基于误比特信息区间斜率的正交频分复用水声通信多普勒估计

针对正交频分复用水声通信中直接误比特率搜索多普勒估计算法存在的高计算复杂度问题,提出了一种基于误比特信息区间斜率的多普勒估计算法,采用计算误比特信息区间斜率取代逐网格搜索最优误比特信息寻优过程,设计根据多普勒估计分辨率动态可变的斜率区间,在进一步提升寻优速率的同时有效减小陷入局部最优解的可能性,并有效降低算法的计算复杂度。仿真实验和海上试验结果表明:所提算法以较低的计算代价实现了与误比特率搜索多普勒估计算法近乎一致的估计性能,在本文试验条件下其相对块多普勒估计、基于互模糊度函数多普勒估计以及准梯度互相关多普勒估计算法可获得不低于14%的误比特率性能改善。

非理想信道估计和相关Nakagami信道条件下空时发送分集的性能分析

深入分析了非理想信道估计和相关Nakagami衰落2种因素对空时发射分集系统性能的影响.首先在高斯信道估计误差的假设条件下,得出了空时发射分集(STTD)接收信号的信噪比公式.在具有任意衰落相关矩阵的相关Nakagami信道条件下,推导出空时发射分集系统误比特率公式.最后通过蒙特卡罗仿真所得结果与理论误比特率相比较,证明了文中所推导的误比特率公式的正确性.结果表明,当信道估计误差与信道增益之比(EGR)不断增大时,误比特率逐渐出现平台现象.当EGR小于-15dB时,非理想信道估计带来的误比特率增加非常缓慢.而当分集支路之间的衰落相关系数小于0.4时,衰落相关带来的误比特率增加量不是很严重.文中还讨论了Nakaga-mi信道衰落参数m对系统性能的影响.

16QAM调制下BICM-ID系统的最优多维映射

研究16QAM星座调制下比特交织编码调制迭代译码(BICM-ID)系统的多维映射设计。通过对渐进误比特概率的分析,得到用以映射设计的距离准则。进一步利用修正的分段二进制切换算法(MBSA)搜索,得到准静态瑞利衰落信道下渐进性能近最优的四维16QAM映射。仿真结果表明,采用四维16QAM映射的BICM-ID系统大幅改善了系统的渐进性能。

分簇频谱检测报告信道的信噪比墙及性能分析

分簇算法是感知无线电频谱检测的重要方案,它包括次级用户到簇头和簇头到融合中心2种报告信道,本文研究这2种报告信道不理想时对系统检测性能的限制。针对目前"误比特率墙"的问题,本文提出"信噪比墙"的指标。首先推导在监听信道不同信噪比和2种报告信道都不理想的情况下,系统检测概率和虚警概率的通式;然后得出报告信道上信噪比墙的存在,并分析在不同信道分布和不同调制方式下,2种报告信道的信噪比墙对系统整体检测性能的影响。仿真结果显示,理论值与仿真结果吻合,所得结论对分簇算法的设计和实际应用具有重要的意义。

Low complexity suboptimal decode algorithms for quasi- orthogonal space time block codes

Due to the high complexity of the pairwise decoding algorithm and the poor performance of zero forcing（ ZF） /minimum mean square error（ MMSE） decoding algorithm, two low-complexity suboptimal decoding algorithms, called pairwisequasi-ZF and pairwise-quasi-MMSE decoders, are proposed. First,two transmit signals are detected by the quasi-ZF or the quasiMMSE algorithm at the receiver. Then, the two detected signals as the decoding results are substituted into the two pairwise decoding algorithm expressions to detect the other two transmit signals. The bit error rate（ BER） performance of the proposed algorithms is compared with that of the current known decoding algorithms.Also, the number of calculations of ZF, MMSE, quasi-ZF and quasi-MMSE algorithms is compared with each other. Simulation results showthat the BER performance of the proposed algorithms is substantially improved in comparison to the quasi-ZF and quasiMMSE algorithms. The BER performance of the pairwise-quasiZF（ pairwise-quasi-MMSE） decoder is equivalent to the pairwiseZF（ pairwise-MMSE） decoder, while the computational complexity is significantly reduced.

