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Author: search.filters.author.Vashistha, Ankush

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    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.
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    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.
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    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.
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    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.
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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.
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    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.
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    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.
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    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.
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    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.
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    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.