KR20030093177A - Apparatus and Design Method of Binary Constant Amplitude CDMA (CA-CDMA) Communication System Using a New Pre-Coding Scheme of code rate 1.0 - Google Patents

Abstract

PURPOSE: A binary CA-CDMA(Constant Amplitude CDMA) system using a new pre-coding technique, of which the code rate is 1, and a method for designing the same are provided to always fix the PAPR(Peak-to-Average Power Ratio) of an output signal as 0 dB by making a signal having a constant amplitude always outputted without a lowering of the bit rate due to a lowering of the code rate. CONSTITUTION: In the transmitter block of a binary 4-user CA-CDMA system, a parity signal extractor(2) extracts a parity signal(5) from b={b0,b1,b2,b3}, each user data(1). The extracted parity signal(5) is multiplied by the fourth user s signal(b3), and a signal inputted from each user has uneven numbers of +1 and -1. As signals composed of uneven numbers of +1 and -1 are multiplied by a Walsh Hardmard sequence Wn(n=1,2,3,4) and the multiplied signals are combined, a signal(S), always composed of ±2, is obtained. As the last bit of the obtained signal(S) is multiplied by the parity signal(5), an output signal(6) satisfying a constant amplitude is outputted.

Description

Apparatus and Design Method of Binary Constant Amplitude CDMA (CA-CDMA) Communication System Using a New Pre-Coding Scheme of code rate 1.0}

In the code division multiple access (CDMA) communication system to which the present invention belongs, a high peak-to-average power ratio is obtained when multiple user data are combined or multiple channels are added at the same time. Ratio: hereinafter referred to as "PAPR". This high PAPR causes nonlinear distortion in the high power amplifier (HPA), causing interference in the band as well as interference to adjacent channels, as well as significantly reducing the power efficiency of the high output amplifier. Therefore, it is very important to reduce the high PAPR to low PAPR that occurs when multiple user channels are combined or data is added.

Examples of Peak to Average Power Ratio (PAPR) reduction techniques invented or reported so far in a CDMA communication system include:

1) In September 2002, K. Sathananthan and C. Tellambura published the Vehicular Technology Conference , vol. A method of reducing PAPR caused by multi-user signals in CDMA as described in Fig. 1 is called a partial transmit sequence ("PTS") and selective mapping ("SLM"). field,

2) In September 2002, O. Vaananen, J. Vankka and K. Halonen published IEEE Seventh International Symposium on Spread Spectrum Techniques and Applications, vol. PAPR reduction technique in CDMA system using clipping method, presented in 2

3) December 1997 by T. Wada, T. Yamazato, M. Katayama and A. Ogawa. Fundamentals, vol. Multi-code CDMA system with constant amplitude using pre-coding, presented in E80-A,

4) In November 2000, S. I. Kim, G. Y. Jung, S. Y. Yoon and H. S. Lee presented IEICE Trans. Commun. vol. A multicode wideband CDMA system with constant amplitude using the more advanced pre-coding presented in E83-B has been presented.

However, the PTS and SLM techniques have the advantage of reducing PAPR without distortion of the signal, but show limitations in the reduction, and have disadvantages such as transmission of side information using a large amount of computation and additional channels. And since the clipping technique distorts the signal itself, it has the advantage of reducing the PAPR as much as desired, but since the clipped signal is not completely recovered by the receiver, the bit error rate (hereinafter referred to as "BER") of the system It has the disadvantage of being very bad.

On the other hand, the precoding technique is the base technology of the present study, and the PAPR reduction performance is excellent because it always outputs a constant signal without distorting the signal. However, the precoding technique presented in the previous studies has two major disadvantages. One is that as the number of users in the system increases, additional channel signals are used instead of user information for precoding, resulting in a loss of signal rate. to be.

The present invention invents a new precoding having a code rate of 1, and in a CDMA communication system, 1) always outputs a signal having a constant amplitude without a decrease in transmission rate due to a decrease in the code rate, thereby making the PAPR of the output signal always 0 dB. 2) Constant amplitude CDMA (Constant Amplitude Code Division Multiple Access (CDMA)) design method and device configuration which is easy to expand the system as the number of users increases. . This method can be applied without extending the bandwidth of the system.

In order to achieve the above object, the present invention implements a 4-user CA-CDMA having a code rate of 1 and always outputting a constant signal by using a parity signal obtained from an input user signal. It's a 4x expansion system.

1 is a block diagram of a transmitter of a binary 4-user CA-CDMA system.

