Note: Descriptions are shown in the official language in which they were submitted.
CA 02614570 2007-12-17
Method and system for controlling radio communications network and radio
network controller
The invention relates to a method and system for controlling a radio communic-
ations network and a radio network controller. Particularly the invention
relates to
the handover procedure in a cellular system. The invention can be
advantageously
applied in broadband radio networks that offer fixed network services to their
users.
Below it will be described the prior art by first illustrating the operation
of a popular
second-generation cellular system and in particular the handover, or change of
active base stations serving a mobile station moving in the cellular network's
coverage area. Then it will be disclosed the characteristics of new, third-
generation
cellular systems and problems related to prior-art handover solutions.
Prior art; second-generation cellular systems
A terminal of a cellular radio system attempts to choose a base station so as
to
operate on said base station's coverage area, or cell. Conventionally, the
choice has
been based on the measurement of the strength of the received radio signal in
the
terminal and base station. For example, in GSM (Global System for Mobile tele-
communications) each base station transmits a signal on a so-called broadcast
control channel (BCCH) and the terminals measure the strengths of the received
BCCH signals and based on that, determine which cell is the most advantageous
one as regards the quality of the radio link. Base stations also transmit to
the
terminals information about the BCCH frequencies used in the neighbouring
cells
so that the terminals know what frequencies they have to listen to in order to
fmd
the BCCH transmissions of the neighbouring cells.
Fig. I shows a second-generation cellular system that comprises a mobile
switching
centre (MSC) belonging to the core network (CN) of the cellular system as well
as
base station controllers (BSC) and base stations (BS) belonging to the a radio
access
network (RAN), to which mobile stations (MS) are linked via radio interface.
Fig. 2
shows the coverage areas C21-C29 of base stations BS21-BS29 of a second-
generation cellular system.
In second-generation cellular systems, such as GSM, communication between base
stations BS and the core network CM occurs via base station controllers BSC.
Usually, one base station controller controls a large number of base stations
so that
when a terminal moves from the area of a cell to the area of another cell, the
base
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2
stations of both the old and the new cell are connected to the same base
station
controller. Thus the handover can be executed in the base station controller.
So, in
the conventional GSM system, for example, there occur fairly few handovers
between a base station of a first base station controller and a base station
of a
second base station controller. In such a case, the switching centre has to
release the
connection with the first base station controller and establish a new
connection with
the new base station controller. Such an event involves a lot of signaling
between
the base station controllers and the switching centre and as the distances
between
the base station controllers and the switching centre may be long there may
occur
disturbances in the connection during the handover.
Third-generation cellular systems
The prior-art handover arrangement is suitable for the so-called second-
generation
digital cellular radio systems such as GSM and its extension DCS1800 (Digital
Communications System at 1800 MHz), IS-54 (Interim Standard 54), and PDC
(Personal Digital Cellular). However, it has been suggested that in future
third-
generation digital cellular systems the service levels offered to the
terminals by the
cells may differ considerably from a cell to another. Proposals for third-
generation
systems include UMTS (Universal Mobile Telecommunications System) and
FPLMTS/IMT-2000 (Future Public Land Mobile Telecommunications System /
International Mobile Telecommunications at 2000 MHz). In these plans cells are
categorised according to their size and characteristics into pico-, nano-,
micro- and
macrocells, and an example of the service level is the bit rate. The bit rate
is the
highest in picocells and the lowest in macrocells. The cells may overlap
partially or
completely and there may be different terminals so that not all terminals
necessarily
are able to utilise all the service levels offered by the cells.
Fig. 3 shows a version of a future cellular radio system which is not entirely
new
compared with the known GSM system but which includes both known elements
and completely new elements. In current cellular radio systems the bottleneck
that
prevents more advanced services from being offered to the terminals comprises
the
radio access network RAN which includes the base stations and base station
controllers. The core network of a cellular radio system comprises mobile
services
switching centres (MSC), other network elements (in GSM, e.g. SGSN and GGSN,
i.e. Serving GPRS Support Node and Gateway GPRS Support node, where GPRS
stands for General Packet Radio Service) and the related transmission systems.
According e.g. to the GSM+ specifications developed from GSM the core network
can also provide new services.
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In Fig. 3, the core network of a cellular radio system 30 comprises a GSM+
core
network 31 which has three parallel radio access networks linked to it. Of
those,
networks 32 and 33 are UMTS radio access networks and network 34 is a GSM+
radio access network. The upper UMTS radio access network 32 is e.g. a
commercial radio access network, owned by a telecommunications operator
offering mobile services, which equally serves all subscribers of said
telecommunications operator. The lower UMTS radio access network 33 is e.g.
private and owned e.g. by a company in whose premises said radio access
network
operates. Typically the cells of the private radio access network 33 are nano-
and/or
picocells in which only terminals of the employees of said company can
operate.
All three radio access networks may have cells of different sizes offering
different
types of services. Additionally, cells of all three radio access networks 32,
33 and
34 may overlap either entirely or in part. The bit rate used at a given moment
of
time depends, among other things, on the radio path conditions,
characteristics of
the services used, regional overall capacity of the cellular system and the
capacity
needs of other users. The new types of radio access networks mentioned above
are
called generic radio access networks (GRAN). Such a network can co-operate
with
different types of fixed core networks CN and especially with the GPRS network
of
the GSM system. The generic radio access network (GRAN) can be defined as a
set
of base stations (BS) and radio network controllers (RNC) that are capable of
com-
municating with each other using signaling messages. Below, the generic radio
access network will be called in short a radio network GRAN.
The terminal 35 shown in Fig. 3 is preferably a so-called dual-mode terminal
that
can serve either as a second-generation GSM terminal or as a third-generation
UMTS terminal according to what kind of services are available at each
particular
location and what the user's communication needs are. It may also be a
multimode
terminal that can function as terminal of several different communications
systems
according to need and the services available. Radio access networks and
services
available to the user are specified in a subscriber identity module 36 (SIM)
connected to the terminal.
Fig. 4 shows in more detail a core network CN of a third-generation cellular
system,
comprising a switching centre MSC, and a radio network GRAN connected to the
core network. The radio network GRAN comprises radio network controllers RNC
and base stations BS connected to them. A given radio network controller RNC
and
the base stations connected to it are able to offer broadband services while a
second
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radio network controller and base stations connected to it may be able to
offer only
conventional narrowband services but possibly covering a larger area.
Fig. 5 shows coverage areas 51a-56a of base stations 51-56 in a third-
generation
cellular system. As can be seen from Fig. 5, a mobile station travelling only
a short
distance can choose from many base stations for the radio link.
New cellular systems can employ a so-called macrodiversity combining technique
related to CDMA systems. This means that on the downlink path a terminal
receives
user data from at least two base stations and correspondingly, the user data
transmitted by the terminal is received by at least two base stations. Then,
instead of
one, there are two or more active base stations, or a so-called active set.
Using
macrodiversity combining it is possible to achieve a better quality of data
com-
munications as momentary fade-outs and disturbances occurring on a given trans-
mission path can be compensated for by means of data transmitted via a second
transmission path.
