Browsing by Author "Vashistha, Ankush"

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Bit error rate and outage analysis of an interference cancellation technique for cooperative spectrum sharing cognitive radio systems
(The Institution of Engineering and Technology, 2016-08) Vashistha, Ankush
In this study, an overlay spectrum sharing scheme has been proposed for a cognitive radio system. To achieve the desired quality of service for the licenced (i.e. primary) system and spectrum access for unlicenced (i.e. secondary) system, a three-phase cooperative decode and forward relaying is used. Furthermore, space–time block coding is used in order to cancel the interference at primary as well as secondary receiver. It has been shown that the proposed scheme helps in achieving diversity gain of three and two for primary and secondary systems, respectively. The performance of both primary and cognitive (secondary) system is appraised by deriving closed-form expression for bit error rate and outage probability. The theoretical and simulation results validate that the proposed scheme improves the performance of both systems as compared with the earlier proposed schemes.
Cooperative spectrum sharing using transmit antenna selection for cognitive radio systems
(Springer, 2015-10) Vashistha, Ankush
In this paper, a spectrum sharing scheme that utilizes the two-phase cooperative decode-and-forward relaying protocol is proposed. The cooperation between primary (i.e. licensed) and secondary (i.e. unlicensed) system helps in achieving the desired target rate for the primary system and spectrum access for cognitive (i.e. secondary) system. In the proposed scheme, secondary transmitter which is equipped with multiple antennas uses transmit antenna selection to improve the primary’s performance by reducing the interference level of secondary signal at primary receiver, while keeping the performance of secondary system unaffected. Closed form expressions for outage probability have been derived for both systems by varying transmit power level at secondary transmitter. The theoretical results have been compared with simulation results to validate the analysis done in this paper.
Defending 5G networks against DDOS attacks using quarantine slice manager architecture
(IEEE, 2024) Vashistha, Ankush
The emergence of 5G technology has opened up new possibilities in the realm of digital applications. However, these technological leaps forward also bring about heightened security risks. This paper investigate the impact of Distributed Denial of Service (DDoS) attacks on 5G network slicing. We introduce a distinctive threat model, tailored specifically for 5G networks. In an effort to combat these vulnerabilities, we present a Quarantine Slice Manager architecture, a two-level hierarchical and distributed network design, capable of effective slice management and prompt response to potential threats. We use an experimental setup consisting of a simulated Radio Access Network (RAN) and an emulated 5G core network to examine the impact of attack to three different network slices—eMBB, uRLLC, and mMTC—under a DDoS attack. Through a series of simulated attack scenarios, we conduct an extensive performance analysis of our system, thereby highlighting the critical importance of securing control plane functions, such as the AMF, for overall network robustness.
E-DTDOA based localization for wireless sensor networks with clock drift compensation
(IEEE, 2020) Vashistha, Ankush
A high time resolution localization scheme, using ultra-wide band ranging signal with bandwidth of 2GHz, is proposed for a fully asynchronous wireless sensor network (WSN). The proposed scheme is specifically useful for sensor nodes which are designed to operate at very low ADC sampling rate, in the order of 2-3 MHz, but still achieves the sampling resolution in the order of sub-nanoseconds. To achieve low sampling rate, equivalent time sampling (ETS) technique is used at the sensor nodes. Reconstructed signal obtained by ETS technique, that require periodic transmission of the same signal repetitively, is severely affected by the variation in transmitter and receiver clock drift as against the real time sampling where the variations are due to receiver node clock drift only. Thus, it requires a protocol to precisely estimate the transmitter and receiver clock parameters. A scheme, which uses a novel mathematical equivalent time of arrival (E-TOA) model for ETS based system, for clock drift estimation is presented. Based on clock drift estimation parameters, receiver nodes are tuned to the same frequency. E-TOA measurements are further used to propose an equivalent differential time difference of arrival (E-DTDOA) based ranging algorithm, which relaxed the time synchronization requirement between the wireless nodes, and still achieving high time resolution. The E-DTDOA range measurements are subsequently used to obtain precise localization of the target node/s. The feasibility of the algorithm proposed is demonstrated experimentally using in house designed wireless sensor nodes.
