MXPA98002945A - Simplifying the decoding of code words in an inalambr communication system - Google Patents

Abstract

The present invention relates to a method and a device for determining whether the reserved bits of a field are assigned or not of a function so that the mobile station can be easily adapted to carry out the improved functions. This determination allows mobile stations of the first generation to perform enhanced functions using bits that were initially reserved but can be assigned to the service or to a function in the subsequent generation of the protocols. An indication of whether the reserved bits have been assigned or not to a function can be sent in a broadcast channel by means of a usage information element. If the usage information element indicates that the reserved bits have not been assigned to any service, such as an energy control, time alignment or short message services, the reserved bits may be used to improve the functions, such as matching or synchronization. The method and the device can further provide improved decoding of the encoded superframe phase / packet channel feedback (CSFP / PCF) field. Because the information of the superframe phase (SFP) is known when viewing the rastant bits from the beginning and the end of the broadcast information, the possible codeword number in the CSFP / PCF field can be reduced by the decoding process. Also, the length of a codeword to be decoded can be reduced based on the usage information element sent in the broadcast channel indicating whether a reserved bit in the CSFP / PCF field is still reserved. More generally, the block code of any coded word of the channel, not necessarily the data of the packet, can be effectively reduced based on the knowledge of certain information in the coded word. The decoding operation is improved by shortening the length of the code words to be decoded because the shorter code words are less susceptible to b errors.

Description

"SIMPLIFYING THE DECODING OF CODE WORDS IN A WIRELESS COMMUNICATION SYSTEM" BACKGROUND Applicants' invention relates to electrical telecommunication, and more particularly to wireless communication systems such as cellular and satellite radio systems, for various modes of operation (analog, digital, dual mode, etc.), and access techniques such as as multiple division frequency access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and FDMA / TDMA / CDMA hybrids. The invention is directed to improve the synchronization, decoding and coding aspects of electrical communication in wireless communication systems. A description follows that is directed to environments in which the invention can be applied. This general description is intended to provide a general overview of the known systems and the associated terminology so that a better understanding of the invention can be obtained. In North America, digital communication and multiple access techniques such as TDMA are currently provided by a digital cellular radiotelephone system called the advanced digital mobile phone service (D-AMPS), some of the characteristics of which are specified in the interim standard TIA / EIA / IS-54-B. The "Dual-Compatibility Mobile Station Compatibility Standard for Base Station", published by the Association of Telecommunications Industry and Electronic Industries Association (TIA / EIA). The TIA / EIA / IS-54-B standard is incorporated in this application by reference. Because a large existing consumer equipment base operates only in the analog domain with frequency division multiple access (FDMA), TIA / EIA / IS-54-B is a dual mode (analogue and digital) standard, providing analog compatibility together with digital communication capability. For example, the TIA / EIA / IS-54-B standard provides both analog voice channels of FDMA (AVC) and digital traffic channels of TDMA (DTC). The AVC and DTC are implemented by radio frequency modulation carrier signals, which have frequencies of about 800 megahertz (MHz) in such a way that each radio channel has a spectral width of 30 kilohertz (KHz). In the TDMA cellular radiotelephone system, each radio channel is divided into a series of time slots, each of which contains a burst of information from a data source, e.g., a digitally coded portion of a voice conversation. The time slots are grouped into successive TDMA frames that have a predetermined duration. The number of time slots of each TDMA frame is related to the number of different users that can simultaneously share the radio channel. If each slot in a TDMA box is assigned to a different user, the duration of a TDMA box is the minimum amount of time between the successive time slots assigned to the same user. The successive time intervals assigned to the same user, which are usually not consecutive time intervals in the radio bearer, constitute the digital traffic channel of the user, which can be considered a logical channel assigned to the user. As described in more detail below, the digital control channels (DCC) can also be provided to communicate the control signals, and this DCC is a logical channel formed by a succession of time intervals not usually consecutive in the carrier of radio. If only one of the many possible modalities of a TDMA system is as described above, the TIA / EIA / IS-54-B standard as long as each TDMA frame consists of six consecutive time intervals, and have a duration of 40 milliseconds (msec). Therefore, each radio channel can carry from three to six DTCs (eg., from three to six telephone conversations), depending on the encoder source schemes / speech decoders (codees) used to digitally code the conversation. These speech codes can work either full-time or half-time. A full-regime DTC requires twice as many time intervals in a given time period as the half-time DTC, and in TIA / EIA / IS-54-B, each full-regime DTC uses two intervals of each frame TDM, that is, the first and fourth, the second and the fifth or the third and sixth of a TDMA table of six intervals. Each half-interval DTC uses a time interval of each TDMA frame. During each DTC time slot, 324 bits are transmitted, of which the predominant portion, 260 bits, is due to the codec speech output, including bits due to error correction coding of the speech output, and Remaining bits are used for protection times and send signals for purposes such as synchronization. It could be seen that the cellular system of TDMA operates in a mode of shock and burst, or discontinuous transmission: each mobile station transmits (and receives) only during its assigned time intervals. At a full rate, for example, a mobile station could transmit during interval 1, receive during interval 2, be inactive during interval 3, transmit during interval 4, receive during interval 5 and be inactive during interval 6 and Then repeat the cycle during the successive TDMA frames. Therefore, the mobile station can be battery powered, it can be disconnected or put to sleep to save energy during the time intervals when it is neither transmitting nor receiving. In addition to the voice and traffic channels, the cellular radio communication systems also provide radiolocation / access channels, or control to carry established messages per call between the base stations and the mobile stations. According to TIA / EIA / IS-54-B, for example, there are twenty one dedicated analog control channels (ACC), which have predetermined fixed frequencies for transmission and reception placed close to 800 MHz. Since these ACCs are always at the same frequencies can be easily located and monitored by mobile stations. For example, when in an inactivated state (ie, connected but not making or receiving a call), a mobile station in a TIA / EIA / IS-54-B system is tuned to and then regularly monitors the control channel more intense (generally, the control channel of the cell where the mobile station is placed at that moment) and can receive or initiate a call through the corresponding base station. When moving between the cells while in the inactive state, the mobile station will eventually "lose" the radio connection in the control channel of the "old" cell and will be tuned to the control channel of the "new" cell . The initial tuning and the subsequent re-tuning to control the channels both are achieved automatically by scanning all available control channels at their own frequencies to find the "best" control channel. When a control channel with good reception quality is found, the mobile station remains tuned to this channel until the quality deteriorates again. In this way, the mobile stations remain "in contact" with the system. While in the inactive state, a mobile station must monitor the control channel to radiolocate messages directed to it. For example, when a regular (land) telephone subscriber calls a mobile subscriber, the call is routed from a public switched telephone network (PSTN) to a mobile switching center (MSC) that analyzes the dialed number. If the desired number is validated, the MSC requests that some or all of the number of the radio base station radiolocate the mobile station called to transmit through its respective control channels the radiolocation messages containing the mobile identification number (MIN) of the mobile station call. Each inactive mobile station that receives a radiolocation message compares the received MIN with the stored MIN itself. The mobile station with the matching stored MIN transmits a radiolocation response through the specific control channel to the base station, which sends the radiolocation response to the MSC. Upon receiving the radiolocation response, the MSC selects an available AVC or DTC to the base station that received the paging response, connects to a corresponding radio transceiver at that base station and causes the base station to send a message through the control channel to the mobile station that instructs the mobile station called to tune to the selected voice or traffic channel. A complete connection for the call establishes once the mobile station has tuned to the selected AVC or DTC.