For selecting an active set an active radio network controller determines, on
the
basis of the geographic location, for example, a candidate set of base
stations,
which is a set of the base stations that are used for measuring general signal
strength
information using e.g. a pilot signal. Below, this candidate set of base
stations will
be called a candidate set (CS) in short. In some systems, such as IS-41,
separate
candidate base stations are used.
Problems related to prior art
Let us consider the application of a prior-art arrangement to a proposed third-
generation digital cellular system. In third-generation systems, base station
handovers and radio network controller handovers are more frequent than in
second-generation systems. One of the reasons behind this is that the cell
sizes may
be remarkably small and that there may occur need to change the service type
e.g.
from narrowband to broadband during a call.
In accordance with the prior art a handover between radio network controllers
would be carried out in such a manner that the user data connection between
the
switching centre and the so-called old active radio network controller/base
station is
released and a new connection is established between the switching centre and
the
so-called new active radio network controller/base station. Then the switching
centre would have to release/set up many connections, which involves a lot of
signaling between the switching centre and the radio network controller.
Further-
.
CA 02614570 2007-12-17
more, there are very many small-sized cells in the area of one switching
centre, and in
broadband applications the amount of user data transmitted is great. This puts
very tight
requirements for capacity and speed on the switching centre hardware, which in
large
systems cannot be met at reasonable costs using current technology.
5
Secondly, known systems have a problem of how to transmit signaling and data
of the
core network CN and signaling of the radio network to a terminal moving in the
radio
network's area. CN signaling and data are specifically meant for the terminal
and routed
via radio network controllers. Radio network signaling may be intended either
for the
terminal or for the radio network itself so that it can arrange optimal use of
radio resources
in the network area. The problem is caused by the moving terminal and its
effect on the
flow of data in the radio network's area.
When using macrodiversity combining the prior art further has the problem that
after a
handover between radio network controllers the new radio network controller
does not
have knowledge of the base stations suitable for macrodiversity combining so
that
macrodiversity combining cannot be used before the new radio network
controller has
established a candidate set of its own. Therefore, transmission power has to
be increased
and only one transmission path can be used temporarily between the system and
the
terminal. This degrades the quality of communications and causes stability
problems
which must be corrected by constant adjustments.
General description of the invention
Handovers between active base stations serving a terminal can be categorised
as follows:
1. handover between base stations (base station sectors) (intra-RNC HO)
2. handover between radio network controllers inside a generic radio network
(inter-RNC
HO) and
3. handover between generic radio networks (inter-GRAN HO).
The present invention primarily relates to handovers between radio network
controllers
inside a generic radio network (item 2 above).
An object of an aspect of the present invention is to provide a radio network
control
arrangement eliminating above-mentioned disadvantages related to the prior-art
arrangements.
One idea of the invention is that a connection is assigned a radio network
controller
through which the user data are directed also when some other radio network
controller is
the active radio network controller. This radio network controller assigned to
a connection
is here called an anchor controller. If during a connection a
CA 02614570 2007-12-17
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base station connected to another radio network controller is chosen the
active base
station, the user data are directed such that they travel to the active radio
network
controller via the anchor controller.
The use of an anchor controller in accordance with the invention brings
consider-
able advantages compared to the prior art. First, the radio network topology
becomes simple and clear, and the network can be easily extended and re-
configured. Second, internal traffic events in the radio network are handled
within
the radio network controlled by the anchor function so that
- a handover between radio network controllers is fast so that it is easier to
meet the
requirements for a seamless and lossless handover and
- the load of the mobile switching centre MSC remains moderate.
A particularly significant advantage is that the operation of the radio
network can be
made optimal as regards the use of radio resources. Furthermore, when using an
anchor controller, data encryption can be performed in the anchor controller
so that
encryption keys need not be transmitted during a connection from a radio
network
controller to another.
Transmission routing from the anchor controller to the active radio network
controller can be performed by means of chaining so that all active radio
network
controllers used during a call remain transmission links for the duration of
the call.
Another alternative is to use optimum routing where radio network controllers
between the anchor controller and the active radio network controller are
bypassed.
Optimum radio network controller routing used in connection with the invention
also brings further advantages. First, the internal signaling load of the
radio network
remains moderate and signaling can be easily made fast enough. In addition,
the
radio network controller's processing requirements remain reasonable, which
makes
the solution practical.
A second idea of the invention is that in preparation for a handover a list is
compiled in a neighbouring radio network controller of those base stations
that
would constitute the candidate set should said neighbouring radio network
controller be made the active radio network controller. Then the active set AS
becomes in conjunction with the handover the new active set AS'. Said list is
here
called an external base station candidate set. When compiling external
candidate
sets it is advantageous to use a boundary base station list (BBSL) that can
help
determine whether a handover is likely. In addition, so-called intense
monitoring
can be used for an external base station set.
CA 02614570 2007-12-17
The use of an external base station candidate set brings e.g. the following
advantages. First, the transmission power change related to the handover is
not great
at the interface but the use of power is "smooth". This results in small total
power
consumption in the interface area and low interference-induced noise level. In
addition, the solution achieves a continuous state as regards the network so
that
handovers will not cause deviations from the normal operation and thus a
stability
problem.
The method according to the invention for controlling radio traffic between a
terminal and a communications system, which comprises radio network
controllers
and base stations to establish a communications connection between the system
and
the terminal connected to it and wherein a first radio network controller and
second
radio network controller serve as active radio network controllers during the
connection, is characterised in that when said second radio network controller
is
active, the connection is routed to said second radio network controller via
said first
radio network controller.
The communications system according to the invention, which comprises radio
net-
work controllers and base stations to establish a communications connection
between the system and the terminal connected to it and wherein a first radio
net-
work controller and second radio network controller serve as active radio
network
controllers during the connection, is characterised in that when said second
radio
network controller is active, the connection is routed to said second radio
network
controller via said first radio network controller.
A communications system radio network controller according to the invention is
characterised in that it comprises means for routing communications to another
radio network controller during a connection.
A second radio network controller according to the invention is characterised
in that
it comprises means for routing the traffic related to a connection between a
base
station and the second radio network controller.
Preferred embodiments of the invention are disclosed in the sub-claims.
"Active" base station here means a base station that has a user data
connection with
a terminal. "Active" radio network controller here means a radio network
controller
with which the active base station is in direct connection so that user data
can be
transmitted to the active base station.
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"Old" base station and radio network controller mean a base station or radio
network
controller that was active before the handover and "new" base station or radio
network controller means a base station or radio network controller which is
active
after the handover. It is also possible that several radio network controllers
are active
simultaneously.
"Handover" here refers to a handover between base stations, radio network
controllers
or radio networks. After the handover it is possible that also the old base
station/ radio
network controller remains active.
"User data" here means information usually transmitted on a so-called traffic
channel
between two cellular system users/terminals or between a cellular system
user/terminal and other terminal via a core network. It may be e.g. coded
voice data,
facsimile data, or picture or text files. "Signaling" refers to communications
related to
the management of the internal functions of the communications system.
Accordingly, in one aspect of the present invention there is provided a method
comprising:
routing communication to another radio network controller during a connection;
and
combining a macrodiversity spread code/macrodiversity signal components
independently or together with another radio network controller in a chain.
