KR20010040855A - Method and apparatus for performing rate determination using orthogonal rate-dependent walsh covering codes - Google Patents

Abstract

The present invention relates to a method and apparatus for rate determination in a communication system using orthogonal rate-dependent Walsh covering codes. Orthogonal rate-dependent Walsh codes are used to cover repeated code symbols prior to transmission over the communication link. Walsh codes include orthogonal binary codes that increase by a power of two for each data rate in the system. Code symbols are repeated using the orthogonal Walsh codes of the present invention and covered at the symbol rate. Symbol error rate (SER) blocks are used to generate a rate-dependent SER metric for each of the candidate rates. SER evaluators 230, 232, 234, 236 associated with soft combiners 204, 206, 208, 210 using incorrect data rate hypotheses may use soft combiners 204, 206, 208, Generate high symbol error rates relative to the symbol error rate generated by the SER evaluators 230, 232, 234, 236 associated with 210. In yet another embodiment, the SER evaluators 230, 232, 234, 236 are replaced with energy metric calculators 250, 252, 254, 256, and rate-dependent re-for each candidate data rate. Used to generate coded energy metrics. Energy metrics produce an estimate of the energy of the symbol, which is used as a data rate indicator.

Description

TECHNICAL AND APPARATUS FOR PERFORMING RATE DETERMINATION USING ORTHOGONAL RATE-DEPENDENT WALSH COVERING CODES}

Wireless communication systems facilitate two types of communication between multiple subscriber mobile stations or “mobile stations” and fixed network infrastructure. One example system is a known Code Division Multiple Access (CDMA) communication system. CDMA systems use unique code sequences to create communication channels in a spread spectrum multiple access digital communication system. The operation and functionality of CDMA systems is described in TIA / EIA / IS-95-A, “Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband,” published in May 1995 by the Telecommunications Industry Association (TIA). Spread Spectrum Cellular System ”is described in the specification of the Telecommunications Industry Association, which administers CDMA operations, which is referred to herein by reference, hereafter referred to as“ IS-95 ”.

Communications from mobile stations to base stations use "reverse CDMA channels" while communications from CDMA base stations to CDMA mobile stations use "forward CDMA channels." The CDMA channels include access channels and traffic channels. These channels distribute the same CDMA frequency assignment using direct-sequence CDMA techniques. Long code sequence numbers of different user channels identify each communication channel. The overall structure of an interfering reverse link CDMA communication channel is shown in FIG. The traffic channel of the proposed forward link that can be adapted for use in the present invention is similar to the reverse traffic channel of FIG. 1, which is described in more detail below. Data transmitted on the reverse CDMA channel is grouped into 20 ms frames. As shown in Fig. 1, prior to transmission, cyclic redundancy codes (CRC) and “tail” bits are added to the reverse channel information bits. The information bit and tail bit are then encoded using conventional coding methods to produce code symbols. Each code symbol is preferably information of digital bits. In one example of the encoder, 4 bits are output for each 1 bit that is input. Such encoders are commonly called quarter encoders. In one particular case, conventional convolutional encoders are used to generate code symbols. The code symbols are repeated, block interleaved, and modulated before transmission. Each of the components of reverse link communication channel structure 100 is briefly described below.

In the exemplary CDMA communication channel structure shown in FIG. 1, the data frames include 9600 (“rate 1”) bits, 4800 (“rate 1/2”) bits, 2400 (“rate 1/4”) bits, It can optionally be transmitted on the reverse traffic channel at 1200 ““ rate 1/8 ”)“ base ”data rates. High data rates such as 19.2 kbps (“rate 2”), 38.4 kbps (“rate 4”), 76.8 kbps (“rate 8”) can be maintained by changing the reverse communication channel structure shown. An example of such an alternative reverse communication channel is described below with reference to FIG. 7. The basic data rates are generated after frame quality indicators, and the “tail bits” of the encoder are added to the information bits by blocks 102 and 104, respectively. The frame quality indicators include cyclic redundancy codes (CRCs) that support two functions: (1) to help determine whether a frame was sent incorrectly (2) to help determine the data rate sent to the receiver. The number of CRC bits added depends on the base data rate used.

Other rate determination metrics are required to perform data rate determination in the receiver. In some systems, not all frames contain CRCs. For example, in the structure of FIG. 1, the two lowest data rates (1.2 and 2.4 kbps) do not include CRC information. In addition to the CRC information, symbol error rates (SERs) evaluated at four candidate elementary data rates have been used for rate determination. In addition, prior art systems have used energy metrics to aid in rate determination in the receiver. Disadvantageously, due to the calibration of data transmitted at various rates (especially for long zero strings), it has proved difficult to determine data rate when using these rate determination metrics.

The encoder tail bits are simply eight logic zeros added to the end of each frame. The tail bits are added to the frames by the tail block 104 of the encoder. The data frames are input to an encoder block 106 as shown in FIG. The reverse channel can use any of the candidate basic data rates to transmit data. The basic data frames include 24 bits (for 1.2 kbps data rate), 48 bits (for 2.4 kbps data rate), 96 bits (for 4.8 kbps data rate), 192 bits (for 9.6 kbps data rate) do. The encoder 106 can be implemented using any known encoding technique that is convenient. For example, the convolutional encoder can be used to implement the encoder 106 of FIG. In this case, the weaving code is preferably at rate 1/4, preferably with a constraint length of nine. The encoder 106 generates code symbols input to the base rate iterator 108 as shown in FIG.

The base rate iterator 108 repeats the information encoded at low rates to ensure transmission at a fixed rate. Thus, the overall radio transmission rate is the same for all users, regardless of the rate at which the actual information is transmitted. The base rate iterator 108 repeats the code symbols before the code symbols are interleaved. In the reverse link traffic channel structure 100 shown in FIG. 1, each code symbol at a rate of 9.6 kbps is repeated once (ie, each symbol occurs twice in succession) each code at a rate of 4.8 kbps. The symbol is repeated three times (ie, each symbol occurs four times in succession). Each code symbol at rate 2.4 kbps is repeated seven times (ie, each symbol occurs eight times in succession). Each code symbol at rate 1.2 kbps is repeated 15 times (ie each symbol occurs 16 times in succession). This results in a constant code symbol rate which is 76,800 code symbols per second. The repeated code symbols generated by the base rate iterator 108 are input to the block interleaver 110 prior to transmission.

The block interleaver 110 functions in a known manner to create a pseudo-random temporal separation between adjacent code symbols. The block interleaver 110 distributes the code symbols for a predetermined time period so that the transmitted data is stronger, further preventing burst errors and reverse channel fading characteristics. This ensures that data can be accurately transceivered under various reverse channel conditions. The code symbols are modulated by modulator 112 prior to transmission.

