Trellis code‐aided high‐rate M‐QAM space‐time labeling diversity using a unitary expansion

In this paper, we present a high‐rate M‐ary quadrature amplitude modulation (M‐QAM) space‐time labeling diversity (STLD) system that retains the robust error performance of the conventional STLD system. The high‐rate STLD is realised by expanding the conventional STLD via a unitary matrix transformation. Robust error performance of the high‐rate STLD is achieved by incorporating trellis coding into the mapping of additional bits to high‐rate codes. The comparison of spectral efficiency between the proposed trellis code‐aided high‐rate STLD (TC‐STLD) and the conventional STLD shows that TC‐STLD with 16‐QAM and 64‐QAM respectively achieves a 12.5% and 8.3% increase in spectral efficiency for each additional bit sent with the transmitted high‐rate codeword. Moreover, we derive an analytical bound to predict the average bit error probability performance of TC‐STLD over Rayleigh frequency‐flat fading channels. The analytical results are verified by Monte Carlo simulation results, which show that the derived analytical bounds closely predict the average bit error probability performance at high signal‐to‐noise ratios (SNR). Simulation results also show that TC‐STLD with 1 additional bit achieves an insignificant SNR gain of approximately 0.05 dB over the conventional STLD, while TC‐STLD with 2 additional bits achieves an SNR gain of approximately 0.12 dB.     

Improved error performance of a 3/4‐Sezginer space‐time block codes

The Alamouti space‐time block code (STBC) achieves full diversity gain at a rate of 1/2. However, the Alamouti scheme does not provide multiplexing gain. The Silver code offers both diversity and multiplexing gain. It has a minimum normalization determinant of . The Golden code is another STBC that offers both diversity and multiplexing gain. The Golden code is ranked higher than the Silver code because of its lower minimum normalization determinant of , however, the golden code suffers from a high detection complexity in the modulation order of M⁴. The 3/4‐Sezginer code is another STBC, which compromises between the Alamouti scheme and the Golden code in terms of diversity gain and multiplexing gain. The 3/4‐Sezginer code achieves full diversity and half of multiplexing gain. The uncoded space‐time labeling diversity (USTLD) is a recent scheme that improves the error performance when applied to the STBC in multiple‐input multiple‐output (MIMO) systems and will be applied to the 3/4‐Sezginer STBC to improve the error performance in this paper. The theoretical error probability for both the 3/4‐Sezginer STBC and the improved system is formulated using the union bound in this paper. The theoretical error probabilities of both 16‐QAM and 64‐QAM are validated through Monte Carlo simulation. The simulation and theoretical results show that the proposed system with 4 N_R can achieve an SNR gain of 1 dB for 16‐QAM and 1.2 dB 64‐QAM at a bit error rate (BER) of 10^?6.     

Space‐time block coded spatial modulation with labeling diversity

Space‐time block coded spatial modulation (STBC‐SM) exploits the advantages of both spatial modulation and the Alamouti space‐time block code. Meanwhile, space‐time labeling diversity has demonstrated an improved bit error rate (BER) performance in comparison to the latter. Hence, in this paper, we extend the application of labeling diversity to STBC‐SM, which is termed STBC‐SM‐LD. Under identical channel assumptions, STBC‐SM‐LD exhibits superior BER performance compared to STBC‐SM. For example, with 4 × 4, 64‐quadrature amplitude modulation (64‐QAM), STBC‐SM‐LD has a BER performance gain of approximately 2.6 dB over STBC‐SM. Moreover, an asymptotic bound is presented to quantify the average BER performance of M‐ary QAM STBC‐SM‐LD over independent and identically distributed Rayleigh frequency‐flat fading channels. Monte Carlo simulations for STBC‐SM‐LD agree well with the analytical framework. In addition to the above, low‐complexity (LC) near‐maximum‐likelihood detectors for space‐time labeling diversity and STBC‐SM‐LD are presented. Complexity analysis of the proposed LC detectors shows a substantial reduction in computational complexity compared to their ML detector counterparts. For example, the proposed detector for STBC‐SM‐LD achieves a 91.9% drop in computational complexity for a 4 × 4, 64‐QAM system. The simulations further validate the near‐maximum‐likelihood performance of the LC detectors.     