The performance of the ACC system that is specified by TIA / EIA / IS-54B has been improved in a system that has digital control channels (DCCH) that is specified in TIA / EIA / IS-136. Using these DCCHs, each TIA / EIA / IS-54B radio signal can carry the DTCs only, the DCCHs only, or a mixture of both DTC and DCCH. Within the framework of TIA / EIA / IS-136-B, each frequency of the radio bearer can have up to three DTC / DCCH of full regime, or six DTC / DCCH of half rate or, any combination between them, for example, a DTC / DCCH of full regime and four of medium regime. Generally speaking, however, the DCCH transmission rate does not need to coincide with the medium and full regime specified in TIA / EIA / IS-54B, and the length of the DCCH intervals may not be uniform and may not coincide with the length of the DTC intervals. The DCCH can be defined in a radio channel of TIA / EIA / IS-54B and can consist, for example, of each n-th interval in the stream of consecutive TDMA intervals. In this case, the length of each DCCH interval may or may not equal 6.67 milliseconds, which is the length of a DTC interval according to TIA / EIA / IS-54B. Alternatively, (and without limitation on other possible alternatives), these DCCH ranges may be defined in other ways known to a person skilled in the art. In cell phone systems, an air link protocol is required in order to allow a mobile station to communicate with the base stations and the MSC. The communications link protocol is used to initiate and receive cell phone calls. The communications link protocol is commonly referred to as within the communications industry as the Layer 2 protocol, and its functionality includes delimiting or framing Layer 3 messages. These Layer 3 messages can be sent between peer entities. of the communication layer 3 that "remain within the mobile stations and the cellular switching systems." The physical layer (Layer 1) defines the parameters of the physical communications channel, eg, radio frequency separation, modulation characteristics, etc. Layer 2 defines the techniques necessary for the exact transmission of information within the constraints of the physical channel, v.gr, correction and error detection, etc., Layer 3 defines the procedures for the reception and processing of the information transmitted through the physical channel, communications between mobile stations and the cellular communication system (the base stations and the MSC) can be described generally with reference to Figures 1 and 2. Figure 1 schematically illustrates the pluralities of messages 11 of Layer 3, frames 13 of Layer 2, channel bursts of Layer 1, or the time slots 15. In Figure 1, each group of channel bursts corresponding to each message of Layer 3 can constitute a logical channel, and as described above, the channel bursts for a message of the Layer 3 determined will usually not be consecutive intervals in a TIA / EIA / 136 carrier. On the other hand, channel bursts could be consecutive; As soon as a time interval ends, the next time interval could begin. Each channel burst 15 of Layer 1 contains a complete Layer 2 box as well as other information such as, for example, error correction information and other information used for the operation of Layer 1. Four Layer 2 each contains at least a portion of a Layer 3 message as well as information used for the operation of Layer 2. Even if not indicated in Figure 1, Layer 3 message layer would include different elements of information that can be considered as the profitable message load, a header portion to identify the respective message type and possibly fill.

