U.S. patent application number 11/515129 was filed with the patent office on 2007-01-04 for methods for determining the gains of different carriers, radio transmission units and modules for such units.
This patent application is currently assigned to Nokia Corporation. Invention is credited to Andre Dekker.
Application Number | 20070004351 11/515129 |
Document ID | / |
Family ID | 8164374 |
Filed Date | 2007-01-04 |
United States Patent
Application |
20070004351 |
Kind Code |
A1 |
Dekker; Andre |
January 4, 2007 |
Methods for determining the gains of different carriers, radio
transmission units and modules for such units
Abstract
The invention relates to methods for determining the separate
radio frequency gains for carriers in a multi-carrier transmitter
of a radio transmission unit of a radio communications system. In
order to enable a simple and accurate estimation of the gains, it
is proposed to determine the individual gains (G.sub.1-G.sub.N) of
the different carriers mathematically from different sets of powers
(REF.sub.1-REF.sub.N) at some point in each single carrier unit and
the corresponding total output powers of the transmitter.
Alternatively, the relation of the powers of the different carriers
to each other is determined just before the carriers are combined
to a single multi-carrier signal. This relation is used for
determining the contribution of the different carriers to the
transmission power of the multi-carrier signal and for therefrom
determining the radio frequency gains for the different carriers.
The invention equally relates to corresponding radio transmission
units and modules of such radio transmission units.
Inventors: |
Dekker; Andre; (Oulu,
FI) |
Correspondence
Address: |
COHEN, PONTANI, LIEBERMAN & PAVANE
551 FIFTH AVENUE
SUITE 1210
NEW YORK
NY
10176
US
|
Assignee: |
Nokia Corporation
Espoo
FI
|
Family ID: |
8164374 |
Appl. No.: |
11/515129 |
Filed: |
September 1, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10297876 |
Feb 3, 2003 |
7110727 |
|
|
PCT/EP01/04292 |
Apr 17, 2001 |
|
|
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11515129 |
Sep 1, 2006 |
|
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Current U.S.
Class: |
455/127.1 |
Current CPC
Class: |
H04W 52/346 20130101;
H04L 27/368 20130101; H04L 27/2626 20130101; H04W 52/52 20130101;
H04B 1/0483 20130101; H04L 5/06 20130101; H04W 52/42 20130101; H04B
2001/0416 20130101 |
Class at
Publication: |
455/127.1 |
International
Class: |
H04B 1/04 20060101
H04B001/04; H01Q 11/12 20060101 H01Q011/12 |
Claims
1. A method for determining separate radio frequency gains for
different carriers in a multi-carrier transmitter of a radio
transmission unit of a radio communications system, the
multi-carrier transmitter comprising means for modulating at least
two different carriers with modulation signals, means for summing
the modulated carriers output by the means for modulating, and a
multi-carrier power amplifier for amplifying the summed modulated
carriers for transmission, the method comprising: determining power
of the summed modulated carriers output by the multi-carrier power
amplifier for at least as many different sets of powers
(REF.sub.1-REF.sub.N) of signals modulated onto the different
carriers as there are carriers; and evaluating the sets of powers
(REF.sub.1-REF.sub.N) of signals used for modulation and
corresponding powers of the summed modulated carriers output by the
multi-carrier power amplifier to mathematically determine a radio
frequency gain (G.sub.1-G.sub.N) between input signals to the means
for modulating and the output of the multi-carrier power
amplifier.
2. The method according to claim 1, wherein radio frequency gain
(G.sub.1-G.sub.N) of each carrier is determined in accordance with
a relationship: P 0 m = i = 1 N .times. REF i m G i ; ##EQU4##
wherein <m> is a number of a respective set, P.sub.0 is a
power of the summed modulated carriers output by the multi-carrier
power amplifier corresponding to the respective set, N is a total
number of carriers, REF.sub.i is the power of the signal used for
modulating an i.sup.th carrier in the respective set, and G.sub.i
is the radio frequency gain to be determined for the i.sup.th
carrier.
3. A method for determining separate radio frequency gains for
different carriers in a multi-carrier transmitter of a radio
transmission unit of a radio communications system, the
multi-carrier transmitter comprising means for modulating at least
two different carriers with modulation signals in a digital domain,
digital-to-analogue converters for converting each of the digital
modulated at least two different carriers into analogue modulated
carriers, means for summing the analogue modulated carriers output
by the digital-to analogue converters, and a multi-carrier power
amplifier for amplifying the summed carriers for transmission, the
method comprising: determining power of the summed carriers output
by the multi-carrier power amplifier for at least as many different
sets of powers of signals input to the digital-to-analogue
converters as there are carriers; and evaluating the sets of powers
of the signals input to the digital-to-analogue converters and the
corresponding powers of the summed carriers output by the
multi-carrier power amplifier to mathematically determine a radio
frequency gain between the input of the digital-to-analogue
converters and the output of the multi-carrier power amplifier for
each of the at least two different carriers.
4. The method according to claim 3, wherein the radio frequency
gain (G.sub.1-G.sub.N) of each carrier is determined in accordance
with the relationship: P 0 m = i = 1 N .times. REF i m G i ;
##EQU5## wherein <m> is a number of a respective set, P.sub.0
is a power of the summed carriers output by the multi-carrier power
amplifier corresponding to the respective set, N is a total number
of carriers, REF.sub.i is the power of the signal input to the
digital to-analogue converters employed for an i.sup.th carrier in
the respective set, and G.sub.i is the radio frequency gain to be
determined for the i.sup.th carrier. carrier in the respective set,
and G.sub.i is the radio frequency gain to be determined for the
i.sup.th carrier.
5. The method according to claim 1, wherein powers used for
determining the radio frequency gain (G.sub.1-G.sub.N) of the
summed modulated carriers correspond to the power of signals
averaged over one measurement time slot.
6. The method according to claim 1, wherein signals of regular
traffic with powers of signals varied according to transmission
requirements are used to obtain powers of signals evaluated for
determining the radio frequency gain (G.sub.1-G.sub.N) of the
summed modulated carriers.
7. The method according to claim 1, wherein dedicated signals with
intentionally varied powers are used to obtain powers of signals
evaluated for determining the radio frequency gain
(G.sub.1-G.sub.N) of the summed modulated carriers.
8. The method according to claim 1, wherein more sets of powers
(REF.sub.1-REF.sub.N) and the corresponding powers of the summed
modulated carriers are determined than carriers are provided by the
means for modulating, for said evaluation a linear equation is set
up for each set of powers (REF.sub.1-REF.sub.N) and the
corresponding power of the summed modulated carriers with the radio
frequency gains (G.sub.1-G.sub.N) as unknown values, and a maximum
likelihood method is used to determine gains that provide a best
equation fit.
9. The method according to claim 1, wherein a characteristic of a
detector used to determine the output power of the multi-carrier
power amplifier is linearised around an operating point.
10. The method according to claim 1, wherein the output power of
the multi-carrier power amplifier is determined by downconverting a
radio frequency signal output by the multi-carrier power amplifier
and by converting it to a digital domain, in which the output power
is determined.
11. The method according to claim 1, wherein means for
downconversion and an analogue-to-digital conversion block
integrated in the multi-carrier power amplifier for monitoring and
controlling linearisation performance detects a power of a signal
output by the multi-carrier power amplifier.
12. The method according to claim 1, further comprising: comparing
the determined radio frequency gains (G.sub.1-G.sub.N) with
predetermined gain values for each carrier; and adjusting radio
frequency gains accordingly for each carrier to control the radio
frequency gains of the at least two different carriers.
13. The method according to claim 1, further comprising: dividing
the power of the summed modulated carriers output from the
multi-carrier power amplifier by a sum of the powers of a single
set of powers to determine a total gain of the at least two
different carriers; and adjusting equally the gain of the summed
modulated carriers for all carriers according to the determined
total gain of the at least two different carriers; wherein gains
(G.sub.1-G.sub.N) of the at least two different carriers are
occasionally determined and used for individual adjustments of the
gains of the at least two different carriers, while during a
remaining time, the total gain of the at least two different
carriers is determined.
14. A method for determining separate radio frequency gains for
different carriers in a multi-carrier transmitter of a radio
transmission unit of a radio communications system, the
multi-carrier transmitter comprising means for modulating at least
two different carriers with modulation signals, means for summing
the modulated at least two different carriers output by the means
for modulating, and a multi-carrier power amplifier for amplifying
the summed at least two carriers for transmission, the method
comprising: determining powers (P.sub.1-P.sub.N) of the modulated
at least two different carriers input to the means for summing
separately for each of the at least two different carriers; and
evaluating a distribution of the determined powers
(P.sub.1-P.sub.N) of the modulated at least two different carriers
to determine a contribution of the at least two different carriers
to a total power (P.sub.0) of the summed at least two different
carriers output by the multi-carrier power amplifier for
determining the radio frequency gains
(G.sub.1G.sub.01-G.sub.NG.sub.ON) for the at least two different
carriers.
15. The method according to claim 14, wherein the radio frequency
gains (G.sub.1G.sub.01-G.sub.NG.sub.ON) for the at least two
different carriers are determined by dividing the contribution of a
respective carrier to the total power by the power of a signal used
for modulating the respective carrier.
