一种新的OVSF码动态有序分配算法

该文通过研究W-CDMA系统下行链路OVSF码的特性,针对传统的随机动态分配算法存 在码阻塞的问题,提出了一种动态有序分配算法,采用先分配低速用户,相同层从低序号码字向高序号码字 顺序分配的原则。并对该算法的流程和系统实现给予了详细的描述。最后通过系统性能的理论分析和数值仿 真,证明该算法大大降低了码字阻塞概率,减少了系统开销,对于工程应用具有重要价值。     

时间相干信道下波束赋形系统的有限反馈方法

该文提出一种新的基于树形码书的有限反馈方法,由于相邻帧的时间相干性,信道向量的量化码字可建模为一阶有限状态马尔可夫链,当前帧信道向量被量化到前一帧最大转移概率码字的子码字上,该子码字的索引以1 bit反馈给发射端。链路仿真结果表明本文所提方法相比普通反馈方法可明显改善误码率性能,某些条件下还可降低反馈速率。     

MIMO系统中的交叉优化调度算法

多入多出（MIMO）系统中在多用户环境下可以在链路级利用空间复用或者在系统级利用多用户调度来提高系统容量。但是仅仅是分别优化MIMO系统链路级性能或是仅仅单纯在系统级进行调度是不够的,将两者联合起来进行优化可以获得更大的系统容量。为此,该文提出了一种新的交叉优化调度算法（Cross Optimization Scheduling Algorithm,COSA）,将系统级的调度策略和链路级的物理层优化相结合,并且采用注水算法动态调整各天线的功率分配。仿真结果表明COSA算法不但在系统级为每个用户提供了公平的接入信道机会,而且在链路级中充分利用MIMO系统的空间复用特点以及动态的功率分配,提高了系统的容量。     

MIMO系统中的交叉优化调度算法

多入多出(MIMO)系统中在多用户环境下可以在链路级利用空间复用或者在系统级利用多用户调度来提高系统容量。但是仅仅是分别优化MIMO系统链路级性能或是仅仅单纯在系统级进行调度是不够的,将两者联合起来进行优化可以获得更大的系统容量。为此,该文提出了一种新的交叉优化调度算法(Cross Optimization Scheduling Algorithm, COSA),将系统级的调度策略和链路级的物理层优化相结合,并且采用注水算法动态调整各天线的功率分配。仿真结果表明COSA算法不但在系统级为每个用户提供了公平的接入信道机会,而且在链路级中充分利用MIMO系统的空间复用特点以及动态的功率分配,提高了系统的容量。     

多用户MIMO-OFDM系统中的一种新的用户调度算法

本文针对多用户环境下的多天线正交频分复用下行系统,提出了一种新的基于迫零波束成型的用户调度算法。迫零波束成型是在发送端消除用户间的干扰生成多个独立的空间子信道,来实现空间复用。由于在多天线正交频分复用下行系统中最优的用户选择算法需要遍历所有可能的用户集合,算法复杂度非常大,本文提出了一种简化算法。所提算法在保证每个用户的速率要求的情况下,通过贪婪算法来选择每个子载波上的用户集合,以最小化系统的发送功率。仿真结果表明在满足用户的速率要求下能达到很好的系统性能。     

TDD大规模MIMO系统中两种新的下行预编码方案

针对时分双工大规模MIMO系统,该文提出两种新的下行链路预编码方案,即新最大比合并(NMRC)和新迫零(NZF)方案,通过理论分析得到两种新预编码方案下目标用户和非目标用户的下行链路信干噪比和频谱效率的表达式,并与传统的迫零(ZF)和最大比合并(MRC)预编码的下行链路信干噪比、频谱效率和误码率性能进行比较.仿真结果表明,所提出的NMRC和NZF预编码与传统的MRC和ZF预编码相比,在不增加运算复杂度的前提下可以获得更好的性能,而且新的预编码方案在提高目标用户性能的同时,对其他非目标用户的性能也有一定的改善.     

