, defined in a unit of subframes. For uplink transmissions both Time Division Multi- plexing (TDM) and Frequency Division Multiplexing (FDM) approaches can be used when supporting CHAPTER 9 The IEEE 802. 16m Physical Layer (Part I) TDD Radio Frame = 5 ms DL (6) DL (7) DL (6) DL (6) DL (6) UL (6) UL (6) UL (7) 6 OFDM Symbols = 0.583 ms 7 OFDM Symbols = 0.680 ms Switching Gaps Idle Time DL/UL (6) DL/UL (7) DL/UL (6) DL/UL (6) DL/UL (7) DL/UL (6) DL/UL (6) DL/UL (7) FDD Radio Frame = 5 ms FIGURE 9-17 The frame structure with CP = 1/16 Tu for FDD and TDD (DL/UL ratio = 5:3) [2] TTG and RTG Gaps Legacy UL Zone Legacy UL Zone New UL Zone New UL Zone Legacy Radio Frame from the Point of View of Legacy BS/MS New Radio Frame from the Point of View of Legacy BS/MS Frame Offset New Frame Duration = 5 ms Legacy Frame Duration = 5 ms FIGURE 9-18 An example of partitioning of the radio frame and the relationship of the new and legacy frames 9.7 The concept of time zones and frequency regions legacy and new mobile stations. The FDM approach is preferred to ensure minimal impact on the uplink link budget of the legacy terminals. 9.7 THE CONCEPT OF TIME ZONES AND FREQUENCY REGIONS As shown in Figure 9-19, a time zone is defined as a time-frequency region which includes the entire transmission bandwidth extended over an integer number of consecutive subframes. Different non- overlapping time zones are time division multiplexed in time. A frequency region is a time-frequency block that occupies a fraction of the transmission bandwidth over one or more consecutive subframes in the downlink or uplink. The concept of time zones is equally applied to TDD and FDD modes. Since many physical and MAC layer features of IEEE 802.16m are new and not backward-compatible with the legacy system, the new and legacy systems are confined within time zones or frequency regions that are time or frequency multiplexed in each radio frame, respectively. The MZones are defined as time zones/frequency regions dedicated to IEEE 802.16m operation, and the L