脉冲噪声和衰落环境下比特交织差分编码调制的性能

根据脉冲噪声产生的机制和Viterbi译码器的要求,提出一种利用比特度量限幅改善比特交织差分编码调制系统性能的新方法,研究结果表明,这种方法可以有效抑制脉冲噪声对差分编码调制系统性能的影响.     

Performance analysis and design optimization of LDPC-coded MIMO OFDM systems

We consider the performance analysis and design optimization of low-density parity check (LDPC) coded multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems for high data rate wireless transmission. The tools of density evolution with mixture Gaussian approximations are used to optimize irregular LDPC codes and to compute minimum operational signal-to-noise ratios (SNRs) for ergodic MIMO OFDM channels. In particular, the optimization is done for various MIMO OFDM system configurations, which include a different number of antennas, different channel models, and different demodulation schemes; the optimized performance is compared with the corresponding channel capacity. It is shown that along with the optimized irregular LDPC codes, a turbo iterative receiver that consists of a soft maximum a posteriori (MAP) demodulator and a belief-propagation LDPC decoder can perform within 1 dB from the ergodic capacity of the MIMO OFDM systems under consideration. It is also shown that compared with the optimal MAP demodulator-based receivers, the receivers employing a low-complexity linear minimum mean-square-error soft-interference-cancellation (LMMSE-SIC) demodulator have a small performance loss (< 1dB) in spatially uncorrelated MIMO channels but suffer extra performance loss in MIMO channels with spatial correlation. Finally, from the LDPC profiles that already are optimized for ergodic channels, we heuristically construct small block-size irregular LDPC codes for outage MIMO OFDM channels; as shown from simulation results, the irregular LDPC codes constructed here are helpful in expediting the convergence of the iterative receivers.     

一种改进的非线性脉冲噪声处理接收机及其性能仿真

脉冲噪声由于其冲击能量和幅度较大,会对通信系统接收机产生严重影响,为了提高通信系统接收机的性能,必须对混有脉冲噪声的接收信号进行处理,需要改进接收机。以MSK信号为例,通过对改进后的接收机性能仿真,验证了采用非线性自适应处理器改进通信接收机的可行性。     

Fourier-Bessel error performance analysis and evaluation of M-aryQAM schemes in an impulsive noise environment

Closed-form expressions are derived for the error rate performance of coherent M-ary quadrature amplitude modulated (QAM) systems in the presence of an additive combination of Gaussian and highly impulsive noise, using the Fourier-Bessel series expansion method. Analytical as well as computed simulated results are presented for 16, 64, and 256 QAM systems. The analytical results demonstrate a negligible truncation error and an accuracy ranging from approximately 1 dB for the 16 QAM scheme up to 3.5 dB for the 256 QAM scheme. The numerical evaluation of the closed-form expressions has been performed much faster than the corresponding computer simulation procedure. Hence, the validity of Fourier-Bessel analysis as a fast and accurate performance evaluation tool for high-level digital modulation schemes in complex interference environments is verified     

A dual protection scheme for impulsive noise suppression in OFDM systems

Orthogonal frequency division multiplexing (OFDM) can be susceptible to impulsive noise arising from numerous sources in a noisy communications environment. Conventional Reed–Solomon (RS) codes are particularly useful for burst-error corrections and have been employed in OFDM systems to manage impulsive noise. The performance gains, however, have been somewhat limited given the sensitivity to other noise types typically present in a noisy channel. In this regard, a novel scheme utilizing a time-domain pre-processing mean filter in combination with RS coding is proposed for impulsive noise suppression in OFDM systems. This scheme is split into two stages. In the first stage, a proposed mean filter effectively detects and removes the impulsive noise using the measured statistics of the impulsive noise. In contrast to a conventional blanking type filter, the traditional mean replacement value is replaced by a composite comparison value (CCV). This principle creates a more accurate estimate of the original OFDM signal after impulsive noise removal. The residual impulsive noise is then managed by a RS decoder in the second stage. Our results show that this dual faceted approach improves OFDM performance when compared to filtering and coding techniques alone.     

