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Amaar Ahmad

Virginia Tech, Electrical Engineering, Alumnus

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Address: Chicago, Illinois, United States

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Universidad de Guanajuato

Troels Markussen

Western Sydney University

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Papers by Amaar Ahmad

On Metropolis Growth

Research Papers in Economics, 2017

We consider the scaling laws, second-order statistics and entropy of the consumed energy of metro... more We consider the scaling laws, second-order statistics and entropy of the consumed energy of metropolis cities which are hybrid complex systems comprising social networks, engineering systems, agricultural output, economic activity and energy components. We abstract a city in terms of two fundamental variables; s resource cells (of unit area) that represent energy-consuming geographic or spatial zones (e.g. land, housing or infrastructure etc.) and a population comprising n mobile units that can migrate between these cells. We show that with a constant metropolis area (fixed s), the variance and entropy of consumed energy initially increase with n, reach a maximum and then eventually diminish to zero as a saturation threshold is reached. These metrics are indicators of the spatial mobility of the population. Under certain situations, the variance is bounded as a quadratic function of the mean consumed energy of the metropolis. However, when population and metropolis area are endogenous, growth in the latter is arrested when n ≤ s 2 log(s) due to diminished population density. Conversely, the population growth reaches equilibrium when n ≥ s log n or equivalently when the aggregate of both over-populated and under-populated areas is large. Moreover, we also draw the relationship between our approach and multi-scalar information, when economic dependency between a metropolis's sub-regions is based on the entropy of consumed energy. Finally, if the city's economic size (domestic product etc.) is proportional to the consumed energy, then for a constant population density, we show that the economy scales linearly with the surface area (or s).

A Waterfilling Algorithm for Multiple Access Point Connectivity with Constrained Backhaul Network

The 4G/5G paradigm offers User Equipment (UE) simultaneous connectivity to a plurality of wireles... more The 4G/5G paradigm offers User Equipment (UE) simultaneous connectivity to a plurality of wireless Access Points (APs). We consider a UE communicating with its destination through multiple uplinks operating on orthogonal wireless channels with unequal bandwidth. The APs are connected via a tree-like backhaul network with destination at the root and non-ideal link capacities. We develop a power allocation scheme that achieves a near-optimal rate without explicit knowledge of the backhaul network topology at transmitter side. The proposed algorithm waterfills a dynamic subset of uplinks using a low-overhead backhaul load feedback.

Marginal Power Efficiency Considerations in Power Control Adaptations for Multihop Cellular Networks

IEEE Transactions on Vehicular Technology, 2014

We propose a Marginal Power Efficiencybased Adaptation (MPEA) scheme for distributed power contro... more We propose a Marginal Power Efficiencybased Adaptation (MPEA) scheme for distributed power control in wireless communication systems. Nodes autonomously adapt their transmit power keeping a differential measure of power efficiency, defined as the additional capacity obtained per unit of transmit power, at a desirable threshold. We combine the MPEA with the Foschini-Miljanic (FM) algorithm [1] into a power control algorithm for a multihop cellular network where nodes can dynamically adapt to both local and global conditions. We derive a fixed point to which the power allocations converge under the scheme and illustrate a significant improvement in the system throughput.

1 Asynchronous Systems and Binary Diagonal Random Matrices: A Proof and Convergence Rate

In a synchronized network of n nodes, each node will update its parameter based on the system sta... more In a synchronized network of n nodes, each node will update its parameter based on the system state in a given iteration. It is well-known that the updates can converge to a fixed point if the maximum absolute eigenvalue (spectral radius) of the n × n iterative matrix F is less than one (i.e. ρ(F) < 1). However, if only a subset of the nodes update their parameter in an iteration (due to delays or stale feedback) then this effectively renders the spectral radius of the iterative matrix as one. We consider matrices of unit spectral radii generated from F due to random delays in the updates. We show that if each node updates at least once in every T iterations, then the product of the random matrices (joint spectral radius) corresponding to these iterations is less than one. We then use this property to prove convergence of asynchronous iterative systems. Finally, we show that the convergence rate of such a system is ρ(F) (1−(1−γ) T) n T , where assuming ergodicity, γ is the lowest bound on the probability that a node will update in any given iteration.

D ec 2 01 7 On Metropolis Growth

We consider the scaling laws, second-order statistics and entropy of the consumed energy of metro... more We consider the scaling laws, second-order statistics and entropy of the consumed energy of metropolis cities which are hybrid complex systems comprising social networks, engineering systems, agricultural output, economic activity and energy components. We abstract a city in terms of two fundamental variables; s resource cells (of unit area) that represent energy-consuming geographic or spatial zones (e.g. land, housing or infrastructure etc.) and a population comprising n mobile units that can migrate between these cells. We show that with a constant metropolis area (fixed s), the variance and entropy of consumed energy initially increase with n, reach a maximum and then eventually diminish to zero as a saturation threshold is reached. These metrics are indicators of the spatial mobility of the population. Under certain situations, the variance is bounded as a quadratic function of the mean consumed energy of the metropolis. However, when population and metropolis area are endogeno...

