Survey on coexistence between wifi and lte

Survey on Coexistence between Wifi and LTE Sally Adil Abd Elrahman1, Dr. Mohamed Abaker Hussein2 1, 2

Telecommunication Engineering,Al Neelain University,Khartoum, Sudan

Abstract:As the demand for more spectrum increases, Mobile operators search for another cost efficient way to increase the capacity and to cope with this increase. Carrier aggregation is a solution presented by the 3rd generation partnership project (3GPP) Release-10 to provide bandwidth up to 100MHz and by extending to the use of unlicensed spectrum in order to increase the efficiency of the network by integrating both LTE and Wifi networks in small cells. In this paper we presented some comparative review of previous studies on LTE/Wifi aggregation and it’s shown that the coexistence between LTE and Wifi can lead to better and efficient network performance.

I. INTRODUCTION Nowadays with the high demand for higher bandwidth in LTE-based technologies and in order to address this problem; the third generation partnership project (3GPP) presented carrier aggregation technology in the unlicensed LTE system (LTE-U) in order to satisfy this high demanding. The LTEU system allows LTE network to make use of the unlicensed band. LTE on the unlicensed band is used in public indoor and outdoor scenarios where there’s a coverage from LTE system in a licensed band [1].

Coexistence between Wifi and LTE allows LTE to operate in the 2.4 GHZ – 5 GHZ bands in order to achieve high spectrum efficiency and to increase the capacity and throughput of the system. Carrier aggregation is a technique presented in LTE- advanced (LTE-A) to allow LTE system to conduct in the unlicensed bands. In carrier aggregation, multiple of component carriers (CC) up to five component carriers can be aggregated to provide maximum of 100 MHz bandwidth [2].

II. LITERATURE SURVEY Rasha et al [3] presented a system-level study on LTE-Wifi carrier aggregation assuming that LTE system borrows carrier components from Wifi spectrum to aggregate with those of LTE system.

They found that LTE and Wifi systems have similarities in terms of access scheme design and channel raster requirements.

Rapeepat Ratasuk et al [4] investigated the coexistence mechanism of LTE in licensed and licensedexempt bands as a part of pico cells and investigated the performance of the LTE system while sharing spectrum with the Wifi system. Their simulation results showed that LTE with LBT implemented can deliver high uplink throughput while maintaining the coexistence with Wifi system and that the performance of the network degrades as the number of users increases due to inter-cell interference and that the random configuration provide higher throughput than the cluster configuration.

Ran Zhang et al [5] presented an overview of the LTE system over the unlicensed spectrum to achieve higher data rates and discussed the LTE-U benefits compared with Wifi system. They conducted a simulation for five different cases and measured the average throughput in each case.

Their results showed that LTE-U can deliver higher throughput while well protecting the performance of Wifi system.

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International Journal of Recent Trends in Engineering & Research (IJRTER) Volume 02, Issue 08; August - 2016 [ISSN: 2455-1457]

Ahmed K. Sadek et al [6] Fan showed through analysis and simulation evaluation the coexistence between LTE and Wifi in the unlicensed band to achieve higher spectral efficiency and per user experience. They presented CSAT and LBT mechanisms for achieving the coexistence. Their results showed that deploying LTE in the unlicensed band can lead to better user experience and higher throughput when more nodes of LTE with CSAT is added.

Xavier Lagrange [7] proposed a coupling solution between LTE and Wifi where Wifi access points are considered as a part of eNodeB to enhance the offloading mechanism using Packet Data Convergence Protocol (PDCP). They found that this coupling solution between LTE and Wifi can lead to better cooperation and management between access points and efficient solution to offloading.

Jonathan Ling et al [8] presented three integration solutions for LTE-Wifi integration, loose, tight and hybrid. They found that those solutions provide efficiency and higher capacity and throughput when offloading from Wifi to LTE and vice versa.

Cristina Cano and Douglas J. Leith [9] proposed a fair allocation scheme for coexistence of LTE and Wifi in the ulicensed spectrum and presented some examples illustrating the results of throughput of Wifi stations and LTE-U UEs. Their results implied that the inefficiency of Wifi system due to random access does not impact the performance of LTE-U system.

Amitav Mukherjee et al [10] presented an overview of LAA LTE, the impact of unlicensed spectrum on the physical layer of LTE system and how LAA, LBT and DFS functions can affect the UL and DL procedures. Their results showed the fair coexistence between Wifi and LAA in both indoor and outdoor scenarios.

While Yingzhe Li [11] proposed a framework for the coexistence of Wifi and LTE systems; they evaluated the analysis under three scenarios. Their results showed that Wifi performance is degraded when LTE transmits and that LTE can improve the performance of Wifi when changing some of LTE features.

III. DISCUSSION In this section we conduct a comparative analysis on the previous papers to explain their strength and weak points.

[3][7][8][10] , conducted a study on the coexistence between Wifi and LTE. [3] presented a design on carrier aggregation where LTE borrows spectrum from Wifi to enhance the system performance.

Both [7] and [8] presented an offloading solution. [7] presented a tight coupling solution for offloading procedures to guarantee better coexistence while in [8] three integrating options were presented not only to achieve better offloading solutions but to also enhance capacity and coverage.

