JP2000032073A - Digital modulation system using orthogonal code deformed for reduction of self-correlation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the multi-bus performance and to maintain the orthogonality of a Walsh code and also the low mutual relation characteristic of Walsh codes by deforming an orthogonal Walsh code by means of plural codes and improving the self-correlation characteristic of the Walsh code by means of the deformed orthogonal Walsh code that has a reduced self- correlation side robe. SOLUTION: Three bits of a 2nd set of 8-bit data symbols which are received from a converter 14 are supplied to a 2nd modulator 34. The modulator 34 generates a Walsh code of length 8 that is deformed by means of plural corresponding codes. The modulator 34 corresponds to a Q-phase modulation branch of an M-array orthogonal modulation MOK system 30, and this branch generates a-QW component of a signal to be transmitted. The modulator 34 also corresponds to the said three data bits and generates a Walsh code of length 8 at a chip speed of about 11 MHz that is controlled by a clock signal of 11 MHz.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wireless communication systems, and more particularly, to digital modulation systems that encode information using modified orthogonal codes, for example, M-array orthogonal modulation (MOK).

[0002]

BACKGROUND OF THE INVENTION Wireless communication channels can rarely be modeled as purely line-of-sight channels. Thus, it is necessary to take into account many independent paths resulting from repeated scattering and reflection of the signal between the transmitting and receiving stations and between many objects lying around them. Due to signal scattering and reflection, there are many different "copies"("multipathsignlas") of the transmitted signal arriving with varying degrees of delay, phase shift, and attenuation at the receiving station. "Is received.
The received signal consists of many signals, each traveling a separate path. The lengths of these propagation paths are unequal, so that the information carried over the wireless link is subject to a spread of delay as it travels between the transmitting and receiving stations. The amount of time dispersion between the earliest received copy and the most recently received copy of a transmitted signal having a signal strength above a certain level is often referred to as delay spread. The spread of the delay causes intersymbol interference (ISI).
In addition to delay spread, the same multipath environment can cause severe local variations in received signal strength because the multipath signals add together or cancel out at the receiving antenna. Become. The multipath component is a combination of multipath signals that arrive at the receiver with approximately the same delay. Such a change in the amplitude (intensity) of the multipath component is usually called Rayleigh fading, and causes a large block of information to be lost.

[0003] Digital modulation techniques are used to enhance wireless communication links by providing greater noise immunity and robustness. In some digital modulation systems, data transmitted over a wireless communication link is represented or encoded as a time sequence of symbols. Each symbol has M finite states, and each symbol represents N bits of information. Digital modulation consists of selecting a particular code symbol from the M finite number of code symbols based on the N-bit information applied to the modulator. In the case of an M-array modulation scheme, log ₂ M bits of information are represented or encoded by M different codes or code symbols, and the encoded code is transmitted. The transmitted code is received as a plurality of delayed replicas of the transmitted code, and the receiver examines the correlation between these delayed versions of the received code and the known code. This is accomplished by summing the autocorrelation values for all possible multipath delays.

The autocorrelation sidelobe indicates the correlation value between a known code and a time-shifted replica of the received code. If the code is the same, ie, a shifted version of itself, the code has a high level of autocorrelation or autocorrelation sidelobes. For example, for code (111-1), the autocorrelation is for zero shift: code 1 1 1 -1 shifted code 1 1 1 -1 multiplication 1 1 1 1 correlation = sum of multiplied values = 4

In the case of one-chip shift, the autocorrelation is: code 11 1 -1 shifted code 11 1 -1 multiplication 11 1 -1 correlation = sum of multiplied values = 1.

In the case of a two-chip shift, the autocorrelation is: code 11 1 -1 shifted code 11 1 -1 multiplication 1 -1 correlation = sum of multiplied values = 0.

In the case of a three-chip shift, the autocorrelation is: code 11 1 -1 shifted code 11 1 -1 multiplication -1 correlation = sum of multiplied values = -1.

A large shift gives an autocorrelation value of zero, so in this example the largest autocorrelation side lobe is one.
Has the value or magnitude of In this example, in the receiver:
Instead of 0, -1 is used. Autocorrelation sidelobes give an indication on multipath performance. If the autocorrelation sidelobe is large, this indicates that some multipath components are strongly interfering with each other.