TDD大规模MIMO系统中两种新的下行预编码方案

针对时分双工大规模MIMO系统,该文提出两种新的下行链路预编码方案,即新最大比合并(NMRC)和新迫零(NZF)方案,通过理论分析得到两种新预编码方案下目标用户和非目标用户的下行链路信干噪比和频谱效率的表达式,并与传统的迫零(ZF)和最大比合并(MRC)预编码的下行链路信干噪比、频谱效率和误码率性能进行比较。仿真结果表明,所提出的NMRC和NZF预编码与传统的MRC和ZF预编码相比,在不增加运算复杂度的前提下可以获得更好的性能,而且新的预编码方案在提高目标用户性能的同时,对其他非目标用户的性能也有一定的改善。     

基于自适应空分复用的分组多用户分集方案

在采用空分复用技术的多用户多输入多输出下行链路中,有限的空域信道资源限制了系统容量.针对这一问题,提出了一种新的基于自适应空分复用的分组多用户分集方案.针对空分复用算法的特点,该方案首先以信道响应矩阵主右奇异向量的互相关大小为度量,将全部用户分为互相关最小的若干组;然后采用一种新的自适应空分复用算法,求出每一组用户传输时所能获得的系统容量,并将信道分配给容量最大的那一组用户.仿真结果表明,所提出的方案不仅能保证信道资源调度的公平性,而且通过引入多用户分集和自适应空域信道分配,显著地提升了系统容量.     

IEEE802.16e系统上行链路初始测距算法研究

该文提出了一种适用于IEEE802.16e的OFDMA系统上行链路的初始测距频域改进算法。频域算法利用测距信号具有连续相位的特点,在频域将接收信号与备选码字共轭相关,按照接入用户信号的强弱依次检测出不同用户发送的码字和定时偏差,从而完成初始测距过程。改进频域算法在频域检测方法的基础上结合了串行干扰抵消的思想,提高了多用户同时接入系统时的正确检测概率,降低了虚警概率。通过仿真比较了改进算法和时域、频域算法的性能。结果表明,所提出的算法在计算复杂度和性能上兼有一定的优势。     

多用户多载波无线携能通信系统的上下行联合资源分配

无线携能通信(SWIPT)技术是解决无线网络能量受限问题的有效方法,该文研究一个由基站(BS)和多用户组成的多载波SWIPT系统,其上行和下行链路均采用正交频分复用(OFDM)技术。在下行链路中,基站向用户同时进行信息与能量传输;在上行链路中,用户利用从基站接收的能量向基站回传信息。该文以最大化上下行加权和速率为目标,联合优化上行和下行的子载波分配和功率分配,提出基于拉格朗日对偶法和椭球法的最优联合资源分配算法。计算机仿真结果证实了该算法的有效性。     

A New Family of Wavelength-Time Optical CDMA Codes Utilizing Programmable Arrayed Waveguide Gratings

A two-dimensional, so-called wavelength-hopping time-spreading, optical code-division multiple-access coding scheme has recently been studied for supporting more subscribers and simultaneous users than conventional one-dimensional techniques. To further improve the numbers of subscribers and simultaneous users without sacrificing performance, a new code, which utilizes the unipolar version of bipolar codes (for wavelength hopping) and optical unipolar codes (for time spreading), is studied and analyzed in this paper. A programmable and integratable coding hardware based on arrayed waveguide gratings is designed for this coding scheme.     

A multicarrier CDMA architecture based on orthogonal complementarycodes for new generations of wideband wireless communications

