Sachitha Kusaladharma

Aggregate Interference Analysis for Underlay Cognitive Radio Networks

This paper investigates the aggregate interference on a primary user caused by a random number of cognitive radio transmitters distributed in a finite ring. A composite model involving path loss, Rayleigh fading, and shadowing is considered. The exact closed-form moment generating function and an accurate approximation are derived. The aggregate interference is shown to be accurately approximated by a Gamma distribution. The exact outage and an asymptotic approximation are derived.

Impact of Beacon Misdetection on Aggregate Interference for Hybrid Underlay-Interweave Networks

The impact of beacon misdetection on the aggregate interference from a hybrid underlay-interweave network is analyzed, for a Poisson field of cognitive radio (CR) nodes distributed over an annular region. This network consists of two types of nodes: underlay, and interweave. The underlay nodes are allowed to transmit anytime, whereas the interweave nodes must first sense an out-of-band beacon. When this sensing is erroneous, interweave node transmissions increase the interference. We analyze the interference statistics by deriving the exact moment generating function, the mean, and the outage probability of the primary receiver, for path loss and Rayleigh fading. Our analysis suggests that hybrid underlay-interweave CR systems are more suitable for areas with low path loss exponents such as rural/suburban environments.

Underlay Interference Analysis of Power Control and Receiver Association Schemes

In this paper, we present a precise comprehensive analysis of the aggregate interference I generated from an underlay network of cognitive radio (CR) nodes employing several transmit power control and receiver association schemes. Importantly, we consider spatial randomness by modeling CR transmitter nodes and receiver nodes as two independent Poisson point processes (PPPs). For the cognitive nodes, we investigate receiver association based on the distance or the instantaneous received power and power control based on the maximum possible transmitter-receiver distance, fixed or location-dependent cutoff power levels, feedback from the primary system, or the maximum number of available receivers. For each of these schemes, the exact moment generating function (mgf) and mean of aggregate I power are derived for links with Rayleigh fading and exponential path loss. The resulting primary outage and the probability of secondary transmitter cutoff are also derived. Numerical results show that the secondary power thresholds and node densities significantly affect the aggregate I, the primary receiver (PR) outage, and the secondary transmitter cutoff arising from the different schemes.

Impact of transmit power control on aggregate interference in underlay cognitive radio networks

This paper analyzes how transmit power control affects the aggregate interference arising from a Poisson field of underlay cognitive radio (CR) transmitter nodes distributed in a finite area. We consider three per-user, location dependent power control schemes, when each CR transmitter is associated with the nearest CR receiver, where the CR receivers form a Poisson field in the entire 2-dimensional space. The 3 schemes are based on: 1) CR transmitter-receiver distance rc 2) rc and a constant cut-off power level 3) rc and a random cut-off power level, respectively. For each of these, the exact moment generating function (MGF) and mean of aggregate interference power are derived. We also investigate the primary system outage due to aggregate interference. Rayleigh fading and exponential path loss links are assumed. Monte-Carlo simulation results validate our analysis and also show that the CR power thresholds and node densities significantly affect the aggregate interference.

On Approximating the Cognitive Radio Aggregate Interference} \IEEEaftertitletextvspace{-1\baselineskip

The aggregate interference caused on a primary receiver by Cognitive Radio (CR) nodes distrbuted uniformly in an annular region around it is investigated, assuming Rayleigh fading and path loss. By approximating the aggregate interference with that caused by the nearest CR interferer, the exact analytical moment generating function for the nearest interferer is derived for cases of no power control and distance based power control. The outage probability based on the approximation is derived, which is a tight lower bound under certain conditions.

