GNSS raw measurements on Android: Does real time/post processing Differential techniques possible?

In short, yes - differential GNSS is now possible on Android, and, as of Android P (on supported devices), real-time kinematic (RTK), or carrier-phase measurements, are also possible.

The May 2018 Google I/O video "How to get one-meter location-accuracy from Android devices (Google I/O '18)" has a really good high-level explanation of the current state on Android as of Oreo, and what's coming that's new in Android P.

The GPS World article Positioning with Android: GNSS observables has a good overview of this topic as well.

The various pieces of data you get from the Android APIs are discussed at 30 min 38 sec: https://youtu.be/vywGgSrGODU?t=30m58s

They are also detailed in the Android GnssMeasurement documentation: https://developer.android.com/reference/android/location/GnssMeasurement.html

...including:

• Pseudorange - https://developer.android.com/reference/android/location/GnssMeasurement.html#getPseudorangeRateMetersPerSecond()
• Accumulated delta range - https://developer.android.com/reference/android/location/GnssMeasurement.html#getAccumulatedDeltaRangeMeters()

The discussion of using reference networks for carrier frequency positioning setup starts at 32 min 31 sec: https://youtu.be/vywGgSrGODU?t=32m31s

The article version of this presentation can be see in the GPS World July 3, 2018 article "How to achieve 1-meter accuracy in Android": http://gpsworld.com/how-to-achieve-1-meter-accuracy-in-android/

If you want a super-deep dive, check out the EU GSA Whitepaper "Using GNSS Raw Measurements on Android Devices" Section 3.4 "Taking It Beyond The Phone - Differential Observations".

All this is possible with single frequency GNSS, although dual-frequency GNSS is now emerging on commercial devices.

And yes, all the necessary data can be save and processed offline. Here are two apps that allow you to log this type of data:

• GnssLogger - the official Google app discussed at https://developer.android.com/guide/topics/sensors/gnss

• GPSTest - Full disclosure, it's my open-source app available on Github