Exploiting multiple antenna cognitive radio system for cooperative spectrum sharing
(IEEE, 2015) Vashistha, Ankush
This paper proposes a cooperative spectrum sharing scheme in which multiple antennas of a secondary (aka cognitive) system is exploited to nullify the interference from the primary (aka licensed) to secondary system and vice versa. The secondary system also acts as a "decode-and-forward" relay for the primary system thus boosting its performance. The performance of primary and secondary system is analyzed by obtaining the closed form expressions for outage probability. The simulation results are also shown to validate the theoretical expressions obtained in this paper.
High precision UWB-IR indoor positioning system for IoT applications
(IEEE, 2018-05) Vashistha, Ankush
This paper presents the design and implementation of an ultra-wideband impulse radio based indoor positioning system and its architecture. The operating mechanism of the complete system along with its hardware and software details are discussed. The system exploits the differential time difference of arrival technique for position estimation. Simulation and experimental results demonstrating the working of this in-house developed positioning system are provided. Good positioning accuracy of around 30 cm has been achieved from the implemented system for line-of-sight setting in a 7 m × 7 m indoor office environment.
IRS-assisted access link-based multihop THz communication
(IEEE, 2024) Vashistha, Ankush
This paper proposes an amplify-and-forward (AF)-based multihop THz backhaul communication integrated with an access THz link. The access link is assisted with an intel-ligent reflecting surfaces (IRS) with an aim to deal with the impediments in THz communication environment. The statistical analysis is presented by deriving the probability density function (PDF) and cumulative distribution function (CDF) of the in-stantaneous signal-to-noise ratio (SNR) for the proposed system. The combined effect of path loss, atmospheric attenuation, and generalized fading is considered for modelling the THz channel. Furthermore, with the aid of PDF and CDF statistics, we propose the exact expressions for outage probability and develop asymptotic analysis in high SNR regime. The simulations are presented to validate the exact analysis and to study various design aspects for the proposed system.
Multiple antenna-based THz communication system with channel correlation
(IEEE, 2024) Vashistha, Ankush
To minimize environmental impairments and channel fading in the THz band, this paper examines a multiple antenna-based THz communication system. The combined effects of path loss, molecular absorption, and statistical fading are considered for the THz system. A comprehensive correlation structure is utilized that uniquely determines the joint probability density function of the THz channel model. The considered correlation structure is a generalization of the correlation models based on hyper-power or power-correlation. The statistical characterizations of channel correlation for the combining schemes such as maximal ratio combining (MRC), selection combining (SC), and equal gain combining (EGC) are presented at the THz receiver. The asymptotic expressions are proposed for the outage probability for the mentioned diversity schemes. The obtained expressions are expressed in closed-form and are highly accurate in the high signal-to-noise ratio (SNR) region. From the analysis, diversity order and degradation due to correlation are determined. The obtained asymptotic expressions enable the easy estimation of the performance especially for more number of antennas, where Monte Carlo simulation takes a long time to execute. Additionally, presented results reveal the factors that can be utilized to optimize the system performance.
A novel E-DTDOA based one-way ranging using uwb-ir with unsynchronized anchors
(IEEE, 2021) Vashistha, Ankush
In this article, a novel analytical equation is proposed to determine the equivalent time of arrival (E-TOA) for achieving sub-ns resolution, with much reduced analog-to-digital converter sampling frequency (in the order of 2-3 MHz). The timing information is extracted from high resolution channel impulse response, which is obtained using an equivalent time sampling (ETS) technique. The proposed E-TOA equation is different from the conventional real-time sampling equation due to the presence of an additional transmitter clock drift, and thus sensitive to both the transmitter and receiver clock drift variations. The validation of the E-TOA equation is carried out numerically using simulations along with experimental validation. The effect of timing uncertainties relating to the transmitter clock start time and the receiver clock offset is analyzed with variations in the transmitter and receiver clock drifts. With E-TOA measurements, an equivalent differential time difference of arrival based one-way ranging scheme for unsynchronized anchors is further proposed. It is thus demonstrated, using in house designed sensor nodes, that high ranging accuracy, in the order of few centimeters, can be achieved by utilizing the proposed analytical E-TOA technique, even with low sampling rate.
