HK1023895B - Methods and system for reduced operation of cellular mobile terminals - Google Patents

Description

Method and system for reducing power operation of cellular mobile terminal

The present invention relates to communication systems, and more particularly to communication systems utilizing wide area cellular networks.

Public cellular networks (public land mobile networks) are commonly used to provide voice and data communications to multiple users, for example, analog cellular radiotelephone networks, such as those known as AMPS, ETACS, NMT-450, and NMT-900, have been successfully deployed worldwide. Recently, digital cellular radiotelephone systems have been introduced, referred to in north america as IS-54B and the pan-european GSM system. These and other systems are described, for example, in a book called "cellular radio system" by Balston et al, published by Norwood, MA, Artech Press 1993.

Conventional analog radiotelephone systems typically employ a system known as Frequency Division Multiple Access (FDMA) to establish a communications channel. As a practical matter well known to those skilled in the art, radiotelephone communications signals of modulated waveform are typically communicated over a predetermined frequency band in the spectrum of carrier frequencies. These discrete frequency bands operate as channels over which cellular radiotelephones communicate with the cell through a base station or satellite serving the cell. For example, in the United states, the Federal authority allocates a block of cellular communication to a system of UHF spectrum further subdivided into narrow band pairs, called EIA-553 or IS-19B. The channel pair is from a frequency duplex device in which the transmit and receive frequencies in each pair are offset by 45 MHZ. There are currently 832 radio channels 30HKZ wide allocated to cellular mobile communications in the united states.

As the number of users increases, the limitation on the number of available frequency bands presents some challenges. Increasing the number of users in a cellular radiotelephone system generally requires more efficient use of the limited available frequency spectrum in order to provide a greater total number of channels while maintaining communication quality. This challenge is exacerbated because users may not be evenly distributed among the cells within the system. More channels may be needed in order for a particular cell to handle the higher local user densities that may occur at any given time. For example, a cell in a downtown area may contain hundreds or thousands of users at any time, easily using up the number of frequency bands available in the cell.

For these reasons, conventional cellular systems employ frequency reuse to increase the potential channel capacity in each cell and to increase spectral efficiency. Frequency reuse involves assigning frequency bands to cells, with cells utilizing the same frequency geographically separated to allow radiotelephones in different cells to use the same frequency simultaneously without interfering with each other. By doing so, only a few hundred frequency bands of the system can serve thousands of users.

Another technique that may further improve channel capacity and spectral efficiency is Time Division Multiple Access (TDMA). A TDMA system may be implemented by subdividing the frequency band utilized in a conventional FDMA system into sequential time slots. While communication on a frequency band typically occurs on a common TDMA frame comprising a plurality of time slots, communication on each frequency band may occur according to a unique TDMA frame, with time slots unique to that frequency band. An example of a system employing TDMA IS the dual analog/digital IS-54B standard employed in the united states, in which each original frequency band of EIA-553 IS subdivided into 3 time slots, while the european GSM standard divides each frequency band into 8 time slots. In these TDMA systems, each user communicates with a base station using bursts of digital data transmitted in time slots assigned to that user.

A channel in a TDMA system typically comprises one or more time slots on one or more frequency bands. As described above, traffic channels are utilized to communicate voice, data, or other information between users, such as between a mobile terminal, such as a wireless telephone, and a network base station. In this way, each traffic channel constitutes one direction of a duplex communication link established by the system from one user to another. Traffic channels are typically allocated dynamically by the system when needed. In addition, systems such as the European GSM system may "frequency hop" traffic channels, i.e., randomly switch frequency bands over which particular traffic channels are transmitted. Frequency hopping reduces the probability of interference events between channels and improves overall communication quality by utilizing interference signal dispersion and averaging.

GB 2,290,399 discusses a method of operating a radio system having a transmitter unit and a receiver unit. At the transmitter unit, at least a part of the address is repeatedly transmitted for a predetermined period of time (T)_w) Followed by a message. The receiver unit does not exceed a predetermined time period (T) in the sleep mode_w) After a period of time, transition from the dormant low power mode to the receive mode. In the receive mode, address information is received and compared bit by bit with a predetermined address stored on the receiver unit. The system described therein, however, relates to paging systems and not TDMA systems utilizing multiple time slots, such as those used in TDMA cellular networks.

Among the dedicated control channels typically included in a cell transmission are forward control channels used in cells of a wide area cellular network, which broadcast control information to wireless telephones that may seek access to the network. The control information broadcast on the forward control channel may include such things as the identity of the cell, the associated network identity, system timing information, and other information needed to access the wide area cellular network from the wireless telephone.

Forward control channels, such as the Broadcast Control Channel (BCCH) of the GSM standard, are typically transmitted on dedicated frequency bands in each cell. A wireless telephone seeking access to a system typically "listens" to a control channel in a standby mode and is not synchronized with a base station or satellite until it acquires the base station or satellite control channel. To prevent undue interference between control channels in adjacent cells, frequency reuse has traditionally been employed, with different dedicated frequency bands being used for control channels in adjacent cells in a frequency reuse pattern that ensures minimal isolation between cells of the same channel. Frequency hopping, which may allow for more dense reuse of the control channel band, is not typically employed, and unsynchronized wireless telephones often have difficulty capturing frequency hopping control channels due to the lack of a reference point for the hopping sequence employed.

Since the mobile terminal must "listen" to the control channel even when not being used for communication, the mobile terminal must expend energy. Energy consumption management is therefore critical to extend the duration of operation of the battery or rechargeable power supply in a mobile terminal. Thus, many mobile terminals are put into a "sleep mode" when not originating or receiving calls. However, the mobile terminal still has to monitor the paging channel in sleep mode to avoid dropping incoming calls. To maximize sleep mode efficiency, the mobile station should be able to detect as early as possible in the reception process whether the received message is a relevant message or an irrelevant message, thereby avoiding as many signal processing steps as possible. The mobile station immediately returns to go to sleep once an extraneous message is detected. To understand the possible power savings from early detection of unrelated pages, consider a typical paging channel in which paging messages are sent once per second. This means that there are 400 paging messages sent to the mobile terminal 60 x 24 x 86 each day. For example, if only 1% of these messages are relevant, the mobile station can avoid processing 99% of paging messages if it can detect irrelevant messages. Thus, for most of the message reception time of the terminal, the mobile terminal can actually spend in the sleep mode.

