Performance Evaluation of LTE and Wi-Fi Coexistence in Unlicensed Bands
02 Jun 2013-pp 1-6
TL;DR: A simulator-based system- level analysis in order to assess the network performance in an office scenario shows that LTE system performance is slightly affected by coexistence whereas Wi-Fi is significantly impacted by LTE transmissions.
Abstract: The deployment of modern mobile systems has faced severe challenges due to the current spectrum scarcity. The situation has been further worsened by the development of different wireless technologies and standards that can be used in the same frequency band. Furthermore, the usage of smaller cells (e.g. pico, femto and wireless LAN), coexistence among heterogeneous networks (including amongst different wireless technologies such as LTE and Wi-Fi deployed in the same frequency band) has been a big field of research in the academy and industry. In this paper, we provide a performance evaluation of coexistence between LTE and Wi-Fi systems and show some of the challenges faced by the different technologies. We focus on a simulator-based system- level analysis in order to assess the network performance in an office scenario. Simulation results show that LTE system performance is slightly affected by coexistence whereas Wi-Fi is significantly impacted by LTE transmissions. In coexistence, the Wi-Fi channel is most often blocked by LTE interference, making the Wi-Fi nodes to stay on the LISTEN mode more than 96% of the time. This reflects directly on the Wi-Fi user throughput, that decreases from 70% to ≈100% depending on the scenario. Finally, some of the main issues that limit the LTE/Wi-Fi coexistence and some pointers on the mutual interference management of both the systems are provided.
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TL;DR: The paper presents a novel analytical model using Markov chain to accurately model the LAA listen-before-talk scheme, as specified in the final technical specification 36.213 of 3GPP release 13 and 14.
Abstract: Long term evolution (LTE) technology leveraging the unlicensed band is anticipated to provide a solution for the challenges stemming from the rapid growth of mobile wireless services, the scarcity of available licensed spectrum, and the expected significant increase in mobile data traffic Ensuring fair operation in terms of spectrum sharing with current unlicensed spectrum incumbents is a key concern relative to the success and viability of Unlicensed LTE (U-LTE) This paper addresses the problem of modeling and evaluating the coexistence of LTE license-assisted-access in the unlicensed band The paper presents a novel analytical model using Markov chain to accurately model the LAA listen-before-talk scheme, as specified in the final technical specification 36213 of 3GPP release 13 and 14 Furthermore, model validation is demonstrated through numerical and simulation results comparison Model performance evaluation is examined and contrasted with IEEE 80211 distributed coordination function Finally, a comprehensive coexistence performance analysis is conducted for both homogeneous and heterogeneous network scenarios and coexistence results are presented and discussed herein
41 citations
Cites background from "Performance Evaluation of LTE and W..."
...BACKGROUND AND RELATED WORK With the initial consideration of permitting licensed LTE to supplement its downlink with unlicensed spectrum, various experimentations indicated LTE would unfairly occupy the unlicensed-band and induce adverse effects on current unlicensed-band occupants [9]–[11]....
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08 Jun 2015
TL;DR: A detailed system-level study on the downlink throughput performance of legacy indoor IEEE 802.11n and LTE-U deployments coexisting in the 5 GHz band shows that in general both Wi-Fi and LTE/U benefit from the large number of available channels and isolation provided by building shielding at 5 GHz.
Abstract: Due to the high expected increase in mobile data traffic and the scarcity of licensed spectrum for cellular networks, 3GPP has started preliminary work for standardizing LTE operation in the 5 GHz unlicensed band (LTE-U). However, LTE-U would interfere with other legacy technologies operating in the unlicensed band, the most important being contention-based Wi-Fi, which would be blocked by conventional LTE, which is designed for dedicated licensed spectrum. Consequently, some coexistence-enabling mechanisms have been proposed for LTE-U, but their evaluation is still at an early stage. In this paper we present a detailed system-level study on the downlink throughput performance of legacy indoor IEEE 802.11n and LTE-U deployments coexisting in the 5 GHz band. We consider several LTE-U coexistence mechanisms (i.e. listen-before-talk and interference-aware channel selection) in indoor LTE-U femtocell and outdoor LTE-U picocell scenarios with a realistic range of network densities and real outdoor picocell locations. We also study coexistence of LTE-U networks deployed by multiple operators, and evaluate the impact of different LTE-U transmit power levels. Our results show that in general both Wi-Fi and LTE-U benefit from the large number of available channels and isolation provided by building shielding at 5 GHz. Additionally, in typical indoor coexistence scenarios, interference-aware channel selection is more efficient for both Wi-Fi and LTE-U than listen-before-talk mechanisms. For outdoor LTE-U picocells and indoor Wi-Fi deployments, the two networks are isolated from each other, but listen-before-talk can increase LTE-U user throughput when multiple outdoor LTE-U networks deployed by different cellular operators coexist.
