Method and apparatus for transmitting and receiving variable rate data

ES 2 380 792 T3

DESCRIPTION

Procedure and apparatus for transmitting and receiving variable speed data

Background of the invention

I. Field of the invention

The present invention relates to communications. More specifically, the present invention relates to a method and apparatus for transmitting and receiving variable rate packets with signals indicating the data rate of those packets.

II. Description of Related Art

The use of code division multiple access (CDMA) modulation techniques is one of several techniques for facilitating communications in which a large number of users of the system are present. Although other techniques are known, such as time division multiple access (TDMA), frequency division multiple access (FDMA) and AM (Amplitude Modulation) modulation schemes, such as compressed and expanded single sideband amplitude (ACSSB), CDMA has significant advantages over these other techniques. The use of CDMA techniques in a multiple access communication system is disclosed in US Patent No. 4,901,307, entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS" ["MULTIPLE ACCESS AND SPECTRUM COMMUNICATION SYSTEM WIDENING USING SATELLITE OR TERRESTRIAL REPEATERS "], assigned to the applicant of the present invention. The use of CDMA techniques in a multiple access communication system is further disclosed in US Patent No. 5,103,459, entitled "SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM" ["SYSTEM AND PROCEDURE FOR GENERATING SIGNAL WAVES IN A CDMA CELLULAR TELEPHONY SYSTEM "], assigned to the applicant of the present invention.

In the aforementioned US Patent No. 5,103,459 (the '459 patent), the use of orthogonal Walsh codes is described to provide channeling to different subscriber stations. This allows a base station to transmit many different channels to a plurality of users in the coverage area of ​​the base station. In the '459 patent, one of the orthogonal Walsh channels being transmitted was a pilot channel that allowed coherent demodulation of traffic channels transmitted over other orthogonal Walsh channels. A method for transmitting a CDMA signal from a mobile station that is capable of coherent demodulation is described in unpublished US Patent Application Serial No. 08 / 856,428 entitled "REDUCED PEAK TO AVERAGE TRANSMIT POWER HIGH DATA RATE IN A CDMA WIRELESS COMMUNICATION SYSTEM. assigned to the applicant of the present invention. In US Patent Application Serial No. 08 / 856,428, the mobile station transmits a plurality of different channels, each channel being distinguished by the use of a short Walsh sequence. Furthermore, in US Patent Application Serial No. 08 / 856,428, a complex pseudo-noise (PN) spreading procedure reduces the maximum to average ratio in the transmission of a QPSK modulated signal.

CDMA systems employ a variable rate vocoder to encode data so that the data rate can vary from one data frame to another. An exemplary embodiment of a variable rate vocoder is disclosed in US Patent No. 5,414,796, entitled "VARIABLE RATE VOCODER", assigned to the assignee of the present invention. The use of a variable speed communications channel reduces mutual interference, eliminating unnecessary transmissions when there is no useful speech to transmit.

Similarly, it is desirable to provide variable rate transmission of digital data in CDMA wireless communication systems. When there is a large amount of digital information to be transmitted and when it is important to minimize delay, then the data should be transmitted at high transmission speeds. However, when there is less data to be transmitted or when minimizing the delay is not so important, it is desirable to reduce the transmission speed of digital data in a wireless communication system, because transmission at speeds lower than the maximum transmission speed can result in increased range and extended battery life, and reduce interference with other users. WO95 / 03652A and US 5,289,476 disclose techniques for enabling high and low data rate channels in data communication systems.

In particular, WO95 / 03652 (QUALCOMM), published on February 2, 1995, discloses a procedure and system for allocating a set of orthogonal PN code sequences of variable length between channels

ES 2 380 792 T3 operating at different data rates, in a spread spectrum communication system. The orthogonal codes of variable length Walsh functions are used to modulate the information signals. The function selection and data rate selection signals are transmitted to the mobile unit by the cell-site. The transmission of a pilot sequence, the adjustment of the gain of the signals at the transmitter, and the use of encryption are also known from this document.

A technique for the receiver to determine the rate of a received data frame is described in US Patent No. 5,566,206, entitled "METHOD AND APPARATUS FOR DETERMINING DATA RATE OF TRANSMITTED VARIABLE RATE DATA IN A COMMUNICATIONS RECEIVER" ["PROCEDURE AND APPARATUS FOR DETERMINING THE DATA SPEED OF DATA TRANSMITTED OF VARIABLE SPEED IN A COMMUNICATION RECEIVER "], assigned to the assignee requesting the present invention. Another technique is described in unpublished US Patent Application Serial No. 08 / 126,477, entitled "MULTIRATE SERIAL VITERBI DECODER FOR CODE DIVISION MULTIPLE ACCESS SYSTEM APPLICATIONS" OF MULTIPLE ACCESS BY CODE DIVISION "], filed on September 24, 1993, assigned to the applicant of the present invention herein. According to these techniques, each received data frame is decoded at each of the possible rates. Error metrics, which describe the quality of the decoded symbols for each decoded frame at each rate, are provided to a processor. Error metrics can include Cyclic Redundancy Check (CRC) results, Yamamoto Quality Metrics, and Symbol Error Rates. These error metrics are well known in communications systems. The processor analyzes the error metrics and determines the most likely rate at which the incoming symbols were transmitted.

