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Why multiple UEs select the same preamble and all of them can receive RAR in random access procedure ?

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In LTE random access procedure, if multiple UEs select the same preamble and send it to BS, there may have two conditions:
First, if these UEs have enough SNR, BS can detect a collision happen, then BS do not send RAR.
Otherwise, second, these UEs have a collision and BS can not detect all of them and send RAR, and all of these collision UEs can receive the same RAR.
My question is about the second one, there are multiple UEs use the same preamble, why BS do not know the collision ? why BS still send RAR to UEs ? why BS can still detect this preamble?

posted Dec 16, 2019 by Lin Unis

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