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what are the steps taken by UE to get know in what configuaration (1.4 Mhz, 5Mhz, 10Mhz etc) eNodeB is running ?

+2 votes
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In LTE FDD mode, eNodeB has two separate earfcn values, one is downlink earfcn and second one for uplink earfcn. Does an UE detect all the possible earfcns(1.4 Mhz, 5 Mhz, 10Mhz etc) of a frequency band ?

posted Sep 21, 2013 by Ganesh Kumar

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3 Answers

+3 votes

If I get the question correctly, you are asking How does a UE knows bandwidth of the cell ?
Answer to it is ,,,In the cell search procedure , a UE looks for all the possible earfcn in the band it supports.It decodes PSS ,SSS and MIB independently without bandwitdth info (MIB occupies the 6 RBs around the center frequency ) .MIB carries bandwidth information.

answer Sep 23, 2013 by Sony Mohanty
+1 vote

In the Master Information Block (MIB), the number of downlink resource blocks is transmitted.

The MIB only occupies the middle 6 resource blocks of the frequency allocation for that reason. Upon initial startup in an unknown region, the UE need only consider the minimum LTE bandwidth before the it can determine the actual bandwidth from the MIB.

answer Sep 23, 2013 by anonymous
+1 vote

In addition to the answer of sony ....
MIB has only 24 bits information but at the transmitter (because it is the most important info of broadcast channel) we made it of 1920 bits by repeating using some algorithm of channel coding,rate matching,interleaving,scrambling etc. and the after QPSK modulation it becomes 960 modulation symbol.
After that we divide this 960 symbols in 4 parts of 240 (which contains the same info but differ only by scrambling with the PN sequence)and placing it in the four symbol of 6 RB length (6*12=72-12 reference symbol=60*4=240 symbols)int second slot of first subframe of four continuous frames of 40 ms time. And then transmit.
At the UE side if he switched on his device in between the four continuous Frame then he descrambles the 240 bits of that frames which he detects first with the PN sequence which he already knows and if it is zero then it knows the correct frame no and a/c to that it waits for the next arrival of first frame and then decoding process starts at UE side and finally gets 24 bits of transport block in which first three bits shows the No. of RB assigned to that system. And UE decides the configuration on which eNodeB is running ac to this...

000--> 6 RB --> 1.4 MHz
001--> 15 RB --> 3 MHz
010--> 25 RB --> 5 MHz
011--> 50 RB --> 10 MHz
100--> 75 RB --> 15 MHz
101--> 100 RB --> 20 MHz

answer Mar 2, 2016 by Shyam Narayan
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