LTE, LTE-Advanced and WiMAX: Towards IMT-Advanced Networks

Relaying

While a variety of MIMO techniques can be utilized at the BS side, the MS options are limited. In fact, it is physically challenging for a MS to support multiple antennas. Consequently, the network designer needs to find a solution to bring the MIMO virtues to MSs especially at the cell-edge. Such a solution has been found in cooperative communications techniques, also known as cooperative diversity, [8, 9]. Using these techniques, single-antenna MSs can enjoy the MIMO advantages through mutually relaying their signals to the BS. However, this cooperation overcomplicates the processing at the BS side as well as the pricing policies. In addition, it will cause a significant reduction in the MSs battery-lives, which is a critical issue for the users. Consequently, dedicated Relay Stations (RSs) have been proposed to replace the user-cooperation. These stations are not given high-processing or decision-making capabilities; hence they are much cheaper than BSs. As a result, they can be used to increase the coverage area, reduce the transmission range from and to the MSs, hence increasing their achievable throughputs by increasing their Signal to Noise Ratios (SNRs). Unlike BSs, RSs access the network backbone through the BSs. Hence, careful resource allocation strategies are needed. For all these reasons, RSs provide a lower Operational Expenditure (OPEX) and Capital Expenditure (CAPEX) option that allows faster roll out and a flexible configuration.

A variety of RS deployment ...