Wimax ofdma
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Wimax ofdma



basic for wimax study

basic for wimax study



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    Wimax ofdma Wimax ofdma Presentation Transcript

    • Basics for WI-MAX Binoy Tomy NexGTech Wireless R & D [email_address] +91 9952170483
    • INTRO
      • WiMAX air interface is based on OFDM/OFDMA physical layer (PHY).
      • To understand how OFDM and OFDMA work, lets start with its "mother" namely FDM (Frequency Division Multiplexing).
    • OFDMA
      • Like OFDM, OFDMA employs multiple closely spaced sub-carriers, but the sub-carriers are divided into groups of sub-carriers.
      • Each group is named a sub-channel.
      • The sub-carriers that form a sub-channel need not be adjacent.
      • 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.
    • Sub-channelization
      • Sub-channelization defines sub-channels that can be allocated to subscriber stations (SSs) depending on their channel conditions and data requirements.
      • 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.
      • 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.
      • This power-saving feature is particularly useful for battery-powered user devices, the likely case in Mobile WiMAX.
    • Cyclic Prefix
      • To avoid ISI and ICI
      • A copy of last part of the OFDM symbol is prepended to the T.Xed symbols and removed at the receiver
      • Data subcarriers for data transmission.
      • Pilot subcarriers for various estimation and synchronization purposes.
      • Null subcarriers for no transmission at all, used for guard bands and DC carriers.
      Type of OFDMA Subcarrier
    • Advantages
      • Effective against ISI and multipath fading
      • Can adjust modulation and coding for each carriers
      • Better spectral efficiency
      • Low complexity modulation that can easily be implemented using IFFT/FFT
    • SOFDMA
      • SOFDMA (S-OFDMA) adds scalability to OFDMA.
      • Scales the FFT size.
      • Smaller FFT size is given to lower bandwidth channels, while larger FFT size to wider channels.
      • OFDMA mode used in IEEE 802.16e.
      • Bandwidth : 1.25 MHz to 20 MHz.
      • Vary the number of subcarriers and control transmission rates and the number of individual users simultaneously.
      • Subcarrier Spacing.
      • Number of Subcarrier scales with Bandwidth.
      • Based on the concept of Subchannel, the smallest unit of Bandwidth allocation is fixed and independent of Bandwidth.
      • Capacity of each individual subchannel remains constant.
    • 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.