MXPA99003949A - Method and apparatus for providing high speed data communications in a cellular environment - Google Patents

Abstract

A method and apparatus for transmitting digital data in a cellular environment. Adjacent cells of the cellular system (1 and 2A-2F) are prevented from simultaneously transmitting data. Because the noise from transmission of adjacent cells is a primary source of interference, the transmission rate of power limited base stations (1-3) can be dramatically increased when the noise from adjacent cells is eliminated. The transmissions to each subscriber station (6) are made at a fixed transmission power level. However, the data rate of transmitted signals differs from one subscriber station (6) to another depending the path loss differences. In a first exemplary embodiment, the data rate of transmissions to a subscriber station (6) is determined by selecting an encoding rate for the transmitted signal while holding the symbol rate constant. In a second exemplary embodiment, the data rate of transmission to a subscriber station (6) is determined by selecting a modulation format for the transmitted signal which directly changes the symbol rate of transmission to a subscriber station (6).

Description

METHOD AND APPARATUS FOR PROVIDING HIGH SPEED DATA TRANSMISSION IN A CELLULAR ENVIRONMENT BACKGROUND OF THE INVENTION I. Field of the Invention The present invention relates to communication systems. The present invention relates, more particularly, to a novel and improved method and apparatus for providing information at high speed, in a wireless cellular communication environment.

II. Description of Related Art As the technology of wireless communication has advanced, the demand for high-speed data transmission services in a wireless environment has increased dramatically.

The use of code division multiple access modulation (CDMA) is one of several techniques for providing wireless digital transmission suitable for the transmission of digital data. Other methods for wireless digital transmission include time division multiple access (TDMA) and frequency division multiple access (FDMA). However, the CDMA dispersion spectrum modulation technique has important advantages different from the modulation techniques P1251 / 99MX digital. The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Patent No. 4,901,307, entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS", assigned to the assignee of the present invention and which is incorporated here as a reference. The use of CDMA techniques in a multiple access communication system is further analyzed in U.S. Patent No. 5,103,459, entitled "SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM", assigned to the transferee of the present invention and which is incorporated herein by reference. The method to provide wireless digital communication using CDMA modulation was standardized by the Telecommunications Industry Association (TIA) in TIA / EIA / IS-95-A Standards for Compatibility of Base Station-Mobile Station for Cellular Spectrum System Broadband Dispersion Dual Mode (hereinafter IS-95). The current wireless communication systems can only provide relatively low transmission speeds. In addition, the most current wireless communication systems have not been optimized for digital data transmission, but have been optimized for the transmission of telephone information. There is therefore, in the P1251 / 99MX industry, the need for a method to provide high-speed digital information transmission in > a wireless environment.

SUMMARY OF THE INVENTION The present invention is a novel and improved method and apparatus for the transmission of digital data in a cellular environment. In the present invention, adjacent cells are prevented from transmitting information at the same time. Therefore, if a first base station on one side of a cell boundary is transmitting, then a second base station on the other side of the boundary of the cell is silent during the transmission period of the cell. first base station. Because noise from adjacent cell transmissions is a primary source of interference, the transmission rate of limited power base stations can be increased significantly when it is eliminated. the noise coming from adjacent cells. In the present invention, all transmissions from a base station are transmitted at a fixed power level and transmissions to each subscriber station in a cell are transmitted in non-overlapping bursts. Therefore, when a base station is transmitting, its transmissions are directed to a station P1251 / 99MX subscriber within the cell, allowing the total amount of available power to be used? to transmit data to that subscribing station that optimizes the speed of information available to the subscriber station. For purposes of clarity, it should be noted that reference is here made to two separate but related speeds. One is the information rate that refers to the binary information speed | 10 generated by the user. The second is the transmission speed, which is the bit rate transmitted by air. When the transmissions are made at a fixed power level, the amount of information that can be transmitted between the base station and the subscriber station varies with the link budget factors that are well known in the art. The most significant link budget factor in a wireless communication system is the path loss between the base station and the subscriber station. Path loss is an important function of the distance between the base station and the subscriber station. In the present invention, the transmissions to each subscriber station are made at a fixed level of transmission power. However, the information speed of transmitted signals P1251 / 99MX differs depending on the distance between the subscriber station and the base station. In the first exemplary embodiment, the information rate of transmissions to a subscriber station is determined by selecting a coding rate for the transmitted signal while maintaining the transmission rate constant. In the second exemplary embodiment, the information rate of transmissions to a subscriber station is determined by selecting a modulation format for the transmitted signal that directly changes the transmission rate to a subscriber station.

