PROPRIETARY STATEMENT: The information contained is this document is Proprietary to DRS...

PROPRIETARY STATEMENT: The information contained is this document is Proprietary to DRS Technologies, Inc.

“High Performance GNU Radio applications: Super or Zero? : A Trade-off Comparison of Superhet vs. Zero IF Radio Architectures in Real World Environments”

2Use or disclosure of data contained on this sheet is subject to the restrictions on the title page. Copyright © 2012, 2015 DRS Technologies, Inc. Proprietary information. .

A/DRF

ConverterGNUDSP

Antenna

In other words - Nasty radio

environments can produce an

undesirable output


DRS Signal Solutions produces radios that meet GNU standards

Zero IF frequency conversion architectures have been proposed to meet the goal of a “radio on a chip” for receivers and transmitters.

This presentation examines zero IF and super-heterodyne approaches, comparing the strengths and weakness in dense signal environments. Particular attention is paid to size, weight, power, price and performance. Real-world operational examples are given to highlight the differences.


Agenda

• Discussion of real world and crowded spectrum issues

• Review dynamic range terminology…NF, IP3, IP2 & NPR

• Super-heterodyne and Zero IF …The difference explained

• How the pros and cons could affect a GNU Radio application

• Testing and evaluation….On-the-Air vs NPR

• Conclusions


The Real World Omni-directional Discone Antenna (30 to 1000 MHz) and Log

Periodic Array ( 1 to 3 GHz) 3 Miles South of Chicago


Real World Spectrum Energy- Chicago

………………


Multiple Signals Require Total Average Power and Crest Factor (CF) Considerations

05

10152025303540

1 10 100Number of Signals

Average PowerAve. Pow. + Theoretical PeakAve. Pow. + Statistical Peak

.…10Log(#Signals), 15Log(#Signals), or 20Log(#Signals)


Simple and Complex Signals and Their Crest Factors (CF)

Tuner Sig Str (dBm)0

-10

-20

-30

-40

-50

-60

10 simple signals

Average power

Plus statistical peak

Complex signal

Example-TV

64 QAM DVT

Average power

Plus statistical peak

Example – FM signals

+10 dB

+10 dB+15 dB

ADC full scale! Needs IF/RF gain change


Note!

Overload of the radio stages before the ADC may require RF/IF attenuation, but the radio control is usually limited to

seeing signals in the ADC IF bandwidth.

The ADC is blind to signals outside its IF spectrum!

What you can’t see can hurt you!

Simulate or calculate first!


Calculating CF Signals at Different Levels and Types

Chicago South, Ill. FM Other significant signals (15Log#) Chicago, Ill. DTVSS -dBm PWR mW Total mW AverageCF total_dBm + 10 dB SS -dBm PWR mW Total mW AverageCF total_dBm SS -dBm PWR mW Total mW Avetotal_dBmCF (dBm + 15dB)

-20.3 9.33E-03 5.70E-02 -2.44 -23 5.01E-03 2.13E-02 -16.72 -15.40 2.88E-02 0.15 -8.38 6.62-21.5 7.08E-03 -21 7.94E-03 -16.40 2.29E-02-22.0 6.31E-03 -25 3.16E-03 -17.20 1.91E-02-22.5 5.62E-03 -23 5.01E-03 -17.70 1.70E-02-22.7 5.37E-03 -38 1.58E-04 -18.20 1.51E-02 FM + Other + DTV (mW) 5.180 mW-22.9 5.13E-03 -52 6.31E-06 -18.60 1.38E-02

-32.1 6.17E-04 2.13E-02 -21.10 7.76E-03 FM + Other + DTV (dBm) 7.14 dBm-23.4 4.57E-03 -21.60 6.92E-03-23.4 4.57E-03 -22.40 5.75E-03-23.7 4.27E-03 5.70E-02 -23.20 4.79E-03-23.8 4.17E-03 -25.00 3.16E-03

1.45E-01FM Crest Factor = Ave. Pwr + Stastical Peak; 20Log #Sig DTV Crest Factor = Ave. Pwr + Stastical Peak; 10Log #Sig + 15 dB


Calculating CF on Cellular Spectrums

• From the above, note RF level and spectral BW of the down links (Cell towers)….about -33 dBm…. over 852 to 864 MHz ~ 22 MHz• TDMA signals are channel spaced at 200 KHz. 22 MHz/200KHz =

110 channels• About 80 % are occupied…88. 15 Log 88 = 29.2 dB• Add 29.2 dB to -33 dBm = -3.8 dBm statistical peak power –

What about other cell bands?


