Method and apparatus for distributing processing load for decoding radio frequency transmissions

A method for receiving a radio communication in a radio communication system (100) shares the downlink processing burden among members of a local group of local stations. The method includes receiving the radio communication (302) at a first mobile station (304) of a plurality of mobile stations (300). The method further includes transmitting a local radio communication (306) from the first mobile station to an intended recipient mobile station (308) of the plurality of mobile stations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to application Ser. No. 09/603,545 entitled Method and Apparatus For Distributing Processing Load For Decoding Paging Messages In A Radio Communication System, Motorola case number CS-10463, filed on even date herewith and commonly assigned to the assignee of the present application.

BACKGROUND OF THE INVENTION

The present invention is related generally to radio communication devices. More particularly, the present invention relates to a method and apparatus for distributing processing load among a group of local radios when receiving radio frequency transmissions from a remote radio.

Radio communication systems have been developed which provide two-way radio communication of voice and data between a mobile station and fixed base stations of the system. Using a mobile station in such a system, a subscriber can initiate calls and receive calls while located in the service area adjacent one or more base stations of the system. The service area may extend a distance of 50 km or more from the base station and transmissions within the system, both from the base station and from mobile stations, are relatively high power. By a process of registration, the system maintains location information for the mobile station so that pages may be sent to alert the mobile station.

To enhance user convenience, mobile stations are portable. The mobile station may register with any base station in the system when transported in the vicinity of the base station. Ongoing radio communication with a given mobile station may be handed off among base stations to provide full mobility within the system. Examples of such systems include cellular telephone systems and trunked radio systems.

To further enhance user convenience, mobile stations are conventionally powered by a depletable energy source such as a battery. Battery power provides true portability for a limited period of time while the battery retains sufficient charge to operate the mobile station. When operated under battery power, the user of the mobile station is free to move about the service area of the system but can still initiate and receive calls.

Various techniques have been developed to reduce the power consumption of a mobile station, thereby extending the time between battery recharges. Some of these techniques are implemented at a system level. For example, in some systems, a mobile station is required only to be active only during a time period associated with transmission of a paging channel by base stations of the system. Otherwise, if not actively engaged in a call, the mobile station enters a low-power sleep mode to extend battery life. After the sleep mode, the mobile station regains synchronization with system timing to receive the paging channel, decode the information contained therein and detect a page intended for the mobile station. Other techniques for extending battery life are implemented in the design of an individual mobile station. For example, improved synchronization methods allow extension of the low power sleep mode while ensuring re-synchronization with system timing.

Even with these techniques, a substantial portion of battery life is expended detecting transmissions that might be intended for the mobile station. For example, in some implementations, when searching for a transmission from a base station, the mobile station must power up its analog front end circuit, its microprocessor or other controller and decoding circuitry. This must be done during each possible transmission of paging information, even though a transmission intended for the mobile station is received only rarely. In next generation radio communication systems, the situation is even more severe, since decoding transmissions will require substantial processing power to decode each received instance of a paging channel. This is referred to as joint detection operation.

Accordingly, there is a need for an improved method and apparatus for reducing power consumption in mobile stations of a radio communication system.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

Referring now to the drawing,FIG. 1is a block diagram showing a radio communication system100. The system100includes a plurality of base stations102,104, a mobile switching center106and a plurality of mobile stations108,110,112. The radio communication system100permits two-way radio communication of voice, data and other information among base stations102,104and mobile stations108,110,112. The system100may include any suitable number of base stations to provide communication capability for any number of mobile stations. The two base stations and the three mobile stations shown in FIG.1are exemplary only. Examples of systems which may embody the system100are cellular radiotelephone systems according to EIA/TIA interim standards IS-95 and IS-136 and next generation systems providing Universal Mobile Telecommunications Service (UMTS) or Wideband Code Division Multiple Access (W-CDMA).

The base stations102,104are fixed and provide radio communication to mobile stations located in a fixed geographic area adjacent to each respective base station. The mobile switching center106is in wire line communication with the base stations102,104and provides supervisory and control functions for the system100. In particular, the mobile switching center106controls handoff of radio communications with a particular mobile station between base stations such as base stations102,104.

