20 research outputs found
Instantly Decodable Network Coding: From Centralized to Device-to-Device Communications
From its introduction to its quindecennial, network coding has built a strong reputation for enhancing packet recovery and achieving maximum information flow in both wired and wireless networks. Traditional studies focused on optimizing the throughput of the system by proposing elaborate schemes able to reach the network capacity. With the shift toward distributed computing on mobile devices, performance and complexity become both critical factors that affect the efficiency of a coding strategy. Instantly decodable network coding presents itself as a new paradigm in network coding that trades off these two aspects. This paper review instantly decodable network coding schemes by identifying, categorizing, and evaluating various algorithms proposed in the literature. The first part of the manuscript investigates the conventional centralized systems, in which all decisions are carried out by a central unit, e.g., a base-station. In particular, two successful approaches known as the strict and generalized instantly decodable network are compared in terms of reliability, performance, complexity, and packet selection methodology. The second part considers the use of instantly decodable codes in a device-to-device communication network, in which devices speed up the recovery of the missing packets by exchanging network coded packets. Although the performance improvements are directly proportional to the computational complexity increases, numerous successful schemes from both the performance and complexity viewpoints are identified
A Tutorial on Environment-Aware Communications via Channel Knowledge Map for 6G
Sixth-generation (6G) mobile communication networks are expected to have
dense infrastructures, large-dimensional channels, cost-effective hardware,
diversified positioning methods, and enhanced intelligence. Such trends bring
both new challenges and opportunities for the practical design of 6G. On one
hand, acquiring channel state information (CSI) in real time for all wireless
links becomes quite challenging in 6G. On the other hand, there would be
numerous data sources in 6G containing high-quality location-tagged channel
data, making it possible to better learn the local wireless environment. By
exploiting such new opportunities and for tackling the CSI acquisition
challenge, there is a promising paradigm shift from the conventional
environment-unaware communications to the new environment-aware communications
based on the novel approach of channel knowledge map (CKM). This article aims
to provide a comprehensive tutorial overview on environment-aware
communications enabled by CKM to fully harness its benefits for 6G. First, the
basic concept of CKM is presented, and a comparison of CKM with various
existing channel inference techniques is discussed. Next, the main techniques
for CKM construction are discussed, including both the model-free and
model-assisted approaches. Furthermore, a general framework is presented for
the utilization of CKM to achieve environment-aware communications, followed by
some typical CKM-aided communication scenarios. Finally, important open
problems in CKM research are highlighted and potential solutions are discussed
to inspire future work
Enabling Cyber-Physical Communication in 5G Cellular Networks: Challenges, Solutions and Applications
Cyber-physical systems (CPS) are expected to revolutionize the world through a myriad of applications in health-care, disaster event applications, environmental management, vehicular networks, industrial automation, and so on. The continuous explosive increase in wireless data traffic, driven by the global rise of smartphones, tablets, video streaming, and online social networking applications along with the anticipated wide massive sensors deployments, will create a set of challenges to network providers, especially that future fifth generation (5G) cellular networks will help facilitate the enabling of CPS communications over current network infrastructure. In this dissertation, we first provide an overview of CPS taxonomy along with its challenges from energy efficiency, security, and reliability. Then we present different tractable analytical solutions through different 5G technologies, such as device-to-device (D2D) communications, cell shrinking and offloading, in order to enable CPS traffic over cellular networks. These technologies also provide CPS with several benefits such as ubiquitous coverage, global connectivity, reliability and security. By tuning specific network parameters, the proposed solutions allow the achievement of balance and fairness in spectral efficiency and minimum achievable throughout among cellular users and CPS devices. To conclude, we present a CPS mobile-health application as a case study where security of the medical health cyber-physical space is discussed in details
Localization and mobility management in heterogeneous wireless networks with network-assistance
The nowadays heterogeneous wireless network (HWN) is a collection of ubiquitous wireless networking elements (WNEs) that support diverse functional capabilities and networking purposes. In such a heterogeneous networking environment, localization and mobility management will play a key role for the seamless support of emerging applications, such as social networking, massive multiplayer online gaming, device-todevice (D2D) communications, smart metering, first-responder communications, and unsupervised navigation of communication-aware robotic nodes. Since most of the existing wireless networking technologies enable the WNEs to assess their current radio status and directly (or indirectly) estimate their relative distance and angle with respect to other WNEs of the same Radio Access Technology (RAT), the integration of such information from the ubiquitous WNEs arises as a natural solution for robustly handling localization between (not necessarily homogeneous) WNEs and mobility management of moving WNEs governed by resource-constrained operation. Under the viewpoint of investigating how the utilization of such spatial information can be used to enhance the performance of localization and mobility management in the nowadays HWN, in this
work we focus and contribute in the following four research areas: i) localization and peer-discovery between non-homogeneous WNEs, ii) network-assisted D2D discovery in cellular networks, iii) energy-efficient handover (HO) decision in the macrocell – femtocell network, and iv) network-assisted vertical handover decision (VHO) for the integrated cellular and WLAN heterogeneous wireless network
On Improving Data Rates of Users in LTE HetNets
The proliferation of smartphones and tablets has led to huge demand for data
services over cellular networks. Cisco VNI mobile forecast (2014-2019) tells that although only 3.9% of mobile connections were Long Term Evolution (LTE) based they
accounted for 40% of the mobile traffic and this will rise to 51% by 2019, by which
the mobile data usage will grow 11 fold to over 15 Exabytes per month. Reports by
Cisco and Huawei tell that 70% of the traffic is generated in indoor environments
such as homes, enterprise buildings and hotspots. Hence, it is very important for
mobile operators to improve coverage and capacity of indoor environments. Indoor
data demand is partly met by intensifying the deployment of Macro Base Stations
(MBSs/eNodeBs) in LTE cellular networks. Owing to many obstacles in the communication path between MBS and users inside the building, radio signals attenuate at a
faster rate as the distance increases. Thus, Indoor User Equipments (IUEs) receive
still low signal strength ( i.e., Signal-to-Noise Ratio, SNR) compared to Outdoor
User Equipments (OUEs). To address this problem, one can deploy a large number
of Low Power Nodes (LPNs) a.k.a. small cells (e.g., Picos and Femtos) under an
umbrella MBS coverage and thereby form an LTE Heterogeneous Network (HetNet).
