scholarly journals Maximal Ratio Combining Using Channel Estimation in Chaos Based Pilot-Added DS-CDMA System with Antenna Diversity

2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Meher Krishna Patel ◽  
Stevan M. Berber ◽  
Kevin W. Sowerby
Keyword(s):  
Channel Estimation ◽  
Bit Error Rate ◽  
Error Rate ◽  
Lms Algorithm ◽  
Maximal Ratio Combining ◽  
Cdma System ◽  
Decision Variable ◽  
Antenna Diversity ◽  
Least Mean Square ◽  
Channel Estimator

This paper presents an adaptive multiuser transceiver scheme for DS-CDMA systems in which pilot symbols are added to users’ data to estimate complex channel fading coefficients. The performance of receiver antenna diversity with maximal ratio combining (MRC) technique is analyzed for imperfect channel estimation in flat fading environments. The complex fading coefficients are estimated using least mean square (LMS) algorithm and these coefficients are utilized by the maximal ratio combiner for generating the decision variable. Probability of error in closed form is derived. Further, the effect of pilot signal power on bit error rate (BER) and BER performance of multiplexed pilot and data signal transmission scenario are investigated. We have compared the performance of added and multiplexed pilot-data systems and concluded the advantages of both systems. The proposed CDMA technique uses the chaotic sequence as spreading sequence. Assuming proper synchronization, the computer simulation results demonstrate the better bit error rate performance in the presence of channel estimator in the chaotic based CDMA system and the receiver antenna diversity technique further improves the performance of the proposed system. Also, no channel estimator is required if there is no phase distortion to the transmitted signal.

scholarly journals Antijamming Performance of Adaptive Chaos Based CDMA System with MRC in Imperfect Channel Estimation Environment

2017 ◽  
Vol 2017 ◽  
pp. 1-5 ◽  
Author(s):  
Meher Krishna Patel ◽  
Stevan M. Berber ◽  
Kevin W. Sowerby
Keyword(s):  
Channel Estimation ◽  
Lms Algorithm ◽  
Maximal Ratio Combining ◽  
Cdma System ◽  
Least Mean Square ◽  
Probability Of Error ◽  
Imperfect Channel Estimation ◽  
Pilot Symbols ◽  
Flat Fading ◽  
Slow Switching

This paper presents the antijamming performance of adaptive multiuser DS-CDMA system using maximal ratio combining technique in slow switching pulse noise jammer. Complex flat fading channel coefficients are assumed to be unknown at the receiver. Pilot symbols are used to estimate the fading coefficients using least mean square (LMS) algorithm, and effect of imperfect channel estimation on bit error rate (BER) is studied. Under the perfect synchronization conditions, probability of error in closed form is derived.

scholarly journals Performance Enhancement of Coherent Optical OFDM System Using LMS Algorithm

2020 ◽  
Vol 1 ◽  
pp. 1-5
Author(s):  
Manisha Bharti
Keyword(s):  
Phase Noise ◽  
Bit Error Rate ◽  
Error Rate ◽  
Orthogonal Frequency Division Multiplexing ◽  
Performance Enhancement ◽  
Lms Algorithm ◽  
Frame Structure ◽  
Least Mean Square ◽  
Ofdm Systems ◽  
Ofdm System

Instability of the local oscillator causes phase noise – a phenomenon that is a disadvantage and is considered to be a major obstacle in the functioning of coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. An attempt has been made in this paper to reduce the effects of common phase errors generated by phase noise. In this paper, a least mean square (LMS) based algorithm is proposed for estimation of phase noise. Using this proposed algorithm, the major problem of phase ambiguity caused by cycle slip is avoided and the bit error rate is greatly improved. Further, there is no requirement for modifying the frame structure of OFDM using this algorithm. A CO-OFDM system with the 8-PSK technique is used to implement the algorithm concerned. Furthermore, the algorithm, using the 8-PSK modulation technique, is analyzed and compared with the existing QPSK technique and with other algorithms. The investigations reveal that 8-PSK outperforms existing LMS algorithms using other techniques and significantly reduces the bit error rate.