According to another aspect of the present invention there is provided a
method
comprising:
establishing communication by a first radio network controller via a second
radio network controller during a connection with a terminal, wherein said
communication is operative with a macrodiversity signal combination and
wherein
said communication_ involves a use of a spread code signal; and
completing the macrodiversity signal combination by combining macrodiversity
spread code signals inspired by said terminal at the first radio network
controller,
wherein the first radio network controller is configured to select between
completing
the macrodiversity signal combination independently and completing the
macrodiversity signal combination together with said second radio network
controller.
= CA 02614570 2012-12-13
8a
According to yet another aspect of the present invention there is provided a
radio
network controller comprising:
a processor configured to establish communication between said radio network
controller and a second radio network controller or a base station during a
connection
with a terminal, wherein said communication is operative with a macrodiversity
signal
combination and wherein said communication uses a spread code signal; and
a processor configured to combine macrodiversity spread code signals inspired
by said terminal by selecting between combining the macrodiversity spread code
signals at said radio network controller and combining the macrodiversity
spread code
signals together with said second radio network controller so that the
macrodiversity
signal combination is completed in said radio network controller.
Detailed description of the invention
The invention is described in more detail with reference to the preferred
embodiments
presented by way of example and to the accompanying drawing wherein
Fig. 1 shows a second-generation cellular system according to
the prior art,
Fig. 2 shows the coverage areas of base stations of a second-
generation
cellular system according to the prior art,
Fig. 3 shows a third-generation cellular system,
Fig. 4 shows the core network CN of a third-generation cellular
system
according to the prior art and the radio network GRAN in connection
with it,
Fig. 5 shows the coverage areas of base stations of a cellular system
according to the prior art,
Fig. 6 shows a flow diagram of the main steps of a method
according to the
invention for performing a handover between base stations, radio
network controllers and radio networks,
Fig. 7 shows a cellular system according to the invention and some
embodiments for arranging communications between radio network
controllers,
Fig. 8 shows an embodiment of the invention for arranging
communications
between radio network controllers of different radio networks by
means of the active protocol of the core network,
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Fig. 9 shows a technique according to the invention for performing the
routing
between radio network controllers by means of chaining,
Fig. 10 shows a technique according to the invention for performing the
routing
between radio network controllers optimally,
Fig. 11 shows a signaling flow chart of a backward handover in a cellular
system
according to the invention,
Fig. 12 shows a signaling flow chart of a forward handover in a cellular
system
according to the invention,
Fig. 13 shows functions of radio network controllers before a handover in
a
cellular system according to the invention,
Fig. 14 shows functions of radio network controllers after a handover in
a
cellular system according to the invention,
Fig. 15 shows a signaling diagram of a procedure according to the
invention for
adding a new neighbour base station to the active set during the
preparation for a handover,
Fig. 16 shows a signaling diagram of a procedure according to the
invention for
removing a neighbour base station from the active set during the
preparation for a handover, and
Fig. 17 shows a signaling flow chart of the execution of a handover in a
cellular
system according to the invention.
Figs. 1 to 5 were discussed above in connection with the description of the
prior art.
Below, a method according to the invention is described briefly with reference
to
Fig. 6. Then, referring to Fig. 7, a cellular system according to the
invention and
embodiments for transmitting signaling and user data between two radio network
controllers will be described. After that, referring to Fig. 8, it will be
disclosed a
handover between a radio network controller in a first radio network and a
radio
network controller in a second radio network.
Next, referring to Figs. 9 and 10, it will be disclosed a chained and an
optimised
embodiment for setting up routing between radio network controllers. Then,
referring to Figs. 11 and 12, two embodiments will be described for realising
optimised routing. After that, two embodiments will be disclosed for realising
macrodiversity combining in a radio network according to the invention.
Next, functions of radio network controllers will be described in conjunction
with a
handover according to the invention with reference to Figs. 13 and 14.
Finally, with
CA 02614570 2007-12-17
reference to Figs. 13 to 17, it will be described the steps related to a
handover in a
radio network employing macrodiversity combining and external candidate set.
The description will be followed by a list of abbreviations used in the
Figures and in
the description.
5 Main steps of a method according to the invention
Fig. 6 shows a flow diagram of a method according to the invention for a
handover
involving the active base station, active radio network controller and active
radio
network. First, a static configuration 600 of the system is performed
comprising the
steps below. In step 601, the connections between a switching centre MSC and
the
10 radio network controllers are detected, and in step 602 a GRAN-wide
routing table
for the radio network controllers is created. Then, the fixed connections in
the radio
network GRAN are established in step 603.
Then it is performed a dynamic configuration 610 of the radio network,
comprising
connection setup steps and connection steps as follows. First, an anchor
controller is
specified, step 611, after which a fixed radio network specific connection
between a
radio network controller RNC[i] and base stations BS[a(i)...k(i)] is
established, step
612. Then, radio connections are set up between radio network controllers
RNC[i]
and mobile station MS [a], and radio links are set up between base stations
BS[a(i)...c(i)] and mobile station MS[a], step 614. After that, possible
handovers
within the radio network controller are carried out in step 615.
If the mobile station receives a strong signal from a base station of an
external radio
network controller, step 620, a new RNC-to-RNC connection is added, step 621,
and the routing is updated and optimised, steps 622 and 623. After that, a
radio net-
work controller specific fixed connection is set up between the radio network
controller RNC[j) and base stations BS[a(j)...f(j)], step 624. Next, radio
connections
are set up between the radio network controller RNC[j] and mobile station
MS[a],
and radio links are established between base stations BS[a(j)...d(j)] and
mobile
station MS[a], step 625. In step 626, handover is executed between radio
network
controllers RNC[i] and RNC[j].
Both radio network controllers can be active as long as it is advantageous to
use
base stations of both radio network controllers. If all signal connections
between the
mobile station and base stations of a radio network controller are terminated,
the
radio network controller can be removed from the chain. A radio network
controller
can also be forced to be removed from the chain when base stations of another
radio
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11
network controller offers better signal connections. In Figure 6 the radio
connection
between the radio network controller RNC[i] and the mobile station is removed
in
step 627, and the radio network controller specific fixed connection between
the
radio network controller RNC[i] and base stations BS[a(i)...c(i)] is also
removed.
Fig. 6 also shows a handover (Inter-GRAN HO) between radio network controllers
belonging to two different radio networks GRAN A and GRAN B. In the case of
such a handover, the dynamic configuration is repeated in the new radio
network
and the same procedures as in the old radio network are carried out in the new
radio
network, steps 631 and 632.
Arranging communications between radio network controllers
Fig. 7 shows in closer detail a cellular system's core network CN which
comprises a
switching centre MSC, and a radio network GRAN connected to the core network.
The radio network GRAN comprises radio network controllers aRNC and bRNC
and base stations BS1 to BS4 connected to them. A terminal TE is connected by
radio to the system, via the base stations. It should be noted that Fig. 7
shows only a
fraction of the usual number of radio network controllers and base stations in
a
radio network.
Fig. 7 illustrates some embodiments of the handover according to the
invention.
When setting up a connection, one radio network controller is made an anchor
controller, which in the case depicted by Fig. 7 also serves as active radio
network
controller at the initial stage of the connection. The anchor controller is
here marked
aRNC. The Figure shows a situation wherein a radio network controller bRNC is
made the active controller during the connection.
