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WLAN

802.11ac Transmitter Block

The description of each block included in these block diagrams is provided in the table at the end of this topic.

 

 

Figure 1 - Transmitter Block Diagram for Single User

 

 

Figure 2 - Transmitter Block Diagram for Multi-User MIMO

Block Description
PHY Padding Appends the PHY pad bits and tail bits to the PSDU.
Scrambler Scrambles the data to prevent long sequences of zeros or ones.
Encoder Parser De-multiplexes the scrambled bits among the number of FEC encoders, in a round robin manner.
FEC Encoder Encodes the data to enable error correction – an FEC encoder may include a binary convolutional encoder followed by a puncturing device.
Stream Parser Divides the output of the encoders into blocks that will be sent to different interleaver and mapping devices. The sequences of the bits sent to the interleaver are called spatial streams.
BCC Interleaver Interleaves the bits of each spatial stream(changes order of bits) to prevent long sequences of adjacent noisy bits from entering the BCC decoder.
Constellation Mapper Maps the sequence of bit in each spatial stream to constellation points (complex numbers).
LDPC Tone Mapping Permutes the stream of constellation points (complex numbers) using LDPC encoding to obtain spatial streams. For 160 MHz, the LDPC tone mapping for LDPC-coded streams is performed separately for the upper and lower 80 MHz frequency segments.
STBC (Space Time Block Coding) The spatial streams are mapped to the space time streams when the number of space time streams is greater than the number of spatial streams.
CSD (Cyclic shift Definition) Applies CSD for each transmit chain.
Spatial Mapping

Maps spatial time streams to different transmit chains. This may include one of the following:

  • Direct mapping – each space time stream is directly mapped to a different transmit chain. When using direct mapping scheme, the number of space time stream must be equal to the number of chains.

  • Spatial expansion – the space time streams are multiplied by a matrix, and then transmitted through different transmit chains. When using spatial expansion mapping scheme, the space time stream can be fewer than the transmit chain. FFT transformation matrix is selected for spatial expansion purpose.

IDFT Converts a block of subcarriers to a time domain block.
Insert GI and Window GI (Guard interval) Inserts the guard interval. Optional windowing – smooths the edges of each symbol to increase spectral decay.
LDPC Encoder The scrambled bits are encoded using the LDPC code with the LENGTH in the TXVECTOR.
BCC Encoder Binary Convolutional Coding (BCC) encoder for the bit error correction.