We move on to a discussion of
Pseudorandom Noise (PN) code generation techniques as well as their properties. A short comparison
will be made and applications will be discussed. Next, the RAKE receiver will be presented and
used as our reference receiver. At this point, we will have developed a baseline understanding to prepare
us for the rest of the chapter, where we discuss the WCDMA standard. We expand this discussion
to include high-speed downlink packet access (HSDPA) and high-speed uplink packet access
(HSUPA) features of the 3GPP standard.
7.1 INTRODUCTION
In a spread spectrum system, the narrowband information signal is transmitted over a larger bandwidth
to overcome the multipath fading channel distortion discussed earlier in Chap. 3. In Fig. 7.1, we provide
an overview of two types of spread spectrum techniques: Direct Sequence (DS) and Frequency Hopping
(FH). This multiple-access scheme is used when all users have a PN sequence code that is ideally uncorrelated
with that assigned to any other user occupying the same channel [1].
Next we provide some general comments for each of the two techniques discussed above. First,
the DS technique is greatly affected by the near-far problem, which, we will see, can be solved by the
use of power control.
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