基于遗传算法的多波束频率复用优化设计北大核心CSCD

高通量卫星中多波束天线的同频率波束之间干扰问题,通常以天线载波干扰比(C/I)表征,提高天线C/I性能是获得更高的通信容量途径之一。文中提出了一种多波束天线频率复用优化设计方法,来解决天线C/I性能与频率规划之间的矛盾。在优化过程中将同频波束的频率分配策略作为优化变量,然后利用遗传算法对其进行优化从而实现更高的C/I性能。最后通过一个实例验证该优化算法的有效性和高效性。     

基于扇区化的OFDM小区选择算法

首先给出了一种基于扇区化（Sectorizing）技术的OFDM蜂窝模型。该蜂窝模型利用定向天线的方向性特点,通过在小区内合理地分配频谱资源,减轻小区间的同频干扰,提高基站和移动终端间传输信号的载干比,从而提高网络总容量。然后将两种应用于全向天线蜂窝网络中的基于下行链路的小区选择模型应用在了该模型上,并通过仿真给出了性能分析结果。     

Iterative interference cancellation and channel estimation in multibeam satellite systems

This paper deals with the use of non‐linear multiuser detection techniques to mitigate co‐channel interference on the reverse link of multibeam satellite systems. These techniques allow more capacity efficient frequency reuse strategies than classical ones, as they make possible to cope with lower C/I. The considered system takes as a starting point the DVB‐RCS standard, with the use of convolutional coding, and the use of the Ka‐band. We propose different iterative interference cancellation schemes, which operate at the beamformer outputs, and which use information from decoders. The proposed receivers assume an initial single‐user synchronization step: frame synchronization and timing recovery, and then perform channel estimation: beamformer coefficients; signal carrier phases and signal amplitudes. In a first step, these receivers are evaluated by simulation in terms of bit error rate and of channel estimation error on two interference configurations. For one of these receivers, sensitivity to imperfect timing recovery and to low‐frequency offsets from user terminals is evaluated. In a second step, since the receiver performances highly depend on the interference configuration, we propose an approach to evaluate performances on a multibeam coverage (by taking into account the variability of interference configurations on the coverage). This method is used to compare different receivers on an example based on a coverage designed on a digital focal array feed reflector antenna. Copyright © 2007 John Wiley & Sons, Ltd.     

一种基于定向天线的自组网多址接入协议

文中提出一种基于定向天线的自组织网多址接入协议DA-STDMA。该协议利用方向性天线定向波束增益特性,保证在高速可靠传输条件下,提升系统的容量,同时可以防止信息截获,提升系统的抗干扰性能。经过理论计算,DA-STDMA协议在信道利用率上与采用全向天线相比有显著提高。文中建立了DA-STDMA协议仿真模型,通过对比空间复用度、网络吞吐量等系统性能,DA-STDMA协议利用定向天线比全向天线性能有明显提升。同时仿真研究也表明,定向天线的定位算法对整个系统建链的收敛时间产生一定影响。     

频率选择性信道下空间相关MIMO的迭代检测技术

给出了一种频率选择性信道下空间相关MIMO的系统模型,其发送端采用准循环系统RA码,接收端采用一种对空间相关和非相关信道均适用的软干扰消除迭代检测算法.该算法首先采用基于最小均方误差检测(MMSE)的滑动窗口模型进行干扰消除,然后采用多天线联合最大似然检测(ML)以得到软信息,再将得到的软信息传递到译码器译码并输出发送比特的软信息作为下一次迭代的先验信息,即完成一次迭代.此模型能够取得比较好的误码率性能(BER),其改进方案既增加了发送端的调制域分集,性能又有提升.作为比较,基于软干扰消除的逐天线MMSE迭代检测的方案(ABA SC/MMSE)性能很差.仿真结果也证明了以上观点.     

Ka‐band HTS channel uplink SNIR probability model

I present a novel analytical study of the signal‐to‐noise‐plus‐interference ratio (SNIR) for Ka‐band high throughput satellite uplink channels. The Ka‐band high throughput satellite systems employ frequency and polarization (color) reuse among the spot beams to achieve throughput increase many times the throughput of the system without reuse. However, color reuse also produces substantial co‐color interference and adding to it, tropospheric precipitation attenuation rises sharply in Ka‐band. The co‐color interference and precipitation induced fading vary randomly; they degrade the system performances. To assess the impact, I develop the uplink channel SNIR probability model in this study. Compared with the known studies of the same topic, this study takes the theoretic approach and is applicable to the urban users in particular. The model is feasible to implement and can provide accurate assessment of the channel SNIR performances statistically in theory for a wide array of system operational scenarios. The SNIR probability model is applied to a model spot beam system of 101 user beams to obtain and compare sample channel performances, which can be used for making system design choices at the early stage of a satellite project. Copyright © 2017 John Wiley & Sons, Ltd.     

