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122 results on '"Khan, Bilal"'

17. Statistical Digital Predistortion of 5G Millimeter-Wave RF Beamforming Transmitter Under Random Amplitude Variations.

Author

Khan, Bilal, Tervo, Nuutti, Jokinen, Markku, Parssinen, Aarno, and Juntti, Markku

Subjects
*TRANSMITTERS (Communication), *FREQUENCY modulation transmitters, *BEAMFORMING, *PHASE shifters, *PHASED array antennas, *5G networks, *POWER amplifiers
Abstract

The nonlinearity of the fifth-generation (5G) millimeter-wave (mmWave) phased array transmitter (TX) depends on the variations in the beamforming coefficients, e.g., due to unwanted amplitude errors of the phase shifters or purposely introduced amplitude variations to shape the beam, as well as other analog component variations. Therefore, also the digital predistortion (DPD) coefficients depend on the beamforming coefficients and require a continuous update for different beamsteering directions in a conventional DPD. We propose a robust DPD approach that uses the average array response for DPD training. The average array response is estimated using the known experimental histogram of power amplifier (PA) input power variation resulting from the amplitude variations due to beamforming. The DPD training based on the average array response makes the DPD coefficients insensitive to beamforming variations. The proposed DPD strategy requires a shared feedback path for training and only a single set of DPD coefficients to linearize the array response in all beamsteering directions. The performance of the proposed DPD strategy is validated by over-the-air (OTA) measurements of a 28-GHz phased array TX over different steering angles. Experimental results show that the proposed DPD method using one set of DPD coefficients provides similar linearization performance across the steering angles compared with the DPD trained to all steering angles through the OTA reference antenna. [ABSTRACT FROM AUTHOR]

Published
2022
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21. Novel Framework for Outdoor Mobility Assistance and Auditory Display for Visually Impaired People

Author

Khan, Wasiq, Hussain, Abir, Khan, Bilal, Nawaz, Raheel, Baker, Thar, Khan, Wasiq, Hussain, Abir, Khan, Bilal, Nawaz, Raheel, and Baker, Thar

Abstract

Outdoor mobility of Visually Impaired People (VIPs) has always been challenging due to the dynamically varying scenes and environmental states. Variety of systems have been introduced to assist VIPs’ mobility that include sensor mounted canes and use of machine intelligence. However, these systems are not reliable when used to navigate the VIPs in dynamically changing environments. The associated challenges are the robust sensing and avoiding diverse types of obstacles, dynamically modelling the changing environmental states (e.g. moving objects, road-works), and effective communication to interpret the environmental states and hazards. In this paper, we propose an intelligent wearable auditory display framework that will process real-time video and multi-sensor data streams to: a) identify the type of obstacles, b) recognize the surrounding scene/objects and corresponding attributes (e.g. geometry, size, shape, distance from user), c) automatically generate the descriptive information about the recognized obstacle/objects and attributes, d) produce accurate, precise and reliable spatial information and corresponding instructions in audio-visual form to assist and navigate VIPs safely with or without the assistance of traditional means.

Published
2020

27. Brain Computer Interface Implementation on Cognitive States

Author

Shah, Bilal Hussain, primary, Sultan, Zamra, additional, Rizvi, Zeeshan, additional, Iqbal, Munnaza, additional, Zaheer, Usama Bin, additional, Huzaif Shah, Syed, additional, Khaliq, Samiya, additional, Zia, Shahrukh, additional, Khan, Bilal Muhammad, additional, and Haider Zaidi, Sajjad, additional

Published
2020
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32. Combined Sidelobe Reduction and Omnidirectional Linearization of Phased Array by Using Tapered Power Amplifier Biasing and Digital Predistortion.

Author

Tervo, Nuutti, Khan, Bilal, Aikio, Janne P., Kursu, Olli, Jokinen, Markku, Leinonen, Marko E., Sonkki, Marko, Rahkonen, Timo, and Parssinen, Aarno

Subjects
*PHASED array antennas, *TRANSMITTERS (Communication), *POWER amplifiers, *LINEAR antenna arrays, *RADIO frequency, *BEAM steering, *SIGNAL processing
Abstract

