Alamouti Space-time Block Code Research Articles

Decoding and Performance Bound of Demodulate-and-Forward Based Distributed Alamouti STBC

In a demodulate-and-forward (DF) based cooperative communication system, erroneous relaying of the data leads to degradation in the performance of the destination receiver. However, a maximum likelihood (ML) decoder in the destination can improve the receiver performance. For achieving a diversity gain, the Alamouti space-time block code (STBC) can be used in the DF based cooperative system in a distributed manner. In this paper, we derive an ML decoder of the distributed Alamouti STBC for the DF based cooperative system with two imperfect relaying nodes. We also consider a DF cooperative communication system in which one out of two relays is in outage. A piece-wise linear (PL) decoder for the DF cooperative system with the distributed Alamouti code and one relay in outage is proposed. The PL decoder provides approximately the same performance as that of the ML decoder with reduced decoding complexity. We derive the pairwise error probability (PEP) of the proposed ML decoder with binary phase-shift keying constellation. An optimized transmit power allocation for the relays is performed by minimizing an upper bound of the PEP. It is shown by simulations that the proposed ML decoder enables the DF protocol based cooperative system to outperform the same rate amplify-and-forward protocol based cooperative system when both systems utilize the distributed Alamouti STBC.

Spectrally efficient multiple‐ARQ scheme for MIMO channel

Proposed is a multiple automatic repeat request (ARQ) scheme for the MIMO channel adopting the structure of space-time block codes (STBCs). With multiple transmissions accompanied by the proposed combing strategy, the input-output relationship of the Alamouti STBC is formed in the receiver. It is observed that the proposed ARQ scheme attains higher throughput than others at all SNR values.

Asymptotic SEP Analysis of Two-Way Relaying Networks With Distributed Alamouti Codes

Asymptotic symbol error probability (SEP) performance with an optimal maximum likelihood (ML) receiver and square quadrature amplitude modulation (QAM) constellations is investigated for two-way amplify-and-forward (AF) half-duplex relaying networks employing distributed Alamouti space-time block codes (DASTCs) recently proposed by Duong By developing a novel strategy to particularly deal with some specific Gaussian integrals, two asymptotic SEP formulas are derived for both fixed- and variable-gain AF protocols. These analytic results reveal that, when the signal-to-noise ratio (SNR) is large, the diversity gain for the variable-gain AF is 2, whereas the diversity gain function for the fixed-gain AF is proportional to SNR <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ln SNR.

Energy-Efficient Collaborative Alamouti Codes

A novel energy-efficient collaborative Alamouti space-time block code (STBC) design is proposed for a wireless communication system having two transmitter antennas and a single receiver antenna. This new design allows us to have more options for variable-rate modulation for fading channels with enhanced performance for signal transmission than the conventional Alamouti coding scheme while having complex-symbol-decodable complexity for the maximum likelihood (ML) detector. Subject to the constraints on a fixed transmission bit rate and unity average energy per each transmitter antenna, the optimal linear constellation combinations with the optimal energy-scales as the coefficients are attained by maximizing the coding gain. It is shown that the optimal coding gain of the newly-designed code is larger than that of the conventional Alamouti code if the transmission bit rate is greater than two bits per channel use.

Research on Coded Cooperative Strategy in Satellite Communications

Aiming at the satellite mobile communication, the cooperative communication technology is applied to the forward downlink in this paper, and one scheme with two satellites based on the coded cooperative which used the Alamouti space time block code is presented. Simulation results show the coded cooperative strategy can obtain better performance than the traditional uncoded systems, which is lower than the MIMO system with two transmit antennas and one receive antenna based on the Alamouti code, but the power of the terminal was decreased. It has the advantage in communication range and low complex mobile terminal, which has a certain application prospects in satellite mobile communications in the future.

BER Analysis of Three-Phase XOR-and-Forward Relaying Using Alamouti STBC

In this paper we investigate the performance of two-way relaying that uses Alamouti space-time block code (STBC) and network coding. In this scheme, two nodes use Alamouti STBC to transmit their symbols to the relay consecutively in two phases. The relay detects and demodulates the transmitted symbols from the nodes, and then uses the bitwise-XOR operation to combine the detected bits. Then the relay modulates and broadcasts the XORed bits to the nodes using Alamouti STBC. In this paper, the bit error rate of the proposed scheme is derived for an uncorrelated Rayleigh fading channel with perfect channel estimation at receivers.

