基于压缩感知的MIMO-OFDM信道估计中一种确定性导频设计

压缩感知理论作为一种新的采样理论,因其采样少,恢复效果好等特点被学术界广泛关注。虽然传统的信道估计算法已经达到了非常不错的效果,但随着科技的发展,人们对信息传输速度和传输质量的需求不断增加,传统算法占用频带资源大、计算复杂度高等缺点就变得越发凸显。于是开始使用压缩感知理论进行信道估计。在使用压缩感知理论对多入多出正交频分复用(MIMO-OFDM)系统进行信道估计的过程中,提出一种导频的设计方法。最后,选定训练序列与几种既有的导频选择法相结合,通过仿真演示提出算法的效果,仿真结果表明提出的方法估计效果较好。     

Symbol-aided channel estimation with nonselective Rayleigh fadingchannels

New algorithms are proposed to implement coherent detection of PSK signals transmitted over frequency-flat Rayleigh channels. Channel gain estimates are derived both from known symbols multiplexed with the data stream and from tentative data decisions. The performance of these algorithms is assessed by computer simulation with uncoded and trellis-coded modulation. Comparisons are also made with differentially coherent detection (DPSK) and with perfect coherent detection (corresponding to ideal knowledge of the fading process). Simulation results demonstrate that these algorithms can track adequately the severe fading fluctuations encountered on a Rayleigh channel and that their superiority over DPSK becomes impressive with fast fading     

A deterministic digital simulation model for Suzuki processes withapplication to a shadowed Rayleigh land mobile radio channel

We present a novel computer simulation model for a land mobile radio channel. The underlying channel model takes for granted non-frequency-selective fading but considers the effects caused by shadowing. For such a channel model we design a simulation model that is based on an efficient approximation of filtered white Gaussian noise processes by finite sums of properly weighted sinusoids with uniformly distributed phases. In all, four completely different methods for the computation of the coefficients of the simulation model are introduced. Furthermore, the performance of each procedure is investigated on the basis of two quality criteria. All the presented methods have in common the fact that the resulting simulation model has a completely determined fading behavior for all time. Therefore, the simulation model can be interpreted as a deterministic model that approximates stochastic processes such as Rayleigh, log-normal, and Suzuki (1977) processes     

Study on application of CMA to land mobile LEO satellite communication systems based on a deterministic channel model

This paper studies the application of the constant modulus algorithm (CMA) in land mobile low earth orbit (LEO) satellite communication systems. Two propagation phenomena prevail in narrow band land mobile LEO satellite channel, namely, adjacent channel interference (ACI) and frequency‐non‐selective fading. The performance of CMA for ACI cancellation and the behaviours of CMA in frequency‐non‐selective fading channels are evaluated using a digital beamforming (DBF) array antenna simulation scheme. All these evaluations are based on a simple but efficient channel model which provides a good and fast simulation method for land mobile LEO satellite channels. The restricted Jakes Doppler power spectral density (psd) function is incorporated into the model to ensure that it will be appropriate for the evaluation of a DBF antenna. Our results reveal that CMA can reject ACI and work well in frequency‐non‐selective fading channels. Copyright © 2002 John Wiley & Sons, Ltd.     

On channel estimation and sequence detection of interleaved codedsignals over frequency nonselective Rayleigh fading channels

Due to the receiver complexity introduced by interleaving, the implementation of maximum likelihood (IML) decoding of interleaved coded signals transmitted over frequency nonselective Rayleigh fading channels has been shown to be practically impossible. As an alternative, a two-stage receiver structure has been proposed, where the channel estimation and sequence decoding are done separately. The channel estimation issue in a two-stage receiver is examined in detail in this paper. It is shown that although an optimum (maximum a posteriori (MAP)) channel estimation is not possible in practice, it can be approached asymptotically by joint MAP estimation of the channel and the coded data sequence. The implementation of the joint MAP estimation is shown to be an ML sequence estimator followed by an minimum mean-square error (MMSE) channel estimator. Approximate fill sequence estimation using pilot symbol interpolation is also studied, and through computer simulations, its performance is compared to receivers using hit sequence estimation. The effect of decision delay (DD), prediction order, and pilot insertion rate (PIR) on the reduced complexity ML sequence estimation is investigated as well. Finally, a practical receiver is proposed that makes the best compromise among the error performance, receiver complexity, DD, and power (or bandwidth) expansion due to pilot insertion     

An adaptive vector quantized flexible precoder for a dynamiccontinuous frequency selective mobile channel

