Wireless communication

2.1Introduction
The term wireless communication was introduced in the 19th century and wireless
communication technology has developed over the subsequent years. It is one of the most
important mediums of transmission of information from one device to other devices. In this
technology, the information can be transmitted through the air without requiring any cable or
wires, or other electronic conductors, by using electromagnetic waves like IR, RF, satellite,
etc. In the present day, wireless communication technology refers to a variety of wireless
communication devices and technologies ranging from smartphones to computers, tabs,
laptops, Bluetooth Technology, and printers [9].

2.2Types of wireless communication

In the present day, the wireless communication system has become an essential part of
various types of wireless communication devices, that permits the user to communicate even
from remote operated areas. There are different types of wireless communication devices like
mobiles. Cordless telephones, Zigbee wireless technology, GPS, Wi-Fi, satellite television,
and wireless computer parts. Current wireless phones include 3 and 4G networks, Bluetooth,
and Wi-Fi technologies.

Figure 2.1: Types of Wireless Communication

communication modes
 The simple wireless communication system is one-way communication. In this type,
communication can be done in one direction.
 The half Duplex communication system is two-way communication, however, it is
not simultaneous. The best example of this type of communication is walkie–talkie.
 The full Duplex communication system is also two-way communication & it is
simultaneous. The best example of this communication system is the mobile phone. In
wireless communication, the devices which are used for communication may change
from one service to others because these are available in different shape, size & data
throughput. The region enclosed through this type of communication system is an
essential factor.
 Figure 2.2 : communication modes

2.2.1 Satellite Communication

Satellite communication is one type of self-contained wireless communication technology, it
is widely spread all over the world to allow users to stay connected almost anywhere on the
earth. When the signal (a beam of modulated microwave) is sent near the satellite then, the
satellite amplifies the signal and sent it back to the antenna receiver which is located on the
surface of the earth. Satellite communication contains two main components like the space
segment and the ground segment. The ground segment consists of fixed or mobile
transmission, reception, and ancillary equipment and the space segment, which mainly is the
satellite itself. [10].

Figure 2.3:
satellite communication

2.2.2 Infrared Communication

Infrared wireless communication communicates information in a device or system through IR
radiation. IR is electromagnetic energy at a wavelength that is longer than that of red light. It
is used for security control, TV remote control, and short-range communications. In the
electromagnetic spectrum, IR radiation lies between microwaves and visible light. So, they
can be used as a source of communication.

Figure 2.4: the electromagnetic spectrum

For successful infrared communication, a photo LED transmitter and a photodiode receptor
are required. The LED transmitter transmits the IR signal in the form of nonvisible light, that
is captured and saved by the photoreceptor. So the information between the source and the
target is transferred in this way. The source and destination can be mobile phones, TVs,
security systems, laptops, etc support wireless communication.

Figure
2.5:infrared wireless communication

2.2.3Broadcast Radio
The first wireless communication technology is open radio communication to seek out
widespread use, and it still serves a purpose nowadays. Handy multichannel radios permit a
user to speak over short distances, whereas citizen’s band and maritime radios offer
communication services for sailors. Ham radio enthusiasts share data and function emergency
communication aids throughout disasters with their powerful broadcasting gear, and can
even communicate digital information over the radio frequency spectrum.
 Figure 2.6:Broadcast radio
Mostly an audio broadcasting service, radio broadcasts sound through the air as radio waves.
The radio uses a transmitter that is used to transmit the data in the form of radio waves to a
receiving antenna. Radio waves are electromagnetic signals, that are transmitted by an
antenna. These waves have completely different frequency segments, and you will be ready
to obtain an audio signal by changing into a frequency segment.

2.2.4Microwave Communication
Microwave wireless communication is an effective type of communication, mainly this
transmission uses radio waves, and the wavelengths of radio waves are measured in
centimeters. In this communication, the data or information can be transferred using two
methods. One is the satellite method and another one is a terrestrial method.

Figure 2.7: microwaves communication

Terrestrial Microwave Transmission System (TMTS)

In these systems, the signals are extremely concentrated and the physical route must be a
line of sight. The signals in these systems are extended with the help of Relay towers.
Terrestrial Microwave Systems need directional parabolic antennas to broadcast and
receive signals in the lower gigahertz range.
Satellite Microwave Transmission System (SMTS)
Satellite Microwave Transmission System uses satellites for broadcasting and receiving of
signals. These systems need satellites which are in the geostationary orbit which is 36000
km above the earth. The satellites operate as repeaters with receiving antenna, transponder
and transmitting of signals [16].

