Quasi-orthogonal Space-time Block Codes Research Articles

Distributed Orthogonal and Quasi-Orthogonal Space-Time Block Code with Embedded AAF/DAF Matrix Elements in Wireless Relay Networks with Four Relays

We consider cooperative networks of one source, four relays, and one destination. Each of them has a single antenna. The four relays use a proposed full rate distributed quasi orthogonal space time...

A Single Symbol Maximum-Likehood Decoder for Four Transimit Antenna QOSTBC

This letter proposes a very low-complexity maximum likelihood (ML) detection algorithm for the quasi-orthogonal space-time block code (QOSTBC) with four transmits antennas. The low-complexity single-complex-symbol detection is based on QR decomposition and the expansion of equalization via a diagonal matrix transformation. The proposed strategy enables the QOSTBC to achieve ML performance with significant reduction in computational load for any high-level modulation scheme.

Novel Distributed Quasi-Orthogonal Space-Time Block Codes for Two-Way Two-Antenna Relay Networks

A half-duplex amplify-and-forward two-way relay network consisting of two single-antenna sources and N relays with each having two antennas is considered in this paper. For such a system, a tight lower bound of pairwise error probability (PEP) of a maximum likelihood (ML) detector for any distributed linear dispersion code with a fixed average amplifier is derived, revealing that diversity gain function cannot decay faster than ln <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</sup> SNR/SNR <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2N</sup> , where rm SNR is signal to noise ratio. Particularly for the network having two relays, a novel distributed quasi-orthogonal space-time block code (QO-STBC) is proposed with two significant advantages. One is that the equivalent channel matrices at both source nodes turn out to be the block-circulant matrices, with each block being a product of the two Alamouti channel matrices. The other is that the equivalent noises at the both source nodes are Gaussian and white. Therefore, like QO-STBC for a multi-antennas system, the proposed code for the relay system still maintains low-decoding complexity for the ML detector. Asymptotic PEP formula is attained to show that the proposed code enables the optimal diversity gain function, i.e., meeting the lower bound of diversity gain, and the optimal coding gain. In addition, a near optimal power allocation that maximizes the received SNR of the worse link is presented and examined through comprehensive computer simulations for various kinds of asymmetric relay channels.

A Novel QO-STBC Scheme with Linear and Single-Symbol Decoding

In this paper, a quasi-orthogonal space time block coding (QO-STBC) scheme with maximum likelihood (ML) decoding via simple linear and single-complex-symbol detection is proposed. We present a fast and simple linear decode processing by embedding a transformed signal space. The method benefits from the reduced maximum likelihood decoding complexity via the pre-interleaving to QO-STBC. We also proposed codes with 3/4 of the full transmission rate for the specific cases of 8 transmit antennas. Finally, the numerical results show the proficiency of our design procedure, demonstrating that significant improvements in BER are achievable when the rate or receive antennas increases.

OFDM-Based STBC with Low End-to-End Delay for Full-Duplex Asynchronous Cooperative Systems

We propose a new space-time block coding (STBC) for asynchronous cooperative systems in full-duplex mode. The orthogonal frequency division multiplexing (OFDM) transmission technique is used to combat the timing errors from the relay nodes. At the relay nodes, only one OFDM time slot is required to delay for a pair-wise symbol swap operation. The decoding complexity is lower for this new STBC than for the traditional quasi-orthogonal STBC. Simulation results show that the proposed scheme achieves excellent performances.

Analysis of Minimum Decoding Complexity Quasi-Orthogonal Space-Time Block Code for 6 Transmit Antennas

Previous work on quasi-orthogonal space-time block code (QO-STBC) has been designed to achieve full rate and full diversity gain for four antennas. However this conventional QO-STBC scheme decoding is complex. For achieving more diversity gains, an extended QO-STBC scheme is provided to achieve full diversity with one rate for six antennas. Furthermore, by transforming the detection matrix to an orthogonal one, this novel scheme can achieve a simple linear decoding. Therefore it proposes an extended minimum decoding complexity QO-STBC (MDC-QO-STBC) for six antennas. Due to eliminate the interference from different equivalent channels, the novel extended MDC-QO-STBC scheme improves transmission reliability and linear decoding complex compared with the conventional QO-STBC scheme. At last extensive simulation results are presented to prove the theoretical analysis.

