Binary data to transmit The faster the bit rate, the more energy is spread on the spectrum + a - a a2T0a2T0 s(t) T0T0 1/T 0 2/T 0 Frequency Time a - a a2T1a2T1 s(t) T1T1 1/T 1 2/T 1 Frequency NRZ coding Time Power spectrum Spread Spectrum Principle 1 - Time - Frequency Duality

T bit T chip 1/T bit T chip = E chip 1/T chip Frequency a 2 T chip 1/T chip +a -a +1 -a +a = x Data sequence a 2 T bit = E bit Data sequence spreading sequence Spreading sequence generator transmitted sequence Transmitted signal Modulation x(t) Power spectrum Spread Spectrum Principle 2 - Transmission

T bit a 2 T bit = E bit Power spectrum 1/T bit 1/T chip Frequency +a -a +1 -a +a = 1/T chip x Data sequence T chip spreading sequence T chip = E chip Spreading sequence generator Demodulation x(t) received sequence a 2 T chip Received signal Spread Spectrum Principle 3 - Reception

User 1 Spreading Code 1 Spread Spectrum Principle 4 - Code Multiplexing Power spectrum User 2 User 3 Code 2 Code 3 User 4 User 5 Code 4 Code 5 Composite signal 5 MHz Codes discriminate users

Unwanted Power from other sources Extraction from the received composite signal Spread Spectrum Principle 5 - Extraction

Maximum noise level Eb/No required Basic W-CDMA Elements Power spectrum Available power to share between users a 2 T bit = E bit gain Unwanted power from other sources 1 - Eb / No E chip

Power spectrum Maximum noise level Power from other users Eb/No a 2 T bit = E bit Eb/No required Power control Power , Interference , Capacity . Basic W-CDMA Elements 2 - Eb / No & Power Control