MXPA00000536A - Communication system and method with orthogonal block encoding - Google Patents

Abstract

A communication system and method with orthogonal block encoding is provided. Encoded signals are transmitted by repeating transmissions of symbol blocks with a phase or sign change selected for each block from a sequence of phase or sign changes. Different symbols are transmitted using orthogonal sequences. The decoding uses different orthogonal sequences for separating the received encoded signals into corresponding separate channels. The orthogonal encoding is removed from the encoded transmitted signals and corresponding ones of the repeated symbols are added in successively received repeated blocks after the orthogonal encoding is removed. A transmitter uses a digital source encoder to encode information into symbols, and each symbol is repeated a preselected number of times to successively produce groups of repeated bits. Each repeat bit is changed in phase or sign by application of a sign or phase change determined by a selected assigned orthogonal code associated with the transmitter. The sign changed bits are interleaved from a number of such groups to successively generate a number of blocks, each composed of the different sign or phase changed bits of the preselected number of repeated groups and having a collective sign or phase change corresponding to a common sign change or phase shared by all bits of the block. The interleaved blocks then modulate a radio signal for transmission.

Description

SYSTEM AND METHOD OF COMMUNICATION WITH CODING OF ORTHOGONAL BLOCKS Background of the Invention The present invention relates generally to a system and method of communication with the transmission of signal coding and particularly to an orthogonal communication method employing orthogonal coding. The deliberate expansion of bandwidth by redundant coding is currently used due to the advantage it gives over the operating parameters. However, this advantage can be lost if the communication channel suffers from delayed echoes, time dispersion or multi-track effects. Code Division Multiple Access, or CDMA, is a known technique often proposed to artificially extend transmission bandwidths. The CDMA is an extension of known redundant coding techniques such as the technique of repeated transmissions with a majority vote in the receiver to combine signal repetitions. In some CDMA applications, also known as Direct Sequence Extended Spectrum, a mixture of simple repeats, or "stupid extension", and error correction coding, or "smart extension", is used to obtain the range of amplitude amplification. of desired band. It is known in the prior art that it is advantageous to use less intelligent coding and replace a stupid extension element in such a way that different signals become orthogonal to each other and then do not interfere with one another. For example: if a signal after an adequate amount of intelligent error correction coding produces a stream of coded bits ai, a2, a3, a4 ... and a second signal produces a stream of coded bits bi, b2, 3, b4 ... Then the first signal is transmitted using an additional four times repeated encoding as ai, ai, - i, -ai, a2, a2, a2, a2 a3, as, -a3, -a3, a, a4 , -a4, ~ a4 ... while the second signal is transmitted with repeated coding four times as bi, -bi, -bi, bi, 2 -b-, -b2, b2, b3, -b3, -b3, b3 , b4, -b4, -b4, b4 ..., then a comparison of the sign pattern of the repeated coding ++ - ++ - ++ - ++ - ... for the first signal and the sign pattern of repetitive coding + - ++ - ++ - ++ - + .... for the second signal, shows that these differ in sign exactly in half of the positions while agreeing in the other half. Therefore, by combining the repetitions with the appropriate signs to improve a signal, the contribution of the signal that interferes is completely canceled, and vice versa. These signals are known as "mutually orthogonal". The U. S. IS95 digital cellular system specifies mutual orthogonality for transmissions from cellular base stations to mobile telephones, using 64 times repeated coding with one of 64 selected sign patterns from a set of mutually orthogonal Walsh-Handamard codes. The IS95 system uses non-orthogonal transmission in the address from the mobile telephone to the cellular base stations, using instead intelligent error correction coding comprising concatenated convolutional coding with Walsh-Handamard orthogonal block coding. In the base mobile address, the orthogonality between different Walsh-Handamard codes is used to discriminate between different 6-bit symbols transmitted from the same mobile phone, while in the base-to-mobile address, the alsh-Handamard codes are used to discriminate between symbols transmitted to different mobile phones. A disadvantage of the IS95 system of non-orthogonal transmissions in the base mobile direction is that these signals interfere with each other if the power of the mobile transmitter is not strictly controlled as a distance function from the base station such as those from different telephones mobile phones received at more or less the same power level. However, the need for strict power control is alleviated when practicing the United States Patent 5, 151,919 assigned to Dent on September 29, 1992, entitled CDMA Restrictive Demodulation. In U.S. Patent 5,218,619 assigned to Dent on June 8, 1993, entitled CDMA Restrictive Demodulation, the already coded signals are subtracted more than once to improve interference subtraction. U.S. Patent 5,353,352 assigned to Dent and Bottomley on October 4, 1994, entitled Multiple Coding for Radio Communications, discloses optimal spectrum distribution access codes, equivalent to the signal patterns discussed above, when orthogonal signaling is employed within a transmission without orthogonality between different transmissions, such as those used in an uplink IS95 in the mobile-to-base direction. The above disclosures in the Patents are incorporated herein by reference in their entirety.

