Gross primary productivity (GPP) through photosynthesis is a crucial ecosystem function that significantly influences food security, carbon cycle, and climate change. Current remote sensing estimates of GPP rely on look-up tables containing biome-specific parameters to model light-use efficiency (ε) using coarse resolution interpolated meteorology data, resulting in significant uncertainties in global GPP estimates. To address this challenge, we propose a simple yet effective ecosystem light-use efficiency (eLUE) model to GPP from FLUXNET tower sites to a global scale. Defined as GPP/PAR, eLUE differs from the traditional LUE (GPP/APAR, or ε) in that eLUE essentially integrates canopy light absorption (fAPAR) and the physiological efficiency of photosynthesis (ε), thus eliminating the need for a separate estimate of ε. eLUE was calibrated as a function of MODIS Enhanced Vegetation Index (EVI), and then GPP can be modelled directly as eLUE × PAR. To quantify the carbon cycle error budget, we analytically derived GPP uncertainty based on the law of error propagation. Cross-validation against 120 global FLUXNET sites, encompassing 11 plant functional types (PFTs), demonstrated satisfactory performance of the eLUE model (R2= 0.74, RMSE = 2.05 g C m-2d-1, NSE = 0.74), outperforming or performing comparably to more sophisticated models. Our estimate of global total terrestrial GPP, averaged between 2001 and 2024, is 135.12±11.02 Pg C yr-1. Meanwhile, we found a significant increasing trend in global total GPP at a rate of 0.26±0.06 Pg C yr-1(p2sequestration in terrestrial ecosystems across the Northern Hemisphere. We suggest that our eLUE model, with its robust performance and clear error representation, will help constrain the global carbon budget and improve the diagnostic analysis of carbon cycle dynamics and climate change feedback. The eLUE-GPP product, available at both global scale and FLUXNET sites, can be accessed for free at: https://doi.org/10.5061/dryad.v9s4mw74h.

Presents corrections to the paper, (“Global Upscaling of Gross Primary Productivity Using a Simple and Robust Modeling Scheme”).

This paper analyzes the effect of distributed time-reversal (DTR) transmission scheme on the signal-to-noise ratio (SNR) at its intended and unintended receivers. By focusing the temporal and spatial signal energy on the intended receiver, DTR can effectively maintain a satisfactory SNR level while lowering received signal level at passive eavesdroppers or unintended co-channel users. The DTR performance is analyzed in terms of a SNR gap between the desired and unintended receivers. The SNR gain of DTR is also analyzed over traditional distributed direct transmission and several cooperative beamforming transmission schemes without time-reversal. Numerical results demonstrate the performance improvement of the time-reversal transmission and the validity of our analytical results.

This paper proposes a joint cooperative relaying and jamming scheme based on distributed beamforming to enhance the secrecy rate of a wireless channel in the presence of an eavesdropper. Specifically, we consider the scenario that a source node transmits messages to a destination with the help of multiple cooperative relays, where a relay might be compromised to become an eavesdropper as an inside attacker. Our joint relaying and jamming approach is to assign some relay nodes to act as jammers to interfere the eavesdropper, while the remaining ones continue relaying information to the destination. We propose a protocol to implement the joint cooperative relaying and jamming. Our protocol further considers the particular challenge brought by the inside attacker: it may know the jamming signal and can use it to remove the interference from the jammers. The issue of phase and frequency synchronization in the distributed beamforming is also taken into account. A mixed integer programming problem is formulated to maximize the secrecy rate with the proposed joint relaying and jamming, by which the optimal role assignment to a relay and the associated optimal power assignment can be solved. Numerical results are presented to demonstrate the efficiency of the proposed joint relaying and jamming in improving the secrecy rate, with comparison to existing approaches.

Device-to-device (D2D) communication brings significant benefits to improve resource utilization and users' throughput as an underlay to cellular networks. This paper first proposes an efficient admission policy based D2D clustering scheme to increase the system rate. By analyzing the interplay between the D2D clusters and the arrival user who intends to join a D2D cluster, we present two attraction functions describing the mutual suitability by considering social interaction, energy balance, and location as well. Further, we formulate the probability of the arrival user joining a certain D2D cluster based on Chinese Restaurant Process (CRP) and utilize a matching function to assign an optimal D2D cluster for each arrival user. On the other hand, we also illustrate how the cluster head can be selected in a D2D cluster. Finally, numerical results demonstrate that our clustering scheme efficiently leads to a good performance on the system rate and the stability of D2D clusters.

This paper proposes a cluster-based optimal relay and jammer selection (CB-ORJ) scheme to deal with interception and improve the secrecy rate in wireless multi-hop networks in the presence of both intra-cluster and inter-cluster eavesdroppers. We first present a novel mathematical model of cluster-based secure transmission. Furthermore, we propose an on-demand relay and jammer selection approach based on the proposed model with power allocation to optimize the secrecy rate subject to a total transmit power constraint under different security requirements. To confuse the intra-cluster eavesdroppers, the cluster heads assign appropriate cluster members as jammers, while for the inter-cluster eavesdroppers, the transmitting cluster and the receiving cluster jointly select their cluster members as jammers. Finally, simulation results demonstrate that our scheme outperforms existing ones in terms of secrecy outage probability (SOP) while guaranteeing a lower desired energy consumption.