scholarly journals MBER Space Time Equalization assisted Multiuser Detection

2012 ◽  
pp. 47-50
Author(s):  
Yogeshwary B.H. ◽  
T.L. Purushottama ◽  
M Z Kurian
Keyword(s):  
Bit Error Rate ◽  
Error Rate ◽  
Minimum Mean Square Error ◽  
Space Time ◽  
Decision Feedback ◽  
Lms Algorithm ◽  
Mean Square ◽  
Least Mean Square ◽  
Estimation Errors ◽  
Time Equalization

A novel minimum bit-error rate (MBER) space–time-equalization (STE)-based multiuser detector (MUD) is proposed for multiple-receive-antenna-assisted space-division multiple-access systems. It is shown that the MBER-STE-aided MUD significantly outperforms the standard minimum mean-square error design in terms of the achievable bit-error rate (BER). Adaptive implementations of the MBER STE are considered, and both the block-databased and sample-by-sample adaptive MBER algorithms are proposed. The latter, referred to as the least BER (LBER) algorithm, is compared with the most popular adaptive algorithm, known as the least mean square (LMS) algorithm. It is shown that in case of binary phase-shift keying, the computational complexity of the LBER-STE is about half of that required by the classic LMS-STE. Our simulation results demonstrate that the MBER ST-DFE assisted MUD is more robust to channel estimation errors as well as to potential error propagation imposed by decision feedback errors, compared to the MMSE ST-DFE assisted MUD.

scholarly journals Smoothing techniques for decision-directed MIMO OFDM channel estimation

2011 ◽  
Vol 9 ◽  
pp. 139-143
Author(s):  
P. Beinschob ◽  
U. Zölzer
Keyword(s):  
Channel Estimation ◽  
Bit Error Rate ◽  
Error Rate ◽  
Error Propagation ◽  
Orthogonal Frequency Division Multiplexing ◽  
Mimo Systems ◽  
Smoothing Techniques ◽  
Time Frequency ◽  
Channel Estimate ◽  
Mimo Ofdm

Abstract. With the purpose of supplying the demand of faster and more reliable communication, multiple-input multiple-output (MIMO) systems in conjunction with Orthogonal Frequency Division Multiplexing (OFDM) are subject of extensive research. Successful Decoding requires an accurate channel estimate at the receiver, which is gained either by evaluation of reference symbols which requires designated resources in the transmit signal or decision-directed approaches. The latter offers a convenient way to maximize bandwidth efficiency, but it suffers from error propagation due to the dependency between the decoding of the current data symbol and the calculation of the next channel estimate. In our contribution we consider linear smoothing techniques to mitigate error propagation by the introduction of backward dependencies in the decision-based channel estimation. Designed as a post-processing step, frame repeat requests can be lowered by applying this technique if the data is insensitive to latency. The problem of high memory requirements of FIR smoothing in the context of MIMO-OFDM is addressed with an recursive approach that acquires minimal resources with virtual no performance loss. Channel estimate normalized mean square error and bit error rate (BER) performance evaluations are presented. For reference, a median filtering technique is presented that operates on the MIMO time-frequency grids of channel coefficients to reduce the peak-like outliers produced by wrong decisions due to unsuccessful decoding. Performance in terms of Bit Error Rate is compared to the proposed smoothing techniques.

Derivation of New Expressions of Bit Error Rate for MC-CDMA System in Nakagami Fading Channel

2003 ◽  
Vol 57 (6) ◽  
pp. 395-402 ◽  
Author(s):  
Ahmed Bouzidi Djebbar ◽  
Ali Djebbari ◽  
Merahi Bouziani ◽  
Jean Michel Rouvaen
Keyword(s):  
Bit Error Rate ◽  
Error Rate ◽  
Fading Channel ◽  
Nakagami Fading ◽  
Cdma System ◽  
Nakagami Fading Channel
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