16. The method according to claim 14, wherein the multi-carrier
transmitter comprises a digital-to-analogue converter for
converting the modulated at least two different carriers into an
analogue domain prior to being summed by the means for summing, and
the radio frequency gains (G.sub.1G.sub.01-G.sub.NG.sub.ON) for the
at least two different carriers are determined by dividing the
contribution of a respective carrier to the total power by the
power of a signal input to the digital-to-analogue converter
employed for the respective carrier.
17. The method according to claim 14, wherein a characteristic of a
detector for determining the output power (P.sub.0) of the
multi-carrier power amplifier is linearised around an operating
point.
18. The method according to claim 14, wherein the output power
(P.sub.0) of the multi-carrier power amplifier is determined by
downconverting a radio frequency signal output by the multi-carrier
power amplifier and by converting it to a digital domain, in which
the output power is determined.
19. The method according to claim 14, wherein means for
downconversion and an analogue-to-digital conversion block
integrated in the multi-carrier power amplifier for monitoring and
controlling linearisation performance is used to detect the power
(P.sub.0) of a signal output by the multi-carrier power
amplifier.
20. The method according to claim 14, further comprising: comparing
the determined radio frequency gains (G.sub.1-G.sub.N) with
predetermined gain values for each of the at least two different
carriers; and adjusting the radio frequency gains accordingly for
each of the at least two different carriers to control the radio
frequency gains of the at least two different carriers.
21. The method according to claim 14, further comprising: dividing
the power of the summed carriers output by the multi-carrier power
amplifier by the sum of the powers of a single set of powers to
determine a total gain of the at least two different carriers; and
adjusting equally the gain of the carriers for all carriers
according to the determined total gain of the different carriers;
wherein gains (G.sub.1-G.sub.N) of the at least two different
carriers are occasionally determined and used for individual
adjustments of the gains of the at least two different carriers,
while during a remainder of time, the total gain of the different
carriers is determined.
22. A radio transmission unit for a radio communications network,
comprising: a multi-carrier transmitter comprising: means for
modulating at least two different carriers with modulation signals,
means for summing the modulated at least two different carriers
output by the means for modulating, and a multi-carrier power
amplifier for amplifying the summed at least two different carriers
for transmission; and power detection and control means receiving
as input at least as many sets of powers (REF.sub.1-REF.sub.N) of
signals used for modulating the at least two different carriers as
there are carriers provided by the means for modulating; wherein
for each set of powers a corresponding power of the summed at least
two different carriers is output by the multi-carrier power
amplifier, and the power detection and control means is configured
to mathematically determine from the received at least as many sets
of powers a radio frequency gain in the multi-carrier transmitter
for each of the at least two different carriers.
23. The radio transmission unit according to claim 22, wherein the
power detection and control means comprise registers for storing
powers of each set of powers (REF.sub.1-REF.sub.N) of the signals
used for modulating the at least two different carriers and a
corresponding total output power of the multi-carrier power
amplifier used for determining radio frequency gains
(G.sub.1-G.sub.N).
24. The radio transmission unit according to claim 22, wherein the
power detection and control means comprise a device configured to
mathematically solve matrix equations for determining radio
frequency gains (G.sub.1-G.sub.N), said device receiving as input
the sets of powers (REF.sub.1-REF.sub.N) of the signals used for
modulating the at least two different carriers and corresponding
powers of the summed at least two different carriers output by the
multi-carrier power amplifier, and outputting an estimated radio
frequency gain (G.sub.1-G.sub.N) for each of the at least two
different carriers.
25. The radio transmission unit according to claim 22, wherein
signals input to the means for modulating are provided by a
separate baseband modulator for each of the at least two different
carriers outputting digital in-phase and digital quadrature
components corresponding to received data symbols and connected to
means for baseband power detection providing the powers
(REF.sub.1-REF.sub.N) of output signals to the power detection and
control means, the means for modulating comprise for each of the at
least two different carriers two digital-to-analogue converters for
converting digital in-phase and quadrature components received from
the baseband modulator for a respective carrier into analogue
in-phase and quadrature components (I,Q), a radio frequency
modulator for modulating a carrier received from a local oscillator
with the analogue in-phase and quadrature components (I,Q) output
by the digital-to-analogue converters, and a radio frequency
amplifier having a gain which can be controlled for at least one
carrier by the power detection and control means.
26. The radio transmission unit according to claim 22, wherein
signals input to the means for modulating are provided by a
separate baseband modulator for each of the at least two different
carriers outputting digital in-phase and digital quadrature
components corresponding to received data symbols and connected to
means for baseband power detection providing the powers
(REF.sub.1-REF.sub.N) of output signals to the power detection and
control means, the means for modulating carriers comprise for each
of the at least two different carriers at least one digital
upconverter connected to a numerically controlled oscillator for
upconverting the digital in-phase and digital quadrature components
output by the baseband modulator for a respective carrier to a
frequency of the respective carrier provided by the numeric
oscillator, a digital-to-analogue converter for converting an
output of the upconverter into an analogue signal, and a radio
frequency amplifier for amplifying a signal output by the
digital-to-analogue converter, the radio frequency amplifier having
a gain which can be controlled for at least one carrier by the
power detection and control means.
27. A radio transmission unit for a radio communications network,
comprising: a multi-carrier transmitter comprising: means for
modulating at least two different carriers with modulation signals
in a digital domain; digital-to analogue converters for converting
each of the digital modulated at least two different carriers into
analogue modulated carriers; means for summing the analogue
modulated carriers output by the digital-to-analogue converters,
and a multi-carrier power amplifier for amplifying the summed
modulated carriers for transmission; and power detection and
control means receiving as input at least as many sets of powers of
signals input to the digital-to-analogue converters as there are
carriers; wherein for each set of powers a corresponding power of
the summed modulated carriers output by the multi-carrier power
amplifier, and the power detection and control means is configured
to mathematically determine from the received at least as many sets
of powers a radio frequency gain in the multi-carrier transmitter
for each of the at least two different carriers.
28. The radio transmission unit according to claim 27, wherein the
power detection and control means comprise registers for storing
powers of each set of powers (REF.sub.1-REF.sub.N) of signals input
to the digital to-analogue converters and a corresponding total
output power of the multi-carrier power amplifier is used for
determining radio frequency gains (G.sub.1-G.sub.N).
29. The radio transmission unit according to claim 27, wherein the
power detection and control means comprise a device configured to
mathematically solve matrix equations for determining radio
frequency gains (G.sub.1-G.sub.N), the device receiving as an input
the sets of powers (REF.sub.1-REF.sub.N) of the signals input to
the digital-to-analogue converters and corresponding powers of the
summed modulated carriers output by the multi-carrier power
amplifier, and outputting an estimated radio frequency gain
(G.sub.1-G.sub.N) for each of the at least two different
carriers.
30. The radio transmission unit according to claim 22, wherein
storage of measured powers and radio frequency gain estimations are
implemented in software.
31. The radio transmission unit according to claim 22, wherein
means for downconversion and an analogue-to-digital conversion
block are integrated in the multi-carrier power amplifier for
monitoring and controlling linearisation performance, and said
means for downconversion and said analogue-to-digital conversion
block are used to detect the power of the summed at least two
different carriers amplified by the multi-carrier power
amplifier.
32. A module for a radio transmission unit of a radio
communications system comprising the power detection and control
means according to claim 22.
33. A radio transmission unit for a radio communications network,
comprising: a multi-carrier transmitter comprising: means for
modulating at least two different carriers with modulation signals;
means for summing the modulated at least two different carriers
output by the means for modulating; and a multi-carrier power
amplifier for amplifying the summed modulated carriers for
transmission; and gain computation and control means receiving as
input values a power (P.sub.0) of the summed modulated carriers
output by the multi-carrier power amplifier; wherein for each
carrier a power (P.sub.1-P.sub.N) of the modulated at least two
different carriers is separately fed by the means for modulating to
the means for summing, and powers (REF.sub.1-REF.sub.N) of signals
used for modulating the at least two different carriers, the gain
computation and control means is configured to evaluate a
distribution of powers of signals input to the means for summing
over the at least two different carriers for determining a
contribution of the at least two different carriers to the power
(P.sub.0) of the summed modulated carriers output by the
multi-carrier power amplifier for determining radio frequency gains
(G.sub.1G.sub.01-G.sub.NG.sub.ON) for the at least two different
carriers.
34. The radio transmission unit according to claim 33, wherein
signals input to the means for modulating are provided by a
separate baseband modulator for each of the at least two different
carriers outputting digital in-phase and digital quadrature
components corresponding to received data symbols and connected to
means for baseband power detection providing powers of output
signals to the power detection and control means, the means for
modulating comprise for each of the at least two different carriers
two digital-to analogue converters for converting digital in-phase
and quadrature components received from the baseband modulator for
a respective carrier into analogue in phase and quadrature
components, a radio frequency modulator for modulating a carrier
received from a local oscillator with the digital in-phase and
quadrature components output by the digital-to analogue converters,
and a radio frequency amplifier for amplifying the modulated
carrier, the radio frequency amplifier having a gain which can be
controlled for at least one carrier by a gain computation and
control means.