The speed by the difference between the uplink IS95, (mobile-to-base), and the downlink IS95, (base to mobile), the transmission schemes is that maintaining the orthogonality between different transmissions requires that they be correctly aligned in time, when the communication schemes of the prior art are employed. Yes, in the example above, the first and second signals are aligned with each other with a deviation from a place presented as follows: The two patterns of example signs given above are now seen to differ only at the beginning and end of the sign blocks, thus severely compromising the orthogonality. In the downlink, or base to mobile, the direction of all the signals originate in the same base station and therefore the time alignment is ensured. When the signals in the uplink or mobile base address originate in different mobile phones that are at different distances from the base station, it is more difficult to obtain time alignment of the signals received in the base station. The cellular European system known as GSM employs dynamic time alignment of mobile transmissions, wherein individual mobile phones are ordered by a base station to advance or delay their time to bring the received signals to a desired time relationship with each other. However, the ability to obtain such synchronization with high precision, for example within fractions of microseconds, is limited by the multi-track signal propagation phenomenon which is a characteristic of the mobile radios environment based on ground. The multi-track signal propagation phenomenon is caused by signal reflections transmitted from large objects such as hills and tall buildings, resulting in delayed echoes. While it may be possible to synchronize the signals transmitted from a mobile transmitter so that a selected signal beam or echo is aligned in time and thus orthogonally to a beam of another mobile transmitter, multi-track propagation, reflected rays or echoes, with track delays different from those of the selected signal rays will not be aligned in time. The GSM system uses Multiple Time Division Access (TDMA) in which each mobile signal is assigned to a time segment that does not overlap with transmissions from other mobiles on the same frequency. A guard time between segments equal to the longest expected echo delays, plus the use of command time delay / advance, reduces the interference between different transmissions caused by multi-track propagation. The interference of an echo with its original signal has been reduced by using an equalizer that beneficially adds energy to different echoes of the same signal. One such equalizer is described, for example, in U.S. Patent 5,331,666 assigned to Dent on July 19, 1994, entitled "Adaptive Maximum Possibility Demodulator" and U.S. Patent 5,335,250 assigned to Dent, et al. On August 2, 1994, entitled Method and Apparatus for Bidirectional Demodulation of Digitally Modulated Signals, the disclosures of which are incorporated herein by reference. The need for a time buffer between time segments reduces the bandwidth capability of the systems while the use of an equalizer does not eliminate the potential problem of multi-track propagation. Therefore a need still exists for a system and a method that constructs and communicates signals that remain mainly orthogonal to each other even when they are delayed by different amounts of time due, for example, to the phenomenon of multi-track propagation. SUMMARY OF THE INVENTION The deficiencies of the prior art described above are alleviated when practicing a communication system and method with orthogonal coding in accordance with the present invention. The communication system and method of the present invention provides for repeatedly transmitting coded signals with mutually orthogonally mutually encoded symbol blocks., the symbols in the repeated blocks representing encoded information. Decoding of the repeated symbol blocks encoded orthogonally of the transmitted encoded signal is provided. In accordance with the present invention, the information signal is divided into a series of information blocks having a plurality of individual information symbols. Each block of information in the information signal is transmitted repeatedly. That is, the entire block of information is transmitted and then the entire block is repeated a predetermined number of times. The number of repetitions of the information block is selected to allow the use of an orthogonal code that extends through all repetitions of the information block. The orthogonal coding is performed by applying a modification factor to each repeated block. The orthogonal coding can be carried out, for example, by inverting or changing the phase of the signal segment corresponding to each information block. In the receiver, the orthogonal encoding is eliminated by applying the orthogonal sequence corresponding to the desired signal and corresponding symbols of each repetition of the information blocks are summed. When the symbols are added, the symbols of the unwanted signal are canceled, leaving only the desired signal. In another aspect of the invention, the communication system of each of the plurality of transmitters may repeat each information bit produced by a digital source encoder a pre-selected number of times to successively produce repeated bit groups. A change of sign is imposed on the repeated bits of each of a second number of successive groups of bits repeated in accordance with an orthogonal code associated with the transmitter.

The interleaving of the bits with change of sign of the second number of groups is then carried out to successively generate a number of blocks equal to said first number containing said second number of symbols and each block comprising different bits of encoded information sharing a change of common sign. A modulated signal is transmitted according to the generated blocks with changes of sign corresponding to the orthogonal code. These and other features and advantages of the present invention will be apparent in the following detailed description, the accompanying drawings and the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a simplified functional diagram of an orthogonal block coding system of the present invention; Figure 2 is an illustration of two blocks of orthogonally encoded signals received in the receiver of Figure 1 which are not synchronized by an amount to which the block encoding receiver is orthogonally totally insensitive; Figure 3 is an illustration like that of Figure 2 but showing a separation of the ideal orthogonality; Figure 4 is an illustration like that of Figure 2 showing the multi-track propagation effect; Figure 5 is a functional block diagram of a transmitter according to the invention; Figure 6 is a functional block diagram of an alternative transmitter array according to the invention; Figure 7 is a functional block diagram of a transmitter according to the invention; Figure 8 (a) presents a pulse of the prior art GSM TDMA and data bit format; and Figure 8 (b) is an illustration like that of Figure 8 (a) but showing the insensitive orthogonal CDMA transmission of data bits according to the invention. Detailed Description of the Invention With reference to Figure 1, the orthogonal block coding communication system 10 of the present invention is presented to include a plurality of transmitters exemplified by a pair of identical block encoding transmitters 11 and 12 which transmit information carrying Sil and S12 signals in the form of electromagnetic waves. Preferably these signals Sil and S12 are digital signals, although the invention contemplates and is usable with analog signals modulated in carrier wave.

