Sum Capacity of Multiuser MIMO Broadcast Channels with Block Diagonalization

The sum capacity of a Gaussian broadcast MIMO channel can be achieved with dirty paper coding (DPC). However, algorithms that approach the DPC sum capacity do not appear viable in the forseeable future, which motivates lower complexity interference suppression techniques. Block diagonalization (BD) is a linear preceding technique for downlink multiuser MIMO systems. With perfect channel knowledge at the transmitter, BD can eliminate other users' interference at each receiver. In this paper, we study the sum capacity of BD with and without receive antenna selection. We analytically compare BD without receive antenna selection to DPC for a set of given channels. It is shown that (1) if the user channels are orthogonal to each other, then BD achieves the same sum capacity as DPC; (2) if the user channels lie in the same subspace, then the gain of DPC over BD can be upper bounded by the minimum of the number of transmit and receive antennas. These observations also hold for BD with receive antenna selection. Further, we study the ergodic sum capacity of BD with and without receive antenna selection in a Rayleigh fading channel. Simulations show that BD can achieve a significant part of the total throughput of DPC. An upper bound on the ergodic sum capacity gain of DPC over BD is proposed for easy estimation of the gap between the sum capacity of DPC and BD without receive antenna selection.     

QoS‐Guaranteed Multiuser Scheduling in MIMO Broadcast Channels

This paper proposes a new multiuser scheduling algorithm that can simultaneously support a variety of different quality‐of‐service (QoS) user groups while satisfying fairness among users in the same QoS group in MIMO broadcast channels. Toward this goal, the proposed algorithm consists of two parts: a QoS‐aware fair (QF) scheduling within a QoS group and an antenna trade‐off scheme between different QoS groups. The proposed QF scheduling algorithm finds a user set from a certain QoS group which can satisfy the fairness among users in terms of throughput or delay. The antenna trade‐off scheme can minimize the QoS violations of a higher priority user group by trading off the number of transmit antennas allocated to different QoS groups. Numerical results demonstrate that the proposed QF scheduling method satisfies different types of fairness among users and can adjust the degree of fairness among them. The antenna trade‐off scheme combined with QF scheduling can improve the probability of QoS‐guaranteed transmission when supporting different QoS groups.     

Simulation Models for Investigation of Multiuser Scheduling in MIMO Broadcast Channels

Spatial correlation is a result of insufficient antenna spacing among multiple antenna elements, while temporal correlation is caused by Doppler spread. This paper compares the effect of spatial and temporal correlation in order to investigate the performance of multiuser scheduling algorithms in multiple‐input multiple‐output (MIMO) broadcast channels. This comparison includes the effect on the ergodic capacity, on fairness among users, and on the sum‐rate capacity of a multiuser scheduling algorithm utilizing statistical channel state information in spatio‐temporally correlated MIMO broadcast channels. Numerical results demonstrate that temporal correlation is more meaningful than spatial correlation in view of the multiuser scheduling algorithm in MIMO broadcast channels. Indeed, the multiuser scheduling algorithm can reduce the effect of the Doppler spread if it exploits the information of temporal correlation appropriately. However, the effect of spatial correlation can be minimized if the antenna spacing is sufficient in rich scattering MIMO channels regardless of the multiuser scheduling algorithm used.     

Achieving Long-Term Fairness and Optimum Multiuser Diversity Gain in Time-Varying Broadcast Channels

In this paper, a downlink system in which a single-antenna base station communicates with k single antenna users over a time-correlated fading channel is considered. It is assumed that each receiver knows its own channel state, while the rate of the channel variation for all users and the corresponding initial fading gains are known to the base station. The average (per channel use) throughput of the system is studied by applying various adaptive signaling schemes. Assuming a large number of users in the system, it is shown that using a scheduling scheme in which the base station transmits to the user with the maximum initial fading gain, while using a fixed codeword length for all users, achieves the order of the maximum throughput. Moreover, an alternative scheduling scheme is proposed (by accounting for users' delays) and shown to achieve the optimum long-term fairness, while preserving the order of the maximum throughput.     

大厂电视台两通道视频服务器播出系统介绍

介绍在专业电视领域中广泛使用的多频道硬盘播出系统,并以大厂电视台采用北京华视恒通数码技术有限公司自行研发的两通道视频播出服务器系统为例,说明视频播出服务器系统在当今电视台频道播出中的重要应用。     

基于正交空分复用的多用户调度策略

为了消除多用户MIMO下行系统的多用户间干扰以及改进系统的误码率性能,研究了块对角化预编码与几何均值分解的联合方案(BD-GMD).针对BD-GMD系统的资源分配和用户调度,对比了等功率分配和注水算法对系统的影响,并基于系统容量最大化,提出了一种根据用户信道的子空间特性的低复杂度的用户调度算法.此外,对比分析了穷举搜索算法和传统的贪婪算法.数值仿真结果表明,文中所提出的基于正交投影的多用户调度算法充在保证系统容量的同时降低了算法复杂度.     

