GB2366138A

GB2366138A - Overhead message updating

Info

Publication number: GB2366138A
Application number: GB0019996A
Authority: GB
Inventors: Gadi Karmi; Matthew S Grob
Original assignee: Qualcomm Inc
Current assignee: Qualcomm Inc
Priority date: 2000-08-14
Filing date: 2000-08-14
Publication date: 2002-02-27
Anticipated expiration: 2020-08-14
Also published as: GB2366138B; GB0019996D0

Abstract

An arrangement for communicating overhead messages in a wireless communication system providing access to a decentralised network, which achieves bandwidth savings as well as minimising power consumption. In one embodiment, a wireless base station which is connected to a decentralised network transmits a sequence of signatures for overhead messages to a mobile unit. The mobile unit wakes up, receives the signatures and compares them to signatures stored at the mobile unit. If the signatures received by the mobile unit are different from the signatures stored at the mobile unit, the mobile unit stays awake to receive the overhead messages to be transmitted by the wireless base station. If the signatures received by the mobile unit are the same as the signatures stored at the mobile unit, the mobile unit may go back to sleep. Alternatively (figure 5) the mobile station may create a signature upon receiving a data signal, compare the signature to a previous signature, and only update the operating parameters of the mobile if the signatures are different.

Description

<Desc/Clms Page number 1> OVERHEAD MIESSAGE UPDATE WITH DECENTRALIZED CONTROL BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates in general to wireless communication systems, and more particularly, to overhead channel information delivery in wireless communication systems.

11. Description of the Related Art In a cellular communications system, the area to be covered is divided up into a number of small areas called cells, with one base station (BS) positioned to give service or coverage to the mobile units within a cell. Each BS is connected to a base station controller (BSQ which is used to control several BSs and the provision of communication service to a mobile unit as it travels from one cell to another. The BSC's are in turn connected to a mobile switching center (MSQ, which is generally a telephone exchange with special software to handle the mobility aspects of tile mobile units. Most cellulx# communications systems consist of a number of MSCs each with their own BSs, and interconnected by means of fixed links. The MSCs interconnect to the public switched telephone network (PSTN) for both outgoing calls to and incoming calls from fixed telephones.

A mobile unit is connected, ultimately, to the MSC through over-the-air radio frequency (RF) reverse (mobile to BS) link to and the RF forward (BS to mobile) link from the BS. RF signals are exchanged between a respective mobile unit and one or more base stations over these links. Mobile units do not communicate directly with one another. Mobile unit to mobile unit communications across the span of one or more cells occurs through the base stations providing service to the mobile units desiring communication. Base

stations communicate with a BSC using various media such as ground based wires or a microwave link, for example. The BSC can route calls to a PSTN through the MSC or can route packets to a packet switched network, such as the Internet. The base station controller also coordinates the operation of base stations within the system during handoff, for example.

A common feature of the RF forward and reverse links of many cellular systems is multiple users using a single communication channel occupying a limited frequency range. Cellular systems employ a variety of techniques for allowing multiple users to use a single communication channel occupying a limited frequency range. Code Division Multiple Access (CDMA) is one such technique. A popular standard for CDMA can be found in the TLkffilA Standard TIA/EIA-95-B entitled "Mobile Station-Base Station Compatibility Standard for Dual Mode Wideband Spread Spectrum Cellular System." In CDMA, multiple users can simultaneously use the whole communication channel without having to coordinate the timing of their transmission or the portion of the communication channel each user utilizes. More details on CDMA and spread spectrum communications can be found in, CDMA Principles of Spread Spectrum Communications, by Andrew J. Viterbi, Addison-Wesley Publishing Company, Reading, M.A., 1996. In contrast to CDMA, two other multiple access techniques either coordinate the timing of user transmissions, time division multiple access (TDMA), or the portion of the communication channel a user uses, frequency division multiple access (FDMA).

Regardless of the technique employed to provide multiple access, in a typical cellular system, the forward communications link includes one or more data channels, a pilot channel, and one or more paging channels, all of which are transmitted from the base station to mobile units. The pilot channel or pilot signal serves to define the boundaries of the cell area served by a base station. In a CDMA cellular system in accordance with IS-95, the pilot signal serves other purposes as well. For example, the pilot signal: provides for time reference and for amplitude and phase tracking; and allows mobile units to identify and become

synchronized with the various base stations that are within range of their communication capability. The set of data channels carry the data associated with the various communication sessions (usually phone calls) and are directed to individual mobile units. These data channels are often called traffic channels. The paging channels are used by the base stations to notify mobile units when a request to communicate has been received. A paging channel is also used to transmit overhead messages. Overhead messages contain information that enables mobile unit-to-base station communication.

Overhead messages are not addressed to any specific mobile unit but are intended for distribution to each mobile unit within the corresponding coverage t5 area. In an IS-95 CDMA cellular system, there are four types of overhead messages: system parameters, access parameters, channel list, and neighbor list overhead messages. Each type of overhead message must be broadcast at least once per second. For example, the neighbor list overhead message continually broadcasts a list of neighboring base stations through which communication may be possible. The mobile units use the neighbor list to monitor signals from the neighboring base stations in the event that the mobile unit enters the coverage area of neighboring base stations. Cellular systems employing other communications standards may have other types of overhead messages.

The overhead messages are typically received and processed by a mobile unit when a mobile unit is not engaged in a call or attempting to engage in a call, (i.e., when it is in an 'idle state'). The term idle state is somewhat of a misnomer because the mobile unit can be very busy in the idle state. During the idle state, the mobile station periodically wakes up and listens to the paging channel and processes the messages on that channel. The overhead messages may remain the same for a substantial period of time during which the mobile station periodically wakes up and listens to the paging channel. Since it is not desirable to have the mobile unit wake up, receive the overhead message, and decode it only to determine that the overhead message is the same as the previous message that was decoded earlier, in the interest of conserving battery power, a sequence number is transmitted along with the overhead message. When the mobile unit wakes up, it

receives the sequence number of the overhead message and decides whether to stay awake and receive the overhead message. In many instances, the mobile unit will go back to sleep after receiving the sequence number because the sequence number is the same as the sequence number received the last time the mobile unit woke up. Since listening for overhead messages requires a certain amount of power and since the listening function is performed frequently (as often as once per second), limiting the amount of time a mobile unit performs the listening function reduces the overall power consumption of that mobile unit and therefore increases the life of any battery or other power storage system utilized by that mobile unit. Significant power savings may occur because in many instances the overhead messages may remain the same for a substantial period of time.

