Operation and administration of mobile station user groups in wireless communications systems

Methods for operating and administering mobile station user groups in a wireless communications system. In one embodiment, a user group identification code is assigned to a plurality of mobile stations to form a user group, wherein the number of mobile stations in the user group is less than the total number of mobile stations in the entire communications system, and wherein the user group identification code is distinguishable from a unique mobile station identification code associated with each mobile station in the user group. A page message from the system to the user group is transmitted using the user group identification code when a terminating call to the user group is requested. A user group specific page indication is then generated at the mobile stations indicating to a user of each mobile station that the page message has been received. A page response message is then transmitted to the system from mobile stations whose users acknowledge the page indication. Finally, a channel assignment for the call is granted to the mobile station which responds first.

FIELD OF THE INVENTION 
The present invention relates to a method for transmitting messages between 
mobile stations and a central switching system, and more particularly to a 
method for transmitting messages such that only a subset of the general 
population of mobile stations are allowed to receive and potentially 
respond to the transmitted messages. 
BACKGROUND OF THE INVENTION 
In a typical cellular radio system, a geographical area, e.g., a 
metropolitan area, is divided into several smaller, contiguous radio 
coverage areas called "cells". The cells are served by a series of fixed 
radio base stations called "base stations". The base stations are 
connected to and controlled by a mobile switching center (MSC). The MSC in 
turn is connected to the landline (wireline) public switched telephone 
network (PSTN). The telephone users (mobile subscribers) in the cellular 
radio system are provided with portable (hand held), transportable (hand 
carried), or mobile (car mounted) telephone units (mobile stations) which 
communicate voice and/or data with the MSC through a nearby base station. 
The MSC switches calls between and among wireline and mobile subscribers, 
controls signalling to the mobile stations, compiles billing statistics, 
and provides for the operation, maintenance, and testing of the system. 
FIG. 1 illustrates the architecture of a conventional cellular radio system 
built according to the Advanced Mobile Phone System (AMPS) standard. In 
FIG. 1, an arbitrary geographic area may be seen divided into a plurality 
of contiguous radio coverage areas, or cells C1-C10. While the system of 
FIG. 1 is, for illustration purposes, shown to include only ten cells, the 
number of cells may be much larger in practice. Associated with and 
located in each of the cells C1-C10 is a base station designated by a 
corresponding one of a plurality of base stations B1-B10. Each of the base 
stations B1-B10 includes a plurality of channel units, each comprising a 
transmitter, a receiver and a controller, as is well known in the art. 
In FIG. 1, the base stations B1-B10 are located at the center of the cells 
C1-C10, respectively, and are equipped with omni-directional antennas 
transmitting equally in all directions. In this case, all the channel 
units in each of the base stations B1-B10 are connected to one antenna. 
However, in other configurations of the cellular radio system, the base 
stations B1-B10 may be located near the periphery, or otherwise away from 
the centers of the cells C1-C10 and may illuminate the cells C1-C10 with 
radio signals directionally. For example, the base station may be equipped 
with three directional antennas, each one covering a 120 degree sector 
cell as illustrated in FIG. 2. In this case, some channel units will be 
connected to one antenna covering one sector cell, other channel units 
will be connected to another antenna covering another sector cell, and the 
remaining channel units will be connected to the remaining antenna 
covering the remaining sector cell. In FIG. 2, therefore, the base station 
serves three sector cells. However, it is not always necessary for three 
sector cells to exist and only one sector cell need be used to cover, for 
example, a road or a highway. 
Returning to FIG. 1, each of the base stations B1-B10 is connected by voice 
and data links to a mobile switching center MSC 20 which is, in turn, 
connected to a central office (not illustrated) in the public switching 
telephone network (PSTN), or a similar facility, e.g., an integrated 
services digital network (ISDN). The relevant connections and transmission 
modes between the mobile switching center MSC 20 and the base stations 
B1-B10, or between the mobile switching center MSC 20 and the PSTN or 
ISDN, are well known to those of ordinary skill in the art and may include 
twisted wire pairs, coaxial cables, fiber optic cables or microwave radio 
channels operating in either analog or digital mode. Further, the voice 
and data links may either be provided by the operator or leased from a 
telephone company (telco). 
With continuing reference to FIG. 1, a plurality of mobile stations M1-M10 
may be found within the cells C1-C10. Again, while only ten mobile 
stations are shown in FIG. 1, the actual number of mobile stations may be 
much larger in practice and will generally exceed the number of base 
stations. Moreover, while none of the mobile stations M1-M10 may be found 
in some of the cells C1-C10, the absence or presence of the mobile 
stations M1-M10 in any particular one of the cells C1-C10 depends on the 
individual desires of each of the mobile subscribers who may travel from 
one location in a cell to another or from one cell to an adjacent or 
neighboring cell. 
