Implementation of a bit error rate tester of a wireless communication system on an fpga

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 03 Issue: 05 | May-2014, Available @ http://www.ijret.org 97
IMPLEMENTATION OF A BIT ERROR RATE TESTER OF A WIRELESS
COMMUNICATION SYSTEM ON AN FPGA
Lakshmy Sukumaran1
, Dharani K G2
1
Student, Electronics and communication, MVJ College of Engineering, Bangalore-560067
2
Assistant Professor, Electronics and communication, MVJ College of Engineering, Bangalore -560067
Abstract
This paper deals with the Field Programmable Gate Array (FPGA) implementation of an entire digital baseband wireless
communication system. The proposed BER tester (BERT) integrates the modules of a typical communication system along with an
AWGN channel into a single FPGA. The BER is calculated for a 2*2 MIMO system also. This FPGA based solution is a more cost
effective, flexible and faster solution compared with the commercially available BER test equipments and software based simulators.
Keywords— BER; BERT; MC simulations; FPGA
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1. INTRODUCTION
Undoubtedly the impact the technology has made on our day
to day life in the last two decade or so is clearly
overwhelming. With ever increasing demand from customers
for better services and increased competition in the market it
becomes absolutely vital for the service providers to ensure
that their systems are subjected to very stringent performance
testing measures. One such most widely used metric for
determining the reliability of a digital communication system
is the bit error rate (BER).[1][2]
This paper performs the bit error rate validation of a digital
baseband wireless communication systems on an FPGA. The
proposed BERT integrates the various modules of a
communication system like the transmitter, receiver and
AWGN channel onto an FPGA. The system performance will
also be evaluated for a 2/2 antenna system. The transmitter
side includes the rate 1/3 convolutional encoder, puncturer,
interleaver and 16 QAM modulator .The receiver includes the
ML detector, demodulator, deinterleaver, depuncturer, and
Viterbi decoder. The output will be exported to MATLAB to
plot the BER curve. The rest of the paper is organized as
follows. Section II describes the literature survey, Section III
contains the overall block diagram and the design details of all
the implemented modules. Section IV shows some simulation
results.
2. LITERATURE SURVEY
Any digital transmission system which transmits a series of
bits over a communication channel is likely to get influenced
by some errors due to various factors like noise, interference
etc. We need to ensure that these errors are reduced to a
minimum so as not to interfere with the working of the
measurements of BER on the test system. BER is a measure of
how effective the system is and indicates the number of bit
errors introduced in the received message. BER Testers are
used to measure this value. These measurements can be done
using either the software based simulations like the MC
(Monte Carlo) simulations and IS (importance sampling) or
using the hardware based prototyping. The various problems
encountered with the existing methods are as follows.[2][3][8]
 The MC simulations are not suitable for communication
systems with low BER, the reason being the fact errors
introduced are less, indicating simulations need to be
run for a longer duration to be able to attain these
BER.[4]
 The fading channel simulators which are used in the
laboratories to replicate the channel are highly costly
and not very accurate. They can also not be scaled to
emerging new standards in the communication
field.[1][5]
 The MC based simulations when done on a simple
AWGN channel takes lesser time when compared to
that for a fading channel. In reality most of wireless
communication systems have fading characteristics
which takes longer run times for the simulations to
estimate the BER.[3]
 For a MIMO channels, the simulation time also is high
as the receiver is highly complex and a lot of possible
configurations in terms of the available coding schemes,
channel, modulation techniques need to be explored
before arriving at the optimum one.[3]
 The BER of a reliable communication link should be
very low .For example IEEE 802.3 10 GB/sec Ethernet
should have a BER of the order of 10(-12
).It means a
single error occurs in approx. 10(12
) samples. This
indicates that a very large number of symbols need to be
processed for software based simulators, over different
SNR ratios to obtain a reliable performance