Toward a Preferred 4 x 4 Space-Time Block Code: A Performance-Versus-Complexity Sweet Spot with Linear-Filter Decoding

We develop a new 4 × 4 Hadamard-precoded quasi-orthogonal space-time block code (QO-STBC) that enables highly effective near-maximum-likelihood (near-ML) reliability-based prioritized symbol detection using linear filters. Approximate block-error-rate minimization is being used to optimize the code rotation angle. Detailed computational complexity evaluation of the decoder in terms of real multiplications and additions shows significant complexity reduction for symbol alphabet sizes of interest. Numerical and simulation studies demonstrate negligible bit-error-rate degradation compared to the state-of-the-art in bit-error-rate by ML decoded 4 × 4 codewords.

A New Approach for OSTBC and QOSTBC

ABSTRACT A new approach for Quasi-Orthogonal space time block coding (QO-STBC) is proposed, with simple linear decoding via maximum likelihood detection. The conventional QO-STBC can achieve the full communication rate, but at the expense of the decoding complexity and the diversity gain due to the interference terms in the detection matrix. In this paper we propose a QO-STBC scheme that will eliminate the interference from the detection matrix. The proposed code improves the diversity gain compared with the conventional QO-STBC scheme; it also reduces the decoding complexity. A full rate full diversity order DiagonalizedHadamard Space Time code (DHSTBC) is presented Keywords Quasi-Orthogonal space time block coding (QO-STBC), full rate, full diversity order,DiagonalizedHadamard Space Time code (DHSTBC). 1. INTRODUCTION In traditional communication systems there is only one antenna at both the transmitter and the receiver. This antenna system is known as Single Input Single Output (SISO). SISO systems have a major drawback in terms of the capacity, as stated by the well-known Shannon-Nyquist criterion. In order to increase the capacity of SISO systems to meet the high bit rate transmission demanded by modern communications, the bandwidth and the power have to increase significantly. Fortunately, using the Multiple-Input Multiple-Output (MIMO) system could increase the capacity of the wireless system without the need to increase the transmission power or the bandwidth. Transmit diversity is a well-known technique to mitigate fading effects over a communication link. Alamouti [1] proposed a transmit diversity scheme that offers maximum diversity gain using two antennas at the transmitter. The pioneering work of Alamouti has been the basis to create Orthogonal space time block coding systems (OSTBCs) for more than two transmit antennas. First of all, Tarokh studied the error performance associated with unitary signal matrices [2]. Sometime later, Ganesan streamlined the derivations of many of the results associated with OSTBC and established an important link to the theory of the orthogonal and ‘amicable orthogonal’ designs [3]. It has been proved that a complex orthogonal design of STBCs that provides full diversity and full transmission rate is not possible for more than two transmit antennas [1]. To achieve full-rate transmission while maintaining much of the orthogonality benefits of OSTBC, Quasi Orthogonal Space Time BlockCode(QO-STBC) has been proposed [4-6]. A QO-STBC can achieve full rate but interference terms will appear from the neighboring signals during the signal detection which will increase the detection complexity and decrease the gain performance.

Performance Evaluation of OSTBC Systems using different Channels

Due to the increased demand of wireless communication systems because of the features of the system which provides a wide coverage, high throughput and reliable services, the MIMO systems communication has come into existence and has been shown to be one of the most promising emerging wireless technologies that can efficiently boost the data transmission rate and capacity of wireless communication system.An effective and practical way to approach these demands of MIMO wireless channel is to employ Space Time (ST) Coding. The performance improvement of MIMO systems can be assessed by using diversity gain and spatial multiplexing gain. Space Time Coding transmits signal across the spatial and time domain simultaneously in order to achieve diversity gain without increasing bandwidth. In this paper, we exploit the space and time diversity to decode the quasi and rotated quasi orthogonal space time block codes (QOSTBC) based on Jakes model and Dent channel model. For Doppler shifting and Rayleigh distribution we make use of dent channel model. This provides fast decoding and gives better performance of communication system as compared to Jakes model. BER analysis has been presented in terms of diversity and code rate.

