Arash Tahmasebi Toyserkani

An analytical approximation to the block error rate in Nakagami-m non-selective block fading channels

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.

An efficient broadcast MAC scheme for traffic safety applications in automotive networks

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 (ERBT) 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

An improved successive interference cancellation multiuser detector for narrowband signals

This paper examines the possibility of reducing error propagation in the successive interference cancellation multiuser detector (SIC-MUD) for a narrowband system. A simple sequence estimation algorithm is employed, working on a symbol by symbol user basis, not affecting the operation of FEC decoding if present. Operating along the stages of the SIC-MUD scheme, this algorithm has a complexity that increases only linearly with the number of users and thus can be used for a larger number of users, as against the optimum joint detection-MUD (JD-MUD), whose complexity increases exponentially with the number of users. Investigation is carried out for both AWGN and Rayleigh fading channels. The obtained results show that the Improved SIC-MUD scheme reduces the error propagation considerably and, with its low complexity, can be a good alternative for the JD-MUD scheme.

A scheduling algorithm for minimizing the packet error probability in clusterized TDMA networks

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.

A Complexity Adjustable Scheduling Algorithm for Throughput Maximization in Clusterized TDMA Networks

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. Earlier work has demonstrated that a significant increase in network throughput can be achieved if all the schedules are optimized 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 complexity to 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 evaluate two 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.

A Low-Complexity Semi-Analytical Approximation to the Block Error Rate in Nakagami-m Block Fading Channels

There are few analytical formulas that can be used for calculating the block error rate (BLER) in block fading channels. Thus, an estimate of the BLER is often obtained using numerical methods. One such method is the threshold method which assigns 0 or 1 to the instantaneous BLER given the signal to noise ratio (SNR) level. It has been shown that utilizing such a method results in an accurate approximation of the BLER in Nakagami-m block fading channels for a wide range of m. In this work, we consider a recently proposed simple method of obtaining the threshold and study the effect of adopting different physical layer and channel parameters on that threshold. We show that, while the value of this threshold depends on the modulation, coding, and block size, it is almost unaffected by the m parameter of Nakagami-m channels for a wide range of practical values. In addition, for a given modulation and coding method, the threshold is shown to be a simple function of block size. As a result, the computational complexity required to obtain the threshold can be significantly reduced.

Topology Aware Link Throughput of Slotted Aloha in Rayleigh Block Fading Channels

In this work, we present an accurate analysis of the probability of successful transmission in a slotted Aloha network with an arbitrary topology, provided that the channel can be accurately modeled as Rayleigh block fading channels. The obtained expression also takes into account the effect of different physical layer parameters such as modulation and coding methods. However, its computational complexity grows quickly as the network size increases. To address this, we also present an accurate approximation method in which the probability of success for a link is predicted by considering only a subset of the interfering nodes. A sufficient condition for the accuracy of this prediction is also presented. The validity of the proposed methods are verified by a series of simulations.