On the other hand, cross-correlation relates to the correlation between different codes. M-array quadrature modulation is a form of digital modulation that provides good cross-correlation between codes by encoding data using orthogonal codes that do not interfere with each other. FIG. 1 shows a schematic block diagram of an M-array quadrature modulation system 10. In this system, input data is transmitted to the Institute of E
Scrambled as specified in the current 802.11 standard by the Electrical and Electronics Engineers (IEEE). This data is then provided to a serial / parallel converter 14, which converts the serial data into eight parallel bits,
From this, one data symbol is formed. The first modulator 16 receives three of the eight parallel bits and generates a first code of eight chips long from the look-up table, and the second modulator 18 generates the first eight bits. Three of the bits are received and a second code of eight chips in length is generated from the look-up table. These chips are actually code bits, but are here referred to as chips to distinguish them from data bits. In this implementation, one of these eight parallel bits is provided to a first exclusive or (XOR) gate 20. XOR gate 2
A 0 inverts the code if the bit has a value of 1. Similarly, the remaining last bit is the second XO
It is supplied to the R gate 22. XOR gate 22 inverts the code from second modulator 18 if that bit has a value of one. In this implementation, the output I _out of XOR gate 20 is provided to signal circuit 21. Signal circuit 21
Converts all 0s to -1 and supplies this to the mixer 24. Kimisa 24 uses this output I _out to generate a frequency ω
Is modulated. In some cases, the signal circuit 21
_May manipulate, transform and / or process the output I _out before using it for modulation. The output Q _out from the XOR gate 22 is supplied to the signal circuit 23. The signal circuit 23 converts all 0s to −1 and supplies this to the Kimisa 26. Kimisa 26 modulates the 90-degree shifted frequency with this output Q _out. In some cases, the signal circuit 23 may operate, convert and / or process the output I _out before using it for modulation. In this particular implementation, the first modulator 16 corresponds to the in-phase (I) component of the output signal, and the second modulator 18 corresponds to the quadrature (Q) component of the output signal.

The modulators 16 and 18 each receive log ₂ M bits of information and perform M-array quadrature modulation or coding to select one code from M orthogonal codes. I do. Since both I and Q components having different codes are prepared and a total of (2M) ² codes can be combined, it is possible to encode a total of 2 + 2 log ₂ M bits into one orthogonal code. it can. In the above example, M is eight. These M codes in an M-array quadrature modulation system are typically M chip Walsh
Based on code. The use of an M-chip Walsh code for an M-array quadrature modulation system is advantageous in the following respects. That is, the M-chip Walsh code is an orthogonal code, which means that the cross-correlation is zero, so that the M-chip Walsh codes can be easily distinguished from each other.

[0011]

However, when a Walsh code is used as an orthogonal code, a new problem occurs.
For example, if Walsh code 0 (all 1s) is selected as the code symbol, Walsh code 0 looks like a carrier signal of unmodulated continuous wave (CW). In order to avoid the problem (Walsh code 0 continuous wave modulation problem) that occurs when modulating with Walsh code 0, the last two bits of the Walsh code are inverted using the cover sequence of (1111100). An M-array quadrature modulation system has been proposed which modifies the Walsh code and uses the Walsh code thus modified. By modifying the Walsh code in this way, the problem that occurs when modulating with Walsh code 0 (Walsh code 0 continuous wave modulation problem) is solved. However, the Walsh code modified in this way is Walsh code.
It has poor autocorrelation and spectral properties inherent in the code. To address this poor autocorrelation and spectral properties of the Walsh code, conventional systems multiply the output signal by a pseudo-random noise (PN) signal. However,
Some systems are based on EGTiedemann, ABSalmasi and
KSGilhousen, “The Design And Development of a Co
de Division Multiple Access (CDMA) System for Cellu
lar and Personal Communications ", Proceedings of IE
As described in EE PIMRC, London, September 23-25, 1991, pp. 131-136, the output signal is multiplied by a PN sequence having a length much larger than the Walsh code.
However, even in this case, the resulting code lacks autocorrelation properties. If the autocorrelation properties of the transmitted code are not sufficient, it will be difficult for the system to detect a delayed or shifted version of the transmitted code, and the multipath performance of the system will be degraded.

