DOCSLIB.ORG

Using Constellation Diagrams to Test Wireless Devices Page | 1 of 3

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Using Constellation Diagrams to Test Wireless Devices Page | 1 of 3 Using Constellation Diagrams to Test TECHNICAL BRIEF Wireless Devices Dr. Michael Lauterbach August 16, 2012 Viewing a QAM Signal on a Constellation Diagram Summary A very common way to transmit wireless data is to use quadrature The number of new cell amplitude modulation (QAM). This method uses two amplitude modulated phones, tablets, laptops and signals, combined into a single channel at the same carrier frequency to many other types of wireless increase the symbol transmission rate. The two signals are out of phase devices coming to market is with each other and are called the In-Phase (I) and Quadrature (Q) very large. A corollary is that components of the transmission. At the transmitter end the two signals the pressure on engineering to are combined and at the receiver end they are separated. A constellation get these products to market diagram is a two-dimensional method of looking at the signal. Shown in in time to beat, or at least Figure 1 is an example of a constellation diagram of a PHP cellular phone meet, the competition is very signal. On the upper left is the voltage vs. time trace of the in-phase signal high. One of the common tools and in the lower left the scope is showing the quadrature signal. The XY used to test the performance plot on the right side of the scope shows the ratio of I/Q. There are eight and quality of wireless devices clearly defined states. is the constellation diagram. This technical brief gives an Making Measurements overview of how to perform these tests using a digital Though there are eight separate states in the XY plot of Figure 1, it is clear oscilloscope. that the signal-to-noise ratio of this transmission is not ideal. A combination of white noise, phase noise, interference and distortion gives a width to each of the states. If a certain symbol receives too much noise, it could be closer to a different state in the constellation diagram and therefore be misinterpreted by the receiver. To capture the I and Q waveforms at the time when symbols are valid, it is mandatory that the symbol clock of the wireless transmission be used as the oscilloscope sampling clock. If a free-running sampling clock inside the oscilloscope is used, then the I and Q signals will be sampled at random times including transition times between states. A unique feature of Teledyne LeCroy oscilloscopes is the ability for the scope user to input an external sampling clock to replace the usual sampling clock of the instrument. Teledyne LeCroy Using Constellation Diagrams to Test Wireless Devices page | 1 of 3 Figure 1: On the left are the voltage vs time traces of the I (upper) and Q (lower) signals. On the right is an XY plot of the same signals Figure 2 shows the setup for the external clock. In this case the symbol clock has a threshold of zero volts (with an amplitude of at least 150 mv peak-to-peak). The external clock can also be ECL or TTL. Figure 2: Setting up the external clock input for a 16 QAM signal. Note that the oscilloscope can be set to use ECL, TTL or 0V external clocks Teledyne LeCroy Using Constellation Diagrams to Test Wireless Devices page | 2 of 3 Figure 3 shows the oscilloscope making a measurement on a 16 QAM signal using a cursor. Note that this waveform has much less noise/distortion than Figure 1, so the widths of the scattering in the XY plot are much smaller. Figure 3: A cursor has been placed on the XY display. The particular data point is at a radius of 164 mV and an angle of -133.3 degrees. On the left side of the display the oscilloscope shows the point in time at which this data occurred The engineer can place a cursor on a data point in the XY plot. The oscilloscope will then show the values of X/Y, X*Y, the radius and the angle of that point. On the left hand side the scope it will show the engineer the time point and the values of the I and Q waveforms that produced that particular point of the XY plot. For example, if there is a point of concern on the XY plot, the engineer can place a cursor on it and then zoom in to view the I and Q waveforms at that point in time. Conversely, the engineer can move a cursor along the I-vs.-Time and Q-vs.-Time waveforms and see where the cursor moves on the XY plot. This ability to have a cursor which tracks on both the XY plot and the signal vs. time traces is a unique feature of Teledyne LeCroy oscilloscopes. A wide variety of other measurements are available. Summary A digital oscilloscope with an input for an external sampling clock can be a very useful tool for capturing and measuring wireless signals. The ability to view I and Q signals versus time while at the same time being able to view and measure the constellation display of the same signals can be very helpful. The scope used for the images in this paper was a Teledyne LeCroy Waverunner 640 Zi. For more information on this topic go to www.lecroy.com and read LAB Brief WM-303C “Constellation Displays – Analyze Quadrature Data Communications Signals Using X-Y Displays,” authored by Art Pini. Teledyne LeCroy Using Constellation Diagrams to Test Wireless Devices page | 3 of 3 .
