An adaptive spatio-temporal coding scheme for indoor wireless communication

Systems that employ multiple antennas in both the transmitter and the receiver of a wireless system have been shown to promise extraordinary spectral efficiency. With full channel knowledge at the transmitter and receiver, Raleigh and Cioffi (1998) proposed a spatio-temporal coding scheme, discrete matrix multitone (DMMT), to achieve asymptotically optimum multiple-input-multiple-output (MIMO) channel capacity. The DMMT can be regarded as an extension of the discrete multitone for a digital subscriber lines (DSL) system to the MIMO wireless application. However, the DMMT is basically impracticable in nonstationary wireless environments due to its high-computational complexity. Exploring second-order statistics, we develop an efficient adaptive blind coding scheme for a high-capacity time-division duplexing (TDD) system with slow time-varying frequency-selective MIMO channels. With this method, neither a training sequence nor feedback of channel information is required in the proposed blind approach. Besides, the computational complexity of the proposed scheme is significantly lower than that of the coding scheme described by Raleigh and Cioffi. Simulation results show that the proposed architecture works efficiently in indoor wireless local area network applications.     

Non-line of Sight Error Mitigation in Ultra-wideband Ranging Systems Using Biased Kalman Filtering

In this paper, a non-line of sight (NLOS) error mitigation method based on biased Kalman filtering for ultra-wideband (UWB) ranging is proposed. The NLOS effect on the measures of signal arrival time is considered one of the major error sources in range estimation and time-based wireless location systems. An improved biased Kalman filtering system, incorporated with sliding-window data smoothing and hypothesis test, is used for NLOS identification and error mitigation. Based on the results of hypothesis test, the estimated ranges are either calculated by smoothing the measured range when line of sight (LOS) status is detected, or obtained by conducting error mitigation on the NLOS corrupted measured range when NLOS status is detected. The effectiveness of the proposed scheme in mitigating errors during the LOS-to-NLOS and NLOS-to-LOS transitions is discussed. Improved NLOS identification and mitigation during the NLOS/LOS variations of channel status are attained by an adaptive variance-adjusting scheme in the biased filter. Simulation results show that the UWB channel status and the transition between NLOS and LOS can be identified promptly by the proposed scheme. The estimated time-based location metrics can be used for achieving higher accuracy in location estimation and target tracking.     

Capacity analysis for LOS millimeter–wave quadrature spatial modulation

Capacity analysis for millimeter-wave (mmWave) quadrature spatial modulation (QSM) multiple-input multiple-output (MIMO) system is presented in this paper. QSM is a new MIMO technique proposed to enhance the performance of conventional spatial modulation while retaining almost all its inherent advantages. Furthermore, mmWave utilizes a license-free wide-bandwidth spectrum and is a very promising candidate for future wireless systems. Detailed and novel analysis of the mutual information and the capacity for line of sight (LOS) mmWave-QSM system are presented in this study. The conditions under which theoretical capacity can be achieved are derived and discussed. Also, mmWave channel design is conducted and a novel algorithm is proposed to overcome existing limitation for unbalanced MIMO configurations, i.e., when the number of receive antennas is less than that of the transmit antennas. Monte Carlo simulation results are provided to corroborate derived formulas. It is shown that significant performance enhancements can be achieved under different system and channel configurations.     

A comparative study of STBC transmissions at 2.4 GHz over indoor channels using a 2 × 2 MIMO testbed

In this paper we employ a 2 × 2 Multiple‐Input Multiple‐Output (MIMO) hardware platform to evaluate, in realistic indoor scenarios, the performance of different space‐time block coded (STBC) transmissions at 2.4 GHz. In particular, we focus on the Alamouti orthogonal scheme considering two types of channel state information (CSI) estimation: a conventional pilot‐aided supervised technique and a recently proposed blind method based on second‐order statistics (SOS). For comparison purposes, we also evaluate the performance of a Differential (non‐coherent) space‐time block coding (DSTBC). DSTBC schemes have the advantage of not requiring CSI estimation but they incur in a 3 dB loss in performance. The hardware MIMO platform is based on high‐performance signal acquisition and generation boards, each one equipped with a 1 GB memory module that allows the transmission of extremely large data frames. Upconversion to RF is performed by two RF vector signal generators whereas downconversion is carried out with two custom circuits designed from commercial components. All the baseband signal processing is implemented off‐line in MATLAB ®, making the MIMO testbed very flexible and easily reconfigurable. Using this platform we compare the performance of the described methods in line‐of‐sight (LOS) and non‐line‐of‐sight (NLOS) indoor scenarios. Copyright © 2007 John Wiley & Sons, Ltd.     