2.3 evolution of wireless communication

Mobile wireless communication system has gone through several evolution stages in past few
decades. This innovation includes a many number of generations and still research going on.
The voyage of wireless network began with 0G, 1G in early 1960s&1980s and followed by
2G, 3G, 4G and upcoming generation 5G [18].
This section provides an overview of the evolution of mobile generations by comparing the
standards, data rates, capacity, challenges, and features generation to the next one

2.3.1 first generation (1G)

The first generation is the wireless telephone technology. It was the analog
telecommunication standard which was introduced in the 1980s and continued till the
invention of 2G technology. The antecedent of 1G technology was mobile radio telephones or
0G. This technology was used in the first wireless mobile phone handsets. When the mobile
phone began to rise in popularity with general public, it replaced 0G network. 1G technology
was first used in Japan and spread quickly to the whole world. 1G technology used the analog
radio signal. Through this network the voice call gets modulated to a higher frequency of
about 150MHz. This was done with the help of Frequency Division Multiple Access
(FDMA). The 1G mobile phones used a single universal network standard which is known as
Advance Mobile Phone System (AMPS). The cell phone networks were intended for the
industrial, military& research application. They used a series of dissimilar network with very
small broadcast areas; the idea of the universal network that started with 1G persists in
today’s worldwide digital network.[17]

- Frequency Division Multiple Access (FDMA)

Frequency division multiple access (FDMA) was employed in the first generation wireless
technology, it assigns individual channels to individual users. It can be seen from Figure 2.8
that each user is allocated a unique frequency band or channel. These channels are assigned
on demand to users who request service. During the period of the call, no other user can share
the same channel The features of FDMA are as follows:

Figure 2.8:FDMA scheme

 The FDMA channel carries only one phone circuit at a time.
 If an FDMA channel is not in use, then it sits idle and cannot be used by other users to
increase or share capacity. It is essentially a wasted resource[19].

2.3.2 SECOND GENERATION (2G)

2G technology means second-generation wireless telephone technology. It was based on the
technology known as the global system for mobile communication which is also called as
GSM. This technology allowed various networks of services likely text messages, picture
messages and MMS (Multi Media messages). The second generation was launched in Finland
in the year 1991. All phone conversations were digitally encrypted.GSM has enabled the
users to utilize the short massage services (SMS) at anywhere and anytime. SMS is a cheap
and easy way to sand a massage to anyone rather than voice call or conference. 2G
technologies were either time division multiple access (TDMA) or code division multiple
access (CDMA). TDMA allows for the division of signal into time slots. CDMA allocates
each user the special code to communicate over a multiplex physical channel. 2G technology
offers improved privacy that was not possible with earlier technologies. 2G technology
introduces the digital data services such as SMS and E-Mail that has allowed the world to
come closer[19].

- time division multiple access (TDMA)

Time Division Multiple Access (TDMA) is a digital modulation technique used in
digital cellular telephone and mobile radio communication . TDMA enables multiple
users to share the same frequency by dividing each cellular channel into different time
slots. In effect, a single frequency supports multiple and simultaneous data
channels[20].

- Code Division Multiple Access (CDMA)

In code division multiple access (CDMA) systems, the narrowband message signal is
multiplied by a very large bandwidth signal called the spreading signal. The spreading
signal is a pseudo-noise code sequence that has a chip rate which is orders of
magnitudes greater than the data rate of the message. All users in a CDMA system, as
seen from , use the same carrier frequency and may transmit simultaneously. Each
user has its own pseudorandom codeword which is approximately orthogonal to all
other codewords. The receiver performs a time correlation operation to detect only the
specific desired codeword. All other codewords appear as noise due to de-correlation.
For detection of the message signal, the receiver needs to know the codeword used by
the transmitter. Each user operates independently with no knowledge of the other
users[19].
 Figure (2.9):TDMA and CDMA schemes

2.3.3 THIRD GENERATION (3G)

Third generation wireless technology is the advanced wireless technology. This technology is
wildly used in mobile phones and data cards. 3G describes updating cellular
telecommunications network around the world to use 3G technologies. Japan was the first
country to commercially launch 3G in 2001. The transition to 3G was completed during
2005-2006 in Japan. In 2005, there were 23 networks worldwide that operating 3G
technology. Some are only for test use and some operators are providing services to
consumers. International Telecommunication Union (ITU) has defined the demand for 3G in
the International Mobile Telecommunication (IMT)-2000 to facilitate growth, increase
bandwidth, support diverse applications. The family of this technology includes 3.5G and
3.75G.[23]

2.3.4 FOURTH GENERATION (4G)

4G wireless systems are a packet-switched wireless system with wide area coverage and high
throughput. It is designed to be cost-effective and to provide high spectral efficiency. The 4G
wireless use the technique of Orthogonal Frequency Division Multiple Access (OFDM),
Ultra Wide Radio Band (UWB) and millimeter wireless. Data rates of 20Mbps are employed.