These signals Sil and S12 are received by an orthogonal block encoding receiver 14 which decodes the orthogonally encoded signals and separates them into different output channels. A portion of the orthogonally encoded block signal Sil of the transmitter 11, as shown by the dotted line, reaches the receiver 14 by means of an indirect track reflecting from a reflective object 13 in the field. Because the reflection path is greater than the length of a direct path of the signal S12, the reflected signal Sil 'reaches 14 some time after the arrival of the directly received signal S12. Accordingly, even if the signal S12 is synchronized to reach the receiver simultaneously with the arrival of the signal Sil, it will not be synchronized with the reflected signal Sil '. With reference to Figure 2, an orthogonal block coding communication system 10 is presented. The first signal Sil comprises blocks of N samples carrying information bir b2, b3 ... bN which are repeated a number of times with inversion indicated by a sign of minus or without inversion indicated by a plus sign on each block. Therefore, as shown in Figure 2, Sll-1, Sll-3 and Sll-4, the first, third and fourth blocks are not inverted, while the second block Sll-2 is inverted. The inversion / non-inversion pattern for Figure 2 is therefore represented by the sign pattern: + - ++. The second signal S12 comprises a block of signal samples ai, a2, as aw which is also repeated with or without inversion. In the case of the second S12 signal there is no investment for the first, second and third repetitions, but inversion of the fourth repetition, represented by the sign pattern +++ -. It can be verified that the sign patterns of the first and second signals + - ++ and +++ - are orthogonal, which means that they agree in as many places as they do not agree with. When the first signal Sil, and the second signal S12, are both transmitted at the same time, the linear sum of the signal samples occurs in the ether. However, as shown in Figure 2, the two signals Sil and S12, or the signal blocks Sll-1 and S12-1, are not necessarily aligned. In the example of Figure 2, samples ai and b? they are not aligned and therefore do not add up, while the samples ai and b (i + 2) are aligned and summed. The receiver 14 is connected to receive the corresponding signal samples that are repeated in the separate transmission time T. The receiver 14 preferably converts the signal samples to a suitable form, such as numeric, which are stored in a sample memory of the receiver 15. The receiver 14 processes and combines the corresponding received signal samples separated by a period of time T reading them in memory 15 if they are previously received samples. At the four sample sampling points in Figure 2, the sum of the sample values of the signals Sil and S12 are respectively a? + B3, a? -b3, a? + B3 and a: + b3. By combining the samples, the receiver 14 uses addition or subtraction according to the pattern of signs associated with the signal. In the example of Figure 2, the sign pattern + - ++ is used to receive the first signal Sil. Alternatively, the sign pattern +++ - is used to receive the second signal S12. Therefore, upon receiving the first signal Sil, receiver 14 forms, + (a? + B5) - (a? -b3) + (a? + B3) + (- a? + B3) = 4b3, which illustrates that the interference of the samples ai and -ai of the second signal S12 are canceled. Alternatively, the receiver 14 combines the samples received using the sign pattern +++ - to form the second signal received S 12, obt enin endo, + (a? + B3) + (a? -b3) + (a? + b3) - (a? + b) = 4 ai, showing that the interference of samples b3 and -b3 of the first signal Sil is canceled. Therefore, the two signals Sil and S12 appear orthogonal despite having a relative time deviation of the two sample intervals. The same orthogonality will remain for other relatively small time deviations compared to the block length of N sample intervals. Differences with the ideal orthogonality when the invention is practiced occur in some repeated bits, the number of bits for which this occurs is equal to the time deviation expressed in sample intervals. Therefore, as shown in Figure 3, when the block duration is large compared to the time deviation, the separation affects the orthogonality only in a small fraction of bits. The receiver 14 combines the samples received to decode the samples using the pattern signs + - ++. For bi, the interference from "a" shows a3 is canceled. However, to decode bN, receiver 14 gets 4bN - a2 + a2 '(1) Interference of the "a" samples to bN does not cancel completely because a2' is a sample of the next set of block repetitions, and not necessarily equal to a2. When the number of repetitions is greater, however, which is greater than four as in the example, the value b will be highlighted by a higher multiplier while the interference of "a" samples will be almost canceled. Additionally, any underlying error correction encoding will tolerate a few corrupted "b" values for uncanceled interference of the "a" signal values without causing transmission errors in the underlying information. Therefore, in practice, with large blocks, a large number of repetitions, such as the 64 repetitions used in IS95, and the use of error correction coding, the invention claims that the orthogonality of the signal is maintained = substantially even when the time deviation between the different signals of several sample intervals. When a signal, such as component "a" of the second signal S12, propagates from a transmitter to a receiver on several propagation paths of different lengths, the signal will be received multiplied by a complex number Co representing phase change and amplitude on a first path and they will be received multiplied by a complex factor Ci representing the phase and amplitude of the delayed path. Figure 4 illustrates this condition for a relative path delay of a sample interval. Therefore, when the sample a2 is decoded, in addition to the phase and amplitude changes to Co.a2 by the first propagation path, it will be additionally corrupted by the addition of the sample to the change in amplitude and phase by the factor Ci of the second path. As shown in Figure 4, the output of receiver 14 is then 4 (Co.a2 + Ci.ai), which is four times the output of the receiver that would occur without repetitions. The output of the receiver 14 is therefore successively: 4C0.a: + C? .aN - C? .aN "(2) 4 (Cc.a2 + 4C? .ai 4C0.a3 + 4C? .a2 4C0.a4 + 4C? .a3 4C0.a + 4C? .a (N-?) Where aN "means the symbol N of the previous block of N symbols. All outputs except the first depends on two samples transmitted. The output sequence can be processed by an equalizer, as described in the incorporated references, designed to handle delayed tracks of one or more delayed samples. Said equalizer processes all samples correctly except those in the boundary between two blocks, such as the first sample given by equation (2) above. The samples in the limit of the blocks are handled appropriately by said equalizer. The degree of approximation is better when the number of combined repetitions "M" is greater than four, so that the first output is: M.C0.a? + (M-3) .Ci .aN-aN "= M. (C0. A? + C?. AN-C?. (AN "+3. AN) / M) (3) where the error Ci. (aN "+ 3.aN) / M tends to zero in relation to Co.ai + Ci.aw because it is M. It is possible, however, to effectively model the receiver's dependence after combining based on three samples, ai , aN and a- 'in the example above in Figure 4, and construct the equalizer that uses this model to decode ai while using a differently dependent model on only two transmitted samples, such an equalizer needs to maintain a larger number of states encoding or "Viterbi states" to resolve the dependence of the signal on the additional symbols In CDMA systems, the receiver 14 of the invention therefore includes extension followed by conventional equalization for propagation on multiple paths. , the receiver 14 may include a Viterbi Maximum Sequence Probability Equalizer type of equalizer or a Feedback Decision Equalizer (DFE), or alternatively, a suitable RAKE receiver. or which responds for the propagation of multi track in the extension process. A suitable RAKE receiver is described in U.S. Patent 5,305,349 assigned to Dent on April 19, 1994 entitled "Coherent Quantized RAKE Receptor", which is incorporated by reference. A transmitter 16 according to the invention is preferably constructed as shown in Figure 5 including a block interleaver 18 which operates on the signal after a final spectrum extension coding operation is carried out by the circuit 20. The circuit 20 includes a bit repeater 22, an orthogonal code sequence generator 24 and a module-2 adder 26. An information source 28 provides information, such as voice or facsimile signals, to a digital source encoder. 30 which converts the information to digital form. The output of the digital source encoder 30 is applied to an error correction encoder 32 to make the transmissions more tolerant to noise and interference. The output bitstream of the encoder 32 (bi, b2, b3 ...) is scattered by the bit repeater 22 which samples each bit M times where M is the desired extension factor. For then the addition of bits, the modulo-2 adder 26 is added in bit form to the bit stream, an orthogonal code feature assigned to the signal and generated by the orthogonal sequence code generator 24. An interleaving operation of MxN block is carried out by the block interleaver 18 on the spectrum spread encoded signal at the output so that the repeated bits are not transmitted adjacently in time but separated by a block of N-bit size. The interleaver of block 18 does not add or delete bits, but it alters the order of transmission, for example: transposing a matrix of NxM bits. Alternatively, the block interleaver 18 is helical, diagonal or diagonal block interleaver instead of just a block interleaver. The spectrum extension encoded block signal is applied to a radio frequency carrier by means of a modulator 33.

