SDMA系统FD方案阻塞率的仿真

现代无线移动通信系统广泛考虑采用空分多址（SDMA）多址接入技术来提高系统容量。比如在频分复用（FDMA）时分复用（TDMA）,码分复用（CDMA）。分析研究SDMA系统中的FD信道分配机制,给出了理论推导,并在此基础上进行了仿真。仿真结果表明：采用该机制以后,用户可以在同一时间共享同一信道。     

CDMA／SDMA系统性能分析

空分多址接入技术（SDMA）可以通过信号不同的空间传播路径来区分用户，从而提高了蜂窝移动通信系统容量．而此技术又可以和其他多址方式相互兼容，比如频分多址，时分多址，码分多址．CDMA／SDMA系统就是码分多址和空分多址两种接入技术相结合的系统．该系统可通过时空编码实现的．文中分析此种系统的性能，并与多用户环境下的CDMA系统进行了比较．     

TD-SCDMA系统所采用的技术(二)

３综合采用各种多址方式TD-SCDMA系统综合使用CDMA、TDMA、FDMA和SDMA四种多址方式，充分发挥码分、时分、频分和空分制式技术优势，最大限度地提高系统容量。TD-SCDMA多址技术原理如图1所示，其三维空间分别为CDMA码道、频率和时间。图1是典型的TD-SCDMA信道结构，三个载波带宽为1.6MHz，用TDMA方式将每个载波分为7个业务时隙（5个下行时隙DL和2个上行时隙UL）和1个DL/UL隔离时隙，采用CDMA技术将每个时隙扩频，最多可得16码道（即扩频系数为16），每个码道可传输一个用户信息。TD-SCDMA的基本信元（RU）由时…     

一种适用于教学实验的SDMA系统设计与实现

本文简要介绍了空分多址(SDMA)的基本原理,设计并实现了一种适用于教学实验的∞MA软件仿真系统.本软件系统可工作在两种模式下,为多个移动用户提供不同的互不干扰的空分信道,以第四维的多址方式接人基站.实验者可设置通信过程中的各种参数并观察其对整个系统性能的影响.该实验系统有助于实验者更好地理解和掌握SDMA技术,同时具有良好的可扩展性,并可与其他多址仿真系统有效地结合.     

移动通信中的空分多址技术

在信息时代，人们对通信业务的需求不断增加，这对通信技术提出了更高的要求，空分多址（SDMA）技术由于其在提高系统容量和频谱利用率方面的独特优势而引起了人们的广泛关注。本文从基本概念、信道模型、系统实现和对通信系统的性能改善等几个方面对空分多址技术进行了较为全面的论述。     

无线多址信道中的协作模型研究

在无线多址信道环境下,为了充分利用协作分集技术提高系统的传输速率和通信质量,引入了多址接入中继信道（MARC）模型。通过加入一个专门的中继节点,MARC模型中的发送节点类似操作在普通的多址信道下,从而使得现有的系统可平滑过渡到协作系统,实用性强。把MARC模型应用在直序扩频CDMA系统中,在Rayleigh信道下对其误码率进行仿真,结果表明,采用MARC模型的协作网络能获得显著的性能增益。     

OFDM/OQAM系统自适应波形设计及多址接入系统

基于传统正交频分复用技术的OFDMA多址接入技术仍然存在循环前缀-正交频分复用(CP-OFDM)技术的固有缺陷,即循环前缀的添加降低了系统频谱利用率,多普勒频移对传统OFDMA系统产生较强的子载波间干扰,且对相邻频带的其他无线传输系统引入较强的相邻信道干扰。该文主要讨论基于扩展高斯函数的正交频分复用系统自适应波形设计,通过信道散射函数选择合适的扩展因子参数,获取更高的频谱利用率和抑制符号间干扰和子载波间干扰。最后该文将自适应波形设计的思想扩展至基于扩展高斯函数的多址接入系统,使每个用户能够根据信道条件选择合适的成形滤波器函数,进而使多址接入系统达到全局最优化。仿真结果验证了该文方法的有效性。     

