Adoption of relay stations has been commonly accepted as a key technique for future IMT-advanced 4G systems to improve the link performance. While study in relay systems is often carried out for individual users independently, in this paper, we present a design termed as relay-based multi-user cooperative communication specifically for the uplink of 4G systems. In this system, data streams from multiple users are coded at the relay with an invertible matrix in finite field. These coded data, with information of one user being spread into other data streams, are forwarded by the RS to the base station (BS). The relayed data received at the BS will work together with those received through the direct links between mobile stations (MS) and BS to implement a cooperative process. This is carried out using a turbo decoding process that alternates the decoding between a multi-user decoder and a number of single-user decoders. It is shown through the simulations that the decoding converges within two or three iterations, yet indeed provides significant gains compared with a reference relay system where each user is processed individually.

The technical feasibility of applying a fiber-optic multilevel QAM (quadrature amplitude modulation) subcarrier multiplexing scheme to a multichannel conventional TV signal transport is explored. This transport scheme has some advantageous features. Because a digital subcarrier modulation scheme is used, a high-quality transmission performance is expected to be achieved, if the bit error is sufficiently small over a transmission line and the required carrier-to-noise ratio (CNR) is relatively small among the many candidates of subcarrier modulation schemes. The use of multilevel modulation allows the bandwidth to be efficiently utilized; consequently, up to 40-channel uncompressed digital TV signals are estimated to be accommodated in the frequency region of the VHF and UHF bands, where well-developed and inexpensive electronics can be easily applied.>