Disadvantageously, the reverse link traffic channel structure shown in FIG. 1 makes it very difficult to perform rate determination at the receiver. Because the symbols are repeated by the base rate iterator 108 rather than the coded or covered, de-interleaved codes are used at different data rates, especially when the codes produce long strings of logical zeros or ones. This is because they are highly correlated. Zero strings are highly correlated because the same zero strings are generated by the base rate iterator 108 when using any of the candidate base data rates. For example, all zero codes repeated eight times at rate 1/4 appear as all zero codes repeated four times at rate 1/2. The same zero string is generated by the base rate iterator 108 in both cases. Disadvantageously, two code symbol sequences cause the receiver to generate an error when trying to determine the rate at which data is transmitted. The rate determination errors cause problems in the receiver to produce decoding errors. Thus, there is a need for an improved traffic channel structure that includes rate covering techniques to facilitate rate determination in the receiver.

In addition, prior art data rate determination metrics have failed to produce reliable results, particularly when the data contains long strings of zero or one. Accordingly, what is needed is a technique to improve the performance of prior art data rate determination metrics.

The present invention provides such an improved rate determination method and apparatus.

Summary of the Invention

Described herein are new methods and apparatus for data rate determination of a wireless communication system. According to one embodiment of the method and apparatus described herein, orthogonal rate-dependent Walsh codes are used to cover sequences of code symbols prior to transmission over a communication link. The Walsh codes increase the length by a power of two for successive low data rates. Individual code symbols are repeated to ensure redundancy and to ensure that each data rate is the same as the rate at which coded information is output from the transmitter. The resulting code symbol sequences are then covered using orthogonal Walsh codes, preferably at symbol rate. Thus, code symbol sequences generated at the first candidate rate are orthogonal to code symbol sequences generated at the second candidate rate. The code symbol repetition and covering method and apparatus thereof described herein are particularly advantageous in encoded data comprising long sequences of logical zeros and ones. The orthogonality of the code symbol sequences covered by the orthogonal codes makes the data rate determination device of the receiver more reliable and less complicated. Thus, rate determination is improved to improve data service capability and reduce decryption errors.

One embodiment of the method and apparatus described herein includes a method and apparatus for rate determination and decoding. The above described data rate determination and decoding method and apparatus provide for the encoded sequence to distinguish between the correct hypothesis and the incorrect hypothesis with respect to the rate at which data is transmitted (ie commonly referred to as "data rate hypotheses"). Take advantage of their orthogonal characteristics. In one embodiment, SER evaluators are used to generate rate-dependent SER metrics for each of the candidate rates. In this embodiment, each SER evaluator receives a first input from an associated soft combiner and a second input from an associated re-encoder. For each SER evaluator associated with the soft combiner used, an incorrect data rate hypothesis produces a high symbol error rate for the symbol error rate generated by the SER evaluator associated with the soft combiner using the correct rate assumption. . The rate discrimination capability of the SER metrics is greatly improved by using orthogonal covering codes that further improves the difference between the SER metrics between correct and incorrect assumptions.

In another embodiment of the rate determination and decoding method and apparatus thereof described herein, energy metric calculators are used to generate a rate-dependent re-encoded energy metric for each candidate rate. In this embodiment of the invention, the energy metric calculators perform a dot product of the soft decision sequence generated by the soft combiners and the re-coded code sequences to generate an energy metric for each candidate rate. . The dot product is generated by adding the dot products resulting from multiplying the re-encoded code sequence by the soft decision sequence output from the soft combiner on a code symbol x code symbol basis. According to this embodiment, the dot product is divided by the total number of symbols to produce an estimate of the symbol energy. The symbol energy is used as another data rate indicator. Due to the orthogonal nature of the method and apparatus of the Walsh cover codes described herein, these soft combiners using inaccurate rate hypotheses produce an energy metric that is nearly zero. However, the soft combiner using the exact rate hypothesis produces an energy metric with a value substantially greater than zero. Thus, according to this embodiment, the energy metrics generated by the energy metric calculators are used to distinguish between correct data rate assumptions and incorrect data rate assumptions.

In another embodiment of the method and apparatus for symbol repetition and Walsh encoding described herein, the block interleaver and repeater / covering blocks are repositioned with respect to each other depending on communication link characteristics and implementation constraints. For example, prior to performing the repeater / covering functions, by performing a block interleave function first, orthogonal characteristics of the transmitted code symbol sequences are emphasized. However, an improvement in the orthogonal characteristics is that a balance is maintained against the degradation of the spatial diversity of the transmitted code symbols. Additionally, for higher data rates, prior to performing the repeater / covering functions, it is a more effective implementation to perform the block interleave function first. In contrast, by performing the block interleave function after performing the repeater / covering functions, the spatial diversity characteristics of the transmitted code symbols are emphasized. However, an improvement in spatial diversity is that balance is maintained against the degradation of the orthogonal properties. Additionally, for lower rates, performing the block interleave function after performing the repeater / covering functions is a more effective implementation. A combination of techniques that can accommodate a wide range of data rates is described.

The present invention relates to code division multiple access (CDMA) communications, and more particularly to rate determination of large capacity CDMA telecommunication systems.

1 is a block diagram illustrating the overall structure of a CDMA communication channel of an exemplary interfering reverse link.

2 illustrates the reverse link CDMA communication channel of FIG. 1 adapted for use with the present invention.

3 is a block diagram of one embodiment of a decoder and rate determination apparatus according to the present invention in which symbol error rate metrics are used as data rate indicators.

4 is a block diagram of one embodiment of a symbol errror rate (SER) block shown in FIG.

5 is a block diagram of an embodiment of a decoder and rate determination apparatus according to the present invention in which re-coded energy metrics are used as data rate indicators.

6 illustrates the reverse CDMA communication channel structure of FIG. 2 adapted for use in an alternative embodiment of the rate determination method and apparatus of the present invention.

7 illustrates an alternative embodiment of a CDMA communication channel of an interfering reverse link adapted for use with the present invention.

Like reference numbers and designations in the various drawings indicate like elements.

Through this description, the preferred embodiments and the examples shown should be considered as embodiments rather than limitations of the invention.

The encoding, symbol repetition and covering method and apparatus described herein facilitate rate determination in the receiver of a communication system. The symbol repetition and encoding apparatus is typically implemented in transmitters of base stations and mobile units designed for use in a communication system. The method and apparatus described herein include the above-described iterative and encoding method and the decoding method and apparatus cooperating with the apparatus so as to correctly decode the data at the transmitted rate. The decoding methods and apparatus described herein are typically implemented in the base station and the receiver of the mobile unit.

