Ramesh Balasubramanyam | Raman Research Institute (original) (raw)

Papers by Ramesh Balasubramanyam

Fading, Coding and Mimo-Ofdm: A Short Review

In Wireless communication, since free space is the medium for communication, it is essential to d... more In Wireless communication, since free space is the medium for communication, it is essential to develop and implement efficient techniques to mitigate the effect of fading that occurs due to multipath propagation. Multi Input Multi Output (MIMO) technology provides diversity, which in turn helps to achieve higher data rates with better error performance. As the data rate increases, the type of fading becomes frequency selective which in turn causes Inter Symbol Interference (ISI). Orthogonal Frequency Division Multiplexing (OFDM) combined with MIMO is the preferred technique in fourth generation wireless communication standards. Fading that occurs in wireless channel is equivalent to burst error in wired channel. Therefore the forward error correcting codes developed for wired channel can be used for wireless fading channel. This paper reviews work done in MIMO communication under different fading environment, considering various coding techniques and symbol mapping schemes. This su...

Building an efficient linear-array imager prototype

2017 IEEE Radio and Antenna Days of the Indian Ocean (RADIO), 2017

Reflecting surfaces constitute telescopes which serve as artificial eyes for astronomers to study... more Reflecting surfaces constitute telescopes which serve as artificial eyes for astronomers to study celestial objects. Their smoothness and figure define the quality of their focusing capacity. Various loads such as wind, thermal and gravity act to deform the figure of the reflectors, especially the primary, and thereby degrade the telescope performance. The back-up structures help to define and retain the desired shapes and relative positions of the reflecting surfaces. The aim of backup structure design is to achieve the desired performance with minimal weight and complexity and thereby with minimal cost. Recently, a new optics entitled Efficient Linear-array Imager has been proposed to optimally use receivers for imaging the skies. A prototype is being made to demonstrate its feasibility. In this paper, we present our backup structure solution for this prototype telescope.

A telescope made with cylinders: constructing a 3 m sub-millimeterwave prototype

... Also to Christien Zier and Raju Varghese for help with photos. ... [5] K. Chandrasekhara, The... more ... Also to Christien Zier and Raju Varghese for help with photos. ... [5] K. Chandrasekhara, Theory of Plates, p 57, 1st ed. University Press (India) Ltd., Hydrebad, 2001. Ramesh Balasubramanyam is currently working as a scientist at the Raman Research Institute. ...

Broad band microwave filters

Recently, a new optics entitled Efficient Linear-array Imager [1] has been proposed to use radio ... more Recently, a new optics entitled Efficient Linear-array Imager [1] has been proposed to use radio receivers efficiently for imaging the skies. The new optics demonstrates that it is possible to trade instantaneous sensitivity to instantaneous field-of-view while conserving the mathrmAOmega\mathrm{A}\OmegamathrmAOmega product. For a dish of size D fitted with N receivers, this product is simD2N\sim D ^ { 2 } NsimD2N. This can be rewritten as 2left(DtimesfracDN/2right)times(N/2)22 \left( D \times \frac { D } { N / 2 } \right) \times ( N / 2 ) ^ { 2 }2left(DtimesfracDN/2right)times(N/2)2. The first part, 2left(DtimesfracDN/2right)2 \left( D \times \frac { D } { N / 2 } \right)2left(DtimesfracDN/2right), implies two orthogonal areas of elliptical cross section with an N/2 aspect ratio. The second part, (N/2)2( N / 2 ) ^ { 2 }(N/2)2, indicates the number of simultaneous beams formed with N receivers. Thus, the resultant configuration is two telescopes of elliptical cross sections laid in a cross-configuration, each fitted with N/2 receivers. Then, by cross correlating each set of receivers with the orthogonal set of receivers, one obtains the $( N /...