In an embodiment of the invention the inter-RNC handover signaling messages,
like
other radio resource management messages within the radio access network as
well
as the user data, are transmitted encapsulated via the core network CN. Then
the
core network CN serves only as a message router and link between two radio
network controllers functioning as tunnelling points. The radio network
controllers
know how to create and decode these messages as well as how to realise the
functions requested in them. An advantage of this embodiment is that no
separate
physical transmission paths are needed between the radio network controllers.
In a second embodiment of the invention there exists a physical link between
two
radio network controllers, such as a cable or radio network connection, for
example.
Then the handover signaling can be transmitted direct from a radio network
CA 02614570 2007-12-17
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controller to another without participation of the core network CN. From the
prior
art it is known signaling between radio network controllers on protocol layers
L1-
L2, which, however, does not take part in the handover signaling proper.
A third embodiment of the invention relates to a situation wherein there is no
continuous connection between two radio network controllers. Then a solution
is
applicable where one base station is connected with two network controllers.
Thus a
base station can actively choose which of the two radio network controllers it
sends
control messages to. Then a base station can also serve as a mediator between
radio
network controllers so that messages from a radio network controller to
another
travel transparently via the base station in both directions. In this case,
identification
codes are used to distinguish between the messages and traffic proper between
the
base station and radio network controller.
Fig. 8 shows a situation wherein it is needed a handover between radio network
controllers of different radio networks. Then the anchor function will not
remain in
the old radio network but a radio network controller of the new radio network
is
made the anchor controller. In such a handover, the signaling between two
radio
networks GRAN can be carried out using an actively participating protocol,
such as
MAP of the GSM system, for instance. MAP will then communicate separately with
the anchor radio network controllers of both GRANs and will process the
signaling
handover messages related to the handover, like other messages between the
core
network CN and radio network GRAN.
Routing between radio network controllers
Let us examine a situation in which a terminal is moving in the coverage area
of a
radio network GRAN. The radio network anchor function then remains in the
radio
network controller specified for the connection, which means that all messages
from
the core network to the terminal are first taken to the anchor radio network
controller which directs them further via other radio network controllers to
the
target radio network controller which delivers them to the terminal via a base
station.
Use of the anchor function requires that the anchor-RNC knows how messages are
transmitted to other radio network controllers of the radio network GRAN. This
may be realised using a GRAN-wide address mechanism such that the anchor-RNC
knows the routing to other radio network controllers, in which case a so-
called fixed
routing table is used. Alternatively, the radio network controller is
connected to
CA 02614570 2007-12-17
13
only one other radio network controller so that messages are always sent
forward
until a radio network controller detects from the address attached to the
message
that the message is addressed to it.
When using such an arrangement, it has to be taken into account that the
anchor-
RNC can be any one of the radio network's radio network controllers. In a
small
radio network it is possible to realise an embodiment of the method that
employs
only one anchor-RNC, common to all terminals, so that no connection-specific
anchor-RNC is needed. Then the anchor-RNC functions as master and the other
network controllers function as slaves. If the radio network controller can be
selected, the anchor decision can be made either in the core network CN or in
the
radio network GRAN. Both the core network and the radio network must know
which radio network controllers serve as anchors in each of the connections
between the terminal TE and switching centre MSC.
Figs. 9 and 10 show two embodiments for realising the routing between radio
network controllers during different stages of connection. Fig. 9 shows an
arrange-
ment for routing the connection by means of chaining, and Fig. 10 shows an
arrangement for routing the connection in an optimised manner. In Figs. 9 and
10,
circles represent radio network controllers and lines represent connections
between
radio network controllers, realised e.g. in one of the above-described methods
according to the invention. A thick line represents active connection routing
between a terminal moving in a radio network and the core network CN. Location
of the terminal is only represented in the Figure by the radio network
controller.
Stages AO and BO in Figs. 9 and 10 represent an initial situation where the
terminal
communicates with the core network through radio network controllers 100 and
900. Stages Al and B1 represent a situation where the terminal is handed over
to
radio network controllers 111 and 911 while the anchor remains in the old
radio
network controller.
The advantage of the optimised embodiment can be seen in the situation where
the
connection of a terminal is further handed over to either an anchor radio
network
controller or some other radio network controller. In stages A2 and B2 the
next
handover is to radio network controller 122 and 922. In the chaining method, a
new
communications link is simply established between the old radio network
controller
921 and the new radio network controller 922. In the optimised solution, a new
communications link is established between the anchor-RNC 120 and the new
radio
CA 02614570 2007-12-17
14
network controller (122), and the link between the anchor-RNC 120 and the old
radio network controller 121 is removed.
Stages A3 and B3 illustrate a situation where the connection of the terminal
has
been handed over back to the anchor-RNC from the initial state of stages A2
and
B2. In the optimised case, the communication link between the old radio
network
controller 132 and the anchor-RNC 130 is removed. Since the new radio network
controller is the anchor-RNC, no new communication link needs to be
established.
In the traditional chaining method, a loop is made from the anchor-RNC 930
back
to the anchor-RNC 930 through all the radio network controllers that the
terminal
has used during the connection.
Optimised handover can be carried out in two ways depending on whether it is
possible to use the signaling connection with the old radio network controller
during
the handover. In a so-called backward handover the old radio network
controller is
used for signaling during the handover, and in a so-called forward handover
the old
radio network controller is not used for signaling during the handover. Figs.
11 and
12 show some ways of carrying out the above-mentioned backward and forward
bandovers. The description to follow also refers to handover situations
according to
Figs. 9 and 10. Abbreviations used in the Figures are listed in the
abbreviation list
that follows the description.
Backward handover
Fig. 11 shows by way of example the signaling flow diagram of an optimised
backward handover between radio network controllers. In a backward handover
the
old connection with the terminal is retained for the whole duration of the
handover
so that the radio path parameters of the new location can be transmitted to
the
terminal via the old radio network controller 111. In our example the terminal
transits from state Al shown in Fig. 10 to state A2, i.e. from the old radio
network
controller 1 1 1 to the new radio network controller 112.
An optimised backward handover according to Fig. 11 between radio network
controllers comprises the following steps:
A terminal TE requiring a handover between base stations sends a message to
the
old radio network controller oRNC. When the old radio network controller finds
that the new base station required by the terminal belongs to another radio
network
controller nRNC, it informs the anchor controller aRNC about the request for a
backward handover.
CA 02614570 2007-12-17
Having received the message from the old radio network controller oRNC the
anchor controller aRNC requests the new radio network controller nRNC to
reserve
fixed and radio connections according to the bearer information (BI) for the
terminal.
5 Having received from the new radio network controller an acknowledge for the
reservation of connections under the new radio network controller nRNC the
anchor
controller aRNC negotiates with the new radio network controller nRNC and they
set up the user data transmission link.
Next, the anchor controller aRNC requests the old radio network controller
oRNC
10 to send the radio path information of the radio path reserved under the
new radio
network controller nRNC to the terminal using the old, still operational
connection.
Having received from the old radio network controller oRNC an acknowledge for
the sending of information of the new radio path to the terminal the anchor-
RNC
requests the new radio network controller to start transmission to the
terminal.
