Zero-rate reliability of the exponential-server timing channel

We determine the reliability function of the exponential-server timing channel (ESTC) in the limit as the data rate approaches zero. The limit shows that at low rates, the ESTC is strictly more reliable than the Poisson channel without dark current, answering a question Arikan posed in these Transactions. The proof employs a distance metric over inputs to timing channels that parallels Euclidean and Hamming distance for conventional channels. A consequence of the proof is that bounded-distance decoding, with distance measured according to this metric, is exponentially optimum for the ESTC in the low-rate regime. We also prove the straight-line bound for the channel and a bound on the reliability of timing channels with general service distributions in the limit as the data rate approaches zero.     

Mismatched decoding revisited: general alphabets, channels withmemory, and the wide-band limit

The mismatch capacity of a channel is the highest rate at which reliable communication is possible over the channel with a given (possibly suboptimal) decoding rule. This quantity has been studied extensively for single-letter decoding rules over discrete memoryless channels (DMCs). Here we extend the study to memoryless channels with general alphabets and to channels with memory with possibly non-single-letter decoding rules. We also study the wide-band limit, and, in particular, the mismatch capacity per unit cost, and the achievable rates on an additive-noise spread-spectrum system with single-letter decoding and binary signaling     

极化码编码器的硬件实现

基于信道的组合和分离,当组合信道的数量趋向于无穷大的时候,一部分信道趋向于完美的信道,而一部分信道则趋向于纯噪声信道,即信道极化现象。基于信道极化现象,可以构造极化码,通过选择性使用比较好的组合信道,其纠错能力理论上可以达到香农限。提出了一种简单的基于部分并行输入的极化码编码器的硬件结构,并进行了设计与实现。     

多片ADC并行采集系统的误差时域测量与校正

并行时间交替采样是提高系统最大采样率的有效方法之一,但由于制造工艺的局限性,并行时间交替采样将不可避免地造成通道失配误差。本文利用正弦采样信号的时域特性,推导出一种快速而精确的算法,用于同时校正通道失配引起的增益误差、偏置误差和时间误差,并通过模拟仿真证明了算法的可行性。     

A Study on Universal Codes With Finite Block Lengths

Based on random codes and typical set decoding, an alternative proof of Root and Varaiya's compound channel coding theorem for linear Gaussian channels is presented. The performance limit of codes with finite block length under a compound channel is studied through error bounds and simulation. Although the theorem promises uniform convergence of the probability of error as the block length approaches infinity, with short block lengths the performance can differ considerably for individual channels. Simulation results show that universal performance can be a practical goal as the block lengths become large.     

Secure Broadcasting Over Fading Channels

We study a problem of broadcasting confidential messages to multiple receivers under an information-theoretic secrecy constraint. Two scenarios are considered: 1) all receivers are to obtain a common message; and 2) each receiver is to obtain an independent message. Moreover, two models are considered: parallel channels and fast-fading channels. For the case of reversely degraded parallel channels, one eavesdropper, and an arbitrary number of legitimate receivers, we determine the secrecy capacity for transmitting a common message, and the secrecy sum-capacity for transmitting independent messages. For the case of fast-fading channels, we assume that the channel state information of the legitimate receivers is known to all the terminals, while that of the eavesdropper is known only to itself. We show that, using a suitable binning strategy, a common message can be reliably and securely transmitted at a rate independent of the number of receivers. We also show that a simple opportunistic transmission strategy is optimal for the reliable and secure transmission of independent messages in the limit of large number of receivers.     

非规则LDPC码在RICE信道中的性能分析

本文对非规则LDPC码在RICE信道的性能进行了分析和仿真,修正了BP译码算法,证明了RICE信道满足对称性,给出了RICE信道译码稳定性条件,推导出了RICE信道的Shannon容量限,采用VC编程对码长N=49512和3072进行了仿真,同时与同码长的Turbo码进行了比较;仿真结果表明LDPC码在码长N＝49512、码率R＝1/3时,与Shannon限相差1dB以内、在低信噪比时其性能优于Turbo码,以及LDPC码本身有很好的交织特性和抗衰落的能力;这进一步表明了LDPC码在包括RICE信道在内的各种信道中的性能都是非常优良的.     

旁瓣对消系统的对消比上限分析

构造了一个理想的旁瓣对消系统和一个理想的信号环境,分析了旁瓣对消系统的对消比上限,推导出了对消比上限的精确表达式及近似表达式,得知对消比的上限取决于辅助通道的干噪比和辅助通道的数量.最后,给出了与理论分析相一致的仿真结果.     

