Zhao Danfeng

Power and bandwidth efficient LDPC coded CPM with iterative decoding

In this paper, in order to improve bit error performance, bandwidth efficiency and reduction of complexity compared to related schemes such as turbo codes, we combine low-density parity-check (LDPC) codes and continuous phase modulation (CPM) and introduce a new scheme, called LDPC coded CPM (LDPCC-CPM). At the receiver, an iterative detection method based on SISO algorithm is proposed. Then the effect of LDPC code length, code rate, iterative number and modulation index on the performance of the system is studied. In our proposed scheme, LDPC and CPM, are considered together to improve both error performance and bandwidth efficiencies. The combination also can achieve better trade-off between power efficiency and bandwidth efficiency than SCCPM. Analysis and simulations show that - among the evaluated systems - the octal 2RC systems provide the highest power/bandwidth efficiency. As an example, rate 1/2-coded octal 2RC with modulation index 1/2 reaches 10−5 bit error probability at Eb/N0=2dB with information block length 768 bits.

Novel joint encoding/decoding algorithms of fountain codes for underwater acoustic communication

Fountain codes are considered to be a promising coding technique in underwater acoustic communication(UAC) which is challenged with the unique propagation features of the underwater acoustic channel and the harsh marine environment. And Luby transform(LT) codes are the first codes fully realizing the digital fountain concept. However, in conventional LT encoding/decoding algorithms, due to the imperfect coverage(IC) of input symbols and short cycles in the generator matrix, stopping sets would occur and terminate the decoding. Thus, the recovery probability is reduced,high coding overhead is required and decoding delay is increased.These issues would be disadvantages while applying LT codes in underwater acoustic communication. Aimed at solving those issues, novel encoding/decoding algorithms are proposed. First,a doping and non-uniform selecting(DNS) encoding algorithm is proposed to solve the IC and the generation of short cycles problems. And this can reduce the probability of stopping sets occur during decoding. Second, a hybrid on the fly Gaussian elimination and belief propagation(OFG-BP) decoding algorithm is designed to reduce the decoding delay and efficiently utilize the information of stopping sets. Comparisons via Monte Carlo simulation confirm that the proposed schemes could achieve better overall decoding performances in comparison with conventional schemes.

Performance of LDPC codes in wideband shortwave channel

To reduce the effect of multi-path and Doppler on the bit error rate performance in the shortwave broadband channel, LDPC code with probable checking matrix and an improved decoding algorithm is introduced to ensure the reliability of the system as channel encoding. Combined with MC-CDMA technology which can inhibit the multi-path interference effectively, the LDPC+OFDM+DSSS scheme is proposed. Using the equalization techniques to recover received signals, the simulation model is built by the analysis of shortwave broadband channel based on ITS model. Simulation results show that: the program not only can inhibit the symbol interference effectively, but also can reduce the sensitivity of the communication system to Doppler frequency and reach a better bit error rate performance.

An 8-Cycle Construction Scheme for Latin Square LDLC

A novel method for constructing the Latin square Low Density Lattice Codes (LDLC) parity check matrix is proposed in this paper. Based on the permutation matrix, a 6-cycle matrix is build firstly. Then the elements involved in the 6-cycle are detected and swapped, which is on the basis of the theory of adjacency matrix. Therefore, we obtain a check matrix, which is 6-cycle free and the nonzero elements obeying random distribution. Simulation results demonstrate that the proposed method has a lower symbol error rate (SER) compared with the previous works.

Joint LDPC-DQPSK iteration system for underwater acoustic communications

To reduce inter-symbol-interference (ISI) in underwater acoustic channels, a communication system based on joint LDPC-DQPSK iterative detection was proposed. Spread spectrum technology was adopted to increase communication distance and to combat multi-path effect. Joint LDPC-DQPSK iteration is essentially a joint demodulation and decoding iterative detection based on Turbo principle. To verify BER performance of proposed system, simulation experiments over typical underwater acoustic channels were carried out. Experiment results show that proposed system outperforms conventional systems. Proposed system with four rounds of joint iterations can obtain 3.5 dB SNR gains compared with conventional systems at BER of 10-4.

The design of variable frame length LT code based on limiting conditions

Because the LT code has the drawback of coding efficiency is not high, decoding time is too long and decoding probability is low, a mathematical method of limiting analysis is introduced to the distribution of LT code, which analysis the effects of different source data frame length, different parameters for LT code from principle, then a system program of variable frame length LT code is proposed, whose core idea is to make a appropriate design of frame length of the source data, split the source data and encode them separately to meet different performance requirements. Theoretical analysis and simulation results show that: Compared with the conventional LT codes, variable frame length LT codes can effectively improve the coding efficiency and decoding probability, enhance the feasibility of LT code in actual system.

Simplified iterative algorithm for OFDM phase noise mitigation

Abstract OFDM has been widely adopted in several communication systems. However, OFDM systems are very sensitive to the phase noise, which causes the CPE (common phase error) and ICI (inter-carrier interference), and thus degrades the system performance significantly. Based on the IEEE 802.11a standard, a simplified iterative phase noise mitigation algorithm is proposed. The proposed algorithm has very low complexity, and requires no additional pilot information. The simulation result shows that good BER performance can be achieved through several few times of iteration.