Performance analysis of discrete feedback schemes for downlink multiuser diversity in OFDMA systems

This paper analyzes discrete feedback of various feedback schemes for multiuser diversity in a multiple subchannel environment. In these schemes of full feedback, fixed feedback, adaptive feedback, and threshold-based feedback, users report a quantized discrete value to indicate their modulation and coding scheme instead of feeding back the full values of the channel state. A closed-form expression of the sum-rate capacity is developed to evaluate the feedback schemes. By comparing the feedback schemes in terms of the sum-rate capacity and the feedback load, this paper provides guidance for the selection of a feedback scheme. Additionally, a mixed-feedback scheme is proposed to reduce the amount of allocated feedback resources in the threshold-based feedback scheme, where the base station adjusts the capacity-feedback tradeoff by controlling two parameters, namely the number of subchannels and a threshold.     

基于SC分集的混合FSO/RF航空通信系统性能分析

研究了基于选择合并(SC)分集的混合激光/射频(FSO/RF)航空通信系统性能,该系统设计简单且在发射端无需信道状态信息(CSI)。激光链路服从平均孔径效应下的Exponentiated Weibull大气湍流分布模型,射频采用Nakagami-m衰落信道模型,推导求出混合FSO/RF航空通信系统接收端信噪比的累积分布函数,进一步利用Meijer′s G函数推导了混合FSO/RF通信系统中断概率以及平均误码率的闭合表达式,通过仿真对比分析了不同湍流强度、调制方式及分集通信方案对系统中断、误码性能的影响。仿真结果表明,混合FSO/RF航空通信系统有效地利用了FSO及RF链路在不同大气信道条件下的互补性质,具有更优的中断和误码性能;采用BPSK调制能有效降低大气湍流对混合FSO/RF航空通信系统的影响;信噪比高时,并行传输、分集接收的通信方案对系统误码性能的改善要优于低阶调制对误码性能的改善。     

Performance analysis of switch‐based multiuser scheduling schemes with adaptive modulation in spectrum sharing systems

This paper focuses on the development of multiuser access schemes for spectrum sharing systems whereby secondary users are allowed to share the spectrum with primary users under the condition that the interference observed at the primary receiver is below a predetermined threshold. In particular, two scheduling schemes are proposed for selecting a user among those that satisfy the interference constraint and achieve an acceptable signal‐to‐noise ratio level. The first scheme focuses on optimizing the average spectral efficiency by selecting the user that reports the best channel quality. In order to alleviate the relatively high feedback required by the first scheme, a second scheme based on the concept of switched diversity is proposed, where the base station (BS) scans the secondary users in a sequential manner until a user whose channel quality is above an acceptable predetermined threshold is found. We develop expressions for the statistics of the signal‐to‐interference and noise ratio as well as the average spectral efficiency, average feedback load, and the delay at the secondary BS. We then present numerical results for the effect of the number of users and the interference constraint on the optimal switching threshold and the system performance and show that our analysis results are in perfect agreement with the numerical results. Copyright © 2014 John Wiley & Sons, Ltd.     

Performance analysis of MIMO systems with multiuser diversity

In this paper, we present a comprehensive performance analysis for multiple‐input multiple‐output (MIMO) systems with multiuser diversity over Rayleigh fading channels. We derive exact closed‐form expressions of the outage probability and the average bit error rate (BER) for different MIMO schemes, including the selective combining (SC), maximum ratio combining (MRC) and space‐time block codes (STBC). We also provide the explicit upper bounds on the BER performance. Finally, the mathematical formalism is verified by numeric results that study the interaction between the antenna diversity and the multiuser diversity. It is observed that the system performance is deteriorated as the number of transmit antennas increases in multiuser scenario, which is unlike the case in single‐user systems. Copyright © 2007 John Wiley & Sons, Ltd.     

空时发射分集在LAS-CDMA中的性能分析

发射分集是克服信道衰落的有效方式,而LAS-CDMA由于特有的智慧编码技术而具有优异的特性.对三种发射分集方式(OTD,STTD,STS)与LAS-CDMA结合的性能进行了研究,从理论上推导了采用这几种方式后的信干比表达式,并且在LAS-CDMA中仿真了其性能,并与传统CDMA进行了比较.表明发射分集与LAS-CDMA相结合能充分的发挥两者的优越特性.     

