Note: Descriptions are shown in the official language in which they were submitted.
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A METHOD FOR ~Y.~ ;~ REGISTRATION AND CELL RESELI~:CTION
BACKGROUND
Applicants' invention relates to electrical telec~.,l""ullication, and more
5 particularly to wireless commllnic~ion systems, such as cellular and satellite radio
systems, for various modes of operation (analog, digital, dual mode, etc.), and access
techniques such as frequency division multiple access (FDMA), time divisional
multiple access (TDMA), code divisional multiple access (CDMA), hybrid
FDMA/TDMA/CDMA, for example.
In North America, digital co... ~ tion and multiple access techniques such
as TDMA are currently provided by a digital cellular radiotelephone system called the
digital advanced mobile phone service (D-AMPS), some of the characteristics of
which are specified in the interim standard TIA/EIA/IS-54-B, "Dual-Mode Mobile
Station-Base Station C~ )alibility Standard", published by the Telecol.. "ir~tions
Industry Association and Electronic Industries Association (TIA/EIA), which is
expressly incorporated herein by reference. Because of a large existing consumerbase of equipment opeldli-lg only in the analog domain with frequency-division
multiple access (FDMA), TIA/EIA/IS-54-B is a dual-mode (analog and digital)
standard, providing for analog compatibility together with digital commllnir~tion
capability. For example, the TIA/EIA/IS-54-B standard provides for both FDMA
analog voice channels (AVC) and TDMA digital traffic channels (DTC). The AVCs
and DTCs are impl~ment~od by frequency mo~ ting radio carrier signals, which have
frequencies near 800 megahertz (MHz) such that each radio channel has a spectralwidth of 30 kilohertz (KHz).
In a TDMA cellular radiotelephone system, each radio channel is divided into
a series of time slots, each of which contains a burst of information from a data
~ source, e.g., a digitally encoded portion of a voice conversation. The time slots are
grouped into successive TDMA frames having a predetermined duration. The number
~ of time slots in each TDMA frame is related to the number of different users that can
simultaneously share the radio channel. If each slot in a TDMA frame is assigned to
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a dirr~re~l user, the duration of a TDMA frame is the minimllrn amount of time
between successive time slots ~igned to the same user.
The successive time slots ~ign~d to the same user, which are usually not
consecutive time slots on the radio carrier, coll~.LiLuLe the user's digital traffic channel,
S which may be considered a logical channel ~ign~-l to the user. As described inmore detail below, digital control channels (DCCs) can also be provided for
commllnic~ting conkol signals, and such a DCC is a logical channel formed by a
succession of usually non-consecutive time slots on the radio carrier.
In only one of many possible embodiments of a TDMA system as described
10 above, the TIA/EIA/IS-54-B standard provided that each TDMA frame consists of six
consecutive time slots and has a duration of 40 milli~econds (msec). Thus, each radio
channel can carry from three to six DTCs (e.g., three to six telephone conversations),
depending on the source rates of the speech coder/decoders (codecs) used to digitally
encode the conversations. Such speech codecs can operate at either full-rate or half-
15 rate. A full-rate DTC requires twice as many time slots in a given time period as a
half-rate DTC, and in TIA/EIA/IS-54-B, each full-rate DTC uses two slots of eachTDMA frame, i.e., the first and fourth, second and fifth, or third and sixth of a
TDMA frame's six slots. Each half-rate DTC uses one time slot of each TDMA
frame. During each DTC time slot, 324 bits are tr,.n~mitfed7 of which the major
20 portion, 260 bits, are allocated for the speech output of the codec, including bits used
for error correction coding of the speech output, and the rem~ining bits are used for
guard times and overhead si~n,.lling for purposes such as synchronization.
It can be seen that the TDMA cellular system operates in a buffer-and-burst,
or discontinuous-tr~n~mi~ion, mode: each mobile station transmits (and receives)25 only during its ,.ccign~od time slots. At full rate, for example, a mobile station might
transmit during slot 1, receive during slot 2, idle during slot 3, transmit during slot 4,
receive during slot 5, and idle during slot 6, and then repeat the cycle during
s~-ccee-1ing TDMA frames. Therefore, the mobile station, which may be battery-
powered, can be switched off, or sleep, to save power during the time slots when it is
30 neither tr,.n~mitting nor receiving.
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In addition to voice or traffic channels, cellular radio comml-nic~tion systems
also provide paging/access, or control, channels for carrying call-setup messages
between base stations and mobile stations. According to TIA/EIA/IS-54-B, for
example, there are twenty-one t~ te-1 analog control channels (ACCs), which have5 predetermined fixed frequencies for transmission and reception located near 800 MHz.
Since these ACCs are always found at the same frequencies, they can be readily
located and monitored by the mobile stations.
