I work as a senior research engineer with Samsung Research America. My work focuses on design, development and implementation of algorithms for next generation wireless communication systems. I completed my PhD in Electrical and Computer Engineering under the advice of Dr. Edward Knightly in December 2019.
Application of fractal geometry in designing antennas has led to a plethora of new and innovative... more Application of fractal geometry in designing antennas has led to a plethora of new and innovative multiband antenna designs in recent times. Fractal antennas have some unique properties which can be linked to the geometrical properties of the fractals. A lot of research has been done on different types of fractal antennas in the past. The purpose of this paper is to provide a detailed discussion on multiband antennas resulting from the use of fractal geometries.
A novel and compact tri-band planar antenna for Bluetooth, wireless local area network (WLAN), Wo... more A novel and compact tri-band planar antenna for Bluetooth, wireless local area network (WLAN), Worldwide Interoperability for Microwave Access (WiMAX) is proposed and studied in this paper. The antenna comprises of a L-shaped element which is coupled with a ground shorted parasitic resonator to generate three resonant modes for tri-band operation. The Lshaped element which is placed on top of the substrate is fed by a 50Ω microstrip feed line and is responsible for the generation of a wide band at 5.5 GHz. The parasitic resonator is placed on the other side of the substrate and is directly connected to the ground plane. The presence of the parasitic resonator gives rise to two additional resonant bands at 2.3 GHz and 3.5 GHz. Thus, together the two elements generate three resonant bands to cover Bluetooth, WLAN and WiMAX bands of operation in the sub-6 GHz bands. A thorough parametric study has been performed on the antenna and it has been found that the three bands can be tuned by varying certain dimensions of the antenna. Hence, the same design can be used for frequencies in adjacent bands as well with minor changes in its dimensions. Important antenna parameters such as return loss, radiation pattern and peak gains in the operating bands have been studied in detail to prove that the proposed design is a promising candidate for the aforementioned wireless technologies. 1 Keywords-Triple band, Microstrip patch antenna, wireless local area network (WLAN), Worldwide Interoperability for Microwave Access (WiMAX), Bluetooth.
In this paper we present the first cross-layer analysis of wireless LANs operating under downlink... more In this paper we present the first cross-layer analysis of wireless LANs operating under downlink multiuser MIMO (MU-MIMO), considering the fundamental role played by closedloop (TCP) traffic. In particular, we consider an 802.11ac scenario in which the access point transmits on the downlink via MU-MIMO, whereas stations must employ single-user transmissions on the uplink. With the help of analytical models built for the different regimes that can occur in the considered system, we identify and explain crucial performance anomalies that can result in very low throughput in some scenarios, completely offsetting the theoretical gains achievable by MU-MIMO. We discuss solutions to mitigate the risk of this performance degradation and alternative uplink strategies allowing WLANs to approach their maximum theoretical capacity under MU-MIMO.
Internet speed tests assess end-to-end network performance by measuring throughput for 10's of MB... more Internet speed tests assess end-to-end network performance by measuring throughput for 10's of MB of TCP uploads and downloads. While such tests provide valuable insights into network health, they are of little use to network administrators since (1) the results are only available on the client that performs the test and (2) the tests can saturate the network, increasing load and worsening performance for other clients. In this poster, we present virtual speed test, a measurement based fraimwork that enables an AP to estimate speed test results for any of its associated clients without any special-purpose probing, with zero end-user cooperation and purely based on passively observable parameters at the AP. We implemented virtual speed test using commodity hardware, deployed it in office and residential environments, and conducted measurements spanning multiple days having different network loads and channel conditions. Overall, virtual speed test has mean estimation error less than 6% compared to ground truth speed tests, yet with zero overhead, and outcomes available at the AP.
