IEEE 802.11介質存取控制器設計與實現：傳輸部分

Abstract

隨著最近無線通訊技術的進步，能同時支援語音與數據服務的無線傳輸已經是下一代通訊網路的趨勢。無線傳輸不會被環境所限制，經由簡單的(無需佈線的)網路拓樸就可以提供等效於有線網路的服務。可以預期的是, 未來的無線網路，將會著重移動性的網路存取支援，以及即時互動服務。 在無線區域網路的相關標準中，IEEE 802.11規格[3] [4]可以說是第一個制定較完整的無線局部數據傳輸標準。它不僅提供了必備的競爭式數據傳輸服務，也制定了可選擇性支援的延遲限制服務(Time-Bounded Service)。IEEE 802.11在1997制訂完成後，數百種相關產品即很快地出現在市場上。在這些產品中, IEEE 802.11介質存取控制器大部分都是採用中央處理器為基礎(或是韌體實作為基礎)的架構設計，例如AMD公司所製造的「以80188為基礎」的79C30晶片。然而，我們注意到以韌體來實現介質存取控制，實際上對區域網路所需之低成本及高傳輸速度要求，並不是符合經濟效益的的設計方法。同時，我們也觀察到IEEE 802.11已經制定完成的介質存取控制規範，於接下來的版本並未有任何修訂。所以，韌體實現架構的易隨標準修訂而修改之彈性化的好處，變成已不是主要的IEEE 802.11介質存取控制器的設計考量。因此，我們認為必須思考一個新的實現架構。 在本論文中，我們提出以專門設計的標準單元式積體電路來實現IEEE 802.11介質存取機制(CSMA/CA)。針對「控制傳輸框架」需要快速回應的需求，一個「控制傳輸框架處理模組」也包含在我們設計的介質存取控制器內。我們的設計---如果與中央處理器為基礎的設計架構作比較---和主系統及基頻處理器的介面就顯的相當簡單。除此之外，我們的設計也能夠很直接的適用於未來IEEE 802.11 5/11Mbps高速的版本上[4] [12]。

With the recent advance of the wireless technologies, wireless transmission is becoming the trend of the next generation communication for voice and data services. It can provide wired-network equivalent services through simple network topology and without being restricted by the environmental space. As anticipated, the future wireless network will focus more on supporting the mobility access, as well as the interactive services. IEEE 802.11 [3] [4] is perhaps the first well-rounded standard on wireless LAN. It not only specifies the basic contention-based data transmission services, but also optionally supports the time-bounded services. After the standardization of IEEE 802.11 in 1997, hundreds of compliant products quickly fill in the market. The current implementations of the IEEE 802.11 Medium Access Control (MAC) are mostly based on a CPU-Based or firmware-based architecture, such as the 80188-based 79C30 chip manufactured by AMD Inc. We, however, notice that the firmware-based implementation is actually not a cost-effect solution for a low-cost and high-speed LAN product. We also observe that the IEEE 802.11 MAC scheme is already finalized (and expects to remain intact in the coming revision). Therefore, the flexibility of a firmware-based implementation somewhat loses its ground. Accordingly, a new implementation architecture should be considered. In this thesis, we propose a specially cell-based IC design to implement the IEEE 802.11 basic medium access mechanism (CSMA/CA). To quickly respond to the control frames, an internal Control Frame Handler is also included in our MAC controller. In our design (if compared with the CPU-based architecture), the interface to the host system, as well as the interface to the Baseband processor, is quite simple. In addition, our design can easily migrate to the coming 5.5/11 Mbps high-speed version of IEEE 802.11 standard [4] [12].