Interference avoidance strategy for ultra dense network with pilot reuse

In the ultra dense network (UDN),the pilot reuse scheme would produce significant interference,which will affect the accuracy of channel estimation.To solve this problem,an interference avoidance strategy for UDN with pilot reuse was proposed.An interference model of subcarriers for UDN was provided and the interference probability of subcarriers was derived.Then,based on the model,a pilot position selection model was proposed and an interference avoidance strategy for UDN with pilot reuse was provided.The simulation results show that compared with the traditional channel estimation algorithm,the channel estimation with proposed interference avoidance strategy can effectively avoid the interference and ensure the accuracy of channel estimation in UDN with pilot reuse.     

无线上行干扰带的设置及优化

无线链路载干比（C／I）决定了无线信道的质量,当干扰信号增强时会导致无线网络质量的下降。通话时MS占用信道的干扰情况将直接影响客户感知,也是决定通话保持性和连续性的先决条件。本文结合空闲信道干扰的测量功能,阐述了无线上行干扰带门限的设置对手机信道分配及通话质量的重要性。     

Co‐channel interference cancelation at the user terminal in multibeam satellite systems

We study the applicability of soft interference cancelation in the forward link of multibeam satellite systems with focus on mobile terminals. We adopt a standard currently used in commercial satellite systems as a reference. The multibeam satellite antenna radiation diagram has been generated using a physical optics reflector model while a widely adopted channel model has been used for the land mobile satellite channel. The interference pattern has been derived using a system simulator developed by the European Space Agency. Starting from the analysis of the interference pattern, we study the application of a low‐complexity soft interference cancelation scheme for commercial applications. Our results show that, under realistic conditions, a two‐colors frequency reuse scheme can be employed while guaranteeing service availability across the coverage and keeping the complexity at the user terminals relatively low. Copyright © 2015 John Wiley & Sons, Ltd.     

Capacity of distributed antenna network by using single‐carrier frequency domain adaptive antenna array

Single‐carrier frequency domain adaptive antenna array (SC‐FDAAA) has been proposed and proved in our previous study to be effective in suppressing multiple access interference in a severely frequency selective fading channel. In this paper, we studied the performance of SC‐FDAAA in a distributed antenna network (DAN). To make it clear whether the performance of SC‐FDAAA can benefit from the distributed nature of DAN or not, we made a comparison between DAN and the traditional cellular network, that is, central antenna network. The bit error rate distribution and the system capacity (both link capacity and cellular link capacity) are presented. It is shown that by using the SC‐FDAAA, cellular link capacity is maximized by using single frequency reuse. In addition, the capacity of SC‐FDAAA can also benefit from the distributed nature of DAN. Copyright © 2012 John Wiley & Sons, Ltd.     

时分双工蜂窝系统的智能天线研究和性能评估

智能天线是移动多媒体通信亟待解决的关键技术,本文研究了一种适用于时分双工蜂窝系统,基于非线性判决反馈空间均衡器和递归最小平方算法的智能天线。提出了双向链路信号对干扰加噪声功率比的算法以及阵列波束方向增益和信干比累积分布函数两种性能评估方法。仿真结果表明：该智能可以抵消同波道干扰,改善信干比,减小频率复用系数。     

Pilot decontamination in massive MIMO system combining time-shifted and cell sectorization pilot assignment

Pilot contamination is appeared in massive MIMO (multiple input multiple output) system when using the same pilot sequences at different cells to get the channel state information.It becomes a bottleneck problem of massive MIMO when the number of antenna goes infinite.In order to dealt with pilot contamination,a new TS-CSPA joint scheme was proposed.This scheme can mitigate pilot contamination by reduce the reuse of pilot sequence through the time domain and space domain.And the closed-form expression for the achieved rates and signal to interference plus noise ratio(SINR) to verify the advantages of the proposed scheme were given.Numerical results show that significant performance gains to mitigate pilot contamination problem compared to other methods.     

非理想信道环境下的多小区干扰对齐技术研究

由于普遍采用频率复用因子为1的方式组网,多小区干扰已成为限制无线通信系统容量的主要因素。为了有效抑制小区间干扰提高小区边缘吞吐量,近年提出了干扰对齐技术,其优势在于可以获得干扰信道的最高自由度。一般的干扰对齐研究仅限于理想信道,研究通过非理想信道环境下的多小区干扰对齐技术,分析了时延信道信息对干扰系统容量的影响。结果表明,信道状态信息的时延大大降低了系统容量,特别是在高信噪比条件下对系统性能的影响更大。     

同信道干扰对多载波CDMA蜂窝系统下行信道的影响

该文主要讨论多载波CDMA蜂窝系统在下行信道中的同信道干扰问题,理论分析了同信道干扰的解析表达式,并通过计算机仿真得出了在一定的传播损耗下多载波CDMA蜂窝系统下行信道的性能。通过仿真发现,即使在有小区间同信道干扰情况下,通过简单的小区布置,多载波CDMA蜂窝系统下行信道就可以有很大的信道容量。     

Performance Evaluation of a Virtual Queuing – Channel Allocation Scheme for Microcellular Networks

This paper deals with the performance evaluation of a novel distributed channel allocation scheme that attains a high resource reuse in cellular networks. A suitable interference model has been envisaged. Resources are nominally assigned to cells with Fixed Channel Allocation (FCA), according to a given reuse distance. Whenever a channel demand from a mobile user does not find a free nominal resource in a cell, a channel is temporarily borrowed violating the reuse distance constraint, provided that the co-channel interference level is acceptable. As soon as a nominal channel becomes available in this cell, the borrowed resource is released (virtual queuing). The performance of the proposed channel allocation scheme has been evaluated considering both uniform and non-uniform traffic patterns. A performance analysis approach has been also developed and validated by simulations. Comparisons with the classical FCA scheme and other dynamic and borrowing channel allocation strategies have permitted to highlight the good performance of the proposed technique.     