For example, when in an idle state (i.e., switched on but not making or
receiving a call), a mobile station in a TIA/EIA/IS-54-B system tunes to and then
10 regularly monitors the strongest control channel (generally, the control channel of the
cell in which the mobile station is located at that moment) and may receive or initiate
a call through the corresponding base station. When moving between cells while in
the idle state, the mobile station will eventually "lose" radio connection on the control
channel of the "old" cell and tune to the control channel of the "new" cell. The15 initial tuning and subsequent re-tuning to control channels are both accomplished
automatically by sc~nning all the available control channels at their known frequencies
to find the "best" control channel. When a control channel with good reception
quality is found, the mobile station remains tuned to this channel until the quality
deteriorates again. In this way, mobile stations stay "in touch" with the system.
While in the idle state, a mobile station must monitor the control channel for
paging messages addressed to it. For example, when an ordinary telephone (land-
line) subscriber calls a mobile subscriber, the call is directed from the public switched
telephone network (PSTN) to a mobile switching center (MSC) that analyzes the
dialed number. If the dialed number is v,.licl,.t~?d, the MSC requests some or all of a
25 number of radio base stations to page the called mobile station by tr~n~mitting over
their respective control channels paging messages that contain the mobile identific~tion
number (MIN) of the called mobile station. Each idle mobile station receiving a
paging message cOlllpal~s the received MIN with its own stored MIN. The mobile
~ station with the m~trhing stored MIN transmits a page response over a control
channel (typically the same control channel on which the mobile station received the
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corresponding paging message) to the base station, which forwards the page response
to the MSC.
Upon receiving the page response, the MSC selects an AVC or a DTC
allocated to the base station that received the page response, switches on a
5 corresponding radio transceiver in that base station, and causes that base station to
send a message, via the control rll~nn~l, to the called mobile station that instructs the
called mobile station to tune to the selected voice or traffic channel. A through-
connection for the call is established once the mobile station has tuned to the selected
AVC or DTC.
The performance of the system having ACCs that is specified by TIA/EIA/IS-
54-B has been improved in a system having digital control channels (DCCs) that is
specified in TIA/EIA/IS-136, which is expressly incorporated herein by reference.
One example of such a system having DCCs with new formats and processes is
described in U.S. Patent Application No. 07/956,640 entitled "Digital Control
Channel", which was filed on October 5, 1992, and which is incorporated in this
application by reference. Using such DCCs, each TIA/EIAtIS-54-B radio channel can
carry DTCs only, DCCs only, or a mixture of both DTCs and DCCs. Within the
TIA/EIA/IS-136 framework, each radio carrier frequency can have up to three full-
rate DTCs/DCCs, or six half-rate DTCs/DCCs, or any combination in between, for
20 example, one full-rate and four half-rate DTCs/DCCs.
In cellular telephone systems, an air link protocol is required in order to allow
a mobile station to cc."",l~ fe with the base stations and MSC. The
col,....l-"i~tions link protocol is used to initiate and to receive cellular telephone calls.
The comml-nic~tions link protocol is commonly referred to within the cc""~ ic~tions
25 industry as a Layer 2 protocol, and its functionality includes the delimiting, or
framing, of Layer 3 messages. These Layer 3 messages may be sent between
commlmic~tin~ Layer 3 peer entities residing within mobile stations and cellularswitching systems. The physical layer (Layer l) defines the parameters of the
physical cornmunications channel, e.g., radio frequency spacing, modulation
30 characteristics, etc. Layer 2 defines the techniques nt-cess~ry for the accurate
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tr~n~mi~ion of information within the constraints of the physical channel, e.g., error
correction and detection, etc. Layer 3 defines the procedures for reception and
processing of information Ll~ (ed over the physical channel using the Layer 2
protocol.
Commllni~ti~ns between mobile stations and the cellular ~wiLchillg system (the
base stations and the MSC) can be described in general with ~ci.,lcl~ce to FIGS. 1 and
2. FIG. 1 sch~m~t~ ly illustrates pluralities of Layer 3 messages 11, Layer 2 frames
13, and Layer 1 channel bursts, or time slots, 15. In FIG. 1, each group of channel
bursts corresponding to each Layer 3 message Coll~LiLulc a logical channel, and as
described above, the channel bursts for a given Layer 3 message would usually not be
consecutive slots on an TIA/EIA/136 carrier. On the other hand, the channel bursts
could be consecutive; as soon as one time slot ends, the next time slot could begin.
Each Layer 1 channel burst 15 contains a complete Layer 2 frame as well as
other inforrnation such as, for example, error correction hlrollllaLion and other
overhead information used for Layer 1 or Layer 2 operation. Each Layer 2 frame
contains at least a portion of a Layer 3 message as well as overhead hlrol~lalion used
for Layer 2 operation. Although not in~ t~1 in FIG. 1, each Layer 3 message
would include various information elements that can be considered the payload of the
message, a header portion for identifying the respective message's type, and possibly
padding.
