在無線隨意網路的環境裡面，雖然利用智慧型天線技術可以有效地大幅提升系統容量，但是卻會引發了兩個嚴重的資源存取問題：其中第一個問題是發生在智慧型天線系統的指向模式，稱作Hidden Terminal Due to Unheard RTS/CTS，其肇因於指向模式輻射型態之高度指向性，此高度指向性無法清楚地分辨重要訊息和其他干擾源，導致網路重要資訊遺失；第二個問題是發生在智慧型天線系統的全向模式，稱作Hidden Terminal Due to Asymmetry in Gain，其肇因於全向模式的天線增益不足(智慧型天線系統的全向模式天線增益遠遠小於指向模式天線增益)，在此模式下，距離較遠的訊號源所發出的網路重要資訊可能會遺失。在本篇論文中，我們將提出一個無線隨意網路媒介擷取控制通訊協定來同時解決這兩個資源存取問題。我們的方法是使用正確的天線增益以及輻射型態讓所有的隱藏節點都能夠收到警告訊息；接收到警告訊息之後，這些隱藏節點必須依照我們所提出的通訊規則來限制自身的傳輸；除了上述兩點之外，在我們的方法中，網路配置向量被區分為網路傳送配置向量和網路接收配置向量兩個部份，如此一來可使得媒介擷取控制通訊協定擁有更佳的效能。理論分析與模擬驗證的結果同時顯示，與其他不同的方法比較起來，我們提出的方法更能夠有效地避免碰撞的發生進而增加無線隨意網路的系統容量。

In ad-hoc multi-hop wireless networks, use of smart antennas can substantially increase system capacity. However, smart antenna technology leads to new channel access problems, such as Hidden Terminal Due to Unheard RTS/CTS and Hidden Terminal Due to Asymmetry in Gain. This paper proposes a MAC protocol that can solve these two problems. The proposed scheme has the following features. First, the antenna pattern used to transmit DATA differs from the antenna pattern used to transmit RTS/CTS/ACK. Second, the gain used to transmit RTS/CTS differs from the gain used to transmit DATA/ACK. Third, the nodes that receive RTS/CTS are limited according to the proposed rules. Finally, the NAV (Network Allocation Vector) timer of the proposed MAC protocol should be separated into two parts: transmitting NAV and receiving NAV. Simulation results show that the proposed MAC protocol can effectively improve network throughput, as compared to other MAC protocols using smart antennas.

[1] M. Takai, J. Martin, A. Ren and R. Bagrodia, “Directional Virtual Carrier Sensing for Directional Antennas in Mobile Ad Hoc Networks,” in ACM MobiHoc, June 2002.
[2] S. Bandyopadhyay, K. Hasuike, S. Horisawa and S. Tawara, “An Adaptive MAC Protocol for Wireless Ad Hoc Community Network (WACNet) Using Electronically Steerable Passive Array Radiator Antenna,” in IEEE GLOBECOM, Volume: 5, 25-29 November 2001, Pages: 2896-2900 vol. 5.
[3] S. Bandyopadhyay, K. Hasuike, S. Horisawa and S. Tawara, “An Adaptive MAC and Directional Routing Protocol for Ad Hoc Wireless Network Using ESPAR Antenna,” in ACM MobiHoc, 4-5 October 2001.
[4] R. R. Choudhury, X. Yang, R. Ramanathan and N. H. Vaidya, “Using Directional Antennas for Medium Access Control in Ad Hoc Networks,” in ACM MOBICOM, September 2002.
[5] T. Korakis, G. Jakllari and L. Tassiulas, “A MAC Protocol for Full Exploitation of Directional Antennas in Ad-hoc Wireless Networks,” in ACM MobiHoc, June 2003.
[6] S. Roy, D. Saha, S. Bandyopadhyay, T. Ueda and S. Tanaka, “A Network-Aware MAC and Routing Protocol for Effective Load Balancing in Ad Hoc Wireless Networks with Directional Antenna,” in ACM MobiHoc, June 2003.
[7] A. Acharya, A. Misra and S. Bansal, “High-Performance Architectures for IP-Based Multihop 802.11 Networks,” in IEEE Wireless Communications [see also IEEE Personal Communications], Volume: 10, Issue: 5, October 2003, Pages: 22-28.
[8] A. Acharya, A. Misra and S. Bansal, “MACA-P: A MAC for Concurrent Transmissions in Multi-hop Wireless Networks,” in IEEE PerCom, 23-26 March 2003, Pages: 505-508.
[9] T. S. Rappaport, “Wireless Communications: Principles & Practice,” Prentice Hall, 1996.
[10] J. C. Liberti and T. S. Rappaport, “Smart Antennas for Wireless Communications: IS-95 and Third Generation CDMA Application,” Prentice Hall, 1999.