In underwater acoustic (UWA) communications, the propagated signal undergoes severe Doppler and m... more In underwater acoustic (UWA) communications, the propagated signal undergoes severe Doppler and multipath distortions. The Doppler estimation/compensation and channel estimation/equalization techniques required to deal with these distortions contribute significantly to the overall complexity of UWA modems. In this paper, we propose a data packet structure for high data rate transmission in time-varying UWA channels with the channel dynamic modelled by velocity and acceleration between the transmitter and receiver. The data packet consists of superimposed data and periodic pilot sequences. The superposition allows achievement of a high spectral efficiency for data transmission. The repeated pilot symbols allow the use of a low-complexity multi-branch autocorrelation method for coarse estimation of Doppler parameters related to the velocity and acceleration. To refine these estimates, we further propose a lowcomplexity fine Doppler estimator based on dichotomous iterations. We also present a low complexity frequency domain channel estimator exploiting the channel sparsity. The proposed modem design has been evaluated using simulation and practical sea trials. The experiments demonstrate high detection performance of the proposed design, in particular in comparison with a more traditional design that ignores the acceleration between the transmitter and receiver.
IEEE Second International Symposium on Spread Spectrum Techniques and Applications
A communication scheme is proposed enabling data to be transmitted over an occupied channel by su... more A communication scheme is proposed enabling data to be transmitted over an occupied channel by superposition of a direct sequence spread spectrum signal of low power spectral density on the existing traffic. Particular attention has been paid to satellite television broadcasting but the principles in this work could be applied to any channel. Applications of this technique include engineering order
IEE Seminar on Broadband Satellite: The Critical Success Factors Technology, Services and Markets
This paper explores an efficient Medium Access Control protocol for carrying data traffic via sat... more This paper explores an efficient Medium Access Control protocol for carrying data traffic via satellite. The Combined Free/Demand Assignment Multiple Access (CFDAMA) protocol combines free assignment of data slots with demand assignment, providing a minimum delay of one round trip time at low loads and the statistical multiplexing gains of demand assignment at high loads. The delay/utilisation performance of CFDAMA is explored for both Poisson and selfsimilar traffic models. It is shown for Poisson traffic that CFDAMA provides both extremely low end-to end delay and variance in delay of packet transmissions over a wide range of loads up to 85% of the channel capacity. For self-similar traffic, it has been found that the scheme is limited to a lower maximum channel loading, but performs better at low channel loads. The importance of an accurate traffic model in network performance evaluation is highlighted. Comparisons are made between CFDAMA and the Slotted ALOHA protocol, and it is shown that CFDAMA outperforms Slotted ALOHA over virtually the entire range of channel utilisation.
ABSTRACT This paper explores some of the techniques and issues associated with the design of an e... more ABSTRACT This paper explores some of the techniques and issues associated with the design of an effective medium access control (MAC) protocol for a geostationary satellite channel. Two satellite MAC schemes are described, combined free/demand assignment multiple access (CFDAMA) and burst targeted demand assignment multiple access (BTDAMA) and their performance is evaluated for both Poisson and self-similar data traffic. Simulation results show that the effectiveness of different MAC techniques is heavily dependent on the nature of the traffic to be supported. It is shown that the CFDAMA scheme can provide good delay/utilisation performance of a satellite channel for Poisson traffic but poorer performance for the highly bursty self-similar traffic. The BTDAMA scheme on the other hand provides good delay/utilisation performance for self-similar traffic but is less suited to handling Poisson traffic.
This Report provides an overview of the principal players and projects involving High Altitude Ai... more This Report provides an overview of the principal players and projects involving High Altitude Aircrafts or Airships (HAAS). It concentrates upon those projects which may be classed as involving 'High Altitude' platforms, although attention is also given to other platforms, such as UAVs, where relevant. Brief summaries are given of various projects together with observations and discussion. All known major
2004 Ieee 15th International Symposium on Personal Indoor and Mobile Radio Communications, Oct 5, 2004
... 2]. A periodogram-based frequency estimator for systems with multi-antenna transmission with ... more ... 2]. A periodogram-based frequency estimator for systems with multi-antenna transmission with Hadamard sequences was proposed by Hong & et a1 in [3]. An autocorrelation-based frequency estimator was proposed by Jeong, Jo and & ... (4) aH+HAH(wo)A(wo)+a __ aHra __ E ...