35. The radio transmission unit according to claim 33, wherein
signals input to the means for modulating are provided by a
separate baseband modulator for each of the at least two different
carriers outputting digital in-phase and digital quadrature
components corresponding to received data symbols and connected to
means for baseband power detection providing the powers
(REF.sub.1-REF.sub.N) of output signals to the gain computation and
control means, the means for modulating carriers comprise for each
of the at least two different carriers at least one digital
upconverter connected to a numeric oscillator for upconverting the
digital in-phase and digital quadrature components output by the
baseband modulator for a respective carrier to a frequency of the
respective carrier provided by the numeric oscillator, a
digital-to-analogue converter for converting an output of the
upconverter into an analogue signal, and a radio frequency
amplifier for amplifying the signal output by the digital-to
analogue converter, the radio frequency amplifier having a gain
which can be controlled for at least one carrier by the gain
computation and control means.
36. A radio transmission unit for a radio communications network,
comprising: a multi-carrier transmitter comprising: means for
modulating at least two different carriers with modulation signals
in a digital domain; digital-to analogue converters for converting
each of the digital modulated at least two different carriers into
analogue modulated carriers; means for summing the analogue
modulated at least two different carriers output by the
digital-to-analogue converters; and a multi-carrier power amplifier
for amplifying the summed carriers for transmission; and gain
computation and control means receiving as input values a power
(P.sub.0) of the summed modulated carriers output by the
multi-carrier power amplifier; wherein for each the at least two
different carriers a power (P.sub.1-P.sub.N) of the analogue
modulated carriers is separately fed by the digital-to-analogue
converters to the means for summing and powers of signals input to
the digital-to analogue converters, the gain computation and
control means is configured to evaluate a distribution of powers of
signals input to the means for summing over the at least two
different carriers for determining a contribution of the at least
two different carriers to the power (P.sub.0) of the summed
modulated carriers output by the multi-carrier power amplifier for
determining radio frequency gains (G.sub.1G.sub.01-G.sub.NG.sub.ON)
for the at least two different carriers.
37. The radio transmission unit according to claim 33, further
comprising means for detecting the powers (P.sub.1-P.sub.N) of the
modulated at least two different carriers fed to the means for
summing, said means for detecting the powers (P.sub.1-P.sub.N)
being a single radio frequency integrated circuit.
38. The radio transmission unit according to claim 33, further
comprising means for detecting the powers (P.sub.1-P.sub.N) of the
modulated at least two different carriers fed to the means for
summing, said means for detecting the powers (P.sub.1-P.sub.N)
including at least one dedicated radio frequency active component
for each of the at least two different carriers; wherein
corresponding dedicated active components employed for the at least
two different carriers are matched components.
39. The radio transmission unit according to claim 33, wherein
means for downconversion and an analogue-to-digital conversion
block are integrated in the multi-carrier power amplifier for
monitoring and controlling linearisation performance, and said
means for downconversion and said analogue-to-digital conversion
block are used to detect the power (P.sub.0) of the summed
modulated carriers amplified by the multi-carrier power
amplifier.
40. The radio transmission unit according to claim 33, wherein
radio frequency gain estimation is implemented in software.
41. A module for a radio transmission unit of a radio
communications system comprising the gain computation and control
means according to claim 33.
42. A module for a radio transmission unit of a radio
communications system comprising means for separately detecting for
each of the at least two different carriers the power of the summed
modulated carriers fed to the means for summing according to claim
33.
43. A radio communications network comprising a radio transmission
unit according to claim 22.
44. The method according to claim 3, wherein powers used for
determining the radio frequency gain (G.sub.1-G.sub.N) of the at
least two different carriers correspond to the power of signals
averaged over one measurement time slot.
45. The method according to claim 3, wherein signals of regular
traffic with powers of signals varied according to transmission
requirements are used to obtain the powers of signals evaluated for
determining the radio frequency gain (G.sub.1-G.sub.N) of the at
least two different carriers.
46. The method according to claim 3, wherein dedicated signals with
intentionally varied powers are used to obtain the powers of
signals evaluated for determining the radio frequency gain
(G.sub.1-G.sub.N) of the at least two different carriers.
47. The method according to claim 3, wherein more sets of powers
(REF.sub.1-REF.sub.N) and the corresponding powers of the summed
carriers are determined than carriers are provided by the means for
modulating, for said evaluation a linear equation is set up for
each set of powers (REF.sub.1-REF.sub.N) and the corresponding
power of the summed carriers with the radio frequency gains
(G.sub.1-G.sub.N) as unknown values, and a maximum likelihood
method is used to determine gains that provide a best equation
fit.
48. The method according to claim 3, wherein a characteristic of a
detector used to determine the output power of the multi-carrier
power amplifier is linearised around an operating point.
49. The method according to claim 3, wherein the output power of
the multi-carrier power amplifier is determined by downconverting a
radio frequency signal output by the multi-carrier power amplifier
and by converting it to a digital domain, in which the output power
is determined.
50. The method according to claim 3, wherein means for
downconversion and an analogue-to-digital conversion block
integrated in the multi-carrier power amplifier for monitoring and
controlling linearisation performance is used to detect the power
of a signal output by the multi-carrier power amplifier.
51. The method according to claim 3, further comprising: comparing
the determined radio frequency gains (G.sub.1-G.sub.N) with
predetermined gain values for each of the at least two carriers;
and adjusting radio frequency gains accordingly for each of the at
least two carriers to control the radio frequency gains.
52. The method according to claim 3, further comprising: dividing
the power of the summed carriers output from the multi-carrier
power amplifier by a sum of the powers of a single set of powers to
determine a total gain of the at least two different carriers; and
adjusting equally the gain of the summed carriers according to the
determined total gain of the at least two different carriers;
wherein the gains (G.sub.1-G.sub.N) of the at least two different
carriers are occasionally determined and used for individual
adjustments of the gains of the at least two different carriers,
while during a remaining time, the total gain of the at least two
different carriers is determined.
53. The radio transmission unit according to claim 27, wherein
storage of measured powers and radio frequency gain estimations are
implemented in software.
54. The radio transmission unit according to claim 27, wherein
means for downconversion and an analogue-to-digital conversion
block are integrated in the multi-carrier power amplifier for
monitoring and controlling linearisation performance, and said
means for downconversion and said analogue-to-digital conversion
block are used to detect the power of the summed modulated carriers
amplified by the multi-carrier power amplifier.
55. A module for a radio transmission unit of a radio
communications system comprising the power detection and control
means according to claim 27.
56. The radio transmission unit according to claim 36, further
comprising means for detecting the power (P.sub.1-P.sub.N) of the
modulated carriers fed to the means for summing, said means for
detecting the power (P.sub.1-P.sub.N) being a single radio
frequency integrated circuit.
57. The radio transmission unit according to claim 36, further
comprising means for detecting the power (P.sub.1-P.sub.N) of the
analogue modulated carriers fed to the means for summing, said
means for detecting the power (P.sub.1-P.sub.N) including at least
one dedicated radio frequency active component for each of the at
least two different carriers; wherein corresponding dedicated
active components employed for different carriers are matched
components.
58. The radio transmission unit according to claim 36, wherein
means for downconversion and an analogue-to-digital conversion
block are integrated in the multi-carrier power amplifier for
monitoring and controlling linearisation performance, said means
for downconversion and said analogue-to-digital conversion block
are used to detect the power (P.sub.0) of the summed at least two
different carriers amplified by the multi-carrier power
amplifier.
59. The radio transmission unit according to claim 36, wherein
radio frequency gain estimations are implemented in software.
60. A module for a radio transmission unit of a radio
communications system comprising the gain computation and control
means according to claim 36.
61. A module for a radio transmission unit of a radio
communications system comprising means for separately detecting for
each of the at least two different carriers the power of the
modulated carriers fed to the means for summing according to claim
36.
62. A radio communications network comprising a radio transmission
unit according to claim 27.
63. A radio communications network comprising a radio transmission
unit according to claim 33.
64. A radio communications network comprising a radio transmission
unit according to claim 36.
65. The method according to claim 1, wherein said means for
modulating at least two different carriers with modulation signals
modulate said at least two different carriers in a digital domain,
a power of said digital modulated carriers is multiplied with a
respective power control level, digital-to-analogue converters
convert each power adjusted digital modulated at least two
different carriers into analogue modulated carriers, said means for
summing sums the analogue modulated carriers output by the
digital-to-analogue converters, and each power in said sets of
powers is multiplied with the power control level which is applied
to a respective digital modulated at least two different carriers
prior to being used in said evaluation, which digital modulated at
least two different carriers have been modulated with a modulating
signal to which the respective power in said sets of powers is
associated.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/297,876 which was filed with the U.S.
Patent and Trademark Office on Feb. 3, 2003, which is a national
stage of PCT application No. PCT/EP01/04292, filed on Apr. 17,
2001.
FIELD OF THE INVENTION
[0002] The invention relates to methods for determining the
separate radio frequency gains for different carriers in a
multi-carrier transmitter of a radio transmission unit of a radio
communications system, the multi-carrier transmitter comprising
means for modulating at least two different carriers with
modulation signals, means for summing the signals output by the
means for modulating, and a multi-carrier power amplifier for
amplifying the summed signals for transmission. The invention
moreover relates to radio transmission units, to modules of such
radio transmission units and to radio communications network
comprising such a radio transmission unit.
BACKGROUND OF THE INVENTION
[0003] In radio communications systems, it is known to employ
cellular base station transmitters outputting signals with
different carrier frequencies. In such transmitters, it is of great
importance to be able to control the radio frequency gains and
accordingly the output powers for each carrier accurately to
predetermined levels.
