L.A. Prashanth

Bio: L.A. Prashanth is an academic researcher from Indian Institute of Science. The author has contributed to research in topics: TCP acceleration & TCP tuning. The author has an hindex of 1, co-authored 2 publications receiving 6 citations.

OFDM-MAC algorithms and their impact on TCP performance in next generation mobile networks

Abstract: Next generation wireless systems employ Orthogonal frequency division multiplexing (OFDM) physical layer owing to the high data rate transmissions that are possible without increase in bandwidth. While TCP performance has been extensively studied for interaction with link layer ARQ, little attention has been given to the interaction of TCP with MAC layer. In this work, we explore cross-layer interactions in an OFDM based wireless system, specifically focusing on channel-aware resource allocation strategies at the MAC layer and its impact on TCP congestion control. Both efficiency and fairness oriented MAC resource allocation strategies were designed for evaluating the performance of TCP. The former schemes try to exploit the channel diversity to maximize the system throughput, while the latter schemes try to provide a fair resource allocation over sufficiently long time duration. From a TCP goodput standpoint, we show that the class of MAC algorithms that incorporate a fairness metric and consider the backlog outperform the channel diversity exploiting schemes.

MAC Design for Heterogeneous Application Support in OFDM Based Wireless Systems

Abstract: With the increasing adoption of wireless technology, it is reasonable to expect an increase in the demand for supporting both real-time multimedia and high rate reliable data services. Next generation wireless systems employ Orthogonal Frequency Division Multiplexing (OFDM) physical layer owing to the high data rate transmissions that are possible without increase in bandwidth. Towards improving the performance of these systems, we look at the design of resource allocation algorithms at medium-access iayer, and their impact on higher layers. While TCP-based elastic traffic needs reliable transport, UDP-based real-time applications have stringent delay and rate requirements. The MAC algorithms while catering to the heterogeneous service needs of these higher layers, tradeoff between maximizing the system capacity and providing fairness among users. The novelty of this work is the proposal of various channel-aware resource allocation algorithms at the MAC layer, which can result in significant performance gains in an OFDM based wireless system.

On cross-layer design of wireless networks

Abstract: Summary form only given. The layered architecture is one of the key reasons behind the explosive and continuing growth of the Internet. There are, however, special networks in which cross-layer design is appropriate and may even be necessary. Two such cases are small wireless LAN and large-scale sensor networks. We consider first the design of medium access control (MAC) for a small wireless LAN based on a multiuser physical layer. We present a complete characterization of the throughput region and present conditions under which ALOHA is optimal. Next we consider the estimation of signal field using data collected from a large scale sensor network. The impact of medium access control on estimation is examined. We show that there exists a threshold on sensor outage probability above which a distributed random access protocol (such as ALOHA) outperforms the centralized deterministic schedulers.

Full-duplex capacity allocation for OFDM-based communication

Abstract: In one embodiment, device determines a quantity of subcarriers available for data frame transmission and data frame receipt based on information included in an acknowledgement data frame. The device transmits a first data frame over at least one of the subcarriers and includes information associated with one or more additional data frames pending transmission. The device then receives a second data frame, subsequent to transmission of the first data frame, and determines a quantity of subcarriers available for transmission of the one or more additional data frames pending transmission based on the information included in the second data frame.

A cross-layer scheduling algorithm with QoS support in wireless networks

Abstract: Scheduling plays an important role in providing quality of service (QoS) support to multimedia communications in various kinds of wireless networks, including cellular networks, mobile ad hoc networks, and wireless sensor networks. The authors propose a scheduling algorithm at the medium access control (MAC) layer for multiple connections with diverse QoS requirements, where each connection employs adaptive modulation and coding (AMC) scheme at the physical (PHY) layer over wireless fading channels. Each connection is assigned a priority, which is updated dynamically based on its channel and service status; the connection with the highest priority is scheduled each time. The authors' scheduler provides diverse QoS guarantees, uses the wireless bandwidth efficiently, and enjoys flexibility, scalability, and low implementation complexity. Its performance is evaluated via simulations.

Hybrid Multi-Radio Transmission Diversity Scheme to Improve Wireless TCP Performance in an Integrated LTE and HSDPA Networks

Abstract: The performance of Transmission Control Protocol (TCP) degrades over wireless links which are characterized by varying channel condition and high error rate. TCP misinterprets these as network congestion. In this paper, we analyze the TCP send rate of parallel multi-radio transmission diversity (MRTD) schemes with and without redundancy in heterogeneous wireless networks (HWNs). Through developing a cross-layer model, MAC layer packet error rate and link rate are taken into consideration. By comparing the performance of these schemes, we propose a hybrid MRTD scheme which aims at obtaining good tradeoff between robustness and efficiency to improve TCP performance. The feasibility of the proposed scheme is validated by user-level simulation. Moreover, system-level simulation results show that hybrid MRTD scheme improves the wireless TCP performance comparing with parallel MRTD schemes.