In this work, an alternative metal-assisted chemical etching method is proposed to fabricate large-area uniform zigzag silicon nanowires. The effects of deposition time, etching time, HF concentration and H2O2 concentration on the nanostructure of nanowires were systematically investigated. The results demonstrate the suitable preparation concentrations in the alternating etching process are HF([SI]/[SII] = 9.2 M/2.3 M) and H2O2{[SI]/[SII] = (0.04 M approximate to 0.26 M)/(0.4 M approximate to 0.65 M)}. Moreover, the anti-reflec-tion properties of the resulting zigzag SiNWs arrays have been studied, the average reflectance is almost lower than 10% at wavelength range of 200 approximate to 1200 nm. The superior anti-reflection performance of zigzag SiNWs shows a huge potential application in high-efficiency silicon solar cells.

为满足多点波束宽带卫星系统各波束不同的业务需求,提高星上功率利用率,对多点波束卫星的功率分配进行优化。在充分考虑卫星下行链路信道条件的不同及各波束最小容量需求的基础上,以服务公平性和容量最大化为目标进行建模,提出了一种波束间功率优化分配算法OIBPA（optimized inter-beam pow-er allocation）,并采用凸优化理论对该优化算法进行分析。通过仿真分析,该算法与传统的功率分配算法相比,在考虑信道条件的基础上提高了卫星的功率利用效率,降低了计算复杂度,且可以根据业务优先级进行灵活地调整,适用于多点波束宽带卫星系统。

The bandwidth management issues in broadband multimedia satellite communication system using multiple frequency-time division multiple access (MF-TDMA) were concerned. The framework of bandwidth management structure was proposed in a hierarchical manner. Some key problems were reviewed from large scale, moderate scale and micro scale aspects respectively.

The existing resource optimization allocation strategies of multi-beam communication satellite don′t take the coupling relationship of power and bandwidth into consideration. In order to further improve the utiliza-tion of satellite resources,a joint optimization algorithm of power and bandwidth is proposed,which gives full consideration to the co-channel interference and the different traffic demands of each beam. This algorithm is proposed on the basis of the system fairness and can be solved by an iterative method. Compared with the tradi-tional fixed allocation method,the joint optimization algorithm is more flexible on the redistribution of on-board resources,which increases the system capacity and improves 10% of the traffic match ratio through simulation results. The joint optimization algorithm improves the efficiency of the on-board resource utilization.

We consider the problem of transmit power allocation for the multi-beam broadband multimedia satellite communication systems. An efficient power allocation strategy based on the different traffic demand of each beam is proposed to guarantee the fairness of the system. First we solve this convex optimization problem by dual methods, and then use a heuristic algorithm to obtain the optimum power allocation of each beam, and also compare the capacity distribution of each beam when the link conditions (rain attenuation) are different.

The Burst Time Plan (BTP) generation is the key for resource allocation in Broadband Satellite Multimedia (BSM) system. The main purpose of this paper is to minimize the system response time to users’ request caused by BTP generation as well as maintain the Quality of Service (QoS) and improve the channel utilization efficiency. Traditionally the BTP is generated periodically in order to simplify the implementation of the resource allocation algorithm. Based on the analysis we find that Periodical BTP Generation (P-BTPG) method cannot guarantee the delay performance, channel utilization efficiency and QoS simultaneously, especially when the capacity requests arrived randomly. The Optimized BTP Generation (O-BTPG) method is given based on the optimal scheduling period and scheduling latency without considering the signaling overhead. Finally, a novel Asynchronous BTP Generation (A-BTPG) method is proposed which is invoked according to users’ requests. A BSM system application scenario is simulated. Simulation results show that A-BTPG is a trade-off between the performance and signaling overhead which can improve the system performance insensitive to the traffic pattern. This method can be used in the ATM onboard switching satellite system and further more can be expended to Digital Video Broadcasting-Return Channel Satellite (DVB-RCS) system or IP onboard routing BSM system in the future.

This paper presents an optimal design for Combined Free/Demand Assignment Multiple Access (CFDAMA) protocol which is widely used in today's broadband satellite system with Multiple Frequency Time Division Multiple Access (MF-TDMA) uplinks. A resource scheduling structure was given. Two important parameters-scheduling period and scheduling latency were analyzed detailed on how they impact the system response ability to traffic requirements. A classical broadband satellite system application scenario was simulated. Results show that both of the parameters have an effect on the delay performance of the system and need to be chosen carefully during system design.

In broadband satellite system providing high-speed multimedia services, it is important to efficiently assign wireless resources according to the user's demands and dynamically take into account the variations of the propagation conditions especially for satellite system operating above 10 GHz. In this paper, a "smart" broadband satellite system was proposed. The system can automatically reconfigurate the transponders according to the channel and traffic states by SDR and adaptive coding and modulation (ACM) technology. By doing so, the system available capacity can be maximized and time-variant (here we call it elastic) while maintaining the QoS. This smart satellite system with elastic capacity can largely improve the spectrum utilization efficiency and better compete with other broadband system in the new century.

With the development of broadband multimedia satellite communication, people focuse more and more on how to make better use of the bandwidth and guarantee the Qos. The bandwidth request methods of different businesses are not the same: When confronted with the real-time demanded multimedia services, the adopt of the peak distribution may waste the bandwidth, thus it's necessary to find more efficient methods; and how to further reduce the transmission delay for the non-real-time business in case of the reliable transmission also need our continuous study. This paper discusses different request and distribution methods in the broadband satellite communication systems: FODA, FEEDERS and DRIFS, and briefly analyzes and compares their performance.