载波聚合下PUCCH格式3的双路RM编译码研究与DSP实现

LTE-A系统中新引入PUCCH格式3,可以反馈最多20个比特的下行ACK/NACK。由于比特数的限制,PUCCH格式3不能用常规的Reed Muller编码,而是用两路的RM编码。文章首先介绍常规双路RM编译码和重叠RM编译码,然后仿真分析不同算法的性能,其中重叠RM具有更好的误码率和吞吐量性能,最后用DSP实现双路RM编译码。

一种降低SC-FDMA信号峰均比的低复杂度方法

针对已有方法复杂度过高或者需要引入额外带宽的缺点,在深入分析单载波频分多址(SC-FDMA)信号大峰值形成原因的基础上,提出了一种不需要额外带宽的简单易行的降峰均比(PAPR)方法。所提方法以引入极少数误比特为代价将造成SC-FDMA信号PAPR值高于给定数值的星座图外部星座点变换为内部星座点,使得发送信号的PAPR大大降低。在收端经过信道译码,可大大减少星座变换带来的极少数误比特。提出的方法所需计算量很低,不会增加额外的带宽开销,同时可有效地降低发送信号的PAPR。

10 Gbit/s PRBS tester implemented in FPGA

The design of an FPGA（ field programmable gate array） based programmable SONET （synchronous optical network） OC-192 10 Gbit/s PRBS （pseudo-random binary sequence） generator and a bit interleaved polarity 8 （BIP-8） error detector is presented. Implemented in a parallel feedback configuration, this tester features PRBS generation of sequences with bit lengths of 2^7 - 1,2^10- 1,2^15 - 1,2^23 - land 2^31 - 1 for up to 10 Gbit/s applications with a 10 Gbit/s optical transceiver, via the SFI-4 （OC-192 serdes-framer interface）. In the OC-192 frame alignment circuit, a dichotomy search algorithm logic which performs the functions of word alignment and STM-64/OC192 de-frame speeds up the frame sync logic and reduces circuit complexity greatly. The system can be used as a low cost tester to evaluate the performance of OC-192 devices and components, taking the replacement of precious commercial PRBS testers.

Downlink BER performance analysis of distributed antenna systems over shadowed Rayleigh fading channels

Due to the complexity of the composite fading channel, a new simplified channel model is proposed to analyze the bit error ratio（BER） performance of the distributed antenna system （DAS）. First, instead of the gamma-log-normal distribution, the log-normal distribution is applied to describe the output signal to noise ratio（SNR） after maximal ratio combining （MRC） at the receiver. Then, assuming that the channel state information（CSI） is available to the transmitter, by employing the Gauss-Hermite integral, an approximate analytical expression of the BER is derived for the downlink of the DAS with antenna selective transmission and MRC. Finally, the results of a Monte Carlo simulation show that the analytical results match the simulation results. Therefore, it can be concluded that the proposed approximate channel model is effective and accurate, and the derived analytical expression can be used to evaluate the real system performance.

A cooperative user selection scheme based on energy efficiency and interference factor in cooperative communication systems

With the rapid development of green communications,energy consumption issue plays more and more important role in cooperative communication strategies and communication systems.Based on cooperative transmission model,a cooperative user selection scheme is proposed in consideration of both energy efficiency and interference factor.With the proposed scheme,the selected cooperative user consumes less energy and receives less interference.Furthermore,the main factor is analyzed to affect system performance,including signal-to-noise ratio(SNR)of source user and cooperative user,distance between source user and cooperative user or base station(BS),and fading factor in the transmission model.Through the proposed scheme,energy consumption and influence of interference are jointly taken into account during the cooperative user selection process.Besides,bit error rate(BER)in proposed scheme is also superior to existing schemes.Simulation results are presented to show the performance improvement of the proposed scheme.

Non-Line-of-Sight Ultraviolet Communication Performance in Atmospheric Turbulence

Non-Line-of-Sight(NLOS)Ultraviolet(UV)communication uses the atmosphere as a propagation medium.As the communication range increases,turbulence becomes a significant atmospheric process that affects the propagation of optical waves.This paper presents a more accurate NLOS channel model by considering turbulence-induced Scintillation Attenuation(SA).Then,the Bit Error Rate(BER)during turbulence of the NLOS UV communication system with On-Off Keying(OOK)modulation and Maximum Likelihood(ML)detection is analysed and compared with that in free space without turbulence.The BER dependence is also analysed for different factors,including the refractive index structure parameter,transceiver range,pointing angles,transmitted power,and data rate.

