This document discusses key concepts of OFDMA and WiMAX including: 1. OFDMA divides subcarriers into groups called sub-channels that can be allocated to different receivers or transmitters. 2. Sub-channelization allows a WiMAX base station to allocate more transmit power to users with lower signal strength and less power to those with higher signal strength. 3. A cyclic prefix is used to avoid intersymbol interference and intercarrier interference.

1. Basics for WI-MAX Binoy Tomy NexGTech Wireless R & D [email_address] +91 9952170483

2. INTRO WiMAX air interface is based on OFDM/OFDMA physical layer (PHY).

3. To understand how OFDM and OFDMA work, lets start with its "mother" namely FDM (Frequency Division Multiplexing).

4. OFDMA Like OFDM, OFDMA employs multiple closely spaced sub-carriers, but the sub-carriers are divided into groups of sub-carriers.

5. Each group is named a sub-channel.

6. The sub-carriers that form a sub-channel need not be adjacent.

7. In the downlink, a sub-channel may be intended for different receivers. In the uplink, a transmitter may be assigned one or more sub-channels.

8. Sub-channelization Sub-channelization defines sub-channels that can be allocated to subscriber stations (SSs) depending on their channel conditions and data requirements.

9. Using sub-channelization, within the same time slot a Mobile WiMAX Base Station (BS) can allocate more transmit power to user devices (SSs) with lower SNR (Signal-to-Noise Ratio), and less power to user devices with higher SNR.

10. Sub-channelization in the up-link can save a user device transmit power because it can concentrate power only on certain sub-channel(s) allocated to it.

11. This power-saving feature is particularly useful for battery-powered user devices, the likely case in Mobile WiMAX.

12. Cyclic Prefix To avoid ISI and ICI

13. A copy of last part of the OFDM symbol is prepended to the T.Xed symbols and removed at the receiver