[0004] In conventional base station transmitters, which comprise a
separate transmitter for each carrier, it is possible to determine
the radio frequency gain for each carrier independently from the
gain of the other carriers.
[0005] For illustration, FIG. 1 shows a block diagram of such a
conventional base station transmitter based on RF (radio frequency)
IQ (in-phase and quadrature) modulators. The base station
transmitter comprises N single-carrier transmitters, of which the
first one and the last one are shown. Signs of components or of
values of the transmitters having an index 1 or N indicate that
they are assigned to the 1.sup.st or N.sup.th single-carrier
transmitter.
[0006] Each of the N single-carrier transmitters includes a
baseband modulator 1 connected at its input to elements (not shown)
of a communications network supplying data symbols and at its
outputs to two digital-to-analogue converters 3, 4. The
digital-to-analogue converters 3, 4 are connected to inputs of an
RF modulator 5. An additional input of the RF modulator 5 is
connected to a local oscillator (LO) 6, while the output of the RF
modulator 5 is connected to an input of a variable gain RF
amplifier 7. The output of the RF amplifier 7 is connected to a
single carrier power amplifier (SCPA) 8 and the output of the SCPA
8 of each single-carrier transmitter is connected via a common
summation unit 10 to a transmit antenna 11. The output of the SCPA
8 is further connected to an input of a power detection and control
unit 9 belonging to the respective single carrier transmitter.
[0007] Equally, the baseband modulator 1 is connected via a
baseband power detection unit 2 to an input of the power detection
and control unit 9. The output of the power detection and control
unit 9 forms a gain controlling input of the RF amplifier 7. In
practice, there can be included more upconversion stages and
amplifiers, and filters may be included as well.
[0008] The baseband modulators 1 of the N single-carrier
transmitters receive symbols from the network that are to be
transmitted via the transmit antenna 11 over the air interface. The
baseband modulator 1 of the respective transmitter generates a
digitised signal trajectory in the complex plain in IQ format and
forwards the signals to the two digital-to-analogue converters
(DAC) 3, 4. Each of the digital IQ signals is converted into an
analogue signal 1, Q by one of the two digital-to-analogue
converters 3, 4 and then fed to the RF modulator 5. In the RF
modulator 5, both signals 1, Q are modulated onto one of N carriers
determined by the local oscillator 6 associated to the respective
single-carrier transmitter. The output signal of the RF modulator 5
is then amplified by the RF amplifier 7 according to the gain set
according to a gain control signal GC.sub.1, GC.sub.N applied to
the respective RF amplifier 7, and fed to the SCPA 8. The powers
output by the N single-carrier transmitters are combined at the
output of the SCPA 8 by the summation unit 10 for transmission by
the transmit antenna 11.
[0009] The power REF.sub.1, REF.sub.N of the output signal of each
baseband modulator 1 is computed in the associated baseband power
detection unit 2 and forwarded to the respective power detection
and control unit 9. Equally, the output of each of the SCPAs 8 is
fed additionally to the respective power detection and control unit
9, where the output carrier power is measured and compared to the
output power provided by the baseband power detection unit 2 of the
corresponding single-carrier transmitter. The quotient of these
powers constitutes the gain of the respective RF path, G.sub.1,
G.sub.N. If the measured gain G.sub.1, G.sub.N on the RF path of
one of the N single-carrier transmitters deviates from the desired
value, the responsible power detection and control unit 9 changes
the gain control signal GC.sub.1 GC.sub.N applied to the respective
RF amplifier 7 for this path in order to steer the gain G.sub.1,
G.sub.N into the direction of the desired gain.
[0010] Equally, an independent power control of the different
carriers is possible in another embodiment of a conventional base
station transmitter shown in FIG. 2. The base station transmitter
corresponds to the one of FIG. 1, except that each baseband
modulator 1 is now connected to the respective RF amplifier 7 via a
digital upconverter 12 and a single digital-to-analogue converter
14. An input of the digital upconverter 12 is further connected to
a numerically controlled oscillator (NCO) 13. To the components of
the single carrier transmitters corresponding to the components of
the single carrier transmitters of FIG. 1, the same reference signs
were assigned.
[0011] In contrast to the example of FIG. 1, here the conversion of
the digital IQ signals output by one of the baseband modulators 1
to a modulated RF signal is carried out in the digital domain by
the respective digital upconverter 12, the frequency of which is
determined by the NCO 13 associated to the digital upconverter 12.
The output of the digital upconverter 12 is then converted to an
analogue signal by the single digital-to-analogue converter 14.
Presently, digital-to-analogue converters 14 are not capable of
generating high quality signals at GHz frequencies. Therefore, the
architecture of FIG. 2 has in practice at least one extra analogue
upconversion stage. However, for the sake of simplicity this is not
shown in the diagram.
[0012] Since the power output by the baseband modulators 1 and the
output of the SCPAs 8 correspond to the outputs of baseband
modulators 1 and SCPAs 8 of FIG. 1 and are fed to the power
detection and control units 9 as in the example of FIG. 1, the RF
gain for each carrier can be determined independently as described
with reference to FIG. 1. Again, gain control signals GC.sub.1,
GC.sub.N are provided by the power detection and control units 9
according to the determined gains G.sub.1, G.sub.N and supplied to
the respective RF amplifier 7 in order to adjust the gain for each
carrier to a predetermined value.
[0013] The base station is required to control the output power
used for each carrier accurately to a predetermined value. At
maximum output power, the GSM (Global System for Mobile
communication) and WCDMA (Wideband Code Division Multiple Access)
standards demand an accuracy of better than .+-.2 dB per carrier.
In order to achieve this accuracy reliably, the power measurement
accuracy should in practice even be better than .+-.dB.
[0014] If a single carrier power amplifier is used for each
carrier, this accuracy can be achieved e.g. with one of the
architectures described with reference to FIGS. 1 and 2, since an
access to the separate output powers of each carrier is given.
Combining the carriers only at the single carrier power amplifier
outputs, though, has several drawbacks. Output power is lost and
changing the number of carriers in a base station takes much
effort. Future base station will therefore combine the carriers
already before power amplification or even earlier. The carriers
are then power amplified by a single multi-carrier power amplifier.
This, however, causes problems for the power control, since the
individual power of the power amplified carriers cannot be accessed
any more but only the multi-carrier signal output by the single
multi-carrier power amplifier. Therefore, an accurate estimation of
the individual carrier RF gains becomes more complicated.
[0015] In a known approach, it is simply assumed that the RF gain
is equal for all carriers. Accordingly, the total output power is
measured and divided by the sum of the output powers of the
baseband modulators. This quotient constitutes the total gain. If
the measured gain deviates from the desired value, the gain control
signals for each RF amplifier are changed equally in order to
adjust the gain to the right value. The drawback of this method is
that there is no way to ensure that the RF gains for the different
carriers are indeed all equal and will stay equal for all values of
the common gain control signal, under all environmental conditions
and during the whole lifetime of the base station. The relation of
the gains to each other can be verified only during the assembly of
the base station and, after putting into operation, by a site visit
to check.
[0016] In an alternative approach, it was proposed to use a
channeliser to separate the individual carriers from each other at
the output of the single multi-carrier power amplifier. The powers
of the separated carriers can then be measured and compared to the
powers of the baseband signals. By division of the respective pair
of values for one carrier, the gain for the individual carriers is
found. If one of the gains deviates from the predetermined gain for
this carrier, the gain can be adjusted individually by a
corresponding gain control signal. The disadvantage of this method
is that a channeliser is needed. The required selectivity is such
that its implementation must be at an intermediate frequency or
baseband. Therefore, one or two downconversion stages are needed,
which increases complexity and adds uncertainty to the measurement.
In practice, the power measurement circuitry moreover needs some
automatic calibration circuit to maintain its accuracy. Therefore,
the power control becomes rather expensive and space consuming.
Moreover, in case frequency hopping transmitters are used, like
e.g. in the GSM, also the channelisers have to be suited for
frequency hopping, which makes the construction even more
complex.
SUMMARY OF THE INVENTION
[0017] It is an object of the invention to provide a method, a
radio transmission unit, a module for a radio transmission unit and
a radio communications network comprising such a radio transmission
unit which enable a simple determination of separate radio
frequency gains for different carriers in a multi-carrier
transmitter of a radio transmission unit of a radio communications
system.
[0018] This object is reached in a first alternative of the
invention on the one hand with a method for determining the
separate radio frequency gains for different carriers in a
multi-carrier transmitter of a radio transmission unit of a radio
communications system, the multi-carrier transmitter comprising
means for modulating at least two different carriers with
modulation signals, means for summing the modulated carriers output
by the means for modulating and a multi-carrier power amplifier for
amplifying the summed carriers for transmission, wherein [0019] the
power of the summed carriers output by the multi-carrier power
amplifier is determined for at least as many different sets of
powers of signals modulated onto the different carriers as there
are carriers; and wherein [0020] the radio frequency gain between
the input of the signals to the means for modulating and the output
of the multi-carrier power amplifier is determined for each carrier
by evaluating the sets of powers of the signals used for modulation
and the corresponding powers of the summed carriers output by the
multi-carrier power amplifier mathematically.