On Metropolis Growth

arXiv: Physics and Society, 2017

We consider the scaling laws, second-order statistics and entropy of the consumed energy of metro... more We consider the scaling laws, second-order statistics and entropy of the consumed energy of metropolis cities which are hybrid complex systems comprising social networks, engineering systems, agricultural output, economic activity and energy components. We abstract a city in terms of two fundamental variables; $s$ resource cells (of unit area) that represent energy-consuming geographic or spatial zones (e.g. land, housing or infrastructure etc.) and a population comprising $n$ mobile units that can migrate between these cells. We show that with a constant metropolis area (fixed $s$), the variance and entropy of consumed energy initially increase with $n$, reach a maximum and then eventually diminish to zero as saturation is reached. These metrics are indicators of the spatial mobility of the population. Under certain situations, the variance is bounded as a quadratic function of the mean consumed energy of the metropolis. However, when population and metropolis area are endogenous, ...

Repeatability of Vehicular Measurements on Public Roadways

Proceedings of the 11th Workshop on Wireless Network Testbeds, Experimental evaluation & CHaracterization, 2017

Connected vehicle applications promise to transform traffic management and safety. Evaluating the... more Connected vehicle applications promise to transform traffic management and safety. Evaluating the performance of vehicular communication systems in real-world settings benefits from detailed propagation models. Developing such models can be challenging due to the dynamic nature of the vehicular environment. This paper presents an experimental methodology to control and monitor key experimental factors and to efficiently conduct real-world measurements. We tested the Dedicated Short Range Communication (DSRC) technology at 5.9 GHz in a week-long experiment involving 10 vehicles on a major highway under one of the most dense traffic conditions in the United States. We study the repeatability of such measurements for different experiment durations, which may help place earlier propagation studies into context. The experiments show that, with orchestrated vehicle movement in a 2 km section of highway, the pathloss exponent estimation is repeatable within a tolerance of +/-0.1 in 11 minu...

Identifying DSRC Channel Loss Factors of Urban Intersections Using RSS Datasets

Channel modeling is critical for evaluating various protocols designed for different network laye... more Channel modeling is critical for evaluating various protocols designed for different network layers, as credibility of the corresponding evaluation largely depends on the accuracy of the propagation models. Dynamic vehicular network topology and propagation environment define the communication channel behavior. In this paper, we study the received signal strength (RSS) based channel characterization dataset collected from an urban intersection scenario for Dedicated Short Range Communication (DSRC) in the 5.9 GHz band. We conducted a large-scale RSS measurement campaign in one of the densest traffic environments in the US. The channel characterization data was collected using ten DSRC-enabled vehicles in an Orange County, CA intersection environment. Using the dataset, we study and identify the key aspects of the network topology and physical environment that collectively describe the channel behavior and determine realistic wireless propagation channel models for urban intersection...

V2V System Congestion Control Validation and Performance

IEEE Transactions on Vehicular Technology

Major international automakers have considered the deployment of the 5.9 GHz Dedicated Short-Rang... more Major international automakers have considered the deployment of the 5.9 GHz Dedicated Short-Range Communications (DSRC) on their vehicle fleets for wireless connectivity. DSRC-enabled Vehicle-to-Vehicle (V2V) communication through broadcast of Basic Safety Messages (BSMs) enables safety applications for crash warning and avoidance. However, in dense traffic conditions as the V2V deployment scales up, the resultant channel load increases and leads to channel congestion and may adversely affect the performance of the safety applications. The Society of Automotive Engineers (SAE) J2945/1 standard that builds atop Institute of Electrical and Electronics Engineers (IEEE) 802.11p and IEEE 1609 standards provides the minimum performance requirements (MPR) for V2V safety communications. Specifically, it provides a Congestion Control (CC) protocol for transmission rate and power adaptations to achieve robust performance in dense vehicular networks. The primary contribution of this paper is that using a congestion generation testbed that emulates channel congestion including a large number of Remote Vehicles (RVs), we can validate and test any V2V equipped vehicle for compliance with the J2945/1 standard. Our paper also demonstrates that under heavy congestion, even with 600 ms of inter-transmit time (ITT), a moving vehicle can be tracked to lane-level accuracy.

