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.

Method for transmitting broadcast information in a digital control channel

Abstract: The present invention provides a method for transmitting information on a communications channel, e.g. , a digital control channel between a base station and a mobile station in a cellular system. The method includes the steps of grouping the information into a plurality of information elements, providing at least one change flag to indicate whether the value of at least one of the information elements has changed and transmitting the change flag and the information element over the communications channel.

Digital communications over fading radio channels

Abstract: A major contribution to system outage in a terrestrial digital radio channel is deep fading of the frequency transfer characteristic, which in addition to causing a precipitous drop in received signal-to-noise ratio (s/n) also causes signal dispersion that can result in severe intersymbol interference. Because the temporal variation of the channel is slow compared to the signaling rate, the information theoretic channel capacity and the “Efficiency Index” in bits/cycle — a figure-of-merit we use for the communication techniques considered — can be viewed as random processes. Starting from an established mathematical model characterizing fading channels (derived from extensive measurements), we estimate the probability distribution of channel capacity and the distributions of efficiency indices for different communications techniques. The repertoire of communication methods considered involves quadrature amplitude modulation with adaptive linear and decision feedback equalization, and maximum likelihood sequence estimation. For specific outage objectives the maximum number of bits per cycle achievable by each technique is estimated. The sensitivity of the distributions to bit-error-rate objective and unfaded s/n is assessed. For certain desired operating points the efficacy of adaptive equalization is demonstrated. There are some operating points where adaptive equalization alone is not adequate and therefore space diversity should be considered. An estimate of the effect of frequency diversity is also included.

On manufacturers complementing the traditional retail channel with a direct online channel

Abstract: With the explosion of the Internet and the reach that it affords, many manufacturers have complemented their existing retail channels with an online channel, which allows them to sell directly to their consumers. Interestingly, there is a significant variation within product categories in manufacturer's use of the Internet as a direct distribution channel. The main objective of this study is to examine the strategic forces that may influence the manufacturer's decision to complement the retail channel with a direct online channel. In particular, we are interested in answering the following questions: (I) Why is it that in some markets only a few firms find it optimal to complement their retail channels with a direct Internet channel while other firms do not? (II) What strategic role (if any), does the direct Internet channel serve and how do market characteristics impact this role?

Ergodic Interference Alignment

Abstract: This paper develops a new communication strategy, ergodic interference alignment, for the K-user interference channel with time-varying fading. At any particular time, each receiver will see a superposition of the transmitted signals plus noise. The standard approach to such a scenario results in each transmitter-receiver pair achieving a rate proportional to 1/K its interference-free ergodic capacity. However, given two well-chosen time indices, the channel coefficients from interfering users can be made to exactly cancel. By adding up these two observations, each receiver can obtain its desired signal without any interference. If the channel gains have independent, uniform phases, this technique allows each user to achieve at least 1/2 its interference-free ergodic capacity at any signal-to-noise ratio. Prior interference alignment techniques were only able to attain this performance as the signal-to-noise ratio tended to infinity. Extensions are given for the case where each receiver wants a message from more than one transmitter as well as the “X channel” case (with two receivers) where each transmitter has an independent message for each receiver. Finally, it is shown how to generalize this strategy beyond Gaussian channel models. For a class of finite field interference channels, this approach yields the ergodic capacity region.

Certain results in coding theory for noisy channels

Abstract: In this paper we will develop certain extensions and refinements of coding theory for noisy communication channels. First, a refinement of the argument based on “random” coding will be used to obtain an upper bound on the probability of error for an optimal code in the memoryless finite discrete channel. Next, an equation is obtained for the capacity of a finite state channel when the state can be calculated at both transmitting and receiving terminals. An analysis is also made of the more complex case where the state is calculable at the transmitting point but not necessarily at the receiving point.