Talk:Quadrature amplitude modulation

message: One issue is - so much talk about N-level QAM, but hardly any talk (or none whatsoever) about how the N-level QAM receiver obtains a normalised N-level QAM map - at least for analog-style 64-QAM. For example, does the transmitter send a signal every once in a while so that the receiver is able to use the incoming transitions to obtain an accurate estimate of the N-level QAM map boundaries? Obviously, if signal strength changes (or environmental conditions change) then the receiver needs to have a new set of calibration data - in order to always have an accurate constellation map to work with. Accurate knowledge of amplitude and phase is important. The question is - how does the receiver calibrate for amplitude and phase? Does the transmitter regularly send out a set of signals that mark out the outer-most boundaries of the N-level map? Here, I'm referring to a scheme that sends out a sinewave having an amplitude (A) and a relative phase (theta) that represents 1 state out of the 64 states of a 64-QAM square grid. I'm not referring to schemes involving digital 64-QAM based on OFDM (and IFFT/FFT). KorgBoy (talk) 21:54, 16 May 2017 (UTC)
thread_title:  64-QAM : receiver calibration? 

message: Hi. Yet another page I want to edit for English usage (my main activity on Wikipedia). I noticed the page uses the word analogue (Commonwealth English spelling) and two words (or forms of words) ending in -ize (American English spelling). The Manual of Style recommends (sensibly) that spelling and usage within an article should be uniform. But I'm not sure which we it should go. It seems that perhaps Commonwealth usage is now dominant, but looking at the page history, I see there were inconsistencies from the beginning. (The very first version has both analog and quantised; perhaps analog is creeping into Commonwealth?) I think at least some comments are necessary before unification is performed. Ddawson 01:10, 26 August 2005 (UTC)
replies: text: I am the editor who rewrote the article into its current form. I speak British English, being English (and British!). However, I've adopted some Americanis(z)ations owing to the journals I write papers in insisting on American English. So I mix them up. Most of the inconsistencies will be my fault, and I do not mind to which version it is harmonized, but harmonized it certainly should be! Thanks for the vigilance. -Splash 01:25, 26 August 2005 (UTC)
replies: text:  -ize can also be used in British English. It's common in British academic publications. SpNeo 02:28, 29 October 2005 (UTC)
replies: text: Yes, though that is largely (in my personal academic writing experience) because many of those publications are in American journals/conferences and the like. For example, the vast majority of electrical engineering journals are published by IEEE which prefers American English spelling. -Splashtalk 06:32, 29 October 2005 (UTC)
thread_title:  Dialectic inconsistency 

message: How can i construct a 64 QAM Constellation diagram?
     For the rectangular case, you would just use an 8x8 grid.  —Preceding unsigned comment added by 75.32.247.201 (talk) 05:24, 6 October 2007 (UTC)
replies: text: TheOriginalPC (talk) 06:27, 19 March 2009 (UTC)
thread_title:  64 QAM Constellation diagram 

message: Although analogue QAM is possible, this article focuses on digital QAM.
This means there's nowhere obvious on Wikipedia to add information about analogue QAM or QAM in general. Perhaps the bulk of this article can be moved to QAM (digital) and the remainder made more mixed? --Dtcdthingy 01:55, 1 June 2006 (UTC)
replies: text: If you want to write about analogue QAM, just remove the 'disclaimer', add a new section heading somewhere and dive in. Unless you feel strongly that they should be in different articles. -Splashtalk 01:57, 1 June 2006 (UTC)
replies: text: The problem is that most of the article has been written as if the page was called Digital QAM. You'd have to put all that under a great big Digital QAM subheading and/or rewrite lots of it to say it only applies to digital. It would be better if we just renamed it, even if that means the article here ends up relatively short. --Dtcdthingy 02:17, 1 June 2006 (UTC)
thread_title:  Analogue QAM 

