Effective Way to Improve Wireless Communication Performance

To improve wireless communication performance, researchers have explored various techniques in Frequency Hopping Spread Spectrum (FHSS) systems. Studies [4-15] have investigated the security enhancement of FHSS using QPSK technique, improved performance evaluation using QAM/FSK modulation techniques, and performance analysis of BER with FHSS system. Other topics covered include jamming-resistant frequency hopping spread spectrum systems, design and implementation of FHSS and DSSS for secure data transmission, and advanced frequency hopping spread spectrum techniques for interference limited fading wireless channels.

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Abstract— Wireless communication is by far the most used
technology today, from wireless networks such as Wi-Fi
connections that transmit information using radio signals
including their most notable application today where they are
used to connect to the worldwide web i.e. the internet. While
wireless communication may offer many benefits and
conveniences, its operation is limited due to the many setbacks of
wireless connections such as interferences and congestions. To
minimize these limitations, operational techniques such as spread
spectrum are used where the information transmitted using radio
signals is spread and augmented to improve its immunity. Now,
Frequency hopping spread spectrum (FHSS) is a good example of
these techniques where signals are moved from one frequency to
another thus nullifying the limitations of wireless
communication. This report provides a critical analysis of this
technique including the emerging trends and applications.
Keywords: Spread spectrum, FHSS, QAM, BW, PN
I. INTRODUCTION
While wired communication may have the benefit of solid
mediums to perform its operations, wireless communication
uses a versatile and dynamic medium to transfer information.
This medium is filled with many elements and conditions that
change abruptly which necessitates the need to improve the
performance of the signals being transmitted. FHSS will
improve the quality of the signals by minimizing signal
interference and fading through hopping technique that carries
information from one signal band to another [1]. Now, to
understand the operation of this technique it’s important to
highlight the entire concept of spread spectrum. In general,
there are two main types of spread spectrum; FHSS and DSSS
(direct sequence spread spectrum). In both instances, the
communication bandwidth i.e. the transmission signal is
enlarged as compared to the bandwidth of the transmitted
signal (original message). This variation accommodates the
limitations of wireless communication particularly in the short
range application improving the quality of the signals [2].
FHSS as a component of spread spectrum will further its
course by utilizing the frequencies of communication and
randomly selected chipping codes. In essence, unique codes
are used to generate spread chips that assign the transmitted
signals carrier frequencies [1]. Through this operational
procedure, the FHSS can be combined with modulation
schemes to convert digital signals to analogue signals, an
added advantage of the technique. However, while these
operations take place, the communication process must ensure
that the hops do not interfere with each other as they would
cancel the entire process. Again, this process is accomplished
using adaptive FH techniques that avoid signal collision and
congestion during the hopping sequences.
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II. LITERATURE REVIEW
Many researchers and scholars who study spread spectrum
techniques compare them to narrow band techniques, where
the difference in the signal spectrum orientation is highlighted
including the advantages of the methods. Now, while narrow
band mobile communication may be efficient to use due to its
operational structure that assigns users (subscribers) fractions
of the communication channel, its allocation process is prone
to many challenges. For one, the allocation process requires a
well-coordinated process to assign the available frequencies to
the different subscribers. Furthermore, having assigned the
resources, the system must be aware of the drawbacks of
jamming and interception of data more so, through
eavesdropping techniques [3]. While there are many solutions
to these problems, they can all be eliminated by the technique
described above where the bandwidth is spread to fulfil the
needs of the subscribers.
FHSS like any other spread spectrum technique will
increase the dimensional attributes of communication signals
thus minimize the incidences of eavesdropping and any other
form of interference. Furthermore, through the chipping codes
that facilitate the hops of the carrier frequencies the transferred
information is only distinguishable to the verified members.
These operational conveniences have led to the application of
the technique in modern wireless infrastructures such as
WLAN (wireless local area networks) and Bluetooth
communication. In all, when using FHSS, the following
advantages are experienced:
 Minimal narrowband interferences.
 No signal interceptions, in fact, it’s very difficult
to eavesdrop on a signal [4].
III. CRITICAL ANALYSIS OF FHSS
FHSS Operation
To understand the FHSS operation, we have to consider the
Capacity formula as put forward by Shannon and Hartley [5].
In their theorem; C = B Log 2(1+S/N). Here, the C is the data
in bits per seconds while the B highlights our required
bandwidth. Therefore, for maximum information transmission,
the value of B (BW) must be high to accommodate the data
quota. Now, shifting back to FHSS, a carrier signal
(encapsulates the message) moving from one frequency
channel to another over a specific period of time. Moreover,
the carrier frequency is accorded a wide range of frequencies
(band) which maximizes the operational bandwidth hence
improving the quality of the communication signals and also
reduces the limitations (interferences and jamming) [5].
Frequency Hopping Spread Spectrum (FHSS)
[First A. Author], and [Second B. Author]
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Fig: FHSS block diagram
Now, during the hop activity, the data session or signal will
remain in a given frequency channel for a specific period of
time, which helps to maintain a consistent level of operation.
According to the IEEE standards, this value should be 300 ms
and is set as so in order to synchronize the operations of both
the transmitter and receiver. In addition to this, the pattern of
operation is dictated by a spreading code that is developed by
a pseudo-random generating program. This program or
generator is again synchronized between the transmitter and
receiver in order to demodulate the signal at the reception
stage. Therefore, when all is said and done, the transmitter and
receiver must have a one to one synchronization for them to
communicate [2].
Fig: FHSS operation
A common feature or attribute that distinguishes FHSS
from DSSS is the signal output given by the technique, instead
of the envelope shaped signal (Sin X)/X)2 a flat output is
given over the different frequencies used. Furthermore, size of
the hopping bandwidth is usually N-times the total number of
slots (frequency bands) available, where N is the bandwidth of
each slot [6].
