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| 2. |
- Tahmasebi Toyserkani, Arash, 1978, et al.
(författare)
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A Scheduling Algorithm for Minimizing the Packet Error Probability in Clusterized TDMA Networks
- 2009
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Ingår i: Eurasip Journal on Wireless Communications and Networking. - : Springer Science and Business Media LLC. - 1687-1499 .- 1687-1472. ; 2009, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- We consider clustered wireless networks, where transceivers in a cluster use a time-slotted mechanism (TDMA) to access a wireless channel that is shared among several clusters. An approximate expression for the packet-loss probability is derived for networks with one or more mutually interfering clusters in Rayleigh fading environments, and the approximation is shown to be good for relevant scenarios. We then present a scheduling algorithm, based on Lagrangian duality, that exploits the derived packet-loss model in an attempt to minimize the average packet-loss probability in the network. Computer simulations of the proposed scheduling algorithm show that a significant increase in network throughput can be achieved compared to uncoordinated scheduling. Empirical trials also indicate that the proposed optimization algorithm almost always converges to an optimal schedule with a reasonable number of iterations. Thus, the proposed algorithm can also be used for bench-marking suboptimal scheduling algorithms.
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| 3. |
- Tahmasebi Toyserkani, Arash, 1978, et al.
(författare)
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On the MAC Protocols of Co-Existing Time-Slotted Sensor Networks
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We consider a joint scheduling approach for clustered sensornetworks, where clusters use a time-slotted mechanism to access a shared medium. It is shown that a significant increase in packet delivery probability can be achieved if the transmission schedules at neighboring clusters are considered jointly. In our consideration of the problem, we include realistic propagation effects, such as Rayleigh fading, something that is often neglected in the literature. For networks with more than two clusters, the scheduling problem is NP-hard, and we therefore approach the problem using Lagrangian relaxation methods. A numerical evaluation of the proposed algorithm show that gains in packet delivery probability up to thirty percent can be achieved over a random scheduling.
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| 4. |
- Tahmasebi Toyserkani, Arash, 1978, et al.
(författare)
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A Complexity Adjustable Scheduling Algorithm for Throughput Maximization in Clusterized TDMA Networks
- 2010
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Ingår i: IEEE Vehicular Technology Conference. - 1550-2252. - 9781424425198
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Konferensbidrag (refereegranskat)abstract
- We consider clustered wireless networks, wheretransceivers in a cluster use a time-slotted mechanism (TDMA) to access a wireless channel that is shared among several clusters.Earlier work has demonstrated that a significant increase innetwork throughput can be achieved if all the schedules areoptimized jointly. However, a drawback of this approach is the prohibitive level of computational complexity is required when a network with a large number of clusters and time-slots is to be scheduled. In this paper, we propose a modification to our previously proposed algorithm which allows for the complexityto be adjusted to the available processing power, provided some minimum processing power is available. This is achieved by carefully reducing the number of interfering clusters considered when scheduling a cluster. In addition, we propose and evaluatetwo heuristic methods of discarding the less significant clusters.While the optimality of the obtained schedule is not proven, our results demonstrate that large gains are consistently attainable.
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| 5. |
- Tahmasebi Toyserkani, Arash, 1978, et al.
(författare)
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A Low-Complexity Semi-Analytical Approximation to the Block Error Rate in Nakagami-m Block Fading Channels
- 2010
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Ingår i: IEEE Vehicular Technology Conference. - 1550-2252. - 9781424435746
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Konferensbidrag (refereegranskat)abstract
- There are few analytical formulas that can be usedfor calculating the block error rate (BLER) in block fadingchannels. Thus, an estimate of the BLER is often obtained usingnumerical methods. One such method is the threshold methodwhich assigns 0 or 1 to the instantaneous BLER given the signalto noise ratio (SNR) level. It has been shown that utilizing sucha method results in an accurate approximation of the BLER inNakagami-m block fading channels for a wide range of m.In this work, we consider a recently proposed simple method ofobtaining the threshold and study the effect of adopting differentphysical layer and channel parameters on that threshold. Weshow that, while the value of this threshold depends on themodulation, coding, and block size, it is almost unaffected bythe m parameter of Nakagami-m channels for a wide range ofpractical values. In addition, for a given modulation and codingmethod, the threshold is shown to be a simple function of blocksize. As a result, the computational complexity required to obtainthe threshold can be significantly reduced.
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| 6. |
- Tahmasebi Toyserkani, Arash, 1978, et al.
