The Maximum-A-Posteriori-probability (MAP) demodulation of recursive FQPSK-B in the presence of Additive White Gaussian Noise (AWGN) channel was first presented. Required in the iterative detection of Serial Concatenation of Convolutional coded Recursive FQPSK (SCCRFQPSK), the bit extrinsic Log-Likelihood Ratio (ex-LLR) of FQPSK demodulation was also derived. Secondly, aiming at weakening the phenomena of positive feedback during the iterative detection of SCCRFQPSK, the bit ex-LLR of FQPSK demodulation was appropriately adjusted by linear weighted processing. By Monte Carlo simulation, it was concluded that the optimal weighting factor of the weighted SCCRFQPSK system was 0.7, and it got 0.3dB Signal-to-Noise Ratio (SNR) gain at a Bit Error Rate (BRE) of 10-5 at 4 iterations. The simulation results indicate that the proposed method can not only accelerate the decoding convergence and improve the performance of the SCCRFQPSK system, but also reduce the delay. To a certain extent, it can deal with the deep space communication with low SNR caused by long distance.

The IEEE 802.11p standard plays an important role in the application and deployment of Vehicular Ad-hoc Network (VANET). Aiming at improving former literature' shortage including the incomplete use of simulation scenes and WAVE (Wireless Access in Vehicular Environments) communication mode, simulation based on NCTUns (National Chiao Tung University network simulation) was conducted to study the effect of transmission power, transmission distance, vehicle density and vehicle velocity on network performance after illustrating the architectures of IEEE 802.11p, NCTUns and the simulation process. The simulation results indicate that node density, transmission power and transmission distance can remarkably influence the packets reception rate and throughput while vehicle velocity has no effect on the node throughput. Finally a method of joint adjustment of packets reception rate and contention window was proposed to enhance the MAC (Media Access Control) performance of the VANET.

To improve the efficiency of the Bit Flipping (BF), a weighted gradient descent bit-flipping decoding algorithm based on average magnitude was proposed for Low Density Parity Check (LDPC) code. The average magnitude of the information nodes was first introduced as the reliability of the parity checks, which was used to weigh the bipolar syndrome, and then an effective bit-flipping function was obtained. Simulation was conducted at Bit-Error Rate (BER) of 10-5 under an Additive White Gaussian Noise (AWGN) channel, and coding gains of 0.08 and 0.29 dB were achieved in comparison to conventional weighted Gradient Descent Bit-Flipping (GDBF) and Reliability Ratio based Weighted Gradient Descent Bit-Flipping (RRWGDBF) algorithms while the average number of decoding iterations was reduced by 72.6% and 9.3%, respectively. The simulation results show that the improved algorithm outperforms the conventional algorithms while average decoding number is also reduced. It indicates that this new scheme can better balance error-correcting ability, decoding complexity and delay, which can be applied to high-speed communication system with high real-time requirement.

OOFDM (Orthogonal Frequency Division Multiplexing) is a focus in research of broadband communications now. The combination of OFDM with ROF (Radio Over Fiber) system can overcome optical dispersion and improve the performance of ROF system。 A generation and transmission system of optical millimeter-wave carrying OFDM signal based on phase modulator was proposed. In the center station, Double SideBand with Suppressed Carrier (DSB-SC) optical millimeter wave signal was generated utilizing phase modulator along with optical filter, while OFDM signal was modulated only onto one of the two optical carriers and transported along optical fiber. The paper set a model about optical carrier OFDM generation and analyzed fiber dispersion influence on phase, and proved the feasibility of the system through the simulation test. The result show the system's eye chart is very clear over 95km optical fiber.