Transmission performance of DS-CDMA with RAKE reception adding time-window control loop (TWCL) in multipath fading environment

This paper presents a code synchronization scheme-the time-window control loop (TWCL)-for postdetection RAKE receiver systems that offers the path-diversity effect. Laboratory test results from a postdetection RAKE receiver system with TWCL under a frequency-selective fading environment are introduced. RAKE combining methods, a simple integral demodulation method within a time window, and a recursive least squares (RLS) demodulation method within the time window that uses the RLS algorithm to realize maximal ratio combining, are investigated. It is found that TWCL performance with delay paths (double-spike frequency-selective Rayleigh-fading model) surpasses the performance of both acquisition and tracking without delay paths (nonfrequency-selective Rayleigh-fading model) because of the path-diversity effect. The laboratory results show that TWCL provides good acquisition and tracking performance under the fading conditions experienced with maximum Doppler frequencies of 5 or 80 Hz. It is also shown that the signal energy per bit to noise-power spectral-density ratio (E/sub b//N/sub 0/) required to achieve the bit error rate (BER) of 10/sup -3/ under the double-spike frequency-selective Rayleigh-fading model is reduced by 10 dB compared to the nonfrequency-selective Rayleigh-fading model. The difference in path-diversity effect between the two RAKE combining methods is only 1 dB. From a structural viewpoint, the simple integral demodulation method supports miniaturization and high-speed data-transmission.

It has been reported that a smart antenna can improve bit error rate (BER) performance significantly in a mobile communications system (Tanaka, S. et al., IEEE JSAC, vol.18, no.8, p.1495-504, 2000). However, the smart antenna has not been applied and analyzed much for the pseudonoise (PN) code tracking loop, which is one of the important aspects in spread spectrum communications receivers. We present a performance analysis of a first order PN-code tracking loop with a smart antenna under a frequency selective fading environment, and show that the smart antenna can also improve the PN code tracking loop significantly, compared to a single antenna element system. We employ the root mean square (RMS) error and mean time to lose lock (MTLL) of the PN code tracking loop as performance criterion.

The transmission quality of mobile radio communications is strongly affected by fading with rapid fluctuations in the envelope and phase of the received signal, in addition to the effect of thermal noise. This paper considers a multiple access system (DS‐CDMA system) using the spread spectrum technique with direct spread, and presents a method of deriving the approximate average bit error rate in a frequency‐selective fading environment (the n‐ray Rayleigh fading model), with the maximum Doppler frequency, the delay time of the delayed wave, and the number of stations simultaneously utilizing the channel as parameters. The two‐wave model and the IMT2000 model are considered as examples, and the validity of the proposed method is demonstrated by the fact that the results obtained by the approximate formula agree well with the simulation results even if the parameters are varied. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(1): 90–100, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1185

Recently, space-time block coded OFDM (ST-OFDM), that applies space-time block codes (STBC) to OFDM, has been proposed. Space-frequency block coded OFDM (SF-OFDM) has also been proposed, where the block codes are formed over the space and frequency domain. ST-OFDM and SF-OFDM achieve good performance over multipath fading environments and fast fading environments, respectively. For systems with two transmit antennas, orthogonal conditions are required to separate the received signals: in ST-OFDM, the frequency responses of two consecutive OFDM symbols are almost identical; in SF-OFDM, the frequency responses of two adjacent subcarriers are almost identical. In practical fading environments, however, these orthogonality conditions sometimes cannot be satisfied. In those environments, the received signals cannot be well separated and the performances are degraded. Recently, a new zero-forcing (ZF) diagonalized maximum likelihood decoder (DMLD) was proposed for the space-time block coded single carrier QPSK system to maintain the orthogonality of STBC under fast fading environments and flat fading environments; the channel separation in DMLD is performed by the ZF algorithm using two receive signals at time index 2n, 2n+1 (STC) or two subcarriers (SFC). The matrix generated after the channel separation is not an identity matrix, but a matrix proportional to an identity matrix. We show that ST/SF-OFDM with DMLD outperform ST/SF-OFDM in terms of bit error rate (BER).

