WO2003071702A1

WO2003071702A1 - Modulating and demodulating methods for increasing the transmitting rate and improving the ber in cdma communication system

Info

Publication number: WO2003071702A1
Application number: PCT/KR2003/000318
Authority: WO
Inventors: Hyung-Yun Kong
Original assignee: Hyung-Yun Kong
Priority date: 2002-02-21
Filing date: 2003-02-14
Publication date: 2003-08-28
Also published as: AU2003207396A1; KR20030069528A; KR100478255B1

Abstract

Modulating and demodulating methods for increasing the transmission rate and improving the BER in the CDMA communication system, wherein the modulating method comprises the steps of: separating data for transmission into plurality of groups, every group comprising predetermined number of data bits; multiplying the predetermined number of data bits belonging to each group by a first set of orthogonal codes to generate a coded signal, the coded signal being created for every group; and multiplying the plurality of the coded signals by a second set of orthogonal codes, wherein the demodulating method comprises the steps of: multiplying received signals by the second set of orthogonal codes to recover the plurality of coded signals; and multiplying the recovered coded signal by the first set of orthogonal codes to recover data bit for each group, wherein the first set of orthogonal codes is a lower half code of a biorthogonal code in the second set of orthogonal codes.

Description

MODULATING AND DEMODULATING METHODS FOR INCREASING THE TRANSMITTING RATE AND IMPROVING THE BER IN CDMA COMMUNICATION SYSTEM

FIELD OF THE INVENTION

The present invention relates to modulating and demodulating methods for a CDMA system and, more particularly, to modulating and demodulating methods for transmitting data with a high transmission rate and a relatively low bit error rate

BACKGROUND OF THE INVENTION

In general, the transmission of digital signals has an advantage in that it is less sensitive to noise, has less distortion and is higher in transmission efficiency On the other hand, there is a disadvantage in that it calls for a broader bandwidth and is complex.

Recently, digital methods have been widely used due to relatively lower error occurrences, higher credibility and development of circuit technologies

In digital communications, there are many kinds of demodulating methods. To begin with, the Quadrature Phase Shift Keying (QPSK) and Quadrature Amplitude Modulation (QAM) methods generally used in CDMA communication systems will be briefly described

First, the QPSK method will be explained with reference to FIG 1 When a data bit stream is inputted to a Seπal-to Parallel (S/P) converter 100, the S/P converter 100 classifies the bit stream into I and Q channels. The signal classified into an I channel is multiplied by a cosine wave at a multiplier 114 to become an I channel signal while the signal classified into Q channel is multiplied by a sine wave at a multiplier 124 to become a Q channel signal. Then, the I channel signal and the Q channel signal are combined at a combiner 102 to be transmitted on a carrier wave.

Meanwhile, a signal processing at a receiving end is performed in a reverse manner to the signal processing at the transmitting end. In other words, a received signal is removed of the carrier wave at the receiving end, and the signal removed of the carrier wave is multiplied by a cosine wave to recover the signal classified as I channel, and the signal removed of the carrier wave is multiplied by a sine wave to recover the signal classified as Q channel.

As noted above, data is phase-modulated for transmission in the QPSK method such that the number of channels is doubled in comparison with the method with no phase-modulation.

In the QAM method, both the phase modulation and amplitude modulation are performed to transmit a much larger amount of data at one time, such that the transmission rate thereof is superior to that of the QPSK method.

Now, the QAM method will be explained with reference to FIG. 2. When data bit streams are inputted into an S/P converter 200, the input signal is converted into a parallel signal to be inputted into a QAM mapper 210. The QAM mapper 210 maps the input signal into an amplitude value, and classifies the value into I channel and Q channel alternatively. The method thereafter is the same as that of the QPSK. A detailed explanation of the mapping process is provided below at Table 1. TABLE 1

When bit streams are inputted into a QAM mapper, the QAM mapper binds input bit streams into a bundle, for example, a bundle of 3 bits each, and changes the value thereof using the Gray code stored in ROM which is used as an amplitude value.

