Alamouti Decoding Research Articles

Generalized Receiver Designs for OFDM Systems with Alamouti Decoding in Fast Fading Channels

In the present paper, the generalized receiver designs for orthogonal frequency-division multiplex-ing (OFDM) systems that exploit the Alamouti transmit diversity technique are addressed. In Alamouti space-time coded OFDM systems, the simple Alamouti decoding at the generalized receiver relies on the assumption that the channels do not change over an Alamouti codeword period (two consecutive OFDM symbol periods). Unfortunately, when the channel is fast fading, the assumption is not met, resulting in severe performance deg-radation. In the present paper, a sequential decision feedback sequence estimation (SDFSE) scheme based on the generalized receiver with an adaptive threshold, a traditionally single-carrier equalization technique, is used to mitigate the performance degradation. A new method to set the threshold value is proposed. For small signal constellations like binary phase-shift keying (BPSK) and quadrature phase shift-keying (QPSK), the SDFSE generalized receiver with the adaptive threshold requires much lower complexity than a previous minimum me-an square error (MMSE) approach based on the generalized receiver at the cost of small performance degradati-on. Furthermore, we show that the performance difference becomes smaller when the channel estimation error is included. Adaptive effort sequence estimation (AESE) scheme based on the generalized receiver is also pro-posed to further reduce the average complexity of the SDFSE generalized receiver scheme with the adaptive threshold. The AESE generalized receiver scheme is based on the observation that a high Doppler frequency does not necessarily mean significant instantaneous channel variations. Simulations demonstrate the efficacy of the proposed SDFSE generalized receiver with the adaptive threshold and AESE generalized receiver schemes.

MIMO-OFDM/OCDM low-complexity equalization under a doubly dispersive channel in wireless sensor networks

In this article, three novel systems for wireless sensor networks based on Alamouti decoding were investigated and then compared, which are Alamouti space–time block coding multiple-input single-output/multiple-input multiple-output multicarrier modulation (MCM) system, extended orthogonal space–time block coding multiple-input single-output MCM system, and multiple-input multiple-output system. Moreover, the proposed work is applied over multiple-input multiple-output systems rather than the conventional single-antenna orthogonal chirp division multiplexing systems, based on the discrete fractional cosine transform orthogonal chirp division multiplexing system to mitigate the effect of frequency-selective and time-varying channels, using low-complexity equalizers, specifically by ignoring the intercarrier interference coming from faraway subcarriers and using the LSMR iteration algorithm to decrease the equalization complexity, mainly with long orthogonal chirp division multiplexing symbols, such as the TV symbols. The block diagrams for the proposed systems are provided to simplify the theoretical analysis by making it easier to follow. Simulation results confirm that the proposed multiple-input multiple-output and multiple-input single-output orthogonal chirp division multiplexing systems outperform the conventional multiple-input multiple-output and multiple-input single-output orthogonal frequency division multiplexing systems. Finally, the results show that orthogonal chirp division multiplexing exhibited a better channel energy behavior than classical orthogonal frequency division multiplexing, thus improving the system performance and allowing the system to decrease the equalization complexity.

Error-Rate Performance of Coded System for MC-IDMA using Spatial Diversity in Cognitive Spectrum

Article entitles the analysis of Cognitive Spectrum based Multi-carrier-IDMA scheme with Multiple-Input and Multiple-Output system (MIMO). We deliberate Space-Time transmits diversity (S-TTD) as MIMO system to procure spatial diversity for up-link communication. We are exploiting frequency-sensitivity device of Cognitive-Radio -Network (CRN) that explore ideal spectrum, disband the radio-spectrum dynamically for the application of mobile communication. In the conventional CDMA, orthogonal code spreading matrix is exploited for user identification. In this article, we invoke IDMA accessing scheme which user’s-specific interleaving pattern in addition to low-spreading sequence, to accommodate large secondary users. At each Mobile station, we use turbo code for channel encoder component and at base station, we consider log-MAP decoding algorithm to alleviate the contrary issues of secondary multi-user interferences(S-MUI) in addition to the Primary users interference (P-MUI). We allocate the radio spectrum dynamically based on Secondary users’ requirement. We invoke S-TTD system to obtain spatial diversity. Simulation results represent coded MIMO-MC-IDMA in the realistic channel environments using Alamouti decoding. The performance curve explicates the benefits of exploiting Cognitive spectrum in real-time environments for MIMO-MC-IDMA in terms of bandwidth achievement. Further, we discern from the graph that S-TTD offers higher capacity with less SNR for coded MC-IDMA system in the context of up-link transmission.

