Ravinder David Koilpillai

In this paper we describe the design and development of the Command and Data Management System (CDMS) of the nano-satellite of IIT Madras, named IITMSAT. The CDMS module uses a 32-bit ARM microcontroller from Freescale - KL46Z256VLL4. This module is responsible for decoding the telecommands sent from the ground station, and transmits the time-stamped payload data back as telemetry packets. The SD card on the CDMS board stores the satellite's health and science data as and when it is acquired in the orbit. The data is transmitted to the ground station (GS) during the satellite's visibility period. The interface board (I/F) links the Flight Computer module and CDMS board along with other electronics onboard. Throughout the design phase, the cost was kept as low as possible, without compromising on performance of the system. Custom-designed protocol and data frame format for communication between the satellite and ground station was completely developed from scratch, based on CCSDS cubesat standards.

Cognitive radio based systems rely on spectrum sensing techniques to detect whitespaces to exploit. For the sake of ease of implementation, simple schemes such as energy detector have been proposed and studied widely. However, such simple schemes perform far from optimally, thereby affecting the performance of the underlying system. On the other hand sophisticated detectors are difficult to implement, giving rise to a trade-off. This paper explores the idea of using spectral estimates for detection. The case of HDTV based cognitive radio is explored and an optimal detection scheme following multi taper estimation is proposed and studied. © 2012 IEEE.

We propose an improved pilot free phase noise mitigation algorithm for CO-OFDM systems using weighted multi-level QPSK partitioning and Kalman filtering. Through extensive Monte Carlo simulations, we demonstrate an improvement in spectral efficiency of >6% in case of 200 Gbps single channel and 1 Tbps multi channel 16QAM CO-OFDM transmission with blind carrier phase estimation. We also experimentally demonstrate the performance of the proposed algorithm against the standard pilot aided algorithm for the transmission of 120 Gbps 16QAM CO-OFDM at different noise levels.

A near maximum a posteriori (MAP)-optimal soft detector that outputs a posteriori probabilities (APP's) for multiple-input multiple-output (MIMO) systems in flat fading channels is proposed. This is referred to as 'reduced state maximum a posteriori (RSMAP)' algorithm. This detection algorithm is based on BCJR algorithm and also uses ideas from reduced state sequence estimation (RSSE) and set partitioning. This algorithm is shown to be near optimal and the computational complexity to implement it is estimated. Finally we also show that applying the well known max-log approximation on this algorithm results in nearly same performance at much lower complexity. © 2012 IEEE.

Faster-Than-Nyquist (FTN) Signaling is a non-orthogonal transmission scheme which violates the Nyquist zero-ISI criterion providing higher throughput and better spectral efficiency than a Nyquist transmission scheme. This comes with a cost of higher transceiver complexity. In this paper, we focus on understanding pulse shapes and their inter-symbol-interference (ISI) and show that, under certain conditions on pulse shapes and τ (time acceleration factor), the ISI can be avoided completely with the help of precoding. This leads to a symbol-by-symbol detection. Further, we extend this idea to Orthogonal Frequency Division Multiplexing (OFDM) FTN systems and show that, under certain conditions, the average performance of OFDM system reaches that of a Nyquist system. Finally, simulation results of the performance of precoded and non-precoded single carrier and OFDM FTN systems are compared to a Nyquist system.

We design a precoder for non-concurrent two-way relaying (ncTWR) where a base station (BS) serves a transmit-only user equipment (TUE) in the uplink and a receive-only user equipment (RUE) in the downlink. The RUE experiences back-propagating interference (BI). The proposed precoder is designed such that it not only cancels the BI experienced by the RUE but more importantly, enables receive data decoding with high diversity. The high diversity precoder is designed by deriving the closed-form pairwise error probability (PEP) expressions, and by optimizing the precoder elements to minimize the PEP. We analytically show that with Nr -antenna relay, Nb-antenna BS, and Nu-antenna TUE and RUE, both BS and RUE decode their respective data with a diversity order of -(Nu2,(Nr-Nu)Nb) at high receive signal-to-noise ratio. We also numerically show that the proposed design has lower bit error rate than the existing state-of-the-art ncTWR designs.

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.

The design of a robust downlink communication system for nanosatellites in UHF amateur radio band involves many challenges like radio spectrum constraints, time-varying Doppler, clock drifts and synchronization in a LEO satellite channel. This paper presents the system designed and implemented for IITMSAT, a student satellite project at IIT Madras, which successfully overcomes these challenges using a robust physical layer design implemented on a generic Software Defined Radio platform. The performance of the proposed design is verified through simulations as well as hardware. The communication system gives a good performance which is only about 1 dB away from theory.

We propose a novel multi-user hybrid precoder design that imitates the bit error rate (BER) performance of a given fully digital precoder by minimizing the Frobenious norm between them. We show that the proposed design equivalently minimizes the chordal distance between the column spaces of the phase-only RF precoder and the given fully digital precoder. The proposed design, in the large antenna regime, has the same BER as that of an existing optimal hybrid precoder design but with much reduced complexity. Furthermore, the proposed design is also shown to approach the BER of a given fully digital precoder.

Spectrum for satellite services are likely to overlap with the ITU 5G spectrum. Critical satellite services may be impacted due to interference between various communication links working in the same frequency band. The worst-case interference scenario between Mobile Base Station (BS) and Satellite Earth Station (ES) is evaluated. Recommendation for path loss for 3.4 GHz operations are given based on ITU-R P.1546-5. Simulations are parameterized by ES height, BS height, terrain, time-variability and location-variability.