Traffic Nonuniformity Research Articles

Traffic Adaptive MAC Mechanism for IEEE 802.15.4 Cluster Based Wireless Sensor Networks with Various Traffic Non-uniformities

This paper proposes a medium access control (MAC) mechanism for the recently developed IEEE 802.15.4 standard, a promising candidate to become the physical (PHY) and MAC layer standard for Wireless Sensor Networks (WSNs). The main concern in WSNs is the energy consumption, and this paper presents a mechanism that adapts properly the duty cycle operation according to the traffic conditions. Various traffic adaption mechanisms have been presented for the MAC layer of the IEEE 802.15.4. However these conventional mechanisms only consider the temporal traffic fluctuations. The proposed mechanism outperforms the conventional mechanism when applied to cluster-tree based WSNs, because it considers not only the temporal fluctuations but also the spatial (geographical) fluctuations, which are intrinsic characteristics of traffic in WSNs with the cluster tree topology. Evaluations showed that the proposed mechanism achieves less energy consumption than the conventional traffic adaptation mechanism, with maintaining almost the same transmission performance.

Nonuniform Traffic Distribution Model in Reverse Link of Multirate/Multiservice WCDMA-Based Systems

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper focuses on the modeling of the reverse link of a wideband code division multiple access system in a nonhomogeneous environment with a single cell. Multiple traffic spatial and service nonuniformities are considered in the analytical model, and then, expressions for required transmitted power and the associated outage probability and block error rate are derived. Special attention is also paid to the effect caused by different transmission bit rates and the spatial location of the traffic nonuniformities. From the presented expressions, it is possible to set appropriate load thresholds to control the desired error rate. Although the model considers a single cell, results in terms of maximum allowable load can also be applicable in multicell scenarios. </para>

A Performance Model of Adaptive Wormhole Routing in k -Ary n -Cubes in the Presence of Digit-Reversal Traffic

Several analytical models of fully adaptive routing in wormhole-routed k-ary n-cubes under the uniform traffic pattern have recently been proposed in the literature. Although the uniform reference model has been widely used by researchers, it is not always true in practice as there are many applications that exhibit traffic nonuniformity. There has hardly been any study that describes an analytical model of fully adaptive routing under nonuniform traffic conditions. This paper describes the first analytical model of fully adaptive routing in k-ary n-cubes in the presence of nonuniform traffic generated by the digit-reversal permutation, which is an important communication operation found in many matrix computation problems. Results obtained through simulation experiments confirm that the model predicts message latency with a good degree of accuracy under different working conditions.

Generalized performance evaluation of low Earth orbit satellite systems

A novel three-dimensional distribution traffic is proposed for low Earth orbit (LEO) satellite systems. The effect of the traffic geographical nonuniformity on the performance of these satellite systems is discussed.

Dynamic cell configuration for CDMA microcell mobile radio communications systems considering nonuniform traffic distribution

In mobile communication systems oriented toward the future, the microcell system, considering the increase of subscribers and the information transfer rates, will be indispensable. When the microcell scheme is introduced, however, the traffic becomes remarkably nonuniform, which affects the communication quality and the subscriber capacity. The authors consider the CDMA microcell mobile communication system, and propose a dynamic cell configuration scheme (DCC) to solve the above problems. The proposed scheme operates as follows. The base station autonomously controls the pilot signal power and the desired uplink power level adaptively, so as to reconfigure the cells flexibly. By this scheme, the communication quality difference among the base stations due to nonuniform traffic is suppressed, and degradation of system efficiency is avoided. This paper describes the equipment architecture and the operating principle of the dynamic cell configuration. The performance of the proposed system is analyzed and is evaluated by simulation. It is shown that the proposed method is useful as a means to cope with traffic nonuniformity in a CDMA microcell system. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(5): 75–89, 2000

Dynamic cell configuration for CDMA microcell mobile radio communications systems considering nonuniform traffic distribution