Golden codeword–based modulation schemes for single‐input multiple‐output systems

The Golden code has full rate and full diversity. The Golden codeword matrix contains two pairs of super symbols. Based on one pair of super symbols, two modulation schemes, Golden codeword–based M‐ary quadrature amplitude modulation (GC‐MQAM) and component‐interleaved GC‐MQAM (CI‐GC‐MQAM), are proposed for single‐input multiple‐output (SIMO) systems. Since the complexities of the maximum likelihood detection for the proposed GC‐MQAM and CI‐GC‐MQAM are proportional to O(M²) and O(M⁴), respectively, low complexity detection schemes for the proposed GC‐MQAM and CI‐GC‐MQAM are further proposed. In addition, the theoretical average bit error probabilities (ABEPs) for the proposed GC‐MQAM and CI‐GC‐MQAM are derived. The derived ABEPs are validated through Monte Carlo simulations. Simulation and theoretical results show that the proposed GC‐MQAM can achieve the error performance of signal space diversity. Simulation and theoretical results further show that the proposed CI‐GC‐16QAM, ‐64QAM, and ‐256QAM with three receive antennas can achieve approximately 2.2, 2.0, and 2.1 dB gain at a bit error rate of 4 × 10^?6 compared with GC‐16QAM, ‐64QAM, and ‐256QAM, respectively.     

Performance analysis of M‐APSK generalised spatial modulation with constellation reassignment

Generalised spatial modulation (GSM) is a recently developed multiple‐input multiple‐output (MIMO) technique aimed at improving data rates over conventional spatial modulation (SM) systems. However, for identical antenna array size and configurations (AASC), the bit error rate (BER) of GSM systems in comparison with SM systems is degraded. Recently, a GSM system with constellation reassignment (GSM‐CR) was proposed in order to improve the BER of traditional GSM systems. However, this study focused on M‐ary quadrature amplitude modulation (M‐QAM) schemes. The focus of this paper is the application of a circular constellations scheme, in particular, amplitude phase shift keying (APSK) modulation, to GSM and GSM‐CR systems. An analytical bound for the average BER of the proposed M‐APSK GSM and M‐APSK GSM‐CR systems over fading channels is derived. The accuracy of this bound is verified using Monte Carlo simulation results. A 4 × 4 16‐APSK GSM‐CR system achieves a gain of 2.5 dB at BER of 10^?5 over the traditional 16‐APSK GSM system with similar AASC. Similarly, a 6 × 4 32‐APSK GSM‐CR system achieves a gain of 2 dB at BER of 10^?5 over equivalent 32‐APSK GSM system.     

V-BLAST系统中采用发射功率分配的MMSE迭代软干扰抵消算法

作为一种软输入软输出的MIMO检测算法,MMSE迭代软干扰抵消算法在MIMO Turbo接收机中得到广泛的关注。为了进一步改善系统性能,采用链路自适应方案是很好的选择。该文给出变发射功率的MMSE迭代软干扰抵消算法,并采用了一种有效的发射功率分配方案,只需要很少的控制信令,就可以获得较大的误码率性能改善。通过没有信道编译码的链路仿真,在4发4收QPSK调制的V-BLAST系统中,如果误码率要求为BER=10-3,MMSE迭代软干扰抵消检测算法迭代次数为2时,采用推荐的发射功率分配方案比不采用发射功率分配方案的系统性能提高了约2dB,如果调制方式为16QAM,系统性能提高了约6dB。     

Spectral efficiency improvement with SISO and SIMO in M‐QAM over millimeter‐wave links

