POSTER XII. TRADIČNÍ WORKSHOP DOKTORANDŮ A MLADÝCH VĚDECKÝCH PRACOVNÍKŮ, VŠB-TU Ostrava, 25. 4. 2012
MEASUREMENT OF DIGITALLY MODULATED SIGNALS BY USING MATHEMATICAL ROLES IN MEASURING INSTRUMENTS 1
Mohamed Al-WOHAISHI1, Radek MARTINEK1 Department of Cybernetics and Biomedical Engineering Faculty of Electrical Engineering and Computer Science VŠB – Technical University of Ostrava 17. listopadu 15, 708 33 Ostrava – Poruba
Abstract Communication systems have covered much ground on its way from simple wired telegraph to today's 4th generation wireless standards. The way full of side cuts, failures and surprises. This article will try to briefly explain, how it was possible to go from first trans-Atlantic cable burned in its middle because of ignoring Ohm's law, to modern ways of transmission of live high-definition movies via DVB-S2 satellite transmission standard, where a lot of data is transmitted using relatively narrow bandwidth. There's one simple word telling the whole very complicated story - mathematics.
Keywords M-PSK, M-QAM, 3D Eye Diagram, LabVIEW, SDR.
1.
Introduction
The first successful bi-directional transmission of clear speech by Bell and Watson was made on March 10, 1876 when Bell spoke into his device, “Mr. Watson, come here, I want to see you.” and Watson answered. The first long distance telephone call was made on 10 August 1876 by Bell from the family homestead in Brantford, Ontario, to his assistant located in Paris, Ontario, some 10 miles (16 km) distant [1]. Nowadays, almost everyone owns a mobile phone or an MP3 player; our cars are equipped with modern navigation systems, which allow a wide range of additional services. These modern devices often use many different technologies to provide customers with a wide array of functionality, Figure 1. Shows the graphically illustrates how many functions can be included in on board system in our car. This system, in addition to the traditional processing of music from CDs and DVDs, is able to communicate with various mobile devices, PDA, navigation, personal computers.
Fig. 1 The diversity of technology
The image below shows a typical generic communications block diagram that every-one will find it in any university textbook on communications. Information flows from the left to right in the top set of blocks as indicated by the arrows. The infor-mation is sent over a transmission medium (a channel) and then flows from the right to the left as the information is decoded and the message recovered. The transmission of information by electrical means using digital communication techniques, the data transmitted in digital form we often use bits (an alphabet consist of 0 and 1). Information may be transmitted from one point to another using either digital or analog communication systems. In a digital communication system, the information is processed so that it can be represented by a sequence of discrete mes-sages [2], as shown in Figure 2. These blocks are for source coding, channel coding, modulation on the transmit side. On the receive side, the blocks include, demodulation, channel decoding and source decoding. A real-world communication link contains a physical channel over which the transmission will occur. Examples of physical channel include, but are not limited to, air (wireless), fiber optic, copper. Source coding block typically involves data compression. For example, the ATSC standard for digital video broadcast (DVB) specifies MPEG-2 encoding for the image to be transmitted. Channel coding block typically involves adding redundant bits to the data stream to increase the receiver’s susceptibility to noise and interference in the channel. The output of the channel coding block is still a series of 0s and 1s. The next block in the chain is the modulation block which converts the bits into an in-phase (I) and quadrature-
Measurement of Digitally Modulated Signals by Using Mathematical Roles in Measuring Instruments M. AL-WOHAISHI, R. MARTINEK
phase (Q) data. This block typically also involves the step of pulse shaping to reduce inter-symbol interference and reduce bandwidth.
frequency response, and M is restricted to 2P so that each symbol can be represented by P bits. Likewise, for MQAM, assuming rectangular QAM signal constellations in which, where is even, I(t) and Q(t) are given as (4) and (5). ∑) $*)
/
02$ 1 √34
/
∑) $*)
(4)
025$ 1 √34 (5)
Where -6 is the minimum symbol energy, and .
Fig. 2. Functional Block Diagram of a Binary Digital Communication System
2.
The difference between QPSK and M-QAM modulation scheme is that QPSK modulation works with constant amplitude of modulated carrier vector and M-QAM modulation works with variable amplitudes and phases of modulated carrier vector [4]. Terrestrial DVB-T broadcasting offers three different modulation schemes QPSK, 16-QAM and 64-QAM, while terrestrial DVB-T2 broadcasting, which allows transmission of high definition picture format, uses 256-QAM modulation scheme. Our Experiment Lab. shown in figure 3 represents the use of Lab VIEW Modulation Toolkit with PXI syntactic instruments.
