Receiver L Losses w when using Quadr drature Ban Bandpas ass - - PowerPoint PPT Presentation

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Receiver L Losses w when using Quadr drature Ban Bandpas ass - - PowerPoint PPT Presentation

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Receiver L Losses w when using Quadr drature Ban Bandpas ass Samplin ling Andrew Dempster, Ediz Cetin How Bandpass Sampling Works exploits aliasing brings all images with it must attenuate out of band images received

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Andrew Dempster, Ediz Cetin

Receiver L Losses w when using Quadr drature Ban Bandpas ass Samplin ling

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IGNSS 2016, UNSW, Sydney 2

How Bandpass Sampling Works

  • exploits aliasing
  • brings all images with it

– must attenuate out of band

received signal “images” sampling frequency

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IGNSS 2016, UNSW, Sydney 3

Bandpass Sampling: GPS L1

  • For GPS L1 signal, with carrier 1.6 GHz,

BW 2MHz:

– Lowpass sampling would require sampling rates of 3.2Gs/s – Bandpass sampling requires a minimum rate of twice the BW, i.e. 4Ms/s

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IGNSS 2016, UNSW, Sydney 4

Bandpass Filter Design

  • For Bandpass sampling:
  • Max subsampling ratio for GNSS is for L1

GPS:

  • Requires Np/N0 of 29dB for 3dB SNR loss

s

) 1 ( SNR N n N S

p

− + =

Np in-band noise N0 out-of-band noise n subsampling ratio

788 1576/2

max max

= =       = B f n

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IGNSS 2016, UNSW, Sydney 5

Bandpass Sampling

  • Sampling rate must be at least twice the

signal bandwidth (Nyquist)

  • It must also, because a virtual

downconversion results, ensure each downconverted band does not:

–

  • verlap dc,

–

  • verlap the Nyquist rate, or

–

  • verlap any other downconverted signal

band

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IGNSS 2016, UNSW, Sydney 6

2B is not to be

  • Need more than twice the bandwidth

sometimes:

Vaughan, R.G.; Scott, N.L.; White, D.R.; “The theory of bandpass sampling”, IEEE Trans Signal Processing, Volume 39, Issue 9, Sept. 1991 Page(s):1973 - 1984

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IGNSS 2016, UNSW, Sydney 7

Sampling at 2B

fs B

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IGNSS 2016, UNSW, Sydney 8

Sampling at the Minimum Rate

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IGNSS 2016, UNSW, Sydney 9

Slide 9

Exceeding the Minimum is not enough either

Vaughan, R.G.; Scott, N.L.; White, D.R.; “The theory of bandpass sampling”, IEEE Trans Signal Processing, Volume 39, Issue 9, Sept. 1991 Page(s):1973 - 1984

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IGNSS 2016, UNSW, Sydney 10

Exceeding the Minimum is not enough either

  • fu=2.5B,

fs=3.5B

  • 1

1 2 3 4 5 6

  • 1
  • 0.5

0.5 1 1.5 2 multiples of bandwidth B

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IGNSS 2016, UNSW, Sydney 11

  • RF signal split into I/ Q by 90° phase shift

in downconversion

“Normal” Quadrature Sampling

ADC

io(n)

X X

0° 90°

~ ~ ~ ~ ~ ~

ADC

qo(n)

Ts

ωLO s(t)

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IGNSS 2016, UNSW, Sydney 12

  • I/ Q from delay in sampling: ∆t = 1/4fc

Quadrature Bandpass Sampling

ADC

i1(n)

ADC

q1(n)

Ts

s(t) ~

~ ~

∆t

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IGNSS 2016, UNSW, Sydney 13

Quadrature Bandpass Sampling

  • Sampling rate must be at least twice the

signal bandwidth (Nyquist)

  • Overlaps are allowed:

–

  • verlap dc,

–

  • verlap the Nyquist rate

–

  • verlap any other downconverted signal

band

  • BPS: no band overlaps
  • QBPS: 2 bands can overlap but not 3
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IGNSS 2016, UNSW, Sydney 14

Dempster, Andrew G., “Quadrature Bandpass Sampling Rules for Single- and Multiband Communications and Satellite Navigation Receivers”, IEEE Transactions on Aerospace and Electronic Systems, vol 47, no 4, Oct 2011, pp 2308 – 2316

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IGNSS 2016, UNSW, Sydney 15

BPS vs QBPS rates

“channel” rate “total” rate

Dempster, Andrew G., “Quadrature Bandpass Sampling Rules for Single- and Multiband Communications and Satellite Navigation Receivers”, IEEE Transactions on Aerospace and Electronic Systems, vol 47, no 4, Oct 2011, pp 2308 – 2316

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IGNSS 2016, UNSW, Sydney 16

  • Signal
  • Sampled I/Q
  • QBPS

Distortion due to QBPS vs Sampled Quadrature Downconversion

distortion

A.G. Dempster, E. Cetin, “QBPS in RF front-ends”, Electronics Letters, vol 52 no 23, 3 Nov 2016, pp1965 - 1967

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IGNSS 2016, UNSW, Sydney 17

Simple Remedy

I/Q QBPS

io(n),qo(n)

∆t

i1(n) q1(n) i’1(n)

Baseband or IF Processing

s(t)

Naïve reconstruction Simple Remedy

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IGNSS 2016, UNSW, Sydney 18

  • For

– x(t) = ejωt input – y(t) = αejωt + βe-jωt output

  • IRR = 20 log10(β/α)

Image Rejection Ratio

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  • Naïve single

frequency

  • Naïve band
  • Simple remedy

IRR for corrected, uncorrected

A.G. Dempster, E. Cetin, “QBPS in RF front-ends”, Electronics Letters, vol 52 no 23, 3 Nov 2016, pp1965 - 1967

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IRR: Naive

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  • GPS L1

IRR: Band

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  • Galileo

E5

IRR: Band

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  • GPS

L1

IRR: remedy

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Achievable IRR

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  • QBPS can readily be used without remedy

and achieve good IRR

  • Remedy improves at some frequencies

Conclusions