Symposium - International Astronomical Union, 2002

We have made a blind survey of SiO masers, of the J=2-1 v = 1 transition, toward 106 bright OH/IR... more We have made a blind survey of SiO masers, of the J=2-1 v = 1 transition, toward 106 bright OH/IR stars which have been previously detected in the OH main line at 1662 MHz with the ATCA in the galactic bulge by Sevenster et al (2000) and in the galactic disk at J=1-0 (v = 1 − 2) line by Miyazaki (2001). A comparison with published data shows that new SiO masers are detected for OH/IR stars in the galactic center, suggesting that those stars are undergoing strong mass loss with dense circumstellar envelopes with apparent angular sizes far smaller than the OH maser shell as obtained by interferometric observations. At the moment, our detection rate is about 23% and it may be increased when the project is completed.

A Systematic Study of Coding Performance in a MIMO–STBC–OFDM Link

IETE Journal of Research, 2014

ABSTRACT MIMO�-STBC-�OFDM systems mitigate inter symbol interference and frequency-selective fadi... more ABSTRACT MIMO�-STBC-�OFDM systems mitigate inter symbol interference and frequency-selective fading caused by multi-path propagation in modern high-data-rate wireless communication. Error correction codes use redundancy to correct errors that still occur. No systematic analysis of their performance using a common link configuration is found in the literature. We fill this gap in this simulation study using a common MIMO-�STBC-�OFDM communication link, transferring data at a symbol rate of 100 Mbps. We find that (a) for all code rates, low-density parity-check code performs best with BPSK and to an extent with QPSK and (b) 1/2-rate convolutional code works well for all symbol mapping schemes.

Monthly Notices of the Royal Astronomical Society, 2014

Large-scale surveys are essential means to leapfrog astronomical understanding. Yet, Galaxywide s... more Large-scale surveys are essential means to leapfrog astronomical understanding. Yet, Galaxywide surveys at millimetre wavelengths are rare and have not benefited much from multiple receivers that provide large instantaneous field of view. If one were to have a large number of millimetre wave receivers, how best to deploy them to maximize survey speed to measure both point and smoothly distributed emission? In this paper, we present a new cross telescope configuration, Efficient Linear-array Imager, and demonstrate that it provides an interesting alternate solution. As an interferometer element, it lends itself for close packing and thereby blends short and long spacing visibilities naturally, improving imaging.

Abstract. Meterwave luminous objects, which are bright at the frequency 74 MHz but very faint at ... more Abstract. Meterwave luminous objects, which are bright at the frequency 74 MHz but very faint at 1.4 GHz in VLA surveys (VLSS and NVSS), have special character-istics: very steep spectra and a distinctive distribution in the sky. They are possibly radio relics, ultra-steep spectrum radio galaxies, and Galactic objects such as pulsars, cool dwarfs, and extrasolar planets. We present a preliminary result of our attempt to identify them with possible astronomical objects. We observed several candidates for electron-cyclotron maser emission from cool dwarfs with GMRT at 235 MHz, and lo-cated the radio source VLSS 0406.1+0251 to be within 0.5′ ′ near the M3 dwarf LSPM 0406+0251. 1.

Holography of the 10.4 m RRI radio telescope using a geo-stationary satellite beacon at 11.699 GHz

... Authors: Raja, Wasim; Balasubramanyam, Ramesh; Gopalkrishna, MR; Deshpande, Avinash A. Affili... more ... Authors: Raja, Wasim; Balasubramanyam, Ramesh; Gopalkrishna, MR; Deshpande, Avinash A. Affiliation: AA(Raman Research Institute, Bangalore), AB(Raman Research Institute, Bangalore), AC(Raman Research Institute, Bangalore), AD(Raman Research Institute ...

The submillimeter waveband (3 to 0.3 mm) is important for photometric and spectroscopic studies o... more The submillimeter waveband (3 to 0.3 mm) is important for photometric and spectroscopic studies of the high redshift Universe and of the deeply embedded star forming regions in our and nearby galaxies. The upcoming Atacama Large Millime- terwave Array (ALMA) will have a large collecting area and high spatial resolution, but small field of view and correlation bandwidth. This creates both an opportunity and a need for an effective complement: a large single dish fitted with a modem pho- ton detector array can be faster than ALMA for continuum source detection. Besides being powerful in its own right, such an instrument can also supply zero-spacing data for making more complete spectral line images with ALMA. Our natural strength in having many high altitude desert sites in the Himalayas can be leveraged to take our nascent submillimeter efforts to the frontiers of this new waveband. BuiIding large submillimeterwave telescopes calls for unconventional approaches. In this paper, we fir...

