Effect of Least Square Channel Estimation Errors on Achievable Rate in MIMO Fading Channels

The achievable rate of a multiple input multiple output (MIMO) fading channel is derived in the form of generalized mutual information (GMI) when least square (LS) channel estimation is employed to gain channel state information at receivers. The derived average GMI of a channel with LS channel estimation is compared with the known average GMI (equivalently, the lower bound on the ergodic capacity) of a channel with linear minimum mean square error channel estimation. An effective approximation method is also proposed to ease the numerical calculation of the average GMI of a MIMO channel with LS channel estimation.     

适合频率选择性MIMO信道的FIR预编码器

改善频率选择性多输入多输出(MIMO)系统的信道容量,具有重要的理论和现实意义。基于最大信道容量准则,提出一种适合MIMO频率选择性衰落信道的预编码新方法。该方法将预编码器建模为一个有限冲击响应(FIR)滤波器,利用秩松弛将原非凸优化问题转换成为半定规划(SDP)问题,并结合特征值分解设计预编码器。仿真实验结果和分析表明,相对于扩展均匀信道分解(EUCD)等其它现有算法,该算法仅需较少的滤波器阶数即可显著提升系统的信道容量,具有较低的实现复杂度。     

基于PSAM的MIMO时间-频率双选择性信道的信道估计

数据的高速率传输以及终端的高速移动,导致无线通信信道具有时间选择性与频率选择性两个特征.本文主要研究了数据分组传输方式下,基于导频符号辅助调制(PSAM)的多输入多输出(MIMO)时间-频率双选择性信道的信道估计问题.首先,将时间-频率双选择性MIMO信道,建模为一个随时间变化的多项式内插信道模型;然后,根据信道Doppler衰落速率、多项式模型中的误差项,确定出模型的阶数以及整个数据块的长度;最后,基于该多项式内插信道模型,提出了采用PSAM的MIMO双选择性信道估计方法.实验结果表明本文的算法在时间-频率双选择性衰落信道下具有较好的性能.     

Performance of MIMO System Through Nakagami Fading Channel with Arbitrary Fading Parameters

In this paper, the analytical and simulation results of the bit error rate (BER) performance for a multiple-input multiple-output (MIMO) system with an arbitrary number of transmit and receive antennas are developed for the uplink transmission. The fading channel is assumed to follow Nakagami-m distribution with correlation among branches. The BER is expressed in terms of Lauricella’s multivariate hypergeometric function for both independent and correlated antenna branches for BPSK system.

Multi-Layer Broadcasting over a Block Fading MIMO Channel

This paper introduces extensions for the broadcast approach for a multi-input multi-output (MIMO) block fading channel, with receiver only channel state information (CSI). Previous works have not been able to fully characterize the fundamental MIMO broadcasting upper bound. As it seems that analytical solution for this problem is quite difficult to achieve, we consider here sub-optimal schemes, for which achievable rates may be computed. In particular, finite level coding over a MIMO channel instead of continuous layering is analyzed, the expressions derived for the decoding probability regions allow numerical computation of finite level coding upper bounds. Noticing that the gains of two level coding over a MIMO channel are rather small, we consider sub-optimal techniques, which are more straightforward to implement. Among these techniques is the multiple-access channel (MAC) approach with single level coded streams, which is similar in concept to V-BLAST. Closed form expressions for probabilities of decoding regions here are derived, allowing numerical evaluation. We further consider multi-access permutation codes (MAPC). A Hadamard transform is compared with a suggested diagonal permutation code, which are shown to have similar performance, while diagonal permutation has lower implementation complexity. For all approaches, we derive information theoretic upper bounds of achievable rates.     

频率选择性衰落MIMO信道容量分析

随着传输速率越来越高,信号所占用的带宽越来越宽,实际信道呈现出频率选择性衰落特性.根据频率选择性衰落信道特性,建立了频率选择性衰落MIMO信道模型,采用频域和时域的方法研究了在频率选择性衰落下,发射端已知和未知信道状态信息的MIMO信道容量,并给出了相关的仿真结果.研究结果表明:在相同发射功率和传输带宽下,MIMO系统可以不牺牲信号带宽而显著提高信道的容量,并且天线数量和输入信噪比的大小对信道容量具有不同的影响.研究结果为如何提高频率选择性衰落环境下MIMO信道容量提供了依据.     

On Achievable Data Rates and Optimal Power Allocation in Fading Channels with Imperfect Channel State Information

Achievable rates of wireless communication systems with pilot-based channel estimation are investigated for the case of time-selective fading. Novel analytical expressions for the maximum achievable rates of such systems are derived in terms of the system signal-to-noise ratio (SNR), fading rate and estimation scheme deployed. The frame size is optimized jointly based on the SNR and the fading rate. The maximum rate achieving coding scheme is suggested and shown to be a modified version of the classical water-filling algorithm that accounts for imperfect channel state information (CSI) at the transmitter. The impact of the estimation scheme and the angular spread of the received signal on the quality of estimation and achievable rates is evaluated. A number of numerical simulations are provided to illustrate the dependence of the optimal block length and achievable rates on SNR, fading rate, estimation scheme and angular spread of the channel.