Load more

Recommended publications
  • Degree Project
    Degree project Performance of MLSE over Fading Channels Author: Aftab Ahmad Date: 2013-05-31 Subject: Electrical Engineering Level: Master Level Course code: 5ED06E To my parents, family, siblings, friends and teachers 1 Research is what I'm doing when I don't know what I'm doing1 Wernher Von Braun 1Brown, James Dean, and Theodore S. Rodgers. Doing Second Language Research: An introduction to the theory and practice of second language research for graduate/Master's students in TESOL and Applied Linguistics, and others. OUP Oxford, 2002. 2 Abstract This work examines the performance of a wireless transceiver system. The environment is indoor channel simulated by Rayleigh and Rician fading channels. The modulation scheme implemented is GMSK in the transmitter. In the receiver the Viterbi MLSE is implemented to cancel noise and interference due to the filtering and the channel. The BER against the SNR is analyzed in this thesis. The waterfall curves are compared for two data rates of 1 M bps and 2 Mbps over both the Rayleigh and Rician fading channels. 3 Acknowledgments I would like to thank Prof. Sven Nordebo for his supervision, valuable time and advices and support during this thesis work. I would like to thank Prof. Sven-Eric Sandstr¨om.Iwould also like to thank Sweden and Denmark for giving me an opportunity to study in this education system and experience the Scandinavian life and culture. I must mention my gratitude to Sohail Atif, javvad ur Rehman, Ahmed Zeeshan and all the rest of my buddies that helped me when i most needed it.
    [Show full text]
  • Bit & Baud Rate
    What’s The Difference Between Bit Rate And Baud Rate? Apr. 27, 2012 Lou Frenzel | Electronic Design Serial-data speed is usually stated in terms of bit rate. However, another oft- quoted measure of speed is baud rate. Though the two aren’t the same, similarities exist under some circumstances. This tutorial will make the difference clear. Table Of Contents Background Bit Rate Overhead Baud Rate Multilevel Modulation Why Multiple Bits Per Baud? Baud Rate Examples References Background Most data communications over networks occurs via serial-data transmission. Data bits transmit one at a time over some communications channel, such as a cable or a wireless path. Figure 1 typifies the digital-bit pattern from a computer or some other digital circuit. This data signal is often called the baseband signal. The data switches between two voltage levels, such as +3 V for a binary 1 and +0.2 V for a binary 0. Other binary levels are also used. In the non-return-to-zero (NRZ) format (Fig. 1, again), the signal never goes to zero as like that of return- to-zero (RZ) formatted signals. 1. Non-return to zero (NRZ) is the most common binary data format. Data rate is indicated in bits per second (bits/s). Bit Rate The speed of the data is expressed in bits per second (bits/s or bps). The data rate R is a function of the duration of the bit or bit time (TB) (Fig. 1, again): R = 1/TB Rate is also called channel capacity C. If the bit time is 10 ns, the data rate equals: R = 1/10 x 10–9 = 100 million bits/s This is usually expressed as 100 Mbits/s.
