A new subspace method for blind estimation of selective MIMO‐STBC channels

In this paper, a new technique for the blind estimation of frequency and/or time‐selective multiple‐input multiple‐output (MIMO) channels under space‐time block coding (STBC) transmissions is presented. The proposed method relies on a basis expansion model (BEM) of the MIMO channel, which reduces the number of parameters to be estimated, and includes many practical STBC‐based transmission scenarios, such as STBC‐orthogonal frequency division multiplexing (OFDM), space‐frequency block coding (SFBC), time‐reversal STBC, and time‐varying STBC encoded systems. Inspired by the unconstrained blind maximum likelihood (UML) decoder, the proposed criterion is a subspace method that efficiently exploits all the information provided by the STBC structure, as well as by the reduced‐rank representation of the MIMO channel. The method, which is independent of the specific signal constellation, is able to blindly recover the MIMO channel within a small number of available blocks at the receiver side. In fact, for some particular cases of interest such as orthogonal STBC‐OFDM schemes, the proposed technique blindly identifies the channel using just one data block. The complexity of the proposed approach reduces to the solution of a generalized eigenvalue (GEV) problem and its computational cost is linear in the number of sub‐channels. An identifiability analysis and some numerical examples illustrating the performance of the proposed algorithm are also provided. Copyright © 2009 John Wiley & Sons, Ltd.     

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.     

Peak‐to‐average power ratio reduction in space frequency block coding multi‐input multi‐output orthogonal frequency division multiplexing systems by tone reservation

In this paper, a tone reservation (TR) method is employed to reduce the peak‐to‐average power ratio (PAPR) in multi‐input multi‐output orthogonal frequency division multiplexing systems with space frequency block coding (SFBC). The key idea of the employed TR method is taking signals on multiple transmit antennas into account to design appropriate peak reduction symbols, which can significantly reduce the PAPR of SFBC multi‐input multi‐output orthogonal frequency division multiplexing signals. With the employed TR scheme, the SFBC structure can be maintained, whereas the traditional TR method would destroy it, resulting in the degradation of bit error rate (BER) performance. Simulation results demonstrate that the employed TR scheme can provide significantly better BER performance than the traditional TR method with slight PAPR reduction degradation. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

Inter‐carrier Interference Reduction Scheme for SFBC‐OFDM Systems

In this paper, we first analyze carrier‐to‐interference ratio performance of the space–frequency block coded orthogonal frequency‐division multiplexing (SFBC‐OFDM) system in the presence of phase noise (PHN) and residual carrier frequency offset (RCFO). From the analysis, we observe that conventional SFBC‐OFDM systems suffer severely in the presence of PHN and RCFO. Therefore, we propose a new inter‐carrier interference (ICI) self‐cancellation method — namely, ISC — for SFBC‐OFDM systems to reduce the ICI caused by PHN and RCFO. Through the simulation results, we show that the proposed scheme compensates the ICI caused by PHN and RCFO in Alamouti SFBC‐OFDM systems and has a better performance than conventional schemes.     

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.     

Iterative nonlinear detection for SFBC SC–FDMA uplink MIMO transmission systems

Single‐carrier frequency division multiple access (SC‐FDMA) systems with space frequency block coding (SFBC) transmissions achieve both spatial and frequency diversity gains in wireless communications. However, SFBC SC‐FDMA schemes using linear detectors suffer from severe performance deterioration because of noise enhancement propagation and additive noise presence in the detected output. Both issues are similar to inter‐symbol‐interference (ISI). Traditionally, SC‐FDMA system decision feedback equalizer (DFE) is often used to eliminate ISI caused by multipath propagation. This article proposes frequency domain turbo equalization based on nonlinear multiuser detection for uplink SFBC SC‐FDMA transmission systems. The presented iterative receiver performs equalization with soft decisions feedback for ISI mitigation. Its coefficients are derived using minimum mean squared error criteria. The receiver configuration study is Alamouti's SFBC with two transmit and two receive antennas. New receiver approach is compared with the recently proposed suboptimal linear detector for SFBC SC‐FDMA systems. Simulation results confirm that the performance of the proposed iterative detection outperforms conventional detection techniques. After a few iterations, bit‐error‐rate performance of the proposed receiver design is closely to the matched filter bound. Copyright © 2016 John Wiley & Sons, Ltd.     

