LETTERS
International Journal of Recent Trends in Engineering, Vol 2, No. 6, November 2009
EE_SP_Mitigation of RFI in Ad Hoc Wireless
Receiver Nodes
P. Banerjee1, D. K. Basu2, and M. Nasipuri 2
ECE Department, Heritage Institute of Technology, Kolkata, India
Email: prabir.banerjee@gmail.com
2
Computer Science & Engineering Department, Jadavpur University, Kolkata, India
dipakkbasu@gmail.com;mitanasipuri@yahoo.com
1
Abstract— The Ad-hoc wireless networks are assuming
great importance because of the ease of operation and their
operation without any infrastructure. On the other hand, it
has its own characteristics like operation from low-capacity
battery, frequent change of routing and connectivity etc..
Bit Error Rate (BER) of any wireless data network is
critically dependent on the signal to noise and
distortion(SINAD) ratio or signal to noise ratio(SNR) or
signal to interference ratio(SIR) parameters of a receiver.
The degradation in receiver performance can be made up
theoretically by boosting the transmitter power level but the
maximum power level is also highly regulated.
Consequently, solution by reducing the interference is more
relevant for Ad-hoc nodes. In this paper, we have analyzed
one of the most critical internal radio interference factor of
a receiver and have tried some circuits successfully to
reduce or remove the difficult-to-remove interference
problem of such receivers.
In this model, the radio receiver, which is an embedded
part of the platform, receives a signal which is the sum of
the propagated signal from the link and the noises
contributed by the noise sources residing in the platform.
Platform noise may be added into the receiver system at a
number of possible locations and for any widespread
wireless network like an Ad Hoc wireless network, the
overall effect of this noise can be analysed only if the
noise from individual sources are analysed and then
summed up. Unfortunately, this is not the model used by
most RF designers in the simulations. They generally
assume a white Gaussian noise source for predicting the
behaviour of the tuned intermediate frequency (IF) stages
of receivers and the modulator stage of transmitters. Such
models seldom match the real time scenario since the
platform-generated noises are typically non-Gaussian.
As such, the present radio design methodology does
not comprehend the impact of such sources of noise at the
time of design of the radio. It may become a cause for
more concern in the wireless designs since they will have
to perform under the following situations:
• Higher processor/controller clock speed
• More mobility of the nodes in the ad hoc
wireless networks
• Increasing density of nodes
The following sub-sections deal with the sources of
interference, modeling of the noise and analysis of the
cause of desensitization of a receiver.
Index Terms— Signal to noise and distortion ratio(SINAD),
Signal to noise ratio(SNR), Signal to interference ratio(SIR),
Phase Locked Loop(PLL)
I. INTRODUCTION
Almost all the modern Radio equipments are
controlled by clock-driven processors or controllers so
that the equipments are versatile. This means that radio
frequency sources inside the compact radios are more
likely to cause electro-magnetic interference (EMI) and
electro-magnetic conduction (EMC) problem. Most of the
radio-frequency (RF) coupling takes place in a radio in
two ways, either through radiation or conduction.
The hardware platform, in our paper, refers to those
digital circuits which are designed around the embedded
radio to provide different functionalities. The EMI and
EMC generated by the hardware platform of the radios
have become integral sources of interference for all
radios.
A realistic radio model in which a part of the radio
transmission channel is associated with the platform of
the wireless radio is depicted in figure 1.
A. SOURCES OF INTERFERENCE
It has been observed that there are quite a few powerful
sources of electro magnetic interference in a modern day
radio. Understanding the spectral content of the different
digital signals helps one to gain an insight into how they
can couple to incidental antennas such as heat sinks, PCB
solder points , power planes etc..
Any clock signal (approximately square with 50%
duty-cycle) in time domain, shows three distinct phases,
namely, rise time, steady-state phase and fall time. To
understand the pattern of interference in a radio, it is
better to translate the time domain clock signal to its
Fourier Transform as one can plan and adjust the signals
to produce less interference only in the frequency
domain. The solution of Fourier Transform is a function
of rise time, fall time, time-period and harmonic order.
The relationship between time and harmonic order is not
the same. It is observed that the first harmonic is the
strongest in terms of amplitude and it varies slowly with
time. On the other hand, higher order harmonics, though
much lower in amplitude, vary more quickly in time and,
Figure 1
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International Journal of Recent Trends in Engineering, Vol 2, No. 6, November 2009
therefore, could appear as a strongly varying interference
source in a receiver. Another serious interference
problem arises because of signal asymmetries i.e., when
even and odd harmonic amplitudes are different.