message: There is a mathematical error on this page in the description of the BER of a M-ary QAM signal in AWGN, where M is even. The BER for a gray coded signal can be directly infered from the PAM signal in each quadrature phase, which are independent from each other.
Thus 64-QAM, which can be regarded as two independent 8-PAM streams, has a BER approximated by 1/3 of symbol error rate of a Gray coded 8-PAM symbol stream.
In general, BER=\frac{4}{k}\times \left( 1-\frac{1}{\sqrt{M}} \right) \times Q\left(\sqrt{\frac{E_b}{N_0}\times \frac{3k}{(M-1)}}\right)
Where k=\log_2{M}
Although it is true that both quadrature PAM symbols must be correct for the final QAM symbol to be entirely correct, there is no such dependancy between the bit errors occuring in each quadrature PAM channel of a QAM system!
--Crazzell 23:38, 13 September 2006 (UTC)
thread_title:  Error in equation for BER of Gray coded M-ary QAM 

message: To be honest, I don't particularly care either way.  But I'm not a fan of changing things for the sake of it (another example would be people who go around Americanising British spellings).
From the MOS:
"It is also acceptable to use “we” in mathematical derivations"
For a few counter-examples to the claim that technical articles don't use "we":
*Gaussian_distribution
*Normalisation_of_a_wavefunction
*Lagrange's_theorem_(group_theory)
*Maximum_likelihood
*Expected_value
*Law_of_total_expectation
*Law_of_total_variance
*Gaussian_elimination
*Augmented_matrix
*Identity_matrix
*Quantum_mechanics
*Cauchy–Schwarz inequality
*Inner_product_space
*Isomorphism
*Bijection
*Permutation_group
*Affine_space
*Linear subspace
*Real number
*Rational number
*...!!!
I could easily go on all night finding counter-examples... Oli Filth 23:23, 15 January 2007 (UTC)
thread_title:  Use of first person 

message: Throughout the article, there are some unclear places whether in QAM only the amplitude of the both carriers is modulated, or both the amplitude and phase is modulated in both carriers. I believe that only the amplitude is modulated, not the phase of each carrier. In this case, I do not quite understand this sentence:
The complicating factor is that the points are no longer all the same amplitude and so the demodulator must now correctly detect both phase and amplitude, rather than just phase.
As said earlier, no change to the phase of either carrier is done. Why should a demodulator need to detect the phase?
Paluchpeter 13:14, 20 July 2007 (UTC)
replies: text: By altering the amplitudes of the I and Q components, the phase of the overall signal is altered.  Oli Filth 13:25, 20 July 2007 (UTC)
replies: text:  Of course, but the phase of the combined signal is not relevant as I understand it. After receiving the combined signal and multiplying it with either sine or cosine signal and filtering the result with a low-pass filter, we will extract the corresponding I or Q component, without paying attention to the phase of the combined signal. Perhaps I am missing something... Paluchpeter 14:59, 20 July 2007 (UTC)
replies: text:  The phase is relevant.  QAM demodulation requires a phase reference, i.e. it can only be demodulated coherently.  Also, it is susceptible to phase noise.  Neither of these apply to simple AM.  Oli Filth 16:34, 20 July 2007 (UTC)
replies: text:  The phase is relevant but not because is required as phase reference for coherent demodulation, but because it actually carries information. And that is why it must be demodulated coherently, because only detecting the envelope would not result in anything (the two modulating signals are merged in the envelope and in the phase).And regarding to simple AM, I don't understand what you say about they don't apply. Because it is possible to detect the "simple AM" (I guess AM-DSB/SSB-LC) with coherent detection rather than envelope detection, and the Rx should also be in sync with the carrier's frequency and is susceptible  to phase and frequency errors as well.--Dhcpy 04:51, 1 December 2007 (UTC)

text: The previous comment is dead on.  Regular AM can be demodulated with simple noncoherent envelope detection, but QAM requires coherent demodulation, i.e. a phase reference is required.  Mathematically speaking, sine and cosine (the two orthogonal carriers that define the quadrature) are just phase-delayed (or equivalently, time-delayed) versions of each other.  The receiver must somehow synchronize (typically via a phase reference) its own local oscillator so that it matches that of the transmitter.  This is necessary because the signal undergoes an unknown time delay (e.g. phase delay) in the channel, and arrives at the receiver with an (at least initially) unknown phase offset (with respect to it's own local oscillator). Any non-zero phase offset (between the transmitter and receiver local oscillators) will rotate the constellation correspondingly.  For instance, a rotation of 90 degrees corresponds to a misidentification (a swapping) of the sine and cosine components, which, in general, would yield a catastrophically high bit error probability, near 1/2.  This requirement for phase synchronization is exactly the same as PSK, and for the same reason.  In fact, the simplest way to view QAM is as a generalization of PSK, e.g. PSK without a constant envelope requirement.  —Preceding unsigned comment added by 75.32.247.201 (talk) 06:28, 6 October 2007 (UTC)

