Comparison of two convolutional orthogonal coding techniques for CDMA radio communications systems (original) (raw)
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1992
{Continue on reverse if necessary and identify by block number) J n this thesis, a new scheme of encoding orthogonal MFSK signals with convolutional codes is proposed. Instead of separating :he code and the signals as is done conventionally, here the m outputs of the convolutic il encoder of rate k/m are used to select the M = 2 m orthogonal FSK signals. This com-)ined coded system is called trellis-coded modulation MFSK (TCM/MFSK). The free distance of TCM/MFSK codes is found computationally. Asymptotic coding gain ;ACG) of several TCM/MFSK systems relative to uncoded MFSK systems having the same bandwidth efficiency (bits/s/Hz) are calculated. Both analytic descriptions and natural mapping implementations of TCM/4-FSK with rat L/2 and TCM/8-FSK with rate 2/3 for several constraint lengths of the convolutional code ire given. The analytic description of TCM/MFSK is also obtained computationally.
2003
The system under study is a convolutionally coded and orthogonally modulated DS-CDMA system in time-varying frequency selective Rayleigh fading channels. After convolutional encoding and block interleaving, information bits are mapped to Mary orthogonal Walsh sequences. In conventional systems, Mary symbol demodulation and convolutional decoding are conducted separately in the receiver, only hard decisions are passed between these two blocks. In this paper, we propose an integrated scheme based on some soft demodulation and decoding algorithms. Instead of making hard decision on the transmitted M-ary symbols from the received observations, we compute the reliability value for the code bits from which orthogonal symbols are formed. This soft information is then deinterleaved and decoded. The detected bits are fed back to demodulator for channel estimation and multiuser detection. For channel decoding, we use Log-MAP algorithm instead of VA (Viterbi algorithm) for better performance. Maximum achievable performance for the system is obtained by iterating this joint soft demodulation and Log-MAP decoding process. The performance of this strategy is evaluated numerically and proved to significantly outperform the conventional partitioned and hard decision based scheme.
New Walsh-Like Non-Linear Phase Orthogonal Codes for Direct Sequence CDMA Communication
International Journal of Linguistics and Computational Applications , 2019
Walsh codes and Gold codes have been used as a spread spectrum codes in Code Division Multiple Access (CDMA) communication because of their ease of generation than the efficiency of these codes. The drawbacks of these codes are that they are limited in number and in their lengths. In this research paper, we relaxed the linear phase requirements of the Walsh code and the new sets of Walsh-like non-linear phase binary orthogonal user codes (transforms) are obtained for the asynchronous and the synchronous spread spectrum multi user communication. We designed the simulink model and performed the algorithm by using MATLAB R 2011 a version in order to obtain this newly proposed Walsh-like code set for the multiuser spread spectrum communication. We compared their performance with the existing codes like the Gold code and the Walsh code families. Our comparisons include their time domain properties like the autocorrelation and the cross correlation along with the bit error rate (BER) performances in the additive white Gaussian noise (AWGN) for the synchronous and asynchronous DS-CDMA communication. We proved that the proposed binary user code family outperforms the Walsh codes significantly and they match in the performance with the popular, nearly orthogonal Gold codes closely for the asynchronous multi user communication in the additive white Gaussian noise (AWGN) channels. We present in this research paper that there are a good number of such desirable code sets which are available in the binary sample space with different transform sizes. These new binary sets with a good performance and flexible code lengths might help us to improve the spread spectrum multiplexing capabilities of future wire line and the wireless CDMA communication systems.
Performance Analysis of Non-Orthogonal Codes for CDMA Wireless Systems
The performance of a CDMA based wireless mobile systems is largely dependent on the characteristics of pseudorandom spreading codes. Thus, the choice of spreading codes is an important parameter to improve the performance of CDMA mobile systems. It is desirable to have a code dictionary consisting of spreading codes which possess both impulsive ACF and all zero CCF characteristics. Therefore, in this paper various non-orthogonal codes have been investigated with special emphasis on their peak as well as mean square correlation properties.
IJERT-Performance Analysis of Non-Orthogonal Codes for CDMA Wireless Systems
International Journal of Engineering Research and Technology (IJERT), 2013
https://www.ijert.org/performance-analysis-of-non-orthogonal-codes-for-cdma-wireless-systems https://www.ijert.org/research/performance-analysis-of-non-orthogonal-codes-for-cdma-wireless-systems-IJERTV2IS70417.pdf The performance of a CDMA based wireless mobile systems is largely dependent on the characteristics of pseudorandom spreading codes. Thus, the choice of spreading codes is an important parameter to improve the performance of CDMA mobile systems. It is desirable to have a code dictionary consisting of spreading codes which possess both impulsive ACF and all zero CCF characteristics. Therefore, in this paper various non-orthogonal codes have been investigated with special emphasis on their peak as well as mean square correlation properties.