15 Finally, the anchor controller aRNC requests the old radio network
controller oRNC
to release the resources allocated to the terminal. This can be a forced
release after
the new base station set offers better signal connections, or alternatively
the release
can be made if none of the base stations of the network controller serves the
mobile
station.
Forward handover
Fig. 12 shows by way of example the signaling flow diagram of an optimised
forward handover between radio network controllers. In a forward handover it
is
assumed that the old connection via the old radio network controller oRNC 111
is
no longer in use. In the example according to Fig. 12 a terminal transits from
state
Al shown in Fig. 10 to state A2, i.e. from the old radio network controller
oRNC
111 to the new radio network controller nRNC 112.
An optimised forward handover according to Fig. 12 between radio network
controllers comprises the following steps:
When the terminal and/or new base station nIIS find that the terminal needs a
handover and the radio network controller nRNC controlling the new base
station
has detected that the old base station belongs to another radio network
controller
oRNC, the new radio network controller nRNC sends a message indicating the
need
CA 02614570 2007-12-17
16
for a forward handover to the old base station oRNC either directly (as in
Fig. 12)
or via the anchor controller aRNC.
The old radio network controller oRNC sends a request-acknowledge to the new
radio network controller nRNC and informs the anchor controller about the need
for
a handover. Then the anchor controller aRNC and the new radio network
controller
nRNC negotiate and set up a dedicated user data transmission link.
Having received from the anchor controller aRNC an acknowledge to its handover
request the old radio network controller releases the fixed and radio
connections
allocated to the terminal. At latest when the new radio network controller has
the
user data connections from the anchor controller aRNC up and operational will
the
new radio network controller nRNC establish the necessary fixed and radio
connections between the base station and terminal.
Finally, the new radio network controller nRNC sends a message to the anchor
controller aRNC indicating that the handover is completed.
Use of macrodiversity combining in radio network according to invention
Used with a CDMA-type radio network, which facilitates the combining of
signals
from multiple base stations, or macrodiversity combining, the arrangement
according to the invention is characterised by some special features.
Macrodiversity
combining employs multiple simultaneous connections, first, between the
terminal
and base station sectors and, second, between the terminal and individual base
stations. On the uplink path the terminal uses one signal and one spread code
which
is received at several base stations. Alternatively, the terminal may use one
signal
with several spread codes received at several base stations. The final signal
is the
result of macrodiversity combination. In the downlink direction, several base
stations transmit one and the same signal spread using different spread codes
to a
terminal that performs the macrodiversity combining. The signal connections
that
provide sufficient signal strength at agreed power levels belong to the so-
called
active set.
If the active set includes base stations connected with different radio
network
controllers, the macrodiversity combining can be carried out separately for
each
radio network controller. Then the final signal combination is completed only
in the
anchor-RNC. In another embodiment the signals are separately routed to the
anchor-RNC where the macrodiversity combining proper is carried out. A
prerequisite for each diversity combining is rough timing information, e.g.
with the
CA 02614570 2007-12-17
17
accuracy of 256 chips, indicating the framework within which bit-level signal
combining can be performed.
Alternatively, macrodiversity combining can be carried out such that the base
stations handle the chip-level timing and make the soft bit decisions. These
bits,
represented by a more detailed representation defined by several bits, are
sent to the
radio network controller where the combining is carried out using the
diversity
teclutique.
In a preferred embodiment, packet transmission can be realised in such a
manner
that same packets are not transmitted via two different base stations. The
solution
may be such that it is decided on the moment of transmission of each packet
which
one of the radio paths is the more advantageous one at that moment. The
decision
may be based e.g. on a prediction on the quality of radio connections, quality
calculations or quality measurements. The advantage of macrodiversity
combining
is then that the better-quality radio transmission path branch is used at each
time.
Retransmissions caused by failed packet receptions can be further directed
e.g.
according to the following selection criteria for the radio transmission path
branch:
- retransmission uses the radio transmission path branch used in the previous
transmission,
- retransmission uses other than the branch used in the previous transmission
or
- retransmission uses the branch the quality of which is estimated the best.
This is to improve the probability of success through retransmission. An
advantage
of this embodiment is e.g. a reduced radio path load as the same data normally
are
not transmitted via two branches.
The active set can be limited such that it includes only the base station
connections
the base stations of which are connected to the same radio network controller.
However, this embodiment has the disadvantage that as the terminal crosses the
boundary between two radio network controllers, the macrodiversity has to be
abandoned momentarily.
In an embodiment in which radio network controllers are connected only through
the core network CN, macrodiversity combining is advantageously realised in
the
nearest radio network controller lest it be necessary to transmit unconnected
signals
via the CN.
If the radio network controllers are directly connected, macrodiversity
combining
according to the invention has two embodiments. The first embodiment covers
the
CA 02614570 2007-12-17
18
cases wherein macrodiversity combining is carried out in successive radio
network
controllers and finally in the anchor-RNC. The second embodiment covers the
cases
wherein all signals are separately gathered in the anchor-RNC and
macrodiversity
combining is carried out there. This embodiment is advantageous in a solution
in
which the anchor-RNC is the same for all connections in the radio network GRAN
and the other radio network controllers are just routers.
Mechanisms according to the present invention easily lead to different radio
net-
work topologies. However, in the preferred embodiment the radio network is not
made topologically complex but it is allowed to utilise as efficiently as
possible the
core network to transmit its own messages, either passively or actively. As
regards
the use of radio network resources, it is advantageous to retain a sufficient
functional distribution because it is preferable that the radio link layers
are located
as close as possible to the base stations the signals of which are best
detected by the
terminal.
Functions according to invention in radio network controller
According to the invention, a radio network controller advantageously has the
following new characteristics.
- means for realising anchor functions,
- means for storing information on routing to other controllers in the radio
network,
- means for realising data routing to the core network CN,
- means for realising data routing to another radio network controller,
- means for communicating with another controller, and
- means for carrying out macrodiversity combining by choosing the momentarily
strongest signal connection or by combining the signals of different
connections
Fig. 13 shows radio network controller functions prior to a handover and Fig.
14
shows radio network controller functions immediately after a handover. In the
situation represented by Figs. 13 and 14, the radio network controller RNCO is
the
anchor controller and the radio network controller RNC I is active before the
hand-
over and RNC2 is active after the handover. In Figs. 13 and 14, a thick line
in the
fixed network represents transmission of user data and a thin line a signaling
connection. A thin line between base stations and a terminal indicates
measurement
operations and a serrated line, or flash symbol, indicates transmission of
user data.
In addition to the anchor RNC functions (ARNCF) the anchor controller RNCO
realises the user data relay (UDR) to the active radio network controller. In
the
CA 02614570 2007-12-17
19
active radio network controller RNC1 there is a macrodiversity controller
(MDC).
The active RNC1 also includes a macrodiversity combination point (MDCP) for
the
uplink direction. The corresponding combination point for the downlink
direction is
located in the terminal TE. The active radio network controller RNC I also
contains
a set controller (SC). For each terminal there is in the active radio network
controller RNC1 a candidate set (CS) and, as a subset of the CS, an active set
(AS).