[0012]

SUMMARY OF THE INVENTION The present invention is directed to a digital (de-) modulation system that improves multipath performance by using a modified orthogonal code having reduced autocorrelation sidelobes. At the same time, the cross-correlation properties of this modified code are maintained. For example, the modified orthogonal code has an autocorrelation side lobe that does not exceed half the length of the modified orthogonal code. In some embodiments, an M-array quadrature modulation (MOK) system is used, which modifies the orthogonal Walsh code with a complement code to improve the autocorrelation properties of the Walsh code. M-array quadrature modulation (MOK)
The multipath performance of the system is improved, while at the same time Walsh
The orthogonality and low cross-correlation properties of the code are maintained.
Other features and advantages of the present invention are described in the following detailed description.
This will become more apparent when read with reference to the drawings.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a digital communication system according to the present invention.
3 illustrates some embodiments of a modulation system. FIG. 2 illustrates a digital modulator 28 according to the principles of the present invention. Modulator 28
Selects the corresponding one of the M codes in response to the data bits. These M codes are generated by transforming the set of orthogonal codes, which gives
The autocorrelation levels associated with these sets of orthogonal codes are reduced, while the orthogonality of these sets of orthogonal codes is maintained. For example, when the same chip in the codes of these orthogonal code sets is inverted, the modified orthogonal code maintains orthogonality. In some embodiments of the present invention, one orthogonal code set is modified with another code, and M orthogonal N chips with autocorrelation sidelobes whose value (length) does not exceed N / 2 Code is generated. Various methods can be considered for generating the modified orthogonal code by the modulator 28. For example, in some embodiments, modulator 28 performs the transformation of the orthogonal code using processing circuitry that implements the logic to perform the transformation, and in some embodiments, , Modulator 28
For example, the modified orthogonal code is stored in a search table. It is also conceivable that the modulator 28 stores a different set of modified orthogonal codes or calculates a different set of modified orthogonal codes in response to a request due to an operation change.
The modification of the orthogonal code is performed by, for example, element-wise multiplication of the orthogonal code and a code having good autocorrelation characteristics. The code thus generated by modulator 28 has low autocorrelation properties, while maintaining at least some orthogonal properties of the original orthogonal code. In the embodiment of FIG. 2, the data bits are shown as being received in parallel, and the code chips are shown as being generated in series. However, depending on the application, conversely, receiving data bits in series and generating code chips in parallel may be considered.

A complement code or a complement sequence used in the present invention is a set having a characteristic that the sum of the autocorrelation of the sequences becomes zero except for the main peak in the case of zero shift even if the sequences are shifted. Is the sequence. By this nature, complement codes can be used to modify the set of orthogonal codes used in connection with modulator 28. For the complement code, see Robert L. Frank, “Polyphase Complementray.
Codes ", IEEE Transactions On Information Theory, Vo
Please refer to l. IT-26, No. 6, Nov. 1980, pp. 641-647. For a length equal to a power of two, the complement code can be easily generated by the following rule: the sequence A = B =
Starting from {1}, the two's complement code is ABA
B '. Here, B ′ means that all elements of the sequence B are inverted. Thus,
For lengths from 2 to 16, the complement sequence is
It looks like this:

{1 0} {1 1 1 0} {1 1 1 0 1 1 0 1} {1 1 1 0 1 1 0 1 1 1 1 0 0 0 1 0}

In addition, by performing another conversion on the complement code, another complement code can be generated from the same length. For example, {11101011} can be obtained as another complement code of length 8 by inverting the first or second half of the code.

The complement code has a low autocorrelation side lobe, and multiplying the complement code by the Walsh function produces another complement code. Thus, the complement code Wals
When used to modify the h code set, the resulting modified Walsh code is a complement and has the same low autocorrelation sidelobe. This modified Walsh code
In addition, maintain orthogonality, which means that the cross-correlation between any different codes will be zero (for zero delay).