[0021] For a variation of this method of the first alternative of
the invention, the multi-carrier transmitter comprises for each
carrier a digital-to-analogue converter for converting digital
modulated carriers into analogue modulated carriers before feeding
them to the means for summing the modulated carriers. Such a
converter can also be comprised in the multi-carrier for the first
presented method. But in the variation, the power of the summed
carriers output by the multi-carrier power amplifier is determined
for at least as many different sets of powers of signals input to
the digital-to-analogue converters as there are carriers. The radio
frequency gain between the input of the digital-to-analogue
converter and the output of the multi-carrier power amplifier is
then determined for each carrier by evaluating the sets of powers
of the signals input to the digital-to-analogue converters and the
corresponding powers of the summed carriers output by the
multi-carrier power amplifier mathematically.
[0022] On the other hand, the object is reached in the first
alternative of the invention with a radio transmission unit for a
radio communications network with a multi-carrier transmitter
comprising means for modulating at least two different carriers
with modulation signals, means for summing the modulated carriers
output by the means for modulating, and a multi-carrier power
amplifier for amplifying the summed carriers for transmission, and
with power detection and control means receiving as input at least
as many sets of powers of signals used for modulating the carriers
as there are carriers provided by the means for modulating, and for
each set the corresponding power of the summed carriers output by
the multi-carrier power amplifier, the power detection and control
means being suited to determine out of the received powers the
radio frequency gain in the multi-carrier transmitter for each
carrier mathematically.
[0023] In a variation of the radio transmission unit corresponding
to the variation of the method, the multi-carrier transmitter of
the radio transmission unit comprises in addition
digital-to-analogue converters for converting each of the modulated
carriers, which are digital modulated carriers, into analogue
modulated carriers, the means for summing the analogue modulated
carriers output by the digital-to-analogue converters. Such
digital-to-analogue converters can also be comprised in the first
proposed radio transmission unit. In contrast to the first proposed
radio transmission unit, in the variation, the power detection and
control means receive as input at least as many sets of powers of
the signals input to the digital-to-analogue converters as there
are carriers, and for each set the corresponding power of the
summed carriers output by the multi-carrier power amplifier. Like
in the first presented radio transmission unit, the power detection
and control means are suited to determine out of the received
powers the radio frequency gain in the multi-carrier transmitter
for each carrier mathematically.
[0024] The object of the invention is moreover reached in the first
alternative with a module for a radio transmission unit in a radio
communications system comprising the power detection and control
unit of a radio transmission unit in one of the presented
variations.
[0025] The methods, the radio transmission units and the modules of
the first alternative of the invention proceed from the idea that
the total power of the summed carriers output by the multi-carrier
power amplifier can be described mathematically with the powers of
predetermined signals in the single carrier units as variable but
known coefficients and the total RF gain for each carrier as
unknown values. The predetermined signals can be either signals
input to the means for modulating the different carriers, or
signals input to digital-to-analogue converters included in the
single carrier units. The powers of the signals in the single
carrier units can be determined easily and each variation in these
powers leads to a corresponding variation in the total output
power. A plurality of sets of different powers of the signals input
to the means for modulating or to the digital-to-analogue
converters respectively and the corresponding total output power
deliver a plurality of equations that can be solved mathematically
in case at least as many sets are supplied as carriers are present.
The proposed methods, radio transmission units and modules
according to the first aspect of the invention therefore enable to
determine the gains of the individual carriers without using a
channeliser, but nevertheless accurately. Avoiding channelisers
means that the implementation can be simpler and there are less
problems in frequency hopping.
[0026] The object of the invention is equally reached in a second
alternative of the invention by a method for determining the
separate radio frequency gains for different carriers in a
multi-carrier transmitter of a radio transmission unit of a radio
communications system, the multi-carrier transmitter comprising
means for modulating at least two different carriers with
modulation signals, means for summing the modulated carriers output
by the means for modulating, and a multi-carrier power amplifier
for amplifying the summed carriers for transmission, wherein the
power of the modulated carriers input to the means for summing is
determined separately for each carrier, and wherein the
distribution of the powers of the modulated carriers input to the
means for summing is evaluated in order to determine the
contribution of the different carriers to the power of the summed
carriers output by the multi-carrier power amplifier for
determining the radio frequency gains for the different
carriers.
[0027] In the second alternative of the invention, the object of
the invention is also-reached by a corresponding radio transmission
unit for a radio communications network with a multi-carrier
transmitter comprising means for modulating at least two different
carriers with modulation signals, means for summing the modulated
carriers output by the means for modulating, and a multi-carrier
power amplifier for amplifying the summed carriers for
transmission, and with gain computation and control means receiving
as input values the total power of the summed carriers output by
the multi-carrier power amplifier, the powers of the modulated
carriers fed by the means for modulating to the means for summing,
and the powers of the signals used for modulating the carriers, the
gain computation and control means being suited to evaluate the
distribution of the powers of the modulated carriers input to the
means for summing for determining the contribution of the different
carriers to the total power of the summed carriers output by the
multi-carrier power amplifier, for determining the radio frequency
gains for the different carriers.
[0028] In a variation of the radio transmission unit for the second
alternative of the invention, the multi-carrier transmitter of the
radio transmission unit comprises in addition digital-to-analogue
converters for converting each of the modulated carriers, which are
digital modulated carriers, into analogue modulated carriers, the
means for summing the analogue modulated carriers output by the
digital-to-analogue converters. Such digital-to-analogue converters
can also be comprised in the first presented radio transmission
unit and in the radio transmission unit used for the presented
method of the second alternative of the invention. The gain
computation and control means receive in the variation as input
values the power of the summed carriers output by the-multi-carrier
power amplifier, for each carrier separately the power of the
modulated carriers fed by the digital-to-analogue converters to the
means for summing, and the powers of the signals input to the
digital-to-analogue converters. The gain computation and control
means are then suited to evaluate the distribution of the powers of
the signals input to the means for summing over the different
carriers for determining the contribution of the different carriers
to the power of the summed carriers output by the multi-carrier
power amplifier for determining the radio frequency gains for the
different carriers.
[0029] Corresponding to these variations of the radio transmission
unit, the gain can be determined in the last presented method based
on the power of the signals used for modulating the respective
carrier or based on the signals input to the respective
digital-to-analogue converter.
[0030] Finally, the object of the invention is reached for the
second alternative of the invention with a corresponding module for
such radio transmission units comprising such a gain computation
and control means and/or means for detecting for each carrier
separately the powers of the modulated carriers fed to the means
for summing.
[0031] The method, radio transmission units and modules according
to the second alternative of the invention are based on the fact
that multi-carrier power amplifiers tend to have by design a very
accurate gain.
[0032] The input powers to a multi-carrier power amplifier are
quite small, typically less than 10 dBm rms (root mean square). In
case a transmitter is not transmitting at maximum power level, the
power may even be significantly smaller, e.g. 0 to -10 dBm. REF
detectors operating at this kind of low input levels are not
particularly accurate and temperature stable. Therefore it is
difficult to perform an accurate carrier power measurement at the
input of a multi-carrier power amplifier. In principle, it would be
possible to generate higher input signals to the multi-carrier
power amplifier, but in case of e.g. WCDMA, this demands extreme
linearity from the driver amplifier. This means, that it is not
advisable to use simply the measured input powers to the
multi-carrier power amplifier, multiplied with the respective gain
in the multi-carrier power amplifier for each carrier, for
calculating the total output power for each carrier.
[0033] According to the second proposed alternative of the
invention, in contrast, the single-carrier powers are determined
before summing of the modulated carriers to a multi-carrier signal,
but only used relatively to each other. Even though it is not
possible to determine the powers of the modulated carriers input to
the multi-carrier power amplifier accurately, it is possible to
mutually track the powers accurately. This makes it possible to
compare the relative strengths of the individual carrier powers at
the output of the low-power part of the multi-carrier transmitter.
The determined relative strengths can then be used to distribute
the total power or the total gain determined for the summed
carriers to the individual carriers. The gains for the different
carriers in the multi-carrier power amplifier can be taken into
account for this distribution. Thus, an accurate individual gain
value for each carrier can be obtained.
[0034] The second proposed alternative of the invention has several
advantages compared to the first proposed alternative. There is no
need to solve a system of equations and the gain information can be
obtained directly after a single measurement, so there is no need
to wait for a series of measurements. Possibly, even less accuracy
is needed in the measurement of the multi-carrier signal. Finally,
the second alternative of the invention is also suited for fixed
carrier powers. The advantage of the first proposed alternative, in
contrast, is that less RF power detectors are needed. Moreover, in
the second alternative, the frequency response of the MCPA, apart
from a constant, has to be known reliably a priory.
[0035] Both alternatives according to the invention use
mathematical evaluations of determined powers in order to allow for
a simple and accurate determination of the individual RF gain of
different carriers in a multi-carrier radio transmission unit.
[0036] It has to be noted that in the respective variation of both
alternatives, in which the gain is determined based on the power of
signals input to the digital-to-analogue converters, the expression
"input to the digital-to-analogue converters" does not necessarily
refer to a direct input to these converters. Rather, the input to
any component of the different single carrier units can constitute
this input to the digital-to-analogue converters to which input the
carriers ate fed while being already modulated but still in the
digital domain.
[0037] The radio transmission units of the invention can be in
particular base stations, but equally any other transmission units
using multi-carrier signals for transmission.
[0038] The object of the invention is also reached with a radio
communications network comprising a radio transmission unit of
either of the alternatives of the invention.
