OLFAR - Orbiting low frequency antennas for radio astronomy

One of the last unexplored frequency ranges in radio astronomy is the frequency band below 30 MHz. New interesting astronomical science drivers for low frequency radio astronomy have emerged, ranging from studies of the astronomical dark ages, the epoch of reionization, exoplanets, to ultra-high energy cosmic rays. However, astronomical observations with Earth-bound radio telescopes at very low frequencies are hampered by the ionospheric plasma, which scatters impinging celestial radio waves

Signal processing aspects of the low frequency array

In the Northern part of the Netherlands ASTRON is building the largest radio telescope in the world for low frequencies. The telescope is based on phased array principles and is known as the LOw Frequency ARray (LOFAR). LOFAR is optimized for detecting astronomical signals in the 30-80 MHz and 120-240 MHz frequency window. LOFAR detects the incoming radio signals by using an array of simple omni-directional antennas. The antennas are grouped in so called stations mainly to reduce the amount of data generated. More than fifty stations will be built, mainly within a circle of 150 kilometres in diameter but also internationally. The signals of all the stations are distributed to the central processor facility, where all the station signals are correlated with each other. In this paper the signal processing aspects on system level will be presented mainly for the astronomical application.\ud \u

Impact of cognitive radio on radio astronomy

The introduction of new communication techniques requires an increase in the efficiency of spectrum usage. Cognitive radio is one of the new techniques that fosters spectrum efficiency by using unoccupied frequency spectrum for communications. However, cognitive radio will increase the transmission power density and cause an increasing level of Radio Frequency Interference (RFI), which may impact other services and particularly passive users of the spectrum. In this paper we present the principles of cognitive radio and introduce a model for its impact on radio astronomy

Optimum design parameters for ultra-low-power RF transceivers in wireless sensor networks

In wireless sensor networks, the need for ultra-low power consuming nodes is one of the main motivations for research in such field. Because radio sections in sensor nodes contribute to a large extent to the overall power consumption, the focus of this study is on the RF transceiver. The aim is to reduce the average power consumption which depends significantly on the circuit architecture design, operating data rate, and duty cycle. In a symmetric communicating system, due to the tradeoff between transmitting power and receiver sensitivity on one hand, as well as between phase noise tolerance and power dissipation in local oscillators on the other hand, the design and operating parameters of the transceiver need to be determined from the perspective of the average power consumption. Therefore, in our study, as an initial step in system design, the optimum for instantaneous data rate, noise figure, and oscillator power budget are analytically determined. The analysis is carried out, taking into consideration an existing in-channel wideband interference, on two transceiver architectures: RF envelope detection and conventional heterodyne. The transceiver in both architectures employs on-off-keying modulation and duty cycling. The optimums are then calculated numerically based on design constants obtained from a frequently-cited RF envelope transceiver, indicating that an energy efficiency improvement of up to 5 dB can still be achieved

Simulation of a ring resonator-based optical beamformer system for phased array receive antennas

A new simulator tool is described that can be used in the field of RF photonics. It has been developed on the basis of a broadband, continuously tunable optical beamformer system for phased array receive antennas. The application that is considered in this paper is airborne satellite reception of digital television. The simulator tool has been developed in LabVIEW. The simulation model comprises a dynamical implementation of the optical beamforming network, such that beamforming can be performed for any number of antenna elements (AEs). The scalability of the model has been investigated by determining the computational complexity relations of the most critical blocks. It was found that a simulation of a full-scale beamformer can be performed within a reasonable amount of time

DARIS, a fleet of passive formation flying small satellites for low frequency radio astronomy

DARIS (Distributed Aperture Array for Radio Astronomy In Space) is a mission to conduct radio astronomy in the low frequency region from 1-10MHz. This region has not yet been explored, as the Earth's ionosphere is opaque to those frequencies, and so a space based observatory is the only solution. DARIS will undertake an extragalactic survey of the low frequency sky, and can also detect some transient radio events such as solar or planetary bursts. To achieve these scientific objectives, DARIS comprises a space-based array, forming a very large effective aperture, as required for such a long wavelength survey. Each station in the array (each required to be a small satellite to ensure several nodes can be flown) carries three orthogonal dipole antennas, each 5m in length. The more station nodes in the array, the more sensitive the antenna. The entire fleet remains within a 100km diameter cloud. \ud A very large data volume is generated by each node, as the antennas have to capture all radio signals, after which the data can be correlated to find the astronomical signal in the noise. As the astronomical signals also have a noise-like nature, no compression is possible on the data captured by the nodes. The data volume is too high to transfer directly to Earth, and will need to be correlated in space. Distributed correlation between the nodes is technically challenging, and therefore a mothership acts as the central correlator and then downlinks the correlated data (lower volume) to Earth. \u

Noise based transmitted reference modulation for wireless sensor networks

Recent advances in the underlying technologies of wireless sensor networks (WSNs) have led to its use in different applications, from fields as diverse as battlefield applications to temperature control to healthcare. Research in the different aspects of WSNs is therefore in full swing, in both academia and the industry. In the Wireless Ad-hoc Links using robust Noise-based Ultra-wideband Transmission (WALNUT) project, modulation concepts (and relevant MAC protocols) are intended to be explored which allow for robust ad-hoc radio links with radio nodes implemented on a single CMOS chip

Vulnerability of terrestrial-trunked radio to intelligent intentional electromagnetic interference

The terrestrial-trunked radio (TETRA) specification is produced by the European Telecommunication Standards Institute for private mobile radio systems. We investigated the resilience of TETRA against intelligent intentional electromagnetic interference (IEMI) with low amplitude. Low power signals interfering with the higher layers of the system have the advantage of staying covert. The analysis shows that if the access assignment channel is corrupted, the mobile stations cannot start conversations with the base station. TETRA’s modulation scheme is also investigated. $pi$/4 differential quadrature phase shift keying (QPSK) is interfered with a continuous wave and a QPSK signal. The results show that a continuous wave created the largest error vector magnitude, but creates a peak in the received spectrum. The power of the QPSK signal, however, is distributed over a bandwidth and is more difficult to detect than the continuous wave in the received spectrum. From this, we conclude that the QPSK signal functions is more effective as an intelligent interference signal compared to a continuous wave. In this paper, it is shown that it is possible to create an IEMI that combines the vulnerability in the TETRA protocol with the QPSK signal to disrupt the service to the communication system, while staying covert

The communication layer for the OLFAR satellite swarm

Recently, new directions in astronomy are investigated as space observations tend to evolve from optical observations to the low-frequency domain. Ultra-long EM waves are the result of planetary emissions from outside and inside the solar system and of high-energy particle interactions. Exploring this band would create an image of our younger universe and uncover a lot of the so called astronomical dark ages(1)