Massive MIMO based underlay networks with power control

While massive MIMO based underlay cognitive radio (CR) networks are a promising concept in the next generation of wireless networks to increase spectral efficiency, reusing the same pilot sequences in both networks cause pilot contamination leading to residual interference. Thus, this paper investigates the affects of pilot contamination on a random CR network underlaid upon a random primary network where both networks employ path loss inversion based power control. A Matern cluster process is considered for the underlay system, while homogeneous Poisson point processes are considered for the primary transmitters and receivers. We derive the moment generating function of the normalized aggregate interference at an underlay receiver, its first two moments, and the outage probability. Finally, it is shown that the underlay cluster radius, ensured received power levels through power control and the different node densities have a significant effect on the outage of an underlay receiver.

A Multiple-Ring Model for Cognitive Radio Aggregate Interference

This paper proposes a new, flexible, multiple ring model for the aggregate interference analysis of a Poisson field of cognitive radio transmitters distributed over an annular region. For Rayleigh fading or composite Rayleigh fading and Gamma shadowing environments, the moment generating function of the aggregate interference and the exact and asymptotic analysis of the outage are derived for the model. Typically, the model is most accurate for larger guard distances and lower path loss exponents. However, its parameters can be tuned such that a required accuracy is obtained for a trade-off in complexity.

Secondary User Interference Characterization for Spatially Random Underlay Networks With Massive MIMO and Power Control

In an underlay (secondary) network, the receiver nodes are subject to both primary and intra-underlay interference. What are the characteristics of this interference when considering the use of massive multiple-input multiple-output (MIMO) systems with pilot contamination, path-loss-inversion power control, receiver association policies, spatially random nodes, and propagation characteristics with power-law path loss and Rayleigh fading? To answer this question, we derive the average and the moment generating function of the aggregate interference and its average due to both primary and underlay transmissions from nodes modeled as Poisson point processes and analyze how the interference impacts the outage performance of an underlay receiver. Our analysis considers all of the above factors and both single antenna type and massive MIMO base stations. We show that massive MIMO improves the outage performance, and a higher path loss exponent reduces the outage probability. This is in contrast to single antenna systems where a higher path loss exponent increases the outage. Furthermore, it is shown that the different node densities and power thresholds significantly affect the outage performance.

Secondary User Interference Characterization for Underlay Networks

In an underlay cognitive radio network, the secondary (underlay) transmitters generate interference to a primary receiver, while an underlay receiver is subject to interference from both the primary transmitters and other underlay transmitters not associated with it. Although guard regions, maximum allowable underlay transmit powers, and contention distances help guarantee a minimum performance to the primary network, no such safeguard exists for the underlay network. To this end, this paper characterizes the aggregate interference on an underlay receiver while considering power control and receiver association schemes for both networks. Transmitters and receivers of both networks are assumed to be distributed as independent Poisson fields in the 2-D plane, and all links undergo exponential path loss and Rayleigh fading. We derive the moment generating function of the aggregate interference on an underlay receiver and its outage probability. We show that the interference from the primary network does not depend on any node density, and that it dominates the aggregate interference. Furthermore, it is shown that increasing primary and underlay receiver densities reduce the outage probability under lower required power thresholds for the primary receivers.

Impact of Transmit Power Control and Receiver Association on Interweave Network Interference

Erroneous beacon detection by interweave secondary nodes generates interference on the primary system. This paper analyzes how the aggregate interference behaves when secondary nodes use transmit power control and receiver association schemes. For this purpose, secondary transmitter nodes and receiver nodes are assumed to be distributed over a circular region and over the entire 2-D plane respectively. Two independent Poisson point processes model these distributions. We propose a receiver association scheme where each secondary transmitter attempts to connect to the closest available receiver. If it is not available, the transmitter attempts to connect with the next closest. This process continues until the M-th closest receivers are scanned. If no receiver is available, the transmitter remains silent. Moreover, a per-user transmit power control scheme is considered in which the transmit power is based on the distance between the transmitter and the associated receiver subject to a cut-off power level. All links are assumed to undergo path-loss and Rayleigh fading. The exact moment generating function (MGF) of the aggregate interference, the outage probability of the primary system, and the average probability of concurrent transmission are derived. Validated by simulations, our results show how the aggregate interference is affected by secondary power thresholds, receiver densities, and availability of the secondary receiver.