Analysis of Multihop Relaying Networks: Communication Between Range-Limited and Cooperative Nodes

The focus of this article is on analyzing the impact of the number of hops and the number of transmit and receive antennas, at the relay nodes, on the performance of multihop networks. The vision of future wireless networks includes a greater role for ubiquitous ad hoc networks based on multihop transmissions between machines and general mobile devices carried around by users. With this in mind, the standards are set to include greater capabilities and specifications regarding ad hoc mesh networks, especially ones that employ multiple antennas for transmissions. Therefore, there is a need for an in-depth analysis of the performance of such networks. In this analysis, we consider equidistant distributed relays between the source and destination. The statistics of the channels of all hops and the noise powers at all terminals are assumed to be the same. The capacity for the amplify-and-forward (AF) and decode-and-forward (DF) relaying schemes over the single-input single-output (SISO) channel is compared. Moreover, we derive a closed-form solution of the ergodic capacity in the presence of Rayleigh fading for multihop wireless transmissions when the DF-relaying scheme and SISO links between the relay nodes are employed. The quality of service (QoS) of the single-input multiple-output (SIMO) and multiple-input multiple-output (MIMO) [Alamouti space-time block code (STBC)-based scheme] multihop networks are studied, and their performance is compared analytically with each other.

On the Vulnerabilities of CSI in MIMO Wireless Communication Systems

Multiple-input multiple-output (MIMO) technologies are a popular choice for emerging wireless systems due to their promised gains in throughput and reliability. In order to realize any gains over traditional non-MIMO communication systems, these systems must possess accurate knowledge of the wireless channel. In this paper, we investigate strategies for disrupting MIMO communications by developing attacks that target the often overlooked, but essential, channel estimation procedure. Our study focuses on the two most popular and well-known MIMO techniques: the capacity achieving SVD-based MIMO scheme, and the Alamouti space-time block code (STBC), which spans many protocols including 802.11n, WiMAX, and 3GPP. We augment theoretical and simulation results with real-world experimentation using the USRP/GNU Radio software defined radio platform. We also present novel methodology to protect the channel estimation procedure from such attacks by embedding authentication messages into physical layer features of the transmissions.

A two‐stage receiver with soft interference cancellation for space–time block code and spatial multiplexing combined systems

AbstractThis paper presents a new space–time two‐stage receiver with the assistance of soft information for the Alamouti space–time block code (STBC) and spatially multiplexing (SM) combined multiple‐input multiple‐output (MIMO) systems, which possess both the advantages of high diversity gain and high data rates to entail the next generation wireless communication systems. The first stage of the receiver, utilizing the inherent structure of the STBC, consists of a bank of soft generalized sidelobe canceller (GSC)‐based detectors, each for every STBC block, and intends to yield a more precise initial estimate of the transmitted symbols. In the second stage, the groupwise detection is conducted successively by using the matched filters (MFs) to simultaneously detect the two consecutive symbols in one STBC block with the removal of the soft interferences in between. Since the interferences have been faithfully reproduced and thoroughly annihilated, the new receiver can yield accurate symbol detection even with simple MFs. Moreover, some extreme cases regarding the soft information employed in the new receiver and its extension to the multiuser (MU) MIMO downlink are addressed as well. Conducted simulations show that the developed receiver, with modest computational load, can provide superior performance compared with pervious works, especially in the MU MIMO downlink. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Spatial Multipath Resolution with Space Time Block Codes

The use of space time block codes (STBCs) over frequency selective multipath multiple-input multiple-output (MIMO) channels is investigated in combination with spatial multipath resolution (SMR) [1], a novel spatial signal processing technique proposed by the authors for mitigating inter-symbol interference. Neither STBC nor SMR requires transmit channel state information. This fact, along with SMR not requiring any modification to the transmitter, makes the MIMO STBC-SMR hybrid effective. Numerical results are presented, illustrating how the scheme fares under the Alamouti STBC scheme, and highlighting the advantage of adaptive SMR - i.e., adapting the number of multipaths resolved based on the channel state. A practical multipath MIMO channel based on the IEEE 802.15.3c NLOS (CM4) model is used for simulation.