System Model
The basic structure of designed communication system comes from the general chain of digital communication system and was implemented using functions from Lab VIEW Modulation Toolkit additional library. Our Experiment Model represent by system based on software defined radio concept was implemented on PXI modular HW platform using Lab VIEW development environment [2]. This Experiment demonstrates continuous acquisition and demodulation of a QAM and PSK signal see figure 1 below. We investigate two families of modulation schemes that are more widespread in digital TV broadcasting [3]. M-PSK and M-QAM, for which the signal can be generally given as (1). st It cos2πf t Qt sin2πf t
(1)
Where f is the carrier frequency, Itand Qt are the baseband signals of the in-phase and quadrature phase components, respectively. For M-PSK given as (2) and (3)
!" #$ %
", #$ %
∑) $*)
+ ∑) $*)
& '
& '
&
( '
&
( '
(2) (3)
Where -. is the symbol energy, T is the symbol interval, In = 0,1, … , M-1, gT(t) has a raised-cosine
Fig. 3. Experiment Lab Bench
3. Concept of the Measuring In the Synthetic Instrumentation Nowadays, the number of communication protocols used in digital transmission systems is increasing dramatically. Some of them are completely new; others are gradually replacing existing ones. The introduction of digital transmission systems of the new generations, accompanied with new and new standards [5], evokes the need for flexible test platform, both in their development stage and in their use. The core of virtual instrument is the addition of an open architecture of personal computer by what it lacks in order to fulfill the role of the measuring instrument. In the hardware is plug multifunction card (plug in the measuring board) equipped with connector for inserting the card into the computer system board personnel (ISA, EISA, PCI bus) [6]. It is suitable in the field of software for a computer
Measurement of Digitally Modulated Signals by Using Mathematical Roles in Measuring Instruments M. AL-WOHAISHI, R. MARTINEK
programs that provides all the functions measuring device and performs the role off the measuring device firmware, and nd prevents duplication that occurs when connecting the measuring device and computer. One of the biggest advantages of this test platform is the ability to respond flexibly to new requirements in the area of testing. In this article the RF vector signal generator and PXIPXI 5670 RF vector signal analyzer PXI-5661 5661 have been used. These two modules are highly flexible solutions for testing of new digital transmission systems. The roles of software soft and hardware are shown in figure 4.
MB throughput via GPIB interface for connection of single vector signal analyzers [8]. Along with the development environment of Lab VIEW with Modulation Toolkit extension libraries and Spectral Measurement Toolkit, this module represents very flexible platform for the automation of usual parameters measurement such as: in-band band power, adjacent channel power, power and frequency-- peak-search. Visualization of measurement results is possible in traditional forms such as 3D spectrograms and constellation diagrams for analysis of digitally modulated signals (I/Q Modulation for Data Analysis).
6.
Fig. 4. Test platform has demarcation between the hardware and software
Results and Discussion
Measurements weree carried out for all the modulation under the same conditions (i.e. with the same performance in different modulation), so they would credibly be compared. Figure 5 below show the positions of symbols in constellation diagram and 3Deye diagram for tested Mdigitally modulated signal (4, 8, 16 and 32) PSK with SNR (20 dB) in transmission channel. channel
4. Vector Signal Generator - NI PXI 5670 Along with the development environment LabVIEW, complemented by extended Modulation Toolkit library, the PXI module could be used to generate the required test signals for verifying the possibilities of digital transmission systems which use the new standards. The whole test system can be easily adapted to new requirements, while the focal point of functionality of such a system is located locate in the software part. The NI PXI-5670RF vector signal generator, represents the generator of user--defined waveform (arbitrary waveform generator) working a resolution of 16 bits and sampling rate of 100MS / s (400MS/s in the interleaved mode) with a depth of memory up to 512 MB and the real bandwidth of 20 MHz Using a digital upconvertor along with this module can generate gene signal in the range of 250 kHz to 2.7 GHz with random modulation scheme such as: AM, FM, PM, ASK, FSK, MSK, GMSK, PSK, QPSK, PAM, and QAM, see [7].
Fig. 5. Constellation and 3D Eye diagram for M-PSK M with SNR (20dB) respectively for (4, 8, 16 and 32)
But, the he simulation of different M-QAM M modulation shows that increasing of the state number, leads to an increase of transfer rate (transfer more bits per symbol). The downside however is that with the growing number of states BER increases at the same transmission power as a result of worse distribution of symbols sym in constellation diagram as shown in figure 6..
