Enabling Mobile mmWave Communication: Achieving Low Power and Delay via a Hybrid RF Design

NeTS Small

List of personnel

  1. Principal Investigator: Can Koksal, Ness Shroff, and Kubilay Sertel

  2. Graduate Students: Syed Saqueb, Yahia Shabara

  3. Postdoctoral Researcher: Morteza Hashemi

Goals

    The goals of the proposed research will be conducted across three major inter-related thrusts:

  1. Scaled-down experimentation for mobile mmWave propagation: Current models of wirelesspropagation are based on a time-scale separation assumption. Based on our preliminary experiments, we demonstrate that this separation does not work for mmWave. We propose a measurement setup that uses small-scale models for the environment of interest and take the measurements at proportionally high frequencies. Our novel framework enables accurate mobile measurements, jointly at the RF and mmWave interfaces without having to build actual real-world systems.

  2. Energy-efficient communication: Despite the availability of huge bandwidths at the mmWave interface, it is not energy efficient to utilize it fully at all times. Furthermore, connection setup and beamforming can consume significant resources. To alleviate these challenges, we will cleverly exploit the correlations across RF and mmWave interfaces in order to achieve mmWave beamforming fully in the analog domain to maximize the achieved rate per unit power consumed.

  3. Low-delay communication: Taking into account the high variability of mmWave channels, we will develop a framework to jointly manage the queues at the RF and mmWave interfaces. Our delay minimization and queue management formulation explicitly takes into account the processor read/write speed relative to the mmWave link rates.

Accomplishments:

In millimeter wave (mmWave) systems, energy is a scarce resource due to the large channel losses and high energy usage by analog-to-digital converters. To mitigate this issue, we propose an integrated architecture that combines RF (i.e., sub-6 GHz)vand mmWave technologies. We investigate the power and bandwidthvallocation jointly across the interfaces in order to maximizevthe achievable sum rate under power constraints. Our optimization formulation explicitly takes the components energy consumptionvinto account, and our results show that despite the availability of huge mmWave bandwidth, it is optimal to utilize it partially undervsome circumstances.

We propose a hybrid architecture to integrate RF (i.e., sub-6 GHz) and millimeter wave (mmWave) interfaces for 5G cellular systems. To alleviate the challenges associated with mmWave communications, our proposed architecture integrates the RF and mmWave interfaces for beamforming and data transfer, and exploits the spatio-temporal correlations between the interfaces. Based on extensive experimentation in indoor and outdoor settings, we demonstrate that an integrated RF/mmWave signaling and channel estimation scheme can remedy the problem of high training overhead associated with mmWave beamforming. In addition, cooperation between two interfaces at the higher layers effectively addresses the high delays caused by highly intermittent connectivity in mmWave channels. Subsequently, we formulate an optimal scheduling problem over the RF and mmWave interfaces where the goal is to maximize the delay-constrained throughput of the mmWave interface. We prove using subadditivity analysis that the optimal scheduling policy is based on a single threshold that can be easily adopted despite high link variations. We design an optimal scheduler that opportunistically schedules the packets over the mmWave interface, while the RF link acts as a fallback mechanism to prevent high delay.

We investigate the problem of beam alignment in millimeter wave (mmWave) systems, and design an optimal algorithm to reduce the overhead. Specifically, due to directional communications, the transmitter and receiver beams need to be aligned, which incurs high delay overhead since without a priori knowledge of the transmitter/receiver location, the search space spans the entire angular domain. This is further exacerbated under dynamic conditions (e.g., moving vehicles) where the access to the base station (access point) is highly dynamic with intermittent on-off periods, requiring more frequent beam alignment and signal training. To mitigate this issue, we consider an online stochastic optimization formulation where the goal is to maximize the directivity gain (i.e., received energy) of the beam alignment policy within a time period. We exploit the inherent correlation and unimodality properties of the model, and demonstrate that contextual information improves the performance. To this end, we propose an equivalent structured Multi-Armed Bandit model to optimally exploit the exploration-exploitation tradeoff. In contrast to the classical MAB models, the contextual information makes the lower bound on regret (i.e., performance loss compared with an oracle policy) independent of the number of beams. This is a crucial property since the number of all combinations of beam patterns can be large in transceiver antenna arrays, especially in massive MIMO systems. We further provide an asymptotically optimal beam alignment algorithm, and investigate its performance via simulations.

We have also complied an extensive database of material properties of commonly available polymers in the mmW and THz bands. This data was collected and processed to lay the foundation for the planned experiments to characterize RF and mmW channels (in a controlled laboratory setting) using THz-band measurements on a scale model of the enviroment, including real-life obstructions, such as buildings and furnature. To do so, we are currently evaluating the RF and mmW properties of common building materials (concrete, wood, drywall, etc.) to create replicas of rooms and buildings for the THz-band measurements.

Significant Results:

Our hybrid mmWave-RF architecture enables a low cost mechanism to achieve mobile wireless communication at mmWave frequences.

Our setup that involves converters, amplifiers, and USRPs enable low to medium bandwidth experimentation without an actual mmWave front end. We show a relatively affordable way of conducting real-world performance measurements to the mmWave community.

We have complied a unique database of the dielectric properties of 7 polymers, commonly used in manufacturing, for the 0-2THz band. The permittvity and loss tangents were characterized and tabulated and concise analytical formulas were developed to aid with the scale model experiments.

Publications:

  1. A. Bakshi, L. Chen, K. Srinivasan, C. E. Koksal, and A. Eryilmaz, “EMIT: An Efficient MAC Paradigm for the Internet of Things”, submitted to IEEE/ACM Trans. on Networking (ToN), 2017.

  2. M. Hashemi, C. E. Koksal, and N. B. Shroff “RF-Assisted Millimeter Wave Beamforming and Communications to Achieve Low Latency and High Energy Efficiency in 5G Systems,” submitted to IEEE Trans. on Communications (TCOM), 2017.

  3. X. Li, Y. Sun, L. Xiao, S. Zhou, and C. E. Koksal, “Analog Beam Tracking in Linear Antenna Arrays: Convergence and Optimality,” ASILOMAR’17, Pacific Grove, CA, Nov. 2017.

  4. M. Hashemi, C. E. Koksal, and N. B. Shroff, “Rate-Optimal Power and Bandwidth Allocation in an Integrated Sub-6 GHz – Millimeter Wave Architecture”, ASILOMAR’17, Pacific Grove, CA, Nov. 2017.

  5. M. Hashemi, C. E. Koksal, and N. B. Shroff, “Hybrid RF-mmWave Communications to Achieve Low Latency and High Energy Efficiency in 5G Cellular Systems,” IEEE WiOpt’17, Paris, France, May 2017.

  6. M. Sahin, N. K. Nahar, and K. Sertel, “Dielectric Properties of Low-loss Polymers for mmW and THz Applications,” IEEE International Symposium on Antennas and Propagation 2017, San Diego, CA Jul. 2017.

Ohio State Engineering:
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