Duplex FDD (H-FDD) Frequency Separation H-FDD with Complementary User Grouping (Group A) (Group B) (Group A) (Group B) Frequency Separation UL (Group B) (Group A) (Group B) (Group A) Radio Frame Radio Frame Listening to DL Broadcast Channels (No UL Transmission) FIGURE 9-14 An illustration of different duplexing scheme concepts The IEEE 802. 16m basic frame structure is illustrated in Figure 9-15. A superframe is defined as a set of four consecutive and equally-sized radio frames. Each 20 ms superframe contains a Primary Superframe Header (P-SFH) and a Secondary Superframe Header (S-SFH). As shown in Table 9-2, the number of subframes per frame varies depending on the cyclic prefix size, the number of available OFDM symbols per frame, and the transmission bandwidth. A subframe is assigned to either DL or UL transmissions subject to the duplexing method. The basic frame structure with CP = 1/8T, due to backward compatibility with the legacy system, is of higher importance. The CP = 1/16T is used when the sum of Round Trip Time (RTT) and the RMS delay spread of the channel is less than 5.71 us, assuming transmission bandwidths of 5, 10, or 20 MHz. There are four types of subframes defined in the IEEE 802.16m standard: (1) type-1 subframe consists of six OFDM symbols; (2) type-2 subframe consists of seven OFDM symbols; (3) type-3 subframe consists of five OFDM symbols; and (4) type-4 subframe consists of nine OFDM symbols. The basic frame structure is applied to both FDD and TDD duplexing schemes including H-FDD operation. The number of switching points in each radio frame in TDD mode is limited to two, where a switching point is defined as a change of transmission direction from DL to UL or from UL to DL. Note that an excessive number of switching points in a radio frame CHAPTER 9 The IEEE 802. 16m Physical Layer (Part I) Superframe = 20 ms Frame = 5 ms Subframe Superframe Headers Symbol FIGURE 9-15 The IEEE 802. 16m basic frame structure [2] would result in inefficient use of radio resources due to consumption of 