Receiver Design for Alamouti Coded FBMC System in Highly Frequency Selective Channels

Alamouti coded filter bank multicarrier systems suffer from severe performance degradation in highly frequency selective channels. To address the above problem, we propose a novel Alamouti decoding receiver based on frequency spreading/despreading, where the Alamouti decoding module is moved to the front of the frequency despreading module. Unlike the traditional subcarrier-based Alamouti decoding scheme, the Alamouti decoding in the proposed receiver could be performed on each frequency point to better combat the frequency selectivity. Moreover, the full diversity is achieved on each frequency point by introducing a phase factor before Alamouti decoding. Simulation results demonstrate the performance advantages of our proposed receiver over the traditional scheme in highly frequency selective channels.

Performance analysis of an OAM multiplexing-based MIMO FSO system over atmospheric turbulence using space-time coding with channel estimation.

The average bit error rate (ABER) performance of an orbital angular momentum (OAM) multiplexing-based free-space optical (FSO) system with multiple-input multiple-output (MIMO) architecture has been investigated over atmospheric turbulence considering channel estimation and space-time coding. The impact of different types of space-time coding, modulation orders, turbulence strengths, receive antenna numbers on the transmission performance of this OAM-FSO system is also taken into account. On the basis of the proposed system model, the analytical expressions of the received signals carried by the k-th OAM mode of the n-th receive antenna for the vertical bell labs layered space-time (V-Blast) and space-time block codes (STBC) are derived, respectively. With the help of channel estimator carrying out with least square (LS) algorithm, the zero-forcing criterion with ordered successive interference cancellation criterion (ZF-OSIC) equalizer of V-Blast scheme and Alamouti decoder of STBC scheme are adopted to mitigate the performance degradation induced by the atmospheric turbulence. The results show that the ABERs obtained by channel estimation have excellent agreement with those of turbulence phase screen simulations. The ABERs of this OAM multiplexing-based MIMO system deteriorate with the increase of turbulence strengths. And both V-Blast and STBC schemes can significantly improve the system performance by mitigating the distortions of atmospheric turbulence as well as additive white Gaussian noise (AWGN). In addition, the ABER performances of both space-time coding schemes can be further enhanced by increasing the number of receive antennas for the diversity gain and STBC outperforms V-Blast in this system for data recovery. This work is beneficial to the OAM FSO system design.

Space-Time Coding for Aeronautical Telemetry: Part II—Decoder and System Performance

This paper describes the use of Alamouti-encoded-shaped offset QPSK version TG (SOQPSK-TG) to solve the two-antenna problem in aeronautical telemetry. The Alamouti space-time block code is used to encode the phase states in the complex exponential representation of SOQPSK-TG. Because SOQPSK-TG possesses memory, the Alamouti decoder is a sequence estimator. Maximum likelihood and least squares sequence decoders are derived. To reduce the number of states, the eight-waveform cross-correlated trellis-coded quadrature modulation (XTCQM) approximate representation of SOQPSK-TG is used. A prototype decoder based on the least squares decoder and the estimators described in Part I and operating at a data rate of 10 Mb/s was tested in the laboratory in test flights at the Air Force Test Center, Edwards AFB. The test flights demonstrate that Alamouti-encoded SOQPSK-TG, as described in this paper, using the least squares decoder based on the estimators described in Part I solves the two antenna problem in aeronautical telemetry.

Intrinsic ICI-Free Alamouti Coded FBMC

Applying Alamouti code to filter bank multicarrier (FBMC) is a challenging issue due to the intrinsic inter-antenna inter-carrier interference (ICI), which does not exist in Alamouti coded orthogonal frequency division multiplexing (OFDM). We propose a frequency reversal Alamouti coded scheme for FBMC. As the frequency reversal symbol arrangement in itself cannot handle the inter-antenna ICI, we carefully consider the signal structure of FBMC and specify the additional requirements to satisfy self-ICI cancellation property. Only with a simple signal modification in the transmitter and the typical Alamouti decoding in the receiver, the proposed scheme achieves ideal (ICI-free) Alamouti code performance if the fading is locally flat over the Alamouti coded block. By properly dividing the total bandwidth into multiple blocks, the proposed scheme achieves near ICI-free performance for the multi-path fading channels.

PERFORMANCE EVALUATION OF RELAYING SCHEMES FOR WIRELESS COMMUNICATION SYSTEMS

The evaluation of MIMO (multiple-input multiple-output) Relay wireless system is carried out and compared against the performance of a SISO (single-input single-output) Relay wireless system. The encoding scheme used in MIMO is Alamouti coding and decoding is done by the Maximum Likelihood (ML) detector. A comparison is made between the SISO non-regenerative amplify-and-forward (AF) and regenerative decode-and-forward (DF) relaying schemes. The plots of bit error rate (BER) versus signal to noise ratio (SNR) are simulated by incorporating Rayleigh fading condition in the presence of additive white Gaussian noise(AWGN) using MATLAB.

