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Papers by Vijitha Weerackody
Proceedings of GLOBECOM '95
Automatic repeat request (ARQ) schemes provide means of transmitting data very reliably. ARQ prot... more Automatic repeat request (ARQ) schemes provide means of transmitting data very reliably. ARQ protocols employ an error detection code and a feedback channel so that the receiver can request retransmission of the erroneous packets, or it can use the feedback channel to acknowledge the correctly received packets. Applications such as image and video usually require very low transmission bit error rates (<10-7) and achieving these low bit error rates in wireless channels is very challenging. We present an ARQ scheme with switched transmitter antenna diversity. In very slow fading channels, this scheme improves the throughput efficiency of the ARQ protocol significantly. The diversity benefit obtained from this scheme reduces the delay in transmitting the data packets and this is attractive in applications such as audio, image and real-time video. We also use this scheme to transmit JPEG coded images
Seamless Interconnection for Universal Services. Global Telecommunications Conference. GLOBECOM'99. (Cat. No.99CH37042)
Orthogonal frequency division multiplexing (OFDM) systems are employed or proposed in many commer... more Orthogonal frequency division multiplexing (OFDM) systems are employed or proposed in many commercial data transmission systems such as high-quality digital audio broadcasting (DAB) and terrestrial HDTV broadcasting. These applications require transmission of very high data rates and OFDM system are capable of providing frequency diversity without resorting to complex equalizers. To improve coverage and efficiency of the system some terrestrial broadcasting systems employ a network of single frequency transmitters all transmitting the same program synchronized in time and frequency. These single frequency networks (SFN) usually provide base station diversity, however, in some cases frequency diversity is not available when the path differences between the stations are very small. We address this situation and introduce a very simple transmit diversity technique. This diversity technique does not introduce any changes at the receiver
2006 40th Annual Conference on Information Sciences and Systems, 2006
ABSTRACT Satellite communications on-the-move systems that operate at the Ku-band (11-14 GHz band... more ABSTRACT Satellite communications on-the-move systems that operate at the Ku-band (11-14 GHz band) and higher frequencies play a significant role in military and civilian communication systems. In order to limit interference to adjacent satellites, regulatory and standards bodies have established strict limits on the effective isotropic radiated power (EIRP) at a particular terminal in its off-axis direction. In communications on-the-move systems, because of the frequent motion of the antenna platform, antenna pointing errors are unavoidable. In this paper we demonstrate that such antenna errors will result in the EIRP exceeding the limit imposed by the standards and regulatory bodies. Also, in order to support mobile antenna terminals, a modification to the existing EIRP spectral density is suggested.
MILCOM 2007 - IEEE Military Communications Conference, 2007
ABSTRACT Mobile satellite communication systems that operate in the Ku-band (11-14 GHz band) and ... more ABSTRACT Mobile satellite communication systems that operate in the Ku-band (11-14 GHz band) and higher frequencies play a significant role in military and civilian communication systems. The satellites of interest are located in the crowded geostationary orbit with a 2 degree separation between adjacent satellites. This close spacing between adjacent satellites may lead to interference effects and, in order to limit interference to adjacent satellites, regulatory agencies have established strict limits on the effective isotropic radiated power (EIRP) from a particular terminal in its off-axis direction. Rugged terrain conditions are commonly encountered in mobile communications applications. In such terrains, the frequent motion of the antenna platform may lead to motion induced antenna pointing errors, which can be characterized by a random variable. It will be shown that such errors will lead to random variations of the terminal's off-axis EIRP spectral density. Since there are strict limits on the off-axis EIRP spectral density it is necessary to quantify these random variation. In this paper we will present a technique to analyze the time-varying interference at the adjacent satellites due to the propagation of the signal from a mobile satellite terminal.
MILCOM 2015 - 2015 IEEE Military Communications Conference, 2015
Earth stations on moving platforms (ESOMPs) are a new generation of satellite terminals designed ... more Earth stations on moving platforms (ESOMPs) are a new generation of satellite terminals designed to provide on-the-move broadband communication services to land vehicles, aircraft, and ships. ESOMPs use very small antennas and require tracking systems to maintain accurate pointing to the target satellite. Because they operate while moving, there may be instances when antenna mispointing may produce interference to other satellites or other radio systems. To account for pointing errors and other time-varying characteristics of a network of ESOMPs, it is necessary to use statistical approaches for interference analysis. This paper provides an overview of ESOMPs, their technical and operational characteristics, statistical approaches for interference analysis, and the standards and regulatory challenges that must be addressed for their successful operation.
