Analysis and Modeling of Realistic Compound Channels in Transparent Relay Transmissions

Analytical approaches for the characterisation of the compound channels in transparent multihop relay transmissions over independent fading channels are considered in this paper. Compound channels with homogeneous links are considered first. Using Mellin transform technique, exact expressions are derived for the moments of cascaded Weibull distributions. Subsequently, two performance metrics, namely, coefficient of variation and amount of fade, are derived using the computed moments. These metrics quantify the possible variations in the channel gain and signal to noise ratio from their respective average values and can be used to characterise the achievable receiver performance. This approach is suitable for analysing more realistic compound channel models for scattering density variations of the environment, experienced in multihop relay transmissions. The performance metrics for such heterogeneous compound channels having distinct distribution in each hop are computed and compared with those having identical constituent component distributions. The moments and the coefficient of variation computed are then used to develop computationally efficient estimators for the distribution parameters and the optimal hop count. The metrics and estimators proposed are complemented with numerical and simulation results to demonstrate the impact of the accuracy of the approaches

An Occupancy Based Cyber-Physical System Design for Intelligent Building Automation

Cyber-physical system (CPS) includes the class of Intelligent Building Automation System (IBAS) which increasingly utilizes advanced technologies for long term stability, economy, longevity, and user comfort. However, there are diverse issues associated with wireless interconnection of the sensors, controllers, and power consuming physical end devices. In this paper, a novel architecture of CPS for wireless networked IBAS with priority-based access mechanism is proposed for zones in a large building with dynamically varying occupancy. Priority status of zones based on occupancy is determined using fuzzy inference engine. Nondominated Sorting Genetic Algorithm-II (NSGA-II) is used to solve the optimization problem involving conflicting demands of minimizing total energy consumption and maximizing occupant comfort levels in building. An algorithm is proposed for power scheduling in sensor nodes to reduce their energy consumption. Wi-Fi with Elimination-Yield Nonpreemptive Multiple Access (EY-NPMA) scheme is used for assigning priority among nodes for wireless channel access. Controller design techniques are also proposed for ensuring the stability of the closed loop control of IBAS in the presence of packet dropouts due to unreliable network links

TCP HACK: TCP Header Checksum Option to Improve Performance Over Lossy Links

In recent years, wireless networks have become increasingly common and an increasing number of devices are communicating with each other over lossy links. Unfortunately, TCP performs poorly over lossy links as it is unable to differentiate the loss due to packet corruption from that due to congestion. In this paper, we present an extension to TCP which enables TCP to distinguish packet corruption from congestion in lossy environments resulting in improved performance. We refer to this extension as the HeAder ChecKsum option (HACK). We implemented our algorithm in the Linux kernel and performed various tests to determine its effectiveness. Our results have shown that HACK performs substantially better than both SACK and NewReno in cases where burst corruptions are frequent. We also found that HACK can co-exist very nicely with SACK and performs even better with SACK enabled

Energy Efficient MAC for QoS Traffic in Wireless Body Area Network

Lifetimes and latencies of devices in wireless body area networks (WBANs) that monitor the health conditions of patients largely determine their utility under such a setup. It is seen that the medium access method used in the body area network can play a significant role in determining the quality of service such medical devices can provide. IEEE 802.15.6 standard for WBAN includes different types of medium access, namely, CSMA/CA, scheduled, and polling access schemes, or a combination of these techniques. In this paper, medium access methods proposed in IEEE 802.15.6 standard are investigated to assess their effectiveness in meeting the lifetime and quality of service requirements of WBANs. We then propose sleeping schedules for contention and polling access schemes to extend the device lifetime. Simulation studies are done for the investigation using a typical configuration of the medical devices found in a hospital setting. It is found that priority polling technique can give a combination of high lifetime and a low latency. Various other results offer important insights into the behaviour of these techniques under WBAN conditions

Comparative Performance of Scheduling Strategies for Switching and Multiplexing in A Hub Based ATM Network: A Simulation Study

We model an ATM network comprising an input queuing cell switching hub. Customer access lines are multiplexed into the relatively faster input links of this hub. Each access multiplexer is fed by on/off sources. Motivated by the fact that an ATM network should support both bursty as well as smooth traffic, we consider the scenario in which some multiplexers are fed by sources with long bursts of cells, and others by sources with short bursts. Here we report the results of a detailed simulation of this hub-based ATM network. Our objective is to compare the performance of various strategies for scheduling cell service in the access multiplexers, and in the ATM switch. The simulation results confirm what might be expected from the results of our earlier analytical modelling of the multiplexer and the switch in isolation (this analysis assumed a particular Markovian model for the aggregate cell arrival processes into the ATM switch). In particular, we find that, if mean burst d..

Saturation throughput analysis of an input queueing ATM switch with multiclass bursty traffic

In this paper we consider an N x N non-blocking, space division ATM switch with input cell queueing. At each input, the cell arrival process comprises geometrically distributed bursts of consecutive cells for the various outputs. Motivated by the fact that some input links may be connected to metropolitan area networks, and others directly to B-ISDN terminals, we study the situation where there are two classes of inputs with different values of mean burst length. We show that when inputs contend for an output, giving priority to an input with smaller expected burst length yields a saturation throughput larger than if the reverse priority is given. Further, giving priority to less bursty traffic can give better throughput than if all the inputs were occupied by this less bursty traffic. We derive the asymptotic (as N --> infinity) saturation throughputs for each priority class