The transmitter of Figure I6 is formed by adding an interleaver 18, which has precise parameters (M, N) adapted to the spectrum extension code produced by the generator 24, to result in a CDMA transmitter according to the invention. Figure 6 presents an alternative transmitter 35 according to the invention which includes the information source 28, a digital source encoder 30 and an error correction encoder 32. The embodiments presented in Figures 5 and 6 may include additional interleaving. on and over to perform interleaving by the interleaver 18, the purpose of the additional interleaving is to avoid errors in the same sample block that appear consecutively in the error correction decoder in the receiver 14. Any additional inter-block interleaving is considered part of the error correction coding process. The output of the error correction encoder 32 is connected to a block repeater unit 36 which stores a block of N consecutive bits and then repeats that block M times. A block sign generator 37 selectively supplies a sign for each repeating block. Therefore, the block sign generator 37 only requires generating orthogonal codes at the block rate, not at the speed at which the samples are generated or "the chip range". The sign of the block signal generator 37 is combined with signal samples, such as bit b3 of the block repeat unit 36 using a unit 38 OR-exclusive or module-2. Alternatively, a module-2 adder is used. A chip rate code is produced in an access code generator 40 to randomize the output of the bit stream of the block sign adder 38. The code produced by the access code generator 40 must be the same for all the codes. signals that are orthogonal, such as signals in the same cell of a cell phone system. The access code generator 40 can operate in a number of different modalities. In a first embodiment, the use of the access code generator 40 is optional, and may be omitted in some systems. Signals which are orthogonal to each other are usually transmitted in the same cell. If spare orthogonal codes are not assigned in an available cell, they are advantageously employed in neighboring cells such that a proportion of the interference from neighboring cells is eliminated. The CDMA systems of the prior art can not employ such orthogonality between cells since the transmission of a cell can not be synchronized with the transmissions of neighboring cells. However, when this invention is put into practice, the lack of precise synchronization is not an impediment to the orthogonality between cells. If, however, the total set of mutually orthogonal codes is used in a first cell, then a neighboring cell uses a second set of codes, orthogonal to each other but not orthogonal to the codes of the first cell. Such a set of additional codes preferably has uncontrolled orthogonality with any set of codes, as can be obtained using the technique of US Pat. No. 5,353,352 indicated above which can be incorporated into the block sign generator 37. In one second mode, the access code generator generates a chip range code of a length equal to the length of the block and is repeated for the repeated blocks. The code is then changed for the next set of repeated blocks, and so on. The property provided by this second technique is that the signal delayed by multi-track by a few chips are scattered by the same pattern of signs produced together by the sign code generator 52 and the block sign generator 52 in the receiver of signals. Figure 7. This multi-track spread causes an additive inter-symbol interference between the output of scattered symbols by the averager 58, which can be determined by the maximum probability equalizer of example 60. The access code is the same preferably for all signals in the same cell while a different access code is used for signals in different cells. The access code is preferably selected in accordance with the technique disclosed in U.S. Patent 5,353,352 to obtain non-orthogonality controlled between cells. In a third embodiment, the access code generator 40 is selected to produce delayed multi-track signals orthogonal to signals not delayed. This is accomplished by applying equal sign changes to any pair of adjacent chips in the middle of the repeats block and not as the sign changes in the other half of the block repeats. This has the effect that the +/- delays of a chip relative to a normal propagation delay results in multi-track signals which are orthogonal to the nominal propagation track. The multi-track signals are then not orthogonal but identically encoded one signal code to the other. This option is preferably used only when half of the available codes are used to discriminate between signals in the cell and the other half of the orthogonal codes are those that appear in + / - a delay chip in the multi track and therefore they discriminate the multi track. In a fourth embodiment, the access code generator 40 is a random code generator or none at the top. Multi-track signals are neither orthogonal to, nor identically encoded with undue signals. If it is desired to demodulate multi-track signals, then a RAKE-type equalizer may be employed, in which the receiver disperses the received signal using different time-shifted outputs of the access code generator 52 and performs different averages for each using instances multiple of the averager 58 to produce multiple averages each corresponding to a signal beam of different propagation delay. The different rays are combined in a RAKE equalizer such as the RAKE receiver using coarse quantized coefficients as described in U.S. Patent 5,305,349 indicated above. This fourth mode is not suggested preferably for application where the degeneracy of code orthogonality is effected by differences of relative propagation delays or by synchronization errors. Advantageously, groups of non-orthogonal signals, such as signals in different cells of a cellular wireless telephone system, are provided with different codes. The receiver 14 of Figures 2, 3 and 4 is preferably constructed in accordance with the invention presented in Figure 7. Signals including desired signals, interference signals, noise and multi-track distortion signals are received from the antenna 44 and applied to an input 45 of a down converter 46. The down converter 46 downconverts the radio frequency signal to a signal suitable for processing, preferably a complex baseband signal. Complex baseband signals may be in Cartesian form (X, Y) having a real component X, or "I", and an imaginary component Y, or "Q", or polar form (R, THETA) or Logpolar form (log (R), THETA) as described in U.S. Patent 5,048,059, assigned to Dent on September 10, 1991, entitled Logpolar Signal Processing, the disclosure of which is incorporated by reference. The samples converted downstream of the output 47 of the down converter 46 are then applied to the sign changer 48 which is connected to an access code coder 52. The downconverted samples are changed by the adder 48 according to the pattern. of signs of an access code provided to the access code generator 52, to eliminate the