As shown in Table 1, in the case of a 64 QAM, the 3-bit bundle is mapped as one amplitude value such that triple the transmitting channels are established in comparison with the QPSK method, and in the case of a 256 QAM, four times the transmitting channels are established.

However, when the QAM level is increased while limiting the transmitting power, the gaps between the Gray code get inevitably narrowed. Then, the correlation between the channels increase and interference of the signals between the channels also increase, which raises the Bit Error Rate (BER) performance at the receiving end. This can be easily noticed via experimental data in FIG. 8 where the BER between 16 QAM, 64 QAM and 256 QAM are compared.

So far, explanations have been made about modulation and demodulation methods mainly used in the CDMA communication system, transmitting efficiency and BER. However, as users' demands on quality, service and convenience in the mobile or Radio Frequency (RF) communication systems vary considerably these days, it has come to the point that the conventional modulation and demodulation methods cannot provide enough transmitting efficiency and BER performance to meet these demands.

Particularly, even the International Mobile Telecommunιcatιon-2000

(I MT-2000) , soon to be commercialized, has a maximum transmitting speed of 2Mbps, and it is expected that this speed can hardly provide a multi-service required by users. With these problems in mind, a variety of studies are being briskly under way in many countries to overcome the limitations on usable frequencies and RF technologies and to improve the transmitting efficiency and the BER performance. Some of the examples now being progressed include Beam-forming antenna technologies, Multiply Input Multiple Output (MIMO) antenna technologies, coding technologies (Space Time Processing Coding (STPC), Turbo Code, Concentrated Coding, etc ) and Space Time Trellis Coding (STTC)

Meanwhile, the present invention will try to overcome the limitations of the conventional technologies by introducing newer and more effective modulation and demodulation methods.

SUMMARY OF THE I NVENTION

The present invention is disclosed to overcome the conventional limitations thus described by increasing the transmission rates and to relatively decrease the BER performance. In other words, the object of the present invention is to provide modulation and demodulation methods configured to establish a larger number of transmission channels in the same frequency bandwidth as that of the prior art to increase the transmission rates and to relatively improve the BER performance. The present invention provides modulating and demodulating methods for increasing the transmission rate and improving the BER in CDMA communication systems, wherein the modulating method comprises the steps of' separating data for transmission into a plurality of groups, every group comprising a predetermined number of data bits; multiplying the predetermined number of data bits belonging to each group by a first set of orthogonal codes to generate a coded signal, the coded signal being created for every group; and multiplying the plurality of the coded signals by a second set of orthogonal codes, wherein the demodulating method comprises the steps of: multiplying received signals by the second set of orthogonal codes to recover the plurality of coded signals; and multiplying the recovered coded signal by the first set of orthogonal codes to recover data bits for each group, wherein the first set of orthogonal codes is a lower half code of a biorthogonal code in the second set of orthogonal codes

BRIEF DESCRIPTION OF THE DRAWINGS

For better understanding of the nature and objects of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a structural drawing for describing QPSK modulating and demodulating methods according to the prior art;

FIG 2 is a structural drawing for describing QAM modulating and demodulating methods according to the prior art;

FIG. 3 is a block diagram for illustrating a signal processing procedure in modulating and demodulating methods according to a first aspect of the present invention;

FIG. 4 is a structural drawing for illustrating a signal processing procedure in a second aspect of the present invention wherein the characteristic structure of the present invention is applied to QPSK modulating and demodulating methods;

FIG. 5 is a signal processing procedure in a third aspect of the present invention wherein the characteristic structure of the present invention is applied to plural QPSK systems;

FIG. 6 is a signal processing procedure in a fourth aspect of the present invention wherein the characteristic structure of the present invention is applied to QAM modulating and demodulating methods;

