# Performance Analysis of LAA and WiFi Coexistence in Unlicensed Spectrum Based on Markov Chain

01 Dec 2016-pp 1-6

TL;DR: This paper presents a new framework to evaluate the downlink performance of coexisting LAA and WiFi networks, and shows that throughput of a WiFi network can be enhanced by adding or replacing WiFi access points with LAA E-UTRAN Node Bs, at the expense of different levels of WiFi performance degradation.

Abstract: License-assisted access (LAA) is a candidate feature in 3GPP Rel-13 to meet the explosive growth of traffic demand. The main idea of LAA is to deploy LTE in the unlicensed band (mainly the 5GHz band), which is abundant with available spectrum. However, the major concern is the coexistence between WiFi and LAA in the same band. This paper presents a new framework to evaluate the downlink performance of coexisting LAA and WiFi networks. By using Markov chain, analytical models are established based on WiFi distributed coordination function (DCF) and two listen-before- talk (LBT) schemes. These two LBT schemes are Cat 3 and Cat 4 LBT, which mainly differ in medium access schemes in terms of backoff procedure. Unlike most existing works, which focus on the impact on WiFi performance posed by LAA, the performance of LAA is also evaluated. Our analysis shows that throughput of a WiFi network can be enhanced by adding or replacing WiFi access points (APs) with LAA E-UTRAN Node Bs (eNBs), at the expense of different levels of WiFi performance degradation. A trade-off between WiFi protection and LAA-WiFi system performance enhancement is observed. WiFi throughput and delay are less affected by Cat 4 LBT scheme, while Cat 3 LBT scheme provides higher LAA-WiFi system throughput. The choice of LBT schemes relies on the network planning priority, WiFi performance protection and LAA system performance requirements.

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TL;DR: This paper evaluates the relevant PHY and MAC techniques for their ability to improve the reliability and reduce the latency and identifies that enabling long-term evolution to coexist in the unlicensed spectrum is also a potential enabler of URLLC in theUnlicensed band.

Abstract: Future 5th generation networks are expected to enable three key services—enhanced mobile broadband, massive machine type communications and ultra-reliable and low latency communications (URLLC). As per the 3rd generation partnership project URLLC requirements, it is expected that the reliability of one transmission of a 32 byte packet will be at least 99.999% and the latency will be at most 1 ms. This unprecedented level of reliability and latency will yield various new applications, such as smart grids, industrial automation and intelligent transport systems. In this survey we present potential future URLLC applications, and summarize the corresponding reliability and latency requirements. We provide a comprehensive discussion on physical (PHY) and medium access control (MAC) layer techniques that enable URLLC, addressing both licensed and unlicensed bands. This paper evaluates the relevant PHY and MAC techniques for their ability to improve the reliability and reduce the latency. We identify that enabling long-term evolution to coexist in the unlicensed spectrum is also a potential enabler of URLLC in the unlicensed band, and provide numerical evaluations. Lastly, this paper discusses the potential future research directions and challenges in achieving the URLLC requirements.

90 citations

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TL;DR: In this paper, the authors developed a new framework for estimating the throughput of Wi-Fi and LTE-LAA in coexistence scenarios via suitable modifications to the celebrated Bianchi model.

Abstract: With both small-cell LTE and Wi-Fi networks available as alternatives for deployment in unlicensed bands (notably 5 GHz), the investigation into their coexistence is a topic of active interest, primarily driven by industry groups. 3GPP has recently standardized LTE licensed assisted access (LTE-LAA) that seeks to make LTE more co-existence friendly with Wi-Fi by incorporating similar sensing and back-off features. Nonetheless, the results presented by industry groups offer little consensus on important issues like respective network parameter settings that promote “fair access” as required by 3GPP. Answers to such key system deployment aspects, in turn, require credible analytical models, on which there has been a little progress to date. Accordingly, in one of the first works of its kind, we develop a new framework for estimating the throughput of Wi-Fi and LTE-LAA in coexistence scenarios via suitable modifications to the celebrated Bianchi model. The impact of various network parameters such as energy detection threshold on Wi-Fi and LTE-LAA coexistence is explored as a byproduct and corroborated via a National Instrument experimental test bed that validates the results for LTE-LAA access priority classes 1 and 3.

