n and physical layer characteristics related to the downlink and uplink channels, respectively. The DCD and UCD messages are transmitted by every BS at regular intervals. The information contained in the DCD and UCD messages is received by the mobile stations within the coverage area of the BS. The mobile stations use the information contained in the DCD and UCD messages to learn about the downlink and uplink channel parameters, respec- tively. The DCD message is always transmitted on a DL burst described by a DL MAP IE with Downlink Interval Usage Code (DIUC) = 0; DIUC = 0 has burst profile parameters that are the same as those used for the transmission of the DL MAP message. Note that HARQ operation is optional in the IEEE 802.16-2009 standard. For FDD/H-FDD operation, if two parameters for a particular type occur in the UCD, the first parameter corresponds to H-FDD Group 1 and the second parameter corresponds to H-FDD Group 2 [1]. The contents of the DCD and UCD messages for the OFDMA physical layer are shown in Table 9-12 and Table 9-13, respectively. The different fields of these two messages are used for different purposes. While some of these fields are present in the DCD/UCD messages in all types of system configurations, other fields are present when certain system configurations are used. This is shown in the second columns of Table 9-12 and Table 9-13 for DCD and UCD messages, respectively. The information fields of the DCD message that are used for all types of system configurations are referred to as mandatory DCD information fields. On the other hand, the information fields of the DCD message that are used only for some system configurations are referred to as configuration-dependent DCD information fields. For example, BS Equivalent Isotropic Radiated Power (EIRP), Transmit/Receive Transition Gap (TTG), Table 9-12 Contents of a DCD MAC Management Message [1] Information Field in DCD Message Usage Description Downlink_Burst_Profile Always The Downlink_Burst_Profile is a compound TLV encoding that de