SIMON NDAYA MAINA

SC212/1012/2019
SOFTWARE ENGINEERING
TITLE: AN INTERNET OF THINGS BASED WIFI RANGE EXTENDER WITH
RASPBERRY PI

CHAPTER 2
LITERATURE REVIEW
2.1 Introduction

Literature review- this is a comprehensive summary of previous research on a topic. It surveys

scholarly articles, books and other sources relevant to a particular area of research.

This chapter provides the literature review of articles, books and other sources of information
that is related to wi-fi range extenders tackling their advantages and disadvantages.
This chapter also justifies the use of the raspberry pi as an extender compared to other extenders.

2.1.1 Overview

Wi-Fi has been widely adopted in homes, offices, and public hot spots. One challenge that often
arises is the range of the network, because Wi-Fi operates under strict transmission power limits,
such that nodes on the edge of the network often get degraded or even interrupted service. This
problem can be alleviated to a degree by range extenders, which extend the range of the network
by capturing and rebroadcasting the packets .However, it is known that the range extenders may
reduce network speed because the node maybe close to the Access Point (AP) and can receive
from the AP directly such that rebroadcasting the packets is unnecessary. Next-generation Home
Wi-Fi networks have to step forward in terms of performance. New applications such as on-line
games, virtual reality or high quality video contents will further demand higher throughput
levels, as well as low latency. Beyond physical (PHY) and medium access control (MAC)
improvements, deploying multiple access points (APs) in a given area may significantly
contribute to achieve those performance goals by simply improving average coverage and data
rates. However, it opens a new challenge: to determine the best access points for each given
station (STA). This article studies the achievable performance gains of using secondary APs,
also called Extenders, in Home Wi-Fi networks in terms of throughput and delay. To do that, we
introduce a centralized, easily implementable channel load aware selection mechanism for Wi-Fi
networks that takes full advantage of( IEEE 802.11k/v )capabilities to collect data from STAs,
and distribute association decisions accordingly.
2.2 Existing wireless network models and protocols

2.2.1 Wireless Networks

Wireless Communication is a method of transmitting information from one point to other,
without using any connection like wires, cables or any physical medium. Generally, in a
communication system, information is transmitted from transmitter to receiver that are placed
over a limited distance.

A wireless network enables people to communicate and access applications and information
without wires. This provides freedom of movement and the ability to extend applications to
different parts of a building, city, or nearly anywhere in the world. Wireless networks allow
people to interact with e-mail or browse the Internet from a location that they prefer.

Wireless communication is the transfer of information between two or more points that do not
use an electrical conductor as a medium for the transfer. The most common wireless
technologies use radio waves. With radio waves, intended distances can be short, such as a few
meters for Bluetooth or as far as millions of kilometers for deep-space radio communications. It
encompasses various types of fixed, mobile, and portable applications, including two-way radios,
cellular telephones, personal digital assistants, and wireless networking. Other examples of
applications of radio wireless technology include GPS units, garage door openers, wireless
computer mouse, keyboards and headsets, headphones, radio receivers, satellite television,
broadcast television and cordless telephones

Wireless transmission dates back into the history of mankind. Even in ancient times, people used
primitive communication systems, which can be categorized as wireless. Examples are smoke
signals, flashing mirrors, flags, fires, etc. It is reported that the ancient Greeks utilized a
communication system comprising a collection of observation stations on hilltops, with each
station visible from its neighboring one. Upon receiving a message from a neighboring station,
the station personnel repeated the message in order to relay it to the next neighboring station.
Using this system messages were exchanged between pairs of stations far apart from one
another. Such systems were also employed by other civilizations. However, it is more logical to
assume that the origin of wireless networks, as we under- stand them today, starts with the first
radio transmission. This took place in 1895, a few years after another major breakthrough: the
invention of the telephone. In this year, Guglie Marconi demonstrated the first radio-based
wireless transmission between the Isle of Wight and a tugboat 18 years later. Marconi
successfully transmitted a radio signal across the Atlantic Ocean from Comwall to
Newfoundland and in 1902 the first bidirectional communication across the Atlantic Ocean was
established. Over the years that followed Marconi's pioneering activities, radio-based
transmission continued to evolve. The origins of radio-based 11 telephony date back to 1915.
When the first radio-based conversation established between ships. IEEE 802.11abgn
Types of wireless network protocols
2.2.2 Wireless Local Area Networks (WLANS) WLANS allow users in a local area, such as a
university campus or library, to form a network or gain access to the internet. A temporary
network can be formed by a small number of users without the need of an access point; given
that they do not need access to network resources. Wi-Fi is a WLAN technology used to connect
computers, tablets, smartphones and other devices to the internet. A Wi-Fi network is simply an
internet connection that's shared with multiple devices in home or business via a wireless router.
The router is connected directly to the internet modem and acts as a hub to broadcast the internet
signal to all your Wi-Fi enabled devices this gives the flexibility to stay connected to the internet
as long as it's in the network coverage area. ( IEEE 802.11k/v)

2.2.3 Wireless Personal Area Networks (WPANS) The two current technologies for wireless
personal area networks are Infra-Red (IR) and Bluetooth (IEEE 802.15). These will allow the
connectivity of personal devices within an area of about 30 feet. However, IR requires a direct
line of site and the range is less.

