共查询到20条相似文献,搜索用时 15 毫秒
1.
Throughput Analysis for Code Division Multiple Accessing of the Spread Spectrum Channel 总被引:1,自引:0,他引:1
We consider the use of error correction codes of rater on top of pseudonoise (PN) sequence coding for code division multiple accessing of the spread spectrum channel. The channel is found to have a maximum throughput of 0.72 and 0.36 based on the evaluation of channel capacity and cutoff rate, respectively. More generally, these two values are derived for given bandwidth expandingn/r versusn/N wheren is the length of the PN sequence andN is the number of simultaneous users. It is found that to achieve the maximum throughput,n should be small. This implies that coding schemes with short PN sequences and low rate codes are superior in terms of throughput or antijam capability. The extreme case ofn = 1 corresponds to using a very low rate code with no PN sequence coding. Convolutional codes are recommended and analyzed for their error rate and decoding complexity. 相似文献
2.
XU Cheng qi 《中国邮电高校学报(英文版)》2000,7(3)
1 IntroductionGAARDERandWOLF[1 ] aswellasCoverandLeunghavedemonstratedthatthecapacityregionofad .m .MultipleAccessChannel(MAC)canbein 相似文献
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In this paper, we propose a robust distant-talking speech recognition by combining cepstral domain denoising autoencoder (DAE) and temporal structure normalization (TSN) filter. As DAE has a deep structure and nonlinear processing steps, it is flexible enough to model highly nonlinear mapping between input and output space. In this paper, we train a DAE to map reverberant and noisy speech features to the underlying clean speech features in the cepstral domain. For the proposed method, after applying a DAE in the cepstral domain of speech to suppress reverberation, we apply a post-processing technology based on temporal structure normalization (TSN) filter to reduce the noise and reverberation effects by normalizing the modulation spectra to reference spectra of clean speech. The proposed method was evaluated using speech in simulated and real reverberant environments. By combining a cepstral-domain DAE and TSN, the average Word Error Rate (WER) was reduced from 25.2 % of the baseline system to 21.2 % in simulated environments and from 47.5 % to 41.3 % in real environments, respectively. 相似文献
4.
Yepuri Sudhakara Rao Madhukumar A. S. Sirigina Rajendra Prasad 《Wireless Personal Communications》2019,104(3):1075-1090
Wireless Personal Communications - Feedback about the channel state information (CSI) enables the transmitter nodes to exploit channel conditions to yield large improvements in almost any... 相似文献
5.
Wing Shing Wong 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2007,53(6):2060-2071
With recent developments in ad hoc networks and sensor networks, random-access protocol without feedback is a technique that deserves a closer look. This paper is based on Massey's model on random-access channel without feedback. A central concept of this model is the idea of protocol sequences. For these sequences, it is desirable that their cross correlation should be as low as possible and that the length of their period should not be too long, even if there is a large number of active users. Another useful feature is to be able to support multirate communication. Based on these considerations, a new family of protocol sequences is proposed in this paper. These new protocol sequences are built on the concept of prime sequences. It is shown that these sequences possess properties that make them suitable candidates for designing random access protocols for certain ad hoc or sensor networks 相似文献
6.
Shrader B. Permuter H. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2009,55(8):3629-3644
In this work, we find the capacity of a compound finite-state channel (FSC) with time-invariant deterministic feedback. We consider the use of fixed length block codes over the compound channel. Our achievability result includes a proof of the existence of a universal decoder for the family of FSCs with feedback. As a consequence of our capacity result, we show that feedback does not increase the capacity of the compound Gilbert-Elliot channel. Additionally, we show that for a stationary and uniformly ergodic Markovian channel, if the compound channel capacity is zero without feedback then it is zero with feedback. Finally, we use our result on the FSC to show that the feedback capacity of the memoryless compound channel is given by infthetas maxQX I(X; Y |thetas). 相似文献
7.
