Optical orthogonal code (OOC) sequences are assigned to optical code-division multiple-access (CDMA) network users, who are then able to transmit data asynchronously through this network. In this work, we present two systematic OOC design techniques based on extended sets. The first technique is a deterministic design approach where the OOC sequences are generated in a single run. We demonstrate that with this design strategy, although not optimal, sequences of relatively short length can be obtained and hence, the required system bandwidth can be feasible for asynchronous intensity-modulation/direct-detection (IM/DD) optical CDMA systems. The second design technique is semi-random and may require multiple iterations until all OOC sequences are generated. Although computationally more cumbersome, this design method is able to converge to the optimal OOC and hence, enables minimum required system bandwidth for the optical CDMA system under consideration.

In this letter, we propose an efficient decoding algorithm for turbo product codes as introduced by Pyndiah. The proposed decoder has no performance degradation and reduces the complexity of the original decoder by an order of magnitude. We concentrate on extended Bose-Chaudhuri-Hocquengem codes as the constituent row and column codes because of their already low implementation complexity. For these component codes, we observe that the weight and reliability factors can be fixed, and that there is no need for normalization. Furthermore, as opposed to previous efficient decoders, the newly proposed decoder naturally scales with a test-pattern parameter p that can change as a function of iteration number, i.e., the efficient Chase algorithm presented here uses conventionally ordered test patterns, and the syndromes, even parities, and extrinsic metrics are obtained with a minimum number of operations.

Multimode fiber links suffer from intermodal dispersion, which, at high data rates, produces intersymbol interference in the received optical signal. Without signal processing or equalization, this limits the achievable data rates. We consider the combination of a spatially resolved equalizer (SRE) (in the optical domain) and forward error correction (FEC) to increase the achievable data rates and reliability on these links. Our performance results obtained with actual measured impulse responses show that SRE and FEC on a multimode fiber link enable a significant increase (about 2.5 times) in data rate and/or a reduction in bit error rate (BER) at relatively low cost. Furthermore, we show that improvements in data rate and reliability are generally not possible using FEC alone, making the SRE/FEC combination a cost-effective, attractive approach.

The application of turbo product codes (TPC) in asynchronous (or synchronous) intensity modulated direct detection optical code division multiple access (CDMA) systems with on-off keying (OOK) is proposed in this study. Optical multiple access interference (OMAI) caused by other users, is the main source of noise that degrades system performance and limits the total number of active users in optical CDMA. The original turbo product decoding algorithm is modified according to the channel model of a direct detection optical CDMA system and it is shown that the implementation of turbo product codes in such a system provides significant improvement of the bit-error rate (BER) permitting a higher number of active users with less complex transmitters and receivers.

This work proposes a new iterative application of the Chase algorithm on Reed-Solomon (RS) product codes. Reliability information of bit positions is calculated only once. Although the bit error rates (BER) achieved are not as good as the results obtained with the recent turbo product decoding (TPD) algorithm, decoding complexity is far less. Simulation results are presented for a communications system using binary phase shift keying (BPSK) on an additive white Gaussian noise (AWGN) channel for both hard and soft decoding iterations and their performances are compared with turbo product decoding.

The partial response channel can be viewed as a rate-1 encoder in which the output alphabet differs from the input alphabet. In serially concatenated coding schemes, the partial response channel can serve as the inner encoder. Recent work has focused on convolutional codes and parity-check codes as the outer code in such serial concatenation schemes. This work focuses instead on the use of product codes as the outer code. Systems using both hard and soft decoding, with both iterative and non-iterative decoding, are presented. Simulation results are presented comparing performance of product codes which use Reed-Solomon and BCH codes as the constituent codes.