BRIEF DESCRIPTION OF THE DRAWINGS The features, objectives and advantages of the present invention will be more apparent from the detailed description set forth below, when taken in conjunction with the drawings, wherein like reference numbers identify processes accordingly, and wherein: Figure 1 is an illustration of a typical cellular diagram for a geographic area; Figure 2 is an illustration of the interrelation of the base station controller, base stations and subscriber stations; Figure 3 is an illustration of the diagram of P1251 / 99MX timing and the exemplary frame format of the present invention; Figure 4 is a block diagram illustrating a cell in the present invention; Figure 5 is a block diagram illustrating the base station of the present invention; Figure 6 is a block diagram illustrating the subscriber station of the present invention; and Figure 7 is an illustration of a cell divided into a large number of narrow sectors.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES In the following description, the same reference number is used to describe both the cell or area served by a base station and the base station itself. In the present invention, two adjacent cells are prohibited from transmitting simultaneously. Thus, in Figure 1, when the base station is transmitting then the base stations 2A-2F are prevented from transmitting. The noise (N0) experienced by a base station that is transmitting in a cellular environment is described by equation (1) below: N0 = Nb + Nm + Nt + Nr, (1) where Nb is the noise coming from base stations P1251 / 99MX in adjacent cells, Nm is the interference of the multiple path reflections and Nt is the thermal noise in the system and Nr counts for all other sources of noise. The value of noise (N0) limits the amount of information that can be transmitted in a limited power wireless communication system. The present invention eliminates the noise that comes from adjacent cells, Nb, preventing any of the two adjacent cells from transmitting simultaneously.

In addition, because a base station transmits only to one subscriber station at a time, all of its available energy can be used for transmissions to that subscriber station. By reducing the total noise (N0) and increasing the available power to transmit to a specific station, the speed of information available for the transmissions to the subscriber station increases significantly. Referring to Figure 2, the base station controller (BSC) 4 controls the operation of a large number of base stations within a geographical region. In the present invention, BSC 4 coordinates the transmission by the base stations 1, 2A-2F and 3A-3L so that neither of the two adjacent cells is transmitting simultaneously. In the present invention, BSC 4 sends a P1251 / 99MX signal to a base station selected from 1, 2A-2F and 3A-3L, directing it to the selected base station to transmit during a predetermined time interval. In a preferred implementation, the cells are grouped into sets of non-adjacent cells where any of the cells within that set can transmit simultaneously. For example, a first set of non-adjacent cells may consist of of cells 2A, 2C, 2E, 3C, 3K and 3G. A second set of non-adjacent cells can consist of cells 2B, 2D, 2F, 3A, 3E and 31. In this preferred implementation, BSC 4 selects the subset of non-adjacent cells that can transmit and to any or all the cells within that set of non-adjacent cells that can transmit during that frame cycle. Referring to the schedule of Figure 3, the BSC 4 sends a transmission message to the base station 1 at time 0. In the preferred implementation, the BSC 4 sends a message to all base stations in the set of non-adjacent base stations, which include the base station 1. In response to that message, the base station 1 transmits during the time interval from 0 a. At time T, the BSC 4 sends a transmission message to the base station 2A indicating to the base station 2A for P1251 / 99MX transmit during the time interval between time T and time 2T. This process is repeated for (^ each base station of the base stations 2B-2F as shown in Figure 3. At time 7T, the BSC 4 5 sends a message to the base station 1 transmitting during the time interval between time 7T and 8T Note that when one of the base stations 2A-2F is transmitting, it is possible for a subset of base stations 2A-2F to be . ^ i iO transmitting, for the time when neither of the two base stations shares a common cell boundary. For example, when the base station 2A is transmitting, then cells 1, 2B, 3F, 3E, 3D and 2F can not transmit since they are not adjacent to the cell 2A. However, cells 2C-2F can transmit during this period as they are not ^^ adjacent to cell 2A. In a preferred embodiment, the time intervals for transmission are the same to reduce the complexity of handling coordination of base station transmissions in the system. It should be noted that the use of variation time intervals is foreseen as a possibility. In the exemplary embodiment illustrated in Figure 3, the transmission cycle of the cells follows a simple deterministic pattern. It is understood that in the simple deterministic transmission cycle, it is not necessary for the base station to operate under the P1251 / 99MX BSC control 4 because each base station can transmit at predetermined times without BSC control 4. In a preferred embodiment, the transmission cycle is not determined by a simple deterministic pattern as illustrated in the Figure 3. In the preferred embodiment, BSC 4 selects a base station or a set of non-adjacent base stations that transmits in accordance with the amount of information that is queued for its transmission at the base station or at the set of stations non-adjacent bases. In the preferred embodiment, the BSC 4 monitors the amount of messages that are in a queue held by each base station or set of non-base stations. adjacent and selects the base station to transmit based on the amount of data in the waiting rows. Within each cell can be found a plurality of subscriber stations, each of the Which require data to be transmitted to them by means of the base station serving that cell. In the exemplary embodiment, the base station designates the identity of the subscriber station to which it is transmitting by means of a header. Doing Referring to Figure 3, in the first time interval (time 0 to T), the base station 1 transmits to a selected subscriber station.

