Radios for Construction HCC20519 Geoffrey Kirk Trimble Who

Radios for Construction HCC-20519 Geoffrey Kirk, Trimble

Who is this session for? • People setting using radios in construction for precision RTK applications • Users of 450 or 900 MHz radios • Focus on GNSS networks, wifi for GNSS and data is not the focus, but will be covered • Applicable to all countries, but we will talk US specific topics • Technical, somewhat but not to much. • And not exactly correct in a few bits. . .

Agenda • • Why we use radios How to get the best performance When they don't work IBSS, when you can't make radios work Legal issues How radios work Channel spacing reduction (Narrow Banding)

Why we use radios? • Because we have to! • The most accurate GNSS position you can get is from a local base station • You can not change the laws of physics closer is better • A Total station is of course more accurate • We have to get the base observations to the rover so it can compute it's position • GNSS Accuracy is impacted by poor radio • 1 mm per sec of latency is a good rule of thumb • x. Fill makes this better

Radio Families § 450 MHz Narrow Band § 900 MHz Frequency Hopping § Wi. Fi § Cellular

Channels and Networks • 450 listen on a single channel which does not change • 900 MHz listens on a single channel that changes 20 times a second • The network number is the pattern that the frequency change.

Performance • The amount of signal received at the rover is what determines if it works. • The required signal is called the sensitivity • Once you are above the sensitivity it works.

Link Budget • The difference between the power you transmit (signal level) and what you need to receive (sensitivity) is the link budget

What reduces signal • • Obstructions Distance Fresnel zone obstructions We allow for multi-path and other random noise with a Fade Margin • Jamming • Cable and connector loss • The Earth (Radio Horizon)

Link with Fade Margin

When you have problems • • • Raise the antenna Better Antenna's More power Repeaters Rebroadcast Cell

Raise the Antenna § If you remember one thing only today remember this! § The Standard Construction Base T-Bar it sub optimal

Clearly Better § Tower § Seco Portable § PCC Radio Tripod

Why does raising the antenna work? § Reduces Obstructions – Clears the Fresnel Zone § Increases the Radio Horizon § Depending on the licensee you may have maximum height

Fresnel Zone § Best Range when nothing is inside the zone § In real life you are trying to minimize things in the zone – Try for 20% or less.

Better Antenna's • Use the external antenna! • You may not exceed the EIRP your license • 450 depends on your license • You can use better antennas and less power • 900 MHz 6 d. Bi • For permanent installations, one piece antennas are better • 2. 4 GHz, must use manufactures antenna’s

More Power § When all else fails power

But it is not as good as you think

More Power § Check your license § 450 MHz, Varies. § 900 MHz – It is at maximum power now § Antenna height!

Repeaters § When you can not get the coverage you need from your base station we use a another radio to transmit it again § Simple § Reliable § Also improves coverage in the overlap area § Only repeats what it hears § Shares radio bandwidth

Link Speed § The speed of the link is a combination of – Bandwidth § More bandwidth = More data – Modulation § Less BPS = More Range

Link Speeds Bandwidth Rate (bps) 450 MHz 12. 5/25 KHz 4800 450 MHz 12. 5/25 KHz 9600 450 MHz 25 KHz 19200 900 MHz 250000 Wi. Fi 20 -40 MHz 1000000 - 5400000 - 48000000

Why do I care about Link Speed § We have to send the base observations § Duty Cycle: The % of time the radio needs to be transmitting to send the CMR’s over the link § Duty Cycle drives: – Power Consumption § Heat – Number of Repeaters – Number of SV’s § Only a 450 Problem

Repeaters § You need enough time to retransmit the base observations § You care about the max data to be transmitted, not the average. § 4800 bps, 0 repeaters § 9600 bps, 1 repeaters § 19200 bps, 2 repeaters

It gets worse § 4800 bps, To many SV’s to Tx § 9600 bps, 0 repeaters § 19200 bps, 1 repeaters

We have solutions § CMRx – Supported by modern equipment – SPS, Any – MS 99 x § Bandwidth Limiting – Send upto the maximum the link can handle § Throw away the lowest SV’s – Automatic § Based on number of repeaters § 1/2 Hz – Send it only every alternate second – Bandwidth Limiting is better generally

900 MHz GNSS Tx § Have 22 available Slots per second § Base uses 4 slots § Each slot can be GPS or GLONASS (or both CMRx) § Will send a packet 2 times – 4 if both fit in a single slot, CMRx only with GLONASS § Improves reliability greatly – 2 chances to get the message – On different freq’s so different jamming, multi-path etc