一种降低OFDM峰均比的编码方法

讨论了一种降低正交频分复用(OFDM)系统峰均比的分组编码方法.对于4载波OFDM系统,通过对已有QPSK调制下具有最小峰均比(PAR)的码字进行分析,表明了能使峰均比降低至少3 dB的码字所满足的相位关系,并以此为基础,研究推广了这类码字在M-PSK调制下的一种一般获取过程.对于子载波个数增大的OFDM系统,讨论了以4载波编码方法为基础降低峰均比的办法,对其进行了理论分析并给出了仿真研究.仿真结果表明文中编码方法不仅能有效降低OFDM系统的PAR,而且具有一定的纠错能力.     

MIMO Frequency Hopping Spread Spectrum Multi-Carrier Multiple Access: A Novel Uplink System for B3G Cellular Networks

In this paper, we propose and give the performance of a novel uplink system based on the combination of multi-carrier (MC), code division multiple access (CDMA) and multiple input multiple output (MIMO) techniques. First, we describe the interests of spread-spectrum multi-carrier multiple access (SS-MC-MA) scheme for uplink, especially compared to MC-CDMA. Classically, with SS-MC-MA, each user spreads its data symbols on a specific subset of adjacent or multiplexed subcarriers, to facilitate the channel estimation and reduce complexity at the reception. In order to compensate for the lack of frequency diversity of SS-MC-MA with adjacent subcarriers, we first combine it with an orthogonal space-time block code (STBC) and demonstrate the resulting spatial diversity gain. Then, we propose to allocate the subsets to the different users by applying a frequency hopping pattern (FH). In that case, each user benefits from the frequency diversity linked to the total bandwidth as with the multiplexed subcarriers solution, while keeping the advantages of the adjacent subcarriers solution. The gain provided by the use of the frequency hopping is stressed on. Finally, the performance of this scheme is evaluated over realistic MIMO channel with channel turbo coding for systems offering asymptotic spectrum efficiency of 1, 2, 3 and 4.5 bit/s/Hz. Thus, the efficiency of the novel proposed STBC FH SS-MC-MA system as a very promising multiple access and modulation scheme for the uplink of the future wideband wireless networks is successfully demonstrated.     

异步OFDM空时协同分集方案

提出一种基于空时分组编码的异步正交频分复用（OFDM,Orthogonal Frequency Division Multiplexing）协同分集方案。提出的方案在中继节点实现OFDM调制及OFDM符号的时间反转和复共轭,信宿节点接收信号的每个OFDM子载波都具有Alamouti空时分组编码结构。信宿节点采用最大似然（ML,Maximum Likelihood）译码准则译码。仿真结果表明,提出的异步OFDM空时协同分集方案无需两个中继节点的同步可获得二阶分集增益,且与其它协同分集方案相比,该方案的误比特率和实现复杂度都更低。     

An Efficient Scheme to Achieve Differential Unitary Space‐Time Modulation on MIMO‐OFDM Systems

Differential unitary space‐time modulation (DUSTM) has emerged as a promising technique to obtain spatial diversity without intractable channel estimation. This paper presents a study of the application of DUSTM on multiple‐input multiple‐output orthogonal frequency division multiplexing (MIMO‐OFDM) systems with frequency‐selective fading channels. From the view of a correlation analysis between subcarriers of OFDM, we obtain the maximum achievable diversity of DUSTM on MIMO‐OFDM systems. Moreover, an efficient implementation strategy based on subcarrier reconstruction is proposed, which transmits all the signals of one signal matrix in one OFDM transmission and performs differential processing between two adjacent OFDM blocks. The proposed method is capable of obtaining both spatial and multipath diversity while reducing the effect of time variation of channels to a minimum. The performance improvement is confirmed by simulation results.     

