Gaussian multiaccess channels with ISI: capacity region andmultiuser water-filling

The capacity region of a two-user Gaussian multiaccess channel with intersymbol interference (ISI) in which the inputs pass through respective linear systems and are superimposed before being corrupted by an additive Gaussian noise process is discussed. A geometrical method for obtaining the optimal input power spectral densities and the capacity region is presented. This method can be viewed as a nontrivial generalization of the single-user water-filling argument. It is shown that, as in the traditional memoryless multiaccess channel, frequency-division multiaccess (FDMA) with optimally selected frequency bands for each user achieves the total capacity of the multiuser Gaussian multiaccess channel with ISI. However, the capacity region of the two-user channel with memory is, in general, not a pentagon unless the channel transfer functions for both users are identical     

Capacity Theorems for the “Z” Channel

We consider the two-user "Z" channel (ZC), where there are two senders and two receivers. One of the senders transmits information to its intended receiver (without interfering with the unintended receiver), while the other sender transmits information to both receivers. The complete characterization of the discrete memoryless ZC remains unknown to date. For the Gaussian ZC, the capacity has only been established for a crossover link gain of 1. In this work, we study both the discrete memoryless ZC and the Gaussian ZC. We first establish achievable rates for the general discrete memoryless ZC. The coding strategy uses rate-splitting and superposition coding at the sender with information for both receivers. At the receivers, we use joint decoding. We then specialize the rates obtained to two different types of degraded discrete memoryless ZCs and also derive respective outer bounds to their capacity regions. We show that as long as a certain condition is satisfied, the achievable rate region is the capacity region for one type of degraded discrete memoryless ZC. The results are then extended to the two-user Gaussian ZC with different crossover link gains. We determine an outer bound to the capacity region of the Gaussian ZC with strong crossover link gain and establish the capacity region for moderately strong crossover link gain     

On the achievable throughput of a multiantenna Gaussian broadcast channel

A Gaussian broadcast channel (GBC) with r single-antenna receivers and t antennas at the transmitter is considered. Both transmitter and receivers have perfect knowledge of the channel. Despite its apparent simplicity, this model is, in general, a nondegraded broadcast channel (BC), for which the capacity region is not fully known. For the two-user case, we find a special case of Marton's (1979) region that achieves optimal sum-rate (throughput). In brief, the transmitter decomposes the channel into two interference channels, where interference is caused by the other user signal. Users are successively encoded, such that encoding of the second user is based on the noncausal knowledge of the interference caused by the first user. The crosstalk parameters are optimized such that the overall throughput is maximum and, surprisingly, this is shown to be optimal over all possible strategies (not only with respect to Marton's achievable region). For the case of r>2 users, we find a somewhat simpler choice of Marton's region based on ordering and successively encoding the users. For each user i in the given ordering, the interference caused by users j>i is eliminated by zero forcing at the transmitter, while interference caused by users j相似文献   

Capacity of Cognitive Interference Channels With and Without Secrecy

Like the conventional two-user interference channel, the cognitive interference channel consists of two transmitters whose signals interfere at two receivers. It is assumed that there is a common message (message 1) known to both transmitters, and an additional independent message (message 2) known only to the cognitive transmitter (transmitter 2). The cognitive receiver (receiver 2) needs to decode messages 1 and 2, while the noncognitive receiver (receiver 1) should decode only message 1. Furthermore, message 2 is assumed to be a confidential message which needs to be kept as secret as possible from receiver 1, which is viewed as an eavesdropper with regard to message 2. The level of secrecy is measured by the equivocation rate. In this paper, a single-letter expression for the capacity-equivocation region of the discrete memoryless cognitive interference channel is obtained. The capacity-equivocation region for the Gaussian cognitive interference channel is also obtained explicitly. Moreover, particularizing the capacity-equivocation region to the case without a secrecy constraint, the capacity region for the two-user cognitive interference channel is obtained, by providing a converse theorem.      

A New Outer Bound and the Noisy-Interference Sum–Rate Capacity for Gaussian Interference Channels

A new outer bound on the capacity region of Gaussian interference channels is developed. The bound combines and improves existing genie-aided methods and is shown to give the sum–rate capacity for noisy interference as defined in this paper. Specifically, it is shown that if the channel crosstalk coefficient magnitudes lie below thresholds defined by the power constraints then single-user detection at each receiver is sum–rate optimal, i.e., treating the interference as noise incurs no loss in performance. This is the first capacity result for the Gaussian interference channel with weak to moderate interference. Furthermore, for certain mixed (weak and strong) interference scenarios, the new outer bounds give a corner point of the capacity region.      

The Two-User Compound Interference Channel

We introduce the two-user finite state compound interference channel. The main contributions involve both novel inner and outer bounds. For the Gaussian case, we characterize its capacity region to within one bit. The inner bound is multilevel superposition coding but the decoding of the levels is opportunistic, depending on the channel state. The genie aided outer bound is motivated by the typical error events of the achievable scheme.     

