Key Technique Research For HF Burst Communication System With Continuous Phase Modulation

High frequcency (HF) communication is an important communication method, especially in military communication; this is attributed to its simplity, moderate cost, ability to provide near global connectivity without repeaters, beyond line-of-sight, and ease of proliferation. But with the development of modern high technolgy war, traditional HF communication is threatened by modern electronic countermeasures, so it is very useful to develop efficient anti-jamming measures in HF communicaiton. The object of this dissertation is to study the applicaiton of continuous phase modulation (CPM) in HF communication and relevant key techniques based on the model of a new HF adaptive burst communication system (ABCS) proposed by academician Lu Jianxun in China Engineering Academy.At the beginning the dissertation introduced the new techniques and methods in modern HF communication, and then put emphasis on the introduction of ABCS, including its basic theories, main characters and advantages over traditional HF communication system.A software HF channel simulator based on Watterson model was presented according to the characters of multipath, fading, Doppler frequency shift and Doppler frequency spread in HF channel. The simulator is simple, movable and low-cost; furthermore, the simulator can also be implanted into modem easily, which makes it easy to test the performaces of HF communication system.Continuous phase modulation (CPM) is an excellent digital modulation scheme with constant envelope, high bandwidth and power efficiency. Just like Trellis-coded modulation (TCM), memory exists among different signal periods in CPM, and it can be described by a finite state machine. Traditional modulation schemes can not use the line amplifier because their envelopes are not constant if their baseband pulses are shaped, such as PSK, QAM, but in CPM, the envelope is always constant and able to use power-effient line amplifier.We discussed the performance of convolutional coded CPM and the performance of RS coded CPM, then based on the decomposed model of CPM, two separate devices: a continuous phase encode (CPE) and a memoryless modulator (MM) were got, using the memory and recursive character of CPE, combined with the convolutional code and interleaver outside, the model of seriallly concatenated CPM (SCCPM) was founded. Apply the SCCPM into HF communication can overcome the shortcomings in traditional Modems and improve the performances.For the reason of anti-jamming in ABCS, the length of frame is short. By experiments and analyses we found that the phenomena of positive feedback during iterative detection were serious in short-frame systems, and led to bad effect on the BER performance of SCCPM. In order to resolve the problem, an improved iterative detection method based on the exchange of weighed extrinsic information probability was proposed. The proposed method can reduce the phenomena of positive feedback in SCCPM system by adaptively adjusting the extrinsic information probability between the decoders. Furthermore, a dynamic iterative method based on the number of change of hard decision was designed; which could detect the positive feedback as well as reduce the average number of iteration. Simulation results show that the proposed methods are effective and feasible.In HF communication the intersymbol interference (ISI) is serious and is the main obstacle of HF high rate communication. An improved iterative interference canceller (IC) for SCCPM was proposed. The traditional IC uses the uniform probability distribution as input on the first iteration, because the CPM Soft-Input Soft-Output (SISO) model can not provide the useful information at that time, so the ISI is not canceled at all and the performance of equalization is poor when the ISI is serious. In order to resolve the problem, the proposed IC uses the priori probability of transmitted signal as input on the first iteration, which can cancel some ISI and improve the performance of equalization. Simulation results show that the proposed IC is more efficient campared with traditional IC.HF communication is bandwidth-limited and high bandwith efficiency is necessary for high rate communication. We disguessed the relationships between the bandwith and parameters of CPM, such as the shape of baseband pulse, modulation index, and cardinality of CPM. We also analysed the power and bandwidth effiecncy using the proposed reciver, and the simulation results show the improved SCCPM is more efficet compared with tradition Modems in HF communication.