基于可重构OTA装置的非平稳多维无线信道重构模型与应用性能分析

大规模多入多出(massive MIMO)天线阵列是5G及下一代移动通信的关键使能技术,可靠可信可行且可按需灵活构建的室内多维度性能测试与验证对推动massive MIMO系统技术的基础理论研究、关键技术突破和商用部署至关重要.为了进行大规模MIMO设备的技术验证、场景完备性测试与技术缺陷评估,发展真实可靠的室内模拟性能测试方法至关重要,其核心挑战是如何为待测设备(Device Under Test,DUT)在测试装置中重建丰富、完备的目标电波传播环境.本文在早期提出的虚拟探头快速位置优化方法及其探头权重计算闭式解和不同信道场景下精确多维度信道重构工作的基础上,提出了一种基于可重构OTA装置的非平稳多维无线信道重构方法,为DUT测试提供了拟真的目标非平稳多维无线信道重构机制,能够有效克服传统多探头微波暗室法(Multi-Probe Anechoic Chamber,MPAC)、辐射两步法(Radiated Two Stage,RTS)以及混响室法(Reverberation Chamber,RC)等三种方法难以满足工作于动态信道环境中大规模MIMO天线系统及其波束性能功能描述问题.本文引进可构建不同比特(bit)数的移相器,重构信道空间谱变化,可开展最大空间相关性误差、加权空间相关性均方根误差(weighted root mean square correlation error)、空间功率角度谱(PAS)相似性(PAS similarity)和固定波束功率损失(fixed beam power loss)评估.本文通过全场景多维度信道重构环境分析表明,4 bit精度移相器可以在保证最佳成本效益的前提下,为室外场景的室内近真实重构提供理想精度的相位矩阵,这也为量化分析移相器误差对虚拟OTA方法影响提供了理论基础和技术途径.本文通过迄今为止未见报道的移相器分辨率因素引入,为传统的相位矩阵虚拟OTA测试装置用于真实复杂电磁传播环境massive MIMO无线设备及其模拟重构,通过相控矩阵调节DUT中各个天线单元的相位响应,模拟探头天线辐射电磁波在自由空间中的传播变化,仿真自适应massive MIMO核心指标与验证,提供了一种有效方法,达成了实际应用场景的信道重构.此外,实验还表明,在虚拟探头数量足够多的情况下,3 bit移相器也能够提供较为理想的信道重构性能,可指导用于室内装置的移相器选择以及低复杂度相控矩阵构建,同时本文也指出虽然4 bit移相器已经能够提供精确信道重构,但也可以选择5 bit移相器提供1 bit安全冗余.进一步,为深入验证本文结果对非标准测量信道场景重构的有效性,本文重构了一个射线追踪模型的动态信道环境,同时,该模型信道在多个空间位置的精确重构也证明了本文方法的广泛适用性与可行性.

移动性受限物联网应用中基于图论的高效数据采集策略

针对物联网数据采集应用,研究移动性受到限制的汇聚节点对数据采集性能和能量有效性造成的影响,提出能量有效的数据采集策略.基于图论基本原理对系统进行分析,建立借助方格的网络分层描述方法.提出数据采集中的能量分层优化HOEE问题,采用基于启发式算法的匹配算法来匹配节点方格,制定能耗均衡的数据包上报策略.NS-3仿真实验结果表明,HOEE数据采集策略具有优越性,与最短路径树、最大数据量最小路径以及随机采集策略相比,网络寿命能够有效提高约30%,维持较高的数据采集性能.在具有移动性受限的汇聚节点的物联网应用中使用HOEE数据采集策略,能够提高网络寿命,保证数据采集性能.

基于惠更斯等效原理的高速高密度PCB分级建模方法

当带宽达到20 GHz以上时(波长从15 mm到无穷小),高速高密度电子系统的内部电路电磁环境变得十分复杂,越来越难以建模和分析预测,进一步当带宽达到40 GHz以上时,电路电磁环境问题将变得更加尖锐.为在设计阶段能够对电磁作用过程、作用效应进行预测评估及控制,需要精确的建模方法和针对大尺度问题的快速计算技术,尤其是超大带宽超高速混合电路和集成电路.本文提出了基于混合电路环境电磁计算基础理论的跨尺度处理技术,通过惠更斯等效原理和电磁奇异性几何结构的电磁收敛降速机理的利用,解决了多维交叉多尺度电路电磁环境场路融合的高效率高精度建模技术挑战;利用惠更斯等效原理和基尔霍夫积分方程,在区域边界面上定义了惠更斯端口,提出了对于任意复杂印制电路板(Printed Circuit Board,PCB)同时垂直方向和水平方向区域分解的一般方法,实现了任意PCB结构的分级分类处理和模块化封装,提高了高速高密度电子系统分析的灵活度;提出了基于几何结构电磁学多重本地本征展开的技术途径,发展了基于模式和区域分解分割的快速并行处理技术,通过电磁锐变区域本征描述及场分布的本征基函数表征,实现了高精度和高计算速度兼得,减少了复杂电子系统的计算时间和设计时间.统计数据表明,本文提出的方法在0~40 GHz大带宽频率范围内频偏误差为3.7%、幅度偏差为±3 dB.本文提出的PCB分级建模分析方法可以应用于高端电子通信系统设计,提升我国宽带高速数模系统的高效电路设计和环境电磁调控能力,缩短产品研发周期.

