Write once memory (WOM) codes allow reuse of a write-once medium. This paper focuses on applying WOM codes to the binary symmetric asymmetric multiple access channel (BS-AMAC). At one specific rate pair, WOM codes can achieve the BS-AMAC maximum sum-rate. Further, any achievable rate pair for a two-write WOM code is also an achievable rate pair for the BS-AMAC. Compared to the uniform input distribution of linear codes, the non-uniform WOM input distribution is helpful for a BS-AMAC. In addition, WOM codes enable “symbol-wise estimation”, resulting in the decomposition to two distinct channels. This scheme does not achieve the BS-AMAC maximum sum-rate if the channel has errors, however leads to reduced-complexity decoding by enabling independent decoding of two codewords. Achievable rates for this decomposed system are also given. The AMAC has practical application to the relay channel and we briefly discuss the relay channel with block Markov encoding using WOM codes. This scheme may be effective for cooperative wireless communications despite the fact that WOM codes are designed for data storage.

In the study of the capacity problem for multiple access channels (MACs), a lower bound on the error probability obtained by Han plays a crucial role in the converse parts of several kinds of channel coding theorems in the information-spectrum framework. Recently, Yagi and Oohama showed a tighter bound than the Han bound by means of Polyanskiy's converse. In this paper, we give a new bound which generalizes and strengthens the Yagi-Oohama bound, and demonstrate that the bound plays a fundamental role in deriving extensions of several known bounds. In particular, the Yagi-Oohama bound is generalized to two different directions; i.e, to general input distributions and to general encoders. In addition we extend these bounds to the quantum MACs and apply them to the converse problems for several information-spectrum settings.

The multiple-access channel (MAC) becomes very popular in various communication systems, because multi-terminal communication systems have been widely used in practical systems, e.g., mobile phones and P2P, etc. For some MACs, it is known that feedback can enlarge the capacity region, where the capacity region is the set of rate pairs such that the error probability can be made arbitrarily small for sufficiently large block length. The capacity region for general MACs, which are not required to satisfy ergodicity and stationarity with perfect feedback was first shown by Tatikonda and Mitter without the proof, where perfect feedback means that the channel output is perfectly fed back to senders. In this paper, we generalize Tatikonda and Mitter's result to the case of deterministic feedback, where the values of deterministic functions of past channel outputs is fed back to senders. We show that the capacity region for general MACs with deterministic feedback can be represented by the information-spectrum formula introduced by Han and Verdu, and directed information introduced by Massey. We also investigate the compound MAC problem, the ε-coding problem, the strong converse property and the cost constraint problem for general MACs with deterministic feedback.

In this paper, we develop linear-programming (LP) decoding for multiple-access channels with binary linear codes. For single-user channels, LP decoding has attracted much attention in recent years as a good approximation to maximum-likelihood (ML) decoding. We demonstrate how the ML decoding problem for multiple-access channels with binary linear codes can be formulated as an LP problem. This is not straightforward, because the objective function of the problem is generally a non-linear function of the codeword symbols. We introduce auxiliary variables such that the objective function is a linear function of these variables. The ML decoding problem then reduces to the LP problem. As in the case for single-user channels, we formulate the relaxed LP problem to reduce the complexity for practical implementation, and as a result propose a decoder that has the desirable property known as the ML certificate property (i.e., if the decoder outputs an integer solution, the solution is guaranteed to be the ML codeword). Although the computational complexity of the proposed algorithm is exponential in the number of users, we can reduce this complexity for Gaussian multiple-access channels. Furthermore, we compare the performance of the proposed decoder with a decoder based on the sum-product algorithm.

This paper generalizes parallel error correcting codes proposed by Ahlswede et al. over a new type of multiple access channel called parallel error channel. The generalized parallel error correcting codes can handle with more errors compared with the original ones. We show construction methods of independent and non-independent parallel error correcting codes and decoding methods. We derive some bounds about the size of respective parallel error correcting codes. The obtained results imply a single parallel error correcting code can be constructed by two or more kinds of error correcting codes with distinct error correcting capabilities.

In this letter, we investigate the sum-rate capacity of a power-controlled multi-user distributed antenna system (DAS) with antennas deployed symmetrically on a circle. The sum-rate capacity, when divided by user number, is proved to converge to an explicit expression as user number and antenna number go to infinity with a constant ratio. We further show how this theoretical result can be used to optimize antenna deployment. Simulation results are also provided to demonstrate the validity of our analysis and the applicability of the asymptotic results to a small-scale system.

In this paper, Information-Spectrum characterization is derived for the reliable transmission of general correlated sources over the general multiple-access channels. We consider the necessary and sufficient conditions for the transmission of general correlated sources over the general multiple-access channels by using Information-Spectrum methods which are introduced by Han and Verdu.

Multihop techniques in CDMA radio access networks, enable dead-spot mobile stations, which cannot communicate with base stations directly, to send data to them via other mobile stations. In this paper, we propose a mechanism for establishing connections and relaying packets between mobile stations. In this mechanism, the mobile stations are connected to one another and relay packets through a random access channel, which is an uplink common channel. In addition, our mechanism satisfies the requirements for applying multihop techniques to third generation radio access networks. Moreover, we also discuss our evaluation of the performance of the mechanism through computer simulations. The results we obtained reveal that it is capable of reducing dead-spot mobile stations and improving throughput with only limited modifications to conventional systems. Furthermore, we propose an adaptive transmission power control to enhance our mechanism and also evaluate this method through computer simulations.

The Joint CDMA/PRMA (JCP) protocol, proposed by Brand and Aghvami, is modified to increase the capacity for mobile communication systems. To reduce multiuser interference, the modified JCP uses an access channel additionally to the traffic channels, on which each mobile terminal reserves a unique slot and code. Furthermore, the modified JCP employs receiver-based code scheme. In the case of voice-only traffic, the throughput increases by up to 15% compared to that of the conventional JCP, when Ploss is 0.01. Also, for the mixed traffic case, the throughput increases about 20%.

A uniquely decodable code pair (C, S) is considered for the two-user binary adder channel. When the first code C is linear, a lower bound of |S| is formulated and a uniquely decodable code pair (C, S) is presented. When a rate R1 of C is less than 1/3, a rate R2of S is greater than the best rate known previously.

A uniquely decodable code (C1, C2, C3) is investigated for the three-user binary adder channel. The uniquely decodable code is constructed as follows: If C1 is an (n, k) linear code with a generator matrix, C2 is a coset of C1 and C3 is a set of all coset leaders, then the code (C1, C2, C3) is uniquely decodable and its total rate is equal to 1k/n, n2k. This code is easily decodable.

A uniquely decodable (UD) code pair (C, S) is considered for the two-user binary adder channel. For a class of linear codes C, the maximum independent set of the graph associated with C, which is the second code S, is evaluated. When the rate R1 of C is less than 0.5, there exist UD codes (C, S)'s such that the rate R2 of S exceeds the Khachatrian's and Guo's results in amount.

It is known that the uniquely decodable code pairs (C1, C2) for the two-user binary adder channel relates to the maximum independent set of a graph associated with a binary code. This paper formulates the independence number of a class of graphs associated with binary linear codes, and presents an algorithm of the maximum independent set for those graphs. Uniquely decodable code pairs (C1, C2)'s are produced, where C1 is a linear code and C2 is a maximum independent set of the graph associated with C1. For the given C1, the transmission rate of C2 is higher than that by Khachatrian, which is known as the best result as so far. This is not rather surprising because the code C2 is a maximum independent set in this paper but not be Khachatrian's.