FTH-PPM多址接入技术在60 GHz脉冲无线通信系统中的性能

针对60 GHz脉冲无线通信系统中存在的多址接入干扰问题,研究了基于FTH-PPM多址接入方案的性能。在IEEE 802.15.3c信道模型下,分析了系统误码率性能与跳频码数量、信噪比、用户数之间的关系,研究了FTH-PPM多址调制系统特性,并与TH-PPM、TH-PAM方案进行比较。仿真结果表明,系统在多址条件下,可以通过改变信噪比、频率跳数、用户数来满足所需的误码率,同时在一定范围内,FTH-PPM的误码率性能优于TH-PAM和TH-PPM的误码率性能,并且可以根据脉冲占空比的值选择合适的多址调制方式,为60 GHz脉冲无线通信的应用提供技术参考。     

KDDI面向4G的无线接入技术利用SDMA增大通信容量

日本KDDI在9月20目开幕的“电子信息通信学会学会大会”上，发表了第4代移动通信系统（4G）无线接入技术的最新研究成果。新成果旨在利用空分多址（SDMA）技术增大通信容量。KDDI与多家厂商联手试制了基于SDMA技术的天线和通信装置，     

OFDMA系统中多波束机会波束成形研究

机会波束成形（Opportunistic Beamforming,OBF）技术通过加大、加快信道的波动来提高多用户分集增益,将之使用在正交频分复用多址接入（OFDMA）系统中,可以使得系统的吞吐量最大化。在OFDMA系统中,通过对所有子载波进行分簇,可以实现在牺牲系统性能很少的情况下,大大降低系统反馈量。研究了对分簇OFDMA系统使用OBF技术来提高系统吞吐量,并进一步研究了在训练阶段使用多个随机加权向量进行多波束成形,然后从中选择最好的一个来实现数据阶段的波束成形。仿真证明,采用多波束机会波束成形技术能提高OFDMA系统吞吐量。     

The impact of space division multiplexing on resource allocation: a unified treatment of TDMA, OFDMA and CDMA

Space division multiple access (SDMA) with an antenna array at the transmitter is a promising means for increasing system capacity and supporting rate-demanding services. However, the presence of an antenna array at the physical layer raises significant issues at higher layers. In this paper, we attempt to capture the impact of SDMA on access layer channel allocation, reflected on channel reuse. This impact obtains different twists in TDMA, CDMA and OFDMA due to the different nature of co-channel and cross-channel interference and the different interaction of user spatial channel characteristics with system channels, namely time slots, codes and subcarriers. We consider these access schemes in a generalized unified framework and propose heuristic algorithms for channel allocation, downlink beamforming and transmit power control so as to increase total provisioned system rate and provide QoS to users in the form of minimum rate guarantees. We study the class of greedy algorithms that rely on criteria such as induced or received interference and signal-to-interference ratio (SIR), and a class of SIR balancing algorithms. Results show superior performance for SIR balancing resource allocation and expose the performance benefits of cross-layer design.     

Information Capacity of the Space Division Multiple Access Mobile Communication System

An expression for the Shannon capacity lower bound of the space division multiple access (SDMA) mobile communication channel with interference is shown. The bound is tightly approaching the Shannon capacity of the orthogonal SDMA system over Gaussian channel with no interference. The information capacity of the SDMA system with adaptive MMSE receivers is presented as well. The SDMA system with MMSE receivers achieves at least 50% of the orthogonal SDMA system capacity for the input signal to noise ratio of practical interest in cellular mobile communications (10–30dB).     

Smart-antenna operation for indoor wireless local-area networks using OFDM

This paper reports link-level Monte Carlo simulations for a system that is compatible with the physical layer of the 5-GHz IEEE 802.11a wireless-local-area network and utilizes an adaptive antenna array at the access point for single-user smart-antenna operation, as well as for space-division multiple access (SDMA). For the spatial indoor radio propagation channel, complex impulse-response recordings are used. These are obtained in wideband channel-sounder measurements in three different buildings at 5.3 GHz. Thus, no unrealistic assumptions about channel conditions are involved. The paper studies how the packet-error-rate performance for the downlink (DL) is affected by time evolution of the radio channel that takes place after the uplink operation in which channel estimation is performed, and before DL operation in which the estimated channel information is utilized. Based on simulations two-user SDMA is possible with four-antenna elements under indoor propagation conditions and with six antennas three users can simultaneously be served. Delay spreads, coherence bandwidths, and correlation properties (in space, frequency, and polarization) of the radio channels obtained in the measurements are also discussed. The results suggest that indoor time-division-duplex systems with access-point-controlled scheduling are desirable communication systems which can benefit from SDMA.     