    [Show full text]
  • Application of 4K-QAM, LDPC and OFDM for Gbps Data Rates Over HFC Plant David John Urban Comcast
    Application of 4K-QAM, LDPC and OFDM for Gbps Data Rates over HFC Plant David John Urban Comcast Abstract Higher spectral density requires mapping more bits into a symbol at the expense of a This paper describes the application of higher signal to noise ratio (SNR) threshold. 4096-QAM, low density parity check codes The new physical layer will map 12 bits per (LDPC), and orthogonal frequency division symbol on the downstream compared to the 8 multiplexing (OFDM) to transmission over a bits per symbol used in DOCSIS 3.0. 4K- hybrid fiber coaxial cable plant (HFC). These QAM (or 4096-QAM) is a modulation techniques enable data rates of several Gbps. technique that has 4,096 points in the constellation diagram and each point is A complete derivation of the equations mapped to 12 bits. The new physical layer used for log domain sum product LDPC will map 10 bits per symbol using 1024-QAM decoding is provided. The reasons for (or 1K-QAM) on the upstream compared to 6 selecting OFDM and 4K-QAM are described. bits per symbol with 64-QAM used in Analysis of performance in the presence of DOCSIS 3.0. noise taken from field measurements is made. INCREASING SPECTRAL EFFICIENCY INTRODUCTION The three key methods for increasing the A new physical layer is being developed for spectral efficiency of the HFC plant in the transmission of data over a HFC cable plant. new physical layer are LDPC, OFDM and The objective is to increase the HFC plant 4K-QAM. LDPC is a very efficient coding capacity.
    [Show full text]
  • A Measurement Instrument for Fault Diagnosis in Qam-Based Telecommunications
    12th IMEKO TC4 International Symposium Electrical Measurements and Instrumentation September 25−27, 2002, Zagreb, Croatia A MEASUREMENT INSTRUMENT FOR FAULT DIAGNOSIS IN QAM-BASED TELECOMMUNICATIONS Pasquale Arpaia(1), Luca De Vito(1,2), Sergio Rapuano(1), Gioacchino Truglia(1,2) (1) Dipartimento di Ingegneria, Università del Sannio, piazza Roma, Benevento, Italy (2) Telsey Telecommunications, viale Mellusi 68, Benevento, Italy Abstract − A method for diagnosing faults in Some techniques for classifying automatically the main communication systems based on QAM (Quadrature faults on QAM modulation via the constellation diagram Amplitude Modulation) modulation scheme is proposed. were proposed. The approach followed in [4] is based on a The most relevant faults affecting this modulation have been Wavelet Network (WN). This method provides very good observed and modelled. Such faults, individually and results on simulated and actual signals. combined, are classified and estimated by analysing the Another method classifies the faults through an image- statistical moments of the received symbols. Simulation and processing approach [5]. The constellation diagram is experimental results of characterisation and validation digitised, then the obtained image is compared with some highlight the practical effectiveness of the proposed method. fault models, by using a correlation method, and a similarity score is provided. Keywords: Fault diagnosis, telecommunication, testing, However, both the WN- and the image processing-based QAM. methods can recognize and eventually measure only the dominating fault, and can not recognize the simultaneous 1. INTRODUCTION presence of several faults. In this paper, a diagnostics method, based on analytical Quadrature Amplitude Modulation (QAM) is an estimation of the statistical moments of the received symbol attractive method for transmitting two data streams in distribution, is proposed for QAM-modulation.
    [Show full text]
  • N9064A & W9064A VXA Signal Analyzer Measurement Application Measurement Guide
    Agilent X-Series Signal Analyzer This manual provides documentation for the following analyzers: PXA Signal Analyzer N9030A MXA Signal Analyzer N9020A EXA Signal Analyzer N9010A CXA Signal Analyzer N9000A N9064A & W9064A VXA Signal Analyzer Measurement Application Measurement Guide Agilent Technologies Notices © Agilent Technologies, Inc. Manual Part Number as defined in DFAR 252.227-7014 2008-2010 (June 1995), or as a “commercial N9064-90002 item” as defined in FAR 2.101(a) or No part of this manual may be as “Restricted computer software” reproduced in any form or by any Supersedes: July 2010 as defined in FAR 52.227-19 (June means (including electronic storage Print Date 1987) or any equivalent agency and retrieval or translation into a regulation or contract clause. Use, foreign language) without prior October 2010 duplication or disclosure of Software agreement and written consent from is subject to Agilent Technologies’ Agilent Technologies, Inc. as Printed in USA standard commercial license terms, governed by United States and Agilent Technologies Inc. and non-DOD Departments and international copyright laws. 1400 Fountaingrove Parkway Agencies of the U.S. Government Trademark Santa Rosa, CA 95403 will receive no greater than Acknowledgements Warranty Restricted Rights as defined in FAR 52.227-19(c)(1-2) (June 1987). U.S. Microsoft® is a U.S. registered The material contained in this Government users will receive no trademark of Microsoft Corporation. document is provided “as is,” and is greater than Limited Rights as subject to being changed, without defined in FAR 52.227-14 (June Windows® and MS Windows® are notice, in future editions.
