in the RN until the UL resources are available for hop one. © 2009 by Taylor & Francis Group, LLC Multihop Extensions to Cellular Networks Therefore, the relaying problem simplifies to the control of resources, which is a task of any central, base-station-controlled cellular system, anyway. Typical scenarios for cellular multihop operation are shown in Figures 8.2 and 8.3. In the coverage extension scenario, the supported area (regarding sufficient SINR) around relay nodes is of the same size as the single-hop area around the base station. The inner hexagon is typically served by BS within its range, and the outer regions are served by one of the three RNs. For capacity extension, the whole hexagonal area can be served by the BS, but in regions closer to the cell border and near the RN, the RN offers a much higher data rate to user terminals than the BS would. Being served by a RN means that an intracell handover has been performed in which the decision has been made that the UT is better supported by the RN than by the BS. "Better" means not only that the UT receives a higher SINR at its current position, but also that the total number of resources needed for hop one (BS-RN) and hop two (RN-UT) is less than what would be required if it were a single-hop transmission between BS and UT. That is, relaying is the most efficient way to handle the UT traffic, both locally for the UT and globally for the spectral efficiency of the cell. Figures in Section 8.5 show the typical SINR conditions and the resulting supported rate around BS and RNs. Another scenario typically used is the city or Manhattan scenario, where base stations placed on road crossings provide coverage only for those two streets with line-of-sight (LOS) contact to the UTs. Other areas are shadowed SO that a trans- mission is not possible. Any relay placed on street corners immediately helps in serving another street [12,19]. Although relays are possible for all kinds of transmission schemes, OFDM has evolved as an efficient multiplex scheme of typicall