多载波码分多址系统在瑞利衰落信道中的性能分析

多载波码分多址(MC-CDMA)是一种把多载波和CDMA相结合的技术方案。在MC-CDMA中,每个数据符号通过N个子载波传输,且根据扩频码对每个子载波以0或π相位偏移进行编码。分别研究了MC-CDMA系统上行链路和下行链路的瑞利衰落信道模型以及采用等增益组合和最大比组合的接收机模型,并对上行链路和下行链路的系统误码率性能进行了分析和计算。数值结果表明,MRC在上行链路中的性能要优于EGC,但在下行链路中的抗干扰性能不如EGC。     

支持MIMO链路的Ad hoc网络中的链路激活型拓扑未知MAC协议

该文提出了支持多输入多输出(MIMO)链路的Ad hoc网络的链路激活型拓扑未知多址接入协议。该协议利用正交拉丁方来为网络链路分配传输时隙,保证每个链路在1帧中至少有1个时隙可以成功传输。推导了该协议的平均吞吐量,并以最大化平均吞吐量为准则给出了选择协议参数的方法。数值结果表明,与已有链路激活型和节点激活型拓扑未知协议相比,本文的协议可以提高网络节点的吞吐量。     

基于DFT扩频的广义多载波频分多址上行链路传输方案——DFT-S-GMC

针对宽带移动通信上行链路传输,提出一种基于离散傅立叶变换(DFT)的广义多载波(GMC)频分多址方案--DFT-S-GMC.该传输方案采用DFT进行频域扩频,采用逆滤波器组变换(IFBT)实现频分复用和频分多址.理论分析和仿真表明,与现有主流上行多址方案(如OFDMA和DFT-S-OFDMA)相比,该方案具有较低的峰均比,并且对由上行用户间的定时和频率同步误差导致的多址干扰有较强的顽健性.     

一类基于分布式多天线的多基站协作传输方案

文章提出了一类基于分布式多天线的多基站协作传输方案，主要分析了该类方案在小区边缘用户链路可靠性方面的性能。仿真表明，该类方案不仅可以显著提高链路可靠性，在保持甚至提高吞吐量的情况下也可以提供优异的性能，未来将有很好的应用前景。     

基于正交变换的广义多载波系统自适应传输方案

针对基于正交变换的广义多载波系统(OT-GMC),提出一种正交变换模式和调制编码方式联合自适应的单载波混合传输方案。该方案以最大化频谱效率为优化准则,依据接收信号的信干噪比(SINR)自适应切换正交变换模式和调制编码方式。当正交变换采用恒等变换时,对子带数据进行独立的链路自适应,提高了频谱效率。当正交变换采用离散傅里叶变换时,发射信号具有较低的峰均比,提高了发射端的功放效率。该传输方案实质上获得了单载波混合传输系统内频谱效率和峰均比的最优化折中性能。仿真表明,多径信道下该混合传输方案的吞吐量性能优于单一传输方案。     

基于多跳协同传输的物联网系统性能研究

针对物联网系统中多跳协同传输的场景,为满足低功耗和高可靠等系统传输要求,提出了目的节点利用收发端直达链路和多跳中继协同链路的最大比合并实现信号的分集接收的传输方案.其中源节点到目的节点的直达径传输和多跳协同传输信道均服从Nakagami-m分布,该分布可涵盖瑞利分布和莱斯分布等信道特性,增加了理论分析的难度.本文在获得接收端信噪比的概率密度函数闭合表达式的基础上,利用概率密度函数分析法和积分特性等方法,在无任何函数近似的条件下,推导出了基于多跳协同传输的物联网系统中断概率和误码率的闭合表达式.通过数值仿真验证了所提方案的有效性和理论分析的正确性.     