MIMO-OFDM信道估计仿真实现

正交频分复用（OFDM）可以有效地将频率选择性衰落信道转化成多个并行平坦衰落信道,从而大大提高传输效率。多输入多输出正交频分复用（MIMO-OFDM）技术可以大幅度地提高无线通信系统的信道容量与传输速率,其信道估计精度对系统性能有着直接的影响。研究了基于导频插入的SISO-OFDM和MIMO-OFDM最小二乘法估计（LS）信道估计方法。采用广义平稳非相关散射下的多径时变瑞利信道模型,对各个算法进行了仿真试验,得出不同算法下信道估计的误比特曲线,比较了各个算法的性能。仿真结果表明：MIMO-OFDMLS算法在误码率性能上优于SISO-OFDM。     

Forward-link capacity in smart antenna base stations with dynamicslot allocation

We consider a base station, which communicates to a set of portable stations using a smart antenna operating in multibeam, packet-switched, space division multiple access (SDMA) mode. We assume that the system operates using time division duplexing (TDD) and focus on the problem of access to the stations by the base station in the forward-link direction. A polling protocol is used which permits efficient access in this type of system. The operation of the protocol is unique in that it permits dynamic slot allocation and accommodates variations in channel time coherence. In the protocol, dynamic slot assignment is integrated into the forward-link beam scheduling. This allows us to explore the value of dynamic station slot assignment when constructing the SDMA/TDMA frames. The results show the improvements in capacity, which are possible in such systems and give insight into the degradation in protocol performance that occurs when channel coherence times decrease. We find that very large improvements in capacity are possible using dynamic slot allocation, especially under harsh channel conditions. We also investigate various base station queueing issues in this type of system. It is shown that care must be taken in how buffering is performed so that blocking effects do not unnecessarily degrade the forward-link capacity     

The performance evaluation of spatial–temporal algorithms in W‐CDMA systems

Differing from FDMA, TDMA, and CDMA, space division multiple access (SDMA) uses space resources to improve communication system performance. Utilizing the smart antenna system is an approach to realize the SDMA technique. Smart antenna systems using the beamforming technique can reduce the co‐channel interference and multipath fading to increase the channel capacity and communication quality. In this study the smart antenna system and rake receiver are integrated. The performance of spatial–temporal structure applied to the W‐CDMA system is evaluated. From the cumulative distribution function simulation results, W‐CDMA system with spatial–temporal algorithm can exactly provide SINR gain to improve the system performance and capacity. Copyright © 2005 John Wiley & Sons, Ltd.     

Dynamic slot allocation (DSA) in indoor SDMA/TDMA using a smartantenna basestation

We introduce and study the use of dynamic slot allocation (DSA) in packet-switched space-division-multiple-access (SDMA) systems. In conventional SDMA, a smart antenna is used at the basestation to simultaneously communicate with multiple stations on the same frequency channel. When dynamic slot allocation is added, the basestation uses uplink channel measurements to intelligently construct future SDMA/TDMA frames. It is shown that under a simple minimum signal-to-interference-plus-noise ratio (SINR) constraint, the problem of performing optimal dynamic slot allocation is NP-complete. Heuristic slot allocation algorithms are introduced which are capable of greatly increasing SDMA/TDMA frame capacity compared with a random allocation of stations. The paper uses both theoretical results and measured data from an experimental testbed to characterize the performance of dynamic slot allocation. The experimental system operates at a carrier frequency of 1.86 GHz and uses an eight-element circular antenna array. It is demonstrated that significant increases in system capacity are possible using DSA in the indoor situations that were tested. Dynamic slot allocation requires the channel to be essentially constant from the time that channel measurements are made until the SDMA/TDMA frame is transmitted. We also present channel measurements which show the effects of channel time coherence in the presence of indoor pedestrian movement. This and other results we have taken suggest that dynamic slot allocation is possible at the frequency considered, provided turnaround times are in the low-to-mid tens of milliseconds