Browsing by Author "Haider, Muhammad Kumail"

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    Geometric Beam Steering via Passive Light Sensing for mmWave WLANs
    (2018-11-30) Haider, Muhammad Kumail; Knightly, Edward W.
    GHz-scale bandwidth in the mmWave spectrum (30 GHz to 300 GHz and beyond) realizes data rates of up to 100 Gb/sec with highly directional links, which can satiate the ever increasing demand for high speed wireless connectivity. However, a key challenge is that end nodes need to continually align their beams to maintain directional links, which incurs significant beam search overhead. This overhead can limit the performance of mmWave networks under nodal or environmental mobility. In this thesis, I present the design, implementation and evaluation of two novel mmWave beam adaptation solutions for achieving out of band steering using passive light sensing with off-the-shelf sensors to completely eliminate the need for in-band training. The key idea is to exploit similar propagation characteristics of higher frequency bands (i.e., light and mmWave bands) to track the dominant component of the mmWave wireless channel solely by using measurements in light band. To this end, I first introduce LiSteer, a system that steers mmWave beams at mobile devices by repurposing indicator LEDs on wireless Access Points (APs) to passively acquire direction estimates. I demonstrate that LiSteer maintains beam alignment at the narrowest beamwidth level even in case of device mobility, without incurring any training overhead at mobile devices. I then present SearchLight, where the key idea is to simultaneously track a mobile device's position and orientation using intensity measurements from lighting infrastructure, and to adapt mmWave beams at both mobile devices and the AP, completely eliminating beam training overhead for mmWave links. My extensive evaluation on a custom dual-band hardware platform comprising highly directional horn antennas as well as practical phased antenna arrays with electronic beam steering shows that both LiSteer and SearchLight achieve direction estimates within 2.5 degrees of ground truth on average. Moreover, both systems track client mobility and achieve up to 3x throughput gains compared to an in-band training strategy, and eliminate milli-second-scale in-band training epochs.
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    Overhead Constrained Joint Adaptation of MCS, Beamwidth and Antenna Sectors for 60 GHz WLANs with Mobile Clients
    (2015-10-27) Haider, Muhammad Kumail; Knightly, Edward
    The 60 GHz frequency band, with its 7 GHz wide unlicensed spectrum, opens up avenues to multi-Gigabit communication. However, the extremely short wavelength (on the order of a few millimeters) results in very high path loss and little diffraction or scattering. To extend range, directional antennas or electronically steerable beam-arrays are used to get directivity gain. This makes links in 60 GHz networks inherently directional and this directivity introduces new challenges in terms of communication link establishment and maintenance. First, the beamwidth of the directional antennas plays an important role in determining the maximum rate, unlike in omni-directional networks. Moreover, 60 GHz links are susceptible to breakage due to misalignment and blockage due to their highly directional nature. In this thesis, I have designed, implemented and evaluated a novel cross-layer protocol, BeamRAP, for adapting the beamwidth of directional antennas and the data rate at the physical layer jointly in 60 GHz directional networks. This joint adaptation is necessary since beamwidth and alignment of directional antennas, are the key determinants of link strength and thereby the data rates. Moreover, misalignment of directional antennas due to nodal mobility or link blockage due to environmental mobility cannot be addressed by existing rate adaptation protocols. Therefore, in BeamRAP, I have implemented a new algorithm for beamwidth adaptation in response to the frequency of blockage and misalignment events, to maximize link throughput. I have also introduced new mechanisms for link breakage detection, and fast recovery to restore links without exhaustive search over all antenna sectors. I have also developed a 60 GHz programmable node and testbed using VubIQ 60 GHz transceivers with WARP baseband, and have conducted an extensive measurement study to collect signal strength traces over-the-air for various LOS, reflection and antenna-misalignment scenario. My experiments under multiple environmental and nodal mobility scenario show that BeamRAP achieves up to 2x gains in throughput as compared to a baseline 802.11ad scheme, which does not implement beamwidth adaptation.