13,068 research outputs found
Advanced Technologies Enabling Unlicensed Spectrum Utilization in Cellular Networks
As the rapid progress and pleasant experience of Internet-based services, there is an increasing demand for high data rate in wireless communications systems. Unlicensed spectrum utilization in Long Term Evolution (LTE) networks is a promising technique to meet the massive traffic
demand. There are two effective methods to use unlicensed bands for delivering LTE traffic. One is offloading LTE traffic toWi-Fi. An alternative method is LTE-unlicensed (LTE-U), which aims to directly use LTE protocols and infrastructures over the unlicensed spectrum. It has also
been pointed out that addressing the above two methods simultaneously could further improve the system performance.
However, how to avoid severe performance degradation of the Wi-Fi network is a challenging issue of utilizing unlicensed spectrum in LTE networks. Specifically, first, the inter-system spectrum sharing, or, more specifically, the coexistence of LTE andWi-Fi in the same unlicensed
spectrum is the major challenge of implementing LTE-U. Second, to use the LTE and Wi-Fi integration approach, mobile operators have to manage two disparate networks in licensed and unlicensed spectrum. Third, optimization for joint data offloading to Wi-Fi and LTE-U in multi-
cell scenarios poses more challenges because inter-cell interference must be addressed.
This thesis focuses on solving problems related to these challenges. First, the effect of bursty traffic in an LTE and Wi-Fi aggregation (LWA)-enabled network has been investigated. To enhance resource efficiency, the Wi-Fi access point (AP) is designed to operate in both the native
mode and the LWA mode simultaneously. Specifically, the LWA-modeWi-Fi AP cooperates with the LTE base station (BS) to transmit bearers to the LWA user, which aggregates packets from both LTE and Wi-Fi. The native-mode Wi-Fi AP transmits Wi-Fi packets to those native Wi-Fi users that are not with LWA capability. This thesis proposes a priority-based Wi-Fi transmission scheme with congestion control and studied the throughput of the native Wi-Fi network, as well as the LWA user delay when the native Wi-Fi user is under heavy traffic conditions. The results
provide fundamental insights in the throughput and delay behavior of the considered network. Second, the above work has been extended to larger topologies. A stochastic geometry model has been used to model and analyze the performance of an MPTCP Proxy-based LWA network with intra-tier and cross-tier dependence. Under the considered network model and the activation conditions of LWA-mode Wi-Fi, this thesis has obtained three approximations for the density of active LWA-mode Wi-Fi APs through different approaches. Tractable analysis is provided for the downlink (DL) performance evaluation of large-scale LWA networks. The impact of different parameters on the network performance have been analyzed, validating the significant gain of using LWA in terms of boosted data rate and improved spectrum reuse. Third, this thesis also takes a significant step of analyzing joint multi-cell LTE-U and Wi-Fi network, while taking into account different LTE-U and Wi-Fi inter-working schemes. In particular, two technologies enabling data offloading from LTE to Wi-Fi are considered, including LWA and Wi-Fi offloading in the context of the power gain-based user offloading scheme. The LTE cells in this work are subject to load-coupling due to inter-cell interference. New system frameworks for maximizing the demand scaling factor for all users in both Wi-Fi and multi-cell LTE networks have been proposed. The potential of networks is explored in achieving optimal capacity with arbitrary topologies, accounting for both resource limits and inter-cell interference. Theoretical analyses have been proposed for the proposed optimization problems, resulting in algorithms that achieve global optimality. Numerical results show the algorithms’ effectiveness and benefits of joint use of data offloading and the direct use of LTE over the unlicensed band. All the derived results in this thesis have been validated by Monte Carlo simulations in Matlab, and the conclusions observed from the results can provide guidelines for the future unlicensed spectrum utilization in LTE networks
A Survey of Resource Allocation Techniques for Cellular Network’s Operation in the Unlicensed Band
With an ever increasing demand for data, better and efficient spectrum operation has become crucial in cellular networks. In this paper, we present a detailed survey of various resource allocation schemes that have been considered for the cellular network’s operation in the unlicensed spectrum. The key channel access mechanisms for cellular network’s operation in the unlicensed bands are discussed. The various channel selection techniques are explored and their operation explained. The prime issue of fairness between cellular and Wi-Fi networks is discussed, along with suitable resource allocation techniques that help in achieving this fairness. We analyze the coverage, capacity, and impact of coordination in LTE-U systems. Furthermore, we study and discuss the impact and discussed the impact of various traffic type, environments, latency, handover, and scenarios on LTE-U’s performance. The new upcoming 5G New Radio and MulteFire is briefly described along with some of the critical aspects of LTE-U which require further research. © 2020 by the authors. Licensee MDPI, Basel, Switzerland
