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Single-side band

# Single-side band

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## Single-side band

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1. Single-side band

2. Intro • Single-sideband modulation (SSB) is a refinement of amplitude modulation that more efficiently uses electrical power and bandwidth. It is closely related to vestigial sideband modulation (VSB). • SSB was also used over long distance telephone lines, as part of a technique known as frequency-division multiplexing (FDM). FDM was pioneered by telephone companies in the 1930s. This enabled many voice channels to be sent down a single physical circuit, for example in L-carrier. SSB allowed channels to be spaced (usually) just 4,000 Hz apart, while offering a speech bandwidth of nominally 300–3,400 Hz. • Depending on which half of DSB-SC signal is transmitted, there are two types of SSB modulation 1. Lower Side Band (LSB) Modulation 2. Upper Side Band (USB) Modulation

3. Mathematical analysis

4. From figure 2, using concept Hilbert transform • But, from complex representation signal • So,

5. Generation of SSB signals A SSB is represented by: • Figure above shown that DSBSC is used in SSB signal generation

6. Coherent Demodulation of SSB signals ΦSSB(t) is multiplied with cos(ωct) and passed through low pass fillterto get back the orignal signal. • The demodulated signal is passed through an LPF to remove unwanted SSB terms

7. BENEFITS of ssb • By eliminating the duplicated side-band and carrier from transmission, the bandwidth has been reduced by half. The formula for predicting bandwidth in a SSB system is BW = fm, where fm is the maximum modulating frequency used. By reducing the bandwidth transmitted, the number of channels (or stations) can be put in the same frequency band. • Because the carrier if also filtered out, there is no transmission unless information is being sent. The efficiency is also improved considerably. Recall that efficiency was the power in the side-bands divided by the total power