面向QoS的UWB分布式MAC协议设计

提出了一种在分布式UWB网络结构中提供QoS服务的MAC协议.该MAC协议能够自适应地协调功耗与速率,设计过程分为资源分配和多路接入两方面.仿真结果表明,通过与功率控制机制及速率控制机制的比较.提出的协议在功率消耗,网络吞吐量及延时方面都有较好的改善.     

LTE系统PRACH详解

PRACH(Physical Random Access Channel),物理随机接入信道,作为非同步用户和LTE无线接入的正交传输方案的接口,主要用于网络接入的初始化,为未得到上行同步或已经失去上行同步的用户实现上行定时同步。本文首先对LTE系统PRACH进行了简单介绍,然后分别从PRACH的初始参数、触发事件、消息流程以及检测等几个方面进行了详解。     

有效提高吞吐量的UPMA+ +协议

本文提出了基于有效竞争接入、高效无冲突传输的多址接入协议—UPMA+ +.该协议采用了有效的冲突分解策略和及时重获信道资源的方法,克服了UPMA(根据用户数目妥善安排传输的多址接入)协议中的开销;通过自适应调整竞争接入周期长度和限制无冲突服务周期长度的方法,很好地解决了激活节点快速接入信道和传输节点尽快传输分组之间的矛盾,从而提高了协议的吞吐量.本文还应用排队论的方法对UPMA+ +协议的性能进行了理论分析,计算结果与仿真结果基本一致.     

基于S-CDMA的HFC网上行信道接入协议

本文着重讨论了一个基于S-CDMA的HFC网上行信道的高效的接入协议--SAMA接入协议，其中包括了请求冲突解决协议和初始化协议两部分，并对这个接入协议的冲突率和吞吐量性能进行了详细分析，最后提出了该接入技术中尚待解决的问题。     

支持话音/数据分组并传的UPMA多址接入协议

本文提出了一种新的、支持数据/话音业务并传的多址接入协议——根据用户数目妥善安排分组传输的多址接入(User-dependent Perfect-scheduling Multiple Access——UPMA)协议,它根据实际需求对上、下行带宽资源实行动态分配.UPMA协议对不同的业务类型赋予不同的优先级,并用轮询方式妥善地安排节点的分组传输;同时,它采用独特的帧结构,使话音业务总是能够得到优先传输.本文还提出了一种高效的竞争接入算法,以保证激活的节点能够快速接入信道.最后,对UPMA协议的性能进行了仿真并与MPRMA协议的性能进行了比较,结果证明UPMA协议有更好的性能.     

在GPON中实现分组业务接入的MAC协议设计

参照ITU-T建议草案——吉比特无源光网络传输汇聚层规范(G.GPON.gtc),提出了一种支持分组业务接入的媒质接入控制(MAC)协议,并对该协议的性能进行了分析。     

GPON的MAC协议设计

参照ITU T建议草案:吉比特无源光网络传输汇聚层规范(G.GPON.gtc),提出了一种支持分组业务接入的媒质接入控制(MAC)协议.通过仿真建模对该协议的性能进行了分析.     

APON的帧结构和MAC协议设计及其性能分析

本文参照以ATM为基础的无源光网络(APON)的G.983建议,提出了一种新的传输帧结构和媒质接入控制(MAC)协议.传输帧长选为125μs,这有利于STM业务的接入.考虑到话音业务对时延敏感并且传输速率较低的特点,MAC协议对话音业务实行固定带宽分配.对其它类型的业务则采用基于预留的动态带宽分配方案.通过建模仿真分析了协议的信元时延(CD)和信元时延变化(CDV)特性.     

