ance improvement. The services and functions of MAC include: mapping between logical channels and physical channels; selection of appropriate transport format for each transport channel, depending on source rate; priority handling between data flows of MT; priority handling between MTs by means of dynamic scheduling; identification of MTs on common transport channels; multiplexing/demultiplexing of upper layer protocol data units (PDUs) into/from transport blocks delivered to/from the physical layer on common transport channels; multiplexing/demultiplexing of upper layer PDUs into/from transport block sets delivered to/from the physical layer on dedicated transport channels; traffic volume measurement; transport channel type of switching; ciphering for transparent mode RLC; and access service class selection for RACH and CPCH (common packet chan- nel) transmission. 2.2.2.4 Intercell Interference Mitigation According to the features of next-generation mobile communication systems, the theory and the corresponding implementation method of soft fractional frequency reuse (SFFR) were first proposed based on the theories of extension set. FuTURE TDD employed SFFR to ensure the QoS for those users at the cell edge under; to resolve the problem of intercell interference exits in the next-generation mobile communication system, which mainly adopted FDMA technology; and to greatly improve the utilization of limited frequency resources. As an important strategy to avoid intercell interference, frequency reuse has already been studied for tens of years. Although CDMA-based systems, with a © 2009 by Taylor & Francis Group, LLC Evolution from TD-SCDMA to FuTURE frequency reuse factor of one, have been developed in 3G systems, it appears that OFDMA-based systems will still play a dominant role in the next-generation mobile systems. Therefore, an efficient frequency reuse strategy, as well as enhanc- ing performance for the cell-edge users, is still left as an open research issue for those FDMA-based systems. To use the spectru