2.2.4Wireless Metropolitan Area Networks (WMANS) This technology allows the connection
of multiple networks in a metropolitan area such as different buildings in a city, which can be an
alternative or backup to laying copper or fiber cabling.

2.2.5 Wireless Wide Area Networks (WWANS) These types of networks can be maintained
over large areas, such as cities or countries, via multiple satellite systems or antenna sites looked
after by an ISP. These types of systems are referred to as 2G (2nd Generation) systems.

2.3 Existing wi-fi Extenders

2.3.1 L2 Relay Extender

This is a novel packet relay protocol for Wi-Fi networks that can improve the performance and
extend the range of the network. A device running L2Relay is referred to as a relayer, which
overhears the packet 13 transmissions and retransmits a packet on behalf of the Access Point
(AP) or the node if no ACK is overheard.

Advantage
One important feature of L2Relay is its ubiquitous compatibility, i.e., it is compatible with any
Wi-Fi devices, such that one or multiple relayers can be installed in any network easily without
any modification to the AP or the nodes .L2Relay is a layer-2 solution that exploits many layer 2
functional it is such as carrier sense. It encompasses unique solutions to link quality
measurement, rate adaptation, and relayer selection. We implement L2Relay in the Open FWWF
platform and compare it against the baseline network without a relayer as well as a popular
commercial Wi-Fi range extender. Our results show that L2Relay achieves overall better
performance than both compared schemes. IEEE 802.11

Disadvantage
These layer 2 devices typically operate only as bridges for the network and might not have an
IPv4 address on the network. Lacking a valid IPv4 source address they cannot relay packets
directly to DHCP server located on another network.

2.3.2 Channel load AP

In presence of multiple AP/Extenders, a new challenge appears: how to determine the best
AP/Extender for each given STA. According to the default Wi-Fi AP selection mechanism, an
STA that receives beacons from several AP/Extenders will initiate the association process with
the AP/Extender with the highest received signal strength indicator (RSSI) value. Though simple
and easy to implement, this mechanism omits any influence of traffic load and, consequently,
can lead to network congestion and low throughput in scenarios with a high number of STAs .
Many research activities have already widely tackled the APs election process in an area
commonly referred to as load balancing, whose goal is to distribute more efficiently STAs
among the available AP/Extenders in a WLAN. Although multiple effective strategies have been
proposed in the literature, most of them lack the prospect of real implementation, as they require
changes in the existing IEEE 802.11 standards and/or in STAs’ wireless cards.

Advantage
It provides home networks with higher capacity lower delay and higher reliability thus
expanding wi-fi.

Disadvantage
There are still many open challenges to properly design and implement real time load balancing
schemes among AP/ Extenders when considering STA and AP mobility and heterogeneity
including UL and DL traffic.

2.3.3 Full Duplex Relays

An existing Wi-Fi network is a common solution when wireless coverage extension is required
in the absence of a connection to the backbone network. Halfduplex (HD) Wi-Fi relays employ
two different frequencies, time slots, or orthogonal spreading codes to prevent the transmitted
signal from interfering with its own receiver. In contrast full-duplex relays (FDR) utilize wireless
resources more efficiently by transmitting and receiving simultaneously on the same frequency
band, creating the potential of doubling the system throughput, when compared to their Half
Duplex (HD) counter parts. Although FDR has higher transmission efficiency, it suffers from
Self Interference (SI) since the transmitted signal by the FDR is received as an in-band blocker
by its own receiver. The SI signal results in system instability, and poor signal to interference
plus noise ratio (SINR) of the signal that is intended to be relayed. In order to use a FDR for
higher efficiency, SI must be coherently cancelled in order to provide stability and a satisfactory
level of SINR of the received signal, before amplifying and forwarding it. To achieve sufficient
SI suppression FDR relies on cancellation across multiple domains (spatial, analog and digital
cancellation. IEEE 802.16, and WIMAX

Advantages

i. Throughput gain: As compared to the HD mode, the FD mode nearly doubles the
throughput of a single-hop wireless link in the physical layer.
 ii. Collision avoidance: In the traditional carrier Sense multiple access with collision
avoidance (CSMA/CA) protocol, each HD node is required to check the channel’s quality
before using it.

