一种基于空时分组编码的MIMO-SC/FDE系统的接收空间分集方案

该文提出了一种基于空时分组编码的多输入多输出频域均衡单载波分组传输(MIMO-SC/FDE)系统的空间分集接收方案,通过在Huang(2004)提出的分集结构中引入使用空时分组编码的发射分集,弥补了因减少DFT块数目而造成的性能损失,同时在接收端进一步减少了IDFT块的数目;通过适当设计空时分组编码,还可以进一步提高数据传输速率。该文详细推导了使用空时分组编码后的处理过程,并对使用空时编码后的MIMO-SC/FDE系统和相应的MIMO-OFDM系统性能进行了仿真比较。仿真结果表明,MIMO-SC/FDE系统的性能从总体上优于MIMO-OFDM系统。     

Performance evaluation of OFDM and single‐carrier systems using frequency domain equalization and phase modulation

In this paper, we study the performance of the continuous phase modulation (CPM)‐based orthogonal frequency division multiplexing (CPM‐OFDM) system. Also, we propose a CPM‐based single‐carrier frequency domain equalization (CPM‐SC‐FDE) structure for broadband wireless communication systems. The proposed structure combines the advantages of the low complexity of SC‐FDE, in addition to exploiting the channel frequency diversity and the power efficiency of CPM. Both the CPM‐OFDM system and the proposed system are implemented with FDE to avoid the complexity of the equalization. Two types of frequency domain equalizers are considered and compared for performance evaluation of both systems; the zero forcing (ZF) equalizer and the minimum mean square error (MMSE) equalizer. Simulation experiments are performed for a variety of multipath fading channels. Simulation results show that the performance of the CPM‐based systems with multipath fading is better than their performance with single path fading. The performance over a multipath channel is at least 5 and 12 dB better than the performance over a single path channel, for the CPM‐OFDM system and the proposed CPM‐SC‐FDE system, respectively. The results also show that, when CPM is utilized in SC‐FDE systems, they can outperform CPM‐OFDM systems by about 5 dB. Copyright © 2010 John Wiley & Sons, Ltd.     

A Reduced-CP Approach to SC/FDE Block Transmission for Broadband Wireless Communications

For conventional cyclic prefix (CP)-assisted single-carrier/frequency-domain equalization (SC/FDE) implementations, as well as for orthogonal frequency-division multiplexing (OFDM) implementations, the CP length is known to be selected on the basis of the expected maximum delay spread. Next, the data block size can be chosen to be large enough to minimize the CP overhead, yet small enough to make the channel variation over the block negligible. This paper considers the possibility of reducing the overall CP assistance, when transmitting sequences of SC blocks, while avoiding an excessively long fast Fourier transform window for FDE purposes and keeping good FDE performances through low-complexity, noniterative receiver techniques. These techniques, which take advantage of specially designed frame structures, rely on a basic algorithm for decision-directed correction (DDC) of the FDE inputs when the CP is not long enough to cope with the time-dispersive channel effects. More specifically, we present and evaluate a novel class of reduced-CP SC/FDE schemes, which takes advantage of a special frame structure for replacing "useless" CP redundancy by fully useful channel coding redundancy, with the help of the DDC algorithm. When using the DDC-FDE technique with these especially designed frame structures, the impact of previous decisions, which are not error-free, is shown to be rather small, thereby allowing a power-efficiency advantage (in addition to the obvious bandwidth-efficiency advantage) over conventional block transmission implementations under full-length CP. Additionally, the DDC algorithm is also shown to be useful to improve the power efficiency of these conventional implementations     

A Turbo FDE Technique for Reduced-CP SC-Based Block Transmission Systems

For conventional cyclic-prefix (CP)-assisted block transmission systems, the CP length is selected on the basis of the expected maximum delay spread. With regard to single-carrier (SC)-based block transmission implementations, a full-length CP is recommendable, since it allows good performances through the use of simple frequency-domain equalization (FDE) techniques. In this letter, a soft-decision-directed correction (SDDC)-aided turbo FDE technique is presented for reduced-CP SC-based block transmission systems using conventional frame structures. The relations with some already known iterative FDE techniques are established, and a set of performance results is reported and discussed. The advantages of the proposed approach are emphasized, namely, the possibility of approximately achieving (besides the obvious bandwidth efficiency gain) the maximum power efficiency gain that a strong CP reduction allows     

