Project Fi / Google Pixel Phone technical aspects

Project Fi is an excellently priced and serviced three LTE carrier + Wifi calling service from Google. It’s not perfect, without VoLTE and requiring specific phones for full functionality. UMA WiFi calling as with every carrier does not always have flawless performance. This is not a big issue since Project Fi phones only use UMA if no cellular signal is available. Overall I strongly recommend Project Fi for those with officially compatible phones.

Project Fi carrier switching

Project Fi phones will sit on the preferred carrier in your area. In much of the US, Project Fi phones prefer Sprint. If Sprint has a very poor signal (say you walk into the basement), Project Fi switches to the next strongest carrier, typically T-Mobile. In rural areas of the US where Sprint and T-Mobile are weak, US Cellular may be used. As of Fall 2016, US Cellular is mostly 3G, with 4G in a limited but growing footprint in rural America.

Project Fi fits sit on the preferred carrier (Sprint) even if say T-Mobile has a much stronger signal. It’s only when the preferred carrier signal is lost that Project Fi “roams” to the less preferred carrier. You can search the internet to find dialer codes that force a particular carrier for the duration of a phone call.

Project Fi coverage maps

Project Fi publishes a map that is roughly a superposition of their host carriers. I compliment Project Fi coverage map for not exaggerating their coverage like AT&T and many other carriers do. In most of the world, Project Fi uses open WiFi where available.

Project Fi behavior on Wifi

Project Fi currently behaves with the following descending priority order for VOICE calls:

  1. If any Fi cellular connection available, use cellular (even if Wifi also available)
  2. If no Fi cellular and connected to WEP/WPA WiFi, use UMA VoIP calling
  3. If no Fi cellular and not connected to WiFi but open good WiFi available, use UMA VoIP over VPN. You’ll see a lock symbol in the status bar.

I think UMA/VoIP calling has the lowest priority since the voice call robustness is lower with UMA than with cellular. I used to use a tablet with Google Hangouts Dialer as my main phone, and eventually the often great, sometimes bad WiFi call quality made me get a regular cell phone.

Project Fi VoLTE not enabled

Currently VoLTE is NOT enabled on Project Fi, so your phone will fall back to a 2G or 3G connection to make a voice call. This is a disadvantage many phones on many carriers suffer, as often the best coverage by a factor of 10 dB or so is on the 700/800 MHz LTE band, yet the phone gets forced to a weak 1.8/1.9 GHz signal for voice calls. Many times, the phone will have an 850 MHz 2G/3G connection available, so the disadvantage is not so large for voice calls vs. LTE.

Project Fi flagship is the Google Pixel

Google Pixel XL FCC ID: NM8G-2PW4100

For brevity the 2G-3.5G GSM/GPRS/EDGE/DTM/UMTS/HSUPA/HSDPA+ 850 MHz and 1900 MHz bands not shown.

  • Pixel LTE is CAT11 (600 Mbps down / 75 Mbps up)
  • LTE-CA (carrier aggregation) is on downlink (receive) only.
  • TDD: time domain duplex: pulsed transmission and reception in same frequency band
  • FDD: frequency domain duplex: transmit and receive in different frequency bands
  • Note: Project Fi does not use AT&T or Verizon, they are just shown for reference.
  • USC: US Cellular, TMO: T-Mobile
  • not every nation is listed, countries listed randomly picked.
  • NFC and UMA (Wifi calling) are also on the Pixel
band mode EIRP (dBm) TX Freq (MHz)
Wifi 2.4/5 GHz n/ac 2x2 MIMO VHT80 867Mbps 16 2402-2480, 5170-5835
BT 4.2 1 MHz BLE / 2 MHz 6 2402-2480
LTE band BW (MHz) EIRP (dBm) TX Freq (MHz) Carrier Notes
1     1920-1980 International
2 1.4 - 20 20 1850-1910 ATT, VZW, TMO
3     1710-1785 International
4 1.4 - 20 20 1710-1755 ATT, VZW, TMO
5 1.4 - 10 20 824-849 ATT, USC
7 5 - 20 20 2500-2570 International
8     880-915 International
12 1.4 - 10 20 699-716 ATT, TMO, USC
13 5 - 10 20 777-787 VZW
17 5 - 10 20 704-716 ATT
20     832-862 International
25 1.4 - 20 20 1850-1915 Sprint nationwide license
26 1.4 - 15 20 814 - 849 Sprint/Nextel ESMR band FDD 5x5 MHz up/down
28     703-748 International
29     N/A International
30 5 - 10 20 2305-2315 ATT
41 5 - 20 20 2496-2690 Sprint Spark TDD two 20 MHz LTE-CA

For Band 26, the FCC license in the USA limits maximum frequency to 824 MHz, thereby allowing two 5x5 MHz (up / down) channels in the old Nextel ESMR (tower transmit 859-869 MHz). In many areas Sprint only has enough ESMR spectrum for one 5x5 MHz LTE band 26 channel.

Non-official phone / LTE smartwatch might work with Project Fi

The Project Fi SIM cards require a phone with appropriate software to be able to switch between the three LTE carriers (currently T-Mobile, Sprint and US Cellular) and VPN-protected Wifi. If you have a non-Project Fi phone, the Project Fi SIM will default to T-Mobile. Some LTE smartwatches work with Project Fi.