Performance of DPSK mobile receiver in impulse noise

The authors present a performance analysis of L-diversity DPSK receivers over frequency non-selective Rayleigh fading channels in Middleton's class A impulse noise. The analysis is exact and is shown by simulation to be accurate     

LDPC-based space-time coded OFDM systems over correlated fadingchannels: Performance analysis and receiver design

We consider a space-time coded (STC) orthogonal frequency-division multiplexing (OFDM) system with multiple transmitter and receiver antennas over correlated frequency- and time-selective fading channels. It is shown that the product of the time-selectivity order and the frequency-selectivity order is a key parameter to characterize the outage capacity of the correlated fading channel. It is also observed that STCs with large effective lengths and ideal built-in interleavers are more effective in exploiting the natural diversity in multiple-antenna correlated fading channels. We then propose a low-density parity-check (LDPC)-code-based STC-OFDM system. Compared with the conventional space-time trellis code (STTC), the LDPC-based STC can significantly improve the system performance by exploiting both the spatial diversity and the selective-fading diversity in wireless channels. Compared with the previously proposed turbo-code-based STC scheme, LDPC-based STC exhibits lower receiver complexity and more flexible scalability. We also consider receiver design for LDPC-based STC-OFDM systems in unknown fast fading channels and propose a novel turbo receiver employing a maximum a posteriori expectation-maximization (MAP-EM) demodulator and a soft LDPC decoder, which can significantly reduce the error floor in fast fading channels with a modest computational complexity. With such a turbo receiver, the proposed LDPC-based STC-OFDM system is a promising solution to highly efficient data transmission over selective-fading mobile wireless channels     

Analysis and comparison of several simple impulsive noise mitigation schemes for OFDM receivers

In this paper, we analyze and compare the performance of OFDM receivers with blanking, clipping and combined blanking-clipping nonlinear preprocessors in the presence of impulsive noise. Closed-form analytical expressions for the signal-to-noise ratio at the output of three types of nonlinearity are derived. Simulation results are provided that show good agreement with theory.     

Decision-directed compensation of phase noise and residual frequency offset in a space-Time OFDM receiver

This letter addresses the simultaneous perturbation of a space-time (ST) OFDM receiver by a PHase Noise (PHN) process plus a fixed but unknown residual frequency offset (RFO), and then proceeds to propose two decision-directed schemes for their joint compensation. Reduced-complexity modifications thereof are also considered, and the corresponding symbol error rate (SER) performance loss is shown to be less than 0.5 dB.     

Robust MMSE receiver employing Hampel-type nonlinear preprocessing for DS-CDMA communication in impulsive noise

A robust minimum mean square error receiver using Hampel-type nonlinear preprocessing is proposed for mitigating both unknown multiple-access interference and impulsive noise. Simulation results are presented to demonstrate the performance of the proposed receiver structure for three distinct nonlinearities in the presence of additive impulsive Gaussian noise.     

Prediction of noise and interference cancellation with a moving compact receiver array in an indoor environment

An interference and noise cancellation technique based on a reference signal is studied for a compact receiver antenna array placed in an indoor environment. The exact active element pattern method is used to model the radiation characteristics of the array, including mutual coupling between the antenna elements. A two-dimensional ray-tracing technique describes the signal propagation in the indoor environment for a moving receiving antenna.     

Performance bounds for optimum and suboptimum reception under Class-A impulsive noise

The transmission over the memoryless additive white Class-A noise (AWCN) channel is considered. For uncoded transmission, an exact expression for the symbol error rate is derived. For coded transmission, the Chernoff bound on the pairwise error probability is calculated and the performance achieved on the real and the complex AWCN channels is compared. Moreover, a low-complexity, suboptimum decoding metric is derived and analyzed employing the cutoff rate as a performance criterion.     

Performance of preamplified direct detection systems underinfluence of receiver noise

We present new results for optically preamplified direct detection systems where the receiver thermal noise is significant. The results obtained with this model is in good agreement with measured results from a system experiment at 10 Gbit/s. It is found that an optical gain of 30 dB is sufficient to keep the penalty due to thermal noise below 0.1 dB for a simple receiver consisting of a photodiode loaded with a broadband amplifier with 50-Ω input impedance     

超宽带Rake接收机的性能分析

超宽带信号经多径信道传播会产生严重的时间弥散，采用Rake接收是提高超宽带接收机性能的重要手段。文中首先介绍了加性高斯白噪声信道模型和IEEE802．15．3a标准信道模型。通过比较分析几种典型调制的超宽带冲激无线电信号的最佳接收机，推广到Rake接收机的性能分析。重点分析并仿真了不同信道、不同调制方式、不同判决方式、不同合并方式、不同速率的情况下Rake接收机的性能。     