access code applied by a corresponding code generator transmitter such as an access code generator 40 in Figure 6. When different codes are applied to samples I, Q in transmitter 16, in Figure 5, codes corresponding ones are used for samples I, Q, respectively, in the receiver 14, in Figure 7. The real I and imaginary components Q of the samples of the sign changer 48 are deinterleaved by the deinterleaver 56 which works by blocking all the chips together corresponding to repetitions of the same signal sample information bit. The individual repetition signs are made the same by applying sign changes in the sign changer 50 according to one of the set of orthogonal sign patterns supplied by a block sign generator 54. Alternatively, block de-mixing is carried out using the access code generator 52 It will be appreciated that two changes of sign, in the sign exchangers 48 and 50 respectively, are equivalent to a single sign change determined by the product of separate signs. Therefore, it does not matter if the net token change is applied before or after de-mixing as long as the access code generator 52 or the block sign generator 54 or a combination thereof generates the appropriate sequence of signs. After the repeats are grouped and the signs of all the repeats are equalized, the repeats are combined together by the averager 58 which averages or prefixes all repetitions in a window of M bits, where M is the number of repetitions Alternatively, the averager 58 is a band pass filter similar to a block mobile averager. The output of the averager 58 is sampled downwards from M samples per bit to one sample per bit to produce the bit series bx, b ^, b3 ... These samples may contain interim interference (ISI) due to multi-track propagation, so that they are sent to a maximum probability equalizer 60. The output values of the equalizer 60 are preferably in a "soft" manner in which ones and zeros are represented by a value indicative of the degree of ones and zeros instead of hard decisions 1/0. U.S. Patent 5,099,499 assigned to Hammar describes soft derivative decisions, the disclosure of which is incorporated by reference. The use of soft decisions improves the operation of an error correction decoder 64 which receives equalized signals and produces hard decisions and "bad frame" indicators to the source decoder 66. The source decoder 66 translates the output bit stream to, for example, speech signals and using bad frame indicators of the error decoder 64 to hide error events, and to prevent noise pulses that corrupt the perceived speech quality. In addition, a mixer 62 is used between the equalizer 60 and the error correction decoder 64 if a corresponding mixer is used in the transmitter 16. The de-mixing by the mixer 62 is not related to the use of the mixer 56 to improve the orthogonality under conditions of time error or multi track. The commonly assigned Patent Application 08 / 305,727 of Dent, entitled Simultaneous Decoder and Demodulator Device integrated on September 14, 1994, discloses a demodulation technique which performs all functions of the equalizer 60, the mixer 62 and the docoder 64 error correction and can be used in place of these individual units. The disclosure is incorporated by reference. Small deviations from the true orthogonality of some symbols transmitted when the transmitters are not exactly synchronized are as described by equation (1). For example: a joint demodulation method for two signals can proceed as follows: If the signals bN and a2 are described as belonging to a vector V (i) of current symbols to be demodulated where and V (il) is similarly composed of bN "and a2" of previous blocks of N transmitted symbols, then by combining the repeats first with the sign pattern for "b" symbols and then for "a" symbols we obtain sums Sa and Sb as follows: Sb = 4bN - a2 + a2 'Sa = 4ba2 - bN + bN' or When all the signals are to be demodulated, as in a cellular base station or satellite earth station, said non-orthogonality remaining can be fully compensated by means of joint demodulation, decision feedback or alternatively the method of demodulation by subtraction of the Patent of United States 5,151,919 which is incorporated above by reference. Therefore, the vector sum Sb, Sa which must be 4Vi is corrupted by a small amount of the previous vector V (il) and the next vector V (itl), the quantities that are described by the coefficients "Inter-Vector Interference" ( IVI) which are matrices MO, Ml and M2 in the following equation: S = MO.V (il) + Ml.Vi + M2.V (Í + 1) (5) The central term is de-mixed multiplying the equation (4 ) by the inverse matrix Ml to get which is equal to equation (4) multiplied by MI "1 The effect of the previous vector V (il) and the following vector V (i + 1) can be eliminated approximately using S_ '(i-1) and S' (i + 1) calculated using equation (6) and replacing them in equation (6) to obtain an improved estimate S_ '(i) of V (i) This process is iterated to the need to obtain the desired precision. generally, IVI expressed in equation (5) of de-mixed by the use of a transverse matrix equalizer described by j = + LS '(i) =? [H (j) .V (i + j)] where L is selectively dimensioned and the equalization matrices H (j) j = -L are selected to obtain the desired equalization accuracy It is not necessary to overcomplicate the process of compensating for non-orthogonalities when only a few of the N symbols per block are affected , particularly when the symbols are further processed by a correction decoder of It may be sufficient to match those symbols which are affected by the non-orthogonality residual a soft value indicative of a larger symbol uncertainty before applying them to the error correction decoder. The present invention can operate with any number of block repeats and not just the power of two by which the alsh-Handamard signature patterns form orthogonal sets. This ability to generalize the invention is supported by the fact that a radio signal is capable of being changed in phase by a desired amount and not only by inverting it 180 degrees. A general phase change, for example, of 120 degrees can be carried out and can be represented by the multiplication of the complex factor: S = EXP (j2pi / 3). Assuming that a block of symbols is to be transmitted in three repetitions according to the invention, a first transmitter transmits its symbol blocks with successive phase deviations of 0, 120 and 240 degrees applied to the three block repeats. Using the symbols where So, Si S ?, represent 0, 120 and 240, respectively-So = 1, Si = EXP (j2pi / 3), and S2 = P (j4pi / 3) = EXP (-j2pi / 3) , a first transmitter transmits So • (bi, b2 / b3 ... bN); Sl. (bi, b2, b3 ... bu); S2 (bi, b2, b3 ... bN); where (bi, b2, b3 ... bN) are the blocks of modulated symbols without the phase change. A second transmitter transmits S0. (ai, a, a3 ... aN); S2. (a?, a2, a3 ... aN); S? (A?, A2, a3 ... aN); where (ax, a2, a3 ... aN) represents its modulated block of symbols, and a third transmitter transmits So • (Ci, C2 / C3 ... CN) / So- (Ci, C2, C3 ... CN), * So.