Summary of the invention

The present invention provides an apparatus and method for transmitting and receiving a variable rate user data packet according to the claims.

Brief description of the drawings

The characteristics, objects and advantages of the present invention will become more apparent from the detailed description set out below, when considered in conjunction with the drawings, in which the like reference characters identify correspondingly in their entirety, and in where:

FIG. 1 is a block diagram of the transmission system of a first example useful for understanding the present invention;

FIG. 2 is a block diagram of an exemplary PN generator;

FIG. 3 is a diagram illustrating the bits used for the long code mask;

FIG. 4 is a block diagram illustrating the first receiver system for receiving variable rate data transmitted by means of the first example;

FIG. 5 is a block diagram illustrating the second receiver system for receiving variable rate data transmitted by means of the first example;

FIG. 6 is a block diagram illustrating the transmitter system of a second example useful in understanding the present invention;

FIGS. 7A through 7H are diagrams illustrating a proposed set of preamble formats for use in the second example;

FIG. 8 is a block diagram illustrating the receiver system of the second example;

FIG. 9 is a block diagram of a remote station of the present invention, illustrating the transmitter system of one embodiment of the present invention; and FIG. 10 is a block diagram illustrating the receiver system of the embodiment of the present invention.

Detailed description of the preferred embodiments

With reference to the figures, FIG. 1 illustrates the transmission apparatus of the first example in block diagram form. The data packet to be transmitted is supplied to the cyclic redundancy control (CRC) and tail bit generator 2. The number of data bits in the data packet determines the effective rate R of the transmission. The CRC and tail bit generator 2 generates a set of CRC bits, such as parity bits, according to procedures that are well known in the art. The CRC bits, along with a set of tail bits, are

ES 2 380 792 T3 attach to data packet.

The data packet with the trailing and CRC bits appended is provided to the early error correction encoder 4. Encoder 4 may be any form of digital forward error correction encoder, such as a convolutional encoder, Reed Solomon encoder, or other known early error correction encoder. In the example, encoder 4 is a turbo-encoder, the design of which is well known in the art, and which is described in detail in US Patent No. 5,446,747, entitled "ERROR-CORRECTION CODING METHOD WITH AT LEAST TWO SYSTEMATIC CONVOLUTIONAL CODINGS IN PARALLEL, CORRESPONDING ITERATIVE DECODING METHOD, DECODING MODULE AND DECODER ”. THE CORRESPONDING ITERATIVE DECODING PROCEDURE, THE DECODING MODULE AND THE DECODING "].

The encoded packet is provided to interleaver 6, which rearranges the encoded symbols in the packet to provide temporal diversity, which provides additional protection against burst errors. The reordered packet is then provided to the repeat generator 8, which provides redundant versions of the symbols interleaved in the packet, in order to output packets of a fixed number of symbols, regardless of the data rate of the R packet. The packet from the repeat generator 8 is provided to the gain element 10, which adjusts the packet gain according to the packet rate R and in order to provide the correct power ratio between the pilot channel and the data channel.

The packet from the gain element 10 is provided to the subchannel spreading element 12. The subchannel spreading element 12 spreads the packet using a short spreading sequence (Wdata) which is used to allow the receiver to separate the pilot channel from the data channel. In the example, the short spreading sequences used are orthogonal Walsh short sequences. The use of short orthogonal Walsh sequences to provide reverse link channeling is described in detail in the aforementioned US Patent Application Serial No. 08 / 856,428. The spread packet from subchannel modulation element 12 is provided to scrambling element 18. The encryption element 18 encrypts the packet according to a pseudo-noise (PN) sequence generated by the long code generator 16.

Turning to FIG. 2, an exemplary embodiment of PN generator 16 is illustrated. The packet is covered using a pseudo-noise (PN) sequence obtained from a FIR filter 50 composed of a linear shift register with associated adder elements and offsets. In the exemplary embodiment, the FIR filter 50 is a diversion FIR filter 42 that is used in encryption of reverse link transmissions in the Telecommunications Industry Association TIA / EIA / IS-95-A standard, entitled Standard Compatibility between Mobile Station and Base Station for a Spread Spectrum, Broadband and Dual Mode Cellular System.

The outputs of the FIR filter 50 are provided to a bank of AND gates 52.

Each of the outputs of the FIR filter 50 is combined by the logical AND operation with a 42-bit Long Code Mask. The results of the AND operations are provided to modulo-2 adding means 54, which performs the addition operation to provide the long code sequence as serial output. Long code generated in this way has important autocorrelation characteristics that are well known in the art. Long codes of this style are used in CDMA cellular systems to distinguish one mobile station from another. When two different long code masks are used, the two resulting long code sequences are uncorrelated, or at least have very limited correlation. The example takes advantage of this property of the generated long codes in order to encode the rate information.