    [Show full text]
  • R&S®FSW-K70 Measuring the BER and the EVM for Signals With
    R&S®FSW-K70 Measuring the BER and the EVM for Signals with Low SNR Application Sheet Signals with low signal-to-noise ratios (SNR) often cause bit errors during demodulation, so that modula- tion accuracy values such as the error vector magnitude (EVM) may not be determined correctly. This application sheet describes: ● The significance of the Bit Error Rate (BER) parameter for signal analysis ● How the R&S FSW VSA application calculates the BER and determines bit errors ● How this knowledge can be used to obtain correct modulation accuracy results (;ÜOÔ2) 1178.3170.02 ─ 01 Application Sheet Test & Measurement R&S®FSW-K70 Contents Contents 1 Introduction............................................................................................ 2 2 How to Create Known Data Files..........................................................3 3 BER Measurement in the R&S FSW VSA application.........................6 4 Tips for Improving Signal Demodulation in Preparation for the Known Data File..................................................................................... 8 5 Measurement Example - Measuring the BER....................................14 6 Additional Information.........................................................................16 1 Introduction What is the Bit Error Rate (BER)? In signal analysis, a bit error occurs when a false symbol decision is made during demodulation. That is: the demodulated symbol does not correspond to the transmitted symbol. Bit errors often occur when demodulating highly distorted signals
    [Show full text]
  • Digital Phase Modulation: a Review of Basic Concepts
    Digital Phase Modulation: A Review of Basic Concepts James E. Gilley Chief Scientist Transcrypt International, Inc. [email protected] August , Introduction The fundamental concept of digital communication is to move digital information from one point to another over an analog channel. More specifically, passband dig- ital communication involves modulating the amplitude, phase or frequency of an analog carrier signal with a baseband information-bearing signal. By definition, fre- quency is the time derivative of phase; therefore, we may generalize phase modula- tion to include frequency modulation. Ordinarily, the carrier frequency is much greater than the symbol rate of the modulation, though this is not always so. In many digital communications systems, the analog carrier is at a radio frequency (RF), hundreds or thousands of MHz, with information symbol rates of many megabaud. In other systems, the carrier may be at an audio frequency, with symbol rates of a few hundred to a few thousand baud. Although this paper primarily relies on examples from the latter case, the concepts are applicable to the former case as well. Given a sinusoidal carrier with frequency: fc , we may express a digitally-modulated passband signal, S(t), as: S(t) A(t)cos(2πf t θ(t)), () = c + where A(t) is a time-varying amplitude modulation and θ(t) is a time-varying phase modulation. For digital phase modulation, we only modulate the phase of the car- rier, θ(t), leaving the amplitude, A(t), constant. BPSK We will begin our discussion of digital phase modulation with a review of the fun- damentals of binary phase shift keying (BPSK), the simplest form of digital phase modulation.