Distributed Concatenated Alamouti Codes for Two-Way Relaying Networks

In this letter, we consider a half-duplex amplify-and-forward two-way relaying network consisting of two sources with each having a single antenna and one relay having two antennas. For such a system, a distributed orthogonal space-time block code (STBC) is proposed by making use of the Alamouti coding scheme and jointly processing the signals from the two antennas at the relay node. Such a code turns out to make the equivalent channel at each source node be a product of the two Alamouti channels and thus, is called distributed concatenated Alamouti STBC. In addition, the asymptotic formula of exact symbol error probability (SEP) for a quadrature amplitude modulation (QAM) constellation with the maximum likelihood (ML) detector is derived. This result shows that the full diversity gain function is achieved and proportional to ln SNR /SNR2.

Cooperative Space Time Coding for Semi Distributed Detection in Wireless Sensor Networks

Parallel distributed detection in wireless sensor networks (WSNs) is considered in this paper. In parallel architecture, sensors process the observations to make local decisions and send them to a central device called fusion center. Parallel architecture is assumed in this paper with cooperative sensors in order to obtain Alamouti space time block codes (STBCs). A similar idea was discussed by Vosoughi and Ahmadi (2009). Although the likelihood ratio provided in that paper is correct, the simulation results don’t make sense. In this paper, we are going to prove that the results provided in (Vosoughi &amp; Ahmadi, 2009) are not correct. Upper bound for the detection performance is also derived. Furthermore, suboptimal fusion rules are derived to support our results. Moreover, correct results are shown in this paper.

Effect of Interleaved FEC Code on Wavelet Based MC-CDMA System with Alamouti STBC in Different Modulation Schemes

In this paper, the impact of Forward Error Correction (FEC) code namely Trellis code with interleaver on the performance of wavelet based MC-CDMA wireless communication system with the implementation of Alamouti antenna diversity scheme has been investigated in terms of Bit Error Rate (BER) as a function of Signal-to-Noise Ratio (SNR) per bit. Simulation of the system under proposed study has been done in M-ary modulation schemes (MPSK, MQAM and DPSK) over AWGN and Rayleigh fading channel incorporating Walsh Hadamard code as orthogonal spreading code to discriminate the message signal for individual user. It is observed via computer simulation that the performance of the interleaved coded based proposed system outperforms than that of the uncoded system in all modulation schemes over Rayleigh fading channel.

Receiver Diversity for Distributed Detection in Wireless Sensor Networks

In this paper, parallel distributed detection in wireless sensor network (WSN) is considered where the sensors process the observations to make local decisions and send these decisions to a central device called fusion center. Receiver diversity technique is proposed here for the distributed detection system in order to enhance the system reliability by improving the detection performance. The fusion center is assumed to be multiple antennas device in order to imply the idea of receiver diversity. Different combining schemes at the fusion center side are used to reduce the fading effects in the case of receiver diversity. Transmitter diversity is also considered in this paper. Cooperative sensors are assumed in order to obtain Alamouti space time block codes. Optimal and sub-optimal fusion rules are derived for each case study. Simulation results show the performance improvement obtained as compared to the conventional distributed detection system in which no diversity is used.

A Simple Layered Space-Time Block Nulling Technique for DSTTD Systems

A double space-time transmit diversity (DSTTD) system employs four transmit antennas to multiplex two Alamouti space-time block code (STBC) units. In this letter, a specially-designed canceling mechanism is presented, which can efficiently separate the two STBC units for such systems. We show that the orthogonal structure, and so the merit of Alamouti STBC, can be kept. Compared with some previous interference cancelation methods, the proposed one requires much fewer floating-point operations (flops) while achieving similar error-rate performance.

Low complexity lattice reduction scheme for STBC two-user uplink MIMO systems

Abstract Recently, a lattice reduction-aided (LRA) multiple-input multiple-output detection scheme has been proposed in junction with linear (as well as nonlinear) detectors. It is well known that these schemes provide a full diversity, and its complexity is comparable to that of linear detectors for the block fading channels. For the fast varying channels, however, the decoding complexity of LRA detection scheme is unreasonably high. This article proposes an efficient iterative lattice reduction (LR) scheme for an uplink system with two receive antennas at the base station and two users, each employing the Alamouti space-time block code (STBC). By taking advantage of the certain inherent STBC structure of transmitted symbols from users, the proposed scheme provides the same performance as a conventional LR while saving about 80% computational complexity. We also show that it can be successfully extended to handle the scenario where another interfering user, who is also employing the Alamouti STBC, is present.

