Aasia Riasat’s research while affiliated with Institute of Business Management and other places

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Publications (54)


A Use of Matrix with GVT Computation in Optimistic Time Warp Algorithm for Parallel Simulation
  • Conference Paper
  • Full-text available

March 2012

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176 Reads

Shalini Potham

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Aasia Riasat

One of the most common optimistic synchronization protocols for parallel simulation is the Time Warp algorithm proposed by Jefferson [12]. Time Warp algorithm is based on the virtual time paradigm that has the potential for greater exploitation of parallelism and, perhaps more importantly, greater transparency of the synchronization mechanism to the simulation programmer. It is widely believe that the optimistic Time Warp algorithm suffers from large memory consumption due to frequent rollbacks. In order to achieve optimal memory management, Time Warp algorithm needs to periodically reclaim the memory. In order to determine which event-messages have been committed and which portion of memory can be reclaimed, the computation of global virtual time (GVT) is essential. Mattern [2] uses a distributed snapshot algorithm to approximate GVT which does not rely on first in first out (FIFO) channels. Specifically, it uses ring structure to establish cuts C1 and C2 to calculate the GVT for distinguishing between the safe and unsafe event-messages. Although, distributed snapshot algorithm provides a straightforward way for computing GVT, more efficient solutions for message acknowledging and delaying of sending event messages while awaiting control messages are desired. This paper studies the memory requirement and time complexity of GVT computation. The main objective of this paper is to implement the concept of matrix with the original Mattern's GVT algorithm to speedups the process of GVT computation while at the same time reduce the memory requirement. Our analysis shows that the use of matrix in GVT computation improves the overall performance in terms of memory saving and latency.

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Figure 1: Internal architecture of an LP. LP maintains one FIFO queue per neighboring LP and one UML. Each LP can have a total of m number of event-messages ( 0 m ≤ ⎯⎯ →∞ ).
Figure 2: An illustration of proposed scheme dealing with the simultaneous reporting problem.
Figure 3: High level architecture of the proposed scheme.
Figure 10: Effect of unacknowledged message list (UML) scheme on the speedup with respect to 4, 8, and 12 processor systems in tree and butterfly barriers. 
An efficient optimistic time management algorithm for discrete-event simulation system

September 2010

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1,007 Reads

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5 Citations

International Journal of Simulation Modelling

Time Wrap algorithm is a well-known mechanism of optimistic synchronization in a parallel discrete-event simulation (PDES) system. It offers a run time recovery mechanism that deals with the causality errors. For an efficient use of rollback, the global virtual time (GVT) computation is performed to reclaim the memory, commit the output, detect the termination, and handle the errors. This paper presents a new unacknowledged message list (UML) scheme for an efficient and accurate GVT computation. The proposed UML scheme is based on the assumption that certain variables are accessible by all processors. In addition to GVT computation, the proposed UML scheme provides an effective solution for both simultaneous reporting and transient message problems in the context of synchronous algorithm. To support the proposed UML approach, two algorithms are presented in details, with a proof of its correctness. Empirical evidence from an experimental study of the proposed UML scheme on PHOLD benchmark fully confirms the theoretical outcomes of this paper.


Figure 2. A constellation diagram consisting of three different vectors
A Low-Complexity Optimum Multiuser Receiver for DS-CDMA Wireless Systems

June 2010

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144 Reads

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2 Citations

Journal of Communications

Multiuser detection is an important technology in wireless CDMA systems for improving both data rate as well as user capacity. However, the computational complexity of multiuser detection prevents the widespread use of this technique. Most of the CDMA systems today and in the near future will continue to use the conventional matched filter with its comparatively low user capacity and a slow data rate. However, if we could lower the computational complexity of multiuser detectors, CDMA systems would offer an increased system capacity with a better data rate. In this paper, a new scheme for reducing the computational complexity of multiuser receivers is proposed. It utilizes the transformation matrix algorithm to improve the performance of multiuser receivers by effectively reducing the bit error rate (BER). In addition to the transformation matrix algorithm, a quantitative analysis of the processing gain for a multiuser DS-CDMA system is presented. The quantitative analysis of the processing gain demonstrates that how the reduced BER could be used to achieve reasonable values of processing gain by which unwanted signals or interference can be suppressed relative to the desired signal at the receiving end. We present that the proposed scheme can reduce the asymptotic computational complexity of multiuser receivers while at the same time effectively eliminates the unwanted signals. The proposed algorithms not only are shown to substantially improve the performance of the multiuser detectors by means of reduced BER but also have a much lower multi-access interference. The performance measure adopted in this paper is the achievable bit rate for a fixed probability of error (10-7) and consistent values of SNR.


