Peshal B. Nayak

Monitoring the network performance experienced by the end-user is crucial for managers of wireless networks as it can enable them to remotely modify the network parameters to improve the end-user experience. Unfortunately, for performance monitoring, managers are typically limited to the logs of the Access Points (APs) that they manage. This information does not directly capture factors that can hinder station (STA) side transmissions. Consequently, state-of-the-art methods to measure such… Show more

Monitoring the network performance experienced by the end-user is crucial for managers of wireless networks as it can enable them to remotely modify the network parameters to improve the end-user experience. Unfortunately, for performance monitoring, managers are typically limited to the logs of the Access Points (APs) that they manage. This information does not directly capture factors that can hinder station (STA) side transmissions. Consequently, state-of-the-art methods to measure such metrics primarily involve active measurements. Unfortunately, such active measurements increase traffic load and if used regularly and for all the STAs can potentially disrupt user traffic, thereby worsening performance for other users in the network and draining the battery of mobile devices.
This thesis enables passive AP-side network analytics. In the first part of the thesis, I present virtual speed test, a measurement based framework that enables an AP to estimate speed test results for any of its associated clients solely based on AP-side observables. Next, I present Uplink Latency Microscope (uScope), an AP-side framework for estimation of WLAN uplink latency for any of the associated STAs and decomposition into its constituent components. Similar to virtual speed test, uScope makes estimations solely based on passive AP-side observations. We implement both frameworks on a commodity hardware platform and conduct extensive field trials on a university campus and in a residential apartment complex. In over 1 million tests, the two proposed frameworks demonstrate an estimation accuracy with errors under 10%. Show less

Internet speed tests assess end-to-end network performance by measuring throughput for 10s 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 paper, we present virtual speed test, a measurement based framework… Show more

Internet speed tests assess end-to-end network performance by measuring throughput for 10s 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 paper, we present virtual speed test, a measurement based framework that enables an AP to estimate speed test results for any of its associated clients without any special-purpose probing, with zero end-user co-operation 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. Show less

In this paper, we present the first cross-layer analysis of wireless LANs operating under downlink multi-user multi-in multi-out (MU-MIMO), considering the fundamental role played by the closed-loop (TCP) traffic. In particular, we consider a scenario in which the access point transmits on the downlink via MU-MIMO, whereas stations must employ single-user transmissions on the uplink, as is the case in IEEE 802.11ac. With the help of analytical models built for different regimes that can occur… Show more

In this paper, we present the first cross-layer analysis of wireless LANs operating under downlink multi-user multi-in multi-out (MU-MIMO), considering the fundamental role played by the closed-loop (TCP) traffic. In particular, we consider a scenario in which the access point transmits on the downlink via MU-MIMO, whereas stations must employ single-user transmissions on the uplink, as is the case in IEEE 802.11ac. With the help of analytical models built for 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. Show less

In this paper we present the first cross-layer analysis of wireless LANs operating under downlink multi-user MIMO (MUMIMO), considering the fundamental role played by closed-loop (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… Show more

In this paper we present the first cross-layer analysis of wireless LANs operating under downlink multi-user MIMO (MUMIMO), considering the fundamental role played by closed-loop (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. Show less

A low cost, dual band antenna has been proposed and studied in this paper. The antenna consists of two elements- a T-shaped element and an F-shaped element. A microstrip feed line with a characteristic impedance of 50? has been used to feed the T-element which is responsible for the generation of the higher band of operation. The F-element is placed on the other side of the dielectric and is coupled with the T-element to generate a lower band of operation. Thus, together the two elements… Show more

A low cost, dual band antenna has been proposed and studied in this paper. The antenna consists of two elements- a T-shaped element and an F-shaped element. A microstrip feed line with a characteristic impedance of 50? has been used to feed the T-element which is responsible for the generation of the higher band of operation. The F-element is placed on the other side of the dielectric and is coupled with the T-element to generate a lower band of operation. Thus, together the two elements generate a dual band performance. Besides, the design has been simpli?ed by doing away with shorting pins and complicated geometries- one of the major disadvantages in existing dual band antenna designs. Furthermore, the dimensions of the two elements have been optimized so that the overall size of the antenna is considerably reduced. Return loss plots, radiation pattern and other antenna parameters have been studied thoroughly and also compared with existing designs to prove that the proposed antenna is a promising design for wireless systems using WiMAX, Bluetooth and also for WLAN applications. Show less

A novel and compact tri-band patch 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… Show more

A novel and compact tri-band patch 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. Show less

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… Show 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. Show less

A novel and compact dual band planar antenna for 2.4/5.2/5.8-GHz wireless local area network(WLAN) applications is proposed and studied in this paper. The antenna comprises of a T-shaped and a F-shaped element to generate two resonant modes for dual band operation. The two elements can independently control the operating frequencies of the two excited resonant modes. The T-element which is fed directly by a 50 Ω microstrip line generates a frequency band at around 5.2 GHz and the antenna… Show more

A novel and compact dual band planar antenna for 2.4/5.2/5.8-GHz wireless local area network(WLAN) applications is proposed and studied in this paper. The antenna comprises of a T-shaped and a F-shaped element to generate two resonant modes for dual band operation. The two elements can independently control the operating frequencies of the two excited resonant modes. The T-element which is fed directly by a 50 Ω microstrip line generates a frequency band at around 5.2 GHz and the antenna parameters can be adjusted to generate a frequency band at 5.8 GHz as well, thus covering the two higher bands of WLAN systems individually. By couple-feeding the F-element through the T-element, a frequency band can be generated at 2.4 GHz to cover the lower band of WLAN system. Hence, the two elements together are very compact with a total area of only 11×6.5 mm2. A thorough parametric study of key dimensions in the design has been performed and the results obtained have been used to present a generalized design approach. Plots of the return loss and radiation pattern have been given and discussed in detail to show that the design is a very promising candidate for WLAN applications. Show less

Cognitive radio is rapidly shaping the future of wireless communications. Research on antenna design is very critical for the implementation of cognitive radio. A special antenna is required in cognitive radio for sensing and communicating. For the purpose of spectrum sensing, an Ultrawideband (UWB) antenna is being considered as a potential candidate by many experts. This paper provides a detailed discussion of the existing UWB spectrum sensing antenna designs for cognitive radio system… Show more

Cognitive radio is rapidly shaping the future of wireless communications. Research on antenna design is very critical for the implementation of cognitive radio. A special antenna is required in cognitive radio for sensing and communicating. For the purpose of spectrum sensing, an Ultrawideband (UWB) antenna is being considered as a potential candidate by many experts. This paper provides a detailed discussion of the existing UWB spectrum sensing antenna designs for cognitive radio system. Simulation results for a promising cognitive radio antenna which provides a reconfigurable function in the range of 5-6 GHz have also been presented and shown to match closely with the measured results. Show less