标题: 基于CRC的轻量化OFDMA网路高可靠度资料递送服务
A CRC-based Lightweight Reliable Data Delivery Services over OFDMA Networks
作者: 陈嘉耀
Chen, Chia-Yao
陈耀宗
文康
资讯科学与工程研究所
关键字: 循环冗余码;校错机制;正交分频多工;多跳中继网路;紧急讯息系统;Cyclic Redundancy Check;error correction;OFDMA;Multi-hop Relay network;Emergency Communications Systems
公开日期: 2013
摘要: 近年来,正交分频多工(Orthogonal Frequency Division Multiplexing Access; OFDMA) 调变编码技术已经被广泛的应用在许多不同类型的无线通讯系统,例如:Wi-Fi、WiMAX和LTE等。为确保传输品质及效率,传统上在Data link Layer,若干个Frame会被集合封装成一Burst,并会附加循环冗余码(Cyclic Redundancy Check; CRC)编码,接收端可以经由检查讯框检查序列(Frame Check Sequence; FCS)得知Burst传送过程中是否发生错误,在经由整合式自动重传机制(Hybrid Automatic Retransmission Request; HARQ) 通知发送端重送错误资料。虽然CRC具备运算速度快的特性,但由于仅能达成错误检测的功能,在错误产生时,仅能以重送全部资料的方式校正错误。
由于在封装时OFDMA 封包必然会产生一些留白(padding),因此本次论文提出一个以CRC为基础的错误码侦测方法,此方法利用的padding空间的大小为基准,动态计算部份封包的FCS值,并将部份封包的FCS值padding在封包内。由于利用的是padding的空间,所以不会增加传送时所需频宽。当网路环境不佳时,封包产生错误比例升高,可能每次传送都会发生错误,此时可以利用额外padding的资讯,判断错误发生的区段,
就算下次重送的封包还是错误,此方法可利用比对前后两次封包资讯的方法,还原成正确的封包,因此本方法可有效在网路环境不佳时,有效下降封包需要重送的次数。
本研究以前述提出的侦错及校错机制,尝试套用在至少三种主要的OFDMA网路应用情境中,如多跳中继(Multihop Relaying)、群播服务(MBS)、高速移动通讯(Telematics)等,这些情境都具备无线节点可能接收到多次相同讯号的特性,符合实现本方法的条件。由模拟结果中发现,本研究提出的方法将有效运用于极端恶劣无线信道环境中,以及对于在高速移动环境中所导致的都普勒(Doppler)效应,由改善其高误码率(BER),提升OFDMA网路的通讯可靠度及频谱效率。
OFDMA-based wireless transmission technologies such as WiMAX are now widely deployed, and the FCS scheme is used to enhance the reliability of OFDMA-based systems. As the padding overhead cannot be completely avoided in such systems when variable-length MAC frames are encapsulated, we propose a novel CRC-based error correction scheme that utilizes the frame padding overhead to carry as much extra segmented FCS information as possible; compared with the legacy FCS scheme, our approach greatly enhance the error detection and correction upon the retransmission. In a multi-hop relay environment, a mobile station might receive a multicast frame more than once, so the error bit correction scheme could be triggered in the first transmission. In the original CRC scheme is optional and only has limited error detection capability in upper MAC layer, but in our work, CRC is compulsory and all sub-FCSs are carried by padding space without using any extra bit. The proposed approach achieves a significant performance improvement over the legacy FCS scheme in terms of error detection and correction of multicast frames in a transparent mode multi-hop relay network. Additionally, in some specific applications, the proposed scheme also achieves a significant performance improvement over the legacy FCS scheme in terms of error detection and correction. For example, the emergency service over Multicast/Broadcast Service (MBS) is a promising technology, because it allows simultaneous delivery of emergency messages to large-scale user communities in a cost-effective manner. In high-mobility environment, mobile station might receive an emergency MBS frame more than once, so the proposed scheme could be cross referenced by duplicated frames received in a WiMAX Mobile Multihop Relay (MMR) network operating in transparent mode. The simulation results show that the mobile stations get significant improvement of goodput and utilization in an error-prone WiMAX network.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT079655825
http://hdl.handle.net/11536/74247
显示于类别:Thesis