模糊聚类CIAP在雷达组网中的应用

随着雷达网络传输技术的发展,雷达网络中的数据拥塞和流量分配不均衡问题亟待解决.文中针对多个被覆线与无线AP所组成的雷达传输网络中的流量分配不均衡问题,对多链路负载均衡算法(CIAP)中的任务调度算法进行改进.算法依据网络传输链路本身的固有特性,在进行链路碎片调度时,采用模糊聚类的思想对任务调度算法进行改进,该算法根据网络中各链路的剩余带宽和链路时延对负载较大的链路的路由碎片进行实时调度.实验结果表明,与传统的基于循环招标任务调度的多链路负载均衡算法比较,改进的算法能够迅速高效地均衡雷达网络中的链路负载.     

民航空地通信中的多链路数据分配算法

针对民航空地通信数据丢失率高、吞吐量低问题,提出了一种基于丢包感知负载均衡(Packet Loss-Aware Load Balancing)的分配算法。在空地多链路通信中,每条链路的数据损失率随着链路状态与传输环境等情况实时变化。该算法通过控制每次空地通信中数据流的分割比率,动态分配给每条链路不同大小的数据流,使每条链路的传输损失率趋于相近,提高了空地通信系统吞吐量并减少了数据传输损失,以应对空地通信中丢包率高与吞吐量低等问题。仿真结果表明,所提算法在数据传输损失率和吞吐量上都优于现有的多链路子流分配算法。     

多跳分集系统中一种新的基于无比率编码的跨层方案

研究了多跳分集系统中由于链路的不可靠传输直接应用实用网络编码存在差错的扩散和传播问题.提出了一种新的基于无比率编码的跨层方案,该方案利用无比率编码的纠错能力及实用网络编码码字随机特性,控制了输入链路的差错扩散和传播.结果表明,在满足每条链路误包率一定的情况下,该方案获得了较好的差错性能.进一步分析了为了使每条链路达到给定的误包率,无比率编码在不同信噪比下的冗余.     

OFDM-ROF下行链路的性能研究

OFDM技术与ROF技术结合为实现低成本、高速数据传输的移动网络提供了可能,但光纤链路的非线性以及无线信道的多径衰落降低了系统性能。在建立ROF下行链路的传输函数模型基础上,分析ROF下行链路对OFDM信号性能的影响。传输模型包括激光器,光纤链路以及无线信道。分析在不同光调制指数、光纤长度及无线多径信道下接收信号的误差矢量、三阶非线性失真和互调失真。仿真结果显示：随着调制指数、光纤长度的增加,以及无线信道的多径衰落使得接收信号性能下降。此分析为OFDM-ROF下行链路的线性化以及无线信道均衡方案选择提供了理论基础。     

Optical Communication Using Subcarrier PSK Intensity Modulation Through Atmospheric Turbulence Channels

This paper studies optical communications using subcarrier phase shift keying (PSK) intensity modulation through atmospheric turbulence channels. The bit error rate (BER) is derived for optical communication systems employing either on/off key (OOK) or subcarrier PSK intensity modulation. It is shown that at BER = 10^-6 and a scintillation level of sigma = 0.1, an optical communication system employing subcarrier BPSK is 3 dB better than a comparable system using fixed-threshold OOK. When sigma = 0.2, an optical communication system employing subcarrier BPSK achieves a BER = 10^-6 at SNR = 13.7 dB, while the BER of a comparable system employing OOK can never be less than 10^-4. Convolutional codes are discussed for optical communication through atmospheric turbulence channels. Interleaving is employed to overcome memory effect in atmospheric turbulence channels. An upper bound on BER is derived for optical communication systems employing convolutional codes and subcarrier BPSK modulation.     

Impact of large Doppler on error performance of FH/MFSK with RS orBCH coding in Rayleigh and Rician fading

The degradation of performance caused by Doppler shift to frequency hopped (FH)/M-ary frequency shift keying (MFSK) Reed-Solomon (RS) coded signal over a Rayleigh and Rician channel is analyzed. The receiver employs a digital processing scheme, consisting of an analog-to-digital (A/D) converter followed by quadrature decomposition and complex-valued envelope discrete Fourier transformation (DFT). Predecoder symbol error probability and post-decoder word error probability are presented as a function of Doppler shift, channel randomness parameter, and the symbol energy-to-noise ratio. The noise is assumed to be white and Gaussian distributed. Results show that for a typical symbol error rate of 10^-3, the margin for 8-ary uncoded transmission must be increased by 8 dB to account for Doppler in a Rician fading channel     