Disadvantage
i. Performance constrained by SI: In an FD device, the RA’s input signal of interest is
usually several orders of magnitude lower in power than the received SI signal imposed
by the device’s TA output. Hence, the interference imposed by the TA upon the RA will
consequently drown out the weak input signal and degrade the FD gains.
ii. Degraded link reliability: The FD mode suffers from a reduced link reliability, regardless
of the SNR. a state-of-the-art of the-shelf radio is capable of achieving 88% of the link
reliability2 compared to its HD mode counterpart. Furthermore, without invoking digital
interference cancellation, an even lower reliability of say 67% may be attainable for the
FD mode.
iii. Suffers from higher PLR: As compared to the HD devices, an FD node has to process
twice the number of packets due to its simultaneous transmission and reception, thus
leading to a higher PLR than the HD mode.
iv. A higher buffer size requirement: To reduce the PLR of the FD mode, a sufficiently large
buffer is required for enabling the packets to be forwarded (that would otherwise have
been discarded due to queue overflow). Since the effects of packet-loss level are more
severe in the FD mode, a larger buffer size is required than for the HD mode.

2.4 Development tools

2.4.1 Raspberry Pi
Raspberry Pi is a series of small, single-board computers developed to teach computer science
basics to school students and other people in low-income countries. It became a popular and easy
to experiment tool to develop school projects, hardware programming, robotics, basic automated
machines, circuits, etc. The Uses of Raspberry Pi is a small, quite affordable, and very much
capable hardware device called a credit card size computer. A Raspberry Pi has the following
types
 Raspberry Pi 1 model B
 Raspberry Pi 1 model A
 Raspberry Pi 1 model B+
 Raspberry Pi 1model A+ 19
 Raspberry Pi Zero
 Raspberry Pi 2
 Raspberry Pi 3 model B
 Raspberry Pi Zero W 2.6.1
Raspberry Pi 3 Model B
2.4.1 Advantages of Raspberry pi
i. The Raspberry Pi3 B is a single-board computer that can connect to a TV and keyboard.
It has Wi-Fi and Bluetooth connectivity.
ii. It boots from the micro-SD card and runs on Linux OS or Windows 10 IoT. It boots
from the micro-SD card and runs on Linux OS or Windows 10 IoT.
 iii. It is supplied without housing, power supply, keyboard, screen and mouse in order to
reduce the cost and promote the use of recovery equipment.
iv. Version 3 is based on a quad-core 64-bit ARM Cortex-A53 processor at 1.2 GHz (about
10x faster than the Pi1 and 50% more capable than the Pi2 model) and has 1 GB of RAM
memory. The Raspberry Pi3 B model has Wi-Fi and Bluetooth connectivity, has 4 USB
ports, a micro-SD port, a 40-pin I/O connector and an HDMI port.
v. Version 3 is physically identical to the Pi 2 version making it compatible with the cases
and other accessories of the Pi 2 version.
vi. This board is based on an ARM processor and allows the running of the
GNU/Linux/Windows 10 IoT operating system and compatible software.
vii. The Raspberry Pi can perform tasks from a desktop PC (spreadsheets, word processing,
games). It can also stream videos in high definition thanks to its Broadcom Video core IV
circuit (allows the decoding of full HD Blu-ray streams).
The Raspberry Pi requires an SD card with an OS, a power supply, a USB keyboard, a USB
mouse, a case and cables. To prepare a bootable SD card, you need to have a PC with a card
reader.
2.4.2 Disadvantages of a Raspberry Pi
i. Because of its processor, it cannot run X86 operating systems. Some common ones like
Windows and Linux distros are not compatible.
ii. Some applications which require high demands on CPU processing are off-limits. An
example “Model B took 107 ms to complete one calculation of the purely synthetic prime
number test; a mid-range desktop Core 2 Duo E8400 took only 0.85ms.” (Collins, 2012)
iii. Users must not use normal computer standards to judge Raspberry Pi. It can work as a
personal computer, but cannot replace it.
2.4.3Characteristics of the Raspberry Pi 3
 Power supply to be provided: 5 V dc/max 2.5 A* via micro-USB socket (* maximum current
if all functions are used).
 CPU: Quad-core ARM Cortex-A53 1.2 GHz (Broadcom BCM2837)
 GPU: Dual Core Video Core IV Multimedia Co-Processor
 Wi-Fi: 2.4GHz, 802.11n (Broadcom BCM43438)
 Bluetooth: 4.1 (Broadcom BCM43438)
 Memory: 1 GB LPDDR2 ( 1024 MB )
 USB: 4 USB 2.0 ports
 Ethernet: 10/100 base T Ethernet port: RJ45
 Bus: SPI, I2C, series
 Card holder: micro-SD
 Audio outputs: HDMI and 3.5mm jack
 Video outputs: HDMI
 Support for distributions: dedicated based on Linux and Windows 10
 Dimensions: 88 x 58 mm
2.5 Conclusion
The raspberry pi wi-fi extender is a reliable model to be used since it’s a low cost and a high-
power device. Since it’s a microprocessor based mini (SBC).It has all features of a computer and
it comes with a fully functional raspberry pi OS and can also use other OS like Linux. It can be
able to perform multiple tasks simultaneously. Therefore it is the most suitable to use in this
project as a wi-fi range extender.