Currently, however, to determine whether a message is relevant, the entire message must be received and at least partially processed. If the message is irrelevant, this reception process alone requires unnecessary energy expenditure by the mobile terminal. Therefore, in view of the above discussion, there is a need to further exploit power savings in mobile terminals.

In view of the above discussion, it is an object of the present invention to provide improved power saving in a mobile terminal.

It is a further object of the invention to provide reduced power consumption without increasing the latency of receiving messages.

In view of the above, the present invention is directed to reducing power consumption in a mobile terminal having a receiver for receiving a time division multiplexed message distributed over a plurality of time slots, a first portion of the time division multiplexed message corresponding to a first subset of the plurality of time slots being received by receiving the first subset of the plurality of time slots. The mobile terminal then determines from the first portion of the time division multiplexed message whether the mobile terminal needs to receive additional time slots of the time division multiplexed message. If the mobile terminal determines from the first portion that the mobile terminal needs to receive an additional portion of the time division multiplexed message, the mobile terminal receives a second subset of the plurality of time slots to receive a second portion of the time division multiplexed message. Thus, the first part of the message is preferably decodable independently of the rest of the message.

In one embodiment of the invention, an address is associated with the mobile terminal and the time division multiplexed message contains an address specifying the intended recipient of the message. In this embodiment, the mobile terminal may determine from the first part of the message whether the time division multiplexed message is addressed to a mobile terminal having an address in an address range containing the mobile terminal and receive further time slots only if the address of the mobile terminal is within the address range.

Alternatively, when the mobile unit identifier comprises multiple bits, the first portion of the time division multiplexed message may comprise a subset of the multiple bits of the mobile unit identifier of the intended recipient of the message. The mobile terminal may then determine whether a subset of the plurality of bits contained in the first portion of the time division multiplexed message is the same as a corresponding subset of the plurality of bits of the mobile unit identifier of the mobile terminal and only receive the remainder of the message if the bits are the same. A subset of bits of the mobile unit identifier may be selected from the plurality of bits such that a random distribution of possible mobile unit identifier values is obtained from the distribution of mobile terminals.

In some embodiments of the invention, the time division multiplexed message comprises a paging message. The time division multiplexed message may also be a broadcast message. In this case, the mobile terminal may determine from the first part of the message whether the time division multiplexed message is a newer version of a previously received time division multiplexed message and receive the rest of the message only if the version is newer.

The present invention enables a mobile terminal to reduce the energy spent receiving a message by receiving only a portion of the message and determining whether to receive the remainder of the message. Furthermore, because only a portion of the message needs to be processed, the energy used to process the entire message can be saved. The invention is particularly suitable for use with paging messages where the mobile terminal typically monitors all paging messages in order to avoid dropping an incoming call.

Those skilled in the art will appreciate that the present invention may be implemented as a method or device.

Figure 1 shows the architecture of a cellular radio system suitable for use in the present invention;

FIG. 2 graphically illustrates channels in a time division multiplexed communication system;

FIG. 3 graphically illustrates a frame in a time division multiplexed communication system;

figure 4 graphically illustrates a combination of frames in a GSM compliant communication system;

figure 5 graphically illustrates a combination of control multiframes in a GSM compliant communication system;

FIG. 6 is a flow chart showing operation of a mobile terminal according to one embodiment of the present invention; and

figure 7 is a flow chart showing operation of a base station in accordance with one embodiment of the present invention; and

fig. 8 is a block diagram of a mobile terminal according to the present invention;

FIG. 8A is a detailed block diagram of one embodiment of the mobile terminal of FIG. 8;

fig. 9 is a block diagram of a base station in accordance with the present invention; and

fig. 9A is a detailed block diagram of one embodiment of the mobile terminal of fig. 9.

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. As will be appreciated by those skilled in the art, the present invention may be embodied as methods or devices. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects.

For purposes of understanding the present invention, a wide area cellular network is described below with reference to the GSM cellular system standard. However, as will be appreciated by those skilled in the art, the advantages and benefits of the present invention can also be obtained in other communication protocols, and thus, the present invention should not be construed as limited to the GSM protocol.

A wide area cellular network utilizing the present invention is shown in fig. 1. In the cellular radio system shown in fig. 1, a geographical area, such as a metropolitan area, is divided into several smaller connected radio coverage areas (called "cells"), such as cells C1-C10. These cells C1-C10 are served by corresponding groups B1-B10 of fixed radio stations (referred to as "base stations"), each operating on a subset of the Radio Frequencies (RFs) allocated to the system. The frequencies assigned to any given cell may be reassigned to distant cells in accordance with a frequency reuse pattern well known in the art. In each cell, at least one frequency (referred to as a "control" or "paging/access" channel) is used to carry control or monitoring messages, while the other frequency (referred to as a "voice" or "speech" channel) is used to carry voice conversations. Cellular telephone subscribers (mobile subscribers) in cellular C1-C10 are provided with portable (hand-held) portable (hand-carried) or automotive (vehicle-carried) telephone units (mobile terminals), such as mobile terminals M1-M9, each of which communicates with nearby base stations, base stations B1-B10 are connected to and controlled by a mobile services switching center (MSC)20, MSC20 is in turn connected to a central office (not shown in FIG. 1) in a landline (landline) Public Switched Telephone Network (PSTN), or similar facility such as an Integrated System Digital Network (ISDN). MSC20 switches calls between and among wireline and mobile subscribers, controls signaling to the mobile terminals, orchestrates operation, maintenance and testing of billing and provisioning systems.

In the united states, two different entities are approved to operate cellular systems in each Metropolitan Statistical Area (MSA). To receive service, the mobile subscriber enters into a subscription contract with one of these local operators (and the local system to which the service is subscribed is referred to as the "local system"). When traveling out of a home system (referred to as "roaming"), a mobile subscriber can obtain service in a remote (referred to as "visited") system if a roaming agreement exists between the home and the operator of the visited system. Access to the cellular system by any of the mobile terminals M1-M9 is controlled based on a Mobile Identification Number (MIN) assigned to each mobile subscriber by the local system operator and an Electronic Serial Number (ESN) permanently stored in the mobile station (the so-called "MIN/ESN pair"). The MIN/ESN pair is sent from the mobile station when a call is originated and is verified for validity by the MSC 20. If the MIN/ESN pair is determined to be illegal, the system may deny mobile station access. The MIN is also sent from the system to the mobile station when notifying the mobile station of an incoming call.

