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We present a new way of operation for the convolutional interleaver of an asynchronous digital subscriber line (ADSL) modem, exploiting the single latency path through the modem. A combined buffer is added after the Reed-Solomon (RS) coders in order to support the parallel way of operation. On the other hand, the combined buffer increases the correcting capabilities of the structure in case the fast path through the modem used, as it serves as an interleaver with a depth of two. The interleaving process is of the double byte kind. The proposed structure offers a performance equivalent to that achieved by a conventional interleaver with a depth of interleaving of double size, reducing thus significantly the delay caused by the interleaver. The gains achieved range from 50% to even a 100%.

The performance of the Reed Solomon coder/decoder for an ADSL modem is studied. The proposal incorporates a new faster parallel structure for the RS coding/decoding part of the modem that exploits the single latency operation of the device. The modem is fully compatible with the existing standard of T1E1.4 ANSI Standard Group and ADSL Forum requirements. The proposed structure was simulated and the results confirmed significant savings. Only the coding/decoding part of the modem was simulated. The simulation results of the parallel structure showed approximately 50% improvement in the speed of the RS coding/decoding operation. The correcting possibilities of the RS code were also confirmed and shown in the simulation results. The paper is organized as follows. The specific structure of the modem is presented. A brief introduction to Reed Solomon codes for ADSL applications is then given. Finally, the simulation results are presented.

A Reed-Solomon coder/decoder combined with a trellis encoder for an ADSL modem for ATM applications is presented and its performance is studied. The proposal incorporates a faster structure for the RS coding/decoding part of the modem that exploits the single latency operation of the device. The modem, as well as the proposed changes in it, is fully compatible with the existing standard of the T1E1.4 ANSI Standard Group. The proposed structure and the results obtained confirmed the significant savings that can be achieved by its application. Here, the coding/decoding part of the modem was simulated, only. The simulation results showed an approximate 50% improvement in the speed of the RS coding/decoding operation. Due to the operation speed up, deeper interleaving or faster transmission could be achieved leading to an improvement in the performance of the whole system. For further gains, a trellis encoder was added to the RS coder in a concatenated scheme. The paper is organized as follows: first, the introduction and the proposed modem structure are given; then follow the Reed Solomon and trellis codes used in the simulations; finally, we give the simulation method, results and conclusions.

In this paper we present the simulation results of a concatenated Reed Solomon-convolutional encoder scheme. The structure proposed was designed with the purpose of being used in ADSL applications. RS (255,239) is used as the outer code, which is proposed by the ANSI T1E1.4 Standard Group. The role of the inner code is undertaken by a convolutional encoder, which protects the outer one from random errors, while the RS code is responsible for the correction of burst errors. The noise model used, AWGN, is generally accepted as the worst case for ADSL transmission. A burst impulsive noise was also simulated proving the correcting capabilities of the RS code. The paper is organized as follows: After the introduction, a description of the simulated system is given. Next, the simulation method is described. The results from the simulation are represented, and, finally, the conclusions and some proposals for the improvement of the system are given.

A faster structure for an asynchronous digital subscriber line (ADSL) modem is presented. The simulation results show an improvement of up to 50%, depending on the application. The structure exploits the path remaining idle in single latency transmission, through the Reed Solomon codecs, improving the correcting capabilities without increasing the latency.