Small cells are mainly being deployed in homes, enterprise buildings and hotspots
like shopping malls and airports to improve indoor coverage and data rates. This is
a win-win situation as telecom operators also benefit by reduction in their CAPEX
and OPEX.
Though the deployment of Femtocells improves indoor data rates, the resulting
LTE HetNet may face a host of problems like co-tier and cross-tier interference (due
to frequency reuse one in LTE) and frequent handovers (due to short coverage areas of
Femtocells). Deployment of Femtos inside a building can lead to signal leakage at the
edges/corners of the buildings. This causes cross-tier interference and degrades the
performance of OUEs in High Interference Zone (HIZone) around the building area,
which are connected to one of the MBSs in the LTE HetNet. Arbitrary placement of
Femtos can lead to high co-channel cross-tier interference among Femtos and Macro
BSs and coverage holes inside buildings. If Femtos are placed without power control,
this leads to high power consumption and high inter-cell interference in large scale deployments. Our goal is to address these problems by developing efficient architecture,
Femto placement and power control schemes in LTE HetNets.
Random or unplanned placement of the Femtos leads to poor SNR and hence
affects achievable data rates of IUEs. Hence, placement of Femtos is important for
the cellular operators to perform planned deployment of minimum number of Femtos
with no coverage holes and guarantee a good signal quality with no co-tier interference. Once the placement of Femtos is done optimally in enterprise environments,
operators need to ensure that traffic load is evenly distributed among neighboring
Femtos for improving Quality of Service (QoS) of IUEs by efficiently utilizing the
network resources. In traditional cellular networks, the uplink access and downlink
access of UEs are coupled to the same (Femto) cell. Suppose a Femto is fully loaded
when compared to its neighboring Femtos, the traditional offloading or load balancing algorithms will try offloading some of the UEs for both their uplink and downlink
access from the loaded cell to one of less loaded neighboring cells (i.e., target cell)
provided that these UEs could get connected to the chosen target cell. This type of
offloading is a forced handover to reduce traffic imbalance and trigger for handover is
not based on better signal strength from the target cell. But, the offloaded UEs are
connected for both their uplink and downlink access to the same target cell. Since
UEs are most likely separated by walls and floors from their connected cells in enterprise environments, these offloaded UEs now have to transmit with higher transmit
power in the uplink and thereby affects their battery lives. In order to reduce the
battery drain for the offloaded UEs while maintaining their QoS, we employ the Decoupled Uplink and Downlink (DUD) access method in such a way that, the uplink
of UE is connected to the closest Femto while the downlink is connected to a less
loaded neighboring Femto.
To maximize the utilization of the limited operating spectrum and provide higher
data rate for IUEs, operators can configure Femtos in open access mode with frequency reuse one (i.e., all Femtos and MBSs operates on a same frequency) in LTE
HetNets. However, this leads to high co-tier interference and cross-tier interference.
Another problem in enterprise buildings having Femtos is frequent handovers, that
happens when IUEs move from one room/floor to another room/floor inside the
building. This leads to degradation of network performance in terms of increased
signaling overhead and low throughputs. In order to reduce this kind of unnecessary
handovers in enterprise buildings, Femtos should be placed optimally with handover
constraints. Hence, we obtain the optimal coordinates from the OptHO model by
adding handover constraints to the Minimize Number of Femtos (MinNF) model
which guarantees threshold Signal-to-Interference plus Noise Ratio (SINR) of -2 dB
for all IUEs inside the building. Such optimized deployment of Femtos reduces the
number of handovers while guaranteeing good SINR to all IUEs.
