 versus Fixed Relays 8.2.5 Theory of Relay-Enhanced Operation 8.2.6 Cross-Layer Issues Reducing Infrastructure Deployment Costs Data Link Layer Algorithms for Multihop 8.4.1 Frame Timing (Radio Frame, TTI Frame) 8.4.2 Scheduling 8.4.2.1 Dynamic Subcarrier Assignment (DSA) 8.4.2.2 Adaptive Modulation and Coding (AMC) 8.4.2.3 Adaptive Power Allocation (APA) © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3 GPP LTE Radio and Cellular Technology 8.4.3 Closed-Loop Control 8.4.4 Forward Error Correction (FEC) 8.4.5 Automatic Repeat Request (ARQ) 8.4.6 Hybrid ARQ (HARQ) 8.4.7 Radio Resource Management (RRM) 8.4.8 Signaling 8.4.9 Handover Decision 8.4.10 Channel Quality Indication (CQI) 8.4.11 Routing 8.4.12 Intercell Interference Mitigation 8.4.13 Full- and Half-Duplex FDD Performance Evaluation 8.5.1 Sequential Multihop Scenario 8.5.2 Ideal Cellular Scenario 8.5.3 Parameter Discussion 8.5.4 Realistic Single-Cell Scenario References Introduction In technologies developed a few years ago, the use of relays has hardly been studied, not to mention any standardization taking place. Long term evolution (LTE) docu- ments SO far do not contain many hints about the use of relays [1,6,7,8]. A relay can be built for a kind of stealth mode SO that it appears exactly like a user terminal (UT) toward the wired base station (BS) and behaves like a BS toward the UTs associated with it [12]. However, radio resources are a scarce good, SO it is much better to inte- grate multihop extensions right from the beginning into the protocol [2,3]. 8.1.1 Motivation for Multihop There will always be a demand for high data rates in large areas. Any public radio communication technology aims at providing high radio capacity and large cover- age. Unfortunately, the properties of radio wave propagation [35] limit the ideals to certain bounds. What the conventional cellular architecture offers does not match the demand for several reasons. The limited power problem. The transmit power of any sender is limited by regulations SO that there is