FIG. 7 is a signal processing procedure in the fourth aspect of the present invention wherein the characteristic structure of the present invention is applied to QAM modulating and demodulating methods;

FIG. 8 is a graph that compares the BER between a case using one to three 16 QAM mappers and a case using two 64 QAM mappers in the fourth aspect of the present invention and a case using the conventional 16, 64 and 256 QAM; and

FIG. 9 is a graph that compares the BER between a case of the conventional QPSK method and a case using two or three QPSK systems in an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In order to classify signals per channel in a conventional CDMA communication, a signal from each channel is multiplied by an orthogonal code at the transmitting end and a signal received from the receiving end is again multiplied by the orthogonal code to recover the original code. However, the number of channels recognizable by the above-mentioned method is only 64 channels when the orthogonal code is a 64x64 Walsh code. However, in the present invention as illustrated in FIG. 3, data to be transmitted from the transmitting end is multiplied by sub Walsh codes (BWl , BW2) and again is multiplied by a main Walsh code, whereby a much larger number of channel classifications is possible such that much larger amount of data can be transmitted at one time. As a result, data can be transmitted at a faster rate even though the same frequency bandwidth is Used. Furthermore, modulating and demodulating methods meeting the users' requirements can be provided by improving the transmission rate.

Hereinafter, a detailed description will be provided with reference to FIG. 3.

BWl and BW2 are sub Walsh codes comprising a first set of orthogonal codes, and MW1 to MWn are main Walsh codes comprising a second set of orthogonal codes.

Data to be transmitted is divided into n groups, and data composed of 2 bits belonging to each group is multiplied by sub Walsh codes (BWl, BW2) and combined. The combined values are respectively multiplied by main Walsh codes corresponding thereto and combined, and transmitted. The original data bits are recovered via reverse procedures thereof at the receiving end.

At this time, the sub Walsh codes should be the lower half codes of the biorthogonal codes of the main Walsh codes to recover the original codes.

If the sub Walsh codes are the upper half codes of the biorthogonal codes of the main Walsh codes, the shape of the sub walsh codes may be identical to that of the main Walsh codes. Then, data cannot be properly recovered.

However, the shape of the lower half codes of the biorthogonal codes is not identical to that of the main Walsh codes, such that the lower half codes of the biorthogonal codes are proper to be used as the sub Walsh codes.

Meanwhile, it is preferable that a sub Walsh code is the shortest orthogonal code of 4x4 for using frequency bandwidth effectively.

The second aspect of the present invention applies the modulating and demodulating methods thus described to the conventional QPSK modulating and demodulating methods. The modulating method comprises the steps of : classifying data bits for transmission into I channel and Q channel; multiplying the plurality of bits classified as I channel by I channel-orthogonal codes and adding the result to generate I channel coded signals; multiplying the plurality of bits classified as Q channel by Q channel orthogonal codes and adding the result to generate Q channel coded signals; and multiplying the I channel coded signals and Q channel coded signals by cosine waves and sine waves, respectively. The demodulating method comprises the steps of multiplying received signals in receiver by cosine waves and sine waves respectively to recover the I channel coded signals and the Q channel coded signals; multiplying the recovered I channel coded signals by the I channel-orthogonal codes to recover the bits classified as I channel and multiplying the recovered Q channel coded signals by the Q channel orthogonal codes to recover the bits classified as the Q channel; and recovering the data bits from the bits classified as I channel and Q channel.

Hereinafter, a detailed description will be explained with reference to FIG. By way of example, when data bit stream of 8 bits is inputted into the S/P converter 300, the S/P converter 300 classifies the data bit stream into the I channel and Q channel each by 4 bits. The signals classified as I channel (11 to 14) are respectively multiplied by I channel orthogonal codes (BW11 to BW14) via multipliers (311 to 314) to be combined by a combiner (350). Meanwhile, the signals classified as Q channel are also combined by a combiner (352) in the same processes as mentioned above.

