Improving performance of far users in cognitive radio: Exploiting NOMA and wireless power transfer

In this paper, we examine non-orthogonal multiple access (NOMA) and relay selection strategy to benefit extra advantage from traditional cognitive radio (CR) relaying systems. The most important requirement to prolong lifetime of such network is employing energy harvesting in the relay to address network with limited power constraint. In particular, we study such energy harvesting CR-NOMA using amplify-and-forward (AF) scheme to improve performance far NOMA users. To further address such problem, two schemes are investigated in term of number of selected relays. To further examine system performance, the outage performance needs to be studied for such wireless powered CR-NOMA network over Rayleigh channels. The accurate expressions for the outage probability are derived to perform outage comparison of primary network and secondary network. The analytical results show clearly that position of these nodes, transmit signal to noise ratio (SNR) and power allocation coefficients result in varying outage performance. As main observation, performance gap between primary and secondary destination is decided by both power allocation factors and selection mode of single relay or multiple relays. Numerical studies were conducted to verify our derivations.Web of Science1211art. no. 220

INTEGRATING MULTI-SOURCE DATA TO QUANTIFY CHANGES IN BIOMASS AND SOIL ORGANIC CARBON DUE TO LAND-USE CHANGE IN THE BOREAL PLAINS ECOZONE, CANADA

Land use and cover change (LUCCs) is the second largest source of global carbon emission and there has been a growing interest in LUCCs to mitigate climate change effects. Global land-use change associated with cropland expansion, which is a major carbon source, was dominant in the last century. Abandoned cropland typically is a carbon sink and was observed in many regions in the recent decades. However, there has been little research on carbon balance resulting from LUCCs in agricultural landscapes, especially under abandoned cropland in Canada. Information on carbon balance resulting from LUCCs is necessary for national greenhouse gas (GHG) inventories as well as emission mitigation options. The primary objective of the study is to quantify carbon stocks and dynamics as consequences of LUCCs in the Boreal Plains Ecozone, Canada. Field measurement on carbon stocks in abandoned cropland was assessed at field sites in Saskatchewan. Vegetation C ranged from 7.6 to 90.1 Mg C ha-1 and increased linearly with stand age. Ecosystem C increased from 74.2 to 137.6 Mg C ha-1 after 41 years of abandonment (or net C sink of 1.9 Mg C ha-1 yr-1). In the agriculture region of the Boreal Plains Ecozone, land-use change accounted for 6.5% of the total area during the 1990-2000 period. Forest to cropland conversion was dominant on well-drained Chernozemic and Luvisolic soil orders. Abandoned cropland occurred mainly on poorly drained and acidic parent materials. LUCCs in agriculture region was estimated to be a net C sink of 0.76 ±0.3 Mg C ha-1 yr-1 during this period. In the agriculture-forest transition region of the Boreal Plains Ecozone, substantial land-use changes occurred in pasture (+76%) and summer fallow (-87.8%) over a 27-year period (1984 - 2011). The shrub and forest area was reduced -31.6% and -16.4%, respectively. Forest disturbances occurred mainly during 2005 – 2011. Substantial changes of summer fallow to annual cropland took place on the higher soil capability land and annual cropland to pasture conversion was more likely on lower capability soil classes. We estimated that LUCCs in the region was a net C source of approximately 552.7 Gg C across the research period or 0.07 Mg C ha-1 yr-1

Enabling non-linear energy harvesting in power domain based multiple access in relaying networks: Outage and ergodic capacity performance analysis

The Power Domain-based Multiple Access (PDMA) scheme is considered as one kind of Non-Orthogonal Multiple Access (NOMA) in green communications and can support energy-limited devices by employing wireless power transfer. Such a technique is known as a lifetime-expanding solution for operations in future access policy, especially in the deployment of power-constrained relays for a three-node dual-hop system. In particular, PDMA and energy harvesting are considered as two communication concepts, which are jointly investigated in this paper. However, the dual-hop relaying network system is a popular model assuming an ideal linear energy harvesting circuit, as in recent works, while the practical system situation motivates us to concentrate on another protocol, namely non-linear energy harvesting. As important results, a closed-form formula of outage probability and ergodic capacity is studied under a practical non-linear energy harvesting model. To explore the optimal system performance in terms of outage probability and ergodic capacity, several main parameters including the energy harvesting coefficients, position allocation of each node, power allocation factors, and transmit signal-to-noise ratio (SNR) are jointly considered. To provide insights into the performance, the approximate expressions for the ergodic capacity are given. By matching analytical and Monte Carlo simulations, the correctness of this framework can be examined. With the observation of the simulation results, the figures also show that the performance of energy harvesting-aware PDMA systems under the proposed model can satisfy the requirements in real PDMA applications.Web of Science87art. no. 81