Outer bounds on the capacity of Gaussian interference channels

Two outer bounds on the capacity region of the two-user Gaussian interference channel (IFC) are derived. The idea of the first bound is to let a genie give each receiver just enough information to decode both messages. This bound unifies and improves the best known outer bounds of Sato and Carleial. Furthermore, the bound extends to discrete memoryless IFCs and is shown to be equivalent to another bound of Carleial. The second bound follows directly from existing results of Costa and Sato and possesses certain optimality properties for weak interference.     

Capacity Regions and Bounds for a Class of Z-Interference Channels

We define a class of Z-interference channels for which we obtain a new upper bound on the capacity region. The bound exploits a technique first introduced by Korner and Marton. A channel in this class has the property that, for the transmitter-receiver pair that suffers from interference, the conditional output entropy at the receiver is invariant with respect to the transmitted codewords. We compare the new capacity region upper bound with the Han/Kobayashi achievable rate region for interference channels. This comparison shows that our bound is tight in some cases, thereby yielding specific points on the capacity region as well as sum capacity for certain Z-interference channels. In particular, this result can be used as an alternate method to obtain sum capacity of Gaussian Z-interference channels. We then apply an additional restriction on our channel class: the transmitter-receiver pair that suffers from interference achieves its maximum output entropy with a single input distribution irrespective of the interference distribution. For these channels, we show that our new capacity region upper bound coincides with the Han/Kobayashi achievable rate region, which is therefore capacity-achieving. In particular, for these channels superposition encoding with partial decoding is shown to be optimal and a single-letter characterization for the capacity region is obtained.     

Graph theoretic approaches to the code construction for the two-user multiple- access binary adder channel

We relate coding for the two-user multiple-access binary adder channel to a problem in graph theory, known as the independent set problem. Graph-theoretic approaches to coding for both synchronized and nonsynchronized two-user adder channels are presented. Using the Tuŕan theorem on the independence number of a simple graph, we are able to improve the lower bounds on the achievable rates of uniquely anddelta-decodable codes for the synchronized adder channel derived by Kasami and Lin. We are also able to derive lower bounds on the achievable rates of uniquely decodable codes for the nonsynchronized adder channel. We show that the rates of Deaett-Wolf codes for the nonsynchronized adder channel fall below the bounds. Synchronizing sequences for the nonsynchronized adder channel are constructed.     

Multicast Capacity of Wireless Ad Hoc Networks

Assume that n wireless nodes are uniformly randomly deployed in a square region with side-length a and all nodes have the uniform transmission range r and uniform interference range R > r. We further assume that each wireless node can transmit (or receive) at W bits/second over a common wireless channel. For each node vi , we randomly and independently pick k-1 points pi,j (1 les j les k-1) from the square, and then multicast data to the nearest node for each pi,j. We derive matching asymptotic upper bounds and lower bounds on multicast capacity of random wireless networks. Under protocol interference model, when a ²/r ²=O(n/log(n)), we show that the total multicast capacity is Theta(radic{n/log n}middot(W/radick)) when k=O(n/log n); the total multicast capacity is Theta(W) when k=Omega(n/log n). We also study the capacity of group-multicast for wireless networks where for each source node, we randomly select k-1 groups of nodes as receivers and the nodes in each group are within a constant hops from the group leader. The same asymptotic upper bounds and lower bounds still hold. We also extend our capacity bounds to d -dimensional networks.     

Interference channels

An interference channel is a communication medium shared by M sender-receiver pairs. Transmission of information from each sender to its corresponding receiver interferes with the communications between the other senders and their receivers. This corresponds to a frequent situation in communications, and defines anM-dimensional capacity region. In this paper, we obtain general bounds on the capacity region for discrete memoryless interference channels and for linear-superposition interference channels with additive white Gaussian noise. The capacity region is determined in special cases.     

On the deterministic-code capacity of the multiple-accessarbitrarily varying channel

A method that allows one to decide whether or not the capacity region of a multiple-access arbitrarily varying channel (AVC) has a nonempty interior is discussed. Using the method of types and an approach different from J.H. Jahn (ibid. vol.27, no.3, p.212-226, 1981) this problem is partially solved. The notion of symmetrizability for the two-user AVC as an extension of the same notion for the single-user AVC is considered. It is shown that if a multiple-access AVC is symmetrizable, then its capacity region has an empty interior. For the two-user AVC, this means that at least one (and perhaps both) users cannot reliably transmit information across the channel. More importantly, it is shown that if the channel is suitably nonsymmetrizable, then the capacity region has a nonempty interior, and both users can reliably transmit information across the channel. The proofs rely heavily on a complicated decoding rule. Conditions under which simpler multiple-message decoding techniques might suffice are therefore examined. In particular, conditions under which the universal maximal mutual information decoding rule will be effective are given     

A New Bound for the Zero-Error Capacity Region of the Two-User Binary Adder Channel

A new uniquely decodable (UD) code pair for the two-user binary adder channel (BAC) is presented. This code pair leads to an improved bound for the zero-error capacity region of such a channel. The highest known rate for a UD code pair for the two-user BAC is thereby improved to$(log_2 240)/6 approx 1.3178$. It is also demonstrated that the problem of finding UD code pairs for the closely related binary XOR channel is in one-to-one correspondence with a certain construction of binary one-error-correcting codes.     