Performance analysis of multiuser selection diversity in SIMO spectrum sharing systems

In this paper, a performance analysis is presented for user selection schemes in a single‐input multiple‐output spectrum sharing system. In the considered system, multiple secondary users try to use the licensed spectrum of a primary user in an opportunistic manner, in which an interference constraint for the primary user is satisfied. In this paper, we first use 2 conventional user selection schemes for single‐input multiple‐output spectrum sharing system and analyze the system performance for each scheme. We then propose a new user selection scheme that can overcome the limitations of those 2 conventional user selection schemes. As for the performance analysis, the average channel capacity, the outage probability, and the bit error rate performances of the system using the presented user selection schemes are analyzed and mathematical closed‐form expressions for the outage probability are derived. The performances of the system are evaluated using the derived mathematical formulas in different cases. In addition, Monte Carlo simulation results are also provided to show the accuracy and correctness of the performed analysis.     

移动通信中发送分集性能分析

发送分集技术是第三代移动通信系统(3G)中的一种关键技术。主要分析了两种基于空时编码的发送分集:STTC和STTD。从成对错误概率角度和误码率等方面讨论了两种发送分集的性能。最后,进行了计算机仿真,并给出结论。     

Performance analysis of multiuser diversity in cooperative multi-relay networks under rayleigh-fading channels

In multiuser cooperative relay networks, cooperative diversity can be obtained with the help of relays, while multiuser diversity is an inherent diversity in multiuser systems. In this letter, the performance analysis of multiuser diversity in cooperative multi-relay networks is presented. Both the case of all relay participating and the case of relay selection are considered. We first derive asymptotic expressions of outage probability and symbol error probability for amplify-and-forward (AF) and decode-and-forward (DF) protocols with joint multiuser and cooperative diversity. Then, the theoretical analysis are validated by Monte Carlo simulations. Both the theoretical analysis and simulations show that a multiuser diversity order of K and a cooperative diversity order of M+ 1 can be achieved simultaneously for both AF and DF protocols (where K is the number of accessing users and M is the number of available relays). These demonstrate that the multiuser diversity can be readily combined with the cooperative diversity in multiuser cooperative relay networks.     

Performance analysis of ONU-wavelength grouping schemes for efficient scheduling in long reach-PONs

Long Reach PONs (LR-PON) were proposed to extend the benefits of Passive Optical Networks (PON) to more users and to a larger area. This paper considers a Dynamic Bandwidth Allocation (DBA) based on a hybrid combination of Time Division Multiplexing (TDM) and Wavelength Division Multiplexing (WDM). The time complexity of the DBA algorithm is typically O(n log n), where n denotes the number of ONUs. Since the maximum number of supported ONUs in an LR-PON can be as high as 2048, the computation time required for computing a schedule will be very high and directly impacts the overall network performance. In this paper, we have presented a grouping strategy to reduce the computation requirements. The number of ONUs is split into mutually exclusive groups with the OLT scheduling each group independently and in parallel. With the static grouping strategy every user is assigned to a group and the assignment of wavelength resources is fixed. However, with non-uniform loads, we observed that static grouping was not found to be suitable as the delay variation was significant across the groups. To address this gap, we introduce the concept of dynamic grouping and define three dynamic grouping heuristics that adapt to the current network load conditions and (re)allocate the ONUs and wavelength resources suitably. The proposed schemes have been compared in terms of delay variation and wavelength utilization. Of the three heuristics, ONU to Least Loaded wavelength group (OLL) and Least Wavelength Resources (LWR) heuristics balance the packet delay across ONUs assigned to different groups and Proportional Wavelength Usage (PWU) heuristic reduces power consumption by allocating fewer wavelength resources.     

Performance analysis of single and multiuser MIMO diversity channels using Nakagami-m distribution

This letter studies the diversity advantage of single and multiuser systems utilizing multiple-input multiple-output (MIMO) antennas for known channels at the transmitter and receiver(s) by investigating the overall distribution of the resulting channel. For the single-user case, the resultant channel is taken as the largest singular value of the MIMO channel whereas for the multiuser scenario, the resultant channel is obtained by a recently proposed joint-channel diagonalization. The channel distribution is studied using hypothesis testing with the hypothesis that the distribution follows a Nakagami-m distribution with given parameters. It is concluded from the chi-square goodness-of-fit test that the distribution of the resultant channel for single or multiuser MIMO channel is well matched with a Nakagami-m distribution.     

