This paper presents a practical technique that uses Ping's interleave(r)-division multiple access and single-user decoding to provide uncoordinated access for a family of binary-input binary-output multiple-access channels (MACs) including the OR-MAC where users' binary transmissions are combined with the logical OR operation. Information theoretic calculations provide the achievable sum-rates and optimal ones densities for these MACs. Because the required ones densities are significantly less than 50%, new nonlinear trellis code analysis and design techniques are introduced to provide the needed codes. Union bound techniques that predict the performance of these codes are also presented. Simulation results and a working FPGA implementation verify the performance and feasibility of the proposed nonlinear codes and overall multiple access scheme.

Low-Density Parity-Check (LDPC) codes are usually decoded by running an iterative belief-propagation (BP), or message-passing, algorithm over the factor graph of the code. The traditional message-passing scheduling, called flooding, consists of updating all the variable nodes in the graph, using the same pre-update information, followed by updating all the check nodes of the graph, again, using the same pre-update information. Recently, several studies show that sequential scheduling, in which messages are generated using the latest available information, significantly improves the convergence speed in terms of number of iterations. Sequential scheduling introduces the problem of finding the best sequence of message updates. We propose Informed Dynamic Scheduling (IDS) strategies that select the message-passing schedule according to the observed rate of change of the messages. In general, IDS strategies require computation to select the message to update but converge in fewer message updates because they focus on the part of the graph that has not converged. Moreover, IDS yields a lower error-rate performance than either flooding or sequential scheduling because IDS strategies overcome traditional trapping-set errors. This paper presents IDS strategies that address several issues including performance for short-blocklength codes, complexity, and implementability.

Parallel concatenated trellis coded modulation (PC- TCM) has been traditionally designed using parallel concatenated convolutional codes with a bits-to-symbol mapper. However, this paper shows that for higher-order modulations using linear codes is too restrictive. Parallel Concatenated Nonlinear Trellis Coded Modulation (PC-NLTCM) that directly assigns constellation points as output-labels to the branches of the trellis can outperform PC-TCM. Simulation results are shown for a 2 bits/s/Hz 16-state nonlinear turbo code with 8PSK. This code is less than 0.43 dB away from the Shannon limit at a BER = 10 5 with an interleaver length of 10000 bits, and outperforms previous published linear turbo code by around 0.2 dB. This paper also provides an extension of Benedetto's uniform interleaver analysis for nonlinear constituent codes, which accurately predicts the BER of the PC-NLTCM at high SNR.

This paper provides an explicit expression for the capacity region of the two-user broadcast Z channel and proves that the optimal boundary can be achieved by independent encoding of each user. Specifically, the information messages corresponding to each user are encoded independently and the OR of these two encoded streams is transmitted. Nonlinear turbo codes that provide a controlled distribution of ones and zeros are used to demonstrate a low-complexity scheme that operates close to the optimal boundary.

This paper presents a design criteria for arbitrarily low-rate parallel concatenated convolutional codes (PCCCs). The purpose of this work is to find a family of turbo codes that work as close to the ultimate low-rate Shannon limit Eb/Nosime -1.59 dB as possible, given a certain constraint in the number of states of the constituent trellis codes and in the interleaver-length. We propose an optimization criteria and reduce the turbo-design problem to the design of block codes for the assignment of output sequences to the trellis branches of the constituent encoders. We show that BCH codes concatenated with repetition codes are optimal for labeling. Moreover, we show that for a fixed number of trellis states these codes achieve arbitrarily low rates, and hence arbitrarily low SNRs, with practically the same performance in terms of Eb/No. Simulation results are shown for 8-state and 16-state turbo codes with rates as low as 1/505, which with an interleaver-length of 8192 provide a BER sime 10-5at an SNR sime -27.6 dB (Eb/Nosime -0.55 dB), around 1 dB away from the ultimate low-rate Shannon limit.