物联网分组数据传输协议研究

在对现有物联网分组数据传输协议分析的基础上,比较了物联网分组数据内网传输协议中的微型区内传输协议和近距离传感区传输协议,提出了接入层传输协议结构模型和接入层传输信道的使用方法及内层传输协议的数据格式。所得结果为物联网接入层传输协议的进一步研究提供了参考。     

一种自组网功率控制算法及分析

无线自组网中的移动节点大多依靠电池提供能量,因此能量是影响无线自组网性能的一个很大的瓶颈,作为事实上的无线自组网媒体接入协议,802.11并没有动态调整传输功率的能力,大大限制了网络的生存时间。采用功率控制可以提高节点的功率使用效率,减少相邻节点间的干扰,改善网络的性能。在802.11基础上提出一种基于信噪比的动态传输功率控制算法。通过进行计算机仿真,与802.11协议相比,在保持吞吐量性能的前提下,大大减少了节点的功率消耗,提高了节点的能量利用率。     

An initialisation protocol for a CDMA based communications schemefor HFC CATV networks

An initialization protocol for a CDMA based communications system for hybrid fiber coax (HFC) central antenna television (CATV) networks is described. HFC CATV networks are shared medium access networks, employing the coaxial bus principle between an optical network terminator and the subscriber. To realize access in the upstream direction, a multiple access scheme based on CDMA can be used. However, before access is granted in the upstream direction, each cable modem connected to the coaxial bus needs to undergo a startup procedure at activation of the modem to determine timing and physical layer related settings. The initialization mechanism described performs time synchronization of a modem and the determination of the power the modem should use. Next to these physical layer settings, also the identity of a modem is determined during the initialization process     

基于HFC网络上行信道CDMA-预约ALOHA多接入方式吞吐量分析

为了在HFC网络上实现交互式业务,人们对基于HFC网络的介质访问协议进行了广泛的研究.已出现的几种基于HFC的MAC协议基本上都采用了竞争与预约相结合的访问机制.基于CDMA的HFC是新一代的HFC系统.本文提出了一种基于CDMA的双向HFC网络竞争与预约相结合的上行信道多址接入方式.并且为该协议系统建立了四状态Markov链分析模型,对该协议进行了性能分析,并给出了计算机实验结果与分析.     

QoS guarantee and provisioning for realtime digital video over mobile ad hoc cdma networks with cross-layer design

In this article we investigate the trade-offs and the constraints for multimedia over mobile ad hoc CDMA networks, and propose a cross-layer distributed power control and scheduling protocol to resolve those trade-offs and constraints in order to provide high-quality video over wireless ad hoc CDMA networks. In particular, a distributed power control and scheduling protocol is proposed to control the incurred delay of video streaming over multihop wireless ad hoc networks, as well as the multiple access interference (MAI). We also investigate the impacts of Doppler spread and noisy channel estimates upon the end-to-end video quality, and provide a relatively robust system which employs a combination of power control and coding/interleaving to combat the effects of Doppler spread by exploiting the increased time diversity when the Doppler spread becomes large. Thus, more robust end-to-end video quality can be achieved over a wide range of channel conditions     

A medium access control scheme for TDD-CDMA cellular networks with two-hop relay architecture

In this paper, we propose a multihop medium access control (mMAC) scheme for time division duplexing-code division multiple access (TDD-CDMA) cellular networks with two-hop relay architecture to support packet data transmission. The proposed mMAC is based on joint CDMA/PRMA (packet reservation multiple access) protocol and it includes BCH code selection, power control and multihop relaying. Simulation results reveal that cellular networks with two-hop relay architecture with the proposed mMAC scheme can substantially provide a good performance as well as larger cell coverage as compared to conventional TDD-CDMA single-hop cellular networks.     

Efficient Radio Resource Management in Integrated WLAN/CDMA Mobile Networks

The complementary characteristics of wireless local area networks (WLANs) and wideband code division multiple access (CDMA) cellular networks make it attractive to integrate these two technologies. How to utilize the overall radio resources optimally in this heterogeneous integrated environment is a challenging issue. This paper proposes an optimal joint session admission control scheme for multimedia traffic that maximizes overall network revenue with quality of service (QoS) constraints over both WLANs and CDMA cellular networks. WLANs operate under IEEE 802.11e medium access control (MAC) protocol, which supports QoS for multimedia traffic. A cross-layer optimization approach is used in CDMA networks taking into account both physical layer linear minimum mean square error (LMMSE) receivers and network layer QoS requirements. Numerical examples illustrate that the network revenue earned in the proposed joint admission control scheme is significantly more than that when the individual networks are optimized independently.     