2 is a receiver block diagram of a binary 4-user CA-CDMA system.

3 is a comparison table of output signals for user inputs of a 4-user system.

4 is a block diagram of a transmitter of a binary 16-user CA-CDMA system.

5 is a block diagram of a transmitter of a binary 16-user CA-CDMA system.

6 shows the output signal level of normal 16-user CDMA

7 shows the output signal level of the proposed 16-user CA-CDMA.

※ Explanation of the code about the main part of FIG.

(1) 4 user input data

(2) parity signal extraction block

(3) serial / parallel conversion block

(4) bottle / serial conversion block

(5) extracted parity signal

(6) output signal

※ Explanation of codes for main parts of Figure 2

(7) received data

(2) parity signal extraction block

(3) serial / parallel conversion block

(4) bottle / serial conversion block

(5) extracted parity signal

(8) User Signal Restoration Block

(9) restored user signal

※ Explanation of codes for main parts of Figure 4

(10) 16 user input data

(11) Binary 4-user CA-CDMA Transmitter

12 output signal

※ Explanation of the code about the main part of FIG.

(13) received signal

(14) Binary 4-user, CA-CDMA Receiver

(15) each restored user signal

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following description focuses on the parts necessary to understand the operation according to the present invention, it should be noted that the description of other parts will be omitted so as not to distract from the gist of the present invention.

In the present invention, the objective of the binary constant amplitude code division multiple access system using a new pre-coding technique is that a high PAPR occurs when multiple user data are combined or multiple channels are added simultaneously in an existing CDMA system. The problem is solved at the binary size level, enabling high performance and high efficiency data transfer. It also solves the problem of lowering the code rate, that is, reducing the data rate or increasing the bandwidth, which occurs in constant amplitude CDMA using other existing precoding.

The use of the present invention additionally solves the limitation of the expansion of the number of system users, which has been a problem in previous studies, which uses a parity signal obtained from the input user signal and has a code rate of 1 and is always constant. By implementing a 4-user CA-CDMA that outputs a signal and using it repeatedly, it can be extended to a system for increased users. As a result, the present invention solves the limitation of system expansion while maintaining the data transmission rate as it is, and solves the high PAPR problem completely by fixing the PAPR of the output signal to 0 dB at all times, and enables more stable and efficient communication.

1 shows a block diagram of a binary 4-user CA-CDMA system transmitter that is the basis of the binary CA-CDMA proposed in the present invention. In order to achieve the above object, the parity signal extractor 2 extracts a parity signal 5 from each input and data 1 b = { b ₀ , b ₁ , b ₂ , b ₃ } input. The parity signal 5 at this time can be obtained by the following equation.

[Equation 1]

The parity signal (5) thus obtained is multiplied by the signal b ₃ of the fourth user. The signal input from each user always has an odd number of + 1's and -1's. The signal S, which is an odd number of + 1's and -1's multiplied by the Walsh Hardmard sequence w _n ( n = 1, 2, 3, 4), is always ± 2. Since the signal S thus obtained always has an odd number of +2 and-, the first input signal can be distinguished by multiplying the parity signal 5 by the last bit, and always outputs an output signal 6 that satisfies the constant amplitude.

As an example, consider the case where the input signal b = [-1 -1 -1 -1]. The parity signal obtained by each data is -1, and the input signal converted by the parity signal is [-1 -1 -1. 1]. If the signal obtained by this process passes through WHT, the WHT output signal S is [-2 -2 -2 2], which is the same result as the first input is [-1 -1 -1 1]. To be done. The distinction between these two input signals can be made by multiplying the last bit of the signal S by the parity signal once again, so that the output signal 6 is S _out = [-2 -2 -2 -2]. In the case of other input signals, an output signal consisting of only ± 2 can be obtained by the same process.

2 shows a receiver block diagram of a binary 4-user CA-CDMA system. The received signal 7 undergoes a serial / parallel conversion (3), and from the parallel converted signal r _n (n = 1, 2, 3, 4), the parity signal extractor 2 receives the parity signal (5) used at the transmitter. Can be found. The parity signal 5 thus found is multiplied by the last bit r ₃ of the received signal 7 as at the transmitter, and the received signal is parallel / serial converted 4. The converted signal R ' is multiplied by each Walsh Hardmard sequence w _n ( n = 1, 2, 3, 4) and then by the user signal recovery block 8 the signal of each user b' _n = { b ' ₀ , b Outputs ' ₁ , b' ₂ , b ' ₃ } and the user signal (9) finally restored by parity signal (5) multiplied by the last bit B = { b' ₀ , b ' ₁ , b' ₂ , } Gets At this time, the user signal recovery block 8 is operated by the following equation.

