Study On Low Complexity Continuous Phase Modulation Transmission Technique For Frequency Hopping Systems

In military communication field, narrowband high speed data transmission technique is the key to improve the bandwidth efficiency, transmission rate, system capacity and the ability to combact interference. There includes more advanced high efficiency code and modulation technique, link adaptation technique and etc..These techniques provide powerful transmission platform for constructing tactical internet and data link. In this dissertation, the low complexity continuous phase modulation transmission technique is studied.The main research works and results are listed as follows:1. The fractional multi-bit differential detector is generalized. The essential of the technique is explained from the physical meaning of phase forming, and theoretical analysis to the upper bound of the fractional bit duration for the maximum performance improvement is given. Analysis and simulation results show that the signal-to-noise ratio is improved. Performance gain is obtained by combining multiple fractional multi-bit differential detector outputs. When the fractional bit duration is the maximal duration in which the symbol decision is not influenced, the maximum performance gain can be achieved.2. A noncoherent RSDSD detector with low complexity for frequency hopping system is proposed. By reasonably choosing state fusing, the reduced detector has no or little degradation in the Euclidean distance compared with the optimum ML detector. Also the exact initial carrier phase need not to be known in the receiver, which is more appropriate to the frequency hopping system and time varying channel. The detector is tolerable to frequency offset within some range and more robust to the situation when the carrier recovery is difficult.3. The CPM modem waveform parameters are designed for the New Generation VHF Narrowband High Speed Data Transmission Radio. The noncoherent RSDSD algorithm is implemented in the experimental system radio. The performance of the modem and the sensitivity of the radio are tested. The far distance communication experiment is made. The results show that the transmission ability of the last negeration equipment is upgraded.4. A quasi-coherent demodulation algorithm based on the direct decision phase synchrionization is studied. The algorithm can further improve the power efficiency of noncoherent CPM detection for frequency hopping system only at little cost. It is more appropriate to the fast frequency hopping system when there is little data in one hop frame.5. The bit error rate union bound and system design criteria of SCCPM system are studied. For SCCPM system with different parameters, the tradeoff between bit error rate union bound and implementation complexity should be consided at the same bandwidth efficiency, and system parameters with good performance should be found.6. For the low complexity iterative decoder of SCCPM system, a reduced state SISO iterative decoding algorithm based on RSSD is proposed. The algorithm avoids the limit of the reduced decoding algorithms based on Laurent decomposition, and the reduced state SISO algorithm based on state truncation is also a special case of the proposed algorithm. At the same computation complexity, the reduced state SISO algorithm based on RSSD provides even little performance loss compared with the SISO decoder based on state truncation.7. The channel quality estimation for adaptive frequency hopping system using nonlinear continuous phase modulation is studied, and a blind channel quality estimation algorithm based on the average signal phase distance is proposed. The algorithm is blind estimation without training symbols and with low complexity, which is appropriate to the fast frequency hopping system when there is little data in one hop frame. For usual frequency hopping interference, the algorithm can efficiently evaluate the channel quality.