In the illustrated embodiment, mobile stations108,110,112together form a local group114of mobile stations. The mobile stations108,110,112are proximally located to permit radio communication among the mobile stations108,110,112by a low power radio communication standard. Any number of mobile stations may be included in the local group114. The size of the local group is, to some extent, defined by the reliable transmission and reception distance for the low power radio communication standard shared by the local group. In one example, this distance is approximately 10 meters.

Mobile station108is shown in detail and is exemplary of the construction and operation of other mobile stations in the system100, such as mobile station110and mobile station112. Mobile station108includes a first radio circuit120, a local radio circuit122and a control circuit124. Operating power in the mobile station is provided by a battery.

The first radio circuit120includes a first receiver126, a decoder circuit128and encoder circuit130, a first transmitter132and a first synthesizer134. The first receiver126and the first transmitter132are electrically coupled with a first antenna136. The first radio circuit120is operable on the radio communication system100to provide two-way radio communication with remote radios of the system100, such as the base station102and the base station104. In one embodiment, the first receiver126and the first transmitter132are operable on a cellular radio communication system. In other embodiments, the radio communication system100may be implemented as a trunked radio communication system.

The receiver126and the transmitter132, in combination with the synthesizer134, form an analog front end of the first radio circuit120. The synthesizer134is operable in response to control signals from the controller150to select a channel or frequency for receiving radio frequency (RF) signals by the receiver126or transmitting RF signals by the transmitter132.

The receiver126receives a downlink127transmitted by a base station such as base station102. The downlink127contains data intended for mobile stations such as mobile station108. The data is formatted and encoded according to an accepted standard. The data are used to modulate a carrier signal at a defined channel frequency.

The decoder128receives analog signals detected by the receiver126and decodes, demodulates and otherwise detects digital data contained in the received RF signals of the downlink127. The data may be embedded in the RF signals in accordance with any suitable radio communication protocol, such as cellular radio telephone systems referred to as IS-95 and IS-136, or next generation radio telephone systems referred to generally as Universal Mobile Telecommunication Systems (UMTS). A radio communication protocol is exemplified by an air interface, which defines the signals and data and formatting for reliable transmission and reception by two radios operating in the system. Other examples are the system defined by the TIA standard IS-2000 and the ITU standard name MC-1X and MC-3X. The detected data is provided by the decoder to the controller150to complete reception of a downlink127of one of the base stations102,104. In some instances, the detected data corresponds to an alert communication such as a paging channel intended to advise the mobile station108of the need to begin communicating with the system100, for example, to receive an incoming call intended for the mobile station108.

In a typical application such as a cellular telephone or UMTS system, the paging channel is the vehicle for communicating with mobile stations when they are not assigned to a traffic channel. As the name implies, its primary purpose is to convey pages, that is, notifications of incoming calls, to the mobile stations. The paging channel carries the responses to mobile station accesses, both page responses and unsolicited originations. Successful accesses are normally followed by an assignment to a dedicated traffic channel. Once on a traffic channel, signaling traffic between base and mobile can continue interspersed with the user traffic. Thus, the paging channel in such as system forms an alert communication.

For transmission of an uplink131to one of the base stations102,104, digital data is provided by the controller150to the encoder130. The encoder formats the data for transmission by the transmitter132. The transmitter modulates a carrier signal provided by the synthesizer134to produce RF signals at the antenna136for transmission to the base station102,104on the uplink131.

The local radio circuit122includes a second or local receiver140, a second or local transmitter142and a second or local synthesizer144. The local radio circuit122preferably operates to provide a low power local radio link. In the illustrated embodiment, the local radio circuit122operates in conjunction with the Bluetooth radio communication standard. The Bluetooth standard has been implemented to provide short distance (such as ten meters), low power (such as 100 mW), two-way radio communication of data among suitably equipped wireless communication devices. Other local radio communication technology may be substituted to provide the local radio links between the mobile station108and mobile stations110,112. This includes equipment such as wireless local area network (LAN) equipment, HyperLAN equipment, and equipment according to IEEE standard 802.111a “Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements—Part 11: Wireless LAN Medium Access Control and Physical Layer Specifications: High Speed Physical Layer in the 5 GHz Band.” Alternatively, non-radio communication technology may be used to provide such communication links, an example being infrared data communication.