Each Layer 1 burst and each Layer 2 frame is divided into a plurality of
dirrt;~ fields. In particular, a limited-length DATA field in each Layer 2 framecontains at least some portion of the Layer 3 message 11. Since Layer 3 messageshave variable lengths depending upon the amount of information contained in the
Layer 3 message, a plurality of Layer 2 frames may be needed for tr~n~mic~it n of a
single Layer 3 message. As a result, a plurality of Layer 1 channel bursts may also
be needed to transmit the entire Layer 3 message as there is a one-to-one
correspondence between channel bursts and Layer 2 frames.
As noted above, when more than one channel burst is required to send a
Layer 3 message, the required bursts are not usually consecutive bursts on the radio
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channel. Moreover, the several bursts are not even usually successive bursts devoted
to the particular logical channel used for carrying the Layer 3 message. Since time is
required to receive, process, and react to each received burst, the bursts required for
tr~n~mi~sion of a Layer 3 message are usually sent in a staggered format, as
5 scllem~tir~lly illustrated in FIG. 2(a) and as described above in connection with the
TIA/EIA/IS-136 standard.
FIG. 2(a) shows a general example of a folwald (or downlink) DCC
configured as a sllcces~ion of time slots 1, 2, . . ., N, . . . included in the
consecutive time slots 1, 2, . . . sent on a radio channel. These DCC slots may be
10 defined on a radio channel such as that specified by TIA/EIA/IS-136, and may
consist, as seen in FIG. 2(a) for example, of every n-th slot in a series of consecutive
slots. Each DCC slot has a duration that may or may not be 6.67 msec, which is the
length of a DTC slot according to the TIA/EIA/IS-136 standard.
As shown in FIG. 2(a), the DCC slots may be org~ni7e~l into superframes
15 (SF), and each superframe includes a number of logical channels that carry different
kinds of information. One or more DCC slots may be allocated to each logical
channel in the superframe. The exemplary downlink superframe in FIG. 2(a) includes
three logical channels: a broadcast control channel (BCCH) in~ln~ing six successive
slots for overhead messages; a paging channel (PCH) including one slot for paging
20 messages; and an access response channel (ARCH) including one slot for channel
~si~nment and other messages. The rem~ining time slots in the exemplary
~u~clr,~lle of FIG. 2 may be dedicated to other logical channels, such as additional
paging channels PCH or other channels. Since the number of mobile stations is
usually much greater than the number of slots in the ~u~lr,~lle, each paging slot is
25 used for paging several mobile stations that share some unique characteristic, e.g., the
last digit of the MIN.
FIG. 2(b) illustrates a ~lef~ d information format for the slots of a ro,~ud
DCC. FIG. 2(b) inflic~tçs the number of bits required for each identified field. The
bits sent in the SYNC information are used in a conventional way to help ensure
30 accurate reception of the CSFP and DATA fields. The SYNC information carries a
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preclPtermined bit pattern used by the base stations to find the start of the slot. The
SCF information is used in conjunction with Layer 2 operation of a random accesschannel (RACH), which is used by the mobile to request access to the system. TheCSFP information conveys a coded superframe phase value that enables the mobile
5 stations to find the start of each superframe. This is just one example for the
information format in the slots of the forward DCC.
For purposes of efficient sleep mode operation and fast cell selection, the
BCCH may be divided into a number of sub-channels. U.S. Patent Application
No. 07/956,640 discloses a BCCH structure that allows the mobile station to read a
10 Illillillllllll amount of information when it is switched on (when it locks onto a DCC)
before being able to access the system (place or receive a call). After being switched
on, an idle mobile station needs to regularly monitor only its assigned PCH slots
(usually one in each superframe); the mobile can sleep during other slots. The ratio
of the mobile's time spent reading paging messages and its time spent asleep is
15 controllable and represents a tradeoff between call-set-up delay and power
consumption.
Since each TDMA time slot has a certain fixed information carrying capacity,
each burst typically carries only a portion of a Layer 3 message as noted above. In
the uplink direction, multiple mobile stations attempt to co-~ ic~te with the system
20 on a contention basis, while multiple mobile stations listen for Layer 3 messages sent
from the system in the downlink direction.
Digital control and traffic channels are desirable because for example, they
support longer sleep periods for the mobile units, which results in longer battery life.
Moreover, digital traffic channels and digital control channels have expanded
25 functionality for optimi7ing system capacity and supporting hierarchical cellstructures, i.e., structures of macrocells, microcells, picocells, etc. The term"macrocell" generally refers to a cell having a size comparable to the si_es of cells in
a conventional cellular telephone system (e.g., a radius of at least about 1 kilometer),
and the terms "microcell" and "picocell" generally refer to progressively smaller
30 cells. For example, a microcell might cover a public indoor or outdoor area, e.g., a
_
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convention center or a busy street, and a picocell might cover an office corridor or a
floor of a high-rise building. From a radio coverage perspective, macrocells,
microcells, and picocells may be distinct from one another or may overlap one
another to handle different traffic patterns or radio environments.
FIG. 3 is an exemplary hierarchical, or multi-layered, cellular system. An
umbrella macrocell 10 represented by a hexagonal shape makes up an overlying
cellular structure. Each umbrella cell may contain an underlying microcell structure.
