In March 2024, Elon Musk posted results of iperf test for Direct to cell system (LTE signal from LEO satellite directly to unmodified LTE phone).
As we can see, results are 16.9 Mbit/s | 1.181ms jitter | 15% packet loss
Spectrum: 1910-1915 MHz and 1990-1995 MHz bands (the “PCS G Block”) of T-mobile USA
This is just for 1 smartphone in a cell (one beam).
There is an info that satellite altitude was about 367km during the test (while regular altitude is 550km)
What is your view on that statistics?
Do you see those results are fissile for providing VoLTE calls?
How did they get it?
Channel BW: 5 MHz
Even though we assume 3 PDCCH symbols for control channel we can get 16Mbps with CQI index 14 and 64QAM modulation.
Do you believe that in DL they managed to get 64QAM to achieve 16Mbps?
Packet loss: 15% is above the threshold where the customer will say “this data does not work”
Latency: Not mentioned - so probably >100ms. Above the threshold where customer will say “this does not sound right”
Large Cells: 16 Mbit/s for one phone is ok - but cellular networks scale by using the same spectrum again and again in many smaller cells. With cells projected from orbit - the cell size will likely be large and capacity per user will be useless.
The speed mentioned is DL and seems great from a satellite eNB operating in 5 MHz BW. However, the packet loss rate is quite high. For VoLTE, data rate requirement is quite low but the packet loss rate should be <1%. I believe, VoLTE calls can be sustained from Satellite utilizing the VoLTE coverage related features and QPSK modulation, the challenge will be more in uplink though as the UE power is limited. I expect another tweet from Elon if they manage to make voice calls.