At power-on (power-on), each mobile terminal M1-M9 enters an idle state (standby mode) and tunes to and continuously monitors the strongest control channel (typically the control channel of the cell in which the mobile station is located at that time). When moving between cells in the idle state, the mobile station will eventually "lose" the radio connection on the control channel of the "old" cell and tune to the control channel of the "new" cell. Both the initial tuning to the control channel and its change are done automatically by scanning all control channels operating in the cellular system to find the "best" control channel. When a control channel with good reception quality is found, the mobile station remains tuned on this channel until the quality deteriorates again. In this manner, the mobile station remains "in contact" with the system and can receive or place telephone calls through one of the base stations B1-B10, which are connected to the MSC 20.

To detect an incoming call, the mobile station continuously monitors the control channel to determine if a paging message addressed to it (i.e., containing its MIN) has been received. When a mobile subscriber is called by a normal (landline) subscriber, a paging message will be sent to the mobile station. The call is directed from the PSIN to MSC20 where the dialed number is analyzed. If the dialed number is valid, the MSC20 requests some or all of the base stations B1-B10 to page the called mobile station throughout their corresponding cells C1-C10. Each base station B1-B10, receiving the request from the MSC20, then sends a paging message containing the MIN of the called mobile station on the control channel of the corresponding cell. Each idle mobile terminal M1-M9 present in the cell compares the MIN in the paging message received on the control channel with the MIN stored in the mobile station. The called mobile terminal with the matching MIN will automatically send a page response on the control channel to the base station, which will forward the page response to MSC 20. Upon receiving the page response, the MSC20 selects an available voice channel in the cell receiving the page response (MSC20 maintains a list of free channels for this purpose) and requests that the base station in the cell command the mobile station to tune to the selected voice channel via a control channel. Once the mobile station has tuned to the selected voice channel, a make connection is established.

On the other hand, when the mobile subscriber initiates a call (e.g., by dialing the general subscriber's telephone number and pressing the "send" button on the telephone handset in the mobile station), the dialed number and the mobile station's MIN/ESN pair are transmitted on the control channel to the base station and forwarded to MSC20, which acknowledges the mobile station, assigns a voice channel and establishes a connection for the session as described above.

If the mobile station moves between cells in the conversational state, the MSC20 will perform a "handoff" of the call from the old base station to the new base station. The MSC20 selects an available voice channel in the new cell and then instructs the old base station to send a handoff message to the mobile station on the current voice channel in the old cell informing the mobile station to tune to the selected voice channel in the new cell. The handover message is sent in a "blank and burst" mode, which results in a short, but hardly noticeable, interruption in the conversation. Upon receipt of the handoff message, the mobile station tunes to the new voice channel and establishes an open connection through the new cell by the MSC 20. The old voice channel in the old cell is marked as idle in the MSC20 and is available for another conversation.

The communication network shown in fig. 1 preferably utilizes a digital standard that employs time division multiplexed messages. For example, GSM systems use time division carriers for messaging. Fig. 2 shows time division of carriers. As shown in fig. 2, the carrier may be divided into 1 to n fixed-length periods called burst periods. Each such burst period may be considered a time slot of a time division carrier.

As seen in fig. 3, a group of sequential slots may be divided into a frame. One frame includes m slots. These time slots are typically designated from 0 to m-1. As also shown in fig. 3, the frames may be repeated such that slot 0 in frame 1 corresponds to slot 0 in frame 2. In a typical time division multiplexed system, a mobile terminal transmits and receives in only one of the slots of a frame. Thus, the mobile terminal may go inactive during the remaining time slots, thereby saving energy.

In a GSM system, as shown in fig. 4, a frame contains 8 time slots labeled 0 through 7. Communications between base stations B1-B10 and mobile terminals M1-M9 are generally divided into two types, traffic channels and common channels. The traffic channel contains 26 GSM frames in a so-called multiframe. The common channel contains 51 GSM frames in a multiframe. The present invention will be described with respect to the 51-frame control channel multiframe shown in fig. 5.

As shown in fig. 5, a GSM multiframe may comprise 51 frames, sequentially numbered 0 through 50. The type of information or function of each frame in fig. 5 is indicated as a frame designated as F indicating a frequency correction burst, a frame designated as S indicating a synchronization burst, a frame designated as BCCH indicating a broadcast control channel, a frame designated as CCCH indicating an example of a common control channel, and a frame designated as I indicating an idle burst. Fig. 5 illustrates the designation of one slot for each frame depicted, such that, for example, the CCCH associated with frames 6-9 represents a message encoded over 4 slots, which is slot 0 for each frame making up the CCCH.

In operation, the mobile terminal M1 is notified of an incoming call with a paging message transmitted in a so-called Paging Channel (PCH). The PCH is carried on one or more instances of the CCCH, as defined in the information carried on the BCCH. A particular PCH may be repeated after every 2 to 9 multiframes. Thus, since there are up to 9 CCCHs per 51-frame multiframe, and these CCCHs repeat over a specified interval of 2 to 9 multiframes, 81 uniquely identifiable PCHs can be specified.

A base station such as B1 assigns a PCH uniquely identified by a mobile terminal such as M1 as its paging channel. The mobile terminal M1 is in standby or sleep mode most of the time it is in use, M1, in which it waits for an incoming call. To avoid dropping incoming calls and to reduce the latency of acknowledging incoming calls, the mobile terminal M1 monitors each occurrence of the assigned PCH for paging messages directed to the mobile terminal M1. In a conventional GSM system, the paging message is convolutionally encoded over the entire CCCH, such that the mobile terminal must receive all 4 slots of the PCH to decode the paging message. Thus, in a conventional system, the mobile terminal M1 receives and decodes all 4 slots of an assigned PCH each time the assigned PCH occurs.

Unlike conventional systems, the system of the present invention allows the mobile terminal M1 to receive only a portion of the time slots associated with the assigned PCH and then determine whether additional time slots should be received. By selectively controlling the signal processing of the receiver and the mobile terminal, power consumption of the mobile terminal is reduced. Thus, the mobile terminal may receive a first subset of the plurality of time slots that make up the entire message and allow the mobile terminal to receive a first portion of the time division multiplexed message. The mobile terminal may then determine from the first portion of the time division multiplexed message whether the mobile terminal needs to receive additional time slots of the time division multiplexed message. The mobile terminal receives the remainder of the time division multiplexed message only if it decides to receive a further portion. In case no further parts are to be received, the mobile terminal saves the energy needed for receiving and processing the further parts.