Experimental investigations of 60 GHz WLAN systems in office environment

This paper presents the results of an experimental investigation of 60 GHz wireless local area network (WLAN) systems in an office environment. The measurement setup with highly directional mechanically steerable antennas and 800 MHz bandwidth was developed and experiments were performed for conference room and cubicle environments. Measurement results demonstrate that the 60 GHz propagation channel is quasioptical in nature and received signal power is obtained through line of sight (LOS) and reflected signal paths of the first and second orders. The 60 GHz WLAN system prototype using steerable directional antennas with 18 dB gain was able to achieve about 30 dB baseband SNR for LOS transmission, about 15-20 dB for communications through the first-order reflected path, and 2-6 dB SNR when using second-order reflection for the office environments. The intra cluster statistical parameters of the propagation channel were evaluated and a statistical model for reflected clusters is proposed. Experimental results demonstrating strong polarization impact on the characteristics of the propagation channel are presented. Cross-polarization discrimination (XPD) of the propagation channel was estimated as approximately 20 dB for LOS transmission and 10-20 dB for NLOS reflected paths.     

Polar codes and polar processing for 6G wireless systems

As the first type of channel code achieving the channel capacity,polar codes are an important candidate for the 6G data transmission.A polarized processing framework for the 6G systems was proposed.In this framework,in order to fulfill the requirement of ultra-reliable transmission,a high-performance coding scheme of concatenated polar code was designed to approach the channel capacity with finite-length.Then,the polar coded MIMO scheme was devised to match the requirement of the high spectrum efficiency.Finally,the scheme of polar coded non-orthogonal multiple access was investigated to improve the transmission capacity.All these schemes indicate that polar processing can dramatically boost the performance of 6G wireless transmission and become a promising direction.     

Layered space–time block code for hybrid satellite–terrestrial broadcasting systems

Multiple‐input multiple‐output (MIMO) is a topic of high interest for the next generation of broadcasting systems. Even if they have begun to be proposed for the second generation of terrestrial digital TV, there are still gaps in the deployment of MIMO schemes in single‐frequency networks. This deployment becomes more critical when a hybrid satellite–terrestrial transmission is adopted because of the different aspects of the respective transmission links. In this paper, we propose to apply a layered space–time block code (LSTBC) for MIMO schemes in this hybrid transmission for next‐generation handheld (NGH) systems. The contribution of this paper is multi‐fold. First, we detail the land mobile satellite channel specifications describing the satellite link. Then, we propose to apply a MIMO scheme between the antennas of the satellite site and the terrestrial site. Then, we introduce the LSTBC scheme for NGH broadcasting systems. The proposed code is based on a layered construction designed to be efficient in shadowing regions. This efficiency is verified in a line‐of‐sight situation but also in low, moderate and deep shadow situations. The LSTBC scheme is then a very promising candidate for NGH systems with MIMO transmission. Copyright © 2012 John Wiley & Sons, Ltd.     

A decision tree‐based NLOS detection method for the UWB indoor location tracking accuracy improvement

Among existing wireless technologies, ultra‐wideband (UWB) is the most promising solution for indoor location tracking. UWB has a great multipath fading immunity; however, great multipath resolvability alone does not eliminate the effect of non‐line‐of‐sight (NLOS) and multipath propagation. NLOS and multipath propagation in indoor environments can easily produce meters of UWB ranging error. This condition gives an enormous impact on the accuracy of indoor location tracking data. To address this problem, we propose an NLOS detection method using recursive decision tree learning. Using the UWB channel quality indicators information, we develop our model with the Gini index and altered priors splitting criteria. We then validate the constructed model using the 10‐fold cross‐validation method. Our experiment shows that the constructed model has correctly detected 90% of both line‐of‐sight (LOS) and NLOS cases on the seven different indoor environments. The result of this work can be used for the UWB indoor location tracking accuracy improvement.     

莱斯衰落信道下大规模MIMO系统中的信道估计方法

日趋重要的高速移动工具,如高速铁路、无人驾驶飞机等,大多都处在开阔地带.由于视距传播的存在,瑞利衰落模型已经不能很好地描述该环境下的信道情况,而莱斯衰落信道模型由视距分量和多径分量组成,更能准确地表述上述信道变化.基于此模型,在大规模天线系统下,在已存在的基于叠加训练序列信道估计方法的基础上,提出了改进的信道估计方法和对应的解码方法.改进后的信道估计方法分为直射分量已知和未知两种情况,分别推导了相应的信道估计公式和解码方法.数值仿真结果验证了本文所提方案性能的优越性.     