DRS Signal Solution in Germantown….total signal power + crest factor

Germantown, MD FM Germantown, MD DTV Germantown Cell towerSS -dBm PWR mW Total mW CF total_dBm + 10 dB SS -dBm PWR mW Total mW total_dBmCF (dBm + 15dB) Total dBm + 10 dB CF= -3.5 dBm

-26.3 2.34E-03 1.32E-02 -8.78 -28.30 1.48E-03 8.36E-03 -20.78 -5.78 88 signals about -33 dBm-26.3 2.34E-03 -28.40 1.45E-03 -3.5-28.9 1.29E-03 -30.10 9.77E-04 FM + DTV + Cell(mW) 0.843 mW

-29.5 1.12E-03 -30.80 8.32E-04 FM + DTV + Cell (dBm) -0.74 dBm-29.9 1.02E-03 -31.30 7.41E-04-29.5 1.12E-03 -31.30 7.41E-04-29.7 1.07E-03 -31.40 7.24E-04-29.7 1.07E-03 -31.90 6.46E-04-31.8 6.61E-04 -33.40 4.57E-04-32.2 6.03E-04 -38.00 1.58E-04-32.3 5.89E-04 -38.00 1.58E-04

1.32E-02 8.36E-03

FM Crest Factor = Ave. Pwr + Stastical Peak; 20Log #SigDTV Crest Factor = Ave. Pwr + Stastical Peak; 10Log #Sig + 15 dB


The Real World is Brutal

Multiple strong signals in an imperfect radio will create false “spurious” signals that will create useless clutter and interfere with the reception of the desired signal.

With many strong signals, the radio may be grossly overloaded and lose sensitivity.


Traditional Dynamic Range Two Tone Tests

Sig Gen 1

Sig Gen 2

Noise Gen

Tuner under test

FFT Display

Sig 1 Sig 2

-IM 2 or 3 +IM 2 or 3

Noise

Tuner ADC

Typical Tests for Noise Figure, IP2, IP3, Phase Noise and Spurious Signals

Frequency

ADC Full Scale

Spurs


Non-linearity in Radios Cause Spurious Issues…IP2 & IP3

Two signals in the non-linear portion of the transfer curve will cause IM2 & IM3 (Intermods)…If a mixer, the spurs can be (Harmonics of RF X LO)


A Better DR Test for Tuners Working with Real World Signals (Used by the telephone companies for 75 years)


Testing and Evaluation…Real World and Simulation

Real World RF Spectra – testing for intermodulation (IM) distortions (spurious signals)…IP2 ~ IM2, IP3 ~ IM3…etc. created by non-linearity in tuner.

Noise Power Ratio NPR testing – Substituting controlled noise for multiple signals and looking into the notch to measure IM’s created by non-linearity in tuner.


Real World Spectrum…Detecting RF Intermods & (XRF times XLO) in Tuners

SignalGenerator

Power Splitter

Antenna

FFT

Tuner Under Test

ADC

Wanted Signal

?? ?

??

Step Attenuator

Amplitude test for real signals Attenuate antenna signals by 3 dB Did ? Signal drop by 3 dB If dropped by 6 dB then it is an IM2 If it dropped by 9 dB than it is an IM3

Frequency test for real signals Tune UUT by 1/10 th FFT bandwidth Did ? Signal move 1/10th

If moved 2X then it is an IM2 If moved 3X then it is an IM3

Note! 1X RF times LO harmonic spurs can only be detected by the frequency test


Noise Power Ratio Testing Comparisons

1. Tune radio UUT #1 & #2 to middle of 1st notch2. Set SG frequency to tuned radio a level of 10 dB SNR3. Reduce attenuator (raise noise) until 7 dB SNR4. Switch out notch and measure noise5. NPR is difference between step 3 and 46. Move tuning to next notch and repeat

SignalGenerator

Power AmpLow Pass Filter

Noisey Resistor

UUT # 1

UUT # 2

Attenuator

-77 dB/Hz

-84 dBm/Hz into UUT

1000 MHz

Home Brew NPR Test Set

Power combiner and

splitter

-78 dB/Hz

(Max of +6 dBm@1GHz BW)

-174 dBm/Hz + R noise


Causes of Out-of-Band Noise Inside Notch :

• Non-linear stages between antenna and mixer/IFA…….