Asynchronous Systems and Binary Diagonal Random Matrices: A Proof and Convergence Rate

In a synchronized network of $n$ nodes, each node will update its parameter based on the system s... more In a synchronized network of $n$ nodes, each node will update its parameter based on the system state in a given iteration. It is well-known that the updates can converge to a fixed point if the maximum absolute eigenvalue (spectral radius) of the $n \times n$ iterative matrix ${\bf{F}}$ is less than one (i.e. $\rho({\bf{F}})<1$). However, if only a subset of the nodes update their parameter in an iteration (due to delays or stale feedback) then this effectively renders the spectral radius of the iterative matrix as one. We consider matrices of unit spectral radii generated from ${\bf{F}}$ due to random delays in the updates. We show that if each node updates at least once in every $T$ iterations, then the product of the random matrices (joint spectral radius) corresponding to these iterations is less than one. We then use this property to prove convergence of asynchronous iterative systems. Finally, we show that the convergence rate of such a system is $\rho({\bf{F}})\frac{(1-(1-\gamma)^T)^n}{T}$, where assuming ergodicity, $\gamma$ is the lowest bound on the probability that a node will update in any given iteration.

A robust hybrid-ARQ protocol for relay networks

This thesis explores wireless relay networks using the hybrid-ARQ protocol. Relay networks exploi... more This thesis explores wireless relay networks using the hybrid-ARQ protocol. Relay networks exploit spatial diversity from 'redundant' nodes in contrast to the single path of classic networks. Thus they show superior performance in dealing with fading and interference. The hybrid-ARQ technique under the constraints of noncoherent orthogonal modulation and hard-decision decoding is the primary focus of the thesis. Information theoretic bounds on the performance for such a system are derived. The extension of hybrid-ARQ from a point-to-point protocol to a broadcast-oriented relaying protocol called HARBINGER (hybrid-ARQ based intra-cluster geographic relaying) was presented in a 2005 paper by Zhao and Valenti. While prior work on this protocol had assumed Gaussian or modulation-constrained inputs, a practical coding technique based on Reed-Solomon codes is now analyzed. The suitability of the proposed protocol to the IEEE 802.15.4/Zigbee based networks using commodity off-the-shelf hardware is shown. Lastly, in order to study the fundamental problem of multiuser interference, the thesis also considers a two-source relay network. The performance of interference avoidance mechanisms such as time-hopping and orthogonal transmissions is explored. iii Acknowledgments I would first like to thank all the professors on my committee. In particular, Dr. Valenti's contribution in assisting me in writing my thesis has been immense. He has arranged the research funding and has helped me find the direction and focus for my work. Furthermore,

Relay feedback based power control for multihop wireless networks

A robust hybrid-ARQ protocol for relay networks [electronic resource] /

System requirements: World Wide Web browser and PDF reader. Mode of access: Available through the... more System requirements: World Wide Web browser and PDF reader. Mode of access: Available through the Internet. Title from document title page. Document formatted into pages; contains vii, 49 p. : ill. (some col.). Thesis (M.S.)--West Virginia University, 2007. Includes abstract. Includes bibliographical references (p. 47-49).

A Waterfilling Algorithm for Multiple Access Point Connectivity with Constrained Backhaul Network

IEEE Wireless Communications Letters, 2015

The 4G/5G paradigm offers User Equipment (UE) simultaneous connectivity to a plurality of wireles... more The 4G/5G paradigm offers User Equipment (UE) simultaneous connectivity to a plurality of wireless Access Points (APs). We consider a UE communicating with its destination through multiple uplinks operating on orthogonal wireless channels with unequal bandwidth. The APs are connected via a tree-like backhaul network with destination at the root and non-ideal link capacities. We develop a power allocation scheme that achieves a nearoptimal rate without explicit knowledge of the backhaul network topology at transmitter side. The proposed algorithm waterfills a dynamic subset of uplinks using a lowoverhead backhaul load feedback.

A Robust Hybrid-ARQ Protocol for Relay Networks

This thesis explores wireless relay networks using the hybrid-ARQ protocol. Relay networks exploi... more This thesis explores wireless relay networks using the hybrid-ARQ protocol. Relay networks exploit spatial diversity from 'redundant' nodes in contrast to the single path of classic networks. Thus they show superior performance in dealing with fading and interference. The hybrid-ARQ technique under the constraints of noncoherent orthogonal modulation and hard-decision decoding is the primary focus of the thesis. Information theoretic bounds on the performance for such a system are derived. The extension of hybrid-ARQ from a point-to-point protocol to a broadcast-oriented relaying protocol called HARBINGER (hybrid-ARQ based intra-cluster geographic relaying) was presented in a 2005 paper by Zhao and Valenti. While prior work on this protocol had assumed Gaussian or modulation-constrained inputs, a practical coding technique based on Reed-Solomon codes is now analyzed. The suitability of the proposed protocol to the IEEE 802.15.4/Zigbee based networks using commodity off-the-shelf hardware is shown. Lastly, in order to study the fundamental problem of multiuser interference, the thesis also considers a two-source relay network. The performance of interference avoidance mechanisms such as time-hopping and orthogonal transmissions is explored. iii Acknowledgments I would first like to thank all the professors on my committee. In particular, Dr. Valenti's contribution in assisting me in writing my thesis has been immense. He has arranged the research funding and has helped me find the direction and focus for my work. Furthermore,