一种非对称馈电的小型化高隔离度分集天线

提出一种基于非对称共面带(ACS)馈电的高隔离度小型化分集天线结构.使用ACS作为天线馈电结构可使天线体积减小约50%.引入地板延伸枝节作为去耦合结构,使天线间端口隔离度大于15 d B,其中最高隔离度达到30 d B.实验结果表明,该分集天线可满足2. 4/5. 2 GHz WLAN和2. 6/3. 5 GHz LTE的通信需求.

Distributed channel assignment combined with routing over multi-radio multi-channel wireless mesh networks

In order to realize the reduction of equipment cost and the demand of higher capacity, wireless mesh network （WMN） router devices usually have several interfaces and work on multi-channels. Jointing channel allocation, interface assignment and routing can efficiently improve the network capacity. This paper presents an efficient channel assignment scheme combined with the multi-radio link quality source routing （MR-LQSR） protocol, which is called channel assignment with MR-LQSR （CA-LQSR）. In this scheme, a physical interference model is established： calculated transmission time （CTT） is proposed as the metric of channel assignment, which can reflect the real network environment and channel interference best, and enhanced weighted cumulative expected transmission time （EWCETT） is proposed as the routing metric, which preserves load balancing and bandwidth of links. Meantime, the expression of EWCETT contains the value of CTT, thus the total cost time of channel assignment and routing can be reduced. Simulation results show that our method has advantage of higher throughput, lower end-to-end time delay, and less network cost over some other existing methods.

Resource scheduling in downlink LTE-advanced system with carrier aggregation

In this paper, we focus on the resource scheduling in the downlink of long term evolution advanced （LTE-A） assuming equal power allocation among subcarriers. Considering the backward compatibility, the LTE-A system serves LTE-A and long term evolution （LTE） users together with carrier aggregation （CA） technology. When CA is applied, a well-designed resource scheduling scheme is essential to the LTE-A system. Joint scheduling （JS） and independent scheduling （INS） are two resource scheduling schemes. JS is optimal in performance but with high complexity. Whereas INS is applied, the LTE users will acquire few resources because they can not support CA technology. And the system fairness is disappointing. In order to improve the system fairness without bringing high complexity to the system, an improved proportional fair （PF） scheduling algorithm base on INS is proposed. In this algorithm, we design a weigh factor which is related with the number of the carriers and the percentage of LTE users. Simulation result shows that the proposed algorithm can effectively enhance the throughput of LTE users and improve the system fairness.

High Data Rate OFDM System with Simplified DAPSK Demodulation

In this paper, a simplified differential amplitude demodulation scheme for high-level Differential Amplitude and Phase Shift Keying （DAPSK） techniqus is proposed, which requires fewer thresholds for demodulation and thus has lower complexity. The performance of the Orthogonal Frequency Division Multiplexing （OFDM） system combined with the simplified DAPSK scheme is investigated over frequency-selective fading channels, then. Compared with coherent QAM-OFDM system, DAPSK-OFDM system has much lower complexity since channel estimation and equalization are unnecessary. Further more, under the condition of the same data rate, DAPSK-OFDM can achieve the performance close to or even better than that of QAM-OFDM system which adopts pilot symbols for channel estimation, by employing the concatenated code and utilizing the additional redundancy for outer coding at high Signal-to-Noise Ratios （SNRs）.

Fairness-oriented routing algorithm joint with power control and channel assignment for multi-radio multi-channel wireless mesh networks

The multi-radio multi-channel wireless mesh network （MRMC-WMN） draws general attention because of its excellent throughput performance, robustness and relative low cost. The closed interactions among power control （PC）, channel assignment （CA） and routing is contributed to the performance of multi-radio multi-channel wireless mesh networks （MRMC-WMNs）. However, the joint PC, CA and routing （JPCR） design, desired to achieve a global optimization, was poor addressed. The authors present a routing algorithm joint with PC and CA （JPCRA） to seek the routing, power and channel scheme for each flow, which can improve the fairness performance. Firstly, considering available channels and power levels, the routing metric, called minimum flow rate, is designed based on the physical interference and Shannon channel models. The JPCRA is presented based on the genetic algorithm （GA） with simulated annealing to maximize the minimum flow rate, an non-deterministic polynomial-time hard （NP-Hard） problem. Simulations show the JPCRA obtains better fairness among different flows and higher network throughput.