In some embodiments, the first radio circuit120and the second radio circuit122may be combined into a single radio circuit which is operable on a cellular or other long range mobile communication system as well as a short range, low power radio system. Alternatively, portions of the two radio circuits120,122, may be combined to provide the necessary functionality while achieving particular design goals, such as reducing power consumption or physical size of the mobile station108.

The first radio circuit120and the second radio circuit122together in the illustrated embodiment form a radio means for receiving radio communication. The first radio circuit120is configurable for two-way radio communication with one or more remote radios such as base stations102,104. The first radio circuit may be so configured by providing operating power and tuning the receiver126and the transmitter132to appropriate communication frequencies and receiving and transmitting according to the controlling air interface standard. Similarly, the local radio circuit122is configurable for low power radio communication with other members of a local group such as the group including mobile stations108,110,112.

The control circuit124includes a controller150, a memory152and a user interface154. The second receiver140and the second transmitter142are coupled to a second antenna145. The control circuit124controls overall operation of the mobile station108. The controller150is implemented as a microprocessor or digital signal processor, or a combination of the two, in the illustrated embodiment. The controller150operates in conjunction with data and instructions stored in the memory152to control the operation of the mobile station108. The user interface154permits user control of the mobile station108. In a typical embodiment, the user interface154includes a display, a keypad, a speaker and a microphone.

In particular, the control circuit124is operable in conjunction with the first radio circuit120to decode a radio communication received as a downlink127from one of the base stations102,104. Further, the control circuit124is operable in conjunction with the local radio circuit122to transmit a local radio communication in response to the radio communication received on the downlink. Still further, the control circuit124is operable to identify an intended recipient of the radio communication and to transmit the local radio communication to an associated mobile station, such as mobile station110or mobile station112, when the intended recipient is the associated mobile station.

Thus, the first radio circuit120including the first receiver126and the decoder128forms a receiving means for receiving downlink radio transmissions. In alternative embodiments, some of the functionality provided by the decoder circuit128may be shared by the controller150. Also, it is known to implement a receiving circuit such as the first receiver circuit120as a zero intermediate frequency (ZIF) receiver or as a direct conversion receiver. Such receiver types translate the relatively high reception frequency of the radio frequency signals on the downlink127to a lower frequency for processing within the mobile station108. The local transmitter142, in conjunction with the synthesizer144, forms a local transmitting means for radio communication of data to an associated portable electronic device in response to the downlink radio transmissions.

In such an embodiment, the mobile station108may be configured as any type of portable electronic device, such as a cellular or other radio telephone, a personal digital assistant including wireless communication capabilities or any electronic processing device with wireless communication capability. Similarly, the other mobile stations in the system100, mobile station110and mobile station112, may be configured as any suitable portable electronic device.

The controller150, in conjunction with the decoder128forms a decoding means for decoding the downlink radio transmission in conjunction with receiving means formed by the receiver126. Similarly, the controller150forms a control means for determining an intended recipient of the downlink radio transmission. As noted, the controller150is preferably a general purpose or dedicated processor operating in response to program code stored in the memory152. As such, the controller150provides a variety of functions at different times and in response to differing stimulus. In place of the controller150, hardwired logic may be provided to provide similar functionality. Any other suitable processor or processing technology may be substituted for the controller150to provide the functionality described herein.

Members of the local group114determine among themselves which radio or radios of the local group will be responsible for receiving downlink radio communications and alert communications from other radios. Thus, the control circuit124forms a control means coupled with the radio means formed by the first radio circuit120and the local radio circuit122for detecting at least one of paging channel information and a local radio communication. If the mobile station108has been assigned to receive paging channel information and other alert communications for the local group114, the paging channel information is received by the radio means such as the first radio circuit120from a remote radio such as a base station102. The paging channel information is intended for a member of a local group of radios such as local group114, including the portable communication device formed by the mobile station108. The control circuit124of the mobile station108subsequently determines if the paging channel information is intended for the mobile station108or another member of the local group114. If another radio of the local group114has been assigned to receive alert communications for members of the local group114, the local radio communication received by the radio means such as the local radio circuit122is received from the other member of the local group and conveys information about received paging channel information received by the other member.