Each burst of Layer 1 and each Layer 2 frame is divided into a plurality of different fields. In particular, a DATA field of limited length in each frame of Layer 2 contains message 11 of Layer 3. Since Layer 3 messages have varying lengths depending on the amount of information contained in the Layer message 3, a plurality of frames of Layer 2 may be required for transmission of a single Layer 3 message. As a result, a plurality of Layer 1 channel bursts may also be necessary to transmit the entire Layer 3 message since there is a one-to-one match between channel bursts and Layer 2 frames. As mentioned above, when more than one channel burst is required to send a Layer 3 message, the different bursts are usually consecutive bursts in the radio channel. Furthermore, the different bursts are not usually successive bursts dedicated to the specific logical channel used to carry the Layer 3 message. Since it takes time to receive, process and react each burst received, the bursts required for transmission of a message of Layer 3 are usually sent in a staggered format as illustrated schematically in Figure 2 (a) and as described above in relation to the TIA / EIA / IS-136 standard. Figure 2 (a) shows a general example of a forward (or downlink) DCCH configured as a succession of time slots 1, 2, ..., N, ... included in the consecutive time slots 1, 2, ... sent on a carrier frequency. These DCC ranges can be defined in a radio channel such as that specified by TIA / EIA / IS-136, and can consist, as can be seen in Figure 2 (a) for example, of each n-th interval in a series of consecutive intervals. Each DCC interval has a duration that may or may not be 6.67 milliseconds, which is the length of a DTC interval according to the TIA / EIA / IS-136 standard. As shown in Figure 2 (a), the DCCH intervals can be arranged in superframes (SF), and each superframe includes a number of logical channels that carry different kinds of information. One or more of the DCCH intervals can be assigned to each logical channel in the superframe. The exemplary downlink superframe in Figure 2 (a) includes three logical channels: a broadcast control channel (BCCH) that includes six successive intervals for messages; a radiolocation channel (PCH) that includes an interval to radiolocate messages; and an access response channel (ARCH) that includes a slot for channel assignment and other messages. The remaining time intervals in the exemplary superframe of Figure 2 (a) can be dedicated to other logical channels, such as additional radiolocation PCH channels or other channels. Since the number of mobile stations is usually much larger than the number of intervals in the superframe, each radiolocation interval is used to radiolocate several mobile stations that share some unique characteristics, eg, the last digit of the MIN. Figure 2 (b) illustrates a preferred information format for the intervals of a front DCCH. The information transferred in each interval comprises a plurality of fields, and Figure 2 (b) indicates the number of bits in each field above that field. The bits sent in the synchronization field (SYNC) are used in a conventional manner to help ensure accurate reception of the CSFP and DATA fields. The synchronization field (SYNC) carries a predetermined bit pattern used by the base stations to find the beginning of the interval. The SCF field is used to control a random access channel (RACH), which is used by the mobile station to request access to the system. The CSFP information transmits a coded superframe phase value that allows mobile stations to find the beginning of each superframe. This is just an example for the information format in the front DCCH ranges. Figure 2 (c) illustrates the 12 bit assignments for the CSFP field that includes the bits d7 ~ dQ and the check bits b3 ~ bo- For purposes of efficient standby mode and fast cell selection, the BCCH can be divided into a number of sub-channels. A BCCH structure is known which allows the mobile station to read a minimum amount of information when it is connected (when hooked into a DCCH) before being able to access the system (place or receive a call). After connecting, an unoccupied mobile station needs to regularly monitor only its allocated PCH intervals (usually one in each superframe); the mobile station can rest during the other intervals. The relation of the time in which the mobile station dedicates to the reading of the radiolocation messages and its time dedicated to rest is controllable and represents a change between the delay of the established call and the energy consumption. Since each TDMA time slot has a certain fixed information bearer capability, each burst typically carries only a portion of a Layer 3 message as mentioned above. In the uplink direction, the multiple mobile stations try to communicate with the system on a containment basis, while the multiple mobile stations listen for the Layer 3 messages sent from the system in the downlink direction. In known systems, any given message from Layer 3 must be carried using as many TDMA channel bursts as required to send the entire Layer 3 message. Digital control channels and traffic are desirable due to reasons, such as sustain longer periods of rest for mobile units, which results in a longer battery life. The digital traffic channels and the digital control channels have expanded functionality to optimize the capacity of the system and support hierarchical cell structures, that is, structures of macrocells, microcells and picocells, etc. The term "macrocell" generally refers to a cell having a size comparable to the sizes of the cells in a conventional cellular telephone system, (e.g., a radius of at least about 1 kilometer), and the terms "microcell" and "picocell" usually refer to progressively smaller cells. For example, a microcell could cover an indoor or outdoor public area, v. gr., a convention center or a busy street, and a picocel could cover a corridor of an office or a floor of a building with multiple floors. From a radio coverage perspective, macrocells, microcells and picocells could be different from one another or they can overlap one another to handle different traffic patterns or different radio environments. Figure 3 is an exemplary hierarchical or multilayer cellular system. A parasol macrocell 10 represented by a hexagonal shape constitutes an overlying cellular structure. Each umbrella cell may contain an underlying microcell structure. The umbrella cell 10 includes microcell 20 represented by an area enclosed within a dotted line and microcell 30 represented by the area enclosed within the dashed line corresponding to the areas along any of the streets of the city, and the 40, 50 and 60 picocells, which cover individual floors of a building. The intersection of two city streets covered by microcells 20 and 30 can be an area of dense traffic concentration and therefore could represent a hot zone. Figure 4 depicts a functional diagram of an exemplary cellular mobile radiotelephone system, including an exemplary base station 110 and a mobile station 120. The base station includes a control and processing unit 130 which connects to the MSC 140 which in turn is connected to the PSTN (not shown). The general aspects of these cellular radiotelephone systems are known in the art as described by US Pat. No. 5,175,867 issued to Wejke et al., Entitled "Neighbor Aided Delivery in a Cellular Communication System", which is incorporated in this application by reference. The base station 110 handles a plurality of voice channels through a voice channel transceiver 150 which is controlled by the control and processing unit 130. Also, each base station includes a control channel transceiver 160 that may be able to handle more than one control channel. The control channel transceiver 160 is controlled by the control and processing unit 130. The control channel transceiver 160 broadcasts the control information through the control channel of the base station or cell to the mobile stations linked to that control channel. It will be understood that transceivers 150 and 160 can be implemented as a single device such as a voice and control transceiver 170, for use with the DCCH and DTC, they share the same radio carrier frequency.