[0039] Preferred embodiments of the invention become apparent from
the subclaims.
[0040] In most radio transmission units, the power of the signals
provided for RF modulation can be varied in time slots in order to
adapt the transmitted power to the needs of the mobile. More
specifically, in TDMA systems, the power of each carrier can be
varied in time slots. In CDMA systems, in contrast, the power of
the user codes can be varied in user specific time slots, the time
slots of different users not being synchronised to each other and
each carrier serving a plurality of users. Accordingly, in the
carrier power of a CDMA signal, the time slots cannot be recognised
any more. The possibility of varying the transmission power reduces
the interference within the network and to other networks.
[0041] It is proposed for the first alternative of the invention
employed in a TDMA system that the power of the signals input to
the means for modulating or to the digital-to-analogue converters
corresponds to the power of signals of one carrier time slot, in
particular the average of the power of one carrier time slot. That
means that used measurement time slots are advantageously
synchronised with the carrier time slots. But also in TDMA systems,
a time slot for measurement does not necessarily have to coincide
with a time slot for power control. The only requirement for the
measurement time slots is that they have to be long enough to allow
a sufficiently accurate power measurement and a mitigation of the
effects of possible small misalignments between the slots for power
of signals input to the means for modulating and the slots for the
power of the RF output signal of the multi-carrier power
amplifier.
[0042] Since in a CDMA system, the power seems to vary in a random
way, there is no need for a synchronisation in such a system, even
though the measurements are preferably also carried out in time
slots.
[0043] The power values of several measurement time slots can be
stored in the first alternative with both systems in registers and
used as input to a mathematical algorithm. On the one hand, the
variations in power employed during regular traffic can be used in
the first proposed alternative for forming continuously sets of
powers and for determining the radio frequency gain based on those
sets continuously. On the other hand, the power of the signals can
be varied intentionally, in particular during times of low traffic.
In the latter case, the RF gains should be so stable that they do
not change significantly over a time span of several hours. During
quiet hours, the carrier powers can be manipulated in e.g. the
following ways: In a CDMA system it is possible to increase
temporarily the power of a carrier by adding dummy traffic
channels. In a TDMA system it is possible to arrange the traffic in
such a way that all carriers will have in turn empty time slots. In
that way a variation between zero (or minimum) power and typical
operating power is created. In the GSM system the BCCH carrier
presents a problem, since all its time slots should be at equal
power. However, if the transmitters have frequency hopping
capability it is possible to redirect the BCCH carrier to another
RF path. In this way it is also possible to arrange zero or minimum
transmit power in the transmitter that normally transmits the
BCCH.
[0044] In order to be able to determine the gains of N different
carriers, in principle, N linear equations with the N gains as N
unknowns in each equation are sufficient in the first alternative
of the invention. But in practice, especially if the carrier powers
are randomly varying according to the needs of the radio network,
there is no guarantee that the system of equations is well
conditioned. Also the measured output power may contain some
errors, even though this may not lead to large errors in the
computed RF gains. In a preferred embodiment of the first
alternative of the invention, therefore more than N sets are
determined and a maximum likelihood method is used to find the
gains that give the best fit to the equations.
[0045] In the second alternative of the invention, the measurement
of the powers of the single carriers before they are summed is best
performed by one or more dedicated active components. If each
carrier is processed by its own active component(s), the components
for the different carriers should be matched. To this end,
corresponding components can e.g. originate from the same area of
the same die so that they have equal electrical properties, and
they should be in close thermal contract, in order to ensure a good
accuracy in the relation of the determined powers. The at least one
dedicated active component can be in particular a single RF
integrated circuit. Still, other active components, like diodes,
can be used as well for realising a detector. In another preferred
embodiment, means for detecting the power of all carriers are
realised in a single radio frequency integrated circuit.
[0046] In the second alternative of the invention, the gain for the
different carriers can be determined by first distributing the
power of the summed carriers output by the multi-carrier power
amplifier to the different carriers according to the relation of
the powers of the different carriers input to the multi-carrier
power amplifier to each other. The individual gains can then be
determined by dividing the determined portion of the output power
assigned to one carrier by the power of the respective signal input
to the means for modulating this carrier or input to the
digital-to-analogue converter of this carrier unit, respectively.
It should be considered that the gain in the MCPA may be different
for the different carriers.
[0047] In both alternatives of the invention, the algorithm used
for determining the RF gains of the different carriers can be
further refined in several ways. For instance, the output signal of
an RF power detector used for detecting the power output by the
multi-carrier power amplifier may be some non-linear function,
constituting the detector characteristic, of the real output power
of the multi-carrier power amplifier. This detector characteristic
can be linearised around some operating point in order to make the
equation set linear again. Even though the linearisation can take
place in the detector itself, it is preferably carried out in
numerical algorithms.
[0048] In a preferred embodiment of both alternatives of the
invention in which the radio frequency gains of the different
carriers is determined based on signals used for modulating the
carriers, baseband signals provided by a baseband modulator are
supplied to the means for modulating the carriers as such signals
used for modulating. In this case, the baseband powers can be
computed numerically inside the baseband modulator or by a separate
processor operating on the digital baseband output of the baseband
modulator.
[0049] When determining in either of the two alternative of the
invention the radio frequency gain of the different carriers based
on the power of signals input to digital-to-analogue converters,
the respective power does not necessarily have to be measured at
the input of the respective digital-to-analogue converter. In NCO
modulator architectures, like the one described with reference to
FIG. 2, it is possible to measure the powers of the signals input
to the digital-to-analogue converters inside of the digital
upconverters preceding the digital-to-analogue converters, or at
the output of such digital upconverters. The power of a signal
input to a digital-to-analogue converter can also be computed as
the power of a complex modulating signal times a multiplication
factor at the output of such a digital upconverter.
[0050] Measuring the output power of the multi-carrier power
amplifier can be carried out in both alternatives of the invention
by an RF integrated circuit, but this may not result in very
accurate measurements. Instead, the radio frequency signal output
by the multi-carrier power amplifier is preferably first
downconverted. The downconverted signal is then converted into the
digital domain, in which the power is determined. Most MCPAs
already have a downconversion and ADC block inside for the purpose
of monitoring and controlling linearisation performance. This block
can be used advantageously as basis for adding digital rms
detection to the MCPA that can be used for detecting the power of
the signal output by the multi-carrier power amplifier.
[0051] In a further preferred embodiment of both alternatives of
the invention, the RF gain estimation is implemented in software.
Additionally, the gain control and, in the first alternative, the
storage of measured values can be implemented in software.
[0052] In both alternatives of the invention, the determined RF
gains are preferably compared with predetermined gain values for
each carrier, so that the gain for each carrier can be adjusted
accordingly.
[0053] The radio transmission units of both alternatives can be
used with various base station architectures. For example, the
means for modulating can be realised with separate RF IQ modulation
or NCO modulation paths for each carrier as described with
reference to FIGS. 1 and 2 respectively from the output of the
baseband modulator to the output of the RF amplifier, the signals
used for modulating the carriers being provided by a baseband
modulator as described with reference to FIGS. 1 and 2. In both
alternatives, additional components may be arranged between the
means for modulating, summing and the power detection and control
means or the gain estimation and control means.
[0054] It is possible to combine one of the proposed methods with
the method mentioned in the background of the invention, in which
the gain is always adjusted equally for all carriers. During normal
operation, the power control works in said conventional way as
described above. As already mentioned, this power control has the
disadvantage that it relies on the equality of the individual RF
gains which can not be guaranteed. Therefore, at certain times,
preferably during low traffic hours, the carrier gains are
determined with one of the methods of the invention with little
error. These gains are used for checking if the RF gains for the
individual carriers are still equal. If this is not the case, some
automatic and individual adjustments can be made to the gains of
the carriers.
[0055] The methods, radio transmission units and modules according
to the invention can be employed in particular, though not
exclusively, with GSM and WCDMA.
[0056] Other objects and features of the present invention will
become apparent from the following detailed description considered
in conjunction with the accompanying drawings. It is to be
understood, however, that the drawings are designed solely for
purposes of illustration and not as a definition of the limits of
the invention, for which reference should be made to the appended
claims. It should be further understood that the drawings are not
necessarily drawn to scale and that, unless otherwise indicated,
they are merely intended to conceptually illustrate the structures
and procedures described herein.
BRIEF DESCRIPTION OF THE FIGURES
[0057] In the following, the invention is explained in more detail
with reference to drawings, of which
[0058] FIG. 1 shows a block diagram of a conventional base station
transmitter based on RF IQ modulation;
[0059] FIG. 2 shows a block diagram of a conventional base station
transmitter based on NCO modulation;
[0060] FIG. 3 shows a block diagram of a multi-carrier base station
transmitter based on RF IQ modulation employed for the first
alternative of the invention;
[0061] FIG. 4 shows a block diagram of a multi-carrier base station
transmitter based on NCO modulation employed for the first
alternative of the invention;
[0062] FIG. 5 illustrates the first method according to the
invention employed in a base station transmitter of FIG. 4 or
5;
[0063] FIG. 6 shows a block diagram of a part of an alternative
multi-carrier base station transmitter based on NCO modulation
employed for the first alternative of the invention; FIG. 7 shows a
block diagram of a multi-carrier base station transmitter based on
NCO modulation according to the second alternative of the
invention; and
[0064] FIG. 8 schematically shows details of a detection and
summation unit of the base station transmitter of FIG. 7.