P1251 / 99MX In the exemplary mode, each frame is 2 ms in duration. The transmitted data is provided with a header identifying the selected subscriber station. In an alternative implementation, each cell is divided into narrow sectors where each sector can be transmitted independently of the transmission to any other sector in the cell. This can be accomplished by means of highly directional antennas, the design of which is well known in the field. Figure 7 illustrates a cell 600 served by the base station 510, which is divided into sectors 500A-500O. In this modality, each cell of the communication system that is divided into sectors in a similar way, transmits to a sector or subset of random sectors in it. The probability of overlapping simultaneous transmissions from adjacent sectors is small insofar as each cell is divided into a sufficiently large number of sectors. It should be noted, with respect to Figure 3, that all forward link transmissions are provided at the same energy E0, which would typically be the maximum transmission energy allowed by government regulations. Equation (2) below illustrates a general link budget analysis that describes the interrelation of parameters P1251 / 99MX in a wireless communication system with fixed power (E0): E0 = R (bits / s) (dB) + (Eb / No) req (dB) + LS (dB) + Lo (dB) (2) where E0 is the fixed transmission power of the base station, R is the transmission speed, (Eb / No) req is the signal required for noise ratio for a given error rate, Ls is the path loss in decibels and L0 is the other loss in decibels. The path loss, Ls, depends to a large extent on the distance between the base station and the subscriber station. In the present invention, either the transmission rate, R, or the signal required for the noise ratio, (Eb / No) req, vary based on the distance between the subscriber station and the base station. Referring to Figure 4, three subscriber stations 6A, 6B and 6C are within the cell boundary 10 and as such, are served by the base station 1. The distances to the subscriber stations 6A, 6B and 6C are rl , r2 and r3, respectively. In an alternative embodiment, an effective distance may be used where the effective distance is a metric that is selected in accordance with the path loss between the base station 1 and the receiving subscriber station.

P1251 / 99MX It will be understood by a person skilled in the art, that the effective distance is related to the physical distance between the base station and the subscriber station, but is not equal to the physical distance between the base station and the subscriber station. The effective distance is a function of both the physical distance and the course of the propagation path. Referring again to the equation ilO (2), it can be observed that the effects of the differences in the trajectory losses (Ls) can be compensated by keeping all the other constants, changing the value of (Eb / No) req. The value (Eb / No) req depends on the techniques of detection and correction of error used to protect the transmission data. The coding rate refers to the ratio of the output number of binary symbols by the encoder to the number of bits output to the encoder. In general, the higher the coding speed of the transmission system, the protection for the transmitted data is greater and the signal required for the signal noise speed is lower (Eb / No) req. In this way, in a first exemplary embodiment of the invention, the speed encoding the transmissions to subscriber stations, is selected based on the distance between the subscriber stations and the base station.

P1251 / 99MX Since communication systems are limited to bandwidth, the higher coding rate used results in lower system data production. 5 In equation (2), it can be seen that the effects of the differences in path loss (Ls) can also be compensated for by changing the value of the transmission speed R. The transmission rate R is determined by the equation : ilO R = Rs • log2M, (3) where Rs is the number of transmitted symbols and M is the number of symbols in the modulation constellation. Thus, if the distance between the base station and the subscriber station is large, the speed is reduced of transmission R. In the present invention, the transmission rate is varied by changing the modulation format to one with more or fewer symbols in the modulation constellation. Whereas, when the distance between the base station and the station subscriber is small, the transmission speed, R, increases. In the second exemplary embodiment, the symbol rate is set by the selection of a modulation format. The information rate is the speed at which the real bits are transmitted of non-coded user information. Assuming physical distance and effective distances are closely related, P1251 / 99 X the base station 1 will transmit at an information rate to the subscriber station 6A lower than the speed it will transmit to the subscriber station 6B, since the effective distance to subscriber station 5A is longer than the effective distance towards Subscriber station 6B. In the exemplary embodiment, each subscriber station transmits a message indicating its location, to the base station that serves the cell in ilO where it is located. In an alternative embodiment, placement methods that are well known in the field can be employed by the communication station to estimate the location of the subscriber station. In an alternative mode, the base station uses a The effective distance determined in accordance with a path loss measurement between the base station and the subscriber station. The measurement of path loss can be done by transmitting a signal of a known power from the station basis and measuring the power received at the subscriber station. Similarly, the path loss measurement can be performed by transmitting a signal of a known power from the subscriber station and measuring the power received at the base station.