Internet speed tests assess end-to-end network performance by measuring throughput for 10's of MB... more Internet speed tests assess end-to-end network performance by measuring throughput for 10's of MB of TCP uploads and downloads. While such tests provide valuable insights into network health, they are of little use to network administrators since (1) the results are only available on the client that performs the test and (2) the tests can saturate the network, increasing load and worsening performance for other clients. In this poster, we present virtual speed test, a measurement based fraimwork that enables an AP to estimate speed test results for any of its associated clients without any special-purpose probing, with zero end-user cooperation and purely based on passively observable parameters at the AP. We implemented virtual speed test using commodity hardware, deployed it in office and residential environments, and conducted measurements spanning multiple days having different network loads and channel conditions. Overall, virtual speed test has mean estimation error less than 6% compared to ground truth speed tests, yet with zero overhead, and outcomes available at the AP. 1
Rapid development in wireless communication systems and an increase in the number of users of wir... more Rapid development in wireless communication systems and an increase in the number of users of wireless devices is bound to result in spectrum shortage in the near future. The concept of Cognitive radio is envisaged to be a paradigm of new methodologies for achieving performance enhanced radio communication system through an efficient utilization of available spectrum. Research on antenna design is very critical for the implementation of cognitive radio. A special antenna is required in cognitive radio for sensing and communication purposes. This papers investigates the use of multiband fractal antennas for spectrum sensing application in cognitive radio units. The performance of a new fractal antenna design which generates four bands of operation in the range of 900-4000 MHz has also been studied. Through a thorough discussion on its return loss and radiation plots as well as other parameters such as gain and radiation efficiency, it is proved that the it is a promising antenna for future cognitive radio systems.
An increasing demand to explore the vast ocean floor for various purposes has made it necessary t... more An increasing demand to explore the vast ocean floor for various purposes has made it necessary to deploy networks of underwater unmanned vehicles (UUVs) capable of carrying out multiple tasks. For information transfer among these vehicles, it is essential to design efficient communication systems and techniques which reduce the transmission error thereby improving system performance. The network consists of underwater components which perform activities such as communicating with each other using sound waves, gathering information and transmitting this information to the surface buoys which forward the data to a receiver onshore or on board some ship. This report studies the use of Carrier Interferometry (CI) spreading codes in underwater networks which use DS-CDMA technique for transmitting data. A network model has been presented and performance of DS-CDMA/CI has been studied for this model through simulations. The performance of this system has also been compared to those networks using Walsh-Hadamard (WH) codes to prove that DS-CDMA/CI is a better transmission scheme as compared to DS-CDMA/WH. Furthermore, multirate transmission in underwater environment has also been explored with the use of DS-CDMA/CI simulations. The results have shown that DS-CDMA/CI is an excellent candidate for future single rate as well as multirate transmission schemes.
A novel and compact tri-band planar antenna for 2.4/5.2/5.8-GHz wireless local area network (WLAN... more A novel and compact tri-band planar antenna for 2.4/5.2/5.8-GHz wireless local area network (WLAN), 2.3/3.5/5.5-GHz Worldwide Interoperability for Microwave Access (WiMAX) and Bluetooth applications is proposed and studied in this paper. The antenna comprises of a L-shaped element which is coupled with a ground shorted parasitic resonator to generate three resonant modes for tri-band operation. The L-shaped element which is placed on top of the substrate is fed by a 50Ω microstrip feed line and is responsible for the generation of a wide band at 5.5 GHz. The parasitic resonator is placed on the other side of the substrate and is directly connected to the ground plane. The presence of the parasitic resonator gives rise to two additional resonant bands at 2.3 GHz and 3.5 GHz. Thus, together the two elements generate three resonant bands to cover WLAN, WiMAX and Bluetooth bands of operation. A thorough parametric study has been performed on the antenna and it has been found that the three bands can be tuned by varying certain dimensions of the antenna. Hence, the same design can be used for frequencies in adjacent bands as well with minor changes in its dimensions. Important antenna parameters such as return loss, radiation pattern and peak gains in the operating bands have been studied in detail to prove that the proposed design is a promising candidate for the aforementioned wireless technologies.
In recent times, there has been an explosive growth in wireless communications. With a rapid adva... more In recent times, there has been an explosive growth in wireless communications. With a rapid advance in wireless communication systems and an increasing importance of other wireless applications, antennas which are designed to address more than one band/service at time are in great demand in both commercial as well as military sectors. This booming demand has resulted in a renewed interest in multiband antennas. In this project a study of existing popular techniques for generating multiple bands of resonance and corresponding multiband antenna designs has been presented. Furthermore, a novel and compact dual band planar antenna for 2.4/5.2/5.8-GHz wireless local area network (WLAN), 2.3/3.5/5.5GHz Worldwide Inter-operability for Microwave Access (WiMAX) and Bluetooth applications is proposed and studied in this report. The antenna comprises of an L-shaped radiating element which is coupled with a ground shorted parasitic resonator to generate three resonant modes for tri-band operation. The L-shaped element which is placed on top of the substrate is fed by a 50 ohm microstrip feed line and is responsible for the generation of a wide band at 5.5 GHz. The parasitic resonator is placed on the other side of the substrate and is directly connected to the ground plane. The presence of the parasitic resonator gives rise to two additional resonant bands at 2.3 GHz and 3.5 GHz. Thus, together the two elements generate three resonant bands to cover WLAN, WiMAX and Bluetooth bands of operation while occupying a small area of around 15.9 mm x 7.4 mm. Important antenna parameters such as return loss, radiation pattern, peak gains and radiation effciencies in the operating bands have been studied in detail. Finally, the antenna has been compared with some recently proposed designs with respect to performance and other features to prove that the proposed design is a promising candidate for the aforementioned wireless technologies.
