Showing papers by "Shivendra S. Panwar published in 2011"

Exploiting MIMO antennas in cooperative cognitive radio networks

Abstract: Recently, a new paradigm for cognitive radio networks has been advocated, where primary users (PUs) recruit some secondary users (SUs) to cooperatively relay the primary traffic. However, all existing work on such cooperative cognitive radio networks (CCRNs) operate in the temporal domain. The PU needs to give out a dedicated portion of channel access time to the SUs for transmitting the secondary data in exchange for the SUs' cooperation, which limits the performance of both PUs and SUs. On the other hand, Multiple Input Multiple Output (MIMO) enables transmission of multiple independent data streams and suppression of interference via beam-forming in the spatial domain over MIMO antenna elements to provide significant performance gains. Researches have not yet explored how to take advantage of the MIMO technique in CCRNs. In this paper, we propose a novel MIMO-CCRN framework, which enables the SUs to utilize the capability provided by the MIMO to cooperatively relay the traffic for the PUs while concurrently accessing the same channel to transmit their own traffic. We design the MIMO-CCRN architecture by considering both the temporal and spatial domains to improve spectrum efficiency. Further we provide theoretical analysis for the primary and secondary transmission rate under MIMO cooperation and then formulate an optimization model based on a Stackelberg game to maximize the utilities of PUs and SUs. Evaluation results show that both primary and secondary users achieve higher utility by leveraging MIMO spatial cooperation in MIMO-CCRN than with conventional schemes.

Scalable Video Multicast in Hybrid 3G/Ad-Hoc Networks

Abstract: Mobile video broadcasting service, or mobile TV, is expected to become a popular application for 3G wireless network operators. Most existing solutions for video Broadcast Multicast Services (BCMCS) in 3G networks employ a single transmission rate to cover all viewers. The system-wide video quality of the cell is therefore throttled by a few viewers close to the boundary, and is far from reaching the social-optimum allowed by the radio resources available at the base station. In this paper, we propose a novel scalable video broadcast/multicast solution, SV-BCMCS, that efficiently integrates scalable video coding, 3G broadcast, and ad-hoc forwarding to balance the system-wide and worst-case video quality of all viewers at 3G cell. We solve the optimal resource allocation problem in SV-BCMCS and develop practical helper discovery and relay routing algorithms. Moreover, we analytically study the gain of using ad-hoc relay, in terms of users' effective distance to the base station. Through extensive real video sequence driven simulations, we show that SV-BCMCS significantly improves the system-wide perceived video quality. The users' average PSNR increases by as much as 1.70 dB with slight quality degradation for the few users close to the 3G cell boundary.

Cooperative Layered Video Multicast Using Randomized Distributed Space Time Codes

Abstract: With the increased popularity of mobile multimedia services, efficient and robust video multicast strategies are of critical importance. Cooperative communications has been shown to improve the robustness and the data rates for point-to-point transmission. In this paper, a two-hop cooperative transmission scheme for multicast in infrastructure-based networks is used, where multiple relays forward the data simultaneously using randomized distributed space time codes (RDSTC). This randomized cooperative transmission is further integrated with layered video coding and packet level forward error correction (FEC) to enable efficient and robust video multicast. Three different schemes are proposed to find the system operating parameters based on the availability of the channel information at the source station: RDSTC with full channel information, RDSTC with limited channel information, and RDSTC with node count. The performance of these three schemes are compared with rate adaptive direct transmission and conventional multicast that does not use rate adaptation. The results show that while rate-adaptive direct transmission provides better video quality than conventional multicast, all three proposed randomized cooperative schemes outperform both strategies significantly as long as the network has enough nodes. Furthermore, the performance gap between RDSTC with full channel information and RDSTC with limited channel information or node count is relatively small, indicating the robustness of the proposed cooperative multicast system using RDSTC.

Interference management using frequency planning in an OFDMA based wireless network

Abstract: In next generation broadband wireless networks, the orthogonal frequency division multiple access (OFDMA) technique provides a flexible physical interface for mobile users (MS) to share the radio resources. Since OFDMA allows MSs in different cells to reuse the same frequency subchannels to increase network spectrum utilization, MSs at the edge of a cell suffer from severe inter-cell interference from co-channel MSs in the neighboring cells. In WiMAX and LTE networks, fractional frequency reuse (FFR) is employed to mitigate the interference for edge users, but may incur a cost in terms of a lower overall spectrum utilization. In this paper, we propose a novel frequency planning scheme to improve the signal-to-interference (SIR) ratio of edge MSs in a multi-cell OFDMA system. A cell is partitioned in a way that minimizes the interference to the edge areas while sustaining a full frequency reuse factor (FRF) for each cell. Simulation results show that our scheme substantially outperforms FFR methods in terms of SIR under the condition of full frequency reuse and high traffic load.

Distributed scheduling for an optical switch

Abstract: Scheduling methods and apparatus for use with optical switches with hybrid architectures are provided. An exemplary distributed scheduling process achieves 100% throughput for any admissible Bernoulli arrival traffic. The exemplary distributed scheduling process may be easily adapted to work for any finite round trip time, without sacrificing any throughput. Simulation results also showed that this distributed scheduling process can provide very good delay performance for different traffic patterns and for different round trip times associated with current switches.

