Description CRC generator
Library cdma2000, Channel Coding
||input frame length
||mode for setting parameters: Choose CRCType from list, User defined
||Choose CRCType from list
||CRC generator polynomial; use when ModeSelect=Choose CRCType from list: CRC16 0x1c867, CRC12 0x1f13, CRC10 0x7d9, CRC8 0x19b, CRC6 0x47, CRC6 0x67
||initial state of encoder(use when ModeSelect=User defined): all 1's, all 0's
||generator polynomial in hex format; used when ModeSelect=User defined
- This model is used to add CRC bits after the input frames.
Each firing, (InputFrameLen + CRCLength) tokens are produced when InputFrameLen tokens are consumed. CRCLength is the length of CRC bits added after the input frame.
- A frame quality indicator is used in many channels. The frame quality indicator (CRC) is calculated on all bits within the frame, except the frame quality indicator itself and the encoder tail bits.
- The generator polynomials for the frame quality indicator are:
- g(x) = x16 + x15 + x14 + x11 + x6 + x5 + x2 + x + 1 for the 16-bit frame quality indicator, where g(x) = 0x1c867 (hex format)
- g(x) = x12 + x11 + x10 + x9 + x8 + x4 + x + 1 for the 12-bit frame quality indicator, where g(x) = 0x1f13 (hex format)
- g(x) = x10 + x9 + x8 + x7 + x6 + x4 + x3 + 1 for the 10-bit frame quality indicator, where g(x) = 0x7d9 (hex format)
- g(x) = x8 + x7 + x4 + x3 + x + 1 for the 8-bit frame quality indicator,
where g(x) = 0x19b (hex format)
- g(x) = x6 + x2 + x + 1( g(x) = 0x47 ) for the 6-bit frame quality indicator
(RC = 2)
- g(x) = x6 + x5 + x2 + x + 1( g(x)= 0x67 ) for the 6-bit frame quality indicator (2 ≤ RC ≤ 9)
- The frame quality indicators are calculated according to the following procedure using the logic shown in the following figure (here g(x) = x6 + x2 + x + 1 used as example)
- Initially, all shift register elements are set to logical one and the switches are set in the up position.
- The register is clocked a number of times equal to the number of reserved and information bits in the frame with those bits as input.
- The switches are set in the down position so that the output is a modulo-2 addition with a 0 and the successive shift register inputs are 0.
- The register is clocked an additional number of times equal to the number of bits in the frame quality indicator (16, 12, 10, 8, or 6).
- To set generation functions, CRC code length, and the initial states of CRC encoder, set ModeSelect to User defined ; then the parameters of InitialState and Polynomial are valid. CRC code length (n) is determined by Polynomial, where 2n ≤ Polynomial ≤ 2n+1.
Frame Quality Indicator Calculation
- TIA/EIA/IS-2000.2 (PN-4428), Physical Layer Standard for cdma2000 Spread Spectrum Systems, July 1999.
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