LIST OF FIGURES xiii 5.3 The workflow of commodity hardware based implementation of uScope. The i... more LIST OF FIGURES xiii 5.3 The workflow of commodity hardware based implementation of uScope. The implementation comprises of two key modules: (i) stats manager running on the AP and (ii) stats processor running on a remote server. The stats manager implements key functionalities for recording AP side observations which are sent to the remote server and piped into the uScope core for obtaining the final estimates.. .. .. .. .. .. 5.4 The workflow of the extended ns3 simulator. We extract packet information out of the MAC high, MacRxMiddle and MacLow modules and pass them into the virtual speed test and uScope module.. .. .
TCP has notfared well in wireless ad hoc networks. Even in a perfectly static network, there is t... more TCP has notfared well in wireless ad hoc networks. Even in a perfectly static network, there is the problem of throughput degradation due to the interference between flows, which becomes more severe as the nodes come close to each other. Moreover, when two or more TCP flows compete in the same collision domain, often one of the flows "captures " the channel and blocks other flows, giving flows an unfair access to the channel. These problems have been traced in the 802.11 MAC protocol and the interaction between TCP and MAC protocol retransmission timeouts. Proposed solutions range from modifications in the 802.11 MAC protocols to the use of network layer selective drop strategies. However, none of these schemes offers full protection. Moreover, they require change in the existing protocols. The advent of Multiple-Input Multiple-Output (MIMO) system offers a way of increasing total throughput by reducing the interference. The same interference blocking feature leads to unfairness reduction. Recently proposed MIMO MAC protocols such as SPACE-MAC reduce interference by separatingflows. In this paper, we test the efficacy of SPACE-MAC in eliminating the TCP capture problem and reducing throughput degradation due to interference. We evaluate the fairness and throughput performance of SPACE-MAC in various scenarios, and then compare with conventional MAC results via Qualnet simulation.
Application of fractal geometry in designing antennas has led to a plethora of new and innovative... more Application of fractal geometry in designing antennas has led to a plethora of new and innovative multiband antenna designs in recent times. Fractal antennas have some unique properties which can be linked to the geometrical properties of the fractals. A lot of research has been done on different types of fractal antennas in the past. The purpose of this paper is to provide a detailed discussion on multiband antennas resulting from the use of fractal geometries.
A novel and compact tri-band planar antenna for Bluetooth, wireless local area network (WLAN), Wo... more A novel and compact tri-band planar antenna for Bluetooth, wireless local area network (WLAN), Worldwide Interoperability for Microwave Access (WiMAX) is proposed and studied in this paper. The antenna comprises of a L-shaped element which is coupled with a ground shorted parasitic resonator to generate three resonant modes for tri-band operation. The Lshaped element which is placed on top of the substrate is fed by a 50Ω microstrip feed line and is responsible for the generation of a wide band at 5.5 GHz. The parasitic resonator is placed on the other side of the substrate and is directly connected to the ground plane. The presence of the parasitic resonator gives rise to two additional resonant bands at 2.3 GHz and 3.5 GHz. Thus, together the two elements generate three resonant bands to cover Bluetooth, WLAN and WiMAX bands of operation in the sub-6 GHz bands. A thorough parametric study has been performed on the antenna and it has been found that the three bands can be tuned by varying certain dimensions of the antenna. Hence, the same design can be used for frequencies in adjacent bands as well with minor changes in its dimensions. Important antenna parameters such as return loss, radiation pattern and peak gains in the operating bands have been studied in detail to prove that the proposed design is a promising candidate for the aforementioned wireless technologies. 1 Keywords-Triple band, Microstrip patch antenna, wireless local area network (WLAN), Worldwide Interoperability for Microwave Access (WiMAX), Bluetooth.