Performance enhancement of multiuser MIMO wireless communication systems

This paper describes a new approach to the problem of enhancing the performance of a multiuser multiple-input-multiple-output (MIMO) system for communication from one base station to many mobile stations in both frequency-flat and frequency-selective fading channels. This problem arises in space-division multiplexing systems with multiple users where many independent signal streams can be transmitted in the same frequency and time slot through the exploitation of multiple antennas at both the base and mobile stations. Our new approach is based on maximizing a lower bound for the product of signal-to-interference plus noise ratio (SINR) of a multiuser MIMO system. This provides a closed-form (noniterative) solution for the antenna weights for all the users, under the constraint of fixed transmit power. Our solution is shown by simulation to have better performance than previously proposed iterative or noniterative solutions. In addition, our solution requires significantly reduced complexity over a gradient search-based method that directly optimizes the product SINRs while still maintaining similar performance. Our solution assumes channel state information is present at the base station or transmitter.     

Performance of multiuser diversity reception in Rayleigh fadingCDMA channels

Error probability of an adaptive multiuser diversity receiver is evaluated in terms of channel fading rate and the number of code-division multiple access users. Fading-induced performance loss, which leads to the error probability floor, is established for the proposed coherent combining scheme and compared to that of the differentially coherent receiver with equal-gain combining     

Capacity of multiuser diversity systems with adaptive transmission and different MIMO schemes

In this paper, we present a comprehensive capacity analysis of the downlink of multiuser diversity (MD) systems with adaptive transmission over Rayleigh fading channels. First, the exact capacity of the single‐input single‐output (SISO) systems with MD and adaptive transmission technique is derived. The optimal power allocation scheme for such a system is shown to be a water‐filling algorithm. Next, we derive the exact closed‐form capacity expressions for different multiple‐input multiple‐output (MIMO) schemes, including the selective combining (SC), maximum ratio combining (MRC) and space‐time block codes (STBC). In order to avoid the cumbersome numerical root finding techniques in solving the optimal cutoff SNR level below which the channel is not used, we also provide the approximate expressions for the cutoff level. For the MD MIMO systems, it is observed that the optimal power allocation strategy is to focus transmit power on a single transmit antenna (e.g. Tx‐MRC/Rx‐MRC scheme) or selecting the best transmit antennas (e.g. Tx‐SC/Rx‐MRC scheme). Copyright © 2007 John Wiley & Sons, Ltd.     

基于跨层策略的60 GHz脉冲多用户通信系统性能分析

由于具备免许可、强方向性、高系统容量和吉比特的高传输速率等优势,60 GHz频段被列为5G新空口（new radio,NR）的候选频段之一。在5G超密集组网场景中,网络节点之间距离的降低引起的节点开关转换的随机性会导致严重的多址干扰、资源失配问题。对此,基于跨层协同设计的思想,提出了一种基于公平性的资源调度策略,在基于TH-PAM（time hopping pulse amplitude modulation）的60 GHz脉冲无线通信系统中对该策略的多址接入性能进行仿真分析。仿真结果表明,相比采用纯物理层优化算法的系统,采用该策略的多址接入系统表现出更强的公平性、更低的系统误码率,但需要额外增加发射功率来满足同等通信系统覆盖范围的要求,即在系统的能量与公平性之间存在一定的折中,可用于指导实际通信系统的构架与布设。     

