  Due to high spectral efficiency and power efficiency, the continuous phase
modulation (CPM) technique with constant envelope is widely used in
aeronautical telemetry in strategic weapons and rockets, which are essential
for national defence and aeronautic application. How to improve the bit error
rate (BER) performance of CPM and keep a reasonable complexity is key for the
entire telemetry system and has been the focus of research and engineering
design. In this paper, a low-complexity noncoherent maximum likelihood sequence
detection (MLSD) scheme for CPM is proposed. In the proposed method, the
criterion of noncoherent MLSD for CPM is derived when the carrier phase is
unknown, and then a novel Viterbi algorithm (VA) with modified state vector is
designed to simplify the implementation of noncoherent MLSD. Both analysis and
experimental results show that the proposed approach has lower computational
complexity and does not need accurate carrier phase recovery, which overcomes
the shortage of traditional MLSD method. What's more, compared to the
traditional MLSD method, the proposed method also achieves almost the same
detection performance.