In mobile communication systems oriented toward the future, the microcell system, considering the increase of subscribers and the information transfer rates, will be indispensable. When the microcell scheme is introduced, however, the traffic becomes remarkably nonuniform, which affects the communication quality and the subscriber capacity. The authors consider the CDMA microcell mobile communication system, and propose a dynamic cell configuration scheme (DCC) to solve the above problems. The proposed scheme operates as follows. The base station autonomously controls the pilot signal power and the desired uplink power level adaptively, so as to reconfigure the cells flexibly. By this scheme, the communication quality difference among the base stations due to nonuniform traffic is suppressed, and degradation of system efficiency is avoided. This paper describes the equipment architecture and the operating principle of the dynamic cell configuration. The performance of the proposed system is analyzed and is evaluated by simulation. It is shown that the proposed method is useful as a means to cope with traffic nonuniformity in a CDMA microcell system. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(5): 75–89, 2000

Soft handoff algorithm with variable thresholdsin CDMA cellular systems

Traffic nonuniformity degrades the performance of CDMA cellular systems. The authors present a new algorithm called the variable threshold soft handoff (VTSH) which reduces the performance degradation due to traffic nonuniformity in CDMA cellular systems. Unlike the conventional fixed handoff thresholds, the proposed algorithm allows the handoff thresholds (T ADD and T DROP) to vary dynamically according to the traffic density of each cell. This algorithm has been implemented by means of computer simulation and the results show that VTSH improves the overall CDMA system performance in terms of outage probability. The VTSH algorithm can easily be applied to CDMA cellular systems without any modification.

The performance of the Cedar multistage switching network

While multistage switching networks for vector multiprocessors have been studied extensively, detailed evaluations of their performance are rare. Indeed, analytical models, simulations with pseudosynthetic loads, studies focused on average-value parameters, and measurements of networks disconnected from the machine, all provide limited information. In this paper, instead, we present an in-depth empirical analysis of a multistage switching network in a realistic setting: We use hardware probes to examine the performance of the omega network of the Cedar shared-memory machine executing real applications. The machine is configured with 16 vector processors. The analysis suggests that the performance of multistage switching networks is limited by traffic nonuniformities. We identify two major nonuniformities that degrade Cedar's performance and are likely to slow down other networks too. The first one is the contention caused by the return messages in a vector access as they converge from the memories to one processor port. This traffic convergence penalizes vector reads and, more importantly, causes tree saturation. The second nonuniformity is the uneven contention delays induced by a relatively fair scheme to resolve message collisions. Based on our observations, we argue that intuitive optimizations for multistage switching networks may not be the most cost-effective ones. Instead, we suggest changes to increase the network bandwidth at the root of the traffic convergence tree and to delay traffic convergence up until the final stages of the network.

A modified power control scheme for remedying the effects of traffic nonuniformity in LEO satellite communications systems

It has been shown in our previous studies that the geographical traffic nonuniformity considerably affects the performance of the low earth orbit satellite communications systems. In this paper, a new scheme for improving the throughput characteristics of these systems at nonuniform traffic distribution is proposed. In this method, some parts of the users under the satellite which is flying over the area with high traffic load are assigned to its neighbor satellites with lower transmitting power levels. It is shown that the method equalizes the traffic loads of the satellites to some degree and, hence, can improve the throughput characteristics of the system.

Cell loss analysis and design trade-offs of nonblocking ATM switches with nonuniform traffic

In practical ATM switch design, a proper dimensioning of buffer sizes and a cost effective selection of speed-up factor should be considered to guarantee a specified cell loss requirement for a given traffic. Although a larger speed-up factor provides better throughput for the switch, increasing the speed-up factor involves greater complexity and cost. Hence, it may not be cost effective to increase the speed-up factor for 100% throughput. Moreover, with a given buffer budget, an increase in the speed-up factor beyond a certain value only adds to the cell loss. The paper addresses design trade-offs existing between finite input/output buffer sizes and speed-up factor in a nonblocking ATM switch. Another important issue is the adverse effect on cell loss performance caused by nonuniform traffic (different traffic intensity and unevenly distributed routing). The paper analyzes cell loss performance of ATM switches with nonuniform traffic, and examines the effect of each nonuniform traffic parameter. The authors also provide an algorithm for effective buffer sharing that alleviates the performance degradation caused by traffic nonuniformity.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>