Study on Improved MAC protocols of VoWLAN system

随着无线通信技术和移动终端技术的迅猛发展，以IEEE802.11为基础的无线局域网（WLAN）得到了越来越广泛的应用。与此同时，VoIP以其价格低廉、资源利用率高等优点成为当今发展最快的网络应用之一。在这两种技术的推动下，VoWLAN（VoiceoverWLAN）逐渐兴起。现在IEEE802.11b已成为WLAN的事实标准，而WLAN又有传输语音业务的需求，然而IEEE802.11b使用竞争信道，主要支持非实时的数据业务，不能满足对时延和时延抖动敏感的语音业务的QoS保证。因此，研究IEEE802.11bWLAN接入环境下的语音传输质量保证方案，具有重要的应用推广意义。本论文就是在这样的背景下...With the rapid development of wireless communications technology and mobile terminal technology, the wireless local area network (WLAN) based on IEEE 802.11 is finding more and more applications. At the same time, with low price and high resource utilization, VoIP becomes one of the network applications experiencing tremendous growth. Driven by both technologies, VoWLAN (Voice over WLAN) is also o...学位：工学硕士院系专业：信息科学与技术学院电子工程系_通信与信息系统学号：20043004

浅谈VDSL(Very High Bit Rate Digital Subscriber Line)

XDSL宽带接入的典型是ADSL和VDSL。本文首先简要介绍VDSL技术及其标准化,然后比较ADSL和VDSL在速率、成本、传输质量和业务等方面的性能,VDSL有其明显的优势。但是实际上,没有任何一种接入技术能够解决所有的问题,它都有其适用范围,所以ADSL与VDSL最终将走向融合,采用DMT调制技术的VDSL2实现与ADSL2+的后向兼容将是VDSL发展的方向

Improved MAC schemes for VoWLAN systems

IEEE 802.11b的dCf接入方式是为无线数据业务提供接入而设计的,不能有效地支持诸如语音之类的实时业务。提出了两种改进的MAC层机制来提高无线局域网上传输语音(VOWlAn)的系统容量和有效性。分析和仿真结果表明,改进机制显著提高了系统容量,并保证了传输延迟、抖动和平均丢包率等服务质量(QOS)要求。IEEE 802.11b DCF was designed to provide wireless data access to support real-time services such as voice.This paper proposed two modified MAC schemes to improve capacity and efficiency of Voice over WLAN(VoWLAN) systems.Analysis and simulation results show that the proposed schemes effectively improve the system capacity,while QoS requirements,such as delay,delay jitter,and average loss rate,are guaranteed.福建省自然科学基金No.2007J0036---

Power Control and Energy Saving of Wireless Ad Hoc Networks

随着无线通信的日益发展,无线自组织网络正逐渐从军用扩大到民用等诸多领域。但是无线自组织网络一般由电池供电,由于提高电池容量的技术进步缓慢,功率控制是一个重要的研究课题。无线自组织网络中的功率控制机制研究主要集中在3个方面,即网络层功率控制、链路层功率控制以及混合功率控制。重点是从分层的角度对功率控制进行阐述,主要介绍了网络层及链路层的功率控制,并介绍了一些节能协议。跨层设计综合考虑了各层性能能更好地为功率控制与节能服务。With the development of wireless communications,wireless Ad Hoc networks are spreading from military areas to lots of civilian areas.However,Ad Hoc networks are supported by batteries,and battery technology of improving capacity progresses slowly,power control enhencement is an important issue.Researches on Power control can be concentrated as follows: power control of Network layer,power control of MAC layer and hybrid power control.The text plays emphasis on the power control of each layer,mostly introduces power control of Network layer and MAC layer.Moreover the text presents some energy saving protocols.The cross layer design takes account of the performance of each layer,may provides better services for power control and energy saving

Amplitude analysis of the decays D0 → π+π−π+π− and D0 → π+π−π0π0*

Using e+e− annihilation data corresponding to an integrated luminosity of 2.93 fb−1 taken at the center-of-mass energy √s = 3.773 GeV with the BESIII detector, a joint amplitude analysis is performed on the decays D0 → π+π−π+π− and D0 → π+π−π0π0 (non-η). The fit fractions of individual components are obtained, and large interferences among the dominant components of the decays D0 → a1(1260)π, D0 → π(1300)π, D0 → ρ(770)ρ(770), and D0 → 2(ππ)S are observed in both channels. With the obtained amplitude model, the CP-even fractions of D0 → π+π−π+π− and D0 → π+π−π0π0 (non-η) are determined to be (75.2 ± 1.1stat. ± 1.5syst.) % and (68.9 ± 1.5stat. ± 2.4syst.)%, respectively. The branching fractions of D0 → π+π−π+π− and D0 → π+π−π0π0 (non-η) are measured to be (0.688 ± 0.010stat. ± 0.010syst.)% and (0.951 ± 0.025stat. ± 0.021syst.)%, respectively. The amplitude analysis provides an important model for the binning strategy in measuring the strong phase parameters of D0 → 4π when used to determine the CKM angle γ(φ3) via the B− → DK− decay

Measurement of integrated luminosity of data collected at 3.773 GeV by BESIII from 2021 to 2024

We present a measurement of the integrated luminosity e+e- of collision data collected by the BESIII detector at the BEPCII collider at a center-of-mass energy of Ecm = 3.773 GeV. The integrated luminosities of the datasets taken from December 2021 to June 2022, from November 2022 to June 2023, and from October 2023 to February 2024 were determined to be 4.995±0.019 fb-1, 8.157±0.031 fb-1, and 4.191±0.016 fb-1, respectively, by analyzing large angle Bhabha scattering events. The uncertainties are dominated by systematic effects, and the statistical uncertainties are negligible. Our results provide essential input for future analyses and precision measurements

Determination of the number of ψ(3686) events taken at BESIII

The number of ψ(3686) events collected by the BESIII detector during the 2021 run period is determined to be (2259.3±11.1)×106 by counting inclusive ψ(3686) hadronic events. The uncertainty is systematic and the statistical uncertainty is negligible. Meanwhile, the numbers of ψ(3686) events collected during the 2009 and 2012 run periods are updated to be (107.7±0.6)×106 and (345.4±2.6)×106, respectively. Both numbers are consistent with the previous measurements within one standard deviation. The total number of ψ(3686) events in the three data samples is (2712.4±14.3)×10^