(Ci, c2, c3 ... cN), where (ci, c2, c3 ... cN) is the symbol block of the third transmitter. The three transmissions are orthogonal because the sequences S? / Sor So, SQ Se, So ».. 'S?, S2, S?, S2, S?, S2 ... and So / S2, S?, So / S2, S? ...; they are mutually orthogonal even when they are deviated in time. Said mutually orthogonal sequences of complex numbers can be called Fourier sequences and can be of any repeating length L of symbols forming them as successive powers of EXP (j2pi / L). The simplest real-value Handamard codes are used when the number of Repetitions L is a power of two. In accordance with one aspect of the invention, other orthogonal sequences can also be constructed, for example: allowing a set of sequential multipliers for successive repetitions so that they are neither complex nor restrictive at binary U / U values. In particular, when the multipliers are selected to be 1 or 0, the orthogonal sequences 1000000100000001000000 .. 0100000010000000100000 .. 0010000000100000001000 .. 0001000000010000000100 .. 0000100000001000000010 .. 0000010000000100000001 .. 0000001000000010000000. .. 0000000100000001000000 ... arise. Similarly when complex weights are selected from orthogonal Fourier sequences, when symbol blocks such as (bl, b2, b3 ... bN) represent N times of repeats of the same symbol "" b "and when the output of each transmitter is filtered , the invention in this special case provides FDMA signaling in which different transmissions are mutually orthogonal independently of the relative delay or time failures by virtue of occupying different and unrelated frequency channels According to another aspect of the invention, TDMA systems and FDMA can be reproduced as special systems and orthogonal CDMA modes insensitive to the delay can be added to FDMA or TDMA systems by modifying their coding methods with reference to Figure 8 (a), a GSM TDMA signal pulse and format The frame consists of eight-time segments, each of which contains signal pulse components of a synchronization word. It is surrounded by data bits. In standard GSM, the data bits in each of the eight time segments belong to different links or telephone call. The evolution of GSM to allow a link to use multiple time segments provides higher bit rates, in which case the data bits in successive segments can form the same communication or call link. Alternatively, Figure 8 (b) shows how, according to the invention, the same data bits of Figure 8 (a) can be repeated successively with or without phase inversion or phase change to form an insensitive orthogonal CDMA signal to the delay. In Figure 8 (b), the placement of each repetition preferably covers two signal pulses, which advantageously avoid the guard time between time segments and prevents a block from being divided by a synchronization word. This has a positive effect on how well the orthogonality is preserved under time deviation conditions, and also avoids the need to apply the orthogonal phase change sequence to the synchronization word S. When a block covers two time segments, the block is divided by the guard time when zero energy is transmitted and not by the synchronization word. This results in less orthogonality reduction under time deviation when the zero energy symbols of the guard time cause less interference than the full power symbols of the synchronization word, when they overlap data symbols. Other arrangements of repetitions within the pulses can be used, and it is not necessary to have eight repetitions. For example: using Fournier sequences, seven repetitions with eight time segments used for reception in the mobile terminal could be used, to avoid a duplication filter to connect the transmitter to the receiver to the same antenna at the same time. Those skilled in the art and who now have the benefit of the present disclosure will appreciate that the present invention can take many forms and modalities. Some embodiments have been presented to provide understanding of the invention. It is the intention that these embodiments are illustrative, and not limiting of the present invention. Instead, it is intended that the invention cover all modifications, equivalents and alternatives that fall within the spirit and scope of the invention in accordance with that defined in the appended claims.

Claims (63)

1. CLAIMS A communication system employing orthogonal block coding, which comprises: a transmitter for repeatedly transmitting encoded signals including repeated blocks of mutually orthogonally coded symbols, the symbols on the repeated blocks represent successive samples of an information source signal; and a receiver for decoding the repeated blocks of mutually orthogonally encoded coded signal symbols.
2. The communication system according to Claim 1 wherein the receiver employs different orthogonal codes to separate the encoded signals into different corresponding channels.
3. The communication system according to claim 1, comprising: a memory for storing an orthogonal code; and a phase changer for responding to the stored orthogonal code to impose a corresponding sequence of phase changes of at least one of the mutually repeated blocks.
4. The communication system according to claim 1 wherein the receiver comprises: an orthogonal block code eliminator to eliminate the orthogonal encoding of the transmitted encoded signals; and an adder to add corresponding symbols between the symbols in repeated blocks received successively from the transmitter after the removal of the orthogonal coding by the orthogonal code eliminator to form a summed signal for each symbol within the repeated blocks.
5. The communication system according to Claim 4, comprising a transmitter for transmitting the repeated blocks at a preselected speed and for adding symbols in successive blocks of the repeated blocks.
6. The communication system according to Claim 4 wherein the receiver comprises an equalizer for processing the summed summer signal to compensate for multi-track propagation.
7. The communication system in accordance with the Claim 1, comprising a digital source encoder for producing the symbols as digital information bits.
8. The communication system according to claim 7, comprising: a bit repeater for repeating each bit of information produced by the digital source encoder a preselected number of times to successively produce groups of repeated bits; a sign setter for selectively imposing a sign change on the repeated bits of each of a number of successive groups of repeated bits equal to the preselected number of bits in each group according to an orthogonal code; an interleaver for interleaving the changed sign bits of the preselected group number to successively generate a number of blocks each consisting of changed bits of sign different from the preselected number of repeated groups and having a collective sign change corresponding to a common sign change shared by all the changed bits of block sign; and a signal modulator for transmitting a modulated signal according to the blocks generated with sign changes corresponding to the orthogonal code.
9. A communication system employing orthogonal block coding, comprising: a plurality of transmissions for repeatedly transmitting coded signals comprised of blocks of repeated symbols orthogonally encoded mutually representing respectively samples of an information source signal in each transmitter; and a receiver for receiving encoded transmitted signals and for decoding orthogonally encoded repeated symbol blocks from the transmitted encoded signals received from the plurality of transmitters, using different codes of a plurality of orthogonal codes respectively associated with different transmitters of the plurality of transmitters for separating the received coded signals into corresponding separate channels.
10. The communication system according to Claim 9 wherein each of the transmitters comprises: a memory for storing the orthogonal code; and an answering machine to respond to the stored orthogonal code to impose a corresponding sequence of phase changes in each of the repeated blocks.
11. 11. The communication system in accordance with the Claim 10 wherein the answering machine selectively imposes a 180 ° phase change on repeated blocks according to the stored orthogonal code.
12. The communication system according to Claim 11 wherein the memory comprises a memory for storing an alsh-Handamard code having a number of bits equal to the number of times the transmitters repeatedly transmit the repeated blocks.
13. The communication system according to Claim 9 wherein the receiver comprises: an orthogonal code eliminator to eliminate the orthogonal encoding of the transmitted encoded signals; and an adder to add the corresponding symbols of the repeated block symbols received successively from one of the plurality of transmitters after the orthogonal coding is eliminated to form a summed signal for each symbol within the repeated blocks.
14. The communication system according to Claim 13, wherein: the blocks are transmitted at a preselected repetition rate which results in a pre-selected repetition period; and the adder comprises another adder to sum the successive repeated block symbols which are separated from each other by an amount equal to the repetition period.
15. The communication system according to claim 14 wherein each of the transmitters comprises: an orthogonal encoder for imposing phase changes to the preselected blocks while they are transmitted according to an associated code of a plurality of different orthogonal codes; and the receiver comprises a block eliminator to remove each of the repeated blocks received from each of the plurality of transmitters according to the orthogonal code associated respectively with the transmitter being decoded before being applied to the adder.