Performance analysis of coherent TCM systems with diversityreception in slow Rayleigh fading

Coherent trellis-coded modulation (TCM) systems employing diversity combining are analyzed. Three different kinds of combining are considered: maximal ratio, equal gain, and selection combining (SC). First, the cutoff rate parameter is derived for equal gain combining (EGG) and SC assuming transmission over a fully interleaved channel with flat slow Rayleigh fading, which permits comparison with previously derived results for maximal ratio combining (MRC). Then, tight upper bounds on the pairwise error probabilities are derived for all three combining techniques. These upper bounds are expressed in product form to permit bounding of the bit error rate (BER) via the transfer function approach. In each case, it is assumed that the diversity branches are independent and that the channel state information (CSI) can be recovered perfectly. Also included is an analysis of MRC when the diversity branches are correlated-the cutoff rate and a tight upper bound on the pairwise error probability are derived. It is shown that with double diversity a branch correlation coefficient as high as 0.5 results in only slight performance degradation     

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.     

An interleaved TCM scheme for single carrier multiple transmit antenna systems

Single carrier (SC) block transmission with frequency domain equalization (FDE) in multi-path fading channels is considered. It is shown that uncoded SC-FDE is resistant to fading even though the multi-path diversity cannot be harnessed. We propose simple schemes based on concatenations of trellis coded modulation (TCM) and interleaving for single and multiple transmit antennas to improve the coding gain, which also exploit spatial diversity in the multi antenna case.     

A New Union Bound on the Error Probability of Binary Coded OFDM Systems in Wireless Environments

Orthogonal Frequency Division Multiplexing (OFDM) systems are commonly used to mitigate frequency-selective multipath fading and provide high-speed data transmission. In this paper, we derive new union bounds on the error probability of a coded OFDM system in wireless environments. In particular, we consider convolutionally coded OFDM systems employing single and multiple transmit antennas over correlated block fading (CBF) channels with perfect channel state information (CSI). Results show that the new union bound is tight to simulation results. In addition, the bound accurately captures the effect of the correlation between sub-carriers channels. It is shown that as the channel becomes more frequency-selective, the performance get better due to the increased frequency diversity. Moreover, the bound also captures the effect of multi-antenna as space diversity. The proposed bounds can be applied for coded OFDM systems employing different coding schemes over different channel models.     

Performance analysis of MIMO systems with multiuser diversity

In this paper, we present a comprehensive performance analysis for multiple‐input multiple‐output (MIMO) systems with multiuser diversity over Rayleigh fading channels. We derive exact closed‐form expressions of the outage probability and the average bit error rate (BER) for different MIMO schemes, including the selective combining (SC), maximum ratio combining (MRC) and space‐time block codes (STBC). We also provide the explicit upper bounds on the BER performance. Finally, the mathematical formalism is verified by numeric results that study the interaction between the antenna diversity and the multiuser diversity. It is observed that the system performance is deteriorated as the number of transmit antennas increases in multiuser scenario, which is unlike the case in single‐user systems. Copyright © 2007 John Wiley & Sons, Ltd.     

SER Analysis of QAM with Space Diversity in Rayleigh Fading Channels

This paper derives the symbol error probability for quadrature amplitude modulation(QAM) with L-fold space diversity in Rayleigh fading channels. Two combining techniques, maximal ratio combining(MRC) and selection combining(SC), are considered. The formula for MRC space diversity is obtained by averaging the symbol error probability of M-ary QAM in an additive white Gaussian noise(AWGN) channel over a chi-square distribution with 2L degrees of freedom. The obtained formula overcomes the limitations of the earlier work, which has been limited only to deriving the symbol error rate(SER) of QAM with two branch MRC space diversity. The formula for SC space diversity is obtained by averaging the symbol error probability of M-ary QAM in an AWGN channel over the distribution of the maximum signal-to-noise ratio among all of the diversity channels for SC space diversity. No analysis for QAM with SC space diversity has been reported yet. Analytical results show that the probability of error decreases with the order of diversity. We can also see that the incremental diversity gain per additional branch decreases as the number of branches becomes larger. On the other hand, the performance of 16 QAM with MRC becomes much better than that of SC as the number of branches becomes larger. By giving the order of diversity, L, and the number of signal points, M, we have been able to obtain the SER performance of QAM with general space diversity. These results can be used to determine the order of diversity to achieve the desired SER in land mobile communication system employing QAM modulation.     