Bandwidth efficient techniques are required to satisfy the demand for future public mobile radio communication systems. Precoding is a nonlinear pre-equalization technique that provides equalization equivalent to a decision-feedback equalizer (DFE) while not being affected by coding. Precoding is shown to be better than conventional equalization over a digital mobile channel that is dynamic in its characteristics. A novel precoding vector quantization scheme is applied to the prediction filter in the precoder and is shown to provide comparable results to the LMS adaptation algorithm while reducing the overheads     

DPA: a deterministic approach to the MAP problem

Deterministic pseudo-annealing (DPA) is a new deterministic optimization method for finding the maximum a posteriori (MAP) labeling in a Markov random field, in which the probability of a tentative labeling is extended to a merit function on continuous labelings. This function is made convex by changing its definition domain. This unambiguous maximization problem is solved, and the solution is followed down to the original domain, yielding a good, if suboptimal, solution to the original labeling assignment problem. The performance of DPA is analyzed on randomly weighted graphs.     

Combined frequency and differential phase shift keying withnon-coherent detection in a satellite mobile channel

We analyze the performance of combined binary frequency and M-ary differential phase shift keying (2FSK/MDPSK) in the satellite mobile channel (SMC). We use two detectors in which the frequency symbol is detected by a limiter discriminator detector (LDD) and the phase symbol by a differential phase detector (DPD). It is shown that this system is power and bandwidth efficient when compared with other systems with constant envelope (or nearly constant envelope) and noncoherent detection like L-ary DPSK (LDPSK), Gaussian minimum shift keying (GMSK) and MSK     

A characterization of the frequency selective fading of the mobile radio channel

An experiment has been designed to determine the frequency selective behavior of a mobile radio channel for a medium bandwidth (maximum of 128 kHz). The measurement technique uses a multitone approach. The transmitted signal consists of several tones (five) with fixed phase and amplitude relationships. Coherent demodulation and separation of each tone is performed at the receiving end. Quantification of the mobile radio channel is conveniently described by its frequency correlation function. Measurements for several types of environments (rural, suburban, urban) were taken and analyzed. The results characterize the amplitude and phase behaviors of a signal for each type of environment. Finally, the computations of the probability of error for a differential phase shift keying (DPSK) modulation scheme in the presence of frequency selective fading show the dominance of this factor as the signal-to-noise ratio (SNR) increases.     

Modelling the land mobile satellite channel: a review

The use of satellite systems in the implementation of third-generation mobile communication systems obviously involves a propagation environment for the signal different from that in the conventional terrestrial first- and second-generation systems. The propagation conditions and phenomena met with are embraced by the expression `land mobile satellite (LMS) channel'. This paper reviews the studies of the LMS channel reported in the literature. The various models are classified and compared in such a way that their similarities and differences are apparent     

A new frequency channel assignment algorithm in high capacity mobile communication systems

A new algorithm for frequency channel assignment in mobile radio communication is proposed. The algorithm uses flexible fixed channel assignment which enables the calls having all their nominal channels busy to borrow channels from the neighboring cells provided that co-channel interference will not result. The borrowed channel cannot be used in three interfering cells; therefore reassignment strategy is used when a call is terminated on a nominal channel to switch a call in progress in a borrowed channel to that nominal one and set free the borrowed channel in the three interfering cells. Thus the traffic carried on borrowed channels is minimized. Also different call switching strategies are proposed to give priority to some channels to be used by the nominal cells and other channels to be borrowed by neighboring cells. These strategies considerably reduce the blocking probability. A simulation study of the algorithm was carried out on 49 hexagonal zones having uniform traffic density. Also a combined telephone and dispatch traffic was included in the simulation study. The results showed that the new algorithm is better than the other channel assignment schemes. This can be applied in high capacity mobile communications systems to utilize the spectrum efficiently.     

Load frequency sampled-data control with unknown deterministic power demand

This letter presents a sampled-data load frequency control method using the Lyapunov function. The proposed method is designed so as to absorb the unknown deterministic power demand. A numerical illustration is presented in order to verify the practicality of the proposed method.     

Characteristics of a digital mobile radio channel

A field test has been made in order to better understand the digital mobile radio channel. At the mobile receiver (450 MHz, 1200 bits/s) recordings were made of the digital signal and the field strength. These recordings were later analyzed by a computer. Some existing models for digital channels have been tested. Theoretically motivated probability density functions for the fading envelope have also been considered. A new model for the digital channel is proposed. This model is a memoryless binary symmetric channel (BSC) with field strength dependent crossover error probability. This model fits very well to the recorded data.     

