reconfiguration
message. The RRC reconfiguration message can be transmitted to the UE.
[0060] Certain implementations may also include identifying the at
least a
subset of the one or more neighboring base stations based on the quality of
service for
the one or more neighboring base stations indicated in the measurement report.
[0061] In certain implementations, the handover request
acknowledgement
message includes one or more of a cell radio network temporary identifier, a
security
algorithm identifier, or a random access channel preamble.
[0062] In certain implementations, the handover request acknowledgement
message includes an intermediate handover state acceptance indicator.
[0063] In certain implementations, the handover request message
includes at
least the IDs of a set of candidate cells.
[0064] In certain implementations, the handover request
acknowledgement
message includes an indicator of whether the uplink synchronization with the
UE is to
be performed.
[0065] In certain implementations, the serving base station is an
anchor base
station of the IHO state.
[0066] Certain implementations may also include transmitting an X2AP
IHO
anchor functionality transfer request message to a target base station. An RRC
reconfiguration message can be transmitted to the UE, the RRC reconfiguration
message including IHO anchor transfer parameters. An RRC reconfiguration
acknowledge message can be received from the UE. An X2AP IHO anchor
functionality transfer response message can be received from the target base
station.
[0067] In certain implementations, the target base station is a IHO
candidate
base station.
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[0068] Certain implementations may also include forwarding DL data to
the
target base station.
[0069] Certain implementations may also include determining a handover
to a
handover target base station. A second X2AP handover request message can be
-- transmitted to the handover target base station, the second X2AP handover
request
message indicating a handover state. A second a second X2AP handover
acknowledge
message can be received from the handover target base station. A second RRC
reconfiguration message can be transmitted to the UE.
[0070] Certain implementations are directed to systems, apparatuses,
and
-- methods performed at a neighboring base station of a wireless
communications
network. An X2AP handover request message can be received from a serving base
station, the serving base station serving a user equipment (UE), the X2AP
handover
request message indicating an intermediate handover state. Admission control
can be
performed to evaluate if the UE can be supported. Responsive to the
performing, a
-- handover request acknowledgement message can be transmitted to the serving
base
station, the handover request acknowledgement message including a radio
resource
control (RRC) reconfiguration message.
[0071] In certain implementations, the handover request
acknowledgement
message includes one or more of a cell radio network temporary identifier, a
security
-- algorithm identifier, or a random access channel preamble.
[0072] In certain implementations, the handover request
acknowledgement
message includes an intermediate handover state acceptance indicator.
[0073] In certain implementations, the handover request
acknowledgement
message includes an indicator of whether the uplink synchronization with the
UE is to
-- be performed.
[0074] Certain implementations may also include receiving a data
packet
destined for the UE from the serving base station and transmitting the data
packet to the
UE.
[0075] Certain implementations may also include receiving a radio
resource
-- control (RRC) reconfiguration message from the UE, the RRC reconfiguration
message
including a cell radio network temporary identifier of the neighboring cell.
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[0076] Certain implementations may also include terminating the
intermediate
handover state in response to the expiration of an intermediate handover state
timer.
[0077] Certain implementations may also include transmitting a message
to the
serving base station indicating that the neighboring base station will
transmit data to the
UE.
[0078] Certain implementations may also include transmitting a message
to the
UE indicating that the neighboring cell will serve the UE.
[0079] Certain implementations may include receiving uplink data from
the UE
and transmitting the uplink data to the serving base station.
[0080] In certain implementations, the neighboring base station is an
anchor
base station of the IHO state.
[0081] Certain implementations may include transmitting an X2AP IHO
anchor
functionality transfer request message to a target base station. An RRC
reconfiguration
message can be transmitted to the UE, the RRC reconfiguration message
including IHO
anchor transfer parameters. An RRC reconfiguration acknowledge message can be
received from the UE. An X2AP IHO anchor functionality transfer response
message
can be received from the target base station.
[0082] In certain implementations, the target base station is the
serving base
station.
[0083] Certain implementations may include transmitting another X2AP IHO
anchor functionality transfer request message to the serving base station.
[0084] In certain implementations, the target base station is another
neighboring
base station.
[0085] Certain implementations may also include receiving a second
X2AP
handover request message, the second X2AP handover request message indicating
a
handover state. A second X2AP handover acknowledge message can be transmitted.
An RRC reconfiguration complete message can be received from the UE.
[0086] Certain aspects are directed to systems, apparatuses, and
methods
performed at a UE in communication with a serving base station of a wireless
communications network. A communications signal may be received from a
neighboring base station, the neighboring base station neighboring the serving
base
station. A first measurement report may be transmitted to the serving base
station , the
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first measurement report including a quality of service indicator of the
communications
signal from the neighboring base station. A radio
resource control (RRC)
reconfiguration message may be received from the serving base station, the RRC
reconfiguration message including configuration information for communicating
with
the neighboring base station. Data packets may be received from the
neighboring base
station. A second measurement report may be transmitted to the serving base
station
after receiving the data packets from the neighboring base station.
[0087] Certain
implementations may include transmitting an RRC
reconfiguration completion message to the neighboring base station.
[0088] Certain aspects of the implementations may also include receiving a
RRC reconfiguration message from an anchor base station, the RRC
reconfiguration
message including IHO anchor functionality transfer parameters, wherein the
IHO
anchor functionality is transferred to a target base station and transmitting
a RRC
reconfiguration acknowledge message to the anchor base station.
[0089] Certain aspects of the implementations may also include determining
a
handover to a handover target base station and
transmitting a RRC reconfiguration
complete message to the handover target base station.
[0090] Certain
aspects of the implementations may also include undergoing
uplink synchronization with the neighboring base station.
[0091] Certain aspects of the implementations may also include transmitting
uplink data to the neighboring cell.
[0092] Certain
aspects of the disclosure are directed to a base station in a
wireless communications network. The base station configured to receive an
indication
that a user equipment (UE) is receiving coverage signal from a second base
station.
The base station may also forward information destined for the UE to the
second base
station. A communications link can be maintained with the UE after forwarding
the
information to the second base station.
[0093] In
certain implementations, the indication is a quality of service
indicator.
[0094] In certain implementations, the coverage signal includes one or more
of:
a reference signal, a system information broadcast signal, or a data
transmission signal
transmitted by a base station.
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[0095] Certain aspects of the implementations also include receiving a
data
packet destined to an Evolved Packet Core (EPC) from the second base station.
A
communications link can be maintained with the UE after receiving the data
packet
from the second base station.
[0096] In certain implementations, forwarding the data packet may also
include
receiving the data packet from the second base station. The data packet can be
decrypted to form Packet Data Convergence Protocol (PDCP) Service Data Unit
(SDU). The encrypted data packet can be forwarded to the EPC.
[0097] In certain implementations, forwarding the information may also
include
receiving a data packet from an EPC, encrypting the data packet to form PDCP
PDU,
and forwarding the encrypted data packet to the second base station.
[0098] In certain implementations, forwarding the information destined
for the
UE to the second base station is performed across one or more of an X2
interface or an
51 interface.
[0099] In certain implementations, maintaining the communication link with
the UE comprises maintaining RRC_connected state with the UE.
1001001 In certain implementations, maintaining the RRC_connected state
with
the UE includes reserving a C-RNTI assigned for the UE.
1001011 Certain aspects of the implementations may also include
receiving an
indication that the coverage signal from the second base station is stronger
than a
coverage signal from the base station, handing over control of communications
for the
UE to the second base station, and terminating the communications link with
the UE.
[00102] In certain implementations, the indication is a quality of
service
indicator.
[00103] FIG. 1 is schematic representation of an example heterogeneous
wireless
communication network 100. The term "heterogeneous wireless communication
network" or "heterogeneous network" may also be referred to as a "Hetnet." The
illustrated heterogeneous network 100 includes a core network 110 and a macro
cell or
overlay cell 120. The term "cell" or "wireless cell" generally refers to an
area of
coverage of wireless transmission by a network or network component, such as
an
access node. The core network 110 can be connected to the Internet 160. In the
illustrated implementation, the macro cell 120 can include at least one base
station.
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The term "base station" can be interchangeably used with a network node, an
access
node, or a network component. Two or more base stations may operate on the
same
radio frequency or on different radio frequencies. In this disclosure, the
term "base
station" is sometimes interchangeably used with the term "cell," where the
base station
provides the coverage of wireless transmission of the cell.
[00104] The base station can be an overlay access node 121 connected to
the
core network 110 via a backhaul link 111a, including optical fiber or cable.