On the performance of multiple antenna cooperative spectrum sharing protocol under Nakagami-m fading
(IEEE, 2015-12) Vashistha, Ankush
In a cooperative spectrum sharing (CSS) protocol, two wireless systems operate over the same frequency band albeit with different priorities. The secondary (or cognitive) system which has a lower priority, helps the higher priority primary system to achieve its target rate by acting as a relay and allocating a fraction of its power to forward the primary signal. The secondary system in return is benefited by transmitting its own data on primary system's spectrum. In this paper, we have analyzed the performance of multiple antenna cooperative spectrum sharing protocol under Nakagami-m Fading. Closed form expressions for outage probability have been obtained by varying the parameters m and Ω of the Nakagami-m fading channels. Apart from above, we have shown the impact of power allocation factor (α) and parameter m on the region of secondary spectrum access, conventionally defined as critical radius for the secondary system. A comparison between theoretical and simulated results is also presented to corroborate the theoretical results obtained in this paper.
Outage analysis of a multiple-antenna cognitive radio system with cooperative decode-and-forward relaying
(IEEE, 2014-12) Vashistha, Ankush
In this paper, we analyze a two-phase hierarchical spectrum sharing protocol based on cooperative decode and forward relay transmission wherein it is assumed that the cognitive (i.e secondary) system is equipped with multiple antennas. The performance of the licensed (i.e. primary) as well as cognitive system is quantified by deriving the closed form expressions for outage probability. The theoretical and simulation results show that by exploiting multiple antennas at secondary transmitter (ST), we can drastically improve the performance of both primary and secondary systems as compared to conventional spectrum sharing schemes.
Robot tele-operations with 5G NR sidelink
(IEEE, 2025) Vashistha, Ankush
5G New Radio (NR) sidelink, introduced in 3GPP Release 16, facilitates direct device-to-device communication, enabling robots to operate independently of traditional cellular networks. As industries increasingly adopt robotic solutions for remote operations, the need for reliable, low-latency communication has become paramount. This paper presents an experimental demonstration of robot tele-operations utilizing 5G NR sidelink technology. Our demonstration showcases the effectiveness of NR sidelink in enhancing robotic tele-operation by integrating real-time video streaming capabilities. We performed a series of experiments in dynamic environments to evaluate the responsiveness, video quality, and operational efficiency of robotic systems utilizing 5G NR sidelink. The results indicate that the low latency and high data rates provided by 5G NR sidelink significantly improve the operator's ability to control robotic systems, particularly in challenging scenarios
Self calibration of the anchor nodes for UWB-IR TDOA based indoor positioning system
(IEEE, 2018-02) Vashistha, Ankush
The problem of anchor nodes placement in indoor positioning systems is labor intensive and time consuming process. A self-calibrating scheme is proposed to determine the position of the anchor nodes using Ultra-Wide band impulse radio (UWB-IR). These positions can be further used to determine the position of the target nodes. The time difference of arrival measurement technique is employed to self-calibrate the anchor nodes. The proposed scheme is verified with the simulation results, as well as with an in house designed sensor nodes experimental setup.
A TDOA measurement technique for asynchronous indoor localization system using UWB-IR
(IEEE, 2016) Vashistha, Ankush
In this paper we have proposed a Time Difference of Arrival (TDOA) measurement scheme for practical asynchronous systems using low cost low power target nodes (called tags). The system performs localization of transmit only tags using an ultra wide band Impulse radio (UWB - IR). We use a known location reference node for synchronization between the receiving (or anchor) nodes. The clock of the reference node is considered to be a perfect clock whereas clocks of all other nodes, anchor nodes as well as target node, is assumed to imperfect. We formulated the equations to synchronize the clocks of the anchor nodes and estimate the TDOA range measurements between the anchor nodes. The equations were analyzed with the practical measurement results.