lecture25 - Lecture Outline(Week 14 lecture 1 Wireless...

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Lecture Outline (Week 14, lecture 1) Wireless Communications – CDMA and 3G Wireless Reading: Focus on these notes. Also text1 9.1-9.2. 1. CDMA Basics Revisited. Use 2PAM or BPSK ) ( ) ( b b n nT t g a t v - = - , where T E t g b 2 ) ( = only in b T t 0 , 1 ± = n a Signal is spread in frequency to ) ( ) ( ) ( t c t v t x = . ) ( t c is periodic and unique for each user. It is the CDMA code for the user. ) ( ) ( 1 c c L k k kT t g c t c c - = = in the period b T t 0 , where 1 ) ( = t g c for in c T t 0 , 1 ± = i c . ) ( ) ( ) ( t c t v t x = is used to modulate a carrier t f c π 2 cos . Users send their signal and the signals are added together at the receiver. Signal is demodulated at the carrier frequency and phase of the intended signal. Receiver for signal ) ( ) ( ) ( t c t v t x = extracts signal by multiplying (de-spreading) with ) ( t c For intended signal, we obtain ) ( ) ( ) ( ) ( ) ( ) ( t v t c t c t v t c t x = = , the signal before spreading. For unintended signal of another user say ) ( ' ) ( ' ) ( ' t c t v t x = , we obtain ) ( ) ( ' ) ( ' ) ( ) ( ' t c t c t v t c t x =
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