Maximum-throughput delivery of SVC-based video over MIMO systems with time-varying channel capacity

In this paper, we present a novel scalable video transmission strategy over multi-input multi-output (MIMO) wireless systems with time-varying channel capacity. It is a great challenge to simultaneously guarantee the QoS for video delivery and maximize the system throughput over time-varying MIMO channel. We demonstrate that, by making full use of estimated channel state information (CSI) through feedback, a cascade of adaptive operations can be designed to satisfy maximum throughput for scalable video over MIMO systems. These operations include power allocation based on water-filling (WF), adaptive channel selection (ACS), and novel throughput maximizing power reallocation (PR). The proposed ACS transmission scheme enables overall increase in data throughput among enhancement layers by adaptively launching base layer bit-stream to proper sub-channel. Then, after initial power allocation with WF and proper adaptive mode selection, we obtain the surplus power across enhancement layer sub-channels which can be reallocated to some sub-channels by the proposed PR scheme. With such power reallocation, certain enhancement layers will be able to reach new level of QAM modulation through PR so as to maximize the system data throughput. We present in this paper some detailed analysis on these adaptive operations. We also present some simulation results to demonstrate that maximum throughput video transmission over MIMO wireless systems indeed can be achieved based on scalable video coding (SVC) and a sequence of appropriately designed adaptive operations.     

An iterative singular vectors estimation scheme for beamforming transmission and detection in MIMO systems

A novel iterative singular vector estimation scheme has been proposed for a beamforming transmission and detection in wireless multiple input multiple output (MIMO) systems. Two singular channel matrix vectors, which correspond to the largest singular value, are iteratively obtained at the transmitter and the receiver without estimating the channel coefficients. The proposed singular vectors estimation strategy has advantages over the conventional MIMO channel estimation schemes in terms of both frame-error-rate performance, bandwidth efficiency and computation complexity.     

Dynamic Resource Allocation for Scalable H.264/AVC Video Transmission over MIMO Wireless Systems

In this study, a channel selection algorithm is proposed to enhance the transmission rate for scalable video coding (SVC) source transmission over multi-input multi-output (MIMO) wireless systems. The proposed algorithm allows each layer of SVC video to choose its appropriate channel in wireless MIMO systems based on channel state information for transmission rate enhancement. Here, this difficult problem is converted into mathematical optimization problem to improve the performance of SVC video transmission. Experimental results show that the transmission rate of the proposed method outperforms the existing scheme.     

室内MIMO系统采用极化分集时的信道容量

典型的室内传播信道为莱斯衰落信道,可将其分解为LOS传播信道和散射信道.本文假设散射信道为瑞利衰落信道,并根据天线的极化特性,给出了存在极化分集时的LOS传播信道.基于此,本文提出了室内MIMO系统采用极化分集时的信道模型.研究表明:极化分集可以有效提高MIMO信道容量.     

A DSFBC-OFDM for a Next Generation Broadcasting System With Multiple Antennas

In this paper, we propose a differential space-frequency block code-orthogonal frequency division multiplexing (DSFBC-OFDM) scheme as a multiple-input multiple-output (MIMO) transmission technique for next generation broadcasting system. A linear decoding method for DSFBC, which performs comparably to the ML decoding method, is derived for the cases of two or four transmit antennas. A simple table lookup method is proposed to improve the efficiency of the encoding/decoding process of DSFBC for the case of non-constant modulus constellations. This not only reduces the computational load, but also removes the necessity of channel estimation. Also, synchronization techniques with a DSFBC-encoded phase reference symbol (PRS) are discussed. Finally, an MIMO channel model for the next generation broadcasting system is developed by extending the 3GPP MIMO model to fit broadcasting environments. The MIMO channel model is then used to compare BER performances of differential space block code schemes for various channel environments. Simulation results show that the DSFBC-16QAM scheme using either four transmit antennas with one receive antenna or two transmit antennas with two receive antennas achieves a performance gain of 12 dB, with a data rate twice faster than that of the conventional DQPSK scheme     

协同信道空时优化MIMO无线传输系统

该文提出一种基于虚拟信道的空时优化多输入多输出(MIMO)无线传输系统。通过在发射端产生不同的空时虚拟信道,与实际空间无线信道级联,构成系统的整体传输信道即协同空分信道。系统可以根据接收端的反馈信息采用模拟退火算法来优化虚拟信道,改善误码率(BER)性能。利用虚拟信道方法,可以使一根MIMO发射天线在同一时间、同一频段传输多路叠加合并后的数据信号,从而可以使发射的不同数据信号的总路数超过发射天线的数量,突破了现有MIMO系统在同一时间、同一频段最多只能发射与发射天线数量相等的不同数据信号的传统方式,可以显著提高系统的频谱效率。仿真结果和基于ZC706和AD9361硬件平台的微波暗室实际测试结果充分验证了新MIMO系统的有效性。     

