Closed-form SER expressions for Star MQAM in frequency non-selective Rician and Nakagami- channels

The theoretical SER of star constellations (M-QAM) is calculated in frequency non-selective slowly fading channels, characterized by either Rician or Nakagami-m statistics and corrupted by AWGN. Closed form expressions for the average SERs for Star M-QAM are derived and analyzed, having the form of a single finite integral composed of elementary functions. Because of their simplicity, these expressions readily allow numerical evaluations in practical cases.     

A lower bound on achievable rate of MRT precoding in multicell multiuser massive MIMO networks with Rician flat fading

A multicell multiuser massive multiple‐input‐multiple‐output (MIMO) network with Rician flat fading is considered. Given channel reciprocity, non‐orthogonal uplink channel training in conjunction with minimum mean square error channel estimation at the base stations are used to acquire channel state information. In the forward link, using maximal ratio transmission precoding, base stations send data to corresponding users. In this paper, first, a closed‐form expression for signal to interference and noise ratio and a lower bound on achievable rate are obtained for arbitrary number of base station antennas. Then, using random matrix theory, a simplified approximate expression for large number of base station antennas (i.e., massive MIMO scenario) are calculated. This simplified expression shows that in a multicell multiuser massive MIMO network with Rician flat fading, like Rayleigh fading, as the number of base station antennas goes to infinity, the effects of uncorrelated noise and intercell and intracell interferences tend to zero. The only factor limiting the performance of system is the correlated intercell interference, that is, pilot contamination, due to non‐orthogonality of channel training sequences in adjacent cells. Numerical results show that our obtained closed‐form expression is a good lower bound on sum‐rate for various system parameters. Copyright © 2016 John Wiley & Sons, Ltd.     

Reflectors for Light Sources

A shape of reflector is calculated to produce a cylindrical radiation pattern over a finite angle, utilizing all the radial radiation from a line source.     

Modelling and simulation of a Ka-band DBPSK/DQPSK mobile satellite channel

For the prospective personal satellite communications in the early 21st century, this paper presents a general exploration of a K_a-band DBPSK/DQPSK land-mobile satellite channel model and its BER performance from system design, modelling and simulation. A forward-link (i.e. outbound from the hub) channel design is introduced in brief. A complete model of channel multipath fading and shadowing is proposed for the first time, including a basic model and various derivative submodels corresponding to different actual propagation environments. Computer simulation results are given for a Rician channel model, a shadowed channel model and different combinational-fading channel models by complete curve sets of BER performance, which coincide with the results of the analysis, and could be used as valuable references in further research and implementation.     

在室内赖斯衰落时数字移动通信系统的性能

论文讨论了在室内赖斯衰落时,数字移动通信系统的性能,并给出了在缓平赖斯衰落时,差分相移键控系统的平均误比特率,损耗功能和误组率及其仿真结果。     

Morphological gradient based adapted selective filter for removal of Rician noise from magnetic resonance images

Feature/edge-preserving noise removal techniques have a strong potential in several application domains including medical image processing. Magnetic resonance (MR) images have a tendency to gain Rician noise during acquisition. In this article, we have presented genetic algorithms based adapted selective non-local means (GASNLM) filter-based scheme for noise suppression of MR images while preserving the image features as much as possible. We have applied GASNLM filter with optimal parameter values for different frequency image regions to remove the noise. Filter parameter values are optimized by genetic algorithm (GA). A change in NLM filter known as selective weight matrix is also proposed to preserve the image features. The results prove soundness of the method. We have compared results with many well known and latest techniques, and the improvements are discussed.     

一种Rician衰落信道快速仿真模型

Rician衰落信道是一种重要的小尺度衰落信道.由于多普勒频移为随机值的Rician衰落信道仿真模型不适用于查表法,因此对多普勒频移进行了改进,设计出一种适用于查表法的Rician衰落信道仿真模型.通过理论及仿真分析,获得当谐波数达到100后,该模型在保持统计特性基本不变的情况下可极大地提高仿真速度.     

相关阴影Rician衰落信道上MPSK的性能

研究多输入多输出相关阴影Rician衰落信道上正交空时分组编码M进制相移键控的平均符号错误概率性能。当信道衰落参数为正整数时,使用矩生成函数方法推导了相关视距分量、独立散射分量条件下的阴影Rician衰落信道上M进制相移键控平均符号错误概率性能的精确闭合表达式。利用获得的精确闭合表达式可以分析信道衰落参数和天线间的相关性对M进制相移键控平均符号错误概率性能的影响。     

Performance analysis of weather-dependent satellite–terrestrial network with rate adaptation hybrid free-space optical and radio frequency link

Due to the rapid development of satellite laser communication technology, free-space optical (FSO) links present a promising alternative to traditional radio frequency (RF) links. In this paper, taking the influence of weather factors into consideration, we investigate the performance of the hybrid FSO/RF links where the feeder link operates in the FSO band and the user link operates in the hybrid FSO/RF band. Specifically, the FSO feeder link is modeled by the gamma–gamma distribution in the presence of beam wander and pointing error, and the detection method adopts either the intensity modulation with direct intensity (IM/DD) or heterodyne detection. The RF user link is assumed to follow the shadowed Rician model. In addition, in order to improve the transmission rate of the link under the time-varying satellite–terrestrial channel, a rate adaptation scheme is proposed. The performance of the system under study is evaluated in terms of the outage probability, average bit error rate (BER), and average transmission rate. Our results provide some important insights, for example, (1) due to the constraints of the feeder link and weather factors, there is an upper limit on the outage performance and bit error rate of the hybrid link; (2) the adaptive transmission strategy can significantly improve the transmission rate of the link compared with traditional design.     

卫星移动通信系统中Turbo均衡性能研究

针对我国天通卫星移动通信系统的传输特点,提出利用Turbo均衡以达到消除衰落信道下码间干扰的目的,针对Turbo均衡Log-MAP算法对信噪比的估计值具有敏感性,提出一种新的信噪比估计方法。根据天通系统特点,利用线性调频(Chirp)信号估计出信噪比值,从而为Turbo均衡器提供准确的信噪比参数,保证均衡器良好的性能。仿真结果表明:利用Chirp信号估计的信噪比误差能保证在0.2 d B范围内,系统在3 d B时误码率可以达到10-3。