This paper proposes a spectral efficiency improvement technique for millimeter wave (mmWave) links. The proposed technique provides an efficient utilization of the mmWave link capacity. This technique is applied in three cases the single‐input single‐output (SISO), single‐input multiple‐output (SIMO) with the maximal ratio combining and with the equal gain combining. The M‐ary quadrature amplitude modulation scheme is used in our work. The power series expansion is used for deriving closed‐form expressions for bit error rate (BER) performances in all studied cases. The BER closed‐form expressions are confirmed by the numerical solution of the integral equations. The simulation results show that a high spectral efficiency can be accomplished by the proposed technique. As well as the derived expressions closely match with the numerical solution of integration expressions at different values of modulations order the Rician factor. For instance, the spectral efficiency gain achievement is 8 at signal‐to‐noise ratio (SNR) equals 34 dB in the case of SISO system whereas in the case of SIMO system, the same gain is achieved at SNR equals 24 dB. As well as the BER performance is enhanced from 1.188 × 10^?4, 7.112 × 10^?4, 4.164 × 10^?3, and 3.286 × 10^?2 to 8.717 × 10^?16, 1.119 × 10^?12, 1.308 × 10^?9, and 4.905 × 10^?6 for M = 4, 16, 64, and 256, respectively, at SNR equals 30 dB.     

Adaptive predistortion of COFDM signals for a mobile satellite channel

In this paper, we consider the optimization of the performance of QPSK and 16‐QAM coded orthogonal frequency division multiplexing (COFDM) signals over the non‐linear and mobile satellite channel. A high power amplifier and Rician flat fading channel produces non‐linear and linear distortions; an adaptive predistortion technique combined with turbo codes will reduce both types of distortion. The predistorter is based on a feedforward neural network, with the coefficients being derived using an extended Kalman filter (EKF). The conventional turbo code is used to mitigate Rician flat fading distortion and Gaussian noise. The performance over a non‐linear satellite channel indicates that QPSK COFDM followed by a predistorter provides a gain of about 1.7 dB at a BER of 3×10^?3 when compared to QPSK COFDM without the predistortion scheme and 16‐QAM COFDM provides a gain of 0.5 dB output back‐off and 1.2 dB signal to noise ratio at a BER of 3×10^?5 when compared with an adaptive predistorter based on the Harmmerstein model. We also investigate the influence of the guard time interval and Doppler frequency effect on the BER performance. When the guard interval increases from 0 to 0.125T samples and the normalized Doppler frequency is 0.001, there is a gain of 0.7 and 1 dB signal to noise ratio at a BER of 6×10^?4 for QPSK and 16‐QAM COFDM, respectively. Copyright © 2003 John Wiley & Sons, Ltd.     

Performance of Two‐User Two‐Way Amplify‐and‐Forward Relaying Systems with Scheduling

In this paper, we study scheduling schemes for two‐user two‐way wireless relaying systems. Two transmission modes are considered: point‐to‐point direct transmission and two‐way amplify‐and‐forward relaying. An optimal scheduling scheme that opportunistically selects the best transmission mode for each user is proposed to minimize the sum bit error rate (BER). The performance lower bound of the optimal scheduling scheme is analyzed, and closed‐form expression of the lower‐bound BER is derived. However, for optimal scheduling, the scheduler requires the knowledge of channel state information (CSI) of all links. To reduce the feedback information of CSI, we also propose a suboptimal scheduling scheme that selects the transmission mode using only the CSI of two direct links. Simulation results show that there are 4 dB to 8 dB gains for the proposed optimal and suboptimal schemes over the fixed direct transmission and fixed two‐way relayed transmission scheme. The performance gap between the optimal and suboptimal scheduling schemes is small, which implies a good trade‐off between implementation complexity and system performance.     