In many cellular systems, the overhead messages and the sequence numbers to be transmitted by a base station are controlled from a central location such as a BSM. One reason for providing this centralized control arises from the nature of the service typically provided by cellular systems. Cellular systems typically provide voice service or connection to and from a land based PSTN. A PSTN typically has a highly concentrated switching structure. As a result, cellular services desirino, to interface to it have had to use central switches for routin- calls. In many cellular systems providing voice service via a PSTN, phone calls are bundled at a central switch (MSC or MSCs) for transmission through the PSTN or unbundled for transmission through the wireless network.

Consequently, due to the existence of a central location (BSM or MSQ at which links from many BSs terminated, it has been logical to take advantage of this central location to control remotely from the central location the programming of overhead messages and sequence numbers at each of the base stations in the cellular system.

In contrast, cellular systems providing packet data service rather than voice service typically interface to a highly decentralized network. An example of a decentralized network is the internet. A cellular system providing packet data service provides a wireless link from the users of the cellular system to a router which links the users to the decentralized network. Technically, the

internet is a collection of standard protocols, such as Transmission Control Protocol/Internet Protocol (TCP/IP), that enable dissimilar computer systems and networks to send and receive information. Some of the more popular protocols include: e-mail (electronic messaging), file transfer protocol (file transferring), World Wide Web (graphical interface utilizing links by hypertext documents), telnet (telephone network connections), IRC (Internet Relay Chat), gopher (information organization).

A message received from a mobile user of the packet data cellular system is forwarded by the base station to a router. The router breaks down the message into smaller pieces, know as packets. The packets travel separately across the network, but are ultimately re-formed together when all the pieces of the message arrive at its destination. During the trip, the packets merely bump along from one router to another router and through bridges and switches. No particular pathway is selected from the outset. Each router or switch looks at the destination address of the packet, but does not inspect its contents, and decides the best way to pass it along.

Since a router typically connects directly to the decentralized network and typically sends data along multiple paths to a destination there is often no need for a switch at a central location to set up a single path to and from a destination. As a result in a wireless data system providing access to a decentralized network there is not likely to be a central location, such as the BSM or MSC, which can also be used to control base stations and the update of overhead messages in the cellular system.

Thus, there has been a need for overhead message delivery in a wireless communication system, such as a cellular system, providing access to a decentralized network. The present invention meets this need.

SUMMARY OF THE INVENTION The system and method of the present invention provide a simple, but effective technique for communicating overhead messages in a wireless communication system providing access to a decentralized network, while achieving bandwidth savings as well as minimizing power consumption. In one embodiment, a wireless base station which is connected to a decentralized network transmits a sequence of signatures for overhead messages to a mobile unit. The mobile unit wakes up receives the signatures and compares them to signatures stored at the mobile unit. If the signatures received by the mobile unit are different from the signatures stored at the mobile unit, the mobile unit stays awake to receive the overhead messages to be transmitted by the wireless base station. If the signatures received by the mobile unit are the same as the signatures stored at the mobile unit, the mobile unit may go back to sleep.

In an alternative embodiment, the mobile unit wakes up and receives a message from a wireless base station. The mobile unit generates a signature using the message. The mobile unit compares the signature to the signature of a previous message received by the mobile unit. If the signature generated for the message received is the same as the signature of the previous message received, then the mobile unit goes back to sleep. If the signature generated for the message 1:D Z# :D received is different from the signature of the previous message received, then the mobile unit updates operating parameters used for communicating with the base station.

BRIEF DESCRIPTION OF THE DRAWINGS Figure I is a block diagram of a wireless communication system according to a preferred embodiment of the invention; Figure 2 shows a structure of a forward link of a wireless communication system in accordance with the invention; Figure 3 shows a process for communicating overhead messages using the structure of the forward link illustrated in Figure 2; Figure 4 shows an alternative structure of a forward link of a wireless communication system in accordance with the invention; and Figure 5 shows an alternative process for communicating overhead messages using the structure of the forward link illustrated in Figure 4.

DETAILED DESCRIPTION OF THE PREFERRED EMMODIMENT Figure I shows a system block diagram of a wireless communications system (CS or System) 200 according to the presently preferred embodiment of the invention. System 200 may include multiple base stations (BS) 210, 220 (only two shown) each of which can communicate wirelessly with a mobile unit (MU) 202 when W 202 is within the geographic area covered by a base station. MU 212 includes terminal equipment 206 and mobile termination 204.

MU is used to refer to the composite entity consisting of the terminal equipment and the mobile termination. In this discussion, the term "mobile unit" is used to refer generally to the remote subscriber station for the purposes of this description. Note, however, that the mobile unit may be fixed in location. The mobile unit may be part of a multiple user concentrated subscriber system. The mobile unit may be used to carry voice, data, or a combination of signal types. The term "mobile unit" is a term of art and is not meant to limit the scope or function of the unit.

Base station 210, 220 includes base station transceiver subsystem (BTS) 212, 222 and radio link protocol and signaling manager (RSM) 214, 224. Base station is used to refer to the composite entity consisting of the BTS and the RSM.

TE 206 is a device providing a user interface: typically, a laptop or notebook computer, or personal digital assistant (PDA). TE 206 is connected to MT 204 which is a wireless device providing a data modulation and demodulation capability. The BTS 214 is connected to the MT 204 through an radio frequency (RF) over-the-air interface. The BTS 214 provides a data modulation and demodulation capability for connecting to MT 206. The RSM 214, 224 serves as the radio link protocol (RLP) endpoint and the signaling endpoint, and maps interent protocol addresses and mobile station identifications to each other. There may be a single RSM or an RSM co-located with each BTS.

System 200 also includes a router 230. Router 230 connects RSM 214, 224 to a decentralized network 250 composed of routers (not shown) and other networks (not shown). One example of a decentralized network is the internet. System 200 may be connected to other types of decentralized and/or centralized networks.