900 MHz Repeaters § 22 Tx Slots, 4 For GNSS § 4 Repeaters (22/4 = 5)? § No only 3 § But. . – If you need more, we support 2 GNSS slots mode (multi cell) – 22 / 2 = 11 Repeaters? – 9 repeaters, 3 chains of 3 repeaters in real life

900 MHz Repeater

Multi-Cell GNSS Repeaters

Out of repeaters § Rebroadcast

Rebroadcast § Rebroadcast is using the internet to get data to a radio § Machines and Rovers use the radio as normal § Project too large for repeaters § Not having a GNSS base station on site § A radio on the site broadcasts data from a Remote base station – VRS can also be used

SNB 900 Rebroadcast Configuration § Connect the SNB 900 to the internet – Wired Ethernet Connection – SNM 940 for Cell connections § Configured Via the Web UI – Enter base details

450 MHz Rebroadcast § Connect the 450 MHz to the internet using a SNM 940 § Configure the SNM 940 § Output via the serial port

Rebroadcast Benefits § Reduced Cost – No Local Base Station – Less Repeaters § Single Internet Connection § Simplified Daily Setup § Control of radio coverage § Ability to use wired internet connection § Standard Rover configuration

When not to use rebroadcast § On a site with only a few devices and good cellular coverage § Using direct cellular connection features may be easier

How do I get my base on the internet? § Use your existing internet connection to put the receiver on the internet – Static IP § SPS 855. com – Port Forward § SPS 855. info – Need IT help § Really hard to do with a cellular base station § Use Internet Base Station Service

IBSS § Uses TCC as a dating service for bases and rovers – Bases connect to TCC – Rover connect to TCC § No IT or cell issues § Need a TCC Device account for the base and rovers § Very Simple

IBSS 2 § Caster changed October 2012 § Rewritten for better operational performance – Better Error Messages to rovers – Better Supportability – Operation over TCC scheduled maintenance and downtimes

Physics § IBSS allows you to connect to a base station 500 miles away – You are not going to get cm’s

GNSS works best close § < 2 -3 Km is most accurate and has least noise § 40 Km base line – Crappy base

Network RTK (VRS) § Same setup on the rovers as IBSS § VRS reduces the effects of the atmosphere § Doesn’t remove them – 0. 5 ppm Vs 1 ppm § Once you are more than 2 -3 km from the base station VRS is better for the same distance to the reference station – It is not constant accuracy across the network!

FCC Narrow banding § Spectrum doesn’t grow on trees, stop wasting it – FCC § Need more channels in densely populated area

What it means to you license § Existing licenses will remain valid and existing radios will remain legal as long as you transmit in either of these narrowband modes: – 4800 or 9600 bps in a 12. 5 KHz Channel – 19200 in a 25 KHz channel

Renewing/modifying a license § When you need to renew or modify an existing license, you may do so online at http: //wireless. fcc. gov/uls/ § If you wish to operate in the 25 k. Hz / 19200 bps narrowband mode, you will be prompted to fill out a special on-line form (see next slide) – Recommended

Applying for a 25 k. Hz/19200 bps license § State “your operation of a data radio complies with the narrowband equivalent efficiency standards under Section 90. 203(j)(3) in that it supports a minimum data rate of 4800 bits per second per 6. 25 k. Hz of channel bandwidth” § Include your radio’s FCC ID# so the FCC can confirm the equipment operates in a narrowbandequivalent mode (see next slide)

What does it really mean? Radios § Old Radios are not legal – Sitenet 450 – TC 450 – SNR 450 – PDL bases

What does it really mean? Over the Air § We are recommending people transmit @ 9600 in a 12. 5 KHz channel – Rovers will work without change – Rovers will work better if you change there configuration to know the channel is 12. 5 KHz

What does it really mean? Range § Range is going to be a bit worse – We lose a few d. B § If you really need range then 4800 may help

What does it really mean? Battery § Same at 9600 § Worse at 4800

What does it really mean? GNSS Internal Radio § There will be new GNSS receiver firmware to support the new US rules § Your units need to go back to the dealer for the country code change § With the firmware and country count everything works with SCS 900 nicely § If you don’t have this firmware – Use autobase or Front Panel – Change the radio configuration after starting with SCS 900

Legal § There are large fines and your equipment can be confiscated – Having your base taken away can ruin your whole day § Don’t – Use the wrong over air format – Use more power than is legal – Use illegal antenna’s – Be dumb

Resources § PCC Range Estimator § http: //www. pacificcrest. com/library/PCC_Range_Esti mator. zip § Meraki Range Estimator § http: //www. meraki. com/lib/tools/meraki_range_calcul ator. xls