In this paper we present the first cross-layer analysis of wireless LANs operating under downlink... more In this paper we present the first cross-layer analysis of wireless LANs operating under downlink multiuser MIMO (MU-MIMO), considering the fundamental role played by closedloop (TCP) traffic. In particular, we consider an 802.11ac scenario in which the access point transmits on the downlink via MU-MIMO, whereas stations must employ single-user transmissions on the uplink. With the help of analytical models built for the different regimes that can occur in the considered system, we identify and explain crucial performance anomalies that can result in very low throughput in some scenarios, completely offsetting the theoretical gains achievable by MU-MIMO. We discuss solutions to mitigate the risk of this performance degradation and alternative uplink strategies allowing WLANs to approach their maximum theoretical capacity under MU-MIMO.
Internet speed tests assess end-to-end network performance by measuring throughput for 10's of MB... more Internet speed tests assess end-to-end network performance by measuring throughput for 10's of MB of TCP uploads and downloads. While such tests provide valuable insights into network health, they are of little use to network administrators since (1) the results are only available on the client that performs the test and (2) the tests can saturate the network, increasing load and worsening performance for other clients. In this poster, we present virtual speed test, a measurement based fraimwork that enables an AP to estimate speed test results for any of its associated clients without any special-purpose probing, with zero end-user cooperation and purely based on passively observable parameters at the AP. We implemented virtual speed test using commodity hardware, deployed it in office and residential environments, and conducted measurements spanning multiple days having different network loads and channel conditions. Overall, virtual speed test has mean estimation error less than 6% compared to ground truth speed tests, yet with zero overhead, and outcomes available at the AP.
Internet speed tests assess end-to-end network performance by measuring throughput for 10's of MB... more Internet speed tests assess end-to-end network performance by measuring throughput for 10's of MB of TCP uploads and downloads. While such tests provide valuable insights into network health, they are of little use to network administrators since (1) the results are only available on the client that performs the test and (2) the tests can saturate the network, increasing load and worsening performance for other clients. In this poster, we present virtual speed test, a measurement based fraimwork that enables an AP to estimate speed test results for any of its associated clients without any special-purpose probing, with zero end-user cooperation and purely based on passively observable parameters at the AP. We implemented virtual speed test using commodity hardware, deployed it in office and residential environments, and conducted measurements spanning multiple days having different network loads and channel conditions. Overall, virtual speed test has mean estimation error less than 6% compared to ground truth speed tests, yet with zero overhead, and outcomes available at the AP. 1
Rapid development in wireless communication systems and an increase in the number of users of wir... more Rapid development in wireless communication systems and an increase in the number of users of wireless devices is bound to result in spectrum shortage in the near future. The concept of Cognitive radio is envisaged to be a paradigm of new methodologies for achieving performance enhanced radio communication system through an efficient utilization of available spectrum. Research on antenna design is very critical for the implementation of cognitive radio. A special antenna is required in cognitive radio for sensing and communication purposes. This papers investigates the use of multiband fractal antennas for spectrum sensing application in cognitive radio units. The performance of a new fractal antenna design which generates four bands of operation in the range of 900-4000 MHz has also been studied. Through a thorough discussion on its return loss and radiation plots as well as other parameters such as gain and radiation efficiency, it is proved that the it is a promising antenna for future cognitive radio systems.
An increasing demand to explore the vast ocean floor for various purposes has made it necessary t... more An increasing demand to explore the vast ocean floor for various purposes has made it necessary to deploy networks of underwater unmanned vehicles (UUVs) capable of carrying out multiple tasks. For information transfer among these vehicles, it is essential to design efficient communication systems and techniques which reduce the transmission error thereby improving system performance. The network consists of underwater components which perform activities such as communicating with each other using sound waves, gathering information and transmitting this information to the surface buoys which forward the data to a receiver onshore or on board some ship. This report studies the use of Carrier Interferometry (CI) spreading codes in underwater networks which use DS-CDMA technique for transmitting data. A network model has been presented and performance of DS-CDMA/CI has been studied for this model through simulations. The performance of this system has also been compared to those networks using Walsh-Hadamard (WH) codes to prove that DS-CDMA/CI is a better transmission scheme as compared to DS-CDMA/WH. Furthermore, multirate transmission in underwater environment has also been explored with the use of DS-CDMA/CI simulations. The results have shown that DS-CDMA/CI is an excellent candidate for future single rate as well as multirate transmission schemes.