As shown in FIG. 3, in the example the exemplary 42-bit long code mask comprises n bits that identify the transmission speed and (42-n) bits that are used to identify the user. For example, if there are two possible baud rates, then a single bit (n = 1) would be sufficient to identify the baud rate. If there were 3 or 4 possible baud rates, then 2 bits (n = 2) would be needed to specify the speed, and so on. In FIG. 3, the bits that identify the transmission speed are the most significant bits (MSB); however, any of the bits would be equally applicable and the bits identifying the speed need not even be consecutive.

Returning to FIG. 1, the information regarding the rate of the information is provided to the mask selector 14 which provides a mask, according to the rate information R and the identity of the transmitting remote station. The mask selector 14 could be implemented using a memory device, such as a RAM or ROM memory device, that stores mask codes that are retrieved according to the speed of the packet to be transmitted. The selected mask is provided to the long code generator 16 which provides the generated long code to the encryption elements 18 and 22.

In the example, the remote station transmits both a data channel and a pilot channel that allows demodulation.

ES 2 380 792 T3 coherent of its transmitted signal. The example is not limited to systems transmitting a data channel with an accompanying pilot channel, nor is it limited to reverse link transmissions. The example is equally applicable to any variable speed transmission system in which the receiver does not know the transmission speed a priori, and in which the data is encrypted using a pseudo-noise sequence.

A set of pilot signal bits is provided to the subchannel spreading element 12. The pilot signal does not carry any information and, in the exemplary embodiment, is simply a string of zeros. The pilot bits are spread with a short Walsh sequence Wpilot, which, in the example, is orthogonal to Wdata, and is used to distinguish the pilot channel from the data channel. The subchannel's spread packet is provided to the encryption element 22 which, as described above, encrypts the packet according to the long code generated by the long code generator 16.

Encrypted PN packets from encryption elements 18 and 22 are provided to IQ complex spreading means 24, which performs a complex spreading operation, as described in the aforementioned US Patent Application Serial No. 08 / 856,428. . The I and Q outputs are spread with complex values ​​by the input pseudo-noise sequences PNi and PNq, to ​​provide the I and Q outputs according to the following equations:

I = I 'PNi - Q'PNq' (1)

Q = I 'PNq + Q' PNi. (2)

The outputs of the PN complex spreading medium 24 are provided to the baseband filters 26 and 28 (BBF), which provide adequate filtering of the resulting waveform. The filtered waves are provided to the frequency boost elements 30 and 32 and their frequency is increased to the carrier frequency (fc) according to a QPSK modulation format. The two waves with increased frequency are added in the summing element 34, the output of which is provided to the transmitter (TMTR) 36, which amplifies and filters the signal and provides it to the antenna 38 for transmission.

FIG. 4 illustrates a first receiver system for receiving the transmitted wave according to FIG. 1. The signal is received at antenna 100 and provided to receiver (RCVR) 102, which filters and amplifies the received signal. The received signal is then provided to frequency buffers 104 and 106, which reduce the frequency of the received signal in accordance with a QPSK down-frequency methodology, as is well known in the art. The I and Q components of the reduced frequency signals are provided to the baseband filters 108 and 110 (BBF), which filter the signals and provide the baseband signals to the complex PN de-spreading medium 112. The implementation of the complex de-spreading means 112 is described in detail in the aforementioned US Patent Application Serial No. 08 / 856,428, and eliminates the PN spreading that was described in equations 1 and 2 above.

Again, the example illustrates a procedure to distinguish between two possible speeds. One skilled in the art will understand that the receiver structure shown can be extended to an arbitrary number of potential rates, increasing the number of demodulator / decoder elements 114. In the example, the de-spread complex packet data is provided to demodulators / decoders 114a and 114b. One skilled in the art will understand that demodulation can also work with a piece of hardware running at a higher speed. In addition, the receiver can decode the pilot using the different long code masks corresponding to the different speed hypotheses, and estimate the resulting energy obtained using each hypothesis.

The demodulator / decoder 114a demodulates the data using a long code mask associated with the first data rate hypothesis, and the demodulator / decoder 114b demodulates the data using a long code mask associated with the second data rate. As described above, the two long PN codes corresponding to the two speed hypotheses will not be correlated. Demodulating and decoding the data, using the correct long code mask (corresponding to the correct rate hypothesis), will demodulate and decode correctly, while decoding the data, using the wrong long code mask (corresponding to the incorrect speed assumption), it will demodulate and decode incorrectly. Correct demodulation and decoding, corresponding to the correct hypothesis of the data, will be detected by the CRC verifier and selector 140. The CRC verifier and selector element 140 will generate a set of CRC bits from the decoded data estimates, and will compare them to the decoded CRC estimates. If the generated CRC bits match the decoded CRC estimates, the data at that rate will be provided to the user.

Turning to the details of demodulators / decoders 114, the PN de-spread complex packets are provided to decryption elements 118 and 120. The packets are decrypted according to long PN codes generated by the long code generators 116, which generate the long codes according to a code mask.

ES 2 380 792 T3 long corresponding to the mobile station being received, and a speed among the set of possible speeds, as described with respect to the transmission process.

