Quasi-orthogonal space-time block coded transceiver systems over frequency selective wireless fading channels

We consider a three-node wireless relay system with frequency selective quasi-static fading channels between the nodes. We assume practical constraints require the relay to operate in half-duplex mode and employ a low-complexity non-orthogonal amplify-forward protocol. Assuming full channel state information and optimal energy allocation between source and relay, we study upper bounds of the outage probability for such channels. Compared to relay systems in flat fading channels, our results reveal that the additional diversity offered by frequency selective fading channels significantly improves outage performance. The results also suggest, however, that relays may offer a limited improvement in diversity when multipath fading in the source-destination link is sufficiently rich.

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.

For the reception of multicode direct sequence (DS)-CDMA signals, the MMSE frequency domain equalisation is applied instead of RAKE combining. The achievable BER performance in a frequency selective Rayleigh fading channel is evaluated by computer simulation. It is shown by computer simulation that the DS-CDMA with MMSE frequency domain equalisation outperforms the DS-CDMA with RAKE combining and shows only slight performance degradation compared to the MC-CDMA with minimum mean square error combining (MMSEC).

This paper presents the performance of turbo codes with multilevel modulation over frequency selective Rayleigh fading channel. The method of turbo equalization with 8-PSK modulation proposed by V. Franz and G. Bauch (1999) is modified here for 8-PSK and 16-QAM modulation in order to be applied to turbo codes. The joint turbo equalization and turbo decoding receiver is presented. From simulation results, good BER performance can be achieved with only 3 iterations.

V-BLAST (Vertically-layered Bell Laboratories Layered Space-Time) is a multiple transmit and receive antenna system that provides very high capacity compared to single antenna systems. However, most research in this area had assumed a flat-fading channel environment. This paper considers a frequency selective Rayleigh fading channel environment for multi-input and multi-output (MIMO) systems. Three different detection techniques with ordered successive interference cancellation are proposed: (1) zero-forcing maximal ratio combining (ZF-MRC); (2) layered maximum likelihood detection (L-MLD); and (3) group maximum likelihood detection (G-MLD). All these schemes consider the delayed elements in each transmit-receive antenna pair as imaginary antennas transmitting delayed versions of the substreams. Constraints on the number of receive antennas are also discussed, with G-MLD requiring the least elements. Simulation results show that G-MLD provides the best performance with ZF-MRC performing the worst.

By transmitting different substreams in different antennas simultaneously, a multiple element antenna array system provides increased capacity that grows linearly with the number of transmit antennas. Layered space-time processing that performs nulling, detection and cancellation for each substream can be used for reception, with a linear growth in receiver complexity. This paper considers this multi-input multi-output system over a slow time-varying frequency selective Rayleigh fading channel environment. With the equivalent channel tap delay line model, each delayed tap in every transmit-receive antenna pair can be considered as an imaginary antenna transmitting a delayed version of the substreams. Based on this idea, we propose a layered maximum likelihood detection (L-MLD) scheme which performs layered processing and maximum likelihood detection for each substream and its delayed elements. To further improve the performance, a group maximum likelihood detection (G-MLD) scheme is also proposed by grouping the substreams and performing layered processing in groups and maximum likelihood detection within the group. However, both schemes increase the required number of receiving antennas, which increases hardware cost and size. To reduce this requirement, we propose the use of oversampling technique to increase the dimension of the received signal. Simulation results show that the L-MLD scheme achieves frequency diversity and outperforms existing schemes such as the V-BLAST system with OFDM and multi-input multi-output decision feedback equalizers (MIMO-DFE). Moreover, the G-MLD scheme performs better than L-MLD with an increased detection complexity. In addition, it was showed that further increasing the oversampling rate beyond the minimum requirement does not improve the performance.

In this paper we propose an interleaved spread spectrum orthogonal frequency division multiplexing (ISS-OFDM) system and investigate its performance over frequency selective multipath fading channels. The purpose is to exploit frequency diversity capability, develop an e±cient spectrum spreading algorithm and improve the system performance over frequency selective multipath fading channels. At transmitter, a spectrum spread ISS-OFDM signal is generated by employing OFDM modulation and interleaving techniques. At the receiver, two solutions including serial demodulation and parallel demodulation for diversity combing are proposed, in which the received signals are combined by using a maximum ratio combining (MRC) technique. The simulation indicates that higher frequency diversity is achieved, and the Bit Error Rate (BER) and Peak-to-Average Power Ratio (PAR) performances of the proposed ISS-OFDM system over frequency selective multipath fading channels are improved signi¯cantly as compared with the conventional OFDM systems. Another unique characteristic is that the spectrum spreading factor and diversity order provided by the system are reconfigurable to achieve cognitive communications.

Multiple-input/multiple-output (MIMO) frequency selective fading channels introduce both the intersymbol interference (ISI) and the inter-(sub)channel interference (ICI) that are the major performance limiting factors for MIMO wireless data communications. This paper focuses on joint suppression of such two interferences in receiver design under the criterion of the minimum mean-squared error (MMSE). The well-known Kalman filtering arises as a natural design tool to achieve the optimum joint suppression of the ISI and ICI in the sense of MMSE that results in a two-stage design method that suppresses the ISI and ICI in series. Specifically, a state-space solution is derived for the optimum decision-feedback equalizer (DFE) based on temporal Kalman filtering, and is shown to be equivalent to a conventional finite length DFE for ISI suppression. A novel spatial Kalman filtering scheme is proposed as the second stage to successively cancel the ICI. It is shown that the proposed two-stage method yields the realizable and optimum joint ISI and ICI suppression, while it admits lower computational complexity than the conventional finite length DFE for ISI suppression and the MMSE V-BLAST receiver for ICI suppression. The results are applicable to any linear channels that admit state-space realizations, including MIMO frequency selective time-varying channels, and are thus the most general. Simulation results show the effectiveness of the proposed two-stage method and its robustness to channel estimation uncertainties that may arise in practical systems.