In this article, a computationally-efficient approach is presented for Bit Error Rate (BER) calculations in multi-user Multiple Input Multiple Output (MIMO) frequency selective fading environments, operating in spatial multiplexing transmission mode. To this end, theoretical expressions for the equivalent Signal to Interference plus Noise Ratio (SINR) per active user and transmission mode, as well as mean BER, are derived. The key idea is that all parameters related to BER calculations can be expressed as sums of identically distributed random variables (RVs). Hence, computational burden can be reduced, since summation formulas take into account the parameters of a standalone RV along with the correlation of an arbitrary pair of RVs. As results indicate, the proposed approach can accurately estimate mean BER in multiuser MIMO orientations with increased reception diversity order, for arbitrary number of transmit/receive antennas, a modulation scheme, and a number of resolvable multi-path components.

In wireless communication, regarding all the multiple access schemes, fading is referred to be major problem in multipath environment. Recently, IDMA scheme has attracted much attention of the researchers all over world as a potential candidate for future generation wireless communication systems. This scheme has also been victim of fading phenomena during communication process. In this paper, the effort has been targeted for mitigation of multipath fading for IDMA scheme in multipath fading environment. For the purpose of performance analysis, maximal ratio combining scheme has been opted with IDMA systems. The simulation results demonstrate the superior performance of tree based interleaver under similar simulation parameters when compared to random interleaver under similar simulation conditions.

This paper analyzes the performance of well known Least-mean-square (LMS) and Recursive-least-squares (RLS) adaptive algorithms in terms of bit error rate (BER) verses signal to noise ratio (SNR) performances on the space-time coded multicarrier CDMA (STC-MC-CDMA) systems in frequency selective environments. For system we consider Alamouti's space-time coding scheme that involves two transmit antennas and provide transmit diversity at transmitting end. We compare the performance of RLS and LMS detector with help of computer simulation. It is found that BER performance of RLS detector is always considerably better than that of LMS detector. Thus, RLS detector outperforms the LMS detector. In this paper, we propose an application of the RLS algorithm for the detection of space-time coded MC-CDMA system. Simulation results presented in this paper confirms the performance analysis.

In this paper, we analyze the Bit Error Rate (BER) performance of Golden coded Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system over Rician multipath fading channel. We also compare the performance of the MIMO-OFDM system using Golden code in Rayleigh and Rician multipath fading channels. We discuss the effects of the presence of line-of-sight (LoS) component in the multipath fading environment which renders the improvement in the overall performance of the Golden coded MIMO-OFDM. This paper discusses the performance of Golden codes in a frequency selective Rician fading channel. To deal with the frequency selective fading channel, we use the OFDM (Orthogonal Frequency Division Multiplexing) modulation. The BER performance of the Golden coded MIMO-OFDM system under several propagation conditions has been evaluated. Keywords—MIMO, OFDM, Golden STBC, Rayleigh fading, Rician fading.

Track-before-detect for Infrared Maneuvering Dim Multi-target via MM-PHD

This paper proposes a novel adaptive differential detection scheme (adaptive DD), which can significantly reduce the irreducible bit-error rate (BER) of M-ary DPSK due to Doppler spread by the adaptive linear prediction of the reference signal. The predictor coefficient is adapted to changing channel conditions by using the recursive least-square (RLS) algorithm. A phase sequence estimation based on the M-state Viterbi algorithm (VA) and another based on the decision feedback algorithm (DFA) are presented. A theoretical BER analysis is presented for adaptive DD-DFA. BER performances of 2 and 4DPSK in Rayleigh fading channels are evaluated by computer simulations. When the RLS forgetting factor of /spl beta/=1 is used, simulation results show that the irreducible BER of 4DPSK can be reduced to 7.2/spl times/10/sup -5/ (3.9/spl times/10/sup -4/) for VA (DFA) while conventional DD offers 3.9/spl times/10/sup -3/ when f/sub D/T/sub b/ (maximum Doppler frequency times bit duration)=0.01 and average E/sub b//N/sub 0/ (signal energy per bit-to-additive white Gaussian noise (AWGN) power spectrum density ratio)=60 dB, where most errors are produced by Doppler spread. Adaptive DD is also effective in AWGN channels-simulations show that for the case of 4DPSK, a performance gain of 1.2 (0.7) dB is achieved over conventional DD for VA (DFA) at BER=10/sup -3/.

