WCDMA Introduction Spreading Code Chia-Chi Yu

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 DL(downlink): Node B(BaseStation) to User Equipment(Mobile) UL(uplink):UE to Node B

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

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

OVSF code generation method

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

Scrambling code generator

Scrambling code(DL) Length: chips(both UL and DL) Use a 10msec radio frame of a 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

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