扩频多符号检测算法及实现

本文研究了差分直接序列扩频多符号检测器算法及实现.基于差分多符号检测算法,导出了差分直接序列扩频多符号检测器算法;采用声表面波(SAW)匹配滤波器和固定延迟线融合设计结构,实现了增益为13、同检符号数N=4的巴克码差分直接序列扩频多符号检测器.并对检测器的解扩解调性能进行了测试和分析.     

NOrth-BDPSK系统的比特软输出算法

本文针对Turbo编码的多进制正交扩频BDPSK复合调制(NOrth-BDPSK)系统,给出了多进制正交扩频调制的比特软值输出算法的推导过程,提出了基于最大后验概率(MAP)准则的BDPSK解调比特软值输出算法,同时给出了BDPSK解调软值的简化算法,最后进行了仿真评估,并与单纯NOrth调制系统进行比较.结果表明:NOrth-BDPSK能以较低的性能损失为代价提供更高的带宽效率.     

一种基于符号级均衡的CDMA接收机

在使用较短扩频码的CDMA系统中,多径干扰会破坏用户扩频码之间的正交性,Rake接收机性能会严重下降.本文提出了一种新的基于Rake的符号级均衡的CDMA接收机,通过分析推导出了基于最小均方误差准则的均衡系数.性能仿真结果表明这种接收机与传统的Rake接收机相比,比特误码率性能有很大的提高,可以有效抑制跨多个符号的多径干扰.     

一种基于准正交空时码的低复杂度 MIMO差分检测方法

针对可实现全速率传输的准正交空时码,提出了一种低复杂度的准正交MIMO差分检测方法.该方法在发射端对数据比特进行联合星座映射,构造准正交空时码进行差分编码;接收端采用最大似然准则对两组星座符号对(symbol pair)并行差分检测.本文提出的星座集合及联合星座映射方法简化了接收端检测算法,降低了检测计算复杂度.     

基于APSK信号的分布式MIMO差分检测方法

提出一种基于APSK信号的分布式MIMO差分编码及检测方法:发送端将待发射的数据符号与前一个发射矩阵中的数据符号进行相位和幅度差分调制,生成新的发射矩阵进行发射;接收端对接收信号匹配滤波之后,利用前后接收量判断相位信息和幅度信息恢复出发送端数据.该方法使得系统无需进行信道估计,频谱效率与V-BLAST (Vertical Bell Laboratories Layered Space-Time)相同,但不受天线数目限制,解决了传统V-BLAST算法无法进行非相干检测的难题.仿真结果显示,该算法在不同信道传播时延情况下的误码率性能不同.     

CO-OFDM系统中相位噪声和频偏的联合补偿

激光器频偏和相位噪声是限制CO-OFDM(相干光正交频分复用)系统性能的重要因素。文章提出了CO-OFDM系统中基于差分预编码和MCDD(多载波差分检测)算法的激光器相位噪声和频偏联合补偿方案。对CO-OFDM系统中的频偏和激光器相位噪声作用机理和基于MCDD的补偿方案机制进行了理论推导,并在不同的光信噪比、激光器频偏和线宽条件下进行了系统仿真。仿真结果表明,基于差分预编码和MCDD的联合补偿方法对CO-OFDM系统中的激光器频偏和相位噪声有较好的补偿效果和较大的补偿范围,在不引入系统开销的同时,可有效改善CO-OFDM系统性能。     

双多进制正交扩频系统的比特软值输出算法

该文针对双多进制正交扩频与Turbo码的联合系统,基于最大后验概率(MAP)准则,提出了双多进制正交扩频输出比特软值的MAP算法,并给出了简化MAP算法;同时,对算法的定点和浮点性能进行了仿真,且与现有的软值算法进行了比较。结果表明,MAP算法能使整个系统获得相当的增益,L=3 的简化MAP算法在基本不增加复杂度情况下好于现有的双最大值算法约0.4dB。     

多进制正交码扩频系统的解扩和同步技术及其实现

本文实现了一个Ｍ进制正交码扩频系统，它能传输２．４Ｋｂｐｓ和１６Ｋｂｐｓ两种信息速率数据并能在低信噪比条件下扩译码，文中首先讨论了该编三扩频和解扩译码的方案，其次讨论了码片采用ＭＳＫ调制时，本地载频和抽样时钟的初始相位的估计方法，然后提出承解扩译码的同时进行相位跟踪的Ｑ支路相关同步法，最后测试了系统的误比特性能。     

声表面波扩频多符号检测器算法研究

基于多符号检测的DMPSK信号处理算法在改善系统检测性能方面是一条行之有效的方法．对于直接序列扩频系统，当采用DMPSK调制方式时，同样会存在检测性能恶化问题．为此，该文提出了基于SAW匹配滤波器的DMPSK直接序列扩频多符号检测器算法，并采用13位巴克码SAW抽头延迟线和固定延迟线组合设计对符号数N=3的DBPSK扩频多符号检测算法进行了实验系统验证，给出了相应结果。     

