387 research outputs found
Joint Backhaul-Access Analysis of Full Duplex Self-Backhauling Heterogeneous Networks
With the successful demonstration of in-band full-duplex (IBFD) transceivers,
a new research dimension has been added to wireless networks. This paper
proposes an interesting use case of this capability for IBFD self-backhauling
heterogeneous networks (HetNet). IBFD self-backhauling in a HetNet refers to
IBFD-enabled small cells backhauling themselves with macro cells over the
wireless channel. Owing to their IBFD capability, the small cells
simultaneously communicate over the access and backhaul links, using the same
frequency band. The idea is doubly advantageous, as it obviates the need for
fiber backhauling small cells every hundred meters and allows the access
spectrum to be reused for backhauling at no extra cost. This work considers the
case of a two-tier cellular network with IBFD-enabled small cells, wirelessly
backhauling themselves with conventional macro cells. For clear exposition, the
case considered is that of FDD network, where within access and backhaul links,
the downlink (DL) and uplink (UL) are frequency duplexed (,
respectively), while the total frequency spectrum used at access and backhaul
() is the same. Analytical expressions for coverage and average downlink
(DL) rate in such a network are derived using tools from the field of
stochastic geometry. It is shown that DL rate in such networks could be close
to double that of a conventional TDD/FDD self-backhauling network, at the
expense of reduced coverage due to higher interference in IBFD networks. For
the proposed IBFD network, the conflicting aspects of increased interference on
one side and high spectral efficiency on the other are captured into a
mathematical model. The mathematical model introduces an end-to-end joint
analysis of backhaul (or fronthaul) and access links, in contrast to the
largely available access-centric studies.Comment: Remodeled using different large-scale path loss exponents for the
Macro Base Station tier and the Pico Base Station Tier. Other formatting
improvements. Submitted to IEEE Transactions on Wireless Communicatio
Sum-Rate Analysis and Optimization of Self-Backhauling Based Full-Duplex Radio Access System
In this article, a radio access system with a self-backhauling full-duplex
access node serving legacy half-duplex mobile devices is studied and analyzed.
In particular, it is assumed that the access node is using the same center
frequency for all the transmissions, meaning that also the backhauling is done
using the same frequency resources as the uplink and downlink transmissions. It
is further assumed that the access node has a massive array to facilitate
efficient beamforming and self-interference nulling in its own receiver. As a
starting point, the signal model for the considered access node is first
derived, including all the transmitted and received signals within the cell.
This is then used as a basis for obtaining the sum-rate expressions, which
depict the overall rates experienced by the mobile users that are served by the
access node. In addition, the data rate for the bi-directional backhaul link is
also derived, since the access node must be able to backhaul itself wirelessly.
The maximum achievable sum-rate is then determined by numerically solving an
optimization problem constructed from the data rate expressions. The
full-duplex scheme is also compared to two alternative transmission schemes,
which perform all or some of the transmissions in half-duplex mode. The results
show that the full-duplex capability of the access node is beneficial for
maximizing the sum-rate, meaning that a simple half-duplex transmission scheme
is typically not optimal. In particular, the highest sum-rate is usually
provided by a relay type solution, where the access node acts as a full-duplex
relay between the mobiles and the backhaul node.Comment: 30 pages, submitted for revie
Integrated Access and Backhaul Optimization for Millimeter Wave Heterogeneous Networks
By allowing a large number of links to be simultaneously transmitted,
directional antenna arrays with beamforming have been envisioned as a promising
candidate to reach unprecedented levels of spatial isolation. To achieve the
high efficiency of spatial reuse in improving system performance, an
optimization problem that maximizes the achievable data rate of a multihop
heterogeneous network, which incorporates the concept of integrated access and
backhaul and supports both downlink and uplink transmissions on access and
backhaul links, is formulated. The optimization problem is then systematically
decomposed and demonstrated as NP-hard, and a heuristic joint scheduling and
resource allocation algorithm is proposed to maximize the achievable data rate.