One way to determine whether the mobile terminal receives the remainder of the time division multiplexed message is to use the mobile unit identifier address MI associated with each mobile terminal. The first part of the message may then contain an address or address range that specifies the intended recipient of the message. The mobile terminal may then compare the address or address range from the first part of the message with its assigned address to determine whether the mobile terminal should receive further parts of the message.

If not all bits of the address assigned to the mobile terminal are included in the first portion of the time division multiplexed message, a subset of bits of the mobile unit identifier of the intended recipient of the message may be included in the first portion of the time division multiplexed message. The mobile terminal may then determine whether to receive additional portions of the message by determining whether a subset of bits of the mobile unit identifier contained in the first portion of the time division multiplexed message is equal to a corresponding subset of the plurality of bits of the mobile unit identifier assigned to the mobile terminal. A subset of these bits may be selected such that a random distribution of possible mobile unit identifier values is obtained from the distribution of mobile terminals. Thus, for all mobile terminals in this distribution, the likelihood that the mobile terminal will correctly determine that the terminal should not receive further portions of the message is approximately equal.

Although the above power saving method may be effective for reducing power consumption of messages intended for a particular mobile terminal, power savings may also be obtained in "broadcast" messages to be received by all mobile terminals in the cell. Broadcast messages are transmitted periodically to all mobile terminals within the cell, however, the content of these messages may be the same for several broadcasts. Thus, further energy savings can be obtained by receiving the entire broadcast message only when the message content is changed in a meaningful way. This determination may be made by determining whether the time division multiplexed message is a newer version of a previously received time division multiplexed message and receiving all messages only if it is the newer version.

The mobile terminal can determine the version of the message by the base station including the version information in the first subset of the time slots of the time division multiplexed message. The mobile terminal now receives and decodes this version information and compares this information with the version information corresponding to the most recently received version of the time division multiplexed message received by the mobile terminal. If the version information indicates a newer version of the message, the mobile terminal may receive the entire message and store the message and its associated version information. So that the mobile terminal receives and processes the entire broadcast message only when the message contains new information and thereby saves energy otherwise required to receive and process redundant information.

The present invention is described below with respect to fig. 6, 7, 8 and 9, which are flowcharts and block diagrams illustrating the operation of a base station and a mobile terminal utilizing the present invention. It will be understood that each block of the flowchart illustrations, and combinations of blocks in the flowchart illustrations, can be implemented by computer program instructions. These program instructions may be provided to a processor to produce a machine, such that the instructions, which execute on the processor, create means for implementing the functions specified in the flowchart block or blocks. Execution of these computer program instructions by a processor may cause a series of operational steps to be performed by the processor to produce a computer implemented process such that the instructions, which execute on the processor, provide steps for implementing the functions specified in the flowchart block or blocks.

Accordingly, blocks of the flowchart illustrations support combinations of means for performing the specified functions, combinations of steps for performing the specified functions and program instruction means for performing the specified functions. It will also be understood that each block of the flowchart illustrations, and combinations of blocks in the flowchart illustrations, can be implemented by special purpose hardware-based systems which perform the specified functions or steps, or combinations of special purpose hardware and computer instructions. It should be noted that many of the components of the mobile terminal 15 shown in fig. 8 can be used to construct the base station 42 shown in fig. 9, where like components are designated with like reference numerals in fig. 8 and are further designated with a prime (') to distinguish the components of the base station 42 from the components of the mobile terminal 15.

The base station 42 shown in fig. 9 encodes and transmits messages to the mobile terminal 15 shown in fig. 8. Figure 7 illustrates the operation of the base station 42 and figure 6 illustrates the operation of the transmission for the mobile terminal 15.

As seen in fig. 8, a mobile terminal 15 according to the present invention includes an antenna 21 connected to a transceiver 22 for transmitting and receiving electromagnetic signals. The transceiver 22 is controlled by a control processor 28. Information to be transmitted using the transceiver 22 is processed by the transmit circuitry 24 which provides transmit signal processing. Similarly, information received by the transceiver 22 is processed by receive circuitry 26, which provides received signal processing. Each of these circuits is also controlled by a control processor 28 having associated memory or other storage 32 for storing data or processing instructions. The mobile terminal 15 also includes a power supply 30, which typically operates from a rechargeable battery or other such portable power storage device. The control processor 28 may selectively provide power from the power supply 30 to the other components of the mobile terminal 15, such as the transmit circuitry 24, receive circuitry 26, and transceiver 22, to reduce power consumption as described herein. The mobile terminal 15 may also include input and output devices such as a keypad 34, speaker 36, microphone 38, and display 40 that are operatively associated with the control processor 28 for interacting with a user.

Similarly, the base station 42 shown in fig. 9 includes an antenna 21 'connected to a transceiver 22'. The transceiver 22 'is controlled by a control processor 28'. Information to be transmitted by the transceiver 22 'is processed by the transmit circuitry 24' which provides transmit signal processing. Similarly, information received by the transceiver 22 'is processed by a receive circuit 26' that provides received signal processing. Each of these circuits is also controlled by a control processor 28 'having associated memory or other storage device 32' for storing data or processor instructions. The base station also includes a power supply 30', which unlike the mobile terminal 15, is not necessarily portable or operated from a power storage device such as a battery. Thus, the base station 42 may not have the same power saving considerations as the mobile terminal 15. The base station 42 also includes an MSC interface 44 for communicating information to and from the MSC 20.

The operation of the base station 42 and the mobile terminal 15 is described below with respect to sending messages from the base station 42 to the mobile terminal 15. For example, the message may be a paging message or a broadcast message received by the MSC interface 44 of base station 42 and provided to the control processor 28' for transmission to one or more mobile terminals. As seen in fig. 7, transmission of the message to the mobile terminal 15 begins with the control processor 28' determining whether the message is intended for a particular mobile terminal or whether the message is a broadcast message (blocks 70 and 72). If the message is a broadcast message, control processor 28' includes the version number of the broadcast message in the first portion of the message (block 74). If the message is intended for a particular mobile terminal, control processor 28 'includes terminal-specific information, such as a portion of the mobile terminal's address or mobile unit identifier described above, in the first portion of the message to be sent (block 76).