The RF over the air interface between BTS 212 and MT 204 includes a forward link for BTS to mobile unit communication and a reverse link for mobile unit to BTS communication, In one embodiment the forward link of System 200 is entirely dedicated to a single mobile unit at any given instant and only a single forward channel is transmitted to a mobile unit at any given instant. There are many types of communications standards with which this invention may be employed. One standard for forward and reverse links in a wireless communications system is specified in TLk/EIA Standard TLA,/EIA-95-B (or IS- 95) entitled "Mobile Station-Base Station Compatibility Standard for Dual Mode Wideband Spread Spectrum Cellular System." In alternative embodiments the forward link of System 200 may be the same as the IS-95 forward channels. In IS-95, multiple forward channels may be received by a mobile unit.

The System 200 forward link also differs from IS-95 in that the pilot channel is burst transmitted and embedded in the data channel as opposed to a continuously transmitted pilot channel as in IS-95. The other overhead channels also differ: the IS-95 continuous synchronization and paging channels have been combined in System 200 to a single control channel whose messages are time multiplexed on the "single user" forward link. Multiplexing is desirable because it avoids splitting the power of a base station between two or more continuously transmitted channels. Using substantially all the power of a base station to transmit a data channel allows higher data rates to be used.

System 200 is designed to operate on a separate CDMA channel (i.e., a different frequency) than an existing IS-95 system. System 200 can be deployed independently of an existing IS-95 system (or in place where no such system

exists) in which case it will contain no interaction with the underlying voice system, or in a location in which a cooperating IS-95 system exists in which case IS-95 system related information will be carried on the System 200 control channel supporting handoffs to the IS-95 system, as well as providing for information delivery from the IS-95 system to System 200 in support of call delivery notifications.

In System 200, where an overhead channel such as the paging channel is time multiplexed with the forward data channel, the less time that is spent on transmitting the paging channel the more time that will be available for transmitting the forward data channel. Since, for a given constant data rate, the data throughput to a mobile unit is directly related to the amount of time that the forward data channel is transmitted to and received by the mobile unit, it is highly desirable to decrease the amount of time spent transmitting the paging channel.

In TWEIA-95, the paging channel is transmitted continuously and takes up part of the total, available bandwidth on the forward channel and the total,available power of the base station. Because some of a base station's total available power is taken up by the paging channel, less power is available for the forward data channels. For a given signal-to-noise ratio (SNR) and a given bit error rate (BER), the maximum data transmission rate on a forward data channel is a function of the power available for a forward data channel. More specifically for a given SNR, as less power becomes available for a forward data channel the maximum data transmission rate on the forward data channel will have to be decreased to satisfy a requirement for a given BER.

For many systems and applications, where it is desirable to have high data transmission rates, it may not be possible to make more power available to the forward data channel by increasing the power at the base station transmitter, Consequently, to achieve the high transmission data rates it is necessary to take power from other channels and make that power available to the forward data channel. Unfortunately, if too much power is taken from the paging channel and

given to the forward data channel, then the SNR on the paging channel may be so detrimentally affected as to also detrimentally affect the BER on the paging channel, making the information sent on the paging channel unintelligible. However, where it is not possible to increase transmitter power, to appreciably increase the data transmission rate it may be necessary to significantly increase the power available to the forward data channel by taking a significant amount of power from the paging channel (or some other channel). To appreciably increase the data transmission rate, it may be necessary to take all the power from the paging channel and give it to the forward data channel and to time multiplex the paging and data channels. For a given transir-Litter power, a system in which the paging channel and data channel are time multiplexed allows for higher transmission data rates to a user than a system in which the paging channel and data channel are transmitted simultaneously and share the given transmit ter power.

While it is true that higher maximum transmission data rates are possible when the paging channel and the forward data channel are time multiplexed, to achieve high effective transmission data rates the time spent transmitting the paging channel must be minimized as the following equation suggests: Effective transmission data rate = Trma, * Tfd/(Tfd +Tpc), where Trmax is the maximum transmission data rate, Tfd is the duration of the transmission of the forward data channel during one period, and Tpc is the duration of the transmission of the paging channel during one period.

Figure 2 generally describes the structure of the forward link of an embodiment in accordance with the invention. The forward link is a periodic cycle of a data stream which includes a paging channel multiplexed with a forward data channel. The paging channel includes a signature capsule and an overhead message capsule. In the embodiment illustrated in Figure 2, the signature and overhead message capsules are transmitted with a period having a duration of 400 milliseconds. In alternative embodiments, the period may have

other durations. The signature capsule contains at least one signature. The signature may represent only one overhead message or may represent a group of more than one message (i.e., the signature is changed whenever at least one message in a group of more than one message is changed).

The overhead message capsule contains at least one overhead message. Overhead messages are not addressed to any specific mobile unit but are intended for distribution to each mobile unit within the corresponding coverage area. Possible overhead messages include system parameters, access parameters, channel list, and neighbor list overhead messages, Each type of overhead message must be broadcast at least once per second. In the preferred embodiment the messages are broadcast every 400 milliseconds. For example, the neighbor list overhead message continually broadcasts a list of neighboring base stations through which communication may be possible. The mobile units use the neighbor list to monitor signals from the neighboring base stations in the event that the mobile unit enters the coverage area of neighboring base stations.

Cellular systems may have other types of overhead messages. It is well-known in the art that overhead messages may include many different parameters which are needed to establish and maintain communication between a mobile unit and a base station.

The overhead message or messages are typically received and processed by a mobile unit when a mobile unit is not engaged in a call or attempting to engage in a call, (i.e., when it is in an 'idle state'). The term idle state is somewhat of a misnomer because the mobile unit can be very busy in the idle state. During the idle state, the mobile station periodically wakes up and listens to the paging channel and processes the messages on that channel. The overhead messages may remain the same for a substantial period of time during which the mobile station periodically wakes up and listens to the paging channel. Since it is not desirable to have the mobile unit wake up, receive the overhead message, and decode it only to determine that the overhead message is the same as the previous message that was decoded earlier, in the interest of conserving battery power, a

sequence number is transmitted along with the overhead message. When the mobile unit wakes up, it receives the signature of the overhead message which will be received later and decides whether to stay awake and receive the overhead message. In many instances, the mobile unit will go back to sleep after receiving the signature because the signature is the same as the sequence number received the last time the mobile unit woke up. Since listening for overhead messages requires a certain amount of power and since the listening function is performed frequently (as often as once per second), limiting the amount of time a mobile unit performs the listening function reduces the overall power consumption of that mobile unit and therefore increases the life of any battery or other power storage system utilized by that mobile unit. Significant power savings may occur because in many instances the overhead messages may remain the same for a substantial period of time.