Distributed Power Allocations in Heterogeneous Networks with Dual Connectivity using Backhaul State Information

LTE release 12 proposes the use of dual connectivity in heterogeneous cellular networks, where a ... more LTE release 12 proposes the use of dual connectivity in heterogeneous cellular networks, where a user equipment (UE) maintains parallel connections to a macrocell base station and to a low-tier node such as a picocell base station or relay. In this paper, we propose a distributed multi-objective power control scheme where each UE independently adapts its transmit power on its dual connections, where the connections could possess unequal bandwidths and non-ideal backhaul links. In the proposed scheme, the UEs can dynamically switch their objectives between data rate maximization and transmit power minimization as the backhaul load varies. To address the coupling between interference and the backhaul load, we propose a low-overhead convergence mechanism which does not require explicit coordination between UEs and also derive a closed-form expression of the transmit power levels at equilibrium. Simulation results show that our scheme performs with higher aggregate end-to-end data rate and significant power saving in comparison to a scheme that employs a greedy algorithm and a scheme that employs only waterfilling.

Asynchronous systems and binary diagonal random matrices: A proof and convergence rate

In a synchronized network of n nodes, each node will update its parameter based on the system sta... more In a synchronized network of n nodes, each node will update its parameter based on the system state in a given iteration. It is well-known that the updates can converge to a fixed point if the maximum absolute eigenvalue (spectral radius) of the n × n iterative matrix F is less than one (i.e. ρ(F) < 1). However, if only a subset of the nodes update their parameter in an iteration (due to delays or stale feedback) then this effectively renders the spectral radius of the iterative matrix as one. We consider matrices of unit spectral radii generated from F due to random delays in the updates. We show that if each node updates at least once in every T iterations, then the product of the random matrices (joint spectral radius) corresponding to these iterations is less than one. We then use this property to prove convergence of asynchronous iterative systems. Finally, we show that the convergence rate of such a system is ρ(F) (1−(1−γ) T) n T , where assuming ergodicity, γ is the lowest bound on the probability that a node will update in any given iteration.

A link adaptive scheme for multihop cellular systems using congestion feedback

2013 IEEE Global Communications Conference (GLOBECOM), 2013

ABSTRACT LTE-Advanced standards contemplate support for heterogeneous networks, through the use o... more ABSTRACT LTE-Advanced standards contemplate support for heterogeneous networks, through the use of relays, as well as the ability to perform carrier aggregation in order to achieve higher data rates. In this paper, we model the User Equipment&#39;s (UE) ability to select its current point-of-access to the network (either a relay or the base station), aggregate additional channels, and perform power adaptations. The adaptations by UEs affect one another, by impacting the interference conditions in the network as well as congestion conditions in the relay-to-base station links. We propose an adaptation mechanism whereby the UEs consider these factors and select their transmit power, channels, and point of access to the network to optimize a combination of achieved data rate and energy consumption. Our results show these adaptations to be more efficient than adaptations that simply consider current channel quality indicators, combined with greedy channel aggregation.

A Practical Hybrid-ARQ Protocol Using Noncoherent Orthogonal Modulation

This paper considers hybrid-ARQ under the constraints of noncoherent orthogonal modulation and ha... more This paper considers hybrid-ARQ under the constraints of noncoherent orthogonal modulation and hard-decision decoding. Information theoretic bounds on the throughput for such systems are derived. A practical coding technique based on Reed-Solomon codes is proposed and analyzed. The proposed hybrid-ARQ protocol is modified to allow relay nodes to service retransmission requests. The proposed protocol is suitable for IEEE 802.15.4/Zigbee networks using commodity off-the-shelf hardware.

Relay feedback-based power control in multihop wireless networks

In this paper, we propose a distributed power control scheme which can take into account the endt... more In this paper, we propose a distributed power control scheme which can take into account the endto-end performance of users in a multihop cellular network. Bottleneck links in a multihop wireless network limit the maximum rate achieved by users along their routes. Under the proposed scheme a link dynamically switches between different power adaptation algorithms based on whether it is a bottleneck or a non-bottleneck link. Specifically, non-bottleneck links iteratively reduce their transmit powers whereas the bottleneck links use power control to exploit the corresponding interference reduction and further increase their signal-to-noise-and-interference ratios (SINRs). We show substantial system throughput performance gain under our scheme and for which, under certain scenarios, we derive a closed-form expression of the converged transmit power levels regardless of their initial values.

