29 research outputs found
User-Centric Interference Nulling in Downlink Multi-Antenna Heterogeneous Networks
In heterogeneous networks (HetNets), strong interference due to spectrum
reuse affects each user's signal-to-interference ratio (SIR), and hence is one
limiting factor of network performance. In this paper, we propose a
user-centric interference nulling (IN) scheme in a downlink large-scale HetNet
to improve coverage/outage probability by improving each user's SIR. This IN
scheme utilizes at most maximum IN degree of freedom (DoF) at each macro-BS to
avoid interference to uniformly selected macro (pico) users with
signal-to-individual-interference ratio (SIIR) below a macro (pico) IN
threshold, where the maximum IN DoF and the two IN thresholds are three design
parameters. Using tools from stochastic geometry, we first obtain a tractable
expression of the coverage (equivalently outage) probability. Then, we analyze
the asymptotic coverage/outage probability in the low and high SIR threshold
regimes. The analytical results indicate that the maximum IN DoF can affect the
order gain of the outage probability in the low SIR threshold regime, but
cannot affect the order gain of the coverage probability in the high SIR
threshold regime. Moreover, we characterize the optimal maximum IN DoF which
optimizes the asymptotic coverage/outage probability. The optimization results
reveal that the IN scheme can linearly improve the outage probability in the
low SIR threshold regime, but cannot improve the coverage probability in the
high SIR threshold regime. Finally, numerical results show that the proposed
scheme can achieve good gains in coverage/outage probability over a maximum
ratio beamforming scheme and a user-centric almost blank subframes (ABS)
scheme.Comment: Transactions on Wireless Communications (under revision). arXiv admin
note: text overlap with arXiv:1504.0528
Analysis and Optimization of Inter-tier Interference Coordination in Downlink Multi-Antenna HetNets with Offloading
Heterogeneous networks (HetNets) with offloading is considered as an
effective way to meet the high data rate demand of future wireless service.
However, the offloaded users suffer from strong inter-tier interference, which
reduces the benefits of offloading and is one of the main limiting factors of
the system performance. In this paper, we investigate an interference nulling
(IN) scheme in improving the system performance by carefully managing the
inter-tier interference to the offloaded users in downlink two-tier HetNets
with multi-antenna base stations. Utilizing tools from stochastic geometry, we
first derive a tractable expression for the rate coverage probability of the IN
scheme. Then, by studying its order, we obtain the optimal design parameter,
i.e., the degrees of freedom that can be used for IN, to maximize the rate
coverage probability. Finally, we analyze the rate coverage probabilities of
the simple offloading scheme without interference management and the
multi-antenna version of the almost blank subframes (ABS) scheme in 3GPP LTE,
and compare the performance of the IN scheme with these two schemes. Both
analytical and numerical results show that the IN scheme can achieve good
performance gains over both of these two schemes, especially in the large
antenna regime
Fast converging robust beamforming for downlink massive MIMO systems in heterogenous networks
Massive multiple-input multiple-output (MIMO) is an emerging technology, which is an enabler for future broadband wireless networks that support high speed connection of densely populated areas. Application of massive MIMO at the macrocell base stations in heterogeneous networks (HetNets) offers an increase in throughput without increasing the bandwidth, but with reduced power consumption. This research investigated the optimisation problem of signal-to-interference-plus-noise ratio (SINR) balancing for macrocell users in a typical HetNet scenario with massive MIMO at the base station. The aim was to present an efficient beamforming solution that would enhance inter-tier interference mitigation in heterogeneous networks. The system model considered the case of perfect channel state information (CSI) acquisition at the transmitter, as well as the case of imperfect CSI at the transmitter. A fast converging beamforming solution, which is applicable to both channel models, is presented. The proposed beamforming solution method applies the matrix stuffing technique and the alternative direction method of multipliers, in a two-stage fashion, to give a modestly accurate and efficient solution. In the first stage, the original optimisation problem is transformed into standard second-order conic program (SOCP) form using the Smith form reformulation and applying the matrix stuffing technique for fast transformation. The second stage uses the alternative direction method of multipliers to solve the SOCP-based optimisation problem. Simulations to evaluate the SINR performance of the proposed solution method were carried out with supporting software-based simulations using relevant MATLAB toolboxes. The simulation results of a typical single cell in a HetNet show that the proposed solution gives performance with modest accuracy, while converging in an efficient manner, compared to optimal solutions achieved by state-of-the-art modelling languages and interior-point solvers. This is particularly for cases when the number of antennas at the base station increases to large values, for both models of perfect CSI and imperfect CSI. This makes the solution method attractive for practical implementation in heterogeneous networks with large scale antenna arrays at the macrocell base station.Dissertation (MEng)--University of Pretoria, 2018.Electrical, Electronic and Computer EngineeringMEngUnrestricte
Separation Framework: An Enabler for Cooperative and D2D Communication for Future 5G Networks
Soaring capacity and coverage demands dictate that future cellular networks
need to soon migrate towards ultra-dense networks. However, network
densification comes with a host of challenges that include compromised energy
efficiency, complex interference management, cumbersome mobility management,
burdensome signaling overheads and higher backhaul costs. Interestingly, most
of the problems, that beleaguer network densification, stem from legacy
networks' one common feature i.e., tight coupling between the control and data
planes regardless of their degree of heterogeneity and cell density.
Consequently, in wake of 5G, control and data planes separation architecture
(SARC) has recently been conceived as a promising paradigm that has potential
to address most of aforementioned challenges. In this article, we review
various proposals that have been presented in literature so far to enable SARC.
More specifically, we analyze how and to what degree various SARC proposals
address the four main challenges in network densification namely: energy
efficiency, system level capacity maximization, interference management and
mobility management. We then focus on two salient features of future cellular
networks that have not yet been adapted in legacy networks at wide scale and
thus remain a hallmark of 5G, i.e., coordinated multipoint (CoMP), and
device-to-device (D2D) communications. After providing necessary background on
CoMP and D2D, we analyze how SARC can particularly act as a major enabler for
CoMP and D2D in context of 5G. This article thus serves as both a tutorial as
well as an up to date survey on SARC, CoMP and D2D. Most importantly, the
article provides an extensive outlook of challenges and opportunities that lie
at the crossroads of these three mutually entangled emerging technologies.Comment: 28 pages, 11 figures, IEEE Communications Surveys & Tutorials 201