[srslte-users] eNodeB does not receive PRACH

[Samie Mostafavi]

Hi,
I have this problem in the timing of the TX radio, I would appreciate if
anyone can help.

My SDR which is an srsUE, sends the PRACH messages after a successful
synchronization process and moving to 5.76 MHz. Then I can see the PRACH
messages every 20ms (20 TTI) on the channel using another receiver. But
eNodeB is not able to receive them. Sometimes by chance it receives one or
two of them but the delay is around 5000 and because of this delay EnodeB
doesn't respond back.

1. I know that PRACH messages should be sent at a specific time, but when
is this time? in other words, when is the correct time of the start of
PRACHs?

2. I have a hardware based timing mechanism on my SDR that tells me the
round trip delay of packets from RX to the user space in the host and again
to the TX (without srsLTE processing time) and it shows that for a buffer
size of 16k samples both for RX and TX, I have 5 ms of end-to-end latency
(2.5 ms from RX to host and 2.5 ms from host to TX). Do you think can I
configure my driver to be able to send the PRACHs at the correct time
points even with this latency?

Best regards,
Samie
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