It should be noted that the references for the distance between the base station and the subscriber station apply equally for the physical distance and for the P1251 / 99MX effective distance based on the measured path loss. In the present invention, the initial coding rate or modulation format is selected and initially provided during the service establishment procedure.

Then, the distance is tracked. If a sufficient change in distance results during the service, a new coding rate or modulation format is selected in accordance with the new distance. In the first exemplary embodiment, the base station selects a coding rate in accordance with the distance between the base station and the subscriber station. The base station transmits an indication of the selected coding rate, towards the subscribing station that receives. The receiving subscriber station, in accordance with the selected encoding rate, selects an appropriate decoding format to be used with the selected encoding rate. In the second exemplary embodiment, the base station selects a modulation format based on the distance between the base station and the subscriber station. The base station then transmits an indication of the selected modulation format to the receiving subscriber station.

P1251 / 99MX The receiving station that receives, according to the selected modulation format, establishes the appropriate demodulator for the reception of the modulated signal, in accordance with the selected modulation format. A block diagram of the exemplary embodiment of the base station 1 is illustrated in Figure 5. Figure 6 illustrates a block diagram of the exemplary embodiment of the subscriber station 6A. In the first exemplary embodiment, the coding rate is selected for transmissions to a subscriber station in accordance with the distance between the base station and the subscriber station. In this way, the transmission rate is varied with the transmission rate R, held fixed by selecting one of a plurality of coding rates. First, the subscriber station 6A registers with the base station 1. In the registration process, the mobile station 6A alerts the base station 1 of its existence and performs basic system establishment or startup tasks as is well known in the field . An exemplary embodiment for the device registration is described in detail in U.S. Patent No. 5,289,527, entitled "MOBILE COMMUNICATION DEVICE REGISTRATION METHOD", assigned to the assignee of the present invention and which P1251 / 99MX is incorporated herein by reference. In the exemplary embodiment, the subscriber station signal generator 218 generates a message indicating its location and provides the message to the transmission subsystem 216. The transmission subsystem 216 encodes, modulates, overconverts and amplifies the message and provides the message through the duplexer 201 for transmission through the antenna 200. The location message is received via the antenna 120 and is provided to the subsystem receiver 118. The receiver subsystem 118 amplifies, subverts, demodulates and decodes the received location message and provides it to the transmission controller 104. In the exemplary embodiment of the present invention, the mobile station 6A transmits a message indicating its location to the base station 1 during the registration process. Further, in the exemplary embodiment, the subscriber station 6A tracks its own movement and, if the distance changes by at least a certain amount, the subscriber station 6A transmits an indication of its new location. As described above, alternative methods for determining the location of the subscriber station or methods based on the path loss measurement can be employed. In the exemplary embodiment, the information of P1251 / 99MX location to the transmission controller 104 of the base station 1, which calculates the distance between the base station 1 and the subscriber station 6A. The transmission controller 104 selects a coding rate in accordance with the distance between the subscriber station 6A and the base station 1. In a preferred embodiment, the distances between the base station 1 and the subscriber station 6A are quantized in discrete values as illustrated in Figure 4. With reference to Figure 4, all subscriber stations that are located between the base station 1 and the circle 7A would receive information at a first coding rate. All subscriber stations that are located between circle 7A and circle 7B would receive information at a second encoding rate. All subscriber stations that are located between circle 7B and circle 7C would receive information at a third encoding rate. For example, referring to Figure 4, the base station 1 may use a speed code of 1/2 when transmitting to the subscriber station 6B which is close to the base station 1. The base station 1 may, however, use a 1/8 speed code when transmitting to the subscriber station 6A which is far from the base station 1. If the distance between the base station and the P1251 / 99MX subscriber station is large, a higher encoding speed will be selected. While, when the distance between the base station and the subscriber station is small, a lower coding rate will be selected. The correction and error detection methods employed in subscriber station 6A will allow a lower signal required for the sound velocity, (Eb / N0) req, for a given error rate. The lower the encoding speed is, the greater the number of errors that can be corrected and the lower the signal required for the noise velocity (Eb / N0) req. In the first exemplary embodiment, the transmission controller 104 selects the speed encoding as described in the above and sending an indication of the selected speed, to the subscriber station 6A. In the exemplary embodiment, the message indicating the coding rate is transmitted by a channel of pager during the registration process. Radio localization channels are used in wireless communication systems to send short messages from a base station to a subscriber station. In a preferred embodiment, the system The communication allows the base station 1 to change the coding rate by subsequent messages transmitted on the traffic channel. A P1251 / 99MX reason to provide the change of the encoding speed is to allow changes in the location of subscriber station 6A. In the exemplary embodiment, the message indicating the selected coding rate is provided by the transmission controller 104 to the encoder 106 encoding the message. The coded symbols from the encoder 106 are provided to the interleaver 108, which reorders the conformance symbols with a predetermined reordering format. In the exemplary embodiment, the interleaved symbols are provided to the mixer 110 that mixes the interleaved signal, in accordance with a CDMA spreading format, as described in the aforementioned US Patents Nos. 4,901,307 and 5,103,459. The spscrambledread signal is provided to the modulator 112 which modulates the signal in accordance with a predetermined modulation format. In the exemplary embodiment, the modulation format for the radiolocation channel is modulation by quadrature phase shift manipulation (QPSK). The modulated signal is provided to the transmitter 114, where it is up-converted and amplified and transmits through the antenna 116. The transmitted message indicating the coding rate is received by the antenna 200 and P1251 / 99MX provided to receiver 202 (RCVR). The receiver 202 downconverts and amplifies the received signal and provides the received signal to the demodulator 204. The demodulator 204 demodulates the received signal. In the exemplary embodiment, the demodulation form for the radio location channel is a QPSK demodulation format. In the exemplary embodiment, the demodulated signal is provided to the equalizer 205.