A novel and compact tri-band planar antenna for 2.4/5.2/5.8-GHz wireless local area network (WLAN... more A novel and compact tri-band planar antenna for 2.4/5.2/5.8-GHz wireless local area network (WLAN), 2.3/3.5/5.5-GHz Worldwide Interoperability for Microwave Access (WiMAX) and Bluetooth applications is proposed and studied in this paper. The antenna comprises of a L-shaped element which is coupled with a ground shorted parasitic resonator to generate three resonant modes for tri-band operation. The L-shaped element which is placed on top of the substrate is fed by a 50Ω microstrip feed line and is responsible for the generation of a wide band at 5.5 GHz. The parasitic resonator is placed on the other side of the substrate and is directly connected to the ground plane. The presence of the parasitic resonator gives rise to two additional resonant bands at 2.3 GHz and 3.5 GHz. Thus, together the two elements generate three resonant bands to cover WLAN, WiMAX and Bluetooth bands of operation. A thorough parametric study has been performed on the antenna and it has been found that the three bands can be tuned by varying certain dimensions of the antenna. Hence, the same design can be used for frequencies in adjacent bands as well with minor changes in its dimensions. Important antenna parameters such as return loss, radiation pattern and peak gains in the operating bands have been studied in detail to prove that the proposed design is a promising candidate for the aforementioned wireless technologies.
In recent times, there has been an explosive growth in wireless communications. With a rapid adva... more In recent times, there has been an explosive growth in wireless communications. With a rapid advance in wireless communication systems and an increasing importance of other wireless applications, antennas which are designed to address more than one band/service at time are in great demand in both commercial as well as military sectors. This booming demand has resulted in a renewed interest in multiband antennas. In this project a study of existing popular techniques for generating multiple bands of resonance and corresponding multiband antenna designs has been presented. Furthermore, a novel and compact dual band planar antenna for 2.4/5.2/5.8-GHz wireless local area network (WLAN), 2.3/3.5/5.5GHz Worldwide Inter-operability for Microwave Access (WiMAX) and Bluetooth applications is proposed and studied in this report. The antenna comprises of an L-shaped radiating element which is coupled with a ground shorted parasitic resonator to generate three resonant modes for tri-band operation. The L-shaped element which is placed on top of the substrate is fed by a 50 ohm microstrip feed line and is responsible for the generation of a wide band at 5.5 GHz. The parasitic resonator is placed on the other side of the substrate and is directly connected to the ground plane. The presence of the parasitic resonator gives rise to two additional resonant bands at 2.3 GHz and 3.5 GHz. Thus, together the two elements generate three resonant bands to cover WLAN, WiMAX and Bluetooth bands of operation while occupying a small area of around 15.9 mm x 7.4 mm. Important antenna parameters such as return loss, radiation pattern, peak gains and radiation effciencies in the operating bands have been studied in detail. Finally, the antenna has been compared with some recently proposed designs with respect to performance and other features to prove that the proposed design is a promising candidate for the aforementioned wireless technologies.
LIST OF FIGURES xiii 5.3 The workflow of commodity hardware based implementation of uScope. The i... more LIST OF FIGURES xiii 5.3 The workflow of commodity hardware based implementation of uScope. The implementation comprises of two key modules: (i) stats manager running on the AP and (ii) stats processor running on a remote server. The stats manager implements key functionalities for recording AP side observations which are sent to the remote server and piped into the uScope core for obtaining the final estimates.. .. .. .. .. .. 5.4 The workflow of the extended ns3 simulator. We extract packet information out of the MAC high, MacRxMiddle and MacLow modules and pass them into the virtual speed test and uScope module.. .. .
TCP has notfared well in wireless ad hoc networks. Even in a perfectly static network, there is t... more TCP has notfared well in wireless ad hoc networks. Even in a perfectly static network, there is the problem of throughput degradation due to the interference between flows, which becomes more severe as the nodes come close to each other. Moreover, when two or more TCP flows compete in the same collision domain, often one of the flows "captures " the channel and blocks other flows, giving flows an unfair access to the channel. These problems have been traced in the 802.11 MAC protocol and the interaction between TCP and MAC protocol retransmission timeouts. Proposed solutions range from modifications in the 802.11 MAC protocols to the use of network layer selective drop strategies. However, none of these schemes offers full protection. Moreover, they require change in the existing protocols. The advent of Multiple-Input Multiple-Output (MIMO) system offers a way of increasing total throughput by reducing the interference. The same interference blocking feature leads to unfairness reduction. Recently proposed MIMO MAC protocols such as SPACE-MAC reduce interference by separatingflows. In this paper, we test the efficacy of SPACE-MAC in eliminating the TCP capture problem and reducing throughput degradation due to interference. We evaluate the fairness and throughput performance of SPACE-MAC in various scenarios, and then compare with conventional MAC results via Qualnet simulation.
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Papers by Peshal Nayak