采用广义正交序列的多载波DS-CDMA系统在瑞利衰落信道中的性能分析

在CDMA系统中，采用正交序列可以有效地减小多址干扰的影响。然后，当由于多径衰落的影响使码片间的相对移位增加时，系统中用户扩频序列间的相互正交性减弱，导致性能大大恶化。本文基于新近提出的广义正交序列，分析了采用该序列的多载波直接序列码多分址系统在瑞利衰落信道中的误比特性能。数值结果表明，当扩频序列间相互移位在零相关区之内时，扩频序列仍可保持正交，因而大大提高了系统误比特性能。     

Differential Detection with Intersymbol Interference and Frequency Uncertainty

In this paper we study differential detection of binary differential phase shift keyed (DPSK) signals with several impairments typical in satellite communication systems. In particular, the bit error rate is determined for bit timing error and frequency offset error at the receiver. The effect of a hard-limiting, band-limited repeater is also considered. The differential detector performance is determined for both conventional DPSK signals (with 0 and π phase shifts) and symmetrical DPSK signals (with- pi/2and+ pi/2phase shifts). With symmetrical DPSK, adjacent bit signals are orthogonal rather than either in or out of phase. Therefore, with intersymbol interference, the error rates for all bits are equal and the average bit error rate is less with symmetrical DPSK, as shown in this paper.     

A UNIVERSAL RECEIVER STRUCTURE FOR MDPSK SIGNALS

In this letter,a universal receiver structure with modu7lation classification and synchronization recovery for MDPSK signal is presented.The universal timing estimation algorith for M-ary DPSK signals is proposed to estimaate the best symbol timing.An identification algorithm based on fourth-order cumulants of signal is used to identify the modulation scheme of the signal.Numerical results of the preformance of the proposed receiver are given.     

Reduced state Viterbi differential phase detection of MDPSK signals

An improved differential phase detection scheme that uses a reduced state Viterbi algorithm (RSVDPD) is proposed for the reception of M-ary differential phase shift keying (MDPSK) signals. The transmitted sequence is estimated from the received signal phases only. The number of trellis states equals that of the signal constellation points M. The branch metric is computed by tracing back the surviving path connected to each state. The bit error rate (BER) performance with RSVDPD is evaluated using computer simulation for 4DPSK transmission in additive white Gaussian noise (AWGN) channels     

Nearly Shot-Noise-Limited Performance of Dual-Channel Linear Optical Sampling for Ultrafast DPSK Signals

This paper describes a newly developed dual-channel linear optical sampling technique for observing ultrafast optical differential phase-shift keying (DPSK) signals. As the proposed measurement scheme offsets two parallel interferometers by a relative delay corresponding to 1-symbol length of the DPSK signal, the measured phase distribution reflects the signal quality which is determined by the phase difference between adjacent symbols. This technique, based on interferometric optical gating by local short-pulses, also offers ultrafast measurement at symbol rates of greater than 100 Gsymbol/s. Moreover, its detection sensitivity can reach the shot noise limit. The waveform degradation caused by the coherence of the light source and the pattern effect of the phase modulator is successfully observed in continuous waves and 10-Gsymbol/s nonreturn-to-zero DPSK signals, and the constellation measurement is demonstrated for a 160-Gsymbol/s return-to-zero DPSK signal. Measurement system noise is also discussed for characterizing the detection sensitivity, and the nearly shot-noise-limited performance is experimentally verified.      

Fast detection and parameter estimation for polyphase-code radar signal

The detection and parameter estimation for polyphase-code radar signal are analysed in this article. In view of the fact that traditional algorithms of signal detection and parameter estimation have enormous computational complexity, a joint fast algorithm employed fractional operation is proposed to detect the polyphase-code radar signal and estimate its modulation parameter. The proposed algorithm firstly detects the signal and estimates the sweep rate with the detection statistics derived from fractional autocorrelation. Then proposed algorithm achieves the estimation of other modulation parameters by using fractional Fourier transform (FrFT). Simulation results have verified the effectiveness of the proposed algorithm. Compared with traditional algorithms, proposed algorithm has identical performance of detection and parameter estimation, but can remarkably reduce computational cost. The proposed algorithm is suitable for the application of practical equipment.     