The mobile station 120 receives the information broadcast on a control channel on its voice channel and control transceiver 170. Then, the processing unit 180 evaluates the received control channel information which includes the characteristics of the cells that are candidates for the mobile station to be linked and determines in which cell the mobile station is to be linked. Advantageously, the information of the received control channel not only includes absolute information related to the cell with which it is associated but also contains relative information related to other cells next to the cell with which the control channel is associated as described in FIG. U.S. Patent No. 5,353,332 issued to Raith et al., Entitled "Method and Apparatus for Control of Communication in a Radiotelephone System", which is incorporated in this application by reference. To increase the "talk time" of the user, i.e. the battery life of the mobile station, a digital front control channel (the base station to the mobile station) can be provided which can carry the specified message types for current analog front control channels (FOCC), but in a format that allows the idle mobile station to read the messages when it is linked to the FOCC and then only when the information has changed; the mobile station rests during all other times. In this system, some types of messages are broadcast by base stations more frequently than other types, and mobile stations do not need to read each broadcast message. The systems specified by the TIA / EIA / IS-54B and TIA / EIA / IS-136 standards are circuit switched technology that is a "connection-oriented" type of communication that establishes a physical call connection and maintains that connection always and when the final communication systems have data to exchange. The direct connection of a circuit switch serves as an open pipeline, allowing the end systems to use the circuit for what they deem appropriate. Even when circuit switched data communication may be appropriate for constant bandwidth application, it is relatively inefficient for low bandwidth and "burst" applications. Packet switched technology, which can be oriented by connection (eg, X.25) or "be free of connection" (eg, Internet Protocol, "IP"), does not require establishment and cancellation of a physical connection that is in remarkable contrast to circuit switched technology. This reduces the latency of the data and increases the efficiency of a channel to handle relatively short, bursty or interactive transactions. A packet-switched switched network distributes the routing functions to multiple routing sites, thus avoiding possible traffic jams that could occur when using a central switching plug. The data is "packaged" with the appropriate address of the final system and then transmitted in independent units along the data path. Intermediate systems, sometimes called "routers" stationed between the final communication systems, make decisions about the most appropriate route to acquire a base per package. Routing decisions are based on a number of features including: lowest cost route or metric cost; link capacity; number of packages awaiting transmission; security requirements for the link; and the current state of operation of the intermediate system (node). The transmission of the packet along a route that does not take into account the path metric, as opposed to a single established circuit, offers flexibility of application and communications. It is also the way in which most of the normal local area networks (LAN) and wide area networks (WAN) have developed in the social environment. Packet switching is appropriate for data communications because many of the applications and devices used, such as keyboard termials, are interactive and transmit the data in bursts. Instead of a channel being inactive while a user admits more data in a terminal or standby to think about a problem, the packet switching intersperses the multiple transmissions from several terminals to the channel. The packet data provides more network robustness due to path independence and the ability of routers to select alternative paths in case of network node failure. The switching of the packet therefore allows the most efficient use of the lines of the network. The package technology offers the option to bill the end user based on the amount of data transmitted instead of the connection time. If the end-user application is designed to make efficient use of the air link, then the number of packets transmitted will be minimal. If each individual user's traffic is kept to a minimum, then the service provider has effectively increased the capacity of the network. Packet networks are usually designed and are based on data standards across the industry such as the open system interface model (OSI) and the TCP / IP prototype stack. These standards have been developed, either formally or de facto, for many years and the applications that use these protocols can usually be obtained easily. The main purpose of standards-based networks is to achieve interconnectivity with other networks. The Internet is currently the most obvious example of the search for the network based on standards of this kind. Packet networks, like the Internet or social LAN, are integral parts of today's media and business environments. As the calculation of the mobile station becomes pervasive in these environments, wireless service providers such as those using TIA / EIA / IS-136 are better positioned to provide access to these networks. However, the data services provided by or proposed for cellular systems are generally based on circuit switched mode of operation, using a dedicated radio channel for each active mobile user. U.S. Patent Number 4,887,265, and "Packet Switching in Digital Cellular Systems", Proc. 38th IEEE Vehicular Technology Conf., Pages 414 to 418 (June 1988) describe a cellular system that provides shared packet data radio channels each being capable of accommodating multiple data calls. A mobile station requesting packet data service is assigned to a specific packet data channel using essentially sending regular cellular signals. The system can include packet access points (PAPS) to interconnect with the packet data networks. Each packet data radio channel is connected to a specific PAP and is therefore capable of multiplexing the data calls associated with PAP. Deliveries are initiated by the system in a way that is greatly similar to the delivery used in the same system for voice calls. A new delivery type is added for those situations where the capacity of a packet channel is insufficient. These documents are all oriented in the data call and are based on delivery initiated by the system in a similar manner as for regular voice calls. Applying these principles to provide packet data services for general purposes in a cellular TDMA system would result in spectrum efficiency and performance disadvantages. U.S. Patent No. 4,916,691 discloses a new cellular radiosystem structure of packet mode and a new method for routing packets (voice and data) to a mobile station. The base stations, the public switches through the trunk interface units, and the cellular control unit are linked together through the WAN. The routing procedure is based on deliveries initiated by the mobile station and adding to the head of any packet transmitted from a mobile station (during a call) an identifier of the base station through which the packet passes. In case of a prolonged period of time between the packets of subsequent user information from a mobile station, the mobile station may transmit extra control packets in order to transport the cell location information. The cellular control unit is mainly involved in a call setup, when a call control number is assigned to the call. It then notifies the mobile station of the call control number and the trunk control number unit of the call control number and the identifier of the initial base station. During a call, the packets are then routed directly between the trunk interface unit, and the base station that currently serves. The system described in U.S. Patent Number 4,916,691 does not directly relate to the specific problems of providing packet data services in TDMA cellular systems.