Quantification of Capacity and Transmission Delay for Mobile Ad Hoc Networks (MANET)

February 2010

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188 Reads

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1 Citation

International Journal of Communications Network and System Sciences

The capacity of mobile ad hoc network (MANET) is typically determined by the size of network, routing protocol, mobility and the interactions that occur between the nodes. Moreover, these critical parameters cause the loss rate that has severed impact on the performance of the MANET. This situation even becomes worst when these critical parameters are chosen inappropriately. This paper presents an analytical model that incorporates most of the critical parameters that can influence the capacity of MANET. Based on the analytical model, an efficient 3-phase algorithm is designed to optimize the performance of MANET in terms of increased capacity and reduced transmission delay. The proposed 3-pahse algorithm considers both delay-tolerant and delay-sensitive network traffics. In addition, the 3-phase algorithm can be used to approximate both the best and worst case capacities of MANET with the relaying and non-relaying nodes.


Fig. 1 IMAGE GOES HERE 
Fig. 2 IMAGE GOES HERE 
The Use of Orthogonal Frequency Code Division (OFCD) Multiplexing in Wireless Mesh Network (WMN)

January 2010

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266 Reads

In the present scenario, improvement in the data rate, network capacity, scalability, and the network throughput are some of the most serious issues in wireless mesh networks (WMN). Specifically, a major obstacle that hinders the widespread adoption of WMN is the severe limits on throughput and the network capacity. This chapter presents a discussion on the potential use of a combined orthogonal-frequency code-division (OFCD) multiple access scheme in a WMN. The OFCD is the combination of orthogonal frequency division multiplexing (OFDM) and the code division multiple access (CDMA). Since ODFM is one of the popular multi-access schemes that provide high data rates, combing the OFDM with the CDMA may yield a significant improvement in a WMN in terms of a comparatively high network throughput with the least error ration. However, these benefits demand for more sophisticated design of transmitter and receiver for WMN that can use OFCD as an underlying multiple access scheme. In order to demonstrate the potential use of OFCD scheme with the WMN, this chapter presents a new transmitter and receiver model along with a comprehensive discussion on the performance of WMN under the new OFCD multiple access scheme. The purpose of this analysis and experimental verification is to observe the performance of new transceiver with the OFCD scheme in WMN with respect to the overall network throughput, bit error rate (BER) performance, and network capacity. Moreover, in this chapter, we provide an analysis and comparison of different multiple access schemes such as FDMA, TDMA, CDMA, OFDM, and the new OFCD. Keywords— Wireless mesh networks, orthogonal frequency code division (OFCD), Code division multiple access (CDMA), Multiple access, Multiple access interference (MAI), Network throughput, Bit error rate (BER), Intersymbol interference (ISI).


Fig. 3: Proposed scheme with primary and secondary path and their links
Fig.4. Number of nodes versus RD
Fig. 6. Time delay versus number of nodes 
A Novel Optimization of the Distance Source Routing (DSR) Protocol for the Mobile Ad Hoc Networks (MANET)

January 2010

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74 Reads

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1 Citation

This paper presents a new scheme for the Distance Source Routing (DSR) protocol which shows the improvement over the two major metrics of the DSR protocol: Route Discovery and Route Maintenance. In addition, we present a mathematical model that includes probability density function for these two observed metrics. Our simulation results demonstrate a significant improvement in the route discovery, transmission time, and the overall network utilization. As an interesting side result, our analysis also shows that the proposed model can be used to effectively reduce the packet losses.


Deterministic Formulization of SNR for Wireless Multiuser DS-CDMA Networks

August 2009

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73 Reads

Wireless Multiuser receivers suffer from their relatively higher computational complexity that prevents widespread use of this technique. In addition, one of the main characteristics of multi-channel communications that can severely degrade the performance is the inconsistent and low values of SNR that result in high BER and poor channel capacity. It has been shown that the computational complexity of a multiuser receiver can be reduced by using the transformation matrix (TM) algorithm [4]. In this paper, we provide quantification of SNR based on the computational complexity of TM algorithm. We show that the reduction of complexity results high and consistent values of SNR that can consequently be used to achieve a desirable BER performance. In addition, our simulation results suggest that the high and consistent values of SNR can be achieved for a desirable BER performance. The performance measure adopted in this paper is the consistent values of SNR. Comment: 9 pages IEEE format, International Journal of Computer Science and Information Security, IJCSIS July 2009, ISSN 1947 5500, Impact Factor 0.423


Fig.1.Multiuser optimal and suboptimal wireless receivers
Fig. 5. The asymptotic computational complexities versus intermediate number of users  
A Low-Complexity Algorithm for Improving Computing Power of Multiuser Receivers for Next Generation Wireless Systems

July 2009

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118 Reads

A new transformation matrix (TM) algorithm for reducing the computational complexity of multiuser receivers for DS-CDMA wireless system is presented. Next generation multiuser wireless receivers will need to use low computational complexity algorithm in order to perform both fast signal detection and error estimation. Several multiuser signal detection algorithms have proposed for next generation wireless receivers, which are designed to give good performance in terms of signal to noise ratio (SNR) and bit error rate (BER), are discarded for a direct implementation as they have high computational complexity. In this paper, we propose a new low-complexity TM algorithm that can be used to perform fast signal detection for multiuser wireless receives. This reduction in computational complexity would likely to give us a considerable improvement in the performance of multiuser wireless receivers such as high computing power and low error rate. In addition, we also present a formal mathematical proof for computational complexities that verifies the low-complexity of the proposed algorithm




Citations (16)


... Conservative protocols fundamentally maintain causality in event execution by strictly disallowing the processing of events out of time-stamp order [4]. Some recent research on conservative algorithms in DES can be found in [11][12][13][14]. An effort to combine conservative and optimistic synchronization algorithms on a common layered architecture framework is proposed in [15]. ...

