This is a broad-scoped standard for systems that operate between 10 and 66 GHz for a fixed point-to-multipoint service. The air interface involves both PHY and MAC sublayers. There is a base station (BS) connected to the PSTN. The BS serves a number of subscriber stations (SS). BS and SSs are stationary. Figure 13.6 is the IEEE 802.16 reference model.
The system provides for broadband channels, 20, 25, or 28 MHz for both downlink and uplink, full-duplex or half-duplex, multiple access TDM/TDMA. The IEEE 802.16 system can tradeoff capacity with robustness in real-time.
On the downlink, the SS (subscriber station) is associated with a specific burst. On the uplink, the SS is allotted a variable length time slot for their transmissions. When using time-division duplex (TDD), the downlink and uplink share the same RF channel. However, for economic design the downlink and uplink do not transmit simultaneously. A typical TDD frame is illustrated in Figure 13.7.
Figure 13.8 shows the IEEE 802.16 TDD downlink subframe. When using the frequency division duplex option, the downlink and uplink are on separate RF channels. For the half-duplex option, the SS does not transmit and receive simultaneously. Figure 13.9 shows FDD burst framing and how it allows scheduling flexibility. Figure 13.10 shows FDD downlink subframe. Table 13.1 gives an overview of IEEE 802.16 modulation rates and channel sizes. It shows a flexible plan allowing manufacturers to choose according to spectrum requirements.
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