The method and apparatus described above preferably use rate-dependent codes to mask or “cover” repeated code symbols before transmitting from the transmitter to the receiver. In this preferred embodiment, the rate-dependent codes are orthogonal (such as Walsh codes) or approximately orthogonal. 2 shows a block diagram of the interfered reverse link CDMA traffic channel of FIG. 1 adapted for use with the methods and apparatus described herein. The code symbols are first repeated as described above with reference to base rate iterator 108 (FIG. 1). The code symbol repetition rate varies with the transmission rate. For example, in one embodiment, the symbols are each rate 1/8 (ie each symbol appears 16 times), rate 1/4 (each symbol appears 8 times), rate 1/2 (each Symbols appear 4 times), 15,7,3,1 times for rate 1 (each symbol appears twice). However, regardless of the transmission data rate, according to the method and apparatus described above, after the code symbols are repeated, the sequences of code symbols are masked or covered by the base rate cover circuit 109. The base rate cover circuit 109 preferably covers repeated code symbols using an appropriate rate-dependent Walsh code operating at the symbol rate. Although the term "circuit" is used herein, it is known that it may be provided by a programmable device, such as a digital signal processor or a general-purpose programmable microprocessor. One embodiment of rate-dependent Walsh codes used to cover the code symbol sequences prior to transmission on the reverse link is shown in Table 1 below.

Data rate label Walsh code pattern One W ₁ ² +- 1/2 W ₂ ⁴ + +-- 1/4 W ₄ ⁸ + + + +---- 1/8 W ₈ ¹⁶ + + + + + + + +---------

Table 1-Preferred reverse link rate-dependent Walsh covers

As used in Table 1, the label “W _x ⁿ ” represents the Walsh code “x” in the “n-ary” Walsh code space. Denotes the negative of W _x ⁿ . Walsh cover codes "+" and "-" represent logic "0" and logic "1", respectively. In one embodiment, rate 1 is the best data rate covered using the methods and apparatus described herein. The rates 1/2, 1/4 and 1/8 are the data rates 1/2, 1/4 and 1/8 with respect to the data rate of rate 1, respectively. In one embodiment of the described method and apparatus, rate 1 is equal to 9.6 kbps. The rates 1/2, 1/4, 1/8 are therefore equal to 4.8, 2.4, 1.2 kbps in this one embodiment. The method and apparatus described above are not limited to the four rates shown in Table 1. Rather, the methods and apparatus described above find utility in many different communication systems using many different rates. Additionally, the embodiment described and shown in Table 1 uses binary Walsh cover codes that increase by two squares of each sub-rate. However, one skilled in the art should understand that any number of Walsh cover codes may be used to implement the methods and apparatus described herein.

The rate-dependent Walsh covering codes described herein are preferably orthogonal or approximately orthogonal to each other, so that any code symbol generated by the first candidate rate is substantially orthogonal to any symbol generated by the second candidate rate. For example, the covering assignments shown in Table 1 are selected so that the resulting Rate 1 code is orthogonal to the resulting Rate 1/2 code. Similarly, the resulting rate 1/2 code is preferably orthogonal to the resulting rate 1/4 and rate 1/8 codes. This is orthogonal even when the symbols include the operations of logic 0 and logic 1. The Walsh codes shown in Table 1 often include operations of 0 and 1, and are useful for coded data that guarantees mutual orthogonality between other data rate assumptions that are independent of the code sequence. That is, attempts to decode such operations of one or zero using different data rate hypotheses result in a relatively large imbalance between the correct data rate assumption and the incorrect rate assumptions.

As shown in Table 1, rate 1 data is covered by a basic rate cover circuit 109 having a Walsh pattern of "+-" or "0 1". Thus, in accordance with Table 1, the rate 1, logic "0" is encoded by the basic rate cover circuit 109 as "0 1" prior to transmission (rate = 1, pattern = 0 1). The logic "1" is encoded by the basic rate cover circuit 109 as "1 0" (rate = 1, pattern = 1 0). As shown in Table 1, rate 1/2 data is preferably covered using a Walsh pattern of "+ +--" or "0 0 1 1". Thus, at a data rate of 1/2, the logic "0" is encoded by the basic rate cover circuit 109 as "0 0 1 1" while the logic "1" is encoded as "1 1 0 0". Rate 1/4 data is preferably covered using a Walsh pattern of "+ + + +----" or "0 0 0 0 1 1 1 1". Thus, at a data rate of 1/4, logic "0" is encoded as "0 0 0 0 1 1 1 1" while logic "1" is encoded as "1 1 1 1 0 0 0 0". The data at rate 1/8 can be converted using the Walsh pattern of "+ + + + + + + +--------" or "0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1" Covered. Thus, at data rate 1/8, logic "0" is encoded as "1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0" while logic "1" is encoded as "0 0 0 0 0 0 0. 0 1 1 1 1 1 1 1 1 1 ”is encoded. According to one aspect of the methods and apparatus described herein, the Walsh code is selected from the 16-ary Walsh code space.

Due to the orthogonal nature of the encoded and covered sequences, the methods and apparatus described herein facilitate reliable rate determination at the receiver. The decoder and rate determination apparatus described above take advantage of the orthogonality of rate-dependent codes to correctly decode the received data. Walsh covering codes are particularly advantageous for data service applications because zero and one operations occur at high frequencies in the transmission of uncompressed and unencrypted data. Thus, since the decoder will decode much less the first selection rate block (eg, rate 1/8 block) as the second selection rate block (eg, rate 1/4 block), or vice versa, Rate determination is improved. Improvements in rate determination provided by the methods and apparatus described herein become more apparent by describing how Walsh covers are used in a receiver. An embodiment of the decoder and rate determination device of the present invention designed to take advantage of the Walsh cover codes of the present invention is described below with reference to FIG.

Rate determination using rate-dependent Walsh covers

One embodiment of the decoder and rate determination apparatus 200 described herein is shown in FIG. 3. As shown in FIG. 3, the decoder and rate determination apparatus 200 includes a “de-interleaver” 202 effectively connected in parallel to one or more matched filters or “soft combiners”. Rate determination apparatus 200 has one soft combiner for each data rate that can be used in a wireless communication system. For example, as shown in FIG. 3, in one embodiment, the rate determining device 200 includes a rate 1 soft combiner 204, a rate 1/2 soft combiner 206, a rate 1/4 soft combiner. 208, rate 1/8 soft combiner 210. The outputs of each soft combiner are connected to the inputs of the same decoders. For example, in the embodiment shown in FIG. 3, the outputs of the soft combiner 204 at rate 1 are provided to the inputs of the decoder 212. Similarly, the outputs of the soft combiners 206, 208, 210 are provided to the inputs of the decoders 214, 216, 218, respectively. The decoders 212, 214, 216, 218 can be implemented using any known decoding technique. In the embodiment shown in FIG. 3, the decoders are implemented as Viterbi decoders.