Massive stars at the end of their lives explode as supernovae. The supernova rate in Milky Way is... more Massive stars at the end of their lives explode as supernovae. The supernova rate in Milky Way is expected to be one in thirty years. Owing to interstellar opacity, they are likely to be visible in optical only if they happen within a few kilo parsec distance. In radio, they can be detected up to the end of the galaxy even with a modest sized telescope. To enable this we are building a dedicated radio Supernova Search Engine (SnSE).

A modern Q-band low noise amplifier (LNA) front-end is being fitted to the 10.4 m millimeter-wave... more A modern Q-band low noise amplifier (LNA) front-end is being fitted to the 10.4 m millimeter-wave telescope at the Raman Research Institute (RRI) to support observations in the 40-50 GHz frequency range. To assess the suitability of the surface for this purpose, we measured the deviations of the primary surface from an ideal paraboloid using radio holography. We used the 11.6996 GHz beacon signal from the GSAT3 satellite, a 1.2 m reference antenna, commercial Ku-band Low Noise Block Convereters (LNBC) as the receiver front-ends and a Stanford Research Systems (SRS) lock-in amplifier as the backend. The LNBCs had independent free-running first local oscillators (LO). Yet, we recovered the correlation by using a radiatively injected common tone that served as the second local oscillator. With this setup, we mapped the surface deviations on a 64 x 64 grid and measured an rms surface deviation of ~350 um with a measurement accuracy of ~50 um.

An MCS with Iterative Multi-dimensional Hamming Product Codes

IETE Journal of Research

Publications of the Astronomical Society of Japan

Publ. Astron. Soc. Aust., 2002, 19, 1--10 A Spectral Line Survey of IRAS 17470-2853 from 86.1 to 92.1 GHz

An Open Voice Command Interface Kit

IEEE Transactions on Human-Machine Systems, 2015

Meterwave luminous objects, which are bright at the frequency 74 MHz but very faint at 1.4 GHz in... more Meterwave luminous objects, which are bright at the frequency 74 MHz but very faint at 1.4 GHz in VLA surveys (VLSS and NVSS), have special characteristics: very steep spectra and a distinctive distribution in the sky. They are possibly radio relics, ultra-steep spectrum radio galaxies, and Galactic objects such as pulsars, cool dwarfs, and extrasolar planets. We present a preliminary result of our attempt to identify them with possible astronomical objects. We observed several candidates for electron-cyclotron maser emission from cool dwarfs with GMRT at 235 MHz, and located the radio source VLSS 0406.1+0251 to be within 0.5 ′′ near the M3 dwarf LSPM 0406+0251.

A modern Q-band low noise amplifier (LNA) front-end is being fitted to the 10.4 m millimeter-wave... more A modern Q-band low noise amplifier (LNA) front-end is being fitted to the 10.4 m millimeter-wave telescope at the Raman Research Institute (RRI) to support observations in the 40-50 GHz frequency range. To assess the suitability of the surface for this purpose, we measured the deviations of the primary surface from an ideal paraboloid using radio holography. We used the 11.6996 GHz beacon signal from the GSAT3 satellite, a 1.2 m reference antenna, commercial K u-band Low Noise Block Convereters (LNBC) as the receiver frontends and a Stanford Research Systems (SRS) lock-in amplifier as the backend. The LNBCs had independent free-running first local oscillators (LO). Yet, we recovered the correlation by using a radiatively injected common tone that served as the second local oscillator. With this setup, we mapped the surface deviations on a 64 × 64 grid and measured an rms surface deviation of ∼ 350 µm with a measurement accuracy of ∼ 50 µm.