(författare)
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A Semi-Analytical Approximation to the Block Error Rate in Nakagami-m Block Fading Channels
- 2009
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- One of the main performance measures of any packet based communicationsystem is the success rate of the packets. A packetis successfully received if the arrival of the packet is detected correctly,header is received successfully, and payload is decoded withouterrors. At the moment, the probability of failure to decode thepayload, i.e., block error rate (BLER), is often obtained by numericalmethods, such as Monte-Carlo simulations due to shortage ofanalytical expressions for BLER.In this work, an approximation method for estimating the BLERin Nakagami-m block-fading channels is proposed. Furthermore, ananalytical expression with a single parameter is derived for Nakagami-m channels. This parameter can be obtained by single simulationat a single signal to noise ratio (SNR) in Rayleigh fading channel.Our simulation results demonstrates that the proposed methods ishighly accurate is estimating the BLER of many important wirelesstechnologies.
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| 7. |
- Tahmasebi Toyserkani, Arash, 1978, et al.
(författare)
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An Analytical Approximation to the Block Error Rate in Nakagami-m Non-Selective Block Fading Channels
- 2010
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Ingår i: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; 9:5, s. 1543-1546
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Tidskriftsartikel (refereegranskat)abstract
- With few exceptions, an analytical closed-form expression for the block error rate (BLER) is lacking in block fading channels. Thus, the BLER is often obtained by numerical methods, such as Monte-Carlo simulations, resulting in additional computational complexity. In this paper, we propose a single-parameter analytical approximation for the BLER in flat, block-fading Nakagami-m channels, which significantly reduces the computational overhead. The low computational cost of the approximation makes it feasible to include the BLER in the objective function of larger optimization problems.
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| 8. |
- Tahmasebi Toyserkani, Arash, 1978, et al.
(författare)
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An Efficient Broadcast MAC Scheme for Traffic Safety Applications in Automotive Networks
- 2006
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Ingår i: Proceedings IEEE Wireless Communications & Networking Conference, Las Vegas, Nevada, USA.
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Konferensbidrag (refereegranskat)abstract
- We consider intelligent transport systems which aim at providing more safety to vehicles by forming a wireless ad-hoc network among the vehicles. To provide safety, each vehicle informs its neighbors about its status by periodically broadcasting data packets. For such a network to provide safety, having an efficient broadcast MAC layer that can provide a low end-to-end delay, regular packet receptions, and fast adaptation to topology changes is essential. We consider CSMA-based broadcast MAC protocols and argue that schemes based on RTS-CTS handshake are not suitable for this type of networks as they suffer from high overhead, long end-to-end delay, and poor adaptation to topology changes. The IEEE 802.11 approach of ignoring RTS-CTS handshake for broadcast packets solves the overhead, delay, and topology adaptation problems. However, it suffers from the hidden terminal problem resulting in low delivery ratio. To address this problem, we propose the Long Range Busy Tone (LRBT) protocol. In this protocol, similar to IEEE 802.11, we ignore the RTS-CTS handshake completely. To provide protection against the hidden terminals, the transmitter sends a packet along with a longer range busy tone to block the hidden terminals. The simulation results confirm that this method offers higher delivery ratio and less inter-packet delay compared to the simple broadcast scheme.
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| 9. |
- Tahmasebi Toyserkani, Arash, 1978, et al.
(författare)
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Improved Model for Transmission and Interference Ranges
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Transmission range (Rtx), carrier sensing range (Rcs), and interference range (Ri) are three important radio ranges in wireless networks. These parameters are defined in [1] and the authors proposed the first analytical model for the interference range based on which new protocols has been proposed [2]–[5]. In this paper, we improve on this model byrelaxing some of the simplifying assumptions. A new formulafor interference range is derived, where noise is not ignored as it was done in [1]. Our formula shows that interference range obtained by ignoring the noise is a good approximation, only for receivers close to the transmitter. While for receivers closer to the transmission range, which suffer from hidden terminal problem, ignoring the noise results in substantially underestimating the interference range.We also study the effect of physical layer parameters on Rtxand Ri, by introducing more general definitions for these ranges. Our study indicates that both Rtx and Ri are influenced by variations in packet size, modulation, and coding. This implies that RTS/CTS packets may have a different Rtx and Ri compared to data packets. Thus, we expect the performance analysis based on the assumption of similar Rtx and Ri for RTS/CTS and data packets, to be inaccurate. Moreover, effects of small-scale fading on Rtx and Ri for the case where fading value is constant during a packet investigated.Our case study indicates that Rayleigh fading has a negative effects on both Rtx and Ri.
