Performance of multiantenna signaling techniques in the presence of polarization diversity

Multiple-input multiple-output (MIMO) antenna systems employ spatial multiplexing to increase spectral efficiency or transmit diversity to improve link reliability. The performance of these signaling strategies is highly dependent on MIMO channel characteristics, which, in turn, depend on antenna height and spacing and richness of scattering. In practice, large antenna spacings are often required to achieve significant multiplexing or diversity gain. The use of dual-polarized antennas (polarization diversity) is a promising cost- and space-effective alternative, where two spatially separated uni-polarized antennas are replaced by a single antenna structure employing orthogonal polarizations. This paper investigates the performance of spatial multiplexing and transmit diversity (Alamouti (see IEEE J. Select. Areas Commun., vol.16, p.1451-58, Oct. 1998) scheme) in MIMO wireless systems employing dual-polarized antennas. In particular, we derive estimates for the uncoded average symbol error rate of spatial multiplexing and transmit diversity and identify channel conditions where the use of polarization diversity yields performance improvements. We show that while improvements in terms of symbol error rate of up to an order of magnitude are possible in the case of spatial multiplexing, the presence of polarization diversity generally incurs a performance loss for transmit diversity techniques. Finally, we provide simulation results to demonstrate that our estimates closely match the actual symbol error rates.     

Generalized Quadrature Spatial Modulation Scheme Using Antenna Grouping

This paper presents a novel generalized quadrature spatial modulation (GQSM) transmission scheme using antenna grouping. The proposed GQSM scheme combines QSM and conventional spatial multiplexing (SMux) techniques in order to improve the spectral efficiency (SE) of the system. Analytical and simulation results show that the proposed transmission scheme has minimal losses in terms of the average bit error probability along with the advantage of an increased SE compared with previous SM and QSM schemes. For the case studies, this advantage represents a reduction of up to 81% in terms of the number of required transmit antennas compared with QSM. In addition, a detection architecture based on the ordered successive interference cancellation scheme and the QR decomposition is presented. The proposed QRD‐M adaptive algorithm showed a near‐maximum‐likelihood performance with a complexity reduction of approximately 90%.     

一种基于分集技术的空时码传输方法

根据分集技术的特点,对以往经典的传输方法进行了改进,提出了一种新的传输方法。在发射端,分成M组天线,每组包含Ti（i=1,2,…,M）根天线,不同组的天线利用不同的频率发射相同的或不同的信息,从而获得发射分集增益和复用增益。在接收端,分成M组天线,每组天线包含Ri（i=1,2,…,M）根天线,每组接收天线负责接收发射端同一组发射天线发射的信息,从而获得接收分集增益,即采用＂多对多＂的传输方式。仿真结果表明：文中方法与典型的传输方法相比,可大大加快传输速率和接收端的译码的速度。同时,在发射端,可以采用正交极化天线,降低了接收端之间的干扰,从而进一步提高了系统的性能。     

Channel estimation for OFDM systems with transmitter diversity inmobile wireless channels

Transmitter diversity is an effective technique to improve wireless communication performance. In this paper, we investigate transmitter diversity using space-time coding for orthogonal frequency division multiplexing (OFDM) systems in high-speed wireless data applications. We develop channel parameter estimation approaches, which are crucial for the decoding of the space-time codes, and we derive the MSE bounds of the estimators. The overall receiver performance using such a transmitter diversity scheme is demonstrated by extensive computer simulations. For an OFDM system with two transmitter antennas and two receiver antennas with transmission efficiency as high as 1.475 bits/s/Hz, the required signal-to-noise ratio is only about 7 dB for a 1% bit error rate and 9 dB for a 10% word error rate assuming channels with two-ray, typical urban, and hilly terrain delay profiles, and a 40-Hz Doppler frequency. In summary, with the proposed channel estimator, combining OPDM with transmitter diversity using space-time coding is a promising technique for highly efficient data transmission over mobile wireless channels     