text: Both of the carriers are only amplitude modulated, and no phase modulation is normally performed for the carriers. However, phase is still relevant at reception (although not the phase of the total signal). The receiver must synchronize to the carrier phase, beacuse the carriers can be only demodulated using coherent demodulation. Alinja 10:56, 8 October 2007 (UTC)

text: This is how I understand it:If you take a look at the block diagram of the analogue QAM you'll see that modulating signal I(t) multiplies cosine and modulating signal Q(t) multiplies the sine. Those I and Q are two different signals from, lets say, two different voice channels.At this point, the 2 resulting signals I(t)cos(wc.t) & Q(t)sin(wc.t) are, as you say, Amplitude Modulated signals, the phase of the carriers isn't changed.But, when they are added, at that point they merge into a complex signal that varies amplitude AND phase. That can be easily shown by writing this complex signal in the "module and argument form" .By writing the QAM signal that way, you'll see that the envelope (amplitude) varies and  the phase varies as well.--Dhcpy 04:51, 1 December 2007 (UTC)

text: Amplitude modulating two carrier waves in quadrature is identical to amplitude and phase modulating a single carrier wave; the two are a trigonometric identity. -Dawn McGatney  —Preceding unsigned comment added by McGatney (talk • contribs) 06:31, 17 January 2008 (UTC)
thread_title:  Is only the amplitude modified in QAM? 

message: A signal in the time domain demonstrating the transmitted signal and how its formed from its data carrying components would be really useful. ~RayLast «Talk!» 18:15, 4 April 2008 (UTC)
replies: text: TheOriginalPC (talk) 07:58, 19 March 2009 (UTC)

text: True, that's the ideal situation.  Many QAM systems though work without ideal equalization, so there may be some inter-symbol interference, rather than ZI functions.  But this is no different from ordinary AM digital channels, BPSK, etc.  If you start by viewing I and Q as piecewise-constant baseband signals (NRZ-like), then you can get to your idealized case, or close to it, by appropriate filtering.  Dicklyon (talk) 04:59, 20 March 2009 (UTC)
thread_title:  Time domain signal 

message: I have a question, how the signals look like in the transmitter, the I and the Q signal? Do they look like sine and cosine wave with varying amplitude (amplitude of 1 and 3) and phase (either 0 or 180)? Something like this http://img266.imageshack.us/my.php?image=16qamprzykvd9.png ?
And how does the receiver "read" the phase? How will the signal look like in the receiver after being filtered by the low-pass filter? Will it be a signal that has a frequency nearly 0Hz, so basically, will it be a constant signal of amplitude -3, -1, 1 or 3? Thank you in advance. WielkiZielonyMelon (talk) 21:12, 5 February 2009 (UTC)
replies: text: Yes, sort of like that.  Each of the I and Q channels looks like a piece of sine wave (I) or cosine wave (Q) of different amplitudes and polarities.  Their sum can therefore have a few more phases and amplitudes.  To demodulate, each is synchronously downconverted to baseband by mixing with a corresponding local oscillator synced to the appropriate I and Q carrier phases, so the two resulting channels looks like baseband signals, and they don't interfere with each other since each channel's signal is orthogonal to the other's local oscillator or recovered carrier.  The only tricky part is how to make a carrier PLL to sync up with something like that.  For that, you need an elaborated Costas loop or something; I don't recall exactly.  Dicklyon (talk) 06:05, 19 March 2009 (UTC)
thread_title: How the signals look like?