空分复用多输入多输出系统中的分组多用户分集

该文针对基于空分复用的多用户多输入多输出系统下行链路,研究了空间衰落相关和信道估计误差对系统容量的影响,提出了两种新的分组多用户分集方案。所提出的方案通过合理选择共道用户,能有效提升系统容量,同时兼顾公平性。分析和仿真结果表明,所提出的方案对衰落相关性以及信道估计误差具有较好的稳健性;其中,第2种方案与第1种相比较,容量性能更优,但具有较高的计算复杂度。     

非高斯信道下的非线性空时多用户检测器

为了减轻冲激噪声和多径干扰的影响,本文提出了一种基于DS-CDMA同步信道的空时非线性接收机。该接收机联合了线性解相关器和带有基于相关匹配M yriad非线性滤波器的非线性前端的天线阵列。将这种M yriad滤波器合并在一起以消除冲激噪声和阻止其进入系统。所提出的检测器采用了一种结构来估计冲激噪声系数和修正非线性滤波器系数。仿真结果表明,这种空时接收机在空时领域的非线性信号处理方面具有很好的性能。     

数字视频广播系统概述

今天 ,尽管我们在家里收看的仍然是模拟电视节目 ,但是当你通过卫星电视网、有线电视网或开路电视网观看电视节目时 ,你已经位于电视数字传输的最后一个环节 ,它正在经历着一场数字化革命 ,以达到电视节目的全数字化传输。在电视数字化的进程中 ,国际组织ＤＶＢ(ＤｉｇｉｔａｌＶｉｄｅｏＢｒｏａｄｃａｓｔｉｎｇ)提出了全套的解决方案 :数字卫星电视 (ＤＶＢ -Ｓ)、数字有线电视 (ＤＶＢ -Ｃ)、数字开路电视 (ＤＶＢ -Ｔ) ,这意味着电视节目数字化的时代已经到来 !在欧洲 ,从 1991年开始 ,电视台、家电产品生产厂家和标准制订者坐到一起 ,…     

Broadcast Channels With Cooperating Decoders

We consider the problem of communicating over the general discrete memoryless broadcast channel (DMBC) with partially cooperating receivers. In our setup, receivers are able to exchange messages over noiseless conference links of finite capacities, prior to decoding the messages sent from the transmitter. In this paper, we formulate the general problem of broadcast with cooperation. We first find the capacity region for the case where the BC is physically degraded. Then, we give achievability results for the general broadcast channel, for both the two independent messages case and the single common message case     

基于广播地面的分层复用系统研究

介绍了基于地面广播的层分复用(Layered Division Multiplexing,LDM)技术的研究与进展.采用层分复用技术可以在不同的接收环境下根据应用需求来选择不同的功率和不同的编码调制方式,能极大地提高频谱的利用率和使用灵活性,且可应用于多个不同的系统中.正是由于该技术的以上特点,层分复用技术被ATSC3.0的专家组选为下一代ATSC3.0标准物理层的核心技术之一,同时被2015年美国广播电视协会展选为最佳技术.首先介绍层分复用技术的初始思想——“云传输”的基本概念,进一步从层分复用系统框架方面,着重介绍层分复用技术在噪声与层间干扰处理、帧结构设计、发射识别和信号消除等方面的设计方法,最后对层分复用技术为地面广播系统带来的性能提升进行了总结.     

移动多媒体广播视频业务复用格式的研究

介绍了H.264视频编码和中国移动多媒体广播(CMMB)信道帧格式,重点讨论了H.264视频流的实时传送协议(RTP)封装格式和CMMB中视频业务的复用封装.     

空间相关信道下的交替多用户调度算法

针对多用户多输入多输出（MIMO）系统,研究了空间相关信道下的多用户调度问题。通过推导用户信道向量夹角的统计特征,分析了多用户调度算法对所调度用户间正交性的影响。分析结果表明在空间相关信道下现有基于串行搜索的调度方法在统计意义上降低了被调度用户之间的正交性,从而导致基于串行搜索的调度算法与最优的穷举搜索之间存在较大的性能差距。为了提高相关信道下多用户MIMO系统的性能,提出了一种基于交替搜索的多用户调度算法及其低复杂度实现方法。仿真结果表明,所提出的用户调度算法能够有效地弥补基于串行搜索的调度方法的性能损失,在空间独立信道和空间相关信道下以较低的计算复杂度获得接近穷举搜索的最优性能。      

Code Design for MIMO Broadcast Channels

Recent information-theoretic results show the optimality of dirty-paper coding (DPC) in achieving the full capacity region of the Gaussian multiple-input multiple-output (MIMO) broadcast channel (BC). This paper presents a DPC based code design for BCs. We consider the case in which there is an individual rate/signal-to-interference-plus-noise ratio (SINR) constraint for each user. For a fixed transmitter power, we choose the linear transmit precoding matrix such that the SINRs at users are uniformly maximized, thus ensuring the best bit-error rate performance. We start with Cover's simplest two-user Gaussian BC and present a coding scheme that operates 1.44 dB from the boundary of the capacity region at the rate of one bit per real sample (b/s) for each user. We then extend the coding strategy to a two-user MIMO Gaussian BC with two transmit antennas at the base-station and develop the first limit-approaching code design using nested turbo codes for DPC. At the rate of 1 b/s for each user, our design operates 1.48 dB from the capacity region boundary. We also consider the performance of our scheme over a slow fading BC. For two transmit antennas, simulation results indicate a performance loss of only 1.4 dB, 1.64 dB and 1.99 dB from the theoretical limit in terms of the total transmission power for the two, three and four user case, respectively.     