16. The communication system according to claim 13 wherein each of the transmitters comprises: an orthogonal encoder to selectively impose phase changes to the repeated blocks while being transmitted in accordance with an associated plurality of orthogonal codes; and the receiver comprises a block eliminator to remove each of the repeated blocks received from the plurality of transmitters according to the associated plurality of different orthogonal codes that are decoded before being applied to the adder.
17. The communication system according to Claim 13 wherein the receiver comprises an equalizer for processing the summed summer signal to compensate for multi-track propagation effects.
18. The communication system according to Claim 9 wherein each of the plurality of transmitters comprises a digital source for producing the symbols as digital information bits.
19. 19. The communication system according to Claim 18 wherein each of the plurality of transmitters comprises: a repeater for repeating each bit of information produced by the digital source encoder a pre-selected number of times to successively produce groups of repeated bits; a token changer for selectively imposing a change of sign in the repeated bits of each of the number of repeating groups equal to a preselected number of bits in each group according to an orthogonal code associated with the transmitter; an interleaver for interleaving the changed bits of the sign of the preselected number of groups to successively generate a number of blocks each composed of different changed bits of sign of a preselected number of repeated groups and having a collective sign change corresponding to a change of sign common shared by all the changed bits of block sign; and a signal modulator to transmit a modulated signal in accordance with the blocks generated with sign changes corresponding to the orthogonal code.
20. The communication system according to Claim 19 wherein each of the transmitters comprises an error correction encoder for imposing an error correction coding on each of the digital source bits of the digital source encoder.
21. The communication system according to claim 19 wherein each of the transmitters comprises: an access code generator for generating access code sequences at a rate at which the digital information bits are produced by the source encoder digital; and an access code setter for imposing the access code on the individual digital bits of each of the blocks orthogonally encoded.
22. 22. The communication system according to claim 21 wherein the receiver comprises an access code decoder for decoding individual digital bits of information received in the receiver.
23. 23. The communication system according to Claim 19 wherein the decoder comprises a deinterleaver for separating the blocks into individual digital bits.
24. 24. The communication system according to Claim 23 comprising a maximum probability equalizer for equalizing individual digital bits of the deinterleaver.
25. 25. The communication system according to Claim 23 wherein the receiver comprises an error correction decoder.
26. 26. A method for orthogonal encoding, comprising the steps of: transmitting respectively mutually encoded signals of orthogonally encoded repeated symbol blocks, the symbols in the repeated blocks representing successive samples; and decoding repeated blocks orthogonally encoded from the transmitted encoded signal.
27. 27. The method according to claim 26 wherein the decoding step comprises the step of using different orthogonal codes respectively to separate the received encoded signals into corresponding separate channels.
28. 28. The method according to claim 26 comprising the steps of: storing the orthogonal code; and imposing a corresponding sequence of phase changes in repeated blocks in response to the stored orthogonal code.
29. 29. The method according to claim 26 comprising the steps of: removing the encoded signals from the transmitted encoded signals; and adding corresponding symbols in the repeated blocks after eliminating the orthogonal coding.
30. 30. The method according to claim 29 comprising the step of transmitting the blocks at a preselected speed and adding symbols in repeated successive blocks.
31. The method according to claim 29 wherein the steps of eliminating the orthogonal encoding comprises the steps of: forming a summed signal for each symbol within repeated blocks; and process the signal added with an equalizer.
32. The method according to claim 26 comprising the step of encoding the symbols as digital bits of information.
33. The method according to claim 32 comprising the steps of: repeating each bit of information produced by the digital source encoder a pre-selected number of times to successively produce groups of repeated bits; imposing a change of sign in the repeated bits of each of the number of successive groups of repeated bits equal to a preselected number of bits in each group in accordance with an orthogonal code; interleaving the changed bits of the sign of the preselected number of groups to successively generate a number of repeated groups and having a collective sign change corresponding to a collective sign change shared by all the changed bits of - ** * > 60 block sign; and transmit a modulated signal according to the blocks generated with a change of sign corresponding to the orthogonal code.
34. 34. In a communication system having a plurality of transmitters and a receiver for communicating with the transmitters, an orthogonal block coding method, comprising the steps of: transmitting respectively each of the plurality of transmitters signals encoded with blocks of repeated symbols mutually orthogonally encoded respectively representing successive samples of an informative signal source produced in the transmitter; and decoding the encoded repeated blocks orthogonally of the encoded signals transmitted from the plurality of transmitters in the receiver employing a plurality of different orthogonal codes associated respectively with different transmitters to separate the encoded signals transmitted in corresponding channels.
35. 35. The method according to claim 34 wherein the transmission step includes the steps of: storing in each transmitter a different code of the plurality of orthogonal codes in each of the plurality of transmitters; and imposing a sequence of phase changes in each of the blocks repeated according to the stored orthogonal code.
36. The method according to claim 35 wherein the step of imposing a sequence comprises the step of selecting a phase change of 180 ° to impose on the repeated blocks according to the stored orthogonal code.
37. The method according to Claim 36 wherein the step of storing comprises the step of: selecting a Walsh-Handamard code having a number of bits equal to the number of times the transmitters repeatedly transmit the repeated blocks.
38. The method according to claim 34 wherein the step of decoding comprises the steps of: eliminating the orthogonal encoding of the transmitted encoded signals; and adding corresponding symbols in repeated blocks received successively from one of the plurality of transmitters after the orthogonal coding is eliminated by the coding to form the summed signal for each symbol within the repeated blocks.
39. The method according to claim 38 comprising the steps of: transmitting the preselected blocks by a repetition rate which results in a preselected repetition period; and adding corresponding symbols in successive repeated blocks which are separated from each other by an amount equal to the repetition period.
40. The method according to claim 39 comprising the steps of: selectively imposing phase changes to the repeated block with an orthogonal encoder while being transmitted according to one of the plurality of different orthogonal codes; and eliminating each of the repeated blocks received from each of the plurality of transmitters according to an orthogonal code associated respectively with the transmitters being decoded before adding one of the corresponding symbols.
41. The method according to claim 38 comprising the steps of: selectively imposing phase changes to the repeated blocks while being transmitted according to one of the plurality of different orthogonal codes with one of the plurality of associated orthogonal codes; and eliminating each of the repeated blocks received from each of the plurality of transmitters according to the orthogonal code associated respectively with the transmitters being decoded before adding the corresponding symbols.