Amplifier-induced crosstalk in multichannel coherent lightwave systems

When an in line semiconductor laser amplifier is used to amplify several channels simultaneously, it can induce inter channel crosstalk if the amplifier gain is channel-dependent. It is shown that modulation of the carrier density at the beat frequency of two neighbouring channels can lead to considerable crosstalk even when the amplifier is operated well below the saturation level. An analytic expression for the channel gains of a travelling-wave amplifier is used to discuss and compare the crosstalk for ASK and FSK systems. The relatively short carrier lifetime in high-gain amplifiers may ultimately limit the channel spacing of such multichannel systems.     

On approaching wideband capacity using multitone FSK

In the wideband limit, certain types of "flash" signaling, such as flash frequency-shift keying (FSK), achieve the capacity of multipath fading channels. It is not clear, however, whether these asymptotic results translate into insights for practical fading channels in the finite-bandwidth, power-limited regime. It is known that, for flash FSK, the size of the input alphabet grows slowly with increasing bandwidth, leading to very high-peak power per tone. Thus, for flash FSK, the codeword probability of error decays very slowly with bandwidth and feasible rates approach the wideband capacity limit extremely slowly. Without contradicting the above results, our results in this paper point to a more optimistic outlook, from the point of view of error exponents and achievable rates, for the applicability of flash techniques in practical scenarios. We consider multitone FSK (MFSK), which has the same asymptotic capacity-achieving property as flash FSK in the wideband limit, but allows a larger input alphabet size with the same bandwidth. First, we show, using an error exponent approach, that multitone FSK allows lower peak power per tone than flash FSK. Next, we present the capacity of single-tone and two-tone FSK schemes with hard-decision detection at finite bandwidths. For typical channel parameters, the capacities are close to the wideband capacity limit.     

Single-mode fused biconical couplers for wavelength divisionmultiplexing with channel spacing between 100 nd 300 nm

The authors report on single-mode fused biconical couplers tailored to the requirements of wavelength-division-multiplexing systems. The wavelengths of the two channels can be chosen arbitrarily for wavelength separations between 100 and 30 nm. For separations between 150 and 300 nm, the couplers can be manufactured with an accuracy of ±5 nm at the two operating wavelengths. For decreasing wavelength separation of the channels, the influence of the state of polarization results in an increased inaccuracy of the two wavelengths, increased far-end crosstalk, and power fluctuations after the coupler. This sets a lower limit for channel separation. Good agreement between theory and experiment is achieved     

多输入多输出（MIMO）系统信道容量技术

本文讨论了在多输入多输出( Multiple- Input Multiple- Output,MIMO)信道上传输的基本容量极限。首先假设信道矩阵是独立的复高斯变量,按照这种理想环境推导出MIMO信道容量;最后通过对几种固定系数信道容量进行分析得出MIMO系统可以大大提高系统的信道容量     

Exploiting Multiple Antennas for Synchronization

Orthogonal frequency-division multiplex (OFDM) offers a low-complexity solution to equalization in multipath channels but does so by increasing the symbol period. This places a limit on the mobility of such systems since time variations in the channel during the symbol period introduce intercarrier interference (ICI), hence, degrading performance. Solutions to reduce ICI in the literature require a high degree of processing. Increasing terminal mobility also places greater requirements on synchronization processing to track the rapidly changing channel. This paper uses multiple antennas at the receiver so that the channel response can be decomposed into a number of more slowly varying channels. Independent synchronization processing and correction can be applied to each of the derived channels before combining the signals prior to the fast Fourier transform (FFT) process. By individually processing the channels, the effective channel is compressed in the time and frequency domains, improving system performance. Perfect tracking of the multipath clusters is initially assumed to show the potential benefits, followed by operation with an idealized tracking algorithm. Operation with more realistic processing algorithms using fixed sectored elements improving the bit error rate (BER) is investigated. Finally, the benefits are then demonstrated with real measured channels from an urban environment.      

The capacity region of broadcast channels with intersymbolinterference and colored Gaussian noise

We derive the capacity region for a broadcast channel with intersymbol interference (ISI) and colored Gaussian noise under an input power constraint. The region is obtained by first defining a similar channel model, the circular broadcast channel, which can be decomposed into a set of parallel degraded broadcast channels. The capacity region for parallel degraded broadcast channels is known. We then show that the capacity region of the original broadcast channel equals that of the circular broadcast channel in the limit of infinite block length, and we obtain an explicit formula for the resulting capacity region. The coding strategy used to achieve each point on the convex hull of the capacity region uses superposition coding on some or all of the parallel channels and dedicated transmission on the others. The optimal power allocation for any point in the capacity region is obtained via a multilevel water-filling. We derive this optimal power allocation and the resulting capacity region for several broadcast channel models     