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measurement .Thus the simulation time can get
extended to months.[3]
 We go for a hardware based prototyping, as it is much
faster than software based simulations. Some of the
BERT available in the market are from various
companies like Data Communications Business Inc.
(DCB), Tektronix, Picosecond Pulse Labs etc. The
drawback of such equipment is the fact that they are
not scalable. Also it can be used for testing the system
designed only at a later stage, after which a lot of
reworks needs to be done if the expectations are not
met. Also there is an additional burden of designing the
custom interfaces for each of the equipment and
communication systems under test.[6]
 Most of the published BERT uses FPGA and Simulink
to integrate the Forward Error Correction (FEC) blocks
onto FPGA. Although use of Simulink reduces the need
for having an extensive knowledge of the hardware, it
has limited resources in its simulation library which
may not be able to keep pace with emerging standards
[6].
 The alternate proposed is where the entire
communication system can be integrated into an FPGA
along with the channel. The speedy calculations are
made possible by the parallel circuitry of FPGA .Also
the memory bandwidth of FPGA is high. These two
features along with flexibility make it a highly likely
candidate for implementing a BERT.[8]
3. PROPOSED SYSTEM
The block diagram of the proposed communication system is
as given in figure1.The implementation has been done using
Verilog HDL in Xilinx ISE 12.2 and simulated using the iSim
simulator M.(63C).
 Convolutional Encoder: The source bit data is given at
the input of the encoder. The encoder used is a rate 1/3
convolutional encoder, which is capable of performing
forward error correction. It differs from the block
coding in its encoding principle. In convolutional
codes, the information bits are spread along the
sequence. Hence it maps the information to code bits
not block wise, but sequentially convolve the sequence
of information bits according to some rule .The encoder
has been implemented using 6 bit shift registers. For
every data input, 3 coded bits will be generated. The
simulation result is given in figure 3.
Fig 1: Block diagram of implemented communication system
 Puncturer: The 3 bit output of encoder is fed to a
puncturer, where some of the output parity bits of the
encoder are deleted as per the puncturing matrix. This
has the same effect as encoding with an error-
correction code with a higher rate, or less redundancy.
Since the same decoder can be employed for decoding,
it considerably increases the flexibility of the system
without significantly increasing its complexity .Using
different puncturing schemes we can adapt to the
channel, ie using the channel state information, send
more redundancy, if the channel quality is bad and send
less redundancy (more information) if the channel
quality is better. We have used a 13 bit puncturing
matrix. The simulation result is given in figure 4.
 Interleaver: The three bit output of puncturer is given to
an interleaver to reduce the burst errors. If the number
of errors within a code word exceeds the error-
correcting code's capability, it fails to recover the
original code word. Interleaving ameliorates this
problem by shuffling source symbols across several
code words, thereby creating a more uniform
distribution of errors. The interleaver concept is
implemented using two temporary 50 bit registers and
counters. The data is written sequentially into these
locations specified by the incrementing counter. At the
other end, the data at locations specified by a specific
logic is taken out. Simulation details are given in figure
5.
 Modulator: The three bit output from the inter leaver is
appended with a zero to make it 4 bits, which is then
mapped to signal constellation as specified by figure 2
using the 16 QAM modulation techniques. The 4 bit
data is mapped into an in phase and quadrature
component, each 16 bits. Simulated results are given by
figure 6.The entire transmitter has been simulated using
figure 7.
 Demodulator: The received signal through the channel
is demodulated using the reverse process, where the 4
bit data is recovered. Simulated results are given in
figure 8.

