标题: | 应用于中继通道之正交振幅调变讯号之放大前送策略研究与设计 Study and Design of Amplify-and-Forward Strategies for QAM- Modulated Signals in Relay Channels |
作者: | 施维庭 Shih, Wei-Ting 陈绍基 Chen, Sau-Gee 电子研究所 |
关键字: | 中继通道;正交振幅调变;网路编码;Relay channel;QAM;Network Coding |
公开日期: | 2010 |
摘要: | 随着通讯产业的发展,各种应用对于高速且稳定的资讯传输的需求也日益增加。 当透过无线通道传输讯息时,多天线传输系统(MIMO system)是已知能够有效增加讯号之多样性(Diversity)进而提高系统效能的一种可行方式,但多天线的通讯设备其复杂度必然高于单天线之设备,因此如何使用单天线之设备达成相近之效果成为了一个值得研究的课题。 合作式通讯( Cooperative communication)是一种利用中继节点(Relay node)来中继网路内传输之资料,以增加数个单天线通讯设备之间讯号传输之多样性之方法。但使用中继节点也同时会造成频谱效率(Spectrum efficiency)的降低。近年来有许多对于合作式通讯之相关研究,证明了将网路编码(Network coding)之概念应用到中继网路(Relay network)架构中,可有效的减少因讯号的中继机制而增加的额外传输时间。但是为维持传输之错误率,中继节点必需加大其传输功率。运用参考资料[19]与[20]的基本概念,此篇论文进一步延伸现有技术与改善传输效能,文中将提出以减少可能出现的符码(Symbol)数量之概念应用于放大前送(Amplify-and-forward)系统之方法,藉以降低中继节点所需之传输功率。 此方法是利用在完美的通道下,经过网路编码处理过的正交振幅调变讯号对复数座标原点具有对称性且其绝对值仍可被接收端(Destination node)解码的特性来减少所有可能出现的符码之数量,但是当介于两个传送端(Source node)与中继节点(Relay node)之间的两通道(Channel)间具有相位差(Phase difference)时,则有可能出现无法将原始讯号还原之情形,本论文尝试同时在两传送端送出讯号之相位上加上一微小的角度,以补偿此现象,模拟结果显示,此方法可一定程度的补偿因通道相位差而造成的效能降低。 本论文也将提出能够延伸应用至多于三个传送端之中继网路的网路编码架构;当一个经过网路编码的讯号中,仅包含一个未知符码时,接收端即可利用已知之资讯对此讯号进行解码,利用此特性可以使用目前已存在之双向中继通道(2-way relay channel)上之网路编码技术,针对多个传送端所传输之讯号进行网路编码以及传送顺序的排序,本论文并将针对传送端之数量与此方法之效能的关系进行分析。 As telecommunication technologies advance rapidly, there are increasing demands in applications that require high speed and stable data transmissions. While transmitting signals through wireless channels, the technique of multiple-input and multiple-output (MIMO) transmission is considered as an effective way to increase the capacity and reliability of general communication systems. However, the complexity of a multi-antenna device is higher than a single-antenna device. Hence, how to achieve similar effect to multi antennae with single-antenna devices is a topic worth investigation. A cooperative communication system can utilize relayed transmission to achieve cooperation diversity by a group of single-antenna devices, at the cost of reduced spectrum efficiency. It has been shown that by applying network coding to relay networks, one can reduce delays in data forwarding processes. However, it demands more transmission power than without network coding, in order to maintain the minimum distance of the resulted data constellation. In this thesis, we will propose a method that reduces the number of candidates of the resulted network-coded constellation for transmitted m-QAM data obeying AF protocol. The proposed method is based on the property that the constellation of network coded QAM signal will be symmetric to the origin, if the channels are perfect. And the absolute value of a signal point in the constellation still can be decoded by the other source in the 2-way relay channel. However, if the two channels from the two sources to the relay have phase difference, decoding performance based on the minimum distance will degrade. This thesis tries to shift the phase of the two signals transmitted by the sources by a small amount so as to compensate the effect of the phase difference between channels. Simulation results shows that, the proposed method can reduce the phase effect, and we will optimize this method for the 4-QAM. We will also propose a network coding scheme that generalizes two-way relay to multi-way relay channels which involves more than three source nodes. Since a destination node can decode a network coded signal if and only if the signal contains only one unknown data symbol, one can use the existing network coding schemes for 2-way relay channels to encode the symbols in the case that more than three sources are involved. We will also analyze the relationship between the amount of sources and the performance while applying this scheme. |
URI: | http://140.113.39.130/cdrfb3/record/nctu/#GT079811612 http://hdl.handle.net/11536/46775 |
显示于类别: | Thesis |