A trapezoidal signal radiates odd harmonics only and
this is why in radio systems, the square waves are
transformed into trapezoidal form by suitable filtering. It
also helps to reduce radiated power since with increase in
rise-time, the number of significant higher-order
harmonics increases. Even then, the symmetry of the
waveform has a role in generating only odd or odd and
even harmonics.
There are multiple sources of radio frequency
emissions in a wireless radio, where the functionality of
the radio is controlled by high- speed processor or
controller. The overall picture can be compared with a
situation, where there is a large number of dipole
radiators. The radiation pattern is not deterministic and it
varies greatly with the frequency of the signals, their
shapes and the number of active radiators at a point of
time and it complicates the things further, as far as
reliable radio performance is concerned.
The RFI, as discussed above, may be taken into
consideration by modifying the model of equation (1), as
suggested in [5]. The modified equation is given below:
B. INTERFERENCE MODEL
In any wireless data network, including Ad-hoc
networks, a key performance metric of any radio link is
its BER. It can be described as a decreasing function of
the SIR observed at its receiver node. We can, therefore,
consider the quality of service (QOS) of a wireless link as
an increasing function of its SIR and we have used the
parameter SIR in our problem formulation.
In any ad-hoc wireless network, the radio link between
the source and the destination has to work satisfactorily in
spite of interference from other sources. Some of the
sources can be exposed and some other may be hidden.
Given N interfering links in a particular channel, the SIR
of the ith link can be denoted by [1]:
C. RESULT OF DESENSITIZATION
The causes of internal RF interference in
communication receivers can be studied by considering a
microcontroller based double super-heterodyne receiver
system. Let us consider a channel frequency f CH of this
receiver.
For such a double super-heterodyne receiver with the
first Intermediate Frequency (IF) equal to 10.7 MHz, the
translation loop equation for the first mixer is
f CH ∼ f LO = 10.7 MHz ------ (3)
where, fLO
is the Local Oscillator frequency
corresponding to the channel frequency, f CH .
In any clock-based receiver, due to the non-linear
characteristics of the mixer device spurious IF can be
generated and this can easily be explained by the
following equation:
G i i Pi
Ri = ---------------------------------N i + ∑ G i j Pj + ∑ Pk
j≠I
where i, j, k Є {1,2,3,……….., N} and Pk denotes the
powers radiated by different clock sources residing in the
hardware platform of the receiver. It is true that out of
these different spurious, undesirable power sources Pk,
the power level of only a few may be strong enough to
degrade the SIR factor but it is impossible to foresee and
isolate those sources. It is true since the degree of
interference is also a function of the frequency.
Therefore, it is required to establish that the factor Pk is
the main additional source of noise that degenerates SIR
and to provide a circuit solution to eliminate this factor of
noise and, ideally, the solution should be independent of
variables like frequency.
G i i Pi
Ri = -------------------------------(1)
N i + ∑ G i j Pj
j≠I
m x f CLK ∼ n x f LO = 10.7 MHz --(4)
where, both m and n are positive integers and start from
1.
If condition stated by equation (4) is met, then spurious
IF is generated and it leads to what is known as
desensitization of receiver.
where i, j Є {1,2,3,……….., N}
In this equation, Pi is the power of the transmitter of
the desired link i, Ni is the thermal noise power at the
receiver of link i, Gi j is the power gain (actually loss)
from the transmitter of the jth link to the receiver of the ith.
one and Pj is the power of the undesired transmitter j
which interferes with the receiver i .
Now this well-known equation takes into consideration
only the radio sources external to the receiver. It has been
observed and established that apart from this cause,
internal signals play a critical role in determining the
performance in terms of receiver SIR of any
microprocessor/microcontroller controlled synthesized
radio. The radio frequency (RF) radiated by the internal
signals can desensitize the receiver to any extent and the
cause of this interference can be analyzed in the
following manner.
