Gaurang Naik
Ph.D., Electrical Engineering

Virginia Tech
900 N Glebe Rd.
Arlington, VA 22203
(540) 449-7603
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  1. The ever-increasing demand for unlicensed spectrum has prompted regulators in the US and Europe to consider opening up the 6 GHz bands for unlicensed access. These bands will open up 1.2 GHz of additional spectrum for unlicensed radio access technologies (RATs), such as Wi-Fi and 5G New Radio Unlicensed (NR-U), in the US and if permitted, 500 MHz of additional spectrum in Europe. The abundance of spectrum in these bands creates new opportunities for the design of mechanisms and features that can support the emerging bandwidth-intensive and latency-sensitive applications. However, coexistence of unlicensed devices both with the bands’ incumbent users and across different unlicensed RATs present significant challenges. In this paper, we provide a comprehensive survey of the existing literature on various issues surrounding the operations of unlicensed RATs in the 6 GHz bands. In particular, we discuss how key features in next-generation Wi-Fi are being designed to leverage these additional unlicensed bands. We also shed light on the foreseeable challenges that designers of unlicensed RATs might face in the near future. Our survey encompasses key research papers, contributions submitted to standardization bodies and regulatory agencies, and documents presented at various other venues. Finally, we highlight a few key research problems that are likely to arise due to unlicensed operations in the 6 GHz bands. Tackling these research challenges effectively will be critical in ensuring that the new unlicensed bands are efficiently utilized while guaranteeing the interference-free operation of the bands’ incumbent users.

    [Download | arXiv | IEEE Xplore]
  2. With the rising interest in autonomous vehicles, developing radio access technologies (RATs) that enable reliable and low latency vehicular communications has become of paramount importance. Dedicated Short Range Communications (DSRC) and Cellular V2X (C-V2X) are two present-day technologies that are capable of supporting day-1 vehicular applications. However, these RATs fall short of supporting communication requirements of many advanced vehicular applications, which are believed to be critical in enabling fully autonomous vehicles. Both DSRC and C-V2X are undergoing extensive enhancements in order to support advanced vehicular applications that are characterized by high reliability, low latency, and high throughput requirements. These RAT evolutions—IEEE 802.11bd for DSRC and NR V2X for CV2X—can supplement today’s vehicular sensors in enabling autonomous driving. In this paper, we survey the latest developments in the standardization of 802.11bd and NR V2X. We begin with a brief description of the two present-day vehicular RATs. In doing so, we highlight their inability to guarantee the quality of service requirements of many advanced vehicular applications. We then look at the two RAT evolutions, i.e., IEEE 802.11bd and NR V2X and outline their objectives, describe their salient features and provide an in-depth description of key mechanisms that enable these features. While both, IEEE 802.11bd and NR V2X, are in their initial stages of development, we shed light on their preliminary performance projections and compare and contrast the two evolutionary RATs with their respective predecessors.

    [Download | arXiv | IEEE Xplore]
  3. As the 2.4 GHz spectrum band has become significantly congested, there is growing interest from the Wi-Fi proponents, cellular operators, and other stakeholders to use the spectrum in the 5 GHz bands. The 5 GHz bands have emerged as the most coveted bands for launching new wireless applications and services, because of their relatively favorable propagation characteristics and the relative abundance of spectrum therein. To meet the exploding demand for more unlicensed spectrum, regulators across the world such as the United States (US) Federal Communications Commission (FCC) and the European Electronic Communications Committee (ECC) have recently started considerations for opening up additional spectrum in the 5 GHz bands for use by unlicensed devices. Moreover, to boost cellular network capacity, wireless service providers are considering the deployment of unlicensed Long Term Evaluation (LTE) in the 5 GHz bands. This and other emerging wireless technologies and applications have resulted in likely deployment scenarios where multiple licensed and unlicensed networks operate in overlapping spectrum. This paper provides a comprehensive overview of the various coexistence scenarios in the 5 GHz bands. In this paper, we discuss coexistence issues between a number of important wireless technologies—viz., LTE and Wi-Fi, radar and Wi-Fi, Dedicated Short Range Communication (DSRC) and Wi-Fi, and coexistence among various 802.11 protocols operating in the 5 GHz bands. Additionally, we identify and provide brief discussions on an impending coexistence issue – one between Cellular V2X and DSRC/Wi-Fi. We summarize relevant standardization initiatives, explain existing coexistence solutions, and discuss open research problems.