FIG. 3 illustrates one embodiment of an M-array quadrature modulation (MOK) system 30 according to the principles of the present invention. The system 30 uses a modulator 32, 34 to generate a length eight code in response to three information bits from the serial / parallel converter 14. In this embodiment, a Walsh code set having a length of 8 is used as the orthogonal code of the set, and the Walsh code set is modified using a complement code. The length 8 Walsh code set is as follows:

1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 1 1 0 0 1 1 0 0 1 0 0 1 1 0 0 1 1 0 1 0 1 0 1 0 1 0 1 0 0 1 0 1 1 0 0 1 0 1 1 0 1 1 0 0 0 0 1 1

As described above, in the conventional system, the Walsh code is transformed element by element by the exclusive OR with the code {11111100}, and the last two chips of each Walsh code (ie, the last two chips of the Walsh code set). The two rows of chips are inverted). However, in the worst case (when -1 is used for 0), this modified code has an autocorrelation side lobe of scale 5, and this autocorrelation value is larger than half the length of the 8-chip code, Degrades multipath performance.

In contrast, in the embodiment of FIG. 3, the M-ary quadrature modulation (MOK) system 30 uses an eight-length complement code to transform the eight-length Walsh code set. For example, the complement sequence {11101101} or {11101011} is used. For the latter code, the modified Wals
The h code set is as follows.

1 1 1 0 1 0 1 1 1 1 1 0 0 1 0 0 1 1 0 1 1 0 0 0 1 0 0 0 1 1 0 1 1 0 1 1 1 1 1 0 1 0 1 1 0 0 0 1 1 0 0 0 0 0 1 0 1 1 0 1 0 1 1 1

In the case of this modified Walsh code set, the autocorrelation side lobe of the generated code has a magnitude or value of only 2 at worst. This variant code is described in Robert L. Frank, “Polyphase Complementray Cod
es ", IEEE Transactions On Information Theory, Vol.IT
-26, No. 6, Nov. 1980, pp. 641-647. That is, the complemented Barker code has autocorrelation sidelobes limited to only one magnitude, provided that the complemented Barker code or sequence has some odd length, eg, length one.
Only exists for one. When comparing the two complement codes shown as an example above, the first code has better cross-correlation characteristics with respect to the time-shifted code.

In the operation of the embodiment shown in FIG. 3, the scrambler 12 receives data and converts the data to IEEE 802.11.
Scramble according to standard. Alternatively, the scrambler 12 is not used, and the data is supplied to the serial / parallel converter 14 after performing other operations on the data, for example, conversion, interleaving, transformation, or the like, or directly. You can also. In the embodiment of FIG. 3, a 1: 8 multiplexer (MUX) is used as the serial / parallel converter 14, and the multiplexer generates eight data bits of data symbols in parallel according to a 1.375 MHz clock signal. The 8-bit data symbol is encoded into a symbol consisting of an I / Q code pair of an 8-chip code or code word, and the interval between the symbols is equal to the code length.
Three bits of the 8-bit data symbol are provided to a first modulator 32, which generates a length-8 Walsh code modified by a corresponding complement code. The first modulator 32 generates this length 8 Walsh code at a chip rate of about 11 MHz controlled by an 11 MHz clock signal. In the above example, each symbol includes eight data bits, which are encoded into independent eight-chip I and Q codes. Chips are actually code bits, but these are referred to herein as chips to distinguish them from data bits. In the embodiment of FIG. 3, the first modulator 32 corresponds to the I-phase modulation branch of an M-ary quadrature modulation (MOK) system 30;
This branch produces the I component of the signal to be transmitted.

The three bits of the second set of 8-bit data symbols from converter 14 are provided to a second modulator 34, which has been modified with the corresponding complement code. Generate a Walsh code of length 8. This second modulator 34 corresponds to the Q phase modulation branch of the M-ary quadrature modulation (MOK) system 30, which generates the Q component of the signal to be transmitted. The second modulator 34 also responds to these three data bits to generate a length 8 Walsh code at a chip rate of about 11 MHz controlled by an 11 MHz clock signal.

