Two very important and active areas of wireless research are multihop relaying and multiple antenna techniques. Wireless multihop relaying can increase the aggregate network data capacity and improve coverage of cellular systems by reducing path loss, mitigating shadowing, and enabling spatial reuse. In particular, multihop relaying can improve the throughput for mobiles suffering from poor signal to interference and noise ratio at the edge of a cell and reduce cell size to increase spectral efficiency. On the other hand, multiple antenna techniques can take advantage of scattering in the wireless channel to achieve higher capacity on individual links. Multiple antennas can provide impressive capacity gains, but the greatest gains occur in high scattering environments with high signal to interference and noise ratio, which are not typical characteristics of cellular systems. Emerging standards for fourth generation cellular systems include both multihop relaying and multiple antenna techniques, so it is necessary to study how these two work jointly in a realistic cellular system. In this paper, we look at the joint application of these two techniques in a cellular system and analyze the fundamental tradeoff between them. In order to obtain meaningful results, system performance is evaluated using realistic propagation models.
Abstract-In this paper we look at the network throughput and efficiency of a cellular system employing multi-hop relaying. It is shown that multi-hop relaying can provide great improvement in the area averaged spectral efficiency (measured in bits/second/Hz per unit area of coverage) of a system. However, the number of relays introduced and the dimensions of coverage areas of relays must be carefully chosen for the specific propagation environment and system parameters, otherwise poorer efficiency may result. Some example designs for the 5 GHz unlicensed band are given to illustrate some design considerations. Realistic simulated throughput, considering physical and medium access control layer overhead, of a HiperMAN or 802.16 system together with noise and interference calculations are used to determine potential real-world performance of such systems. Calculations for one to four relay hops are presented and designs' area averaged spectral efficiencies are compared.
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