This article is a review of our ongoing research effort to construct a new multicarrier CDMA architecture based on orthogonal complete complementary codes, characterized by its innovative spreading modulation scheme, uplink and downlink signaling design, and digital receiver implementation for multipath signal detection. There are several advantages of the proposed CDMA architecture compared to conventional CDMA systems pertinent to current 2G and 3G standards. First of all, it can achieve a spreading efficiency (SE) very close to one (the SE is defined as the amount of information bit(s) conveyed by each chip); whereas SEs of conventional CDMA systems equal 1/N, where N denotes the length of spreading codes. Second, it offers MAI-free operation in both upand downlink transmissions in an MAI-AWGN channel, which can significantly reduce the co-channel interference responsible for capacity decline of a CDMA system. Third, the proposed CDMA architecture is able to offer a high bandwidth efficiency due to the use of its unique spreading modulation scheme and orthogonal carriers. Lastly, the proposed CDMA architecture is particularly suited to multirate signal transmission due to the use of an offset stacked spreading modulation scheme, which simplifies the rate-matching algorithm relevant to multimedia services and facilitates asymmetric traffic in up- and downlink transmissions for IP-based applications. Based on the above characteristics and the obtained results, it is concluded that the proposed CDMA architecture has a great potential for applications in future wideband mobile communications beyond 3G, which is expected to offer a very high data rate in hostile mobile channels     

Adaptive power and rate allocation for service curve assurance in DS-CDMA network

This paper describes schemes for forward and reverse links in a direct sequence code-division multiple-access-based cellular network. The primary objective is to meet the diverse quality-of-service (QoS) needs of mobile hosts (MHs), and the secondary objective is to maximize the system throughput. The QoS needs of the MHs are modeled using the notion of a service curve. Furthermore, a notion of deviation is introduced as a measure of meeting service curve. The scheme proposed in this paper jointly adapts the transmitted power and the number of spreading codes assigned to each MH for receiving/transmitting its data bits. The scheme imposes practical constraints including bounds on the transmitted power for a base station and MHs, a bound on the number of spreading codes that an MH can handle, and minimum signal-to-interference-plus-noise ratio at the receiver. The proposed solutions are evaluated using discrete event simulations. The simulation results characterize the performance of the proposed solutions for several instances of the practical constraints.     

OVSF code channel assignment with dynamic code set and buffering adjustment for UMTS

The Universal Mobile Telecommunications System (UMTS) provides users variable data rate services, which adopts wide-band code-division multiple-access (WCDMA) as the radio access technology. In WCDMA, orthogonal variable spreading factor (OVSF) codes are assigned to different users to preserve the orthogonality between users' physical channels. The data rate supported by an OVSF code depends on its spreading factor (SF). An OVSF code with smaller SF can support higher data rate services than that with larger SFs. Randomly assigning the OVSF code with a large SF to a user may preclude a larger number of OVSF codes with small SFs, which may cause lots of high data rate call requests to be blocked. Therefore the OVSF code assignment affects the performance of the UMTS network significantly. In this paper, we propose two OVSF code assignment schemes CADPB1 and CADPB2 for UMTS. Both schemes are simple and with low system overhead. The simulation experiments are conducted to evaluate the performances for our schemes. Our study indicates that our proposed schemes outperform previously proposed schemes in terms of the weighted blocking probability and fairness index. Our schemes improve the call acceptance rate by slightly introducing call waiting time.     

A Medium Access Control Protocol for Voice/Data Integrated Wireless CDMA Systems

In this paper, a medium access control protocol is proposed for integrated voice and data services in wireless local networks. Uplink channels for the proposed protocol are composed of time slots with multiple spreading codes per slot based on slotted code division multiple access (CDMA) systems. The proposed protocol uses spreading code sensing and reservation schemes. This protocol gives higher access priority to delay‐sensitive voice traffic than to data traffic. The voice terminal reserves an available spreading code to transmit multiple voice packets during a talkspurt. On the other hand, the data terminal transmits a packet without making a reservation over one of the available spreading codes that are not used by voice terminals. In this protocol, voice packets do not come into collision with data packets. The numerical results show that this protocol can increase the system capacity for voice service by applying the reservation scheme. The performance for data traffic will decrease in the case of high voice traffic load because of its low access priority. But it shows that the data traffic performance can be increased in proportion to the number of spreading codes.     