《IEEE transactions on information theory / Professional Technical Group on Information Theory》2008,54(11):5059-5067
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《Communications, IEEE Transactions on》2006,54(3):574-574
Outage Minimization With Limited Feedback for the Fading Relay Channel In this paper, we consider practical methods to approach the theoretical performance limits in the fading relay channel under different assumptions of transmitter channel knowledge. Specifically, we consider two degrees of transmitter channel knowledge: 1) perfect feedback is available and power control is employed; and 2) no channel-state knowledge is available at the transmitters, and only spatial power allocation is possible. First, when perfect feedback is available, the optimal power-control policy determines the ultimate limits of performance for constant-rate transmission in the slow fading environment. However, in practice, perfect channel knowledge is not possible at the transmitters due to the finite capacity of the feedback links. We find practical methods to approach this performance limit through the use of power control with finite-rate feedback. The finite-rate feedback results are shown for the low-complexity, full-diversity amplify-and-forward (AF) protocol. Interestingly, we see that only a few feedback bits are needed to achieve most of the gains of the optimal perfect feedback power-control algorithm. Second, we consider the performance limit when the transmitter has no channel-state knowledge, and derive the optimal spatial power allocation between the source and relay for a given sum power constraint for the AF protocol. In the foremost practical cases of interest, equal power allocation between the source and relay is shown to be nearly optimal. Our work suggests that there is minimal power savings from using spatial power allocation at the transmitters. To obtain large performance improvements over constant power transmission, it is imperative to have feedback for each realization of the channel state to allow for temporal power control. 相似文献
10.
Permuter H. Cuff P. Van Roy B. Weissman T. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2008,54(7):3150-3165
We establish that the feedback capacity of the trapdoor channel is the logarithm of the golden ratio and provide a simple communication scheme that achieves capacity. As part of the analysis, we formulate a class of dynamic programs that characterize capacities of unifilar finite-state channels. The trapdoor channel is an instance that admits a simple closed-form solution. 相似文献
11.
数字集群中信道争用问题的ALOHA协议研究 总被引:1,自引:0,他引:1
目前在数字集群通信系统中采用时分多址技术,通过信道共用的方法,较好的解决了频率资源紧张的问题.然而信道共用必须要解决好信息"碰撞"问题.ALOHA算法是运用比较普遍的一种解决信道争用算法,文中对ALOHA算法及其衍生算法进行研究,并提出优化的防碰撞算法,采用动态估算碰撞时隙数,满足在呼叫时以最大吞吐量进行工作. 相似文献
12.
This paper employs a high resolution quantization framework to study the effects of finite-rate quantization of the channel state information (CSI) on the performance of MISO systems over correlated fading channels. The contributions of this paper are twofold. First, as an application of the general distortion analysis, tight lower bounds on the capacity loss of correlated MISO systems due to the finite-rate channel quantization are provided. Closed-form expressions for the capacity loss in high-signal-to-noise ratio (SNR) and low-SNR regimes are also provided, and their analysis reveals that the capacity loss of correlated MISO channels is related to that of i.i.d. fading channels by a simple multiplicative factor which is given by the ratio of the geometric mean to the arithmetic mean of the eigenvalues of the channel covariance matrix. Second, this paper extends the general asymptotic distortion analysis to the important practical problem of suboptimal quantizers resulting from mismatches in the distortion functions, source statistics, and quantization criteria. As a specific application, two types of mismatched MISO CSI quantizers are investigated: quantizers whose codebooks are designed with minimum mean square error (MMSE) criterion but the distortion measure is the ergodic capacity loss (i.e., mismatched design criterion), and quantizers with codebook designed with a mismatched channel covariance matrix (i.e., mismatched statistics). Bounds on the channel capacity loss of the mismatched codebooks are provided and compared to that of the optimal quantizers. Finally, numerical and simulation results are presented and they confirm the tightness of theoretical distortion bounds. 相似文献
13.
