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Communication channel

About: Communication channel is a research topic. Over the lifetime, 137411 publications have been published within this topic receiving 1715077 citations. The topic is also known as: communication channel & communications channel.


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Journal ArticleDOI
TL;DR: In this article, the authors show that at least 12 degrees-of-freedom is achievable for all values of complex Gaussian channel coefficients except for a subset of measure zero for the class of linear beamforming and interference alignment schemes considered in this paper.
Abstract: It has been conjectured by Ho-Madsen and Nosratinia that complex Gaussian interference channels with constant channel coefficients have only one degree-of-freedom regardless of the number of users While several examples are known of constant channels that achieve more than 1 degree-of-freedom, these special cases only span a subset of measure zero In other words, for almost all channel coefficient values, it is not known if more than 1 degree-of-freedom is achievable In this paper, we settle the Host-Madsen-Nosratinia conjecture in the negative We show that at least 12 degrees-of-freedom are achievable for all values of complex channel coefficients except for a subset of measure zero For the class of linear beamforming and interference alignment schemes considered in this paper, it is also shown that 12 is the maximum number of degrees-of-freedom achievable on the complex Gaussian 3 user interference channel with constant channel coefficients, for almost all values of channel coefficients To establish the achievability of 12 degrees-of-freedom we use the novel idea of asymmetric complex signaling - ie, the inputs are chosen to be complex but not circularly symmetric It is shown that unlike Gaussian point-to-point, multiple-access and broadcast channels where circularly symmetric complex Gaussian inputs are optimal, for interference channels optimal inputs are in general asymmetric With asymmetric complex signaling, we also show that the 2 user complex Gaussian X channel with constant channel coefficients achieves the outer bound of 4/3 degrees-of-freedom, ie, the assumption of time-variations/frequency-selectivity used in prior work to establish the same result, is not needed

260 citations

01 Jan 1994
TL;DR: In this article, a method of maximum likelihood sequence estimation is proposed for data that a re transmitted over unknown linear channels, which does not require a start-up sequence for estimating the channel impulse response.
Abstract: A novel method of maximum likelihood sequence estimation is proposed for data that a re transmitted over unknown linear channels. Unlike conventional sequence es- timation techniques, this procedure does not require a start- up sequence for estimating the channel impulse response. Rather, the data and the channel are simultaneously esti- mated. In principle this is accomplished by finding the least squares channel estimate between the received sequence and every possible data sequence that can be transmitted, and choosing that pair of data sequence and the corresponding estimated channel with the overall least squares error. This simple but exhaustive search technique is non-instrumentable because of the exponential growth in complexity with the length of the data sequence. In practice it is implemented, without any loss of optimality, by a trellis search algorithm which searches for the best data sequence from among a number of hypothesized trellises which are constructed from the observed sequence. The number of states in each trel- lis as well as the number of trellises grows exponentially with the channel memory. A sub-optimal trellis search al- gorithm is proposed whose complexity in the best of situa- tions is slightly higher than that of the conventional adaptive Viterbi algorithm operating with a known channel response. A simplified channel estimation algorithm when the number of data alphabets is greater than 2 is also proposed. Fast convergence of the algorithm in estimating the chan- nel is demonstrated for binary pulse amplitude modulation (%PAM) over a variety of channels. Convergence over a wide range of signal-to-noise ratios occurs within 100 sym- bols. The channel estimation algorithm for multi-level (greater than 2) Signals is shown to converge within 500- 1000 symbols. We finally present an application of this al- gorithm to the problem of sequence estimation in the pres- ence of rapidly time-varying intersymbol interference. The algorithm provides reliable zero-delay decisions which re- sults in a better channel tracking algorithm when compared to previously proposed schemes.

260 citations

Journal ArticleDOI
Hisashi Kobayashi1, D. T. Tang1
TL;DR: A conventional NRZI method of recording is shown to be equivalent to the "precoding" of this particular partial-response channel, the purpose of which is to limit the propagation of error in the channel output, and an error detection scheme is presented that takes full advantage of the inherent redundancy in the three-level channel output.
Abstract: A magnetic recording channel can be regarded as a "partial-response" channel because of its inherent differentiation in the readback process. The conventional NRZI method of recording is shown to be equivalent to the "precoding" of this particular partial-response channel, the purpose of which is to limit the propagation of error in the channel output. Using this new viewpoint, one can readily adopt an error detection scheme (developed for general partial-response channels) that takes full advantage of the inherent redundancy in the three-level channel output. The detection scheme is optimum in the sense that it detects all detectable errors with minimum delay. The paper also describes a new high-density recording method, named the "Interleaved NRZI," which is obtained by molding an ordinary recording channel into a different type of partial-response channel, resulting in a potential increase in information density. Implementation of the corresponding optimum error detection scheme is also presented. Finally, performance of these error detection schemes is evaluated in terms of probabilities of detecting single and double errors within a certain finite delay.

260 citations

Journal ArticleDOI
TL;DR: A conceptual framework for omni-channel systems, configured by three dimensions of channel stage, channel type and channel agent is developed, which can be applied to a wide range of retail supply chains.

260 citations

Journal ArticleDOI
TL;DR: A channel estimation framework based on the parallel factor decomposition to unfold the resulting cascaded channel model is proposed and it is demonstrated that the sum rate using the estimated channels always reach that of perfect channels under various settings, thus, verifying the effectiveness and robustness of the proposed estimation algorithms.
Abstract: Reconfigurable Intelligent Surfaces (RISs) have been recently considered as an energy-efficient solution for future wireless networks due to their fast and low-power configuration, which has increased potential in enabling massive connectivity and low-latency communications. Accurate and low-overhead channel estimation in RIS-based systems is one of the most critical challenges due to the usually large number of RIS unit elements and their distinctive hardware constraints. In this paper, we focus on the uplink of a RIS-empowered multi-user Multiple Input Single Output (MISO) uplink communication systems and propose a channel estimation framework based on the parallel factor decomposition to unfold the resulting cascaded channel model. We present two iterative estimation algorithms for the channels between the base station and RIS, as well as the channels between RIS and users. One is based on alternating least squares (ALS), while the other uses vector approximate message passing to iteratively reconstruct two unknown channels from the estimated vectors. To theoretically assess the performance of the ALS-based algorithm, we derived its estimation Cramer-Rao Bound (CRB). We also discuss the downlink achievable sum rate computation with estimated channels and different precoding schemes for the base station. Our extensive simulation results show that our algorithms outperform benchmark schemes and that the ALS technique achieves the CRB. It is also demonstrated that the sum rate using the estimated channels always reach that of perfect channels under various settings, thus, verifying the effectiveness and robustness of the proposed estimation algorithms.

260 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202270
20214,425
20206,535
20197,160
20187,052
20176,315