An Overview

The assignment content discusses encoding techniques used in data transmission. The first part of the content explains the limitations of delta modulation and the required condition for avoiding slope overload. It also introduces the concept of orthogonal frequency division multiplexing (OFDM) as a recent technique for encoding used in various applications such as audio and television broadcasting, wireless networks, and power line networks. The second part discusses multiplexing, which is a technique for combining multiple digital and analog signals into a single signal. The content also highlights the importance of encoding frequency modulation to improve cochlear implant performance.

ADVANCED NETWORKING
Encoding Techniques
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Abstract—This paper discusses and critically analyzes
techniques for data encoding. The paper reviews the concept of
data and signal transmission over networks through encoding.
Encoding can be achieved through two level or three level
methods. Signals are transmitted using a continuous signal that
varies in phase, amplitude, or other property in direct proportion
to that of a variable. Encoding can be analog to analog (AM, FM,
PSM), digital to digital (NRZ, NRZI, ME), analog to analog, and
digital to digital (ASK FSK PSK QAM). Some of the significant
recent developments include Orthogonal frequency division
multiplexing and Multiplexing
Keywords—discusses; critical analysis; encoding; techniques;
I. INTRODUCTION
Communication in networks requires at least two parties;
the sender and recipient, along with the medium for
transmission and the message/ data to be transmitted. All
communications start with the sender, who must figure out
how to encode the data/ information to be sent, so as to convey
meaning. Encoding refers to the process of putting a character
sequence, such as numbers, symbols, and letters into a special
format to enable efficient transmission and in some cases,
storage. The encoded information is then decoded at the
recipient end where the encoded information is encoded
(converted) back into the original character sequence. The
encoding aims at producing a signal from the encoded data
stream to be transmitted over a specific medium; the encoding
must take into consideration the medium for transmission.
Encoding is the process of using a code to convert original
information/ data into a form usable by an external process.
The process of encoding defines the way that signals are
represented on a given (physical) line of communication;
hence, there is a need to have a format that is standard for
seamless communication [1]. The encoded signal is
manipulated in such a way that the sender and the recipient can
recognize the changes (encoding) made. Information to be sent
over a network can be analog (such as voice and video data) or
digital.
II. LITERATURE REVIEW
Networks have become more complex and highly
interconnected; for instance, the World Wide Web is among
the biggest network of interconnected computers and servers.
Copious volumes of data are exchanged at any given time
within networks, hence the need for encoding. Further, new
transmission models, such as fiber optic have been developed,
requiring a standardized method of transmitting information
over different mediums until they reach their destination in a
desirable format [2]. To ensure transmission is optimized, a
signal has to be encoded to facilitate transmission over a
physical medium that can be a copper cable, a network cable,
or a fiber cable; wireless mediums also necessitate encoding.
Encoding is essential in keeping the lines balanced even if the
data keeps changing its state often enough and to make it
distinguishable from a line that is dead. For instance, if the data
stream has uneven 1s and 0s, an unbalanced offset voltage will
be developed by the receiver. Encoding also ensures that long
1s or 0s strings are eliminated and that over time, the total
number of 1s and 0s remains balanced all the time. Further,
signals cannot be sent just in the forms of 0s or 1s; the signals
have to be encoded into signals having two states, such as;
 The absence or presence of current in a wire
 Two different voltage levels relative to the earth
 Difference in voltage between two mediums
(wires)
 The absence or presence of light
There are two main ways in which encoding can be
achieved; two level encoding and three level encoding. In two-
level encoding, the signal is encoded in such a way that it can
only take on a value that is either strictly positive (+x) or
strictly negative (-x), where x is a value of the physical
quantity that is being used to transport signals (the physical
medium). In three level encoding, the signal can take on a
value that is strictly positive (+x), strictly negative (-x), or null
(0). There are various methods for signal encoding, as
discussed in the next section [3].