频域均衡的单载波传输方案研究

无线信道的信道干扰主要表现为多径衰落和多普勒衰落对信道的影响。我们可以采用均衡技术来补偿信道中由于多径效应产生的码间干扰（ISI）。现引入频域均衡的单栽波传输（SC／FDE）方案，探讨了其实现机理，并对采用SC／FDE的高速率无线通讯系统实例进行系统整体建模和仿真计算。     

Adaptive Frequency-Domain Equalization with Narrowband Interference Suppression

Frequency-domain equalization (FDE) is an effective technique that exhibits the property of relatively low complexity which grows with increasing the number of symbols of dispersion in multipath propagation environments for broadband wireless communications compared with the conventional time-domain equalization. However, in practical broadband wireless communications, there exists not only multipath but also narrowband interference (NBI). The conventional FDE methods do not consider NBI and their performance degrades obviously in such case. In this paper, we propose a new optimization criterion which can effectively suppress NBI to obtain the maximum decision signal-to-noise ratio. The proposed scheme employs a conventional adaptive algorithm such as least-mean-square or recursive-least-square and operates in the spatial-frequency domain, which is concerned with the use of FDE and space diversity within block transmission schemes jointly. The simulation results show that the proposed schemes have better error-rate performance with low complexity and can be used even in the presence of strong NBI, compared to other existing adaptive FDE algorithms.     

A Comparison of Frequency-Domain Block MIMO Transmission Systems

Block transmission techniques, with appropriate cyclic prefix and frequency-domain processing schemes, have been shown to be excellent candidates for digital transmission over severely time-dispersive channels, allowing good performance with implementation complexity that is much lower than traditional time-domain processing schemes. Orthogonal frequency-division multiplexing (OFDM) modulation is the most popular block transmission technique. Single-carrier (SC) modulation using frequency-domain equalization (FDE) is an attractive alternative approach based on this principle. In this paper, we propose two new receiver structures for multiple-input-multiple-output (MIMO) channels employing SC (MIMO-SC) modulation and FDE schemes. These receivers have a hybrid structure with frequency-domain feedforward and time-domain feedback filters for intersymbol interference (ISI) and interference cancellation. The proposed schemes are compared with different MIMO systems employing OFDM modulation (MIMO-OFDM) receivers in terms of performance [bit error rate (BER) and throughput] and complexity. Our performance results show the superiority of MIMO-SC approaches relative to MIMO-OFDM in terms of the BER performance for the simulated scenarios. Also, the simulation results show that the proposed hybrid MIMO-SC receivers yield a higher throughput than a MIMO-OFDM system.     

Subblock processing in MMSE-FDE under fast fading environments

Frequency domain equalization (FDE) has been studied for reducing inter-symbol interference (ISI) caused by frequency selective fading in single carrier systems. When a high-mobility terminal exists in the system, the channel state may change within a DFT block. Then, the ISI reduction performance of FDE degrades since cyclicity of the channel matrix is lost. We propose to divide a received data block into multiple subblocks to decrease the channel transition within the DFT block in fast fading environments. Also, to satisfy periodicity of the received signal in each subblock, we introduce a pseudo cyclic prefix technique. The results of numerical analysis show that the proposed method can effectively decrease the error floor in fast fading environments.     

基于散射信道的单载波频域均衡算法仿真

从对流层散射通信信道的特点出发,介绍了单载波频域均衡技术原理与系统结构,研究了可适用于对流层散射通信且易于工程实现的几种频域均衡算法,并创新性地研究了将单载波频域均衡技术与分集接收技术相结合的可行性及系统性能,在理论分析的基础上借助Matlab软件进行了仿真验证,给出了仿真结果,并对其进行了分析。仿真结果验证了算法的有效性以及单载波频域均衡技术与分集接收技术相结合的可行性,为其在散射通信系统中的应用和工程实现提供参考和指导。     