© 2009 ACADEMY PUBLISHER
(2)
D. MITIGATION OF RFI
The basic method for getting rid of a RFI source is to
remove the radiating mechanism. Conversion of
electromechanical contacts, for example, to solid state
would remove the arc-generated RFI. Electrostatic
discharge (ESD) generated RFI could be reduced by
removing the charge generating mechanism or by
providing a method to bleed off the charge. If the sources
of RFI are global and are identifiable, then it is relatively
easier to eliminate the sources. If the RFI from a source,
which is essential for the operation of the total radio
system, is responsible for the desensitization of the
receiver channel, then the solution cannot be a straightforward one. The communication systems must be able to
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International Journal of Recent Trends in Engineering, Vol 2, No. 6, November 2009
function in the presence of high-frequency interfering
clock signals. There are four basic methods, which can be
used to minimize RFI effects:
•
Eliminate the radiating source;
•
Shield either the source or the receiver;
•
Separate distance between the source of
radiation and the receiver ; and
•
Improve circuit design.
The following block diagram (Fig.2) represents a
double-super-heterodyne FM receiver and it also shows
the different functional blocks of a Phase-locked-loop
(PLL). The signal picked up by the antenna is fed to the
Low Noise Amplifier (LNA), the output of which is
mixed with the first Local Oscillator (LO) signal. This
local oscillator signal is the locked output of the Voltage
Controlled Oscillator (VCO).
Shielding is probably the most common means used to
reduce the effects of RFI. The effectiveness of the
shielding depends on the frequency of the incident waves,
the thickness of the shielding plates, the property of the
shielding material and slots or apertures in the cage.
Efficient shielding in present day wireless radios,
particularly ad hoc wireless nodes is very difficult to
achieve in the presence of very high frequency clocks.
Another alternative is to use absorbers instead of RF
shields. The best approach as far as passive mitigation of
RF interference is concerned, is to design the layout of
the radio with a technique so that the sensitive radio part
is located away from the noisy components
Administrative controls can also be used to prohibit RFI
sources from being operated near sensitive equipment.
The first three approaches are not effective in present day
designs of receivers because of the requirements of
miniaturization and lesser weight. So, removing or
reducing the interference by circuit design approach has
become the accepted solution. In the present work, the
sources of RFI have been analyzed and experiments
have been carried out with an existing microcontroller
based communication system. Finally, circuit based
solutions have been proposed strongly for the reduction
of the RFI problem caused by hardware platform of the
radio.
Figure 2
The first mixer output can be represented
mathematically by:
IF1 = {fCH + fm} ∼ fLO1 ,
where, fCH is the channel or carrier frequency;
fm is the modulating frequency and fLO1 represents the
first local oscillator frequency. For PLL schemes, fLO1 is
equal to the voltage controlled oscillator (VCO) output in
the locked condition. This frequency is programmed in
such a way that the first Intermediate Frequency (IF), IF1
becomes independent of the channel frequency. As an
example, if fCH = 80.0 MHz, IF1= 10.7 MHz (for the
receiver) and fm= 1 KHz then fLO1 = 90.7 MHz.
IF1 signal is then mixed with second local oscillator
signal, LO2 which is fixed for a given receiver. For our
system, it is 10.245 MHz so that the second intermediate
frequency (IF2) becomes (455 KHz +fm). The detector
stage extracts the modulating signal fm. For the PLL, IC of
Philips numbered SAA 1057 was used. It contains the
voltage controlled oscillator (VCO), the mixer, the low
pass filter and the reference oscillator. The division ratio,
N, is to be supplied to the PLL chip by suitable intelligent
circuit
which, in turn, is multiplied by the internal
reference frequency to generate the channel dependent
frequency for the mixer. The value of N in transmit
mode (NTX) of operation of PLL is given by:
NTx = (fCH / fref)
where, fCH represents the transmit channel frequency of
the set at a given point of time. In receive mode, the value
of N in receive mode (NRX) is calculated by:
NRx = (fCH ± 1st. IF / fref ) ,
where, fCh is the channel frequency, 1st.IF stands for the
first intermediate frequency of the super-heterodyne
receiver, fref is PLL chip specific reference frequency and
is equal to 12.5 KHz.. The NTx as well as NRx are
obviously decimal numbers and are to be converted to
binary format before loading into memory. In the
memory, blocks are to be earmarked for receive and
transmit operation .The NTx(binary) and the NRx(binary)
values are to be stored in appropriate blocks.
LTX uses 8051family microcontroller to control
receive and transmit operation. Since it is a simplex
II. RFI MITIGATION BY HARDWARE APPROACH
To establish Pk as the major source of noise, we have
experimented with a microcontroller based Very High
Frequency
(VHF)
band
set
of
Philips
Telecommunication. The model had the following
characteristics.
