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Wimax ofdma
- 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
- 14. Data subcarriers for data transmission.
- 15. Pilot subcarriers for various estimation and synchronization purposes.
- 16. Null subcarriers for no transmission at all, used for guard bands and DC carriers. Type of OFDMA Subcarrier
- 17. Advantages Effective against ISI and multipath fading
- 18. Can adjust modulation and coding for each carriers
- 20. Low complexity modulation that can easily be implemented using IFFT/FFT
- 21. SOFDMA SOFDMA (S-OFDMA) adds scalability to OFDMA.
- 22. Scales the FFT size.
- 23. Smaller FFT size is given to lower bandwidth channels, while larger FFT size to wider channels.
- 24. OFDMA mode used in IEEE 802.16e.
- 25. Bandwidth : 1.25 MHz to 20 MHz.
- 26. Vary the number of subcarriers and control transmission rates and the number of individual users simultaneously.
- 28. Number of Subcarrier scales with Bandwidth.
- 29. Based on the concept of Subchannel, the smallest unit of Bandwidth allocation is fixed and independent of Bandwidth.
- 30. Capacity of each individual subchannel remains constant.
- 31. Features 1, Advanced Modulation & Coding. 2, Hybrid Automatic Repeat Request. 3, High-efficiency uplink subchannels structures. 4, Multiple input Multiple output diversity. 5, Inter operability.
- 33. PARAMETERS