the meaning of pa、pb and rs power

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23/4/19

The Meaning of Pa 、 Pb and RS power

HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential


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.

EA means the energy of resource element of A OFDM symbol.

EB means the energy of resource element of B OFDM symbol.



The meaning of ρA and ρB ：

ρA = EA/ERS ， ρB = EB/ERS

The relationship between mW, dBm and dB can be decided by the following formulas:

The relationship between Pa 、 Pb 、 ρA and ρB:

Pa= ρA = EA/ERS

Pb is decided by ρA /ρB （ equal to EA/EB ）， There is a mapping relationship between ρA /ρB and Pb:

mW

P

mW

P

P

PdB inout

in

out

1lg*10

1lg*10lg*10

mW

PdBm r

1lg*10

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:

It can also be calculate by the following steps:

First, , with RS power and PA, 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.

121000

10 10

max

RB

PP

NP

ARS



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:

It can also be calculate by the following steps:

First, with RS power and PA, so we can calculate the power of per resource element of A OFDM symbol.

Second, with PB, so we can know the value of ρA /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.

RB

P

A

B

PP

NP

RSARS

)21000

108

1000

10(

1010

max



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

the meaning of pa、pb and rs power

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