2004 IEEE 15th International Symposium on Personal, Indoor and Mobile Radio Communications (IEEE Cat. No.04TH8754), 2000
ABSTRACT The burst targeted demand assignment multiple access (BTDAMA) protocols incorporate an o... more ABSTRACT The burst targeted demand assignment multiple access (BTDAMA) protocols incorporate an original approach to DAMA, which eliminates the fundamental end-to-end delay bound associated with the traditional DAMA techniques. Whilst they offer significant improvements in the achievable delay/utilisation performance for bursty packet transmission over satellite, they are constrained by the initial build up of packets at the start of traffic bursts. In this paper, we introduce the adaptivity to the uplink frame that enables the proportion of alternative types of capacity allocation to be varied on a dynamic basis. Sufficient demand assigned capacity is assigned to meet the instantaneous user requirements, with spare capacity allocated by an alternative strategy to assist with initial throughput at the start of bursts. Results show that this approach enhances the end-to-end delay distribution and delay jitter performance compared with the conventional static frame BTDAMA schemes.
A technique is described to reduce the probability of false-lock in Costas loops. This is where a... more A technique is described to reduce the probability of false-lock in Costas loops. This is where a frequency offset arises at a multiple of half the incoming data rate due to finite bandwidth of the arm filters. A modification is described to process components of this offset so as to augment the feedback control voltage. The performance is analyzed and
EURASIP Journal on Wireless Communications and Networking, 2008
The Swiss-based "StratXX" project during 2006-2007 has been developing a stratospheric lighter-th... more The Swiss-based "StratXX" project during 2006-2007 has been developing a stratospheric lighter-than-air platform for deployment of telecommunications and environmental monitoring services. In support of a first round of experimental trials, a WiMAX communications subsystem, including platform payload and ground stations, has been developed. The communications system design and results of terrestrial pretrials are reported.
In underwater acoustic (UWA) communications, the propagated signal undergoes severe Doppler and m... more In underwater acoustic (UWA) communications, the propagated signal undergoes severe Doppler and multipath distortions. The Doppler estimation/compensation and channel estimation/equalization techniques required to deal with these distortions contribute significantly to the overall complexity of UWA modems. In this paper, we propose a data packet structure for high data rate transmission in time-varying UWA channels with the channel dynamic modelled by velocity and acceleration between the transmitter and receiver. The data packet consists of superimposed data and periodic pilot sequences. The superposition allows achievement of a high spectral efficiency for data transmission. The repeated pilot symbols allow the use of a low-complexity multi-branch autocorrelation method for coarse estimation of Doppler parameters related to the velocity and acceleration. To refine these estimates, we further propose a lowcomplexity fine Doppler estimator based on dichotomous iterations. We also present a low complexity frequency domain channel estimator exploiting the channel sparsity. The proposed modem design has been evaluated using simulation and practical sea trials. The experiments demonstrate high detection performance of the proposed design, in particular in comparison with a more traditional design that ignores the acceleration between the transmitter and receiver.
IEEE Second International Symposium on Spread Spectrum Techniques and Applications
A communication scheme is proposed enabling data to be transmitted over an occupied channel by su... more A communication scheme is proposed enabling data to be transmitted over an occupied channel by superposition of a direct sequence spread spectrum signal of low power spectral density on the existing traffic. Particular attention has been paid to satellite television broadcasting but the principles in this work could be applied to any channel. Applications of this technique include engineering order
IEE Seminar on Broadband Satellite: The Critical Success Factors Technology, Services and Markets
This paper explores an efficient Medium Access Control protocol for carrying data traffic via sat... more This paper explores an efficient Medium Access Control protocol for carrying data traffic via satellite. The Combined Free/Demand Assignment Multiple Access (CFDAMA) protocol combines free assignment of data slots with demand assignment, providing a minimum delay of one round trip time at low loads and the statistical multiplexing gains of demand assignment at high loads. The delay/utilisation performance of CFDAMA is explored for both Poisson and selfsimilar traffic models. It is shown for Poisson traffic that CFDAMA provides both extremely low end-to end delay and variance in delay of packet transmissions over a wide range of loads up to 85% of the channel capacity. For self-similar traffic, it has been found that the scheme is limited to a lower maximum channel loading, but performs better at low channel loads. The importance of an accurate traffic model in network performance evaluation is highlighted. Comparisons are made between CFDAMA and the Slotted ALOHA protocol, and it is shown that CFDAMA outperforms Slotted ALOHA over virtually the entire range of channel utilisation.