Design, Implementation, and Characterization of a Cooperative Communications System

Cooperative communications is a class of techniques that seek to improve reliability and throughput in wireless systems by pooling the resources of distributed nodes. Although cooperation can occur at different network layers and time scales, physical-layer cooperation at symbol time scales offers the largest benefit in combating losses due to fading. However, symbol-level cooperation poses significant implementation challenges, particularly in synchronizing the behavior and carrier frequency of distributed nodes. We present the implementation and characterization of a complete real-time cooperative physical-layer transceiver built on the Rice University Wireless Open-Access Research Platform (WARP). In our implementation, autonomous nodes employ physical-layer cooperation without a central synchronization source and can select between non-cooperative and cooperative communications per packet. Cooperative transmissions use a distributed Alamouti space-time block code (STBC) and employ either amplify-and-forward (AF) or decode-and-forward (DF) relaying. We also present experimental results of our transceiver's real-time performance under various topologies and propagation conditions. Our results clearly demonstrate significant performance gains (more than 40× improvement in packet error rate in some topologies) provided by physical-layer cooperation, even when subject to the constraints of a real-time implementation. Finally, we present methodologies for isolating and understanding the sources of performance bottlenecks in our design. As with all our work on WARP, our transceiver design and experimental framework are available through the open-source WARP repository for use by other wireless researchers.

A Near-Optimum Multiuser Receiver for STBC MC-CDMA Systems Based on Minimum Conditional BER Criterion and Genetic Algorithm-Assisted Channel Estimation

The implementation of efficient baseband receivers characterized by affordable computational load is a crucial point in the development of transmission systems exploiting diversity in different domains. This would be a crucial point in the future development of 4G systems, where space, time, and frequency diversity will be combined together in order to increase system throughput. In this framework, a linear multiuser detector for MC-CDMA systems with Alamouti's Space-Time Block Coding (STBC), which is inspired by the concept of Minimum Conditional Bit Error Rate (MCBER), is proposed. The MCBER combiner has been implemented in adaptive way by using Least-Mean-Square (LMS) optimization. The estimation of Channel State Information (CSI), necessary to make practically feasible the MCBER detection, is aided by a Genetic Algorithm (GA). The obtained receiver scheme is near-optimal, as both LMS-based MCBER and GA-assisted channel estimation perform closely to optimum in fulfilling their respective tasks. Simulation results evidenced that the proposed receiver always outperforms state-of-the-art receiver schemes based on EGC and MMSE criterion exploiting the same degree of channel knowledge.

The Scheme and Performance Analysis of Combined Beamforming with Space-Time Block Coding

Alamouti空时块码与波束形成相结合的方案只使用了两个功率均分的波束,在很多情况下并非最优。该文提出了新的空时块码与波束形成相结合的方案,新方案能够根据信道互相关矩阵的特征值,展开不超过发射端天线数量的波束,在满足空时块码发射天线数量等于波束数量的条件下,与任意码率空时块码结合。该文还利用Gauss-Chebyshev积分对线性调制下新方案的误符号率进行了性能分析,得出了简单的数值计算表达式。新方案由于同时获得了分集增益和波束形成增益,显著提高了系统的性能。

On the Performance Analysis of a MIMO-Relaying Scheme With Space–Time Block Codes

This paper presents performance analysis of a cooperative multiple-input-multiple-output (MIMO) relaying system with a single relay. In this scheme, each link uses MIMO Alamouti space-time block coding (STBC) over Rayleigh flat-fading channels. The particularity of the proposed scheme is that, during a first time slot, the source node broadcasts each STBC to the relay and destination nodes. During the second time slot, the relay node amplifies-and-forwards (AF) the received STBCs. Finally, the receiver at the destination node exploits the diversity gain that is obtained through the direct and indirect links simultaneously by applying maximum ratio combining (MRC) on the received signals. Using the SNR for the direct link and an upper bound of the SNR for the indirect link, the moment-generating function (MGF) of the SNR for the cooperative link is derived. Since this MGF is based on an upper bound of the SNR, it is then employed to derive a lower bound of the symbol error probability (SEP) for a particular signal of M-ary quadrature-amplitude modulation (M-QAM). Subsequently, simulation results of the SEP are presented to illustrate the performance improvement given by the MIMO cooperative diversity system based on the STBC scheme.