The umbrella cell 10 includes microcell 20 represented by the area enclosed within
the dotted line and microcell 30 represented by the area enclosed within the dashed
line corresponding to areas along city streets, and picocells 40, 50, and 60, which
cover individual floors of a building. The intersection of the two city streets covered
by the microcells 20 and 30 may be an area of dense traffic concentration, and thus
might represent a hot spot.
FIG. 4 represents a block diagram of an exemplary cellular mobile
radiotelephone system, including an exemplary base station 110 and mobile station
120. The base station includes a control and processing unit 130 which is connected
to the MSC 140 which in turn is connected to the PSTN (not shown).
The base station 110 handles a plurality of voice channels through a voice
channel transceiver 150, which is controlled by the control and processing unit 130.
Also, each base station includes a control channel transceiver 160, which may becapable of h~n-lling more than one control channel. The control channel transceiver
160 is controlled by the control and processing unit 130. The control channel
transceiver 160 broadcasts control information over the control channel of the base
station or cell to mobiles locked to that control channel. It will be understood that the
transceivers 150 and 160 can be implemented as a single device, like the voice and
control transceiver 170, for use with DCCs and DTCs that share the same radio
carrier frequency.
The mobile station 120 receives the information broadcast on a control channel
at its voice and control channel transceiver 170. Then, the processing unit 180
evaluates the received control channel h~r ~ laLion, which includes the characteristics
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of cells that are c~n~ tes for the mobile station to lock on to, and determines on
r which cell the mobile should lock. Advantageously, the received control channel
information not only includes absolute information concerning the cell with which it is
associated, but also contains relative information concerning other cells proximate to
the cell with which the control channel is associated, as described in U.S. Patent
No. 5,353,332 to Raith et al., entitled "Method and Apparatus for Co.. -.. -ic~ti~-n
Control in a Radiotelephone System".
To increase the user's "talk time", i.e., the battery life of the mobile station, a
digital forward control channel (base station to mobile station) can be provided that
can carry the types of messages specified for current analog forward control channels
(FOCCs), but in a format which allows an idle mobile station to read overhead
messages when locking onto the FOCC and thereafter only when the information haschanged; the mobile sleeps at all other times. In such a system, some types of
messages are broadcast by the base stations more frequently than other types, and
mobile stations need not read every message bro~-lc~t
The systems specified by the TIA/EIA/IS-54-B and TIA/EIA/IS-136 standards
employ circuit-switched technology, which is a type of "connection-oriented"
co....,.l...ic~tion that establishes a physical call connection and m~int~in~ that
connection for as long as the cu---------~ic~ting end-systems have data to exchange. The
20 direct connection of a circuit switch serves as an open pipeline, permitting the end-
systems to use the circuit for whatever they deem ~lo~liate. While circuit-switched
data Coll--llu- ication may be well suited to constant-bandwidth applications, it is
relatively inefficient for low-bandwidth and "bursty" applications.
Packet-switched technology, which may be connection-oriented (e.g., X.25) or
25 "connectionless" (e.g., the Internet Protocol, "IP"), does not require the set-up and
tear-down of a physical connection, which is in marked contrast to circuit-switched
technology. This reduces the data latency and increases the efficiency of a channel in
hz~nl1ling relatively short, bursty, or interactive transactions. A connectionless packet-
switched network distributes the routing functions to multiple routing sites, thereby
30 avoiding possible traf~lc bottlenecks that could occur when using a central switching
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hub. Data is "packetized" with the ~ fo~liate end-system addressing and then
tr~n~mitte-l in independent units along the data path. Intermediate systems, s-)m~tim~s
called "routers", stationed between the co~lllllunicating end-systems make decisions
about the most ~prc,~liate route to take on a per packet basis. Routing decisions are
based on a number of characteristics, inr.hlfling: least-cost route or cost metric;
capacity of the link; number of packets waiting for tr~n~mi.s~ion; security
requirements for the link; and intermediate system (node) operational status.
Packet tr~n~mi.~inn along a route that takes into consideration path metrics, asopposed to a single circuit set up, offers application and commllnic~tions flexibility.
It is also how most standard local area networks (LANs) and wide area networks
(WANs) have evolved in the corporate ~nvilolllllent. Packet switching is ~ro~liate
for data commnnications because many of the applications and devices used, such as
keyboard terminals, are interactive and transmit data in bursts. Instead of a channel
being idle while a user inputs more data into the terminal or pauses to think about a
problem, packet switching interleaves multiple tr~n~mi~ ns from several terminals
onto the channel.
Packet data provides more network robustness due to path independence and
the routers' ability to select alternative paths in the event of network node failure.
Packet switching, therefore, allows for more efficient use of the network lines.Packet technology offers the option of billing the end user based on amount of data
tr~n~mitte(l instead of connection time. If the end user's application has been
designed to make efficient use of the air link, then the number of packets tr~n~mittf d
will be minim~l. If each individual user's traffic is held to a minimnm, then the
service provider has effectively increased network capacity.