In the embodiment shown in FIG. 3, the outputs of the decoder are input to an associated re-encoder. In particular, the outputs of the decoder 212 are re-encoded by the rate 1 re-encoder 220 before being output to the first input of the rate 1 SER evaluator 230. Similarly, the outputs of decoders 214, 216, 218 are each converted by rate 1/2 re-encoder 222, rate 1/4 encoder 224, rate 1/8 re-encoder 226. Re-encoded. The re-encoded data output by the re-encoder 222 at rate 1/2, the rate 1/4 re-encoder 224 and the re-encoder 226 at rate 1/8 are each of rate 1/2. SER evaluator 232, SER evaluator 234 at rate 1/4, and SER evaluator 236 at rate 1/8 are provided at a first input. Outputs of the soft combiners 204, 206, 208, 210 are provided to the second input of the SER evaluators 230, 232, 234, 236, respectively. The operation of the rate determination and decoding apparatus shown in FIG. 3 is now described in more detail.

The data provided to the input line 240 of the de-interleaver 202 is first demodulated and filtered before being input into the rate determining device 200 of the present invention. The operation of the modulator and filter is well known and therefore not further described. Demodulated and filtered soft decisions that once indicated adjacent information in time (prior to transmission) are now separated in time by the operation of the interleaver 110 in the transmitter (FIG. 2). Thus, the deinterleaver 202 operates in a known manner to timely re-set or re-align soft decisions that once in time indicate adjacent information. In the embodiment of the invention shown in Fig. 3, the de-interleaver 202 outputs re-arranged soft crystals such that the soft crystals representing the initially adjacent information are once again adjacent in parallel to the input of the soft combiners. Provide this information.

One soft combiner is provided for each rate hypothesis. Soft combiners function to cancel symbol repetition and the covering functions at the transmitter to generate soft decision inputs to the decoder. Soft combiners “de-cover” repetitive code symbols originally covered by rate cover circuitry 109 in the transmitter using orthogonal rate-dependent Walsh codes as described above with reference to FIG. 2. do. Each soft combiner shown in FIG. 3 performs a de-covering function by multiplying each soft decision by a Walsh covering code of a given rate and accumulating successive symbols to cancel the repeating code. For example, rate 1 soft combiner 204 multiplies soft decisions by the Walsh cover code of "+-". Similarly, rate combiner 206 at rate 1/2 multiplies soft decisions by the Walsh cover code of “+ +--” at the symbol rate. The soft combiner 208 of rate 1/4 multiplies the soft crystals by the Walsh cover code of “+ + + +----”. The soft combiner 210 at rate 1/8 multiplies the soft crystals by the Walsh cover code of “+ + + + + + + +--------".

When data is transmitted at a given data rate, only one of the soft combiners 204, 206, 208, 210 outputs accurate and de-covered soft decisions. Since the Walsh cover codes of the method and apparatus of the present invention are orthogonal, three soft combiners using wrong rate hypotheses have a soft decision meaning approximately zero. In contrast, a soft combiner using an accurate rate hypothesis outputs a soft decision sequence that represents the original coded code sequence plus noise. As shown in FIG. 3, the outputs of the soft combiners are connected to the inputs of the associated SER evaluators and Viterbi decoders.

SER metrics for use in rate determination

As described below with reference to FIG. 3, the orthogonal rate-dependent Walsh cover codes of the present invention facilitate the rate determination of the receiver by improving the rate determining power of at least two rate determination metrics (SER metric, energy metric). Let's do it. Two rate determination metrics are described in turn.

In one embodiment of the present invention, the SER metric is generated by rate re-encoders 220, 222, 224, 226 and operates in cooperation with rate SER evaluators 230, 232, 234, 236. Each rate soft combiner has an associated SER evaluator, re-encoder, and decoder. For example, the output of rate 1 soft combiner 204 is provided to rate 1 SER 230, decoder 212, and the output of the decoder is provided to rate 1 re-encoder 220. . Each decoder decodes the soft decisions produced by the associated soft combiner using a known Viterbi algorithm. As shown in FIG. 3, the decoder outputs are fed back to rate re-coders associated with them. The rate re-coders 220, 222, 224, 226 re-encode the outputs of the decoders 212, 214, 216, 218, respectively. The rate re-coders re-encode decoder outputs using the same encoding technique used by encoder 106 of FIG. The re-coded code symbols are provided to a first input of an SER evaluator associated with each re-encoder.

The outputs of the soft combiners are provided to a second input of the SER evaluators associated with them. Each SER evaluator 230, 232, 234, 236 compares the re-coded code symbols output by the re-encoder associated with the soft decisions output by the associated soft combiner. In an ideal transport channel environment (i.e., the channel is low noise and decoded by accurate rate assumptions), the soft decisions output by the soft combiners and input to the decoders are applied to the respective re-coders that yield zero SER. Same as re-encoded by However, since there is noise in the transmission channel, the noise is added to the soft decisions output by the soft combiners. Thus, even if there is no error in the decoded code sequence, the SER is not zero. This is due to introducing errors into soft decisions due to noise and the error correction nature of the code that corrects these introduced errors.

4 illustrates one embodiment of the SER evaluators of FIG. 3. The SER evaluator preferably includes a threshold decision circuit 302, an exclusive OR (“XOR”) gate 304, and a sign mismatch adder 306. The threshold determination circuit can be implemented in either hardware or software. As shown in FIG. 4, in accordance with one embodiment of the methods and apparatus described herein, each SER evaluator 230, 232, 234, 236 is characterized by the sine of soft decisions and the evaluator 230. Compare the re-coded code symbols provided at the inputs of 232, 234, 236. For example, the SER evaluator 232 of rate 1/2 has a sine of each soft decision generated by the soft combiner of rate 1/2 and each of the outputs from the re-encoder 222 of rate 1/2. Compare the sine of the re-coded code symbols. The sine soft decision is determined by performing a simple threshold decision function in the threshold decision circuit 302. Since the re-encoder of rate 1/2 introduces a small time delay (the time required to re-encode the symbol), the soft decisions output by the soft combiner 206 are not determined by the threshold decision circuit (sigma) before the sine comparisons are performed. 302 is delayed with the same delay period. In the embodiment shown in FIG. 4, the sine comparison function is implemented using a simple XOR gate 304.

