Wavelets for improving spectral efficiency in a digital communication system

In this paper, two types of wavelet based schemes to improve the spectral efficiency (SE) of a digital communication system are presented. First one is wavelet based pulse shaping and the other is wavelet based digital modulation called wavelet shift keying (WSK). In pulse shaping scheme, orthonormal wavelets and their translates are used as base band shaping pulses. To improve spectral efficiency and coding gain, dyadic expansions and their translates are used for signaling. Since wavelets have zero average value, they can be transmitted using single side-band (SSB) transmission. By comparing with raised-cosine (RC) signaling, this wavelet approach offers more data rate at the same bandwidth. RC systems offers only 0.83 b/S/Hz for low pass transmission where as transmission using the first two dyadics offers 1.12 b/S/Hz. More over, it is shown that wavelets obey Nyquist pulse shaping conditions. Using a dyadic expansion to support a channel code there is a coding gain over the RC system, with essentially no bandwidth penalty. In modulation scheme, the user data stream is transformed into sequence of scaled mother wavelets to indicate which version of the mother wavelet is transmitted. This modulation offers more spectral efficiency as number of users increases keeping the power efficiency as constant.

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