Prasanna Herath

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.

Outage probability analysis of two-hop MIMO relay networks with interference at the relay

In this paper, the outage probability analysis of two-hop amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay networks is presented. The source and the destination are equipped with multiple antennas and communicate with each other, with the help of a single antenna relay which is subject to interference. Two systems are considered; transmit antenna selection with maximal ratio combining (TAS/MRC) and transmit antenna selection with selection combining (TAS/SC). We derive closed form expressions for the cumulative distribution function (CDF) for an arbitrary number of interferences under flat Rayleigh fading channels. Analytical and Monte Carlo simulation results are presented to validate the analysis and to demonstrate the effect of interference.

Stochastic Geometry Modeling of Cellular Uplink Power Control under Composite Rayleigh-Lognormal Fading

Power control for uplink transmission in a randomly laid-out cellular network operating over an environment with path loss and composite Rayleigh-lognormal shadowing is investigated. Each mobile station (MS) adjusts its transmit power to completely remove shadowing and to partially invert the effect of path loss. Using stochastic geometry tools, we derive an approximate coverage probability expression and validate it via simulations. With the power control scheme considered, shadowing with lower standard deviation improves the coverage probability. Also the severity of shadowing of local and surrounding environments has the same effect on the coverage probability. It was also observed that at low signal-to-interference-plus-noise ratio (SINR) thresholds, complete compensation of shadowing and partial compensation of path loss improves coverage, while at high SINR thresholds inverting only the effect of shadowing gives a better coverage probability.

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.

Mixed Rayleigh and Rician fading with partial relay selection

The performance of a two hop amplify-and-forward relay system, where the source-relay and the relay-destination channels experience Rayleigh and Rician fading, respectively, is investigated with relay selection. Partial relay selection is considered, where the relay is selected based on instantaneous and partial knowledge of the channel (source-relay). We derive an exact expression for the outage probability and a lower bound for the average bit error probability, where the bound becomes tight at medium to high signal-to-noise ratios. Also we provide simulation results to support the theoretical analysis.

A Novel Base Stations-Mobile Stations Association Policy for Cellular Networks

We propose a novel base stations (BSs) - mobile stations (MSs) association policy for cellular networks. In this policy, the BS which provides the highest signal-to-interference ratio (SIR) among those located within a predetermined maximum association distance of the MS is selected as the serving BS. This policy encompasses the conventional highest-SIR association as a special case. Application of the new policy in 2- and 3- dimensional single-tier (homogeneous) and 2-dimensional two-tier (heterogeneous) networks is discussed. Coverage probability expressions are derived assuming BSs in each tier are distributed according to an independent homogeneous Poisson point process (PPP). Rayleigh fading and exponential path-loss radio channels are assumed. Analysis is validated by Monte-Carlo simulations. For single-tier networks, two methods are proposed for the selection of the maximum association distance. With such selection, the proposed association policy performs similarly to the highest-SIR association. It is shown that this policy can also be used to manage user offloading to small cells in two-tier heterogeneous networks.

Aggregate Interference Analysis for Interweave Cognitive Networks

This paper investigates the aggregate interference from interweave cognitive secondary nodes spatially distributed in a finite Poisson field. These secondary nodes sense an out-of-band beacon to initiate their transmissions, which can be concurrent with those of the primary system if a sensing error is made. The resulting aggregate interference is analyzed in this paper. For this purpose, general Nakagami-m fading and path-loss are assumed for all relevant channels. Moreover, we incorporate random secondary node transmit powers with any probability distribution. The analysis includes the exact moment generating function (MGF) of the aggregate interference along with the exact outage probability of the primary system. Furthermore, we develop a simple MGF approximation which is valid for severely fading channels and for lower beacon reception threshold to beacon transmit power ratios. Finally, we show that a lower fading severity significantly improves the diversity order of the PR due to more accurate spectrum sensing by the secondary nodes.

Distributed switch-and-examine combining with threshold-based relaying

We study the distributed switch-and-examine combining with threshold-based relaying (DSEC-T). In this scheme, relay selection is performed in a similar fashion to switch-and-examine combining (SEC) considering the source-relay channel signal-to-noise ratio (SNR) in conjunction with threshold-based relaying. In particular, the same relay remain selected as long as its SNR is above a predefined threshold; should this condition be violated, the remaining relays are tested against the threshold in a predefined order. This testing process is repeated until either an acceptable relay is found or no relay is left to be examined. In the latter case none of the relay is chosen for communication. On the other hand, if an acceptable relay is identified, the switch-and-examine process is interrupted and the identified relay assists the source-destination communication working as an amplify-and-forward (AF) relay. Lower bounds for the outage probability and symbol error rate (SER) are derived assuming Rayleigh multi-path fading channels. Numerical results demonstrate that the proposed DSEC-T scheme achieves the same diversity order as the partial relay selection (PRS) where the best relay is selected based on source-relay SNR for earch transmission.