Figure 3 illustrates a process for updating overhead messages for an embodiment in accordance with this invention and having the forward link with the structure illustrated in Figure 2. Referring to Figure 3, an overhead message is changed at step 302 at the BS 210. At step 304, at the BS 210 a signature is generated for the overhead message that was changed. A signature can be generated by hashing the message is a well-known hashing function to produce a sixteen or thirty-two bit signature. Hashing a message to generate a signature can 0 ZD be performed by a signature generator using well-known arithmetic logic (not shown) or a general purpose microprocessor (not shown) and need not be described in detail here. One of ordinary skill in the art would recognize that the signature may be generated using other forms of logic not described herein. The length of the signature in bits depends on system requirements that two consecutive messages share different signatures (i.e., avoid collisions). There is a definite but small probability that two different consecutive messages may share the same signature because hashing only ser-ves to compress the message space into a smaller signature space in which more than one message may have the same signature. In the event that two consecutive messages are different but the

hashing produces the same signature for both, at step 304, the hashing may be repeated with a random number until a signature that is different from the signature of a predetermined number of previous messages is generated. Alternatively, the signature can be generated by incrementing a counter.

At step 306 the MU 202 wakes up and listens. At step 308 the BS 210 transmits the signature to the MU 202. At step 3 10, the MU 202 receives the signature. At step 312, the MU 202 retrieves a previous signature from memory (not shown). At step 312, the MU 202 compares the signature received at step 3 10 with the previous signature. The circuitry or signature comparison element required for performing the comparison at step 312 can be realized by a variety of components including microprocessors as well as combinatorial logic and other logiccircuits. If the signature received at step 310-is the same as the previous signature, at step 314 the MU 202 goes back to sleep. If the signature received at step 3 10 is different from the previous signature, at step 3 16, the MU 202 stays awake and listens to receive the message. After the MU 202 receives the message it updates the operating parameters of the MT 204 so that it will be able to communicate effectively with System 200.

The structure of the overhead messages on the paging channel may be in accordance with the structure required by a technique known as slotted paging. Slotted paging is useful for reducing power consumption by a mobile unit. More information on slotted mode operation is disclosed in U.S. Pat. No. 5,392,287 entitled "APPARATUS AND METHOD FOR REDUCING POWER CONSUMPTION R,; A MOBILE COMMUNICATIONS RECEIVER" issued Feb. 21, 1995, assigned to the assignee of the present invention, and incorporated herein by reference.

Figure 4 generally describes the structure of the forward link of an alternative embodiment in accordance with the invention. The forward link is a periodic cycle of a data stream which includes a paging channel multiplexed with a forward data channel. The paging channel includes an overhead message

capsule. In the embodiment illustrated in Figure 4, the overhead message capsules are transmitted with a period having a duration of 400 milliseconds. In alternative embodiments, the period may have other durations.

Figure 5 illustrates a process for updating overhead messages for an alternative embodiment in accordance with this invention and having the forward link with the structure illustrated in Figure 4. Referring to Figure 5, an overhead message is changed at step 502 at the BS 2 10. At step 504, the MU 202 wakes up and listens. At step 506 the BS transmits the message to the MU 202 and the MU 202 receives the message. At step 508 the MU 202 generates a signature for the message using a hashing function as described with regards to Process 300 in Figure 3. Hashing a message to generate a signature can be performed by a signature generator using well-known arithmetic logic (not shown) or a general purpose microprocessor (not shown) and need not be described in detail here. One of ordinary skill in the art would recognize that the signature may be generated using other forms of logic not described herein. At step 512, the MU 202 retrieves a previous signature from storage (not shown) at the MU 202. At step 512, the MU 202 compares the previous signature with signature generated at step 508. The circuitry or signature comparison element required for performing the comparison at step 512 can be realized by a variety of components including microprocessors as well as combinatorial logic and other logic circuits. If the signature generated at step 508 is the same as the previous signature, at step 514 the MU 202 goes back to sleep. If the signature generated at step 508 is different from the previous signature, at step 416, the MU 202 updates its operating parameters with the infon-nation contained in the message received at step 506.

The generation and receipt of CDMA signals is disclosed in U.S. Patent No. 4,401,307 entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEMS USING SATELLITES OR TERRESTRIAL REPEATERS" and in U.S. Patent No. 5,103,459 entitled "SYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULAR

TELEPHONE SYSTEM", both of which are assigned to the assignee of the present invention and incorporated herein by reference.

Demodulation of multiple signals is disclosed in U.S. Patent No. 5,490,165 entitled "DEMODULATION ELEMENT ASSIGNMENT IN A SYSTEM CAPABLE OF RECEIVING MULTIPLE SIGNALS" and in U.S. patent No. 5,109,390 entitled "DIVERSITY RECEIVER IN A CDMA CELLULAR TELEPHONE SYSTEM", both of which are assigned to the assignee of the present invention and incorporated herein by reference.

Although the invention has been described in conjunction with particular embodiments, it will be appreciated that various modifications and alterations may be made by those skilled in the art without departing from the spirit and scope of the invention. The invention is not to be limited by the foregoing illustrative details, but rather is to be defined by the amended claims.

Claims

CLAIMS The invention claimed is: I . A method for communicating messages to a mobile station by a wireless communication system providing access to a decentralized data network, the method comprising the steps of: providing a sequence of messages; providing for each respective message a respective signature; and comparing the respective signature for any given respective message with at least one signature. 2. The method of claim 1, further comprising receiving the respective signature for a respective message. 3. The method of claim 1, further comprising: receiving the respective signature for a respective message; and sleeping after receiving the signature. 4. The method of claim I further comprising: receiving the respective signature for a respective message; and sleeping after receiving the respective signature if the respective signature matches a corresponding signature from the at least one signature. 4# ID 5. The method of claim I further comprising: receiving the respective signature for a respective message; sleeping after receiving the respective signature if the respective signature matches a corresponding signature from the at least one signature; and transmitting the respective message, wherein sleeping occurs while the respective message is being transmitted.