One of the remaining two bits of the 8-bit data symbol from the serial / parallel converter 14 is the first XO
It is supplied to the R gate 36. If the bit is 0, the first XOR gate 36 changes the sign (polarity) of the length 8 Walsh code from the first modulator 32. The resulting modified Walsh code I _out is supplied to the signal circuit 21. The signal circuit 21 converts all 0's to 1's and performs additional signal processing and / or conversion before supplying them to the first mixer 24. The first mixer 24 modulates the carrier having the frequency ω with this code. The last bit is provided to a second XOR gate 38. When the bit is 0, the second XOR gate 38 changes the sign of the length 8 Walsh code from the second modulator 34. The resulting modified Walsh code _Qout is supplied to the signal circuit 23. The signal circuit 23 changes all 0's to 1's and performs additional signal processing and / or conversion before supplying it to the second mixer 26. The second mixer 26 modulates with this code a 90 ° shifted version of the carrier at frequency ω. If -1 is used instead of 0, a multiplexer can be used instead of the first and second XOR gates 36 and 38 to change the sign of _Iout and _Qout . Finally, the carrier modulated at I _out and Q _out
Are combined and transmitted. Thus, the M-array quadrature modulation (MO
K) In system 30, 8 bits of incoming data are divided into 4 bits for the I branch and 4 bits for the Q branch. The three data bits on the I branch are encoded into an 8-chip code, and the three data bits on the Q branch are encoded into an 8-chip code in parallel. Each of the last two bits encodes information by determining the sign of an 8-bit symbol, so that the M-Array Quadrature Modulation (MOK) system 30
The data bits are encoded into two codes, both of which are picked up from a set of 16 possible codes. In the embodiment of FIG. 3, there are eight modified Walsh codes, and by inverting them, 16 codes can be obtained. 1.375 MSps symbol rate and 8 bits /
With symbols, the data rate of the M-ary quadrature modulation (MOK) system 30 is 11 MBps.

FIG. 4 shows the relationship between packet error rate and delay spread for a multi-fading channel under the condition that 8 bits per symbol, 11 Mbps, and a 4-tap channel matched filter known to those skilled in the art. -A comparison is made between a case where an array orthogonal modulation (MOK) system uses a Walsh code modified by a conventional cover sequence and a case using a modified orthogonal code according to the present invention. Curve 40 is similar to conventional system 10.
Cover sequence (11111100) as in the method of
Curve 42 corresponds to the case where digital modulation is performed using the Walsh code modified with the complement code (11101011), as in the case of the present invention, corresponding to the case where digital modulation is performed using the modified Walsh code. Corresponding. The channel model used for comparison assumes an exponentially decaying power delay characteristic and an independent Rayleigh fading path. From FIG. 4, it can be seen that the system achieves a packet error rate of about 1% or 10% when using the complement code (curve 42) compared to using other codes (curve 40). It can be seen that the delay spread can be increased by 50%.

FIG. 5 shows an M-array quadrature modulation (MOK) system 50 that can be used as a fallback mode for M-array quadrature modulation (MOK) system 30 (FIG. 3).
Is shown. Also in this embodiment, the input data is scrambled by the scrambler 12 according to the IEEE 802.11 standard. This data is supplied to the serial / parallel converter 52. In this embodiment, converter 52 generates 5-bit data symbols in parallel at a data symbol rate of 1.375 MSps. Three bits from this 5-bit data symbol are received by modulator 54. Modulator 54 encodes the three bits into a modified Walsh code of length 8 according to the principles of the present invention. This Walsh of length 8
The code is provided to both the I branch 56 and the Q branch 58. In this particular embodiment of FIG. 5, the same code is provided to a plurality of phase modulation paths or branches, and thus, on a plurality of phase modulation paths (in this embodiment, on I branch 56 and Q branch 58). 2), a fallback mode using independent phase modulation of the same code, for example, quadrature phase shift modulation (QPSK) or 8-phase shift modulation (8-PSK) is possible. On the I branch 56, the 8-chip modified Walsh code is supplied in series to the first XOR gate 60, and on the Q branch 58, the 8-chip modified Walsh code is supplied in series to the second XOR gate 62. One of the remaining two bits from the serial / parallel converter 52 is supplied to a first XOR gate 60, based on which the sign of the modified Walsh code of length 8 is adjusted, and consequently , I branch is generated on the I branch 56. The other bit is provided to a second XOR gate 62, based on which the sign of the modified Walsh code of length 8 is adjusted, resulting in Q _out on Q branch 58.
Is generated. Depending on the implementation, a multiplexer may be used instead of the first and second XOR gates 60, 62 if -1 is used instead of 0. Thus, a data symbol of 5 bits / symbol and 1.375 MBp
When the symbol rate of s is used, the data rate of this embodiment is 6.8 MBps.