The term
"overlay access node" generally refers to a network element or component that
at least
partly serves to form a wireless cell. In one implementation in which the
network 100
is an LTE network, the overlay access node 121 can be a Universal Terrestrial
Radio
Access Network (UTRAN) node B or "eNB" which is part of an evolved Universal
Terrestrial Radio Access Network (E-UTRAN). An eNB that forms an overlay
access
node of a macro cell can be generally referred to as a "macro eNB." The term
"eNB"
may be interchangeably used with an "evolved node B." The eNBs may cooperate
to
conduct a handover procedure for User Equipment (UE) in the network 100. To
conduct the handover procedure, the eNBs may exchange control information via
the
backhaul link 111a or 111b or 111c or 111d.
[00105] The network 100 can also include one or more underlay cells,
for
example, a pico cell 130 and a femto cell 140. The underlay cells can have a
coverage
at least partially overlapping with the coverage of the macro cell 120. While
the term
"underlay cell" is described herein in the context of the long term evolution
(LTE)
standard, other wireless standards can also have components similar to
underlay cells.
The implementations described herein can be adapted for such standards without
departing from the scope of this disclosure. Although FIG. 1 illustrates only
one pico
cell and only one femto cell, the network 100 can include more or less cells.
The
underlay cells 130, 140 have a smaller coverage than the overlay cell 120. For
example, in a suburban environment, the overlay cell 120 may have a coverage
radius
of 0.5 kilometer, while the underlay cells 130, 140 may have a coverage radius
of 0.2
kilometer. Access nodes 131, 141 forming the underlay cells 130, 140 can use a
lower
transmission power than that of the overlay access node 121. The underlay
cells 130,
140 may further include a range expansion area used for increasing the
coverage area
for the cells having a smaller coverage.
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[00106] The pico cell 130 can include a pico eNB 131 connected to the
core
network 110 via a backhaul link 111b and to the macro eNB 121 via a backhaul
link
111c. The backhaul links 111b and 111c may include cable, fiber, wireless
links, or
others. In some implementations, the pico eNB 131 can have a transmission
power that
is, for example, about 30 dBm, which is about 13 dB lower than that of the
macro eNB
121.
[00107] The femto cell 140 can include a femto eNB 141 connected to the
core
network 110 via the Internet 160 via a wired or wireless connection. The term
"femto
eNB" can also be referred to as a "home eNB (HeNB)." The femto cell 140 is a
subscription based cell. Three access modes can be defined for HeNBs: closed
access
mode, hybrid access mode and open access mode. In closed access mode, HeNB
provides services only to its associated closed subscription group (CSG)
members. The
term "closed subscription group (CSG)" can be interchangeably used with closed
subscriber group. Hybrid access mode allows HeNB to provide services to its
associated CSG members and to non-CSG members. In some implementations, the
CSG members are prioritized to non-CSG members. An open access mode HeNB
appears as a normal eNB.
[00108] The network 100 can also include a relay node 150 which serves
to
wirelessly relay data and/or control information between the macro eNB 121 and
user
equipment 170. The macro eNB 121 and the relay node 150 can be connected to
each
other via a wireless backhaul link 111d. In such an instance, the macro eNB
121 can be
referred to as a donor eNB. In some implementations, the relay node 150 can
have a
transmission power that is, for example, about 30 or 37 dBm, which is about 13
dB or 6
dB lower than that of the macro eNB 121. The term "underlay access node"
generally
refers to pico eNBs, femto eNBs, or relay nodes.
[00109] The user equipment 170 can communicate wirelessly with any one
of
the overlay access nodes 121 or the underlay access nodes 131, 141, 150,
depending on
the location or the existence of subscription in the case of the femto cell
140. The term
"user equipment" ("UE") can refer to various devices with telecommunications
capabilities, such as mobile devices and network appliances. The UE 170 may
switch
from the coverage of one cell to another cell, for example, from the coverage
of the
pico cell 130 to the coverage of the macro cell 120, i.e., a pico-to-macro
cell change, or
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from the coverage of a macro cell 120 to the coverage of the pico cell 130,
i.e., a
macro-to-pico cell change. A handover procedure may be conducted to ensure
that the
UE does not lose connection with the network while switching between cells.
[00110] Examples of user equipment include, but are not limited to, a
mobile
phone, a smart phone, a telephone, a television, a remote controller, a set-
top box, a
computer monitor, a computer (including a tablet computer such as BlackBerry
Playbook tablet, a desktop computer, a handheld or laptop computer, a netbook
computer), a personal digital assistant (PDA), a microwave, a refrigerator, a
stereo
system, a cassette recorder or player, a DVD player or recorder, a CD player
or
recorder, a VCR, an MP3 player, a radio, a camcorder, a camera, a digital
camera, a
portable memory chip, a washer, a dryer, a washer/dryer, a copier, a facsimile
machine,
a scanner, a multi-functional peripheral device, a wrist watch, a clock, a
game device,
etc. The UE 170 may include a device and a removable memory module, such as a
Universal Integrated Circuit Card (UICC) that includes a Subscriber Identity
Module
(SIM) application, a Universal Subscriber Identity Module (USIM) application,
or a
Removable User Identity Module (R-UIM) application. In some implementations,
the
UE 170 may include the device without such a module. The term "UE" can also
refer
to any hardware or software component that can terminate a communication
session for
a user. In addition, the terms "user equipment," "UE," "user equipment
device," "user
agent," "UA," "user device," and "mobile device" can be used synonymously
herein.
[00111] FIG. 2 is a schematic block diagram 200 illustrating various
layers of
access nodes and user equipment in an example wireless communication network.
The
illustrated system 200 includes a macro eNB 215, a pico eNB 225, a macro UE
205,
and a pico UE 235. Here macro UE 205 and Pico UE 235 are UEs which are either
actively communicating or camping on macro eNB 215 and pico eNB 225
respectively.
The macro eNB 215 and the pico eNB 225 can be collectively referred to as a
"network," "network components," "network elements," "access nodes," or
"access
devices." FIG. 2 shows only these four devices (also referred to as
"apparatuses" or
"entities") for illustrative purposes, and the system 200 can further include
one or more
of these devices without departing from the scope of this disclosure. The
macro eNB
215 can communicate wirelessly with the macro UE 205. The pico eNB 225 can
communicate wirelessly with the pico UE 235. The macro eNB 215 can communicate
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with the pico eNB 225 via a backhaul link, for example, an X2 backhaul link, a
wireless connection, or a combination thereof In some implementations, the
macro
eNB 215 and pico eNB 225 may exchange handover control information via the
backhaul link.
[00112] Each of the devices 205, 215, 225 and 235 includes a protocol stack
for
communications with other devices via wireless or wired connection. The macro
eNB
215 can include a physical (PHY) layer 216, a medium access control (MAC)
layer
218, a radio link control (RLC) layer 220, a packet data convergence protocol
(PDCP)
layer 222, and a radio resource control (RRC) layer 224. In the case of user
plane
communications for data traffic, RRC layer is not involved. The macro eNB 215
can
also include one or more transmit and receive antennas 226 coupled to the PHY
layer
216. In the illustrated implementation, a "PHY layer" can also be referred to
as "layer
1 (L1)." A MAC layer can also be referred to as "layer 2 (L2)." The other
layers (RLC
layer, PDCP layer, RRC layer and above) can be collectively referred to as a
"higher
layer(s)."
[00113] Similarly, the pico eNB 225 includes a PHY layer 228, a MAC
layer
230, a RLC layer 232, a PDCP layer 234, and an RRC layer 236. The pico eNB 225
can also include one or more antennas 238 coupled to the PHY layer 228.
[00114] The macro UE 205 can include a PHY layer 202, a MAC layer 204,
a
RLC layer 206, a PDCP layer 208, an RRC layer 210, and a non-access stratum
(NAS)
layer 212. The macro UE 205 can also include one or more transmit and receive
antennas 214 coupled to the PHY layer 202. Similarly, the pico UE 235 can
include a
PHY layer 240, a MAC layer 242, a RLC layer 244, a PDCP layer 246, an RRC
layer
248, and a NAS layer 250. The pico UE 235 can also include one or more
transmit and
receive antennas 252 coupled to the PHY layer 240.
