This paper proposes a multihop mobile communications system using an MC-CDMA transmission technique in the forward links. In the system, it is assumed that each mobile station has a relaying function where a frequency band is used both in the 1st and 2nd hops henceforth. Then, we examined a radio resource allocation method in the forward links. In this method, an orthogonal codeword is assigned for each group that consists of one or more mobile stations and the resources of time and frequency are distributed to each link within a group. To clarify the characteristics of this method, we compared the proposed system and a conventional one without relaying, in terms of the base station connection rate and throughput, and so on. Simulation results indicate that the proposed system improves the connection rate without further orthogonal codewords consumption, and user throughput in an appropriate mobile station density.
I. IRealization of an even greater high-speed wireless transmission service is expected because Internet access in the mobile communications environment has become widespread, and the range of applications such as pictures and animations has increased. The next generation mobile communications system, which realizes wideband and high-speed transmission, has been examined recently, and various transmission methods have been proposed. Above all, multi-carrier transmission systems, such as orthogonal frequency division multiplexing (OFDM) and multi-carrier code division multiple access (MC-CDMA) have attracted particular attention from the viewpoints of frequency efficiency and robustness against multipath propagation. Research aimed at adoption of these transmission systems in the next generation mobile communications system is ongoing [1]. However, in the process of improvement in data transmission speed, increase in the required electric power of received signals caused by high-speed transmission, and system deployment in high frequency bands are assumed. These two factors lead to reduction of the coverage area, and therefore many base stations are needed in order to deploy cells without dead spots. This issue must be examined in establishing next generation systems [2].In order to solve this coverage reduction problem, research has focused on a multihop mobile communications system in which a user terminal connects to a base station via other user terminals or relay terminals, and application to access methods, such as time division multiple access (TDMA) and code division multiple access (CDMA), have been proposed[3]- [5]. It is necessary to examine the feasibility of the multihop system, which is based on multi-career transmission methods. In particular, if the same frequency band as direct transmission between base station and user terminals is used for relay transmissions, signal transmissions by relay cause interference, and it is necessary to show clearly how the interference affects the system, which is based on multi-career transmissions.This paper proposes a multihop mobile communi...