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Femtocells: Past, Present, and Future
- IEEE Journal on Selected Areas in Communications
, 2012
"... Abstract—Femtocells, despite their name, pose a potentially large disruption to the carefully planned cellular networks that now connect a majority of the planet’s citizens to the Internet and with each other. Femtocells – which by the end of 2010 already outnumbered traditional base stations and at ..."
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Cited by 91 (18 self)
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Abstract—Femtocells, despite their name, pose a potentially large disruption to the carefully planned cellular networks that now connect a majority of the planet’s citizens to the Internet and with each other. Femtocells – which by the end of 2010 already outnumbered traditional base stations and at the time of publication are being deployed at a rate of about five million a year – both enhance and interfere with this network in ways that are not yet well understood. Will femtocells be crucial for offloading data and video from the creaking traditional network? Or will femtocells prove more trouble than they are worth, undermining decades of careful base station deployment with unpredictable interference while delivering only limited gains? Or possibly neither: are femtocells just a “flash in the pan”; an exciting but short-lived stage of network evolution that will be rendered obsolete by improved WiFi offloading, new backhaul regulations and/or pricing, or other unforeseen technological developments? This tutorial article overviews the history of femtocells, demystifies their key aspects, and provides a preview of the next few years, which the authors believe will see a rapid acceleration towards small cell technology. In the course of the article, we also position and introduce the articles that headline this special issue.
Seven Ways that HetNets are a Cellular Paradigm Shift
, 2012
"... Imagine a world with more base stations than cell phones: this is where cellular technology is headed in 10-20 years. This mega-trend requires many fundamental differences in visualizing, modeling, analyzing, simulating and designing cellular networks versus the current textbook approach. In this pa ..."
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Cited by 64 (10 self)
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Imagine a world with more base stations than cell phones: this is where cellular technology is headed in 10-20 years. This mega-trend requires many fundamental differences in visualizing, modeling, analyzing, simulating and designing cellular networks versus the current textbook approach. In this paper, the most important shifts are distilled down to seven key factors, with the implications described and new models and techniques proposed for some, while others are ripe areas for future exploration.
Analytical modeling of uplink cellular networks
- IEEE Trans. Wireless Commun
, 2013
"... Abstract—Cellular uplink analysis has typically been under-taken by either a simple approach that lumps all interference into a single deterministic or random parameter in a Wyner-type model, or via complex system level simulations that often do not provide insight into why various trends are observ ..."
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Cited by 34 (5 self)
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Abstract—Cellular uplink analysis has typically been under-taken by either a simple approach that lumps all interference into a single deterministic or random parameter in a Wyner-type model, or via complex system level simulations that often do not provide insight into why various trends are observed. This paper proposes a novel middle way using point processes that is both accurate and also results in easy-to-evaluate integral expressions based on the Laplace transform of the interference. We assume mobiles and base stations are randomly placed in the network with each mobile pairing up to its closest base station. Compared to related recent work on downlink analysis, the proposed uplink model differs in two key features. First, dependence is considered between user and base station point processes to make sure each base station serves a single mobile in the given resource block. Second, per-mobile power control is included, which further couples the transmission of mobiles due to location-dependent channel inversion. Nevertheless, we succeed in deriving the coverage (equivalently outage) probability of a typical link in the network. This model can be used to address a wide variety of system design questions in the future. In this paper we focus on the implications for power control and show that partial channel inversion should be used at low signal-to-interference-plus-noise ratio (SINR), while full power transmission is optimal at higher SINR. Index Terms—Uplink, cellular networks, SINR, outage prob-ability, stochastic geometry, fractional power control.
Joint Resource Partitioning and Offloading in Heterogeneous Cellular Networks
, 2013
"... In heterogeneous cellular networks (HCNs), it is desirable to offload mobile users to small cells, which are typically significantly less congested than the macrocells. To achieve suffi-cient load balancing, the offloaded users often have much lower SINR than they would on the macrocell. This SINR d ..."