[00115] Communications between the devices, such as between the macro
eNB
215 and the macro UE 205, generally occur within the same protocol layer
between the
two devices. Thus, for example, communications from the RRC layer 224 at the
macro
eNB 215 travel through the PDCP layer 222, the RLC layer 220, the MAC layer
218,
and the PHY layer 216, and are sent over the PHY layer 216 and the antenna 226
to the
macro UE 205. When received at the antenna 214 of the macro UE 205, the
communications travel through the PHY layer 202, the MAC layer 204, the RLC
layer
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206, the PDCP layer 208 to the RRC layer 210 of the macro UE 205. Such
communications are generally done utilizing a communications sub-system and a
processor, as described in more detail below.
[00116] Some typical functionality of different protocol layers is
briefly
described below. The NAS protocol, which runs between a core network and the
UE,
can serve for control purposes such as authentication, session management, and
UE
mobility management. The RRC layer in the eNB may be capable to make handover
decisions based on neighbor cell measurements sent by the UE, broadcasts
system
information, controls UE measurement and allocate cell-level temporary
identifiers to
active UEs. The functionality of PDCP layer includes, among other things,
encryption
of user data stream and header compression and decompression. The RLC layer
can be
used to format and transport traffic between the UE and the eNB. The MAC layer
is
responsible for, among other things, control of random access procedure,
scheduling of
data packets, and mapping of logical channels to transport channels. The PHY
layer
may involve modulation and demodulation, error protection of data package by
utilizing coding, radio frequency (RF) processing, radio characteristics
measurements
and indications to higher layers, and support for multiple input multiple
output (MIMO)
if multiple antennas are equipped with the eNB or the UE.
[00117] In the implementations described in this disclosure, various
steps and
actions of the macro eNB, macro UE, pico eNB, and pico UE can be performed by
one
or more of the layers described above in connection with FIG. 2. For example,
handover procedure for the macro UE 205 can be performed by one or more of the
layers 202-212 of the macro UE 205. Handover procedure by the pico UE 235 can
be
performed by one or more of the layers 240-250 of the pico UE 235. Channel
quality
measurement may be performed by the PHY layer and MAC layer of the macro UE
205 and pico UE 235. For another example, handover of UE may be initiated by
the
RRC layer 224 of the macro eNB 215 and the RRC layer 236 of the pico eNB 225.
[00118] FIG. 3 is a schematic block diagram 300 illustrating an access
node
device. The illustrated device 300 includes a processing module 302, a wired
communication subsystem 304, and a wireless communication subsystem 306. The
wireless communication subsystem 306 can receive data traffic and control
traffic from
the UE. The wired communication subsystem 304 can be configured to transmit
and
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receive control information between other access node devices via backhaul
connections. The processing module 302 can include one or more processing
components (also referred to as "processors" or "central processing units"
(CPUs))
capable of executing instructions related to one or more of the processes,
steps, or
actions described above in connection with one or more of the implementations
disclosed herein. The processing module 302 can also include other auxiliary
components, such as random access memory (RAM), read only memory (ROM),
secondary storage (for example, a hard disk drive or flash memory). The
processing
module 302 can form at least part of the layers described above in connection
with FIG.
2. In particular, the processing module 302 may be configured to receive
signal quality
indicators from the UE. The processing module 302 may also be configured to
determine a handover or an intermediate handover based on the received signal
quality
indicators, and to transmit a handover or an intermediate handover command.
The
processing module 302 can execute certain instructions and commands to provide
wireless or wired communication, using the wired communication subsystem 304
or a
wireless communication subsystem 306. A skilled artisan will readily
appreciate that
various other components can also be included in the device 300.
[00119] FIG. 4 is a schematic block diagram 400 illustrating user
equipment
device. The illustrated device 400 includes a processing unit 402, a computer
readable
storage medium 404 (for example, ROM or flash memory), a wireless
communication
subsystem 406, a user interface 408, and an I/0 interface 410.
[00120] Similar to the processing module 302 of FIG. 3, the processing
unit 402
can include one or more processing components (also referred to as
"processors" or
"central processing units" (CPUs)) configured to execute instructions related
to one or
more of the processes, steps, or actions described above in connection with
one or more
of the implementations disclosed herein. In particular, the processing module
402 may
be configured to estimate signal quality associated different cell and
transmit signal
quality indicators to an access node. The processing module 402 may also be
configured to receive signaling from access nodes and perform operations
accordingly,
such as transitions between a handover state and an intermediate handover
state. The
processing module 402 can form at least part of the layers described above in
connection with FIG. 2. The processing unit 402 can also include other
auxiliary
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components, such as random access memory (RAM) and read only memory (ROM).
The computer readable storage medium 404 can store an operating system (OS) of
the
device 400 and various other computer executable software programs for
performing
one or more of the processes, steps, or actions described above.
[00121] The wireless communication subsystem 406 is configured to provide
wireless communication for data and/or control information provided by the
processing
unit 402. The wireless communication subsystem 406 can include, for example,
one or
more antennas, a receiver, a transmitter, a local oscillator, a mixer, and a
digital signal
processing (DSP) unit. In some implementations, the subsystem 406 can support
multiple input multiple output (MIMO) transmissions.
[00122] The user interface 408 can include, for example, one or more of
a screen
or touch screen (for example, a liquid crystal display (LCD), a light emitting
display
(LED), an organic light emitting display (OLED), a microelectromechanical
system
(MEMS) display), a keyboard or keypad, a trackball, a speaker, and a
microphone. The
I/0 interface 410 can include, for example, a universal serial bus (USB)
interface. A
skilled artisan will readily appreciate that various other components can also
be
included in the device 400.
[00123] FIG. 5 is a schematic presentation 500 of an example deployment
of a
heterogeneous network. As shown in FIG. 5, a macro eNB 510 provides a macro
coverage area 512. Pico cells 520a and 520b and a femto cell cluster 530a-c
may be
situated within the coverage of a macro cell 512. The pico cell eNBs 521a and
521b
and macro cells eNB 510 are connected to EPC (Evolved Packet Core) network
through the MME (Mobility Management Entity)/S-GW (Serving Gateway) 515 via
backhaul connections 540a-c. The backhaul connection can be, for example, an
51
interface. Femto cell eNBs (HeNBs) 53l a-c are connected to an intermediate
gateway
HeNB-GW 550 through backhaul links 560a-c such as 51 interfaces. The HeNB-GW
550 can be connected with the MME/S-GW 515 via an 51 interface 540d as well.
Backhaul connections may exist between different types of eNBs. For example,
the
macro eNB 510 and the pico eNBs 521a-b can be connected through an X2
interference
(not shown). The femto eNBs 53l a-c may be connected with each other via the
X2
interface 572a-b. Moreover, an X2 interference 570 can be also introduced
between the
macro eNB 510 and HeNB-GW 550 in order to facilitate communications and
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coordination between the macro cell 512 and the femto cells 53 la-c and
provide
seamless service coverage for UEs in this area.
[00124] When a UE moves around in the area of 512, it may traverse
different
cells and trigger multiple handovers. In one example, a UE 580a may move along
a
trajectory 590a where it starts from the pico cell 520a, gets exposed to the
coverage
area of the macro cell 512 when it arrives at cell edge of the pico cell 520a,
and then
enters another pico cell 520b. During this trajectory, two handovers may
occur: a first
one from the pico cell 520a to the macro cell 512 and a second one from macro
cell 512
to the next pico cell 520b. In another example, if UE 580b moves along a
trajectory
490b, similarly, there can be multiple handovers between the macro cell 512
and the
femto cells 530a-c. Frequent handovers between multiple cells can result in
increases of
signalling overhead and delay, prolonged data interruptions, and degradation
of the
QoS of UEs.
[00125] In heterogeneous communication networks, especially under a
small cell
cluster deployment as shown in FIG. 5, large overlaps in coverage between
macro and
femto/ pico cells are generally expected. Cell boundaries between the macro
and femto/
pico cells can have acceptable coverage for control signaling receipt.
Furthermore,
some type of interference cancellation and/ or coordination methods is
generally used
in this type of deployments. Therefore a UE may receive control signaling from
multiple cells and collaborate with multiple cells for handover operations
accordingly.
The UE may maintain downlink (DL) and uplink (UL) transmissions
synchronization
within the cluster deployment. The UE may control its transmit power and
timing on
the uplink based on the receive point at any given time. In an alternate
embodiment, the
UE may be capable of maintaining separate UL and DL synchronization with the
multiple neighboring cells within an acceptable range simultaneously.