• It is a programmable, 16-channel set
• It is a synthesized radio using phase locked
loop( PLL) technique
• The receiver section is double superheterodyne type with first IF equal to 10.7
MHz
• It is a low band set working in 66-88 MHz
range
For generating the reference frequency, the PLL chip
requires a stable 4.0 MHz temperature controlled crystal
oscillator (TCXO).
This reference frequency is multiplied by a factor
N(the division ratio) which, in turn, is supplied to the
SAA1057 chip.
A. DETAILS OF EXPERIMENT
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International Journal of Recent Trends in Engineering, Vol 2, No. 6, November 2009
of the receiver but due to the reasons stated in this section
itself.
transceiver set, the single VCO and PLL are switched
between receive and transmit modes. It fetches with the
help of the microcontroller the NRx(binary) from receive
memory block and sends to the multiplier section of the
PLL for locking in receive mode.
When the set is switched to the transmit mode, the
controller fetches the NTx (binary) string from transmit
block of memory and sends to the multiplier of the PLL
for locking to the transmit frequency. The very high
frequency synthesized set, code-named LTX, has two
variants – low-band(68 to 88 MHz) and high-band(146 to
174 MHz). For our experimentation, the low-band LTX
set was selected. The justification for this choice is
explained below.
With reference to equation (4), it is seen that spurious
intermediate frequency (IF) is generated if:
m x f CLK ∼ n x f LO = 10.7 MHz, as 1st. IF for LTX is
10.7 MHZ.
Now, for simplicity, let us consider that there is no
received signal at the antenna and let us assume that the
microcontroller clock frequency is 4.0 MHz.
Hence, putting the values of fCLK = 4.0 MHz and fLO =
90.7 MHz corresponding to the channel frequency of 80.0
MHz, in equation (3), we obtain :
m= 20 and n=1.
With increase in channel frequency, the value of ‘m’
will increase and this means that the intensity of spurious
harmonic emission due to the clock signal will decrease.
Therefore, to observe the performance in the worst
possible condition, the low-band LTX set was chosen.
C. FIRST SOLUTION
It may be noted from the experimental results of
section III, that only if the interference factor is nil
(equation (4)), the SINAD or SNR will determine the
receiver performance of a radio receiver. The following
approaches were tried in the LTX to achieve the best
possible result:
• To eliminate the interfering factor, RF-shielding
of the microcontroller Printed Circuit Board
(P.C.B.) along with the Voltage Controlled
Oscillator (V.C.O.) was done. It reduced the
intensity of interference but the readings were
well below the 12 dB mark for the interfering
frequencies.
• The microcontroller clock was made separate
from the PLL clock and a different value of this
clock immediately increased the SINAD values
for the frequencies which were earlier giving
low SINAD
This second approach was studied further with
different frequency combinations and some other
disturbing data were exposed. It was observed that the
different address bus lines(A0 – An) and data bus signals
and other digital signal lines can also become sources of
RFI .Hence, we thought that it will be best if the microcontroller system could be forced into idle/sleep mode
once the receiver channel is locked.
The following circuit was developed to sense the
locked condition and the circuit was geared to track
change in the channel. The schematic is shown here in
Fig .3.
B. EXPERIMENTS AND ANALYSIS
To check the signal to noise and distortion ratio
(SINAD expressed as S+N+D/N+D) at different
frequencies over the entire band, the LTX was
programmed with different frequencies.The SINAD was
measured using the method described in CEPT standard
MPT 1323 :1996[7]. The method asks for application of
0.3µV (pd) signal strength from a suitable radio
frequency(RF) generator at the correct channel frequency
to the antenna socket of the receiver.
The receiver output has to be measured with the help
of a suitable audio distortion analyzer and the
(S+N+D/N+D) ratio should be more than or equal to
20dB if measured through a telephone psophometric
network or better than 12dB without the network.
The SINAD was recorded for all the frequencies at
input signal strength of 0.3µV (pd) with the help of
Rohde & Scharwz CMS-91 model and the readings are
shown in the same table. It is to be noted that for
professional voice-grade communication equipment, the
minimum requirement for receiver sensitivity is 12 dB
SINAD for 0.3µV (pd) RF signal input. After some
abruptly changing pattern with frequency, it was analysed
that:
• the SINAD has become a function of the
receive frequency
• the SINAD degrades sharply when the
receive frequency is a multiple of 4
To establish the points, the set was re-programmed
with a new set of frequencies and readings were taken. It
proved that the degradation was not due to the detuning
© 2009 ACADEMY PUBLISHER
Channel Sensor
Circuit
Control
Module
Micro- controller
Block
PLL
Block
Figure 3
This scheme worked satisfactorily and the system
became very stable and RFI was totally eliminated. The
final results obtained are tabulated in the table I below.
