Deployment cost efficiency in broadband delivery with fixed wireless relays

University dissertation from Stockholm : KTH

Abstract: Although radio repeaters and wireless routers are commonly used, relaying techniques have received a lot of attention in academic publications the last decade. Most of the techniques proposed in the literature are based on relaying terminals. For instance groups of mobile terminals cooperate so as to jointly communicate with an access point, or to another group of mobiles in an (infrastructure-less) mobile ad-hoc network MANET. However, it has also been suggested that these techniques can be applied to hybrid cellular-relaying architecture with fixed relays and that this would reduce the infrastructure costs.The literature shows that the coverage or capacity of a cellular network is enhanced when using relays. A common assumption in these studies is that relays are very low cost, but little attention has been given to how cheap these relays need to be in order for the technical enhancements to translate into an economic gain. It is not obvious that the techniques proposed for mobile relaying are economically feasible when applied to fixed relays.This thesis examines the conditions under which large scale usage of fixed relays leads to lower infrastructure cost than in a purely cellular architecture, how large the benefits of these new techniques are, compared with existing repeater/router techniques, and how sensitive the results are to traditional network design parameters.The analysis is done by means of several study cases in which coverage should be provided for broadband services by building a network from scratch. The results are expressed in terms of how cheap a relay must be with respect to a base station's cost so that the hybrid infrastructure provides the desired service at a lower cost. If in practice this relative relay cost is much lower, then high economic gains are expected.None of the study cases considered yield substantial cost savings when using fixed relays on a large scale. When access points are placed as high as in a cellular network, the hybrid system is feasible only if the total relay cost is 3-20% of the total base station cost. When unplanned relay deployment is used, the impact of the antenna height and/or gain on the results is much greater than the particular type of amplify-and-forward relaying scheme. Planned deployment of a few relays should be used unless the cost of planning is 1-2 times larger than all the other relay costs. A proper trade-off between route-length and how tight the radio channel can be reused is essential for the feasibility of the hybrid system. The results confirm that the planned usage of few relays together with macro-like base stations is an efficient way of providing coverage. Analysis of other scenarios, such as the use of pico base stations for coverage, is left for further studies.