Performance Analysis of OCDMA System with Unipolar Walsh Coding
The success of a radiofrequency in CDMA depends on well designed bipolar codes with good correlation properties. These sequences of (+1,-1) values exist in the RF domain because the phase of the electromagnetic field can be detected directly. The unipolar optical coding is studied as optical system is nonnegative and unipolar in nature and detects and processes the signal intensity. The strict orthogonality of bipolar Walsh codes shows cross correlations to be equal to zero while auto correlations have large magnitudes. Unipolar Walsh coding have been studied and constructed in the previous published papers. In this work, the performance of the proposed codes has been analyzed and it has been observed that performance is better than modified frequency hopping & Hadamard code, Random Diagonal codes. Theoretical results for SNR and BER and Simulation results are shown.
IEEE Transactions on Vehicular Technology, 1998
The probability of error performance of a directsequence code-division multiple-access (DS/CDMA) system employing noncoherent M-ary orthogonal signaling in a Nakagami multipath fading channel is analyzed. A RAKE receiver structure with square-law demodulation is used at the receiver. The multiple-access interferences are modeled as Gaussian and expressions derived for the exact probability of error. The performance is also evaluated in terms of the number of users that can be supported by the system at a given probability of error. The effect of correlated fading on system performance is also investigated by considering two correlation models, which can be characterized by a single correlation coefficient. In the first model, the correlation coefficient between any two diversity branches is constant. In the second model, it is assumed that the correlation coefficient between any two diversity branches decreases exponentially as the separation between them increases. For both models, it is found that the presence of correlation deteriorates system performance. The use of larger signal alphabets than binary modulation in conjunction with diversity reception provides a considerable performance improvement even in the presence of correlated fading. Index Terms-Correlated Nakagami fading, DS-CDMA system, M-ary noncoherent orthogonal modulation. I. INTRODUCTION T HE ABILITY of direct-sequence code-division multipleaccess (DS/CDMA) systems to mitigate the effect of multipath and suppress interference has made them popular in recent years. Especially, CDMA has been shown to offer more system capacity than time-division multiple access (TDMA) or frequency-division multiple access (FDMA) in cellular networks [1]. In a multiuser DS/CDMA system, a pilot signal must usually be included in the forward/reverse link for each user so that coherent demodulation can be performed at the receiver. Such is the case, for example, in the wideband CDMA system authorized as the air interface of IS-665, which uses coherent detection and interference cancellation techniques to improve system capacity [2]. However, the reverse link is more vulnerable to interference and, therefore, has less capacity than the forward link. Also, on the reverse channel it may be difficult to recover the pilot signal from Manuscript
IEEE Journal on Selected Areas in Communications, 2000
The performance of Reed-Solomon (RS) coded direct-sequence code division multiple-access (DS-CDMA) systems using noncoherent-ary orthogonal modulation is investigated over multipath Rayleigh fading channels. Diversity reception techniques with equal gain combining (EGC) or selection combining (SC) are invoked and the related performance is evaluated for both uncoded and coded DS-CDMA systems. "Errors-and-erasures" decoding is considered, where the erasures are based on Viterbi's so-called ratio threshold test (RTT). The probability density functions (PDF) of the ratio associated with the RTT conditioned on both the correct detection and erroneous detection of the-ary signals are derived. These PDFs are then used for computing the codeword decoding error probability of the RS coded DS-CDMA system using "errors-and-erasures" decoding. Furthermore, the performance of the "errors-and-erasures" decoding technique employing the RTT is compared to that of "error-correction-only" decoding refraining from using side-information over multipath Rayleigh fading channels. As expected, the numerical results show that when using "errors-and-erasures" decoding, RS codes of a given code rate can achieve a higher coding gain than without erasure information.
Low-complexity multiuser detector for coherent and incoherent CDMA mobile radio communications
Seamless Interconnection for Universal Services. Global Telecommunications Conference. GLOBECOM'99. (Cat. No.99CH37042), 1999
This paper deals with a multiuser detector based on a decorrelating approach for asynchronous up-link DS/CDMA communications in which QPSK modulation schemes are used in transmission and coherent and incoherent receivers in reception. It is shown here that the receivers proposed are near-far resistant and exhibits lower complexity than the optimum detector. The incoherent realization allows a lighter complexity overhead