Research On The Modem Technique For Continuous Phase Modulation Signal

With the development of society, various public and private communications systemspursuit a longer communication distance, greater capacity and higher power efficiency,especially in mobile communication system, satellite communications and the spacecraftmeasurement, tracking and control system，these systems are now widely used, which madethis need become more urgent. Frequency band and communication system that can be usedhave a direct impact on the capacity of the communication system, but the available frequencyband is non-renewable resource, and also has certain limitation. So we need to look for somemodulation techniques that require a higher spectral efficiency.So as a highly efficient modulation technology, Compared with other modulationtechnology, continuous phase modulation (CPM) develops very fast. CPM has outstandingadvantages, has a very high bandwidth and power efficiency, these characteristics make it hasplayed an important role in all kinds of communication system, it is becoming more and moreattention by people. CPM signals contain many forms, but there are some commoncharacteristics, these signals have constant signal envelope and continuous phase, they areparticularly suitable for applications in digital wireless communications. Gaussian minimumfrequency shift keying (GMSK) as one kind of CPM signals often been used commonly, hasvarious advantages of the CPM modulation technology, and has been widely applied tovarious kinds of wireless communication system, especially in the field of mobilecommunications, GMSK signal played a huge role. This article mainly used GMSK signal asan example analyzed CPM signal modem technology.In this paper, first of all, on the basis of the analysis of continuous phase modulationtechnique, we studied the production of the GMSK modulation technology and signal model;Secondly, focus on the GMSK signal demodulation scheme, first we studied the Viterbialgorithm performance of the GMSK signal, and then the multi-branch fractional multi-bitdifferential detection technique with decision feedback is proposed, which is used in GMSKsystem. This method is based on the combination of decision feedback technique and themulti-branch fractional multi-bit differential detection technique. Simulation results andfurther analysis show that the new detection technique reduces the inter-symbol interference, which leads to the performance improvement.Finally, combined the GMSK modulation anderror correcting code, analyzed the demodulation performance of Serial Concatenated GMSK(SCGMSK) system.