One or more radio network controllers (RNC2) that control base stations in the
immediate vicinity (handover likely) of the base station set of the active
radio
network controller RNC1 may control an external candidate set (ECS). The
external
candidate set ECS may include one or more base stations controlled by the
radio
network controller RNC2. The radio network controller RNC2 includes an
external
candidate set controller (ECSC) to control the external candidate set.
The anchor controller RNCO or the active RNC1 (location selectable) includes a
so-
called set control function (SCF) that monitors the need for handover between
radio
network controllers, prepares the necessary external candidate set ECS and
executes
the handover.
An anchor controller can be established in two alternative manners:
* The radio network controller RNC through which the connection was originally
set up is chosen the anchor controller. Then, in principle, all radio network
controllers may function as the anchor. In practice, this alternative calls
for logical
RNC-to-RNC connection facilities between all radio network controllers RNC in
the radio network GRAN.
* Within a radio network GRAN, all anchors are always established in one and
the
same radio network controller, so-called master-RNC, which at the same time is
probably the only radio network controller connected with the core network CN.
The master-RNC includes the anchor-RNC functions (ARNCF). The master-RNC
facilitates a star-like topology for the connections between radio network
controllers.
The examples illustrated by Figs. 13 and 14 are based on a situation where the
anchor has been selected and one active RNC is connected with it which is not
an
anchor-RNC.
The anchor controller RNCO shall have a logical communications connection with
both the radio network controller RNC1 and the RNC2. The physical realisation
of
the logical RNC-to-RNC communications connection between the radio network
CA 02614570 2007-12-17
controllers RNC1 and RNC2 may be a direct RNC1-RNC2' link or, optionally, the
communications between the radio network controllers RNC1 and RNC2 can be
realised by relaying via the anchor controller RNCO.
In Fig. 13 the set control function SCF is located in the anchor controller
RNCO so
5 that a logical connection between radio network controllers RNC1 and RNC2
is not
needed. Other logical RNC-to-RNC connections can be physically realised in the
three manners described above (via CN, using RNC-to-RNC cable/radio link, or
via
base stations). A logical RNC-to-RNC communications connection is in principle
independent of the physical implementation. E.g. in optimised routing, where
the
10 logical communications connection exists between the anchor controller and
the
active radio network controller, the physical connection can even be relayed
via
previous active radio network controllers if necessary.
The anchor-RNF function ARNCF comprises tasks as follows:
- Setting up logical RNC-to-RNC connections between the anchor controller and
the
15 active radio network controller,
- User data relay UDR, i.e. directing the downlink data to radio network
controller
RNC2 and receiving the uplink data from macrodiversity combination point
MDCP-up/RNC2 of the radio network controller RNC2, and
- Setting up, controlling and releasing a logical connection between core
network
20 CN and radio network.
The user data relay UDR comprises tasks as follows:
- Relaying traffic between a terminal TE and core network CN instead of base
stations controlled by own radio network controller to another radio network
controller according to instructions from the anchor-RNC function ARNCF.
The user data relay controls the user data stream directly or controls the
operation of
the logical link control LLC. The logical link control LLC controls the radio
connections between the radio network controller and a terminal. The tasks of
the
logical link control LLC include error detection, error correction and
retransmission
in error situations. In addition, the logical link control LLC comprises
control for
the necessary buffers and acknowledge windows. The logical link control unit
LLC
has a generalised meaning; it may terminate the corresponding LLC protocol of
the
terminal, but it can alternatively serve as an LLC relay. In an LLC relay
function
the locical link control unit may terminate the messages of the radio network
in a
normal manner, but it relays the core network messages (core network data and
signaling) further to a defined node of the core network CN. An example of
this is
CA 02614570 2007-12-17
21
relaying messages between a terminal and core network of the General Packet
Radio Service GPRS. In this case the Serving GPRS Support Node (SGSN) would
serve as a terminating unit.
The logical link control LLC can be located such that it is always in the
anchor
controller. Then there is no need to transmit big LLC buffers within the radio
network in connection with a handover of an active radio network controller.
Alternatively, the logical link control may be located always in the active
radio
network controller, in which case the LLC buffers have to be transferred in
conjunction with a handover between radio network controllers. Possible
transfer of
the logical link control from a radio network controller to another is carried
out
under the control of the user data relay UDR in the anchor controller. The
location
of the logical link control in the active radio network controller is shown by
dashed
lines in Figs. 13 and 14.
The user data relay UDR carries out data relaying also in cases where the role
of the
logical link control is small, e.g. in the so-called minimum mode, or when the
logical link control has no role at all. Possible locations of the logical
link control
are also determined in part by the macrodiversity combining used.
Radio network controller managers create or remove, depending on the internal
implementation method, terminal-specific functions (e.g. ECSC, MDC and MDCP)
in the radio network controller and direct the signaling messages to the
correct
function in the radio network controller.
The macrodiversity combination point MDCP and macrodiversity controller MDC
represent ordinary functions related to the macrodiversity implementation
used. The
user data relay UDR is related to inter-RNC communications within the radio
network. The anchor-RNC function (ARNCF), which is active only during a
handover, belongs to the disclosed anchor-based handover arrangement according
to the invention. The set control function SCF, set controller SC and the
external
candidate set controller ECSC belong to the disclosed arrangement according to
the
invention that uses an external candidate set.
In a macrodiversity implementation which comprises on the uplink transmission
path only one transmission in the terminal, the macrodiversity combination
point
MDCP/up is located in the radio network controller. On the downlink
transmission
path with multiple transmissions (each base station having its own) the
macrodiversity combination point MDCP/down is located in the terminal.
CA 02614570 2007-12-17
22
The macrodiversity combination point MDCP and macrodiversity controller MDC
perform the functions that belong to macrodiversity combining according to the
macrodiversity implementation used. The functions add and remove base stations
from the internal candidate set and from the active set.
Furthermore, the macrodiversity controller MDC according to the invention
shall be
capable of
- indicating to the set controller SC the completed additions or removals of
base
stations to and from the active set of base stations,
- adding to/removing from the candidate set visible to the terminal the base
stations
added to/removed from the external candidate set,
- producing for the set controller the necessary radio path quality reports
comparable with the external candidate set controller ECSC, and
- indicating on request of the set controller SC to the terminal that an
entirely new
active set (former external candidate set) has been taken into use.
The set controller SC carries out tasks as follows:
- Checks using the boundary base station list BBSL whether a base station
added
to/removed from the active set belongs to the so-called boundary base stations
of a
neighbour radio network controller.
- Requests the set control function SCF to realise a creation/removal of an
external
candidate set in a neighbour radio network controller and to provide the
necessary
information such as the identity of the base station that triggered the
request, the
identity of the terminal, etc.
- When the external candidate set changes, transmits via the macrodiversity
controller MDC to the terminal the information needed by the terminal in the
external candidate set measurement.
- Provided that intense monitoring is used, produces and transmits information
to
the set control function SCF that is comparable with intense monitoring
controlled
by the external candidate set controller ECSC.
- Conveys to the macrodiversity controller MDC the radiotechnical parameters
of
the external base station set that is about to become active. The
macrodiversitv
controller MDC sends them further to the terminal like the parameters it
produced
itself.
- On request of the set control function SCF, terminates the operation of a
terminal
in its own radio network controller RNC1 or, alternatively, converts the
active set of
its own radio network controller to the external candidate set of the new
active radio
network controller RNC2.