In either case, the first portion of the message and the remainder of the message are provided to the transmit circuitry 24', which independently encodes the first portion of the message and the remainder of the message (block 78). The transmit circuitry 24 ' then provides the two independently encoded portions of the message to the transceiver 22 ' for transmission on the antenna 21 ', which completes the message transmission operation (blocks 80, 82 and 84).

As seen in fig. 6, the mobile terminal 15 receives a message from the base station 42 beginning with a time slot in which the transceiver 22 is activated to receive the message (blocks 50 and 52). The mobile terminal 15 then deactivates the transceiver 22 for the received time slot (block 54). The mobile terminal 15 then determines whether enough messages have been received to decode a portion of the message (block 56). If a message has not been received that is sufficient to decode a portion of the message, the activation and deactivation of the transceiver 22 is repeated at the appropriate timing to continue receiving the slots of the message (blocks 56, 52, and 54).

When a time slot is received that is sufficient to decode a portion of the message, control processor 28 causes receive circuitry 26 to process the received information to decode the portion of the message (block 58). The control processor 28 then determines from the decoded message part whether a new version of the broadcast message is being transmitted or whether the message is directed to the mobile terminal 15. If either is the case, the process of activating and deactivating the transceiver 28 and receive circuitry 26 continues until the entire message is received, as seen in block 62. If, however, the message does not contain new information or is directed to a different mobile terminal, the message reception process for the current message is terminated (block 64). As shown in fig. 6, if the control processor determines at any point in the message monitoring process that the mobile terminal does not need to fully receive the message, the process can be terminated and energy otherwise expended receiving and decoding the message saved.

In addition to the targeted messaging system described above for transmitting messages to mobile terminals, the use of base station 42 and mobile terminal 15 may generally conform to known cellular communication methods such as the GSM described above. These general aspects of the operation of the mobile terminal 15 and the base station 42 are known to those skilled in the art. Accordingly, general operation of the base station 42 and the mobile terminal 15 beyond that which is relevant to the present invention is not described.

A more detailed block diagram of one embodiment of a mobile terminal in accordance with the present invention is provided in fig. 8A. Also, a more detailed block diagram of one embodiment of a base station in accordance with the present invention is provided in figure 9A. As with mobile terminal 15 and base station 42, many of the components are common to both devices and perform the same functions in each device. The following describes the operation of the mobile terminal of fig. 8A and the base station of fig. 9A for both transmit and receive control and voice messages, highlighting the number of operations and the amount of savings that can be achieved by using the present invention. As the discussion becomes clearer, the large number of components and operations required to receive and decode a message exacerbates the need to detect early whether a message distributed over several slots should be received and decoded in its entirety.

Referring initially to fig. 8A, a block diagram of an exemplary mobile terminal generally compliant with IS-54B and usable in accordance with the present invention IS shown. In fig. 8A, some components are shown that are associated with communicating over a digital channel, although it should be understood that other digital or analog components may be used in addition to or instead of some of these components. The exemplary mobile terminal of fig. 8A is capable of sending and receiving voice and control data. The transmit circuitry is generally depicted in the upper half of fig. 8A and the receive circuitry is generally depicted in the lower half of fig. 8A.

In the mobile terminal of fig. 8A, the microphone 100 detects speech from the user as an analog speech signal and then passes it through one or more speech processing stages (not shown in fig. 8A) before providing it as input to the speech encoder 101. The pre-coding processing stage may include audio level adjustment, band pass filtering and analog to digital conversion (such as 13 bit PCM format or 8 bit μ law format) followed by additional high pass filtering. The speech encoder 101 compresses the speech signal into a low-rate data bit stream (e.g., from 64kbps to 8kpbs) using a speech compression algorithm (e.g., RELP or VSELP). The output of the speech encoder 101 is fed to a channel encoder 104 which applies one or more error protection and/or correction techniques to the data stream. For example, the channel encoder 104 may utilize half the convolutional code rate to protect the more vulnerable bits of the speech encoder data stream. The channel encoder 104 may also use a Cyclic Redundancy Check (CRC) on some of the most significant bits of the vocoder frame.

As shown in fig. 8A, control data is generated in a Fast Associated Control Channel (FACCH) generator 102 and a Slow Associated Control Channel (SACCH) generator 103 in the mobile terminal and error correction coded in channel encoders 105 and 106, respectively. FACCH messages are transmitted in a "blank and burst" mode whereby bursts of voice data are emptied and replaced with high rate FACCH bursts. In contrast, SACCH is transmitted continuously at a slower rate with bursts of voice data. In the exemplary embodiment shown in fig. 8A, the SACCH message is fed to a 22-burst interleaver (interleaver)110, which distributes the SACCH data over 22 slots before transmission.

The encoded voice bits from the channel encoder 104 and the encoded FACCH message from the channel encoder 105 are provided to respective inputs of a time division multiplexer 107 which formats the voice data or FACCH message into transmission time slots. The output of the multiplexer 107 is fed to a 2-pulse digital multiplexer 108 which interleaves the coded voice or FACCH data over the two time slots in order to ameliorate the degrading effects of Rayleigh fading (thereby providing further protection against channel errors in addition to error correction coding). This means that each voice slot contains data from two consecutive voice encoder frames or similarly each FACCH message is spread over two slots. The output of the 2-burst interleaver 108 is provided as an input to a modulo-2 adder 109 where the data is encrypted on a bitwise basis using logical modulo-2 addition with a pseudorandom keystream provided by a cryptography unit 115. The input to the cryptographic unit 115 may contain the value of the frame counter 114 incremented once every 20ms (i.e., once for each TDM frame of the full-rate channel), and a secret key 116 unique to the mobile terminal. The frame counter 114 is used to update the cipher (pseudo-random key stream) once every 20ms (i.e., once per transmitted TDM frame). The password is generated using an encryption algorithm that operates on the bits of the secret key 116.