MIMO Broadcast Channels With Finite-Rate Feedback

Multiple transmit antennas in a downlink channel can provide tremendous capacity (i.e., multiplexing) gains, even when receivers have only single antennas. However, receiver and transmitter channel state information is generally required. In this correspondence, a system where each receiver has perfect channel knowledge, but the transmitter only receives quantized information regarding the channel instantiation is analyzed. The well-known zero-forcing transmission technique is considered, and simple expressions for the throughput degradation due to finite-rate feedback are derived. A key finding is that the feedback rate per mobile must be increased linearly with the signal-to-noise ratio (SNR) (in decibels) in order to achieve the full multiplexing gain. This is in sharp contrast to point-to-point multiple-input multiple-output (MIMO) systems, in which it is not necessary to increase the feedback rate as a function of the SNR     

Multidestination Protocols for Satellite Broadcast Channels

Two retransmission procedures, the go-back-N(GBN) scheme and the selective repeat (SR) scheme, have been analyzed for data transfer from one transmitter to many receivers. We consider transfer of error-controlled bulk data over a satellite broadcast channel. Two retransmission strategies, the dynamic retransmission group reduction (DRGR) technique and the fixed retransmission group (FRG) technique, are proposed. We study the GBN and SR schemes for both strategies. Analytic expressions are derived for the throughput performance of the GBN scheme and of the SR scheme with infinite resources, while discrete event simulation is used to estimate the throughput of the selective repeat scheme with finite resources. Only the SR scheme using the DRGR technique provides acceptable performance for high-speed bulk data transfer. For the DRGR technique, the throughput falls logarithmically with an increase in the number of receivers. In contrast, the throughput for the FRG technique falls exponentially with an increase in the number of receivers.     

Rate Regions for Relay Broadcast Channels

A partially cooperative relay broadcast channel (RBC) is a three-node network with one source node and two destination nodes (destinations 1 and 2) where destination 1 can act as a relay to assist destination 2. Inner and outer bounds on the capacity region of the discrete memoryless partially cooperative RBC are obtained. When the relay function is disabled, the inner bound reduces to an inner bound on the capacity region of broadcast channels that includes an inner bound of Marton, and GePfand and Pinsker. The outer bound reduces to a new outer bound on the capacity region of broadcast channels that generalizes an outer bound of Marton to include a common message, and that generalizes an outer bound of GePfand and Pinsker to apply to general discrete memoryless broadcast channels. The proof for the outer bound simplifies the proof of GePfand and Pinsker that was based on a recursive approach. Four classes of RBCs are studied in detail. For the partially cooperative RBC with degraded message sets, inner and outer bounds are obtained. For the semideterministic partially cooperative RBC and the orthogonal partially cooperative RBC, the capacity regions are established. For the parallel partially cooperative RBC with unmatched degraded subchannels, the capacity region is established for the case of degraded message sets. The capacity is also established when the source node has only a private message for destination 2, i.e., the channel reduces to a parallel relay channel with unmatched degraded subchannels.     

Fundamental Limits in MIMO Broadcast Channels

This paper studies the fundamental limits of MIMO broadcast channels from a high level, determining the sum-rate capacity of the system as a function of system parameters, such as the number of transmit antennas, the number of users, the number of receive antennas, and the total transmit power. The crucial role of channel state information at the transmitter is emphasized, as well as the emergence of opportunistic transmission schemes. The effects of channel estimation errors, training, and spatial correlation are studied, as well as issues related to fairness, delay and differentiated rate scheduling.     

Diversity–Multiplexing Tradeoff in ISI Channels

The optimal diversity–multiplexing tradeoff curve for the intersymbol interference (ISI) channel is computed and various equalizers are analyzed using this performance metric. Maximum-likelihood signal decoding (MLSD) and decision feedback equalization (DFE) equalizers achieve the optimal tradeoff without coding, but zero forcing (ZF) and minimum mean-square-error (MMSE) equalizers do not. However if each transmission block is ended with a period of silence lasting the coherence time of the channel, both ZF and MMSE equalizers become diversity-multiplexing optimal. This suggests that the bulk of the performance gain obtained by replacing linear decoders with computationally intensive ones such as orthogonal frequency-division multiplexing (OFDM) or Viterbi, can be realized in much simpler fashion—with a small modification to the transmit scheme.