FIG. 6 shows the relationship between the packet error rate of the multipath fading channel and the spread of the delay (ns) by (1) a Walsh code modified by a cover sequence (111111000) as in the case of the conventional system. And when quadrature phase shift modulation (QPSK) is used at a fallback rate of 6.8 Mpbs (curve 63), (2) Walsh code modified with complement code (for example, 11101011) and 8-phase shift modulation When (8-PSK) is used at a speed of 8.25 Mbps (curve 64), and (3) a complement code (for example, 111010)
The Walsh code modified in 11) and quadrature phase shift keying (QPSK) at 6.8 Mbps using the same code on the I and Q branches (curve 65) are shown for comparison. The channel model used in this comparison assumes an exponentially decaying power delay profile and an independent Rayleigh fading path.
FIG. 6 shows that the use of the code proposed by the present invention more than doubles the resistance to the spread of delay. In addition, as can be seen from FIG. 6 (from curve 64), this digital modulation system replaces quadrature phase shift modulation (QPSK) with an alternative modulation scheme, eg, 8-phase shift modulation (8-PSK). Can be used with a higher data rate (8.25Mbps)
Can be obtained without significant loss of delay spread performance.

FIG. 7 illustrates another M-array quadrature modulation (MO) that can be used as a fallback mode for the M-array quadrature modulation (MOK) system 30 (FIG. 3).
K) System 66 is shown. The input data is scrambled by the scrambler 12 according to the IEEE 802.11 standard. The scrambled data is supplied to a serial / parallel converter 68. The serial / parallel converter 68 in this embodiment converts the 4-bit data symbol to 1.37.
Generated in parallel at a symbol rate of 5 MSps. Three bits from this 4-bit data symbol are received by modulator 70. Modulator 70 encodes these three bits into a modified Walsh code of length 8 according to the principles of the present invention. The modulator 70 generates this length 8 Walsh code in series at a rate of 11 MHz. This modified Walsh code of length 8 is
XOR gate 72 corresponding to both branch and Q branch
Supplied to By multiplying the modified Walsh code of length 8 by the remaining one bit of the data symbol from the serial / parallel converter 68, the sign of the code of length 8 is adjusted, and I _out and Q _out are connected in series. Generated. By realization, 0
If -1 is used instead of, a multiplexer can be used instead of the XOR gate 72. Thus, a data symbol of 4 bits / symbol and 1.375 MBp
When the symbol rate of s is used, the data rate of this embodiment is 5.5 MBps.

FIG. 8 shows a digital demodulation system 76 used at a receiver (not shown) for receiving a code transmitted from a transmitter (not shown) that uses the digital modulation system described above. This digital demodulation system 7
6 receives the modified orthogonal code according to the principles of the present invention. The digital demodulation system 76 generates a corresponding data symbol in response to the modified orthogonal code. Depending on the implementation, the code chips and / or data bits can be parallel or serial.