The "Radio Package in GSM", European Telecommunications Standards Institute (ETSI) T Doc SMG 4 58/93 (February 12, 1993) and "A Proposed General Package Radio Service for GSM" presented during a seminar called "GSM in a Competitive Future Environment ", from Helsinki, Finland (October 13, 1993) indicates a possible packet access protocol for voice and data in GSM. These documents are directly related to the TDMA cellular systems, ie, GSM, and even when they point out a possible organization of shared packet data channel carried to the optimum they do not deal with the aspects of the integration packet data channels in a total system solution. The "Data packet through the GSM network", T Doc SMG 1 238/93, ETSI (September 28, 1993) describes a concept of providing packet data services in GSM based on regular GSM using first sending signals and authentication to establish a virtual channel between a mobile packet station and an "agent" that handles access to packet data services. With the sending of regular signals modified for fast channel setup and release, the regular traffic channels are then used for packet transfer. This document is directly related to the TDMA cellular systems, but since the concept is based on using a "fast switching" version of the existing GSM traffic channels, it has disadvantages in terms of spectrum efficiency and transfer delays. package (especially for short messages) compared to a concept based on the optimized shared packet data channels. The Cellular Digital Package Data System (CDPD) Release 1.0 Specification (July 1993), describes a concept for providing packet data services using radio channels available in current Advanced Mobile Phone Service systems (AMPS), that is, the North analogue cellular system America. The CDPD is a comprehensive open specification endorsed by a group of cell phone operators in the United States. Covered articles include external interfaces, air link interfaces, services, network architecture, network administration and administration. The CDPD system specified is based to a considerable degree on an infrastructure that is independent of the existing AMPS infrastructure. Things common with AMPS systems are limited to the use of the same type of radio frequency channels and the same base station sites (the base station used by CDPD may be new and specific CDPD) and the use of a radio interface. sending signals to coordinate the channel assignments between the two systems. The routing of a packet to a mobile station is based on first routing the packet to a base network node (Base Mobile Data Intermediate System, MD-IS) equipped with a base location register (HLR) based on the address of the mobile station; then, when necessary, route the packet to a visited service MD-IS, based on the HLR information; and finally transferring the packet from the serving MD-IS through the current base station based on the mobile station disclosing its cell location to the service MD-IS. Even though the CDPD System Specification does not directly relate to the specific problems of providing packet data services in the TDMA cellular systems that are addressed by this application, the network aspects and concepts described in the CDPD System Specification may used as a basis for the network aspects necessary for an air link protocol in accordance with this invention. The CDPD System Specification is incorporated in this application by reference. The CDPD network is designed to make an extension of existing data communications networks and the network - 2Í AMPS cellular Existing connection-free network protocols can be used to provide access to the CDPD network. Since the network is always considered as developing, it uses an open network design that allows the addition of new network layer protocols when appropriate. The services and protocols of the CDPD network are limited to the Network Layer of the OSI model and below. Doing so allows the protocols of the upper layer and application development without changing the underlying CDPD network. From the perspective of the mobile subscriber, the CDPD network is a wireless mobile extension of traditional data and voice networks. Using a CDPD service provider network service, the subscriber is able to provide access to data applications, many of which can be left in traditional data networks. The CDPD system can be seen as two interrelated service sets: the support services of the CDPD network and the services of the CDPD network. The CDPD network supports the services carried out necessary to maintain and administer the CDPD network. These services are: account servers; network management system; message transfer server; authentication server. These services are defined to allow interoperability between service providers. Since the CDPD network is technically developed beyond its original AMPS infrastructure, it is anticipated that the support services will remain unchanged. The functions of network support services are necessary for many mobile networks that are independent of radio frequency (RF) technology. The CDPD network services are data transfer services that allow subscribers to communicate with data applications. In addition, one or both ends of the data communication can be mobile. To summarize, there is a need for a system that provides packet data services for general purposes in D-AMPS cellular systems, based on providing shared packet data channels optimized for the package data. This application is directed to systems and methods that provide the combined advantages of a connection-oriented network similar to that specified by the TIA / EIA / IS-136 standard and a connection-free packet data network. In addition, the invention is directed to improve the synchronization, decoding and coding of aspects of electrical communication in wireless communication systems.

