Feedforward Synchronization Schemes for MSK-Type Signals

Feedforward algorithms are investigated for estimating carrier frequency, carrier phase and symbol timing in MSK-type modulations. Their derivation is based on maximum likelihood criteria and leads to synchronization schemes that are suitable for full digital implementation. The operation of these algorithms is decoupled, meaning that the frequency parameter is measured first and independently of the others. Subsequently, phase and timing are computed through simple formulas. The performance of the proposed algorithms is investigated analytically and by simulation and the results are compared with Cramer-Rao bounds. It turns out that the estimation accuracy is very close to the theoretical limits. The frequency estimation range is in the order of 20% of the symbol rate for MSK and 10% for GMSK. A frequency estimation threshold lower that 4 dB is achieved with fairly short observation windows.