Power amplifier (PA) efficiency and linearity are among the key drivers to reduce energy consumption while enabling high data rates in the fifth-generation (5G) millimeter-wave phased array transmitters. Analog per-branch phase and amplitude control is used to steer the beam, suppress the sidelobes, and form zeros to the desired spatial directions. The amplitude control of individual PA inputs makes nonlinearity vary from antenna to antenna, which challenges the common digital predistortion (DPD) used to linearize the array. In this article, we implement an amplitude control for beamforming by tuning the PA gate bias. Varying the output powers via PA biasing makes the nonlinear characteristics observed at the individual PA outputs similar that helps the array DPD to linearize also individual PAs. The technique is validated by both simulations and measurements. As a measurement platform, we use a 28-GHz phased array transceiver equipped with 64 antenna elements and 16 radio frequency chains. The desired beam shape is synthesized by controlling the per-antenna over-the-air-power with PA gate bias. Then, the system is linearized by training DPD with a reference antenna. The DPD is demonstrated with 100-MHz-wide 5G new radio modulated waveform. The best example case showed −23.5-dB maximum sidelobe level (SLL) with 4.9% error vector magnitude and −40.8-dB total radiated adjacent channel power ratio with DPD. The proposed approach enables simultaneous reduction of beam pattern SLL, achieves good linearity in all directions, and maintains the PA efficiency. [ABSTRACT FROM AUTHOR]

Published
2021
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40. An Iris based Smart System for Stress Identification

Author

Haider, Amna, primary, Hussain, Tassadaq, additional, Agha, Areeb, additional, Khan, Bilal, additional, Rashid, Fawad, additional, Muzamil, Sohail, additional, Taleb Ahmed, Abdelmalik, additional, Alharbi, Soltan Abed, additional, and Ayguade, Eduard, additional

Published
2019
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44. Retraction Notice: An Iris based Lungs Pre-diagnostic System

Author

Hussain, Tassadaq, primary, Haider, Amna, additional, Muhammad, Abdul Malik, additional, Agha, Areeb, additional, Khan, Bilal, additional, Rashid, Fawad, additional, Raza, Muhammad Saad, additional, Din, Moainud, additional, Khan, Mehran, additional, Ullah, Sami, additional, Ahmed, Abdelmalik Taleb, additional, and Ayguade, Eduard, additional

Published
2019
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45. An Iris based Lungs Pre-diagnostic System

Author

Hussain, Tassadaq, primary, Haider, Amna, additional, Muhammad, Abdul Malik, additional, Agha, Areeb, additional, Khan, Bilal, additional, Rashid, Fawad, additional, Raza, Muhammad Saad, additional, Din, Moainud, additional, Khan, Mehran, additional, Ullah, Sami, additional, Ahmed, Abdelmalik Taleb, additional, and Ayguade, Eduard, additional

Published
2019
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49. Digital Predistortion of Phased-Array Transmitter With Shared Feedback and Far-Field Calibration.

Author

Tervo, Nuutti, Khan, Bilal, Kursu, Olli, Aikio, Janne P., Jokinen, Markku, Leinonen, Marko E., Juntti, Markku, Rahkonen, Timo, and Parssinen, Aarno

Subjects
*PHASED array antennas, *TRANSMITTERS (Communication), *PSYCHOLOGICAL feedback, *CALIBRATION, *POWER amplifiers, *SIGNAL processing, *MIMO radar
Abstract

Digital predistortion (DPD) of a phased array requires that multiple transmit paths must be measured by a feedback (FB) receiver (Rx). In this article, we propose an FB concept for DPD in a time-division-duplex (TDD) phased arrays. We use a single FB line to collect the waveform samples from the parallel transmit paths to the FB Rx. The TDD switches are used to enable and disable individual transmit paths. The FB is calibrated by comparing the FB outputs from individual power amplifiers (PAs) to over-the-air (OTA) measurement reference performed with a frequency-modulated continuous-wave (FMCW) signal. The individual PA measurements are postequalized before the DPD training to model the far-field signal. Three alternative strategies are considered for training the DPD through the calibrated FB line and compared with the OTA DPD. The performance is verified by OTA measurements of a 28-GHz phased-array transmitter and with fifth-generation new radio waveform in terms of total radiated adjacent channel power ratio (TRACPR), cumulative absolute ACP (CACP), and main lobe error vector magnitude (EVM). The best EVM and ACPR performance is achieved by the strategy where the individual PA responses are treated independently. The methods were comparable to the OTA DPD performance, achieving all < −37-dB TRACPR, −29-dBm/MHz CACP, and ≤7 % EVM. [ABSTRACT FROM AUTHOR]

Published
2021
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