Adaptive Transmission Scheme for Mixed Multicast and Unicast Traffic in Cellular Systems

Wireless communication systems have been developed to support users' various requirements. Multicast and unicast transmission schemes are proposed for various types of services. The multicast transmission is known as an efficient method for group-data transmission. The data rate for multicast transmission depends on the instantaneous worst channel user. On the other hand, unicast transmission exploits wireless channel variation and achieves a multiuser diversity gain. In this paper, we evaluate and compare the system performance of multicast and unicast transmission schemes in terms of system capacity, worst average channel user's capacity, and outage probability for varying cell environments. We also propose a novel hybrid scheduling scheme for mixed multicast and unicast traffic services and compare the proposed scheme with the conventional scheme.      

Interference Cancellation with Space Diversity for Downlink MC-CDMA Systems

Modern wireless communications require an efficient spectrum usage and high channel capacity and throughput. Multiple-input and multiple-output (MIMO), Linear equalizers, multi-user detection and multicarrier code-division multiple access (MC-CDMA) are possible solutions to achieve spectral efficiency, high channel capacity, eliminate multiple access interference (MAI), eliminate Inter symbol interference (ISI) and robustness against frequency selective fading. In this paper, we combine all these techniques and investigate BER performance. We propose a low complexity receiver structure for Single-input Multiple-output (SIMO) downlink MC-CDMA systems. It employs an interference cancellation scheme to suppress the interference caused by the multipath fading channel. Also, the proposed scheme is developed for MIMO MC-CDMA system. The performance analysis of Downlink MIMO MC-CDMA systems with V-BLAST over frequency selective fading channel is investigated under various number of transmit and receive antennas. The simulation results show proposed SIMO equalization with parallel interference cancellation scheme is effective in reducing the ISI and the MAI. It improves the performance significantly and the simulation results show that MIMO MC-CDMA with V-BLAST multi-user detection provides high data rate and the BER significant improvement.     

3D大规模MIMO系统中莱斯信道下的传输方案

针对三维(3D)大规模多输入多输出(MIMO)系统中莱斯信道模型,通过研究分析获得简单易行、频谱效率高的传输方案。考虑到莱斯信道中的散射信道获取较为困难,而视距信道获取较为容易,仅利用视距信道进行传输方案研究。首先通过用户调度算法解决了相邻用户之间干扰过大的问题,从而提升了系统的和速率;接着充分利用3D MIMO系统中水平和垂直维度的特点,采用域选择的预编码方法消除不同用户间的干扰并最大化信噪比,进一步提升了系统和速率。经过仿真验证,提出的3D大规模MIMO传输方案比以往方案具备更大的频谱效率。     

A low-complexity space-time OFDM multiuser system

Exploiting the Fourier basis structure both in the space and the time domains, we develop a low-complexity multiuser space-time coding scheme, multiuser (MU) angle-frequency coding scheme (MU-AFCS), to properly schedule the data streams of each user with respect to its corresponding angle-frequency channel structure for downlink wireless systems. With the proposed approach, a large amount of space resource left over by one user, in clustered multipath wireless channels, can be easily identified and used by the others without serious signal collision in the space domain. In doing so, low channel capacity resulting from poor channel structures in systems, allowing only single-user transmission at a time, can be greatly boosted. The key advantage of this approach is that only limited feedback of channel state information to the transmitter is required while multiuser macro-diversity is sufficiently exploited. In addition, the complexity of the proposed approach is much lower than that of the existing ones serving similar purposes. Through theoretical analyses and computer simulations, we demonstrate that the MU-AFCS can significantly increase the channel capacity as compared to the traditional orthogonal resource division MU multiple-input multiple-output (MIMO) systems.     

Capacity enhancement in coherent optical MIMO (COMIMO) multimode fiber links

In this paper, we study a coherent optical MIMO (COMIEMO) multi-mode fiber link proposed for enhancing the fiber information capacity. We examine the statistical characterization of the equivalent MIMO channel and the improvement in the fiber capacity due to MIMO transmission. It is shown that the equivalent channel behaves similarly to a complex Gaussian MIMO channel, suggesting that the available results on wireless MIMO communication systems can be applied to optical fiber links for capacity enhancement.