Research

EMvelop stimulation: minimally invasive deep brain stimulation using temporally interfering electromagnetic waves

 

EMvelop stimulation methodology.

Superposition of GHz electric fields from two antenna arrays, shown in green and blue, differing by a small frequency offset creates the EMvelop signal, shown in red, whose amplitude is modulated at E1 and E2 are electric fields generated by each array, and EAM is the peak-to-peak value of the dashed envelope.

 

EMvelop stimulation representative result for a center target deep inside the brain tissue.

We show that when we optimize for intensity of EMvelop stimulation, we can deliver an E-field of 11.98 V/m with a focality of 3.59 cm, whereas when we optimize for focality of EMvelop stimulation, we can deliver 3.04 V/m with a focality of 2.78 cm at the target, while obeying safety limits.

Publications: 

  • Fatima Ahsan, Taiyun Chi, Raymond Cho, Sameer A. Sheth, Wayne Goodman,
    and Behnaam Aazhang, “EMvelop stimulation: minimally invasive deep
    brain stimulation using temporally interfering electromagnetic waves”,
    Journal of Neural Engineering, July 2022 [paper] 
  • Fatima Ahsan, Taiyun Chi, Raymond Cho, Sameer Anil Sheth, Wayne Goodman and Behnaam Aazhang, “ Non-invasive Deep Brain Stimulation using Electromagnetic Waves”, IEEE Asilomar 2020, Monterrey, CA, USA [paper]

Leveraging Massive MIMO Spatial Degrees of Freedom to Reduce Random Access Delay

Random access is a crucial building block for nearly all wireless networks, and impacts both the overall spectral efficiency and latency in communication. In this work, we analytically show that the spatial degrees of freedom, e.g. available in massive MIMO systems, can potentially be leveraged to reduce random access latency. Using one-ring propagation model, we evaluate how the random access collision probability depends on the aperture size of the array and the spread of user’s signal Angle-of-Arrivals (AoAs) at the base-station, as a function of the user-density and the number of random access codes. Our numerical evaluation shows that for practically sized large arrays in outdoor environments, a significant reduction in collision probability is possible, which in turn can decrease the random access latency.

Publication:

Fatima Ahsan and Ashutosh Sabharwal, “Leveraging Massive MIMO Spatial Degrees of Freedom to Reduce Random Access Delay”, IEEE Asilomar 2017, Monterrey, CA, USA [paper]

Stalkers: A physical-layer solution towards co-existence with WiFi

In this work, we present a prototype implementation of Stalkers; a physical layer solution that lets a pair of opportunistic secondary nodes to co-exist with a primary IEEE 802.11-type transmitter-receiver pair using simultaneous in-band transmissions. For this co-existence, the secondary system first stalks the primary system, following which it shapes its own transmissions so as to cause no degradation in the primary network’s performance while at the same time not necessitating any change in the primary nodes’ physical layer. Drawing inspiration from existing information theoretic literature, the secondary transmissions of the implemented solution rely on (a) forwarding of the primary system’s signal by the secondary system to compensate for the interference caused by the latter at the former, and (b) Tomlinson-Harashima precoding to mitigate the primary interference seen by the secondary network. The solution prototype is built with software-defined radios, using which we experimentally demonstrate that the performance of the primary 802.11-type system remains unaffected with the introduction of the secondary system, thereby acquiring throughput for the in-band co-existing solution.
Publication:
Fatima Ahsan and M. Uppal, “Stalkers: Co-existing Nodes within Unlicensed WiFi Band”, IEEE WCNC 2018, Barcelona, Spain [paper]