On Metropolis Growth

Research Papers in Economics, 2017

We consider the scaling laws, second-order statistics and entropy of the consumed energy of metro... more We consider the scaling laws, second-order statistics and entropy of the consumed energy of metropolis cities which are hybrid complex systems comprising social networks, engineering systems, agricultural output, economic activity and energy components. We abstract a city in terms of two fundamental variables; s resource cells (of unit area) that represent energy-consuming geographic or spatial zones (e.g. land, housing or infrastructure etc.) and a population comprising n mobile units that can migrate between these cells. We show that with a constant metropolis area (fixed s), the variance and entropy of consumed energy initially increase with n, reach a maximum and then eventually diminish to zero as a saturation threshold is reached. These metrics are indicators of the spatial mobility of the population. Under certain situations, the variance is bounded as a quadratic function of the mean consumed energy of the metropolis. However, when population and metropolis area are endogenous, growth in the latter is arrested when n ≤ s 2 log(s) due to diminished population density. Conversely, the population growth reaches equilibrium when n ≥ s log n or equivalently when the aggregate of both over-populated and under-populated areas is large. Moreover, we also draw the relationship between our approach and multi-scalar information, when economic dependency between a metropolis's sub-regions is based on the entropy of consumed energy. Finally, if the city's economic size (domestic product etc.) is proportional to the consumed energy, then for a constant population density, we show that the economy scales linearly with the surface area (or s).

A Waterfilling Algorithm for Multiple Access Point Connectivity with Constrained Backhaul Network

The 4G/5G paradigm offers User Equipment (UE) simultaneous connectivity to a plurality of wireles... more The 4G/5G paradigm offers User Equipment (UE) simultaneous connectivity to a plurality of wireless Access Points (APs). We consider a UE communicating with its destination through multiple uplinks operating on orthogonal wireless channels with unequal bandwidth. The APs are connected via a tree-like backhaul network with destination at the root and non-ideal link capacities. We develop a power allocation scheme that achieves a near-optimal rate without explicit knowledge of the backhaul network topology at transmitter side. The proposed algorithm waterfills a dynamic subset of uplinks using a low-overhead backhaul load feedback.

Marginal Power Efficiency Considerations in Power Control Adaptations for Multihop Cellular Networks

IEEE Transactions on Vehicular Technology, 2014

We propose a Marginal Power Efficiencybased Adaptation (MPEA) scheme for distributed power contro... more We propose a Marginal Power Efficiencybased Adaptation (MPEA) scheme for distributed power control in wireless communication systems. Nodes autonomously adapt their transmit power keeping a differential measure of power efficiency, defined as the additional capacity obtained per unit of transmit power, at a desirable threshold. We combine the MPEA with the Foschini-Miljanic (FM) algorithm [1] into a power control algorithm for a multihop cellular network where nodes can dynamically adapt to both local and global conditions. We derive a fixed point to which the power allocations converge under the scheme and illustrate a significant improvement in the system throughput.

1 Asynchronous Systems and Binary Diagonal Random Matrices: A Proof and Convergence Rate

In a synchronized network of n nodes, each node will update its parameter based on the system sta... more In a synchronized network of n nodes, each node will update its parameter based on the system state in a given iteration. It is well-known that the updates can converge to a fixed point if the maximum absolute eigenvalue (spectral radius) of the n × n iterative matrix F is less than one (i.e. ρ(F) < 1). However, if only a subset of the nodes update their parameter in an iteration (due to delays or stale feedback) then this effectively renders the spectral radius of the iterative matrix as one. We consider matrices of unit spectral radii generated from F due to random delays in the updates. We show that if each node updates at least once in every T iterations, then the product of the random matrices (joint spectral radius) corresponding to these iterations is less than one. We then use this property to prove convergence of asynchronous iterative systems. Finally, we show that the convergence rate of such a system is ρ(F) (1−(1−γ) T) n T , where assuming ergodicity, γ is the lowest bound on the probability that a node will update in any given iteration.

D ec 2 01 7 On Metropolis Growth

We consider the scaling laws, second-order statistics and entropy of the consumed energy of metro... more We consider the scaling laws, second-order statistics and entropy of the consumed energy of metropolis cities which are hybrid complex systems comprising social networks, engineering systems, agricultural output, economic activity and energy components. We abstract a city in terms of two fundamental variables; s resource cells (of unit area) that represent energy-consuming geographic or spatial zones (e.g. land, housing or infrastructure etc.) and a population comprising n mobile units that can migrate between these cells. We show that with a constant metropolis area (fixed s), the variance and entropy of consumed energy initially increase with n, reach a maximum and then eventually diminish to zero as a saturation threshold is reached. These metrics are indicators of the spatial mobility of the population. Under certain situations, the variance is bounded as a quadratic function of the mean consumed energy of the metropolis. However, when population and metropolis area are endogeno...

