Design And Implementation Of a Digital Direct Sequence Spread Spectrum (DSSS) System For Four Users Using FPGA

Abstract: In this paper, we design a digital DSSS System using Cyclone II EP2C20F484C7 FPGA from ALTERA placed on education and development board DE-1 for the DSSS system with the transmitting and receiving sections according to the following parameters: -Clock frequency of the system 10 KHz.
-Length of spreading pseudo-noise code (PNC): is 16 chips.

Type generation of spreading code: Walsh codes (H16).
-Length of data bit: is 2bits with 16 chips for every one bit.
-spread operation: X -Number of users: is four -User 1 with Data (00) and pseudo-noise code:

Code 1=[ 1111111111111111]

1 → +1 , 0 → −1 ⟹ Code 1=[ 1111111111111111]

-User 2 with Data (01) and pseudo-noise code:

Code 2=[ 1010101010101010]

1 → +1 , 0 → −1 ⟹ Code 2=[ 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1]

-User 3 with Data (10) and pseudo-noise code:

Code 3=[ 1100110011001100]

1 → +1 , 0 → −1 ⟹ Code 3=[ 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1]

-User 4 with Data (11) and pseudo-noise code:

Code 4=[ 1001100110011001]

1 → +1 , 0 → −1 ⟹ Code 4=[ 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1]

These codes must be orthogonal to each other, so they are chosen according to Welch's codes via the HADAMARD matrix, for a 16-bit codes, the H16 array should be chosen.

Keywords: CDMA, DSSS, Walsh Codes, PNC, PNCG, FPGA.