Performance of Space Time Block Codes and Quasi Orthogonal Space Time Codes on Fading Channel

In this paper the performance of Space Time Codes (STC) & Quasi Orthogonal Space Time Block Codes (QOSTBC) has been analyzed. Use of multiple antennas is an emerging approach for recovering fading and reducing the bit error rate. Space diversity is introduced in space time codes. In Alamouti Space Time Code (STC) two transmit antennas are used that provide relatively better results than no coding approach. Alamouti uses a code matrix at transmitter and at receiver end it uses MLD and estimates the output signals. Space time block codes are with arbitrary number of antennas. It uses a huge code matrix at encoder and decodes using MLD. QOSTBC is one of the latest variants of the STBCs. The encoded symbols are mapped in the transmission matrix which is decoded at the receiver end using pair wise maximum likelihood decoding (MLD). Pair wise MLD is the specialty of the QOSTBC. The performance of STBC is far better than Alamouti and has no match with no coding. The performance comparison of QOSTBC, Alamouti, STBC and no coding is showed using simulations in MATLAB. Space time codes works with the price of redundancy bits and extra antenna price. Simulation results for QOSTBC also shows better performance with the price of slightly increased decoding complexity.

A Grouped Decoding Algorithm for Non-binary LDPC code with Quasiorthogonal STBC in MIMO System

A Grouped Decoding Algorithm for Non-binary LDPC code with Quasiorthogonal STBC in MIMO System

Fastest-Known Maximum-Likelihood Decoding of Quasi-Orthogonal STBCs with QAM Signals

We present a maximum-likelihood (ML) decoder with the lowest computational complexity known to-date for full-diversity, arbitrary size Quasi-Orthogonal Space-Time Block Codes (QO-STBCs) with symbols from square or rectangular quadrature amplitude modulation (QAM) constellations. We start with the formulation of an explicit joint two-complex-symbol decoder for general QO-STBCs with arbitrary complex symbols and then derive the proposed ML decoder for QO-STBCs with QAM symbols. The complexity savings are made possible by a simplified quadratic ML decoding statistic that utilizes algebraically the structure of the signal points of the QAM constellation. Comparative computational complexity analysis with existing ML implementations and simulation studies are included herein for illustration and validation purposes.

Low‐complexity symbol timing error detection for quasi‐orthogonal space–time block codes

The author presents the design and analysis of low-complexity symbol timing error detectors (TEDs) for timing synchronisation in quasi-orthogonal space-time block code (QOSTBC) receivers. The estimators operate on data symbols and approximate decision variables, producing timing error measurements which are shown to be robust to channel fading. In evaluating the detector S-curve for the general form of the estimator, the author shows that the result is independent of the constellation rotation angle employed by the code. The expressions for the estimation error variance and TED signal-to-noise ratio are also obtained, with the analysis carried out under the assumptions of perfect data and channel knowledge at the receiver. Through system simulations, the effects of decision errors on the detector characteristics are examined, and the overall system performance is evaluated, where the proposed TEDs are incorporated into the receiver timing loop. Receivers with perfect channel knowledge and pilot-based channel estimation are considered. Symbol error rate results show timing synchronisation loss of less than 0.5 dB for a receiver with perfect channel information. In addition, it is shown that the receiver is able to track the timing variations two orders of magnitude faster than required by the present-day hardware oscillators.

Single‐symbol decodable space‐time block code for multi‐input–multi‐output systems with four transmit antennas

This study presents an orthogonal design of space-time block code (STBC) that is single symbol decodable and enables full diversity and full rate transmission in a quasi-static channel environment. In the proposed scheme, full diversity is achieved by use of constellation rotation and co-ordination interpolation as is the case for the co-ordinate interleaved orthogonal design, whereas the transmission matrix of the proposed code consists of orthogonal columns with all non-zero elements, alleviating the concern about high peak-to-average power ratio. In particular, the proposed code offers lower complexity of channel estimation, and exhibits lower symbol error rate than the conventional quasi-orthogonal STBC when an maximum-likelihood decision-directed channel estimator is assumed. The advantages of the proposed code over the conventional codes are demonstrated through computer simulations. In addition, the selection of the angle of rotation for the proposed design is also presented, regarding the impact of channel estimation error.