CA 02614570 2007-12-17
23
The set control function SCF comprises tasks as follows:
- On request of the set controller SC, allows/forbids, possibly negotiating
with, say,
the target radio network controller, the creation of an external candidate set
ECS.
- Requests that a neighbour radio network controller create an external
candidate set
for a certain terminal, transmitting the information (say, base station
identity)
produced by the active radio network controller to the neighbour radio network
controller RNC2.
- When creating or modifying an external base station set transmits to the set
controller SC the data needed by the terminal in the measurement.
- Receives the connection quality reports of the set controller SC and
external
candidate set controller and makes a handover decision based on them.
- Decides on a handover to a neighbour radio network controller or on intense
monitoring.
- If intense monitoring is possible, requests the external candidate set
controller
ECSC to start intense monitoring. Requests from the macrodiversity controller
the
data required for intense monitoring and sends them to the external candidate
set
controller. Requests the macrodiversity controller to produce data comparable
with
the intense monitoring data produced by the external candidate set controller
ECSC
if said data differ from normal reference data. Receives the intense
monitoring
results from the external candidate set controller ECSC and compares them with
the
quality data received from the set controller SC.
- Indicates to the external candidate set controller ECSC that the handover
has been
completed and receives the radiotechnical parameters of the active external
base
station set of the external candidate set controller ECSC and sends them
further to
the set controller SC.
- Indicates to the anchor-RNC function ARNCF that the handover has been
completed between the two radio network controllers.
- When the base station set of the radio network controller RNC2 has become
the
active set, requests the set controller SC/RNC I of the old radio network
controller
RNC I to terminate operation and to remove the rest of the functions related
to the
terminal from the radio network controller RNC1 or, alternatively, convert the
radio
network controller RNC1 into an external candidate set controller for the
radio net-
work controller RNC2.
The external candidate set controller ECSC has tasks as follows:
- When starting for a given terminal it creates for the base station BS/RNC I,
which
triggered the preparation, a suitable external candidate set ECS based e.g. on
geo-
graphic and/or propagation technical location data and, when the external
candidate
CA 02614570 2007-12-17
24
set ECS exists, updates it constantly according to the base stations added
to/removed from the active set.
- Conveys to the set control function SCF the data required for the external
candidate set ECS measurement at the terminal.
- In intense monitoring, on the basis of the terminal-specific information
produced
by the set control function, sets up in the radio network controller RNC2 the
functions that are needed in the uplink quality sampling and reports the
results of
the sampling to the set control function SCF.
- As handover starts, sends the radiotechnical parameters of the external base
station
set becoming active to the set control function SCF. Starts in the radio
network
controller RNC2 the uplink macrodiversity controller MDC/RNC2 and the macro-
diversity combination point MDCP-up/RNC2 needed in the active radio network
controller, using the external candidate set as the initial state for the new
active set.
At the same time establishes the fixed and radio connections needed by the
active
set.
Execution of handover between radio network controllers
Let us consider the execution of a handover between radio network controllers
in
the exemplary situation depicted by Figs. 13 and 14. Two phases can be
discerned
in the handover between radio network controllers:
- inter-RNC handover preparation phase and
- inter-RNC handover execution phase.
Handover preparation phase
The following example of the preparation phase assumes that the set control
function SCF is in the anchor controller RNCO, so a connection between radio
network controllers RNC1 and RNC2 is not needed. The preparation phase is the
same in the uplink and downlink directions.
In the situation depicted in Figs. 13 and 14 the handover preparation
comprises the
following steps:
First, the radio network controller RNC I adds a base station to the active
set AS.
The signaling flow diagram in Fig. 15 shows one method of adding a base
station to
the active set. Then the set controller SC/RNC1 detects on the basis of the
boundary
base station list BBSL that a base station has been added to the active set
which is
located in the immediate vicinity of the base stations controlled by a
neighbour
radio network controller RNC2. The set controller SC/RNC1 sends a message
about
CA 02614570 2007-12-17
this to the set control function SCF. If this is the first such base station,
the set
control function SCF requests that an external candidate set controller ECSC
be
started in the neighbour radio network controller RNC2.
Next the radio network controller RNC2 starts the external candidate set
controller
5 ECSC for the terminal. Based e.g. on the geographic location data the
external
candidate set controller ECSC determines a suitable external candidate set ECS
for
the terminal and sends information about the base stations belonging to the
external
candidate set to the radio network controller RNC I via the set control
function SCF.
Alternatively, if there is a direct signaling connection between the radio
network
10 controllers RNC1 and RNC2. this can be done direct to the set controller
SC/RNC I.
The set controller SC/RNC1 adds the external candidate set ECS to the set of
base
stations to be measured at the terminal. This is done controlled by the
macrodiversity controller MDC/RNC I as in the case of an internal candidate
set.
After that the terminal uses e.g. pilot signals to perform usual measurements
for the
15 base station set that includes the candidate set CS and the external
candidate set
ECS. In this example it is assumed that the terminal makes a decision or
proposition
for transferring base stations between the active set and the candidate set,
and the
transfer can be carried out by the macrodiversity combination point MDCP and
macrodiversity controller MDC. The set controller SC/RNC1 is informed about
the
20 transfer. When the macrodiversity controller MDC/RNC1 detects the request
of
transferring a base station belonging to an external candidate set ECS to the
active
set, the request is transmitted to the set controller SC/RNC1 to be further
considered
or to be executed.
If the only boundary base station toward the radio network controller RNC2 is
25 removed from the active set, the set controller SC/RNC1, having detected
the
situation, removes the external candidate set controller ECSC from the radio
network controller RNC2 by sending a removal request to the set control
function
SCF/RNCO, Fig. 16. The set control function SCF/RNC then conveys the request
to
the radio network controller RNC2 which removes the external candidate set
controller ECSC. The procedure then starts over again. Otherwise the set
controller
(SC/RNC1) requests for external candidate set update in the radio network
controller RNC2.
If the set control function SCF finds that a base station/base stations
controlled by
the radio network controller RNC2 give(s) a better signal, the set control
function
SCF may alternatively order a handover between radio network controllers RNC I
CA 02614570 2007-12-17
26
and RNC2 or only start optional intense monitoring in the radio network
controller
RNC2.
In intense monitoring, a preprocess MDCP' like the macrodiversity combination
point is set up in the radio network controller RNC2 for the uplink
transmission
path, and said preprocess once in a while receives data from the tenninal but
does
not itself transmit data further but only the connection quality report to the
set
control function SCF.
Having found on the basis of measurements or intense monitoring that a
handover is
necessary to base station(s) controlled by the radio network controller RNC2,
the
set control function SCF starts the execution phase of a handover between
radio
network controller RNC1 and radio network controller RNC2.
Handover execution phase
An inter-RNC handover can be carried out as follows:
- The active set is completely transferred to the new radio network controller
RNC2.
Thus only one radio network controller is active at a time. In the handover
execution phase the external candidate set ECS2 of the radio network
controller
RNC2 completely becomes the terminal's active set AS, and the active set AS1
and
candidate set CS1 of the radio network controller RNC1 are removed.