56 citations

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TL;DR: In one of the first works of its kind, a new framework for estimating the throughput of Wi-Fi and LTE-LAA in coexistence scenarios via suitable modifications to the celebrated Bianchi model is developed.

Abstract: With both small-cell LTE and Wi-Fi networks available as alternatives for deployment in unlicensed bands (notably 5 GHz), the investigation into their coexistence is a topic of active interest, primarily driven by industry groups. 3GPP has recently standardized LTE Licensed Assisted Access (LTE-LAA) that seeks to make LTE more co-existence friendly with Wi-Fi by incorporating similar sensing and back-off features. Nonetheless, the results presented by industry groups offer little consensus on important issues like respective network parameter settings that promote "fair access" as required by 3GPP. Answers to such key system deployment aspects, in turn, require credible analytical models, on which there has been little progress to date. Accordingly, in one of the first work of its kind, we develop a new framework for estimating the throughput of Wi-Fi and LTE-LAA in coexistence scenarios via suitable modifications to the celebrated Bianchi \cite{Bianchi} model. The impact of various network parameters such as energy detection (ED) threshold on Wi-Fi and LTE-LAA coexistence is explored as a byproduct and corroborated via a National Instrument (NI) experimental testbed that validates the results for LTE-LAA access priority class 1 and 3.

45 citations

### Cites background from "Performance Analysis of LAA and WiF..."

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TL;DR: This paper presents an overview of the work appeared in the literature analyzing the impact of LTE on the performance of Wi-Fi and proposing solutions to mitigate such an impact and describes the main solutions that are currently being developed by standardization bodies and telecom industry.

Abstract: To overcome the lack of spectrum resources, the proposal of extending LTE (Long Term Evolution) to the readily available unlicensed spectrum is receiving much attention. However, gaining capacity in a band where Wi-Fi is widely used and guaranteeing fairness between systems is not an easy to address issue. Analyzing the impact of operating LTE in the unlicensed band on the performance of Wi-Fi and devising solutions to minimize such an impact have been the goals of a considerable amount of work carried out by the research community, standardization bodies and telecom operators. In this paper, we first present a basic overview of Wi-Fi and LTE, which serves the purpose of illustrating why the fair coexistence of the two technologies in the unlicensed band is an issue. Basically, since LTE has been designed to operate in licensed bands, the centralized scheduling performed by LTE eNodeBs saturates all the channel resources, while Wi-Fi stations refrain from transmitting if the channel is sensed busy. Then, we illustrate the main approaches proposed to ensure a fair coexistence between Wi-Fi and LTE in the unlicensed band, namely Listen Before Talk (LBT) and Almost Blank Subframe (ABS), along with some other minor techniques. We describe the main solutions that are currently being developed by standardization bodies and telecom industry: LTE–U, Licensed Assisted Access (LAA) and MuLTEfire. Finally, we present an overview of the work appeared in the literature analyzing the impact of LTE on the performance of Wi-Fi and proposing solutions to mitigate such an impact.

42 citations

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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

34 citations

##### References

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TL;DR: In this paper, a simple but nevertheless extremely accurate, analytical model to compute the 802.11 DCF throughput, in the assumption of finite number of terminals and ideal channel conditions, is presented.

Abstract: The IEEE has standardized the 802.11 protocol for wireless local area networks. The primary medium access control (MAC) technique of 802.11 is called the distributed coordination function (DCF). The DCF is a carrier sense multiple access with collision avoidance (CSMA/CA) scheme with binary slotted exponential backoff. This paper provides a simple, but nevertheless extremely accurate, analytical model to compute the 802.11 DCF throughput, in the assumption of finite number of terminals and ideal channel conditions. The proposed analysis applies to both the packet transmission schemes employed by DCF, namely, the basic access and the RTS/CTS access mechanisms. In addition, it also applies to a combination of the two schemes, in which packets longer than a given threshold are transmitted according to the RTS/CTS mechanism. By means of the proposed model, we provide an extensive throughput performance evaluation of both access mechanisms of the 802.11 protocol.

7,899 citations

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01 Jan 2008

TL;DR: In this paper, the authors present an axiomatic approach to a theory of probability, based on the axiomatization of probability models, for the analysis and design of wireless networks.