The I channel coded signals and the Q channel coded signals thus obtained are respectively multiplied by a sine wave and cosine wave at multipliers (370, 372). The I channel coded signals and the Q channel coded signals multiplied by the cosine wave and sine wave are combined by a combiner (380), and the combined signals are multiplied by the carrier wave at a multiplier (390) to be transmitted.

Meanwhile, the received signals are removed of the carrier wave at the receiving end and are respectively multiplied by a cosine wave and sine wave Then, the I channel coded signals and the Q channel coded signals are recovered. The recovered I channel coded signals are multiplied by the I channel orthogonal codes to recover signals classified as Q channel, and the recovered Q channel coded signals are multiplied by Q channel orthogonal codes to recover signals classified as Q channel. Original data bit stream is recovered from the signals recovered and classified as I channel and Q channel.

The present invention includes the step of multiplying data by the I channel orthogonal codes and Q channel orthogonal codes at the transmitting end and the receiving end such that data can be transmitted in channels the number of which are double the number of I channel orthogonal codes (or the number of Q channel orthogonal codes). As a result, it is determined that the transmission rate is far superior to that of the prior QPSK and the BER performance is also excellent.

As described above, the reason the present invention has an excellent transmission rate is that channels can be further classified by the I channel orthogonal codes and the Q channel orthogonal codes.

Meanwhile, it should be noted that the I channel orthogonal codes and Q channel orthogonal codes may be identical because the I channel coded signals and Q channel coded signals are respectively multiplied by a cosine wave and sine wave to be modulated in phases by as much as 90 degrees, whereby channels can be classified even though the I channel orthogonal codes and Q channel orthogonal codes are identical.

Furthermore, it is preferable that the shortest orthogonal code of 4x4 walsh code should be used for orthogonality and efficiency. If the above described second aspect of the present invention is summarized as the principal structure of the present invention applied to a single QPSK system, a third aspect of the present invention is the same as the principal structure of the present invention applied to a plurality of QPSK systems.

Hereinafter, the third aspect of the present invention will be described with reference to FIG. 5.

The third aspect of the present invention couples plural QPSK systems in parallel and each QPSK system uses I channel orthogonal codes and Q channel orthogonal codes. Each QPSK system uses different modulated frequencies such that additional channels as many as the number of QPSK systems can be further formed.

The operational principle of the third aspect is the same as that of the second aspect of the present invention except that a plurality of QPSK systems are used and a step of combining plural I channels and combining plural Q channels is add wherein frequencies modulating the channels are different among the channels. Therefore, further explanation thereto is omitted.

Next, a fourth aspect of the present invention is an application where the featured structure of the present invention is applied to QAM modulation and demodulation methods and is described with reference to FIG. 6.

When data bit streams (0, 1, 1, 1, 0, 1, 0, 0) to be transmitted are inputted into an S/P converter 400, some of the signals (for example, 0, 1, 0, 0) among the input signals are inputted into a first mapper (412) (16 QAM mapper) and the input signals are converted into a single symbol per every 2 bit.

T A B L E 2

In other words, the input signals (0, 1 , 0, 0) are converted into, by way of example, (I I, 12)= (3, 1) according to the Gray code disclosed in Table 2. Meanwhile, some signals (1, 1 , 1, 0) among the input signals are converted into a single symbol per every 2 bits by a second mapper (422). In other words, the input signals (1, 1, 1, 0) are converted into (Ql, Q2)=(-3, -1) as per the Gray code disclosed in Table 2. As a result, 8 signals are converted into 4 signals through these mapping processes. Thereafter, serial signals (I I, 12) and (Ql, Q2) are classified into parallel signals respectively by two S/P converters (414) and (424).