On the Performance of Quasiorthogonal STBC with Relay Selection and Phase Rotation Techniques for Decode and Forward Cooperative Communications

The performance of quasiorthogonal space-time block code with relay-selection and phase-rotation techniques applied to cooperative communications for four communication nodes is investigated. Specifically, by applying relay-selection and phase-rotation techniques, a diversity gain of four can be achieved. In addition, a symbol error rate (SER) performance analysis with closed-form expression and power allocation are investigated and compared with simulation results. The results show that theoretical SER curves are close to the simulation results. In addition, a code rate of the proposed scheme is two times higher than ordinary cooperative communications. The computer simulation results also show a significant probability of error improvement of about 2.8 dB over the conventional decode-and-forward protocol.

Improved QO-STBC OFDM System Using Null Interference Elimination

The quasi-orthogonal space time block coding (QO-STBC) over orthogonal frequency division multiplexing (OFDM) is investigated. Traditionally, QO-STBC does not achieve full diversity since the detection matrix of QO-STBC scheme is not a diagonal matrix. In STBC, the decoding matrix is a diagonal matrix which enables linear decoding whereas the decoding matrix in traditional QO-STBC does not enable linear decoding. In this paper it is shown that there are some interfering terms in terms of non-diagonal elements that result from the decoding process which limit the linear decoding. As a result, interference from the application of the QO-STBC decoding matrix depletes the performance of the scheme such that full diversity is not attained. A method of eliminating this interference in QO-STBC is investigated by nulling the interfering terms towards full diversity for an OFDM system. It was found that the interference reduction technique permits circa 2dB BER performance gain in QO-STBC. The theoretical and simulation results are presented, for both traditional QO-STBC and interference-free QO-STBC applying OFDM

Quasi-Orthogonal Space-Time Block Code with Givens Rotation for SC-FDE Transmission in Frequency Selective Fading Channels

Conventional space-time block codes are normally designed and studied for Rayleigh flat fading channels. As Single Carrier Frequency-Domain Equalization (SC-FDE) can help to combat the Inter-Symbol Interference (ISI) caused by multipath radio channels, this paper investigates quasi- orthogonal space-time block code (QOSTBC) with Givens rotation in order to enhance the reliability of the SC-FDE transmission in the frequency selective fading channels. To use QOSTBC with Givens rotation for the SC-FDE system, the encoding is performed on the data block basis, and we derive the corresponding decoding method performing in the frequency domain at the receiver. With Givens rotation, the correlation of channel equivalent matrix is eliminated, and the decoding can be performed with linear combiner at the receiver. Such a proposed scheme can achieve full rate transmission and provide high diversity gain. Simulation results show that the BER performance of the proposed scheme is better than QOSTBC for four transmit antennas, and is better than OSTBC (orthogonal space-time block code) in the low SNR regime. 1

Low Complexity Decoder Design for Non-binary LDPC Coded MIMO System Using Quasi-Orthogonal STBC

Low Complexity Decoder Design for Non-binary LDPC Coded MIMO System Using Quasi-Orthogonal STBC

An Improved Low Complexity Detection Algorithm for Quasi-Orthogonal STBC

In this paper, based on QR decomposition, an improved detection algorithm for quasi-orthogonal space-time block code (QOSTBC) using square QAM constellation is presented. In the proposed method, by executing single complex symbol twi-detection for each block and selecting the optimal result, the BER performance is much better than that of the linear receivers. Compared with conventional maximum-likelihood (ML) decoding, though the bit error rates (BER) performance is with a slight loss, the improved detection algorithm reduces the decoding complexity significantly. The derivation and simulation results of the proposed algorithm are presented.

A simple asynchronous distributed STBC network scheme with full diversity

In this article, we propose a simple distributed space-time block code (STBC) network scheme for asynchronous relay network, where every two traditional relay nodes are combined to one node to amplify and forward the processed signals via the same transmission antenna. In the proposed distributed network scheme, we consider a wireless scenario with frequency selective fading channels. The orthogonal frequency division multiplexing (OFDM) symbols are broadcast from source to relay nodes in the first step, and in the second step, the received signals at the relay nodes are implemented with a simple operation and mixed partially and forwarded to destination. In this network scheme, the four by four quasi-orthogonal STBC (QO-STBC) is applied, and the orthogonal decoding algorithm can be used at the receiver because of the orthogonality of the re-constructed equivalent transmission matrix. Thus, the full rate and the full diversity are achieved at the transmitter and the receiver of the proposed distributed network scheme, respectively. Simulation result shows that the proposed distributed STBC network scheme has better performance than other network schemes.