The encrypted data from modulo-2 adder 109 and the interleaved SACCH data from 22-burst interleaver 110 are provided as inputs to burst generator 111, which is also provided with a Sync (Sync) word and a digital check color code (DVCC) from Sync word/DVCC generator 112. Burst generator 111 formats data bursts that each include a sync word, DVCC, SACCH data, and voice or FACCH data. The sync word is used for slot identification and synchronization, as well as equalizer training at the remote receiver (i.e., base station). The DVCC is used to distinguish the current traffic channel from the traffic cochannel and to ensure that the receiver is decoding the correct RF channel. The DVCC may be error correction coded, such as with Haming codes. As will be seen below, DVCC and Sync words are also included in each burst transmitted from the base station to the mobile station.

With further reference to fig. 9A, each message burst from the burst generator 111 is transmitted in one of the time slots of the TDM frame. The burst generator 111 is connected to an equalizer 113 which provides the timing required to synchronize the transmission of one time slot with the transmission of the other time slots. Equalizer 113 detects the timing signals transmitted from the base station (master) to the mobile terminal (slave) and synchronizes burst generator 111 accordingly. The equalizer 113 may also be used to check the values of the Sync word and DVCC from the base station, and both the burst generator 111 and the equalizer 113 are connected to the frame counter 114 for timing purposes.

The message burst generated by the burst generator 111 is provided as input to an RF modulator 117 which is used to modulate the carrier frequency according to a modulation technique known as pi/4 phase-shifted differential encoder phase shift keying (pi/4 DQPSK). Using this technique implies that the information to be transmitted by the mobile terminal is differentially encoded, so that the 2-bit symbols are transmitted as four possible variations in phase (± pi/4 and ± 3 pi/4) rather than absolute phase. To reduce errors caused by noise in the selected RF channel, Gray coding can be used to map adjacent phase variations onto symbols that differ by only one bit (since most possible errors cause the receiver to select adjacent phases, these errors will be limited to single-bit errors). The carrier frequency of the selected RF channel is provided to the RF modulator 117 by the transmit frequency synthesizer 118. The pulse train modulated carrier signal output from the RF modulator 117 is amplified by a power amplifier 119 and then transmitted to a base station via an antenna 120.

Reception at the mobile terminal is essentially the inverse of the transmission. The mobile terminal receives the burst modulated signal from the base station via an antenna 121 connected to a receiver 122. The receive frequency synthesizer 123 generates a receiver carrier frequency for the selected RF channel and provides it to an RF demodulator 124, which demodulates the received carrier signal to an Intermediate Frequency (IF) signal. IF demodulator 125 further demodulates the IF signal to recover the original digital information prior to pi/4-DQPSK modulation. The digital information is then passed to equalizer 113 which formats the information into two-bit symbols and then to symbol detector 126 which converts the symbols into a single-bit data stream containing voice or FACCH data and SACCH data. The symbol detector 126 distributes the FACCH or voice data to the modulo-2 adder 127 and the SACCH data to the 22-burst deinterleaver 135.

A modulo-2 adder 127 is connected to the cipher unit 115 and is used to decrypt the encrypted voice or FACCH data on a bit-by-bit basis by subtracting the same pseudorandom keystream used by the transmitter in the base station to encrypt the data. The decrypted output of the modulo-2 adder 127 is fed to a 2-burst deinterleaver 128 which reconstructs the voice or FACCH data by combining bits from two successive frames of digital data. The 2-burst deinterleaver 128 is coupled to two channel decoders 129 and 130 that decode the convolutionally encoded voice or FACCH data and check the CRC bits to determine if any errors have occurred (the CRC bits also provide a means of distinguishing between the voice data and the FACCH data). The voice data from the channel decoder 129 is fed to a voice decoder 131 which recovers the original digital voice signal. The signal is then converted to analog and filtered before being broadcast by the speaker 133. The FACCH detector 132 detects any FACCH messages and submits them to the microprocessor 134 for appropriate action.

The 22-burst deinterleaver 135 reassembles the SACCH data distributed over 22 concatenated frames. The output of the 22-burst deinterleaver 135 is provided as an input to a channel decoder 136. The SACCH detector 137 detects any SACCH message and passes it to the microprocessor 134 for appropriate action.

The microprocessor 134 controls the activities of the mobile station and the communications between the mobile station and the base station. The microprocessor 134 makes the determination based on the messages received from the base station and the measurements performed by the mobile terminal. The microprocessor 134 is provided with a memory (not shown) and is also connected to a terminal keypad input and display output unit 138. The keypad and display unit 138 allow the user to initiate and answer calls, and enter information into the mobile terminal memory.

The base station of fig. 9A communicates with the mobile terminal of fig. 8A. As will be appreciated by those skilled in the art, there may be some differences in the construction of base stations and mobile terminals. For example, as shown in fig. 9A, a base station may have multiple receive antennas 121 ' and associated radio hardware 122 ' -125 ' for distributed reception. Furthermore, since the base station supports three (full rate) Digital Traffic Channels (DTCH) per RF channel, the base station may have three times as much baseband processing hardware in the base station (the frame in fig. 9A), while IF demodulator 125' may have more than one but three outputs, one for each of the three digital traffic channels. In addition, since the base station typically operates on multiple RF channels, it may include multiple sets of radio channel hardware (baseband processing and radio hardware) and a programmable frequency combiner 118A' to make the selection of the RF channel to be used by the base station according to the applicable cellular frequency reuse plan. Alternatively, the base station may not include the user keypad and display unit 138, but may include a signal level meter 100 ' to determine the received signal strength of each of the two antennas 121 ' and provide an output to the microprocessor 134 ' (for handover purposes). Other differences between a mobile terminal and a base station will be readily apparent to those skilled in the art. Otherwise, the operation of the base station is substantially the same as that described above for the mobile terminal with respect to transmission and reception of control and voice messages.

By utilizing the present invention, the number of slots received by receiver 122, demodulated by RF demodulator 124, demodulated by IF demodulator 125, and decoded by symbol detector 126, modulo-2 adder 127, 2-burst and 22-burst deinterleavers 128 and 135, channel decoders 130 and 136, and FACCH and SACCH detectors 132 and 137 is reduced. Thus, if the microprocessor 134 determines that the remainder of the message need not be received while the first portion of the message is being received, operation of these modules is avoided. Thus, not requiring activation of these modules may save energy that would otherwise be used to receive and decode any remaining portion of the message.