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| 10. |
- Tahmasebi Toyserkani, Arash, 1978
(författare)
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On Medium Access for Wireless Ad-hoc and Sensor Networks
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The medium access control (MAC) is a sub-layer of the data link layer, thesecond layer of the open system interconnection (OSI) model. The MAC sub-layeris responsible for organizing the access to the shared channel and it is due tothis important responsibility that the performance of networks is substantiallyinfluenced by the MAC protocol. This thesis is based on three contributions,addressing different issues related to the MAC layer of a variety of wirelessnetworks.The first contribution in this thesis, paper A, deals with the problem ofdesigning a MAC protocol for vehicle-to-vehicle (V2V) communication for trafficsafety purposes. Traffic safety applications often require to broadcastinformation or warning packets to all the vehicles in a close vicinity with aslittle delay as possible. CSMA-based protocols, which is one of the candidatesfor the V2V communication MAC, suffer from lack of an efficient and reliablebroadcast method. To address this problem, a new broadcast scheme called LongRange Busy Tone (LRBT) is proposed. Two important ranges in the MAC layer, namely the transmission andinterference ranges, are the topics of the second contribution of this thesis.Weaknesses of the current model for interference range are discussed and animproved model is obtained by removing some of the simplifying assumptions.Additionally, the effects of physical layer parameters and a fading channel ontransmission and interference ranges are discussed. The last part of this thesis is devoted to scheduling co-existingtime-slotted clusters in a Rayleigh fading channel. In this fading channel, nodistance separation guarantees interference free communication. Therefore, theco-channel interference can be only minimized, if a joint scheduling among allthe clusters is considered. In paper C, this joint scheduling problem, which isknown to be NP-hard, is sub-optimally solved based on Lagrangian relaxation andthe auction algorithm.
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| 11. |
- Tahmasebi Toyserkani, Arash, 1978
(författare)
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The Block Error Rate in Block Interference Channels and its Applications to Medium Access Control
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis may be distinguished into two interdependentparts. The first part outlines the outcome of our efforts toconstruct accurate and yet simple models that account for the probability of successful reception of a packet for a wide range of physical layer parameters. The probability of successful reception of a packet in many applications can be accurately approximated by the probability of successfully receiving the payload, which in turn is a simple function of the block error rate (BLER). The presented studies are limited to block interference fading channels for which there exists few analytical solutions to the BLER. Therefore when needed, various numericalsolutions are employed to obtain an approximation of the BLER. A large part of this thesis is devoted to a detailed study of one of these numerical methods, known as the threshold method. We study the applicability of this method to Nakagami-$m$ block fading channels and to Rayleigh block interference channels. We also investigate the effect of physical layer and channel parameters on the accuracy of this approximation method and the value of thethreshold. As a result, a low complexity method of approximating the BLER in Nakagami-$m$ block fading channels is developed which is shown to be accurate for a wide range of different physical layer parameters and the practical values of $m$.The second part of the thesis is devoted to applications of above models towards the study of various issues at the medium access control (MAC) layer. For instance, we formulate the scheduling problem in TDMA based clustered ad hoc networks as an optimization problem for which the cost function is obtained from the BLER models. The optimum schedule for maximizing the network throughput was obtained using the Lagrangian relaxation method. In addition, a simpler sub-optimum version of this algorithm with adaptablecomplexity is proposed.The developed BLER model is also utilized to obtain both anaccurate solution and a less-complex estimate of the linkthroughput in slotted Aloha networks. The main advantage of these methods is that the detailed state of all nodes in the network is taken into account. Therefore, the obtained results are applicable to arbitrary topologies and traffic models.
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| 12. |
- Tahmasebi Toyserkani, Arash, 1978, et al.
(författare)
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Topology Aware Link Throughput of Slotted Aloha in Rayleigh Block Fading Channels
- 2010
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Ingår i: GLOBECOM - IEEE Global Telecommunications Conference. - 9781424456383
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Konferensbidrag (refereegranskat)abstract
- In this work, we present an accurate analysis ofthe probability of successful transmission in a slotted Alohanetwork with an arbitrary topology, provided that the channelcan be accurately modeled as Rayleigh block fading channels.The obtained expression also takes into account the effect ofdifferent physical layer parameters such as modulation andcoding methods. However, its computational complexity growsquickly as the network size increases. To address this, wealso present an accurate approximation method in which theprobability of success for a link is predicted by considering onlya subset of the interfering nodes. A sufficient condition for theaccuracy of this prediction is also presented. The validity of theproposed methods are verified by a series of simulations.
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