Design of a High Capacity, Scalable, and Green Wireless Communication System Leveraging the Unlicensed Spectrum
The stunning demand for mobile wireless data that has been recently growing at an exponential rate requires a several fold increase in spectrum. The use of unlicensed spectrum is thus critically needed to aid the existing licensed spectrum to meet such a huge mobile wireless data traffic growth demand in a cost effective manner. The deployment of Long Term Evolution (LTE) in the unlicensed spectrum (LTE-U) has recently been gaining significant industry momentum. The lower transmit power regulation of the unlicensed spectrum makes LTE deployment in the unlicensed spectrum suitable only for a small cell. A small cell utilizing LTE-L (LTE in licensed spectrum), and LTE-U (LTE in unlicensed spectrum) will therefore significantly reduce the total cost of ownership (TCO) of a small cell, while providing the additional mobile wireless data offload capacity from Macro Cell to small cell in LTE Heterogeneous Networks (HetNet), to meet such an increase in wireless data demand. The U.S. 5 GHz Unlicensed National Information Infrastructure (U-NII) 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 co-exist and share the same 20 MHz unlicensed channel with each other and with the incumbent Wi-Fi.
This dissertation presents a proactive small cell interference mitigation strategy for improving the spectral efficiency of LTE networks in the unlicensed spectrum. It describes the scenario and demonstrate via simulation results, 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 co-channel co-existence in countries such as U.S. that do not mandate Listen-Before-Talk (LBT) regulations. An unlicensed spectrum Inter Cell Interference Coordination (usICIC) mechanism is then presented as a time-domain multiplexing technique for interference mitigation for the sharing of an unlicensed channel by multi-operator LTE-U small cells. Through extensive simulation results, it is demonstrated that the proposed usICIC mechanism will result in 40% or more improvement in the overall LTE-U system performance (throughput) leading to increased wireless communication system capacity.
The ever increasing demand for mobile wireless data is also resulting in a dramatic expansion of wireless network infrastructure by all service providers resulting in significant escalation in energy consumption by the wireless networks. This not only has an impact on the recurring operational expanse (OPEX) for the service providers, but importantly the resulting increase in greenhouse gas emission is not good for the environment. Energy efficiency has thus become one of the critical tenets in the design and deployment of Green wireless communication systems. Consequently the market trend for next-generation communication systems has been towards miniaturization to meet this stunning ever increasing demand for mobile wireless data, leading towards the need for scalable distributed and parallel processing system architecture that is energy efficient, and high capacity. Reducing cost and size while increasing capacity, ensuring scalability, and achieving energy efficiency requires several design paradigm shifts.
This dissertation presents the design for a next generation wireless communication system that employs new energy efficient distributed and parallel processing system architecture to achieve these goals while leveraging the unlicensed spectrum to significantly increase (by a factor of two) the capacity of the wireless communication system. This design not only significantly reduces the upfront CAPEX, but also the recurring OPEX for the service providers to maintain their next generation wireless communication networks
Wi-Fi Coexistence with Duty Cycled LTE-U
Coexistence of Wi-Fi and LTE-Unlicensed (LTE-U) technologies has drawn
significant concern in industry. In this paper, we investigate the Wi-Fi
performance in the presence of duty cycle based LTE-U transmission on the same
channel. More specifically, one LTE-U cell and one Wi-Fi basic service set
(BSS) coexist by allowing LTE-U devices transmit their signals only in
predetermined duty cycles. Wi-Fi stations, on the other hand, simply contend
the shared channel using the distributed coordination function (DCF) protocol
without cooperation with the LTE-U system or prior knowledge about the duty
cycle period or duty cycle of LTE-U transmission. We define the fairness of the
above scheme as the difference between Wi-Fi performance loss ratio
(considering a defined reference performance) and the LTE-U duty cycle (or
function of LTE-U duty cycle). Depending on the interference to noise ratio
(INR) being above or below -62dbm, we classify the LTE-U interference as strong
or weak and establish mathematical models accordingly. The average throughput
and average service time of Wi-Fi are both formulated as functions of Wi-Fi and
LTE-U system parameters using probability theory. Lastly, we use the Monte
Carlo analysis to demonstrate the fairness of Wi-Fi and LTE-U air time sharing
Survey of Spectrum Sharing for Inter-Technology Coexistence
Increasing capacity demands in emerging wireless technologies are expected to
be met by network densification and spectrum bands open to multiple
technologies. These will, in turn, increase the level of interference and also
result in more complex inter-technology interactions, which will need to be
managed through spectrum sharing mechanisms. Consequently, novel spectrum
sharing mechanisms should be designed to allow spectrum access for multiple
technologies, while efficiently utilizing the spectrum resources overall.