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6. The method of claim 1 further comprising: receiving the respective signature for each respective message; and t) t# t# sleeping if each respective signature matches a corresponding signature from the at least one signature. 7. The method of claim I further comprising: receiving the respective signature for each respective message; sleeping if each respective signature matches a corresponding signature from the at least one signature; and transmitting each respective message, wherein sleeping occurs while each respective message is being transmitted. 8. The method of claim 1, further comprising: receiving the respective signature for a respective message; and listening for the respective message if the respective signature does not match a corresponding signature from the at least one signature. 9. The method of claim 1, further comprising: receiving the respective signature for a respective message; and listening for the respective message if the respective signature does not match a corresponding, signature from the at least one signature, wherein listening is done only until the respective message is received. 10. The method of claim 1, further comprising: receiving the respective signature for a respective message; listening for the respective message if the respective signature does not match a corresponding signature from the at least one signature, wherein listening is done only until the respective message is received; and sleeping after the respective message is received.

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11. The method of claim 1, further comprising: receiving the respective signature for a respective message; listening for the respective message if the respective signature does not match a corresponding signature from the at least one signature; sleeping after the respective message is received; and waking up after sleeping. 12. The method of claim 1, further comprising: receiving the respective signature for a respective message; listening for the respective message if the respective signature does not match a corresponding signature from the at least one signature; sleeping after the respective message is received; and waking up after sleeping for 5.2 seconds. 13. The method of claim 1, further comprising: receiving at the mobile station the respective signature for a respective message; listening at the mobile station for the respective message if the respective signature does not match a corresponding signature from the at least one signature; and sleeping at the mobile station after the respective message is received. 14. The method of claim 1, further comprising: receiving the respective signature for each respective message. 15. The method of claim 1, further comprising: receiving the respective signature for each respective message; and listening for a respective message whose respective signature does not match a corresponding signature from the at least one signature. 16. The method of claim 1, further comprising:

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receiving the respective signature for each respective message; and listening for a respective message whose respective signature does not match a corresponding signature from the at least one signature; wherein listening is done only until the respective message is received. 17. The method of claim 1, further comprising: receiving the respective signature for each respective message; listening for a respective message whose respective signature does not match a corresponding signature from the at least one signature; and sleeping after the respective message is received. 18. The method of claim 1, further comprising: receiving the respective signature for each respectivemessage; listening for a respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening is done only until the respective message is received; and sleeping for 5.2 seconds after the respective message is received. 19. The method of claim 1, further comprising: receiving the respective signature for each respective message; listening for a respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening is done only until the respective message is received; and sleeping after the respective message is received; and waking up after sleeping. 20. The method of claim 1, further comprising: receiving the respective signature for each respective message; C> listening for a respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening is done only until the respective message is received;

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sleeping after the respective message is received; and waking up after sleeping for 5.2 seconds. 21. The method of claim 1, further comprising: receiving at the mobile station the respective signature for each respective message; listening at the mobile station for a respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening is done only until the respective message is received; sleeping at the mobile station after the respective message is received; and waking at the mobile station up after sleeping. 22. The method of claim 1, further comprising: receiving at the mobile station the respective signature for each respective message; listening at the mobile station for a respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening is done only until the respective message is received; sleeping at the mobile station after the respective message is received; and waking at the mobile station up after sleeping for 5.2 seconds. 23. The method of claim 1, further comprising: receiving at the mobile station the respective signature for each respective message, wherein the respective signature for each respective message was transmitted by the wireless communication system; listening at the mobile station for a respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening is done only until the respective message is received; wherein the respective message was transmitted by the wireless communication system; sleeping at the mobile station after the respective message is received; and

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waking at the mobile station up after sleeping. 24. The method of claim 1, further comprising: receiving at the mobile station the respective signature for each respective message, wherein the respective signature for each respective message was transmitted by the wireless communication system; listening at the mobile station for a respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening is done only until the respective message is received; wherein the respective message was transmitted by the wireless communication system; sleeping at the mobile station after the respective message is received; and waking at the mobile station up after sleeping for 5.2 seconds. 25. The method of claim 1, further comprising: receiving the respective signature for each respective message; listening for a first respective message whose respective signature does not match a corresponding signature from the at least one signature; and listening for a second respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening is done until the second respective message is received, and wherein listening for the second respective message occurs after listening for the first respective message. 26. The method of claim 1, further comprising: receiving the respective signature for each respective message; listening for a first respective message whose respective signature does not match a corresponding signature from the at least one signature; listening for a second respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening is done until the second respective message is received, and wherein C)

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listening for the second respective message occurs after listening for the first respective message; and sleeping after the second respective message is received. 27. The method of claim 1, further comprising: receiving the respective signature for each respective message; listening for a first respective message whose respective signature does not match a corresponding signature from the at least one signature; listening for a second respective message whose respective signature does not match a corresponding signature from the at least one signature, and wherein listening for the second respective message occurs after listening for the first respective message; listening for a third respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening for the third respective message is done after listening for the second respective message; and wherein listening for the third respective message is done until the third respective message is received; and sleeping after the third respective message is received. 28. The method of claim 1, further comprising: receiving the respective signature for each respective message; listening for each respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening stops if there are no more messages whose respective signature does not match a corresponding signature from the at least one signature; and sleeping after listening stops. 29. The method of claim 1, further comprising: receiving the respective signature for each respective message; listening for each respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening 0 C:'

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stops if there are no more messages whose respective signature does not match a corresponding signature from the at least one signature; sleeping after listening stops; and waking up after sleeping. 30. The method of claim 1, further comprising: receiving the respective signature for each respective message; listening for each respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening stops if there are no more messages whose respective signature does not match a corresponding signature from the at least one signature; sleeping after listening stops; and waking up 5.2 seconds after sleeping. 31. The method of claim 1, further comprising: receiving at the mobile station the respective signature for each respective message, wherein the respective signature for each respective message is transmitted by the wireless communication system; listening at the mobile station for each respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening stops if there are no more messages whose respective signature does not match a corresponding signature from the at least one signature; wherein each respective message is transmitted by the wireless communication system; sleeping at the mobile station after listening stops; and waking up at the mobile station after sleeping. 32. The method of claim 1, further comprising:

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receiving at the mobile station the respective signature for each respective message, wherein the respective signature for each respective message is transmitted by the wireless communication system; listening at the mobile station for each respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening stops if there are no more messages whose respective signature does not match a corresponding signature from the at least one signature; wherein each respective message is transmitted by the wireless communication system; sleeping at the mobile station after listening stops; and waking up at the mobile station 5.2 seconds after sleeping. 33. The method of claim 1, further comprising: waking up at the mobile station; and receiving the respective signature for a respective message at the mobile station. 34. The method of claim 1, further comprising: waking up at the mobile station; receiving the respective signature for a respective message at the mobile station; and listening for the respective message if the respective signature does not match a corresponding signature from the at least one signature, wherein listening is done only until the respective message is received. 35. The method of claim 1, further comprising: waking up at the mobile station; receiving the respective signature for a respective message at the mobile station;

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listening for the respective message if the respective signature does not match a corresponding signature from the at least one signature, wherein listening is done only until the respective message is received; and sleeping after the respective message is received. 36. The method of claim 1, further comprising: waking up at the mobile station; receiving the respective signature for each respective message at the mobile station; listening for a respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening is done only until the respective message is received; and sleeping after the respective message is received. 37. The method of claim 1, further comprising: waking up at the mobile station; receiving the respective signature for each respective message at the mobile station; listening for each respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening stops if there are no more messages to be whose respective signature does not match a corresponding signature from the at least one signature; and sleeping at the mobile station listening stops. 38. The method of claim 1, wherein the sequence of messages is a sequence of overhead messages. 39. The method of claim 1, wherein the sequence of messages is periodically transmitted by the wireless communication system.

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40. The method of claim 1, wherein the sequence of messages is aperiodically transmitted by the wireless communication system. 41. The method of claim 1, wherein the sequence of messages is transmitted to at least one mobile station. 42. The method of claim 1, wherein each message is embedded in a message capsule having a plurality of messages. 43. The method of claim 1, wherein providing for each respective message a respective signature comprises hashing each message. 44- The method of claim 1, wherein providing for each message a respective signature comprises hashing each message to generate a first hash, wherein hashing comprises rehashing any message if the first hash of any message matches any of at least one corresponding signature from the at least one signature, wherein the at least one corresponding signature was generated within a time period TEftabefore commencing providing for each message a respective sianature. 1-# 45. The method of claim 1, wherein providing for each message a respective signature comprises hashing each message to generate a first hash, wherein hashing comprises adding a random value to the first hash if the first hash of any message matches any of at least one corresponding signature from the at least one signature, wherein the at least one corresponding signature was generated within a time period Tr,,# before commencing providing for each message a respective signature. 46. The method of claim 1, wherein providing for each message a respective signature comprises hashing each message to generate a first hash, wherein hashing comprises rehashing any message with a random value if the first hash of

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any message matches any of at least one corresponding signature from the at least Z:' one signature, wherein the at least one corresponding signature was generated within a time period TDej. before commencing providing for each message a respective signature. 47- The method of claim 1, wherein providing for each message a respective signature comprises hashing each message to generate a first hash, wherein hashing comprises rehashing any message with a random value if the first hash of any message matches any of at least one corresponding signature from the at least one signature, wherein the at least one corresponding signature was generated within a time period TD,,,a before commencing providing for each message a respective signature, and wherein the time period TDelta is larger than the largest allowed sleep time of any mobile station communicating with the wireless conimunication system. 48. The method of claim 1, wherein providing for each respective message a respective signature comprises hashing each message to generate a sixteen bit value for the respective signature. 49. The method of claim 1, wherein providing for each message a respective signature comprises hashing each message to generate a thirty-two bit value for the respective signature. 5E) - The method of claim 1, wherein providing for each message a respective signature comprises giving the respective signature a value stored in a counter. 51- The method of claim 1, wherein providing for each message a respective signature comprises: incrementing a counter; and giving the respective signature a value stored in the counter. C)

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52. The method of claim 1, wherein providing for each message a respective signature comprises: Z:I incrementing a counter if any given message does not match a C# corresponding first message, wherein the corresponding first message was Z# 4:1 0 generated at a time before commencing providing a sequence of messages; and giving the respective signature a value stored in the counter. 53. The method of claim 1, wherein one of the sequence of messages includes an overhead message indicative of base station parameters in the wireless communication system. 54. The method of claim 1, wherein one of the sequence of messages includes an overhead message indicative of base station parameters in the wireless communication system, and wherein the base station parameters include system parameters, access parameters, channel list, and neighbor list parameters. 55. The method of claim 1, wherein one of the sequence of messages includes an overhead message indicative of the wireless communication system's system wide parameters. 56. The method of claim 1, wherein one of the sequence of messages includes an overhead message indicative of the wireless conununication system's system wide parameters, and wherein the system wide parameters include system parameters, access parameters, channel list, and neighbor list parameters. 57. The method of claim I further comprising receiving the sequence of messages at the mobile station. 58. The method of claim I further comprising receiving the sequence of messages at the mobile station, and wherein providing for each message a C> respective signature comprises hashing each message at the mobile station.

