IP Paging for Mobile Hosts in Distributed and Fixed Hierarchical Mobile IP

The concept of Paging has been found useful in existing cellular networks for mobile users with low call-to-mobility ratio (CMR). It is necessary for fast mobility users to minimize the signaling burden on the network. Reduced signaling, also, conserves scarce wireless resources and provides power savings at user terminals. However, Mobile IP (MIP), a base protocol for IP mobility, does not support paging concept in its original form. Several paging schemes and micro-mobility protocols, centralized and distributed, have been proposed in literature to alleviate the inherent limitations of Mobile IP. In this paper, the authors propose three paging schemes for Distributed and Fixed Hierarchical Mobile IP (DFHMIP) and develop analytical models for them. Performance evaluations of these schemes have been carried out and results have been compared with DFHMIP without paging and with Dynamic Hierarchical Mobile IP (DHMIP) for low CMR values.

BER Fairness and PAPR Study of Interleaved OFDMA System

For an OFDMA system, the role of interleavers is analyzed to ensure fairness of BER performance among the active users and investigate their respective PAPR properties. In this paper, the authors consider a generic system and show that for a slowly changing multipath channel, individual user’s BER performance can vary, implying that the propagation channel effect is unfairly distributed on the users. Applying different types of frequency interleaving mechanisms, the authors demonstrate that random interleaving can ensure BER fairness on an individual user basis but the associated system overhead for de-interleaving is very high. In this context, the authors introduce the application of cyclically shifted random interleaver and demonstrate its effectiveness in achieving BER fairness (dispersion in individual users BER reduced by 94% compared to no interleaving at 20dB SNR) with little system overhead. The authors also explore the comparative performance of different interleavers for scenarios with varying number of total subcarriers and subcarriers per user. Based on the scenario specific results, the authors conclude that for a heavily loaded system, i.e., relatively low number of subcarriers per user, cyclically shifted random interleavers can effectively ensure uniform performance among active users with reduced system complexity and manageable PAPR.

Improving WLAN Performance by Modifying an IEEE 802.11 Protocol

One of the limitations of the IEEE 802.11 distributed coordination function (DCF) protocol is its low bandwidth utilization under medium-to-high traffic loads resulting in low throughput and high packet delay. To overcome performance problems, traditional IEEE 802.11 DCF (“DCF”) protocol is modified to the buffer unit multiple access (BUMA) protocol. The BUMA protocol achieves a better system performance by introducing a temporary buffer unit at the medium access control (MAC) layer to accumulate multiple packets and combine them into a single packet (with a header and a trailer) before transmission. This paper provides an in-depth performance evaluation (by simulation) of BUMA for multiuser ad hoc and infrastructure networks. Results obtained show that the BUMA is more efficient than that of DCF. The BUMA protocol is simple and its algorithm (software) can be upgraded to 802.11 networks requiring no hardware changes. The BUMA protocol is described and simulation results are presented to verify the performance.

Insights from Experimental Research on Distributed Channel Assignment in Wireless Testbeds

This article presents the DES-Chan framework for experimental research on distributed channel assignment algorithms in wireless mesh testbeds. The implementation process of channel assignment algorithms is a difficult task for the researcher since common operating systems do not support channel assignment algorithms. DES-Chan provides a set of common services required by distributed channel assignment algorithms and eases the implementation effort. The results of experiments to measure the channel characteristics in terms of intra-path and inter-path interference according to the channel distance on the DES-Testbed are also presented. The DES-Testbed is a multi-radio WMN with more than 100 nodes located on the campus of the Freie Universität Berlin. These measurements are an important input to validate common assumptions of WMNs and derive more realistic, measurement-based interference models in contrast to simplified heuristics.

Wireless Transport Layer Congestion Control Evaluation

The performance of transport layer protocols can be affected differently due to wireless congestion, as opposed to network congestion. Using an active network evaluation strategy in a real world test-bed experiment, the Transport Control Protocol (TCP), Datagram Congestion Control Protocol (DCCP), and Stream Control Transport Protocol (SCTP) were evaluated to determine their effectiveness in terms of throughput, fairness, and smoothness. Though TCP’s fairness was shown to suffer in wireless congestion, the results showed that it still outperforms the alternative protocols in both wireless congestion, and network congestion. In terms of smoothness, the TCP-like congestion control algorithm of DCCP did outperform TCP in wireless congestion, but at the expense of throughput and ensuing fairness. SCTP’s congestion control algorithm was also found to provide better smoothness in wireless congestion. In fact, it provided smoother throughput performance than in the network congestion.

An Efficient Data Dissemination Scheme for Warning Messages in Vehicular Ad Hoc Networks

Vehicular ad hoc networks (VANETs) are expected to be used for the dissemination of emergency warning messages on the roads. The emergency warning messages such as post crash warning notification would require an efficient multi hop broadcast scheme to notify all the vehicles within a particular area about the emergency. Such emergency warning applications have low delay and transmission overhead requirements to effectively transmit the emergency notification. In this paper, an adaptive distance based backoff scheme is presented for efficient dissemination of warning messages on the road. The proposed scheme adaptively selects the furthest vehicle as the next forwarder of the emergency message based on channel conditions. The detailed performance figures of the protocol are presented in the paper using simulations in the OPNET network simulator. The proposed protocol introduces lower packet delay and broadcast overhead as compared to standard packet broadcasting protocols for vehicular networks.

Mobile WiMAX Bandwidth Reservation Thresholds

This paper addresses the issue of wireless bandwidth partitioning of a Mobile WiMAX cell. The authors consider a Complete Partitioning strategy, where the wireless bandwidth capacity of a cell is divided into trunks. Each partition is strictly reserved to a particular type of connection. Four IEEE 802.16e 2005 service classes are distinguished: UGS, rtPS, nrtPS, and ErtPS. The authors consider mobility and differentiate new call request from handoffs. In addition, the authors take into consideration the Adaptive Modulation and Coding (AMC) scheme, through the partition of the cell into different areas associated to a particular modulation and coding scheme. The purpose of the paper is to determine, using an analytical model and a heuristic approach, the nearly optimal sizes of the partition sizes dedicated to each type of connection, which is characterized by its service class, type of request and modulation, and coding scheme.

Synchronous Relaying in Vehicular Ad-Hoc Networks

In this paper, the authors propose a simple concept for emergency information dissemination in vehicular ad-hoc networks. Instead of competing for the shared wireless medium when transmitting the emergency information, the authors’ proposed method requires nodes to cooperate by synchronizing their transmissions. The proposed scheme is backward compatible with IEEE 802.11p carrier sense multiple access with collision avoidance. The authors also briefly address some of the implementation issues of the proposed scheme.

Performance Evaluation of a Three Node Client Relay System

In this paper, the authors examine a client relay system comprising three wireless nodes. Closed-form expressions for mean packet delay, as well as for throughput, energy expenditure, and energy efficiency of the source nodes are also obtained. The precision of the established parameters is verified by means of simulation.

HTTP Traffic Model for Web2.0 and Future WebX.0

This article presents a method of estimation for HTTP traffic quality service parameters mean delay and lost packets percentage. This method, based on statistic measurements, includes simulation and analytical modeling. Statistical HTTP traffic models presented earlier take into account typical features of WEB2.0 Internet traffic, which were used for the simulation model. Developed universal simulation models make it possible to research service quality parameters under setting network conditions over a wide range considering Internet development. The presented analytical method based on batch packet arrival model allows an accuracy estimation of mean HTTP-packets delay in Core Router by simple calculations. Objective results of HTTP traffic quality service parameters can be used in QoS standard development for WEB traffic and model QoE standard development.