FIG. 2is a diagram illustrating local communication among a plurality200of mobile stations202,204,206,208,210,212. InFIG. 2, each of the mobile stations is in at least intermittent radio communication with each of the other mobile stations, which together form a local group214. For radio communication, the local group214uses a low power radio communication technology, such as Bluetooth. Other suitable radio communication technologies or protocols may be used. In the illustrated embodiment, each of the mobile stations is able to communicate over a relatively short distance with each of the other mobile stations. For example, when the mobile stations are all within ten meters of each other, reliable radio communication may be established, providing two-way transmission of data and other information. In addition to the radio links illustrated inFIG. 2, cross-links may also be established. For example, mobile station206may communicate with mobile station210and mobile station204may communicate with mobile station208.

Thus, the local radio circuits of each mobile station permit ongoing local radio communication of data and other information. Preferably, membership of the group is monitored and a list of members is maintained at at least one group member. As new members are added to the group, they may join the conversation as well. As members leave, their departure may be noted or may go unannounced. Preferably, this level of radio communication is largely invisible to the users of each mobile station. However, the radio links established between the mobile stations provide a resource which may be utilized by the respective radios or their users for file transfer or transfer of other information.

FIG. 3illustrates a method for sharing processing load among members of a local communication group300in the radio communication system100ofFIG. 1. The local group300includes a first mobile station304and associated mobile stations such as mobile station308. The first mobile station304has been assigned to receive transmissions from remote radios on behalf of the members of the group. This assignment has been made by cooperation among the members of the group.

WhileFIG. 3shows the assigned mobile station304in the approximate center of the group300, this is for convenience only. The members of the group300may be distributed over any appropriate distance limited only by reliable radio transmission and reception. The members of the group300may be in separate rooms or on separate floors of a building.

In the embodiment illustrated inFIG. 3, the first mobile station304receives a downlink radio transmission302. In the illustrated embodiment, the downlink radio transmission302is transmitted by a remote radio such as a base station of a radio telephone system using a mobile communication protocol, such as a cellular telephone system. The downlink radio transmission302may include data representative of voice or other information. In addition or instead, the downlink radio transmission may include an alert communication such as a paging channel.

The first mobile station304determines an intended recipient of the downlink radio transmission. This is accomplished, for example, by demodulating and decoding the downlink transmission302and reading the data embedded in the downlink302. The embedded data define a recipient for the downlink302. The recipient may be defined by an embedded mobile identification number corresponding to the recipient, data in the paging channel or in a voice channel, or by any other suitable method.

When the intended recipient corresponds to an associated mobile station or other member of the group300, the first mobile station304transmits information about the downlink radio transmission302to the associated mobile station on a low power local radio link such as link306transmitted to second mobile station308. In one embodiment, the information is broadcast to all members of the group300. In another embodiment, the information is encoded or encrypted for reception only by the intended recipient, mobile station308.

The associated mobile station, second mobile station308, may be associated with the first mobile station304in any convenient manner. It is envisioned herein that the members of the local communication group300will share identification information with other radios of the local group300of radios. The members of the group coordinate reception of downlink transmissions such as downlink transmission302among them and assign a receiving mobile station such as mobile station304to receive the downlinks. Subsequently, the assigned mobile station receives, decodes and processes downlink transmissions such as downlink transmission302for conveyance to an intended recipient among the radio communication group300.

In the particular case of a paging channel on the downlink302, subsequently the assigned mobile station receives a paging channel from a remote radio of the radio communication system in which the mobile stations operate. The assigned mobile station identifies in the paging channel the intended recipient of the paging channel and then determines correspondence between the intended recipient and respective identification information for one or more radios of the group. For example, the shared identification information may be stored in memory at the assigned mobile station. When a paging channel or other communication is received, the stored information is searched for a match with the information in the downlink identifying the intended recipient. If there is a match, information about the downlink or paging channel is transmitted to the intended recipient. If there is no match or correspondence, the downlink or paging channel is discarded. Thus, the first mobile station304, in conjunction with the other members of the radio communication group, coordinates reception of subsequent downlink radio transmissions among a plurality of mobile radio communication stations, the group300, including at least the associated mobile station, second mobile station308.