5. Vector Signal Analyzer - NI PXI 5661 The NI PXI- 5660 module was used for the analysis of digitally modulated dulated signals. This module is a very compact solution (30% of normal weight and cubature of separate devices in this class), allowing very rapid measurement of digitally modulated signals in the range from 9 kHz to 2.7 GHz. With the real bandwidth of 20 MHz, but with possible flow of data 132 Mb/s over the PCI bus, this solution represents tremendous progress in the contrast of 1
Fig. 6. Constellation and 3D Eye diagram for M-QAM M with SNR (20dB) respectively for (, 8, 16, 32 and 64)
Measurement of Digitally Modulated Signals by Using Mathematical Roles in Measuring Instruments M. AL-WOHAISHI, R. MARTINEK Table 1. Measured BER vs. SNR
[5]
J.S. Wilson, S. Ball, "Test and measurement", ISBN: 978-185617-530-2, USA, Paperback: 968 pages, Publisher: Newnes, Illustration: NL language: ENG, Complete Title: Test and Measurement: Know It All, 2009.
[6]
S.K. Vasudevan, R. Sivaraman, Z.C. Alex, "Software Defined Radio Implementation (With simulation & analysis)", International Journal of Computer Applications (0975 – 8887), Volume 4– No.8, August 2010
[7]
[7] National Instruments: RF Vector Signal Generator NI PXI-5671,katalog list, 2005 http://www.ni.com/pdf/products/us/20055170101dlr.pdf
[8]
National Instruments: RF Vector Signal Analyzer NI PXI5660,katalog list, 2005
[9]
http://www.ni.com/pdf/products/us/4mi469-471.pdf
BER
SNR [dB] 4-QAM
8-QAM
16-QAM
32-QAM
0
0,0761
0,2054
0,25817
0,31779
2
0,0388
0,1489
0,21275
0,28123
4
0,0134
0,0958
0,15531
0,24034
6
0,0023
0,0517
0,10306
0,18916
8
0,0002
0,0204
0,05729
0,13475
10
0
0,0055
0,02302
0,08237
12
0
0,0008
0,00630
0,04066
14
0
0
0,00072
0,01392
16
0
0
0
0,00232
18
0
0
0
0,00026
20
0
0
0
0
7. Conclusion The main contribution of this paper is introduction to new approach in measurement of digitally modulated signals by using mathematical roles in measuring instruments. In this paper we described the case study of software defined radio communication system implemented on National Instruments PXI modular HW platform using graphically oriented development environment LabVIEW. The synthetic instrument for analysis of digitally (PSK QAM) modulated signal was implemented on the same platform. Some basic advantages of SDR concept were demonstrated by SW configuration of basic parameters of the communication system. Basic features of different types of digital signal modulation were demonstrated by results of measurements, which were executed on implemented synthetic instrument. The results of these measurements are compared with results of measurement from standalone specialized measuring instruments.
Literatura [1]
Invention of the telephone [online]. 8 April 2009 [cit. 2009-0424]. .
[2]
B. Sklar, Digital Communications: Fundamentals and Applications, Prentice Hall Inc., Englewood Cliffs, NJ, 1998.
[3]
J.Lu, K.B. Lefaief, J.C.-I. Chunng and M L. Liou. "M-PSK and M-QAM BER computation using signal-space concepts". IEEE Transactions on communications, vol. 47, no, 2, pp. 181-184, 1999, ISSN: 0090-6778, NSPEC Accession Number: 6212385.
[4]
E. Martos-Naya, J.F. Paris, U. Fernandez-Plazaola, A. Goldsmith, " Exact BER analysis for M-QAM modulation with transmit beam forming under channel prediction errors", Wireless Communications, On page(s): 3674, ISSN: 15361276, 2008.
About the Authors ... Mohamed Al-WOHAISHI was born on 1710-1972 in Aden, Yemen. In 2008 he earned the title Eng. from the Technical University of Ostrava in the field of Measuring and Control Technology. He is currently doing his PhD at the Department of measurement and control technology engineering. He is interested in digital signal processing and Communication Systems using virtual instrumentation. Radek MARTINEK was born on August 10, 1984 in Nové Město na Moravě, Czech Republic. He received the Bc. degree in Electrical, Electronic, Communication and Control Technology from Faculty of Electrical Engineering and Communication Brno University of Technology in 2007, the Ing. degree in Communication Technology from Faculty of Electrical Engineering and Computer Science VŠB – Technical University of Ostrava in 2009. He is pursuing his Ph.D. in Department of Measurement and Control. His current research interests include Digital Signal Processing and Communication Systems.