If the sine of the soft decisions compared by the SER evaluators 230, 232, 234, 236 and the associated and re-coded code symbols are equal (e.g. they are both positive), the soft decisions are error free. Assumptions are made. However, if the sine of the soft decision and the re-coded code symbol do not match, the soft decision output from the soft combiner 204, 206, 208, 210 may result in noise, introduction of fading or other distortions in the transmission channel. Because of this, it is assumed that the transmitted sequence is not represented exactly. The total number of detected sign mismatches is added together by the sign mismatch adder 306 to produce the total number of symbol errors. Note that there is one such whole for each adder 306 (ie, the associated soft combiner 204, 206, 208, 210 for each rate hypothesis). By taking the total number of sine mismatches and dividing by the number of decoded code symbols (N) compared, the SER rate is calculated for each soft combiner 204, 206, 208, 210 (and therefore for each rate). Is generated.

As described above, orthogonal codes are used to cover code symbols prior to transmission, so soft combiners using inappropriate rate hypotheses generate AWGN signals meaning zero at their outputs. Decoders attempt to decode AWGN signals, and the re-encoders attempt to generate re-coded code symbols based on the AWGN signal. In general, decoders find the sequence that best matches the input AWGN signal. Thus, since the outputs of the decoders are somewhat arbitrary, the probability that the sine of incoming Gaussian noise signals and the sine of the re-coded Gaussian noise signals do not match is relatively high. In contrast, the sine of the soft decisions output by the soft combiner using the correct rate hypothesis match the sine of the re-coded code symbols associated with it more often. Thus, SER evaluators associated with the soft combiners using an incorrect data rate hypothesis produce higher symbol error rates than symbol error rates produced by SER evaluators associated with the soft combiner using an accurate rate assumption.

Rate determination can thus be improved by using SER outputs as a data rate indicator. The SERs allow the receiver to more easily distinguish between the rates. The higher the symbol error rate generated by the SER evaluator, the more incorrect rate is used to decode soft decisions. In contrast, the lower the symbol error rate produced by the SER evaluator, the more the associated soft combiner uses the correct rate assumption.

If the Walsh covering codes of the method and apparatus of the present invention are not used to cover code symbols (such as the transmitter shown in FIG. 1), the SER evaluators 230, 232, 234, 236 include zero long operation. Note that very similar symbol error rates occur for sequences that do. The worst case is a code sequence that is all zeros. For example, consider the case when data is transmitted at rate 1/2. When a sequence of all zeros is transmitted, rate combiner 206 generates a sequence of zeros (zero sequence is simply repeated in this case and not covered with Walsh cover codes). Disadvantageously, all other soft combiners also generate sequences that are all zero (since the input sequence is simply repeated using Walsh covers but not covered). Sequences that are all zero are decoded by the decoders and re-encoded by the re-encoders. Each SER evaluator matches the sine of each input signal (since the sequence of all zeros output by the encoders matches the sequence of all zeros output by the soft combiners), and each SER The evaluator thus indicates that each symbol error rate is approximately zero. Thus, symbol error rates cannot be used as a reliable metric for rate determination in this case.

In contrast, by using the orthogonal Walsh cover codes of the present invention, only a soft combiner using an exact rate hypothesis yields relatively small symbol error rates. The orthogonality of the Walsh covers allows the AWGN signal, meaning zero, to be generated by soft combiners using incorrect rate assumptions. This is especially useful when the input sequence is all zero sequence. Instead of inputting a sequence that is all zeros to the SER inputs (as described above and as produced by prior art soft combiners), an AWGN signal meaning zero is input. Gaussian noise signals generated by soft combiners using inaccurate rate hypotheses produce higher symbol error rates than symbol error rates produced by the soft combiner using the correct rate hypothesis. In short, an improved rate difference can be achieved using the rate-dependent Walsh covers of the present invention. The present invention uses the re-coded code symbols to produce an estimate of symbol error rates at decoder inputs. Advantageously, the symbol error rate metric generated by the present invention can be used as an indicator to simplify the rate determination task of the receiver.

Re-encoded energy metric for use in rate determination

In addition to the SER metric described above, the rate-dependent Walsh cover codes of the present invention improve the reliability of use of re-coded energy metrics to perform rate determination. The re-encoded energy metric is generated in a manner similar to the generation of the SER metric described above with reference to FIG. 3. 5 illustrates an embodiment of a decoder and rate determination apparatus of the present invention that uses a re-encoded energy metric to facilitate rate determination. The apparatus 200 of FIG. 5 is similar to that shown in FIG. 3 except that the energy metric calculators 250, 252, 254, 256 replace the SER evaluators 230, 232, 234, 236, respectively. same. The energy metric calculators are used to project the re-coded sequences output backward by the rate re-encoders onto the soft crystals generated by the soft combiners to produce a rate-dependent energy metric. As described in more detail below, each energy metric calculator produces a rate dependent energy metric that can be used by the receiver with the aid of rate determination processing. The energy metric is thus another indicator that can be used to distinguish between accurate rate assumptions and incorrect rate assumptions. Energy metric calculators are now described in more detail.

As described above with reference to FIG. 3, the outputs of the soft combiners are input to decoders associated with them. The decoders can be implemented using any known convenient decoding technique. For example, the decoders shown in FIG. 5 can be implemented using known Viterbi decoders. The outputs of the soft combiner are also provided to a first input of an associated energy metric calculator. The re-coded code symbols (output by the rate re-encoder) are provided as inputs to the second input of the energy metric calculators. For example, as shown in FIG. 5, the output of the soft combiner 206 at rate 1/2 is coupled to the first input of the energy metric calculator 252 and the Viterbi decoder 214. The Viterbi decoder 214 is re-encoded by the re-encoder 222 at rate 1/2 and provided to a second input of the energy metric calculator 252.