Equalizer 205 is a channel equalizer that reduces the effects of the propagation environment such as multipath effects. Channel EQs are well known in the field.

The design and implementation of a channel equalizer is discussed in co-pending US Patent Application No. 08 / 509,722 entitled "Adaptive Despreader", filed on July 31, 1995, which was assigned to the assignee of the present invention. and is incorporated here as a reference. The equalized signal is provided to the demixer 206 which demixes the signal in accordance with a CDMA de-dispersion format described in detail in the aforementioned U.S. Patent Nos. 4,901,307 and 5,103,459. Dispersed symbols are provided to deinterleaver 208 and reordered in accordance with a predetermined deinterleaving format. Reordered symbols are provided to the decoder P1251 / 99 X 210 which decodes the message indicating the selected coding rate and provides the decoded message to the control processor 212. In response to the decoded message, the control processor 212 provides a signal to the decoder 210 indicating a decoding format that it will be used for high-speed data transmissions. In the exemplary embodiment, the decoder 210 is capable of decoding a received signal in accordance with a plurality of grid decoding formats, wherein each decoding format corresponds to a corresponding different coding format. Referring again to Figure 5, the data to be transmitted to the subscriber stations in cell 1 (subscriber stations 6A, 6B and 6C) are provided to queue 100. Data is stored in the row of subscribers. wait 100 in accordance with the subscribing station to which they are going to be transmitted. The data for subscriber station 6A is stored in memory 102A, data for subscriber station 6B is stored in memory 102B, data for subscriber station 6C is stored in memory 102C, and so on. The various memory elements (102A-102N) are for illustrative purposes only, it will be understood that the queue consinormally P1251 / 99MX from a single memory device and the separate memory devices illustrated refer simply to the memory locations within the device. In the first time interval (t = 0) in Figure 3, the BSC 4 sends a message to the transmission controller 104 indicating the base station 1 to transmit. In response, the transmission controller 104 selects a receiving subscriber station within its coverage area and the period of time that the data has been waiting in the queue. In a preferred embodiment, the selection of the receiving subscriber station is based on the amount of data waiting for transmission to the subscriber stations in the coverage area. The transmission controller 104 selectively provides a signal to one of the memory elements 102A-102N based on its selection from the receiving subscriber station. In addition, in accordance with the selected receiving subscriber station, the transmission controller 104 provides a signal to the encoder 106 indicating the coding rate to be used for transmissions to the selected subscriber station. The transmission controller 104 provides, to the encoder 106, a header message identifying the receiving subscriber station. In an exemplary embodiment, encoder 106 encodes P1251 / 99MX the header message using an encoding format that will be used to encode the headers for transmissions to all subscriber stations. In an exemplary embodiment, the header information is encoded separately from the rest of the data, so that a subscriber station does not need to decode the very large amount of data transmitted during the transmission interval if it is not addressed to that subscriber station. The transmission controller 104 then provides a signal to the memory element 102A for use in providing data and specifying the maximum amount of data that can be transmitted to the receiving subscriber station 6A during the predetermined time interval. The predetermined maximum is the maximum information that can be transmitted to the subscriber station 6A within the time interval T, at the selected coding rate (Renc) # - for the fixed transmission rate, R, as shown in the equation (4) next: Max Data = (R • T) / Rene (4) In response to the signal from the transmission controller 104, the memory element 102A provides the encoder 106 with a data amount less than or equal to Max Data.

