e other direction (upstack), measurement reports about the received signal strength on certain subchannels must be sent in regular intervals from the PHY layer SO that CQI messages can be prepared in higher-layer control plane units. These issues are on a link basis (i.e., there is no need to handle relays in any special way). The UT side of a relay (RNUT) acts like a UT and sends CQI information back to its base station. The BS side of a relay (RNBS) receives CQI messages from its UTs and uses this information for its local downlink scheduling. 8.3 Reducing Infrastructure Deployment Costs Multihop networking claims to reduce deployment costs because it is assumed that RNs are much cheaper than BSs. Regarding CAPEX and OPEX, there is no need for any fixed line access to RNs, but BSs require expensive fiber lines. It is hard to get real expenditure numbers from operators. A simple analysis can help here. Let CBS be the cost of a BS and CRN that of an RN. All costs include CAPEX and OPEX over a period of, say, 8 years. For a coverage extension scenario with three RNs, we know that the covered multihop area is AMH=3X ASH. Thus, the costs for serving this area with multihop are CMH CBS+3X CRN compared to CSH = 3 X CBS. Therefore, it is an advantage of multihop if CMH CSH-that is, It is not hard to meet this cost requirement. There is more on this topic in Timus [28]. 8.4 Data Link Layer Algorithms for Multihop The data link layer functionality is what makes a radio system characteristic [5]. Typically, each radio system has its own timing; that is, frames look different- some are frequency division duplex (FDD) and some are time division duplex [10]. (TDD), the number of resources in frequency and time direction is different, and SO on. Also, the functional units inside layer 2 differ a lot. In this section, the detailed units in layer 2 are shown and discussed with respect to their importance for relaying. © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology 8.4.1 Frame T