Optionally,
the active set AS of the radio network controller RNC1 may remain as candidate
set
ECS I. This arrangement avoids the problem of RNC synchronisation found in
hierarchic combining.
- In hierarchic combining, each radio network controller has an active set of
its
own. All active radio network controllers perform their own combining for the
data
in the uplink direction. Final uplink combining can be carried out in radio
network
controller RNCO. Then it is not necessary to establish a macrodiversity
controller
proper MDC/RNCO in the radio network controller RNCO or functions equivalent
to
a macrodiversity combination point MDCP-up/RNCO, if the combination points of
the active radio network controllers are able to preprocess the final result
for fixed
transmission in such a manner that final combining is easy to perform in the
radio
network controller RNCO. Alternatively, one of the active radio network
controllers
may serve as a so-called combination anchor, combining the user data of the
other
active radio network controllers prior to the transmission to the radio
network
controller RNCO. The user data relay UDR/RNCO has to duplicate the downlink
user data for the downlink connection combined in the terminal. Additionally,
the
CA 02614570 2007-12-17
27
base stations of the active sets of the different radio network controllers
must be
synchronised as required by the CDMA method used. Hierarchic combining may
comprise several hierarchy levels.
- A combination of the alternatives described above is used e.g. in such a
manner
that the downlink direction employs complete transfer of active set and the
uplink
direction employs hierarchic combining. Then in the downlink direction user
data
are transmitted via the previous active set until measurements show that the
new
base station set is better. Then the downlink data will be transmitted via the
new set.
By means of this solution, the advantages of hierarchic combining are retained
in
the uplink direction but data duplicating is avoided in the downlink
direction.
Following example of the execution phase of an inter-RNC handover is based on
the complete transfer of the active set both in the uplink and in the downlink
directions (alternative 1). The execution phase example assumes that the set
control
function SCF is located in the anchor controller RNCO so that no logical RNC-
to-
RNC connection is needed between the radio network controllers RNC1 and RNC2.
The execution phase example is based on the use of macrodiversity in a generic
CDMA system. The example is illustrated by the message flow diagram in Fig.
17.
In the example discussed here the handover execution comprises the following
steps
after the set control function (SCF) has made the handover decision.
First, the anchor function ARNCF of the anchor controller RNCO sets up a
logical
RNC-to-RNC connection between the anchor controller RNCO and the new active
radio network controller RNC2. Then the set control function SCF informs the
radio
network controller RNC2 about the execution of the handover. The external
candidate set controller ECSC sends to the set control function SCF or,
alternative-
ly, direct to the old set controller SC/RNC1 the radiotechnical parameters of
the
active-to-be base station set to be further transmitted to the terminal.
Internal
operation of the radio network controller RNC2 is mostly the same as in con-
junction with the set-up of a normal call with the difference that the
external candi-
date set is immediately made the final active set. Instead of an external
candidate
set, a set controller SC/RNC2, macrodiversity controller MDC/RNC2 and macro-
diversity combination point MDCP/RNC2 are established for the uplink
direction.
Controlled by the radio network controller RNC2 it is reserved or created
terminal-
specific fixed bearers needed for user data transmission between the radio
network
controllers and the base stations in the active set as well as radio bearers
between
base stations and the terminal in manners used in the radio network unless
such
CA 02614570 2007-12-17
28
connections have already been completely created in intense monitoring of the
preparation phase.
On request of the set control function SCF the user data relay UDR in the
anchor-
RNC function ARNCF modifies its operation as follows. The user data relay UDR
prepares to receive the uplink user data from the macrodiversity combination
point
MDCP-up/RNC2 of the radio network controller RNC2. The user data relay UDR
directs the downlink user data also to the radio network controller RNC2.
Next, the set control function SCF/RNC2 sends to the set controller SC/RNC1 of
the radio network controller RNC I the parameters (such as the time reference
and
the scrambling and/or spreading code used) of the pilot signals of the base
stations
in the active set of the radio network controller RNC2. The set controller
SC/RNC1
in the radio network controller RNC I sends to the terminal the parameters of
the
new active set.
Then the macrodiversity combination point MDCP/RNC2 in the radio network
controller RNC2 starts transmission with the new active set AS/RNC2. This is
ac-
knowledged to the anchor-RNC function ARNCF via the set control function SCF.
Finally, the anchor function ARNCF may request the radio network controller
RNC I to remove the terminal's set controller SC/RNC1, macrodiversity
controller
MDC/RNC1 and macrodiversity combination point MDCP/RNC1 as well as to
release the terminal-specific fixed bearers between the radio network
controllers and
base stations and possible remaining radio path reservations. Alternatively,
the
anchor controller may request the radio network controller RNC1 to turn the
active
set of the radio network controller RNC I into an external candidate set ECS.
This
having been acknowledged, the inter-RNC handover is completed.
In the examples discussed above it is assumed that the frequency of the
external
candidate set ECS complies with re-use I, typical of a CDMA system, so that
the
external candidate set has the same frequency as the candidate set proper. It
is
however possible to establish an external candidate set at another frequency.
Then,
the active set AS of only one candidate set can be in use. Even if
macrodiversity
combining were not an advantageous solution between different frequencies,
this
embodiment still facilitates the change from candidate set AS to new candidate
set
AS' in accordance with the principles set forth above.
=
CA 02614570 2007-12-17
29
Applications of invention
The present invention can be used in connection with a great number of
applications. These include e.g. database search seivices, data downloading,
video
conferencing, "on demand" data purchases from a communications network, use of
world wide web services in the Internet including web browsing etc.
The embodiments discussed above are naturally exemplaiy and do not limit the
invention. For example, the terminal may comprise a mobile station, portable
terminal or a fixed terminal, such as the terminal of a cordless subscriber
connection.
Particularly it should be noted that the creation of an external candidate set
for an
inter-RNC handover can be carried out independently of whether data communic-
ations will be routed to the new active base station via another radio network
controller, such as an anchor controller.
The steps of the above-described method according to the invention can also be
carried out in an order other than that given above and some steps may be
skipped
as unnecessary.
Above it was discussed embodiments wherein the radio network employs the
CDMA system. However, it should be noted that the present invention is in no
way
limited to the CDMA system but it can be utilised in other systems as well,
such as
the TDMA system. for example.
CA 02614570 2007-12-17
List of abbreviations used in Figures and description
CN Core Network
GRAN Generic Radio Access Network
TDMA Time Division Multiple Access
5 CDMA Code Division Multiple Access
TE Terminal Equipment
BS Base Station
nBS new Base Station
oBS old Base Station
10 BSC Base Station Controller
RNC Radio Network Controller
raNC new Radio Network Controller
oRNC old Radio Network Controller
aRNC anchor Radio Network Controller
15 aRNCF anchor Radio Network Controller Function
bRNC active Radio Network Controller which is not anchor RNC
UDR User Data Relay
CS Candidate Set
AS Active Set
20 ECS External Candidate Set
ECSC External Candidate Set Controller
MDC MacroDiversity Controller
SC Set Controller
SCF Set Control Function
25 BBSL Boundary Base Station List
MDCP MacroDiversity Combination Point
RI Radiopath Information
BI Bearer Information
ID IDentity
30 HO HandOver
ack acknowledge
up uplink
down downlink
req request
resp response
