Aditya Trivedi

Priority based MAC scheme for cognitive radio network: A queuing theory modelling

In the cognitive radio networks (CRNs), primary user (PU) has higher priority to access the spectrum band over the secondary user (SU). In this paper, new multichannel priority based cognitive radio (CR) architecture is presented for medium access control (MAC). This multichannel CRN architecture is designed with pre-emptive, non-preemptive resume, and pooling priority based systems. Main objective of this modelling is to minimize the overall transmitting or processing time for all the users. We have derived the optimal system time, waiting time, and channel selection probability (conditional, and unconditional probabilities) for the priority-based spectrum decision schemes. We have also designed and simulated multichannel priority CRN system with various cases, i.e., multichannel with priorities and opportunistic selection of best available channel from multichannel systems. Simulation results and observations verify our mathematical model that, system or processing time depends on the number of users in the system and queue, and number of channels in the CRN system. Moreover, processing time for the primary users is much lower than the secondary users, because waiting time of secondary users is higher than the primary users.

Joint Routing and Stream Control Scheduling in MIMO-Based WMNs

Wireless Mesh Networks (WMNs) have emerged as a cost effective and promising technology to provide broadband connectivity in several environments. In this work, we consider a cross layer optimal design of routing, medium access control (MAC) scheduling, and physical layer resource allocation for WMNs, where nodes are equipped with Multiple Input Multiple Output (MIMO) antennas. MIMO antennas can greatly im- proves the throughput by transmitting multiple independent data streams and/or suppressing the interference from neighboring links. To address the MAC and stream control at the physical layer, we consider the notion of Transmission Configurations (TCs). By incorporating the TCs in the cross-layer design, we formulate a Joint Routing and Stream Control Scheduling (JRSCS) problem as a linear program (LP), with the objective of finding a minimum length schedule that satisfies the traffic demand of a set of end-to-end sessions. A column generation based method is proposed to solve the JRSCS problem. The simulation results are presented to verify the performance of the scheme. We have also evaluated the impact of the physical layer capabilities such as number of antennas, single and multi-user radios on the scheduling time of the network.

Adaptive Equalization of Space-Time Coded MC-CDMA Systems

This paper considers applying the well known least-mean-square (LMS) adaptive algorithm on the detection for space-time coded multicarrier CDMA (STC-MC-CDMA) systems in frequency selective environments. In particular, we consider the Alamoutis space-time coding scheme that involves two transmit antennas. The performance of the LMS detector is evaluated with computer simulations. The performance of the LMS detector is compared with minimum mean-square error (MMSE) detector and the performances of both the schemes are found to be almost identical.

Exploiting opportunistic decode-and-forward cooperation for cognitive radio relay channels in multi-antenna cognitive radio networks

In this paper, we investigate the performance of an opportunistic decode-and-forward cooperation (ODFC) strategy for cognitive radio relay channels (CRRCs) in multi-antenna cognitive radio network. The key feature of the proposed strategy is that, via opportunistically decode-and-forward cooperation strategy, the cognitive users can maximize its end-to-end throughput by utilizing opportunistic cooperation. The proposed ODFC strategy maintains full diversity. Simulation results demonstrate the effectiveness of the proposed approach as compared to no power no channel allocation scheme (NPNCA), power allocation scheme (PA), and channel allocation scheme (CA). Opportunistic cooperation significantly improves the end-to-end throughput of the system and performs very close to channel allocation scheme in single antenna case and increases the end-to-end throughput in multi-antenna case without using additional transmit power or bandwidth requirement.

Performance of Pilot Symbol Assisted Channel Estimation Techniques for Uplink MC-CDMA Systems using MMSE Receiver

In order to attain near-single user performance in uplink multicarrier code division multiple access (MC-CDMA) systems, multiuser detection (MUD) methods may be employed. However, most of MUD methods rely on simultaneous estimation of the channel frequency response of multiple users. In this paper, performance of a MC-CDMA system employing minimum mean-square error (MMSE) MUD at receiver is evaluated using three different pilot symbol assisted (PSA) channel estimation techniques. The MMSE estimation is superior in performance but it requires prior information about the channel. Other two methods: the maximum likelihood estimation (MLE) and the inverse discrete Fourier transform (IDFT) based channel estimation are simple to implement as they do not depend upon the knowledge of the channel statistics.