III. CRITICAL ANALYSIS OF ENCODING
The network uses standard protocols for the transmission
and delivery of data over a distance, with the network designed
in layers, each performing a specific function. The standard
network has various layers including the physical layer (layer
1), the data link layer (layer 2), and the presentation layer
(layer 3). The Transmission of data is based on the TCP
(Transmission Control Protocol) and it is found in layer one
(physical layer), where cannel coding takes place. Data

transmission refers to the transfer of data over a point to
another point or multipoint communication channels. The
channels used for transmissions include optical fiber, copper
wires, computer buses, wireless communication channels, and
storage media. The data being transmitted is presented in the
form of electromagnetic signals, for example radio waves,
microwaves, infrared signals, or electrical voltages. There are
various kinds of data transmission, including analog
transmission where data, voice, image, video information or
signals are transmitted using a continuous signal that varies in
phase, amplitude, or other property in direct proportion to that
of a variable [2]. The messages are represented by a set of
limited continuous varying wave forms (a process termed pass
band transmission) through digital modulation, or by a pulse
sequence using a line code (a method termed baseband
transmission). Modem equipment undertakes the process of
passband modulation and its corresponding demodulation. The
bit streams represented by both passband and baseband
transmission are both considered digital transmission. The
transmitted data can be an analog source, such as from video or
phone call digitized into bit stream signals or digital such as
from a keyboard. Before being transmitted over networks,
information/ data must be encoded before being transported
across a given media such as copper or fiber optic. This implies
that the current or voltage waveform pattern used for
representing 1s and 0s are encoded by adjusting them. There
are various ways in which encoding of signals for transmission
over networks can be achieved;
 Analog to digital
 Digital to analog
 Analog to analog
 Digital to digital [4]
The chosen mechanism for encoding depends largely
on the technology available at a given time and the application
needs.
IV. ANALOG TO ANALOG ENCODING
This is one of the oldest methods for encoding and entails
converting analog data into digital signals and was (is)
employed in telephony to transmit voice data over telephone
(copper) lines. Analog data is represented in their baseband as
analog frequencies. For instance, when using a telephone,
there are two ways in which the data is sent; the analog voice
signal is transmitted at the baseband signal. Alternatively, the
data can be transmitted by combining the signals into another
signal which acts as the carrier and the combined signals
transmitted at a different frequency. When the pitch of a signal
wave is modified, its termed frequency modulation; modifying
a wave’s strength is termed amplitude modulation, while
modifying its (wave) natural flow is termed phase modulation
[4]
A. Amplitude Modulation
AM works by having the data/ message encoded in the
amplitude of a signal pulse series; the amplitudes of carrier
pulses train are varied based on the sample value of the data/
message signal. The bulk of carrier signals and and a waveform
in the baseband with the lower sideband being slightly lower
than the frequency of the carrier while the upper side band is
slightly higher [5]. AM can is expressed as;
s(t) = [1+na x(t)] cos 2 πfc t
The resulting signal envelope is 1+na x (t)
As long as na <1, the envelope becomes the original
signal’s exact reproduction. If na >= 1, the standard AM
modulator will fail since as the wave envelop negative
excursions cannot fall below zero; therefore, the received
modulation becomes distorted. Because of its nature, the author
feels it’s more suited for wide area applications but unsuitable
for situations where quality is required as it has levels of noise.
Further, it’s unsuitable for data or multimedia because of a
limited bandwidth and has a weaker signal
B. Frequency modulation (FM)
Is an analog data encoding method in which data is
encoded into an alternating current (AC) wave through
changing the waves instantaneous frequency and can be
used for encoding either digital or analog data. In digital
FM, the data is in the form of 0s and 1s, and there are
abrupt signal changes of the carrier frequency. The number
of carrier frequencies is represented in powers of two (2),
corresponding with the ON/OFF frequency states. Analog
FM has a continuous/ smooth AC carrier wave that can be
represented as a sine wave [6]. If the baseband signal is x m
(t) and the sinusoidal carrier wave is
Xc (t) = Ac cos (2 π fc t)
Where fc is the base frequency of the carrier and
Ac is its amplitude the modulator combines the
baseband data signal with the carrier to obtain the
transmitted signal;
The author feels FM is suitable for data transfers over short
distances due to a larger bandwidth, low noise, is more

efficient as it requires less amplification during transmission
and compression (photo-acoustic) can be applied to it.
However, it requires complicated demodulators due to the need
for amplitude limiter.