The decrypted data packets from decryption elements 118 and 120 are provided to subchannel de-spreading elements 122, 124, 126 and 128, which remove the Walsh subchannel coverages from the received data stream. Subchannel de-spreading elements 122 and 124 remove the data subchannel coverage from the decrypted data, according to the Walsh sequence (Wdata) of the data subchannel. The subchannel de-spreading elements 126 and 128 remove the data subchannel coverages from the decrypted data according to the Walsh sequence (Wpilot) of the pilot subchannel.

The output of subchannel de-spreading elements 126 and 128 is provided to pilot filter 132, which performs a moving average filtering operation on the signal in order to reduce the effects of noise on the received pilot signal. The I and Q components from pilot filter 132 are provided to vector product circuit 130, which performs coherent demodulation of the QPSK data channel. The design of vector product elements is well known in the art, and is described in detail in US Patent No. 5,506,865, entitled "PILOT CARRIER DOT PRODUCT CIRCUIT". which is assigned to the applicant of the present invention.

The demodulated data signal from vector product element 130 is provided to repeat combiner 134. The repeating combiner 134 combines the repeating symbols in the packet according to the rate hypothesis being tested by the demodulator / decoder 114. The deinterleaver 136, which reorders the symbols according to a rate dependent de-interleaving format, and provides the symbols combined. The rearranged symbols are provided to decoder 138, which decodes the symbols. In the example, decoder 138 is a turbo decoder, the implementation of which is well known in the art, and is described in detail in US Patent No. 5,446,747. The example is equally applicable to other decoder structures, such as lattice decoders and block decoders.

The decoded data packets from demodulator / decoder 138a and 138b are provided to the CRC checker and selector 140. In the example, the CRC bits are checked and the data that passes the CRC check is output as the demodulated and decoded data. at the correct speed. The example also anticipates the use of other procedures for packet selection, such as those involving the use of the accumulated metric from decoder 138, the estimates of the pilot energy received following de-spreading by the various long code masks or the use of symbol error rate (SER), which depend on the number of symbol corrections made by decoder 138.

FIG. 5 illustrates a second receiver system for receiving the transmitted wave according to FIG. 1. The signal is received at antenna 200 and provided to receiver (RCVR) 202, which filters and amplifies the received signal. The received signal is then provided to frequency bumps 204 and 206, which reduce the frequency of the received signal in accordance with a QPSK frequency down-reduction methodology, as is well known in the art. The I and Q components of the reduced frequency signals are provided to the baseband filters 208 and 210 (BBF), which filter the signals and provide the baseband signals to the complex PN de-spreading means 212, which de-spread the signals. signals according to the PNi and PNq pseudo-noise sequences. The implementation of complex PN de-spreading means 212 is described in detail in the aforementioned US Patent Application Serial No. 08 / 856,428, and eliminates the PN spreading that was described in equations 1 and 2 above.

Again, the example illustrates a procedure to distinguish between two possible speeds. One skilled in the art will understand that the receiver structure shown can be extended at an arbitrary number of potential speeds, increasing the number of demodulator elements 214. In the example, the PN de-spread complex packet data is provided to the demodulators 214a and 214b.

The demodulator 214a demodulates the data using a long code mask associated with the first data rate hypothesis, and the demodulator 214b demodulates the data using a long code mask associated with the second data rate hypothesis. As described above, the two long PN codes corresponding to the two speed hypotheses will not be correlated. Demodulating the data using the correct long code mask (corresponding to the correct rate hypothesis) will demodulate correctly, producing a high energy demodulated signal, while decoding the data using the wrong long code mask (corresponding to the incorrect speed assumption) will incorrectly demodulate, producing low energy noise. The correct demodulation, corresponding to the correct speed hypothesis, will be detected by selector 236, which will compare the energies of the two demodulated data streams.

The selector element 236 will provide the correctly demodulated data packet to the replay combiner 238, which combines the data according to the detected rate of the received data. The combined symbols are provided to deinterleaver 240, which reorders the symbols according to a selected deinterleaving format based on the determined rate. The rearranged symbols are provided to decoder 242, which decodes the

ES 2 380 792 T3 symbols according to a predetermined error correction format. In the example, decoder 242 is a turbo decoder, although the example is equally applicable to other decoders, such as lattice or block encoders. The decoded data packet is then broadcast to the user.

Turning to the details of demodulators 214, complex PN de-spread packets are provided to decryption elements 218 and 220. The packets are decrypted according to long PN codes generated by long code generators 216 which generate the long codes according to a long code mask corresponding to a rate from the set of possible rates, as described with respect to the transmission process.

The decrypted data packets from decryption elements 218 and 220 are provided to subchannel de-spreading elements 222, 224, 226 and 228, which remove the Walsh subchannel coverages from the received data stream. The subchannel de-spreading elements 224 and 224 remove the subchannel coverage of the data decrypted according to the Walsh sequence (Wdata) of the data subchannel. Subchannel de-spreading elements 226 and 228 remove the subchannel coverages from the decrypted data, according to the Walsh (Wpilot) sequence of the pilot subchannel.

The output of subchannel de-spreading elements 226 and 228 is provided to pilot filter 232, which performs a moving average filtering operation on the signal to reduce the effects of noise on the received pilot signal. The I and Q components from pilot filter 232 are provided to vector product circuit 230, which performs coherent demodulation of the QPSK data channel. Vector product element design is well known in the art and is described in detail in US Patent No. 5,506,865, entitled "PILOT CARRIER DOT PRODUCT CIRCUIT", which is assigned to the applicant of the present invention.