Parametric channel modeling based OFDM channel estimation

A simplified parametric channel estimation approach was proposed for orthogonal frequency division multiplexing （OFDM） systems. Based on parametric channel model, this algorithm is composed of two parts： the estimation of channel parameters and channel interpolation. The exponentially embedded family （EEF） criterion is exploited to determine the number of channel paths as well as the multipath time delays. Consequently, the channel frequency responses is acquired via the estimated parameters. Additionally, the authors＇ scheme is computationally efficient owing to the needless of the eigenvalue decomposition or the estimation of signal parameters by the rotational invariance technique （ESPRIT）. Simulations are provided to validate the performance of this algorithm from perspectives of the probability of correct estimation and the mean square error （MSE）. It is demonstrated that this approach exhibits a superior performance over the existing algorithms.

Efficient wireless multicast retransmission using network coding

In wireless multicast, network coding has recently attracted attentions as a substantial improvement to packet retransmission schemes. However, the problem of finding the optimal network code which minimizes the retransmissions is hard to solve or approximate. This paper presents two schemes to reduce the number of retransmissions for reliable multicast efficiently. One is retransmission using network coding based on improved Vandermonde matrix （VRNC）, the other is retransmission using network coding based on adaptive improved Vandermonde matrix （AVRNC）. Using VRNC scheme the sender selects the packets all receivers have lost and encodes them with improved Vandermonde matrix; when receivers receive enough encoded retransmission packets, all the lost packets can be recovered. With AVRNC scheme, the sender can obtain the recovery information from all the receivers after sending out per retransmission packet, and then the improved Vandermonde matrix can be updated, thus reducing the complexity of encoding and decoding. Our proposed schemes can achieve the theoretical lower bound assuming retransmission packets lossless, and approach the theoretical lower bound considering retransmission packets loss. Simulation results show that the proposed algorithms can efficiently reduce the number ofretransmissions, thus improving transmission efficiency.

New predistorter using triangular memory polynomial for power amplifier of OFDM-based wireless broadband communication system

A triangular memory polynomial （TMP） predistorter is presented in this paper to linearize a power amplifier＇s nonlinear with memory effects. Compared with the traditional memory polynomial （MP） predistorter, the coefficients of TMP predistorter is reduced more than 75%, which can effectively decrease the implementation complexity. The coefficients of predistorter are directly extracted from an offline system identification process by an open-loop structure in our approach. Several signals with data rate 5 MHz, 10 MHz, 15 MHz and 20 MHz are used to verify the performance of the proposed predistorter. Experimental results show that the proposed TMP predistorter and the traditional MP predistorter almost have the same performance.

Energy efficiency of massive MIMO wireless communication systems with antenna selection

Massive multiple-input multiple-output（MIMO） requires a large number（tens or hundreds） of base station antennas serving for much smaller number of terminals, with large gains in energy efficiency and spectral efficiency compared with traditional MIMO technology. Large scale antennas mean large scale radio frequency（RF） chains. Considering the plenty of power consumption and high cost of RF chains, antenna selection is necessary for Massive MIMO wireless communication systems in both transmitting end and receiving end. An energy efficient antenna selection algorithm based on convex optimization was proposed for Massive MIMO wireless communication systems. On the condition that the channel capacity of the cell is larger than a certain threshold, the number of transmit antenna, the subset of transmit antenna and servable mobile terminals（MTs） were jointly optimized to maximize energy efficiency. The joint optimization problem was proved in detail. The proposed algorithm is verified by analysis and numerical simulations. Good performance gain of energy efficiency is obtained comparing with no antenna selection.

Joint relay selection and power allocation algorithm in two-way relay networks with proportional fair constraint

In this paper, we consider the joint relay selection and power allocation problem for two-way relay systems with multiple relay nodes. Traditionally, relay selection schemes are primarily focused on selecting one relay node to maximize the transmission sum rate or minimize the outage probability. If so, it is possible to cause certain relay nodes overloaded. In addition, the joint relay selection and power allocation problem is a mixed integer program problem and prohibitive in terms of complexity. Therefore, we propose a novel low complexity joint relay selection and power allocation algorithm with proportional fair scheduling to get the load-balancing among potential relays. Simulation results turn out that, compared with round-robin schemes and max sum rate schemes, the proposed algorithm can achieve the tradeoff between system transmission sum rate and load-balancing.

