One of the main OPEX (operational expenditure) drivers in mobile networks today is the requirement to connect each base station directly to the network. In most cases this means installing a cable or microwave connection at each base station site. For fixed line connections, UMTS/HSPA base stations mostly use a number of E-1 or T-1 links today, each being capable of transmitting about 2 MBits/s. With rising bandwidths, however, using several E-1 links for each base station will soon become difficult for both cost and availability of wires. Alternatives are fiber or using a transmission technology which can get more out of a pair of copper cables. Nevertheless, it will remain expensive.
For WiMAX networks, the IEEE has started in 2006 to work on 802.16j "Mobile Multihop Relay" (MMR). The basic idea behind MMR is to allow WiMAX base stations which do not have a backhaul connection to communicate with base stations that do. On the one hand this will of course reduce the bandwidth available to users in the cells involved in relaying packets. On the other hand it's an elegant way to save costs and extend network coverage into areas where connecting a base station directly to the network via a fixed line connection is economically or technically not feasible.
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