The soft combiners 204, 206, 208, 210 produce soft crystals that include sine and size information. Thus they are commonly referred to as having "soft" decision values. As shown in FIG. 5, the soft decision values are input to the energy metric calculators and the Viterbi decoders. The Viterbi decoders try to find a sequence that matches the soft values, and the output of the Viterbi decoders is re-encoded by the rate re-coders. The re-coded code symbols are provided as input to the associated energy metric calculators. The energy metric calculators project the re-coded sequences produced by the rate re-coders behind the soft decision values output by the soft combiners. For example, as shown in FIG. 5, the energy metric calculator 250 generates the re-generator generated by the rate re-encoder 220 over the soft decision values output by the soft combiner 204. Project the encoded sequences. Similarly, the energy metric calculators 252, 254, 256 rearrange the re-coded sequences generated by the rate re-coders 222, 224, 226 on the soft decision values output by the soft combiners 206, 208, 210, respectively. Project from

The re-coded sequences are projected onto combiner outputs in the energy metric calculators. The energy metric calculators perform a dot product of the re-coded sequences and the soft decision values output by the soft combiners. The re-encoded sequences generated by each re-encoder are multiplied by the soft code values output by the soft combiner in association with the re-encoder. For example, the energy metric calculator 252 takes the re-encoded sequences generated by the re-encoder 222 of the rate 1/2 and adds to the soft combiner 206 of the rate 1/2. Multiply them by the associated soft code values generated by The energy metric calculator 252 performs this multiplication on the basis of the symbol x symbol and adds the results to produce a dot product. Each energy metric calculator divides this dot product by the total number N of soft crystals produced by its associated soft combiner, and then squares the result of the division. Accordingly, each energy metric calculator produces an estimate of the energy per soft decision (“E _s ”) output by its associated soft combiner.

The energy E _s can be used as an additional indicator for the purposes of rate determination. As described in more detail below, due to the orthogonal nature of the Walsh covering codes of the present invention, the soft combiners using inaccurate rate hypotheses produce near zero energy metrics. In contrast, the soft combiner using the exact rate hypothesis produces an energy metric proportional to the square root of energy E _s under best conditions. Since the energy metric generated by the soft combiner using the correct rate hypothesis is distinguished from zero, it is sufficiently distinguishable from the energy metrics produced by the soft combiners using inaccurate rate hypotheses. Thus, the energy metrics generated by each energy metric calculator 250,252,254,256 can be used to distinguish between accurate rate assumptions and incorrect rate assumptions.

As described above with reference to FIG. 3, due to the orthogonal nature of the Walsh covering codes of the present invention, the soft combiners using incorrect rate hypotheses output AWGN signals meaning approximately zero. When noise signals are input to the Viterbi decoder, the Viterbi decoder will find a coded sequence of encoder inputs that best matches the noise. The energy metric is evaluated by calculating the dot product of the noise sequence and the re-coded sequence. Since the re-coded sequences are weakly correlated with soft decisions, the inner product of the soft combiner sequences and the re-coded sequences is likely to cancel. That is, the dot products of the AWGN outputs of the soft combiners and the associated and re-coded code symbol sequences approach zero.

Due to the orthogonal nature of the Walsh covering codes, a significant amount of energy of the AWGN signals generated by the soft combiners is removed from the re-encoded energy metric. The dot products are not exactly equal to zero since the Viterbi decoder finds some that are correlated with AWGN signals. Using incorrect rate hypotheses, the energy is likely to be zero. In contrast, a soft combiner using an accurate rate hypothesis produces valid soft crystals at its output. As described above, these soft decisions are decoded, re-encoded, and projected back onto the code symbols to produce an energy metric. In this case, however, the re-coded sequences do not cancel the valid code symbols. Rather, as described above, the inner product is proportional to the square root of the energy E _s . Thus, the energy metric generated by the energy metric calculator using the correct rate hypothesis is distinguishable from these metrics generated using the incorrect rate hypotheses. Thus, by using the Walsh covering codes of the method and apparatus of the present invention at the transmitter, an energy metric associated with each useful data rate can be generated by the receiver. The energy metrics can be used as another indicator that allows the receiver to distinguish between the correct rate hypothesis and the incorrect rate hypothesis. One embodiment of the present invention has been described above with reference to FIGS. 2 is a hardware implementation of the Walsh covering and encoding apparatus of the present invention adapted for use in a wireless receiver. 3-5 are hardware implementations of the decoder and rate determination apparatus of the present invention adapted for use in a wireless receiver. Those skilled in the telecommunications art can appreciate that the invention can also be implemented in software execution on some other data sequencing device or processor in the receiver and transmitter. In particular, in one embodiment, the Walsh covering and encoding method of the present invention described above with reference to FIG. 2 is executed on a microprocessor or other data processing apparatus in the transmitter. Similarly, in one embodiment, the rate determination and decoding method of the present invention is executed on a microprocessor or other data processing apparatus in the receiver. Alternatively, the methods may be implemented using any convenient or desired sequencing device, such as a state device, current state-to-state state discrete logic or field programmable gate array device.

Many embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the base rate repeater block 108 and the base rate covering block 109 of FIG. 2 may be located before or after the block interleaver 110 (as shown in FIG. 2). That is, the code symbols generated by the encoder 106 can be repeated first, covered with the Walsh cover codes of the present invention and interleaved (as shown in FIG. 2) or alternatively they are first interleaved and repeated May be covered with the Walsh cover codes.

An alternative embodiment of reverse link CDMA communication channel structure 100 'is shown in FIG. As shown in FIG. 6, the positions of the block interleaver 110 ′ and the repeater / cover circuits 108 ′ and 109 ′ are exchanged with one another in comparison to the relative positions of the traffic channel structure 100 of FIG. 2. Thus, after code symbols are generated by the encoder 106, the symbols are repeated by the repeater block 108 'and the cover using the method and apparatus described above with reference to FIGS. It is first block interleaved by the block interleaver 110 'before it is covered by the circuit 109'.

The decision to locate the block interleaver before or after the iterator / cover function depends on whether the orthogonal characteristics of the transmitted code symbols are more important than the diversity characteristics of a given system configuration. The transport channel environment in which the transmitter and receiver operate determines which characteristics should be emphasized. For example, in a mobile environment, the fading characteristics of the transport channel cause errors in the transmitted data. Thus, in a mobile environment, the diversity characteristics of the transmitted symbols become more important than these orthogonal characteristics. However, fading is not a big problem for wireless local loop applications.

Positioning the block interleaver after the base rate iterator 108 and the base rate cover 109 (as shown in FIG. 2) improves the diversity characteristics of the transmitted codes. However, an improvement in diversity characteristics is that there is a balance against degradation of orthogonal characteristics of the transmitted code symbols. If fading occurs during transmission, this adversely affects the orthogonality of the code symbols. When the codes are de-interleaved and soft combined at the receiver, the resulting code symbols are less orthogonal than when transmitted by fading errors. However, this reduced orthogonality can be accommodated in an environment where diversity should be emphasized.

In contrast, the block interleaver 110 '(as shown in FIG. 6) located before the base rate repeater 108' and the base rate cover 109 'improves the orthogonal characteristics of the transmitted codes. However, the improvement of the orthogonal characteristics is balanced against the degradation of the diversity characteristics of the transmitted code symbols. If fading occurs during transmission, the entire code symbols may be lost. However, reduced diversity can be accommodated in environments where diversity is less important.