40 citations
Cites background from "Performance Evaluation of LTE and W..."
...Consistent results are presented in [4], where a single-building indoor scenario in the 900 MHz band is analyzed based on simulations, but no mechanism to enable coexistence is considered....
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TL;DR: This paper proposes a matching theory framework to tackle the unlicensed resource allocation problem under both LTE and Wi-Fi transmission requirements and proposes two semi-distributed solutions, namely, the Gale–Shapley and the random path to stability algorithms.
Abstract: LTE-Unlicensed has recently captured intense attention from both academic and industrial fields. By integrating the unlicensed spectrum with the licensed spectrum, using carrier aggregation, LTE-Unlicensed users can experience enhanced transmission while maintaining the seamless mobility management and predictable performance. However, due to different transmission regulations, the coordination between LTE and Wi-Fi systems requires careful design. It is especially important to understand how to guarantee the transmission quality for LTE users and reduce Wi-Fi users’ performance degradation, under the impact of the co-channel interference. In other words, how can we solve the unlicensed resource allocation problem under both LTE and Wi-Fi transmission requirements? In this paper, we propose a matching theory framework to tackle this problem. Specifically, the coexistence between LTE and Wi-Fi systems, i.e., the interaction between LTE and Wi-Fi users, is modeled as a stable marriage game. The coexistence constraints are interpreted as the preference lists. Two semi-distributed solutions, namely, the Gale–Shapley and the random path to stability algorithms are proposed. In addition, to address the external effect in matching, the inter-channel cooperation algorithm is introduced. Last but not least, the resource allocation problem is studied with network dynamics and the proposed mechanisms are evaluated under two typical user mobility models.
39 citations
Cites background from "Performance Evaluation of LTE and W..."
...are done in [10], which again observes about 70% to 100%...
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TL;DR: This paper presents the unlicensed spectrum intercell interference co-ordination (usICIC) mechanism as a time-domain multiplexing technique for interference mitigation for the sharing of an unlicensed channel by multioperator LTE-U small cells and demonstrates that the proposed usICIC mechanism will result in 40% or more improvement in overall LTE- U system performance.
Abstract: The deployment of long term evolution (LTE) in the unlicensed spectrum (LTE-U) has been gaining significant industry momentum in recent months. The US 5-GHz Unlicensed National Information Infrastructure (UNII) bands that are currently under consideration for LTE deployment in the unlicensed spectrum contain only a limited number of 20 MHZ channels. Thus, in a dense multi-operator deployment scenario, one or more LTE-U small cells have to coexist and share the same 20 MHz unlicensed channel with each other and with the incumbent Wi-Fi. In this paper, we present the scenario and demonstrate that in the absence of an explicit interference mitigation mechanism, there will be a significant degradation in the overall LTE-U system performance for LTE-U cochannel coexistence in countries that do not mandate listen-before-talk (LBT) requirements. We then present the unlicensed spectrum intercell interference co-ordination (usICIC) mechanism as a time-domain multiplexing technique for interference mitigation for the sharing of an unlicensed channel by multioperator LTE-U small cells. Through extensive simulation results, we also demonstrate that our proposed usICIC mechanism will result in 40% or more improvement in overall LTE-U system performance.
39 citations
Cites background from "Performance Evaluation of LTE and W..."
...which are considered far inferior to those offered by licensed cellular wireless technologies such as LTE [14], [17] that offers higher spectral efficiency [10]....
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...In [10], the performance of LTE and Wi-Fi was compared in the unlicensed spectrum to demonstrate that in general, LTE outperforms Wi-Fi in similar scenarios....
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TL;DR: Numerical results show that the proposed dynamic sharing scheme outperforms static sharing, which in turn achieves much higher revenue than uncoordinated full-spectrum sharing.
