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• Enabling Multi-User Transmissions in 60 GHz WLANs                                 M.Sc. project, Rice University

The millimeter scale carrier wavelength of the 60 GHz spectrum makes it feasible to pack two order of magnitudes more antennas into the same form factor compared to legacy bands (i.e. 2.4 and 5 GHz band). Prior works in 60 GHz have exploited this large antenna arrays to enhance the link budget of a single user transmission, which suffers from high path loss in 60 GHz. We are proposing a scalable multi-user scheme in 60 GHz WLANs in order to serve multiple clients with multi-Gbps data rate simultaneously in the same environment using the same frequency channel. To this end, we first propose a scalable beam training protocol, which tracks the users for directional transmissions. Then we have designed and evaluated incremental policies that add clients to a transmission sequentially until the AP’s resources are exhausted or client link budgets, including interference, are exceeded. We further target polarization diversity and non-uniform antenna partitioning as mechanisms to dramatically reduce inter-stream interference enabling vastly improved aggregate rate. At lower bands, multi-user aggregation is typically achieved by zero-forcing inter-user interference via sender-side digital pre-coding using channel state information at the source. Unfortunately, such techniques do not scale to 60 GHz since (i) 60 GHz transmission is highly directional and lacks the rich scattering propagation environment assumed for most prior work; (ii) even efficient mechanisms for CSIT collection do not scale to large antenna arrays; (iii) prior techniques employ a large number of radio frequency chains (up to one per antenna) which are not feasible in our scenario. Our experiments through over-the-air testbed built over WARP platform and trace-driven simulations show that our methodology can achieve performance near to that of exhaustive search of all possible client combinations, yet with substantially less overhead.

The details of this project cannot be provided yet.

• Managing mmWave Cellular Networks                                                     Internship project, NEC labs America

The details of this project cannot be provided yet.

• Robust 60 GHz Indoor Connectivity with Cooperative Access Points       Ph.D. Qualifier project (ELEC 599)

The 60 GHz frequency band achieves very high data rate (in the order of Gb/s) since it has 7-9 GHz unlicensed bandwidth. However, high free-space path loss and penetration loss necessitate use of steerable directional antennas to overcome these losses by additional antenna gain. The directional nature of 60 GHz links makes them sensitive to misalignment that can cause by nodal movement. In this project, we propose and evaluate a novel method for improving the connectivity of indoor 60 GHz links. The key idea is to allocate multiple coordinated Access Points (AP) for each transmission in downlink. Since these APs are widely spaced in the environment and transmit simultaneously, the link remains stable by the translational or rotational movement of the client or obstacles. There are many challenges related to this method that need to be addressed. The exhaustive research protocol for discovering the best “sector” for a pair of nodes require more time with increasing the number of APs. This large amount of overhead time may affect the throughput significantly. Having more transmitters is not sufficient enough since there are other parameters like beamwidth that affect the link robustness. We evaluate the performance of our proposed method and compare it with normal point to point data transmission as defined in IEEE 802.11ad standard. Our simulation results show that by having three APs transmitting concurrently to a mobile client whose antenna beamwidth is ??°, packet delivery ratio is 99% while in a similar situation with one AP this ratio is 61%.

The details of this project can be found here.

• mmTrace: Modeling Millimeter-wave Indoor Propagation with Image-based Ray-tracing                                                                                                             In collaboration with TU Darmstadt university in Germany

Current mm-wave indoor propagation analysis techniques have limited options when it comes to more than one transmitter and receiver, large antenna arrays and polarized antennas. Experimental testbed hardware is expensive and state-of-the-art simulation methods, as statistical channel models, are limited to specific scenarios. To overcome this problems, we present mmTrace, a fast deterministic image-based ray-tracing simulation framework for mm-wave propagation. It supports developing mm-wave specific protocols and, in contrast to common statistical models, deals with multiple transceivers. The strengths of mmTrace constitute signal variations at different receivers and interference of multiple transmitters, which are crucial in specific situations. We implement our framework in MATLAB and validate simulated channel impulse responses against over-the-air measurements using WARP platform in well defined scenarios. Our results indicate that image-based ray-tracing is a feasible tool to predict interference in mm-wave communication systems.

The details of this project are available on request.