The impact of impulse postfix length on the BER performance of IP‐OFDM systems

The impulse postfix OFDM (IP‐OFDM) system exploits the IP, which consists of a high power impulse sample and several zero samples at the end of a zero padded‐OFDM symbol block, to estimate channel impulse response (CIR) in time domain. In this paper, the impact of IP length on the BER performance of the IP‐OFDM system is analyzed. According to the analytic results, the BER performance can be significantly degraded with both a shorter length of IP as well as a longer length of IP than that of the CIR. Thus, an adaptive IP scheme, which adjusts the length of IP adaptively depending on the length of CIR, is proposed to enhance the BER performance of IP‐OFDM systems and its effectiveness is demonstrated by computer simulations. The BER performance of the IP‐OFDM systems with the proposed adaptive scheme is compared with that of the conventional IP‐OFDM system over various modulation schemes. Simulation results show that the IP‐OFDM with the proposed scheme can achieve about 2 dB performance enhancement compared with that of conventional systems at BER=10^?2. Copyright © 2010 John Wiley & Sons, Ltd.     

Enhancing spectral efficiency of FSO system using adaptive SIM/M‐PSK and SIMO in the presence of atmospheric turbulence and pointing errors

This paper proposes an adaptive transmission modulation (ATM) technique for free‐space optical (FSO) links over gamma‐gamma turbulence channels.The ATM technique provides efficient utilization of the FSO channel capacity for improving spectral efficiency, by adapting the order of the phase‐shift keying modulation scheme, according to the channel conditions and the required bit error rate (BER). To overcome the channel degradation resulting from the turbulence effects as well as the pointing errors (PEs), single‐input multiple‐output (SIMO) system with maximal ratio combining (MRC) is proposed. Exact closed‐form expressions of BER and upper bound of the capacity are derived and verified by Monte Carlo simulations. The numerical results show that the proposed adaptive technique improves the spectral efficiency (SE) five times higher than the nonadaptive technique at the same BER threshold (10^?3).This improvement is achieved at signal‐to‐noise ratio (SNR) equals 27 and 42  dB in the case of atmospheric turbulence without and with PE, respectively. Furthermore, this SE could be obtained while the SNR = 30  dB by using ( 1 × 4 ) SIMO scheme with MRC and PE and having the same transmitting optical power.     

A Time‐Varying Modified MMSE Detector for Multirate CDMA Signals in Fast Rayleigh Fading Channels

In this paper, we propose a time‐varying modified minimum mean‐squared error (MMSE) detector for the detection of higher data rate signals in a multirate asynchronous code‐division multiple‐access (CDMA) system which is signaled in a fast Rayleigh fading channel. The interference viewed by a higher data rate symbol will be periodic due to the presence of a lower data rate symbol which spans multiple higher data rate symbols. The detection is carried out on the basis of a modified MMSE criterion which incorporates differential detection and the ratio of channel coefficients in two consecutive observation intervals inherently compensating the fast variation of the channel due to fading. The numerical results obtained by the MMSE detector with time‐varying detection show around 3 dB (M=2) and 6 dB (M=4) performance improvement at a BER of 10^?3 in the AWGN channel, while introducing more computational complexity than the MMSE detector without time‐varying detection. At a higher Eb/N0, the proposed scheme can achieve a BER of approximately 10^?3 in the presence of fast channel variation which is an improvement over other schemes.     

High‐rate uncoded space‐time labelling diversity with low‐complexity detection

Uncoded space‐time labelling diversity (USTLD) is a recent scheme that improved the error performance compared to conventional multiple‐input, multiple‐output systems. Thus far, USTLD has suffered from limited achievable data rates, as the original model uses only two transmit antennas. This motivates for the work in this paper, where the USTLD model is extended to allow for any desired number of transmit antennas. An analytical bound for the average bit error probability of this high‐rate USTLD (HR‐USTLD) system is derived. This expression is verified using the results of Monte Carlo simulations, which show a tight fit in the high signal‐to‐noise ratio region. The increased data rates associated with larger transmit antenna arrays in HR‐USTLD systems come at the cost of increased detection complexity. Therefore, this paper studies the application of low‐complexity detection algorithms based on the popular QR decomposition technique and proposes a new algorithm specifically designed for HR‐USTLD systems. Analysis of this algorithm in terms of accuracy and computational complexity is also provided and benchmarked against maximum‐likelihood detection (MLD). It is shown that the proposed algorithm achieves near‐MLD accuracy, while reducing complexity by 79.75% and 92.53% for the respective 4 × 4 16QAM and 4 × 5 16PSK HR‐USTLD systems investigated.     