Those skilled in the art will appreciate that the present invention is particularly useful when the message is transmitted on a common control channel and is more particularly useful when the message is a paging message. The present invention is particularly useful for paging messages because mobile terminals typically monitor each paging message to avoid dropping incoming calls. Thus, as the frequency of types of messages, such as paging messages, that the mobile terminal must monitor increases, the chances of avoiding receiving unnecessary slots also increase.

The amount of savings achievable by using the present invention can be seen by using one example. In the asian cellular satellite system (ACeS), a 19-slot long paging message structure (H-PACH) and an 81-slot broadcast control channel (S-HMBCH) are defined. For GSM, a frame contains 8 slots but a control multiframe contains 102 frames numbered 0 through 101. One or more time slots are allocated to the paging channel in the control multiframe. The paging channel structure of one slot contains 5 paging channels. Each paging channel has a duration of 19 slots and can carry one paging message per multiframe. For GSM, the paging message contains the mobile unit identifier of the mobile terminal being paged. Each mobile terminal monitors a paging channel for mobile unit identifier messages with identifiers matching itself.

According to the invention, the paging message can be divided into two unequal parts. The smaller of the two portions contains only a portion of the mobile unit identifier. This first part may be transmitted over the first 4 slots and encoded such that it can be decoded independently. The first 4 bursts may contain, for example, 7 bits of a 56 bit mobile unit identifier. The mobile terminal then first receives the 4 bursts, decodes them and compares the received bits with the corresponding bits in its mobile unit identifier. If there is an exact match, it receives the remaining 15 slots of the paging message.

Using a 7-bit comparison and selecting the 7 bits from the mobile unit identifier allows to find a universal random distribution of possible values from the typical distribution of mobile terminals, a terminal in standby mode on average only having to read 1/2 of the message⁷All 19 time slots above. This allows the number of time slots read by the phone to be reduced from 19To 4.12 time slots on average 4+ 15/128. Both reception and signal processing can reduce this factor resulting in power savings.

Although the present invention has been described with respect to a particular standard for cellular communications, the present invention should not be construed as limited to any particular communication standard. The invention has also been described as separating a message into two independently decodable portions, however, as will be appreciated by those skilled in the art, a message may be separated into any number of portions while still benefiting from the advantages of the invention. Furthermore, if the message format can be decoded upon reception, the message need not be divided into parts prior to transmission, but can be evaluated by the receiving mobile terminal upon its reception. Thus, the term message portion as used herein refers to any independent distinguishable subset of information of the entire message.

In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.

Claims (15)

1. A method of communicating to a mobile terminal (15) having a receiver (26) for receiving a time division multiplexed message distributed over a plurality of time slots in a time division multiple access cellular network, wherein an address is associated with the mobile terminal (15), and wherein the time division multiplexed message contains addresses distributed over a plurality of time slots that specify intended recipients of the message, the method comprising:

receiving a first subset of the plurality of time slots to receive a first portion of a time division multiplexed message corresponding to the first subset of the plurality of time slots, wherein the first portion of the time division multiplexed message includes at least a portion of an address specifying an intended recipient of the message;

determining from at least a part of the address contained in the first part of the time division multiplex message whether the mobile terminal (15) needs to receive a further time slot of the time division multiplex message; and

receiving a second subset of the plurality of time slots for receiving a second portion of the time division multiplexed message if said determining step determines that the mobile terminal (15) is to receive a further portion of the time division multiplexed message;

wherein the address associated with the mobile terminal (15) is a mobile unit identifier comprising a plurality of bits, and wherein the first portion of the time division multiplexed message comprises a subset of the plurality of bits of the mobile unit identifier of the intended recipient of the message; and

wherein the determining step comprises determining whether a subset of the plurality of bits contained in the first portion of the time division multiplexed message is equal to a corresponding subset of the plurality of bits of the mobile unit identifier of the mobile terminal (15).

2. A method according to claim 1, wherein said determining step comprises determining whether the time division multiplex message is addressed to an address in an address range containing the mobile terminal (15); and

wherein said step of receiving a second subset of the plurality of time slots comprises receiving the second subset of the plurality of time slots for receiving a second portion of the time division multiplexed message if said determining step determines that the message is addressed to a mobile terminal (15) having an address in an address range containing the mobile terminal (15).

3. The method according to claim 1, wherein the bits making up the subset of the multiple bits of the mobile unit identifier contained in the first part of the time division multiplex message are selected from the multiple bits such that a random distribution of possible mobile unit identifier values is obtained from the distribution of mobile terminals (15).

4. A method as claimed in any one of claims 1, 2 or 3, wherein the time division multiplex message comprises a paging message.

5. A method as claimed in any one of claims 1, 2 or 3, wherein the first part of the message is decodable separately from the second part of the message.

6. A method of communicating to a mobile terminal (15) having a receiver (26) for receiving a time division multiplexed message distributed over a plurality of time slots in a time division multiple access cellular network, wherein an address is associated with the mobile terminal (15), and wherein the time division multiplexed message contains addresses distributed over a plurality of time slots that specify intended recipients of the message, the method comprising:

separating the message into at least a first independently decodable portion of the message and a second independently decodable portion of the message, wherein the first independently decodable portion of the message and the second independently decodable portion of the message each comprise at least a portion of an address specifying an intended recipient of the message from which the mobile terminal (15) can determine whether the mobile terminal (15) needs to receive the second independently decodable portion of the message;

transmitting a first independently decodable portion of the message at a predetermined time corresponding to a first subset of the plurality of slots; and

transmitting a second independently decodable portion of the message at a predetermined time corresponding to a second subset of the plurality of slots;

receiving a first subset of the plurality of time slots to receive a first portion of the time division multiplexed message corresponding to the first subset of the plurality of time slots, wherein the first portion of the time division multiplexed message includes at least a portion of an address defining an intended recipient of the message;

determining from at least a portion of the address included in the first portion of the time division multiplexed message whether the mobile terminal needs to receive additional time slots of the time division multiplexed message; and

if the determining step determines that the mobile station (15) is to receive the additional portion of the time division multiplexed message, a second subset of the plurality of time slots is received to receive the second portion of the time division multiplexed message.

7. The method of claim 6, wherein the time division multiplexed message contains an address comprised of a plurality of bits that specify the intended recipient of the message;

wherein the dividing step comprises dividing the time division multiplexed message into a first independently decodable portion of the message that includes at least a subset of the plurality of bits of the address.