Packet networks are usually de~ign~d and based on industry-wide data
standards such as the open system interface (OSI) model or the TCP/IP protocol
stack. These standards have been developed, whether formally or de facto, for many
years, and the applications that use these protocols are readily available. The main
objective of standards-based networks is to achieve interconnectivity with other
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networks. The Internet is today's most obvious example of such a standards-basednetwork pursuit of this goal.
Packet networks, like the Internet or a corporate LAN, are integral parts of
today's business and c~ r~tion~ envho~llcnts. As mobile co~ uLillg becomes
S pervasive in these environments, wireless service providers such as those using
TIA/EIA/IS-136 are best positioned to provide access to these networks.
Nevertheless, the data services provided by or proposed for cellular systems aregenerally based on the circuit-switched mode of operation, using a dedicated radio
channel for each active mobile user.
FIG. S shows representative architect -re used for c-~.. l.-.-iczlting across an air
link that comprises the protocols which provide connectivity between a mobile end
system (M-ES), a mobile data base station (MDBS), and a mobile data intermediatesystem (MD-IS). An exemplary description of the elements in FIG. 5 and a
recommended approach for each element when considering alternative RF
technologies follows.
The Internet Protocol/Connectionless Network Protocol (IP/CLNP) are
network protocols that are connectionless and widely supported throughout the
traditional data network co.ll",-.~ y. These protocols are independent of the physical
layer and preferably are not modified as the RF technologies change.
The Security Management Protocol (SMP) provides security services across the
air link interface. The services furnished include data link confi~entizllity, M-ES
authentication, key management, access control, and al~,olilhlll upgradability/
replacement. The SMP should remain unch~nged when implementing alternative RF
technologies.
The Radio Resource Management Protocol (RRMP) provides management and
control over the mobile unit's use of the RF resources. The RRMP and its associated
procedures are specific to the AMPS RF infrastructure and require change based on
the RF technology implemented.
The Mobile Network Registration Protocol (MNRP) is used in tandem with a
Mobile Network Location Protocol (MNLP) to allow proper registration and
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authentication of the mobile end system. The MNRP should be llnrh~nged when
using alternative RF technologies.
The Mobile Data Link Protocol (MDLP) provides efficient data transfer
between the MD-IS and the M-ES. The MDLP supports efficient mobile end system
S movement, mobile end system power conservation, RF channel resources sharing, and
efficient error recovery. The MDLP should be lln~h~nged when using alternative RF
technologies.
The Medium Access Control (MAC) protocol and associated procedures
control the methodology M-ESs use to manage shared access to the RF channel. This
10 protocol and its functionality must be supplied by alternative RF technologies.
Modulation and encoding schemes are used at the physical layer. These
schemes are specific to the RF technology employed, and therefore should be replaced
with schemes ~lopliate for the alternative RF technology. The adoption of
alternative RF technologies can be implemented with a minimllm amount of change to
15 the CDPD system arrhitec~lre. The required changes are limited to the radio
resource management protocol, the MAC, and physical layers; all other network
services and support services remain llnrh~nged.
A few exceptions to data services for cellular systems based on the circuit-
switched mode of operation are described in the following docum~nts, which include
20 the packet data concepts.
U.S. Patent No. 4,887,265 and "Packet Switching in Digital Cellular
Systems", Proc. 38th IEEE Vehicular Technolo~y Conf.. pp. 414-418 (June 1988)
describe a cellular system providing shared packet data radio channels, each onecapable of accommodating multiple data calls. A mobile station requesting packet25 data service is assigned to a particular packet data channel using essentially regular
cellular ~i~n~lling. The system may include packet access points (PAPS) for
interfacing with packet data nc~Lw~lh~. Each packet data radio channel is connected to
one particular PAP and is thus capable of multiplexing data calls associated with that
PAP. Handovers are initiated by the system in a manner that is largely similar to the
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handover used in the same system for voice calls. A new type of handover is added
for those situations when the capacity of a packet channel is insufficient.
These document.c are data-call oriented and based on using system-initi~te-l
handover in a similar way as for regular voice calls. Applying these principles for
5 providing general purpose packet data services in a TDMA cellular system would result in spectrum-efficiency and performance disadvantages.
U.S. Patent No. 4,916,691 describes a new packet mode cellular radio system
architecture and a new procedure for routing (voice and/or data) packets to a mobile
station. Base stations, public switches via trunk interface units, and a cellular control
10 unit are linked together via a WAN. The routing procedure is based on mobile-station-initi~te~l handovers and on adding to the header of any packet tr~n~mitte~l from
a mobile station (during a call) an identifier of the base station through which the
packet passes. In case of an extended period of time between subsequent user
information packets from a mobile station, the mobile station may transmit extra15 control packets for the purpose of conveying cell location information.