Then, signals classified as I channel are multiplied by I channel orthogonal codes at the multiplier (416, 418) and combined at combiner (430) to generate I channel coded signals. Signals classified as Q channel are multiplied by Q channel orthogonal codes at the multiplier (426, 428) and combined at combiner (440) to create Q channel coded signals. I channel coded signals are multiplied by a cosine wave at the multiplier (436) and Q channel coded signals are multiplied by a sine wave at the multiplier (446) and combined, and again multiplied by a carrier wave to be transmitted.

With reference to FIG. 7, a demodulating process is performed in the reverse way of the modulating one, where signals classified as I channel and Q channel are recovered and are demapped through a QAM demapper, thereby recovering the original transmitted data signals.

In other words, the carrier wave is initially removed from the received signals to which cosine wave and sine wave are respectively multiplied and , passed through a Low Pass Filter (LPF) to recover I channel coded signals and Q channel coded signals.

The I channel coded signals pass through multipliers (518, 519) and integrators (514, 516) to become (I I, 12), and the Q channel signals pass through multipliers (528, 529) and integrators (524, 526) to become (Ql , Q2).

These values are demapped by a demapper (500) to become original data bit streams.

Although the fourth aspect of the present invention has used two 16

QAM mappers, it is noted that the number of QAM mappers can be increased to form further channels ( the number of I channel orthogonal codes or Q channel orthogonal codes are the same as that of QAM mappers ) and either the 64 QAM or 256 QAM mapper can be used instead of the 16 QAM mapper. FIG. 8 is a graph for illustrating the performance between the conventional QAM method and the present invention. In other words, BERs are illustrated for a case of the conventional 16,64,256 QAM, a case where one to three 16 QAM mappers are used in the fourth aspect of the present invention and a case where two 64 QAM mappers are used.

According to FIG. 8, it can be shown that as the number of bit of QAM is increased, the transmission rate is increased, and the BER is also increased. It can be also noticed in the present invention that, when the number of QAM mappers is increased, the transmission rate and the BER are increased However, it should be noted that the increase of the transmission rate in relation to the increase of the number of the QAM mappers demonstrates a much more excellent effect even though a degradation of BER is taken into account.

For example, if a comparison is made between a case where one to three 16 QAMs are used in the modulating and demodulating methods disclosed in the fourth aspect of the present invention and a case where 16 QAM is used in the prior art, it can be noted that the BER is much lower in the present invention, and the transmission efficiency is increased as the number of QAM is increased in the fourth aspect of the present invention. These results are also identically demonstrated in 64 QAM and 256 QAM as illustrated in the figure drawings

Meanwhile, Fig. 9 is a graph for illustrating a comparison between performance of the present invention and that of the conventional QPSK method, where QPSK (two w2) indicates a case when two QPSK systems and two sub Walsh codes are used and possesses four times the transmission rate of the conventional QPSK method. However, although there is shown a high transmission rate, it can be noted in FIG. 9 that the BER is not so high compared with that of the conventional QPSK method.

Furthermore, QPSK (three 3w) shows a case when three QPSK systems and three sub Walsh codes are used and has nine times the transmission rate of the conventional QPSK method. However, as described in the foregoing, it can be noticed that the present invention boasts an excellent performance of modulating and demodulating methods with a rapid increase of transmission rate albeit relatively less BER.

Although the present invention may be embodied in several other forms without departing from the spirit or essential characteristics thereof, the present embodiments are therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than the description preceding same, and those skilled in the art will recognize with considerable modification within the scope of the appended claims.

As mentioned in the foregoing, there is an advantage in the modulating and demodulating methods for increasing the transmission rate and improving the BER in a CDMA communication system thus described in that the transmission rate is increased and the BET is improved compared with those of the conventional art, thereby enabling to transmit data at a higher speed.