Abstract: 1. Probability Models in Electrical and Computer Engineering. Mathematical models as tools in analysis and design. Deterministic models. Probability models. Statistical regularity. Properties of relative frequency. The axiomatic approach to a theory of probability. Building a probability model. A detailed example: a packet voice transmission system. Other examples. Communication over unreliable channels. Processing of random signals. Resource sharing systems. Reliability of systems. Overview of book. Summary. Problems. 2. Basic Concepts of Probability Theory. Specifying random experiments. The sample space. Events. Set operations. The axioms of probability. Discrete sample spaces. Continuous sample spaces. Computing probabilities using counting methods. Sampling with replacement and with ordering. Sampling without replacement and with ordering. Permutations of n distinct objects. Sampling without replacement and without ordering. Sampling with replacement and without ordering. Conditional probability. Bayes' Rule. Independence of events. Sequential experiments. Sequences of independent experiments. The binomial probability law. The multinomial probability law. The geometric probability law. Sequences of dependent experiments. A computer method for synthesizing randomness: random number generators. Summary. Problems. 3. Random Variables. The notion of a random variable. The cumulative distribution function. The three types of random variables. The probability density function. Conditional cdf's and pdf's. Some important random variables. Discrete random variables. Continuous random variables. Functions of a random variable. The expected value of random variables. The expected value of X. The expected value of Y = g(X). Variance of X. The Markov and Chebyshev inequalities. Testing the fit of a distribution to data. Transform methods. The characteristic function. The probability generating function. The laplace transform of the pdf. Basic reliability calculations. The failure rate function. Reliability of systems. Computer methods for generating random variables. The transformation method. The rejection method. Generation of functions of a random variable. Generating mixtures of random variables. Entropy. The entropy of a random variable. Entropy as a measure of information. The method of a maximum entropy. Summary. Problems. 4. Multiple Random Variables. Vector random variables. Events and probabilities. Independence. Pairs of random variables. Pairs of discrete random variables. The joint cdf of X and Y. The joint pdf of two jointly continuous random variables. Random variables that differ in type. Independence of two random variables. Conditional probability and conditional expectation. Conditional probability. Conditional expectation. Multiple random variables. Joint distributions. Independence. Functions of several random variables. One function of several random variables. Transformation of random vectors. pdf of linear transformations. pdf of general transformations. Expected value of functions of random variables. The correlation and covariance of two random variables. Joint characteristic function. Jointly Gaussian random variables. n jointly Gaussian random variables. Linear transformation of Gaussian random variables. Joint characteristic function of Gaussian random variables. Mean square estimation. Linear prediction. Generating correlated vector random variables. Generating vectors of random variables with specified covariances. Generating vectors of jointly Gaussian random variables. Summary. Problems. 5. Sums of Random Variables and Long-Term Averages. Sums of random variables. Mean and variance of sums of random variables. pdf of sums of independent random variables. Sum of a random number of random variables. The sample mean and the laws of large numbers. The central limit theorem. Gaussian approximation for binomial probabilities. Proof of the central limit theorem. Confidence intervals. Case 1: Xj's Gaussian unknown mean and known variance. Case 2: Xj's Gaussian mean and variance unknown. Case 3: Xj's Non-Gaussian mean and variance unknown. Convergence of sequences of random variables. Long-term arrival rates and associated averages. Long-term time averages. A computer method for evaluating the distribution of a random variable using the discrete Fourier transform. Discrete random variables. Continuous random variables. Summary. Problems. Appendix: subroutine FFT(A,M,N). 6. Random Processes. Definition of a random process. Specifying of a random process. Joint distributions of time samples. The mean, autocorrelation, and autocovariance functions. Gaussian random processes. Multiple random processes. Examples of discrete-time random processes. iid random processes. Sum processes the binomial counting and random walk processes. Examples of continuous-time random processes. Poisson process. Random telegraph signal and other processes derived from the Poisson Process. Wiener process and Brownian motion. Stationary random processes. Wide-sense stationary random processes. Wide-sense stationary Gaussian random processes. Cylostationary random processes. Continuity, derivative, and integrals of random processes. Mean square continuity. Mean square derivatives. Mean square integrals. Response of a linear system to random input. Time averages of random processes and ergodic theorems. Fourier series and Karhunen-Loeve expansion. Karhunen-Loeve expansion. Summary. Problems. 7. Analysis and Processing of Random Signals. Power spectral density. Continuous-time random processes. Discrete-time random processes. Power spectral density as a time average. Response of linear systems to random signals. Continuous-time systems. Discrete-time systems. Amplitude modulation by random signals. Optimum linear systems. The orthogonality condition. Prediction. Estimation using the entire realization of the observed process. Estimation using causal filters. The Kalman filter. Estimating the power spectral density. Variance of periodogram estimate. Smoothing of periodogram estimate. Summary. Problems. 8. Markov Chains. Markov processes. Discrete-time Markov chains. The n-step transition probabilities. The state probabilities. Steady state probabilities. Continuous-time Markov chains. State occupancy times. Transition rates and time-dependent state probabilities. Steady state probabilities and global balance equations. Classes of states, recurrence properties, and limiting probabilities. Classes of states. Recurrence properties. Limiting probabilities. Limiting probabilities for continuous-time Markov chains. Time-reversed Markov chains. Time-reversible Markov chains. Time-reversible continuous-time Markov chains. Summary. Problems. 9. Introduction to Queueing Theory. The elements of a queueing system. Little's formula. The M/M/I queue. Distribution of number in the system. Delay distribution in M/M/I system and arriving customer's distribution. The M/M/I system with finite capacity. Multi-server systems: M/M/c, M/M/c/c, and M/M/infinity. Distribution of number in the M/M/c system. Waiting time distribution for M/M/c. The M/M/c/c queueing system. The M/M/infinity queueing system. Finite-source queueing systems. Arriving customer's distribution. M/G/I queueing systems. The residual service time. Mean delay in M/G/I systems. Mean delay in M/G/I systems with priority service discipline. M/G/I analysis using embedded Markov chains. The embedded Markov chains. The number of customers in an M/G/I system. Delay and waiting time distribution in an M/G/I system. Burke's theorem: Departures from M/M/c systems Proof of Burke's theorem using time reversibility. Networks of queues: Jackson's theorem. Open networks of queues. Proof of Jackson's theorem. Closed networks of queues. Mean value analysis. Proof of the arrival theorem. Summary. Problems. Appendix A. Mathematical Tables. Appendix B. Tables of Fourier Transformation. Appendix C. Computer Programs for Generating Random Variables. Answers to Selected Problems. Index.