Pilot symbol assisted channel estimation for uplink MC-CDMA systems using parametric Channel Modeling

In order to attain near-single user performance in uplink multicarrier code division multiple access (MC-CDMA) systems, multiuser detection (MUD) methods may be employed which rely on simultaneous estimation of the channel frequency response of multiple users. In this paper, performance of a MC-CDMA system employing minimum mean-square error (MMSE) MUD at receiver, is evaluated using two pilot symbol assisted (PSA) channel estimation schemes: the maximum likelihood (ML) estimation and the MMSE estimation. In simplified design where multipath fading channels are assumed to have sample-spaced path time delays, the MMSE estimator (MMSEE) slightly outperforms the ML estimator (MLE) at low signal to noise ratios (SNR). At intermediate and high SNRs, both estimators show almost identical performance. We find that the MMSEE provides significant performance gain when path delays are not sample-spaced and channel estimation is carried out considering a general parametric model of the multipath channel.

Outage performance of decode-forward and amplify-forward protocols in cooperative wireless communication

In this paper, outage performance of Decode-forward (DF) and Amplify-forward (AF) protocols in cooperative wireless communication is evaluated in terms of outage probability. In particular, a new outage analysis for AF protocol has been carried out. Results obtained using this analysis matches with the simulated results. Outage probability analysis helps in deciding whether the targeted quality of service (QoS) is achievable or not. Performance of DF protocol will be better in case of low SNR while performance of AF protocol will be better in case of high SNR. Effect of increase in number of cooperating nodes equipped with single antenna is described, which indicate that as the number of cooperating nodes increases outage performance will improve.

An access strategy selection in Cognitive Radio networks and QoS provisioning

The basic notion behind Cognitive Radio (CR) is that secondary users (SU) access the under-utilized licensed spectrum of primary users (PU) in an opportunistic manner. It assuages the problem of spectrum scarcity, which is a major concern as many applications and devices nowadays are using wireless medium. Before carrying on any transmission, the SU senses the licensed spectrum and predicts whether the spectrum is preoccupied by PU. Access strategy selection is a very crucial issue for CR networks, because the SU needs to satisfy the interference constraint caused to the PU as well as the quality-of-service (QoS) requirements. In this paper the access strategies for the spectrum access, i.e., the underlay strategy and the overlay strategy have been discussed for low and high transmit power of SU transmitter. The relationship between effective capacity and the quality of service exponent has also been presented in this paper.

Joint Routing and Scheduling in Wireless Mesh Networks based on Traffic Prediction Using ARIMA

Wireless Mesh Networks offer a high-performance and low-cost solution to last-mile broadband Internet access. Routing and Scheduling play a critical role in determining the performance of a wireless mesh network. Efficiency of Routing and Scheduling algorithms is highly dependent on the availability of accurate traffic information. In this paper, we predict network traffic based on past data using ARIMA model, and provide that input to the routing and scheduling algorithm. Joint routing and scheduling results in significant performance improvement over the routing only algorithms. So, we provide predicted network traffic information to a Joint routing and scheduling algorithm known as Traffic Oblivious Routing and Scheduling. Traffic Oblivious Routing and Scheduling algorithm optimizes the worst case performance under traffic uncertainty but when accurate traffic information is available to the algorithm, its performance is enhanced. In the Traffic Oblivious Routing and Scheduling algorithm, computing the routing and the scheduling values is a one time overhead. In this paper, we present a system where we predict network traffic information using past data, then use the predicted information to formulate the input for the Traffic Oblivious routing and scheduling algorithm and finally we evaluate the performance of the algorithm using simulations.

Outage and energy efficiency analysis for cognitive based heterogeneous cellular networks

Cognitive radio and small cells are the promising techniques to minimize energy consumption and satisfy the exponentially increasing data rates for the heterogeneous cellular network (HCN). In this paper, a theoretical framework is developed to calculate the outage probability of the HCN based on the opportunistic utilization of the traditional cellular bandwidth and television white space (TVWS) for the cognitive femto base stations. This work investigates overlay, underlay, mixed overlay-underlay based two tiers cognitive HCN. It also investigates the impact of the TVWS in the overlay-TVWS mixed spectrum sharing technique (SST). Tools from stochastic geometry are used to model cognitive HCN. Furthermore, the tier selection probability, average ergodic rate, area spectral efficiency (ASE), and energy efficiency (EE) of the HCN are also calculated for different SSTs. Numerical results show that mixed SST achieves a significant reduction in tier outage probability and total outage probability as compared to underlay and overlay techniques alone. It is also demonstrated that compared to the traditional single tier network, cognitive based HCN can improve the total ASE and EE of the order of