This study presents a new effective layout method considering space-saving for a type of U-shaped folded dipole antenna (UFDA), namely, a vertical U-shaped folded dipole antenna (VUFDA) that projects from a small ground plane, designed for WiMAX applications. Moreover, by applying a suitable formulation of the objective function in a particle swarm optimization (PSO), the VUFDA shape is optimized to achieve desired broadband properties that include the use of two WiMAX frequency bands, and reduce the physical antenna area by roughly 23% compared to that of an optimized UFDA reported in a previous study.
We propose a grid-based routing protocol which divides the network area for large side lengths of square cells and exploits cell rotation. The proposed scheme divides each cell into multiple sub-cells, and because the maximum transmission range is a fixed value, side lengths of square cells can be enlarged. Therefore, the number of relay nodes between the source node and the mobile sink is reduced. Simulation results show that the proposed scheme improves the packets latency and energy consumption efficiency.
In this letter, we introduce a simple analytical model for wireless distributed networks (WDNs) using IEEE 802.11 distributed coordination function (DCF), which considers contending and hidden nodes. Furthermore, we derive simple formulas of throughput for maximum and saturated cases, and discuss the characteristics of the influence of the contending and hidden nodes. We also compare the analytical results with the simulation of 802.11 DCF. Although our analytical model simplifies the behavior of 802.11 DCF, analytical results coincide with the simulation.
Safety application to notify emergency events and non-safety application to improve the transport efficiency are provided at the same time. The emergency events should be transmitted as quickly as possible and vehicle’s driving status is collected by a road-side unit periodically. In a congested road, the road-side unit cannot collect vehicle information periodically because this is transmitted only on the service channel. In this letter, we proposed channel interval adjustment scheme to improve capacity of road-side unit. Simulation results show that the proposed scheme provides the improved performance in congested traffic condition.
This paper proposes a new retransmission scheme for achieving high-speed transmission by reducing the retransmission delay time caused by packet loss. High-speed data packet transmission can be realized by sending user datagram protocol (UDP) packets continuously over long-distance wireless systems. The UDP characterizes connectionless communication, requiring the use of a retransmission scheme for reliable quality. However, the transmission speed will reduce with repeated retransmissions over time. The key advantage of the proposed scheme is that the retransmission waiting time can be dramatically reduced by transmitting data packets in descending order from the last data packet. It is verified via a computer simulation that the average peer-to-peer network configuration receiving time can be approximately halved and a 20% improvement in throughput with a packet error rate of 0.1 can be achieved by the proposed scheme.
This article provides an analytical consideration of transmission control protocol (TCP) characteristics when under the sleep control of passive optical networks (PON) systems. We show that the TCP’s initial throughput growth is delayed by sleep control with a large round trip time (RTT), where the guard time used to make the sleep decision expires before the next packet train arrives. We modeled the adverse impact caused by sleep control in terms of congestion window growth. We confirmed that our model successfully approximated the experimental result obtained in an actual environment. We also provide a guideline for solving this problem that takes account of power-saving efficiency.
This letter presents a mathematical model that minimizes the number of wavelengths required for wavelength assignment in a wavelength-reusable multi-carrier-distributed (WRMD) wavelength division multiplexing mesh network. None of the source nodes in the WRMD network is equipped with laser diodes. It receives carrier wavelengths from a multi-carrier light source or reuses carrier wavelengths from other established lightpaths. The loop problem may occur in mesh topologies when a source node selects a reused carrier wavelength from a destination lightpath node, if we consider only flow conservation constraints, which are usually adopted in conventional network design. We solve the loop problem by formulating constraints that reflect the special characteristics of the WRMD network. To support the development of heuristic algorithms towards large-scale networks, our mathematical model, which can provide reference values including upper and lower bounds, is useful for benchmarks.
Closed-form error probability expressions for a L(≥ 2) branch post-detection switch-and-examine combiner (SEC), using non-coherent M-ary frequency shift keying (ncMFSK) modulation and operating over independent and identically distributed (IID) Hoyt fading channel, are derived. Under similar channel and receiver constraints, derived error rates are compared with results available for pre-detection combining. It was observed that an additional diversity gain is achievable with post-detection scheme when the average channel signal-to-noise ratio (SNR) exceeds some crossover SNR value that depends on modulation order (M), fading parameter (q), and number of diversity branches (L).