COMPENDIUM In accordance with an aspect of the invention there is provided a method for determining whether or not reserved bits of a field are assigned to a function so that the mobile station can be easily adapted to improve other functions. This determination allows first generation mobile stations to improve functions using bits that are usually initially reserved but can be assigned to feature services in later protocol generations. An indication of whether the reserved or non-allocated bits of a function can be sent in a broadcast channel by means of a usage information element. If the usage information element indicates that the reserved bits have not been assigned from any service, such as power control, time alignment or short message services, the reserved bits can be used to improve functions such as equalization and synchronization. In accordance with another aspect of the invention, the decoding of the decoded / packet channel superframe phase field (CSFP / PCF) is improved. Because the superframe phase information (SFP) is already known when looking at the remaining bits, the number of possible code words in the CSFP / PCF field can be reduced in the decoding process. Also, the length of a codeword to be decoded can be reduced based on a usage information element indicating whether a reserved bit in the CSFP / PCF field is still reserved. For more general mañerea, the block code of any coded word of channel, not necessarily a packet data, can be effectively reduced based on the knowledge of certain information in the coded word. The decoding operation is improved by shortening the length of the code words to be decoded because the shorter codewords are less susceptible to bit errors.

BRIEF DESCRIPTION OF THE DRAWINGS The particularities and advantages of the Applicants' invention will be understood by reading this description together with the drawings in which: Figure 1 schematically illustrates the pluralities of the Layer 3 messages, the Layer 2 frames and the channel bursts of Layer 1, or the time intervals; Figure 2 (a) shows a front DCC configured as a succession of time slots included in the consecutive time slots sent on a carrier frequency; Figure 2 (b) shows an example of a DCCH field interval format of IS-136; Figure 2 (c) shows an example of a bit allocation of CSFP; Figure 3 illustrates an exemplary jeriarchic cell or multilayer system; Figure 4 is a functional diagram of an exemplary cellular mobile radiotelephone system including an exemplary base station and mobile station; Figure 5 illustrates an example of a possible message map stroke sequence through the layers; Figure 6 illustrates an example of an interval format for BMI messages - > MS in PDCH; and Figure 7 illustrates an example of a CSFP / PCF field having eight information bits.