A New Approach to Achieve High Spectral Efficiency in Wavelength-Time OCDMA Network Transmission

We design a new wavelength-time optical code-division multiple-access (OCDMA) modulation scheme that does not use spreading sequences for information transmission, i.e., the spreading length is N=1. The proposed transmitter sends (error-control) coded data directly through the optical channel and exploits a probabilistic method to reduce the amount of multiuser interference. Simulation results show that by using turbo codes, Reed-Solomon codes, and soft-decision demodulation, the proposed OCDMA scheme can support hundreds of active users at target bit-error rate =10^-9. Furthermore, the achieved spectral efficiency of 0.740 bits per channel use is almost twice as large as the best previous OCDMA results     

Code-spread CDMA using maximum free distance low-rate convolutionalcodes

In code division multiple-access (CDMA) systems, maximum total throughput assuming a matched filter receiver can be obtained by spreading with low-rate error control codes. Previously, orthogonal, bi-orthogonal and super-orthogonal codes have been proposed for this purpose. We present in this paper a family of rate-compatible low-rate convolutional codes with maximum free distance. The performance of these codes for spectrum spreading in a CDMA system is evaluated and shown to outperform that of orthogonal and super-orthogonal codes as well as conventionally coded and spread systems. We also show that the proposed low rate codes will give simple encoder and decoder implementations. With these codes, any rate 1/n, n⩽512, are obtained for constraint lengths up to 11, resulting in a more flexible and powerful scheme than those previously proposed     

可分解的RC-LDPC码以及HARQ的设计

该文提出了一种可分解的码率兼容LDPC码的构造方法, 该方法构造所得到的一个高码率LDPC码的校验矩阵中包含有若干低码率LDPC码的校验矩阵,而且一个高码率的LDPC码又可以分解成多个性能优异的低码率的LDPC码进行编译码;结合该特性设计了一种基于可分解的码率兼容LDPC码的混合自动重传方案。与普通的ARQ方案相比,该重传方案不单能够通过重传获得更多的信息,而且能够通过降低纠错码的码率来提高纠错码的性能。仿真结果表明,当所采用LDPC码的码长为2000左右,码率为1/2和2/3时,与一般的ARQ相比,该方案的误帧率以及吞吐量(小于0.5的时候)均能获得近1.5dB的增益。     

On the comparisons of system performance and capacity of asynchronous STBC MC‐CDMA multirate access schemes

Three multirate access schemes, multicode, variable spreading gain (VSG), and spectral overlaid multiple‐symbol‐rate (MSR), for asynchronous space‐time block coded (STBC) multicarrier code division multiple access (MC‐CDMA) systems are proposed. The three possible spectral overlaid configurations for MSR systems are also investigated. The expressions to evaluate the multiple access interferences, bit error rate (BER) performances, and system capacities of a antenna STBC MC‐CDMA using the three multirate access schemes are obtained. Transmit power allocation is adjusted according to the service rates and the number of active users in each service class to maintain the link quality and to improve the system capacity. Our numerical results show that systems with multicode access scheme using orthogonal Gold spreading codes and with VSG access scheme have similar system performance and capacity, and both perform in general better than systems with MSR access scheme of any spectrum configurations. In case when non‐orthogonal Gold codes are used, multicode access scheme shows degradation in the system capacity as compared to VSG, due to the presence of larger self‐interference (SI) among the codes used by each user. The achievable capacities for the three spectral overlaid configurations of MSR multirate systems are also compared. Copyright © 2007 John Wiley & Sons, Ltd.     

一种改进的准正交空时分组码设计方案

基于MIMO天线系统的空时编码技术是改善无线通信性能、提高带限系统数据速率的一种理想选择。但是由于正交空时分组码不能保证数据全速率传输,为此提出一种改进的准正交空时分组码设计方案。该编码方法利用准正交准则,能够保证数据以全速率传输。并在此基础上具体讨论和分析了编码的编、译码算法和误码性能。该编码方法既不降低分集增益也不增加译码复杂度,并且可以获得一定的编码增益。仿真结果表明,这种方法的误比特率无论在低信噪比还是在高信噪比条件下都要优于已有的准正交空时分组码——Jafarkhani码。