message: One or more portions of this article duplicated other source(s).  Infringing material has been rewritten or removed and must not be restored, unless it is duly released under a compatible license. (For more information, please see "using copyrighted works from others" if you are not the copyright holder of this material, or "donating copyrighted materials" if you are.) For legal reasons, we cannot accept copyrighted text or images borrowed from other web sites or published material; such additions will be deleted. Contributors may use copyrighted publications as a source of information, but not as a source of sentences or phrases. Accordingly, the material may be rewritten, but only if it does not infringe on the copyright of the original or plagiarize from that source. Please see our guideline on non-free text for how to properly implement limited quotations of copyrighted text. Wikipedia takes copyright violations very seriously, and persistent violators will be blocked from editing. While we appreciate contributions, we must require all contributors to understand and comply with these policies. Thank you.  Ozob (talk) 00:28, 23 December 2009 (UTC)
replies: text: It's not clear why you removed as much as you did; yes the definitions are very close to what's in that cited source, and perhaps should be paraphrased more or rewritten in light of other sources.  I'm going to put back the main paragraph, and try to make a sensible section heading.  Dicklyon (talk) 08:06, 23 December 2009 (UTC)
thread_title:  Copyright problem removed 

message: The analog and digital cases are not same. I suggest to split this article into 2. `a5b (talk) 21:46, 12 September 2010 (UTC)
replies: text: What great differences would suggest a need for separate articles?  Dicklyon (talk) 04:26, 13 September 2010 (UTC)
thread_title:  Split analog and digital QAM 

message: Is the first section, named "Digital QAM", describing digital modulation? It is talking about QAM generally, or even some about analog QAM. Why is it named "Digital"?
As far as I know, "digital" means discrete in time domain and quantized in amplitude. Is that right?  —Preceding unsigned comment added by Zhaixm (talk • contribs) 13:16, 28 November 2010 (UTC)
thread_title:  Should the first section named "Digital" ? 

message: The line about VDSL2 using 32768-QAM needs to be removed. VDSL2 only uses DMT line code. VDSL1 gave the option of using QAM or DMT but it was removed in the later VDSL2 specification. An article that backs up the removal of QAM from the spec: http://www.rubytech-brasil.ws/whatsnewtxt/rubytech_vdsl.html scroll down to: VDSL2 Band Plan and Profiles  — Preceding unsigned comment added by 63.117.216.50 (talk) 17:18, 20 March 2014 (UTC)
replies: text: I find this statements about QAM vs. DMT confusing. DMT is not a modulation scheme: it's a multiplexing scheme, i.e. a way to split the channel into several subchannels. You still need a modulation scheme in those subchannels, which may be QAM or another. Does anyone have some information about the modulation used in VDSL2? —Edgar.bonet (talk) 19:35, 20 March 2014 (UTC)
replies: text:  *Sigh*. VDSL does use QAM for each individual OFDM carrier (DMT carrier, if you want to use the archaic term). From Orthogonal_frequency-division_multiplexing: Each sub-carrier is modulated with a conventional modulation scheme (such as quadrature amplitude modulation). I suggest taking a course on Fundamentals of Wireless Communication 101 before offering opinions about the technical content of this article, and not learning about VDSL and QAM from random articles on the Internet. 93.173.234.150 (talk) 19:17, 11 August 2015 (UTC)
thread_title:  VDSL2 and QAM 

message: QAM was originally known as AMPQM (amplitude modulated phase quadrature modulation).  this is nothing but a fancy way of saying every word has an amplitude and phase assigned to it with a constant center carrier.  It was originally invented by Codex corporation which was later on bought out by Motorola.  If you need any technical reference information on this refer to DCA (defense communications circular) circular 310-70-1 volume 2 supplement 1 (which is still classified so you can't access it).
Robert Dell (talk) 19:43, 25 November 2014 (UTC)
thread_title:  FYI QAM has a beginning 

message: Hello fellow Wikipedians,
I have just added archive links to  on Quadrature amplitude modulation. Please take a moment to review my edit. If necessary, add  after the link to keep me from modifying it. Alternatively, you can add  to keep me off the page altogether. I made the following changes:
*Added archive http://web.archive.org/web/20060810085319/http://www.blondertongue.com:80/QAM-Transmodulator/QAM_defined.php to http://www.blondertongue.com/QAM-Transmodulator/QAM_defined.php
When you have finished reviewing my changes, please set the checked parameter below to true to let others know.
Cheers.—cyberbot IITalk to my owner:Online 13:26, 27 February 2016 (UTC)
thread_title:  External links modified 

message: In figure of section Quantized QAM, there is a table representing amplitude, phase and data. In the second record, the data is 1001 with amplitude 75% and phase of 135 degree. Is that phase angle correct? or it should be 113 degree?
Ru7w1k (talk) 06:31, 14 May 2016 (UTC)
replies: text: Yes, that angle is wrong as you note.  The amplitudes are not very close to right either.  Dicklyon (talk) 06:49, 14 May 2016 (UTC)
thread_title:  Is phase angle wrong in figure 'Digital 16-QAM with example constellation points' ? 

