Lte Prach Channel

LTE PRACH Channel-Physical Random Access Channel This page on LTE PRACH describes LTE Physical Random Access Channel(PRACH).It mentions links or !C"#A PRACH and $%# RACH cha nnel basics. This channel is &sed to carry random access preambles &sed or initiation o random access  proced&re. The basic str&ct&re is mentioned in the ig&re. As sho'n a random access preamble incl&des a CP a se&ence and a g&ard time. This carries the random access preamble. The RACH transport channel is mapped to this. * Carries the random access preamble a +E sends to access the net'ork  * It consists o ,- s&bcarriers in the re&ency domain * There are / dierent RA(random access) preamble ormats deined deined in LTE LTE 0"" speciications. The same ha1e been mentioned in the table2 belo'. It consists o dierent  preamble and CP d&ration to accommodate dierent cell si3es. si3es.

LTE PRACH Preamble Format

4 2 6

CP Length

4.24ms 4.95ms 4.-ms 4.95ms

Sequence Guard length 4.5ms 4.5ms 2.9ms 2.9ms

Total Length

Time 4.24ms 2ms 4.8-ms -ms 4.-ms -ms 4.,-ms 6ms

Guard time

Ty"ical #a$! equi!dist! cell range 647m 287m 289km ,5km 947m 647m -297m 2457m

The preamble ormat to be &sed in a speciic cell is inormed to the +E &sing & sing PRACH conig&ration inde:. This is broadcasted in %I;-. PRACH conig&ration inde: also indicates %0< and s&brames. This gi1es the e:act position o random access preamble. TableTable- beloe mentions LTE LTE PRACH channel conig&ration inde: preamble ormat allo'ed %0< and allo'ed s&brames. Preamble Format

PRACHCon%iguration &nde$

4 2 6 / 8

4 4 4 4 4 4

SF'

E1en E1en E1en Any Any Any

Sub%rame number

2 / , 2 / ,

9 , 5 = 24 22 226 2/ 28 29 2, 25 2= -4 -2 --6 -/ -8 -9 -, -5 -= 64 62 666 6/ 68 69 6, 65 6= /4 /2 //6 // /8 /9 /,

4 4 4 4 4 4 4 4 4 4 2 2 2 2 2 2 2 2 2 2 2 2 2 2  2  -

Any Any Any Any Any Any Any Any Any E1en E1en E1en E1en Any Any Any Any Any Any Any Any Any Any Any  E1en E1en E1en E1en Any Any Any Any Any Any Any Any Any Any Any  E1en

29 -, 65 2/, -85 69= 4-/95 268,= 4 to = = 2 / , 2 / , 29 -, 65 2/, -85 69= 4-/95 268,=  4 2 / , 2 / , 29 -, 65 2/, -85 69= 4-/95 268,=  =

/5 /= 84 82 886 8/ 88 89 8, 85 8= 94 92 996

6 6 6 6 6 6 6 6 6 6 6 6    6

E1en E1en E1en Any Any Any Any Any Any Any Any Any    E1en

2 / , 2 / , 29 -, 65 2/, -85 69=    =

The preamble &ses s&bcarrier spacing o 2.-87H3 instead o 287H3. The random access  preamble occ&pies 2- or 6 s&brames in the time domain(2-6ms) and 56= s&bcarriers in re&ency domain(2.48#H3) . There 'ill be 287H3 g&ard band on both the sides and hence it &ses total o 2.45#H3 (e&al to 9 R;s). The position o LTE random access preamble is deined  by PRACH re&ency oset parameter carried in %I;-.

There is a ma:. o 2 random access preamble in a s&brame b&t more than one +Es can &se it. #<iple +Es &sing same preamble reso&rce allocations are dierentiated by their &ni&e  preamble se&ences. As mentioned in table- ma:. o 9/ preamble se&ences are di1ided into gro&pA and gro&p;. LTE +E selects the se&ence rom these t'o gro&ps based on si3e o &plink packet and radio conditions. This helps e 6$PP T% 69.-22

PRACH RELATE( L&')S !C"#A PRACH channel $%# RACH channel +E RACH not reaching to the $%# net'ork 

LTE RELATE( L&')S "ierence bet'een %C0"#A and ?0"#A LTE Cyclic "elay "i1ersity LTE e
LTE ;earer types LTE +E E1ent #eas&rement Reporting LTE R%RP 1s R%R@ LTE %ignalling radio bearers LTE @o% LTE EP% mobility management states LTE EP% connection management states LTE +E cell selection LTE +E PL#< selection LTE +E Paging Proced&re

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