P1251 / 99MX The encoder 106 encodes the data using the selected coding format and combines the encoded symbols of the header message with the encoded data symbols. In the exemplary embodiment 5, the encoder 106 is capable of encoding the data in a plurality of convolutional coding rates. For example, the encoder 106 may be capable of encoding the data using convolutional coding formats at ilO speeds of 1/2, 1/3, 1/4 and 1/5. The coding rates can be varied at virtually any speed using a combination of commonly used encoders and data drilling. The encoder 106 provides the coded symbols at interleaver 108. The interleaver 108 reorders the symbols in accordance with a predetermined reordering format and provides the reordered symbols to the mixer 110. The mixer 110 mixes the symbols in accordance with a predetermined CDMA spreading format and provides scattered symbols to the modulator 112. It should be noted that since only one subscriber station 6A is being transmitted, the use of the mixer 110 is for purposes of data mixing for security purposes and to increase signal immunity to narrow band noise and not for the purposes of P1251 / 99 X multiple access communications. The modulator 112 modulates the scattered symbols in accordance with a predetermined modulation format. In the exemplary embodiment, the modulator 112 is a 16-year QAM modulator. The modulator 112 provides the modulated symbols to the transmitter (TMTR) 114. The transmitter 114 overconverts and amplifies the signal and transmits the signal through the antenna 116. The transmitted signal is received by the subscriber station 6A on the antenna 200. The signal received is provided to receiver 202 (RCVR). The receiver 202 downconverts and amplifies the received signal. The received signal is provided to the demodulator 204 which demodulates the signal in accordance with a predetermined demodulation format. The demodulated signal is provided to the equalizer 205 which is a channel equalizer as described above. The equalized channel signal is provided to the demixer 206 that demixes the signal in accordance with a predetermined CDMA de-dispersion format, as described above. The deinterleaver 208 rearranges the scattered symbols and provides them to the decoder 210. In the exemplary embodiment, the decoder 210 first decodes the header message contained in the reordered symbols. He P1251 / 99MX header message is provided to the header verification means 214 which verifies that the information being transmitted is destined to the subscriber station 6A. If the data is destined for the subscriber station 6A, then the rest of the data is decoded. When the header indicates that the data is intended for the user of the subscriber station 6A, the header verifier 214 sends a signal to the decoder 210 indicating that the excess information must be decoded. In an alternative mode, all the information is decoded and then the header is verified after the decoding process. The decoder 210 decodes the symbols in accordance with the decoding format selected from the control processor 212. In the exemplary embodiment, the decoder 210 decodes the reordered symbols according to one of a plurality of grid decoding formats selected based on the encoding speed selected. The decoded symbols are then provided to the user of the subscriber station 6A. In the second exemplary embodiment, the transmission controller 104 selects the modulation format in accordance with the distance between the base station and the mobile station. The base station 1 P1251 / 99MX sends an indication of the selected modulation format to the subscriber station. The modulation format directly effects the transmission speed R. Referring to equation (2), all parameters are fixed in this case, except the path loss Ls, and the transmission speed R. The highest transmission rates R are transmitted using a modulation format containing a Largest set of modulation symbols. For example, the 28-aria quadrature amplitude modulation (QAM) can be used for transmission to the subscriber station near the base station. While QAM 16-aria modulation would be used for transmission to subscriber stations in addition to the base station. In the exemplary embodiment, the subscriber station 6A transmits a message indicating its location to the base station 1. In response, the base station 1 selects a modulation format.

As described with respect to the above embodiment, the distances calculated by the transmission controller 104 are quantized. The modulation format is selected in accordance with the quantized distances. Referring to the Figure 4, all the subscriber stations that are located between the base station 1 and the circle 7A would receive information using a first format of P1251 / 99MX modulation. All subscriber stations that are located between circle 7A and circle 7B f would receive information using a second modulation format. All subscriber stations that are located between circle 7B and circle 7C would receive information using a third modulation format. For example, referring to the Figure 4, the base station 1 can use a QPSK modulation format when it is transmitting to the subscriber ilO station 6B which is close to the base station 1.

