An Approach To The PHY Layer
The PHY layer must be able to adapt to different conditions and also needs to be flexible for jumping from channel to channel without errors in transmission or losing clients (CPEs). This flexibility is also required for being able to dynamically adjust the bandwidth, modulation and coding schemes. OFDMA will be the modulation scheme for transmission in up and downlinks. With OFDMA it will be possible to achieve this fast adaptation needed for the BS's and CPEs. By using just one TV channel (a TV channel has a bandwidth of 6 MHz; in some countries they can be of 7 or 8 MHz) the approximate maximum bit rate is 19 Mbit/s at a 30 km distance. The speed and distance achieved is not enough to fulfill the requirements of the standard. The feature Channel Bonding deals with this problem. Channel Bonding consists in using more than one channel for Tx / Rx. This allows the system to have higher bandwidth which will be reflected in a better system performance.
Read more about this topic: IEEE 802.22
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