Study of C-V2X & coexistence with Wi-Fi
C-V2X is a vehicle-to-everything (V2X) communications technology developed by 3GPP and standardized in it's Rel. 14 in 2017. The development of it's evolution---NR V2X---is now underway, and is expected to be standardized by Dec. 2019. In this project, we look at several issues surrounding the performance of C-V2X, especially in the sidelink mode 4, i.e. scenarios where C-V2X-equipped vehicles operate outside cellular coverage. We also look at the impact of Wi-Fi transmissions on C-V2X performance, both in co-channel and adjacent-channel scenarios.
- We have developed an ns-3 simulator that simulates the physical and medium access control layers of C-V2X sidelink mode 4.
- Using this simulator, we have studied the performance of C-V2X in various scenarios, i.e. urban/highway and low load/high load scenarios.
- We have also studied the impact of co-channel and adjacent-channel Wi-Fi transmissions on C-V2X performance.
Performance Analysis of IEEE 802.11ax
Description: IEEE 802.11ax is the next generation of Wi-Fi. 802.11ax is a major overhaul of it's predecessor Wi-Fi standard (802.11ac) and introduces many new features to the 802.11 family. Among these features is the use of Multi-User Orthogonal Frequency Division Multiple Access (MU-OFDMA) in the downlink and uplink. This mode of transmission is significantly different from the currently-used Carrier Sense Multiple Access (CSMA) protocol, and requires the Wi-Fi Access Point to co-ordinate transmissions among it's associated clients. The design of MU-OFDMA is challenging, especially, in the uplink where the Access Point may be unaware of the buffer occupancy status of it's clients. To facilitate this, 802.11ax introduces Uplink OFDMA-based random access (UORA), which allows ALOHA-like contention on Wi-Fi sub-channels (a.k.a. Resource Units, RUs). In this project, we look the performance of uplink OFDMA in 802.11ax.
- We perform the performance analysis of uplink MU-OFDMA in 802.11ax in the combined random access/scheduled access mode of transmission.
- We propose an algorithm to achieve the optimal balance between random access RUs and scheduled access RUs and validate the algorithm using ns-3 simulations.
- Uplink resource allocation in IEEE 802.11ax, IEEE ICC 2019.
- Performance Analysis of Uplink Multi-User OFDMA in IEEE 802.11ax, IEEE ICC 2018.
Coexistence of DSRC and Wi-Fi
Description: The 5.9 GHz band (5.85 - 5.925 GHz) has been allocated for Intelligent Transportation Systems (ITS) applications in the US. The under-utilization of this band has lead to interests in sharing the spectrum with unlicensed technologies such as Wi-Fi. Under this spectrum sharing scenario, DSRC devices will be the primary users of the spectrum, while Wi-Fi users will be allowed to use the spectrum opportunistically. In this project, we look at the impact of Wi-Fi on DSRC and vice-versa.
- Using Monte Carlo and System-level simulations, we evaluate the impact of Wi-Fi users on the system-wide performance of DSRC.
- We observe that by changing certain contention parameters of Wi-Fi transmitters (e.g. Inter-frame space), the impact of Wi-Fi users on the DSRC performance can be alleviated.
- We verify this claim using test-bed experiments and propose a real-time channelization algorithm that can be used at Wi-Fi devices in order to maximize Wi-Fi performance under the spectrum sharing scenario.
- Coexistence of DSRC and Wi-Fi: Impact on the performance of vehicular safety applications , IEEE ICC 2017.
- Coexistence of Dedicated Short Range Communications (DSRC) and Wi-Fi: Implications to Wi-Fi performance , IEEE INFOCOM 2017.
TV White Spaces in India
Description: The Ultra High Frequency (UHF) TV band is extremely lucrative in delivering services over long distances. Terrestrial TV transmitters operating in this band typically re-use frequencies over large distances, creating geographical regions where certain TV channels may be unused. These "voids" constitute TV White Spaces. In many countries, this band has been explored for delivering Internet services, especially in rural areas, where Internet coverage may be sparse. In this project, we evaluate the potential of the use of TV White Spaces in India.
- Toward Enabling Broadband for a Billion Plus Population with TV White Spaces, IEEE Communications Magazine, 2016.
- OpenPaws: An Open Source PAWS and UHF TV White Space Database Implementation for India, IEEE NCC 2015.
- Quantitative Assessment of TV White Space in India, IEEE NCC 2014.