The demodulated data signal from vector product element 230 is provided to energy calculator 234 and selector 236. Energy calculator 234 calculates the energy of the demodulated packet and provides the energy value to selector 236. Selector 236 selects the demodulated packet with the highest magnitude of energy. The selected packet is provided to the repeat combiner 238, which combines the redundant symbol energies and provides the combined energies to deinterleaver 240. Deinterleaver 240 reorders the combined symbol energies and supplies them to decoder 242. Decoder 242 decodes the data and provides them to the user.

FIG. 6 illustrates a transmission system for the second example. In the second example, each data packet is transmitted with a preamble indicating the data rate of the transmitted packet. The data packet is provided to the CRC and tail bits generator 300. The CRC and tail bit generator 300 generates a set of redundant check bits and appends those check bits, along with a set of tail bits, to the packet.

The packet emitted by the CRC and tail bit generator 300 is provided to the encoder 302, which performs early error coding on the packet. In the example, encoder 302 is a turbo encoder. The encoded symbols are provided to interleaver 304, which reorders the symbols according to a predetermined interleaving format. The reordered symbols are provided to the repeat generator 306, which generates a set of redundant symbols to output a packet of a fixed number of symbols, regardless of the data rate of the packet.

The packet from the repeat generator 306 is provided to the gain adjusting means 308, which adjusts the packet gain based on the packet data rate, and the Eb / Nü ratio required for proper transmission of the link signal. reverse. The adjusted gain packet is provided to multiplexer 312. In the example, multiplexer 312 performs a simple switching operation that punctures a rate indication preamble in the data packet, overwriting a first portion of the frame. The overwritten data could be recovered by means of a look-ahead decoder in the receiver. In an alternative embodiment, the length of the packet could be adjusted such that none of the data required to be overwritten by the preamble.

In the current example, the set of rate indication preambles have lengths that vary according to the data rate of the packet to be transmitted. In the example, the lower the data rate of the packet, the higher the preamble included with the packet. In the example, the set of possible speeds differ from each other by factors of two, for example, 9.6 Kbps, 19.2 Kbps, 38.4 Kbps, and 76.8 Kbps. In the example, the length of the preamble varies inversely with the data rate of the packet, and thus the proportion of the data in the packet that is overwritten by the preamble remains constant, due to the varying duration of the packets. to transmit as a function of the data rate.

Turning to FIG. 7, an exemplary set of four preambles is illustrated. In the example, FIG. 7A illustrates the proposed preamble for the highest possible speed in the set of speeds (ie 76.8 Kbps). FIG. 7B illustrates the proposed preamble for the second highest possible speed in the speed set (ie 36.4 Kbps). FIG. 7C illustrates the proposed preamble for the third highest possible speed in the speed set

ES 2 380 792 T3 (i.e. 19.2 Kbps). FIG. 7D illustrates the proposed preamble for the lowest possible speed in the set of speeds (ie 9.6 Kbps).

The important feature to note with respect to the proposed preamble structure is that the preamble sequences are orthogonal over selected time periods. For example, the preamble sequence illustrated in FIG. 7A is orthogonal to the preamble sequences illustrated in FIGS. 7B, 7C and 7D over the period of its duration (0 to 4T). Similarly, the preamble sequence illustrated in FIG. 7B is orthogonal to the preamble sequences illustrated in FIGS. 7C and 7D over the period of their duration (0 to 8T). Finally, the preamble sequence illustrated in FIG. 7C is orthogonal to the preamble sequence illustrated in FIG. 7D over the period of its duration (0 to 16T). The benefit of the orthogonality of the preamble waves is realized at the receiver, making the preamble detection more accurate, because the correlation between two orthogonal sequences is zero. Thus, passage of the preamble sequence through a correlator, such as an associated filter, will produce zero energy for all preamble rate hypotheses except for the correct preamble rate hypothesis. FIGS. 7E through 7H illustrate an alternate set of proposed preamble waves exhibiting the same orthogonal properties as illustrated in 7A through 7D.

The data packet is provided to the subchannel spreading element 310 which covers the packet according to the Walsh sequence Wdatos. Furthermore, the speed indication signal is covered according to Walsh by the subchannel spreading element 311. The data signal and the preamble signal are combined by multiplexer 312. In an alternative example, the data packet could be combined with the preamble prior to performing the Walsh coverage operation. The combined Walsh covered packet is then provided to encryption means 314, which encrypts the packet according to a long code sequence provided by the long code generator and mask 316. The long code is uniquely assigned to the remote station and is used. to distinguish the transmission of different remote stations simultaneously communicating with a given base station.