[00126] To restrict the handover and reduce unnecessary and unwanted
data
interruptions, an intermediate handover (IHO) state can be introduced. With an
enablement of the IHO state, the number of handovers can be reduced to one for
both
trajectories 590a-b mentioned above. For example, for the trajectory 590a
where the
UE 580a is traversing between the pico cells 520a and 520b, the handover
to/from
macro cell 512 can be avoided by keeping the UE 580a to the pico cell 520a
until the
UE 580a completely enters the coverage area of pico cell 520b. Then, the UE
580a can
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only be handed over once from the pico cell 520a to the pico cell 520b.
Implementations of the IHO state will be described in further details below.
[00127] FIG. 6a is a schematic state diagram 600 illustrating a
handover
mechanism involving the IHO state. In general, when a UE is registered with a
serving
cell, it has RRC (Radio Resource Control) connection with the serving cell and
can
actively communicate with the core network. A UE in "STAY/ ACTIVE" 610 is in
RRC ACTIVE state with the serving cell and can transmit and receive, for
example,
Packet Data Control Protocol (PDCP) packets, from the serving eNB. The UE may
send a signal quality indicator to the serving base station. The signal
quality indicator
can be a measurement feedback, such as Channel Quality Information (CQI)
reports of
a target cell. The serving cell may send an RRC message so that the UE may
transition
to "HO" state 620 or "IHO" state 630 based on the measurement reports from the
UE.
From the "IHO" state 630, the UE may transition back to RRC_ACTIVE state 610
with
the serving cell or to a "HO" state. This transition may happen at the request
of the
serving cell or can be triggered autonomously. Once the HO is performed the UE
goes
into "STAY/ ACTIVE" state with a target cell.
[00128] In the IHO state 630, the UE is not handed over to any of the
target cells
completely. These target cells are referred to as IHO candidate cells during
the IHO
state. An example method to select IHO candidate cells will be discussed in
further
details below. The PDCP packets from the serving eNB are routed to the IHO
candidate
eNB(s) over a backhaul link, such as the X2 interface, which connects eNBs. If
the QoS
of a candidate cell is expected to be better than that of the serving cell,
the PDCP
packets are scheduled and transmitted by that candidate cell to the UE. Recall
that the
PDCP processing can provide encryption of the data packets for security and
identity
protection. During the IHO state, the encryption of the data packets may
remain
unchanged and still be conducted by the serving cell. Therefore, the data
rerouting from
the serving cell to the candidate cell is completely transparent to the EPC
network.
Moreover, most control signaling of the RRC and NAS may also originate from
the
serving eNB and be rerouted to the candidate eNB(s), for example, through
backhaul
links. Therefore, the IHO state in this disclosure can also be referred as a
network
agnostic mobility management (NA-MM) state, which means the state is
transparent to
the core network. When the expected QoS difference with respect to serving
cell and
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IHO candidate cell is larger than a threshold, the UE may be instructed to
handover
completely to one of the candidate cells (i.e. exits the intermediate handover
state).
[00129] In the intermediate handover state, the UE may transmit/
receive packets
to/ from either the target cell or the serving cell. The cell which actively
transmits the
data to the UE is referred to as the Anchor cell. The switching of
transmission/ receipt
between the cells may be decided by the Anchor cell. The packet transmission/
receipt
cell may be indicated in an RRC message transmitted by the anchor cell.
[00130] Normally the switching of anchor cell can occur at the start of
a new IP
packet/ PDCP SDU transmission. For DL, the anchor eNB is aware of the
transmission
of a new PDCP SDU. In the case of UL, UE may be aware of this condition and
inform
the completion of the IP packet/ PDCP SDU so that new resources are assigned
by the
new anchor cell. The IP packet segmentation is done independently at each
candidate
cell. Normally the switching between the candidate cells is not expected to be
very
frequent. The switching times are typically dependent on the application type.
For
example, for Gaming applications, the IP packets tend to be small. In this
case the
switching between the cells may be faster (if the signal quality with respect
to each cell
varies very rapidly).
[00131] The IHO state may be time limited. Because each candidate cell
participating in the IHO state may reserve resource for the UE, configuring a
timer
associate with the IHO state can avoid excessive system resource reserved for
one UE
whereas qualify of service of other UEs in the network may be affected. The
value of
the timer Tilio can be implementation specific, for example, depending on a
deployment
scenario. The network operator can have the freedom to configure the time
limit for the
IHO state to optimize the system performance. In some implementations, the
serving
eNB may send the value of the timer to the candidate cells during the IHO
request.
[00132] The system operator can determine under what scenarios the IHO
state
can be enabled. For example, it might be set that IHO state can be only
enabled if one
or more of the neighboring cells are low power cells, i.e. pico/ femto/ relay
cells/ nodes.
The IHO state may be enabled or disabled by the operator through OAM
(Operations,
Administration, and Maintenance) settings.
[00133] FIG. 6b is a schematic flow chart 640 illustrating a method may
be
performed by a serving cell of a UE for IHO candidate cell selection. In a
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heterogeneous network, a UE may receive and measure downlink (DL) signal
quality
with respect to the serving cell, as well as a plurality of neighboring cells.
A
neighboring cell can be, for example, a macro cell, a pico cell, or a femto
cell. The UE
may send a DL signal quality indicator to the serving cell. The DL signal
indicator may
indicate the serving cell that the UE is proximate to one or more neighboring
base
stations and can receive data packets from the neighboring base stations. In
some
implementations, the DL signal indicator can be signal quality measurement
feedback,
such as Channel Quality Information (CQI) reports of the neighboring cells, or
any
other channel quality parameters. For example, the receive signal quality can
include at
least one of the following: reference signal receive quality, reference signal
receive
power, signal to interference plus noise ratio, or average packet delay.
[00134] Upon the receipt of the signal quality indicator at step 642,
the serving
cell may determine whether a condition for an IHO state is satisfied based on
the signal
quality indicator from the UE at step 644. Given the condition satisfied, in
step 646, the
serving cell may select one or more neighboring base stations whose DL signal
quality
report is above a predefined threshold. The predefined threshold can be a UE
specific
parameter and selected to guarantee the promised Quality of Service (QoS) to
the UE.
Then, at step 648, the serving cell can send IHO request messages to the one
or more
neighboring base stations. The neighboring base stations can determine whether
to
participate in the IHO state based on several factors , such as, whether the
base station
has enough resource to allocate to the UE, and/or whether the UE is a
subscription
group (CSG) member if neighboring base station is a HeNB with closed access or
hybrid access mode.
[00135] If a neighboring base station agrees to join the IHO state, it
may reserve
DL resource for the UE. The neighboring base stations may inform the serving
cell
their respective decisions via the IHO responses. After receiving the IHO
responses
from the neighboring cells in step 650, the serving cell can further select
one or more
potential IHO candidate base stations in step 652 out of the neighboring base
stations
that respond positively to the IHO request. Thus a group of potential IHO
candidate
base stations is formed.
[00136] In some implementations, the serving base station may compare
the
number of potential IHO candidate base stations with a maximum allowed number
of
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IHO candidate base stations in step 654. The maximum allowed number can be a
network configuration dependent parameter and be set by the network operator.
If the
number of potential IHO candidate base stations is above the maximum allowed
number of IHO candidate base stations, the serving base station may remove one
or
more base stations from the group of potential IHO candidate base stations in
step 656
and send cancellation messages to those base stations in step 658. If the
number of
potential IHO candidate base stations does not exceed the maximum allowed
number
of IHO candidate base stations, the base station can start an IHO timer and
send a
control information to the UE to initiate the IHO state. In some
implementations, the
control information can be sent via a radio resource control (RRC) message.
[00137] During the IHO state, the UE can be connected to the serving
cell as
well as at least one candidate target cell. Enabling the RRC_ACTIVE state with
both
the eNBs may require some changes to the existing standards. As illustrated in
FIG. 5,
depending on system deployment, in some embodiments, pico/femto cells (e.g.,
pico
cells 520a and 520b) can be directly connected to the network and have an X2
interface
with other eNBs; in other embodiments, femto cells (e.g., femto cells 530a-c)
can be
connected to the network via H-GW and H-GW and eNB are connected over an X2
interface. Proper protocol and signaling changes can be made to incorporate
IHO state
in handover procedures under different system deployments.
