Changes between Version 8 and Version 9 of OFDM/MIMO/Docs/PHYDetails/FrameFormat


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Timestamp:
Aug 30, 2009, 1:09:29 PM (13 years ago)
Author:
murphpo
Comment:

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  • OFDM/MIMO/Docs/PHYDetails/FrameFormat

    v8 v9  
    1111
    1212'''SISO Frame Format'''[[BR]]
    13 [[Image(OFDM/MIMO/Docs/Images:SISO_Frame_Format.png, 684)]]
     13[[Image(OFDM/MIMO/Docs/Images:FrameFormat_SISO.png, 684)]]
    1414
    1515'''Alamouti Frame Format'''[[BR]]
    16 [[Image(OFDM/MIMO/Docs/Images:SISO_Frame_Format.png, 684)]]
     16[[Image(OFDM/MIMO/Docs/Images:FrameFormat_Alamouti.png, 684)]]
    1717
    1818'''Multiplexing Frame Format'''[[BR]]
    19 [[Image(OFDM/MIMO/Docs/Images:MIMO_Frame_Format.png)]]
     19[[Image(OFDM/MIMO/Docs/Images:FrameFormat_Multiplexing.png)]]
    2020
    2121=== Preamble ===
     
    2424In SISO mode, the preamble is transmitted only from the active antenna. In Alamouti and multiplexing modes, the preamble is always transmitted from antenna A and optionally from antenna B. This option is controlled by user software.
    2525
    26 In both modes, the preamble is scaled by a programmed constant. This scaling allows the full-scale swing of the preamble (+/-1 default) to match the swing of the IFFT output. The scaling constant is programmed by user software.
     26The preamble is scaled by a programmed constant. This scaling allows the full-scale swing of the preamble (+/-1 default) to match the swing of the IFFT output. The scaling constant is programmed by user software.
    2727
    2828[[Image(OFDM/MIMO/Docs/Images:preamble.png, 500)]]
    2929
    3030=== Training ===
    31 The OFDM core uses hard-coded sequence of BPSK symbols for channel training. Each repetition of the sequence is treated as a full OFDM symbol at the receiver. The number of repetitions is programmable but must be known to both the transmitter and receiver ahead of time. The training sequence is defined in the OFDM model's initialization script.
     31The OFDM core uses hard-coded sequence of pseudo-random BPSK symbols for channel training. Each repetition of the sequence occupies a full OFDM symbol period, including the usual cyclic extension. The number of repetitions is programmable but must be known to both the transmitter and receiver ahead of time. The training sequence is defined in the OFDM model's initialization script.
    3232
    33 For SISO mode, the programmed number of training symbols are inserted between the preamble and base-rate symbols. For Alamouti and multiplexing modes, the programmed number of training symbol periods are dedicated to channel estimation and are split evenly between the transmit antennas. See the frame format section below for more details.
     33For SISO mode, the programmed number of training symbols are inserted between the preamble and base-rate symbols. For Alamouti and multiplexing modes, the programmed number of training symbol periods are dedicated to channel estimation and are split evenly between the transmit antennas. In all modes, the number of training symbols must be even.
    3434
    3535=== Base Rate ===
    36 In order to maintain compatibility with nodes communicating over various distances (i.e. capable of communicating at various rates), the OFDM core allows a number of OFDM symbols to be modulated using a base-rate. The number of base-rate symbols and the assignment of base-rate modulation schemes to subcarriers must be known to both the transmitter and receiver ahead of time. In multiplexing mode, the base-rate symbols are transmitted only from antenna A.
     36In order to maintain compatibility with nodes communicating over various distances (i.e. capable of communicating at various rates), the OFDM core uses a number of OFDM symbols modulated using a base-rate. The number of base-rate symbols and the assignment of base-rate modulation schemes to subcarriers must be known to both the transmitter and receiver ahead of time. In multiplexing mode, the base-rate symbols are transmitted only from antenna A. In Alamouti mode, the base-rate symbols are transmitted from both antennas using the Alamouti STBC (just like the full-rate symbols).
    3737
    3838Generally, these base-rate symbols contain the packet's header, which enables every receiving node to know the packet's source, destination, full-rate modulation and length.
     
    4343The remaining OFDM symbols in each packet contain data modulated at the full-rate. The full-rate modulation schemes are programmable across subcarriers and antennas. The assignment of full-rate modulation schemes to subcarriers and antennas must be known to both the transmitter and receiver ahead of time.
    4444
    45 The number of full-rate symbols is calculated automatically by the transmitter based on the modulation rate and packet length specified by user code. The maximum number of full-rate symbols is 2047 (way more than enough for very long packets).
     45The number of full-rate symbols is calculated automatically by the transmitter based on the modulation rate and packet length specified by user code. The maximum number of full-rate symbols is 2047 (more than enough for very long packets).
    4646
    47 The number of full-rate symbols can be zero. This enables header-only packets. User code selects this mode by transmitting a packet whose length equals the number header bytes specified during the OFDM core initialization.
     47The number of full-rate symbols can be zero, enabling the transmission of header-only packets. User code selects this mode by transmitting a packet whose length equals the number header bytes specified during the OFDM core initialization.
    4848
    4949== Checksums ==
    50 The OFDM transmitter subsystem includes a checksum calculation and insertion block. This block will overwrite the last two bytes of the header with a 16-bit CRC calculated over the full contents of the base-rate symbols. The checksum block will overwrite the last four bytes of the packet with a 32-bit CRC calculated over the full packet, including the header. The 32-bit full-packet checksum is not used for header-only packets.
     50The OFDM transmitter subsystem includes a checksum calculation and insertion block. This block will overwrite the last two bytes of the header with a 16-bit CRC calculated over the full contents of the base-rate symbols. For packets with full-rate symbols (not header-only packets), the checksum block will overwrite the last four bytes of the packet with a 32-bit CRC calculated over the full packet, including the header. The receiver uses these checksums to assert its good/bad header/packet outputs.
    5151
    52 User code must accommodate these checksum insertions by leaving the corresponding bytes empty in packets loaded for transmission, and by ignoring these bytes when processing received packets.
     52User code must accommodate these checksum insertions by leaving the corresponding bytes empty in packets loaded for transmission, and by ignoring these bytes when processing received packets. The 2-byte header and 4-byte packet checksums must be included in the header and packet lengths provided by user code. This is handled automatically when using [source:/PlatformSupport/WARPMAC/ WARPMAC].
     53