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Cited by 23 (2 self)
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In heterogeneous cellular networks (HCNs), it is desirable to offload mobile users to small cells, which are typically significantly less congested than the macrocells. To achieve suffi-cient load balancing, the offloaded users often have much lower SINR than they would on the macrocell. This SINR degradation can be partially alleviated through interference avoidance, for example time or frequency resource partitioning, whereby the macrocell turns off in some fraction of such resources. Naturally, the optimal offloading strategy is tightly coupled with resource partitioning; the optimal amount of which in turn depends on how many users have been offloaded. In this paper, we propose a general and tractable framework for modeling and analyzing joint resource partitioning and offloading in a two-tier cellular network. With it, we are able to derive the downlink rate distribution over the entire network, and an optimal strategy for joint resource partitioning and offloading. We show that load balancing, by itself, is insufficient, and resource partitioning is required in conjunction with offloading to improve the rate of cell edge users in co-channel heterogeneous networks.
Improving the Energy Efficiency of Two-Tier Heterogeneous Cellular Networks through Partial Spectrum Reuse
"... Abstract—Partial Spectrum Reuse (PSR) in the second tier of two-tier heterogeneous cellular networks has a potential to improve spectrum efficiency by reducing inter-cell interference, and thus energy efficiency as well by deploying less or switching off more Base Stations (BSs). In this paper, we a ..."
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Cited by 3 (0 self)
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Abstract—Partial Spectrum Reuse (PSR) in the second tier of two-tier heterogeneous cellular networks has a potential to improve spectrum efficiency by reducing inter-cell interference, and thus energy efficiency as well by deploying less or switching off more Base Stations (BSs). In this paper, we analyze the optimal PSR factor, defined as the portion of spectrum reused by micro cells in two-tier heterogeneous networks, which is not in an explicit form generally. Then, a closed-form limit of the optimal PSR factor is derived as the ratio of the user rate requirement over the whole system spectrum bandwidth is approaching zero, based on which a threshold of the micro-BS energy cost is also derived to determine which type of BSs is preferable. Specifically, one should deploy more micro BSs or switch off more macro BSs if the micro-BS energy cost is lower than the threshold. Otherwise, the optimal choice is the opposite. This threshold with the PSR scheme is higher than that without PSR scheme, i.e., PSR can improve both spectrum efficiency and energy efficiency. Numerical results show that adopting PSR can reduce the network energy consumption by up to 50 % when the transmit power of macro BSs is 10dB higher than that of micro BSs. Index Terms—Heterogeneous cellular networks, partial spec-trum reuse, poisson point process, energy efficiency. I.
Distributed InterBS Cooperation Aided Energy Efficient Load Balancing for Cellular Networks
- IEEE Transactions on Wireless Communications
, 2013
"... We propose a distributed inter-base station (BS) cooperation assisted load balancing framework for improving energy efficiency of OFDMA-based cellular access networks. Proposed cooperation is formulated following the principle of ecological self-organization. Based on the network traffic, BSs mutual ..."
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Cited by 3 (1 self)
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We propose a distributed inter-base station (BS) cooperation assisted load balancing framework for improving energy efficiency of OFDMA-based cellular access networks. Proposed cooperation is formulated following the principle of ecological self-organization. Based on the network traffic, BSs mutually cooperate for distributing traffic among themselves and thus, the number of active BSs is dynamically adjusted for energy savings. For reducing the number of communications among BSs, a three-step measure is taken by using estimated load factor (LF), initializing the algorithm with only the active BSs and differentiating neighboring BSs according to their operating modes for distributing traffic. An exponentially weighted moving average (EWMA)-based technique is proposed for estimating the LF in advance based on the historical data. Various selection schemes for finding the best BSs to distribute traffic are also explored. Furthermore, we present an analytical formulation for modeling the dynamic switching of BSs. A thorough investigation under a wide range of network settings is carried out in the context of an LTE system. Results demonstrate a significant enhancement in network energy efficiency yielding up to 30 % higher savings than the compared schemes. Moreover, frequency of correspondence among BSs can be reduced up to 80%.
A Framework for Uplink Intercell Interference Modeling with Channel-Based Scheduling
, 2012
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Load Balancing by Dynamic Base Station Relay Station Associations in Cellular Netwroks
- IEEE Wireless Commun. Lett
, 2013
"... Abstract—In this paper, we propose a relay-assisted load balancing scheme in cellular networks. The relay stations can be dynamically associated with different base stations. The load transferring from over-loaded cells to neighboring under-loaded cells is realized by dynamically changing the base s ..."