    [Download | IEEE Xplore]
  4. One of the major impediments to providing broadband connectivity in semi-urban and rural India is the lack of robust and affordable backhaul. Fiber connectivity in terms of backhaul that is being planned (or provided) by the Government of India would reach only till rural offices (named Gram Panchayat) in the Indian rural areas. In this exposition, we articulate how TV white space can address the challenge in providing broadband connectivity to a billion plus population within India. The villages can form local Wi-Fi clusters. The problem of connecting the Wi-Fi clusters to the optical fiber points can be addressed using a TV white space based backhaul (middle-mile) network.

    The amount of TV white space present in India is very large when compared with the developed world. Therefore, we discuss a backhaul architecture for rural India, which utilizes TV white spaces. We also showcase results from our TV white space testbed, which support the effectiveness of backhaul by using TV white spaces. Our testbed provides a broadband access network to rural population in thirteen villages.The testbed is deployed over an area of 25km2 , and extends seamless broadband connectivity from optical fiber locations or Internet gateways to remote (difficult to connect) rural regions. We also discuss standards and TV white space regulations, which are pertinent to the backhaul architecture mentioned above.

    [arXiv | IEEE Xplore]


  1. Multi Link Aggregation (MLA) is a feature likely to be introduced in Wi-Fi 7, the next-generation of Wi-Fi, which will be based on the IEEE 802.11be specifications. MLA will allow Wi-Fi devices that support multiple bands (such as the 2.4 GHz, 5 GHz, and 6 GHz bands) to operate on them simultaneously. The resulting throughput and latency gains are likely to bring Wi-Fi one step closer to supporting emerging real-time applications like augmented and virtual reality. While throughput gains resulting from the use of MLA are mostly linear, the latency gains exhibit interesting characteristics and are the subject of this paper. We use our in-house simulator to study the latency enhancements resulting from MLA and seek to answer whether Wi-Fi 7 devices can meet the challenging latency requirements demanded by most real-time applications. In this pursuit, we observe that allowing Wi-Fi devices to contend on even a single additional link without changing any physical layer parameters can lead to an order of magnitude improvement in the worst-case latency in many scenarios. In addition, we highlight that even in dense conditions, MLA can help Wi-Fi devices meet the challenging latency requirements of most real-time applications.

    [Download | IEEE Xplore]
  2. Regulators in the US and Europe have stepped up their efforts to open the 6~GHz bands for unlicensed access. The two unlicensed technologies likely to operate and coexist in these bands are Wi-Fi 6E and 5G New Radio Unlicensed (NR-U). The greenfield 6~GHz bands allow us to take a fresh look at the coexistence between Wi-Fi and 3GPP-based unlicensed technologies. In this paper, using tools from stochastic geometry, we study the impact of Multi User Orthogonal Frequency Division Multiple Access, i.e., MU OFDMA---a feature introduced in 802.11ax---on this coexistence issue. Our results reveal that by disabling the use of the legacy contention mechanism (and allowing only MU OFDMA) for uplink access in Wi-Fi 6E, the performance of both NR-U networks and uplink Wi-Fi 6E can be improved. This is indeed feasible in the 6~GHz bands, where there are no operational Wi-Fi or NR-U users. In so doing, we also highlight the importance of accurate channel sensing at the entity that schedules uplink transmissions in Wi-Fi 6E and NR-U. If the channel is incorrectly detected as idle, factors that improve the uplink performance of one technology contribute negatively to the performance of the other technology.