SERIAL
NO.
1
2
3
4
5
6
7
8
9
10
118
TABLE I
FREQUENCY
(MHz)
66.5
67
68
71
74
77
79
80
84
87.5
MEASURED
SINAD(dB)
16
15.6
16.1
15.9
15.3
16.1
15.5
16.2
15.8
16.2
LETTERS
International Journal of Recent Trends in Engineering, Vol 2, No. 6, November 2009
The first plot shown in figure 4 shows the wide
variation in SINAD ratios when the internal controller
clocks are running, marked especially by low SINAD at
frequencies like 68 and 80 MHz. When the internal clock
is stopped by the control circuit, the SINAD for the entire
band of frequencies improves remarkably and the
consistency is indicated by a very narrow band of SINAD
variation in the figure 5.The shortcoming of this approach
is that the microcontroller cannot execute any other
operation once the frequency is locked.
SINAD in dB
20
Figure 6
15
One of the most important output of such versatile
design is the Radio Signal Strength Indicator (RSSI)
output from the IF processor IC. This is a dc signal and is
proportional to the IF signal strength. Therefore, this
signal can be used to measure the level of platform noise
in the receiver, which includes interference from the
controller clocks also. In our scheme, we have utilized the
RSSI output from the IF processor IC, NJM2537. The
operation of the circuit is controlled by a micro-controller
80C51. The entire sequence of operation is as follows.
The RSSI output of NJM2537 is connected to the noninverting input of an OP-AMP, functioning in comparator
mode. The inverting input of the same is held at 0.6 volts
dc. This is to ensure that the selection of the crystal
frequency gives the best possible result since RSSI=0.6
Volts is generated only for IF signal strength of
60dBµV(emf)[9].When the RSSI level equals or exceeds
the reference voltage, the comparator output becomes
more or less equal to the positive supply voltage of the
OP-AMP IC. The reference voltage varies with IC
types[8].
This output is used to control the Enable pin of 4066,a
CMOS analog transmission gate which transfers +5V dc
to the Port 2.4 of 80C51.On the controller side, instead of
the conventional practice of connecting a fixed frequency
crystal across the pins X1 and X2 of the controller, our
circuit uses 4 crystals, all of different frequencies. It is
better if the frequencies are not whole numbers. We used
two crystals of frequencies 3.58 MHz and 4.0 MHz to
check whether our hardware and software schemes work
properly. One end of the two crystals are shorted and
connected to the terminal X1 of the controller. The other
ends of the crystals are connected to the Y inputs of the
individual section of analog transmission gates(4066
IC).The outputs(Z terminals) of all the 4066 sections are
shorted and the shorted terminal is connected to the
terminal X2 of the controller IC. This is possible since the
4066 is a tri-stated device and each of the gate will be
enabled individually under software control. Port lines
P2.0 to P2.3 are utilized to control the individual enable
pins of 4066 gates.The software algorithm works in the
following manner.
In the power up condition, P2.0 enables crystal XL1 by
default. If this frequency ensures +5V to P2.4, the
controller does not change the active crystal for the
controller. Otherwise, the software with the help of port
lines P2.1 to P2.3, switches the crystal selection till P2.4
10
5
66
.5
67
68 68
.0
68 25
.0
5
74
77
80 80
.0
2
87 5
.5
0
Freq. in MHz
80
84
87
.5
77
79
66
.
71
74
16.4
16.2
16
15.8
15.6
15.4
15.2
15
14.8
5
67
68
SINAD in dB
Figure 4
Freq. in MHz
Figure 5
D. SECOND SOLUTION
A more dynamic solution can be implemented if the
check for spurious IF is made progressive with the help
of software and the result is utilized to switch on the noninterfering oscillator frequency for the microcontroller.
We have tried this second solution and have obtained
almost same result as was obtained with our first
approach. However, it involves some extra hardware as
shown in Fig.6. This solution may be explained as
follows. Most of the Intermediate Frequency (IF) stage
operations in a radio receiver is executed by the hybrid IF
processor chips in most of the new designs. Apart from
the classical modules like the Mixers and the Band Pass
Filters, these processors also are designed with signal
processing blocks.