In LTE HetNets, even though planned deployment of Femtos in open access mode
boosts the IUEs performance, the power leakage from indoor Femtos create interferix
ence to the OUEs in the HIZone in the buildings surrounding areas. We propose
an efficient placement and power control SON (Self organizing Network) algorithm
which optimally places Femtos and dynamically adjusts the transmit power of Femtos
based on the occupancy of Macro connected OUEs in the HIZone. To do this, we
use the same MinNF model to place the Femtos optimally and solve Optimal Femto
Power (OptFP) allocation problem (Mixed Integer Linear Programming (MILP))
which guarantees threshold SINR of -4 dB for IUEs with the Macro users SINR
degradation as lesser than 2 dB. In the OptFP model, Femto’s transmit power is
tuned dynamically according to the occupancy of OUEs in the HIZone. But the
presence of even a single OUE in the HIZone decreases SINR of numerous IUEs,
which is not fair to IUEs. In order to address this issue, we propose two solutions
a) On improving SINR in LTE HetNets with D2D relays and b) A novel resource
allocation and power control mechanism for Hybrid Access Femtos in LTE HetNets,
which we describe in the following two paragraphs.
To guarantee certain minimum SINR and fairness to both IUEs and OUEs in
HIZone, we consider a system model by applying the concept of Device-to-Device
(D2D) communication wherein free/idle IUEs connected to Femto act like UE-relays
(i.e., UE-like BS, forwarding downlink data plane traffic for some of the HIZone
users connected to MBS). We formulate a Mixed-Integer Linear Programming (MILP)
optimization model which efficiently establishes D2D pairs between free/idle celledge IUEs and HIZone users by guaranteeing certain SINRT h for both IUEs and
HIZone users. As D2D MILP model takes more computation time, it is not usable
in real-world scenarios for establishing D2D pairs on the fly. Hence, we propose a
two-step D2D heuristic algorithm for establishing D2D pairs.
In above works, we assume that Femtos are configured in open access mode. But
Hybrid Access Femtocells (HAFs) are favored by the operators because they ensure
the paid Subscribed Group (SG) users certain QoS and then try to maximize the system capacity by serving near-by Non Subscribed Group (NSG) users in a best-effort
manner. To reap in the benefits of HAFs, the operators need to employ effective
resource sharing and scheduling mechanisms to contain co-tier and cross-tier interference arising out of reuse one in the HetNet system. Towards this, we address various
challenges in terms of deployment and operation of HAFs in indoor environments. We
propose an Optimal Placement of hybrid access Femtos (OPF) model which ensures
a certain SINRT h inside the building and a certain SINRT h in the HIZone of the
building. Unlike in previous optimization models, in this model, users in HIZone are
connected to HAF s deployed inside the building. Also we propose a decentralized
Dynamic Bandwidth Allocation (BWA) mechanism which divides the available HAF
bandwidth between the two sets of user groups: SG and NSG. In order to mitigate
co-tier and cross-tier interference, we then propose a dynamic Optimal Power Control
(OPC) mechanism which adjusts the transmit powers of HAFs whenever the users in
the HIZone cannot be served by the HAFs. In such a case, HIZone users connect
to an MBS instead. Since the OPC problem is hard to solve in polynomial time,
we also present a Sub-Optimal Power Control (SOPC) mechanism. To maintain fair
resource allocation between SG and NSG users, we propose an Enhanced Priority
(EP) scheduling mechanism which employs two schedulers which are based on the
Proportional Fair (PF) and the Priority Set (PS) scheduling mechanisms.
In above works, placement of Femtos is optimized to reduce co-channel co-tier
interference among neighboring Femtos and transmit power of Femtos is optimized
to reduce cross-tier interference between MBSs and Femtos. But, for arbitrary deployed Femtos, Inter Cell Interference Coordination (ICIC) techniques could be employed to address co-tier interference problem among Femtos which are connected with
each other over X2 interface. Hence, in this work, we propose an ICIC technique,
Variable Radius (VR) algorithm which dynamically increases or decreases the cell
edge/non-cell edge regions of Femtos and efficiently allocates radio resources among
cell edge/non-cell edge regions of Femtos so that the interference between neighboring Femtos can be avoided. We implement the proposed VR algorithm on top of PF
scheduler in NS-3 simulator and find that it significantly improves average network
throughput when compared to existing techniques in the literature
Recent Developments on Mobile Ad-Hoc Networks and Vehicular Ad-Hoc Networks
This book presents collective works published in the recent Special Issue (SI) entitled "Recent Developments on Mobile Ad-Hoc Networks and Vehicular Ad-Hoc Networks”. These works expose the readership to the latest solutions and techniques for MANETs and VANETs. They cover interesting topics such as power-aware optimization solutions for MANETs, data dissemination in VANETs, adaptive multi-hop broadcast schemes for VANETs, multi-metric routing protocols for VANETs, and incentive mechanisms to encourage the distribution of information in VANETs. The book demonstrates pioneering work in these fields, investigates novel solutions and methods, and discusses future trends in these field