All but one mobile stations are not the assigned station. As is the case with the assigned mobile station, the non-assigned mobile stations share identification information with other radios of the local group of radios. Subsequently, such a non-assigned radio receives information about a received paging channel or other downlink transmission intended for the non-assigned radio from the one radio which has been assigned by the local group for receiving paging channels and other downlink transmissions for all radios of the local group.

Thus, whenever a group of subscribers congregate in close proximity, the illustrated method and apparatus operates to reduce the processing load placed on any given mobile station in the group by sharing the processing load among mobile stations of the group. For example, when users of the mobile stations of the group congregate in a busy public location, or in a private location such as a meeting in a conference room, these users have access to two separate radio communication systems. The first radio communication system provides two-way radio telephone service for voice and data transmission. A local communication system, such as Bluetooth, provides a second radio communication system.

In accordance with the illustrated embodiments, instead of each respective mobile station independently demodulating and decoding the downlink from the base station on the first radio communication, the decoding task is distributed among all the members of the group of mobile stations that are within range of each other's local radio communication circuit. In this way, only one mobile station has to decode the downlink at a given time. Other mobile stations do not have to energize the analog front end circuitry, decoders, controllers, and so forth, needed to receive the downlink. If a downlink transmission intended for reception by a member of the group is detected by the assigned mobile station, information about the downlink transmission may be conveyed over the local radio link to the intended recipient. After the assigned mobile station receives and decodes the information, the results are sent to all the proximal devices of the group via the short-range, low power local radio communication link.

The decoding operation may be distributed among the group of users in any suitable fashion. In one embodiment, among the plurality of mobile stations of the group, one mobile station is selectively assigned as the first mobile station for receiving the downlink transmission. In another embodiment, among the plurality of mobile stations of the group, the decoding task may be accomplished by sequentially assigning one mobile station of the plurality of mobile stations as the first mobile station to decode the downlink transmission.

In a first example of this embodiment, each mobile station sequentially is assigned to receive the downlink during a predetermined time period. After the time period has elapsed, responsibility for receiving the downlink transmission is passed to another mobile station in the sequence.

In a second example, each mobile station receives a predetermined number of downlink transmissions, such as one transmission. After the predetermined number is reached, responsibility for receiving downlink transmissions passes to a subsequent mobile station in the group.

In still another embodiment, the plurality of mobile stations among them may identify one mobile station having best radio reception characteristics. One example is identifying a best received signal strength indication (RSSI). The identified mobile station may then be assigned among the group as the first mobile station for receiving downlink transmissions. This embodiment may be especially suitable, for example, in a situation where the group of users of the mobile stations is located in a conference room with one of the users being near a window and having better reception of downlink transmissions from a remote radio.

In still another embodiment, the plurality of mobile stations among them may identify one mobile station having particular battery capabilities. This could include identifying a mobile station having best battery capabilities, such as most stored charge or longest time to discharge, or this could include identifying a mobile station having worst battery capabilities, such as least stored charge or shortest time to discharge. One example is determining at each mobile station an indication of remaining battery power. Each mobile station in turn communicates its respective remaining battery power to members of the local group. Based on this information, one mobile station is identified as having the particular battery capabilities. Using this information, the identified mobile station may be assigned as the first mobile station for receiving downlink transmissions, for example, if it has best battery capabilities. Conversely, the identified mobile station, if it has worst battery capabilities, may be designated as not to be assigned as the first mobile station for receiving downlink transmissions.

