Swetank Kumar Saha

Power-throughput tradeoffs of 802.11n/ac in smartphones

This paper presents the first, to the best of our knowledge, detailed experimental study of 802.11n/ac throughput and power consumption in modern smartphones. We experiment with a variety of smartphones, supporting different subsets of 802.11n/ac features. We investigate the power consumption in various states of the wireless interface (sleep, idle, active), the impact of various features of 802.11n/ac (PHY bitrate, frame aggregation, channel bonding, MIMO) on both throughput and power consumption, and the tradeoffs between these two metrics. Some of our findings are significantly different from the findings of previous studies using 802.11n/ac wireless cards for laptop/desktop computers. We believe that these findings will help in understanding various performance and power consumption issues in todays smartphones and will guide the design of power optimization algorithms for the next generation of mobile devices.

X60: A Programmable Testbed for Wideband 60 GHz WLANs with Phased Arrays

This paper introduces X60, the first SDR-based testbed for 60 GHz WLANs, featuring fully programmable MAC/PHY/Network layers, multi-Gbps rates, and a user-configurable 12-element phased antenna array. Combined these features provide an unprecedented opportunity to re-examine the most important aspects of signal propagation and performance expected from practical 60 GHz systems. Leveraging the testbeds capabilities, we conduct an extensive measurement study, looking at different aspects of indoor 60 GHz links. We find that the presence of reflective surfaces and imperfect beams generated by practical phased arrays together can result in multiple NLoS paths supporting Gbps rates. Additionally, our comparison of different beam adaptation strategies reveals how beam steering even at one end of the link can often be sufficient to restore link quality.

Poster: X60: A Programmable Testbed for Wideband 60 GHz WLANs with Phased Arrays

We introduce X60, the first SDR-based testbed for 60 GHz WLANs, featuring fully programmable MAC/PHY/Network layers, multi-Gbps rates, and a user-configurable 12-element phased antenna array. These features provide us with an unprecedented opportunity to revisit the most important aspects of 60 GHz signal propagation and obtain new insights on performance expected from practical 60 GHz systems. X60s unique capabilities make it an ideal platform for experimentation and prototyping across layers.

A detailed look into power consumption of commodity 60 GHz devices

The millimeter-wave technology is emerging as an alternative to legacy 2.4/5 GHz WiFi, offering multi-Gigabit throughput. While a lot of attention has been paid recently to analyzing the performance of the 60 GHz technology and adapting it for indoor WLAN usage, the power consumption aspect has largely been neglected. Given that mobile devices are the next target for 60 GHz, any discussion about this technology is incomplete without considering power consumption. In this work, we present the first, to our best knowledge, detailed study of the power consumption of 60 GHz commodity devices. We evaluate the power and energy consumption of two standard-compliant 60 GHz wireless adapters in different operating states and under a number of different configurations. We also compare our results against 802.11ac and discuss power-performance tradeoffs for the two technologies.

A first look at TCP performance in indoor IEEE 802.11ad WLANs

Radio communication in the millimeter-wave (mmwave) frequency bands, recently standardized by the IEEE 802.11ad specification, is emerging as an alternative to the traditional 2.4/5GHz wireless systems, promising multi-Gigabit throughput. Most work in this area until now has focused on PHY/MAC layer design. In contrast, little attention has been paid towards transport layer performance. In this work, we experimentally characterize TCPs behavior and its interplay with the lower layers of the protocol stack over 60GHz links in a typical office environment. Our results differ significantly from the those reported in the past for 60GHz links in a stable datacenter environment.

Revisiting 802.11 power consumption modeling in smartphones

WiFi activity is a major source of power consumption in todays smartphones. Consequently, accurately WiFi power consumption models are extremely useful for researchers and app developers. Among a large number of models proposed recently, a model introduced by Serrano et al. was the first to add a new component - a per-frame energy toll incurred as a frame traverses the protocol stack - to the power consumption of the wireless NIC. The authors called this new component cross-factor and validated the accuracy of the model on a large number of devices, mostly 802.11g wireless routers and APs. This paper examines the validity of the model introduced by Serrano et al. on todays smartphones. We try to answer two questions: (i) Can the model accurately estimate the power consumption due to WiFi activity in todays smartphones given the complexity of modern smartphone architectures? (ii) Does the model remain valid in the case of 802.11n/ac interfaces, and if yes, can it reflect the impact of the new MAC features (e.g., MIMO, channel bonding) on the WiFi power consumption? Additionally, we study the impact of the power saving mode (PSM) which was ignored in the original model and show that ignoring PSM results in significant overestimation of the total power consumption at low frame generation rates. Accordingly, we propose a new model that works across the full range of frame generation rates and verify its accuracy for a wide range of parameters and devices.

A Feasibility Study of 60 GHz Indoor WLANs

This paper presents a feasibility study of 60 GHz indoor WLANs. We evaluate 60 GHz performance in a typical academic office building under the primary assumption that 60 GHz WLAN APs and clients will be equipped with wider beam antennas to cope with client mobility. In contrast to previous works which measured performance at a single layer using custom, non-standard compliant hardware, we investigate performance across multiple layers using 802.11ad-compliant wide beam COTS devices. Our study shows that the large number of reflective surfaces in typical indoor WLAN environments combined with wider beams makes performance highly unpredictable and invalidates several assumptions that hold true in static, LOS scenarios. Additionally, we present the first measurements, to our best knowledge, of power consumption of an 802.11ad NIC and examine the impact of a number of factors on power consumption.

Improving Connectivity, Coverage, and Capacity in 60 GHz Indoor WLANs Using Relays

60 GHz technology, standardized by IEEE 802.11ad, has emerged as an alternative to 2.4/5 GHz legacy WiFi for building multi-Gigabit general purpose home/enterprise WLANs. However, limited range and high vulnerability to blockage of millimeter-wave (mmWave) links can severely affect WLAN performance. These problems coupled with long re-connection time for a broken link pose a major challenge to the realization of 60 GHz WLANs. In this work, we look at the relay architecture defined in the 802.11ad standard as a solution to these issues and propose extensions to it for achieving gains in both WLAN coverage and capacity.

Multipath TCP in Smartphones: Impact on Performance, Energy, and CPU Utilization

This paper explores the potential benefits and pitfalls of Multipath TCP (MPTCP) in smartphones via an extensive experimental study over real Android applications. We consider different types of applications - upload vs. download intensive, network intensive vs. interactive - and a variety of network conditions, and we study the impact of MPTCP on performance, energy consumption, and CPU utilization. Our results reveal that the benefits of MPTCP in smartphone apps are lower than expected in theory; in several cases, MPTCP in fact can hurt both performance and energy consumption. Our findings can provide insights to smartphone designers and mobile app developers towards improving user experience and extending smartphone battery life.

Multi-Gigabit indoor WLANs: Looking beyond 2.4/5 GHz

This work explores the idea of building multi-Gigabit indoor enterprise WLANs using the millimeter-wave technology. Instead of the legacy 2.4/5 GHz band, we look at the unlicensed band around 60 GHz and the new 802.11ad standard, which supports PHY data rates of up to 6.76 Gbps. Through a set of measurements with commercial hardware, we show the feasibility of building multi-Gigabit WLANs. Using observations from our experiments and results reported in recent studies, we point out both the advantages and drawbacks of the 60 GHz technology, and identify the research challenges towards making multi-Gigabit 60 GHz indoor WLANs a reality.