在巨量天線通訊系統中，嚴重的領航訊號汙染問題將大幅度限制其系統容量。為此，傳統的軟式頻譜重複使用機制被應用於解決領航訊號不足所可能造成汙染問題。其主要概念在於限制鄰近細胞以重複使用配置於細胞內圍之低汙染領航訊號。此外，應用加權式著色理論適當的選擇使用者以減少重複利用領航訊號而產生的汙染也是文獻中所採行的方案。在本篇論文中，我們結合上述兩解決方案之精神以進一步重複利用配置於細胞外圍之領航訊號。為控制其可能增加的汙染量，我們將細胞外圍區域劃分為安全邊界區及危險邊界區。顧名思義，配置於安全邊界區之領航訊號可重複被鄰近細胞使用；反之，配置於危險邊界區之領航訊號則不可被重複使用。藉由此汙染增量的控制方法，系統將能容納較多的使用者，因而大幅度的提升整體的系統傳輸率。再者，依使用者所處之區域適應性的調整其功率同時增加天線配置數量能更一步提升使用者之傳輸率。

In the massive multiple-input multiple-output (MIMO) systems, the serious pilot contamination problem severely restricts its ability to boost the spectrum utilization. To tackle this problem, the conventional concept of softly reusing the spectrum resources for the inner regions of the neighboring cells has been extended to reuse the pilot resources so as to accommodate more users. Alternatively, properly selecting the users to reuse the pilots among the neighboring cells can alleviate the pilot contamination problem as well. In this thesis, we delicately integrate these two concepts to properly reuse the pilots allocated to the outer regions of the cells. By well designing the hazard- and secure-edge regions to manage the pilot reuse, the increment of interference can be effectively suppressed; and, consequently, the more accommodated users can contribute to the remarkably higher sum data rates.Furthermore, via some adaptive power adjustment for the users within different regions, the user data rates
can further be significantly enhanced.

[1] T. L. Marzetta,"Massive MIMO an introduction," Bell Labs Technical Journal,vol. 20, pp.11-22, Mar. 2015.
[2] -,"Noncooperative cellular wireless with unlimited numbers of base station antennas," IEEE Transactions Wireless Communication, vol. 9, no. 11, pp. 3590-3600, Nov. 2010.
[3] L. Lu, G. Y. Li, A. L. Swindlehurst, A. Ashikhmin, and R. Zhang, "An overview of massive MIMO benefits and challenges," IEEE Journal of Selected Topics in Signal Processing, vol. 8, no. 5, pp. 742-758, Oct. 2014.
[4] F. Fernandes, A. Ashikhmin, and T. L. Marzetta, "Inter-cell interference in noncooperative tdd large scale antenna systems," IEEE Journal On Selected Areas In Communications, vol. 31, no. 2, pp. 192-201, Feb. 2013.
[5] H. Yin, D. Gesbert, M. Filippou, and Y. Liu, "A coordinated approach to channel estimation in large-scale multiple-antenna systems," IEEE Journal on Selected Areas in Communications, vol. 31, no. 2, pp. 264-273, Feb. 2013.
[6] X. Zhu, Z. Wang, L. Dai, and C. Qian, "Smart pilot assignment for massive MIMO," IEEE Communications Letters, vol. 19, no. 9, pp. 1644-1647, Sept. 2015.
[7] H. Q. Ngo and E. G. Larsson, "EVD based channel estimation in multicell multiuser MIMO systems with large antenna arrays," in IEEE International Conference on Acoustics Speech, Signal Processing (ICASSP), Mar. 2012, pp. 3249-3252.
[8] M. Li, S. Jin, and X. Gao, "Spatial orthogonality-based pilot reuse for multicell massive MIMO transmission," in IEEE International Conference on Wireless Communications and Signal Processing (WCSP), Oct. 2013, pp. 1-6.
[9] M. Alkhaled, E. Alsusa, and K. A. Hamdi, "Adaptive pilot allocation algorithm for pilot contamination mitigation in tdd massive MIMO systems," in IEEE Wireless Communications and Networking Conference (WCNC), May. 2017, pp. 1-6.
[10] X. Zhu, Z. Wang, C. Qian, L. Dai, J. Chen, S. Chen, and L. Hanzo, "Soft pilot reuse and multicell block diagonalization precoding for massive MIMO systems," IEEE Transaction on Vehicular Technology, vol. 65, no. 5, pp. 3285-3298, May.2016.
[11] X. Zhu, L. Dai, Z. Wang, and X. Wang, "Weighted graph coloring based pilot decontamination for multicell massive MIMO systems," IEEE Transaction on Vehicular Technology, vol. 66, no. 3, pp. 2829-2834, Mar. 2017.
[12] G. L. Stuber, Principles of mobile communication, 2nd ed. Kluwer Academic Publishers, 2002.
[13] Y. S. Cho, J. Kim, W. Y. Yang, and C. G. Kang, MIMO-OFDM Wireless Communications with MATLAB. John Wiley & Sons (Asia) Pte. Ltd., 2010.
[14] W. Chang, C.-Y. Yang, S.-L. Su, and Y. Lee, "Adaptive network MIMO architecture based on dynamic user-oriented frequency allocation scheme: Part i homogeneous network," in IEEE Vehicular Technology Conference (VTC Spring), May.2016.
[15] L.-C. Wang and C.-J. Yeh, "3-cell network MIMO architectures with sectorization and fractional frequency reuse," IEEE Journal on Selected Areas in Communications, vol. 29, no. 6, pp. 1185-1199, June. 2011.
[16] F. Fernandes, A. Ashikhmin, and T. L. Marzetta, "Intercell interference in noncooperative TDD large antenna systems," IEEE Journal on Selected Areas in Communications, vol. 31, no. 2, pp. 192-201, Feb. 2013.
[17] W. A. W. M. Mahyiddin, P. A. Martin, and P. J. Smith, "Performance of synchronized and unsynchronized pilots in finite massive MIMO systems," IEEE Transactions on Wireless Communications, vol. 14, no. 12, pp. 6763-6776, Dec. 2015.