Optimal diversity allocation in multiuser communication systems.II. Optimization

For pt.I see ibid., vol.47, no.1828-36 (1999). In Part I, a class of multicarrier systems was proposed to study the effect of the method of diversity allocation on the performance of coherent multiuser communication systems operating over fading channels. In this paper, optimization over the proposed class of systems is considered for a fixed number of users per unit bandwidth. The first case studied is a system where the only noise not attributable to users in the system is additive white Gaussian noise. It is observed that either a system employing exclusive allocation, where users are allocated time-bandwidth resources that are not simultaneously shared with other users, or a system employing maximum resource sharing, where all users simultaneously share time-bandwidth resources, is optimal. Next, the preferable of these two extreme forms of resource allocation is determined. For any reasonable signal-to-noise ratio (SNR) and user density, it is shown that the system employing exclusive resource allocation is optimal in a single-cell environment with perfect subchannel separation at the receiver. Finally, the optimization is repeated in the presence of partial-band interference (PBI). Once again, either a system employing exclusive resource allocation or a system employing a maximum resource sharing scheme is observed to be optimal. The presence of the PBI increases the range of user densities and SNRs where a system employing a maximum resource sharing scheme is optimal, particularly when the probability of a particular time-bandwidth slot experiencing interference is high     

Performance analysis of multi-user diversity in heterogeneous cooperative communication systems

The heterogeneous cooperative relaying technique can be utilized to complete the hierarchical convergence for the multi-radio access networks, where the single heterogeneous cooperative relay is selected and the maximal-ratio combining (MRC) scheme is utilized to achieve the cooperative diversity gain. In order to evaluate performances of the hierarchical convergence mechanism, this paper theoretically investigates the key factors of the multi-user diversity (MUD) gain, the heterogeneous cooperative diversity gain and the large scale fading of the first and second links. The tight closed-form expressions in terms of the outage probability and the average symbol error rate are derived for evaluating how and with what factors impact on the system performance. The analytical and simulation results show that the number of heterogeneous cooperative relay nodes (HCRNs)M and the number of destination stations (DSs)K have great impacts on performances, and the order of outage probability is (M + 1)K. The large scale fading ratio of the first hop to the second hop also has a big impact on performances. Thus in the real network, we can utilize advanced radio resource management schemes to achieve a high multi-user diversity, instead of configuring too many HCRNs for the heterogeneous cooperative diversity gain. Furthermore, we can guarantee the transmission quality between the BS and HCRNs via the network planning to optimize the overall network performance.     

两类混沌激光保密通信方案的性能分析

半导体激光器在外加扰动下,可以产生高维宽带的混沌激光信号,是实现高速保密通信的理想载波。本文数值研究了混沌调制和混沌隐藏两种信息加载方式下的混沌激光保密通信系统的性能,分析了两种信息加载方式下系统分别传输正弦信息和数字信息时的信噪比和Q因子的变化情况,研究了两种信息加载方式下系统的相关系数随调制深度的变化趋势。结果表明,不同的调制深度或调制频率/速率都会影响系统的性能,且混沌调制方式的系统性能优于混沌隐藏方式。     

相关MIMO信道下空间分集系统中多用户分集性能

多用户MIMO(Multi-input multi-output)系统中,研究空间相关对联合空间分集和多用户分集的性能影响.推导了接收天线之间存在相关的多用户MIMO STBC(Space-time block coding)和MIMO MRT/MRC(Maximum-ratio-transmis-sion/maximal-ratio-combining)系统的中断容量、平均容量表达式,并由此进行性能分析.计算机仿真验证了理论分析的有效性.结果表明,相对于闭环的多用户MI-MO MRT/MRC系统,空间相关下开环的多用户MIMO STBC系统具有较低的平均容量和较高的调度增益.     

Exact capacity analysis of multiuser diversity combined with transmit diversity

Expressions for the average channel capacity of a multiuser diversity system combined with transmit diversity at each link are presented under the assumption of independent Rayleigh fading. The analysis results exactly agree with the simulation results and definitely show the impact of transmit diversity on multiuser diversity.     

Optimal diversity allocation in multiuser communication systems. I.System model

A class of multiuser multicarrier communication systems is introduced to study the influence of resource allocation on the performance of multiuser communication systems operating over fading channels. This class of systems includes both systems that employ exclusive allocation schemes, where users are allotted time-bandwidth slots without interference from other users, and systems that employ shared allocation schemes, where users are allotted time-bandwidth slots that are also employed by other users. The optimal weighting factors used in the combining of the received signals from the slots of a single user for the conventional receiver is derived, and the performance of systems in the class is characterized. For each of a number of popular multiuser architectures, it is shown that there exists a system in the class with nearly identical performance. Based on these relations, it is concluded that a class of systems has been introduced that allows the study of the merits of different types of time-bandwidth allocation under a single framework