534 citations

### "Performance Analysis of LAA and WiF..." refers methods in this paper

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Nokia

^{1}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.

310 citations

### "Performance Analysis of LAA and WiF..." refers background in this paper

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TL;DR: A throughput analysis of the IEEE 802.11 protocol at the data link layer in non-saturated traffic conditions taking into account the impact of both transmission channel and capture effects in Rayleigh fading environment is provided.

Abstract: In this paper, we provide a saturation throughput analysis of the IEEE 802.11 protocol at the data link layer by including the impact of both transmission channel and capture effects in Rayleigh fading environment. Impacts of both non-ideal channel and capture effects, specially in an environment of high interference, become important in terms of the actual observed throughput. As far as the 4-way handshaking mechanism is concerned, we extend the multi-dimensional Markovian state transition model characterizing the behavior at the MAC layer by including transmission states that account for packet transmission failures due to errors caused by propagation through the channel. This way, any channel model characterizing the physical transmission medium can be accommodated, including AWGN and fading channels. We also extend the Markov model in order to consider the behavior of the contention window when employing the basic 2-way handshaking mechanism. Under the usual assumptions regarding the traffic generated per node and independence of packet collisions, we solve for the stationary probabilities of the Markov chain and develop expressions for the saturation throughput as a function of the number of terminals, packet sizes, raw channel error rates, capture probability, and other key system parameters. The theoretical derivations are then compared to simulation results confirming the effectiveness of the proposed models.

287 citations

### "Performance Analysis of LAA and WiF..." refers background in this paper

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Nokia

^{1}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.

256 citations

### "Performance Analysis of LAA and WiF..." refers background in this paper

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