On Metropolis Growth

arXiv: Physics and Society, 2017

We consider the scaling laws, second-order statistics and entropy of the consumed energy of metro... more We consider the scaling laws, second-order statistics and entropy of the consumed energy of metropolis cities which are hybrid complex systems comprising social networks, engineering systems, agricultural output, economic activity and energy components. We abstract a city in terms of two fundamental variables; $s$ resource cells (of unit area) that represent energy-consuming geographic or spatial zones (e.g. land, housing or infrastructure etc.) and a population comprising $n$ mobile units that can migrate between these cells. We show that with a constant metropolis area (fixed $s$), the variance and entropy of consumed energy initially increase with $n$, reach a maximum and then eventually diminish to zero as saturation is reached. These metrics are indicators of the spatial mobility of the population. Under certain situations, the variance is bounded as a quadratic function of the mean consumed energy of the metropolis. However, when population and metropolis area are endogenous, ...

Repeatability of Vehicular Measurements on Public Roadways

Proceedings of the 11th Workshop on Wireless Network Testbeds, Experimental evaluation & CHaracterization, 2017

Connected vehicle applications promise to transform traffic management and safety. Evaluating the... more Connected vehicle applications promise to transform traffic management and safety. Evaluating the performance of vehicular communication systems in real-world settings benefits from detailed propagation models. Developing such models can be challenging due to the dynamic nature of the vehicular environment. This paper presents an experimental methodology to control and monitor key experimental factors and to efficiently conduct real-world measurements. We tested the Dedicated Short Range Communication (DSRC) technology at 5.9 GHz in a week-long experiment involving 10 vehicles on a major highway under one of the most dense traffic conditions in the United States. We study the repeatability of such measurements for different experiment durations, which may help place earlier propagation studies into context. The experiments show that, with orchestrated vehicle movement in a 2 km section of highway, the pathloss exponent estimation is repeatable within a tolerance of +/-0.1 in 11 minu...

Identifying DSRC Channel Loss Factors of Urban Intersections Using RSS Datasets

Channel modeling is critical for evaluating various protocols designed for different network laye... more Channel modeling is critical for evaluating various protocols designed for different network layers, as credibility of the corresponding evaluation largely depends on the accuracy of the propagation models. Dynamic vehicular network topology and propagation environment define the communication channel behavior. In this paper, we study the received signal strength (RSS) based channel characterization dataset collected from an urban intersection scenario for Dedicated Short Range Communication (DSRC) in the 5.9 GHz band. We conducted a large-scale RSS measurement campaign in one of the densest traffic environments in the US. The channel characterization data was collected using ten DSRC-enabled vehicles in an Orange County, CA intersection environment. Using the dataset, we study and identify the key aspects of the network topology and physical environment that collectively describe the channel behavior and determine realistic wireless propagation channel models for urban intersection...

V2V System Congestion Control Validation and Performance

IEEE Transactions on Vehicular Technology

Major international automakers have considered the deployment of the 5.9 GHz Dedicated Short-Rang... more Major international automakers have considered the deployment of the 5.9 GHz Dedicated Short-Range Communications (DSRC) on their vehicle fleets for wireless connectivity. DSRC-enabled Vehicle-to-Vehicle (V2V) communication through broadcast of Basic Safety Messages (BSMs) enables safety applications for crash warning and avoidance. However, in dense traffic conditions as the V2V deployment scales up, the resultant channel load increases and leads to channel congestion and may adversely affect the performance of the safety applications. The Society of Automotive Engineers (SAE) J2945/1 standard that builds atop Institute of Electrical and Electronics Engineers (IEEE) 802.11p and IEEE 1609 standards provides the minimum performance requirements (MPR) for V2V safety communications. Specifically, it provides a Congestion Control (CC) protocol for transmission rate and power adaptations to achieve robust performance in dense vehicular networks. The primary contribution of this paper is that using a congestion generation testbed that emulates channel congestion including a large number of Remote Vehicles (RVs), we can validate and test any V2V equipped vehicle for compliance with the J2945/1 standard. Our paper also demonstrates that under heavy congestion, even with 600 ms of inter-transmit time (ITT), a moving vehicle can be tracked to lane-level accuracy.