C. Phase Shift Modulation (PSM)
This involves conveying digital signals by shifting phases;
this technique is basically used for satellite communication and
digital signaling. The phase numbers used in representing the
information being transmitted can significantly impact the
amount of transmitted information. When more than two
phases are used, it is termed multi-level signaling [7]. This, on
further evaluation, is an easier encoding method compared to
FM and more information such as Doppler can be obtained
with PSM. However, extending its modulation beyond 180
degrees results in phase ambiguity and it requires frequency
multipliers, limiting its application for modern data transfer
needs
V. DIGITAL TO DIGITAL ENCODING
This is a method of encoding that is at present, commonly
used in transmitting data over digital facilities, such as
computer data over networks. This model uses less complex
equipment as well as being less expensive, compared to
methods such as digital to analog. Digital signals are discrete
sequences of discontinuous voltage pulses with every pulse
having a signal element. It entails encoding binary data bit into
signal elements in order to transmit data. The encoding scheme
entails mapping signal elements from data bits; a mark is the
binary digit 1 while the binary digit 0 signifies a space. The
common techniques used in digital to digital encoding include
NRZ (no return to zero) encoding, NRZI (no return to zero
inverted) encoding, Bipolar AMI (alternate mark inversion),
and Manchester Encoding.
A. NRZ Encoding
This is among the simplest and earliest used encoding
systems for digital to digital encoding; it entails transforming
the 1s into -X and the 0s into +X resulting into a bipolar
encoding where the signal can never be null. As a consequence,
the recipient of the message/ data can determine easily whether
there is a signal present or not. NRZ is often used in slow speed
type of communications interfaces for asynchronous and
synchronous data transmissions [13]. I think this technique
makes synchronization difficult and causes higher power losses
for transmitted DC power and adds costs to transmission as the
lines must be DC coupled. Further, it’s difficult to achieve
clock recovery from signals and errors may be introduced over
long distances
B. NRZI Encoding
This type of digital to digital encoding entails the signal
changing state after ticking of the clock when the bit value is 1.
When value of the bit is 0, there is no change in state of the
signal value. This type of encoding is advantageous because it
enables detecting whether there is a signal or not and the
transmission current is low voltage, albeit with the problem of
continuous current during sequences of 0s [8]. This method is
suitable for data transmissions over long distances because
many transitions can be introduced to enable clock recovery
from the signal and so limit errors; a clear advantage over
NZR.
C. Manchester Encoding (ME)
This is a digital to digital encoding where transitions from
one logical state to another state represents data bits and each
data bit length is set by default. It entails an exclusive
performance of the OR (XOR) of a signal with the clock signal
that results into a raising edge when the value of the bit is 0 and
a falling edge in the opposite case. The direction of the
transition determines the state of a bit. Data encoded using
Manchester Encoding contains frequent transition levels that
allow the extraction of the clock signal by the receiver using
the DPLL (digital phase locked loop) [8]. Manchester encoding
works based on the rules shown below;
TABLE I.
Original data Sent value
Logic 1 1 to 0; downward transition
at the bit center

Logic 0 0 to 1; transition at the bit
center
VI. DIGITAL TO ANALOG ENCODING
There are various types of digital data to analog signal data
encoding for data transmission. Digital to analog encoding
works on the principle of shift keying using the following
techniques;
 ASK- Amplitude Shift keying
 FSK- Frequency Shift keying
 PSK- Phase Shift keying
 QAM-Quadrature Amplitude modulation [10]
A. Amplitude Shift Keying
This equates the digital to analog encoding of AM
(amplitude modulation) in which digital data is represented as
variations in the carrier wave amplitude. With ASK, the 1
(binary symbol) representation is attained by transmitting a
carrier wave with a fixed amplitude and fixed frequency for T
seconds of bit duration period. If the signal has a value of 1, the
carrier signal is transmitted; however, if the value of the signal
is 0, then a 0 value signal is transmitted. Digital data
transmission over optical fiber is achieved using the ASK
technique. In LED transmission, a short light pulse represents
the binary 1 with the absence of light represented by the binary
0. in Laser transmission, there is a fixed bias current that results
in the device emitting light at low levels; the low level light
represents the binary 0 while binary 1 is represented by higher
amplitude light [10].