Importantly, it is not trivial to design such efficient mechanisms, not only
due to technical aspects, but also due to regulatory and business model
constraints. In this survey we address spectrum sharing mechanisms for wireless
inter-technology coexistence by means of a technology circle that incorporates
in a unified, system-level view the technical and non-technical aspects. We
thus systematically explore the spectrum sharing design space consisting of
parameters at different layers. Using this framework, we present a literature
review on inter-technology coexistence with a focus on wireless technologies
with equal spectrum access rights, i.e. (i) primary/primary, (ii)
secondary/secondary, and (iii) technologies operating in a spectrum commons.
Moreover, we reflect on our literature review to identify possible spectrum
sharing design solutions and performance evaluation approaches useful for
future coexistence cases. Finally, we discuss spectrum sharing design
challenges and suggest future research directions
LTE in Unlicensed Bands is neither Friend nor Foe to Wi-Fi
Proponents of deploying LTE in the 5 GHz band for providing additional
cellular network capacity have claimed that LTE would be a better neighbour to
Wi-Fi in the unlicensed band, than Wi-Fi is to itself. On the other side of the
debate, the Wi-Fi community has objected that LTE would be highly detrimental
to Wi-Fi network performance. However, there is a lack of transparent and
systematic engineering evidence supporting the contradicting claims of the two
camps, which is essential for ascertaining whether regulatory intervention is
in fact required to protect the Wi-Fi incumbent from the new LTE entrant. To
this end, we present a comprehensive coexistence study of Wi-Fi and
LTE-in-unlicensed, surveying a large parameter space of coexistence mechanisms
and a range of representative network densities and deployment scenarios. Our
results show that, typically, harmonious coexistence between Wi-Fi and LTE is
ensured by the large number of 5 GHz channels. For the worst-case scenario of
forced co-channel operation, LTE is sometimes a better neighbour to Wi-Fi -
when effective node density is low - but sometimes worse - when density is
high. We find that distributed interference coordination is only necessary to
prevent a "tragedy of the commons" in regimes where interference is very
likely. We also show that in practice it does not make a difference to the
incumbent what kind of coexistence mechanism is added to LTE-in-unlicensed, as
long as one is in place. We therefore conclude that LTE is neither friend nor
foe to Wi-Fi in the unlicensed bands in general. We submit that the systematic
engineering analysis exemplified by our case study is a best-practice approach
for supporting evidence-based rulemaking by the regulator.Comment: accepted for publication in IEEE Acces
Risk-Informed Interference Assessment for Shared Spectrum Bands: A Wi-Fi/LTE Coexistence Case Study
Interference evaluation is crucial when deciding whether and how wireless
technologies should operate. In this paper we demonstrate the benefit of
risk-informed interference assessment to aid spectrum regulators in making
decisions, and to readily convey engineering insight. Our contributions are: we
apply, for the first time, risk assessment to a problem of inter-technology
spectrum sharing, i.e. Wi-Fi/LTE in the 5 GHz unlicensed band, and we
demonstrate that this method comprehensively quantifies the interference
impact. We perform simulations with our newly publicly-available tool and we
consider throughput degradation and fairness metrics to assess the risk for
different network densities, numbers of channels, and deployment scenarios. Our
results show that no regulatory intervention is needed to ensure harmonious
technical Wi-Fi/LTE coexistence: for the typically large number of channels
available in the 5 GHz band, the risk for Wi-Fi from LTE is negligible,
rendering policy and engineering concerns largely moot. As an engineering
insight, Wi-Fi coexists better with itself in dense, but better with LTE, in
sparse deployments. Also, both main LTE-in-unlicensed variants coexist well
with Wi-Fi in general. For LTE intra-technology inter-operator coexistence,
both variants typically coexist well in the 5 GHz band, but for dense
deployments, implementing listen-before-talk causes less interference
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