Abstract
■■■Continuous phase modulation (CPM) is a popular frequency modulation technique used in mobile communications due to its power efficiency and constant modulus properties. Conventional narrowband CPM demodulation employs the Viterbi algorithm after phase demodulation and requires that the phase states be rational and contain additive white noise. The complexity of the Viterbi approach further increases with the number of phase states. Frequency discrimination approaches that estimate the instantaneous frequency provide a simpler suboptimal approach but are primarily for full response CPM and are not well known for wideband partial response CPM.In this paper, we investigate an approach that combines multirate frequency transformations for wideband CPM demodulation with decision feedback equalization for memory removal. This combined approach avoids the problems of complexity and restrictive requirements of the Viterbi approach. Simulation results are used to demonstrate the validity of the combined approach.
Highlights
Continuous phase modulation (CPM) [1,2,3] is a popular form of frequency modulation employed in mobile communications [4] and has desirable spectral efficiency [5] and constant modulus properties that facilitate use of class-C amplifiers
5 Conclusions In this paper, we have presented an approach towards wideband CPM demodulation by extending the MFTESA approach developed by the authors
The characteristic features of the proposed multirate frequency transformations (MFT)-energy separation algorithm (ESA) approach are (1) unlike the Viterbi algorithm whose complexity increases with the number of phase states induced by m and p as in Eq 8, the complexity of the proposed approach is independent of the modulation index; (2) the proposed approach does not require prior knowledge of the carrier frequency and this parameter can be extracted from the instantaneous frequency (IF) estimates; and (3) the proposed approach accommodates large modulation indices and multilevel signaling making it conducive to the large bandwidth requirements proposed in the M-ary fequency-shift keying (FSK) system for satellite communications [15]
Summary
Continuous phase modulation (CPM) [1,2,3] is a popular form of frequency modulation employed in mobile communications [4] and has desirable spectral efficiency [5] and constant modulus properties that facilitate use of class-C amplifiers. In prior work [10, 11], it was shown that frequency discrimination for full response CPM demodulation has the same performance as that of binary phase-shift keying (BPSK) detection in additive white Guassian noise (AWGN). Liu and Santhanam EURASIP Journal on Wireless Communications and Networking (2018) 2018:91 approach. These approaches do not require prior knowledge of the carrier frequency. We investigate the approach that combines the MFT and energy separation algorithm (ESA) [13, 14] with decision feedback equalization (DFE) to effectively demodulate wideband CPM with memory. The wideband CPM signal is first converted into narrowband via the MFT and demodulated by the ESA to obtain the IF estimates.
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