By contrast, the base station 1 can use a Quadrature Amplitude Modulation (QAM) 64-ary when it is transmitting to subscriber station 6A which is far from the base station 1. In the mode exemplary, the message indicating the selected modulation format, is transmitted by a radio location channel during the registration process. Again, in a preferred embodiment, the communication system allows the base station 1 to change the modulation format by subsequent messages transmitted by the radio location channel. The transmitted signal indicating the modulation format is received by the subscriber station 6A as described above and is provided to the control processor 212. Control processor 212 provides a signal to demodulator 204 indicating a demodulation format to be used. He P12S1 / 99MX demodulator 204, of the second exemplary embodiment, is capable of demodulating a received signal in accordance with a plurality of demodulation formats. In response to the signal from the control processor 212, an appropriate demodulation format is selected. Referring again to Figure 5, the data that will be transmitted to the subscriber stations in cell 1 (subscriber stations 6A, ilO 6B and 6C) is provided to queue 100. In the first time slot (t = 0), the BSC 4 sends a message to the transmission controller 104 sending to the base station 1 to transmit. In response to the signal, the transmission controller 104 selects a receiving subscriber station as described in the above. The transmission controller 104 selectively provides a signal to one of the memory elements 102A-102N based on its selection of the subscriber station. In addition, in accordance with In the selected subscriber station, the transmission controller 104 provides the modulator 112 with a signal indicating the selected modulation format. The transmission controller 104 provides, to the decoder 106, a header message that identifies the subscriber station to which the data is being sent. The encoder 106 encodes the header message as described in FIG.

P1251 / 99MX previous. The transmission controller 104 then provides a signal to the memory element 102A sending it to provide data and specifying the maximum amount of data that can be transmitted 5 to the receiving subscriber station 6A during the predetermined time interval. The predetermined maximum is the maximum information that can be transmitted to the subscriber station 6A within the time interval T, at the selected rate, 11O as shown in the following equation (4). Max Data = M • Rs • T, (5) where M is the number of modulation symbols used in the selected modulation format and Rs is the symbol rate. In response to the signal from transmission controller 104, memory element 102A provides encoder 106, a data amount less than or equal to Max Data. In the second exemplary embodiment, the encoder 106 encodes the data at a speed of coding and combining the coded symbols of the header message with the coded data symbols. The encoder 106 provides the coded symbols to the interleaver 108. The interleaver 108 rearranges the conformance symbols with a predetermined reordering format and provides the reordered symbols to the mixer 110. The mixer 110 mixes the symbols in accordance with P1251 / 99MX a predetermined CDMA spreading format and provides the mixed symbols to the modulator 112.

) The modulator 112 modulates the mixed symbols according to the modulation format selected. In the exemplary embodiment, the modulator 112 is capable of configuring the mixed symbols into modulation symbols in accordance with a plurality of modulation formats. The modulator 112 provides the modulated symbols to the ilO 114 transmitter (TMTR). The transmitter 114 overconverts and amplifies the signal and transmits the signal through the antenna 116. The transmitted signal is received by the subscriber station 6A on the antenna 200. The signal received is provided to receiver 202 (RCVR). The receiver 202 downconverts and amplifies the received signal. The received signal is provided to the demodulator 204 which demodulates the signal in accordance with the selected demodulation format. The signal demodulated is provided to the equalizer 205 whose channel equalizes the received signal as described above. The equalized signal is provided to the demixer 206 which demixes the signal in accordance with a predetermined CDMA de-dispersion format.

The deinterleaver 208 reorders the demixed symbols and provides them to the decoder 210. In the exemplary embodiment, the P12S1 / 99MX decoder 210 first decodes the header message contained in the reordered symbols. The header message is provided to the header verification means 214 which verifies that the information being transmitted is destined to the subscriber station 6A. If the data is destined to subscriber station 6A then the rest of the data is decoded. When the header indicates that the data is intended for the user of the subscriber station IO 6A, the header verifier 214 sends a signal to the decoder 210 indicating that the remaining information must be decoded. In an alternative mode, all the information is decoded and then the header is verified after the decoding process was finished. The decoder 210 decodes the symbols. The decoded symbols are then provided to user of the subscriber station 6A. It should be noted that those systems that use both the variation of coding speed, and the technique of variation of modulation format, simultaneously. The above description of the preferred modalities is provided to train any person skilled in the art to make or use the present invention. The various modifications to these modalities will be easily P1251 / 99MX are obvious to those with skill in the art, and the generic principles defined here can be applied to other modalities without the use of the 'inventive faculty'. In this way, it is not intended that the present invention be limited to the modalities shown here, but that it will be in accordance with the broadest scope consistent with the principles and novel features discussed herein.

