David Koilpillai

Bio: David Koilpillai is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Payload & Van Allen radiation belt. The author has an hindex of 3, co-authored 13 publications receiving 26 citations.

Design of Electrical Power Subsystem for IITMSAT

Abstract: This paper describes the design, development and test results of the Electrical Power Subsystem (EPS) of IITMSAT — the nano-satellite project of Indian Institute of Technology Madras (IITM). IITMSAT's payload comprises of an indigenously designed and developed Space based Proton Electron Energy Detector (SPEED). It is designed to measure the high energy particle precipitations just below the Van Allen Belts. Apart from SPEED, the satellite electronics include the health monitoring sensors, attitude sensors, three 32-bit ARM microcontrollers to process the data, communication module, Beacon, Command and Data Management System (CDMS) and electromagnetic actuators (Torque Rods) to align the satellite along the Earth's local magnetic field in the Low Earth Orbit (LEO). This indigenous EPS was designed and developed using low-cost, high-performance commercial off-the-shelf (COTS) components of industrial grade, to power loads of about 6 Watts. This paper describes the satellite power requirements, EPS hardware design, simulation results followed by practical results obtained from the prototype hardware.

Performance analysis of optical front-hauling for 5G Waveforms

Abstract: Multicarrier modulation based schemes — Universally Filtered Orthogonal Frequency Division Multiplexing (UF-OFDM) and Generalized Frequency Division Multiplexing (GFDM) have emerged as potential candidate waveforms for 5G mobile communication [1]. Fronthauling (the delievry of services between centralized baseband unit (C-BBU) and radio element at antenna site) of the 5G signals in the optical domain is an obvious choice, considering the ultra-dense deployment of small cell antenna sites that will be required to provide an aggregated data rate of 1000 times larger than 4G systems with low latency, high capacity and flexibility, coupled with energy efficient low cost centralized radio access network (C-RAN) architecture [2]. Analog intermediate frequency over fiber (AIFoF) fronthauling technique provides more flexibility and uses lower bandwidth optical components compared to radio/mmW frequency signal over fiber techniques [2]. In this work, we experimentally study the suitability of optical transmission of 5G waveforms, UF-OFDM and GFDM, for fronthauling applications using an AIFoF technique, and compare their performances with OFDM.

Limited-Feedback Low-Encoding Complexity Precoder Design for Downlink of FDD Multi-User Massive MIMO Systems

Abstract: We investigate a limited feedback precoder based on symbol pairwise error probability (PEP) for a block-faded $K \times n_{t}$ downlink multiple-input multiple-output (MIMO) channel. In the considered system, $K=\lfloor n_{t}^{\alpha }\rfloor $ single-antenna users feedback quantized channel state information to the $n_{t}$ -antenna transmitter using $B$ bits per-transmit-antenna per user. We analytically show that for $\alpha , $B \geq 1$ and $n_{t}\rightarrow \infty $ , both symbol PEP and achievable rate of each of the $K$ downlink users almost surely converge to the symbol PEP and achievable rate of $K$ parallel additive white Gaussian noise (AWGN) channels, respectively. We show that the encoding complexity of the precoder is $O(n_{t}K)$ . We also show that if channel coefficients estimated by the user are corrupted by AWGN noise, the symbol PEP and achievable rate of each user almost surely converge to the symbol PEP and achievable rate in a scaled AWGN channel with $B>1$ and $n_{t}\rightarrow \infty $ . For correlated channels, we derive a condition, which enables the proposed precoder almost surely to cancel multi-user interference for large $n_{t}$ values. Finally, we numerically compare the bit error rate, encoding complexity, and per-user achievable rate of the proposed scheme with the existing designs.

Broadband to Empower Rural India

Abstract: (2007). Broadband to Empower Rural India. IETE Technical Review: Vol. 24, No. 4, pp. 195-201.

IITMSAT Communications System : A LeanSat Design Approach

Abstract: IITMSAT is a student-built nano satellite mission of Indian Institute of Technology Madras, Chennai, India. The objective is to study the precipitation of high energy electrons and protons from Van-Allen radiation belts to lower altitude of 600-900 km due to resonance interaction with low frequency EM waves. The unique communications system design of IITMSAT evolves from the challenging downlink data requirement of 1 MB per day in the UHF band posed by the mission and the satellite's payload, SPEED (Space based Proton and Electron Energy Detector). To ensure continuous downlink data stream in the short Low earth Orbit passes, a robust physical layer protocol was designed to counter time-varying aspects of a Space-Earth telecom link. For the on-board communications system, two types of design alternatives exist for each module. The first option is a custom design wherein a module is developed from scratch using discrete components.The other option is an integrated design wherein an electronics COTS module can be directly plugged into the subsystem. This module is evaluated by carrying out vibration and thermal tests. If an integrated module is low-cost and meets the design requirements, it is preferred over a custom design. In order to carry out performance tests under simulated link conditions, an RF attenuation test setup was designed that can work at extreme temperatures. Burn-In tests for 72 hours at ambient and extreme temperatures were carried out. Integrated tests indicate all IITMSAT design requirements have been met. Hence a robust communications system has been validated. The time taken for development of on-board telecom and GS was less than a year and was achieved at a low cost which agrees to a LeanSat approach.