Space-time signaling for high data rates in EDGE

Several space-time coding and processing techniques have been introduced in the literature for enhancing the capacity of wireless systems through antenna diversity or spatial multiplexing. We study the application of such techniques to an adaptive coded modulation system in multipath channels with intersymbol interference. One of the key requirements for application of these schemes is the use of appropriate training symbols for channel estimation at the receiver. We determine the training requirements for coherent receiver operation when multiple transmit antennas are used. We show that for the special case of the delay diversity scheme, transmitting the same training sequence from the two antennas is optimal. For more general schemes, we present training sequences that have good auto-correlation and cross-correlation properties that can be used in a practical system such as Enhanced Data for GSM Evolution (EDGE). We present detailed link level simulations that include channel estimation for the proposed schemes. We then determine the system throughput that is achieved for packet data with ideal link adaptation for deployment scenarios with 1/3, 3/9, 4/12, and 7/21 frequency reuse. We conclude that the gains from transmit diversity are not significant when there is frequency hopping as in an EDGE system and that a factor of 3 gain in throughput can be achieved when four transmit and four receive antennas are available using simple space-time transmission and receiver processing.     

Antenna Selection for MIMO–OFDM WLAN Systems

This paper discusses the packet error rate (PER) performance of multiple-input multiple-output (MIMO) wireless systems. We focus our discussion on communication systems based on the IEEE 802.11a/g standard. In particular, we study the performance of spatial multiplexing systems with joint encoding at the transmitter and linear detection at the receiver. We show that spatial multiplexing systems based on minimum mean square error (MMSE) or zero forcing (ZF) demultiplexing benefit greatly from antenna subset selection. These results agree with recent analytical results showing the equivalence in diversity order between a full system (all receive antennas) and a system with antenna selection.     

Performance analysis and design of STBCs for frequency-selective fading channels

In this paper, space-time block-coded transmission over frequency-selective fading channels is investigated. A lower bound for the pairwise error probability for optimum detection is given. Also, an approximation for the bit-error rate is derived and compared with simulation results for maximum-likelihood sequence estimation (MLSE) for the GSM/EDGE (Enhanced Data Rates for GSM Evolution) system. Furthermore, a novel design rule for space-time block codes (STBCs) for frequency-selective fading channels is provided. A corresponding code is designed and shown to yield higher performance than Alamouti's code. It is demonstrated that for fading channels with L independent impulse response coefficients, STBCs designed for the flat fading channel can achieve at most a diversity order of (N/sub T/+L-1)N/sub R/ if N/sub T/ transmit antennas and N/sub R/ receive antennas are used. On the other hand, the maximum diversity order employing the proposed code design rule is LN/sub T/N/sub R/.     

Exploiting Multipath Diversity in Multiple Antenna OFDM Systems With Spatially Correlated Channels

Multiple antennas are useful in orthogonal frequency division multiplexing (OFDM) systems for providing transmit and receive diversity to overcome fading. Typically, these designs require considerable separation between the antennas. Spatial correlation is introduced when antennas are not well separated, and it often leads to performance degradation in a flat fading environment. However, in frequency selective fading channels with rich multipath diversity, OFDM receivers can overcome this performance degradation due to antenna correlation. This is due to transformation of a highly spatially correlated channel impulse response to a less spatially correlated channel frequency response inherently by an OFDM system in the presence of rich multipath diversity. We illustrate this for a simple receive diversity OFDM system and hence introduce the concept of space sampling at the receiver where antennas are placed relatively close to each other. The minimum separation required between the antennas under such circumstances is derived analytically, and it is shown that even with a separation of only$0.44lambda$, the required spatial correlation in the channel frequency response becomes sufficiently low. Simulated performance results with such spacing for various multiple antenna OFDM systems corroborate the analytical results.     

TD-SCDMA HSPA+中的单双流MIMO技术的研究

多输入多输出(MIMO)技术是近年来移动通信的热门研究领域,它的特征在于无线发射机和接收机都引入了多根天线.MIMO技术除了通过空间分集方式获得容量的提升外,还可以通过空间复用方式,利用不同天线信道的独立性建立多个空间子信道来提高容量.但是,无论是基于空间分集的单流模式还是基于空间复用的双流模式,单独在TD-SCDMA...     