ABSTRACT This paper explores some of the techniques and issues associated with the design of an e... more ABSTRACT This paper explores some of the techniques and issues associated with the design of an effective medium access control (MAC) protocol for a geostationary satellite channel. Two satellite MAC schemes are described, combined free/demand assignment multiple access (CFDAMA) and burst targeted demand assignment multiple access (BTDAMA) and their performance is evaluated for both Poisson and self-similar data traffic. Simulation results show that the effectiveness of different MAC techniques is heavily dependent on the nature of the traffic to be supported. It is shown that the CFDAMA scheme can provide good delay/utilisation performance of a satellite channel for Poisson traffic but poorer performance for the highly bursty self-similar traffic. The BTDAMA scheme on the other hand provides good delay/utilisation performance for self-similar traffic but is less suited to handling Poisson traffic.
This Report provides an overview of the principal players and projects involving High Altitude Ai... more This Report provides an overview of the principal players and projects involving High Altitude Aircrafts or Airships (HAAS). It concentrates upon those projects which may be classed as involving 'High Altitude' platforms, although attention is also given to other platforms, such as UAVs, where relevant. Brief summaries are given of various projects together with observations and discussion. All known major
2004 Ieee 15th International Symposium on Personal Indoor and Mobile Radio Communications, Oct 5, 2004
... 2]. A periodogram-based frequency estimator for systems with multi-antenna transmission with ... more ... 2]. A periodogram-based frequency estimator for systems with multi-antenna transmission with Hadamard sequences was proposed by Hong & et a1 in [3]. An autocorrelation-based frequency estimator was proposed by Jeong, Jo and & ... (4) aH+HAH(wo)A(wo)+a __ aHra __ E ...
2004 IEEE 15th International Symposium on Personal, Indoor and Mobile Radio Communications (IEEE Cat. No.04TH8754), 2000
ABSTRACT The burst targeted demand assignment multiple access (BTDAMA) protocols incorporate an o... more ABSTRACT The burst targeted demand assignment multiple access (BTDAMA) protocols incorporate an original approach to DAMA, which eliminates the fundamental end-to-end delay bound associated with the traditional DAMA techniques. Whilst they offer significant improvements in the achievable delay/utilisation performance for bursty packet transmission over satellite, they are constrained by the initial build up of packets at the start of traffic bursts. In this paper, we introduce the adaptivity to the uplink frame that enables the proportion of alternative types of capacity allocation to be varied on a dynamic basis. Sufficient demand assigned capacity is assigned to meet the instantaneous user requirements, with spare capacity allocated by an alternative strategy to assist with initial throughput at the start of bursts. Results show that this approach enhances the end-to-end delay distribution and delay jitter performance compared with the conventional static frame BTDAMA schemes.
A technique is described to reduce the probability of false-lock in Costas loops. This is where a... more A technique is described to reduce the probability of false-lock in Costas loops. This is where a frequency offset arises at a multiple of half the incoming data rate due to finite bandwidth of the arm filters. A modification is described to process components of this offset so as to augment the feedback control voltage. The performance is analyzed and
EURASIP Journal on Wireless Communications and Networking, 2008
The Swiss-based "StratXX" project during 2006-2007 has been developing a stratospheric lighter-th... more The Swiss-based "StratXX" project during 2006-2007 has been developing a stratospheric lighter-than-air platform for deployment of telecommunications and environmental monitoring services. In support of a first round of experimental trials, a WiMAX communications subsystem, including platform payload and ground stations, has been developed. The communications system design and results of terrestrial pretrials are reported.
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Papers by Tim C Tozer