[00138] FIG. 7 is a schematic 700 illustrating an example heterogeneous
network
where pico or femto cells are directly connected to the core network and
having an X2
interface with other eNBs. As shown in FIG.7, three UEs, UEO 702, UE1 704 and
UE2
706, are connected to the EPC 705 via a pico cell (Cell-N) 708 and a macro
cell (Cell-
S) 710. Cell-S 710 is the serving cell (a first cell) of the UE1 704. In some
implementations, the UE1 704 may receive coverage signal from a second cell,
say,
Cell-N 708 when UE1 704 is in the common coverage of both cells. The coverage
signal can include one or more of a reference signal, a system information
broadcast
signal, or a data transmission signal transmitted by a base station. The UE
may send a
signal quality indicator to the serving cell. The signal quality indicator may
represent
the quality of the received signal at the UE from the serving cell and the
second cell
Cell-N 708. Some example signal quality indicator can be RSRP (Reference
Signal
Received Power), RSRQ (Reference Signal Received Quality), Channel Quality
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Information (CQI), or any other channel quality parameters. Based on the
indicator
from the UE, the serving base station may decide and initiate an IHO state of
the UE
with the serving cell and the second cell.
[00139] During the IHO state, both the serving cell Cell-S 710 and the
second
cell Cell-N 708 can maintain a communication link with the UE. The
communication
link can be, for example, a RRC connection. UE1 704 may transmit/ receive data
packets to/ from either one of the cells. The transmission from the core
network/base
station to the UE is referred to as downlink (DL) transmission; and
transmission from
the UE to the core network/base station is referred to as uplink (DL)
transmission. In
the following, some example process or signaling flow are discussed in
accordance
with DL transmission. Corresponding process and signaling flow for UL
transmission
can be readily appreciated by a skilled artisan in the art.
[00140] In one example, if the UE1 704 gets a better signal quality
from Cell-N
708, the Cell-S 710 can transmit the encrypted data packets (such as Packet
Data
Convergence Protocol (PDCP) packets) destined to the UE to the Cell-N 708 via
a
backhaul link (such as the X2 interface 712 in FIG. 7). Note that this data
packet
rerouting is not visible to the EPC 705. The encryption keys associated with
the data
and control signaling (including the data scrambling function) are also not
affected
since the data sent by the Cell-N 708 is already encrypted by Cell-S 710. As
an
example, the Cell-S 710 can receive a data packet from the EPC, encrypts the
data
packet form PDCP Service Data Unit (SDU), and forward the encrypted data
packet to
the second cell Cell-N 708. After transmitting the data packet to the second
cell, the
serving cell can still maintain a communications link with the UE during the
IHO state.
[00141] In some embodiments, the IHO state can be established based on
control
signal exchange between the two cells via X2-C interface 712. During the IHO
state,
the data packets can also be exchanged over the X2-U interface.
[00142] In other embodiments, X2 may not exist between the two cells
(or
eNBs); the information exchange can be performed via 51 interface such as 714a-
b
involving the MME/SGW 716 as shown by the dotted line 718 in FIG. 7.
[00143] Note that FIG. 7 only shows an example IHO state involving a
serving
cell and a neighboring cell. A skilled artisan can readily appreciated that an
IHO state
can also involve a serving cell and a plurality of neighboring cells.
Moreover, in FIG.
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7, the two cells, namely, Cell-S 708 and Cell-N 710, are connected to a same
MME and
SGW 716. In other implementations where the cells are connected to multiple
MMEs
and/or S-GWs, the IHO state can also be enabled without departing from the
scope of
this disclosure. In such aspects of implementations, the related control
information and
data packets can go through, for example, backhaul links that connect the
multiple
MMEs and/or S-GWs.
[00144] In some implementations, the serving base station may receive
an
indication that the signal quality from the second base station is stronger
than the signal
from the serving base station such that a handover can be triggered. In this
case, the
serving base station can hand over control of communications for the UE to the
second
base station and exit the IHO state by terminating the communications link
with the
UE.
[00145] To look at the enablement of an IHO state from a protocol
perspective,
FIGS. 8a-8b illustrate example user plane protocol stacks of access nodes and
UE
during the IHO state. Wireless networks may distinguish between user plane
protocol
and control-plane protocol. Various examples of user-plane traffic and
services carried
by the user plane include voice, video, internet data, web browsing sessions,
upload/download file transfer, instant messaging, e-mail, navigation services,
RSS
feeds, and streaming media. Control-plane traffic signaling may be used to
enable or
support transfer of the user plane data via the wireless network, including,
for example,
mobility control and radio resource control functionality. Various examples of
control
plane traffic include core-network mobility and attachment control, (e.g., Non-
Access
Stratum (NAS) signaling), radio access network control (e.g., Radio Resource
Control
(RRC)), and physical layer control signaling such as may be used to facilitate
advanced
transmission techniques and for radio link adaptation purposes.
[00146] FIG. 8a is a schematic block diagram 800 showing the user plane
protocol stack when a UE 805 is communicating with its serving cell 815. The
serving
cell 815 is further connected to a Serving Gateway (SGW)/Packet Data Network
Gateway (PGNGW) 825. The SGW can serve as a mobility anchor for the user plane
during inter-eNB handovers and as the anchor for mobility between LTE and
other
3GPP technologies. PGNGW can serve as the anchor for mobility between 3GPP and
non-3GPP technologies such as WiMAX and 3GPP2 (e.g., CDMA lx and EvD0).
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[00147] The user plane protocol stack of UE 805 includes a Li (Layer 1)
802,
also known as a PHY layer, an upper layer 804 (including a MAC layer, a RLC
layer,
and a PDCP layer), an IP layer 806, a TCP/UDP layer 808 and an Application
layer
810. Similarly, the serving cell 815 (e.g., the macro Cell-S 710 in FIG. 7)
includes a Li
812, a MAC layer 814, a PDCP layer 818 to communicate with the UE.
[00148] On the other hand, there may be a backhaul connection such as
an Si
user interface between the serving cell and the SGW/PDNGW. The serving cell
815
may include a Li 818, a L2 (Layer 2, also known as MAC layer) 820, an UDP/IP
layer
822, a GPRS Tunneling Protocol (GTP) layer 824 to communicate with the
SGW/PDNGW 825. Accordingly, the SGW/PDNGW 825 can have a user plane stack
containing a Li 826, a L2 828, a UDP/IP layer 830, a GTP layer 832 and an IP
layer
834.
[00149] The Application layer 810 of UE 805 provides end-to-end
connectivity
between the UE and a remote host such as another UE, or a remote internet
server. For
example, a navigation application may utilize TCP for file transfer of mapping
data
from an internet server to a device. The application, may utilize Internet-
based
protocols (IP) to establish an end-to-end connection.
[00150] In the illustrated example, the IP layer 834 of the SGW/PDNGW
825
may receive IP packets intended for the UE 805 from the internet server. The
data
packets can be transmitted between the backhaul connection (e.g., Si user
interface)
between the SGW/PDNGW 825 and the serving cell 815 through the GTP layer 832,
the UDP/IP layer 830, the L2 828 and the Li 826 on the SGW/PDNGW side, and the
Li 818, the L2 820, the UDP/IP layer 822, and the GTP layer 824 on the serving
cell
side. The serving cell 815 may encrypt the data packets at the PDCP layer 816,
pass the
PDCP packets to the MAC layer 814, and be sent over the Li 812 to the UE 805.
[00151] The signal received at the UE 805 can be processed through the
Li 802,
the RLC/MAC/PDCP layer 804, the IP layer 806, the TCP/UDP layer 808, and
eventually reach the Application layer 810 and complete an end-to-end
communication.
[00152] FIG. 8b is a schematic block diagram 850 showing the user plane
protocol stack when a UE 835 is communicating with a neighboring cell 845
(e.g.,
pico/femto cell Cell-N 708 in FIG. 7). In this embodiment, the neighboring
cell 845 has
a backhaul connection such as an X2 interface between the serving cell 855
(e.g., the
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macro Cell-S 710 in FIG. 7) that is further connected to a SGW/PDNGW 865. The
protocol stack between the serving cell 855 and the SGW/PDNGW 865 is the same
as
the one between the serving cell 815 and the SGW/PDNGW 825 shown in FIG.8a,
including a GTP layer 884, a UDP/IP layer 882, a L2 880 and a Li 878 on the
serving
cell 855 side, and a Li 886, a L2 888, a UDP/IP layer 890, a GTP layer 892,
and an IP
layer 894 on the SGW/PDNGW 865 side.