Integration of a GFDM-Based 5G Transceiver in a GPON Using Radio Over Fiber Technology

Abstract: This paper reports the integration and experimental performance analysis of a GFDM-based 5G transceiver in a gigabit passive optical network (GPON), using radio over fiber technology. The proposed architecture enables to simultaneously transport two 5G candidates RF signals through an active GPON under real channel conditions. One signal is generated by a GFDM-based 5G prototype transceiver at 735 MHz, whereas the second one is synthetized by a vector signal generator at 26 GHz. A dual-drive Mach–Zehnder modulator has been utilized in the optical line terminal to modulate both signals, with the purpose of mitigating the interference between them. Particularly for the GFDM-based 735 MHz signal, a modulation error ratio (MER) of 40 dB has been obtained at RF-driven signal up to –9 dBm. Furthermore, the use of a digital predistortion scheme has been efficiently employed to reduce the impact of the nonlinear distortions and enhance MER. The 26-GHz RF signal, aimed for the 5G millimeter wave band, has been investigated as a function of error vector magnitude (EVM) for bitrates up to 1 Gbit/s. ${\text{EVM}}_{{\text{RMS}}}$ of 2.18% and 5.70% have been obtained for 100 Mbit/s and 1 Gbit/s, respectively. Finally, the latency and throughput measurements of the baseband signal originally running over GPON have shown no significant penalties.

The Application of Relay to Massive Non-Orthogonal Multiple Access

Abstract: This paper considers the application of relay to enhance the performance of massive non-orthogonal multiple access (NOMA) systems and solve the challenge of channel state information acquisition in the case of a massive number of users. First, we design a general framework for a multiple-relay-aided massive NOMA system. Then, we analyze the performance of the multiple-relay-aided massive NOMA system, and derive a closed-form expression for a lower bound on the spectral efficiency. In particular, we reveal the impact of system parameters on the spectral efficiency via asymptotic analysis in three important scenarios, e.g., a large number of antennas at the base station (BS), a high transmit power at the BS or the relays, and a large number of relays. To further improve the spectral efficiency in the context of massive access, we propose two effective schemes to optimize the transmit power at the BS and relays, respectively. Finally, extensive simulation results validate the effectiveness of the proposed multiple-relay-aided massive NOMA scheme.

High Speed 4 × 2.5 Gbps-5 GHz AMI-WDM-RoF Transmission System for WLANs

Abstract: Abstract Radio-over-fiber (RoF) is revolutionary technique to transmit radio signals over optical fiber. It can be also suitable to distribute wireless local area networks (WLANs) due to its low-cost implementation. WLANs generally operate on 5 GHz radio signals. Thus in this work, four high speed radio channels, each carrying 2.5 Gbps data and 5 GHz radio signal, are transmitted by incorporating alternate mark inversion (AMI) scheme and wavelength division multiplexing (WDM) scheme over optical fiber having span of 50 km. The performance of proposed AMI-WDM-RoF transmission system is reported in terms of Q-factor, bit error rate, signal-to-noise ratio, total received power and eye diagrams.

On the Performance of Energy Harvesting Non-Orthogonal Multiple Access Relaying System with Imperfect Channel State Information over Rayleigh Fading Channels.

Abstract: In this paper, we propose a non-orthogonal multiple access (NOMA) relaying system, where a source node communicates simultaneously with multiple users via the assistance of the best amplify-and-forward (AF) relay. The best relay is selected among N relays which are capable of harvesting the energy from radio frequency (RF) signals. We analyze the performance of the proposed NOMA relaying system in the conditions of imperfect channel state information (CSI) and Rayleigh fading by deriving the exact expressions of the outage probability (OP) and the approximate expression of the ergodic capacities of each user and the whole system. We also determine the optimal energy harvesting duration which minimizes the OP. Numerical results show that, for the same parameter settings, the performance of the proposed NOMA relaying system, especially the ergodic capacity of the whole system, outperforms that of the orthogonal-multiple-access (OMA) relaying system. Monte-Carlo simulations are used to validate the correctness of the analytical results.

The factors that contribute to the continuous usage of broadband technologies among youth in rural areas: A case of northern region of Malaysia

Abstract: Despite the benefits of broadband technology in education and healthcare services, its usage in the rural areas is still low and Malaysia is not excluded. This situation leads to raising the question of long-term usage of the technology. Presently, there are less empirical study on the continuous usage of broadband technology among the youths particularly school children in the rural areas of Malaysia. The objective of this study is to determine the contributing factors for continuous usage of broadband technology among youths in the rural areas. Therefore, a research model was proposed consisting of eight contributing factors for continuous usage of broadband technology. Moreover, the study used quantitative approach by distributing 450 questionnaires to respondents in the northern region of Malaysia. However, only 393 questionnaires were returned which represent 87.33% response rate. The data collected were analyzed using a Structural Equation Model to investigate the relationship between contributing factors. The results showed that performance expectancy, effort expectancy, social influence, compatibility, facilitating condition, service quality, user behavioural intention and user satisfaction are the significant contributing factors that must be in place to ensure the continuous usage of broadband among youth in the rural areas. Hence, this study contributes to the body of knowledge in Community Informatics by providing a framework for achieving long-term use of broadband technology among youths in the rural areas, through the integration of Information System Continuance Post Acceptance and Unified Theory of Acceptance and Use of Technology models. The factors identified may contribute as input to the government policy formulations and service providers to ensure continuous demand for broadband from the evidence extracted from this study. Continuous usage of broadband technology in the rural areas would have positive contributions on the academic performance, literacy among youths, bridging the digital divide in broadband usage, increase home business and national productivity.