針對無線行動通訊之回程網路所提出分時多工之介質存取控制協定

Abstract

對於一個手機網路(Mobile Network)來說，很重要的一個議題是覆蓋率(Coverage)的問題，使用無線的方式去擴充基地臺(Base Station)，相較於傳統的有線方式，可以更快速且方便來達到高覆蓋率，以節省成本。特別是在偏遠的山區，用有線的方式去佈建將會更加困難，成本更高，此時使用無線的技術更可以顯現其優點。然而，無線的方式會面臨到許多困難。其中最主要的問題是，由於是在同一個區域之下，使用同一個介質，因此導致容易發生碰撞。所以在這些基地臺之間，我們需要有一個移動交換中心(Mobile Switch Center)，來控制與協調這些基地臺，讓他們在整個無線行動通訊之回程網路(Wireless Mobile Backhaul Network)中，可以有效率地使用共享的介質並且避免碰撞發生。 在本篇論文中，我們設定了此網路，其最遠連接距離是2英哩，最多可連接8個基地臺，並具有QoS控管以及高吞吐量。所以我們針對這樣的一個無線行動通訊之回程網路，提出了一個分時多工之介質存取控制協定(MAC Protocol)，在MAC層上面來控制與協調這些基地臺的傳輸。 此MAC Protocol的傳輸過程當中是以superframe為單位作傳輸。每個superframe時間長度為65 ms，包含了Beacon period、UL Groups以及DL Groups。每4個superframe提供一次的入網時段，來允許一個基地臺入網。 我們也針對此MAC Protocol來進行模擬，來得知此MAC protocol的相關資訊。最後將此MAC Protocol利用兩張FPGA板子來進行整個傳輸行為的驗證。資料的來源是從Host上面傳給MAC Protocol，我們將MAC Protocol利用軟體的方式實作在其中一張FPGA板子上，而另外一張板子則是使用硬體來模擬成通道，讓MAC Protocol所傳輸的資料在經過此通道時，有機率的會發生錯誤。在資料傳輸方面，兩張FPGA板子的傳輸協定為I2C Protocol，而MAC Protocol所在的FPGA與Host之間是使用Ethernet來進行資料的傳輸。 在實作的平臺運作過程當中，會印出每個frame的狀態與資訊，我們根據這些資訊來對此系統進行每個功能的驗證，包含了入網功能、時間同步功能、ACK與重送功能、錯誤偵測、失去連線之偵測，以及QoS的驗證。來確保此平臺的正確性以及穩定性。

For a mobile network, the most important issue is coverage. Using wireless method to extend the base station is better than the traditional wired method. It is quicker and easier to achieve the high coverages, and saving costs. Especially extend base stations in the suburbs by using the wired method, it will be more difficult and more expensive. So using the wireless technology can show its advantages significantly. However, wireless method faced many challenges. The most important problem is that all the base stations are using the same medium in the local area, it maybe cause the collision. So we need a mobile switch center to control and coordinate these base stations, to efficiently use the share medium and avoid collision in the entire wireless mobile backhaul network. In this paper, we set up a network which farthest distance is 2 miles, can connect up to eight base stations, and has a QoS control and high throughput. So we focused on such a wireless mobile bakchaul network, proposed a TDMA MAC protocol, on the MAC layer to control and coordinate the transmission of these base stations. The transmission unit in the MAC protocol is superframe. Each superframe duration is 65 ms, including the beacon period, UL groups and DL groups. Every four superframes provide a joinable period to allow one base station to join the network. We also simulated the MAC protocol to learn more information. Finally, we verified the entire transmission behavior of the MAC protocol via two FPGA boards. The data resource was from host to MAC protocol. We used the software method to program the MAC protocol on a FPGA, and the another FPGA was used to simulate the channel by hardware. When the the data was transmitted to the channel by MAC protocol, it had the probability to occur the propagation error. In the data transmission, the transmission protocol was I2C protocol between the two FPGA boards, and we used Ethernet to transmit data between the host and the FPGA which was running the MAC protocol. During the system platform operating, the system will print out the status and information for each frame transmission. According to these messages, we can verify the correctness of each function which includes the join function, time sync function, ACK and retransmittion function, error detection, the disconnection detection, and the QoS verification. To ensure the correctness and stability of this platform.