臺灣博碩士論文加值系統

為了滿足日漸增長流量需求，行動網路營運商將免執照頻段引入到LTE中，使其得到更大的頻寬。但若沒有公平的共存方法，將會嚴重危害目前在免執照頻段中Wi-Fi的效能。在本篇論文，我們提出一套利用Wi-Fi競爭視窗大小來分配占空比的共存方法。我們在LTE基地台中安裝虛擬Wi-Fi傳送節點，利用該節點來模擬分散式協調功能，得到目前網路中競爭視窗大小，根據平均競爭視窗大小估算目前Wi-Fi網路的流量，分配合適的占空比。我們提出的共存方法可以保證Wi-Fi與LTE之間的公平性，並提高頻譜使用效率。最後，我們利用NS3這套模擬軟體去評估我們與其他共存方法的效能。

In order to satisfy increasing traffic demands, LTE-U offloads its traffic on unlicensed channels by aggregating its licensed and unlicensed carriers. However, coexistence of LTE-U and unlicensed users such as WiFi causes significant interference, which degrades the throughput of WiFi systems. In this paper, we propose fair coexistence scheme that allocates LTE-off period (i.e., time for WiFi transmissions) according to Wi-Fi traffic volume. We can estimate Wi-Fi traffic level based on average contention window size. Simulation results show that our coexistence scheme outperforms state-of-the-art techniques in terms of fairness.

1 Introduction 1
2 Background 3
2.1 Related Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2 Preliminary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3 Research goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3 Coexistence scheme 6
3.1 Main idea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2 Window Traffic Estimation . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2.1 Average Contention Window Size . . . . . . . . . . . . . . . . . 7
3.2.2 Contention window size based traffic estimation . . . . . . . . . 8
3.3 Duty cycle allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4 Performance evaluation 12
4.1 Scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.2 WiFi traffic vs. Contention Window . . . . . . . . . . . . . . . . . . . . 13
4.3 Impact of Upload WiFi traffic . . . . . . . . . . . . . . . . . . . . . . . 14
4.4 Throughput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5 Conclusion 18
Bibliography 19

[1] I. Ericsson, Ericsson Mobility Report, Novenber 2016, available at https://www.ericsson.com/assets/local/mobility-report/documents/2016/ericssonmobility-report-november-2016.pdf.
[2] A. M. Cavalcante, E. Almeida, R. D. Vieira, F. Chaves, R. C. Paiva, F. Abinader, S. Choudhury, E. Tuomaala, and K. Doppler, “Performance evaluation of lte and wi-fi coexistence in unlicensed bands,” Vehicular Technology Conference, pp. 1–6, 2013.
[3] Q. Technologies, Qualcomm research LTE in unlicensed spectrum: Harmonious coexistence with Wi-F, June 2014, available at https://www.qualcomm.com/media/documents/files/lte-unlicensed-coexistence-whitepaper.pdf.
[4] B. Jia and M. Tao, “A channel sensing based design for lte in unlicensed bands,”IEEE International Conference on Communication Workshop (ICCW), pp. 2332–2337, 2015.
[5] E. ETSI, “301 893 broadband radio access networks (bran); 5 ghz high performance rlan; harmonized en covering the essential requirements of article 3.2 of the r&tte directive,” 2014.
[6] E. Almeida, A. M. Cavalcante, R. C. Paiva, F. S. Chaves, F. M. Abinader, R. D.Vieira, S. Choudhury, E. Tuomaala, and K. Doppler, “Enabling lte/wifi coexistence by lte blank subframe allocation,” IEEE International Communications Conference (ICC), pp. 5083–5088, 2013.
[7] I. C. S. L. M. S. Committee et al., “Wireless lan medium access control (mac) and physical layer (phy) specifications,” IEEE Standard 802.11-1997, 1997.
[8] Z. Guan and T. Melodia, “Cu-lte: Spectrally-efficient and fair coexistence between lte and wi-fi in unlicensed bands,” IEEE International Conference on Computer Communications (INFOCOM), pp. 1–9, 2016.
[9] C. Cano and D. J. Leith, “Unlicensed lte/wifi coexistence: Is lbt inherently fairer than csat?” IEEE International Communications Conference (ICC), pp. 1–6, 2016.
[10] E. Chai, K. Sundaresan, M. A. Khojastepour, and S. Rangarajan, “Lte in unlicensed spectrum: are we there yet?” Proceedings of the 22nd Annual International Conference on Mobile Computing and Networking (MobiCom ’16), pp. 135–148, 2016.
[11] 3GPP, “Study on Licensed-Assisted Access to Unlicensed Spectrum,” 3rd Generation Partnership Project, (Release 12) TR 36.889v1.0.1, 2015.
[12] C. Cano and D. J. Leith, “Coexistence of wifi and lte in unlicensed bands: A proportional fair allocation scheme,” IEEE International Communications Conference (ICC), pp. 2288–2293, 2015.