[00153] In the illustrated example, since the Cell-S 855 is still the
serving cell of
the UE 835, the SGW/PDNGW 865 may still route data packets destined for the UE
835 to Cell-S 855. The Cell-S 855 can then send the encrypted data packets to
the Cell-
N 845 via the X2 interface. The user plane protocol between the Cell-S 855 and
Cell-N
845 can include a PDCP layer 876, a GTP/UDP/IP layer 874, a L2 872 and a Li
870 at
the Cell-S 855 and a PDCP layer 868, a GTP/UDP/IP layer 866, a L2 864 and a Li
862
at the Cell-N 845 accordingly. As mentioned above, this data packet rerouting
is not
visible to the EPC. The encryption keys associated with the PDCP data packets
and
control signalling (including the data scrambling function) are also not
affected since
the data sent by the Cell-N is already encrypted by Cell-S.
[00154] Between the neighboring cell 845 and the UE 835, the user plane
protocol is similar to the one between the serving cell 815 and the UE 805 in
FIG. 8a.
For instance, the downlink user plane traffic may go through a PDCP layer 860,
a
RLC/MAC layer 858, and transmit over a Li 856 to the UE 835 where the received
user traffic is processed through a Li 842, a RLC/MAC layer 844, a PDCP layer
848,
an IP layer 851, a TCP/UDP layer 852, and arrives at an Application layer 854.
[00155] FIG. 9a is a schematic block diagram 900 showing an example
control
plane protocol stack of access nodes and UE during the IHO state. In
particular, a UE
905 is communicating with its serving cell 915 that is further connected to a
MME
(Mobility Management Entity) 925. On top of the protocol stack of the UE and
the
MME are Non-Access Stratum (NAS) layers 908 and 932 respectively. The NAS
protocols support the mobility of the UE and the session management procedures
to
establish and maintain IP connectivity between the UE and a PDN GW. Under the
NAS
layer 908 of the UE, there can be a RRC PDCP layer 906, a RLC/MAC layer 904
and a
Li 902. Accordingly, there are a RRC PDCP layer 914, a RLC/MAC layer 912 and a
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Li 910 at the serving cell 915, supporting the transmission of control plane
traffic
between the UE 905 and the serving cell 915.
[00156] Between the serving cell 915 and the MME 925, there may exist
backhaul connection such as an Si control interface. In such a case, the
control plane
protocol stacks of the serving cell 912 and the MME 925 contains Si-AP (Si
Application Protocol) layers 922 and 930, SCTP (Stream Control Transmission
Protocol) layers 920 and 928, IP layers 918 and 926, and Li/L2 916 and 924,
respectively. The Si-AP is the application layer protocol between an eNB and
MME. It
can support, among other things, mobility functions for UE, Paging, and NAS
signaling
transport function. SCTP is a common transport protocol that uses the services
of IP to
provide a reliable datagram delivery service to the adaptation modules, such
as the
S 1AP. SCTP can provide reliable and sequenced delivery on top of the existing
IP
framework.
[00157] FIG. 9b is a schematic block diagram 950 showing an example
control
plane protocol stack of access nodes and UE during the IHO state. In
particular, a UE
935 is communicating with a neighboring cell Cell-N 945. There can be a
backhaul
connection such as an X2 interface between the neighboring cell Cell-N 945 and
the
UE's serving cell Cell-S 955. The serving cell 955 is further connected to an
MME
(Mobility Management Entity) 965 via an Si interface. The control plane
protocols
between the serving cell 955 and the MME 965, similar to the ones in FIG. 9a
between
the serving cell 915 and the MME 925, can include Si-AP layers 978 and 986,
SCTP
layers 976 and 984, IP layers 974 and 982, and Li/L2 972 and 980, at the
serving cell
955 and the MME 965, respectively. The top layer of the control plane at the
MME can
be a NAS layer 988.
[00158] Between the neighboring cell 945 and the serving cell 955, the
control
plane on the X2 interface (X2-C interface) may include RRC/PDCP layers 960 and
970, X2-AP layers 958 and 968, SCTP layers 956 and 966, IP layers 954 an 964
and
Li/L2 952 and 962, at the neighboring cell 945 and the serving cell 955,
respectively.
X2-AP protocol can be used to handle the UE mobility within E-UTRAN. During
the
RRC connection between the two cells, the PDCP packets carrying X2-AP message
can
be encrypted by the serving cell 9 and rerouted to the neighboring cell 9.
SCTP is
supported as the transport layer of between eNB-eNB pairs for transporting
various
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signaling protocols over IP network. The IHO state can be established based on
control
signal exchange between the two cells via the X2-C interface.
[00159] Similar to the control plane protocols where the UE 905 is
communicating with the serving cell 915 in FIG. 9a, the control plane
protocols may
include RRC PDCP layers 938 and 948, RLC/MAC layers 936 and 946, and Li 934
and 942 at the UE 935 and the neighboring cell 945. After receiving the PDCP
packets
containing control information from the serving cell 955, the neighboring cell
945 may
process and send the PDCP packets to the UE 935. The data packets may go
through
various protocol layers between the neighboring cell and the UE and eventually
reach a
NAS layer 940 at the UE 935.
[00160] The protocol stacks shown in FIGS. 8 and 9 may be more relevant
to the
case where the pico/femto cells are directly connected to the network and
having an X2
interface with other eNBs. In some other embodiments where there may be no
direct
X2 interface between the pico/femto cells (or eNBs), the information exchange
can be
performed via Si interface involving the MME/SGW. Corresponding modifications,
variations, and enhancement can be made to the example protocol stacks in
FIGS. 8 and
9. For instance, protocol stacks related to the Si interface between the eNB
and the
SGW/PDNGW/MME can replace the protocols related to the X2 interface as shown
in
FIGS. 8b and 9b between the neighboring cell and the serving cell where the UE
is
communicating with the neighboring cell.
[00161] In some embodiments, femto cells are connected to the network
via H-
GW such as shown in FIG. 5 where femto cells 530a-c are connected to the H-GW
550
via Si interface 560a-c. In this case, the HeNB GW appears to the MME as an
eNB.
The HeNB GW appears to the eNB as another eNB. The HeNB GW shall connect to
the EPC in a way that inbound and outbound mobility to cells served by the
HeNB GW
may not necessarily require inter MME handovers. X2 connections (e.g., 572a-b)
may
exist between HeNBs in a set. Under this scenario, X2-based handover between
HeNBs
is allowed if no access control at the MME is needed, i.e. when the handover
is
between closed/hybrid access HeNBs having the same CSG ID or when the target
HeNB is an open access HeNB. An X2 connection (e.g., 570 in FIG. 5) can be
introduced between HeNB GW and eNB. With this arrangement, the eNB that is
within
the coverage range of the HeNB which is supported by the HeNB GW can operate
with
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the HeNB to execute the handoff process as described above. For example,
handover
process with enablement of IHO state can be established between the macro eNB
510
and the femto eNB 531a with corresponding control plane and user plane
protocol
stacks in place.
[00162] To facilitate the communications among the UE, the serving cell,
and
one or more neighboring cells, a pool of C-RNTIs (Cell Radio Network Temporary
Identifier) can be allocated among neighboring cells for IHO operation. During
the IHO
state, the UE will be assigned to one of these C-RNTIs by the serving cell. In
some
implementations the C-RNTIs can be assigned dynamically. If the neighboring
cell has
the specific C-RNTI assigned by the serving cell to the UE available, then the
same C-
RNTI is used during the IHO. If there is a conflict, a new C-RNTI is
negotiated with
the serving cell and/ or the neighboring cells.
[00163] To implement a HO procedure with IHO state, certain changes in
signaling can be incorporated to coordinate the UE, the serving cell, and one
or more
candidate cells in initiating the IHO state, during the IHO state, and state
transitions
among the IHO, HO and STAY states.
[00164] FIG. 10 is a schematic flow diagram 1000 illustrating an
example
method for performing a handover mechanism involving an IHO state in a
wireless
communication network. The communication network may include a UE 1002, a
serving cell/eNB 1004 of the UE, one or more IHO candidate cell/eNB 1006, MME
1008 and SGW 1010. The example HO procedure includes three stages: HO/IHO
preparation stage 1005 where the network entities collaborate in initiating
the IHO
state, IHO state 1015, and HO to target cell stage 1025 where the UE in IHO
state may
exit the IHO state and move to a target cell (as shown in FIG. 10). In some
other
implementations, the UE may stay with the serving cell after exiting the IHO
state (not
shown).