This study presents an experimental evaluation of bit-error-rate (BER) performances of a single carrier IEEE 802.16 (WiMax) radio channels. A packet which contains five sub data packets with different modulation techniques is used at transmitter end able to compare BER performances of these modulations in the same communication channels. Results are presented before and after channel coding. Two conventional adaptive equalizer training methods, the least mean squares (LMS) and the recursive least squares (RLS), are implemented. In experimental trails the obtained BER performance of receiver using LMS training has been quite close to whom using RLS particularly after coding, in real-time channel conditions.

Filter-bank Multicarrier (FBMC) modulation is the most promising 5th Generation (5G) waveform candidate in order to fulfill modern day requirements of ultra-high data rates with minimum latency. With lower side-lobes and faster spectral decay, FBMC is also well suited for reconfigurable radios such as Software Defined Radio (SDR) or Cognitive Radio (CR) for efficient spectrum utilization. In this paper, a performance as well as a parametric analysis of FBMC over Stanford University Interim (SUI) channel models has been analyzed. Performance is evaluated on the basis of Bit error rate (BER) using multipath fading environment that is characterized by Rician distribution, under different scenarios. The evaluation provides a useful basis for FBMC-based dynamic link adaptation in SDR wideband waveform.

The performance of optimum combining (OC) operating over a non-Gaussian, so called spherically invariant random process, multipath fading environment has been investigated. This non-Gaussian process has been normally used to characterize the clutters and multipath fading due to its Gaussian-like properties. The closed-form expression of average bit error rate (BER) in the presence of multiple equal-power interferers is then derived.

Orthogonal frequency division multiplexing (OFDM) is a very attractive technique for high-bit-rate data transmission in a multipath fading environment that causes intersymbol interference (ISI). There are many error-correcting codes applied to OFDM, convolutional codes, Reed-Solomon codes, turbo codes, and so on. Low-density parity-check (LDPC) codes have attracted much attention particularly in the field of coding theory. LDPC codes were proposed by Gallager (1962) and the performance is very close to the Shannon limit with practical decoding complexity like turbo codes. We propose LDPC coded OFDM (LDPC-COFDM) systems to improve the bit error rate (BER) of OFDM. We show that the BER of the LDPC-COFDM is worse than that of the TCOFDM on an AWGN channel, while that of the LDPC-COFDM is better than that of the turbo-coded OFDM (TCOFDM) on a frequency-selective fading channel.

Orthogonal Frequency Division Multiplexing (OFDM) is a advance bandwidth efficient digital modulation technique highly adopted for the broadband wireless services because it gives high performance in the multipath fading environments. It is very robust against narrowband interference, but it is not totally free from drawbacks. There are timing and frequency synchronization error for which this technique is very sensitive. These errors are quite detrimental to the mutual orthogonality among the subcarriers which is main condition of the OFDM technique. If it is not resolved properly, it creates inter-symbol interference (ISI) and inter-channel interference (ICI). ISI and ICI increase the Bit Error Rate (BER) and creates packet loss in the transmission. Means, OFDM System has no proper use without precise synchronization technique to assure reasonable system performance. This paper provides an overview on the causes and the effects of these synchronization errors. It focuses on various symbol timing and carrier frequency acquisition schemes including coarse and fine synchronization techniques, using cyclic prefix or training symbols. It has also discussed the attention to implement different standards in the same wireless device using common frequency synchronization structure.