Difference of RF-Waveform between DSB-ASK and SSB-ASK

pancho_hideboo · Jun 23, 2018

Attached figure shows RF-Waveforms in RFID.
DSB-ASK, SSB-ASK, PR-ASK.

PR-ASK is no more than BPSK with amplitude variation at symbol transition.

My questions are :
(1) What RF-Wavwform does show SSB-ASK ?
I don't think RF-Waveform of SSB-ASK is same as DSB-ASK.

(2) What advantage does have PR-ASK than DSB-ASK or SSB-ASK ?
It gives small required CNR than DSB-ASK or SSB-ASK ?

FvM · Jun 23, 2018

The commonly understood technical terms for the shown modulation methods are ASK and BPSK. They are e.g. used in RFID standard documents. A differentiation between "DSB" AND "SSB" doesn't seem to make sense for binary modulation. PR-ASK makes no sense either, a contradiction in terms, PSK is clearly distinguished from ASK.

13.56MHz RFID ISO/IEC14443 and related NFC standard are e.g. using BPSK subcarrier modulation for tag to reader ("PICC to PCD") transmission at higher data rates.

pancho_hideboo · Jun 23, 2018

FvM said:
A differentiation between "DSB" AND "SSB" doesn't seem to make sense for binary modulation.

No.
It does make sense surely.

{I(t) + j*Ih(t)} * exp(j*omega*t)
Ih(t) is a hilbert transfomation of I(t)

This is an image rejection upmixer.

DSB-ASK has a real envelope, I(t).
On the other hand, SSB-ASK has a complex envelope, I(t) + j*Ih(t).

My question is a behavior of this I(t) + j*Ih(t) or
sqrt{I(t)**2 + Ih(t)**2}.

FvM said:
PR-ASK makes no sense either

No. It also surely makes sense.

DSB-ASK, SSB-ASK and PR-ASK are defined in "EPCglobal Class 1 Generation 2 (C1G2)".

https://books.google.com/books?id=V...84ChDoAQglMAE#v=onepage&q=pr-ask rfid&f=false

https://www.edaboard.com/showthread.php?145945#2

FvM · Jun 24, 2018

O.K, the terms are in fact used in the Gen2 EPC specification, I forgot about it.

I think there's no problem with "PR-ASK" which is just a synonym of more commonly used term BPSK.

SSB-ASK is a modulation specific to Gen2 EPC, curiously there seems to be no exact description throughout the spec, at least in the documents that I reviewed.

A broad idea what they mean can be found in the air interface specification document

If an Interrogator uses SSB-ASK modulation, the transmit spectrum shall be centered in the channel during R=>T signaling

The below shown spectrum illustrates the usage of the SSB signal.

This looks like they are cutting the lower sideband after performing a usual ASK modulation, centering the transmitter spectrum in the occupied band by shifting the carrier.

The time domain waveform of the "SSB" signal will be of course different from the Annex H waveform, in so far the modulated waveform picture is misleading.

pancho_hideboo · Jun 26, 2018

FvM said:
The time domain waveform of the "SSB" signal will be of course different from the Annex H waveform,
in so far the modulated waveform picture is misleading.

Attached figure shows DSB, LSB, USB for one-tone sinusoidal modulation.
Waveform of SSB is very similar to DSB.

So I think Waveform of SSB-ASK will be very similar to DSB-ASK.

Code:

`include "constants.vams"
`include "disciplines.vams"

module V_SSB_ASK(dsb, lsb, usb);
output dsb, lsb, usb;
electrical dsb, lsb, usb;

parameter real fc = 1G from (0.0:inf);
parameter real fm = 1M from (0.0:inf);
parameter real Ac = 1.0 exclude 0;
parameter real init_phase = 0.0; //Initial phase for Sinusoid

parameter real ASK_Mod_Index=100.0; //from [10:100];

real wc, wm, wlsb, wusb;
real init_phase_rad, m;
real vc, vlsb, vusb;

analog begin
   @(initial_step) begin
      wc = `M_TWO_PI * fc;
      wm = `M_TWO_PI * fm;
      wlsb = wc - wm;
      wusb = wc + wm;
      m = ASK_Mod_Index / 100.0;
      init_phase_rad = (`M_PI/180.0) * init_phase;
   end //initial_step

   //to ensure at least 25 points in an output cycle
   $bound_step( (1/fc) / 25 );

   vc = Ac * cos(wc * $abstime + init_phase_rad);
   vlsb = m * (Ac/2) * cos(wlsb * $abstime + init_phase_rad);
   vusb = m * (Ac/2) * cos(wusb * $abstime + init_phase_rad);