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59. The method of claim I further comprising receiving any given one of the ZD sequence of messages at the mobile station; wherein providing for each message a respective signature comprises hashing each message at the mobile station to generate a first hash for each message, wherein hashing comprises rehashing any message using a random value if the first hash of any message matches any of at least one corresponding signature from the at least one signature; and wherein the at least one corresponding signature was generated within a time period TDeft,, before commencing providing for each message a respective signature. 60. The method of claim I further comprising receiving any given one of the sequence of messages at the mobile station; wherein providing for each message a respective signature comprises hashing each message at the mobile station to generate a first hash for each message, wherein hashing comprises rehashing any message using a random value if the first hash of any message matches any of at least one corresponding sianature from the at least one signature; CD wherein the at least one corresponding signature was generated within a time period T,,,,. before commencing providing for each message a respective signature; and wherein TD,Ia is longer than the longest allowed sleep time for any mobile station communicating with the wireless communication system. 61. The method of claim I further comprising: providing at least one stored message at the mobile station; 0 receiving the sequence of messages at the mobile station;

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wherein each of the at least one stored message has a corresponding message in the sequence of messages; wherein providing for each respective message a respective signature comprises hashing each message at the mobile station to generate a first hash for each message; wherein hashing comprises rehashing any message using a random value if the first hash of any message matches any of at least one corresponding signature from the at least one signature; wherein the at least one corresponding signature was generated within a time period T,,,,t, before commencing providing for each message a respective signature; wherein T#,,,. is longer the longest allowed sleep time of any mobile station communicating with the wireless system; and replacing any message from the at least one stored message with a corresponding message from the sequence of messages received at the mobile station if the respective signature of the corresponding message does not match a corresponding signature from the at least one signature. 62. The method of claim 1 further comprising: providing at least one stored message at the mobile station; receiving the sequence of messages at the mobile station; wherein each of the at least one stored message has a corresponding message in the sequence of messages; and replacing any message from the at least one stored message with a corresponding message from the sequence of messages received at the mobile station if the respective signature of the corresponding message does not match a corresponding signature from the at least one signature.

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Amendments to the claims have been filed as F'ollows CLAIMS I . A method for communicating messages to a mobile station by a wireless communication system providing access to a decentralized data network, the method comprising: providing a sequence of messages; providing for each respective message a respective signature, the respective signature being separate from the respective message; and comparing the respective signature for any given respective message with at least one signature. 2. The method of claim 1, further comprising receiving the respective signature for a respective message. 3. The method of claim 2, further comprising sleeping after receiving the signature. 4. The method of claim 2, further comprising sleeping after receiving the respective signature if the respective signature matches a corresponding signature from the at least one signature. 5. The method of claim 4, further comprising transmitting the respective message, wherein sleeping occurs while the respective message is bemig transmitted. 6. The method of claim 1 further comprising: receiving the respective signature for each respective message; and sleeping if each respective signature matches a corresponding signature from the at least one signature.

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7. The method of claim 6, Rather comprising transmitting each respective message, wherein sleeping occurs while each respective message is being transmitted. 8. The method of any of claims 2 to 7, Rather comprising listening for the respective message if the respective signature does not match a corresponding signature from the at least one signature. 9. The method of claim 8, wherein listening is done only until the respective message is received. 10. The method of claim 8 or 9, flirther comprising sleeping after the respective message is received. 11. The method of claim 10, further comprising waking up after sleeping. 12. The method of claim 10, Rather comprising waking up after sleeping for 5.2 seconds. 13. The method of any preceding claim, further comprising: receiving at the mobile station the respective signature for a respective message; listening at the mobile station for the respective message if the respective signature does not match a corresponding signature from the at least one signature; and sleeping at the mobile station after the respective message is received.

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14. The method of any of claims 2 to 12, further comprising listening for a respective message whose respective signature does not match a corresponding signature from the at least one signature. 15. The method of claim 13 or 14, wherein: the respective signature for each respective message was transmitted by the wireless communication system; and the respective message was transmitted by the wireless communication system. 16. The method of claim 1, further comprising: receiving the respective signature for each respective message; listening for a first respective message whose respective signature does not match a corresponding signature from the at least one signature; and listening for a second respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening is done until the second respective message is received, and wherein listening for the second respective message occurs after listening for the first respective message. 17. The method of claim 16, further comprising sleeping after the second respective message is received. 18. The method of claim 17, further comprising listening for a third respective message whose respective signature does not match a correspondin,cly signature from the at least one signature, wherein listening for the third respective message is done after listening for the second respective

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message; and wherein listening for the third respective message is done until the third respective message is received; and sleeping after the third respective message is received. 19. The method of any of claims 6 to 12, further comprising: receiving the respective signature for each respective message; listening for each respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening stops if there are no more messages whose respective signature does not match a corresponding signature from the at least one signature; and sleeping after listening stops. 20. The method of claim 19, further comprising waking- up after sleeping. 21. The method of claim 19, further comprising waking up 5.2 seconds after sleeping. 22. The method of claim 1, further comprising: receiving at the mobile station the respective signature for each respective message, wherein the respective signature for each respective message is transmitted by the wireless communication system; listening at the mobile station for each respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening stops if there are no more messages

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whose respective signature does not match a corresponding signature from the at least one signature; wherein each respective message is transmitted by the wireless communication system; sleeping at the mobile station after listening stops; and waking up at the mobile station after sleeping. 23. The method of claim 22, comprising waking up at the mobile station 5.2 seconds after sleeping. 24. The method of claim 1, further comprising: waking up at the mobile station; and receiving the respective signature for a respective message at the mobile station. 25. The method of claim 24, further comprising listening for the respective message if the respective signature does not match a corresponding signature from the at least one signature, wherein listening is done only until the respective message is received. 26, The method of claim 25, further comprising sleeping after the respective message is received. 27, The method of claim 24, further comprising: listening for a respective message whose respective signature does not match a corresponding signature from the at least one signature, wherein listening is done only until the respective message is received; and sleeping, after the respective message is received. I

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providing for each message a respective signature, and wherein the time period TDelta is larger than the largest allowed sleep time of any mobile station communicating with the wireless communication system. 39. The method of any preceding claim, wherein providing for each respective message a respective signature comprises hashing each message to generate a sixteen bit value for the respective signature. 40. The method of any of claims I to 38, wherein providing for each message a respective signature comprises hashing each message to generate a thirty-two bit value for the respective signature. 41. The method of any of claims I to 39, wherein providing for each message a respective signature comprises giving the respective signature a value stored in a counter. 42. The method of claim 41, flifther comprising incrementing the counter. 43. The method of any of claims 1 to 38, wherein providing for each message a respective signature comprises: incrementing a counter if any given message does not match a corresponding first message, wherein the corresponding first message was generated at a time before commencing providing a sequence of messages; and giving the respective signature a value stored in the counter.