FIG. 9 illustrates a demodulation system 80 that uses a digital demodulation system according to the principles of the present invention. In this particular embodiment, the received signal is provided to both I branch 82 and Q branch 84 of demodulation system 80. The first mixer 86 adds cosωt to the received signal.
(Where ω represents the frequency of the carrier) to extract the modulated I information, and the second mixer 88
The modulated Q information is extracted by multiplying the received signal by sinωt. After low-pass filtering, these I and Q information are
0, 92. In the embodiment shown in FIG.
Each of the correlator blocks 90, 92 includes eight correlators for correlating the time delayed versions of the I and Q information. Code discovery blocks 94, 96
Finds a known modified orthogonal code that gives the highest correlation magnitude to the I and Q information, respectively, according to the principles of the present invention. A demodulator 76 (FIG. 8), or a portion thereof, for decoding a known orthogonal code into corresponding data bits, depending on the implementation, may have code discovery blocks 94, 96.
Performing the operations within the code discovery block 94,
It is also conceivable to receive the output from 96. Further, depending on the implementation, the digital demodulation system 76 (FIG. 8), or a portion thereof, may be implemented within the code discovery blocks 94, 96 to decode the modified orthogonal code into corresponding data bits, and the code detection block 98. , 100, at a location branched off from the I path 82 and the Q path 84, or at the output of the code detection blocks 98, 100. In the embodiment of FIG.
8, 100 each decode additional data bits from each code of the discovered modified orthogonal code.

FIG. 10 illustrates a fallback mode for a demodulation system 80 (FIG. 9) that receives code symbols from a modulator system 50 (FIG. 5) in which the same code is transmitted on multiple modulation paths. 2 shows a demodulation system 110 that can be used (at back speed). Demodulation system 110 is a full-speed demodulation system 88 of FIG.
The difference is that the code finding block 112 uses the I correlator 9
The sum of the squared correlation output of the 0 and Q correlators 92 is to detect a modified orthogonal code according to the principles of the present invention that gives the highest composite correlation magnitude. In this particular embodiment, the same codes for digital demodulation are
In both of the paths 84, the phase detection block 114
Find the modified orthogonal code with the highest composite correlation magnitude. The demodulator 76, or a portion thereof, for decoding the modified orthogonal code into corresponding data bits may perform operations within the code discovery block 112, or may operate upon receiving output from the code discovery block 112, depending on the implementation. It is also conceivable to carry out. Further, depending on the implementation, the digital demodulation system 76 (FIG. 8) or a portion thereof may be implemented within the code discovery block 112 to decode the modified orthogonal code and generate corresponding data bits. It may be realized in the path 114, at a place branched off from the path 115, or at the output of the phase detector 114. The phase detector 114 detects the phase of the composite correlation output and composites 2 additional bits per code for QPSK and 3 additional bits per code symbol for 8-PSK.

In addition to the embodiments described above, omissions, additions, and / or additions to elements of the described system may be made without departing from the principles of the present invention.
Various alternative configurations of the digital (demodulation) modulation system are possible, including variations or only partial use.
For example, in the above application, the digital modulation scheme includes a quadrature phase shift modulation (QPSK) phase shift modulation scheme (FIGS. 1, 3, and 5) and a binary phase shift modulation (BPSK) scheme (FIG. 6). Although used, as will be appreciated by those skilled in the art, digital modulation schemes include amplitude modulation, including quadrature amplitude modulation (QAM), and other phase modulation schemes, including 8-phase shift modulation (8-PSK). Can also be used. In addition, although the above description of the digital modulation system has described that the orthogonal code of 1 and 0 is used and this is modified by 1 and 0, the digital modulation system according to the present invention includes:
Depending on the implementation, orthogonal codes of 1 and −1 may be used and modified by 1 and 0. Further, in the above description of the embodiment, the codes of 1 and -1 are received at the receiver, and 1 and -1 are used in determining the correlation.
However, this demodulation system may have 1 and 0 depending on the implementation.
At the receiver, and 1 and -1 can be used in determining the correlation.

Furthermore, while the digital modulation system has been described above as using particular elements in a particular configuration, the digital modulation system according to the present invention may have a different configuration than the description. It may also operate in connection with a different process than described. In addition, various elements that make up the digital modulation system according to the invention,
The operating parameters and characteristics of each of these elements are properties that must be properly adapted to the operating environment so that correct operation can be ensured. The digital modulation system according to the present invention and portions thereof, as will be readily understood by those skilled in the art, can be implemented in application specific integrated circuits, software driven processing circuits, firmware, lookup tables, and other arrays of discrete elements,
Optionally, it can be realized without detracting from the benefits of the present invention. The above description is intended solely to illustrate the application of the principles of the present invention, and will be understood by those skilled in the art to have a strict sense of the several embodiments described above for purposes of explanation. However, various other modifications to the above described apparatus and method of the present invention are possible without departing from the spirit and scope of the present invention.