Analytical performance evaluation of the OFDM systems in the presence of jointly fifth order nonlinearity and phase noise

This paper presents an exact theoretical analysis of the performance degradation in an orthogonal frequency division multiplexing (OFDM) system when the signal including phase noise is passed through a nonlinear circuit such as high power amplifier (HPA). This circuit is modeled as a fifth order memory-less nonlinear polynomial model (5th order MLNPM). The nonlinear model is derived from important electrical parameters such as gain, 1-dB compression and 3rd order intercept point. Theoretical analysis shows that the detected data symbol at the receiver consists of attenuated version of the original transmitted data symbol, common phase error (CPE), inter-sub-carrier interference (ICI), third and fifth order intermodulation (IM) components. The analytical expressions for intermodulation noise term are derived using combinatorial methods. By use of the derived expressions, a closed-form output signal to noise ratio (SNR), degradation factor (DF) and probability of error can be evaluated theoretically. For verifying the accuracy of our analysis, comparisons between the theoretical and simulated results with electrical parameter of an actual and applicable HPA are presented. The comparisons show that bit error rate (BER) of analytical results is closely match with simulation results for OFDM system using M-QAM modulation.     

Measurement of the impulsive noise environment for satellite-mobileradio systems at 1.5 GHz

Noise amplitude distribution measurements relevant to satellite-mobile radio systems are reported. The rationale for the measurements is outlined and the choice of measurement parameters justified. The measurement equipment and measurement methodology are described in detail. Results characterizing the elevation angle distribution of impulsive noise are presented for rural, suburban and urban environments and also for an arterial road (U.K. motorway) carrying high density, fast moving traffic. Measurements of the levels of impulsive noise to be expected in each environment for high- and low-elevation satellite scenarios using appropriate antenna configurations are also presented     

Particle filter with ant colony optimization for frequency offset estimation in OFDM systems with unknown noise distribution

Orthogonal frequency division multiplexing (OFDM) is sensitive to carrier frequency offset (CFO) that causes inter-carrier interference (ICI). In this paper, a particle filter (PF) method augmented with ant colony optimization (ACO) is developed to estimate the CFO. The ACO for continuous domains is incorporated into PF to optimize the sampling process. Unlike the standard PF, resampling is not required in the method. Moreover, it does not require the noise distribution. Simulation results show that the proposed method is effective when estimating the CFO and can effectively combat the effect of ICI in OFDM systems.     

突发OFDM接收机同步算法研究与实现

根据突发OFDM系统的特点,提出了一种具有实用价值的OFDM帧同步方法。在经典SC算法的基础上,提出了改进型SC算法和基于时域PN序列的改进型SC算法。对这两种算法进行了仿真对比,仿真结果表明基于时域PN序列的SC算法能够实现突发帧的精同步,而改进型SC算法只能实现粗同步。但是改进型SC算法更适合FPGA实现,采用Verilog HDL语言,在Quartus Ⅱ上完成开发,同时给出了其在ModelSim 6.5b下的仿真结果,结果表明,方案是完全可行的。     

Performance analysis of deliberately clipped OFDM signals

We analyze the performance of the clipped orthogonal frequency division multiplexing (OFDM) system in terms of peak power reduction capability and degradation of channel capacity. The clipping is performed on the baseband OFDM signals with and without oversampling, followed by the ideal low-pass filter. First, the effect of the envelope clipping on the peak-to-average power ratio (PAPR) and the instantaneous power of the band-limited OFDM signal is studied. We then discuss the channel capacity of the oversampled and clipped OFDM signals over the additive white Gaussian noise and ideally interleaved Rayleigh fading channels. The capacity is calculated based on the assumption that the distortion terms caused by the clipping are Gaussian. It is shown that the SNR penalty due to the clipping can be considerably alleviated by using optimal coding and reducing the information data rate. The results are justified by the simulation results using near optimal turbo codes     

OFDM接收机的系统设计和DSP实现

设计了一个OFDM接收机，并采用TI公司的TMS320C6416芯片进行实现。在假设理想同步的前提下，该系统进行了FFT变化、使用了LS（最小二乘法）进行信道估计，并且采用了QPSK算法进行解调。最后将接收机输出数据与发端数据进行比较，在不同信噪比情况下计算其误码率，得出了比较理想的结果。