The cellular control unit is primarily involved at call establishment, when it
assigns to the call a call control number. It then notifies the mobile station of the call
control number and the trunk interface unit of the call control number and the
identifier of the initial base station. During a call, packets are then routed directly
20 between the trunk interface unit and the currently serving base station.
The system described in U.S. Patent No. 4,916,691 iS not directly related to
the specific problems of providing packet data services in TDMA cellular systems.
"Packet Radio in GSM", Eulu~ean Telecommnnic~tions Standards Tn~ti1~-tf
(ETSI) T Doc SMG 4 58/93 (Feb. 12, 1993) and "A General Packet Radio Service
25 Proposed for GSM" presented during a stomin~r entitled "GSM in a Future
Competitive Environment", Helsinki, Finland (Oct. 13, 1993) outline a possible
packet access protocol for voice and data in GSM. These documents directly relate to
TDMA cellular systems, i.e., GSM, and although they outline a possible or~ ion
of an optimized shared packet data channel, they do not deal with the aspects of in-
30 tegrating packet data channels in a total system solution.
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"Packet Data over GSM Network", T Doc SMG 1 238/93, ETSI (Sept. 28,
1993) describes a concept of providing packet data services in GSM based on first
using regular GSM sign~lling and authentic~tion to establish a virtual channel between
a packet mobile station and an "agent" h~n-lling access to packet data services. With
5 regular .~ign~lling modified for fast channel setup and release, regular traffic channels
are then used for packet transfer. This document directly relates to TDMA cellular
systems, but since the concept is based on using a "fast switching" version of existing
GSM traffic channels, it has disadvantages in terms of spectrum efficiency and packet
transfer delays (especially for short messages) compared to a concept based on
10 optimized shared packet data channels.
Cellular Digital Packet Data (CDPD) System Specification, Release 1.0 (July
1993), which is expressly incorporated herein by reference, describes a concept for
providing packet data services that utilizes available radio channels on currentAdvanced Mobile Phone Service (AMPS) systems, i.e., the North American analog
15 cellular system. CDPD is a comprehensive, open specification endorsed by a group
of U.S. cellular operators. Items covered include external interfaces, air link
interfaces, services, network architectllre, network management, and a-lmini.ctration.
The specified CDPD system is to a large extent based on an infrastructure that
is independent of the existing AMPS infrastructure. Commonalities with AMPS
20 systems are limited to ~ltili7~ti~n of the sarne type of radio frequency channels and the
same base station sites (the base station used by CDPD may be new and CDPD
specific) and employment of a ~ign~lling interface for coor lin~ting channel
assignments between the two systems.
Routing a packet to a mobile station is based on, first, routing the packet to a25 home network node (home Mobile Data Intermediate System, MD-IS) equipped with a
home location register (HLR) based on the mobile station address; then, when
necessary, routing the packet to a visited, serving MD-IS based on HLR information;
and finally transferring the packet from the serving MD-IS via the current base
station, based on the mobile station reporting its cell location to its serving MD-IS.
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Although the CDPD System Specification is not directly related to the specific
problems of providing packet data services in TDMA cellular systems that are
addressed by this application, the network aspects and concepts described in theCDPD System Specification can be used as a basis for the network aspects needed for
an air link protocol in accordance with this invention.
The CDPD network is rlesigneC~ to be an extension of existing data
co~ lullications networks and the AMPS cellular network. Existing connectionlessnetwork protocols may be used to access the CDPD network. Since the network is
always considered to be evolving, it uses an open network design that allows the10 addition of new network layer protocols when a~plo~liate. The CDPD network
services and protocols are limited to the Network Layer of the OSI model and below.
Doing so allows upper-layer protocols and applications development without ch~nging
the underlying CDPD network.
From the mobile subscriber's perspective, the CDPD network is a wireless
15 mobile extension of traditional networks, both data and voice. By using a CDPD
service provider network's service, the subscriber is able to seamlessly access data
applications, many of which may reside on traditional data networks. The CDPD
system may be viewed as two interrelated service sets: CDPD network support
services and CDPD network services.
CDPD network support services perform duties n~cess~ry to m~int~in and
mini~ter the CDPD network. These services are: accounting server; network
management system; message lldl~rel server; and authentication server. These
services are defined to permit interoperability among service providers. As the
CDPD network evolves technically beyond its original AMPS infrastructure, it is
25 anticipated that the support services shall remain llnch~nged. The functions of
network support services are necessary for any mobile network and are independent of
radio frequency (RF) technology.
CDPD network services are data ~ r~l services that allow subscribers to
col,l",l~"ic~te with data applications. Additionally, one or both ends of the data
30 collllllullications may be mobile.
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To ~ul~ lal.~e, there is a need for a system providing general purpose packet
data services in D-AMPS cellular systems, based on providing shared packet-data
channels optirnized for packet data. This application is directed to systems andmethods that provide the combined advantages of a connection-oriented network like
5 that specified by the TIA/EIA/IS-136 standard and a connectionless, packet data
network. Furthermore, the present invention is directed to accessing the CDPD
network, for example, by existing connection1ess network protocols with low
complexity and high throughput.
