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Wimax ofdma
Wimax ofdma
Wimax ofdma
Wimax ofdma
Wimax ofdma
Wimax ofdma
Wimax ofdma
Wimax ofdma
Wimax ofdma
Wimax ofdma
Wimax ofdma
Wimax ofdma
Wimax ofdma
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Wimax ofdma


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basic for wimax study

basic for wimax study

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  • 1. Basics for WI-MAX Binoy Tomy NexGTech Wireless R & D [email_address] +91 9952170483
  • 2. INTRO <ul><li>WiMAX air interface is based on OFDM/OFDMA physical layer (PHY).
  • 3. To understand how OFDM and OFDMA work, lets start with its &quot;mother&quot; namely FDM (Frequency Division Multiplexing). </li></ul>
  • 4. OFDMA <ul><li>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. </li></ul>
  • 8. Sub-channelization <ul><li>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. </li></ul>
  • 10. <ul><li>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. </li></ul>
  • 12. Cyclic Prefix <ul><li>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 </li></ul>
  • 14. <ul><li>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. </li></ul>Type of OFDMA Subcarrier
  • 17. Advantages <ul><li>Effective against ISI and multipath fading
  • 18. Can adjust modulation and coding for each carriers
  • 19. Better spectral efficiency
  • 20. Low complexity modulation that can easily be implemented using IFFT/FFT </li></ul>
  • 21. SOFDMA <ul><li>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. </li></ul>
  • 27. PRINCIPLE <ul><li>Subcarrier Spacing.
  • 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. </li></ul>
  • 31. Features <ul>1, Advanced Modulation & Coding. 2, Hybrid Automatic Repeat Request. 3, High-efficiency uplink subchannels structures. 4, Multiple input Multiple output diversity. 5, Inter operability. </ul>
  • 32.