Question

Suppose there are three UE who are trying to access the network through the RACH procedure but the network dont have that much resource to provide it to all three. It have only resource for two UE from which parameter network will decide to which two UE the resource will allocate

Answer 1

Hi,

There is no rejection in RACH procedure. If current SF doesn't have resource then it will be scheduled on next available SF. If ENB wants to reject the UE then RRC will take a call after receiving an connection request it can send an connection reject.

Comments

Thanks for the answer #jaganathan but this is not the right answer for this question.. Please go through this question again and help me in finding the right answer.

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So it can be implementation specific
But normally it would go by RACH power
eNB calculates the SNR of the recieved RACH
So it can choose the top two of all the detected RACH

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Hey SNR can't be a reason it is a part of RF

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Hi,
Let me understand your question .
1. All three UE trying to access ENB. (Is this in same SF?)
   If yes, then all three UE cannot access the RACH resource in same SF, it gets corrupted and ENB itself cannot receive the rach signal. So UE's will re select the preamble and resend the request again. Incase any UE's RACH signal receives at ENB side the it sends back RAPID to UE's so that other UE can re-initate the RACH again.
   If no, Then all three UE's are sending request in different SF then there is no priority handling between these UE's. Each UE gets the resource in different SF.

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it is not about the subframe UE is initialising the rach before registration

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UE sends the RACH in subframe, Before registration it selects the subframe based on SIB2 parameter, Please refer the Specification 36.321 RACH procedure to get more details about RACH initialization.

Answer 2

So it can be implementation specific
But normally it would go by RACH power
eNB calculates the SNR of the recieved RACH
So it can choose the top two of all the detected RACH

Comments

How eNB will calculate the SNR value of UE?

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May be i am not the correct person to comment here how eNB calculates the SNR but there is some values documented depending which modulation scheme is being used and depends on code rate there are SNR value defined. Fow more info please refer this link http://www.techplayon.com/lte-reference-sensitivity-calculation-how-it-depends-on-snr-why-throughput-decrease-at-the-cell-edge/