    [Download | IEEE Xplore]
  3. The 3rd Generation Partnership Project (3GPP) is actively designing New Radio Vehicle-to-Everything (NR V2X)—--a 5G NR-based technology for V2X communications. NR V2X, along with its predecessor Cellular V2X (C-V2X), is set to enable low-latency and high-reliability communications in high-speed and dense vehicular environments. A key reliability-enhancing mechanism that is available in C-V2X and is likely to be re-used in NR V2X is packet re-transmissions. In this paper, using a systematic and extensive simulation study, we investigate the impact of this feature on the system performance of C-V2X. We show that statically configuring vehicles to always disable or enable packet re-transmissions either fails to extract the full potential of this feature or leads to performance degradation due to increased channel congestion. Motivated by this, we propose and evaluate Channel Congestion-based Re-transmission Control (C2RC), which, based on the observed channel congestion, allows vehicles to autonomously decide whether or not to use packet re-transmissions without any role of the cellular infrastructure. Using our proposed mechanism, C-V2X-capable vehicles can boost their performance in lightly-loaded environments, while not compromising on performance in denser conditions.

    [Download | IEEE Xplore | Slides]
  4. The 5.9 GHz band has been earmarked in many countries for Intelligent Transportation Systems (ITS) applications. Cellular V2X (C-V2X)---a recently developed access technology for vehicle-to-everything (V2X) communications---is a candidate technology to provision ITS applications using the 5.9~GHz band. Due to the ever-increasing popularity of Wi-Fi and search for additional unlicensed bands, in the US and Europe, regional regulators have previously considered allowing co-channel Wi-Fi operations in the ITS band on a secondary basis to the incumbent ITS technology. Additionally, there are several Wi-Fi channel configurations, some already in operation while others still under consideration, which place Wi-Fi and C-V2X devices in adjacent bands. It is, therefore, likely that C-V2X users may be susceptible to interference from Wi-Fi devices operating both in co-channel scenarios and in adjacent bands. To make an informed decision on future Wi-Fi channelization in and around the ITS band, a detailed study on the impact of these Wi-Fi transmissions on the system performance of C-V2X is extremely essential. In this paper, through a comprehensive and systematic simulation study, we investigate the impact of Wi-Fi transmissions on the performance of C-V2X, both in co-channel and adjacent channel scenarios. Our simulations reveal that if Wi-Fi devices are to coexist with C-V2X in the same spectrum, existing mechanisms either fall short of sufficiently protecting C-V2X performance or render the spectrum unusable for Wi-Fi operations. On the other hand, all Wi-Fi channels that are adjacent to the ITS band can significantly degrade the system-wide C-V2X performance. In such scenarios, to adequately protect the C-V2X network performance, either certain restrictions need to be put in place on Wi-Fi operations, or the operations of Wi-Fi in such channels must be prohibited.

    [Download | IEEE Xplore | Slides]
  5. One of the notable features of the upcoming Wireless Fidelity (Wi-Fi) standard---namely, IEEE 802.11ax---is the use of Multi-User Orthogonal Frequency Division Multiple Access (MU-OFDMA). MU-OFDMA facilitates multiple users to transmit simultaneously in smaller sub-channels (a.k.a. resource units (RUs)), thereby improving the 802.11ax MAC efficiency. The 802.11ax MAC enables MU-OFDMA transmissions in the uplink (UL) by using two types of RUs: i) Random Access (RA) RUs, and ii) Scheduled Access (SA) RUs. In this paper, we investigate the impact of different distributions of RA RU and SA RU on the MAC layer performance. We leverage our analysis in devising a practical UL RU allocation scheme that maximizes the overall 802.11ax network throughput. We implement the 802.11ax MAC in network simulator-3 (NS-3) and perform extensive simulations to validate the efficacy of our proposed scheme.

