d, namely transparent and non-transparent. A non-transparent RS can operate in both centralized and distributed scheduling mode, while a transparent RS can only operate in centralized scheduling mode. A transparent RS communicates with the base station and subordinate mobile stations using the same carrier frequency. A non-transparent RS may commu- nicate with the base station and the subordinate mobile stations via the same or different carrier frequencies. CHAPTER 3 IEEE 802.16m Reference Model and Protocol Structure Packets Packets Reports Service Flow Service Flow Classification Declassification Header Compression Header Decompression Payload Selection and ARQ and ARQ and Sequencing Packet Segmentation Packet Reassembly PDU Formation and PDU Retrieval and Priority Handling Multiplexing De-multiplexing Encryption Dercryption Re-transmission Control Redundancy Redundancy Version Version Channel Coding Channel Decoding Modulation Scheme Data Modulation Data Demodulation MIMO Mode Selection MIMO Encoding MIMO Decoding Resource/Power Resource Mapping Resource Demapping Assignment Antenna Mapping Antenna Mapping Antenna Demapping FIGURE 3-15 IP Packet processing and retrieval in the BS and MS 3.2 The IEEE 802. 16m protocol structure Relaying in the IEEE 802.16m system is performed using a decode-and-forward paradigm and supports TDD and FDD duplex modes. In TDD deployments, the relay stations operate in time-division transmit and receive (TTR) mode, xii whereby the access and relay link communications are multiplexed using time division multiplexing over a single RF carrier. In the IEEE 802.16m system, the relay stations operate in non-transparent mode, which essentially means that the relay stations compose and transmit the synchronization channels, system information, and the control channels for the subordinate stations. In any IEEE 802.16m deployment supporting relay functionality, a distributed scheduling model is used where each infrastructure station (BS or RS) schedules the radio resources on its subordinat