Abstract: Facing the challenge of meeting ever-increasing demand for wireless data, the industry is striving to exploit large swaths of unlicensed spectrum, which supports open access. Major standards bodies are currently considering a proposal to retool and deploy long term evolution (LTE) technologies in unlicensed bands. This paper studies the fundamental question of how the unlicensed spectrum can be shared by strategic operators to mitigate suffering from the tragedy of the commons. A class of general utility functions is considered. The spectrum sharing problem is formulated as a repeated game over a sequence of time slots. It is first shown that a simple static sharing scheme allows a given set of operators to reach a subgame perfect Nash equilibrium for mutually beneficial sharing. The question of how many operators will choose to enter the market is also addressed by studying an entry game. A sharing scheme, which allows dynamic spectrum borrowing and lending between operators, is then proposed to address time-varying traffic and proved to achieve perfect Bayesian equilibrium. Numerical results show that the proposed dynamic sharing scheme outperforms static sharing, which in turn achieves much higher revenue than uncoordinated full-spectrum sharing. Implications of the results for the standardization and deployment of LTE in unlicensed bands (LTE-U) are also discussed.
38 citations
Cites background from "Performance Evaluation of LTE and W..."
...Interference between these two systems needs to be managed, otherwise WiFi systems will be severely impacted due to WiFi protocol's " politeness " [5], [6]....
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References
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TL;DR: An overview of the techniques being considered for LTE Release 10 (aka LTEAdvanced) is discussed, which includes bandwidth extension via carrier aggregation to support deployment bandwidths up to 100 MHz, downlink spatial multiplexing including single-cell multi-user multiple-input multiple-output transmission and coordinated multi point transmission, and heterogeneous networks with emphasis on Type 1 and Type 2 relays.
Abstract: LTE Release 8 is one of the primary broadband technologies based on OFDM, which is currently being commercialized. LTE Release 8, which is mainly deployed in a macro/microcell layout, provides improved system capacity and coverage, high peak data rates, low latency, reduced operating costs, multi-antenna support, flexible bandwidth operation and seamless integration with existing systems. LTE-Advanced (also known as LTE Release 10) significantly enhances the existing LTE Release 8 and supports much higher peak rates, higher throughput and coverage, and lower latencies, resulting in a better user experience. Additionally, LTE Release 10 will support heterogeneous deployments where low-power nodes comprising picocells, femtocells, relays, remote radio heads, and so on are placed in a macrocell layout. The LTE-Advanced features enable one to meet or exceed IMT-Advanced requirements. It may also be noted that LTE Release 9 provides some minor enhancement to LTE Release 8 with respect to the air interface, and includes features like dual-layer beamforming and time-difference- of-arrival-based location techniques. In this article an overview of the techniques being considered for LTE Release 10 (aka LTEAdvanced) is discussed. This includes bandwidth extension via carrier aggregation to support deployment bandwidths up to 100 MHz, downlink spatial multiplexing including single-cell multi-user multiple-input multiple-output transmission and coordinated multi point transmission, uplink spatial multiplexing including extension to four-layer MIMO, and heterogeneous networks with emphasis on Type 1 and Type 2 relays. Finally, the performance of LTEAdvanced using IMT-A scenarios is presented and compared against IMT-A targets for full buffer and bursty traffic model.
1,044 citations
"Performance Evaluation of LTE and W..." refers background in this paper
...4GHz band has already been established [7], and the recent inclusion of features on LTE standard [12] are promoting its usage on pico and femto cells, it is possible that in the near future coexistence between LTE (-ADV) and Wi-Fi will become important....
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TL;DR: Concepts underlying the "property" and "commons" debate are presented, options for spectrum reform are clarified, and the trade-offs of spectrum sharing are described.
Abstract: Many complain about severe spectrum shortage. The shortage comes from outdated spectrum policies that allows for little sharing. Regulators have granted licenses that offer exclusive access to the spectrum. When these licensees are not transmitting, the spectrum sits idle. A new technology regarding spectrum shortage enables more spectrum sharing that unleashes innovative products and services, provided that we adopt the appropriate spectrum policies. Two camps are pushing for extreme reform, one for "property rights" and the other for "spectrum commons". This article presents concepts underlying the "property" and "commons" debate, clarifies options for spectrum reform, and describes the trade-offs of spectrum sharing
592 citations
"Performance Evaluation of LTE and W..." refers background in this paper
...One of the most promising techniques for dealing with the lack of available spectrum is the concept of spectrum sharing [1] ....