[00165] In the HO/IHO preparation stage 1005, the UE 1002 maybe
triggered to
send a MEASUREMENT REPORT at step 1031 by the rules set by the system
information, specification etc. The measurement report may contain a signal
quality
indicator that indicating quality of service (QoS) for the source base station
and one or
more neighboring base stations. As shown in FIG. 10, the MEASUREMENT REPORT
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is received by the serving cell 1004. Then the serving cell can make decision
based on
MEASUREMENT REPORT to initiate HO or IHO 1032.
[00166] The HO algorithm can be implementation specific. For example,
QoS
values with respect to the serving cell and neighbouring cells may be measured
by the
UE. In some implementations, the eNB may obtain a representation of the QoS by
modifying the existing UE measurements, such as RSRP and/or RSRQ, with the
additional performance monitoring on UE ACK/NACK feedback. Based on the
measurements, the HO algorithm can determine what scenarios an IHO state
should be
initiated. During this procedure, if IHO is an appropriate state, at least a
subset of the
one or more neighboring base stations can be selected as candidate cells for
enabling
IHO state. The at least a subset of the one or more neighboring base stations
can be
identified based on the quality of service for the one or more neighboring
base stations
indicated in the measurement report. In some implementations, the IHO
candidate cell
selection method illustrated in FIG. 6b can be used.
[00167] In step 1033, the serving cell can issue a X2AP: HANDOVER
REQUEST message to the IHO candidate cells. The serving cell may include
necessary
information in the handover request message to prepare the IHO at the
candidate
cell(s). For example, the handover request message may include at least the
IDs of a set
of candidate cells. The message may indicate, for instance, whether the
intermediate
HO (IHO) state is enabled or not, the expected duration of the IHO state, or
any other
appropriate indications.
[00168] Admission Control 1034 may be performed by the candidate cells
dependent on the received E-RAB (EUTRAN Radio access bearers) QoS information
to increase the likelihood of a successful HO/ IHO, if the resources can be
granted by
the candidate cell. The candidate cell configures the required resources
according to the
received E-RAB QoS information and reserves a C-RNTI and optionally a RACH
(Random Access Channel) preamble. The AS-configuration to be used in the
candidate
cell can either be specified independently (i.e. an "establishment") or as a
delta
compared to the AS-configuration used in the serving cell (i.e. a
"reconfiguration"). If
the X2AP: HANDOVER REQUEST message indicates that IHO is enabled, the
admission control performed by the candidate cells may be different. The
resources
reserved at the candidate cells are normally time limited only for the
duration of IHO.
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Furthermore, a scaling factor is used to estimate the fraction of the time
that these
resources are actually used. This scaling factor may be a function of the
deployment
scenario and configured by the OAM. For example, the scaling factor for three
candidate cells may be set to 1/3. In this example, it is assumed that each
candidate cell
transmits/ receives 1/3 of the IP packets to the UE during the IHO state.
[00169] Candidate cell prepares HO with L1/L2 and sends the HANDOVER
REQUEST ACKNOWLEDGE to the serving cell in step 1035. The X2AP:
HANDOVER REQUEST ACKNOWLEDGE message includes a transparent container
to be sent to the UE as an RRC message to perform the handover/ IHO. The
container
includes a new C-RNTI, target eNB security algorithm identifiers for the
selected
security algorithms, may include a dedicated RACH preamble, and possibly some
other
parameters i.e. access parameters, SIBs (System Information Blocks), etc. The
X2AP:
HANDOVER REQUEST ACKNOWLEDGE message may also include RNL (Radio
Network Layer)/TNL (Transport Network Layer) information for the forwarding
tunnels, if necessary. In this message the candidate eNB may also include an
IHO state
acceptance indicator. Basically the IHO state acceptance indicator can
indicate whether
the target eNB's willingness to participate in the support of IHO state.
Furthermore, the
candidate cell may indicate whether the UE is required to perform UL
synchronization
with the candidate cell or not. Normally this decision is dependent on the
location of
the UE and the coverage overlap of the serving and candidate cells.
[00170] The candidate eNB generates the RRC message to perform the
handover
or IHO, i.e RRCConnectionReconfiguration message including the
mobilityControlInformation, to be sent by the serving eNB towards the UE. In
step
1036, the serving eNB transmits the RRC reconfiguration message received from
the
target cell(s) to the UE. The RRC Reconfiguration message may include
additional
information to enable IHO state. The additional parameter may include the list
of the
IHO candidate cells, IHO timer, etc.
[00171] The serving eNB may start transmitting the unacknowledged data
packets to the target eNB over X2_U interface in step 1037. These data packets
may
not be transmitted to the candidate cell if the UE stays in IHO state before
performing
HO to the candidate cell. However, any new IP packets (PDCP SDUs) are
forwarded to
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the candidate cell's eNBs. The new IP packet forwarding can be performed
selectively
or multi-casted to all the candidate cells during the IHO duration.
[00172] After receiving the RRC Connection Reconfiguration message
including
the mobility Control Information, UE may enter IHO state if enabled. Before
entering
IHO state, the UE may optionally perform UL synchronization with the target
cell(s)
1038. UL sync is performed only if the UE is instructed to do so. Upon
entering the
IHO state, the UE sends the RRC Connection Reconfiguration Complete to
indicate
that it has successfully accessed the candidate cell at step 1038a. This RRC
Connection
Reconfig Complete message is sent to all candidate cells after successfully
accessing
those cells. This message to each candidate cell may include the C-RNTI
assigned by
the respective candidate cell. If RRC Reconfig Complete message is not
received by the
candidate cell within a predefined time, the candidate cell may cancel UE's
IHO state
and inform that to the serving cell over X2 by sending X2: IHO Cancel message.
[00173] During the IHO state 1015, the UE receives from, and transmits
to, only
the anchor cell. The anchor cell is basically the cell actively transmitting
to or
receiving from the UE. Also while in the IHO state, any candidate cell,
including the
serving cell, may become the anchor cell. As illustrated in step 1038b-1038h,
during
the IHO state, the anchor cell may decide a next anchor cell based on the
measurement
reports from the UE 1002. If the anchor cell changes, there are corresponding
IP
packets forwarding to enable the anchor cell actively transmitting to or
receiving from
the UE. The steps 1038b-1038f illustrate an example IHO anchor transfer
procedure
where the first anchor cell is the serving cell 1004 and the second anchor
cell is another
candidate cell 1006. Further details are illustrated in FIGS. ha-c in the
following.
[00174] FIG. 1 la is a schematic flow diagram 1100 illustrating an
example IHO
anchor transfer procedure where the first anchor cell is the serving cell 1104
and the
second anchor cell is another IHO candidate cell 1106. The UE 1102 may measure
the
signal quality with respect to the candidate cells, preferably periodically
and report
these measurements to the current anchor cell 1104 in step 1108. The anchor
cell 1104
may further evaluate these measurements and may select a second anchor cell
based on
the used HO/IHO algorithm in step 1110. In this case, a candidate cell 1106 is
selected
as the second anchor cell. Then the first anchor cell 1104 may send X2AP: IHO
anchor
functionality transfer request message to the newly selected anchor cell in
step 1112
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and forward all the new downlink IP packets to the second anchor cell 1106
from the
serving cell 1104 in step 1114. The first anchor cell 1104 may send an RRC
Reconfiguration message to the UE to inform about the new anchor cell in step
1116.
This RRC reconfiguration message is much shorter than the RRC reconfiguration
message for initiating IHO or HO. Normally this message is shorter and just
informs
the UE about the ID of the second anchor cell. UE can listen to one of the
candidate
cells from a future subframe. Upon receiving this RRC Reconfiguration message
with
the candidate cell ID and the time to switch to the new anchor cell, the UE
1102 may
send RRC reconfiguration acknowledgement to the current anchor cell 1104 in
step
1118 and RRC reconfiguration of complete message to the new anchor cell 1106
in step
1120. Upon receiving the RRC reconfiguration complete message, the second
anchor
cell 1106 may send X2AP: IHO Anchor Functionality Transfer Response message to
the first anchor cell in step 1122 and starts transmitting the data to the UE.
[00175] FIG. 1 lb is a schematic flow diagram 1130 illustrating an
example IHO
anchor transfer procedure where the first anchor cell is an IHO candidate cell
1134 and
the second anchor cell is the serving cell 1136. The anchor transfer procedure
can
follow a series of steps 1138-1150 similar to the steps 1108 to 1122 except
step 1114 in
FIG. lla because in this case the second anchor control is the serving cell
1136; and the
new IP packets do not need to be forwarded.