DETAILED DESCRIPTION To help understanding, it is illustrated in the Figure 5 a possible sequence for mapping the messages of the upper layer of messages of the lower layer, showing an example of the dedicated packet data channel (PDCH) in the manner in which the message of Layer 3 (which by it can be derived from higher layers, such as a table in accordance with the protocol of the mobile data link CDPD) is plotted on a map in several tables of Layer 2, an example of a map stroke of the Layer 2 chart in a time interval and an example of time slice map stroke to a PDCH channel. (See also Figures 2 (a), 2 (b), 2 { C).) The length of the time slots (FPDCH) of forward packet data channel and reverse packet data channel bursts. (RPDCH) are set even though there are three forms of RPDCH bursts that have different fixed lengths. For explanation purposes, the FPDCH interval and the full-regime PDCH are assumed to be in the physical layer of Figure 5, and the time division multiple access (TDMA) frame structure is assumed to be the same as the control channel IS-136 digital (DCCH) and the digital traffic channel (DTC). The TIA / EIA / IS-136 standard is incorporated by reference in this application. In the interest of maximum performance when using a multiple rate channel (double-rate PDCH and triple-rate PDCH), a slightly different FPDCH interval format is specified as shown in Figures 5 and 6. Figure 6 isolates the interval format used to send front messages from the interworkings of the mobile switching center of the base station (BMI) to a mobile station (MS) sending messages in a PDCH. The interval format illustrated in Figure 6 differs from the DCCH BMI interval format? IS-136 MS in which those packet channel (PCF) feedback fields replace the shared signal feedback fields (SCF). Another difference is a coded superframe phase / packet channel (CSFP / PCF) field replaced by the CSFP field in a DCCH format of IS-136. The CSFP / PCF field is used to transmit the information related to the SFP phase of the superframe so that the mobile stations can find the beginning of a superframe. In one aspect of the invention, an information element in the broadcast channel informs the mobile station whether the reserved or non-reserved bits in a field have any of the functions assigned to them. By definition, no assumptions can be made about the values of the reserved bits in the field, and the values of the reserved bits are typically assigned to zero. Due to initial versions of many specifications that set the bits reserved to zero and do not assign any functions to them, these bits can not be used by the mobile station even when future versions of the specifications can never assign functions to these bits. However, it is desirable to make use of these bits for improved functions such as synchronization or equalization, even when functions of these bits are not assigned. Accordingly, the invention provides an information element in the broadcast channel to indicate whether the reserved bits have been assigned or not of a function. The interval format shown in Figure 6 includes a reserved bit field RSVD which, in accordance with IS-136, includes two reserved bits. The value of the RSVD bits is typically both initially graduated to a fault 1. Normally, the mobile station does not make the assumption as to the values of the bits. According to the invention, an information element sent in a broadcast channel message indicates that the reserved bits can be used by the mobile station for a function such as demodulation or decoding, based on whether the reserved bits are used, such services as energy control, time alignment or short messages. If the information element sent in the message of the broadcast channel indicates that the reserved bits have been assigned to any function, the mobile station may depend on the RSVD bits that have their failure values and may use that information to improve the performance of a demodulation function (synchronization or equalization), for example. If the information element indicates that the RSVD bits have been assigned to a service, the mobile station can not depend on these bits having their failure values. As shown in Figure 6, the two RSVD bits can be effectively combined with the synchronization field (SYNC) in the next burst, yielding a 30 bit synchronization word (SYNC). It will be appreciated, of course, that the mobile station can apply this technique to any of the bits that have known values. In accordance with another aspect of this invention, knowledge of some of the CSFP / PCF bits is used (by, eg, eg, an appropriate processor) to improve the decoding of the remaining CSFP / PCF bits. As illustrated in Figure 7, the CSFP / PCF field includes a twelve-bit code word representing eight information bits. In Figure 7, the information bits comprise a reserved bit, two bits of the space echo qualifier (PEQ) and five SFP bits, but it will be appreciated that these are just a specific example and this invention is not limited to this example. When the mobile station is in the process of reading the bits, the mobile station has already been synchronized to the superframe, and therefore, the correct values of the five SFP bits are known by the mobile station. (The PEQ bits are used by the mobile station in a manner similar to that in which the SCF is IS-136 used when transmitting). As a result, the number of possible code words is that they represent the bits of PEQ and RSVD is reduced from 28 = 256 to 23 = 8, in the process of decoding the remaining three bits. In fact, the code word (12, 8) has been reduced to a code word of (7, 3) that must be decoded. In addition, the protection of the CSFP / PCF field is improved because a code word (7, 3) is less susceptible to bit errors than a code word of (12, 8). According to the invention, the decoding performance in this way is improved compared to the normal coding method which retrieves all eight bits of information but then discards the five bits of SFP. An example of a decoding strategy for a codeword (12, 8) will be described below. In this exemplary method, the received check bits can be reversed if reversed by the transmitter. Then, a 12 bit code word of a "predicted" SFP value, determined from the internal clock of the mobile station (ie, the mobile station knows the "phase" of the time slot it is reading), is generated. add known values (e.g., of O) to the bit positions that correspond to the remaining information bits to form a resulting word, and encoding the resulting word as necessary to generate a code word of 12 bits A logical operation (eg, from "0" exclusive) is then carried out in these two 12-bit sectors (ie, the field received from CSFP / PCF in the code word produced from the SFP value) As a result of the logical operation, the impact of the SFP values on the bits at the four-bit check position is removed, discriminating between a digital control channel (DCCH), a digital traffic channel (DTC) and a PDCH is described in Applicant's Patent Application Number 08 / 544,835, filed October 18, 1995, for "Discriminating Between Channels in Wireless Communication Systems", which is incorporated in this application by reference. which correspond to the bit positions of SFP are then discarded and the remaining seven bits are a code word (7, 3) .This code word (7, 3) which is derived from the same code (15, 11) as the code word (12, 8), it is finally decoded. e the Hamming distance (3) is not changed since the code words (7, 3) is a shortened version of the code word (12, 8). However, only one-bit errors can be corrected by this technique. The soft information can be used to further improve the decoding performance and shorten the codeword. As described above, the decoding performance can further be improved by analyzing (e.g., in an appropriate detector) a usage information element sent in the broadcast channel indicating whether some of the CSFP / PCF bits are reserved ( and therefore have predetermined values or assigned specific functions, if the use information element of the broadcast channel indicates that the bit or bits are reserved, the bit or reserved bits of the CSFP / PCF bits are known to have fault values. Using this knowledge, the code word (7, 3) can be shortened to a codeword (6, 2) or, alternatively, a codeword (12, 8) can be shortened to a codeword (11, 7) . (The latter may be useful when the mobile station does not know the value of SFP, such as before synchronization of the superframe). However, if the usage information element indicates that the bit (s) is no longer reserved, no assumption is made about its values and the code word can not be shortened. In general, the length of any channel code word not only the code words in a packet data channel may be reduced based on the knowledge of certain information in the code word. It will be appreciated that the term "reduced length" as used herein refers to reducing the number of bits of information to be decoded, thereby improving the decoding accuracy. Having thus described the invention, it will be apparent that it can be varied in many ways. These variations should not be considered as a deviation from the spirit and scope of the invention, and all these modifications that will be evident to a person skilled in the art are intended to be included within the scope of the following claims.

Claims (27)

CLAIMS;

1. A method for analyzing reserved bits in a signal received from a wireless communion system, comprising the steps of: (a) determining the state of a usage information element in a broadcast channel; and (b) performing the enhanced functions in the received signal with the reserved bits in response to the state of the usage information element determined in step (a).

2. A method according to claim 1, wherein the improved functions are performed by a mobile station with the reserved bits when the usage information element indes that the reserved bits are not used to perform any other functions.