    [Download | IEEE Xplore]
  6. With the new emerging throughput-intensive ultralow latency applications, there is a need for a transport layer protocol that can achieve high throughput with low latency. One promising candidate is TCP BBR, a protocol developed by Google, with the aim of achieving high throughput and low latency by operating around the Bandwidth Delay Product (BDP) of the bottleneck link. Google reported significant throughput gains and much lower latency relative to TCP Cubic following the deployment of BBR in their high-speed wide area wired network. As most of these emerging applications will be supported by Millimeter Wave (mmWave) wireless networks, BBR should achieve both high throughput and ultra-low latency in these settings. However, in our preliminary experiments with BBR over a mmWave wireless link operating at 60 GHz, we observed a severe degradation in throughput that we were able to attribute to high delay variation on the link. In this paper, we show that “throughput collapse” occurs when BBR's estimate of minimum RTT is less than half of the average RTT of the uncongested link (as when delay jitter is large). We demonstrate this phenomenon and explain the underlying reasons for it using a series of controlled experiments on the CloudLab testbed. We also present a mathematical analysis of BBR, which matches our experimental results closely. Based on our analysis, we propose and experimentally evaluate potential solutions that can overcome the throughput collapse without addina sianificant latency.

    [IEEE Xplore]
  7. IEEE 802.11ax is the upcoming standard of the IEEE 802.11 wireless local area networks (WLAN) family. Until its most recent standard, i.e. 802.11ac, the primary focus of the 802.11 Working Group has been to increase the overall throughput of the physical (PHY) layer using innovative mechanisms such as multi-user multiple input multiple output (MU- MIMO), higher order modulation and coding schemes etc. However, these PHY layer gains often fail to translate to high throughput at the medium access control (MAC) layer, particularly in dense deployment scenarios. To address this limitation, IEEE 802.11ax introduces new features, most notably the use of Orthogonal Frequency Division Multiple Access (OFDMA), thereby enabling concurrent MU transmissions. In this paper, we first provide an overview of the uplink MU OFDMA in IEEE 802.11ax. Second, we provide an analytical model for characterizing the performance of the 802.11ax MAC layer. We investigate the trade-off between providing high network throughput and supporting new users using a metric-namely, BSR delivery rate. Finally, we validate our analyses using extensive NS-3 simulations, and present the resulting findings.

    [Download | IEEE Xplore | Slides]
  8. To adequately support high-throughput applications in next-generation WLANs, more spectrum will be needed to accommodate wider channels. To address this issue, spectrum regulators and stakeholders from the wireless industry and the intelligent transportation system communities are exploring possible band sharing approaches in the 5.9 GHz band. Such approaches include techniques that enable the harmonious coexistence of Dedicated Short Range Communications (DSRC) networks and IEEE 802.11ac networks. In this paper, we provide in-depth discussions on how the coexistence of DSRC and 802.11ac impacts the performance of DSRC applications, with a particular focus on vehicular safety applications. We propose an analytical model that provides valuable insights on DSRC network performance and its vulnerability to interference induced by other DSRC nodes as well as 802.11ac nodes. Using the analytical results derived from the model and extensive simulation results, we also propose a methodology for adjusting 802.11ac parameters that enables a DSRC network to meet the performance requirements of safety applications. Using simulations, we also analyze the throughput of the coexisting 802.11ac network.

    [Download | IEEE Xplore | Slides]
  9. The 5.9 GHz band is being actively explored for possible spectrum sharing opportunities between Dedicated Short Range Communications (DSRC) and IEEE 802.11ac networks in order to address the increasing demand for bandwidth-intensive Wi-Fi applications. In this paper, we study the implications of this spectrum sharing to the performance of Wi-Fi systems. Through experiments performed on our testbed, we first investigate band sharing options available for Wi-Fi devices. Using experimental results, we show the need for using conservative Wi-Fi transmission parameters to enable harmonious coexistence between DSRC and Wi-Fi. Moreover, we show that under the current 802.11ac standard, certain channelization options, particularly the high bandwidth ones, cannot be used by Wi-Fi devices without causing interference to the DSRC nodes. Under these constraints, we propose a Real-time Channelization Algorithm (RCA) for Wi-Fi Access Points (APs) operating in the shared spectrum. Evaluation of the proposed algorithm using a prototype implementation on commodity hardware as well as via simulations show that informed channelization decisions can significantly increase Wi-Fi throughput compared to static channelization schemes.