MIMO Signaling over the MMF Optical Broadcast Channel with Square-Law Detection

This paper proposes an architecture for using multiple-input multiple-output techniques for a multimode fiber broadcast channel, allowing simultaneous transmission of unique streams to different users on the same fiber while using squarelaw detection. The resulting system throughput scales nearly linearly with the number of transmitters and receivers. The paper also proposes a training scheme appropriate for use with squarelaw detection.     

A Note on Discrete-Time Triply-Selective MIMO Rayleigh Fading Channel Models

We discuss recent results on discrete-time models for triply-selective multiple-input multiple-output (MIMO) Rayleigh fading channels. Our key finding is that a previously proposed model (Xiao et al., 2004), which allows for efficient computer simulations, is sufficiently accurate for a wide range of practical scenarios.     

用于MIMO广播信道的带多波束选择的正交随机波束成形算法

本文提出一种基于有限反馈的波束和用户选择方案,在这种方案中,用户端利用一个随机正交码本对其信道方向信息(CDI)进行量化,计算其最大信号与干扰加噪声功率比(SINR),并把这些信息反馈给基站;基站根据接收到的这些反馈信息,按照和容量最大的准则选择出多个正交波束以及相应的多个用户.和sharif等人最近提出的方案相比,我们提出的方案能根据系统参数,如用户数和信噪比(SNR),对选择的波束成形矢量及其对应的用户的数量和集合进行调整,当用户数量较小时,和容量性能得到了很大的提升,同时避免了选择波束成形矢量时的用户冲突,另外,基站也不需要广播波束成形矢量给各个用户.     

Degrees of Freedom Region of the MIMO X Channel

We provide achievability as well as converse results for the degrees of freedom region of a multiple-input multiple-output (MIMO) X channel, i.e., a system with two transmitters, two receivers, each equipped with multiple antennas, where independent messages need to be conveyed over fixed channels from each transmitter to each receiver. The inner and outer bounds on the degrees of freedom region are tight whenever integer degrees of freedom are optimal for each message. With M = 1 antennas at each node, we find that the total (sum rate) degrees of freedom are bounded above and below as 1 les eta*x les 4/3. If M > 1 and channel matrices are nondegenerate then the precise degrees of freedom eta*x = (4/3)M. Thus, the MIMO X channel has noninteger degrees of freedom when M is not a multiple of 3. Simple zero forcing without dirty paper encoding or successive decoding, suffices to achieve the (4/3)M degrees of freedom. If the channels vary with time/frequency then the channel with single antennas (M = 1) at all nodes has exactly 4/3 degrees of freedom. The key idea for the achievability of the degrees of freedom is interference alignment-i.e., signal spaces are aligned at receivers where they constitute interference while they are separable at receivers where they are desired. We also explore the increase in degrees of freedom when some of the messages are made available to a transmitter or receiver in the manner of cognitive radio.     

An Achievable Rate Region for the Asynchronous Multiple Access Channel with Feedback

1　ＩｎｔｒｏｄｕｃｔｉｏｎＧＡＡＲＤＥＲａｎｄＷＯＬＦ[1 ] ａｓｗｅｌｌａｓＣｏｖｅｒａｎｄＬｅｕｎｇｈａｖｅｄｅｍｏｎｓｔｒａｔｅｄｔｈａｔｔｈｅｃａｐａｃｉｔｙｒｅｇｉｏｎｏｆａｄ .ｍ .ＭｕｌｔｉｐｌｅＡｃｃｅｓｓＣｈａｎｎｅｌ(ＭＡＣ)ｃａｎｂｅｉｎ     

On the User Selection for MIMO Broadcast Channels

In this paper, a downlink communication system, in which a base station (BS) equipped with $M$ antennas communicates with $N$ users each equipped with $K$ receive antennas, is considered. An efficient suboptimum algorithm is proposed for selecting a set of users in order to maximize the sum–rate throughput of the system, in a Rayleigh-fading environment. For the asymptotic case when $N$ tends to infinity, the necessary and sufficient conditions in order to achieve the maximum sum–rate throughput, such that the difference between the achievable sum–rate and the maximum value approaches zero, is derived. The complexity of our algorithm is investigated in terms of the required amount of feedback from the users to the BS, as well as the number of searches required for selecting the users. It is shown that the proposed method is capable of achieving a large portion of the sum–rate capacity, with a very low complexity.      