Asynchronous Systems and Binary Diagonal Random Matrices: A Proof and Convergence Rate

In a synchronized network of $n$ nodes, each node will update its parameter based on the system s... more In a synchronized network of $n$ nodes, each node will update its parameter based on the system state in a given iteration. It is well-known that the updates can converge to a fixed point if the maximum absolute eigenvalue (spectral radius) of the $n \times n$ iterative matrix ${\bf{F}}$ is less than one (i.e. $\rho({\bf{F}})<1$). However, if only a subset of the nodes update their parameter in an iteration (due to delays or stale feedback) then this effectively renders the spectral radius of the iterative matrix as one. We consider matrices of unit spectral radii generated from ${\bf{F}}$ due to random delays in the updates. We show that if each node updates at least once in every $T$ iterations, then the product of the random matrices (joint spectral radius) corresponding to these iterations is less than one. We then use this property to prove convergence of asynchronous iterative systems. Finally, we show that the convergence rate of such a system is $\rho({\bf{F}})\frac{(1-(1-\gamma)^T)^n}{T}$, where assuming ergodicity, $\gamma$ is the lowest bound on the probability that a node will update in any given iteration.

A robust hybrid-ARQ protocol for relay networks

This thesis explores wireless relay networks using the hybrid-ARQ protocol. Relay networks exploi... more This thesis explores wireless relay networks using the hybrid-ARQ protocol. Relay networks exploit spatial diversity from 'redundant' nodes in contrast to the single path of classic networks. Thus they show superior performance in dealing with fading and interference. The hybrid-ARQ technique under the constraints of noncoherent orthogonal modulation and hard-decision decoding is the primary focus of the thesis. Information theoretic bounds on the performance for such a system are derived. The extension of hybrid-ARQ from a point-to-point protocol to a broadcast-oriented relaying protocol called HARBINGER (hybrid-ARQ based intra-cluster geographic relaying) was presented in a 2005 paper by Zhao and Valenti. While prior work on this protocol had assumed Gaussian or modulation-constrained inputs, a practical coding technique based on Reed-Solomon codes is now analyzed. The suitability of the proposed protocol to the IEEE 802.15.4/Zigbee based networks using commodity off-the-shelf hardware is shown. Lastly, in order to study the fundamental problem of multiuser interference, the thesis also considers a two-source relay network. The performance of interference avoidance mechanisms such as time-hopping and orthogonal transmissions is explored. iii Acknowledgments I would first like to thank all the professors on my committee. In particular, Dr. Valenti's contribution in assisting me in writing my thesis has been immense. He has arranged the research funding and has helped me find the direction and focus for my work. Furthermore,

Relay feedback based power control for multihop wireless networks

A robust hybrid-ARQ protocol for relay networks [electronic resource] /

System requirements: World Wide Web browser and PDF reader. Mode of access: Available through the... more System requirements: World Wide Web browser and PDF reader. Mode of access: Available through the Internet. Title from document title page. Document formatted into pages; contains vii, 49 p. : ill. (some col.). Thesis (M.S.)--West Virginia University, 2007. Includes abstract. Includes bibliographical references (p. 47-49).

A Waterfilling Algorithm for Multiple Access Point Connectivity with Constrained Backhaul Network

IEEE Wireless Communications Letters, 2015

The 4G/5G paradigm offers User Equipment (UE) simultaneous connectivity to a plurality of wireles... more The 4G/5G paradigm offers User Equipment (UE) simultaneous connectivity to a plurality of wireless Access Points (APs). We consider a UE communicating with its destination through multiple uplinks operating on orthogonal wireless channels with unequal bandwidth. The APs are connected via a tree-like backhaul network with destination at the root and non-ideal link capacities. We develop a power allocation scheme that achieves a nearoptimal rate without explicit knowledge of the backhaul network topology at transmitter side. The proposed algorithm waterfills a dynamic subset of uplinks using a lowoverhead backhaul load feedback.

A Robust Hybrid-ARQ Protocol for Relay Networks

This thesis explores wireless relay networks using the hybrid-ARQ protocol. Relay networks exploi... more This thesis explores wireless relay networks using the hybrid-ARQ protocol. Relay networks exploit spatial diversity from 'redundant' nodes in contrast to the single path of classic networks. Thus they show superior performance in dealing with fading and interference. The hybrid-ARQ technique under the constraints of noncoherent orthogonal modulation and hard-decision decoding is the primary focus of the thesis. Information theoretic bounds on the performance for such a system are derived. The extension of hybrid-ARQ from a point-to-point protocol to a broadcast-oriented relaying protocol called HARBINGER (hybrid-ARQ based intra-cluster geographic relaying) was presented in a 2005 paper by Zhao and Valenti. While prior work on this protocol had assumed Gaussian or modulation-constrained inputs, a practical coding technique based on Reed-Solomon codes is now analyzed. The suitability of the proposed protocol to the IEEE 802.15.4/Zigbee based networks using commodity off-the-shelf hardware is shown. Lastly, in order to study the fundamental problem of multiuser interference, the thesis also considers a two-source relay network. The performance of interference avoidance mechanisms such as time-hopping and orthogonal transmissions is explored. iii Acknowledgments I would first like to thank all the professors on my committee. In particular, Dr. Valenti's contribution in assisting me in writing my thesis has been immense. He has arranged the research funding and has helped me find the direction and focus for my work. Furthermore,

