10.1

Explain the statements made in the text that, at a CDMA chip rate of 3.84 Mcps, path differences of 78 meters or 240 ft can be resolved, while, for a chip rate of 1.2288 Mcps, path differences of 240 meters can be resolved.

10.2

1. Explain how multi-code CDMA allows transmission at higher bit rates without reducing the spreading gain. What is meant by the statement that the codes used in parallel must be orthogonal to one another ? What is meant by the phrase self-interference at the receiver ? How does othogonality prevent self-interference?

2. Draw a diagram of multi-code CDMA for the case of tripling the basic bit rate, showing how serial-to-parallel conversion is used to obtain the rate tripling.

3. Explain why multi-code CDMA results in wider envelope variations. Why would multiple RAKE receivers be required, one for each code?

10.3

Explain the statement that, for a RAKE receiver to be effective, the spread signal bandwidth must be greater than the coherence bandwidth. Why does this result in frequency-selective fading, and why is frequency-selective fading necessary for the resolution of multipath echoes?

10.4

Consider the W-CDMA system.

1. Explain why the rates of transmission of user data are less than half of the rate of transmission over the air interface. Why would a local-area environment allow a much higher transmission rate than a wide-area environment?

2. Explain how a bit rate of 5.76 Mps can be attained on the uplink radio channel.