A Distributed Scheduling Algorithm for High-Speed Switching Systems

Abstract: Given the rapid increase in traffic, greater demands have been put on research in high-speed switching systems. Such systems have to simultaneously meet several constraints, e.g., high throughput, low delay and low complexity. This makes it challenging to design an efficient scheduling algorithm, and has consequently drawn considerable research interest. However, previous results either cannot provide a 100% throughput guarantee without a speedup, or require a complex centralized scheduler. In this paper, we design a distributed 100% throughput algorithm for crosspoint buffered switches, called DISQUO, with very limited message passing. We prove that DISQUO can achieve 100% throughput for any admissible Bernoulli traffic, with a low time complexity of O(1) per port and a few bits message exchanging in every time slot. To the best of our knowledge, it is the first distributed algorithm that can provide a 100% throughput for a crosspoint buffered switch.

Distributed scheduling for variable-size packet switching system

Abstract: Scheduling methods and apparatus are provided for an input-queued switch The exemplary distributed scheduling process achieves 100% throughput for any admissible Bernoulli arrival traffic The exemplary distributed scheduling process includes scheduling variable size packets The exemplary distributed scheduling process may be easily implemented with a low-rate control or by sacrificing the throughput by a small amount Simulation results also showed that this distributed scheduling process can provide very good delay performance for different traffic patterns The exemplary distributed scheduling process may therefore be a good candidate large-scale high-speed switching systems

The Urge to Merge: When Cellular Service Providers Pool Capacity

Abstract: As cellular networks are turning into a platform for ubiquitous data access, cellular operators are facing a severe data capacity crisis due to the exponential growth of traffic generated by mobile users. In this work, we investigate the benefits of sharing infrastructure and spectrum among two cellular operators. Specifically, we provide a multi-cell analytical model using stochastic geometry to identify the performance gain under different sharing strategies, which gives tractable and accurate results. To validate the performance using a realistic setting, we conduct extensive simulations for a multi-cell OFDMA system using real base station locations. Both analytical and simulation results show that even a simple cooperation strategy between two similar operators, where they share spectrum and base stations, roughly quadruples capacity as compared to the capacity of a single operator. This is equivalent to doubling the capacity per customer, providing a strong incentive for operators to cooperate, if not actually merge.

Characterization of a shared buffer optoelectronic packet router

Abstract: The rapid increase in Internet traffic is forcing packet routers to grow in capacity to meet the demand. Optical packet routers with less buffering and a greater degree of optical transparency are actively being researched as a way to improve energy efficiency and capacity scaling over traditional electronic routers. Since it is difficult to buffer packets in the optical domain, in this paper we analyze the performance of a hybrid optoelectronic packet router. The router architecture has multiple optical switch planes and a shared electronic buffer to resolve output-port contention. By using multiple ports on the switch planes for each input and output fiber, and by using some switch-plane ports to inter-connect the planes, we can achieve a relatively low packet loss ratio in a router with no buffer. In this case, most traffic can be switched using only the through optical paths of the router without entering the shared buffer. The shared electronic buffer is primarily used to reduce the packet drop ratio under periods of heavy loads and occasionally for optical regeneration of a packet.We run extensive simulations to evaluate the performance of the router with varying number of switch plane ports, number of connections to the electronic buffer, and number of interconnections between the switch planes. We show that the router can provide good throughput, with realistic on-off bursty traffic and asynchronous packet arrivals.

STiCMAC: A MAC Protocol for Robust Space-Time Coding in Cooperative Wireless LANs

Abstract: Relay-assisted cooperative wireless communication has been shown to have significant performance gains over the legacy direct transmission scheme. Compared with single relay based cooperation schemes, utilizing multiple relays further improves the reliability and rate of transmissions. Distributed space-time coding (DSTC), as one of the schemes to utilize multiple relays, requires tight coordination between relays and does not perform well in a distributed environment with mobility. In this paper, a cooperative medium access control (MAC) layer protocol, called \emph{STiCMAC}, is designed to allow multiple relays to transmit at the same time in an IEEE 802.11 network. The transmission is based on a novel DSTC scheme called \emph{randomized distributed space-time coding} (\emph{R-DSTC}), which requires minimum coordination. Unlike conventional cooperation schemes that pick nodes with good links, \emph{STiCMAC} picks a \emph{transmission mode} that could most improve the end-to-end data rate. Any station that correctly receives from the source can act as a relay and participate in forwarding. The MAC protocol is implemented in a fully decentralized manner and is able to opportunistically recruit relays on the fly, thus making it \emph{robust} to channel variations and user mobility. Simulation results show that the network capacity and delay performance are greatly improved, especially in a mobile environment.

A system-theoretic approach for epidemic networks with time-varying population

Abstract: In this paper, a modern system-theoretic approach is applied to analyze the dynamics of epidemic networks with time-varying population. Specifically, cooperative system theory, nonnegative matrix theory and large-scale system theory are jointly invoked to study the global asymptotic stability of an equilibrium of interest. The obtained results may provide biologically-meaningful measures for how to control the disease and explain why the disease fades out in the population. An explicit estimate is given to describe how the recovery rate affects the epidemic level.