In addition, implementation considerations associated with the data rates supported by the channel also serve to determine where to place the two functions. For high data rates, placing the block interleaver 110 'before the iterator 108' and cover circuit 109 'as shown in FIG. 6 is a more efficient implementation. In contrast, for low data rates, as shown in FIG. 2, it is a more efficient implementation to place the block interleaver 110 after the repeater and cover circuit 108, 109, respectively.

An alternative embodiment of an interfering reverse link CDMA communication channel 100 ″ that is adapted for use with the present invention is shown in FIG. 7. As shown in FIG. 7, in order to achieve high bit rates (multiple of the bit rate of rate 1), multiple rate 1 blocks are packaged into a single frame. As described above with reference to FIGS. 1 to 2, the information bits are CRC by CRC blocks (e.g., 102, 102 ', etc.) and tail blocks (e.g., 104. 104', etc.), respectively. And tail bits are added. The blocks are multiplexed together into a single stream by the multiplexer 130. As described above, the data is then encoded by encoder 106 and repeated at base rates (rate 1/8, 1/4, 1/2, 1) by base rate iterator 108. . The repeated codes are then covered by the base rate cover 109 as described above such that the base rate codes are orthogonal. The covered codes are then bit interleaved using the bit inversion block interleaver 110. Thereafter, in order to reduce the complexity of the implementation, high rate codes are repeated using the medium rate iterator 132. The codes are increased to a symbol rate of 12,2888 symbols per frame. The codes are covered by the media rate cover 134 so that all rate codes are orthogonal. In theory, the covering blocks 109 and 130 may be implemented in one block before the block interleaver 110. However, such an arrangement makes the block interleaver undesirably large. Thus, the covering functions are preferably separated as shown (one of the lower rates, one of the higher rates).

In summary, the invention described above includes means for repeating and covering code symbols with orthogonal rate-dependent Walsh cover codes prior to transmission over the communication link. The invention also includes means for determining and decoding the data rate at which the code symbols are transmitted. The present invention advantageously improves data rate determination and reduces error rates associated with decoding processing. By improving the coding reliability, the present invention also advantageously allows operation at a reduced signal-to-noise ratio (SNR), which in turn increases system capacity. Improvements in reliability reduce the latency of transport protocols, which provide reliable end-to-end links using ARQ schemes. The present invention is particularly useful in wide area wireless digital communication systems, such as CDMA systems, but it is also useful in other digital communication systems.

While one particular set of rate-dependent orthogonal Walsh cover codes is described, those skilled in the art understand that a number of alternative codes may be used to practice the present invention. For example, the invention may be practiced using covers that are not strictly orthogonal but have low cross correlation. One example is referred to as "gold" codes in the above description. Substantially orthogonal pseudo-orthogonal codes may also be used to practice the present invention. In addition, the present invention has been described above with reference to preferred reverse link Walsh cover codes. In one embodiment of the present invention, the forward link may use a slightly different set of Walsh cover codes to ensure backward compatibility with previous CDMA communication systems (e.g., systems configured with IS-95). Can be. In this embodiment, the forward link uses the Walsh cover codes shown in Table 2 below.

Data rate label Walsh code pattern One W ₀ ¹ + 1/2 W ₁ ² +- 1/4 W ₂ ⁴ + +-- 1/8 W ₄ ⁸ + + + +----

Table 2-Forward Link Rate-Dependent Walsh Covers

As used in Table 2, the label "W _x ⁿ " represents the Walsh code "x" in the "n-ary" Walsh code space. ^Represents the negative of W _x ⁿ . The Walsh covers of the forward link are due to the 8-ary Walsh code space. The Walsh codes are selected for two reasons. First, assignments are selected such that rates less than rate 1 are orthogonal to each other. Secondly, allocations are selected such that the rate 1 code is orthogonal to all other rates when the frame of rate 1 includes zero or one operation. As a result of the Walsh code covering using the Walsh codes shown in Table 2, the decoder is less likely to mistake a high rate block with 0 or 1 operations as a low rate block with 0 or 1 operations. As described above, this is important during data transmission, since zero or one operations frequently occur during the transmission of uncompressed and unencrypted data. In addition, using the Walsh cover codes shown in Table 2, the decoder is much less likely to decode a block smaller than a rate 1 block into another block smaller than a rate 1 block.

As described above, in one embodiment, the method and apparatus use orthogonal binary Walsh cover codes to code code symbols prior to transmission. Binary Walsh cover codes increase in length by a power of two for each data transmission sub-rate used by the transmitter. The present invention decodes the coded code symbols by deriving an SER and a re-encoded energy metric that aid in rate determination at the receiver. Other rate-dependent metrics, such as state metric re-normalization of Viterbi decoders, can be used to assist in rate determination processing when Viterbi decoders are used to implement the present invention.

Accordingly, it is to be understood that the invention is not limited by the scope of the appended claims as well as the specific depicted embodiments.

Claims (31)

