| Summary: | 碩士 === 中華大學 === 電機工程學系碩士班 === 87 === WCDMA will play an important role in the communication systems of the next generation. Spread spectrum, the modulation technique that CDMA is based on, possesses many features such as antijam, low probability to detect, low power spectrum density, multipath diversity, and soft limit for capacity. These features make it suitable to develop the third generation wireless communications. From the pointview of system users, multi-media service will be more heavily emphasized, and this makes up the mainstream of this thesis.
When considering the multi-media service in a CDMA system, the conventional CDMA scheme seems to be the most straightforward way to employ. In other words, all types of digital input signals with different data rates are spread over the same total transmission bandwidth. This scheme with multiple processing gains will not utilize the bandwidth efficiently. Instead, we adopt the FDM scheme with CDMA to reallocate the spectrum in such a way that different input signals obtain the same single processing gain value.
We will analyze the multi-media with three different data rates, i.e. , high, medium, and low rate. When combined with two power control methods, namely, the equal signal strength (ESS) method and equal error probability(EEP) method, we will demonstrate that when compared with conventional CDMA, FDM/DS-CDMA will obtain higher capacity in most conditions. For different values of BER, EEP gets higher capacity than ESS.
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