Distributed Power Allocations in Heterogeneous Networks with Dual Connectivity using Backhaul State Information

LTE release 12 proposes the use of dual connectivity in heterogeneous cellular networks, where a ... more LTE release 12 proposes the use of dual connectivity in heterogeneous cellular networks, where a user equipment (UE) maintains parallel connections to a macrocell base station and to a low-tier node such as a picocell base station or relay. In this paper, we propose a distributed multi-objective power control scheme where each UE independently adapts its transmit power on its dual connections, where the connections could possess unequal bandwidths and non-ideal backhaul links. In the proposed scheme, the UEs can dynamically switch their objectives between data rate maximization and transmit power minimization as the backhaul load varies. To address the coupling between interference and the backhaul load, we propose a low-overhead convergence mechanism which does not require explicit coordination between UEs and also derive a closed-form expression of the transmit power levels at equilibrium. Simulation results show that our scheme performs with higher aggregate end-to-end data rate and significant power saving in comparison to a scheme that employs a greedy algorithm and a scheme that employs only waterfilling.

Asynchronous systems and binary diagonal random matrices: A proof and convergence rate

In a synchronized network of n nodes, each node will update its parameter based on the system sta... more In a synchronized network of n nodes, each node will update its parameter based on the system state in a given iteration. It is well-known that the updates can converge to a fixed point if the maximum absolute eigenvalue (spectral radius) of the n × n iterative matrix F is less than one (i.e. ρ(F) < 1). However, if only a subset of the nodes update their parameter in an iteration (due to delays or stale feedback) then this effectively renders the spectral radius of the iterative matrix as one. We consider matrices of unit spectral radii generated from F due to random delays in the updates. We show that if each node updates at least once in every T iterations, then the product of the random matrices (joint spectral radius) corresponding to these iterations is less than one. We then use this property to prove convergence of asynchronous iterative systems. Finally, we show that the convergence rate of such a system is ρ(F) (1−(1−γ) T) n T , where assuming ergodicity, γ is the lowest bound on the probability that a node will update in any given iteration.

A link adaptive scheme for multihop cellular systems using congestion feedback

2013 IEEE Global Communications Conference (GLOBECOM), 2013

ABSTRACT LTE-Advanced standards contemplate support for heterogeneous networks, through the use o... more ABSTRACT LTE-Advanced standards contemplate support for heterogeneous networks, through the use of relays, as well as the ability to perform carrier aggregation in order to achieve higher data rates. In this paper, we model the User Equipment&#39;s (UE) ability to select its current point-of-access to the network (either a relay or the base station), aggregate additional channels, and perform power adaptations. The adaptations by UEs affect one another, by impacting the interference conditions in the network as well as congestion conditions in the relay-to-base station links. We propose an adaptation mechanism whereby the UEs consider these factors and select their transmit power, channels, and point of access to the network to optimize a combination of achieved data rate and energy consumption. Our results show these adaptations to be more efficient than adaptations that simply consider current channel quality indicators, combined with greedy channel aggregation.

A Practical Hybrid-ARQ Protocol Using Noncoherent Orthogonal Modulation

This paper considers hybrid-ARQ under the constraints of noncoherent orthogonal modulation and ha... more This paper considers hybrid-ARQ under the constraints of noncoherent orthogonal modulation and hard-decision decoding. Information theoretic bounds on the throughput for such systems are derived. A practical coding technique based on Reed-Solomon codes is proposed and analyzed. The proposed hybrid-ARQ protocol is modified to allow relay nodes to service retransmission requests. The proposed protocol is suitable for IEEE 802.15.4/Zigbee networks using commodity off-the-shelf hardware.

Relay feedback-based power control in multihop wireless networks

In this paper, we propose a distributed power control scheme which can take into account the endt... more In this paper, we propose a distributed power control scheme which can take into account the endto-end performance of users in a multihop cellular network. Bottleneck links in a multihop wireless network limit the maximum rate achieved by users along their routes. Under the proposed scheme a link dynamically switches between different power adaptation algorithms based on whether it is a bottleneck or a non-bottleneck link. Specifically, non-bottleneck links iteratively reduce their transmit powers whereas the bottleneck links use power control to exploit the corresponding interference reduction and further increase their signal-to-noise-and-interference ratios (SINRs). We show substantial system throughput performance gain under our scheme and for which, under certain scenarios, we derive a closed-form expression of the converged transmit power levels regardless of their initial values.