Demodulation of Wideband, Low-Power FM Signals*

Abstract

Some theoretical aspects of the demodulation of wideband, low‐power FM signals are discussed. It is assumed that a band‐limited, continuous, analog signal is supplied to the modulator and is recovered to a fidelity suitable for television, telephone, or carrier telephone. Much of the paper assumes that the baseband signal is sampled and clamped before it is applied to the frequency modulator. The combination has been called PAM‐FM and is characterized by a piecewise constant transmitted frequency. PAM‐FM can be demodulated by spectrum analysis means not suitable for continuously varying frequencies. It is shown that a spectrum generator can be derived from the techniques of radar pulse compression, and is equivalent to an infinite set of correlators or matched filters plus means for scanning their terminals. The spectrum analysis circuit forms are compared with demodulators using frequency detectors, with and without FM feedback, in regard to theoretical noise sensitivities. The theoretical sensitivities are quite similar for spectrum analysis and FMFB under conditions assumed. The comparisons disclose that frequency detectors (followed by filters) enjoy a disguised but efficient use of a differential phase coherence which is a characteristic of FM signals. A combination of spectrum analysis and frequency detection is described which has some of the theoretical advantages of both.

Orthogonal Chirp Division Multiplexing

“…In spread-spectrum systems, digital binary information is encoded by modulating the frequency of a carrier, sweeping the frequency linearly from low to high as 'up-chirp' for bit '1' or from high to low as 'down-chirp' for bit '0', as shown in Fig. 1 (c) and (d) [8][9][10][11][12][13]. The chirp signal uses a wideband spectrum for transmission and is resistant to detrimental effects, such as channel noise, multipath fading and Doppler effects within the mobile radio channel.…”

Orthogonal Chirp Division Multiplexing for Coherent Optical Fiber Communications

“…It guarantees secure and robust communications for specific purposes, including military and underwater communications [26]- [28]. One commercial example is the CSS scheme in the 802.15a standard for ultra-wideband communication.…”

Detection of FSK and DPSK data signals by pulse compression

“…The signal may occasionally be masked for short periods by a noise component which causes an error in the received signal. The error rate for the FSK detection scheme can be determined approximately from the probability that the spectrum of a random noise component exceeds the component of signal at the wanted frequency [13]. Thus…”

“…It is possible, however, to adapt the pulse-compression techniques widely used in radar systems [10][11][12][13] to facilitate the implementation of a matched filter in the form of a pulse-compressor matched filter (PCMF). This has led to a new approach for detecting FSK data signals [14], which hinges on two operations at the receiver comprising a mixer-PCMF combination as shown in Fig.…”