In modulating the pilot signal, a set of predetermined pilot symbols is provided to the Walsh covering means 318. In the exemplary embodiment, the pilot symbol sequence is a string of all zeros. The Walsh covering means 318 covers the pilot symbols according to the Walsh Wpilot sequence. The Walsh covered pilot symbols are provided to the encryption means 320, which encrypts the Walsh covered pilot symbols according to a long PN sequence from the long code generator and mask 316. The outputs of the ciphers 314 and 320 PN complex spreading element 322 is entered, along with the PNi and PNq pseudo-noise sequences. The complex PN spreading element 322 performs a complex PN spreading on the input signal, according to the above equations 1 and 2.

The I and Q channel outputs from PN complex spreading element 322 are provided to baseband filters 324 and 326 (BBF). Baseband filters 324 and 326 filter the baseband signals and provide the filtered signals to frequency boosters 328 and 330. The frequency boosters 328 and 330 increase the frequency of the signals, according to a QPSK modulation format, in which the resulting frequency-increased signals are 90 degrees out of phase with each other. The frequency-increased signals are summed at summing element 332 and provided to transmitter (TMTR) 334, where the signal is amplified and filtered, and transmitted through antenna 336.

FIG. 8 illustrates the receiver system of the second example. The signal is received at antenna 400 and provided to receiver (RCVR) 402, which filters and amplifies the received signal. The received signal is then provided to frequency reducers 404 and 406, which reduce the frequency of the received signal in accordance with a QPSK frequency reduction methodology, as is well known in the art. The I and Q components of the reduced frequency signals are provided to baseband filters 408 and 410 (BBF), which filter the signals and provide the baseband signals to PN complex de-spreading element 412: The implementation of the complex PN widening element 412 is described in detail in the aforementioned US Patent Application Serial No. 08 / 856,428, and eliminates the complex PN widening that was described in the above equations 1 and

2.

The de-spread I and Q signals are provided to decryption elements 416 and 418. Decryption elements 416 and 418 decrypt the signals according to a long code provided by long code and mask generator 414. The decrypted I and Q signals are provided by decryption elements 416 and 418 to subchannel de-spreading elements 426, 428, 430 and 432, which remove the Walsh subchannel coverages from the received signals. The subchannel de-spreading elements 426 and 428 remove the subchannel coverage from the decrypted data, according to the Walsh sequence (Wdatos) of the data subchannel. The subchannel de-spreading elements 430 and 432 remove the coverages of the pilot subchannel from the decrypted data, according to the Walsh sequence (Wpilot) of the pilot subchannel.

The output of subchannel de-spreading elements 430 and 432 is provided to pilot filter 434, which performs a moving average filtering operation on the signal to reduce the effects of noise on the received pilot signal. The I and Q components from pilot filter 434 are provided to vector product circuit 436,

ES 2 380 792 T3 that performs a coherent demodulation of the QPSK data channel. The design of vector product elements is well known in the art and is described in detail in US Patent No. 5,506,865, entitled "PILOT CARRIER DOT PRODUCT CIRCUIT", which is assigned to the applicant of the present invention.

The demodulated data signal from vector product element 436 is provided to demultiplexer (De-Mux) 420. Demultiplexer 420 initially outputs the data to preamble detector 424. Preamble detector 424 determines the speed indicated by the de-spread preamble. Many implementations of the preamble detector are possible. For example, preamble detector 424 can be implemented using a bank of associated filters or other correlators. Upon finding a preamble with sufficient correlation energy with one among the predetermined set of preambles, the speed is declared to have been successfully detected. In an alternative example, the preamble could be detected non-coherently, in which case the despread data would be provided directly to the preamble detector through multiplexer 420 from subchannel de-spreading elements 426 and 428.

Upon successful detection of one of the candidate preambles, preamble detector 424 sends a signal indicating the detected rate to repeat combiner 438, deinterleaver 440, and decoder 442, which perform their operations based on this information. Furthermore, upon detection of the end of the preamble message, the preamble detector sends a signal indicating the detection of the end of the preamble to the demultiplexer 420, in response to which the demultiplexer 420 begins to output the despread data to the repeat combiner 438. .

The repeat combiner 438 combines the repeating symbol energies in the packet according to the detected rate of the received packet. The combined symbol energies are provided to deinterleaver 440, which rearranges the symbol energies according to a selected deinterleaver pattern according to the velocity signal from preamble detector 424. The reordered symbols are provided to decoder 442, which decodes the symbols. In the example, decoder 442 is a turbo decoder, the implementation of which is well known in the art, and is described in detail in US Patent No. 5,446,747. The example is equally applicable to other decoder structures, such as lattice decoders and block decoders. The decoded data estimates are broadcast by decoder 442 to the user.

FIG. 9 illustrates the preferred embodiment of the present invention for transmitting variable rate data. In the preferred embodiment, packets at different data rates contain a different number of bits of information, but span the same time duration (ie, 2 frames = 32 slots = 53 msec). The data transmission system again transmits a control channel other than a data channel. In the embodiment of the present invention, the control channel includes three types of information, which are multiplexed together in time. The first type of information provided by the control channel is the pilot signal. The second is a rate indication message that indicates the rate of the data packet that is being transmitted concurrently with the control channel information. The third is a rate request message which is the request by the remote station for a serving base station to provide data up to that rate.