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 Deinterleaver: Here the reverse operation of the
interleaver takes place. The simulation results are given
in figure9.
Fig 2: 16 QAM signal constellation
 De puncturing: The same puncturing matrix is used at
the receiver side. De puncturing just introduces dummy
bits. The simulated result is given in figure 10.
 Viterbi decoder: The three bit output of the depuncturer
is fed to Viterbi decoder. There are three different parts
to a Viterbi decoder. They are the path metric unit
(PMU) which contains the Add Compare Select (ACS),
the branch metric unit (BMU) and the survivor memory
management unit. The block diagram of the basic
Viterbi decoder is shown in figure 3.The first branch
metric unit compares the received data symbols with
the ideal output of the encoder at transmitter side. A
hard decision decoding is performed using hamming
distance as the metric. The path metric unit calculates
the path metric by adding the branch metric associated
with the received symbols with the path metrics from
the previous stage. The last stage is the register
exchange or the trace back unit, where the survivor
path and the output data are identified. The simulated
result of the Viterbi decoder is shown in figure 12 and
the integrated receiver in figure 13.[7]
Fig 3: Block Diagram of Viterbi Decoder
4. SIMULATION RESULTS
The coding has been done using Verilog language in Xilinx
ISE 12.2 and simulated using ISim Simulator.
Fig 4: Simulation result of a rate 1/3 convolutional encoder
Fig 5: Simulation result of puncturer
Fig 6: Simulation result of interleaver
Fig 7: Simulation result of 16 QAM modulator

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Fig 8: Simulation result of the integrated transmitter
Fig 9: Simulation result of demodulator
Fig 10: Simulation result of deinterleaver
Fig 11: Simulation result of de puncturer
Fig 12: Simulation result of Viterbi decoder
Fig 13: Simulation result of integrated receiver

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5. CONCLUSIONS AND FUTURE SCOPE
The FPGA based BERT is a flexible and cost effective
solution compared to the conventional bit error rate
measurement techniques. The transmitter and receiver have
been completely simulated successfully.
As an extension to the project, Verilog coding for different
coding schemes and different modulations may be put on
FPGA.A user friendly GUI may be developed through which
the parameters of the BERT can be altered, as per choice. The
main advantage of this BERT is the flexibility that it offers in
terms of scalability to the new emerging technology standards
and thus poses a very cost friendly and effective method.
REFERENCES
[1] A. Alimohammad, S. F. Fard, and B. F. Cockburn,
“FPGA-based accelerator for the verification of
leading-edge wireless systems,” in Proc.IEEE Int
DAC,Jul 2009,pp 844-847.
[2] Breed, G. (2003, January). Bit ErrorRate: Fundamental
concepts and measurement issues. Retrieved April 07,
2014, from highfrequencyelectronics:
http://www.highfrequencyelectronics.com/Archives/Ja
n03/HFE0103_Tutorial.pdf[
[3] Bohdanowicz, A. (n.d.). On Efficient BER Evaluation
of Digital Communication Systems via Importance
Sampling. Retrieved April7,2014,fromCiteSeerx:
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.
1.1.118.2785&rep=rep1&type=pdf
[4] Peter J. Smith, Mansoor Sha_ and Hongsheng Gao,
Quick sim-ulation: A review of importance sampling
techniques in communication systems," IEEE Journal
on Selected Areas in Communications, vol. 15, pp.
597{613, May 1997.
[5] A. Alimohammad, S. F. Fard, and B. F. Cockburn,
“FPGA-accelerated baseband design and verification of
broadband MIMO wireless systems,”in Proc. IEEE 1st
Int. Conf. Adv. Syst. Testing Validation, Sep. 2009,pp.
135–140.
[6] Lakshmy Sukumaran, D. K. (2014). Bit Error Rate
Testers - A Study. International Journal For
Engineering Research and Applications, ISSN : 2248-
9622, Vol. 4, Issue 4( Version 8), April 2014, pp.122-
125.
[7] Anubhuti Khare, Manish Saxena, Jagdish Patel(2011
October)- An FPGA based Efficient
implementation of Viterbi decoder, International
Journal of Engineering and Advanced Technology
(IJEAT):ISSN:2249-8958,Volume-1,Issue-1.
[8] Amirhossein Alimohammad and Saeed Fouladi
Fard:’FPGA based bit error rate performance
measurement of FPGA systems.’ IEEE transactions on
very large scale integrated systems. 1063-8210@2013
IEEE – DOI: 10.1109/TVLSI.2013.2276010

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