Adaptive modulation for space–frequency block coded OFDM systems

The growing popularity of both multiple-input multiple-output (MIMO) and orthogonal frequency division multiplexing (OFDM) systems has created the need for adaptive modulation to integrate temporal, spatial and spectral components together. In this article, an overview of some adaptive modulation schemes for OFDM is presented. Then a new scheme consisting of a combination of adaptive modulation, OFDM, high-order space-frequency block codes (SFBC), and antenna selection is presented. The proposed scheme exploits the benefits of space–frequency block codes, OFDM, adaptive modulation and antenna selection to provide high-quality transmission for broadband wireless communications. The spectral efficiency advantage of the proposed system is examined. It is shown that antenna selection with adaptive modulation can greatly improve the performance of the conventional SFBC–OFDM systems.     

瑞利衰落下的空时频(STF)分组编码OFDM系统

基于正交频分复用(OFDM)系统，提出了一种发射分集方案——比特交织空时频(BI—STF)分组编码。其基本思路是：应用子载波分群方法并选择合适的系统参数，将OFDM系统转化成分群OFDM(G-OFDM)，对每个群分别进行空时频分组编码(GSTFBC)；在编码比特被重组和映射成GSTF分组编码前进行合理的比特交织，并按一定的规则分配给各个单群子载波进行酉星座旋转(CR)预编码。随后讨论了该方案的频谱利用率和成对错误概率(PEP)。仿真结果表明，同其它编码方案相比，提出的方案能在频率选择性瑞利衰落信道下获得最大的空间分集和频率分集增益，且只有较低的解码复杂性。     

Progressive image transmission over differentially space‐time coded OFDM systems

In this paper, we consider progressive image transmission over differentially space‐time coded orthogonal frequency‐division multiplexing (OFDM) systems and treat the problem as one of optimal joint source‐channel coding (JSCC) in the form of unequal error protection (UEP), as necessitated by embedded source coding (e.g., SPIHT and JPEG 2000). We adopt a product channel code structure that is proven to provide powerful error protection and employ low‐complexity decision‐feedback decoding for differentially space‐time coded OFDM without assuming channel state information. For a given SNR, the BER performance of the differentially space‐time coded OFDM system is treated as the channel condition in the JSCC/UEP design via a fast product code optimization algorithm so that the end‐to‐end quality of reconstructed images is optimized in the average minimum MSE sense. Extensive image transmission experiments show that SNR/BER improvements can be translated into quality gains in reconstructed images. Moreover, compared to another non‐coherent detection algorithm, i.e., the iterative receiver based on expectation‐maximization algorithm for the space‐time coded OFDM systems, differentially space‐time coded OFDM systems suffer some quality loss in reconstructed images. With the efficiency and simplicity of decision‐feedback differential decoding, differentially space‐time coded OFDM is thus a feasible modulation scheme for applications such as wireless image over mobile devices (e.g., cell phones). Copyright © 2006 John Wiley & Sons, Ltd.     

IEEE 802.11n: Joint modulation‐coding and guard interval adaptation scheme for throughput enhancement

IEEE 802.11n is a high‐speed wireless broadband local area networking standard. IEEE 802.11n‐based devices are using some kind of adaptive modulation‐coding (AMC) scheme to adjust its transmission rate according to the radio channel condition. In these devices, however, the concept of guard interval adaptation is not been considered. Normally, orthogonal frequency division multiplexing (OFDM) technology‐based systems are using the guard interval much greater than the length of the channel impulse response. However, many previous works have shown that the choice of the larger guard interval is inefficient in terms of achievable throughput. IEEE802.11n supports using two guard intervals (short = 400 ns or long = 800 ns). Indeed, the shorter guard interval evidently results in intersymbol interference (ISI) and intercarrier interference (ICI), but the gain offered by shortened guard interval may exceed the loss caused by interference. In this paper, we propose a novel but simple solution for the guard interval adaptation joint with an adaptive modulation‐coding scheme to optimize the throughput performance of a wireless local area network (WLAN) system. This paper aims to analyze the effect of joint adaptive modulation‐coding and the guard interval (JAMCGI) algorithm on the WLAN system under bit‐error‐rate (BER) constraints. Simulation results and their analysis show a significant increase in the throughput performance of the WLAN system with our proposed algorithm.     