FIG. 4illustrates a prior art method of transmitting radio communications in a time division duplex (TDD) radio communication system. In a TDD system, uplink transmissions from a mobile station to a base station alternate with downlink transmissions from a base station to mobile stations. Thus, the first uplink transmission402is followed by a downlink transmission406. The downlink transmission406is followed by a subsequent uplink transmission408. Each downlink transmission is further subdivided into a plurality of slots. InFIG. 4, the downlink transmission406includes a first slot410, a second slot412, a third slot414and a fourth slot416. In the illustrated system, multiple users are assigned to each respective time slot410,412,414,416. Thus, referring to the group300of mobile stations inFIG. 3, the first mobile station304, designated S1, is assigned a downlink time slot in the first slot410. In this type of radio communication system, each mobile station must receive the transmission in its assigned time slot and decode the time slot information to locate a transmission for which it is the intended recipient. The area in the first time slot410labelled S1corresponds to the transmission of information intended for the first mobile station S1. The cross-hatched area of the time slots shows communication assigned to other users in the system. In a similar fashion, the mobile stations designated S2and S3are assigned to second downlink time slot412. Still further, the other members of the group, mobile stations designated as S4, S5and S6, are assigned to the third and fourth time slots414,416. In the prior art embodiment ofFIG. 4, time slot assignment at a base station is random for any given mobile station.

With the mobile stations of the group assigned this way, the mobile station which is assigned by the group for receiving downlink transmissions must receive all time slots of the downlink406but need not be powered up for the uplinks402,408The assigned mobile station enjoys reduced power consumption in that its receiving circuitry may be powered down during the uplinks402,408.

FIG. 5illustrates a timing diagram showing time slot assignments in the radio communication system of claim1. InFIG. 5, the uplink transmission times402,408again alternate with the downlink transmission time410. Similarly, inFIG. 5as inFIG. 4, the downlink410is divided into four time slots, including time slots410,412,414,416. However, in the system illustrated inFIG. 5, radio communications intended for any local station of the plurality or group of mobile stations are transmitted during a common predefined time period. Any time could be chosen for the common time period. In the embodiment ofFIG. 5, the chosen time period is time slot410. As is illustrated, the transmissions, if any, intended for the mobile stations designated S1, S2, S3, S4, S5, S6are all assigned for transmission during the first time slot410.

In this manner, optimal assignments of time slots have been made, insuring that all users in the group are sent in the same time slot410. This simplifies decoding of information intended for all mobile stations of the group within a single mobile station of the group. This prevents the situation shown inFIG. 4of spreading the proximal users' information across several time slots410,412,414,416. InFIG. 5, all the users share the same time slot410, meaning that the assigned mobile station need only energize its receive circuitry during the first time slot410.

Implementation of this requires that the base stations transmitting to the mobile stations have information about the identities of the mobile stations forming the group. Thus, one of the mobile stations in the group preferably transmits from the one mobile station of the plurality of mobile stations to a remote radio of the radio communication system identification information for each mobile station of the plurality of mobile stations.

FIG. 6is a flow diagram illustrating a method of operating the radio communication system ofFIG. 1. The method begins at block600.

At block602, all local group radios are identified to each other. This is preferably done using low power, short distance local radio links established among the radios of the group. An example of such a radio communication system for establishing such links is the Bluetooth radio standard. However, other wireless communication techniques, including infrared transmission and use of the cellular transmitter and receiver of the mobile stations may be used.

At block604, the mobile stations of the local group coordinate reception of downlink transmissions and transmission of uplink transmissions among local radios. For example, if it is desired to have all transmissions or paging channels intended for the local group consolidated into a single time slot, as is illustrated atFIG. 5, this information is aggregated and one local station of the group is assigned to transmit the information to a base station for subsequent processing. At block606, one mobile station is assigned for downlink reception. As described above, assignment of a mobile station to receive downlink transmissions for the entire group may be made in any suitable fashion. Responsibility for downlink reception may be passed around in a round robin fashion after lapse of predetermined time intervals or after detection of a predetermined number of downlinks.

At block608, it is determined if RF signals have been received at the assigned mobile station. The assigned mobile station remains in a loop waiting for receipt of a downlink containing information intended for one or more of the members of the group. The assigned mobile station may activate its receiver circuit only during predetermined times, such as during transmission of a paging channel by a base station in order to reduce or minimize battery drain.

Once radio signals have been received at block610, it is determined if the radio signals are intended for the receiving mobile station. If not, the receiving mobile station transmits a local radio communication to the intended recipient, block612. This is done using the low power, local radio link such as Bluetooth. Control then returns to block606. At block606, if appropriate, a new mobile station may be assigned for downlink reception. Assignment of one mobile station generally includes de-assignment of the previously assigned mobile station.