- OFDMA (Orthogonal Frequency Multiple Access)

OFDMA is the multi-user variant of the OFDM scheme where multiple access is achieved by
assigning subsets of time-frequency resources to different users, allowing simultaneous data
transmission from several users. In OFDMA, the radio resources are 2D regions over time (an
integer number of OFDM symbols) and frequency (a number of contiguous or non-
contiguous subcarriers). Similar to OFDM, OFDMA employs multiple closely spaced
subcarriers that are divided into groups of subcarriers where each group is called a resource
block. The grouping of subcarriers into groups of resource blocks is referred to as sub-
channelization. The subcarriers that form a resource block do not need to be physically
adjacent. In the downlink, a resource block may be allocated to different users. In the uplink,
a user may be assigned to one or more resource blocks. Sub-channelization defines
subchannels that can be allocated to mobile stations depending on their channel conditions
and service[24].

Figure 2.10:OFDM vs OFDMA scheme

2.3.5 FIFTH GENERATION (5G)

5G is the 5th generation mobile network. It is a new global wireless standard after 1G, 2G,
3G, and 4G networks. 5G enables a new kind of network that is designed to connect virtually
everyone and everything together including machines, objects, and devices.
5G wireless technology is meant to deliver higher multi-Gbps peak data speeds, ultra low
latency, more reliability, massive network capacity, increased availability, and a more
uniform user experience to more users. Higher performance and improved efficiency
empower new user experiences and connects new industries[25].

Fifth-generation of wireless cellular systems has the potential to increase capacity, spectral
efficiency, and fairness among users. The Non-Orthogonal Multiple Access based wireless
networks (NOMA) is the next generation multiplexing technique. NOMA breaks the
orthogonality of traditional multiple access to allow multiple users to share the same radio
resource simultaneously. The main challenge in designing NOMA is the selection of the
resource allocation algorithms since user pairing and power allocation are coupled[26].

2.4 Non-orthogonal multiple access (NOMA)

Non-orthogonal multiple access (NOMA) is one of the most promising radio access
techniques in next-generation wireless communications. Compared to orthogonal frequency
division multiple access (OFDMA), which is the current standard orthogonal multiple access
(OMA) technique, NOMA offers a set of desirable potential benefits, such as enhanced
spectrum efficiency, and reduced latency with high reliability, and massive connectivity. The
baseline idea of NOMA is to serve multiple users using the same resource in terms of time,
frequency, and space. The available NOMA techniques can broadly be divided into two
major categories, i.e., power-domain NOMA and code-domain NOMA. Code-domain
NOMA can further be classified into several multiple access techniques that rely on low-
density spreading and sparse code multiple access. Other closely related multiple access
schemes in this context are lattice-partition multiple access, multi-user shared access, and
pattern-division multiple access[28].

Figure 2.11: difference between OMA & NOMA scheme.

2.5.1 Power domain (NOMA)

The main concept of power domain NOMA is multiple users are multiplexed in the power-
domain at the transmitter side and multi-user signal separation is conducted at the receiver
side From an information-theoretic perspective, it is well-known that non-orthogonal user
multiplexing using superposition coding at the transmitter and successive interference
cancellation (SIC) at the receiver not only outperforms orthogonal multiplexing, but also is
optimal in the sense of achieving the capacity region of the downlink , different users are
allocated different power coefficients according to their channel conditions in order to
achieve a high system performance, this means signal power levels for users are allocated
depending on their distance, more power is allocated to user that is farthest from BS and
least power is allocated to the nearest user from BS.

Figure 2.12: main concept of NOMA

2.5.3Superposition coding(SC)
SC is a technique of simultaneously communicating information to several receivers by a single
source. In other words, it allows the transmitter to transmit multiple users’ information at the same
time. NOMA uses SC at the transmitter side, that superimposes the signals or users in one complex
signal and then transmits this signal from BS figure 2.13 shows how the transmitter composes the
user’s data into one signal so it is ready for transmission.

Figure 2.13: superposition coding technique

The transmitted signal can be expressed as :
M
S= ∑ √ a m p x m (2.1)
m=1

where am is the power allocation coefficient of user m, x m is the modulated signal of user m,
M is the number of users and p is the total power.

2.5.4 successive interference cancellation (SIC)

In order to decode the user m message from the superimposed signal s, the SIC scheme is regarded as
a rudimental approach. The basic structure of SIC is presented in Figure (3.2). The key operating
principle of SIC relies on exploiting the power differences among users participating in SC The
working principle of SIC can be explained as follows SIC is an iterative algorithm where data is
decoded in the order of decreasing power levels. That is, data corresponding to the user who is
given the highest power is decoded first, then the data of the user who is given the next highest
power is decoded. This process repeats till we have decoded all user's data.

Figure 2.14:principle of SIC