In addition, an efficient dynamic routing algorithm is proposed to further
enhance the data rate. With extensive system-level simulations, it is
demonstrated that the proposed algorithms achieve significant gain over
benchmark schemes, in terms of data rate, and closely approach the theoretical
optimum, yet with lower latency. Besides, the proposed algorithms enable a
flexible adjustment of downlink and uplink transmission duration allocation and
support both half- and full-duplex modes with considerable performance
enhancement. In particular, the proposed algorithms are capable of fulfilling
different performance requirements for both point-to-point and
point-to-multipoint communications.Comment: IEEE Transactions on Wireless Communication
Analysis of Massive MIMO-Enabled Downlink Wireless Backhauling for Full-Duplex Small Cells
Using tools from stochastic geometry, we develop a framework to model the
downlink rate coverage probability of a user in a given small cell network
(SCN) with massive MIMO-enabled wireless backhauls. The considered SCN is
composed of a mixture of small cells that are configured in either in-band or
out-of-band backhaul modes with a certain probability. The performance of the
user in the considered hierarchical network is limited by several sources of
interference such as the backhaul interference, small cell base station
(SBS)-to-SBS interference and the SI. Moreover, due to the channel hardening
effect in massive MIMO, the backhaul links experience long term channel effects
only, whereas the access links experience both the long term and short term
channel effects. Consequently, the developed framework is flexible to
characterize different sources of interference while capturing the
heterogeneity of the access and backhaul channels. In specific scenarios, the
framework enables deriving closed-form coverage probability expressions. Under
perfect backhaul coverage, the simplified expressions are utilized to optimize
the proportion of in-band and out-of-band small cells in the SCN in
closed-form. Finally, few remedial solutions are proposed that can potentially
mitigate the backhaul interference and in turn improve the performance of
in-band FD wireless backhauling. Numerical results investigate the scenarios in
which in-band wireless backhauling is useful and demonstrate that maintaining a
correct proportion of in-band and out-of-band FD small cells is crucial in
wireless backhauled SCNs.Comment: 15 pages, 7 figures, IEEE Transactions on Communication
Ultra-Dense 5G Small Cell Deployment for Fiber and Wireless Backhaul-Aware Infrastructures
In this paper, we study the cell planning problem for a two-tier cellular
network containing two types of base stations (BSs)-- i.e. with fiber backhaul,
referred to as wired BSs (W-BSs), and BSs with wireless backhaul, referred to
as unwired-BSs (U-BSs). In-band full-duplex wireless communications is used to
connect U-BSs and W-BSs. We propose an algorithm to determine the minimum
number of W-BSs and U-BSs to satisfy given cell and capacity coverage
constraints. Furthermore, we apply our proposed non-dominated sorting genetic
algorithm II (NSGA-II) to solve both cell planning and joint cell and backhaul
planning problem to minimize the cost of planning, while maximizing the
coverage simultaneously. Additionally, the considered cell planning program is
developed into an optimization by including the problem of minimizing the cost
of fiber backhaul deployment. In order to analyze the performance of the
proposed algorithm, we study three different deployment scenarios based on
different spatial distributions of users and coverage areas. The results show
the superiority of our proposed NSGA-II algorithm for both cell planning and
joint cell and backhaul planning to other well-known optimization algorithms.
The results also reveal that there is a trade-off between cell deployment costs
and SINR/rate coverage, and W-BSs are placed in congested areas to consume less
resources for wireless backhauls. Similarly, a trade-off between cell and fiber
deployment costs and SINR/rate coverage is observed in planning. We show that
for realistic scenarios desirable solutions can be selected from the Pareto
front of the introduced multi-objective problem based on given cellular
operator policies
Max-Min Rates in Self-backhauled Millimeter Wave Cellular Networks
This paper considers the following question for viable wide-area millimeter
wave cellular networks. What is the maximum extended coverage area of a single
fiber site using multi-hop relaying, while achieving a minimum target per user
data rate? We formulate an optimization problem to maximize the minimum
end-to-end per user data rate, and exploit unique features of millimeter wave
deployments to yield a tractable solution. The mesh network is modeled as a
ring urban-canyon type deployment, where is the number of hops back to
the fiber site. The total number of relays per fiber site grows as . We
consider both integrated access-backhaul (IAB) and orthogonal access-backhaul
(OAB) resource allocation strategies, as well as both half and full duplex base
stations (BSs). With a few validated simplifications, our results are given as
simple closed-form expressions that are easy to evaluate even for large
networks. Several design guidelines are provided, including on the choice of
routing and scheduling strategy, the maximum allowable self-interference in
full duplex relays and role of dual connectivity to reduce load imbalance
across BSs. For example, we show that for certain load conditions there is very
little gain to IAB (as considered for 5G) as opposed to tunable OAB (using
separate spectrum for access and backhaul links); the latter being
significantly simpler to implement.Comment: under review, major revision, submitted to IEEE Trans. Wireless
Commu
Distributed Virtual Resource Allocation in Small Cell Networks with Full Duplex Self-backhauls and Virtualization
Wireless network virtualization has attracted great attentions from both
academia and industry. Another emerging technology for next generation wireless
networks is in-band full duplex (FD) communications. Due to its promising
performance, FD communication has been considered as an effective way to
achieve self-backhauls for small cells. In this paper, we introduce wireless
virtualization into small cell networks, and propose a virtualized small cell
network architecture with FD self-backhauls. We formulate the virtual resource
allocation problem in virtualized small cell networks with FD self-backhauls as
an optimization problem. Since the formulated problem is a mixed combinatorial
and non-convex optimization problem, its computational complexity is high.
Moreover, the centralized scheme may suffer from signaling overhead, outdated
dynamics information, and scalability issues. To solve it efficiently, we
divide the original problem into two subproblems. For the first subproblem, we
transfer it to a convex optimization problem, and then solve it by an efficient
alternating direction method of multipliers (ADMM)-based distributed algorithm.