Each of the mobile stations M1-M10 includes a transmitter, a receiver, a 
controller and a user interface, e.g., a telephone handset, as is well 
known in the art. Each of the mobile stations M1-M10 is assigned a mobile 
identification number (MIN) which, in the United States, is a digital 
representation of the telephone directory number of the mobile subscriber. 
The MIN defines the subscription of the mobile subscriber on the radio 
path and is sent from the mobile station to the MSC 20 at call origination 
and from the MSC 20 to the mobile station at call termination. Each of the 
mobile stations M1-M10 is also identified by an electronic serial number 
(ESN) which is a factory set, "unchangeable" number designed to protect 
against the unauthorized use of the mobile station. At call origination, 
for example, the mobile station will send the ESN to the MSC 20. The MSC 
20 will compare the received ESN to a "black list" of the ESN's of mobile 
stations which have been reported to be stolen. If a match is found, the 
stolen mobile station will be denied access. 
Each of the cells C1-C10 is allocated a subset of the radio frequency (RF) 
channels assigned to the entire cellular system by the concerned 
government authority, e.g., the Federal Communications Commission (FCC) in 
the United States. Each subset of RF channels is divided into several 
voice or speech channels which are used to carry voice conversations, and 
at least one paging/access or control channel which is used to carry 
supervisory data messages, between each of the base stations B1-B10 and 
the mobile stations M1-M10 in its coverage area. Each RF channel comprises 
a duplex channel (bidirectional radio transmission path) between the base 
station and the mobile station. The RF channel consists of a pair of 
separate frequencies, one for transmission from the base station 
(reception by the mobile station) and one for transmission by the mobile 
station (reception by the base station). Each channel unit in the base 
stations B1-B10 normally operates on a preselected one of the radio 
channels allocated to the corresponding cell, i.e., the transmitter TX and 
receiver RX of the channel unit are tuned to a pair of transmit and 
receive frequencies, respectively, which does not change. The transceiver 
(TX/RX) of each mobile station M1-M1O, however, may tune to any of the 
radio channels specified in the system. 
In typical land line systems, remote stations and control centers are 
connected by copper or fiber optic circuits which have a data through put 
capacity and performance integrity that is generally significantly better 
than the data through put capacity and performance integrity provided by 
an air interface in a cellular telephone system. As a result, the 
conciseness of overhead required to manage any selected communication link 
protocol for land line systems is of secondary importance. In cellular 
telephone systems, an air interface communications link protocol is 
required in order to allow a mobile station to communicate with a cellular 
switching system. A communications link protocol is used to initiate and 
to receive cellular telephone calls. 
The electromagnetic spectrum available for use by cellular telephone 
systems is limited and is divided into units called channels. Individual 
channels are used as communication links either on a shared basis or on a 
dedicated or reserved basis. When individual channels are used as 
communication links on a shared basis, multiple mobile stations may either 
listen to or contend for the same channels. In the contending situation, 
each shared channel can be used by a plurality of mobile stations which 
compete to obtain exclusive use of the channel for a limited period of 
time. On the other hand, when individual channels are used as 
communication links on a dedicated basis, a single mobile station is 
assigned the exclusive use of the channel for as long as it is needed. 
In light of the generally reduced data through put capacity and performance 
integrity afforded by an individual channel in a channel sharing situation 
in a cellular telephone environment, the selection of an efficient air 
interface protocol to serve as the basis for the communication link and 
its economic use by cellular applications becomes paramount. The 
communication link protocol is commonly referred to as a layer 2 protocol 
within the communications industry and its functionality includes the 
delimiting and framing of higher level messages. Layer 2 protocol framing 
mechanisms of bit stuffing and flag characteristics are commonly used in 
land line networks today to frame higher layer messages, which are 
referred to as layer 3 messages. These layer 3 messages may be sent 
between communicating layer 3 peer entities residing within the mobile 
stations and cellular switching systems. The specific types of layer 3 
messages and their sequence of exchange between a mobile station and a 
cellular switching system is what defines a cellular application. 
The present invention relates to a method for transmitting messages between 
mobile stations and a central switching system, and more particularly to a 
method for transmitting these messages such that only a subset of the 
general population of mobile stations are allowed to receive and 
potentially respond to these messages. This subset of the general 
population of mobile stations may be considered as a user group having 
membership requirements that must be satisfied for participation in the 
user group. 
SUMMARY OF THE INVENTION 
According to one embodiment of the present invention, a method for user 
group operation is disclosed whereby a single member of the user group is 
deemed the winner of a user group terminating call attempt and as such is 
granted the terminating call. 