3. A method according to claim 1, wherein the improved functions include synchronization and equalization functions.

4. A method for decoding information fields in a wireless communion system, comprising the steps of: (a) giving access to a codeword of a data field; and (b) reducing the length of the codeword to be encoded, based on a usage information element sent in a broadcast channel.

5. A method according to claim 4, wherein the data field comprises a coded superframe phase / packet channel feedback field (CSFP / PCF).

6. A method according to claim 4, wherein the code word is reduced in step (b) by performing a log operation.

7. A method according to claim 6, wherein the code word that has received access in step (a) is a code word (12, 8).

8. A method according to claim 6, wherein the log operation is a "0" operation exclusive of the code word and a vector derived from a predicted value increased with known bits, and the bit positions corresponding to the expected value are discarded to remove the impact of the expected value.

9. A method according to claim 8, wherein the predicted value is an expected value of the bits of the superframe phase (SFP) and the known bits are 0.

10. A method according to claim 9, wherein the known bits are added to the value provided for deriving a known codeword having the same length and encoding of the received codeword.

11. A method for decoding a control data in a wireless communion system, comprising the steps of: receiving a code word; forming a vector of known control values appended with the known bits; encode the vector using the same encoding as the received codeword; perform a log operation on the vector and the received codeword; shortening the resulting code word by discarding the bit positions corresponding to the known bits; and decoding the shortened code word.

The method of claim 11, wherein the control data is a CSFP / PCF data, the known control values are 5 SFP values of the CSFP / PCF data, and the known bits are three 0.

13. The method of claim 12, wherein the code word is a 12-bit codeword encoded with a code (12, 8).

14. The method of claim 12, wherein the log operation is a unique "0" operation.

The method of claim 14, wherein the shortening step is carried out by discarding 5 bits corresponding to the SFP values to derive a code word (7, 3) as the shortened code word.

16. A method for decoding a control data in a wireless communion system comprising the steps of: (a) determining the state of the usage information element sent in a broadcast channel; (b) receiving a code word of the control data; and (c) reducing a length of the code word when the state of the usage information element indes that one or more bits in the control data has been graduated to a known value.

17. A method according to claim 16, wherein the code word that has been accessed in step (b) is a code word (7, 3) and is reduced in step (c) to a code word (6, 2) when the code element Use information indicates that one bit is reserved, and is reduced to one code word (5, 1) when the usage information element indicates that two bits are reserved.

18. A method according to claim 16, wherein the received codeword is a codeword (15, 11) and is reduced in step (c) to a code word (14, 10) when the usage information element indicates that the reserved bit is reserved.

19. A device for analyzing bits in a signal received in a wireless communication system comprising: a detector for determining the state of a use information element in a broadcast channel; and a processor for performing enhanced functions on the received signal in response to the state of the usage information element determined by the detector.

20. A device according to claim 19, wherein the enhanced functions are performed by a mobile station, when the usage information element indicates that reserved bits are not used to perform any other functions.

21. A device according to claim 19, wherein the improved functions include synchronization and equalization functions.

22. A device for decoding information fields in a wireless communication system, comprising: means for receiving a code word from a data field; and a processor for reducing the length of the received codeword to be decoded based on the usage information element sent in a broadcast channel.

23. A device according to claim 22, wherein the data field comprises a coded superframe phase / packet channel feedback (CSFP / PCF) field.

24. A device according to claim 22, wherein the code word is reduced by the processor carrying out a logical function.

25. A device according to claim 24, wherein the received codeword to which access has been given is a code word (12, 8).

26. A device according to claim 25, wherein the logical function carried out is an exclusive "O" of the predicted superframe phase information values (SFP) augmented with known bits to generate a codeword of 12. bit, and the bits corresponding to the SFP information values are discarded to derive a code word (7, 3).

27. A method for decoding a control data in a wireless communication system, comprising the steps of: reducing a length of the code word received from the control data based on a predicted value of the received codeword, an element of usage information sent in a broadcast control channel or both the predicted value and the usage information element; and decode the reduced code word. SUMMARY OF THE INVENTION A method and a device for determining whether the reserved bits of a field are assigned or not of a function are described so that the mobile station can be easily adapted to carry out the improved functions. This determination allows mobile stations of the first generation to perform enhanced functions using bits that were initially reserved but can be assigned to the service or to a function in the subsequent generation of the protocols. An indication of whether the reserved bits have been assigned or not of a function can be sent in a broadcast channel by means of a usage information element. If the usage information element indicates that the reserved bits have not been assigned to any service, such as an energy control, time alignment or short message services, the reserved bits may be used to improve the functions, such as matching or synchronization. The method and the device can further provide improved decoding of the encoded superframe phase / packet channel feedback (CSFP / PCF) field. Because the information of the superframe phase (SFP) is known when viewing the rastant bits from the beginning and the end of the broadcast information, the possible codeword number in the CSFP / PCF field can be reduced in the process of decoding. Likewise, the length of a codeword to be decoded can be reduced based on the usage information element sent in the broadcast channel indicating whether a reserved bit in the CSFP / PCF field is still reserved. More generally, the block code of any coded word of the channel, not necessarily the data of the packet, can be effectively reduced based on the knowledge of certain information in the coded word. The decoding operation is improved by shortening the length of the code words to be decoded because the shorter codewords are less susceptible to bit errors.