Low-density parity-check (LDPC) codes are usually decoded by running an iterative belief-propagation, or message-passing, algorithm over the factor graph of the code. The traditional message-passing schedule consists of updating all the variable nodes in the graph, using the same pre-update information, followed by updating all the check nodes of the graph, again, using the same pre-update information. Recently several studies show that sequential scheduling, in which messages are generated using the latest available information, significantly improves the convergence speed in terms of number of iterations. Sequential scheduling raises the problem of finding the best sequence of message updates. This paper presents practical scheduling strategies that use the value of the messages in the graph to find the next message to be updated. Simulation results show that these informed update sequences require significantly fewer iterations than standard sequential schedules. Furthermore, the paper shows that informed scheduling solves some standard trapping set errors. Therefore, it also outperforms traditional scheduling for a large numbers of iterations. Complexity and implementability issues are also addressed.

Though it promises high bandwidths, the optical medium is not popular in local area networks. This is because current optical networks do not offer the ease of use and setup that an uncoordinated multiple access network such as Ethernet offers. By careful design and implementation of high speed channel coding architectures, we show that it is possible for optical networks to exhibit these desirable properties while maintaining high optical transmission rates. This paper presents an interleaver-division multiple access (IDMA) architecture implemented with a rate 1/20, 64-state Viterbi decoder and a word-based interleaver. These structures allowed us to achieve optical data rates of 2Gbps in FPGA implementation and 5.4Gbps for 0.18mum ASIC implementation. The techniques presented can be adapted for other similar architectures

This paper presents an interleaver-division multiple access (IDMA) based architecture with single-user decoding using parallel concatenated non-linear trellis codes (PC-NLTCs). These PC-NLTCs are designed specifically for the Z-Channel that arises in a multiple-user OR channel when each user treats the other users as noise. Over the OR multiple access channel (OR-MAC) single-user decoding permits operation at about 70% of the full multiple access channel sum capacity. In order to reach the sum capacity of the OR-MAC, these codes employ a ones density of much less than 50%. A union bound technique that predicts the performance of these codes under maximum- likelihood (ML) decoding is presented. The uniform interleaver analysis presented in this paper can be applied to any asymmetric channel, as long as an additive distance can be defined. Results for different numbers of users and a sum-rate of 60% are presented.

This paper presents trellis codes for the Z channel designed to maintain a relatively low ones density. These codes have applications in pulse-position modulation systems and as a solution for uncoordinated communication on the binary OR multiple-access channel (MAC). In this paper we consider the latter application to demonstrate the performance of the codes. The OR channel provides an unusual opportunity where single-user decoding permits operation at about 70% of the full multiple-access channel sum capacity. The interleaver-division multiple access technique applied in this paper should approach that performance with turbo solutions. However, the current paper focuses on very low latency codes with simple decoding, intended for very high speed (gigabits per second) applications. Namely, it focuses on nonlinear trellis codes that provide about 30% of the full multiple-access sum capacity at high speeds and with very low latency. These trellis codes are designed specifically for the Z-Channel that arises in a multiple-user OR channel, when the other users are treated as noise. In order to optimize the sum-capacity of the OR-MAC, the trellis code transmits codewords with a ones density much less than 50%. Also, a union bound technique that predicts the performance of these codes is presented. Results from simulations and a working FPGA implementation are shown.

This paper describes an implementation, analysis and improvements to MATE (MPLS adaptive traffic engineering) algorithm. MATE is an on-line load balancing algorithm. As MATE was originally thought for constant average incoming traffic, the first improvement is the usage of an adaptive update step size for time varying traffic. The second one modifies the time interval between updates to adequate itself to the traffic characteristics and calculates the amount of measurements in each interval to have a reliable statistic. The original algorithm and the new version, which would be called MATE-TV (MATE for time-varying traffic), were implemented in a LINUX-MPLS network, using the 'mpls-linux' packet distributed by Source Forge.