Iterative Interference Suppression Technique For Wireless Communications

In the severe interference environment of electronic warfare, it is important to suppress interference for reliability of systems. Iterative detection is an effective and promising signal processing method. The a prior information and the extrinsic information can be exchanged between soft-in soft -out (SISO) blocks, so that the optimal detection can be approached by introducing iterative detection. Moreover, jamming state information (JSI) can be calculated by iterative estimation. Combining the estimator and detector together, the receiver can greatly suppress the jamming signals with the help of JSI.On the other hand traditional Frequency-hopping (FH) techniques are widely used in the military communication systems to achieve reliable information transmission. In the FH system, the information sequences are transmitted over time variable carrier frequency. If the FH technique and the iterative detection method are both effectively implied in the system, the performance - including jamming suppression performance, the reliability of the system, the spectrum efficiency - can be greatly improved. Therefore the iterative detection method and the iterative estimation method to suppress jamming in FH systems are studied in this paper.In chapter two, the iterative detection principles and applications are introduced. The FH-CPM system model with serially connected channel coder is adopted. It's well known that continuous phase modulation (CPM) signals take on some attractive merits: high spectrum efficiency, fixed complex envelop, and it can be modulated by non-linear amplifier to avoid the cost of linear amplifier.In Chapter three, the jamming suppression method of coherent FH-CPM is studied. By introducing an exact construction of digital phase modulations by superposition of amplitude modulated pulses (Laurent decomposition of CPM), the SISO algorithm is improved, and the complexity increasing caused by the response length of CPM is greatly reduced. Due to the interleaver between the modulator and the coder, the probability density function of the extrinsic information is difficult to be calculated. Here, extrinsic information transmission chart (EXIT) is employed to analyze the convergence character of the iteration. The simulation results demonstrate the system takes on good bit error rate (BER) performance in partial-band jamming (BPJ) and multi-tone jamming (MTJ) environment as well as in AWGN channel.Chapter four is mainly about the SISO algorithm when non-coherent detection of CPM signals is applied. In this chapter, we propose an iterative tree search (ITS) algorithm based on Laurent decomposition, which can reduce the complexity of the demodulator while non-coherent detection is achieved. The convergence character analysis is also accomplished using EXIT. From the simulation results, we can see that the loss of BER performance is within 1.5dB compared to that of the system with coherent detector in AWGN channel.In Chapter five, the partial-band jamming information (PBJSI) method is studied and the multi-tone jamming information (MTJSI) estimation method is proposed. The iterative estimation method of partial-band jamming is firstly studied, which brings nearly 3dB gain at aimed BER10^-4. Secondly a multi-tone jamming estimation method is proposed in this paper. In this method the JSI and the threshold of deciding are iteratively updated, hence the problem of determining the threshold in frequency-domain estimation method is avoided. Meanwhile, the parameter of MTJ is estimated so that the jamming can be reconstructed and removed from the received signals. The simulation results prove that by introducing this method the receiver is almost free from MTJ.