The second subproblem is a convex problem, which can be solved by each
infrastructure provider. Extensive simulations are conducted with different
system configurations to show the effectiveness of the proposed scheme
User-Centric Joint Access-Backhaul Design for Full-Duplex Self-Backhauled Wireless Networks
Full-duplex self-backhauling is promising to provide cost-effective and
flexible backhaul connectivity for ultra-dense wireless networks, but also
poses a great challenge to resource management between the access and backhaul
links. In this paper, we propose a user-centric joint access-backhaul
transmission framework for full-duplex self-backhauled wireless networks. In
the access link, user-centric clustering is adopted so that each user is
cooperatively served by multiple small base stations (SBSs). In the backhaul
link, user-centric multicast transmission is proposed so that each user's
message is treated as a common message and multicast to its serving SBS
cluster. We first formulate an optimization problem to maximize the network
weighted sum rate through joint access-backhaul beamforming and SBS clustering
when global channel state information (CSI) is available. This problem is
efficiently solved via the successive lower-bound maximization approach with a
novel approximate objective function and the iterative link removal technique.
We then extend the study to the stochastic joint access-backhaul beamforming
optimization with partial CSI. Simulation results demonstrate the effectiveness
of the proposed algorithms for both full CSI and partial CSI scenarios. They
also show that the transmission design with partial CSI can greatly reduce the
CSI overhead with little performance degradation.Comment: to appear in IEEE Trans. on Communication
Wireless Backhaul in 5G and Beyond: Issues, Challenges and Opportunities
With the introduction of new technologies such as Unmanned Aerial Vehicle
(UAV), High Altitude Platform Station (HAPS), Millimeter Wave (mmWave)
frequencies, Massive Multiple-Input Multiple-Output (mMIMO), and beamforming,
wireless backhaul is expected to be an integral part of the 5G networks. While
this concept is nothing new, it was shortcoming in terms of performance
compared to the fiber backhauling. However, with these new technologies, fiber
is no longer the foremost technology for backhauling. With the projected
densification of networks, wireless backhaul has become mandatory to use. There
are still challenges to be tackled if wireless backhaul is to be used
efficiently. Resource allocation, deployment, scheduling, power management and
energy efficiency are some of these problems. Wireless backhaul also acts as an
enabler for new technologies and improves some of the existing ones
significantly. To name a few, rural connectivity, satellite communication, and
mobile edge computing are some concepts for which wireless backhauling acts as
an enabler. Small cell usage with wireless backhaul presents different security
challenges. Governing bodies of cellular networks have standardization efforts
going on especially for the Integrated Acces-Backhaul (IAB) concept, and this
is briefly mentioned. Finally, wireless backhaul is also projected to be an
important part of the beyond 5G networks, and newly developed concepts such as
cell-free networking, ultra-massive MIMO, and extremely dense network show this
trend as well. In this survey, we present the aforementioned issues,
challenges, opportunities, and applications of wireless backhaul in 5G, while
briefly mentioning concepts related to wireless backhaul beyond 5G alongside
with security and standardization issues
Joint Downlink Cell Association and Bandwidth Allocation for Wireless Backhauling in Two-Tier HetNets with Large-Scale Antenna Arrays
The problem of joint downlink cell association (CA) and wireless backhaul
bandwidth allocation (WBBA) in two-tier cellular heterogeneous networks
(HetNets) is considered. Large-scale antenna array is implemented at the macro
base station (BS), while the small cells within the macro cell range are
single-antenna BSs and they rely on over-the-air links to the macro BS for
backhauling. A sum logarithmic user rate maximization problem is investigated
considering wireless backhauling constraints. A duplex and spectrum sharing
scheme based on co-channel reverse time-division duplex (TDD) and dynamic soft
frequency reuse (SFR) is proposed for interference management in two-tier
HetNets with large-scale antenna arrays at the macro BS and wireless
backhauling for small cells. Two in-band WBBA scenarios, namely, unified
bandwidth allocation and per-small-cell bandwidth allocation scenarios, are
investigated for joint CA-WBBA in the HetNet. A two-level hierarchical
decomposition method for relaxed optimization is employed to solve the
mixed-integer nonlinear program (MINLP). Solutions based on the General
Algorithm Modeling System (GAMS) optimization solver and fast heuristics are
also proposed for cell association in the per-small-cell WBBA scenario. It is
shown that when all small cells have to use in-band wireless backhaul, the
system load has more impact on both the sum log-rate and per-user rate
performance than the number of small cells deployed within the macro cell
range. The proposed joint CA-WBBA algorithms have an optimal load approximately
equal to the size of the large-scale antenna array at the macro BS. The cell
range expansion (CRE) strategy, which is an efficient cell association scheme
for HetNets with perfect backhauling, is shown to be inefficient when in-band
wireless backhauling for small cells comes into play.Comment: IEEE Transactions on Wireless Communications, to appea
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