Complex Envelope Second-Order Statistics in High-Altitude Platforms Communication Channels

High-altitude platforms are one of the most promising alternative infrastructures for realizing next generation high data rate wireless networks. This paper presents a three-dimensional (3-D) scattering model for land mobile stratospheric multipath-fading channel with its complex faded envelope. From the scattering model and the complex envelope second-order statistics are derived for a 3-D non-isotropic scattering environment. When we discuss on the second-order statistics we refer to the level crossing rate and the average fade duration, whichare two main parameters in describing the fading severity over time and are very important in assess system characteristics such as hand off, velocities of the transmitter and receiver and fading rate. Numerical calculations have been carried out to demonstrate theoretical derivations and the utility of the proposed model.     

Green optical backbone networks: virtual topology adaptation using a page rank‐based rating system

An energy‐aware virtual topology rating system is proposed in this work, which can be utilized as a tool during the virtual topology reconfiguration procedure in an optical backbone network in order to reduce its energy consumption. It is well known that maintaining a static virtual topology in Internet Protocol (IP)‐over‐Wavelength Division Multiplexing (WDM) networks is not energy‐efficient. To that end, virtual topology adaptation algorithms have been developed to adjust the virtual topology to the constantly fluctuating traffic load. While these algorithms achieve significant energy savings, further reduction on the total network energy consumption can be achieved through the proposed rating system. The proposed rating system is a modified version of the page rank algorithm, which ranks websites in the Internet based on their importance. The proposed rating system attributes ratings to lightpaths, which indicate the relative significance of a lightpath in the virtual topology in terms of energy consumption. The rating can be used during the routing procedure as an energy efficiency indicator, in order to increase the number of lightpaths that are deactivated from the reconfiguration mechanism and increase the utilization per lightpath. The proposed reconfiguration scheme (page rank‐based virtual topology reconfiguration) achieves up to 12% additional energy savings in comparison to an existing virtual topology reconfiguration algorithm at the cost of slightly increased average hop distance. Copyright © 2015 John Wiley & Sons, Ltd.     

A virtual circuit deflection protocol

We propose a communication protocol, called the virtual circuit deflection (VCD) protocol, which combines some of the individual characteristics of virtual circuit switching and deflection routing. An advantage of the VCD protocol over previous (datagram) deflection schemes is that deflections in the former occur on a per session basis (or a per subsession basis, if sessions need to be split to find adequate capacity on the outgoing links), while in the latter, they occur on a per packet basis. This makes packet resequencing at the destination considerably easier to accomplish in the VCD protocol than in datagram deflection schemes. The VCD protocol exploits the storage arising from the high bandwidth-delay product of optical fibers to provide lossless communication with little buffering at the switches and without the need for advance reservations. This makes it particularly suitable for networks that use optical switching, where buffers are expensive to implement with current optical technology. We present a simple implementation of the VCD protocol for such networks, which requires only limited buffering, accomplished through the use of a minimal number of optical delay lines. We also analyze the performance of the protocol for the Manhattan Street network topology by using new analytical models. In particular, we examine the effect of the traffic load and the network size on the throughput and the length of the paths followed by the sessions, and compare the analytical results obtained with corresponding simulation results. The results indicate that the VCD protocol is efficient under both light and heavy traffic conditions, especially when the link capacities are large compared to the basic rate of individual sessions, as is expected to be the case in future multigigabit networks     

Performance engineering of metropolitan area optical networks through impairment constraint routing

We demonstrate the use of impairment constraint routing for performance engineering of transparent metropolitan area optical networks. Our results show the relationship between blocking probability and different network characteristics such as span length, amplifier noise figure, and bit rate, and provide information on the system specifications required to achieve acceptable network performance.     

A new burst assembly scheme based on the average packet delay and its performance for TCP traffic

We propose and evaluate a new burst assembly algorithm based on the average delay of the packets comprising a burst. This method fixes the average delay of the packets belonging to an assembled burst to a desired value $T_{\mathrm{AVE}}$ that may be different for each forwarding equivalence class (FEC). We show that the proposed method significantly improves the delay jitter experienced by the packets during the burst assembly process, when compared to that of timer-based and burst length-based assembly policies. Minimizing packet delay jitter is important in a number of applications, such as real-audio and streaming-video applications. We also find that the improvement in the packet delay jitter yields a corresponding significant improvement in the performance of TCP, whose operation depends critically on the ability to obtain accurate estimates of the round-trip times (RTT).