The Poisson multiple-access channel

The Poisson multiple-access channel (MAC) models many-to-one optical communication through an optical fiber or in free space. For this model we compute the capacity region for the two-user case as a function of the allowed peak power. Focusing on the maximum throughput we generalize our results to the case where the users are subjected to an additional average-power constraint and to the many-users case. We show that contrary to the Gaussian MAC, in the Poisson MAC the maximum throughput is bounded in the number of users. We quantify the loss that is incurred when time-division multiple access (TDMA) is employed and show that while in the two-user case and in the absence of dark current the penalty is rather mild, the penalty can be quite severe in the many-users case in the presence of large dark current. We introduce a generalized TDMA technique that mitigates this loss to a large extent     

Capacity of time-slotted ALOHA packetized multiple-access systems over the AWGN channel

We study different notions of capacity for time-slotted ALOHA systems. In these systems, multiple users synchronously send packets in a bursty manner over a common additive white Gaussian noise (AWGN) channel. The users do not coordinate their transmissions, which may collide at the receiver. For such a system, we define both single-slot capacity and multiple-slot capacity. We then construct a coding and decoding scheme for single-slot capacity that achieves any rate within this capacity region. This coding and decoding scheme for a single time slot combines aspects of multiple access rate splitting and of broadcast codes for degraded AWGN channels. This design allows some bits to be reliably received even when collisions occur and more bits to be reliably received in the absence of collisions. The exact number of bits reliably received under both of these scenarios is part of the code design process, which we optimize to maximize the expected rate in each slot. Next, we examine the behavior of the system asymptotically over multiple slots. We show that there exist coding and decoding strategies such that regardless of the burstiness of the traffic, the system is stable as long as the average rate of the users is within the multiple access capacity region of the channel. In other words, we show that bursty traffic does not decrease the Cover-Wyner capacity region of the multiple access channel. A vast family of codes, which includes the type of codes we introduce for the single-slot transmission, achieve the capacity region, in a sense we define, for multiple-slot transmissions. These codes are stabilizing, using only local information at each of the individual queues. The use of information regarding other queues or the use of scheduling does not improve the multiple-slot capacity region.     

On the diversity gain region of the dynamic decode-and-forward relay-assisted Z-channel

In an interference-limited system, the interference forwarding by a relay enhances the interference level and thereby enables the cancellation of the interference. In this work, interference forwarding by a half-duplex dynamic decode-and-forward (HD DDF) relay in a two-user Z-channel is considered. In the two-user Z-channel, one user is interference-limited while the other user is interference-free. The diversity gain region (DGR), which characterizes the tradeoff between the achievable diversity orders between the two users, is an appropriate performance metric for the Z-channel. Closed-form expression for the achievable DGR with the interference forwarding by the HD DDF relay is presented. The multiplexing gain regions (MGRs) where the HD DDF protocol achieves better DGR over the direct transmission scheme, full-duplex decode-and-forward (FD DF) and FD partial DF relay assisted Z- channel are identified. The HD DDF protocol is shown to achieve better DGR than the FD DF and FD PDF relay for a large range of MGR. The achievable DGRs for the HD DDF, FD DF, and FD PDF relay-assisted Z-channel and direct transmission scheme are presented for various interference levels and multiplexing gain pairs.     

Selfishness and altruism on the MISO interference channel: the case of partial transmitter CSI

We study the achievable ergodic rate region of the two-user multiple-input single-output interference channel, under the assumptions that the receivers treat interference as additive Gaussian noise and the transmitters only have statistical channel knowledge. Initially, we provide a closed-form expression for the ergodic rates and derive the Nash-equilibrium and zero-forcing transmit beamforming strategies. Then, we show that combinations of the aforementioned selfish and altruistic, respectively, strategies achieve Pareto-optimal rate pairs.     

The capacity of the white Gaussian multiple access channel with feedback

Since the appearance of [10] by Gaarder and Wolf, it has been well known that feedback can enlarge the capacity region of the multiple access channel. In this paper a deterministic feedback code is presented for the two-user Gaussian multiple access channel, which is shown to allow reliable communication at all points inside a region larger than any previously obtained. An outer bound is given which is shown to coincide with the achievable region, thus yielding the capacity region of this channel exactly.     

The Capacity Region of Frequency-Selective Gaussian Interference Channels Under Strong Interference

This paper presents the capacity region of frequency-selective Gaussian interference channels under the condition of strong interference, assuming an average power constraint per user. First, a frequency-selective Gaussian interference channel is modeled as a set of independent parallel memoryless Gaussian interference channels. Using nonfrequency selective results, the capacity region of frequency-selective Gaussian interference channels under strong interference is expressed mathematically. Exploiting structures inherent in the problem, a dual problem is constructed for each independent memoryless channel, in which both mathematical and numerical analysis are performed. Furthermore, three suboptimal methods are compared to the capacity-achieving coding and power allocation scheme. Iterative waterfilling, a suboptimal scheme, provides close-to-optimum performance and has a distributed coding and power allocation scheme, which are attractive in practice.