[Equation 2]

Where b _'n is the reconstructed n-th output signal, R' and N ', and w _n is the number of hand signals, conversion of users by the parity signals, respectively, and represents the n-th Walsh sequence Hardmard.

3 shows the output of each system according to the information input from the conventional 4-user CDMA transmitter and binary 4-user CA-CDMA transmitter.

4 shows the configuration of a 16-user CA-CDMA transmitter. First input user signal (10) b = { b ₀ , b ₁ , ..., b ₁₄ , b ₁₅ } is input into four binary 4-user CA-CDMA transmitters (11) divided by 4 bits, Signals S _n = { S _n , ₀ , S _n , ₁ , S _n , ₂ , S _n , ₃ } Output from each of the four binary 4-user CA-CDMA transmitters 11 ( n = 1, 2, 3, 4) are again input to one of the four binary 4-user CA-CDMA transmitters 11 and output signals 12 having constant amplitude S _tx = { S _tx , ₀ , S _tx , _{2 ,.} ., S _tx , ₁₄ , S _tx , ₁₅ } Since the signals S _n ( n = 1, 2, 3, 4) output from the four binary 4-user CA-CDMA transmitters 11 are 4 signals each having a length of 4 and are composed of ± 2, one again two four 2 The output signal 12 S _tx through the true 4-user CA-CDMA transmitter 11 is 16 in length and consists of ± 4.

5 shows a binary 16-user CA-CDMA receiver. The received signal 13 R = { R ₀ , ..., R ₁₅ } is four bit strings R 'of length 4 and made up of ± 2 by one binary 4-user CA-CDMA receiver 14. _n = { R ' _n , ₀ , R' _n , ₁ , R ' _n , ₂ , R' _n , ₃ }, which are then input to four binary 4-user CA-CDMA receivers 14, respectively And each restored user signal 15 B = { b ' ₀ , ..., b' ₁₅ }.

6 shows the level of a transmission signal output from a conventional CDMA transmitter, and the number of users is 16. FIG. As shown in the figure, it can be seen that the signal fluctuates greatly from -16 to +16. Since the large signal level changes, the signal has a large PAPR.

7 shows the output signal level of binary CA-CDMA proposed in this study. Again, the number of users is 16, and the signal appears at binary levels of +4 and -4 as shown. It has a PAPR of 0 dB and no nonlinear distortion occurs through the HPA.

As described above, the present invention is a system for always outputting a signal having a constant size by applying a new precoding scheme to an existing 4-user CDMA system. Alternatively, there is no bandwidth expansion problem, and the number of system users can be extended by using binary 4-user CA-CDMA repeatedly. The present invention solves the problem of data transmission rate degradation or bandwidth expansion of the system and system scalability for more users, and nonlinear distortion occurs in a high power amplifier (HPA) by outputting a signal having a PAPR of 0 dB. This makes it possible to transmit data more efficiently and with stable BER performance. In addition, the high-power amplifier can be used at maximum power efficiency.

Claims (2)

In the structure and method of a binary constant amplitude code division multiplexing (CA-CDMA) communication system proposed by the present invention, 1) A method and apparatus for implementing binary constant amplitude 4-user CA-CDMA using a new precoding scheme having a code rate of 1; 2) A method and apparatus for expanding user capacity by four times by using parallel iteration based on binary constant amplitude 4-user CA-CDMA. A new precoding scheme with a code rate of 1 for 4-user CA-CDMA, which is the basis of the binary constant-width code division multiplexing (CA-CDMA) communication system, described in the above 1, the configuration of a transceiver and the number of users, A method and apparatus for expanding, A) an apparatus for obtaining a parity signal from the signal of each user input to the transmitter of 4-user CA-CDMA, and a method and apparatus for multiplying the signal with the signal of the fourth user; B) In 4-user CA-CDMA transmitter, when the input signal converted by parity signal is output through WHT (Walsh Hardmard transform), the parity signal is multiplied by multiplying the last bit of the output signal by the parity signal. Identifying processes and devices, C) A method and apparatus for finding a parity signal used in a transmitter from each parallel data by serially / parallel converting a signal input to a 4-user CA-CDMA receiver. D) A method and apparatus for expanding to four times the size by inputting the output signals of four identical CA-CDMA transmitters into another CA-CDMA.