Proposal for Beyond 100-Gb/s Optical Transmission Based on Bit-Interleaved LDPC-Coded Modulation

An iterative bandwidth-efficient coded modulation scheme based on bit-interleaving low-density parity-check (LDPC) codes, and M-ary differential phase-shift keying is proposed. A bit-interleaved LDPC-coded scheme, carrying 3 bits/symbol, provides the coding gain of 8.3 dB at a bit-error rate (BER) of 10^-7. The expected coding gain at BER of 10^-12 is 12.8 dB. Possible applications include 100G Ethernet, and high-speed (>100 Gb/s) long-haul transmission     

Data detection of MPSK in the presence of rapidly changing carrierphase

We present a novel method for data detection of M-ary phase shift keying (MPSK) in the presence of unknown carrier phase and additive white Gaussian noise. Here, the unknown carrier phase is rapidly changing and random. That is, the unknown phase changes from symbol to symbol in a nondeterministic manner. The rate of phase change is such that phase change over two symbol intervals is negligible, but it is not necessarily negligible over a longer interval. Our proposed system outperforms traditional differential phase shift keying (DPSK) by 1.5 dB at error probabilities of 10^-3 and 10^-4. We also compare the performance of our scheme with that of multiple symbol differential detection (MSDD). Except under very slow phase change conditions, our scheme outperforms MSDD. Our decoder is well suited to mobile communication systems. Here, receivers usually move with different speeds at different times     

An adaptive modulation scheme for simultaneous voice and datatransmission over fading channels

We propose a new adaptive modulation technique for simultaneous voice and data transmission over fading channels and study its performance. The proposed scheme takes advantage of the time-varying nature of fading to dynamically allocate the transmitted power between the inphase (I) and quadrature (Q) channels. It uses fixed-rate binary phase shift keying (BPSK) modulation on the Q channel for voice, and variable-rate M-ary amplitude modulation (M-AM) on the I channel for data. For favorable channel conditions, most of the power is allocated to high rate data transmission on the I channel. The remaining power is used to support the variable-power voice transmission on the Q channel. As the channel degrades, the modulation gradually reduces its data throughput and reallocates most of its available power to ensure a continuous and satisfactory voice transmission. The scheme is intended to provide a high average spectral efficiency for data communications while meeting the stringent delay requirements imposed by voice. We present closed-form expressions as well as numerical and simulation results for the outage probability, average allocated power, achievable spectral efficiency, and average bit error rate (BER) for both voice and data transmission over Nakagami-m fading channels. We also discuss the features and advantages of the proposed scheme. For example, in Rayleigh fading with an average signal-to-noise ratio (SNR) of 20 dB, our scheme is able to transmit about 2 bits/s/Hz of data at an average BER of 10 ^-5 while sending about 1 bit/s/Hz of voice at an average BER of 10^-2     

A 6-Gb/s Wireless Inter-Chip Data Link Using 43-GHz Transceivers and Bond-Wire Antennas

A 43-GHz wireless inter-chip data link including antennas, transmitters, and receivers is presented. The industry standard bonding wires are exploited to provide high efficiency and low-cost antennas. This type of antennas can provide an efficient horizontal communication which is hard to achieve using conventional on-chip antennas. The system uses binary amplitude shift keying (ASK) modulation to keep the design compact and power efficient. The transmitter includes a differential to single-ended modulator and a two-stage power amplifier (PA). The receiver includes a low-noise amplifier (LNA), pre-amplifiers, envelope detectors (ED), a variable gain amplifier (VGA), and a comparator. The chip is fabricated in 180-nm SiGe BiCMOS technology. With power-efficient transceivers and low-cost high-performance antennas, the implemented inter-chip link achieves bit-error rate (BER) around 10^-8 for 6 Gb/s over a distance of 2 cm. The signal-to-noise ratio (SNR) of the recovered signal is about 24 dB with 18 ps of rms jitter. The transmitter and receiver consume 57 mW and 60 mW, respectively, including buffers. The bit energy efficiency excluding test buffers is 17 pJ/bit. The presented work shows the feasibility of a low power high data rate wireless inter-chip data link and wireless heterogeneous multi-chip networks.     