Fast turbo codes with space‐time block codes in fast fading channels

In this paper, space‐time block coding has been used in conjunction with Turbo codes to provide good diversity and coding gains. A new method of dividing turbo encoder and decoder into several parallel encoding and decoding blocks is considered. These blocks work simultaneously and yield a faster coding scheme in comparison to classical Turbo codes. The system concatenates fast Turbo coding as an outer code with Alamouti's G2 space‐time block coding scheme as an inner code, achieving benefits associated with both techniques including acceptable diversity and coding gain as well as short coding delay. In this paper, fast fading Rayleigh and Rician channels are considered for discussion. For Rayleigh fading channels, a fixed frame size and channel memory length of 5000 and 10, respectively, the coding gain is 7.5 dB and bit error rate (BER) of 10^?4 is achieved at 7 dB. For the same frame size and channel memory length, Rician fading channel yields the same BER at about 4.5 dB. Copyright © 2013 John Wiley & Sons, Ltd.     

Nonlinear Product Codes and Their Low Complexity Iterative Decoding

This paper proposes encoding and decoding for nonlinear product codes and investigates the performance of nonlinear product codes. The proposed nonlinear product codes are constructed as N‐dimensional product codes where the constituent codes are nonlinear binary codes derived from the linear codes over higher order alphabets, for example, Preparata or Kerdock codes. The performance and the complexity of the proposed construction are evaluated using the well‐known nonlinear Nordstrom‐Robinson code, which is presented in the generalized array code format with a low complexity trellis. The proposed construction shows the additional coding gain, reduced error floor, and lower implementation complexity. The (64, 24, 12) nonlinear binary product code has an effective gain of about 2.5 dB and 1 dB gain at a BER of 10^?6 when compared to the (64, 15, 16) linear product code and the (64, 24, 10) linear product code, respectively. The (256, 64, 36) nonlinear binary product code composed of two Nordstrom‐Robinson codes has an effective gain of about 0.7 dB at a BER of 10^?5 when compared to the (256, 64, 25) linear product code composed of two (16, 8, 5) quasi‐cyclic codes.     

A novel bandwidth efficient SOC-based turbo coding scheme mid reduced complexity MUD for SA-based MC-CDMA systems

Multiuser-detection (MUD), turbo coding and smart-antennas (SA) are powerful techniques for enhancing the performance and capacity of MC-CDMA systems. Among the MUD algorithms, the maximum-likelihood (ML) method has the best performance but its complexity increases exponentially with the number of users and constellation size. In this paper, we first propose a novel bandwidth-efficient-channel-coding-scheme (BECCS) for a super-orthogonal-code (SOC)-based serially concatenated turbo code (SCSOC) so that by using it, the coded system without extra bandwidth significantly improves the performance of an uncoded system over a fading channel. Second, in order to reduce the complexity of the ML-based turbo MUD technique, an ML algorithm based on the sensitive-bits-algorithm (SBA) and a less-complex-norm-approximation (LCNA) based Euclidean distance is proposed for a SCSOC-based BECCS assisted coded MC-CDMA system accompanied by SA techniques at the receiver. Our analytical and simulation results show that from a performance perspective, at BER=10^?2, the proposed SCSOC-based BECCS assisted MC-CDMA system performs 4?dB better than SOC-based coded systems. The latter system has 5?dB gain in comparison with an uncoded one, all in the same bandwidth and over fading channels.     