• 1st and 2nd IF responses

• 1st and 2nd image responses

• All possible third order responses

• All possible second order responses

• Reciprocal mix of LO phase noise

• All M X N mixer combinations that make a 1st IF response


Super-heterodyne Architecture

RFOutput

PostselectorPower amp

1st mixer2nd IF BPF2nd mixer1st IF IF amp DAC

1st LO synthesizer2nd LO

synthesizer

ADC clock

Data

Rx

Tx


Zero IF Architecture

Optional BPF

Optional BPF

Rx

Tx Amp

DAC

ADC clock

Amp

DAC

RFOutput

Power amp

LO synthesizer

LPF

LPF

0

90

Powercombiner

“I” mixer

“Q” mixer

"Q”data

“I”data


Super-heterodyne vs. Zero IF

Pros:• High quality fixed frequency IF

bandpass filtering• 1/f noise at IF is negligible• Good image and spurious signal

rejection• Good (Superior) dynamic range

Cons:• Higher complexity• Larger size• Higher cost• May be higher power

Pros:• Low cost, small• Simple receiver

architecture• Baseband filtering can

be done digitally or with active filters

Cons:• 1/f noise is amplified• DC offset spur caused by LO rectification

in mixer• Requires image rejecting mixer – Image

(false signal) Tx/Rx spurs about - 45 dB dBc (vs. superhets -90 dBc)

• Second order distortion, nonlinearity creates a signal at 2f.

• Both Rx & Tx respond/transmit LO harmonics

Superhet

Zero IF


Types of Preselection to Reduce Out-of-Band (OOB) Interference

Antenna

Preamp

IP2, IP3 & NF Ultimate OOB rejection

Simple Preselection

Protect

200 to 350MHz

350 to 550MHz

550 to 850MHz

850 to 1500MHz

RF in RF

out

Low pass filter for image noise & LO rejection

IP2 , IP 3 & NF

I.L . IP2 , IP3 , Shape factor

Tracking Preselector

Switched Sub-octave Preselection

Number of Bands and IP2 Shape factor

1

2

3

Low pass filter for image noise & LO rejection

Ultimate OOB rejection

Least cost but no 2nd order protection and multiple signal overload issues

2nd order protection but loss problems…Higher Noise Figure

Most protection from OOB interferers & 2nd IMs but higher cost and PCB real estate


Issues to Consider…

Product data sheets; general specifications do not adequately predict radio performance in the real world.

Which of the following matter for your specific application?

Cost: A simple lower cost product may fit the need for a specific requirement. – But even with limited frequency applications, zero IF requires a tight preselector BPF to reduce spurious

RF environment: Real world spectral evaluation and testing is essential to avoid damage from RF interferers. Many combinations of large signals can produce “Single Signal Spurious”.

Spurious signals: The presence unwanted signals in a crowded RF spectrum may result in false signals or interference with desired signals.

Performance: It is very difficult to define the metrics to determine “Good Enough” when each surveillance site has varying spectra. Knowledge is key


Zero IF vs. Super-heterodyne: Tuners at low signal spectra (300 MHz) On-the-Air Intermod Spurs

A 3 dB change in antenna level resulted in a 6 dB drop in IM’s ….therefore IM2’s

SPURS

Zero IF Superhet

Signal


Conclusions• GNU Radio provides a framework for very diverse RF application

development, including specialized, high-performance designs

• In high density signal environments, super-heterodyne Tx/Rx have higher dynamic range – Fewer IMs (Spurious signals)

• Both Zero IF and Superhets benefit from preselection filters that reduce the total number of signals

• In a low signal density environment, a Zero IF may be OK and less expensive but an RF bandpass filter is recommended

• On-the-Air testing for IMs is easy but difficult to quantify

• Noise Power Ratio testing gives the best indication on how radios perform in a high density signal environments vs IP2 and IP3 test

THANK YOU FOR YOUR ATTENTION

PROPRIETARY STATEMENT: The information contained is this document is Proprietary to DRS...

Documents

Transcript of PROPRIETARY STATEMENT: The information contained is this document is Proprietary to DRS...