If, at block610, it was determined that the received RF signals were intended for the assigned mobile station, at block614the received transmission is processed. Control then proceeds to block606for assignment of a different mobile station, if necessary, and subsequent processing.

FIG. 7is a flow diagram illustrating an alternative embodiment of the acts illustrated in block606ofFIG. 6. InFIG. 7, assignment of a mobile station to receive downlink transmissions for the local group is done in a round robin fashion with reassignment after elapse of a timer. Thus, at block702, an initial mobile station is assigned for downlink reception. At block704, a timer is started to time duration during which the mobile station will be assigned. The timer may be maintained at the assigned mobile station, another mobile station or more mobile stations in the local group. At block706, it is determined if time has elapsed. If so, control returns to block702for de-assignment of the presently assigned mobile station and assignment of a new mobile station for receiving downlink transmissions intended for one or more members of the group. If, at block706, the timer had not elapsed, at block708it is determined if RF signals have been received. If not, control returns to block706to again test the timer. If RF signals are received at block708, control then proceeds to block610,FIG. 6.

FIG. 8illustrates an alternative embodiment of block604,FIG. 6. In the embodiment illustrated inFIG. 8, the assignment of a mobile station to receive downlink transmissions intended for one or more members of the local group is made according to reception characteristics of the respective mobile stations. Thus, at block802, each mobile station of the group measures a reception characteristic, such as received signal strength indication (RSSI). At block804, the mobile stations of the local group share their respective RSSI values using the local radio link. At block806, each mobile station determines if its respective RSSI value is the best of all respective RSSI values for the local group. If so, at block810, the mobile station is assigned to receive downlinks. If not, and another mobile station has the best RSSI value, at block12, the other mobile station is assigned to receive downlinks on behalf of the group.

As noted above, acts similar to those shown inFIG. 8could be taken to identify a mobile station having particular battery characteristics. Assignment of a mobile station having best battery characteristics or specific non-assignment of a mobile station having worst battery characteristics could be made based on the identification and shared information. The blocks ofFIG. 8can be readily modified by those ordinarily skilled in the art to produce method steps describing this process.

It is to be noted that the techniques for assigning one mobile station for reception of downlinks on behalf of all mobile stations in the local group may be combined in a particular situation. Thus, it may be initially determined if any mobile station of the group possesses particularly good reception characteristics. If not, then assignment may be made on some other basis, such as by random assignment or assignment in sequence.

FIG. 9is a portion of a flow diagram illustrating an alternative embodiment of steps of the flow diagram ofFIG. 6. At block902, the received downlink is decoded by the assigned mobile station on behalf of the rest of the local group. At block904, the intended recipient of the downlink is identified using data or other information embedded within the downlink. For example, a mobile identity number may be read from the embedded data. At block906, it is determined if the intended recipient is a member of the local group. If so, control proceeds to block610,FIG. 6. However, if the intended recipient is not a member of the local group, at block908the received downlink transmission is discarded and no further processing occurs for that downlink.

FIG. 10illustrates an alternative embodiment of the acts of block604,FIG. 6. At block1002, the assigned mobile station transmits identification information for members of the local group to one or more base stations in proximity to the local group. This identification information is preferably used by the radio communication system including the mobile switching center and the base stations of the system for controlling and combining downlink transmissions intended for members of the group. At block1004, a time slot is identified for group communication. This is similar to the aggregation of downlink transmissions in a common time slot illustrated inFIG. 5.

From the foregoing, it can be seen that the present embodiments provide an improved method and apparatus for operating a mobile station as part of a local group of mobile stations in a radio communication system. Mobile stations of the local group use a low power local radio network for communicating information about their capabilities and for assigning one mobile station of the group for receiving downlink transmissions. Assignment of the mobile station may change over time to share the processing load among the members of the local group. In this manner, the processing power and battery drain required by each individual mobile station of the local group is reduced.

While a particular embodiment of the present invention has been shown and described, modifications may be made. It is therefore intended in the appended claims to cover such changes and modifications which follow in the true spirit and scope of the invention.