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Modulation and demodulation
Published in Geoff Lewis, Communications Technology Handbook, 2013
ISB (independent sideband). As the information to be transmitted is contained in each sideband of the normal double sideband AM signal, it is only necessary to transmit a single sideband. By using a pair of balanced modulators driven by the same carrier signal, two DSBSC signals can be generated. If the upper sideband is filtered from one and the lower sideband from the other, when the two modulation products are combined, each sideband contains independent information. This automatically doubles the channel capacity but at the expense of halving the signal power at the receiver. Thus the received signal to noise ratio will be 3 dB worse than for a double sideband transmission.
From the Top Down: Layer 1–Populating the OFDM Waveform with Information
Published in David P. Maxson, The IBOC Handbook, 2007
Early HD Radio receivers would select all four matrices (ML, MU, BL and BU) in a complementary mode discussed further in Chapter 8, or switch to selecting the best sideband (ML and BL, or MU and BU), an independent sideband mode, depending on which method is performing best. Later HD Radio receiver versions employ maximum ratio combining to eke extra performance out of the fact that there is gain to be obtained from combining the weighted results of both decoding methods.
Practical method for nullifying ripple effect from FIR-Hilbert transformer
Published in International Journal of Electronics Letters, 2023
The developed asynchronous demodulation method for RZ SSB may be extended to four SSB signals arranged on the frequency axis to achieve greater data and support burst mode transmission (Daikoku, 2021b). When a reduced pilot carrier is placed at the centre of the four SSB signals, it is guarded by the Lower Sideband (LSB) and Upper Sideband (USB) signals; that is, this scheme is classified into the Tone-In-Band (TIB; Rappaport, 1996). The transmitting four SSB signals comprise multiplexing two Independent Sideband (ISB) signals on the frequency axis with the same carrier frequency, and both ISBs possess the real part described by a sum signal and the imaginary part described by a Hilbert-transformed difference signal, which are produced from the ISB modulation process with four independent information signals. In the demodulation process, we obtain the sum signal and the difference signal that has been Hilbert-transformed on the receiver side. We can finally separate four information signals by calculating the sum and difference signals on a sum-difference calculation circuit. For real-time signal processing, we must introduce a Finite Impulse Response (FIR)-Hilbert transformer (Hahn, 1996). This inevitably requires a delay line to compensate for the delay time of the FIR-Hilbert transformer. The FIR-Hilbert transformer produces a ripple whose level strongly depends on the filter order N and the transition bandwidth. However, there was no ripple on the delay line. It has been reported that the separation performance is degraded by the ripple (Daikoku, 2021b).