Performance of an Improved One-Way Error Reconciliation Protocol Based on Key Redistribution

In data post-processing for quantum key distribution, it is essential to have a highly efficient error reconciliation protocol. Based on the key redistribution scheme, we analyze a one-way error reconciliation protocol by data simulation. The relationship between the error correction capability and the key generation efficiency of three kinds of Hamming code are demonstrated. The simulation results indicate that when the initial error rates are （0,1.5%], （1.5,4%], and （4,11%], using the Hamming （31,26）, （15,11）, and （7,4） codes to correct the error, respectively, the key generation rate will be maximized. Based on this, we propose a modified one-way error reconciliation protocol which employs a mixed Hamming code concatenation scheme. The error correction capability and key generation rate are verified through data simulation. Using the parameters of the posterior distribution based on the tested data, a simple method for estimating the bit error rate （BER） with a given confidence interval is estimated. The simulation results show that when the initial bit error rate is 10.00%, after 7 rounds of error correction, the error bits are eliminated completely, and the key generation rate is 10.36%; the BER expectation is 2.96×10^-10, and when the confidence is 95% the corresponding BER upper limit is 2.17×10^-9. By comparison, for the single （7,4） Hamming code error reconciliation scheme at a confidence of 95%,the key generation rate is only 6.09%, while the BER expectation is 5.92x 10＂9, with a BER upper limit of 4.34×10^-8. Hence, our improved protocol is much better than the original one.

BER ANALYSIS OF A GMSK SYSTEM USING DECISION FEEDBACK

There are considerable literatures on the Bit Error Rate(BER)evaluation of DifferentialDetection of Gaussian Minimum Shift Keying(DDGMSK)system using Decision Feedback(DF),butmost of them give the performance based on the Monte Carlo Error Counting(MCEC)technique.Fromthe probability distribution of the phase angle between two vectors perturbed by Gaussian noises,theformulae of BER are derived for the performance analysis of DDGMSK system with DF in this letter.Considering the m-bit dock-tailed sequence,the new formulae of Gaussian Minimum Shift Keying(GMSK)modulated phase and the Time-Varying Signal to Noise Ratio(TVSNR)of the demodulatedsignal are presented,and it is proved that the relationship between the TVSNR of the demodulatedsignal and the size of eye opening is not inevitable.Simulation results show that the theoretical in-vestigation gives analogous results with the MCEC technique.The formulae presented are useful for theperformance analysis of systems using GMSK as modulating and demodulating method,for instance,the analysis of synchronous performance of frequency-hopping communication system.

A High-Speed Bi-Directional Visible Light Communication System Based on RGB-LED

In this paper, we propose and experimentally demonstrate a bi-directional indoor communication system based on visible light RGB-LED. Spectrally efficient modulation formats （QAM-OFDM）, advanced digital signal processing, pre- and post- equalization are adopted to compensate the severe frequency response of indoor channel. In this system, we utilize red-green-blue Light emitting diodes （LEDs）, of which each color can be used to carry different signals. For downlink, the low frequencies of each color are used while for uplink, the high frequencies are used. The overall data rate of downlink and uplink are 1.15-Gb/s and 300-Mb/s. The bit error ratios （BERs） for all channels after 0.7 m indoor delivery are below pre-forward- error-correction （pre-FEC） threshold of 3.8×10-3. To the best of our knowledge, this is the highest data rate in bi-directional visible light communication system.

THE PERFORMANCE OF MT-CDMA SYSTEM IN THE PRESENCE OF CARRIER FREQUENCY OFFSET

In this letter,the sensitivity of an uplink Multi-Tone Code-Division Multiple Access (MT-CDMA) system to the Carrier Frequency Offset (CFO) is investigated. The analytical expression for the Bit Error Rate (BER) of uplink MT-CDMA in the presence of CFO is derived in a multipath Rayleigh fading channel which is verified through simulations. Both Maximal Ratio Combining (MRC) and Equal Gain Combining (EGC) are considered in combining multipath signals in the analysis. It is found that the BER performance can be improved with the number of multipath increasing in the presence of CFO.

