Abstract
In this paper we show how a graph-based systemcan be designed for an N-FSK T-user multiple access channel withnoise. The channel is a frequency selective fast fading channelwith additive white Gaussian Noise. The system does not knowor attempt to determine the fading incurred at a given moment.The system is composed of a multiuser detector and T differentRepeat-Accumulate (RA) decoders. The decoders are optimizedas a set and consequently have the same parameters. A structuralvariation between the users’ encoders/decoders is sufficient toallow for multiple access and channel error correction, whileproviding rates close to channel capacity.
Highlights
Wideband channels are an option when high data rate and multiple users are desirable
In this paper we show that it is possible to transmit information using this channel with rates close to sum capacity without the need of hopping patterns
Let IAB(·) be the EXIT function that indicates how much information is transmitted from layer A to layer B, where A and B can assume the values of V (VND), C (CND), A (ACC) and D (MUD)
Summary
Wideband channels are an option when high data rate and multiple users are desirable. For this type of channel, fading is seldom flat. A drawback of traditional FFH-CDMA systems is that its hopping code with length L, used to mitigate the multiuser interference, has spectral efficiency equivalent to a repetition code with rate 1/L. This results in a sum rate that is considerably lower than the channel’s sum capacity. Some remarks about mathematical notation: P (·) is a probability mass function (p.m.f) and p(·) is a probability density function (p.d.f.) For both cases, function arguments are sufficient to identify them.
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