(A)

1. sx(t) = A x(t) cos wt x(t) BPSK modulator BPSK modulator Data s(t) = A x(t) g(t) cos wt A cos wt g(t) Carrier x(t) BPSK modulator s(t) = A x(t) g(t) cos wt A cos wt g(t) r(t) = A’A x(t - td) g(t - td) cos [ w(t – td) + f ] BPSK demod Filter ~ Output of correlator ~ g(t - td) Correlator (A) (B) (C) s(t) = A’A x(t - td)

2. Data “A” Locally generated PN bit stream “B” A xor B transmitted “C” Received “C” same as above Locally generated PN bit stream “D” same as “B” above C xor D original data signal

3. Important Code Properties • Must be easily generated at the transmitter and receiver (i.e. deterministic) • Behave as much as possible like a random sequence • Be difficult to exploit • Support multiple access • Provide ease of synchronization

4. + Mod-2 Adder PN sequence 4 – Stage shift register Simple Shift Register Generator (SSRG) • Data at first stage is shifted once toward the right each time clock pulse occurs • Clock input are normally not shown

5. 55

8. RUN PROPERTIES OF M-SEQUENCES • In one period there a 2(n-1) runs of consecutive 1’s or 0’s. • ½ are of length 1 • ¼ are of length 2 • 1/2lare of length l • Or equivalently: • 1 run of 1’s of length n • 1 run of 0’s of length n-1 • 1 run of 1’s and 1 run of 0’s of length n-2 • 2 runs of 1’s and 2 runs of 0’s of length n-3 • 4 runs of 1’s and 4 runs of 0’s of length n-4 • 2n-3 runs of 1’s and 2n-3 runs of 0’s of length. 1 61