Relaying systems with reciprocity mismatch : impact analysis and calibration

Cooperative beamforming can provide significant performance improvement for relaying systems with the help of the channel state information (CSI). In time-division duplexing (TDD) mode, the estimated CSI will deteriorate due to the reciprocity mismatch. In this work, we examine the impact and the calibration of the reciprocity mismatch in relaying systems. To evaluate the impact of the reciprocity mismatch for all devices, the closed-form expression of the achievable rate is first derived. Then, we analyze the performance loss caused by the reciprocity mismatch at sources, relays, and destinations respectively to show that the mismatch at relays dominates the impact. To compensate the performance loss, a two-stage calibration scheme is proposed for relays. Specifically, relays perform the intra-calibration based on circuits independently. Further, the inter-calibration based on the discrete Fourier transform (DFT) codebook is operated to improve the calibration performance by cooperation transmission, which has never been considered in previous work. Finally, we derive the achievable rate after relays perform the proposed reciprocity calibration scheme and investigate the impact of estimation errors on the system performance. Simulation results are presented to verify the analytical results and to show the performance of the proposed calibration approach

NOMA-enhanced computation over multi-access channels

Massive numbers of nodes will be connected in future wireless networks. This brings great difficulty to collect a large amount of data. Instead of collecting the data individually, computation over multi-access channels (CoMAC) provides an intelligent solution by computing a desired function over the air based on the signal-superposition property of wireless channels. To improve the spectrum efficiency in conventional CoMAC, we propose the use of non-orthogonal multiple access (NOMA) for functions in CoMAC. The desired functions are decomposed into several sub-functions, and multiple sub-functions are selected to be superposed over each resource block (RB). The corresponding achievable rate is derived based on sub-function superposition, which prevents a vanishing computation rate for large numbers of nodes. We further study the limiting case when the number of nodes goes to infinity. An exact expression of the rate is derived that provides a lower bound on the computation rate. Compared with existing CoMAC, the NOMA-based CoMAC not only achieves a higher computation rate but also provides an improved non-vanishing rate. Furthermore, the diversity order of the computation rate is derived, which shows that the system performance is dominated by the node with the worst channel gain among these sub-functions in each RB

Phosphorus-Containing Polyisocyanurate Elastomers for Flame Retardant Application

Polyurethane (PU) is one of the most common and versatile polymers in many applications especially in the construction and automotive industry where the improvement of thermal stability and flame retardancy is crucial. As polyisocyanaurate (PIR) is well known to have a high decomposition temperature and phosphorus motifs are usually used as flame retardants in polymers, the introduction of PIR and phosphorus motifs in polyurethanes can lead to PUs with high thermal stability and flame retardancy. We investigated a synthetic pathway to introduce polyisocyanurate (PIR) and phosphorus motifs in polyurethanes via co-trimerization of 4,4′-methylene diphenyl diisocyanate (4,4′-MDI) and monoisocyanate, which was synthesized from the reaction between diethyl (hydroxymethyl)phosphonate (DEHP) and 4,4′-MDI. The resulting PIR-DEHP prepolymer was used to prepare PIR-DEHP elastomers in both solvent and solvent-free conditions. The elastomer with polyester polyol and 15 wt % 1,4-butanediol in the polyol component showed high char formation (25.5 wt %) and 55% reduction in the total heat release (THR) relative to the reference elastomer without PIR and phosphorus content. It is expected that the use of the PIR-DEHP prepolymer can be extended to other applications, such as rigid PU foams and compact thermosets where the flame retardancy and bulk reaction conditions are required

Power consumption optimization and delay based on ant colony algorithm in network-on-chip

With a further increase of the number of on-chip devices, the bus structure has not met the requirements. In order to make better communication between each part, the chip designers need to explore a new NoC structure to solve the interconnection of an on-chip device. For the purpose of improving the performance of a network-on-chip without a significant increase in power consumption, the paper proposes a network-on-chip that selects NoC (Network-On-Chip) platform with 2-dimension mesh as the carrier and incorporates communication power consumption and delay into a unified cost function. The paper uses ant colony optimization for the realization of NoC map facing power consumption and delay potential. The experiment indicates that in comparison with a random map, single objective optimization can separately account for (30%~47%) and (20%~39%) of communication power consumption and execution time, and joint objective optimization can further excavate the potential of time dimension in a mapping scheme dominated by the power