ICC 2001. IEEE International Conference on Communications. Conference Record (Cat. No.01CH37240), 2001
High quality multimedia streaming applications over the Internet require very low packet loss rat... more High quality multimedia streaming applications over the Internet require very low packet loss rates. The Internet is characterized by long bursts of packet losses and delays. A large receive buffer can be used to mitigate the effects of packet losses and delays. However, a large receive buffer introduces a large delay in the playback of a packet. This large delay could be annoying at the start of a program or during switch over to another channel in a multi-channel broadcast. We introduce a separate low-delay tuning stream to address this start-up problem. In the steady state, this tuning stream is synchronized appropriately with the high-delay steady state stream to give an enhanced composite signal
2007 41st Annual Conference on Information Sciences and Systems, 2007
Very high-speed data links from fast-moving mobile terminals to satellites are attractive in many... more Very high-speed data links from fast-moving mobile terminals to satellites are attractive in many military applications. In order to provide such high-speed data rates we consider a multiple-input multiple-output (MIMO) free space optical (FSO) system for the earth-to-satellite link. In this case the signal is transmitted via closely-spaced multiple transmit apertures and the receiver consists of multiple apertures. Mobility of
Proceedings of GLOBECOM '95
Automatic repeat request (ARQ) schemes provide means of transmitting data very reliably. ARQ prot... more Automatic repeat request (ARQ) schemes provide means of transmitting data very reliably. ARQ protocols employ an error detection code and a feedback channel so that the receiver can request retransmission of the erroneous packets, or it can use the feedback channel to acknowledge the correctly received packets. Applications such as image and video usually require very low transmission bit error rates (<10-7) and achieving these low bit error rates in wireless channels is very challenging. We present an ARQ scheme with switched transmitter antenna diversity. In very slow fading channels, this scheme improves the throughput efficiency of the ARQ protocol significantly. The diversity benefit obtained from this scheme reduces the delay in transmitting the data packets and this is attractive in applications such as audio, image and real-time video. We also use this scheme to transmit JPEG coded images
Seamless Interconnection for Universal Services. Global Telecommunications Conference. GLOBECOM'99. (Cat. No.99CH37042)
Orthogonal frequency division multiplexing (OFDM) systems are employed or proposed in many commer... more Orthogonal frequency division multiplexing (OFDM) systems are employed or proposed in many commercial data transmission systems such as high-quality digital audio broadcasting (DAB) and terrestrial HDTV broadcasting. These applications require transmission of very high data rates and OFDM system are capable of providing frequency diversity without resorting to complex equalizers. To improve coverage and efficiency of the system some terrestrial broadcasting systems employ a network of single frequency transmitters all transmitting the same program synchronized in time and frequency. These single frequency networks (SFN) usually provide base station diversity, however, in some cases frequency diversity is not available when the path differences between the stations are very small. We address this situation and introduce a very simple transmit diversity technique. This diversity technique does not introduce any changes at the receiver
2006 40th Annual Conference on Information Sciences and Systems, 2006
ABSTRACT Satellite communications on-the-move systems that operate at the Ku-band (11-14 GHz band... more ABSTRACT Satellite communications on-the-move systems that operate at the Ku-band (11-14 GHz band) and higher frequencies play a significant role in military and civilian communication systems. In order to limit interference to adjacent satellites, regulatory and standards bodies have established strict limits on the effective isotropic radiated power (EIRP) at a particular terminal in its off-axis direction. In communications on-the-move systems, because of the frequent motion of the antenna platform, antenna pointing errors are unavoidable. In this paper we demonstrate that such antenna errors will result in the EIRP exceeding the limit imposed by the standards and regulatory bodies. Also, in order to support mobile antenna terminals, a modification to the existing EIRP spectral density is suggested.
MILCOM 2007 - IEEE Military Communications Conference, 2007
ABSTRACT Mobile satellite communication systems that operate in the Ku-band (11-14 GHz band) and ... more ABSTRACT Mobile satellite communication systems that operate in the Ku-band (11-14 GHz band) and higher frequencies play a significant role in military and civilian communication systems. The satellites of interest are located in the crowded geostationary orbit with a 2 degree separation between adjacent satellites. This close spacing between adjacent satellites may lead to interference effects and, in order to limit interference to adjacent satellites, regulatory agencies have established strict limits on the effective isotropic radiated power (EIRP) from a particular terminal in its off-axis direction. Rugged terrain conditions are commonly encountered in mobile communications applications. In such terrains, the frequent motion of the antenna platform may lead to motion induced antenna pointing errors, which can be characterized by a random variable. It will be shown that such errors will lead to random variations of the terminal's off-axis EIRP spectral density. Since there are strict limits on the off-axis EIRP spectral density it is necessary to quantify these random variation. In this paper we will present a technique to analyze the time-varying interference at the adjacent satellites due to the propagation of the signal from a mobile satellite terminal.
MILCOM 2015 - 2015 IEEE Military Communications Conference, 2015
Earth stations on moving platforms (ESOMPs) are a new generation of satellite terminals designed ... more Earth stations on moving platforms (ESOMPs) are a new generation of satellite terminals designed to provide on-the-move broadband communication services to land vehicles, aircraft, and ships. ESOMPs use very small antennas and require tracking systems to maintain accurate pointing to the target satellite. Because they operate while moving, there may be instances when antenna mispointing may produce interference to other satellites or other radio systems. To account for pointing errors and other time-varying characteristics of a network of ESOMPs, it is necessary to use statistical approaches for interference analysis. This paper provides an overview of ESOMPs, their technical and operational characteristics, statistical approaches for interference analysis, and the standards and regulatory challenges that must be addressed for their successful operation.
ICC 2001. IEEE International Conference on Communications. Conference Record (Cat. No.01CH37240), 2001
High quality multimedia streaming applications over the Internet require very low packet loss rat... more High quality multimedia streaming applications over the Internet require very low packet loss rates. The Internet is characterized by long bursts of packet losses and delays. A large receive buffer can be used to mitigate the effects of packet losses and delays. However, a large receive buffer introduces a large delay in the playback of a packet. This large delay could be annoying at the start of a program or during switch over to another channel in a multi-channel broadcast. We introduce a separate low-delay tuning stream to address this start-up problem. In the steady state, this tuning stream is synchronized appropriately with the high-delay steady state stream to give an enhanced composite signal
2007 41st Annual Conference on Information Sciences and Systems, 2007
Very high-speed data links from fast-moving mobile terminals to satellites are attractive in many... more Very high-speed data links from fast-moving mobile terminals to satellites are attractive in many military applications. In order to provide such high-speed data rates we consider a multiple-input multiple-output (MIMO) free space optical (FSO) system for the earth-to-satellite link. In this case the signal is transmitted via closely-spaced multiple transmit apertures and the receiver consists of multiple apertures. Mobility of