Integration Interval Determination and Decision Threshold Optimization for Improved TRPC-UWB Communication Systems

Integration interval and decision threshold issues were investigated for improved transmitted reference pulse cluster （iTRPC-） ultra-wideband （UWB） systems. Our analysis shows that the bit error rate （BER） performance of iTRPC-UWB systems can be significantly improved via integration interval determination （IID） and decision threshold optimization. For this purpose, two modifications can be made at the autocorrelation receiver as follows. Firstly, the liD processing is performed for autocorrelation operation to capture multi-path energy as much as possible. Secondly, adaptive decision threshold （ADT） instead of zero decision threshold （ZDT）, is used as estimated optimal decision threshold for symbol detection. Performance of iTRPCUWB systems using liD and ADT was evaluated in realistic IEEE 802.15.4a UWB channel models and the simulation results demonstrated our theoretical analysis.

Performance of Physical-Layer Network Coding in Asymmetric Two-Way Relay Channels

In this paper, we study the performance of physical-layer network coding in asymmetric two-way relay channels using four different cases having different poor channels:phase asymmetry, downlink asymmetry, uplink asymmetry and node asymmetry. The decision and mapping rule for symmetric and asymmetric cases are studied. The performance in terms of bit error rate for each case will be studied and analysed by computer simulation. Analytical and simulation results show that uplink asymmetry is the worst case;intra-phase asymmetry and unreliable uplink channels will more severely affect the performance degradation, which is caused by channel asymmetry.

A new support vector machine based multiuser detection scheme

In order to suppress the multiple access interference (MAI) in 3G, which limits the capacity of a CDMA communication system, a fast relevance vector machine (FRVM) is employed in the multiuser detection (MUD) scheme. This method aims to overcome the shortcomings of many ordinary support vector machine (SVM) based MUD schemes, such as the long training time and the inaccuracy of the decision data, and enhance the performance of a CDMA communication system. Computer simulation results demonstrate that the proposed FRVM based multiuser detection has lower bit error rate, costs short training time, needs fewer kernel functions and possesses better near-far resistance.

Guaranteeing Wireless Communication Secrecy via a WFRFT-Based Cooperative System

In this paper, a weighted fractional Fourier transform(WFRFT) based cooperative overlay system, aiming to guarantee physical layer(PHY) security, is proposed. The paper elaborates how WFRFT and physical layer properties of the wireless medium are collaborated to guarantee the secrecy of wireless transmissions. In the proposed system, WFRFT is first preform on the secret data, such that the transmitted signal is distorted and can only be neutralized by inverse-WFRFT with the same parameter. And then two streams of the transformed sequences that bearing different messages are cooperatively and simultaneously transmitted to two legitimate receivers via a beamforming-liked method, respectively. In general, both the rapid spatial decorrelation property and the inherent security features of WFRFT are leveraged, such that only the eavesdropper's is degraded, and hence, the wireless communication secrecy is reliably guaranteed. Numerical simulations are conducted to evaluate the performance of the proposed system in terms of the average bit error rate and the secrecy capacity.

Quality of Service Improvement for High-Speed Railway Communications

With the fast development of highspeed railways,a call for fulfilling the notion of communication at "anytime,anywhere" for high-speed train passengers in the Train Operating Control System is on the way.In order to make a realization of that,new railway wireless communication networks are needed.The most promising one is the Long Term Evolution for Railway which will provide broadband access,fast handover,and reliable communication for high mobility users.However,with the increase of speed,the system is subjected to high bit error rate,Doppler frequency shift and handover failure just like other system does.This paper is trying to solve these problems by employing MIMO technique.Specifically,the goal is to provide higher data rate,higher reliability,less delay,and other relative quality of services for passengers.MIMO performance analysis,resource allocation,and access control for handover and various services in a two-hop model are proposed in this paper.Analytical results and simulation results show that the proposed model and schemes perform well in improving the system performances.