扩展空间调制技术的低复杂度检测算法

针对发射天线数可变的扩展空间调制技术(Extended Spatial Modulation,ESM)提出了相应的低复杂度检测算法。传统的空间调制技术(Spatial Modulation,SM)将信息调制在发射的天线上,但是在一个符号周期内活跃的天线数为常数。而ESM允许在不同符号周期以不同数目的发射天线进行组合,不仅能够承载更多信息,同时对发射的天线也有了更多优选的空间,但是传统的检测算法在发射天线数固定时才能正常使用,针对ESM的特殊情况提出了阈值法检测天线,并通过数值实验给出了性能分析。     

多用户MIMO系统下行链路的随机多波束复用技术

该文提出了一种随机多波束多用户复用技术,充分利用多用户分集以及基站多天线的空间自由度来提高系统吞吐量。不同于传统的随机波束形成技术,该技术首先在给定预编码码本内随机选取一个码字,然后调度多个空分复用用户以及其余预编码矩阵。该文采用了一种逐次调度的方式,第一次训练调度一个主发送用户并确定一个次发送预编码矩阵,通过第二次训练选择次发送用户,这种方式能以很小的反馈开销有效控制复用用户之间的相互干扰。同时,该文所提技术能进一步推广到用户具有不同天线配置的异构情形。仿真结果表明,该文技术在具有不同相关性的信道环境下都能获得较优的系统吞吐量。     

On achievable performance of spatial diversity fading channels

Channel time-variation and frequency selectivity [causing intersymbol interference (ISI)] are two major impairments in transmission for a wireless communication environment. Spatial diversity on the transmitter or the receiver side has been traditionally used to combat multipath fading. Previous results indicate significant gains in using multiple transmitter and receiver antenna diversity. By deriving the mutual information and cutoff rate we characterize the gains on these channels. We show that gains linear in the number of antennas can be achieved either when the signal-to-noise ratio (SNR) becomes very large or when the number of antennas becomes large. We show that some of these gains can be achieved by lower complexity linear receiver structures. By evaluating the cutoff rate for phase-shift keying (PSK) constellations we further quantify the gains of using spatial diversity at both the transmitter and the receiver. Next, we examine the expected mutual information for slowly fading ISI channels where the channel is assumed to be block time-invariant. We then examine the impact of fast channel time variation (time variation within a transmission block) on multicarrier transmission schemes. We derive the average mutual information for orthogonal frequency-division multiplexing (OFDM) in time-varying ISI environments. Using this we examine the impact of transmitter and receiver diversity on OFDM transmission over time-varying ISI channels. We also study the effect of time variation on OFDM packet-size design     

On the Diversity Order of Spatial Multiplexing Systems With Transmit Antenna Selection: A Geometrical Approach

In recent years, the remarkable ability of multiple-input-multiple-output (MIMO) wireless communication systems to provide spatial diversity or multiplexing gains has been clearly demonstrated. For MIMO diversity schemes, it is well known that antenna selection methods that optimize the postprocessing signal-to-noise ratio (SNR) can preserve the diversity order of the original full-size MIMO system. On the other hand, the diversity order achieved by antenna selection in spatial multiplexing systems, especially those exploiting practical coding and decoding schemes, has not thus far been rigorously analyzed. In this paper, a geometrical framework is proposed to theoretically analyze the diversity order achieved by transmit antenna selection for separately encoded spatial multiplexing systems with linear and decision-feedback receivers. When two antennas are selected from the transmitter, the exact achievable diversity order is rigorously derived, which previously only appears as conjectures based on numerical results in the literature. If more than two antennas are selected, we give lower and upper bounds on the achievable diversity order. Furthermore, the same geometrical approach is used to evaluate the diversity-multiplexing tradeoff in spatial multiplexing systems with transmit antenna selection     

Space–Time/Space–Frequency/Space–Time–Frequency Block Coded MIMO-OFDM System with Equalizers in Quasi Static Mobile Radio Channels Using Higher Tap Order

In 4G broadband wireless communications, multiple transmit and receive antennas are used to form multiple input multiple output (MIMO) channels to increase the capacity (by a factor of the minimum number of transmit and receive antennas) and data rate. In this paper, the combination of MIMO technology and orthogonal frequency division multiplexing (OFDM) systems is analyzed for wideband transmission which mitigates the intersymbol interference and hence enhances system capacity. In MIMO-OFDM systems, the coding is done over space, time, and frequency domains to provide reliable and robust transmission in harsh wireless environment. Also, the performance of space time frequency (STF) coded MIMO-OFDM is analyzed with space time and space frequency coding as special cases. The maximum achievable diversity of STF coded MIMO-OFDM is analyzed and bit error rate performance improvement is verified by simulation results. Simulations are carried out in harsh wireless environment, whose effect is mitigated by using higher tap order channels. The complexity is resolved by employing sphere decoder at the receiver.     

