In this paper, we examine a cognitive spectrum access scheme in which secondary users exploit the primary feedback information. We consider an overlay secondary network employing a random access scheme in which secondary users access the channel by certain access probabilities that are function of the spectrum sensing metric. In setting our problem, we assume that secondary users can eavesdrop on the primary link's feedback. We study the cognitive radio network from a queuing theory point of view. Access probabilities are determined by solving a secondary throughput maximization problem

In this paper we study the problem of buffer-aware power control in underlay cognitive radio networks. In particular, we investigate the role of buffer state information, manifested through the secondary users' queue lengths, along with channel state information in the cognitive radio power control problem. Towards this objective, we formulate a constrained optimization problem to find the set of secondary user transmit powers that maximizes the sum of rates weighted by the respective buffer lengths subject to signal-to- interference-and-noise-ratio (SINR) and maximum power constraints

A fundamental problem in cognitive radio systems is that the secondary user is ignorant of the primary channel state and the interference it inflicts on the primary license holder. We consider a secondary user that can eavesdrop on the ACK/NACK Automatic Repeat reQuest (ARQ) fed back from the primary receiver to the primary transmitter. Assuming the primary channel states follow a Markov chain, this feedback gives the secondary user an indication of the primary channel quality. Based on the ACK/NACK received, we devise optimal transmission strategies for the secondary user so as to maximize a

In this paper, we propose fractional sequential sensing (FSS) as a novel cooperative sensing scheme for cognitive radio networks. FSS compromises a tradeoff between sensing accuracy and efficiency by formulating an optimization problem whose solution identifies FSS sensing parameters. These parameters include the sensing period and channels allocated for each user. Our simulation results show that FSS successfully improves the sensing accuracy while maintaining a low power profile. Additionally, we show that the sensing accuracy performance gap between FSS and other traditional schemes

This paper proposes a new cooperative protocol which involves cooperation between primary and secondary users. We consider a cognitive setting with one primary user (PU) and multIPle secondary users (SUs). The time resource is partitioned into discrete time slots. Each time slot, one of the SUs is scheduled for transmission according to time division multIPle access scheme, and the remainder of the SUs, which we refer to as secondary relays, attempt to decode the primary packet. If more than one relay can decode the primary packet, the secondary relays then employ cooperative beamforming to

In this paper, a multiple-access wireless network consisting of two transmitters and one receiver is considered. The transmitters can access the same channel simultaneously and the receiver performs successive interference cancellation (SIC) to decode the messages from both senders. A two-dimensional Markov chain is used to model the medium access control layer behavior of the system, where the state represents the queue length of the transmitters. In this model a general number of packets can be transmitted from any user in a single time slot. A probabilistic cross-layer scheme is proposed to

We consider a cognitive radio system that consists of primary user, secondary user, and their destinations. The secondary user has a relaying capability, i.e., it transmits the relayed packets from the primary user. Unlike most of the previous works that restrict the secondary user to transmit only in the idle time slots, we assume that the secondary user interferes on the primary user with certain probability that is optimized to maximize the stable throughput of the secondary network under certain level of quality of service constraints for the primary one. We show how significantly our

This paper characterizes the performance of a generic K-tier cache-aided heterogeneous network (CHN), in which the base stations (BSS) across tiers differ in terms of their spatial densities, transmission powers, pathloss exponents, activity probabilities conditioned on the serving link and placement caching strategies. We consider that each user connects to the BS which maximizes its average received power and at the same time caches its file of interest. Modeling the locations of the BSS across different tiers as independent homogeneous Poisson Point processes (HPPPs), we derive closed-form

In this paper, we characterize optimal resource allocation for the uplink and downlink of wireless powered cellular networks (WPCNs). In particular, we investigate a time-slotted WPCN, where a hybrid access point (HAP) is in charge of energy replenishing of M cellular users (CUs), along with transmission/reception of information to/from them. Unlike prior works, which give attention to information transmission in only one direction (either uplink or downlink), our work incorporates information transmission in both directions, along with energy transfer over the downlink. Besides harvesting

Centralized coded caching and delivery is studied for a partially-connected fog radio access network (F-RAN), whereby a set of H edge nodes (ENs) (without caches), connected to a cloud server via orthogonal fronthaul links, serve K users over the wireless edge. The cloud server is assumed to hold a library of N files, each of size F bits; and each user, equipped with a cache of size MF bits, is connected to a distinct set of r ENs; or equivalently, the wireless edge from the ENs to the users is modeled as a partial interference channel. The objective is to minimize the normalized delivery time