P1251 / 99MX

Claims (24)

1. NOVELTY OF THE INVENTION Having described the present invention, it is consid as a novelty and, thore, the content of the following 3 CLAIMS is claimed as property: 1. A method for the transmission of digital data from a first communication station to a second communication station, comprising the steps of: i determining a distance between the first communication station and the second communication station; select an information rate for transmission in accordance with distance; and 15 transmitting the digital data at the information rate. The method according to claim 1, whn the step of selecting the information rate comprises selecting a speed of 20 coding for digital data. The method according to claim 1, whn the step of selecting the information rate comprises selecting a modulation format for the digital data. 4. The method according to claim 2, whn the step of selecting a coding rate comprises selecting one of a set P1251 / 99MX predetermined convolutional encoding rates. 5. The method according to claim 1, whn the step of determining the distance comprises the 5 stages of: transmitting a location message from the first communication station to the second communication station; and determine the distance in accordance with the location message. The method according to claim 1, whn the step of determining the distance comprises the steps of: transmitting a refce signal to a known power; measure the received power of the refce signal; and calculating a value for the distance, in accordance with the known power and the received power. The method according to claim 1, whn the step of transmitting the digital data at the data rate is effected at a fixed maximum transmission power. 8. The method according to claim 1, further comprising the step of preventing at least one first adjacent communication station from transmitting. P1251 / 99MX when the first communication station is transmitting. 9. In a communication system in which a first communication station transmits digital data to a second communication station, whn the information speed of the digital data is determined in accordance with the path loss between the first communication station and the second communication station, a method for receiving the digital data comprising the steps of: receiving in the second communication a signal indicating the information rate; selecting in the second communication station, a reception format in accordance with the speed of the data; and receive the digital data in accordance with the selected reception format. The method according to claim 9, whn the step of selecting a reception format comprises selecting a decoder format. The method according to claim 10, whn the step of selecting a reception format comprises selecting a grid decoding format. The method according to claim 9, whn the step of selecting a reception format P1251 / 99MX comprises selecting a demodulation format. 13. An apparatus for transmitting digital data from a first communication station to a second communication station, which 5 comprises: a transmission controller for selecting a transmission format in accordance with the distance between the first communication station and the second communication station and for providing ilO with a transmission format signal indicating the selected transmission format; and a transmission system for the reception of the digital data and the transmission format signal and for transmitting the digital data in accordance with the selected transmission format. 14. The apparatus according to claim 13, wherein the transmission controller selects a coding rate for the digital data. 15. The apparatus according to claim 13, wherein the transmission controller selects a modulation format for the digital data. The apparatus according to claim 14, wherein the transmission controller selects a speed from a predetermined set of speeds 25 convolutional coding. 17. The apparatus according to claim 13, further comprising: P1251 / 99MX a receiving subsystem for receiving a location message from the second communication station; and wherein the transmission controller serves to receive the location message and to calculate the distance between the first communication station and the second communication station, in accordance with the location message. The apparatus according to claim 13, further comprising: a receiving subsystem for receiving a known transmission energy signal from the second communication station; and wherein the transmission controller serves to measure the energy of the received signal and to calculate the distance between the first communication station and the second communication station, in accordance with the measured energy of the received signal. 19. The apparatus according to claim 13, wherein the transmission system transmits digital data at a fixed maximum transmission power. The apparatus according to claim 13, wherein the first communication station is a cellular base station serving a first cell and wherein the transmission controller is further to receive a transmission signal indicating a time interval in the cell. that transmits, and where the P12S1 / 99MX transmission signal is provided so that when the first communication station is transmitting it is prohibited to transmit other base stations serving the cells adjacent to the first cell. 21. In a communication system in which a first communication station transmits digital data to a second communication station, wherein the information speed of the digital data is determined in accordance with the distance between the first communication station and the second communication station, an apparatus for receiving the digital data, comprising the steps of: receiving subsystem to receive in the second communication a signal indicating the information rate; control processor for selecting in the second communication station a reception format, in accordance with the information rate; and wherein the receiving subsystem is in addition to receive the digital data, in accordance with the selected reception format. 22. The apparatus according to claim 21, wherein the control processor selects a decoder format. 23. The apparatus according to claim 22, in P1251 / 99MX where the control processor selects a grid decoding format. 24. The apparatus according to claim 21, wherein the control processor selects a demodulation format. P1251 / 99MX