Collision Resolution in RFID Systems Using Antenna Arrays and Mix Source Separation

In this letter, we propose an efficient mix source separation algorithm for collision resolution in radio frequency identification (RFID) systems equipped with an antenna array at the reader. We first introduce an approach that exploits the zero constant modulus (ZCM) criterion to separate colliding tags through gradient descent, without using pilot symbols. We show that the ZCM characteristic, considered alone, in the design of the objective function can lead to significant ambiguities in the determination of the beamformers used in the recovery of tag messages. To address this limitation, we propose a more sophisticated approach, relying on a hybrid objective function, incorporating a new ambiguity-raising criterion in addition to the ZCM criterion.

Randomized Power Transmission with Optimized Level Selection Probabilities in Uncoordinated Uplink NOMA

We consider uncoordinated random uplink non-orthogonal multiple access (NOMA) systems using a set of predetermined power levels. We propose to optimize the probabilities of selection of power levels in order to minimize performance metrics as block error probability (BLEP) or bit error probability (BEP). When the multiuser detection algorithm at the BS treats at most two colliding users' packets, our optimization problem is a quadratic programming problem. For more colliding users' packets, we solve the problem iteratively. Our solution is original because it applies to any multiuser detection algorithm and any set of power levels.

Uncoordinated Cooperative OFDM Multi-Hop UAV Relay Networks Using Virtual Channels Based on All-Pass Filters

In this paper, we propose an efficient transmission scheme for autonomous cooperative Orthogonal Frequency Division Multiplexing (OFDM) based multi-hop Unmanned Aerial Vehicle (UAV) relay networks. These systems often suffer from destructive interference at the destination node due to uncoordinated transmissions of common packets by cooperating UAVs. To address this issue, we introduce the concept of virtual transmit channels at each UAV, implemented using truncated all-pass filters (APFs). This approach ensures that all subcarriers benefit from comparable transmit powers, guaranteeing excellent performance when a single UAV is transmitting. In scenarios where multiple UAVs cooperate without coordination, the inherent randomness of the generated virtual channels facilitates cooperative diversity, effectively mitigating destructive interference. We further integrate this method with the distributed randomized space-time block coding (STBC) scheme to enhance transmission reliability. Additionally, we propose efficient algorithms for estimating the composite channels that combine both the true propagation channels and the virtual channels. Simulation results demonstrate that our proposed scheme significantly outperforms the classical phase dithering scheme across various scenarios.