A method of determining data rates of code symbols transmitted over a communication link, the method comprising: The code symbols are repeated a predetermined number of times per symbol depending on the data rate used for transmission, Wherein the code symbols are transmitted at a selected one of a number of useful rates, a) covering the code symbols with a selected one of a plurality of rate-dependent orthogonal Walsh covering codes, b) transmitting the covered code symbols over the communication link at the selected data rate, c) deriving a rate-dependent metric based on the covered code symbols transmitted, d) determining the selected data rate based on the derived rate-dependent metrics. 2. The method of claim 1 wherein the rate-dependent Walsh covering codes are selected from 16-ary Walsh code spaces. 2. The method of claim 1 wherein the rate-dependent Walsh covering codes are binary. 4. The method of claim 3 wherein the rate-dependent Walsh covering codes comprise binary codes that increase by a power of two with respect to the sub-rate of each successive data. 2. The method of claim 1, wherein said communication link comprises a wireless link. 6. The method of claim 5, wherein said communication link is part of a digital cellular communication system. 7. The method of claim 6, wherein said digital cellular communication system is a CDMA system. The method of claim 1, wherein the rate-dependent orthogonal Walsh covering codes having a value of W _x ^n, _x ⁿ is the W data rate determination method indicates the "n-ary" Walsh code in the Walsh code space "x". The method of claim 8, Is a data rate determinant representing W _x ⁿ . 9. The method of claim 8 wherein the Walsh covering codes have the following values for four predetermined rates including rates of one, one-half, one-fourth, and one-eighth: Data rate label Walsh code pattern One W ₁ ² +- 1/2 W ₂ ⁴ + +-- 1/4 W ₄ ⁸ + + + +---- 1/8 W ₈ ¹⁶ + + + + + + + +--------- 11. The method of claim 10, wherein "+" represents logic 0 and "-" represents logic 1. 11. The data of claim 10, wherein rate 1 comprises 9.6 kbps, rate 1/2 comprises 4.8 kbps, rate 1/4 comprises 2.4 kbps, and rate 1/8 comprises 1/2 kbps. Rate determination method. 2. The method of claim 1, wherein one of the derived rate-dependent metrics is a symbol error rate (SER) metric. 14. The method of claim 13, wherein an SER metric is derived for each useful rate. The method of claim 14, wherein deriving the SER metric comprises: a) de-interleaving the covered code symbols transmitted and providing the de-interleaved code symbols to a plurality of soft combiners as inputs, each associated soft combiner having a respective useful data rate. Wow, b) combining the de-interleaved code symbols for each useful rate; c) decoding the combined code symbols; d) re-coding the decoded code symbols; e) comparing the combined code symbols with the re-coded code symbols on the basis of a symbol x symbol; f) generating an SER for each useful rate based on the comparison made in step e). 2. The method of claim 1, wherein one of the derived rate-dependent metrics is a re-coded energy metric. 17. The method of claim 16, wherein the re-encoded energy metric is derived for each useful rate. 18. The method of claim 17, wherein deriving the re-encoded energy metric comprises: a) de-interleaving the covered code symbols transmitted and providing the de-interleaved code symbols to a plurality of soft combiners as inputs, each associated soft combiner having a respective useful rate; , b) combining the de-interleaved code symbols for each useful rate; c) decoding the combined code symbols; d) re-coding the decoded code symbols; e) projecting the re-coded code symbols onto the combined code symbols on a symbol x symbol basis; f) generating an energy metric for each useful rate based on the comparison made in step e). 19. The method of claim 18, wherein projecting step e) comprises performing a dot product of the re-coded code symbols and the combined code symbols on a symbol x symbol basis. 20. The energy per symbol (Es) for each useful data rate according to claim 19, wherein the generating step f) adds the dot products for the total number of code symbols and divides the sum by the total number of code symbols. Generating an estimate of the data rate. 15. The method of claim 14, wherein the SER metrics are used to distinguish between accurate rate assumptions and incorrect rate assumptions. 22. The method of claim 21, wherein the incorrect data rate hypotheses produce SER metrics that are significantly greater than the SER metric produced by the correct data rate hypothesis. 18. The method of claim 17, wherein the re-encoded energy metrics are used to distinguish between correct data rate assumptions and incorrect data rate assumptions. 24. The method of claim 23, wherein the incorrect data rate hypotheses produce re-encoded energy metrics that approach zero, and wherein the re-encoded energy metric generated by the correct rate hypothesis is significantly greater than zero data data. Rate determination method. A rate determining apparatus adapted for use in a communication system having a communication link, comprising: a) means for covering code symbols using a selected one of a plurality of rate-dependent orthogonal Walsh covering codes, b) means for effectively connecting the covering code symbols associated with the selected one Walsh covering code at the selected useful data rate via the communication link, effectively connected to the covering means; c) means for deriving, in response to the transmitting means, data rate dependent metrics based on the transmitted code symbols; d) means for determining, in response to the derivation means, the selected useful data rate based on the derived metrics. A system for performing data rate determination in a communication system having a communication link, comprising: In the system, code symbols are transmitted over the communication link at a selected one of a number of useful data rates. a) code symbols are symbol repetition and coding blocks that are repeated and covered with a selected one of a plurality of rate-dependent orthogonal Walsh covering codes; b) means for transmitting over the communication link the covered code symbols associated with the selected one Walsh covering code at the selected useful data rate, effectively coupled to the symbol repetition and coding block; c) a plurality of soft combiners with said transmitting means in wireless communication, each soft combiner having a respective data rate associated therewith, said soft combiners being de-interleaved to output combined code symbol sequences; d) a plurality of Viterbi decoder and re-encoder pairs that are effectively coupled to respective associated soft combiners, wherein the rate re-encoders comprise the decoder and re-encoder pairs that output re-coded code symbols, e) a plurality of SER blocks having a first input effectively coupled to each associated soft combiner and a second input effectively coupled to each associated re-encoder output, wherein each SER evaluator is based on a symbol x symbol basis; Said blocks for generating an SER metric by comparing code symbols generated by an associated re-encoder with code symbols generated by an associated soft combiner; f) means for determining, in response to the SER evaluators, the selected useful data rate based on the SER metrics generated by the SER evaluators. A system for performing rate determination in a communication system having a communication link, the code symbols being transmitted over the communication link at a selected one of a number of useful rates, wherein: a) symbol repetition and coding block, wherein code symbols are repeated and covered with a selected one of a plurality of rate-dependent orthogonal Walsh covering codes; b) means for effectively connecting the symbol repetition and coding block and transmitting over the communication link the covered code symbols associated with the selected one Walsh covering code at the selected useful rate; c) in wireless communication, a plurality of soft combiners having said transmitting means, each soft combiner having a respective data rate associated therewith, said soft combiners being de-interleaved to output combined code symbol sequences; d) a plurality of Viterbi decoder and rate re-encoder pairs effectively coupled to respective associated soft combiners, the rate re-encoders being the decoder and rate re-encoder pairs that output re-coded code symbols; e) a number of energy metric calculators having a first input effectively coupled to each associated soft combiner and a second input effectively coupled to each associated re-encoder output, each energy metric calculator being based on a symbol × symbol basis. Said calculators for generating an energy metric by multiplying code symbols generated by a re-encoder associated with code symbols generated by an associated soft combiner; f) means for determining, in response to the energy metric calculators, the selected useful data rate based on the energy metrics generated by the energy metric calculators. A computer program executable on a general purpose computing device, The program may determine data rates of code symbols transmitted over a communication link, the code symbols being repeated a predetermined number of times per symbol, depending on the data rate used during transmission, the code symbols being a number of useful symbols. For the program being transmitted at a selected one of the rates, a) a first set of instructions to cover the code symbols with a selected one of a plurality of rate dependent orthogonal Walsh cover codes, wherein the selected cover code is associated with the selected transmission data rate; b) a second set of instructions for deriving rate-dependent metrics based on the covered code symbols; c) a third set of instructions for determining the selected transmission rate based on the derived rate-dependent metrics. 29. The computer program of claim 28, wherein the program is executed by a general purpose computing device at a mobile station. 29. The computer program of claim 28, wherein the program is executed by a general purpose computing device at a base station. 29. The computer program of claim 28, wherein the program is executed in a field programmable gate array device.