SUMMARY
According to one embodiment of the present invention, a method for
registering a mobile station when the mobile station first enters a commnnic~tion
system which supports packet data channels is disclosed. The mobile station receives
system information bro~c1c~te~1 on a digital control channel from which it determines
15 its assigned beacon packet data channel. The mobile station then registers with the
collllllunication system over the packet data channel to activate packet data service.
The mobile station measures the signal strength of digital control ch~nnel~ of
neighboring cells listed on a neighbor list included in the system information as well
as the signal strength of the channel the mobile station is ~ y camping on. The
20 mobile station can then decide to switch to a digital control channel of a neighboring
cell, e.g., when the signal strength of the neighboring digital control channel is higher
than the signal strength of the first digital control channel. Furthermore, each packet
data channel can provide an inrlir~ti~n to mobile stations regarding which neighboring
cells support packet data channels.
~5
BRIEF DESCRIPTION OF THE DRAWINGS
The features and advantages of Applicants' invention will be understood by
reading this description in conjunction with the drawings in which:
FIG. 1 schem~ticz-11y illustrates pluralities of Layer 3 messages, Layer 2
30 frames, and Layer l channel bursts, or time slots;
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FIG. 2(a) shows a fol~d DCC configured as a succec~ n of time slots
included in the consecutive time slots sent on a carrier frequency;
FIG. 2(b) shows an example of an IS-136 DCCH field slot format;
FIG. 3 illustrates an exemplary hierarchical, or multi-layered, cellular system;FIG. 4 is a block diagram of an exemplary cellular mobile radiotelephone
system, including an exernplary base station and mobile station;
FIG. 5 shows a protocol architectllre for commlmic~ting across an air link;
FIG. 6 illustrates one example of a possible mapping sequence;
FIG. 7 illustrates an example of a slot format for BMl ~ M5 on PDCH;
FIG. 8 illustrate a mobile station activating a CDPD mode of operation; and
FIG. 9 illustrates a PDCH selection and cell reselection process according to
one embodiment of the present invention.
DETAILED DESCRIPTION
To aid in the underst~n~1ing of the present invention, a description for one
possible mapping sequence is illustrated in FIG. 6. FIG. 6 shows a dedicated PDCH
example of how one L3 message is mapped into several layer 2 frames, an example of
a layer 2 frame mapping onto a time slot, and an example of time slot mapping onto a
PDCH channel. The length of the FPDCH time slots and RPDCH bursts are fixed.
There are three possible forms of RPDCH bursts (i.e., normal abbreviated and
auxiliary) which have dirr~,elll fixed lengths. FPDCH slots on a full-rate PDCH are
"~.sllme-l to be on the physical layer in FlG. 6. In the present invention, the TDMA
frame structure is the same as for IS-136 DCCH and DTC. In the interest of
maximal throughput when a multi-rate channel is used (double rate PDCH and triple
rate PDCH), an additional FPDCH slot format is specified. FIG. 7 illustrates an
additional slot format which is provided by this invention, specifically a slot format
for BMI ~ MS on a PDCH. The difference between the slot format illustrated in
FIG. 7 and the IS-136 DCCH BMI MS slot format is that the PCF field is used in
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the present embodiment instead of SCF and the CSFP/PCF field in the present
embodiment has replaced the CSFP field in the IS-136 DCCH format.
In this embodiment of FIG.7, the slot format is divided into seven fields; a
synchronization field (SYNC) for providing syncl~luni~a~ion information to the mobile
5 station, a packet channel feedback field (PCF), a first data (DATA) field, a coded
superframe phase/packet channel feedback (CSFP/PCF)field, a second data field, asecond packet channel feedback (PCF) field, and a reserved (RSVD) field.
The PCF fieldis used to control access on the RPDCH and includes
busy/reserved/idle (BRI), received/not received (R/N), partial echo (PE) and partial
10 echo qualifier (PEQ) information. The B~I, PE, and R/N data are as specified in IS-
136. The CSFP/PCF field contains the additional PEQ data in the present
embodiment. The CSFP/PCF fieldis used to convey information regarding the
superframe phase SFPso that mobile stations can find the start of the superframe.
Also, the CSFP/PCF field provides the PEQ information, which is used to
15 dynamically assign the subchannels of the RPDCH so as to provide an efficient means
for inte~ ing tr~n~mi~ions by a first mobile station so as to allow for tr~n~mi~sions
from other mobile stations that are either attempting to access the system or have
already ~cce~e-l the system and are in the process of sending packet data information.