Adaptive power loading with BER-constraint for OFDM systems

A novel adaptive power loading algorithm with the constraint of target overall bit error rate （BER） for orthogonal frequency division multiplexing （OFDM） systems is proposed in this article. The proposed algorithm aims to minimize the required transmit power with fixed data rate and uniform （nonadaptive） bit allocation, while guaranteeing the target overall BER. The power loading is based on the unequal-BER （UBER） strategy that allows unequal mean BERs on different subcarriers. The closed-form expressions for optimal BER and power distributions are derived in this article. Simulation results indicate the superiority of the proposed algorithm in terms of BER performance and algorithmic complexity.

A Novel Multiuser Detection Algorithm for CDMA-Based MIMO-OFDM System

This paper investigates QR matrix decomposition based successive interference cancellation multiuser detection algorithms in synchronous uplink for code division multiple access based multiple input multiple output orthogonal frequency division multiplexing ,system. The Symbol Error Rate＇（SER） performance of the optimal order and the suboptimal order QR-SIC MUD algorithms are compared with conventional zero forcing and minimum mean ,square error multiuser detection algorithms by Monte Carlo .simulations. Complexity analysis is presented at the end of the paper. Both our .simulation results and complexity analysis show that SER performance of QR-Successive Interference Cancellation （QR-SIC） algorithms is superior to those of zero forcing （ZF） and minimum mean .square error algorithms, and the ,suboptimal order Q-R-SIC algorithm hos a good trade-off between SER performance and computation complexity.

User Identification Detector Based on Power of R Technique

To avoid the inaccurate estimation of the active user＇ s number and the corresponding performance degradation, a novel POR-based User Identification Detector （UID） is proposed for the Code Division Multiple Acces （CDMA） systems. The new detector adopts the Power of R （POR） technique and the Multiple Signal Classification （MUSIC） method, which does not require the estimation of active users＇ number, and obtains lower false alarm probability than the subspace-based UID in the multipath channels. However, from our analysis, increasing the order m does not improve the performance. Therefore, when m is one, the performance of the new detector is maximal.

Throughput oriented forwarders selection analysis for opportunistic routing in wireless mesh network

Opportunistic routing explicitly takes advantage of the broadcast nature of wireless communications by using a set of forwarders to opportunistically perform packet forwarding. A key issue in the design of opportunistic routing protocols is the forwarder list selection problem. This paper proposes a novel routing metric which shows the end-to-end throughput and a corresponding throughput oriented opportunistic routing forwarder-selecting algorithm throughput oriented forwarders selection （TOFS） through analyzing forwarding characteristics of forwarders. The algorithm puts forward a constraint mechanism that controls the number of forwarders by constraint of throughput for forwarders selection, achieving a better balance between number of forwarders and effective link stability by introducing the factor of transmission time. Simulation results show that the algorithm can improve the network end-to-end throughput effectively over existing methods.

Suboptimal resource allocation with MMSE detector for grouped MC-CDMA systems

This article puts forward two novel user-grouping algorithms for grouped multi-carrier （MC）-code division multiple access （CDMA） systems. As is well known, the adaptive assignment for user-grouping plays an important role for link quality of multi-access transmissions. In the study, the capacity-maximizing problem of user-grouping is formulated. By using the Kuhn-Tucker condition, the optimal criterion is deduced and found to have a similar form with signal to noise plus interference （SINR）. However SINR includes the signal power that can only be determined after user-grouping. Therefore the optimal criterion will lead to an impractical application. To deal with it, the user＇s equivalent SINR for minimum mean square error （MMSE） detector is proposed and served as a suboptimal assignment criterion, based on which two kinds of user-grouping algorithms are proposed. In the algorithms, only partial channel information is needed at the base station, which saves a large part of the bandwidth occupied by feedback information. Computer simulations have evaluated an excellent performance of the proposed algorithms at both link quality and data rate. Meanwhile, the proposed algorithms have lower implementation complexity for practical reality.

AAA authentication for network mobility

Network mobility （NEMO） is a protocol proposed for the mobility management of a whole network. It offers seamless Internet connectivity to the mobile end users. However, the NEMO protocol has not been widely used in Internet, because it has not considered the secure problem about authentication and authorization. The proposed framework designed an access control scheme especially used for the NEMO network environment. It is based on the authentication, authorization, and accounting （AAA） system. It can make use of the mobile router to authenticate for all the mobile nodes at the same time, and uses the mobile network node （MNN）-list synchronization mechanism to control the secure access of the MNN. By using the foreign AAA server cache mechanism, this scheme can decrease the authentication time delay and improve the efficiency of the network. The advantages are proved by the comparison with other recent related studies via the OPNETsimulations.