The Capacity Region of the Gaussian Multiple-Input Multiple-Output Broadcast Channel

The Gaussian multiple-input multiple-output (MIMO) broadcast channel (BC) is considered. The dirty-paper coding (DPC) rate region is shown to coincide with the capacity region. To that end, a new notion of an enhanced broadcast channel is introduced and is used jointly with the entropy power inequality, to show that a superposition of Gaussian codes is optimal for the degraded vector broadcast channel and that DPC is optimal for the nondegraded case. Furthermore, the capacity region is characterized under a wide range of input constraints, accounting, as special cases, for the total power and the per-antenna power constraints     

On the Discrete Memoryless Partially Cooperative Relay Broadcast Channel and the Broadcast Channel With Cooperating Decoders

We derive two inner bounds on the rate region of the partially cooperative relay broadcast channel. The first inner bound is based on the Cover and El Gamal generalized strategy for the original relay channel, while the second inner bound is based on the strategy proposed recently by Chong, Motani, and Garg, for the relay channel, which combines backward decoding and simultaneous decoding. Both rate regions subsume the inner bound reported by Liang and Kramer which is based just on the decode-and-forward strategy for the common message. A broadcast channel with cooperating decoders is a broadcast channel wherein the receivers, once observing their outputs, may exchange messages via a pair of channels with specified capacities. An achievable rate region for this model is derived based on the first coding strategy for the partially cooperative relay broadcast channel. This region subsumes the Dabora and Servetto rate region. A converse result is proved for this model based on the converse result of Nair and El Gamal for the broadcast channel and Willems's converse proof for the multiple-access channel with cooperating encoders.     

Achievable Rates Over Time-Varying Rayleigh Fading Channels

This paper investigates achievable rates for a wireless communication system when neither the transmitter nor the receiver has a priori knowledge of the channel state information (CSI). The dynamics of the flat fading channel are characterized by a known Doppler spectrum. Quantitative results are provided for independent and identically distributed (i.i.d.) Gaussian signals and long data blocks. Expressions for the achievable rates include a lower bound on mutual information, and the achievable rates of pilot-aided systems with optimized resource allocation. A simple, low-duty-cycle signaling scheme is proposed to improve the information rates in the low signal-to-noise ratio (SNR) regime, and the optimal duty cycle is expressed as a function of the fading rate and SNR. It is demonstrated that the resource allocation and duty cycle developed for Gaussian signals can also be applied to systems using other signaling formats.     

The Capacity Region of the Degraded Multiple-Input Multiple-Output Compound Broadcast Channel

The capacity region of a compound multiple-antenna broadcast channel is characterized when the users exhibit a certain degradedness order. The channel under consideration has two users, each user has a finite set of possible realizations. The transmitter transmits two messages, one for each user, in such a manner that regardless of the actual realizations, both users will be able to decode their messages correctly. An alternative view of this channel is that of a broadcast channel with two common messages, each common message is intended to a different set of users. The degradedness order between the two sets of realizations/users is defined through an additional, fictitious, user whose channel is degraded with respect to all realizations/users from one set while all realizations/users from the other set are degraded with respect to him.     

On the Gaussian MIMO Relay Channel With Full Channel State Information

This paper addresses the problem of source and relay transmit covariance optimization on the Gaussian MIMO relay channel with full channel state information (CSI), i.e., assuming perfect knowledge of all channels. For full-duplex relaying, we show that the cut-set bound on capacity can be computed as the solution of a convex problem, thus providing a tighter bound than previously published. For time division duplex (TDD) relaying, both upper and lower bounds on capacity are derived, and the transmit covariance matrices are optimized for decode-and-forward (DF) strategies with either partial or full decoding at the relay. A generic procedure is introduced to formulate these problems into a standard convex form, and to solve them efficiently. Suboptimum precoders are also proposed which have a specific matrix structure that either leads to a closed-form expression or at least reduces the dimension of the optimization problem. Practical aspects related to transmit power constraints and CSI availability are then discussed. Finally, simulations in a cellular downlink scenario show that the partial DF strategy can achieve a rate very close to capacity for realistic values of the source to relay SNR, and that the rate loss due to suboptimum precoder structures remains small for typical antenna configurations.      

Capacity Region of a Class of Gaussian Cognitive Degraded Broadcast Channel

This paper studies the cognitive broadcast channel in which the primary user com- municates to the primary receiver, while the secondary user has noncausal knowledge of the primary radio＇s codeword and expects to communicate to two secondary receivers. Comparing with the existing cognitive radio channel which considers only one secondary receiver, cognitive broadcast channel studies the case that there are multiple secondary receivers. To this end, we investigate the fundamental limits of the performance of the Gaussian cognitive broadcast channel from the information theoretic perspective. Specifically, we derive the capacity region of the Gaussian cognitive degraded broadcast channel with weak interference.