Yang Mingchuan

Design and Analysis of Printed Yagi-Uda Antenna and Two-Element Array for WLAN Applications

A printed director antenna with compact structure is proposed. The antenna is fed by a balanced microstrip-slotline and makes good use of space to reduce feeding network area and the size of antenna. According to the simulation results of CST MICROWAVE STUDIO software, broadband characteristics and directional radiation properties of the antenna are explained. The operating bandwidth is 1.8 GHz–3.5 GHz with reflection coefficient less than −10 dB. Antenna gain in band can achieve 4.5–6.8 dBi, and the overall size of antenna is smaller than . Then the antenna is developed to a two-element antenna array, working frequency and relative bandwidth of which are 2.15–2.87 GHz and 28.7%, respectively. Compared with antenna unit, the gain of the antenna array has increased by 2 dB. Thus the proposed antenna has characteristics of compact structure, relatively small size, and wideband, and it can be widely used in PCS/UMTS/WLAN/ WiMAX fields.

A Random Number Generator Based Software Channel Simulator for Land Mobile Satellite Channel

A two-state statistical channel model is proposed for predicting the propagation characteristics of land mobile satellite channel (LMSC) according to propagation scattering theory. The underlying channel model takes for granted non- frequency-selective fading but considers the effects caused by shadowing. For such a channel model, a software channel simulator is designed. The simulator is based on a random number generator (RNG) that generates data sets to compute fading statistics of the propagation channels. Compared with the filter method and the Rice method, the RNG method can be realized precisely in engineering. Furthermore, the operating frequency band of the simulator is not restricted to any particular frequency band, for the random numbers used in the simulator are independent of frequency. The validity of the simulator is confirmed by comparing fading statistics from the analytical model and the measured data.

Congestion-aware and hybrid routing protocol for vehicular ad hoc network

In vehicular ad hoc network (VANET), nodes have to cooperate to forward each others packets through the networks. Every node, including source and intermediate nodes, has a fair opportunity to transmit a packet. Consequence, the hot spot may incur traffic congestion. The packet loss rate and the transmission delay are increased, but the throughput is decreased. On account of the contention for the shared channel, the throughput of each single node is limited not only by the channel capacity, but also by the transmissions in its neighborhood. Additionally, the network throughput still restrict by the channel capacity. Some other related works using multiple channels simultaneously to transmit packets without interfering each other increases the throughput. But if the traffic load is heavy, these schemes may trigger off more serious packet loss on the contrary because they do not consider the congestion problem especially in VANET environment. In this paper we use cross layer approach to design routing protocol for VANET with aim to restrict the number of packets of every flow passing by congested nodes. Firstly, we estimate congested probability at each node by using MAC overheads, quality of link, and data rate. Subsequently, we use congested probability assessment as route metric. This method enhances link stable and network throughputs. For building routing protocol operation we use hybrid model (inherit good chacters from proactive and reactive routing protocols). It helps restrict route overheads and fast convergence of route discovery process. The simulation results illustrate our prominent proposed routing protocol.