According to one exemplary embodiment of the present invention, the digital
20 control channel (DCCH) of the IS-136 specification can be used to inrlir~tr support
for packet data channel operation. In the present co~ ic~ti-~n systems, different
cells within the comml-nic~tion system have different digital control channels. When
a mobile station powers on or enters the coll""~ ic~tion system, the mobile station
will receive information about the c-,llll"llllic~tion system which is being broadcast on
25 the DCCH on which the mobile station decides to acquire service. FIG.8 illustrates
an activation process for a mobile station at power-up. The mobile station first finds
a DCCH and then reads the BCCH to find a pointer to the beacon PDCH. A mobile
station interested in packet data operation locks onto the beacon PDCH, and enters an
active mode whereby it registers with the commlmiczlti~ n system. The mobile station
30 may be redirected to a different PDCH in response to its registration. The mobile
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station stays in an active mode on the inllic~tr-l PDCH until an activity timer has
expired. The mobile station then enters a passive mode on the PDCH.
FIG. 9 illustrates the relationship between packet data channels belonging to
one cell or more specifically, having a common mother DCCH, and digital control
channels in different cells. FIG. 9 illustrates a co.. ~ r~tion system with a plurality
of digital control channels (DCCHl, DCCH2, ..., DCCHn, DCCHm). When a
mobile station is activated or enters the col~ iC~ti~ n system, the mobile station
camps on one of the digital control charmels, for example, DCCHl. While the
mobile station is camped on DCCHl, the system will send hl~ollllation to the mobile
10 station such as a neighbor list, which lists m-l frequencies of the digital control
channels used by neighboring cells and whether the cell encompassed by DCCHl
supports packet data channels. If DCCHl inrlir~trs support for one or more dedicated
PDCHs, the carrier frequency of one PDCH, i.e., a beacon PDCH, is also provided
as part of the broadcast information sent on the BCCH of DCCHl. The mobile
15 station is directed toward the beacon PDCH by a PDCH pointer. If interested in
packet data operation, the mobile station camps and registers on the beacon PDCH.
The mobile station may continue to be ~e~ignrd to the beacon PDCH or the mobile
station may be ~ignto-l to another derlir~tçd PDCH depending upon the
co."".ll..ir~tion system. For example, the digital control channel DCCHl may
20 support a plurality of packet data channels (Beacon PDCH, PDCH2, , PDCHr,
PDCHq). As a result, while the mobile station is first ~signt?d to the beacon PDCH,
the mobile station can be reassigned to another packet data channel as part of the
registration process. The mobile station may be reassigned to another packet data
channel for a variety of reasons, such as traffic control.
There are several benefits to having just one PDCH pointer per digital control
channel. First of all, if each digital control channel were to have more than one
pointer, extra bandwidth on each digital control channel would have to be provided
for each additional pointer. In addition, rç~igning mobile stations from the beacon
- PDCH allows the system to be more flexible than systems which must reassign mobile
stations to new PDCHs directly from the DCCH. For example, a system with
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multiple pointers on each digital control channel can only assign the mobile stations to
the packet data channels as a function of each mobile stations phone number or
icientific~tion number (MSID). Thus, the assignment process would be static.
However, according to the present invention, the beacon PDCH can perform
S individual rçS~cignments to other PDCHs based on a mobile station's past history
and/or current request.
The mobile station performs cell reselection measurements by measuring the
signal strengths of digital control channels of neighboring cells using the neighbor list
acquired while initially camped on the digital control channel. According to one10 embodiment of the present invention, information on the PDCH in~Tiç~tes whether a
neighboring DCCH supports packet data tr~n~mi~ ns. Each packet data channel
contains local PDCH information which in-licat~s whether neighbor cells support
packet data channels. Each packet data cnannel inrhl-le~ a vector, i.e., a bit map,
having a length reflecting the length of the neighboring cell list. The vector may
15 in-lic~te which channels in the neighboring cell list support packet data channels. For
example, a "1" in the first bit position in the bit map could in~lic~t~ that the first cell
in the neighbor list supports packet ch~nn~l~. It will be understood that the bit map is
not limited to binary bits and could include multiple bits. In such a case, the multiple
bits could also int1i~te other features of the neighboring cells, e.g., CDPD with
20 original CDPD air interface. When a cell reselection takes place, the mobile station
first camps on the new DCCH such as DCCH2. The mobile station is then directed
to a beacon PDCH by a PDCH pointer specified for DCCH2. Likewise, the beacon
PDCH can reassign the mobile station to another PDCH.
According to one embodiment of the present invention, the beacon may be the
25 only PDCH channel which carries broadcast information. In this situation, when the
broadcast information is changed, all of the mobile stations assigned to non-beacon
packet data channels must be returned to the beacon PDCH so that the mobile stations
can receive the new broadcast information. In the alternative, all of the PDCH
channels may provide broadcast information. In this situation, the broadcast
30 information should be the same for all PDCH channels. Thus, if a mobile station
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reads broadcast hlroll-la~ion on one channel, the mobile station can be assigned to
another PDCH channel wherein the mobile station will not have to first reread the
broadcast inforrnation.
It will be understood that Applicants' invention is not limited to the particular
S embo-liment~ that have been described and illustrated. This application contemplates
any and all mollific~tinns that fall within the spirit and scope of Applicants' invention
as defined by the following claims.