    [Download | IEEE Xplore | Slides]
  10. Cooperative transmit beamforming (CTB) is a practical approach for addressing the challenging problem of spectrum scarcity in broadband 5G wireless communication systems. It is a technique that allows a group of secondary users (SUs), each equipped with a single omni-directional antenna, to collaborate and steer the signal towards the intended receiver. CTB allows SUs to co-exist with primary users in the same spectrum, which helps to significantly improve the efficiency of spectrum utilization. One of the key factors that affect the performance of CTB is the selection of participatory nodes. In this paper, we first formulate the CTB as an optimization problem, and then investigate the impact of different node-selection schemes on the performance of CTB. Our findings illustrate that exhaustive search based optimal node-selection scheme is computationally infeasible for real-time systems, while simple random-selection and highest-channel-state based selection often result in poor performance. Motivated by these findings, we propose a computationally efficient node-selection scheme for CTB that achieves a near-optimal performance. The proposed scheme is based on iterative node-replacement and is computationally scalable to large system size. Results from extensive simulations show that the proposed scheme asymptotically approaches the exhaustive search based optimal system performance. In our example, the performance of the proposed scheme is approximately 98.5% of the optimal system performance while limiting the required computations to only 1.67%.

    [IEEE Xplore]
  11. TV white space (TVWS) geolocation database is being used for the protection of the terrestrial TV broadcast receivers, and the coexistence of secondary devices. To the best of our knowledge, though TV White Space calculations are available, an active online database does not exist for India. In this paper, the development of the first TVWS database for India is detailed and is released for public access. A standardized protocol to access the TVWS database on a readily available hardware platform is implemented. A hardware prototype, which is capable of querying the TVWS database and operating in the TV band without causing harmful interference to the TV receivers in UHF TV bands, is developed. The source code of our implementation has been released under the GNU general public license version 2.0.

    [IEEE Xplore]
  12. Licensed but unutilized television (TV) band spectrum is called as TV white space in the literature. Ultra high frequency (UHF) TV band spectrum has very good wireless radio propagation characteristics. The amount of TV white space in the UHF TV band in India is of interest. Comprehensive quantitative assessment and estimates for the TV white space in the 470-590 MHz band for four zones of India (all except north) are presented in this work. This is the first effort in India to estimate TV white spaces in a comprehensive manner. The average available TV white space per unit area in these four zones is calculated using two methods: (i) the primary (licensed) user and secondary (unlicensed) user point of views; and, (ii) the regulations of Federal Communications Commission in the United States. By both methods, the average available TV white space in the UHF TV band is shown to be more than 100 MHz! A TV transmitter frequency reassignment algorithm is also described. Based on spatial-reuse ideas, a TV channel frequency allocation scheme is presented which results in insignificant interference to the TV receivers while using the smallest bandwidth for existing transmission across the four zones. In the proposed reassignment, it is found that four TV band channels (or 32 MHz) are sufficient to provide the existing UHF TV band coverage in India.

    [arXiv | Extended Version | IEEE Xplore]


  1. "Coexistence of Vehicular Communication Technologies and Wi-Fi in the 5 and 6 GHz Bands" Doctoral Dissertation, Virginia Tech, USA, October 2020.
    [Download | Slides]
  2. "On the Feasibility of Providing Affordable Broadband Services using Backhaul in TV White Spaces" Masters Thesis, Indian Institute of Technology Bombay, India, June 2015.