Optimal predistortion of Gaussian inputs for clipping channels

For a clipped channel with a Gaussian input, a predistortion/restoration technique to reduce clipping-induced nonlinear distortion is proposed and analyzed. The input signal is processed by a nonlinear predistorter circuit, reducing the probability of clipping. The receiver output signal passes through a restorer having an inverse transfer characteristic, which yields the original signal. For both one-sided and two-sided limiter channels, the optimal predistortion curves are determined analytically. A limiter channel with Gaussian input may be used to model clipping-induced nonlinear distortion in optical-fiber common antenna television (CATV) distribution systems using multiple intensity-modulated subcarriers. When applied to an amplitude-modulated vestigial-sideband (AM-VSB) CATV system, the optimal predistortion curves yield sensitivity improvements of 5.3 and 4.4 dB for oneand two-sided limiter channels, respectively     

The impact of CSO/CTB distortion on BER characteristics by hybridmultichannel analog/QAM transmission systems

The FEC limit (uncorrectable errors) with CSO/CTB (composite second order/composite triple beats) distortion presence in a channel is not for modulated lasers only, but for coaxial networks with amplifiers too. The system quality reserve depends not only on CNR, but is more limited on CSO/CTB. It is important, for the definition of the system quality reserve, to calculate the CSO/CTB spectrum caused by analogue channels within analogue and digital QAM channels and also to calculate the changing of CNR from the intermodulation interaction between analog and digital channels in a CATV network     

多智能体自组织语音识别

语音感知是无人系统的重要组成部分,已有的工作大多集中于单个智能体的语音感知,受噪声、混响等因素的影响,性能存在上限。因此研究多智能体语音感知,通过多智能体自组织、相互协作,提高感知性能非常必要。假设每个智能体输出一个通道的语音流条件下,本文提出一种多智能体自组织语音系统,旨在综合利用所有通道提高感知性能;并进一步以语音识别为例,提出能处理大规模多智能体语音识别的通道选择方法。基于Sparsemax算子的端到端语音识别流注意机制,将带噪通道权重置零,使流注意力具备通道选择能力,但Sparsemax算子会将过多通道权重置零。本文提出Scaling Sparsemax算子,只将带噪较强的通道权重置零;同时提出了多层流注意力结构,有效降低了计算复杂度。在30个智能体的无人系统环境下,基于conformer架构的识别系统实验结果表明,在通道数失配的测试环境下,提出的Scaling Sparsemax在仿真数据集上的文字差错率(WER)相比Softmax降低30%以上,在半真实数据集上降低20%以上。     

一种针对转发式欺骗干扰信号的负延时补偿方法

针对卫星导航转发式欺骗干扰中转发信号存在负延时需求而工程上又无法实现的问题,提出了一种负延时补偿方法。该方法根据预设欺骗位置,通过转发式欺骗干扰延时算法,获得各卫星信号通道所需转发延时量;然后基于接收机钟差最小化原则选取最优的延时修正量添加到所有通道的转发信号中。理论分析和仿真结果表明,该方法不影响接收机的定位结果,消除了负延时无法实现的问题对转发式欺骗干扰的限制。     

Analysis of the effects of time delay spread on TCM performance

We investigate the effect of time delay spread on trellis coded modulation (TCM) in a wireless radio environment where equalization is not employed to mitigate the effects of frequency selective fading when the time delay spread is small. Using a random variable decomposition technique and a Gaussian approximation of the intersymbol interference terms, we obtain explicit bounds for the pairwise error probability of TCM over multipath Rayleigh fading channels characterized by various power delay profiles. A method to calculate an upper bound of the bit error rate (BER) based on Jamali and LeNgoc (1995) bound is also presented. These bounds are used to evaluate TCM performance as well as investigate the delay spread tolerance limit of TCM, including I-Q TCM, over frequency selective fading channels     

Channel addition/removal response in cascades of strongly invertederbium-doped fiber amplifiers

Signal power steady-state and transient fluctuations due to gain cross saturation in erbium-doped fiber amplifiers (EDFA's) in multiwavelength optical networks caused by addition or removal of channels due to network reconfigurations or line failures must be minimized to avoid error bursts in the surviving channels. The effects of addition and/or dropping of wavelength channels in a multiwavelength network comprising six concatenated strongly inverted two-stage EDFA's have been analyzed by numerical simulation. A large-signal numerical model which incorporates time variation effects and the downstream and upstream propagation of signal, pump and amplified spontaneous emission has been used. Power excursions caused in an eight channel wavelength division multiplexing (WDM) network by the loss/addition of one, three, or six channels will be lower than 0.6 dB if the length average normalized population density of the metastable level does not drop below 0.76. No additional measures need to be taken to limit the power excursions of the surviving channels