Satyam Agarwal

DSAT-MAC: Dynamic slot allocation based TDMA MAC protocol for Cognitive Radio Networks

Cognitive Radio Networks (CRN) have enabled us to efficiently reuse the underutilized radio spectrum. The MAC protocol in CRN defines the spectrum usage by sharing the channels efficiently among users. In this paper we propose a novel TDMA based MAC protocol with dynamically allocated slots. Most of the MAC protocols proposed in the literature employ Common Control Channel (CCC) to manage the resources among Cognitive Radio (CR) users. Control channel saturation in case of large number of CR users is one of the main drawbacks of the CCC based MAC protocols. In contrast with CCC based MAC protcols, DSAT-MAC protocol is based on the TDMA mechanism, without using any CCC for control information exchange. The channels are divided into time slots and CR users send their control or data packets over their designated slot. The protocol ensures that no slot is left vacant. This guarantees full use of the available spectrum. The protocol includes the provision for Quality of Service, where real-time and safety critical data is transmitted with highest priority and least delay. The protocol also ensures a fair sharing of available spectrum among the CR users, with the mechanism to regulate the transmission of malicious nodes. Energy saving techniques are also presented for longer life of battery operated CR nodes. Theoretical analysis and simulations over ns-2 of the proposed protocol reveal that the protocol performs better in various CR adhoc network applications.

eDSA: Energy-Efficient Dynamic Spectrum Access Protocols for Cognitive Radio Networks

In this paper, we propose a class of energy-efficient dynamic spectrum access (DSA) protocols for secondary user (SU) communication over a single primary user (PU) channel. The proposed variants of DSA can be optimized with respect to different backoff strategies and SU packet lengths. Via Markov chain models and numerical analysis, we derive the optimal SU packet length and inter-sensing time for optimal SU performance in the DSA variants. We evaluate the protocol performance in terms of SU goodput, SU energy efficiency, and PU collision ratio. Adaptability of the proposed SU operation protocol in practical scenarios is tested over cellular GSM band as well as under real-time video over IP based PU traffic in ISM band. Our performance studies demonstrate that the proposed protocols offer significantly high channel utilization while keeping the PU collisions below an acceptable threshold. The proposed protocol operation is also outlined, where the protocol adapts to the changing PU traffic load for optimized performance.

QoS-Aware Downlink Cooperation for Cell-Edge and Handoff Users

In this paper, we present a quality-of-service (QoS)-aware cooperative downlink scheduling approach for cell-edge and handoff users that offers more reliability and higher effective capacity. The cooperation (handoff) region is defined for active handoff users between two adjacent base stations (BSs) as a function of the user QoS requirements and network load. In addition, the proposed technique inherently acquires intercell interference (ICI) coordination by adjusting the position and size of the cooperation window suitably. Numerical results are presented showing reliability, user QoS and capacity gain performance, and the region for cooperative scheduling in a coded communication scenario. Our analysis indicates that cooperation provides relatively less gain in effective capacity, i.e., up to about 40% with respect to noncooperative handoff, when the QoS requirement is loose. On the other hand, when the QoS requirement is more stringent, the effective capacity gain can increase up to nearly 100%. Additionally, we show that, while for applications with a loose QoS requirement the cooperation window size is small, i.e., nearly 1% of the total area of the BSs participating in cooperation, it increases quite significantly, i.e., up to nearly 25%, for the applications with stringent QoS. Although the outage performance of the proposed approach is poorer than the joint transmission mode of a cooperative multipoint scheme in lightly loaded networks, its effective capacity is significantly higher under varying network traffic load and QoS constraints.

Impact of Channel Switching in Energy Constrained Cognitive Radio Networks

In this letter, we investigate the energy efficiency of multichannel spectrum access in cognitive radio networks. We consider two channel access schemes. In one case, a secondary user (SU) is assigned multiple channels and the channels are switched whenever a primary user (PU) returns. In the other, the SU operates on a single channel without switching to other channels. We develop an analytic framework on achievable channel utilization and energy consumption performance of the SU. From the results, we examine the trade-off between SU channel utilization and energy consumption, and identify the PU traffic conditions where one scheme outperforms the other.