A wavelet packet function based multiple access (WPMA) system is developed in this paper to maximize capacity and improve receiver performance over frequency selective multipath fading channels. To design an efficient receiver that mitigates residual multiple access interference (MAI) and intersymbol interference, while improving receive signal-to-interference and noise ratio (SINR) simultaneously on the uplink; a multichannel decision feedback equalizer (DFE) following a wavelet packet function based RAKE receiver is proposed. Simulation results show that, over GSM TU channels the developed receiver performs quite well if the power of each user is perfectly controlled or the space diversity combining (SDC) technique is applied.

An estimator-correlator receiver structure using wideband signaling using PN sequences is developed for multipath frequency selective fading channels. Expressions for the error performance of the receiver for binary and M-ary FSK signaling schemes, for equal and unequal average SNR per path, are presented. Results of analytical performance evaluation of the receiver are presented and a comparison with a square law Rake correlator receiver is made.

This work addresses the problem of coherently detecting turbo coded orthogonal frequency division multiplexed (OFDM) signals, transmitted through frequency selective Rayleigh fading channels. A single transmit and receive antenna is assumed. The channel output is distorted by a carrier frequency and phase offset, besides additive white Gaussian noise (AWGN). A new frame structure for OFDM, consisting of a known preamble, cyclic prefix and data is proposed. A filter that is matched to the preamble is used for start-of-frame (SoF) detection. A two-step ML detector for frequency-offset estimation is proposed, which has a much lower complexity compared to the single step ML detector. Turbo decoding and data interleaving is used to significantly enhance the bit-error-rate (BER) performance of the coherent receiver. Simulation results show that the BER performance of the practical coherent receiver is close to the ideal coherent receiver, for data length equal to the preamble length, and attains a BER of about 4× 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> at an SNR of just 8 dB. It is also shown that the probability of erasure is less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> for a preamble length of 512 QPSK symbols. The proposed algorithms are well suited for implementation on a DSP-platform.

The reverse link performance of direct sequence code division multiple access (DS-CDMA) system in wireless communication over a frequency selective multipath fading channel has been investigated in this paper. The channel has been modeled as Nakagami-m distributed frequency selective multipath fading channel. A conventional correlator type receiver has been considered for the analysis. Noise is taken as additive white Gaussian noise (AWGN) with two sided power spectral density N/sub 0//2 . To model multiple access interference (MAI), standard Gaussian approximation (SGA) has been considered in this paper. To mitigate the near-far problem, a power control scheme, but imperfect has been assumed in this paper. The bit error rate (BER) expression for the system has been derived and simulated by varying number of users, number of fading path, processing gain, fading parameter, SNR per bit E/sub b//N/sub 0/ and variation in the amplitude of the received signal. The analysis shows that as the number of simultaneous active user, the number of fading path and the variation in the power of the received signal increases, the BER of the system increases indicating the performance degradation. As the value of the processing gain, the ratio E/sub b//N/sub 0/ and the fading parameter increases, the BER performance of the system improves.

Space-time modulation exploiting diversity or/and coding gains has been a major focus in high-speed wireless communications systems against channel fading. We employ noncoherent space-time modulation in cyclic-prefix (CP) based single-carrier (SC) block systems over frequency selective Rayleigh block fading channels, where channel order, upper-bounded by the CP length, is assumed known. Capitalizing on multi-channel input-output relation for time-domain processing, we reveal that employing complex orthogonal m-sequences can enable a simplified maximum-likelihood (ML) detector. Further, code construction is addressed so as to adaptation of a variety of transmission rates and trellis-coded unitary space-time modulation is also investigated. Numerical results suggest that this noncoherent space-time modulation for SC block system, coupled with time-domain ML detection, can realize multipath diversity under certain circumstances.

In this paper, a pilot-assisted minimum mean square error (MMSE) multiuser channel estimation algorithm is proposed for quasi-synchronous code-division multiple-access (CDMA) systems that undergo frequency-selective channel fading. The frequency-selective multiuser fading channel is represented as a symbol-wise time-varying chip-spaced tapped delay line filter with correlated filter taps. The multiuser channel tap coefficients at pilot symbol positions are estimated under the MMSE criterion with the help of the channel intertap correlation matrix, which is determined by the combined effects of the physical fading channel, transmit filter, and receive filter. In the development of the estimation algorithm, the channel intertap correlation matrix is deemed as an essential factor, and a novel iterative method is proposed for the joint estimation of the channel intertap correlation and filter tap timing based on the received pilot samples. Simulations show that the information of the channel intertap correlation is critical to the performance of the channel estimation, and the channel taps at different delays cannot be assumed uncorrelated for CDMA systems experiencing frequency-selective fading.

Time varying channels have memory due to the correlation between successive channel impulse responses. By using finite state Markov chains, this memory can be exploited to improve the receiver performance. A channel estimation scheme for time varying frequency selective fading channel is developed and used in a maximum ratio combining RAKE receiver for a QPSK WCDMA downlink. The receiver only requires a sequence of pilot symbols to start. The channel estimation algorithm models the amplitude as well as the phase of the recombined paths of the RAKE receiver and makes use of maximum a posteriori metrics and an efficient arrangement of Viterbi algorithms.