DETAILED DESCRIPTION OF THE INVENTION
[0065] FIGS. 1 and 2 have already described with reference to the
background of the invention.
[0066] FIGS. 3 and 4 each show a block diagrams of a different
embodiment of multi-carrier base station transmitters in which the
first alternative of the invention can be employed
advantageously.
[0067] FIG. 3 is a multi-carrier base station transmitter based on
RF IQ modulation like the conventional base station transmitter
shown in FIG. 1. It equally comprises for each of N carriers a
baseband modulator 1 connected via two digital-to-analogue
converters 3, 4 and an RF modulator 5 to a gain variable radio
amplifier 7. Each baseband modulator 1 is moreover connected to a
baseband power detection unit 2 and each RF modulator 5 to a local
oscillator (LO) 6. In contrast to FIG. 1, however, the output of
each RF amplifier 7 is not connected to a dedicated SCPA but via a
summation unit 10 to a single multi-carrier power amplifier (MCPA)
15. The output of the MCPA 15 is connected to a transmit antenna 11
and to a common power detection and control unit 16. The power
detection and control unit 16 is connected at further inputs to the
outputs of the baseband power detection units 2 and at outputs to
the gain control inputs of the RF amplifiers 7.
[0068] FIG. 4 is a multi-carrier base station transmitter based on
NCO modulation like the conventional base station transmitter shown
in FIG. 2. It equally comprises for each of N carriers a baseband
modulator 1 connected via a digital upconverter 12 and a
digital-to-analogue converter 14 to an RF amplifier 7. Each
baseband modulator 1 is moreover connected to a baseband power
detection unit 2 and each digital upconverter 12 to an NCO 13. In
contrast to FIG. 2 and equal to FIG. 3, the output of each RF
amplifier 7 is connected via a summation unit 10 to a common MCPA
15. The output of the MCPA 15 is connected to the transmit antenna
11 and to a common power detection and control unit 16. Further
inputs and outputs of the power detection and control unit 16 are
connected to the baseband power detection units 2 and the RF
amplifiers 7 as in the base station transmitter of FIG. 3
respectively.
[0069] In the multi-carrier base station transmitters of FIGS. 3
and 4, symbols fed to the baseband modulators 1 are processed as
described with reference to FIGS. 1 and 2 respectively, until they
leave the RF amplifiers 7. In both examples, the output signals of
the RF amplifiers 7 are then summed in the summation unit 10 and
fed as a multi-carrier signal to the MCPA 15, which amplifies the
received signal.
[0070] The power detection and control unit 16 arranged at the
output of the MCPA 15 receives as input the total power output by
the MCPA 15 and the output powers of the digital baseband
modulators 1 via the baseband power detection unit 2. To this end,
the summed RF signal is on the one hand forwarded after power
amplification to the transmit antenna 11 for transmission and on
the other hand downconverted and converted to the digital domain
inside of the MCPA 15, in order to enable a digital rms detection
of the output power. Alternatively, there could be an RF detector
or a downconversion path and a digitisation outside of the MCPA.
Each baseband power detection unit 2 forms a processor operating on
the digital baseband output of the baseband modulator 1 to which it
is connected and computes the baseband powers numerically in order
to be able to provide the power detection and control unit 16 with
the power value output by the respective baseband modulator 1.
According to the first method of the invention, the power detection
and control unit 16 is able to set the gain control signal GC, to
GCN for each carrier individually based on this power information
as explained in the following with reference to FIG. 5.
[0071] FIG. 5 illustrates the basic principle of the processing in
the power detection and control unit 16 according to the first
method of the invention employed for a multi-carrier base station
transmitter as depicted in FIG. 3 or 4.
[0072] An rms power detector 20 is connected on the one hand to the
output of the MCPA 15 of the employed base station transmitter and
on the other hand via a sampler 21 to a first register 22. Equally,
the output of each baseband power detection unit 2 of the base
station transmitter is connected via a dedicated sampler 23 to a
dedicated further register 24 providing storage room for a
plurality of values. Each register 22, 24 has for each stored value
a separate output to a device 25 that is able to solve matrix
equations. The device 25 has N outputs, each connected via a
separate summation element 26 to a separate controller 27. Each
summation element 26 has a further input to which a predetermined
gain value is provided. The output of each controller 26 is
connected to the gain control input of one of the RF amplifiers 7.
Although presented as a hardware block diagram, most of the
implementation is advantageously realised in software in the power
detection and control unit 16.
[0073] Symbols that are to be transmitted by the base station
transmitter over the air interface are fed to the baseband
modulators 1. The output powers of the baseband modulators 1 are
varied in several measurement time slots, the respective rms power
value REF.sub.1 to REF.sub.N being determined in the baseband power
detection unit 2 and forwarded to the respective sampler 23 of the
power detection and control unit 16. Each sampler 23 averages the
received baseband power over one measurement time slot and forwards
an averaged power value per measurement time slot to the connected
baseband register 24, until the values for N measurement time slots
are stored for the respective carrier. Thus, for each measurement
time slot, a set of baseband power values REF.sub.1 to REF.sub.N is
stored distributed over the N baseband registers 24.
[0074] The signals output by the baseband modulators 1 are moreover
processed either by digital-to-analogue converters 3, 4 and RF
modulator 5, or by digital upconverter 12 and digital-to-analogue
converter 14, depending on the base station transmitter employed,
and, in both cases, by RF amplifier 7, summation unit 10 and MCPA
15, as described above.
[0075] The rms value of the power of the signals output by the MCPA
15 is detected by the power detector 20 and forwarded to the
associated sampler 21. The sampler 21 averages the received power
over one measurement time slot and stores in register 22 an
averaged MCPA 15 output power value for each measurement time slot
for which a set of averaged baseband power values is being stored
in the baseband power registers 24. When at least N sets of
baseband power values and the corresponding MCPA 15 output power
values are stored in the registers 24, 22, the contents of the
registers 22, 24 are fed to the device 25, which is able to solve a
system of N equations with N unknowns. In case the base station
transmitter is used in a TDMA system, the measurement time slots
are advantageously synchronised with the carrier time slots.
[0076] Each power P.sub.0.sup.<m> of an RF signal output by
the MCPA 15 during a given measurement timeslot m is the sum of the
amplified baseband reference powers during that timeslot, as
expressed by the following equation:
P.sub.O.sup.<m>+REF.sub.1.sup.<m>G.sub.1+REF.sub.2.sup.<m&-
gt;G.sub.2+ . . . +REF.sub.N.sup.<m>G.sub.N,
REF.sub.i.sup.<m>
[0077] being the power of the i.sup.th (i=1 . . . N) of N carriers
averaged over the measurement time slot m at the output of the
baseband modulator, and G.sub.i (i=1 . . . N) being the to be
estimated RF power gain for the i.sup.th carrier. Given N sets of
baseband powers and N corresponding MCPA output powers stored in
the registers, a system of N equations with N unknowns is obtained,
from which the unknown RF gain G.sub.i for each carrier can be
calculated. The device 25 that is able to solve matrix equations is
used to solve this system of equations, providing as solution of
the system of equations an estimated gain G.sub.i of the radio
frequency path for each carrier.
[0078] The estimated gain G.sub.i is compared with a predetermined
gain for each carrier by a dedicated summation element 26, in which
the estimated gain G.sub.i is subtracted from the predetermined
gain. The resulting difference is used by a controller 27 connected
to the respective summation element 26 to control the gain for the
respective carrier by adjusting the gain control signal GC.sub.i
(i=1 to N) fed to the gain control input of the respective RF
amplifier 7 accordingly.
[0079] In one preferred embodiment, the described procedure is
applied regularly, in order to set the gain for each carrier
accurately. In between, the total gain is determined by simply
dividing the total output power by the sum of the input powers. The
total gain is compared to a desired total gain and the difference
is used to change the gain of all RF amplifiers 7 equally, as
described as one possibility known from the state of the art. The
setting of the gain according to the first method of the invention
is carried out during low traffic hours by varying the carrier
powers systematically. If dummy code channels are added during
which the carrier powers are varied in a way that the matrix
equation gets well conditioned, the individual RF gains can be
solved with little error, while at the same time the data
transmission is not influenced.
[0080] In a variation of the embodiment of FIG. 4, it is not the
power of the baseband signals that is fed to the power detection
and control unit 16, but rather the power of the signals input to
the digital-to-analogue converters 14. The power of these signals
can be determined either already within the digital upconverter 12
or at its output. The determination of the RF gains of the
different carriers corresponds to the determination described with
reference to FIGS. 4 and 5. In this case, however, the determined
gain does not include the gain in the digital upconverter 12.
[0081] FIG. 6 illustrates a further variation of such a
multi-carrier base station transmitter that can be employed as GSM
multi-carrier base station transmitter, while the previous
embodiments can be employed in particular for WCDMA. The
multi-carrier base station transmitter corresponds to the
transmitter of FIG. 4, except for modifications in the respective
part between the baseband power detection unit 2 and the
digital-to-analogue converter 14 in each single carrier unit.
Therefore, only this part is shown, and only for the first
carrier.