The error performance of CD900-like cellular mobile radio systems

The symbol error performance of CD900-like digital cellular mobile radio systems over narrowband and urban wideband transmission channels was investigated. The basic performance is presented for Gaussian, flat-fading Rayleigh, and log-normal channels in the presence of selection and ratio combining space diversity schemes. For wideband channels having more than one resolvable fading path, a CD900-like system without diversity reception suffers from large residual symbol error probabilities P_R(≈10^-1). The introduction of adaptive correlation diversity (ACD) mitigates the effects of multipath, yielding a P_R of 6×10^-5. Although this P_R value is relatively low, the probability of symbol error (P_e) versus signal-to-noise ratio (SNR) is significantly poorer than for the Gaussian channel. By combining the ACD scheme with space diversity, the P_R is eliminated by P_e >10^-5, and the channel SNR is within 5 dB of the Gaussian channel performance when P_e is 10^-10     

Nakagami衰落信道上组合SC/MRC的性能分析

研究Nakagami衰落信道上组合发射机选择合并(SC)/接收机最大比合并(MRC)天线分集系统的性能.使用矩生成函数方法,推导采用组合SC/MRC天线分集和相干检测的MPSK(M进制相移键控)、MQAM(M进制正交幅度调制)、MPAM(M进制脉冲幅度调制)、BFSK(二进制频移键控)、最小相关BFSK(BFSKmin)、差分编码BPSK(DE-BPSK)和预编码MSK(最小频移键控)等几种M进制数字调制方式在Nakagami衰落信道上的误符号率性能,获得了M进制数字调制系统误符号率性能的精确数学表达式.数值计算结果阐明了发射天线和接收天线数目以及衰落参数对数字调制系统误符号率性能的影响.     

Symbol Error Probabilities for M-ary CPFSK: Coherent and Noncoherent Detection

Continuous-phase frequency shift keying (CPFSK) is discussed and theoretical predictions for symbol error probabilities are derived, where the memory inherent in the phase continuity is used to improve performance. Previously known results concluded that binary CPFSK can outperform coherently detected PSK at high SNR. New results presented here show thatM-ary CPFSK outperforms more tranditionally usedM-ary modulation systems. Specifically, coherently detected quaternary CPFSK with a five-symbol interval decision can outperform coherent QPSK by 3.5 dB, and octal coherent CPFSK with a three- symbol decision can outperform octal orthogonal signaling by 2.6 dB at high SNR. Results for coherently detected and noncoherently detected CPFSK are derived. These performance improvements are estimates derived from symbol error probability upper bounds. Monte Carlo simulation was performed which then verified the results.     

Differential space time block codes using nonconstant modulus constellations

We propose differential space time block codes (STBC) using nonconstant modulus constellations, e.g., quadrature amplitude modulation (QAM), which cannot be utilized in the conventional differential STBC. Since QAM constellations have a larger minimum distance compared with the phase shift keying (PSK), the proposed method has the advantage of signal-to-noise ratio (SNR) gain compared with conventional differential STBC. The QAM signals are encoded in a manner similar to that of the conventional differential STBC. To decode nonconstant modulus signals, the received signals are normalized by the channel power estimated forgoing training symbols and then decoded with a conventional QAM decoder. Assuming the knowledge of the channel power at the receiver, the symbol error rate (SER) bound of the proposed method under independent Rayleigh fading assumption is derived, which shows better SER performance than the conventional differential STBC. When the transmission rate is more than 3 bits/channel use in time-varying channels, the simulation results demonstrate that the proposed method with the channel power estimation outperforms the conventional differential STBC. Specifically, the posed method using the channel power estimation obtains a 7.3 dB SNR gain at a transmission rate of 6 bits/channel use in slow fading channels. Although the performance gap between the proposed method and the conventional one decreases as the Doppler frequency increases, the proposed method still exhibits lower SER than the conventional one, provided the estimation interval L is chosen carefully.