While manufacturers and operators keep introducing evolutions of voice communications standards in order to improve voice quality, it feels like mobile voice quality is often lagging behind VoIP apps such as Messenger, WhatsApp, Viber.
Codec performance and compression levels
The algorithms used in 2G and 3G to compress voice calls have not evolved much during the years: Full Rate, Half Rate and Adaptative Multi Rate – for 2G – AMR and AMR Wideband – for 3G – offer compression between around 5 Kbps and 24 Kbps.
Here is an example of voice quality index (MOS or Mean Opinion Score, between 1 = poor and 5 = good) for usual narrow band 2G codecs:
Narrowband codecs will cut out all noises that are not within a 300-3400 Hz frequency band, while wideband codecs, such as AMR-WB, will consider a wider speech bandwidth of 50–7000 Hz, offering a better listening quality.
However, while AMR and AMR-WB in 3G can offer a decent voice quality in good conditions, the compression level of the speech becomes stronger as the network load increases, thus degrading the speech quality, especially in Busy Hour.
So the voice quality you will experience on a network will greatly depend on what time you make your calls, and not only whether you are on 2G, 3G, or a 3G network that advertises “HD Voice” on its billboards.
As a comparison, VoIP apps use more robust codecs and can use more bandwidth to establish the calls and provide better quality. For instance WhatsApp is known to be using Opus. The chart below compares the voice quality of Opus with AMR and AMR-WB for various bitrates:
International calls are probably the worst situation for a mobile operator to compare itself with an OTT VoIP app. The mobile operator of the caller party does not control the call circuit established end-to-end, and the call can be transcoded several times along the way to save international bandwidth, degrading the voice quality and introducing delays.
On the other hand, VoIP apps being over-the-top, they have a better control of the codec selection end-to-end depending on the data connection quality.
What’s next? VoLTE?
I personnally don’t believe in VoLTE and it seems that I am not the only one: out of 521 LTE networks launched as of last July, less than 10% have actually implemented VoLTE, meaning that the others rely on CS Fallback on 3G or 2G to make voice calls, bringing additional delay in the call setup time.
Source: ©GSA 2016 – 521 LTE networks as of July 2016
Let’s see how things develop next year. 5G also does not seem to put voice as a critical requirement for its development and it seems VoLTE will be the only way that will be maintained there to allow voice calls, if (1) people still want to do cellular voice calls instead of VoIP calls – i doubt it, or (2) if it remains a regulatory requirement for emergency services and public services, if those cannot be migrated into the OTT VoIP apps.
Feel free to comment!