基於IEEE 802.11n多點協調網路系統之媒體存取控制層實作

Abstract

隨著人們對於無線通訊的需求越來越大，依賴程度也越來越高，不只是因為手攜式手持裝置的蓬勃發展，同時也是來自應用程式越來越多元化所帶來的影響，因此網路需要更完善的協定以及機制來滿足需求，多點協調網路(Coordinated Multipoint) 便是一個相當創新的技術，也稱作Network MIMO，能透過提升基地台涵蓋範圍內邊際用戶的吞吐量，使整個無線網路的使用上更有效率。 在本論文中，因為設計的無線傳輸節點僅配置一根Tx天線和一根Rx天線，因此本論文嘗試在盡量符合IEEE 802.11n的規格之下，試著實作出能夠以CoMP技術中的聯合處理技術(Joint Processing)進行傳輸的系統，這樣多個傳輸節點可以同時間同頻帶傳送多筆資料給多個用戶。本論文主要針對幾個方向進行修改，首先是針對IEEE 802.11n的封包格式進行簡化以及小幅度的修改，接著本論文設計了能在系統上面使用的MAC Protocol以便能夠拿到所要的資訊，特別是通道資訊的部分，以用來控制整個CoMP系統，最後再針對同步問題找出相對應的方法來減少誤差。而因應軟體定義網路(Software Defined Network)的興起，本論文在骨幹網路的部分加入了Openflow的交換器以加快網路速度並且預留功能以便往後繼續開發。

In recent years, because of the wireless communication product innovation, the number of handheld devices has continuously increased, thus the wireless systems require better network protocol and mechanism in the future. In response to the trend of the future, we used the technique of Coordinated Multipoint(CoMP), also called Network MIMO, to increase the throughputs of the edge user. In the paper, we designed a wireless device configured with 1 transmitting antenna and 1 receiving antenna. The modified MAC protocol was implemented based on IEEE 802.11n to accomplish the Joint Processing(JP) mechanism in our system, which is one of the techniques of CoMP. In this way, more than one wireless device could transmit the data stream to the user who is associated with the device in the same time and frequency without interfering with each other. To achieve the goal, we first modified the frame format based on IEEE 802.11n, and then we designed a new MAC protocol in furtherance of getting the channel coefficient. In addition, the issue of synchronization is important too. Therefore, the network time protocol and precision time protocol daemon were applied to decrease the clock offsets between the devices. Finally, we deploy the Openflow Switch to improve the speed of backbone network.