Performance improvement of fixed wireless access networks by conjunction of dual polarization and time domain radio resource allocation technique

This paper considers the impact of dual polarization adoption on the performance for a fixed wireless access (FWA) network. The major limiting factor of the performance in these systems is co‐channel interference (CCI) originating from intracell and intercell concurrent transmissions. The proposed framework combines an appropriate time domain radio resource allocation technique with a dual polarization pattern to mitigate CCI and enhance the obtained signal to interference plus noise ratio (SINR). Simulation results present the performance of the proposed framework against various terrain categories and sector antenna characteristics. Copyright © 2010 John Wiley & Sons, Ltd.     

Effects of correlated shadowing signals on channel reuse in mobileradio systems

The authors present a study to evaluate the cochannel interference probability for the desired and interference signals which are correlated due to shadowing. The effects of correlation on the normalized reuse distance are investigated. A generalized expression for the cochannel interference probability is derived by combining uncorrelated (fast) Rayleigh fading and correlated (slow) log-normal signals. The cochannel interference probability for sectorized cell layouts is compared with the lower bound of cochannel interference probability for omnidirectional antenna systems. It is found that omnidirectional cell layouts cause the highest level of cochannel interference probability. An omnidirectional system requires a higher cluster size than a directional system to maintain acceptable cochannel interference     

Interference Avoidance through Pilot‐Based Spectrum Sensing Algorithm in Overlaid Femtocell Networks

Co‐channel interference between macro–femtocell networks is an unresolved problem, due to the frequency reuse phenomenon. To mitigate such interference, a secondary femtocell must acquire channel‐state knowledge about a co‐channel macrocell user and accordingly condition the maximum transmit power of femtocell user. This paper proposes a pilot‐based spectrum sensing (PSS) algorithm for overlaid femtocell networks to sense the presence of a macrocell user over a channel of interest. The PSS algorithm senses the pilot tones in the received signal through the power level and the correlation metric comparisons between the received signal and the local reference pilots. On ensuring the existence of a co‐channel macrocell user, the maximum transmit power of the corresponding femtocell user is optimized so as to avoid interference. Time and frequency offsets are carefully handled in our proposal. Simulation results show that the PSS algorithm outperforms existing sensing techniques, even at poor received signal quality. It requires less sensing time and provides better detection probability over existing techniques.     

Joint carrier frequency offset and channel estimation for OFDM systems with two receive antennas

Carrier frequency offset (CFO) in OFDM systems results in loss of channel orthogonality and hence degrades the system's performance. In this paper, we propose a new method for joint CFO/channel estimation for OFDM systems with two receive antennas. Our method avoids the complexity of full search methods in one or two dimensions. Using one training OFDM symbol and utilizing the knowledge of the structure of the inter‐channel interference that results from CFO, we develop a two‐stage estimation procedure. The first stage derives an initial CFO/channel estimate based on a one shot minimization step. The second stage refines this joint estimate by conducting a small CFO search in the vicinity of the initial estimate. This procedure provides CFO estimates over a full range of −N /2–N /2, (N : number of subcarriers), as well as the channel estimates. Computer simulations show an excellent performance that is very close to the Cramer–Rao lower bound and superior to some existing methods. The effect of antenna correlation on performance is also investigated through computer simulations, showing small performance degradation even at medium correlation coefficients (0.3–0.6). Copyright © 2015 John Wiley & Sons, Ltd.     

Comparison between the Spectral Efficiency of SDMA Systems and Sectorized Systems

In this paper we present a comparison of the spectral efficiency of Spatial Division Multiple Access systems with conventional omni-directional and sectorized systems. Our analysis attempts to incorporate the effect of co-channel interference (CCI) for users sharing the same channel within a cell (intra-cell interference) as well as the CCI from other cells (inter-cell interference). To determine the outage probability we utilize exact results for combined Rayleigh and Log-normal shadowing in conjunction with a generic antenna pattern. The study is limited to the forward link only and the switched-beam approach. Results are provided for the outage probability and spectral efficiency for various reuse distances and blocking probabilities. These demonstrate that under most conditions, SDMA systems have higher spectral efficiency than conventional omni-directional or sectored systems. Nevertheless under certain conditions such as high blocking probabilities or large reuse distances, the spectral efficiency of SDMA systems is lower than conventional systems.