Surface metrology using one-element interferometry

2015 1st URSI Atlantic Radio Science Conference (URSI AT-RASC), 2015

Fading, Coding and Mimo-Ofdm: A Short Review

In Wireless communication, since free space is the medium for communication, it is essential to d... more In Wireless communication, since free space is the medium for communication, it is essential to develop and implement efficient techniques to mitigate the effect of fading that occurs due to multipath propagation. Multi Input Multi Output (MIMO) technology provides diversity, which in turn helps to achieve higher data rates with better error performance. As the data rate increases, the type of fading becomes frequency selective which in turn causes Inter Symbol Interference (ISI). Orthogonal Frequency Division Multiplexing (OFDM) combined with MIMO is the preferred technique in fourth generation wireless communication standards. Fading that occurs in wireless channel is equivalent to burst error in wired channel. Therefore the forward error correcting codes developed for wired channel can be used for wireless fading channel. This paper reviews work done in MIMO communication under different fading environment, considering various coding techniques and symbol mapping schemes. This su...

Building an efficient linear-array imager prototype

2017 IEEE Radio and Antenna Days of the Indian Ocean (RADIO), 2017

Reflecting surfaces constitute telescopes which serve as artificial eyes for astronomers to study... more Reflecting surfaces constitute telescopes which serve as artificial eyes for astronomers to study celestial objects. Their smoothness and figure define the quality of their focusing capacity. Various loads such as wind, thermal and gravity act to deform the figure of the reflectors, especially the primary, and thereby degrade the telescope performance. The back-up structures help to define and retain the desired shapes and relative positions of the reflecting surfaces. The aim of backup structure design is to achieve the desired performance with minimal weight and complexity and thereby with minimal cost. Recently, a new optics entitled Efficient Linear-array Imager has been proposed to optimally use receivers for imaging the skies. A prototype is being made to demonstrate its feasibility. In this paper, we present our backup structure solution for this prototype telescope.

A telescope made with cylinders: constructing a 3 m sub-millimeterwave prototype

... Also to Christien Zier and Raju Varghese for help with photos. ... [5] K. Chandrasekhara, The... more ... Also to Christien Zier and Raju Varghese for help with photos. ... [5] K. Chandrasekhara, Theory of Plates, p 57, 1st ed. University Press (India) Ltd., Hydrebad, 2001. Ramesh Balasubramanyam is currently working as a scientist at the Raman Research Institute. ...

Broad band microwave filters

Recently, a new optics entitled Efficient Linear-array Imager [1] has been proposed to use radio ... more Recently, a new optics entitled Efficient Linear-array Imager [1] has been proposed to use radio receivers efficiently for imaging the skies. The new optics demonstrates that it is possible to trade instantaneous sensitivity to instantaneous field-of-view while conserving the mathrmAOmega\mathrm{A}\OmegamathrmAOmega product. For a dish of size D fitted with N receivers, this product is simD2N\sim D ^ { 2 } NsimD2N. This can be rewritten as 2left(DtimesfracDN/2right)times(N/2)22 \left( D \times \frac { D } { N / 2 } \right) \times ( N / 2 ) ^ { 2 }2left(DtimesfracDN/2right)times(N/2)2. The first part, 2left(DtimesfracDN/2right)2 \left( D \times \frac { D } { N / 2 } \right)2left(DtimesfracDN/2right), implies two orthogonal areas of elliptical cross section with an N/2 aspect ratio. The second part, (N/2)2( N / 2 ) ^ { 2 }(N/2)2, indicates the number of simultaneous beams formed with N receivers. Thus, the resultant configuration is two telescopes of elliptical cross sections laid in a cross-configuration, each fitted with N/2 receivers. Then, by cross correlating each set of receivers with the orthogonal set of receivers, one obtains the $( N /...