Cognitive Multihoming System for Energy and Cost Aware Video Transmission

To alleviate the spectrum scarcity problem in the licensed cellular networks (LCNs), we introduce a new paradigm called cognitive multihoming (CM), where a cognitive radio (CR)-enabled base station transmits to the users simultaneously over the licensed cellular bands and primary user bands in CR networks (CRNs). The CR aspect incurs lower cost, however, at the expense of higher energy consumption due to intermittent channel sensing. On the other hand, transmission via LCN is expensive because of its licensing premium. To minimize the transmission cost while meeting the users energy and received video quality constraints, sensing duration and transmission rate over CRN, transmission rate over LCN, and network selection for retransmission of lost packets are adjusted. Solution to the multiuser resource allocation optimization problem is obtained by solving the cost minimization problem of a single-user system. The problem is nonconvex which is solved using convex-concave procedure. The proposed scheme is compared with the cases where a user operates over a single network, either LCN or CRN. The system performance results indicate that the proposed CM strategy significantly decreases the cost to the users as well as serves a higher number of users while maintaining the desired video quality and energy consumption constraints.

Cognitive Multihoming: Maximizing Network Utility over CR-Assisted Cellular Network

Demand for wireless data bandwidth has been increasing explosively so that the present licensed cellular networks (LCNs) themselves are no longer competent to provide high quality service to the users at a reasonable cost. In this paper, we propose a cost-effective system, called cognitive multihoming (CM), that enables high quality service and at the same time incurs low cost. The proposed system considers a cellular base station with added cognitive radio (CR) functionality. The heterogeneous resources are organized into a single centrally- managed virtual system to allocate the heterogeneous users with varying quality and cost constraints. Multiple multihoming-capable heterogeneous users request downlink unicast data from the system. Transmissions to these users are performed simultaneously via LCN and CR network (CRN). This cooperative approach aids lowering service cost to the users. The possibility of loss in quality of service is mitigated by optimally distributing the traffic load between LCN and CRN, based on the users rate requirements. To evaluate the CM performance we consider a benchmark system with the same total channel resource from LCN and CRN, where a user is served via either LCN or CRN depending on the users quality and cost preferences. Numerical results show that, on average the network utility of the proposed system is nearly 17% higher than the benchmark.

Dynamic spectrum access for energy-constrained CR: single channel versus switched multichannel

In energy-constrained cognitive radio networks (CRNs), the choice on single channel access versus switched multichannel access is critical for energy saving and sustainable network operation. In this study, the authors study and compare the energy efficiency of switched (probabilistic) multichannel access (pMCA) and fixed single-channel access (SCA) in CRNs. In pMCA, a secondary user (SU) switches channel with certain probability whenever it encounters a busy channel. In SCA on the other hand, the SU stays on the same channel for its usage and waits for its availability. Via an analytical framework the authors derive the channel utilisation and energy efficiency of the two schemes. From the results the authors examine the primary user (PU) traffic dependent optimum switching probability in pMCA and the regime of PU activity dynamics where SCA outperforms pMCA.

Poster: Rural Broadband Access via TVWs

Wireless broadband access has become a necessity rather than luxury. However, a significant proportion of rural population in the developing countries are deprived of this basic necessity. Rural area in the developing countries is characterized by low population density in sparsely located villages and modest income of the villagers. Cellular services are mostly unavailable in remote rural areas due to low return on investment the operators experience with a relatively low user density and data demands. Cost of deploying fiber optic/copper-lines is high. Thus, in order to make Internet available to the rural populace, an efficient and low-cost network setup is required. Measurement studies have revealed that most of the TV bands are unused due to TV transmissions shifting from analog to digital domain. These unused TV bands or white space (TVWS) are being considered for enabling rural broadband due to their low-loss propagation characteristics.

A New Spectrum Occupancy Model for 802.11 WLAN Traffic

We report characterization of busy and idle periods in 802.11 wireless local area network via experiments in software-defined radio. A new channel occupancy model, called the Gaussian mixture (GM) model, is proposed and shown to fit the empirical data significantly better than the other available models. Further simulation results demonstrate that utilizing the GM model highly improves secondary user goodput and energy efficiency.

A persistent link layer transmission strategy for efficient dynamic spectrum access

In this paper, we propose an efficient dynamic spectrum access protocol for secondary users (SU) communication over an agile single primary user (PU) channel. The proposed access scheme is optimized with respect to different SU back-off times and SU packet length. Via Markov chain models and numerical analysis, we derive the optimal SU packet length for optimal SU performance at a given PU traffic load. We evaluate the protocol performance in terms of SU goodput and PU collision ratio. An outline of the proposed protocol operation is also given, where the protocol adapts to the changing PU traffic load for optimized spectrum access performance. Our performance studies demonstrate that the proposed protocol offers significantly high channel utilization while keeping the PU collisions below a predefined acceptable threshold.