1. ECE 442 COMMUNICATION SYSTEM DESIGN LECTURE 4. SPREAD SPECTRUM Husheng Li Dept. of EECS The University of Tennessee

2. THE MOTHER OF CDMA Hedy Lamarr (1913---2000): a famous actress in Holly Wood. She invented CDMA in 1941

3. DIRECT-SEQUENCE CDMA The signal of DS-CDMA: Informati on signal Wideband PN waveform

4. PN WAVEFORM C(T) We consider rectangle pulses (called chips) The correlation function is given by

5. OUTPUT SPECTRUM The spectrum of the output signal is given by is called the bandwidth expansion factor (also called processing gain), which ranges from 10 to 10,000. The wideband noise-like signal would be hard to distinguish from background noise at an authorized receiver.

6. DS-CDMA RECEIVER

7. PERFORMANCE OF RECEIVER When there is noise, the bit error rate is given by When there is a single-tone jammer, the big error rate is given by is called the jamming margin. Processing gain

8. MULTIPLE ACCESS Suppose a user shares the spectrum with M-1 other users. The interference is given by The bit error rate is then given by (noiseless case) The interference is like background noise.

9. HOMEWORK Problem 1: Problem 15.1-1 Problem 2: Problem 15.1-2 Problem 3: Compute the bit error rate of DS- CDMA using QPSK in presence of noise (we have obtained the expression for BPSK in Eq. (6), page 726)