聚丙烯酸酯弹性体/聚乳酸共混物的结晶性能

通过种子乳液聚合合成了以丙烯酸丁酯(BA)为核、甲基丙烯酸甲酯(MMA)共聚甲基丙烯酸缩水甘油酯(GMA)为壳的聚丙烯酸酯冲击改性剂(Poly(BA)/poly(MMA-co-GMA),PBMG),以此改性聚乳酸,并对共混物的非等温结晶性能进行了研究。结果表明,质量分数10%的PBMG的加入能改善聚乳酸共混物的力学性能,冲击强度由2.6kJ/m^(2)增加到10.45kJ/m^(2)。同时采用差示扫描量热仪及偏光显微镜对共混物的结晶性能进行了研究,并利用Jeziorny修订的Avrami方程和莫志深方程探究了共混物的非等温结晶动力学。PBMG作为成核剂,在共混物中提供了更多的成核位点,从而提高了结晶度并加快了共混物的结晶速率。

Civil Aircraft Assisted Space-Air-Ground Integrated Networks: Architecture Design and Coverage Analysis

In this paper, we propose a novel AIenabled space-air-ground integrated networks(SAGIN). This new integrated networks architecture consists of LEO satellites and civil aircrafts carrying aerial base stations, called "civil aircraft assisted SAGIN(CAA-SAGIN)". The assistance of civil aircrafts can reduce the stress of satellite networks, improve the performance of SAGIN, decrease the construction cost and save space resources. Taking the Chinese mainland as an example, this paper has analyzed the distribution of civil aircrafts, and obtained the coverage characteristics of civil aircraft assisted networks(CAAN). Taking Starlink as the benchmark, this paper has calculated the service gap of CAAN, and designed the joint coverage constellation. The simulation results prove that the number of satellites in CAASAGIN can be greatly reduced with the assistance of civil aircrafts at the same data rate.

Asymptotic Analysis and Precoding Design of Integrated Access and Backhaul in Full-Duplex mmWave Networks

In this paper,we consider a full-duplex(FD)millimeter wave(mmWave)multiuser integrated access and backhaul(IAB)system with massive MIMO,and the system asymptotic performance and interference cancellation schemes are investigated.First,the asymptotic performance of the IAB system with massive MIMO is analyzed.As the number of macro base station(MBS)and small base station(SBS)antennas approaches infinity,the FD selfinterference(SI),inter-tier interference and noise can be eliminated,which means that only multiuser interference remains in the system.Then,multiuser interference can be suppressed by the base band(BB)precoders.Since all interference and noise are suppressed,the spectral efficiency of the SBS and users are infinite in theory.Then,two interference suppression precoding schemes are proposed.A block diagonalization(BD)-based interference cancellation scheme is designed based on the channel characteristics and null space projection.The FD SI,intertier interference and multiuser interference are eliminated by BB precoders.Instead of eliminating interference completely,a signal to leakage and noise ratio(SLNR)-based precoding scheme is derived to suppress both interference and noise.By utilizing the Rayleigh-Ritz theorem,the SLNRs of the SBS and users are optimized.Simulation results show that all the interference can be effectively eliminated by the BD-based scheme at the cost of spectral efficiency performance loss,while the SLNR-based scheme can balance interference and noise and achieve higher spectral efficiency with comparatively low interference level.Therefore,the BD-based scheme is more suitable for interference elimination cases,and the SLNRbased scheme can improve the system performance in low interference scenarios.

User Fairness Scheme with Proportional Fair Scheduling in Multi-user MIMO Limited Feedback System

In Multi-user MIMO (MU-MIMO) downlink system, suitable user selection schemes can improve spatial diversity gain. In most of previous studies, it is always assumed that the base station (BS) knows full channel state information (CSI) of each user, which does not consider the reality. However, there are only limited feedback bits in real system. Besides, user fairness is often ignored in most of current user selection schemes. To discuss the user fairness and limited feedback, in this paper, the user selection scheme with limited feedback bits is proposed. The BS utilizes codebook precoding transmitting strategy with LTE codebook. Furthermore, this paper analyzes the influence of the number of feedback bits and the number of users on user fairness and system sum capacity. Simulation results show that in order to achieve better user fairness, we can use fewer bits for feedback CSI when the number of user is small, and more feedback bits when the number of users is large.

A New Family of Optical Codes Based on Complementary Theory for OCDMA System

A new family of optical codes for Optical Code-division Multiple Access (OCDMA) systems, named as Optical Complementary Codes (OCCs), is proposed in this paper. The constructions of these codes consist of multiple sub-codes, and the codes have an auto-correlation interference constraint as 0 and a cross-correlation interference constraint as 1. Compared with conventional optical codes such as OPCs, OOCs and 2-D OOCs, the OCC has a shorter code length and higher code efficiency with better correlation property.

Spatio-Temporal Service Analysis in Multi-Layer Non-Terrestrial Networks

In the advent of the 6G era, non-terrestrial networks (NTN) with expansive coverage are being increasingly recognized as a vital supplement to cellular networks for facilitating seamless communication. The intricate interplay between network performance and service quality necessitates a thorough investigation into the modeling and analysis of services for efficient construction of NTN.Previous studies on service analysis, predominantly focused on terrestrial networks,fall short in addressing the unique challenges posed by NTN,particularly those related to platform distribution and antenna gain modeling. This deficiency in research,coupled with the varying preferences of users for different network types, forms the basis of this study. This paper explores the spatio-temporal characteristics of services within a multi-layered NTN framework.In this context,the spatial distribution of the platforms is modeled using a binomial point process, and the antennas are characterized by a sectorized beam pattern. We derive the closed-form expressions for the association probability,the number of accessed users, and the arrival rate of services with certain delay requirements towards different types of NTN. Simulation results are provided to evaluate the influence of various parameters on the association probability, the number of accessed users, and the total arrival rate of services. The number of satellites can be determined to achieve the optimal system utility,balancing the accessed services, offloading effects, and launching costs. This initial investigation lays the groundwork for further theoretical progress in the service analysis and platform deployment of NTN.

Resource allocation algorithm for multi-user MIMO-OFDM downlink with correlated channels

To minimize transmitting power,an adaptive resource allocation algorithm is proposed for multi-user multiple input multiple output-orthogonal frequency division multiplexing(MIMO-OFDM)downlink with correlated channels,which,based on the user’s grouping according to their spatial correlations,combines the shared manner and the exclusive manner to allocate sub-carriers.Between different groups the shared manner with a null steering method based on group marginal users is applied,whereas within a group the exclusive manner is applied.The simulations show that the power efficiency and spectral efficiency are improved;the base station transmitting antenna number and the computational complexity is decreased.