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International Journal of Recent Trends in Engineering, Vol 2, No. 6, November 2009
standard code- named Version Envy which will be more
RFI proof. We would like to carry out further work in this
direction so that more power sensitive solution can be
implemented and transmitter power level can be reduced
still further in ad hoc wireless networks.
is +5V.One has to remember that in this total scheme of
operation of a receiver, the reference crystal for the PLL
is a separate entity and this modified scheme is in no way
interfering with this crystal.
For operations like key-pad scanning and display
interfacing, the change in source frequency of oscillation
is not a factor. For communication softwares, the change
in oscillator frequency is to be taken care of properly by
designing suitable divider chain or by modifying the
software.
The two solutions are not strictly comparable since the
second solution requires more circuit and is reactive. The
advantage
of
this
solution
is
that
the
microprocessor/microcontroller can be kept alive for
other operations like display multiplexing.
Therefore, the choice of the solution will depend on the
versatility of the ad hoc network node and we are
confident that this solution for RF interference mitigation
will give much better and stable result from the point of
view of consistent SINAD value which, in turn, is related
to bit error rate in data communication.
ACKNOWLEDGMENT
The authors are indebted to CMATER and SRUVM
projects of the Computer Science and Engineering (CSE)
department, Jadavpur University for allowing them to use
the laboratory and other facilities.
Prabir Banerjee is grateful to the authorities of
Heritage Institute of Technology, Kolkata for allowing
him to work on the research paper, and Dr. D. K. Basu to
AICTE, New Delhi for providing him with an Emeritus
fellowship.
REFERENCES
[1] A. Ephremides, “Energy concerns in wireless networks”,
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[2] A. Pal, Mehmet Akar, Michael G. Safonov, U. Mitra,
“Adaptive Power Control for Wireless Networks Using
Multiple Controllers and Switching”.
[3] J. Rabaey, J. Ammer, J. L. da Silva Jr., D. Patel, “Ad-Hoc
Wireless Networking of Ubiquitous Low-Energy
Sensor/Monitor Nodes”.
[4] M.
Ibnkahla,
“Signal
Processing
for
Mobile
Communications Handbook”
[5] Intel StrongARM SA-1110 Microprocessor Developer’s
Manual, June 2000
[6] xapp 347-application note of m/s Xilinx
[7] Performance specification; Angle modulated radio
equipment for use at fixed and mobile in the private mobile
radio service operating in the VHF band, Revised and
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[8] www.datasheetcatalog.org/datasheet/rohm/bh4127fv.pdf
[9] http://www.datasheetcatalog.org/datasheet/newjapanradio/
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[10] C.C. Goodyear, Signals and Information, WileyInterscience,1971
[11] R. P. Feynman, R. B. Leighton and M. Sands, Feynman
Lectures on Physics, Vol.2,Addison-Wesley 2006
[12] B. Skalar, Digital Communication, Prentice Hall PTR,2001
[13] K. Slattery, J. Muccioli, T. North, Modeling the Radiated
Emissions from Microprocessors and other VLSI devices,
IEEE 2000 EMC Symposium, Washington DC
[14] H. W. Ott, Noise Reduction Techniques in Electronic
Systems (2nd. Ed.),Wiley,1988
[15] A. F. Molisch, Wireless Communications, Wiley,2005
[16] M. Mardiguian, Controlling Radiated Emissions by
Design, Springer, 2001
III. COMPARISON
The solutions which have been described in this paper,
have been compared with the following patents and
commercial radio product. The comparisons with each of
these have been enumerated.
1.
US Patent number 7116958
2.
US Patent number 7197291
3.
US Patent number 6148039
4.
Diversity UHF receiver UCR205D
It has been established that these solutions have some
weaknesses, which render those unsuitable for use as ad
hoc wireless network nodes.
IV. CONCLUSION
In many Ad Hoc wireless networks, the nodes need not
be proactive and it is sufficient if they are reactive only.
This is true since power consumption is a critical issue
for ad hoc network nodes or sensors. Hence, the first
solution can be the solution for RFI mitigation inmost of
the Ad Hoc wireless network nodes. However, depending
on the roles the nodes play in a dynamic situation like
changing the routes, transmission power level control
etc., the second solution will be more acceptable.
Lots of research work is going on to reduce or
eliminate RFI from wireless receivers. In the Bluetooth
standard , the receiver sensitivity level is kept as low as 70 dBm to take care of RFI and work is on for a new
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