Differential detection of quadrature frequency/phase modulatedsignals

This paper proposes a pilot-symbol-assisted (PSA) signaling format that enables the differential detection of the differentially phase-encoded quadrature frequency/phase modulated (NDQFPM) signal using N orthogonal frequencies. The PSA-NDQFPM signal is transmitted on a frame-by-frame structure. The channel considered is an additive white Gaussian noise channel where the channel phase varies so slowly that it is assumed constant over one frame duration. Each frame consists of J NQFPM pilot symbols and I data blocks, each containing L NDQFPM symbols, with the first symbol differentially phase encoded with respect to pilot symbols. Based on the maximum-likelihood sequence estimation principle, the maximum-likelihood differential-detection (ML-DD) algorithm is developed to detect the PSA-NDQFPM signal on a block-by-block basis. Tight upper and asymptotic bounds are derived and verified by simulation to evaluate the bit error performance of the ML-DD algorithm. Both bandwidth and power efficiencies of PSA-NDQFPM with ML-DD are compared to NQFPM with coherent detection, constant-envelope NQFPM with coherent detection, constant-envelope NDQFPM (also known as NFSK/4DPSK) with ML-DD, and conventional 2DQFPM (also known as DQ²PSK) with ML-DD. It is analytically shown that PSA-NDQFPM with ML-DD has lower power efficiency than NQFPM with coherent detection and NFSK/4DPSK with ML-DD, but still can provide noticeably higher power efficiency than DQ ²PSK with ML-DD when a medium frame length is used. Due to the use of pilot symbols, PSA-NDQFPM with a medium frame length has marginally lower bandwidth efficiency than its coherent counterpart NQFPM, but still yields significantly higher bandwidth efficiency than constant-envelope NQFPM and NFSK/4DPSK     

A WDM-PON with DPSK modulated downstream and OOK modulated upstream signals based on symmetric 10 Gbit/s wavelength reused bidirectional reflective SOA

We investigate a wavelength-division-multiplexing passive optical network (WDM-PON) with centralized lightwave and direct detection. The system is demonstrated for symmetric 10 Gbit/s differential phase-shift keying (DPSK) downstream signals and on-off keying (OOK) upstream signals, respectively. A wavelength reused scheme is employed to carry the upstream data by using a reflective semiconductor optical amplifier (RSOA) as an intensity modulator at the optical network unit (ONU). The constant-intensity property of the DPSK modulation format can keep high extinction ratio (ER) of downstream signal and reduce the crosstalk to the upstream signal. The bit error rate (BER) performance of our scheme shows that the proposed 10 Gbit/s symmetric WDM-PON can achieve error free transmission over 25-km-long fiber transmission with low power penalty.     

Adaptive Spectrum Sensing Algorithm in Cognitive Ultra-wideband Systems

Energy detection is a simple spectrum sensing technique that compares the energy in the received signal with a threshold to determine whether a primary user signal is present or not. Setting the threshold is very important to the performance of the spectrum sensing. This paper proposes an adaptive spectrum sensing algorithm where an optimal decision threshold of energy detection is derived based on minimizing the weighted sum of probabilities of detection and false alarm. Since the optimal decision threshold is dependent on the noise power and signal power, a simple, practical frequency domain approach is devised to estimate both. The algorithm can be used for the detection of various kinds of signals without any prior knowledge of the signal, channel or noise power, and is able to adapt to noise fluctuation. Simulations for detecting narrow-band and wideband signals (phase shift keying signal, frequency shift keying signal, orthogonal frequency division multiplexing signal) and ultra-wideband (UWB) signals (direct sequence spread spectrum signals) in an IEEE 802.15.3a UWB band are presented. The results show that the proposed algorithm has excellent robustness to noise uncertainty and outperforms the existing spectrum sensing algorithms in the literature.     

Semiblind Channel Estimation and Signal Detection for OFDM System with Receiver Diversity

In this paper, we address the problem of channel estimation and signal detection for orthogonal frequency division multiplexing (OFDM) system with multiple receive antennas. The received signal can be denoted as a trilinear model, and then a trilinear decomposition-based channel estimation and signal detection algorithm is proposed. Scalar ambiguity which is inherent in the blind algorithms can be easily resolved by insertion fewer pilots in the proposed algorithm. Compared with conventional subspace approaches, the proposed algorithm has improved estimation performance, and the signal detection performance of the proposed algorithm is very close to non-blind minimum mean square error (MMSE) receiver. Furthermore, our proposed algorithm works well in the presence/absence of virtual carriers, and it does not require knowledge of statistical characteristics. Simulation results illustrate performance of the algorithm.     

平面天线阵快速正交投影波束形成算法

针对大型平面天线阵列下样本数据含有期望信号时，正交投影（OP）波束形成算法不再适用的问题，提出一种新的基于阻塞矩阵的正交投影快速波束形成算法。该算法首先构造阻塞矩阵从样本信号中阻塞掉期望信号，再对阻塞后的样本信号进行施密特（GS）正交化得到重构后的干扰子空间，最后在此基础上实现正交投影波束形成。新算法适用于任意阵型的二维均匀平面阵，在小快拍数下能快速计算出自适应权重。仿真结果表明，无论是弱干扰信号还是强干扰信号，该算法都具有很好的抗干扰性能。