Time Synchronization for Cooperative Communication in Wireless Sensor Networks

Time synchronization is crucial for the implementation of cooperative communication in wireless sensor networks. In this paper, we explore the effect of synchronization error on cooperative communication utilizing distributed Alamouti code. The analysis and simulation results show that small synchronization error has negligible effect on bit error rate (BER) performance. In order to synchronize the distributed sensor nodes within an acceptable error, we propose a physical layer synchronization scheme. This scheme consists of an initial synchronization of the cooperative transmitters, synchronization error estimation at the cooperative receiver and finally a feedback phase. A maximum likelihood method is proposed to make the synchronization error estimation. It achieves better performance than the matched filter method at the price of moderate increase in computational complexity and memory space. Two strategies after synchronization error estimation have been analyzed. They provide better BER performance in the existence of initial synchronization error. They are practical to be implemented in the sensor nodes before the Alamouti decoding.

Spectral efficient cooperative transmission for half-duplex relay communications

A new transmission protocol using MIMO (Multiple Input Multiple Output) half-duplex relays is proposed to improve the capacity and the diversity gain of uplink relay communication systems. The proposed protocol employs two half-duplex DF (Decode-and-Forward)relays and Alamouti coded 2×2 MIMO communication for links between each relay and the destination. A low complexity receiver using maximum ratio combining and Alamouti decoding is introduced to detect the signal of the proposed protocol. Performance is evaluated by theoretical analysis and computer simulations, and the results show that the proposed protocol outperforms conventional IEEE 802.16j systems in terms of ergodic capacity and outage probability.

Improved linear group detection for combined spatial multiplexing/STBC systems

Wireless architectures combining the use of spatial division multiplexing (SDM) and space-time block coding (STBC) have begun to appear in the latest communications standards. In recent years, different detection strategies for these schemes have been proposed which can be broadly categorised as group-based or direct-detection techniques. While the former class aims at separating the different STBC streams and then apply conventional simple Alamouti decoding, the latter type directly estimates the transmitted symbols without fully exploiting the Alamouti structure. Previous publications have shown that direct-detection outperform group-based detectors with the penalty of a higher computational complexity. This letter presents a unified view of the detection strategies for hybrid SDM/STBC systems and presents two new families of group-based detectors. It is shown that linear group detection, when properly implemented, attains the same performance as linear direct detectors at a significant lower complexity.

On the performance of concatenated convolutional code and Alamouti space-time code with noisy channel estimates and finite-depth interleaving

In this paper, performance of the Alamouti space- time code (STC) [1] and performance of the concatenation between the convolutional code and the Alamouti STC are derived. In order to describe realistic performance issues, we assume that the channel estimates are calculated from linear filters using noisy pilot symbols. We also assume non-quasi- static channels, spatially correlated transmit antennas and finite- depth interleaving. Two types of receivers are investigated for the Alamouti STC, namely, the linear-combining space-time decoder (LC-STD) and the maximum-likelihood space-time decoder (ML- STD). Two types of receivers are investigated for the concatenated system, namely, the LC-STD with the ML convolutional decoder and the joint Alamouti and convolutional ML decoder. The results have shown that the LC-STD is more sensitive to the Doppler spread than the ML-STD. However, since the ML- STD is very sensitive to the channel estimation error, the gains provided by the decoder in fast fading channels will be offset unless an optimized channel estimator is employed. Performance comparisons between the Alamouti systems and the SISO systems indicate that, when the system environment is not ideal, the SISO systems may outperform the Alamouti systems. Lastly, analytical results are compared with simulation results to illustrate the accuracy of the analysis.

Recursive Decoding for OFDM Systems with Multiple Transmit Antennas

In this letter, we propose a recursive space time decoding method for orthogonal frequency division multiplexing (OFDM) systems exploiting multiple transmit antenna diversity when the channels are fast fading. We first develop a computationally efficient space-time decoding method involving a matrix inversion to mitigate the channel variation effect. We then further reduce the computational complexity of the matrix inversion decoding method via a recursive formulation. Computer simulation results show that the proposed recursive decoding has much better BER performance than Alamouti decoding, requiring much less computation than the matrix inversion decoding. Moreover, the relative advantage in BER performance of the proposed scheme over Alamouti decoding stands out as the Doppler frequency increases.