According to one embodiment of the present invention, a method for 
completing a call in a cellular communication system to a mobile station 
which is part of a user group is disclosed. First, a user group 
identification code is assigned to a first plurality of mobile stations, 
wherein said first plurality is less than the total number of mobile 
stations in said system. A page message from said cellular system to said 
user group is transmitted using said user group identification code when a 
terminating call has been requested to the user group. A user group 
specific page indication is then generated at the first plurality of 
mobile stations in response to receiving the page message. A page response 
message is then transmitted to said cellular system from mobile stations 
whose users acknowledge the page indication. Finally, a channel assignment 
for said call is granted to the mobile station which sends the first 
received page message received at said cellular system.

DETAILED DESCRIPTION 
Although the description hereinafter focuses on systems which comply with 
IS-54B and its successors, the principles of the present invention are 
equally applicable to a variety of wireless communication systems, e.g., 
cellular and satellite radio systems, irrespective of the particular mode 
of operation (analog, digital, dual mode, etc.), the access technique 
(FDMA, TDMA, CDMA, hybrid FDMA/TDMA/CDMA, etc.), or the architecture 
(macrocells, microcells, picocells, etc.). As will be appreciated by one 
skilled in the art, the logical channel which carries speech and/or data 
may be implemented in different ways at the physical layer level. The 
physical channel may be a relatively narrow RF band (FDMA), a time slot on 
a radio frequency (TDMA), a unique code sequence (CDMA), or a combination 
of the foregoing. For purposes of the present invention, the term 
"channel" means any physical channel which can carry speech and/or data, 
and is not limited to any particular mode of operation, access technique 
or system architecture. 
FIG. 3 represents a block diagram of an exemplary cellular mobile radio 
telephone system according to one embodiment of the present invention. The 
system illustrates an exemplary base station 110 and a mobile station 120. 
The base station 110 includes a control and processing unit 130 which is 
connected to the mobile switching center MSC 140 which in turn is 
connected to the public switch telephone network (not illustrated). 
The base station 110 for a cell includes a plurality of voice channels 
handled by a voice channel receiver 150 which is controlled by the control 
and processing unit 130. Also, each base station includes a control 
channel transceiver 160 which may be capable of handling 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. 
When the mobile 120 is in an idle mode, the mobile periodically scans the 
control channels of base stations like base station 110 to determine which 
cell to lock onto or camp to. The mobile 120 receives the absolute and 
relative information broadcast on a control channel at its voice and 
control channel transceiver 170. Then, the processing unit 180 evaluates 
the received control channel information which includes the 
characteristics of the candidate cells and determines which cell the 
mobile should lock onto. 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 
approximate to the cell which the control channel is associated. 
According to one embodiment of the present invention, a mobile subscriber 
can request participation in a user group in a variety of ways. For 
instance, a mobile station may be preregistered for user group operation 
within one or more specific user groups as a result of its service 
subscription in its home MSC. Such a mobile station could then attempt to 
activate user group operation by requesting participation in a specific 
user group during registration with any visited MSC that broadcast support 
for user group operation in general. When a MSC receives a registration 
wherein the mobile subscriber is requesting that the mobile station be 
actively included in a specific user group, the serving MSC can contact 
the home MSC to determine whether or not the requesting mobile station is 
allowed to activate user group operation for the requested user group. The 
home MSC informs the visited MSC of the home MSC's decision to either 
approve or deny service for the requested user group. If the home MSC 
decides to approve the request, the serving MSC sends back a registration 
acceptance message to the requesting mobile station. If the mobile station 
does not receive a registration accept message, the mobile station will 
know that its request has been denied and will not activate user group 
operation for that user group. 
In order to send layer 3 messages to distinct user groups, a user group 
identity field (UGID) can be included in the SH layer 2 protocol. By 
using this group identity, the communication system can page the entire 
user group in any given paging area by sending only one page message. A 
user group ID frame is illustrated in FIG. 4. A further description of 
layer 2 protocol can be found in U.S. patent application Ser. Nos. 
08/331,816 and 08/332,114, both of which are incorporated herein by 
reference. 
The present invention will now be described from two different 
perspectives: from the perspective of a MSC; and from the perspective of a 
mobile station. First, the user group operation from the MSC's perspective 
will be described with reference to FIG. 5 and then the user group 
operation from the mobile station's perspective will be described with 
reference to FIG. 6. 