In the preferred embodiment, the rate request information provides an indication both of the rate at which the remote station wants data to be downloaded to it, and of the base station, or base station sector, that the remote station wants to perform. data transmission. In the preferred embodiment, the indication of which base station, or sector, of a predetermined set of base stations, or sectors, is based on a spreading function that will only be properly decoded by the searched base station to transmit to the remote station.

When identifying the Walsh function, the superscript identifies the order of the Walsh function, and the subscript identifies the index of the Walsh function of that order. Tables 1 through 3 below provide the Walsh function used in the current description.

Table 1

<td>W0²</td><td> 00</td>

<td>WT</td><td> 00</td>

Table 2

<td>W0⁴</td><td> 0000</td>

<td>WT</td><td> 0101</td>

ES 2 380 792 T3

<td>W2⁴</td><td> 0011</td>

<td>WT</td><td> 0110</td>

Table 3

<td>Wq^B</td><td> 0000 0000</td>

<td>W1⁸</td><td> 0101 0101</td>

<td>W2⁸</td><td> 0011 0011</td>

<td>W3⁸</td><td> 0110 0110</td>

<td>W4⁸</td><td> 0000 1111</td>

<td>W₅⁸</td><td> 0101 1010</td>

<td>W6⁸</td><td> 00111100</td>

<td>W7⁸</td><td> 01101001</td>

As in the previous two embodiments, the pilot channel symbols are a predetermined single sequence. In the exemplary embodiment, the pilot symbols are a string of all zeros that are provided to multiplexer (MUX) 500. In the exemplary embodiment, the speed indication signal is a bio-orthogonal wave. Thus, the input to the Walsh cover element 502 is a binary value, the switching of which will result in the inversion of the resulting wave. The symbols from the Walsh cover element 502 are provided to the Walsh cover element 504, which provides a second Walsh cover of the data, in which the used Walsh cover index provides the second part of the speed indication value. In the exemplary embodiment, the second Walsh coverage can take eight different forms which, in combination with the input bit, allow the specification of up to 16 different speeds. The Walsh symbols from the Walsh cover element 504 are provided to the multiplexer 500. In the exemplary embodiment, the rate indication is punctuated at the pilot symbols, once per slot for 32 consecutive slots (2 frames) spanned by a packet. reverse link. This is to provide temporary diversity in a fading environment.

Turning to the rate request message, the exemplary embodiment provides the specification of up to 16 possible forward link data rates (from base station to remote station). A 4-bit index is provided to the block encoder 506. In the exemplary embodiment, the block encoder 506, which associates the 4-bit input to a set of 8 possible Walsh symbols, or the reverse, using a block code (8, 4, 4), the design and implementation of which are well known in the art. The block-coded rate request is then provided to replay generator 508, which provides redundancy for temporal diversity purposes, to protect against burst errors. The rate request message is then provided to gain adjusting element 510, which adjusts the gain to provide proper reception of the rate request message. The adjusted gain signal is provided to the Walsh cover element 512, which provides additional redundancy to the rate request message.

The Walsh covered message from the Walsh cover element 512 is then provided to the Walsh cover element 514. The purpose of the Walsh coverage element 514 is to indicate the best base station, or base station sector, from which to receive forward link data. In the exemplary embodiment, the remote station measures the C / I ratio of transmissions from a set of base stations, from which it is capable of receiving data. The base station that can provide data to the remote station with the highest C / I ratio is selected by the remote station to download data to the remote station. The selected base station is indicated using a Walsh sequence that will only be properly demodulated by the selected base station. All base stations, and the sector in the active set of remote stations (or set of base stations, or sectors, capable of transmission to the remote station), will attempt to demodulate the signal using an assigned sequence Wi⁸. However, only the selected base station will correctly demodulate the request and transmit to the remote station. The encoded rate request information, rate indication, and pilot data are multiplexed together in time by multiplexer 500. The multiplexed control signal is provided to subchannel spreading element 516, which covers the resulting signal with a Walsh coverage that is orthogonal to that used to cover the data subchannel.

Over the data subchannel, variable rate data packets are provided to the CRC and tail bit generator 518. The CRC and tail bit generator 518 generates a set of redundant check bits and appends those check bits together with a set of used tail bits to the packet.

ES 2 380 792 T3

The packet emitted by the CRC and tail bit generator 518 is provided to the encoder 520, which performs early error coding on the variable rate data packet. In the exemplary embodiment, encoder 520 is a turbo encoder. The encoded symbols are then provided to interleaver 522, which reorders the symbols according to a predetermined interleaving format. The reordered symbols are then provided to the repeat generator 524, which generates a set of redundant symbols to output a packet containing a fixed number of symbols, regardless of the data rate of the packet.

The packet from the repeat generator 524 is provided to the gain adjusting means 526, which adjusts the packet gain based on the packet data rate, and the Eb / N0 ratio required for proper transmission of the link signal. reverse. The adjusted gain packet is provided to subchannel spreading element 528, which covers the packet with a Walsh sequence that is orthogonal to the Walsh sequence used to cover the control packet.

The data packet and the control packet are provided to the encryption means 534 and 532, respectively. Encryption elements 532 and 534 encrypt the packets according to a long code sequence provided by the long code generator and mask 530. The outputs from encryption elements 532 and 534 are input to complex spreading element 536 of PN, together with the PNi and PNq pseudo-noise sequences. The PN complex spreading element 536 performs a PN complex spreading on the input signal, according to the above equations 1 and 2.

