56 research outputs found
Coverage in Multi-Antenna Two-Tier Networks
In two-tier networks -- comprising a conventional cellular network overlaid
with shorter range hotspots (e.g. femtocells, distributed antennas, or wired
relays) -- with universal frequency reuse, the near-far effect from cross-tier
interference creates dead spots where reliable coverage cannot be guaranteed to
users in either tier. Equipping the macrocell and femtocells with multiple
antennas enhances robustness against the near-far problem. This work derives
the maximum number of simultaneously transmitting multiple antenna femtocells
meeting a per-tier outage probability constraint. Coverage dead zones are
presented wherein cross-tier interference bottlenecks cellular and hotspot
coverage. Two operating regimes are shown namely 1) a cellular-limited regime
in which femtocell users experience unacceptable cross-tier interference and 2)
a hotspot-limited regime wherein both femtocell users and cellular users are
limited by hotspot interference. Our analysis accounts for the per-tier
transmit powers, the number of transmit antennas (single antenna transmission
being a special case) and terrestrial propagation such as the Rayleigh fading
and the path loss exponents. Single-user (SU) multiple antenna transmission at
each tier is shown to provide significantly superior coverage and spatial reuse
relative to multiuser (MU) transmission. We propose a decentralized
carrier-sensing approach to regulate femtocell transmission powers based on
their location. Considering a worst-case cell-edge location, simulations using
typical path loss scenarios show that our interference management strategy
provides reliable cellular coverage with about 60 femtocells per cellsite.Comment: 30 Pages, 11 figures, Revised and Resubmitted to IEEE Transactions on
Wireless Communication
Optimal decentralized spectral resource allocation for OFDMA downlink of femto networks via adaptive gradient vector step size approach
For the orthogonal frequency division multiple access (OFDMA) downlink of a femto network, the resource allocation scheme would aim to maximize the area spectral efficiency (ASE) subject to constraints on the radio resources per transmission interval accessible by each femtocell. An optimal resource allocation scheme for completely decentralized femtocell deployments leads to a nonlinear optimization problem because the cost function of the optimization problem is nonlinear. In this paper, an adaptive gradient vector step size approach is proposed for finding the optimal solution of the optimization problem. Computer numerical simulation results show that our proposed method is more efficient than existing exhaustive search methods
Decentralized spectral resource allocation for OFDMA downlink of coexisting macro/femto networks using filled function method
For an orthogonal frequency division multiple access (OFDMA) downlink of a spectrally coexisting macro and femto network, a resource allocation scheme would aim to maximize the area spectral efficiency (ASE) subject to constraints on the radio resources per transmission interval accessible by each femtocell. An optimal resource allocation scheme for completely decentralized deployments leads however to a nonconvex optimization problem. In this paper, a filled function method is employed to find the global maximum of the optimization problem. Simulation results show that our proposed method is efficient and effective
Analytical Evaluation of Coverage-Oriented Femtocell Network Deployment
This paper proposes a coverage-oriented femtocell network deployment scheme,
in which the femtocell base stations (BSs) can decide whether to be active or
inactive depending on their distances from the macrocell BSs. Specifically, as
the areas close to the macrocell BSs already have satisfactory cellular
coverage, the femtocell BSs located inside such areas are kept to be inactive.
Thus, all the active femtocells are located in the poor macrocell coverage
areas. Based on a stochastic geometric framework, the coverage probability can
be analyzed with tractable results. Surprisingly, the results show that the
proposed scheme, although with a lower defacto femtocell density, can achieve
better coverage performance than that keeping all femtocells in the entire
network to be active. The analytical results further identify the achievable
optimal performance of the new scheme, which provides mobile operators a
guideline for femtocell deployment and operation.Comment: 6 pages, 7 figures, published in IEEE International Conference on
Communications (ICC'13
Designing Wireless Broadband Access for Energy Efficiency: Are Small Cells the Only Answer?
The main usage of cellular networks has changed from voice to data traffic,
mostly requested by static users. In this paper, we analyze how a cellular
network should be designed to provide such wireless broadband access with
maximal energy efficiency (EE). Using stochastic geometry and a detailed power
consumption model, we optimize the density of access points (APs), number of
antennas and users per AP, and transmission power for maximal EE. Small cells
are of course a key technology in this direction, but the analysis shows that
the EE improvement of a small-cell network saturates quickly with the AP
density and then "massive MIMO" techniques can further improve the EE.Comment: Published at Small Cell and 5G Networks (SmallNets) Workshop, IEEE
International Conference on Communications (ICC), 6 pages, 5 figures, 1 tabl
Coverage performance of MIMO-MRC in heterogeneous networks:a stochastic geometry perspective
We study the coverage performance of multi-antenna (MIMO) communications with maximum ratio combining (MRC) at the receiver in heterogeneous networks (HetNets). Our main interest in on multi-stream communications when BSs do not have access to channel state information. Adopting stochastic geometry we evaluate the network-wise coverage performance of MIMO-MRC assuming maximum signal- to-interference ratio (SIR) cell association rule. Coverage analysis in MIMO-MRC HetNets is challenging due to inter-stream interference and statistical dependencies among streams' SIR values in each communication link. Using the results of stochastic geometry we then investigate this problem and obtain tractable analytical approximations for the coverage performance. We then show that our results are adequately accurate and easily computable. Our analysis sheds light on the impacts of important system parameters on the coverage performance, and provides quantitative insight on the densification in conjunction with high multiplexing gains in MIMO HetNets. We further observe that increasing multiplexing gain in high- power tier can cost a huge coverage reduction unless it is practiced with densification in femto-cell tier
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