    [Show full text]
  • Phase Jitter in DTV Signals
    BROADCASTING DIVISION Application Note Phase Jitter in DTV Signals Products: TV Test Transmitter R&S SFQ TV Test Receiver R&S EFA 7BM30_0E Contents Phase Jitter in DTV Signals 1 Introduction ................................................................................................... 3 2 Measurement Capabilities of TV Test Transmitter R&S SFQ ................. 3 2.1 Phase Jitter Generation and Test Setup ................................................... 3 2.2 What Phase Jitter is Produced at What Modulation Frequency fMOD? ..... 4 2.3 Examples of Phase Jitter in a Constellation Diagram ............................ 5 2.4 Phase Jitter as a Function of Modulation Frequency ............................ 6 2.5 Phase Jitter Limits for 16QAM and 64QAM ................................................... 6 3 Summary ................................................................................................ 6 Appendix – Technical Data of Mixer R&S MUF2-Z2 ....................................... 7 2 BROADCASTING DIVISION Phase Jitter in DTV Signals 2 Measurement Capabilities of 1 Introduction TV Test Transmitter R&S SFQ Today's state-of-the-art TV test transmitters for TV Test Transmitter R&S SFQ meets the digital TV provide signals fully complying with requirements of DVB and ATSC. Multistandard the European DVB (digital video broadcasting) test capability is provided through options. The standard and the U.S. ATSC (advanced three DVB substandards – DVB-C (cable), television systems committee) standard. DVB-S (satellite) and DVB-T (terrestrial) – are Featuring calibrated settings for each of these also implemented by means of options. Another standards, the transmitters cover all parameters option is available for fading simulation. stipulated by the respective specifications. Configured in this way, the test transmitter is TV test transmitters must not only be capable of capable of setting and varying all of the above generating signals in conformance with signal parameters except for phase jitter.
    [Show full text]
  • Lecture 10 Digital I/Q Transceiver
    Lecture 10 Digital I/Q Transceiver Digital I/Q Transceiver • Constellation Diagram •SNR • Eye Diagram Lab 5 • Transmitter • Analog Receiver • Digital Receiver 10/17/2006 Digital Modulation Baseband Input Receiver Output Lowpass it(t) ir(t) t t π π 2cos(2 f1t) 2cos(2 f1t) π π 2sin(2 f1t) 2sin(2 f1t) Lowpass qt(t) qr(t) t t Decision Boundaries Sample Times • I/Q signals take on discrete values at discrete time instants corresponding to digital data – Receiver samples I/Q channels • Uses decision boundaries to evaluate value of data at each time instant • I/Q signals may be binary or multi-bit – Multi-bit shown above 10/17/2006 L Lecture 10 Fall 2006 2 Constellation Diagram-16QAM Q 00 01 11 10 Receiver Output 00 01 Decision t Boundaries I 11 10 t Decision Sample Boundaries Times • We can view I/Q values at sample instants on a two- dimensional coordinate system • Decision boundaries mark up regions corresponding to different data values • Gray coding used to minimize number of bit errors that occur if wrong decisions made due to noise 10/17/2006 L Lecture 10 Fall 2006 3 Impact of Noise on Constellation Diagram High Power Low Power • Sampled data values no longer land in exact same location across all sample instants while decision boundaries remain fixed • Significant noise causes bit errors to be made • Increasing signal power increases distance between decision boundaries i.e., increased SNR 10/17/2006 L Lecture 10 Fall 2006 4 Transition Behavior Between Constellation Points Q 00 01 11 10 00 Decision 01 Boundaries I 11 10 Decision Boundaries • Constellation diagrams provide us with a snapshot of I/Q signals at sample instants • Transition behavior between sample points depends on modulation scheme and transmit filter 10/17/2006 L Lecture 10 Fall 2006 5 Need for Transmit Filter data(t) x(t) Td O-Order t t Track & Hold • Steps in waveform x(t) have high frequency components.
    [Show full text]
  • Chapter 5 Analog Transmission
    Chapter 5 Analog Transmission 5.1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 5-1 DIGITAL-TO-ANALOG CONVERSION Digital--tto--analoanalog conversion is the process of changing one of the characteristics of an analog signal based on the information in digital data.. Topics discussed in this section: Aspects of Digital-to-Analog Conversion Amplitude Shift Keying Frequency Shift Keying Phase Shift Keying Quadrature Amplitude Modulation 5.2 Figure 5.1 Digital-to-analog conversion Digital-to-analog modulation (or shift keying): changing one of the characteristics of the analog signal …… based on the information of the digital signal (carrying digital information onto analog signals) Changing any of the characteristics of the simple signal (amplitude, frequency, or phase) would change the nature of the signal to become a composite signal 5.3 Figure 5.2 Types of digital-to-analog conversion 5.4 Asppgects of Digital-to-Analog Conversion Data Element vs. Signal Element Data Rate vs. Signal Rate S = N/r r=logr = log2 L, where L is the number of signal elements Bandwidth: The required bandwidth for analog transmission of digital data is proportional to the signal rate Carrier Signal: The digital data changes the carrier signal by modifying one of its characteristics This is called modulation (or Shift Keying) The receiver is tuned to the carrier signal’s frequency 5.5 Note Bit rate is the number of bits per second. Baud rate is the number of signal elements per second . In the analog transmission of digital data, the baud rate is less than or equal to the bit rate.