The I and Q channel outputs from PN complex spreading element 536 are provided to baseband filters 538 and 540 (BBF). Baseband filters 538 and 540 filter the baseband signals and provide the filtered signals to frequency boosters 542 and 544. The frequency boosters 542 and 544 increase the frequency of the signals, according to a QPSK modulation format in which the resulting frequency-increased signals are out of phase with each other by 90 degrees. The frequency-increased signals are summed at summing element 546 and provided to transmitter (TMTR) 548, where the signal is amplified and filtered, and provided, through duplexer 549, for transmission through antenna 550 .

In addition, remote station 554 includes a variable rate receiving subsystem 552 for receiving variable rate data of the forward link from a base station, or a plurality of base stations, capable of transmitting to remote station 554. The rate data Forward link variables are received through antenna 550 and provided, through duplexer 549, to variable rate receive subsystem 552.

FIG. 10 illustrates an exemplary embodiment of the receiver for the preferred embodiment. The signal is received at antenna 600 and provided to receiver (RCVR) 602, which filters and amplifies the received signal. The received signal is then provided to frequency buffers 604 and 606, which reduce the frequency of the received signal in accordance with a QPSK frequency downgrading methodology, as is well known in the art. The I and Q components of the reduced frequency signals are provided to baseband filters 608 and 640 (BBF), which filter the signals and provide the baseband signals to complex PN de-spreading element 612. The implementation of complex PN widening element 612, which eliminates the complex PN widening that was described in equations 1 and 2. An implementation of the complex PN de-spreading element 612 is described in detail in the aforementioned US Patent Application Serial No. 08 / 856,428.

Complex PN de-spread packets are provided to decryptors 614 and 618. The packets are decrypted according to the long PN codes generated by the long code generators 618 that generate the long code sequence, as described above with respect to the above embodiments.

The decrypted data packets from decryptors 614 and 616 are provided to subchannel de-spreading elements 620, 622, 624, and 626, which remove the Walsh subchannel coverages from the received data stream. Subchannel de-spreading elements 620 and 622 remove the data subchannel coverage from the decrypted data, according to the sequence (W2⁴) of Walsh of the data subchannel. Subchannel de-spreading elements 624 and 626 remove the data subchannel coverages from the decrypted data, according to the sequence (W0⁴) of Walsh from the pilot subchannel.

The output from subchannel de-spreaders 624 and 626 is provided to demultiplexer (DeMux) 628. Demultiplexer 628 separates the various parts of the received control channel corresponding to pilot symbols, rate indication symbols, and request symbols data, and outputs that data to three different outputs.

The pilot symbols provided by the demultiplexer 628 by a first output are provided to the pilot filter 632, which performs a moving average filtering operation on the signal in order to reduce the effects of noise on the received pilot signal. The I and Q components from pilot filter 632 are provided to vector product circuit 630, which performs coherent demodulation of the QPSK data channel. The design of vector product elements is well known in the art and is described in detail in US Patent No. 5,506,865,

ES 2 380 792 T3 entitled "PILOT CARRIER DOT PRODUCT CIRCUIT", which is assigned to the applicant of the present invention.

The demodulated data signal from vector product element 630 is provided to repeat combiner 638. The repeat combiner 638 combines the repeating symbols in the packet according to the detected reverse link speed signal, provided by the speed indication decoder 634. The combined symbol energies are provided to deinterleaver 640, which reorders the symbols according to the detected rate indication signal, provided by rate indication decoder 634. The reordered symbols are provided to decoder 642, which decodes the symbols according to the detected rate indication signal. In the exemplary embodiment, decoder 642 is a turbo decoder, the implementation of which is well known in the art and is described in detail in US Patent No. 5,446,747. The present invention is equally applicable to other decoder structures, such as lattice decoders and block decoders.

The demultiplexer 628 provides the received symbol energies corresponding to the rate indication signal on a second output to the rate indication decoder 634. Rate indicating decoder 634 can be implemented in a wide variety of ways, such as using a bank of correlators to correlate received symbol energies with possible rate indicating waves. The wave with the highest correlation energy would be detected as the transmitted wave, thus determining the speed indication value. The rate indication value is provided to repeat combiner 638, deinterleaver 640, and decoder 642 to assist in the operation of those items.

The demultiplexer 628 provides the received symbol energies corresponding to the rate request message signal, at a third output, to the rate request decoder 636. Each base station in the remote station's active set would attempt to decode the rate request message using an assigned Walsh sequence.

Only the base station to which the remote station wishes to transmit the data will be able to correctly decode the rate request message. After the selected base station, or sector, removes the Walsh coverage from the rate request message, the message is block-decoded to provide the requested rate information to the base station. This information is provided to a control processor in selected base stations, or sectors, which schedule data transmissions to the remote station according to this rate request.

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. The various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of inventiveness. Therefore, the present invention is not intended to be limited to the embodiments shown herein, but is to be granted the widest scope, as defined in the appended claims.