MIMO系统中的部分信道状态信息反馈 总被引:1,自引:0,他引:1
根据有关多输入对输出(MIMO)系统的相关特征可知,在发射端完全知道信道状态信息(CSI)的情况下,遵循注水定理可以实现最优的发射设计。对于有线通信系统来说,这种情况是完全合理的。但是,在无线通信中,基于完全的信道状态信息的自适应发送仅仅在信道变化足够慢的情况下才有效。现有的关于MIMO的研究,主要集中于信道状态未知的情况下发射端的设计,这种设计并不能获得太令人满意的性能。然而为了减低信道信息反馈带来的信令开销,实时地更新完全信道状态信息对于MIMO系统来说是不太现实的。近来,越来越多的研究更集中于部分信道状态信息,该技术具有极大的应用价值,因为它为上述两种情况提供了一个很好的折衷。 相似文献
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Mehdi Ansari Sadrabadi Amir K. Khandani Farshad Lahouti 《Wireless Communications, IEEE Transactions on》2006,5(12):3335-3338
In this work, we study a multiple-input multiple-output (MIMO) wireless system where the channel state information is partially available at the transmitter through a feedback link. Based on singular value decomposition, the MIMO channel is split into independent sub-channels. Effective feedback of the required spatial channel information entails efficient quantization/encoding of a unitary matrix. We propose two schemes for quantizing unitary matrices via Givens rotations and examine the performance for a scenario where the rates allocated to the sub-channels are selected according to their corresponding gains. Numerical results show that the proposed schemes offer a significant performance improvement as compared to that of MIMO systems without feedback, with a negligible increase in the complexity 相似文献
15.
Multiple-input multiple-output (MIMO) wireless systems can achieve significant diversity and array gain by using transmit beamforming and receive combining techniques. In the absence of full channel knowledge at the transmitter, the transmit beamforming vector can be quantized at the receiver and sent to the transmitter using a low-rate feedback channel. In the literature, quantization algorithms for the beamforming vector are designed and optimized for a particular channel distribution, commonly the uncorrelated Rayleigh distribution. When the channel is not uncorrelated Rayleigh, however, these quantization strategies result in a degradation of the receive signal-to-noise ratio (SNR). In this paper, switched codebook quantization is proposed where the codebook is dynamically chosen based on the channel distribution. The codebook adaptation enables the quantization to exploit the spatial and temporal correlation inherent in the channel. The convergence properties of the codebook selection algorithm are studied assuming a block-stationary model for the channel. In the case of a nonstationary channel, it is shown using simulations that the selected codebook tracks the distribution of the channel resulting in improvements in SNR. Simulation results show that in the case of correlated channels, the SNR performance of the link can be significantly improved by adaptation, compared with nonadaptive quantization strategies designed for uncorrelated Rayleigh-fading channels 相似文献
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为了降低网络接入单位连接多个VPN网络的费用,通过采用mpls/BGP VPN技术、vlan技术和IEEE802.1q协议相结合的方法,设计出一种使网络接入用户只用一条接入线路和一台二层交换机就能连接多个VPN的技术方案。 相似文献
18.
Channel Modeling for Multiple Satellite Broadcasting Systems 总被引:2,自引:0,他引:2
《Broadcasting, IEEE Transactions on》2009,55(4):705-718
19.
波束形成技术是MIMO无线通信系统的关键技术之一,它能够使系统有效性与可靠性都得到显著地提高,但它需要系统所有在线用户反馈其全部瞬时变化的信道状态信息,这将使拥挤的无线频谱资源更加紧张.为了降低系统所需的反馈量,本文结合LTE系统MIMO下行链路环境,将采用DFT基码本对信道状态信息进行量化,仅需要用户给基站反馈其最优码本索引;同时本文也首次提出基于信道质量干扰比为量化准则的一种新波束形成方案,并给出了质量干扰比的详细计算公式.此量化准则能够兼顾到量化信道的质量信息和子信道之间的互干扰信息,比传统的量化准则更具优良的性能.仿真结果表明,本文提出方案不仅可以明显降低系统反馈量,而且其性能超过随机波束形成,尤其在低信噪比场景下甚至优于特征波束形成的系统性能.理论分析和仿真验证表明本文方案是一种比较好的波束形成方案. 相似文献
20.
Gabbai Y. Bross S.I. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2006,52(11):4989-5007
Achievable rates over the discrete memoryless relay channel with partial feedback configurations are proposed. Specifically, we consider partial feedback from the receiver to the sender as well as partial feedback from the relay to the sender. These achievable rates are calculated for the general Gaussian and the Z relay channels and are shown to improve on the known one-way achievable rates 相似文献