Selected mapping technique for reducing PAPR of single‐carrier signals

Single‐carrier transmission with frequency‐domain equalization (SC‐FDE) is widely known as a promising transmission technique providing low error probability with low peak‐to‐average power ratio (PAPR) of transmit signal. However, the low‐PAPR property of SC‐FDE cannot be maintained if multi‐level data modulation is introduced. The low‐PAPR property of SC‐FDE can be maintained by applying transmit filtering with roll‐off factor at the expense of spectrum efficiency. In this paper, we propose two types of selected mapping (SLM) to reduce the PAPR of SC‐FDE transmit signal. The first SLM technique is conducted in the frequency domain, where the phase rotation is applied to subcarriers similar to the SLM technique for orthogonal frequency division multiplexing transmission. The second SLM technique is conducted in the time domain, where the phase rotation is applied directly to data‐modulated symbol sequence. Computer simulation confirms that both SLM techniques are able to reduce the PAPR of SC‐FDE signal without significant degradation of bit‐error rate performance and spectrum efficiency. Copyright © 2016 John Wiley & Sons, Ltd.     

移动通信中一种自适应时隙结构的新方法

在基于时分导频体制的单载波频域均衡系统平台上,我们利用有效到达径上信道参数的估计值,统计其包络的电平通过率,据此估计出时变多径信道的多普勒频移;进而利用跟踪多普勒频移变化与所需导频密度之间的关系,自适应地调整导频密度,使得通信系统在各种移动速度下都具有较高的信息传输速率和良好的接收性能。     

Average probability of packet error with diversity reception over arbitrarily correlated fading channels

Closed form expressions for the average probability of packet error (PPE) are presented for no diversity, maximum ratio combining (MRC), selection combining (SC) and switch and stay combining (SSC) diversity schemes. The average PPE for the no diversity case is obtained in two alternative expressions assuming arbitrarily correlated Nakagami and Rician fading channels. For the MRC case, L diversity branches are considered and the channel samples are assumed to follow Nakagami distribution and to be arbitrarily correlated in both time and space. For the SC diversity scheme with L diversity branches, two bounds on the average PPE are derived for both slow and fast fading channels. The average PPE in this case is obtained in an infinite integral form for Nakagami channels while it is reduced to a closed form expression for the Rayleigh case. The average PPE is also derived in the case of SSC diversity with dual branches for both slow and fast Rayleigh fading channels. The new formulas are applicable for all modulation schemes where the conditional probability of error has an exponential dependence on the signal‐to‐noise ratio. The average PPE is then used to obtain a modified expression for the throughput for network protocols. In general, the diversity gain exhibits a little diminishing effect as the number of diversity branches increases. In addition, the system is found to be more sensitive to the space correlation than to the time correlation. The effects of different system parameters and diversity schemes are studied and discussed. Specific figures about the system performance are also provided. Copyright © 2004 John Wiley & Sons, Ltd.     

Distributed antenna network for gigabit wireless access

For gigabit wireless data services, there are three important technical issues to be addressed: limited bandwidth, severe frequency-selective fading, and limited transmit power. A distributed antenna network (DAN) is a promising solution to the above three technical issues. In DAN, each mobile user is served by using multiple distributed antennas close to it. In this paper, recent advances in various distributed multi-input/multi-output (MIMO) techniques combined with single-carrier (SC) frequency-domain signal processing are presented for DAN. Particular attention is paid to SC frequency-domain MIMO diversity, relay, beamforming, and multiplexing jointly used with frequency-domain equalization (FDE) to significantly improve the signal transmission performance.     

Iterative frequency-domain channel estimation and equalization for single-carrier transmissions without cyclic-prefix

Compared to conventional time-domain equalization, frequency-domain equalization (FDE) presents a computationally efficient alternative for the reception of single carrier (SC) transmissions. In this paper, we consider iterative FDE (IFDE) with explicit frequency-domain channel estimation (FDCE) for non-cyclic-prefixed SC systems. First, an improved IFDE algorithm is presented based on soft iterative interferencecancellation. Second, a new adaptive FDCE (AFDCE) algorithm based on per-tone Kalman filtering is proposed to track and predict the frequency-domain channel coefficients. The AFDCE algorithm employs across-tone noise reduction, exploits temporal correlation between successive blocks, and adaptively updates the auto-regressive model coefficients, bypassing the need for prior knowledge of channel statistics. Finally, block-overlapping is used to facilitate the joint operation of IFDE and AFDCE. Simulation results show that, compared to related IFDE and adaptive channel estimation schemes, the proposed schemes offer lower mean-square error (MSE) in channel prediction, lower bit error rate (BER) after decoding, and robustness to non-stationary channels.