Decision feedback detection with error compensation for hybrid space-time block codes

Spatial division multiplexing (SDM) techniques increase the total throughput by transmitting independent information streams through multiple transmit antennas whereas space time coding (STC) techniques utilize diversity gain. Hybrid space-time block code (STBC) schemes proposed combine the above two techniques to maximize the link performance. We propose a decision feedback detection method to improve the performance of the hybrid STBC scheme for orthogonal frequency division multiplexing (OFDM). In this scheme, we take the error propagation effect into account to enhance the detection performance. Simulation results show that the proposed method outperforms the conventional hybrid STBC detection algorithm by more than 3dB at 1% frame error rate for frequency selective fading channels.     

Spatial multiplexing with transmit antenna and constellation selection for correlated MIMO fading channels

We consider spatial multiplexing systems in correlated multiple-input multiple-output (MIMO) fading channels with equal power allocated to each transmit antenna. Under this constraint, the number and subset of transmit antennas together with the transmit symbol constellations are determined assuming knowledge of the channel correlation matrices. We first consider a fixed data rate system and vary the number of transmit antennas and constellation such that the minimum margin in the signal-to-noise ratio (SNR) is maximized for linear and Vertical Bell Laboratories Layered Space-Time (V-BLAST) receivers. We also derive transmit antenna and constellation selection criteria for a successive interference cancellation receiver (SCR) with a fixed detection order and a variable number of bits transmitted on each substream. Compared with a system using all available antennas, performance results show significant gains using a subset of transmit antennas, even for independent fading channels. Finally, we select a subset of transmit antennas to maximize data rate given a minimum SNR margin. A lower bound on the maximum outage data rate is derived. The maximum outage data rate of the SCR receiver is seen to be close to the outage channel capacity.     

A practical transmit beamforming strategy for closed‐loop MIMO communication

A new beamforming strategy is proposed for multiuser systems with N transmit antennas at the transmitter and M ? N single antenna receivers. The proposed scheme remarkably improves on the classical spatial division multiple access, and achieves the same data rates as spatial multiplexing for all users but with significantly superior performance/diversity gain. When compared with the Bell labs layered space–time system, the symbol rate is the same and the performance is much superior because of the presence of diversity gain. In addition, unlike the Bell labs layered space–time system, the receivers do not need to know each other's vector channels. Finally, the proposed algorithm is based on dirty‐paper coding, but does not require much complexity and is implementable. Copyright © 2011 John Wiley & Sons, Ltd.     

Detection schemes for space-time block code and spatial multiplexing combined system

Space-time block code is combined with spatial multiplexing technique over multiple-input multiple-output system to take advantages of both schemes. The transmit antennas are divided into groups and each group transmits space-time coded blocks in parallel. At receiver side, three types of group receivers are proposed to separate the filtered version of the multiplexed space-time coded symbol blocks followed by space-time decoder. Error rate performances of the detection schemes are evaluated in correlated channels. The diversity order of the combined system is compared with that of the SM system and the STBC system.     

A new high-rate differential space-time block coding scheme

A new high-rate differential space-time transmission scheme based on spatial multiplexing of Alamouti-encoded information streams is developed. At the receiver, joint space-time differential interference cancellation and decoding is performed, realizing diversity and rate gains, without requiring channel knowledge or bandwidth expansion. Our focus is on the case of two information streams with two transmit antennas per stream on flat-fading channels for simplicity. However, using previously published techniques, the development readily extends to more than two information streams, to more than two transmit antennas per stream, and to frequency-selective channels.     

Contour-Based Priority Scheduling in Optical Burst Switched Networks

Optical burst switching (OBS) is an emerging technology that allows variable size data bursts to be transported directly over dense wavelength division multiplexing links. Although several quality-of-service (QoS) schemes have been proposed for OBS networks, how to provide QoS at the high speed required by the OBS network is still an open question. In this paper, we propose a novel O(1) runtime contour-based priority algorithm that provides complete priority isolation among different priorities. This is the first practical O(1) runtime priority algorithm proposed for OBS, and it is well suited to high-speed hardware implementation.