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CyclicPrefix.md

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Cyclic Prefix

Josh Sanz [email protected]

Overview

The cyclic prefix block can add or remove cyclic prefixes from OFDM symbols. It uses the pktStart and pktEnd flags to determine where symbols occur for alignment purposes.

When removing prefixes, the block simply drops the first prefixLength samples it receives and passes the next symbolLength samples in a cycle.

When adding prefixes, the block first buffers in symbolLength samples. It then sends out the final prefixLength samples of the buffer, then flushes the buffer from the beginning.

An example with prefixLength=2 and symbolLength=6 is shown below

Add = True
           |-------------|
fedcba --> |Cyclic Prefix| --> fedcbafe
           |-------------|
           
Add = False
             |-------------|
fedcbafe --> |Cyclic Prefix| --> fedcba
             |-------------|

Parameters

  • protoIQ: DspComplex[T] - prototype for IQ data
  • prefixLength: Int - number of samples in the prefix/guard interval of an OFDM symbol
  • symbolLength: Int - number of samples in an OFDM symbol

Inputs

Decoupled interface

  • add: Bool - block will add cyclic prefixes when true and remove them when false; the flag should only be changed between packets
  • iq: Vec[DspComplex[T]] - incoming IQ, vector has width 1
  • pktStart: Bool - packet start flag
  • pktEnd: Bool - packet end flag

Outputs

Decoupled interface

  • iq: Vec[DspComplex[T]] - outgoing IQ, vector has width 1
  • pktStart: Bool - packet start flag
  • pktEnd: Bool - packet end flag

Tests

sbt test The block's tests include whether it

  • Removes the prefix from a single symbol
  • Removes the prefixes from multiple symbols
  • Adds a prefix to a single symbol
  • Adds a prefix to multiple symbols
  • Can switch between adding and removing prefixes betwen packets