message: Hi,
I wanted to drop a shameless plug here in case this could be helpful for generating graphics for this article, or if it'd be handy to link to.
I've put together a javascript library that passes data through sound, and it includes QAM schemes. I have a live interactive demo of it useful for tuning. It displays the received constellation, and you can also view the received waveform. This might be a handy tool for someone curious about QAM.
The link is https://quiet.github.io/quiet-profile-lab/
Brian-armstrong (talk) 23:34, 22 June 2016 (UTC)
thread_title:  Interactive demo 

message: Hello fellow Wikipedians,
I have just modified  on Quadrature amplitude modulation. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
*Added archive http://web.archive.org/web/20140817034950/http://www.scte.org/FileDownload.aspx?A=3445 to http://www.scte.org/FileDownload.aspx?A=3445
*Added archive http://web.archive.org/web/20140416220641/http://webdemo.inue.uni-stuttgart.de/webdemos/02_lectures/uebertragungstechnik_1/qam_constellation_diagram_from_snr/ to http://webdemo.inue.uni-stuttgart.de/webdemos/02_lectures/uebertragungstechnik_1/qam_constellation_diagram_from_snr
*Added archive http://web.archive.org/web/20150904013227/http://www.etti.unibw.de/labalive/experiment/qam/ to http://www.etti.unibw.de/labalive/experiment/qam/
*Added archive https://web.archive.org/web/20060810085319/http://www.blondertongue.com:80/QAM-Transmodulator/QAM_defined.php to http://www.blondertongue.com:80/QAM-Transmodulator/QAM_defined.php
When you have finished reviewing my changes, please set the checked parameter below to true or failed to let others know (documentation at ).
Cheers.—InternetArchiveBot (Report bug) 16:14, 16 July 2016 (UTC)
thread_title:  External links modified 

message: Hello fellow Wikipedians,
I have just modified  on Quadrature amplitude modulation. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
*Added archive http://web.archive.org/web/20110430132506/http://www.barnardmicrosystems.com:80/L4E_comms_2.htm to http://www.barnardmicrosystems.com/L4E_comms_2.htm
*Added archive http://web.archive.org/web/20110713175309/http://www.kylia.com/QAM.html to http://kylia.com/QAM.html
When you have finished reviewing my changes, please set the checked parameter below to true or failed to let others know (documentation at ).
Cheers.—InternetArchiveBot (Report bug) 12:10, 21 July 2016 (UTC)
thread_title:  External links modified 

message: The following Wikimedia Commons file used on this page has been nominated for speedy deletion:
* 
You can see the reason for deletion at the file description page linked above. —Community Tech bot (talk) 14:07, 18 November 2019 (UTC)
thread_title:  A Commons file used on this page has been nominated for speedy deletion 

message: In the Digital QAM section, see the "Digital 16-QAM with example constellation points" GIF. It includes a table of 8 points with amplitudes all either 25% or 75%. I think all 8 amplitude values are incorrect. For example the last point shown, data 1111 in the lower-left corner, is identified as Amplitude 75%. It should be sqrt(2)*75% = 106% = the distance from the origin. I think the correct amplitude values are sqrt(2)*25%=35.4% (4 points), sqrt(2)*75%=106% (4 points), and sqrt(10)*25%=79.1% (8 points). Please agree or disagree. I don't have the means to correct the GIF. Rick314 (talk) 20:15, 18 November 2023 (UTC)
replies: text: I might have known some necessary details a long time ago but they are forgotten now. If the diagram is a polar graph of amplitude and phase, you are obviously correct. But I'm wondering if Constellation diagram suggests that the diagram is just a logical depiction showing how the binary numbers (each four bits for this diagram) are encoded—that would make the diagram correct. It looks like this page does not get much attention. You could ask at WP:RD/S or possibly WP:RD/C. Johnuniq (talk) 02:57, 21 November 2023 (UTC)
thread_title:  Digital 16-QAM GIF Errors