FHSS Features:
 Identified by the IEEE 802.11 standard
 Operates within the 2.4 GHz band while having 79
frequencies (2.402 – 2.480GHz).
 Each of the frequencies outlined above is modulated
(FSK) with a width of 1MHz [7].
FHSS Modulation
After highlighting the general operation method, its time to
outline the modulation process used i.e. the transmission of the
signal from a common FSHH transceiver. First, any signal
interval can be chosen to highlight the process occupying one
or even more frequency slots. Moreover, the frequency slot
occupation is designated by the code generator which is
usually a pseudo-noise (PN) sequence. Now, the most
commonly used modulation method is usually M-ary FSK
(frequency shift keying) and QAM (quadrature amplitude
modulation). Therefore, the FSK is used to generate a signal at
the start of transmission, with the output signalling the start of
the modulation process. After, the FSK signal is converted
into a frequency that is then synthesized with the frequency
synthesizer. The resultant frequency is then combined with the
overall output of the modulator forming a frequency-translated
communication signal. This is the final product of the
modulation process and is the signal transmitted over the
channel [8].
NB: Note that, the PN generator produces N bits which are
usually used to make the final 2N-1 frequency translations.
Furthermore, the modulated signal is then transmitted using an
AWGN (Additive white Gaussian noise) channel.
FHSS Demodulation (receiver section)
In the receiver section of the transceiver, a similar PN
generator is used to match the code used at the modulation
stage. Furthermore, the generator at this end is synchronized
with that of the input in order to match the operational
frequency and slots used [9]. Moreover, its operation (PN
generator) is also synchronized with the received signal so as
to control the outcome of the resulting frequency synthesizer.
Therefore, all the operations conducted at the transmitter are
removed at this section, first, pseudorandom frequency
conversion introduced is removed by mixing the product of
the synthesizer with that of the received signal. Thereafter, the
resulting product is demodulated using an M-FSK
demodulator that matches the one at the transmitter [2].
NB: To maintain a synchronized operation, a signal or
matching method is required between the PN generator and
the frequency translated signal. This matching is usually done
by the received signal as it dictates the terms of operation for
it is the subject of the demodulation process. Furthermore, the
improvements in FHSS operation and QAM as supported by
Viterbi decoders which decrease the overall bit error rate [10].
FHSS Application
As outlined before, FHSS offer improved signal
performance as compared to narrow band technologies. This
outcome makes its suitable for applications that use its
corresponding operational frequency as highlighted in the
figure above. Therefore, it’s mostly used for applications that
require the operational frequencies of 2.4GHz and 3G. These
applications are common among the military whose operations
not only requires efficient systems bust also the utmost
security. Now, both of these conditions are met by FHSS,
where security is implemented using cryptographic structures
and algorithms that generate unique chipping codes which are
shared amongst the communicating parties. Moreover, FHSS
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is also used in wireless area networks (WLAN) where again it
operates using the 97 frequency channels identified before.
Now, in WLAN, it follows the operational band between 2.40
GHz and 2.480 GHz as highlighted in the figure above [11].
FHSS is also used in the modern digital systems, more so in
the global positioning systems that outline objects positions. In
all, the overall GPS system consists of several sections i.e.
control unit, space unit and the user unit. Now, all these units
exist independently and will use wireless communication to
connect with each other which is where FHSS comes in hand
offering its quality networking procedures. Moreover, FHSS is
also used in other forms of wireless communication mostly
because of its modulation process [12]. Finally, FHSS is also
used in Bluetooth technologies.
IV NEW FINDINGS
Optimized matched frequency hopping (OMFH) and
optimized advanced frequency hopping (OAFH) are
considered in this section. Now, traditional FHSS will just
divide the overall communication band and spread the signal
across them (hopping sequences). Moreover, the random
pseudo code is used to deliver the allocation, however, this
operational method is sometimes inefficient which has led to
the new developments highlighted above. In essence, the
overall performance of FHSS is improved by fading the
frequency selection process and by use of adaptive frequency
band jamming [13]. This outcome is accomplished by
optimizing the control factors through matching hops and
advanced frequency matching which improves the overall
signal throughput.
OMFH: In this technique, the regulation parameters of the
FHSS are optimized and in this case, the only available factor
is usually the sub-band frequencies for the hops. In essence, as
one increases the number of sub-bands (hops) the signal
interference decreases. In fact, an optimal operation is
achieved when the sub-band frequencies are greater than 7
[14].
OAFH: Similarly, the regulation of FHSS parameters in
done in this case, however, unlike the previous technique the
respective sub-band frequencies are also regulated and
optimized. Again, several sub-band are chosen but now each
sub-band is regulated and optimized to increase the individual
throughput which enhances the performance of FHSS beyond
that of OFMH [15].
V CONCLUSION
From the analysis given in this report, FHSS has been
outlined as a modulation technique that spread the
communication spectrum based on the operational frequency.
In all, in the technique, a number of sub-band frequencies are
selected randomly using pseudorandom generators (PN) which
designate the path for the transferred signals. After identifying
the sub-frequencies, the signals are then hopped from one
band to another which increases the operation bandwidth
hence minimizing the limitation of wireless communication.
Furthermore, the hops are strictly monitored based on a
specific time interval, an outcome that makes the transiting
signal immune to noises, distortions, jamming and
interceptions. In addition to this, the presence of the chipping
code generator (PN) makes the FHSS technique secure as it
can be deployed using cryptographic parameters which can
only be known by the communicating parties. Again, these
operational conveniences make FHSS suitable for applications
that require secure systems such as those of the military as
identified above.
VI. REFERENCES
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