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Abstract—In this paper, we propose a relay-assisted load balancing scheme in cellular networks. The relay stations can be dynamically associated with different base stations. The load transferring from over-loaded cells to neighboring under-loaded cells is realized by dynamically changing the base station-relay station associations. A distributed algorithm, in which each relay station only needs to exchange information with its neighboring base stations and makes a re-association decision by itself, is proposed. Simulation results show that the overall call blocking probability can be reduced significantly when our distributed algorithm is applied. Index Terms—Cellular networks, load balancing, dynamic relay station association. I.
On cognitive small cells in two-tier heterogeneous networks
- in Proc. 9th Workshop on Spatial Stochastic Models for Wireless Networks (SpaSWiN 2013), Tsukuba Science City
"... Abstract-In a two-tier heterogeneous network (HetNet) where small base stations (SBSs) coexist with macro base stations (MBSs), the SBSs may suffer significant performance degradation due to the inter-and intra-tier interferences. Introducing cognition into the SBSs through the spectrum sensing (e. ..."
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Abstract-In a two-tier heterogeneous network (HetNet) where small base stations (SBSs) coexist with macro base stations (MBSs), the SBSs may suffer significant performance degradation due to the inter-and intra-tier interferences. Introducing cognition into the SBSs through the spectrum sensing (e.g., carrier sensing) capability helps them detecting the interference sources and avoiding them via opportunistic access to orthogonal channels. In this paper, we use stochastic geometry to model and analyze the performance of two cases of cognitive SBSs in a multichannel environment, namely, the semi-cognitive case and the full-cognitive case. In the semi-cognitive case, the SBSs are only aware of the interference from the MBSs, hence, only inter-tier interference is minimized. On the other hand, in the full-cognitive case, the SBSs access the spectrum via a contention resolution process, hence, both the intra-and intertier interferences are minimized, but at the expense of reduced spectrum access opportunities. We quantify the performance gain in outage probability obtained by introducing cognition into the small cell tier for both the cases. We will focus on a special type of SBSs called the femto access points (FAPs) and also capture the effect of different admission control policies, namely, the openaccess and closed-access policies. We show that a semi-cognitive SBS always outperforms a full-cognitive SBS and that there exists an optimal spectrum sensing threshold for the cognitive SBSs which can be obtained via the analytical framework presented in this paper.
Ergodic Capacity Analysis of Downlink Distributed Antenna Systems Using Stochastic Geometry
"... Abstract—This paper studies the ergodic capacity of a multicell distributed antenna system (DAS), where remote antenna ports are spread within each cell to cooperatively transmit to user terminals. Unlike most prior studies which assume the antenna ports to be deployed at fixed locations, this paper ..."
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Abstract—This paper studies the ergodic capacity of a multicell distributed antenna system (DAS), where remote antenna ports are spread within each cell to cooperatively transmit to user terminals. Unlike most prior studies which assume the antenna ports to be deployed at fixed locations, this paper assumes the antenna ports to be distributed as a spatial Poisson point process (PPP) to account for the fact that in practice the antenna ports are randomly placed to cover wherever the dead spots are. We first model DAS within each cell as a downlink multiple-input single-output (MISO) channel with per-antenna power constraint while accounting for inter-cell (inter-cluster) interference. Two DAS layouts are considered: the “regular ” layout where the antenna ports are randomly deployed within regular cellular boundary to serve a given user, and the “user-centric ” layout where the antenna ports are distributed over a wide area and the users choose the surrounding antenna ports to form a “virtual cell” as its own serving antenna subset. Using the tool of stochastic geometry, we analytically derive efficiently computable ergodic capacity expressions for the two layouts of DAS. Using these expressions, the cell-edge capacity of DAS under the regular layout is shown to be upper-bounded by α 2, where α is the pathloss exponent. Numerical results show that the proposed analytical model can accurately model the first layout, and can well approximate the second layout when the serving radius of users is not large. Compared to the traditional cellular system where all antennas are co-located at the cell center, DAS has better cell-edge performance. Further, the user-centric DAS has higher capacity than the DAS under regular layout. I.
