Guo Daoxing

A modified water-filling algorithm of power allocation

OFDMA is a multiple access based on orthogonal frequency division multiplexing of multi-users. As a method, conventional iterative water-filling algorithm satisfies the convergent condition by constantly closing to the optimum value. Therefore, the application of the algorithm is limited for the huge computations and complex algorithm. Aiming at solving the problem, a modified water-filling algorithm based on limitations of total power and capacity of each subcarrier is proposed. The iterative computations are avoided by the modified algorithm, and the simulation results show that the modified algorithm has a great advantage in complexity of operations compared with conventional iterative water-filling algorithm in the same condition. Meanwhile, the impacts on the two algorithms of the BER and the numbers of subcarriers are discussed.

Performance analysis of dual-hop satellite relay networks with hardware impairments and co-channel interference

In this paper, we investigate the impact of hardware impairments on the outage performance and the instantaneous capacity of dual-hop decode-and-forward (DF) satellite relay networks in the presence of co-channel interference. Specifically, the exact closed-form expression for the outage probability and the analytical expression for the instantaneous capacity of the system are derived over a shadowed-Rician fading channel, which provides a fast means to evaluate the impact of hardware impairments on the system performance. Our results demonstrate that the outage floor occurs and the capacity upper bound appears when the hardware impairments exist. In addition, simulation results were provided to verify the correctness of the analytical results.

A simplified code aided carrier frequency-off set estimation algorithm

The EM algorithm in low SNR systems employs optimal search to perform the carrier frequency-offsets ML estimation, and involves high complexity. In this paper, the Three-Line-Interpolation (TLE) algorithm with high frequency offset estimation precision is replaced by the optimal search algorithm. And a simplified algorithm is proposed. The simulation results show that the computation complexity is greatly reduced and the accuracy is improved by using the TLE algorithm. And the simplified algorithm exchanges little performance loss for high computational complexity.

The optimized design of degree distribution of fountain codes in DTN with relays

Apparently, the degree distribution of fountain codes has strong impact on the performance of the codes, such as the success rate of decoding and the complexity of encoding and decoding. And robust soliton distribution on the codes has the advantage of good performance. However, the problem of optimization on degree distribution in specific network models should be further studied. In this paper, the links interruption characteristics of DTN (Disruption Tolerate Network) is considered, and the design of the degree distribution of fountain codes in two information source and a relay DTN is optimized, which has not been studied before. Simulation results show that the optimized degree distribution effectively improves the performance of fountain codes in DTN.

Performance of LDPC Coded SFH System with Partial-Band Interference

The application of Low Density Parity Check (LDPC) code in the anti-interference systems has drawn an increasing attention, due to its admiring performance which is very close to the theory limit. This paper focuses on a LDPC encoded slow frequency hopping (SFH) communication system with partial-band interference. Firstly, a modified soft-decision algorithm based on the utilization of interference information is proposed, and its performance is compared with some other soft-decision methods. Secondly, with numerical simulation, the influence of code rate, code length and the number of symbols per hops on the performance of the system with partial band noise interference is illustrated and examined in detail. Considering the great influence of hops per symbol on the performance, interleaver should be used and its influence on the performance is further examined by simulation. Finally, some constructive advices for the design of LDPC coded SFH system are given. Simulation results show that, with a reasonable design, the SFH system with LDPC code could achieve a desirable performance.

Performance of transparent transponder satcom system with interference

The robustness of transparent transponder satcom to uplink interference is investigated. First, the performance of transparent transponder satcom system is analyzed to uplink interference (or jamming) and the closed expression for calculating BER performance is given. Also the simulation is done for the two typical cases. It is shown that narrow-band multiple access combined with backoff of HPA provide robustness to jamming. The jamming level needed to cause all users unacceptable error bit rates must be comparable to the sum of the users power. And it was found that this level is generally slightly lower than that to cause transponder saturation.