In present cellular systems, mobile stations are allowed to roam into areas 
covered by MSCs other than their home MSC and also into other cellular 
systems administered by other cellular operators. When a mobile station 
roams, the mobile station will register with the MSC responsible for the 
area in which the mobile station is located in step S100. During the 
registration, the mobile station can request activation for a specific 
user group as described above. If a roaming mobile station successfully 
registers for user group operation in a visited MSC, the visited MSC may 
track the whereabouts of the registered mobile station according to the 
mobile station's identity (MSID) and its assigned user group 
identification (UGID) in step S110. An MSC tracking a mobile station's 
location using MSID and UGID will maintain a list of all paging areas in 
which there exists one or more mobile stations that have registered for 
user group operation for a specific UGID. As a result, an MSC may track 
multiple UGIDs in parallel, where each tracked UGID may translate into a 
different set of paging areas. 
When a mobile station registers with a visited MSC, the location of the 
mobile station is sent back to the home MSC where it is stored. As a 
result, when the home MSC receives a page request for a specific user 
group in step S120, the page request can be routed to one or more visited 
MSCs which serve the areas in which the mobile stations, having that user 
group activated, have roamed. It will be apparent to one skilled in the 
art that the home MSC can specify whether a single call assignment should 
be made to a single mobile station or whether each visited MSC can grant a 
channel assignment to one mobile station, thus resulting in a conference 
call. The visited MSCs then transmit, in step S130, a user group page 
message over the appropriate radio channels (control channels) determined 
according to MSID/UGID tracking performed by the MSCs. The visited MSCs 
then start a page response timer in step S140 and wait for a mobile 
station to send a page response message in step S150. If a page response 
message is received before a time out condition is experienced, the MSC 
grants a channel assignment, over which the call takes place, to the 
mobile station identified by the first received page response message in 
step S160. The MSC then transmits an UGID specific release message in step 
S170, which tells the other mobile stations to abort the user group call 
attempt. Finally, the MSC completes the necessary call processing for the 
winning mobile station in step S180. 
However, if the MSC does not receive a page response message in step S150 
before the MSC determines that a time out condition has occurred in step 
S190, the MSC transmits a UGID specific release message in step S200 which 
indicates that all of the mobile stations in the user group should abort 
the user group call attempt. 
Furthermore, the MSC could receive an unexpected UGID page response. For 
example, the MSC could receive a page response message from a second 
mobile station after having already granted the channel assignment to a 
first mobile station. When the MSC receives an unexpected page response 
message in step S210, the MSC transmits a UGID specific release message in 
step S220 which indicates that all of the mobile stations in the user 
group should abort the user group call attempt. 
The user group operation from the perspective of the mobile station will 
now be described with reference to FIG. 6. When the mobile station 
receives a user group page message, in step S300, the mobile station 
determines whether the mobile station is active in the identified user 
group in step S310. If the mobile station is not active in the identified 
user group, then the mobile station ignores the user group page message in 
step S320. However, if the mobile station is active in the identified user 
group, the mobile station responds in step S330 by providing some form of 
alerting to the mobile station user. According to one embodiment of the 
present invention, a special tone or signal is used to indicate that a 
user group call termination is being attempted. The specific form of 
alerting the mobile station user (tones and cadences) may be identified in 
the received page message. When a mobile station is in the process of 
alerting the user to the fact that a user group page message has been 
received, the mobile station is considered to be in a user group alerting 
state. Upon first entering the user group alerting state a mobile station 
starts a timer in step S340. The mobile station then waits for the user to 
acknowledge the user group page message in step S350. While the mobile 
station is waiting for an acknowledgement, the mobile station determines 
whether a user group release message has been received or if a time out 
condition exists in steps S430 and S440. If either a user group release 
message is received or a time out condition exists before the user 
acknowledges the user group page message, the mobile station aborts the 
user group call attempt. When a mobile station is in the user group 
alerting state and the user responds in step S350 to the special paging 
tone or signal by pushing at least one button, the mobile station resets 
the time out timer in step S360 and transmits a page response message to 
the serving MSC in step S370, wherein the page response contains, among 
other information, the identity of the responding mobile station and its 
active UGID. Of all the mobile stations that transmit a page response 
message, only one mobile station (the winner) is granted a channel 
assignment over which the call takes place. Thus, the mobile station waits 
for a channel assignment in step S380. While the mobile station is waiting 
for a channel assignment, the mobile station determines whether a user 
group release message has been received or a time out condition exists in 
steps S400 and S410. If a user group release message is received or a time 
out condition exists before a channel assignment is received, the mobile 
station aborts the user group call attempt. However, if the mobile station 
does receive a channel assignment, the mobile station and the serving MSC 
complete the call processing in step S390. 
While a particular embodiment of the present invention has been described 
and illustrated, it should be understood that the invention is not limited 
thereto since modifications may be made by persons skilled in the art. The 
present application contemplates any and all modifications that fall 
within the spirit and scope of the underlying invention disclosed and 
claimed herein.