Non deterministic caches: a simple and effective defense against side channel attacks

Side channel cryptanalysis has received significant attention lately, because it provides a low-cost and facile way to reveal the secret information held on a secure computing system. One particular type of side channel attacks, called cache-based side channel attacks, aims to deduce information about the state of a cryptographic algorithm or its key by observing the data-dependent behavior of a microprocessor’s cache memory. These attacks have been proven successful and very hard to protect against. In this paper, we introduce the use of the Cache Decay approach as an aid to guard against cache-based side channel attacks. Cache Decay controls the lifetime (called decay interval) of the cache items and was initially proposed for cache power leakage savings. By randomly selecting the decay interval of the cache, we actually create caches with non-deterministic behavior in regard to their statistics. Thus, as we demonstrate, multiple runs of the same algorithm (performing on the same input) will result in different cache statistics, defending against the attacker and reinforcing the protection offered by the system. In our work, we use a cycle-based processor simulator, enhanced with the required modifications, in order to evaluate our proposal and show that our technique can be used effectively to protect against cache-based side channel attacks.     

Performance analysis of a deterministic channel estimator for blocktransmission systems with null guard intervals

A deterministic algorithm was proposed for channel identification in block communication systems. The method assumed that the channel has a finite impulse response (FIR) and that null guard intervals of length greater than the channel order are inserted between successive blocks to prevent interblock interference and allow block synchronization. In the absence of noise, the algorithm provides error-free channel estimates, using a finite number of received data, without requiring training sequences and without imposing a restriction neither on the channel, except for finite order and time invariance, nor on the symbol constellation. Using small perturbation analysis, we derive approximate expressions of the estimated channel covariance matrix, which are used to quantify the resilience of the estimation algorithm to additive noise and channel fluctuations. Specifically, we consider channel fluctuations induced by transmitter/receiver relative motion, asynchronism, and oscillators' phase noise. We also compare the channel estimation accuracy with the Cramer-Rao bound (CRB) and prove that our estimation method is statistically efficient at practical SNR values for any data block length. Finally, we validate our theoretical analysis with simulations and compare our transmission scheme with an alternative system using training sequences for channel estimation     

同频同调制信号的瑞利信道系统仿真设计

为了解决通信系统仿真模型的不完备性,利用Matlab的组件Simulink搭建了一套模拟信号的传输、接收、分离的接收机通信仿真模型。该模型以同频同调制信号为信源,选取多径瑞利衰落信道模拟仿真实际接收机的工作流程,并且包括信源模块、调制解调模块、信道模块、模拟接收模块、采样滤波模块、信号分离模块等。此外,系统测试了瑞利信道的路径增益对信号盲分离的影响,仿真结果表明信道增益越大,信号越集中,分离效果也相对较好。因此,该仿真系统可以与硬件系统原型相结合,为测试信号提供功能验证,为实际接收机系统运行环境提供参考建议。     

Multicarrier transmission in a mobile radio channel

A multicarrier modulation system designed for communication in a multipath, mobile radio channel is described. The effect of introducing channel coding is investigated and the improvement in BER performance is shown. A comparison is made between the modulation schemes of DPSK and DQPSK     

Optimal detection of digital data over the nonselective Rayleighfading channel with diversity reception

Based on the criterion of minimum symbol error probability, an analysis is made of symbol-by-symbol detection of a sequence of digital data transmitted using linear suppressed-carrier modulation over L independent diversity channels with AWGN (additive white Gaussian noise) and slow nonselective Rayleigh fading. The optimal receiver is derived, but is found to be difficult to implement in practice because of its exponential growth in complexity as a function of sequence length. Suboptimal decision-feedback approximations are then suggested which are linear and readily implementable and can be integrated as generalized differentially coherent receivers. The exact bit error probabilities of these suboptimal receivers are obtained. Tight upper bounds on these error probabilities are also obtained which show simply how they behave as a function of signal-to-noise ratio and order of diversity. A main conclusion of this work is that optimal data detection on a fading channel should be performed using MMSE (minimum mean squared error) estimates of the quadrature amplitudes of the channel fading processes as a coherent reference     

Implementation of a digital wide-band mobile channel simulator

This paper addresses the implementation of a powerful wide-band mobile channel simulator, which is based on two state-of-the-art 32-bit floating point DSP processors. A key feature of this simulator is the ability to be reconfigured through a common serial interface and virtually simulate a wide variety of different channel models. Additionally, this simulator can be useful to the study of space diversity for it can be arranged to provide two groups of Rayleigh fading signals whose correlation coefficient can be adjusted between zero and one