[Brief description of the drawings]

FIG. 1 shows a block diagram of an M-array quadrature modulation (MOK) system using a Walsh code modified by a cover sequence (11111100).

FIG. 2 shows in a block diagram a digital modulation system using a modified orthogonal code according to the invention to reduce the autocorrelation side lobes of the orthogonal code.

FIG. 3 is a block diagram illustrating one embodiment of a MOK system according to the principles of the present invention.

FIG. 4 shows the relationship between the packet error rate and the delay spread achieved by the MOK system using the Walsh code modified by the cover sequence and the modified orthogonal code according to the present invention for reducing the autocorrelation side lobe. It is a graph shown comparatively about the case where it was used.

FIG. 5 is a block diagram illustrating another embodiment of a MOK system according to the principles of the present invention.

FIG. 6 shows the relationship between the packet error rate and delay spread of the MOK system, which is transformed by a cover sequence into Walsh.
5 is a graph showing a comparison between a case where a code is used and a case where a modified orthogonal code according to the present invention for reducing autocorrelation side lobes is used.

FIG. 7 is a block diagram illustrating another embodiment of a MOK system according to the principles of the present invention.

FIG. 8 illustrates a digital demodulator according to some principles of the present invention.

FIG. 9 illustrates a demodulation system using a digital demodulator according to some principles of the present invention.

FIG. 10 illustrates another embodiment of a demodulation system using a digital demodulator according to some principles of the present invention.

[Explanation of symbols]

 12 Scrambler 14 Serial / Parallel Converter 21, 23 Signal Circuit 24, 26 Mixer 28 Digital Modulator 30 M-Array Quadrature Modulation (MOK) System 32, 34 Modulator 36, 38 XOR Gate 76 Demodulator 80 Demodulation System 82 I Branch 84 Q branch 86 Mixer 90, 92 Correlator block 94, 96 Code discovery block 98, 100 Code detection block

Claims (12)

[Claims] 1. A method for processing information bits, the method comprising: responsive to said information bits of a set,
Generating a modified code, wherein the modified code is obtained by modifying an orthogonal code, and wherein an autocorrelation side lobe of the modified code is less than half the length of the modified code. 2. The method of claim 1, wherein the step of generating a modified code comprises: modifying the orthogonal code using a complement code. 3. The method of claim 1, wherein the step of generating a modified code comprises: using a Walsh code as the orthogonal code. 4. The method of claim 1 wherein said step of generating a modified code comprises: generating said modified code as one of M modified codes in response to log ₂ M bits of a set. 5. The modified code generating step includes: a length M.
5. The method according to claim 4, wherein the modified code is generated.
the method of. 6. The method of claim 5, wherein said length M is eight. 7. The method according to claim 1, further comprising the step of supplying the modified code to a plurality of modulation paths, wherein the modified code is modulated on the plurality of modulation paths.
the method of. 8. A method for demodulation, wherein a demodulator generates a corresponding set of data bits in response to a modified orthogonal code, wherein the modified orthogonal code is obtained by modifying the orthogonal code. The method wherein the autocorrelation side lobe of the modified code is less than half the length of the modified orthogonal code. 9. A method for processing information bits, the method comprising: generating a modified Walsh code in response to the set of information bits, wherein the modified Walsh code is generated.
A method wherein the sh code is transformed from the Walsh code using a complement code. 10. A method for demodulation, the method comprising: generating a corresponding set of information bits in response to a modified Walsh code, wherein the modified Walsh code uses a complement code from the Walsh code. A method characterized by having been deformed. 11. A digital modulation system, the system comprising: a modulator responsive to a set of information bits to generate a modified code, wherein the modified code is obtained by modifying an orthogonal code. A digital modulation system, wherein the autocorrelation sidelobe of the code is less than half the length of the orthogonal code. 12. A digital modulation system, comprising: a modified Walsh in response to a set of information bits.
A digital modulation system, comprising a modulator for generating a code, wherein the modified Walsh code is modified using a complement code from the Walsh code.