衰落信道上空频分组码的性能分析

对于任意抽头数的多输入多输出(MIMO)频率选择性Nakagami衰落信道,利用矩生成函数(MGF)方法和高斯Q函数的指数近似表达式,推导采用矩形M进制正交幅度调制(MQAM)的空频分组编码(SFBC)正交频分复用(OFDM)系统的平均误符号率(SER)性能的精确和近似解析表达式。数值计算和仿真结果证明了理论分析的正确性和近似分析的准确性。     

MQAM-OFDM系统中降低峰均比与残余载波频偏同步联合算法

针对OFDM系统对频偏敏感及峰均比高的问题,提出一种用MQAM调制值的共轭码对残余载波频偏进行跟踪的方法,该共轭码同时可以降低系统峰均比.用频域MQAM数值的共轭来调制导频子载波以抵消相位,降低系统的峰值功率.同时利用这种共轭关系估计残余载波频偏引起的相位旋转,在时域或频域进行纠正.仿真结果表明利用这种共轭码可有效的跟...     

Comparison of coded orthogonal frequency division multiplexing and multicarrier code division multiple access systems for power line communications

Orthogonal frequency division multiplexing (OFDM) and multicarrier code division multiple access (MC‐CDMA) systems are comparatively evaluated for power line communications (PLC) in a frequency‐selective fading environment with additive coloured Gaussian noise which is used to model the actual in‐home power line channel. OFDM serves as a benchmark in order to measure the performance of various MC‐CDMA systems, since multicarrier modulation systems are considered the best candidate for this kind of channel. Both single‐user and multi‐user cases are taken into account, making use of the appropriate combiner schemes to take full advantage of each case. System efficiency is enhanced by the application of different coding techniques, a fact which shows that powerful coding can make the difference under such a hostile medium. The impact of block interleaving is investigated, while the simulation examines how different modulation schemes fair under the imposed channel conditions as well. The performance of the system is assessed by the commonly used bit error rate vs signal‐to‐noise ratio diagrams and there is also a comparison regarding throughput efficiency among all the tested systems. As stated in Section 4, a promising PLC application is attained. Copyright © 2004 John Wiley & Sons, Ltd.     

Performance Investigation of Space‐Time Block Coded Multicarrier DS‐CDMA in Time‐Varying Channels

In this letter, we evaluate the system performance of a space‐time block coded (STBC) multicarrier (MC) DS‐CDMA system over a time selective fading channel, with imperfect channel knowledge. The average bit error rate impairment due to imperfect channel information is investigated by taking into account the effect of the STBC position. We consider two schemes: STBC after spreading and STBC before spreading in the MC DS‐CDMA system. In the scheme with STBC after spreading, STBC is performed at the chip level; in the scheme with STBC before spreading, STBC is performed at the symbol level. We found that these two schemes have various channel estimation errors, and that the system with STBC before spreading is more sensitive to channel estimation than the system with STBC after spreading. Furthermore, derived results prove that a high spreading factor (SF) in the MC DS‐CDMA system with STBC before spreading leads to high channel estimation error, whereas for a system with STBC after spreading this statement is not true.     

多层空时编码方案的MIMO-OFDM系统研究

结合STBC和VBLAST混合编码结构的优点,提出将块分组编码应用于MIMO-OFDM系统.在发射端数据流分成两层输入块分组编码器后进行OFDM调制,在接收端,采用MMSE干扰抑制算法译码.块分组编码将数据符号按层分块后交叉通过不同的天线对发射,数据流之间产生了一定交织效果,使编码获得了更好的分集增益.