[0082] In the depicted single carrier unit, two multipliers 40, 41
are arranged between the digital upconverter 12 and the
digital-to-analogue converter 14, the latter two being present also
in FIG. 4. The output of the baseband power detection unit 2 is
moreover connected to an input of a third multiplier 42. Further, a
common source of a power control level signal is connected to an
input of the second multiplier 41 and an input of the third
multiplier 42, which is indicated in FIG. 6 by a double arrow
between the second and the third multiplier 41,42.
[0083] In operation, the first multiplier 40 multiplies the output
of the digital upconverter 12 with a ramping profile signal 43. The
ramping profile is used to separate the timeslots of the modulated
carrier signal from each other. The resulting signal is then
provided to an input of the second multiplier 41. The power control
level signal, which is constant within a time slot and which
corresponds to the needed transmitter output power in each
individual time slot, is provided as second input signal to the
second multiplier 41. Accordingly, the second multiplier 41
multiplies the ramped and modulated carrier signal received from
the first multiplier 40 with the received power control level and
forwards the result to the digital-to-analogue converter 14. The
third multiplier 42, on the other hand, receives as first input
signal the output power of the digital baseband modulator 1 via the
baseband power detection unit 2 and as second input signal as well
the power control level signal. The third multiplier 42 multiplies
both received signals and outputs as result a reference power
REF.sub.1.
[0084] Assuming that the gain of the digital upconverter times the
peak value of the ramping profile is unity, i.e. the gain of the
digital upconverter is compensated by the peak value of the ramping
profile in the multiplication, the power REF, output by the third
multiplier 42 is equal to the power input to the
digital-to-analogue converter 14. The power REF, and the
corresponding powers for the other carriers are then fed to the
power detection and control unit 16, where they are used to
determine the RF gain for the different carriers as described with
reference to FIGS. 3 to 5.
[0085] FIG. 7 shows a block diagram of an embodiment of a
multi-carrier base station transmitter based on NCO modulation that
can be used according to the second alternative of the
invention.
[0086] The base station transmitter comprises like the one in FIG.
4 a separate transmitter part for each of N carriers. Each of these
separate transmitter parts includes a baseband modulator 1, a
digital upconverter 12, a digital-to-analogue converter 14 and an
RF amplifier 7. Again, in practice, the architecture will have more
upconversion stages, amplifiers, filters, etc. The outputs of the
RF amplifiers 7 are connected via a detection and summation unit 17
and an MCPA 15 to a transmit antenna 11. Further outputs of the
detection and summation unit 17 are connected to the inputs of a
gain computation and control unit 18. Additionally, the output of
the MCPA 15 is connected via a rms power detector 19 to an input of
the gain computation and control unit 18. Finally, a digital output
of each baseband modulator 1 is connected via a baseband power
detection unit 2 to an input of the gain computation and control
unit 18. Each of the N outputs of the gain computation and control
unit 18 is connected to the gain control input of one of the RF
amplifiers 7 of the N separate transmitter part.
[0087] FIG. 8 shows in more detail the detection and summation unit
17 of FIG. 7. The detection and summation unit 17 comprises a bank
of detectors 30 in a single integrated circuit. However. the use of
a single integrated circuit for the detectors 30 is only a
preferred implementation. As an alternative, it would also be
possible to use separate circuits for each detector. The input of
each detector 30 is connected to the output of one of the RF
amplifiers 7. The outputs of the detectors 30 are connected to
inputs of the gain computation and control unit 18. Additionally,
the detection and summation unit 17 comprises a summation element
31 via which the output of each RF amplifier 7 is connected to the
input of the MCPA 15. The bank of detectors 30 of the detection and
summation unit 17 could be located anywhere, but in order to
minimise the cabling in the transmitter, the detectors are located
where the single-carrier signals are brought together anyway, i.e.
near the summing element 31 at the input of the MCPA 15.
[0088] The processing of symbols that are to be transmitted by the
base station transmitter in baseband modulators 1, digital
upconverters 12, digital-to-analogue converters 14 and RF
amplifiers 7 corresponds to the processing described with reference
to FIG. 4.
[0089] In contrast to the architecture in FIG. 4, however, the
individual carrier powers are detected separately in the detection
and summation unit 17 before the modulated carriers are summed by
the summing element 31. The N detectors 30, each used for detecting
the power P.sub.1-P.sub.N of one of the N carriers, are well
matched to each other in order to be able to track the power of
each carrier in relation to the power of the other carriers
accurately. The detected powers P.sub.1-P.sub.N are fed to the gain
computation and control unit 18 and the summed multi-carrier signal
is forwarded to the MCPA 15 for power amplification.
[0090] The multi-carrier signal output by the MCPA 15 is forwarded
on the one hand to the transmit antenna 11 for transmission.
[0091] On the other hand, the power P.sub.0 of the multi-carrier
signal is determined by the rms power detector 19. The detected
power P.sub.0 is input to the gain computation and control unit
18.
[0092] Moreover, the powers REF.sub.1-REF.sub.N of the baseband
signals output by the N baseband modulators 1 are determined in the
baseband power detection unit 2 and input to the gain computation
and control unit 18.
[0093] The gain computation and control unit 18 comprises a
mathematical algorithm for estimating the individual RF gains of
the different carriers out of the different power values P.sub.0,
P.sub.1-P.sub.N, REF.sub.1-REF.sub.N received. All powers are
averaged over the same measurement time slot before being used by
the algorithm.
[0094] Because the measured powers P.sub.1-P.sub.N determined by
the detectors 30 have only a multiplicative error that is common
for each carrier, their ratios have no error. Referencing the
detected powers of the single-carrier signals arbitrarily to the
power P.sub.1 of the first carrier, the normalised output powers of
the carrier are given by P i P 1 = REF i G i REF 1 G 1 ,
##EQU1##
[0095] where P.sub.i (i=1 . . . N) is the power of the i.sup.th
carrier determined by the respective detector 30, REF.sub.1 (i=1 .
. . N) the power of the signal output by the i.sup.th baseband
modulator 1 for modulation of the i.sup.th carrier, and G.sub.i
(i=1 . . . N) the RF gain of the i.sup.th carrier until the
summation. Proceeding from the above equation, the gains normalised
with the RF gain G.sub.1 of the first carrier until summation are:
G i G 1 = REF 1 P i REF 1 P 1 , ##EQU2##
[0096] Moreover, the multi-carrier output power in a given
measurement time slot P.sub.0 is the sum of the amplified baseband
powers and given by the equation:
P.sub.O=REF.sub.1G.sub.1G.sub.01+REF.sub.2G.sub.2G.sub.02+ . . .
+REF.sub.NG.sub.NG.sub.ON
[0097] The total amplification for the i.sup.th carrier in this
equation is given by G.sub.i*G.sub.0i (i=1 . . . N), with G.sub.0i
being the RF power gain for the i.sup.th carrier in the summation
element 31 of the detection and summation unit 17 and in the MCPA
15. The values of G.sub.0i are assumed to be known a priory apart
from an unknown common factor. The latter equation can be rewritten
as: G 1 G 01 = P 0 REF 1 + REF 2 G 2 G 1 G 02 G 01 + + REF N G N G
1 G 0 .times. N G 01 ##EQU3##
[0098] As shown above, the ratios G.sub.i/G.sub.1 are easily
derived from the measured single-carrier RP powers P.sub.i and the
baseband powers REF.sub.i. The ratios G.sub.0i/G.sub.01 are assumed
to be known a priori from the frequency response of the MCPA 15.
Therefore, G.sub.1*G.sub.01, which constitutes the gain of the
1.sup.st RF path used by the 1.sup.st carrier, can readily be
solved from the above equation. The gain G.sub.i*G.sub.0i of the
i.sup.th RF path can be computed from the gain of the 1.sup.st
path, since the gain ratios are known. If the RF gains deviate from
values predetermined for the gains, the gain computation and
control unit 18 adjusts the gain control signals GC.sub.i (i=1 . .
. N) input to the RF amplifiers 7 in order to approach the
estimated gains to the desired gains.
[0099] The base station transmitter of FIG. 7 is based on NCO
modulation, which could also be varied for this embodiment of the
second alternative of the invention according to FIG. 6. The second
method according to the invention can moreover equally be employed
for a base station transmitter based on RF IQ modulation as
presented in FIG. 3.
[0100] Even though the described embodiments of the invention all
proceed from a conventional base station transmitter based on RF IQ
modulation or from a conventional base station transmitter based on
NCO modulation, the features of the invention can be combined with
any conceivable base station architecture. Also when proceeding
from a base station transmitter based on RF IQ modulation or on NCO
modulation, various amendments can be carried out without exceeding
the scope of the invention.
[0101] Thus, while there have shown and described and pointed out
fundamental novel features of the invention as applied to a
preferred embodiment thereof, it will be understood that various
omissions and substitutions and changes in the form and details of
the devices illustrated, and in their operation, may be made by
those skilled in the art without departing from the spirit of the
invention. For example, it is expressly intended that all
combinations of those elements and/or method steps which perform
substantially the same function in substantially the same way to
achieve the same results are within the scope of the invention.
Moreover, it should be recognized that structures and/or elements
and/or method steps shown and/or described in connection with any
disclosed form or embodiment of the invention may be incorporated
in any other disclosed or described or suggested form or embodiment
as a general matter of design choice. It is the intention,
therefore, to be limited only as indicated by the scope of the
claims appended hereto.
* * * * *