A dynamic control scheme for the IEEE 802.14 draft MAC protocolover CATV/HFC networks

We first describe the draft multiple/random access protocol for IEEE 802.14 over the cable TV/hybrid fiber coaxial (CATV/HFC) networks. To best fit this draft protocol into the target network, we propose a dynamic control scheme to adequately adjust the parameters. Simulations of the draft protocol are then presented to depict the effectiveness of the proposed scheme and further highlight the directions for the design of MAC protocols over the CATV/HFC networks     

Performance evaluation of a joint CDMA/NC-PRMA protocol forwireless multimedia communications

A joint code division multiple access and noncollision packet reservation multiple access (CDMA/NC-PRMA) technique is proposed and investigated as an uplink protocol for the third-generation (3G) mobile systems. Being the underlying time division multiple access (TDMA) architecture of the CDMA transmissions, NC-PRMA enables the base station (BS) to have a centralized control over the slot allocation policy. In order to reduce the multiple access interference (MAI) variation in a CDMA transmission, two different slot assignment schemes, referred to as load-balancing (LB) and power-grouping (PG) schemes, are proposed and evaluated. Simulation results show that considerable improvement can be achieved over the joint CDMA/PRMA scheme, in which the MAI variation is reduced by way of a dynamic permission probability for contending terminals. Especially when an imperfect power control mechanism is considered, the proposed PG assignment scheme achieves significant performance advantages     

On IEEE 802.14 medium access control protocol

In this article we present a comprehensive survey on the architecture, protocol issues, and standard of the hybrid fiber coaxial (HFC) networks which are evolving from the existing residential CATV networks. We first describe the HFC architecture and discuss the problems in providing two-way communication. Then, we identify three important medium access control (MAC) issues in designing the IEEE 802.14 standard; namely, synchronization, upstream channel access modes, and collision resolution. Resolutions adopted by the IEEE 802.14 Committee are illustrated after giving a protocol overview. Key resolutions include compensating round trip correction (RTC), interleaving minislots of data and request concurrently, and resolving collisions by multiple collision resolution engines, using the n-ary tree plus p-persistence algorithm with a first transmission rule. A comparative summary of some draft proposals that lead to the standard is given. Finally, we pinpoint two headend algorithms, minislot allocation and request scheduling, which are left open in the standard. They do not affect interoperability but may have a critical impact on performance.     

Optimal Joint Session Admission Control in Integrated WLAN and CDMA Cellular Networks with Vertical Handoff

This paper considers optimizing the utilization of radio resources in a heterogeneous integrated system consisting of two different networks: a wireless local area network (WLAN) and a wideband code division multiple access (CDMA) network. We propose a joint session admission control scheme for multimedia traffic that maximizes overall network revenue with quality of service (QoS) constraints over both the WLAN and the CDMA cellular networks. The WLAN operates under the IEEE 802.11e medium access control (MAC) protocol, which supports QoS for multimedia traffic. A novel concept of effective bandwidth is used in the CDMA network to derive the unified radio resource usage, taking into account both physical layer linear minimum mean square error (LMMSE) receivers and characteristics of the packet traffic. Numerical examples illustrate that the network revenue earned in the proposed joint admission control scheme is significantly larger than that when the individual networks are optimized independently with no vertical handoff between them. The revenue gain is also significant over the scheme in which vertical handoff is supported, but admission control is not done jointly. Furthermore, we show that the optimal joint admission control policy is a randomized policy, i.e., sessions are admitted to the system with probabilities in some states