Thursday, 5 November 2015

LTE Central Frequency and EARFCN

We usually see one parameter “EARFCN” in our project network optimization test. The full name is “E-UTRA Absolute Radio Frequency Channel Number”. This parameter is the central frequency that the LTE system used. Generally the EARFCN is calculated by the 3GPP defined formula, so we don’t know directly what the central frequency is. This document mainly gives introduction about how to calculate EARFCN by central frequency and how to calculate central frequency by EARFCN.
 When we do drive test by using TEMS Investigation tool, we can only see EAUFCN through the test tool. When we use CNT in drive testwe can both see the DL,UL central frequency and the matched EARFCNlike figure 2-1. What’s the relation between central frequency and EARFCN? That is our main subject about how to calculate the relation result. 

The professional name of EARFCN is defined detailed in 3GPPTS 36.104 protocol
Table 2-1  Protocol definition
The carrier frequency in the uplink and downlink is designated by the E-UTRA Absolute Radio Frequency Channel Number (EARFCN) in the range 0 - 65535. The relation between EARFCN and the carrier frequency in MHz for the downlink is given by the following equation, where FDL_low and NOffs-DL are given in table 5.7.3-1 and NDL is the downlink EARFCN.
         FDL = FDL_low + 0.1(NDL – NOffs-DL)
The relation between EARFCN and the carrier frequency in MHz for the uplink is given by the following equation where FUL_low and NOffs-UL are given in table 5.7.3-1 and NUL is the uplink EARFCN.
         FUL = FUL_low + 0.1(NUL – NOffs-UL) 
The referred table 5.7.3-1 is below table 2-2. From the description of the protocolwe can see the central frequency has one - to - one correspondence relation with EARFCN.  NDL/uL is defined as DL/UL EARFCN. The range is 0-65535 and the value is changed from low to high according to the operating band that the central frequency in. 0-6599 are belong to FDD downlink use, 18000-245999 are belong to up link use,36000-45589 are both used by down link and up link.
Table 2-2  E-UTRA operating band
E-UTRA Operating Band
Downlink
Uplink
FDL_low [MHz]
NOffs-DL
Range of NDL
FUL_low [MHz]
NOffs-UL
Range of NUL
1
2110
0
0 – 599
1920
18000
18000 – 18599
2
1930
600
6001199
1850
18600
18600 – 19199
3
1805
1200
12001949
1710
19200
19200 – 19949
4
2110
1950
1950 – 2399
1710
19950
19950 – 20399
5
869
2400
2400 – 2649
824
20400
20400 – 20649
6
875
2650
2650 – 2749
830
20650
20650 – 20749
7
2620
2750
2750 – 3449
2500
20750
20750 – 21449
8
925
3450
3450 – 3799
880
21450
21450 – 21799
9
1844.9
3800
3800 – 4149
1749.9
21800
21800 – 22149
10
2110
4150
4150 – 4749
1710
22150
22150 – 22749
11
1475.9
4750
47504949
1427.9
22750
22750 – 22949
12
729
5010
5010 – 5179
699
23010
23010 – 23179
13
746
5180
5180 – 5279
777
23180
23180 – 23279
14
758
5280
5280 – 5379
788
23280
23280 – 23379







17
734
5730
5730 – 5849
704
23730
23730 – 23849
18
860
5850
5850 – 5999
815
23850
23850 – 23999
19
875
6000
6000 – 6149
830
24000
24000 – 24149
20
791
6150
6150 - 6449
832
24150
24150 - 24449
21
1495.9
6450
64506599
1447.9
24450
24450 24599







33
1900
36000
36000 – 36199
1900
36000
36000 – 36199
34
2010
36200
36200 – 36349
2010
36200
36200 – 36349
35
1850
36350
36350 – 36949
1850
36350
36350 – 36949
36
1930
36950
36950 – 37549
1930
36950
36950 – 37549
37
1910
37550
37550 – 37749
1910
37550
37550 – 37749
38
2570
37750
37750 – 38249
2570
37750
37750 – 38249
39
1880
38250
38250 – 38649
1880
38250
38250 – 38649
40
2300
38650
38650 – 39649
2300
38650
38650 – 39649
41
2496
39650
39650 – 41589
2496
39650
39650 – 41589
42
3400
41590
41590 – 43589
3400
41590
41590 – 43589
43
3600
43590
43590 – 45589
3600
43590
43590 – 45589
NOTE:       The channel numbers that designate carrier frequencies so close to the operating band edges that the carrier extends beyond the operating band edge shall not be used. This implies that the first 7, 15, 25, 50, 75 and 100 channel numbers at the lower operating band edge and the last 6, 14, 24, 49, 74 and 99 channel numbers at the upper operating band edge shall not be used for channel bandwidths of 1.4, 3, 5, 10, 15 and 20 MHz respectively.

Since now we have known the relation and formula, we can try to calculate central frequency and EARFCN.
For example: the central frequency is 2664 MHz, Band=7 FDD LTE system, what is the down link EARFCN?
Calculation progress is shown as below, from the formula:
FDL = FDLlow + 0.1(NDL – NOffs-DL),
We know:
NDL=FDL – FDLlow×10+ NOffs-DL
Check from table 2-2 we can know when band =7, FDLlow=2620 NOffs-DL=2750, we can put the correspondence relation to the formula, the calculation result is,
NDL=2664 – 2620×10+ 2750=3190
Finally we get the result when the central frequency is 2664MHz FDD LTE system, the down link EARFCN is 3190.
From EARFCN to central frequency
Then we can make a backward calculate. When we do LTE test, we know the EARFCN and how to calculate the central frequency?
For example down link EARFCN is 37762, what is the central frequency?
We can calculate as below, 37762 correspondence band is 38, we can check from table 2-2 that FDLlow=2570NOffs-DL=37750we can put the correspondence relation to the formula , the calculation result is:
FDL = 2570 + 0.1(37762 – 37750)=2571.2
Finally we get the result that the central frequency is 2571.2MHz.
 
Through above calculation and formula we can get almost all the EARFCN and Central frequency. But we must observe one important and detail in our calculation: BAND. From below table 2 and 3 we can see that the same down link and up link frequency may be in different band. In table 2, band 3 and band 4 indicate that DL and UL bandwidth have overlap. So when we calculate EARFCN, we should confirm the system band first, then we can calculate them accurately and correctly.
Table 3-1  FDD LTE highest and lowest frequency
E-UTRA Band
UL frequencies (MHz)
DL frequencies (MHz)
lowest
highest
lowest
highest
1
1920
1980
2110
2170
2
1850
1910
1930
1990
3
1710
1785
1805
1880
4
1710
1755
2110
2155
5
824
849
869
894
6
830
840
875
885
7
2500
2570
2620
2690
8
880
915
925
960
9
1749.9
1784.9
1844.9
1879.9
10
1710
1770
2110
2170
11
1427.9
1452.9
1475.9
1500.9
Table 3-2  TDD LTE highest and lowest frequency
E-UTRA band
UL/DL frequencies (MHz)
lowest
highest
33
1900
1920
34
2010
2025
35
1850
1910
36
1930
1990
37
1910
1930
38
2570
2620
 
Tool make
From the formula calculation and the detail progress shownwe can make the EARFCN and central frequency search tool, which can give immediately and convenient search in our network planning and optimization work.
 EARFCN and central frequency is one important parameter for us to know LTE system. When we in one trial or commercial project. We must know the FDD LTE system frequency and bandwidth. If we know the operator’s frequency information detailed, that can help us to give some professional advice to our customers.

Budi Prasetyo

About Budi Prasetyo

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