Claims

WHAT IS CLAI MED IS:

1. Modulating and demodulating methods for increasing transmission rate and improving BER in the CDMA communication system, wherein the modulating method comprises the steps of:

separating data for transmission into a plurality of groups, every group comprising predetermined number of data bits;

multiplying the predetermined number of data bits belonging to each group by a first set of orthogonal codes to generate a coded signal, the coded signal being created for every group; and

multiplying the plurality of the coded signals by a second set of orthogonal codes,

wherein the demodulating method comprises the steps of:

multiplying received signals by the second set of orthogonal codes to recover the plurality of coded signals; and

multiplying the recovered coded signal by the first set of orthogonal codes to recover data bit for each group,

wherein the first set of orthogonal codes is a lower half code of a biorthogonal code in the second set of orthogonal codes.

2. The modulating and demodulating methods as defined in claim 1 , wherein the first set of orthogonal codes and the second set of orthogonal codes are

Walsh codes.

3. The modulating and demodulating methods as defined in claim 2, wherein the first set of orthogonal codes comprises 4x4 orthogonal codes.

4. Modulating and demodulating methods for increasing the transmission rate and improving the BER in a communication system, the modulating method comprising the steps of:

classifying data bits for transmission into I channel and Q channel;

multiplying the plurality of bits classified as I channel by I channel- orthogonal codes and adding the result to generate I channel coded signals;

multiplying the plurality of bits classified as Q channel by Q channel- orthogonal codes and adding the result to generate Q channel coded signals; and

multiplying the I channel coded signals and Q channel coded signals by cosine waves and sine waves, respectively,

the demodulating method comprising the steps of multiplying received signals in a receiver by cosine waves and sine waves respectively to recover the I channel coded signals and the Q channel coded signals;

multiplying the recovered I channel coded signals by the I channel- orthogonal codes to recover the bits classified as I channel and multiplying the recovered Q channel coded signals by the Q channel-orthogonal codes to recover the bits classified as the Q channel; and

recovering the data bits from the bits classified as I channel- and Q channel.

5. The modulating and demodulating methods as defined in claim 4, wherein the classifying step comprises a step of : classifying the data bits for transmission into a plurality of I channels and a plurality of Q channels, and the frequencies of the cosine waves (or sine waves) which is multiplied to plurality of I channel coded signals (or Q channel coded signals), respectively, are different from each other, and the modulating method further comprises a step of combining the plurality of I channel coded signals and Q channel coded signals multiplied by the cosine waves and the sine waves, respectively, and the modulating and the demodulating methods are performed in parallel relatively to the plurality of I channels and the plurality of Q channels.

6. The modulating and demodulating methods as defined in claim 4 or 5, wherein the I channel orthogonal codes and the Q channel orthogonal codes are

Walsh codes

7. The modulating and demodulating methods as defined in claim 4 or 5, wherein I channel orthogonal codes and the Q channel orthogonal codes are 4x4 codes.

8. Modulating and demodulating methods for increasing the transmission rate and improving the BER in a CDMA communication system, wherein the modulating method comprises the steps of : mapping data bits stream for transmission via a plurality of QAM mappers and classifying mapped signals into I channel and Q channel; multiplying the plurality of signals classified as I channel by I channel orthogonal codes and combining the same to generate I channel coded signals; multiplying the plurality of signals classified as Q channel by Q channel othogonal codes and combining the same to generate Q channel coded signals; and multiplying the I channel coded signals and Q channel coded signals by cosine waves and sine waves, respectively, wherein the demodulating method comprises the steps of : multiplying received signals by cosine waves and sine waves respectively to recover the I channel coded signals and the Q channel coded signals; multiplying the recovered I channel coded signals by the I channel orthogonal codes to recover the signals classi fied as I channel and multiplying the recovered Q channel coded signals by the Q channel orthogonal codes to recover the signals classified as the Q channel; and demapping the signals classified as the I channel and Q channel via QAM demapper to recover the data bit stream.

9. The modulating and demodulating methods as defined in claim 8, wherein the I channel codes and the Q channel codes are Walsh codes.

10. The modulating and demodulating methods as defined in claim 8 or 9, wherein I channel codes and the Q channel codes are 4x4 codes.