RF Recording and Playback: An expanding technology for RF

receiver development and validation

Dominique Fortin eng.Montreal April 12th 2012

Agenda

The real life environment of RF receiversStandard equipment for testing receivers: Channel emulators and signal generatorsCommercially available RF recorders today: General specifications and limitationsExamples of use cases for commercial applicationsQ&A

The real life of receiverBasic Parmeters: Noise (C/N, C/No) InterferenceMultipath

Interference types:Intentional (jamming) Non-intentionalStatic: Continuous broadcastDynamic: TDMA, Pulsed, radarMan-made: Power line, electrical motor, engine,…Natural: lightning, solar flare

The real life of (mobile) receiverMulti-path: Its effects include constructive and destructive interference, and phase shifting of the signal

The real life of (mobile) receiver

Rate of selective fading is proportional to speed and signal frequency

The real life of (mobile) receiverExample of multipath on a signal and its interferer

The real life of (mobile) receiver

In real life, both signal AND interferences are affected by multipath.For commercial application, signal usually varies from -100 dBm to +10 dBm. So can be the interference(s)Interference can be co-channel or adjacent channelIn complex urban environment, there can be up to 40 multipath for a same signal

Terrestrial

The real life of (mobile) receiver

In the case of multi-satellites constellation such as GPS or the Russian GLONASS, there are other complex mechanisms such as signal blocking or obscuration which vary dynamicallyThese adds up to the multipath of each satelliteSome radar interference in some bands

Satellite constellation

The real life of (mobile) receiverSignal obscuration in urban canyon

The real life of (mobile) receiverThe effect of multipath and signal obscuration

Standard equipment for testing receiver

Standard equipment for testing receiver

Generating Continuous Wave or simple modulation interferer is easy but more complex ones requires high end generatorGenerating multiple interferers = $Generating one interferer with multipath = $$Generating multiple interferers with multipath= $$$

Interference

Standard equipment for testing receiver

Requires expert usersDifferent models for different modulation, band, environment such as COST XYZ (urban, semi-urban…)Typically 6/12 paths, some up to 24/48 per channelMany models: Constant, Rayleigh, Rice, Nakagami, Lognormal, Suzuki, Doppler, Gaussian, JakesMany settable parameters: Doppler, K factor, Slow fading, CW interference, Noise, etc

Channel emulation

Commercial RF Recorders todayRationale for using RF recorders

Can capture a specific RF environment at a specific location known to be “difficult” for RF receiversCapture the full complexity of the environment with all its impairments. Can considerably reduce lengthy and costly test driveWell adapted for broadcast, limited application for two-ways telecom.

The technology breakthroughCommercial RF Recorders today

PCI Express bus allow multi GB/s transfer at low cost. Can use PC architecture with WindowsRAID technology: RAID 0 allowed byte strippingStorage drive keep growing. Today: 4 TB drive are available. They double every 2 years

Commercial RF Recorders todayGeneral Specification

20 MHz of bandwidth standard, up to 50-110 MHzDynamic range of Analog to Digital converter >80 dBMany Terabytes of storage capacityPortable (11-23 Kg) 120-200 Watts 12 Volts optionsOften have a playback options integrated for validation in the fieldMulti-channel for MIMO starting to be available (at same frequency) Calibration is difficultMeta-data: Geo-tagging, video, data in parallel,…

The data rate and sizeCommercial RF Recorders today

Format is usually in IQ format. ( 2 X 2 Bytes) since the samples are 16 bitsNeed 20% of guard band for filtering so for 20 MHz Bandwidth, we need 25 MSamples/Sec of I&QSustained rate for 20 MHz at 16 bits= 100 MB/sec1 hour of recording is 360 GbytesNeed to back up at home….

Commercial RF Recorders today

Limitations of RF Recorders

Linearity

Limitations of RF Recorders: linearity

Limitations of RF Recorders: linearity

Capturing 93.9 on the FM band 3rd Order IM: 2*(94.7)-95.5 = 93.9 MHz 4th Order IM: 105.9+93.1-105.1 = 93.9 MHz

Limitations of RF Recorders: Input RF filter

Inadequate filtering can brings artefacts caused by strong interference out of band or from the image.

Limitations of RF Recorders: Oscillator

Phase noise is additive using the Root Mean SquareIn a playback mode, you have to add the noise of recorder and player. This can be a factor of degradation but it is typically fairly small.

Limitations of RF Recorders: AGCAGC needs to change continuously because the total power change continuously for mobile terrestrial application. While settling, the AGC is causing an impairment.

AGC at work

Noise from digitizer

Thermal noise (-174dBm/Hz)

Limitations of RF Recorders: The effect of AGC

AGC can be slow such as a few times per second or be adjusted every millisecond or even less. In that case, you need to include the AGC information in the IQ file.

Other consideration: HeadroomThe headroom is required to take in account the distribution of the peak to average signal when there is more than one present. Typical value for recorder is 10 dBThis 10 dB reduces the useful dynamic range by an equivalent factor.

Headroom {

Commercial examplesRF Broadcast receiver validation

AM/FM Radio: Radio Data System (RDS), Traffic Message Channel) TMC

Digital radio: DAB, HD RadioCable problems in hotels for TV makersDigital Video (DVB-T, ISDB-T, ATSC,…) In some

cases there are many flavours of DVB-T per country on both modulation and content

Recording GPS signal: Low end (Automotive) High end: Precision (Multi-Frequencies)

Q & A