[10] presented an overview for DL physical layer for LTE with LAA to show the fair coexistence between Wifi and LAA. [4][5][6][9], analyzed the coexistence in terms of throughput. [4] analyzed the system performance in two placements, random and cluster, each with 10 users. They analyzed their results according to wifi factor which specifies the time in which wifi is transmitting and uplink performance with that factor, their results showed that LTE can coexist with wifi and provide high throughput. While [5] presented a simulation where 50 users were dropped randomly in each cluster, they used full buffer for traffic model. The throughput in simulation was analyzed for 5 cases scenarios stated as: case1: LTE/Wifi interworking, case2: Hetnet, case3: LTE-U, case4: LTE-U with duty cycle and case5: LTE-U with CSAT. In [9] they focused on the coexistence on the physical layer level and that the

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International Journal of Recent Trends in Engineering & Research (IJRTER) Volume 02, Issue 08; August - 2016 [ISSN: 2455-1457]

coexistence is achieved by assigning channel times to every entity in order to achieve successful transmissions and no interference or collisions. Their proposed approach is easy to implement while the fourth paper focused on release-10 in SDL mode with CSAT and frequency selection, with different number of Aps, they have advantage over the previous papers for testing the coexistence in both simulation and indoor lab test. While in [11] the coexistence is analyzed in terms of SINR, rate coverage and density of successful transmission DST in different coexistence scenarios. Both results of [4] and [11] papers showed that Wifi performance degrades. [4] showed that with the increasing number of users the performance of the network degrades due to inter cell interference while [11] showed that Wifi performance degrades when LTE is transmitting but they presented a solution to address this problem by modification of the LTE duty cycle, sensing threshold and the priority of channel access.

IV. CONCLUSION With the increasing demand on higher capacity and throughput, the need for higher spectrum increases. Coexistence between Wifi and LTE is considered to address the problem. From the papers reviewed and analyzed, it is shown that the coexistence between LTE and Wifi can be in a fair and friendly manner. Some papers presented a study on the coexistence between Wifi and LTE and presented solutions to offloading problems while in the other papers, their presented simulation results showed that LTE can deliver high throughput while maintaining the coexistence with Wifi network. Some results showed that LTE deliver high throughput when coexisting with Wifi but not higher than the throughput of only LTE network and some papers showed that the performance of Wifi degrades when LTE is transmitting.

REFERENCES Nokia,“LTE for Unlicensed Spectrum” , “networks.nokia.com/sites/default/files/.../nokia_lte_unlicensed_white_paper.pdf “,2014.

2. R. Zhang, Z. Zheng, M. Wang, X. Shen, and L. Xie, “Equivalent capacity in carrier aggregation-based LTE-A systems: A probabilistic analysis ” ,IEEE Trans. on Wireless Communications, 2014.

3. R. Alkhansa, H. Artail, D. M. Gutierrez-Estevez, “LTE-WiFi Carrier Aggregation for Future 5G Systems: A Feasibility Study and Research Challenges”, “www.Sciencedirect.com”, FNC, 2014.

4. Rapeepat Ratasuk, Mikko A. Uusitalo, Nitin Mangalvedhe, Antti Sorri, Sassan Iraji, Carl Wijting and Amitava Ghosh, “License-Exempt LTE Deployment in Heterogeneous Network”, International Symposium on Wireless Communication Systems (ISWCS), 2012.

5. Ran Zhang, Miao Wang, Lin X. Cai, Zhongming Zheng, Xuemin (Sherman) Shen and Liang-Liang Xie, “LTEUnlicensed: The Future of Spectrum Aggregation for Cellular Networks”, IEEE Wireless Communications 22(3):150-159, 2015.

6. A. K. Sadek, T. Kadous, K. Tang, H. Lee and M. Fan, “Extending LTE to Unlicensed Band – Merit and Coexistence”, IEEE International Conference on Communication Workshop (ICCW), 2015.

7. Xavier Lagrange, “Very Tight Coupling between LTE and Wi-Fi for Advanced Offloading Procedures”, Wireless Communications and Networking Conference Workshops (WCNCW) IEEE, 2014.

8. J. Ling, S. Kanugovi, S. Vasudevan and A. K. Pramod, “Enhanced capacity & coverage by Wi-Fi LTE Integration”, IEEE Communications Magazine, 2014.

9. Cristina Cano and Douglas J. Leith, “Coexistence of WiFi and LTE in Unlicensed Bands: A Proportional Fair Allocation Scheme”, IEEE International Conference on Communication Workshop (ICCW), 2015.

10. A. Mukherjee, J.Cheng, S.Falahati, L. Falconetti, A. Furuskär, B. Godana, Du Ho Kang, H. Koorapaty, D. Larsson, and Yu Yang, “System Architecture and Coexistence Evaluation of Licensed-Assisted Access LTE with IEEE 802.11”, IEEE International Conference on Communication Workshop (ICCW) , 2015.

11. Y. Li, F. Baccelli, J. G. Andrews, T. D. Novlan, Jianzhong and Ch. Zhang, “Modeling and Analyzing the Coexistence of Wi-Fi and LTE in Unlicensed Spectrum”, “www.arxiv.org/abs/1510.01392 “, 2015.

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