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22 Apr 2007
TL;DR: An adjusted Shannon capacity formula is introduced, where it is shown that the bandwidth efficiency can be calculated based on system parameters, while the SNR efficiency is extracted from detailed link level studies.
Abstract: In this paper we propose a modification to Shannon capacity bound in order to facilitate accurate benchmarking of UTRAN long term evolution (LTE). The method is generally applicable to wireless communication systems, while we have used LTE air-interface technology as a case study. We introduce an adjusted Shannon capacity formula, where we take into account the system bandwidth efficiency and the SNR efficiency of LTE. Separating these issues, allows for simplified parameter extraction. We show that the bandwidth efficiency can be calculated based on system parameters, while the SNR efficiency is extracted from detailed link level studies including advanced features of MIMO and frequency domain packet scheduling (FDPS). We then use the adjusted Shannon capacity formula combined with G-factor distributions for macro and micro cell scenarios to predict LTE cell spectral efficiency (SE). Such LTE SE predictions are compared to LTE cell SE results generated by system level simulations. The results show an excellent match of less that 5-10% deviation.
580 citations
"Performance Evaluation of LTE and W..." refers methods in this paper
...For physical layer (PHY) abstraction, Shannon-fitting [14] is employed to predict the PHY performance at the system-level....
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09 Jun 2013
TL;DR: This paper considers two of the most prominent wireless technologies available today, namely Long Term Evolution (LTE), and WiFi, and addresses some problems that arise from their coexistence in the same band, and proposes a simple coexistence scheme that reuses the concept of almost blank subframes in LTE.
Abstract: The recent development of regulatory policies that permit the use of TV bands spectrum on a secondary basis has motivated discussion about coexistence of primary (e.g. TV broadcasts) and secondary users (e.g. WiFi users in TV spectrum). However, much less attention has been given to coexistence of different secondary wireless technologies in the TV white spaces. Lack of coordination between secondary networks may create severe interference situations, resulting in less efficient usage of the spectrum. In this paper, we consider two of the most prominent wireless technologies available today, namely Long Term Evolution (LTE), and WiFi, and address some problems that arise from their coexistence in the same band. We perform exhaustive system simulations and observe that WiFi is hampered much more significantly than LTE in coexistence scenarios. A simple coexistence scheme that reuses the concept of almost blank subframes in LTE is proposed, and it is observed that it can improve the WiFi throughput per user up to 50 times in the studied scenarios.
324 citations
"Performance Evaluation of LTE and W..." refers background in this paper
...This kind of approach has started to be investigated in [16], where LTE/Wi-Fi coexistence is enabled by LTE blank subframe allocation....
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27 Aug 2007
TL;DR: A channel hopping design is prototype using PRISM NICs, and it is found that it can sustain throughput at levels of RF interference well above that needed to disrupt unmodified links, and at a reasonable cost in terms of switching overheads.
Abstract: We study the impact on 802.11 networks of RF interference from devices such as Zigbee and cordless phones that increasingly crowd the 2.4GHz ISM band, and from devices such as wireless camera jammers and non-compliant 802.11 devices that seek to disrupt 802.11 operation. Our experiments show that commodity 802.11 equipment is surprisingly vulnerable to certain patterns of weak or narrow-band interference. This enables us to disrupt a link with an interfering signal whose power is 1000 times weaker than the victim's 802.11 signals, or to shut down a multiple AP, multiple channel managed network at a location with a single radio interferer. We identify several factors that lead to these vulnerabilities, ranging from MAC layer driver implementation strategies to PHY layer radio frequency implementation strategies. Our results further show that these factors are not overcome by simply changing 802.11 operational parameters (such as CCA threshold, rate and packet size) with the exception of frequency shifts. This leads us to explore rapid channel hopping as a strategy to withstand RF interference. We prototype a channel hopping design using PRISM NICs, and find that it can sustain throughput at levels of RF interference well above that needed to disrupt unmodified links, and at a reasonable cost in terms of switching overheads.
300 citations
"Performance Evaluation of LTE and W..." refers background in this paper
...However, it is observed that the coexistence of heterogeneous systems in the same frequency bands causes a meaningful degradation on the system performance (e.g., Wi-Fi and Bluetooth [3], Wi-Fi and ZigBee [4], Wi-Fi and WiMAX [5])....
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..., Wi-Fi and Bluetooth [3], Wi-Fi and ZigBee [4], Wi-Fi and WiMAX [5])....
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