Reference:

A Logical Process Simulation Model for Conservative Distributed Simulation Systems
Minimizing the Null Message Exchange in Conservative Distributed Simulation

... Source Routing (DSR) [24], and Temporarily Ordered Routing Algorithm (TORA) [25]. Hybrid protocols are a mix between the previous types where routes are kept proactively for nearby nodes and reactively 2.2. ...

A Novel Optimization of the Distance Source Routing (DSR) Protocol for the Mobile Ad Hoc Networks (MANET)

... • the Medium Access Delay based on the MAC access schemes used in each frequency band. The Switching Delay occurs when a node in a path switches from one frequency band to another [27] ; • Queueing Delay based on the output transmission capacity of a node on a given frequency band Regarding the routing transmission of packets from the source to the destination, the symbol is assigned to depict the ratio of the packet arrival rate and the packet service rate µ of MN [28]. When ≤ , we assume ( ) the probability of having packets queuing in the system ( ≤ . ...

A Mathematical Model for Evaluating the Performance of Multicast Systems

... The end to end packet delay in mobile ad-hoc network is complex because it depends on many influential factors as path length from source to destination, average neighbours of intermediate hops and interference. [5] [6] On the basis of available papers, it has been review in [7] that delay is a dynamic metric which is built upon the following factors multi-hop nature of network, Mobility, path length, Dynamic topology, Link-Breakage, limited battery life, bandwidth issues and Selfish behaviour of nodes. And in a dense network these factors show their affect even more than in a sparce network. ...

Quantification of Capacity and Transmission Delay for Mobile Ad Hoc Networks (MANET)

International Journal of Communications Network and System Sciences

... Processors use EBs to record the number of events sent and received by LPs, as well as the LVT of each LP and the timestamps of events in transit. GVT computation via the EB approach can avoid message acknowledgement, which is a common solution for the problem of transient event in distributed GVT algorithms [16,17,20,21]. In our algorithm, the size of Event-Bulk is negatively correlated with the accuracy of GVT computation but positively correlated with the performance of GVT computation. ...

An efficient optimistic time management algorithm for discrete-event simulation system

International Journal of Simulation Modelling

... Due to its nature, it requires the definition of some artificial events with the aim of making the simulation proceed. The number of such messages introduced by the synchronization algorithm can be very large [74,75]. Obviously, this communication overhead has a big effect on the WCT. ...

Minimizing the Null Message Exchange in Conservative Distributed Simulation

... The solution to the system Cz + W ′ = D may not yield unique solution because D does not lie in the column space of C. So, an approximate solution is needed in this scenario. Basically, this approximate solution is projected solution onto the column space of C. It is at the minimum distance from all the column vectors of C. Therefore, a least square approach [33] is used in this context. The advantage of this approach lies in the fact that non-linear Equations 16 can be converted to linear one by subtracting out two equations. ...

A New Methodology for Self Localization in Wireless Sensor Networks

... This approach produced the highest message delivery percentage as seen in Message Delay and Hop count: Another evaluation criteria is the average hop count of the multicast messages. The hop count of a packet is defined as the number of routers traversed by a packet between its source and destination [17], which is in this case the number of hosts that a message passes from the source to the destination [18]. As seen in Figures 8 and 9 and Tables 2 and 3 when the number of users is small, the average hop count of LA-NICE and NICE, as well as the maximum hop count is almost the same, however as the number of users increase LA-NICE has less number of hops leading to less delay in delivering the messages. ...

Deterministic formulization of bandwidth efficiency for multicast systems

... In order to collect the information, two methods of scanning are commonly available in the literature: active scanning and passive scanning [42]. Active scanning refers to keeping on all the interfaces continuously active while passive scanning refers to the periodic activation of the interfaces for verifying the availability of new networks. ...

Active scanning: A better approach to reduce handover time at MAC layer for wireless networks

... Consequently, the use of matrix with the Mattern's algorithm provides several advantages such as it reduces the number of memory fetches, saves memory, increases the processor speed, and improves the latency. We incorporated the butterfly barrier as it has great performance when compared to the other broadcast and the centralized barriers [7,19,20]. ...

Implementation of Tree and Butterfly Barriers with Optimistic Time Management Algorithms for Discrete Event Simulation