8. A mobile terminal (15) for use in a mobile communication network having a time division multiplexed message distributed over a plurality of time slots in a time division multiple access cellular network, wherein an address is associated with the mobile terminal (15), and wherein the time division multiplexed message contains addresses distributed over a plurality of time slots and indicates an intended recipient of the message, the mobile terminal (15) comprising:

a receiver circuit (26) for selectively receiving wireless communications at predetermined times corresponding to time division multiplexed messages;

means responsive to said receiver circuit (26) for determining from a subset of said plurality of time slots corresponding to a first portion of said time division multiplexed message whether a mobile terminal (15) requires reception of additional time slots of the time division multiplexed message, wherein the first portion of the time division multiplexed message includes at least a portion of an address specifying a recipient of the message, and wherein said determining means (28) determines from the at least a portion of the address whether additional time slots are required;

receiver control means operatively associated with said decision means (28) for selectively causing said receiver circuit (26) to receive radio communications at a predetermined time corresponding to a second subset of the plurality of time slots, wherein said second subset of the plurality of time slots corresponds to a second portion of the time division multiplexed message if said decision means (28) decides that the mobile terminal (15) is to receive additional time slots of the time division multiplexed message;

wherein said determining means (28) comprises means for determining whether the time division multiplex message comprises an address within an address range, said address range comprising the address of said mobile terminal (15); and

wherein said receiver control means further comprises means for selectively causing said receiver circuit (26) to receive wireless communications at predetermined times corresponding to a second subset of the plurality of time slots, wherein said second subset of the plurality of time slots corresponds to a second portion of the time division multiplexed message if said decision means (28) decides that the message includes an address that is within an address range that includes said mobile terminal (15).

9. A mobile terminal (15) for use in a mobile communication network having a time division multiplexed message distributed over a plurality of time slots in a time division multiple access cellular network, wherein an address is associated with the mobile terminal (15), and wherein the time division multiplexed message contains addresses distributed over a plurality of time slots and indicates an intended recipient of the message, the mobile terminal (15) comprising:

a receiver circuit (26) for selectively receiving wireless communications at predetermined times corresponding to time division multiplexed messages;

means responsive to said receiver circuit (26) for determining from a subset of said plurality of time slots corresponding to a first portion of said time division multiplexed message whether a mobile terminal (15) requires reception of additional time slots of the time division multiplexed message, wherein the first portion of the time division multiplexed message includes at least a portion of an address specifying a recipient of the message, and wherein said determining means (28) determines from the at least a portion of the address whether additional time slots are required;

receiver control means operatively associated with said decision means (28) for selectively causing said receiver circuit (26) to receive radio communications at a predetermined time corresponding to a second subset of the plurality of time slots, wherein said second subset of the plurality of time slots corresponds to a second portion of the time division multiplexed message if said decision means (28) decides that the mobile terminal (15) is to receive additional time slots of the time division multiplexed message;

wherein the mobile terminal (15) has associated therewith a mobile unit identifier comprised of a plurality of bits, and wherein said determining (28) means comprises means for determining whether a subset of the plurality of bits of the mobile unit identifier associated with the time division multiplexed message is equal to a corresponding subset of the plurality of bits of the mobile unit identifier of the mobile terminal (15).

10. The mobile terminal (15) according to claim 9, wherein the bits making up the subset of the plurality of bits of the mobile identifier associated with the time division multiplexed message are selected from the plurality of bits such that a random distribution of possible mobile unit identifier values is derived from the distribution of mobile terminals (15).

11. A mobile terminal (15) for use in a mobile communication network having a time division multiplexed message distributed over a plurality of time slots in a time division multiple access cellular network, wherein an address is associated with the mobile terminal (15), and wherein the time division multiplexed message contains addresses distributed over a plurality of time slots and indicates an intended recipient of the message, the mobile terminal (15) comprising:

a receiver circuit (26) for selectively receiving wireless communications at predetermined times corresponding to time division multiplexed messages;

means responsive to said receiver circuit (26) for determining from a subset of said plurality of time slots corresponding to a first portion of said time division multiplexed message whether a mobile terminal (15) requires reception of additional time slots of the time division multiplexed message, wherein the first portion of the time division multiplexed message includes at least a portion of an address specifying a recipient of the message, and wherein said determining means (28) determines from the at least a portion of the address whether additional time slots are required;

receiver control means operatively associated with said decision means (28) for selectively causing said receiver circuit (26) to receive radio communications at a predetermined time corresponding to a second subset of the plurality of time slots, wherein said second subset of the plurality of time slots corresponds to a second portion of the time division multiplexed message if said decision means (28) decides that the mobile terminal (15) is to receive additional time slots of the time division multiplexed message;

wherein a portion of a message and a second portion of a message are independently decodable, and wherein said receiver circuit (26) of said mobile terminal (15) comprises decoder means (129 ', 130 ', 136 ') operatively associated with said receiver circuit (26) for selectively decoding said first portion and said second portion of said message.

12. A base station (42) for use in a Time Division Multiple Access (TDMA) cellular network utilizing time division multiplexing distributed over a plurality of time slots, the base station (42) comprising:

means (26') for dividing the message into at least a first independently decodable portion of the message and a second independently decodable portion of the message, wherein the first independently decodable portion of the message and the second independently decodable portion of the message each contain at least a portion of an address associated with the message from which the mobile terminal (15) can determine whether the mobile terminal (15) needs to receive the second independently decodable portion of the message;

means for transmitting (24') a first independently decodable portion of the message at a predetermined time corresponding to a first subset of the plurality of slots; and

means for transmitting (24') a second independently decodable portion of the message at a predetermined time corresponding to a second subset of the plurality of slots.

13. The base station (42) of claim 12 wherein an address is associated with a mobile terminal (15), and wherein the time division multiplexed message includes an address comprised of a plurality of bits specifying the intended recipient of the message; and

wherein said dividing (26') means comprises a first independently decodable portion of the message that divides the time division multiplexed message into at least a subset of the plurality of bits of the address.

14. The base station (42) of claim 13 wherein the address is a mobile unit identifier.

15. The base station (42) according to claim 13 wherein the bits that form the subset of the plurality of bits of the mobile identifier associated with the first portion of the time division multiplexed message are selected from the plurality of bits such that a random distribution of possible mobile unit identifier values is obtained from the distribution of mobile terminals (15).