Symposium - International Astronomical Union, 2002

We have made a blind survey of SiO masers, of the J=2-1 v = 1 transition, toward 106 bright OH/IR... more We have made a blind survey of SiO masers, of the J=2-1 v = 1 transition, toward 106 bright OH/IR stars which have been previously detected in the OH main line at 1662 MHz with the ATCA in the galactic bulge by Sevenster et al (2000) and in the galactic disk at J=1-0 (v = 1 − 2) line by Miyazaki (2001). A comparison with published data shows that new SiO masers are detected for OH/IR stars in the galactic center, suggesting that those stars are undergoing strong mass loss with dense circumstellar envelopes with apparent angular sizes far smaller than the OH maser shell as obtained by interferometric observations. At the moment, our detection rate is about 23% and it may be increased when the project is completed.

A Systematic Study of Coding Performance in a MIMO–STBC–OFDM Link

IETE Journal of Research, 2014

ABSTRACT MIMO�-STBC-�OFDM systems mitigate inter symbol interference and frequency-selective fadi... more ABSTRACT MIMO�-STBC-�OFDM systems mitigate inter symbol interference and frequency-selective fading caused by multi-path propagation in modern high-data-rate wireless communication. Error correction codes use redundancy to correct errors that still occur. No systematic analysis of their performance using a common link configuration is found in the literature. We fill this gap in this simulation study using a common MIMO-�STBC-�OFDM communication link, transferring data at a symbol rate of 100 Mbps. We find that (a) for all code rates, low-density parity-check code performs best with BPSK and to an extent with QPSK and (b) 1/2-rate convolutional code works well for all symbol mapping schemes.

Monthly Notices of the Royal Astronomical Society, 2014

Large-scale surveys are essential means to leapfrog astronomical understanding. Yet, Galaxywide s... more Large-scale surveys are essential means to leapfrog astronomical understanding. Yet, Galaxywide surveys at millimetre wavelengths are rare and have not benefited much from multiple receivers that provide large instantaneous field of view. If one were to have a large number of millimetre wave receivers, how best to deploy them to maximize survey speed to measure both point and smoothly distributed emission? In this paper, we present a new cross telescope configuration, Efficient Linear-array Imager, and demonstrate that it provides an interesting alternate solution. As an interferometer element, it lends itself for close packing and thereby blends short and long spacing visibilities naturally, improving imaging.

Abstract. Meterwave luminous objects, which are bright at the frequency 74 MHz but very faint at ... more Abstract. Meterwave luminous objects, which are bright at the frequency 74 MHz but very faint at 1.4 GHz in VLA surveys (VLSS and NVSS), have special character-istics: very steep spectra and a distinctive distribution in the sky. They are possibly radio relics, ultra-steep spectrum radio galaxies, and Galactic objects such as pulsars, cool dwarfs, and extrasolar planets. We present a preliminary result of our attempt to identify them with possible astronomical objects. We observed several candidates for electron-cyclotron maser emission from cool dwarfs with GMRT at 235 MHz, and lo-cated the radio source VLSS 0406.1+0251 to be within 0.5′ ′ near the M3 dwarf LSPM 0406+0251. 1.

Holography of the 10.4 m RRI radio telescope using a geo-stationary satellite beacon at 11.699 GHz

... Authors: Raja, Wasim; Balasubramanyam, Ramesh; Gopalkrishna, MR; Deshpande, Avinash A. Affili... more ... Authors: Raja, Wasim; Balasubramanyam, Ramesh; Gopalkrishna, MR; Deshpande, Avinash A. Affiliation: AA(Raman Research Institute, Bangalore), AB(Raman Research Institute, Bangalore), AC(Raman Research Institute, Bangalore), AD(Raman Research Institute ...

The submillimeter waveband (3 to 0.3 mm) is important for photometric and spectroscopic studies o... more The submillimeter waveband (3 to 0.3 mm) is important for photometric and spectroscopic studies of the high redshift Universe and of the deeply embedded star forming regions in our and nearby galaxies. The upcoming Atacama Large Millime- terwave Array (ALMA) will have a large collecting area and high spatial resolution, but small field of view and correlation bandwidth. This creates both an opportunity and a need for an effective complement: a large single dish fitted with a modem pho- ton detector array can be faster than ALMA for continuum source detection. Besides being powerful in its own right, such an instrument can also supply zero-spacing data for making more complete spectral line images with ALMA. Our natural strength in having many high altitude desert sites in the Himalayas can be leveraged to take our nascent submillimeter efforts to the frontiers of this new waveband. BuiIding large submillimeterwave telescopes calls for unconventional approaches. In this paper, we fir...

