The Meaning of Pa、Pb and RS power
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The Meaning of Pa、Pb and RS power...
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2017/8/28
The Meaning of Pa Pb and RS power
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The Meaning of Pa
Pb and RS power
、
Before understanding the meaning of Pa
Pb and RS Power, we should know:
What is OFDM symbol?
The classification of OFDM symbols
The meaning of ρA and ρB
OFDM symbol means all the resource elements and RS with the same slot in time
、
domain, it can be divided into type A (A OFDM symbol) and type B (B OFDM symbol). One B OFDM Symbol has reference signals, but one A OFDM symbol does not have any reference signals.
ERS means the energy of RS.
E A means the energy of resource element of A OFDM symbol.
EB means the energy of resource element of B OFDM symbol.
The Meaning of Pa
Pb and RS power
、
The meaning of ρ A and ρB ：
ρ A = E A/ERS， ρB = EB/ERS The relationship between mW, dBm and dB can be decided by the following formulas: dBm
P r 10 * lg 1mW
P out P out P in 10 * lg 10 * lg P mW mW 1 1 in
dB 10 * lg
The relationship between Pa、Pb 、 ρ A and ρB: Pa= ρ A = E A/ERS Pb is decided by ρ A /ρB （equal to E A/EB），There is a mapping relationship between ρ A /ρB and Pb: PB
ρB /ρA
One Antenna Port
Two or Four Antenna Ports
0
1
5/4
1
4/5
1`
2
3/5
3/4
3
2/5
1/2
How to calculate the RRU power
The RRU power is equal to the power of all the resource elements and RS with the same slot, so it can be calculate by power of A OFDM symbol and B OFDM symbol respectively.
How to calculate the power of A OFDM symbol
It can be calculate by the following formula: P RS P A
P max
10
10
1000
N RB 12
It can also be calculate by the following steps:
First, , with RS power and P A, so we can calculate the power of per resource element of A OFDM symbol.
Second, we can add the powers of all the resource element s belong to one A OFDM symbol, the result is power of A OFDM symbol For example, RS=15.2dbm, Pa=-3dB, the power of per resource element of A OFDM symbol is 12.2dbm, equal to 16.6mw. There are 100 RBs in 20m cell, and each RB include 12 sub-carriers, so in 20m cell, there are 12×100 resource elements in one A OFDM symbol. So the Power of A OFDM symbol is 16.6mw×12×100=20W.
How to calculate the RRU power
How to calculate the power of B OFDM symbol
For RRU with two antennas, the power of B OFDM symbol can be calculate by the following formula: P RS P A
P max
10 10 ( 1000
P RS
B
8
A
10 10 1000
2) N RB
It can also be calculate by the following steps:
First, with RS power and P A, so we can calculate the power of per resource element of A OFDM symbol.
Second, with P B, so we can know the value of ρ A /ρB and we can calculate the power of per resource element of B OFDM symbol.
Third, we can add the powers of all the resource elements (exclude the resource elements not used) and reference signals belong to one B OFDM symbol, the result is power of B OFDM symbol.
For example, RS=15.2dbm, Pa=-3dB, Pb=1, the power of per resource element of B OFDM symbol is 12.2dbm, equal to 16.6mw. because there are two antennas, so Pa=1 means ρB/ρA is 1. That means EPRE(do not include RS and RE with no power) of B OFDM symbol is 16.6mw, and there are 12
100 REs in one B OFDM symbol.
×
2×100 RS in them and 2 ×100 REs are not used, RS power is 33.1mw. So the Power of B OFDM symbol is 16.6mw×8×100+33.1mw ×2×100=20W.
How to calculate the RRU power
The maximum output power of RRU
If the power of A OFDM is equal to the power of B OFDM symbol, the maximum output power of RRU is the power of A(or B) OFDM symbol.
If the power of A OFDM is unequal to the power of B OFDM symbol, the maximum output power is the bigger one.
The recommended power configuration is PA=-3dBm, PB=1. Under this configuration, the power of A OFDM symbol is equal to the power of B OFDM symbol, RRU can fully use the power. For the power of RS is stronger than the power of resource element, it is good for the coverage of the cell.
The parameter configuration table of Pa
Pb and RS
、
PRS(dBm)
PA(dB)
PB
Recommendation 1
15.2
0
0
default value（Huawei suggestion）
18.2
-3
1
recommendation 2
19.9
-4.77
2
recommendation3
21.2
-6
3
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