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WCDMA Introduction Spreading Code

WCDMA Introduction Spreading Code. Chia-Chi Yu 2004.8.13. Outline. WCDMA two layer Spreading Channelization code – OVSF code How to generate OVSF code? Scrambling code – Gold sequence Conclusions. Spreading. Two layer spreading. Define DL and UL.

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WCDMA Introduction Spreading Code

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  1. WCDMA IntroductionSpreading Code Chia-Chi Yu 2004.8.13

  2. Outline • WCDMA two layer Spreading • Channelization code – OVSF code • How to generate OVSF code? • Scrambling code – Gold sequence • Conclusions

  3. Spreading • Two layer spreading

  4. Define DL and UL • DL(downlink): Node B(BaseStation) to User Equipment(Mobile) • UL(uplink):UE to Node B

  5. Channelization Code • Usage◇Uplink: Separation of DPDCH and DPCCH from the same terminal◇Downlink: Separation of downlink connections to different users within one cell • Using OVSF code • Length◇Uplink: 4~256 chips same as SF ◇Downlink:4~512 chips same as SF

  6. OVSF code • Orthogonal Variable Spreading Factor→The Spreading Factor can be changed (e.g.,for variable bit rate service) • Orthogonality preserved across the different symbol rates

  7. OVSF code generation method

  8. Scrambling code • Usage◇Uplink: Separation of UE(Mobile) ◇Downlink: Separation of Base Station(cell) • Since WCDMA uses different scrambling codes to separate user from cells, it is not necessary to be synchronous between BS • Gold Sequence

  9. Scrambling code generator

  10. Scrambling code(DL) • Length: 38400 chips(both UL and DL) • Use a 10msec radio frame of a 218-1 shortened Gold sequence • Total number of codes : 262,143 • Use only 8,192 codes→ Broken into 512 sets of codes • Each set has 1 primary code with 15 secodary codes • Primary codes are further broken into 64 code groups, each with 8 primary codes

  11. Conclusions • Limited OVSF codes must be reused in every cell→Interference if two cells use the same code→Scrambling codes provide solutions • Asynchronous BS

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