Where
ht(f) = transmission carrier signal
hc(f)= channel impulse response
n(t) = channel introduced noise
hr(f) = the receiver filter
L = level numbers used in transmission
Ts = Time taken between two symbols generation
When data is coming out of a transmitter, the signal s(t) is
expressed using the relation;
s(t) = v[n] . ht (t- nTs)
After filtering in the receiver, the hr (t), the signal is
expressed as
z(t) = nr(t) + . gt (t- nTs) [11]
I think it is useful for digital data transmission over optical
fibers due to high bandwidth efficiency and the modulation-
demodulation processes are inexpensive along with simple
receiver design. This means it can be efficiently applied to
networks such as large data-centers and WANs. Frequency
Shift Keying (FSK)
In FSK, only the frequency changes with the phase and
amplitude remaining unchanged. In this modulation scheme,
the digital data is transmitted via discrete changes in frequency
of the carrier signal. FSK is used in applications such as remote
metering and in caller ID in telephone lines. FSK helps solve
the line noise challenges posed by ASK since the receiver is
tuned to a specific frequency. FSK needs two carrier signals,
the lower frequency for the binary 0s and the higher frequency
one for the 1s binary signals. FSK is used for encoding in
applications such as modems, to a maximum frequency of
1200 bps; it works by making guard bands whose role is to
avoid overlap in signals [11]. Using low power micro
controllers, the binary FSK signal can be demodulated fast and
efficiently using the Goertzel algorithm which has two stages;
the first to compute the intermediate sequence y[n];
s[n] = x[n] + 2 cos (w0)s [n-1] – s [n-2]
and the second stage that applies the filter s[n] to generate
the output sequence y[n];
y[n] = s[n] – e -jwo s [n-1]
The image below depicts FSK operation ;
B. Phase Shift Keying (FSK)
Digital to analog encoding works by converting data using
modulation, by changing the reference signal phase (carrier
wave). The cosine and sine inputs are varied at precise times to
attain modulation. Binary bit 0 has a phase shift of 0, but the
binary bit 1 has a phase shift of 180. The wave shift in signals
is achieved through delaying the signal while retaining its

frequency and/ or amplitude. The modified signal is assigned a
given binary value, such as 1, while the carrier signal that
remains unchanged has the binary value 0. A finite number of
well-defined signals are used to represent data [11]. The two
binary phases are represented by 0 and 180 degrees and the
resulting one bit time transmitted signal is given by the
equation. Its characteristics make it highly suitable in modern
data transfer needs such as RFID, Bluetooth, and WLANs
(wireless local area networks); the diagram shows the process;
C. Quadrature Amplitude Modulation (QAM)
This is a method of encoding that can be used to either
decrease or increase the amounts of data sent without the need
for increasing bandwidth. QAM operates by combining PSK
and ASK to give maximum contrast between tri-bits, di-bits,
and quad bits. The recommended QAM is the 16 QAM in
which three amplitudes and twelve phases are combined; this is
because it is the most efficient model for reducing noise
because the ratio of phase shifts to amplitude is the highest.
The bit rate then becomes thrice the baud rate to further
enhance its efficiency [12]. Two signals transmitted through
QAM modulation will be in the form;
S(t) = Re {[I(t) + iQ (t)] e12πF0t }
= I(t) cos (2πf0t) – Q(t) sin 2 πf0t
Where i2 is -1, I(t) and Q(t) are modulating signals,
Re{} is the real section, and f0 is carrier frequency. Analog to
Digital Encoding
This is a form of encoding popularly known as digitization
and is achieved either by pulse code modulation or delta
modulation. Quantization and sampling are the main important
factors in analog to digital modulation
VII. ANALOG TO DIGITAL ENCODING
This is a form of encoding popularly known as digitization
and is achieved either by pulse code modulation or delta
modulation. Quantization and sampling are the main important
factors in analog to digital modulation Pulse Code Modulation
(PCM)
This is a technique of converting analog data into digital
signals such as in computer digital audio, digital telephony, and
CDs (compact discs). In the PCM stream, the analog signals’
amplitude is regularly sampled at uniform intervals, with every
sample being quantized within a given range of digital steps, to
the nearest value. PCM enables analog data to be converted
into digital signals to enable the transmission of the analog
signal through digital communication channels and networks.
