在干擾環境下具適應性的藍芽封包選擇及排程策略

Abstract

藍芽是一個應用於無線個人區域網路的技術。它旨在消除各種裝置之間裝設電纜和連接器的需求。它可應用在個人電腦及其週邊設備，隨身聽及其連接的耳機等。藍芽提供具強韌性、安全性且支援數據和聲音的無線電通訊，而這些裝置不需要彼此都在視線之內。藍芽使用2.4 GHz ISM 頻帶，與IEEE 802.11系列的無線區域網路共用同一頻帶。此兩種網路本是互補而非互相競爭關係，然而它們互相干擾可能會不預期發生，此將嚴重降低彼此效能。在本論文中，我們提出根據頻道狀況進行藍芽資料分割和重組的方案(CSD-SAR)及根據佇列狀況作排程的策略(QSD-PR)。CSD-SAR 會建構一個接收頻道表(receiving frequency table)，並根據此表去預測頻道狀況及選擇最適合的封包格式和封包大小來傳輸資料。透過這個方法，不僅可以在不延遲傳輸下，避用不好的頻道，並且在易於發生錯誤的環境下有較好的鏈路使用率及較好的效能表現。此外，QSD-PR 也利用這個接收頻道表去避免在不好的頻道傳送封包，且給予彼此之間有較多資料要傳送的主從對 (master-slave pair) 較高的優先權，以避免時槽的浪費。常見的排程策略如輪詢排程(RR)，在分時雙工(TDD)的存取控制通訊協定下，不能提供較好的效能，此造成時槽的浪費，也不能確保公平性。模擬結果顯示，與RR比較，無論在無錯誤或易於發生錯誤的環境下，我們提出的封包選擇及排程策略能達到較好的鏈路使用率及較高的效能。我們提出的方案因為避免使用其他網路所佔用的頻道，所以也能消除對其他共用同一頻帶的無線區域網路之干擾。

Bluetooth is a new technology for Wireless Personal Area Networks (WPANs). It intends to eliminate the need of wires and connectors between a variety of devices, like PCs and their peripherals, walkmans and their earphones, and etc. Bluetooth provides robust and secure wireless radio communication of both data and voice, even when the devices are not within line-of-sight. Bluetooth employs the 2.4 GHz ISM band, sharing the same band with the Wireless LAN (WLAN) implementing the IEEE 802.11 series standard. While WLANs and WPANs are complementary rather than competing technologies, the likelihood of mutual interference may occur unexpectedly, which may impact the performance of either severely. In this thesis, we propose a Bluetooth channel state dependent data segmentation and reassembly (CSD-SAR) scheme and a queue state dependent priority (QSD-PR) scheduling policy. The CSD-SAR maintains a receiving frequency table to predict channel conditions and selects the best packet type and packet size to transmit data. In this way, it not only masks bad frequencies without delaying transmission but also leads to the best performance with high link utilization in error-prone environments. In addition, the QSD-PR also uses the receiving frequency table to avoid bad frequencies and gives a selected master-slave pair, which has more queued data to send between each other, a higher priority to eliminate the wastage of slots. The conventional scheduling policy, Round Robin (RR), yields poor performance with the time division duplex (TDD) based MAC protocol and results in slot wastage and may not ensure fairness. Simulation results show that our proposed scheme achieves better link utilization and higher throughput with bounded delay compared to the RR scheme in error-free and error-prone environments. Our scheme can also eliminate interference to other wireless networks that share the same spectrum, such as WLANs, by avoiding selecting channels occupied by other networks.