Vaibhav Singh - Academia.edu (original) (raw)
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Papers by Vaibhav Singh
This thesis investigates the performance of broadcast systems in which the transmitted signal is ... more This thesis investigates the performance of broadcast systems in which the transmitted signal is obtained by superposition of the independent user signals. We first focus on single-input single-output systems in additive white Gaussian noise channel. We study the performance of a superposition coding based transmission scheme for a 2-user broadcast system when the power allocated to each user is varied. Using a simple scheme, we achieve near-capacity performance. When the power is split equally between the users, superposition coding leads to severe erasure at the transmitter. It is seen that this degrades the performance significantly. Next we focus on multiple-input multiple-output broadcast systems. We compare the performance of a transmission scheme based on superposition of user signals with a orthogonal transmission scheme. By using an outer turbo code and performing iterative joint detection and decoding, it is seen that linear dispersion code clearly outperforms orthogonal code. This improved performance is however obtained at the cost of increased receiver complexity. We finally study some receiver structures with reduced complexity. It is also seen that the labelling map used to map the bits to symbols has a significant impact on the performance. i
Transmitter diversity at the base station has been included in WCDMA standard for third generatio... more Transmitter diversity at the base station has been included in WCDMA standard for third generation mobile systems as a means of increasing the downlink system capacity. In previous works, it has been shown that open loop transmitter diversity can significantly increase the downlink capacity. However, the performance in multipath environment is not known. In our study, we present the simulation results for downlink system capacity taking into account the effect of Doppler frequency and multipath fading. The results show that even in severe multipath wireless channel, diversity scheme can greatly improve the system capacity when no soft handover is used.
Resource allocation algorithm in a multiuser access scenario plays a vital role in efficient util... more Resource allocation algorithm in a multiuser access scenario plays a vital role in efficient utilization of limited channel resource and supporting quality-of-service (QoS) of users. Dynamic resource allocation at the physical layer has been extensively studied in recent years. Orthogonal ...
Optical Switching and Networking, 2010
Efficient uplink scheduling in Ethernet passive optical networks (EPONs) is very important for ma... more Efficient uplink scheduling in Ethernet passive optical networks (EPONs) is very important for maximizing the network capacity while maintaining the required quality of service (QoS). Several variants of dynamic bandwidth resource allocation have been proposed in recent research literature. However, the available techniques do not fully exploit the elastic properties of the user traffic. In this paper, we explore optimal predictive resource allocation strategies by exploiting the elasticity of QoS-constrained traffic and using the knowledge of traffic patterns of different service classes. We propose a predictive dynamic uplink bandwidth allocation scheme that offers lower access delay and packet loss rate, yet achieves a higher overall network throughput. We formulate a model for determining the traffic burstiness-dependent optimum prediction order that would enhance the quality of prediction with a minimum possible prediction-related processing overhead. We then demonstrate that, in a multi-class access scheduling, with respect to the conventional dynamic allocation strategies, our priority scheduling with judicious prediction of individual traffic classes can enhance the system performance significantly. Our analytic observations are supported by extensive simulation results.
This thesis investigates the performance of broadcast systems in which the transmitted signal is ... more This thesis investigates the performance of broadcast systems in which the transmitted signal is obtained by superposition of the independent user signals. We first focus on single-input single-output systems in additive white Gaussian noise channel. We study the performance of a superposition coding based transmission scheme for a 2-user broadcast system when the power allocated to each user is varied. Using a simple scheme, we achieve near-capacity performance. When the power is split equally between the users, superposition coding leads to severe erasure at the transmitter. It is seen that this degrades the performance significantly. Next we focus on multiple-input multiple-output broadcast systems. We compare the performance of a transmission scheme based on superposition of user signals with a orthogonal transmission scheme. By using an outer turbo code and performing iterative joint detection and decoding, it is seen that linear dispersion code clearly outperforms orthogonal code. This improved performance is however obtained at the cost of increased receiver complexity. We finally study some receiver structures with reduced complexity. It is also seen that the labelling map used to map the bits to symbols has a significant impact on the performance. i
Transmitter diversity at the base station has been included in WCDMA standard for third generatio... more Transmitter diversity at the base station has been included in WCDMA standard for third generation mobile systems as a means of increasing the downlink system capacity. In previous works, it has been shown that open loop transmitter diversity can significantly increase the downlink capacity. However, the performance in multipath environment is not known. In our study, we present the simulation results for downlink system capacity taking into account the effect of Doppler frequency and multipath fading. The results show that even in severe multipath wireless channel, diversity scheme can greatly improve the system capacity when no soft handover is used.
Resource allocation algorithm in a multiuser access scenario plays a vital role in efficient util... more Resource allocation algorithm in a multiuser access scenario plays a vital role in efficient utilization of limited channel resource and supporting quality-of-service (QoS) of users. Dynamic resource allocation at the physical layer has been extensively studied in recent years. Orthogonal ...
Optical Switching and Networking, 2010
Efficient uplink scheduling in Ethernet passive optical networks (EPONs) is very important for ma... more Efficient uplink scheduling in Ethernet passive optical networks (EPONs) is very important for maximizing the network capacity while maintaining the required quality of service (QoS). Several variants of dynamic bandwidth resource allocation have been proposed in recent research literature. However, the available techniques do not fully exploit the elastic properties of the user traffic. In this paper, we explore optimal predictive resource allocation strategies by exploiting the elasticity of QoS-constrained traffic and using the knowledge of traffic patterns of different service classes. We propose a predictive dynamic uplink bandwidth allocation scheme that offers lower access delay and packet loss rate, yet achieves a higher overall network throughput. We formulate a model for determining the traffic burstiness-dependent optimum prediction order that would enhance the quality of prediction with a minimum possible prediction-related processing overhead. We then demonstrate that, in a multi-class access scheduling, with respect to the conventional dynamic allocation strategies, our priority scheduling with judicious prediction of individual traffic classes can enhance the system performance significantly. Our analytic observations are supported by extensive simulation results.