The signal is transported in digital format and then converted
again into analog signals at the receiving end. PCM entails
three main steps; sampling, followed by quantization, and then
coding. Before sampling, the signal must be filtered first before
sampling so the maximum signal frequency is limited as this
has a direct effect on the rate of sampling. Sampling occurs
when every Ts seconds (sampling interval), an analog signal is
sampled [15].
Fs = 1/Ts becomes the sampling frequency. Sampling
can be ideal, natural, or flat top. Sampling is a form of PAM
(pulse amplitude modulation) that results in an analog signal. It
is can be applied to fields such as video streaming and VOIP
very well, however, it needs a large bandwidth.
The PCM signal bit rate can be computed from the relation
Bit rate = nb x fs
Where fs is sampling rate and nb is the numbers of bits in
each sample
A. Delta Modulation (DM)
This is a technique for converting analog data into digital
signals and is frequently used for transmitting voice data in
applications where the quality is not of primal importance.
Oversampling techniques are utilized to ensure the signal to
noise ratio is high; meaning less noise in the transmitted data
by sampling the signal at rates several times higher than
Nyquist rate [14]. Delta modulation restricts the input signal
amplitude since if the transmitted signal possesses a large
derivative, the modulated signal will fail to follow the input
signal, resulting in slope overload.
If input signal is m(t) = A cos (wt),
The input signal derivative becomes
{m (t)] max = wA

The required condition for avoiding slope overload is
[m (t)]max = wA < afs
As such, the the input signal maximum amplitude becomes
Amax = afs/w
Where;
fs = sampling frequency
w = input signal frequency
a = quantization step size
Amax = maximum possible amplitude that can be
transmitted by DM without causing slope overload [15].
VIII.NEW TRENDS AND ADVANCES IN ENCODING
A. Orthogonal frequency division multiplexing (OFDM)
This is a recent technique for encoding used in wide band
digital communication in applications such as audio and
television broadcasting, wireless networks, DSL internet
access, 4 G mobile communication, and power line networks. It
is a frequency division multiplexing scheme employed as a
multi carrier method of modulation. It work s by using a large
number of orthogonal sub carrier signals that are closely
spaced for carrying data on multiple parallel data channels/
streams. A conventional modulation scheme such as PSK or
QAM is used for modulation each carrier at low symbol rates.
This ensures total data rates are maintained in a way similar to
schemes used in single carriers on the same bandwidth. OFDM
has benefits over single carrier schemes such as FM is that it
can cope well with channel conditions that are severe such as
high frequency attenuation in very long copper wire mediums
or narrow band interference [16]
B. Multiplexing
This is a technique for combining multiple digital and
analog signals into a single signal over shared mediums in
which case the medium is a scarce resource. This entails
dividing the channel into several logical channels, with each
channel handling a single data stream or signal. At the r3ceiver
end, de-multiplexing reverses this process to recover the signal.
A common approach to multiplexing is the frequency division
multiplexing which can be considered an analog method.
Several distinct signal frequencies are sent over a single
channel using electrical signals and is applied in cable
television and TV channel broadcasting [17]
IX. CONCLUSION
Encoding is an integral and highly essential component in
networks and data transmission to enable transmission of data
between two or more terminals. Encoding also ensures the lines
are balanced even when there are changes in the state of the
data as to be indistinguishable from a dead line or has uneven
numbers. Encoding allows different media to be transmitted,
from voice to videos and computer data in a standardized
manner. Different techniques are used for data transmission,
depending on the type of data, the medium, and distance as
well as the application. There are four major ways of encoding,
namely analog to analog (AM, FM, PSM), digital to digital
(NRZ, NRZI, ME), analog to analog, and digital to digital
(ASK FSK PSK QAM). These are standard/ regularly used
methods; however, as applications become more resource
intensive such as video streaming and cloud computing new
approaches to handle such demands are necessary. New
techniques include orthogonal frequency division multiplexing
and advanced methods of multiplexing
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