How PN Codes are used in IS-95 Systems
By Dr. Ernest Simo

24.0 Reception processes at the cell site using Long PN Codes.

  • Let us examine the simplified reception processes at cell site A. The received or input to cell A is:

    Input = di(t)• LC(t- A) + dj(t)•LC(t- B)


  • Cell A is assumed to have synchronized with Mobile A. So, it is tuned to Mobile A with its local Long PN code set to LC(t- A).

  • Cell A will then “multiply” its local code LC(t- A), with the received or incoming input signal . The resulting output signal is:

    Output = di(t)• LC(t- A)• LC(t- A) + dj(t)• LC(t- B)•LC(t- A)


    As noted earlier, the normalized Auto-correlation LC(t- A)• LC(t- A) is 1. And the normalized Cross-correlation LC(t- B)• LC(t- A) is -1/L. For large values of L therefore, the second term can be ignored. This simply reduces the output to di(t). (Note that the signal from Mobile B is nicely ignored !)

    Click here to view Figure 14




    © 2001 DR. ERNEST SIMO - SPACE2000
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