According to 3GPP standards "3GPP TS 36.211 version 13.2.0 Release 13" in section 10.1.6:
"The preamble consisting of 4 symbol groups transmitted without gaps shall be transmitted NPRACHrep N times"
Does the mentioned "without gaps" means only for one preamble itself, it should be transmitted without gaps? (all 4 symbol groups one after another without time gaps)
Or does it means all repetitions should be transmitted one after another without any gaps in between?
This question arises as many papers consider the second case (no time gaps between all repetitions). However, this is against the standards which mentioned clearly in the same section:
"The transmission of a random access preamble, if triggered by the MAC layer, is restricted to certain time and frequency resources.
NPRACH transmission can start only NNPRACHstart ⋅30720T time units after the start of a radio frame fulfilling nf mod( NNPRACHperiod /10)=0"
This means that NPRACH happens only in certain frames fulfilling mentioned conditions. Thus, preamble repetitions can be transmitted only in those frames. which means it can't be transmitted continuously without gaps because we can never have two consequent frames which fulfil the condition.
The attached figure shows which frames in time domain do have NPRACH.
Kindly, if my previous notation is wrong and repetitions should be transmitted continuously without gaps can you explain to me how that comply with the standards especially with "NNprachPeriodicity"?
Dear Anas,
ACCORDING TO THE COMMUNICATION PRINCIPLES,The function of the preample is for timing and synchronization in addition to channel estimation. So, the preample symbols must be sent continuously without interruption inside the preample. As for the preamble itself it is sent whenever one needs to send it to synchronize data and assess the channel. It depends on the channel conditions.The preamples must not sent periodically.
Best wishes
Dear Anas,
ACCORDING TO THE COMMUNICATION PRINCIPLES,The function of the preample is for timing and synchronization in addition to channel estimation. So, the preample symbols must be sent continuously without interruption inside the preample. As for the preamble itself it is sent whenever one needs to send it to synchronize data and assess the channel. It depends on the channel conditions.The preamples must not sent periodically.
Best wishes
Dear Anas,
I agree that the standard is not clear.
NPRACH preamble and repetitions are transmitted continuously.
NPRACH transmission can start only NNPRACHstart ⋅30720T time units after the start of a radio frame fulfilling nf mod( NNPRACHperiod /10)=0"
-> it gives the rule for the start of the NPRACH transmission, i.e. the first group of symbols of the first repetition. Other repetitions are then transmitted one after the other continuously.
A time gap of 40 ms occurs only after the transmission of 64 preambles (cf TS 36.211). Then the remaining repetitions, if they exist, are continuously transmitted again until the total number of repetitions is reached. If the eNB does not detect the preambles, i.e. the UE does not get random access response, then it starts transmission again after periodicity is reached. Thus, the N_rep repetitions occur within the periodicity window.
Hope this is clear.
Best regards,
Vincent
Hi.,
preamble detection, estimating uplink timing is another main ... to the time of the start of the NPRACH transmission is. ... Outer hopping is across repetitions with a different start ... There is no sampling rate below 1.92 MHz that can.
For More info:
https://www.etsi.org/deliver/etsi_ts/136300_136399/136321/13.06.00_60/ts_136321v130600p.pdf
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