42. 42. The method according to claim 38 comprising the step of processing the summed signal to compensate for multi-track propagation effects.
43. 43. The method according to claim 34 comprising the step of producing the symbols as digital bits of information.
44. 44. The method according to claim 43 comprising the steps of: repeating each information bit produced a pre-selected number of times to successively produce groups of repeated bits; and selectively imposing a sign change on the repeated bits of each of a number of successive groups of repeated bits equal to the preselected number of bits in each group according to an orthogonal code associated with the transmitter; interleaving the changed bits of the sign of the preselected group number to successively generate a number of blocks each consisting of different bits changed sign of the preselected number of repeated groups and having a collective sign change corresponding to a collective sign change shared by all the changed bits of the block sign; and transmit a modulated signal according to the blocks generated with sign changes corresponding to the orthogonal code.
45. The method according to claim 44 comprising the step of imposing error correction coding on each of the digital information bits.
46. The method according to claim 44 comprising the steps of: generating access code sequences at a rate at which the digital information bits are produced by the digital source encoder; and imposing the access code on the individual digital bits of each of the orthogonally encoded blocks.
47. 47. The method according to claim 46 comprising the step of decoding the individual digital information bits received in the receiver.
48. 48. The method according to claim 44 comprising the step of separating the blocks into individual digital bits.
49. 49. The method according to claim 48 comprising the step of equalizing the individual digital bits with a maximum probability equalizer.
50. 50. The method according to claim 49 comprising the step of including an error correction decoder for the receiver.
51. 51. A method for transmitting a spread spectrum encoded signal with improved multi-track propagation tolerance, comprising the steps of: encoding information to produce blocks of symbols containing a first predetermined number of symbols; repeat the transmission of each block of symbols a selected number of times; and changing the sign to each successive block repeated according to a preselected sequence of sign changes.
52. 52. The method according to claim 51, wherein the distribution of the coded signal spectrum is additionally conditioned prior to transmission by combining with a spectrum distribution access code.
53. 53. The method according to claim 52, wherein the spectrum distribution access code is used in common by different transmitters.
54. 54. The method according to claim 51 wherein the selected sequence of sign or phase changes is different for a different transmitter.
55. 55. The method according to claim 54 wherein the different sequences are orthogonal to each other.
56. 56. A method for decoding a spectrum spread encoded signal, comprising the steps of: receiving a composite signal, the composite signal being a sum of a number of overlapping spectrum spread signals including said coded signal and sampling the composite signal to produce signal samples; combining selected signal samples separated by a predetermined number of samples using a selected phase change from a pre-assigned pattern of phase changes associated with a particular overlapping spread signal to produce scattered samples; and process the scattered samples using an equalizer to compensate for multi-track propagation.
57. A transmitter to be used in a communication system employing orthogonal block coding, the transmitter comprises: a producer of signal source of information; a transmitter circuit for repeatedly transmitting coded signals composed of orthogonally encoded repeated symbol blocks respectively representing samples of the information source signal; a memory for storing an orthogonal code; and a phase changer that responds to the stored orthogonal code to impose a corresponding sequence of phase changes in each repeated block.
58. The transmitter according to Claim 57 comprising a digital source encoder for producing the symbols as digital information bits.
59. The transmitter according to Claim 58 comprising: a repeater for repeating each bit of information produced by the digital source encoder a pre-selected number of times to successively produce groups of repeated bits; a token changer to selectively impose a sign change on the repeated bits of each of the successive groups of repeated bits equal to the preselected number of bits in each group according to an orthogonal code associated with the transmitter; an interleaver for interleaving the changed sign bits of the preselected group number to successively generate a number of blocks each consisting of the changed sign bits of the preselected number of repeating groups having a collective sign change corresponding to a common sign change shared by all the changed bits of block sign; and a signal modulator for transmitting a modulated signal according to the blocks generated with a change of sign corresponding to the orthogonal code.
60. The transmitter in accordance with the Claim 59 comprising an error correction encoder for imposing an error correction coding on each of the digital source bits of the digital source encoder.
61. 61. A receiver for use in the processing of transmitted encoded signals having mutually orthogonally encoded repeated symbol blocks, the receiver comprising a receiver circuit for receiving the transmitted coded signals, and for decoding the repeated blocks of orthogonally encoded symbols of the transmitted signals received of the transmitters, employing different orthogonal codes respectively associated with a plurality of different orthogonal codes associated with different transmitters to separate the received coded signals into separate corresponding channels.
62. 62. The receiver according to claim 61 comprising: an orthogonal code eliminator for eliminating the orthogonal encoding of the transmitted encoded signals; and an adder to sum corresponding symbols in repeated blocks received successively after the orthogonal coding is eliminated by the orthogonal code eliminator to form a summed signal for each symbol within the repeated blocks.
63. 63. The receiver according to Claim 62 wherein the blocks are transmitted at a preselected block repetition rate which results in a preselected repetition period; and the adder comprises another adder to sum the corresponding symbols in successive repeated blocks which are separated from each other by an amount equal to the repetition period. The receiver according to Claim 63 wherein the receiver comprises a block eliminator to eliminate each of the repeated blocks received from the transmitter according to the orthogonal code associated with the transmitter before being applied to the adder. SUMMARY OF THE INVENTION A communication system and method with orthogonal block coding is provided. Coded signals are transmitted by repetitive transmissions of symbol blocks with a change of phase or sign selected for each block from a sequence of phase or sign changes. Different symbols are transmitted using orthogonal sequences. The decoding employs different orthogonal sequences to separate the received encoded signals into corresponding separate channels. The orthogonal coding is removed from the transmitted encoded signals and the corresponding symbols between the repeated symbols are added in repeated blocks received successively after the removal of the orthogonal coding. A transmitter employs a digital source encoder to encode information in symbols, and each symbol is repeated a preselected number of times to successively produce groups of repeated bits. Each repeated bit is changed in terms of phase or sign by applying a change of sign or phase determined by a selected assigned orthogonal code associated with the transmitter. The bits with change of sign are interleaved from several groups of this type to successively generate several blocks, each block composed of the different bits with change of sign or phase of the preselected number of repeated groups and having a change of sign or phase collective that corresponds to a change of common sign or phase shared by all the bits of the block. The interleaved blocks then modulate a radio signal for transmission.