[00176] FIG. 11c is a schematic flow diagram 1100 illustrating an example
IHO
anchor transfer procedure where neither the first anchor cell nor the second
anchor cell
is the serving cell. As shown in FIG. 11c, the downlink data is first
forwarded to the
first anchor cell 1164 from the serving cell 1168. The UE 1162 reports quality
measurements to the first anchor cell 1164 that performs anchor cell decision
making
1174. If a candidate cell 1166 is determined to be the second anchor cell, the
first
anchor cell 1164 may send X2AP: IHO Anchor Functionality Transfer Request to
the
new anchor cell 1166 and the serving cell 1168 in steps 1176 and 1178,
respectively.
With the notice of the anchor cell change, the serving cell then forward
downlink data
to the second anchor cell 1166 in step 1180. The first anchor cell may also
send an
RRC Reconfiguration message to the UE in step 1182 to inform about the second
anchor cell 1166. The UE 1162 may send RRC reconfiguration acknowledgement to
the current anchor cell in step 1118 and RRC reconfiguration of complete
message to
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the new anchor cell 1166 in step 1194. Upon receiving the RRC reconfiguration
complete message, the second anchor cell 1166 may send X2AP: IHO Anchor
Functionality Transfer Response message to the first anchor cell 1162 in step
1188 and
starts transmitting the data to the UE.
[00177] Referring back to the FIG. 10, while in the IHO state, if UE
determines
that the QoS from the candidate cell is consistently above the required QoS
requirement
and also significantly better than the QoS that can be obtained from the
serving cell, UE
may send an updated measurement report to the anchor cell in step 1038j.
Subsequently, the anchor cell may perform HO/IHO algorithm in step 1038h and
trigger HO to one of the candidate cells (i.e. HO target cell) as shown in HO
to
handover stage 1015 including steps 1038j to 1038m. In the illustrated example
in FIG.
10, the serving cell 1004 may send the X2AP: HO request to the target cell
1006 in step
1038k. When the UE is handed over to one of the candidate cells, the X2AP: HO
request is simplified since the UE context is already available at the target
cell. In step
1138i, the target cell 1006 may reply to the serving cell 1004 with a X2AP: HO
Request acknowledgement. The serving cell can then send a RRC reconfiguration
message to the UE 1002 informing about the handover to the target cell 1006 in
step
1038m.
[00178] When the UE has successfully accessed the target cell, the UE
1102
sends the RRC Connection Reconfiguration Complete message (including a C-RNTI)
to confirm the handover in step 1139, along with an uplink Buffer Status
Report,
whenever possible, to the target eNB to indicate that the handover procedure
is
completed for the UE. The target eNB verifies the C-RNTI sent in the RRC
Connection Reconfiguration Complete message. When the UE is moving to the
target
cell from IHO state and the target cell is one of the IHO candidate cells,
then the above
messages are simplified since the UE context is already available at the
target cell.
[00179] Subsequently, path switch 1040 can be performed among the
source
eNB, the target eNB and the MME. Specifically, the target eNB 1006 sends a S
1AP:
PATH SWITCH message to MME to inform that the UE has changed cells. The MME
sends an UPDATE USER PLANE REQUEST message to the Serving Gateway. The
Serving Gateway switches the downlink data path to the target side. The
Serving
gateway sends one or more "end marker" packets on the old path to the source
eNB and
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then can release any U-plane/TNL resources towards the source eNB. Serving
Gateway
sends an UPDATE USER PLANE RESPONSE message to MME. The MME confirms
the SlAP: PATH SWITCH message with the SlAP: PATH SWITCH
ACKNOWLEDGE message. The target eNB starts making the scheduling decisions on
the new packets received for this point.
[00180] By sending X2AP: UE CONTEXT RELEASE in step 1041, the target
eNB 1006 informs success of HO to source eNB 1004. The target eNB 1006 sends
this
message after the SlAP: PATH SWITCH ACKNOWLEDGE message is received from
the MME. Now the target cell is the new serving cell of the UE 1002 and the
uplink/downlink data packets of the UE 1002 are routed through the new serving
cell
1006 to/from MME 1008.
[00181] Note that in the example of FIG. 10, UE reports the
measurements to the
serving cell. In some embodiments, the UE can report the measurements to one
of the
candidate cells and thus the HO decision is made at the candidate cell. In
some
implementations, the measurement report may be forwarded to the serving cell.
[00182] FIG. 12 is a schematic flow diagram 1200 illustrating an
example
handover procedure where the measurement report is received by one of the IHO
candidate cell. The handover procedure with IHO state shown in FIG. 12 is
substantially the same as the one of FIG. 11, except that the measurement
report is
received by the IHO candidate cell 1206 from the UE 1202; and hence the IHO to
HO
algorithm is performed at the candidate cell 1206 in step 1238h, rather than
at the
serving cell 1004 in step 1038h in FIG. 10.
[00183] As shown in FIGS. 10 and 12, the decision of moving to one of
the
candidate cells (i.e. a target cell) or staying with the serving cell when the
UE is IHO
state is made by the network (either the serving cell or on candidate cell).
In some other
embodiments, the UE can determine whether to perform HO when it is in IHO
state.
[00184] FIG. 13 is a schematic flow diagram 1300 illustrating an
example
handover procedure with IHO state with UE initiated HO. In the illustrated
example is
for scenario, the UE requests HO to a candidate cell, when the candidate cell
is the
current anchor cell. The steps 1331-138f are substantially the same as steps
1031-103f
in FIG. 10 described above and hence will be described further only to the
extent
necessary to illustrate the UE initiated HO case.
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[00185] After the IHO state is established, in step 1338g, after
measuring the
expected signal quality with respect to all the candidate cells, the UE 1302
may
evaluate a HO criterion and decide to indicate to the candidate cell 1306 that
HO is
preferred. Since the UE context is already available at the candidate cell, HO
procedure is simplified. The HO criterion may be partially controlled or
suggested by
the EPC/ serving eNB.
[00186] In step 1339a, the UE 1302 can send the RRC Connection
Reconfiguration Complete message to the target eNB 1306 indicating that the
handover
is preferred. The target eNB 1306 may respond by sending an RRC
Reconfiguration
response to the UE in step 1339b and further sends X2AP: UE HO Update to the
UE's
serving cell 1304 in step 1339c. This may trigger cancellation of the IHO by
the UE's
serving cell 1304.
[00187] In step 1340, the target eNB 1306 can send a PATH SWITCH
message
to MME 1308 to inform that the UE has changed cells. The MME sends an UPDATE
USER PLANE REQUEST message to the Serving Gateway. The Serving Gateway
switches the downlink data path to the target side. The Serving gateway sends
one or
more "end marker" packets on the old path to the source eNB and then can
release any
U-plane/TNL resources towards the source eNB. Serving Gateway sends an UPDATE
USER PLANE RESPONSE message to MME. The MME confirms the PATH
SWITCH message with the PATH SWITCH ACKNOWLEDGE message. The target
eNB starts making the scheduling decisions on the new packets received for
this point.
[00188] By sending UE CONTEXT RELEASE, the target eNB 1306 informs
success of HO to source eNB 1304. The target eNB 1306 sends this message after
the
PATH SWITCH ACKNOWLEDGE message is received from the MME in step 1340.
[00189] While several implementations have been provided in the present
disclosure, it should be understood that the disclosed systems and methods may
be
embodied in many other specific forms without departing from the scope of the
present
disclosure. The present examples are to be considered as illustrative and not
restrictive,
and the intention is not to be limited to the details given herein. For
example, the
various elements or components may be combined or integrated in another system
or
certain features may be omitted, or not implemented. Variations,
modifications, and
37
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enhancements to the described examples and implementations and other
implementations can be made based on what is disclosed.
[00190] Also, techniques, systems, subsystems and methods described and
illustrated in the various implementations as discrete or separate may be
combined or
integrated with other systems, modules, techniques, or methods without
departing from
the scope of the present disclosure. Other items shown or discussed as coupled
or
directly coupled or communicating with each other may be indirectly coupled or
communicating through some interface, device, or intermediate component,
whether
electrically, mechanically, or otherwise. Other examples of changes,
substitutions, and
alterations are ascertainable by one skilled in the art and could be made
without
departing from the spirit and scope disclosed herein.
[00191] While the above detailed description has shown, described, and
pointed
out the fundamental novel features of the disclosure as applied to various
implementations, it will be understood that various omissions and
substitutions and
changes in the form and details of the system illustrated may be made by those
skilled
in the art, without departing from the intent of the disclosure.
38