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44, The method of any preceding claim, wherein one of the sequence of messages includes an overhead message indicative of base station parameters in the wireless communication system. 45. The method of claim 44, wherein the base station parameters include system parameters, access parameters, channel list, and neighbour list parameters. 46. The method of any preceding claim, wherein one of the sequence of messages includes an overhead message indicative of the wireless communication system's system wide parameters. 47. The method of claim 40, wherein the system wide parameters include system parameters, access parameters, channel list, and neighbour list pa rameters. 48. The method of any preceding claim, further comprising receiving the sequence of messages at the mobile station. 49. The method of claim I further comprising: p rovi 'ding at least one stored message at the mobile station; receiving the sequence of messages at the mobile station wherein: each of the at least one stored message has a corresponding message in the sequence of messages; providing for each respective message a respective signature comprises hashing each message at the mobile station to generate a first hash for each message;

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hashing comprises rehashing any message using a random value if the first hash of any message matches any of at least one corresponding signature from the at least one signature; the at least one corresponding signature was generated within a time period TDelt# before commencing providing for each message a respective signature; and wherein TD,It# is longer the longest allowed sleep time of any mobile station communicating with the wireless system; and the method further comprises: replacing any message from the at least one stored message with a corresponding message from the sequence of messages received at the mobile station if the respective signature of the corresponding message does not match a corresponding signature from the at least one signature. 50. The method of claim 1, further comprising: providing at least one stored message at the mobile station; receiving the sequence of messages at the mobile station wherein each of the at least one stored message has a corresponding message in the sequence of messages; and replacing any message from the at least one stored message with a corresponding message from the sequence of messages received at the mobile station if the respective signature of the corresponding message does not match a corresponding signature from the at least one signature.

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51. The method of any preceding claim, wherein the sequence of messages is transmitted in a message capsule; a signature is generated for the message capsule; and the signature is transmitted in a separate signature capsule; comparing the signature with one or more signatures previously stored at the mobile station. 52. An apparatus for communicating messages to a mobile station by a wireless communication system providing access to a decentralised data network, the apparatus comprising: a base station configured to: transmit a message capsule over a forward channel; generate a signature for the message capsule; and transmit a signature in a separate signature capsule over the forward channel; and a mobile station configured to compare the signature with one or more signatures previously stored at said mobile station. 53. An apparatus as claimed in claim 52, wherein said mobile station is configured to sleep if the signature matches one of the previously stored signatures. 54. An apparatus as claimed in claim 52 or 53, wherein said mobile station is configured to sleep while the message capsule is being transmitted over the forward channel.

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55. An apparatus as claimed in claim 52, wherein said mobile station is further configured to listen for the message capsule if the signature does not match one of the previously stored signatures. 56. An apparatus as claimed in claim 55, wherein said mobile station isconfigured to listen only until the message capsule is received. 57. An apparatus as claimed in claim 56, wherein said mobile station is configured to sleep after the message capsule is received. 58. An apparatus as claimed in claim 57, wherein said mobile station is confi-,ured to wake up after sleeping. 59. An apparatus as claimed in claim 57, wherein said mobile station is configured to wake up after sleeping for 5.2 seconds. 60. An apparatus as clainied in any of claims 52 to 59, wherein said mobile station is configured to listen for a second message capsule whose signature does not match one of the previously stored signatures, wherein the listening is done until the second message capsule is received. 61. An apparatus as claimed in claim 60, wherein said mobile. station is configured to sleep after the second message capsule is received. 62. An apparatus as claimed in claim 60 or 61, wherein said mobile station is further configured to listen for a third message capsule whose signature does not match one of the previously stored signatures, wherein the listening is done until the third message capsule is received. 63. An apparatus as claimed in claim 62, wherein said mobile station is configured to sleep after the third message capsule is received.

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64. An apparatus as claimed in any of claims 52 to 63, wherein said mobile station is configured to stop listening if there are no more message capsules whose signatures do not match one of the previously stored signatures. 65. An apparatus as claimed in any of claims 52 to 64, wherein the message capsule is one of a sequence of message capsules carrying overhead messages. 66. An apparatus as claimed in claim 65, wherein the sequence is periodically transmitted by the wireless communication system. 67. An apparatus as claimed in claim 65, wherein the sequence is aperiodically transmitted by the wireless communication system. 68. An apparatus as claimed in any of claims 52 to 67, wherein the signature is generated by hashing the message capsule. C 69. An apparatus as claimed in claim 68, wherein the hashing comprises hashing the message capsule to generate a first hash and rehashing the message capsule if the first hash of the message matches a signature of a previous message capsule. 70. An apparatus as claimed in claim 69, wherein the rehashing comprises adding a random value to the first hash. 71. An apparatus as claimed in claim 69, wherein the rehashing is done if the signature of a previous message capsule was generated within a time period TDelw-

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72. An apparatus as claimed in claim 71, wherein the time period TDelta is laraer than the largest allowed sleep time of any mobile station that could be communicated with the wireless communication system. 73. An apparatus as claimed in any of claims 68 to 72, wherein the hashing is. arranged to generate a sixteen bit value for the signature. 74. An apparatus as claimed in any of claims 68 to 72, wherein the hashing is arranged to generate a thirty-two bit value for the signature. 75. An apparatus as claimed in any of claims 52 to 74, wherein the signature is generated by assigning a value stored in a counter. 76. An apparatus as claimed in claim 75, wherein the counter is incremented after a signature is generated. 77. An apparatus as claimed in claim 75, wherein the counter is incremented if the message capsule is different than a previously transmitted message capsule. 78. An apparatus as claimed in any of claims 52 to 77, wherein the message capsule comprises an overhead message indicative of base station parameters in the wireless communication system. 79. An apparatus as claimed in claim 78, wherein the base station parameters include system parameters, access parameters, channel list, and neighbour list parameters. 80. An apparatus as claimed in any of claims 52 to 77, wherein the message comprises an overhead message indicative of system-wide parameters of the wireless communication system.

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81. An apparatus as claimed in claim 80, wherein the system wide parameters include system parameters, access parameters, channel list, and neighbour list parameters. 82. An apparatus as claimed in any of claims 52 to 91, wherein said mobile station is configured to generate a signature from the message capsule and compare the signature with said one or more signatures previously stored at the mobile station.