   V(dsb) <+ vc + vlsb + vusb;
   V(lsb) <+ vc + 2 * vlsb;
   V(usb) <+ vc + 2 * vusb;
end //analog

endmodule

FvM · Jun 27, 2018

For sinusoidal modulation, the DSB and SSB waveforms envelope waveforms look similar, difference is only in the instantaneous carrier phase. But as far as I see, the "equal shape" isn't maintained when switching to more complex, e.g. binary bitstream modulation signals.

pancho_hideboo · Jun 28, 2018

FvM said:
But as far as I see,
the "equal shape" isn't maintained when switching to more complex,
e.g. binary bitstream modulation signals.

Tag of RFID does not know what modulation RF waveform comes from reader/writer.
However Tag of RFID can decode RF waveform by same envelope detector.

We can decode any of DSB-ASK, SSB-ASK and PR-ASK by one same envelope detector without any additional information.
This is a remarkable feature of RF Modulation in RFID.

T0 : Time duartion for Bit=0
T1 : Time duration for Bit=1

T1 > T0

In https://www.edaboard.com/attachment.php?attachmentid=147463&d=1529731132
"DSB- or SSB-ASK Baseband Data : 010" is correct.
But "PR-ASK Baseband Data : 010" is wrong.

FvM · Jun 28, 2018

We can decode any of DSB-ASK, SSB-ASK and PR-ASK by one same envelope detector without any additional information.

How do you decode "PR-ASK" (BPSK) modulated signal with envelope detector? It's usually decoded with Costas Loop PLL.

pancho_hideboo · Jun 29, 2018

FvM said:
It's usually decoded with Costas Loop PLL.

Such power hungry circuit can not be acceptable for passive RFID Tag.
Moreover any phase information of carrier is not required for demodulating at all.

FvM said:
How do you decode "PR-ASK" (BPSK) modulated signal with envelope detector?

See RF waveform in https://www.edaboard.com/attachment.php?attachmentid=147463&d=1529731132

We can distinguish T0 and T1 by simple envelope detector.

T0 : Time duartion for Bit=0
T1 : Time duration for Bit=1

T1 > T0

This is a remarkable feature of modulation scheme in RFID.

FvM · Jul 2, 2018

We can distinguish T0 and T1 by simple envelope detector.

Yes, it's possible in the context of the EPC specific bit coding. They are generating different modulating waveforms for ASK and BPSK to achieve similar RF envelopes.

I assume that this property is the motivation for introducing the uncommon term "PR-ASK", using phase shift keying to produce a specific envelope.

This is a remarkable feature of modulation scheme in RFID.

I see the advantage. EPC is not a synonym of RFID in general, it's one of many used RFID standards.

"DSB- or SSB-ASK Baseband Data : 010" is correct.
But "PR-ASK Baseband Data : 010" is wrong.

Not exactly wrong, just sketched inaccurately, cutting part of the waveforms for the first data symbol. Ratio of 0 and 1 duration can be different in EPC, here's the exact specification

A side remark referring to the initial question, if you modulate square wave with sufficient bandwidth using SSB-ASK, the envelope isn't exactly rectangular. This can't be seen in your previous experiment with sine SSB modulation.

pancho_hideboo · Jul 2, 2018

FvM said:
Not exactly wrong,
just sketched inaccurately,
cutting part of the waveforms for the first data symbol.

No.
Surely see and compare "PR-ASK Baseband Data : 010" and "PR-ASK Modulating Waveform" in https://www.edaboard.com/attachment.php?attachmentid=147463&d=1529731132.

FvM said:
Ratio of 0 and 1 duration can be different in EPC,
here's the exact specification

Wrong.
This(https://www.edaboard.com/attachment.php?attachmentid=147627&d=1530513989) is true for DSB-ASK and SSB-ASK.
But this is not true for PR-ASK, although T0 and T1 are different even in PR-ASK.

FvM said:
EPC is not a synonym of RFID in general,
it's one of many used RFID standards.

Right.

FvM said:
A side remark referring to the initial question,
if you modulate square wave with sufficient bandwidth using SSB-ASK,
the envelope isn't exactly rectangular.

Right.

FvM said:
This can't be seen in your previous experiment with sine SSB modulation.

However I think RF envelope of DSB-SSK and SSB-ASK is still very similar.
And we can still distinguish T0 and T1 of DSB-SSK, SSB-ASKand PR-ASK by same simple envelope detector.

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Difference of RF-Waveform between DSB-ASK and SSB-ASK

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