Method of controlling the relative power of radio signals transmitted in macrodiversity mode and a radio network controller for implementing the method
The radio network controller estimates respective attenuation ratios of radio signals received by a terminal from transmitters of an active set. It commands at least some of the transmitters of the active set to transmit to the terminal with respective powers such that the difference p i -p j between the respective transmission powers p i and p j of two transmitters i and j is substantially proportional to 1 L j - 1 L i , where L i and L j designate the attenuation ratios estimated for the transmitters i and j, respectively.
1. A method of controlling power of radio signals transmitted in macrodiversity mode from a plurality of radio transmitters of an active set to a radio terminal, the method comprising the steps of:
estimating respective attenuation ratios of radio signals received by the terminal from the transmitters of the active set; and
controlling at least some of the transmitters of the active set to transmit to the terminal at respective powers such that the difference p i -p j between the respective transmission powers p i and p j of two transmitters i and j is substantially proportional to
1
L
j
-
1
L
i
,
where L i and L j , designate attenuation ratios estimated for transmitters i and j, respectively.
2. The method of claim 1 , wherein said transmitters i and j are controlled so that said difference p i -p j between the respective transmission powers is substantially equal to
NO
·
(
1
L
j
-
1
L
i
)
,
where NO is an estimate of the power of the noise affecting the receiving radio terminal.
3. The method of claim 2 , further comprising the steps of:
estimating a total power P to be transmitted to the terminal from the transmitters of the set;
evaluating the sign of a quantity
p
n
-
a
i
+
1
n
∑
j
a
j
for each transmitter j of the active set, where n is the number of transmitters of the active set and for each transmitter j of the active set
a
j
=
N0
L
j
;
and
if the evaluated sign is negative, controlling the transmitter i not to transmit to the terminal.
4. The method of claim 3 , further comprising the step of supplying the quantity
p
n
-
a
i
+
1
n
∑
j
a
j
as a parameter of a decision process for retaining the transmitter i in the active set or eliminating it therefrom.
5. The method of claim 1 , wherein the steps of estimating the attenuation ratios and of controlling the transmitters of the active set are executed periodically.
6. A radio network controller for a cellular radio network infrastructure, comprising means for communicating with fixed radio transmitters serving respective cells and with at least one radio terminal and means for monitoring radio resources assigned to a call between the terminal and a plurality of radio transmitters belonging to an active set, wherein the radio resource control means comprise means for estimating respective attenuation ratios of radio signals received by the terminal from the transmitters of the active set in accordance with measurements relating to conditions of reception of said radio signals by the terminal and means for controlling at least some of the transmitters of the active set to transmit to the terminal at respective powers such that the difference p i -p j between the respective transmission powers p i , and p j of two transmitters i and j is substantially proportional to
1
L
j
-
1
L
i
,
where L 1 and L j designate the attenuation ratios estimated for the transmitters i and j, respectively.
7. The radio network controller of claim 6 , wherein said transmitters i and j are controlled so that said difference p i -p j between the respective transmission powers is substantially equal to 26
NO
·
(
1
L
j
-
1
L
i
)
,
where N0 is an estimate of the noise received by the radio terminal.
8. The radio network controller of claim 7 , wherein the radio resource control means comprise means for estimating a total power P to be transmitted to the terminal from the transmitters of the set and means for evaluating the sign of the quantity
p
n
-
a
i
+
1
n
∑
j
a
j
for each transmitter i of the active set, where n is the number of transmitters of the active set, and
a
j
=
N0
Lj
for each transmitter j of the active set, the transmitter i being controlled not to send to the terminal if the evaluated sign is negative.
9. The radio network controller of claim 8 , wherein the radio resource control means comprise active set determination means receiving the quantity
p
n
-
a
i
+
1
n
∑
j
a
j
as a parameter to eliminate from the active set a transmitter for which said parameter is negative.