Massive stars at the end of their lives explode as supernovae. The supernova rate in Milky Way is... more Massive stars at the end of their lives explode as supernovae. The supernova rate in Milky Way is expected to be one in thirty years. Owing to interstellar opacity, they are likely to be visible in optical only if they happen within a few kilo parsec distance. In radio, they can be detected up to the end of the galaxy even with a modest sized telescope. To enable this we are building a dedicated radio Supernova Search Engine (SnSE).

A modern Q-band low noise amplifier (LNA) front-end is being fitted to the 10.4 m millimeter-wave... more A modern Q-band low noise amplifier (LNA) front-end is being fitted to the 10.4 m millimeter-wave telescope at the Raman Research Institute (RRI) to support observations in the 40-50 GHz frequency range. To assess the suitability of the surface for this purpose, we measured the deviations of the primary surface from an ideal paraboloid using radio holography. We used the 11.6996 GHz beacon signal from the GSAT3 satellite, a 1.2 m reference antenna, commercial Ku-band Low Noise Block Convereters (LNBC) as the receiver front-ends and a Stanford Research Systems (SRS) lock-in amplifier as the backend. The LNBCs had independent free-running first local oscillators (LO). Yet, we recovered the correlation by using a radiatively injected common tone that served as the second local oscillator. With this setup, we mapped the surface deviations on a 64 x 64 grid and measured an rms surface deviation of ~350 um with a measurement accuracy of ~50 um.

An MCS with Iterative Multi-dimensional Hamming Product Codes

IETE Journal of Research

Publications of the Astronomical Society of Japan

Publ. Astron. Soc. Aust., 2002, 19, 1--10 A Spectral Line Survey of IRAS 17470-2853 from 86.1 to 92.1 GHz

An Open Voice Command Interface Kit

IEEE Transactions on Human-Machine Systems, 2015

Meterwave luminous objects, which are bright at the frequency 74 MHz but very faint at 1.4 GHz in... more Meterwave luminous objects, which are bright at the frequency 74 MHz but very faint at 1.4 GHz in VLA surveys (VLSS and NVSS), have special characteristics: very steep spectra and a distinctive distribution in the sky. They are possibly radio relics, ultra-steep spectrum radio galaxies, and Galactic objects such as pulsars, cool dwarfs, and extrasolar planets. We present a preliminary result of our attempt to identify them with possible astronomical objects. We observed several candidates for electron-cyclotron maser emission from cool dwarfs with GMRT at 235 MHz, and located the radio source VLSS 0406.1+0251 to be within 0.5 ′′ near the M3 dwarf LSPM 0406+0251.

A modern Q-band low noise amplifier (LNA) front-end is being fitted to the 10.4 m millimeter-wave... more A modern Q-band low noise amplifier (LNA) front-end is being fitted to the 10.4 m millimeter-wave telescope at the Raman Research Institute (RRI) to support observations in the 40-50 GHz frequency range. To assess the suitability of the surface for this purpose, we measured the deviations of the primary surface from an ideal paraboloid using radio holography. We used the 11.6996 GHz beacon signal from the GSAT3 satellite, a 1.2 m reference antenna, commercial K u-band Low Noise Block Convereters (LNBC) as the receiver frontends and a Stanford Research Systems (SRS) lock-in amplifier as the backend. The LNBCs had independent free-running first local oscillators (LO). Yet, we recovered the correlation by using a radiatively injected common tone that served as the second local oscillator. With this setup, we mapped the surface deviations on a 64 × 64 grid and measured an rms surface deviation of ∼ 350 µm with a measurement accuracy of ∼ 50 µm.

Surface metrology using one-element interferometry

2015 1st URSI Atlantic Radio Science Conference (URSI AT-RASC), 2015