Channel‐estimate‐based frequency‐domain equalization (CE‐FDE) for broadband single‐carrier transmission

A channel‐estimate‐based frequency‐domain equalization (CE‐FDE) scheme for wireless broadband single‐carrier communications over time‐varying frequency‐selective fading channels is proposed. Adaptive updating of the FDE coefficients are based on the timely estimate of channel impulse response (CIR) to avoid error propagation that is a major source of performance degradation in adaptive equalizers using least mean square (LMS) or recursive least square (RLS) algorithms. Various time‐domain and frequency‐domain techniques for initial channel estimation and adaptive updating are discussed and evaluated in terms of performance and complexity. Performance of uncoded and coded systems using the proposed CE‐FDE with diversity combining in different time‐varying, multi‐path fading channels is evaluated. Analytical and simulation results show the good performance of the proposed scheme suitable for broadband wireless communications. For channels with high‐Doppler frequency, diversity combining substantially improves the system performance. For channels with sparse multi‐path propagation, a tap‐selection strategy used with the CE‐FDE systems can significantly reduce the complexity without sacrificing the performance. Copyright © 2004 John Wiley & Sons, Ltd.     

Performance improvement of 60‐GHz wireless optical systems with reverse‐parallel hybrid modulation scheme

This paper improves the performance of 60‐GHz wireless optical system including radio over fibre (RoF) and radio over free space optics (RoFSO), based on novel reverse‐parallel (RP) hybrid modulation scheme. This scheme combines the chromatic dispersion compensation technique of parallel modulation with energy efficiency manipulation technique of reverse modulation. Superior functioning of RoFSO is provided with reverse modulation compared with normal modulation. Comparative investigations are performed by loading 60‐GHz RF signal with 2.5 and 10‐Gbps data and modulating it with both reverse and hybrid modulators. Hybrid modulation performed better with improved BER of 10^?23 at distance of 51 km for 2.5‐Gbps data compared with reverse modulation with BER of 10^?7.     

Combined ML and QR Detection Algorithm for MIMO‐OFDM Systems with Perfect ChanneI State Information

An effective signal detection algorithm with low complexity is presented for multiple‐input multiple‐output orthogonal frequency division multiplexing systems. The proposed technique, QR‐MLD, combines the conventional maximum likelihood detection (MLD) algorithm and the QR algorithm, resulting in much lower complexity compared to MLD. The proposed technique is compared with a similar algorithm, showing that the complexity of the proposed technique with T=1 is a 95% improvement over that of MLD, at the expense of about a 2‐dB signal‐to‐noise‐ratio (SNR) degradation for a bit error rate (BER) of 10⁻³. Additionally, with T=2, the proposed technique reduces the complexity by 73% for multiplications and 80% for additions and enhances the SNR performance about 1 dB for a BER of 10⁻³.     

Performance of coded DS‐CDMA system using reduced rank MMSE receiver in Rayleigh fading channels

This paper examines the performance of a reduced rank minimum mean square error (MMSE) receiver‐based direct sequence code division multiple access (DS‐CDMA) system. For such system, when a large processing gain is employed, substantial time is consumed in computing the filter tap weights. Many schemes for reducing the complexity of the MMSE have been proposed in recent years. In this paper, computational complexity reduction of the MMSE receiver is achieved by using the K‐mean classification algorithm. The performance of the uncoded and coded systems are investigated for the full rank MMSE receiver and reduced rank MMSE receiver and results are compared in terms of bit error rate at different loading levels in both AWGN and fading channels. A system with the matched filter (MF) receiver is also presented for the purpose of comparison and an analytical pair‐wise error bound for the coded system is derived. In the adaptive implementation of the receivers, results show that good performance is achieved for the reduced rank receiver when compared to the full rank receiver in both coded and uncoded systems, while in the optimum implementation of the tap weights, the reduced dimension receiver performance experiences degradation when compared to the full rank scheme. Over the band‐limited channels considered, results for the reduced rank receiver also reiterate the fact that higher code rates tend to yield lower BER than that of low rate codes. Copyright © 2006 John Wiley & Sons, Ltd.