    [Show full text]
  • Critical RF Measurements in Cable, Satellite and Terrestrial DTV Systems
    Application Note Critical RF Measurements in Cable, Satellite and Terrestrial DTV Systems The secret to maintaining reliable and high-quality services over different digital television transmission systems is to focus on critical factors that may compromise the integrity of the system. This application note describes those critical RF measurements which help to detect such problems before viewers lose their service and picture completely. Critical RF Measurements in Cable, Satellite and Terrestrial DTV Systems Application Note Modern digital cable, satellite, and terrestrial systems behave The Key RF parameters quite differently when compared to traditional analog TV as the signal is subjected to noise, distortion, and interferences RF signal strength How much signal is being received along its path. Todays consumers are familiar with simple analog TV reception. If the picture quality is poor, an indoor Constellation diagram Characterizes link and modulator antenna can usually be adjusted to get a viewable picture. performance Even if the picture quality is still poor, and if the program is of MER An early indicator of signal degradation, MER enough interest, the viewer will usually continue watching as (Modulation is the ratio of the power of the signal to the long as there is sound. Error Ratio) power of the error vectors, expressed in dB DTV is not this simple. Once reception is lost, the path EVM EVM is a measurement similar to MER but to recovery isn t always obvious. The problem could be (Error Vector expressed differently. EVM is the ratio of the caused by MPEG table errors, or merely from the RF power Magnitude) amplitude of the RMS error vector to the dropping below the operational threshold or the cliff point.
    [Show full text]
  • Vector Signal Analyzer R&S FSQ-K70
    Product brochure Version 02.00 July 2004 Vector Signal Analyzer ¸FSQ-K70 Universal demodulation, analysis and documentation of digital radio signals ◆ For all major mobile radio communica- ◆ For all common digital modulation ◆ Optimum representation of results: tion standards: modes: – In-phase and quadrature signals –GSM & EDGE – BPSK, QPSK, OQPSK versus time –WCDMA-QPSK – π/4 DQPSK – Magnitude and phase versus time – cdma2000-QPSK – 8PSK, D8PSK, 3π/8 8PSK –Eye diagram – Bluetooth® –(G)MSK – Vector diagram –TETRA –2, 4, (G)FSK – Constellation diagram –PDC – 16, 32, 64, 128, 256 (D)QAM – Table with modulation errors –PHS – 8VSB – Demodulated bit stream –DECT ◆ 25 MHz symbol rate expandable up to – Statistical evaluation of modula- –NADC 81.6 MHz tion parameters ◆ 28 MHz I/Q demodulation bandwidth – Spectral evaluation expandable up to 120 MHz – Amplifier distortion measurements Universal analysis of digital Fit for future standards Multiple test functions radio signals integrated in one unit The option ¸FSQ-B72 allows the The vector signal analyzer option standard demodulation bandwidth of The Signal Analyzers ¸FSQ in con- upgrades the high-quality Signal 28 MHz to be expanded to 60 MHz for junction with the option ¸FSQ-K70 Analyzers ¸FSQ, adding universal frequencies below 3.6 GHz and above replace several individual instruments: demodulation and analysis capability 120 MHz. down to bit stream level for digital radio ◆ High-grade spectrum analyzer signals. The option supports all common ◆ Vector demodulator mobile radio communications standards. Efficient in production ◆ Constellation analyzer The high measurement speed of Measurement and analysis of 60 sweeps/s in the analyzer mode and Principle of vector signal digital modulation signals typically 20 measurements/s using the analysis vector signal analyzer function is ideal for You want to measure and analyze digi- applications in production.
    [Show full text]