Telecommunications – Transmitter – Plural separate transmitters or channels
Reexamination Certificate
2000-12-27
2004-03-02
Nguyen, Lee (Department: 2682)
Telecommunications
Transmitter
Plural separate transmitters or channels
C455S069000, C455S127100
Reexamination Certificate
active
06701135
ABSTRACT:
The present invention relates to a multi-carrier radio transmitter and a method of power control in a multi-carrier radio transmitter. It has particular application to power control in a base station of a cellular radio network.
In a cellular radio network a geographic area is divided into separate cells. Each cell has a base station for communicating with mobile terminals or the like which are within that cell. Each base station has a receiver for receiving signals from the mobile terminals and a transmitter for sending signals to the mobile terminals. The transmitter communicates with the mobile terminals by modulating a carrier wave. In time division multiple access (TDMA) the transmitter transmits a series of TDMA frames where each frame comprises a succession of time slots and each time slots is associated with a separate communication channel. As an example in GSM the number of time slots per frame is eight. A mobile terminal is assigned a particular communication channel and the base station transmits to that mobile terminal in successive frames by sending signal bursts which occupy an assigned time slot.
Each mobile terminal is in a different environment and at a different distance from the base station. The power level of the signal burst from the base station occupying the slots in a TDMA frame may therefore need to be varied from slot to slot (i.e. from mobile terminal to mobile terminal) or from frame to frame (i.e. as the environment of a mobile terminal changes). Each of the signal bursts will be sent with a predetermined transmit power level which will generally differ from slot to slot. In addition, the transmitter is switched off between signal bursts for a predetermined period of time (the guard period) to separate the individual communication channels. Consequently, on the initiation of a burst, transmitted power must be ramped up from a low value to the predetermined transmit level for that communication channel. Furthermore, at the end of the burst the power level must be ramped down from the predetermined transmit level to a low level. According to the GSM standard guard periods have a duration of about 30 &mgr;s, time slots are 577 &mgr;s, and the time to ramp a signal burst up to its predetermined level or to ramp it down from its predetermined level is approximately 10 &mgr;s. The up and down ramping periods are included in the guard period, the remaining portion of the guard period being a constant low power level period.
To increase the number of channels in a cell it is possible to use a number of single carrier narrow band transmitters in a base station where each transmitter is operating with a particular carrier frequency. The allocation of different carrier frequencies to different channels is referred to as frequency division multiple access (FDMA). In each such narrow band, single carrier, transmitter power control is typically achieved by comparing a sample of output power with a reference signal, the output power being adjusted in dependence upon that comparison. U.S. Pat. Nos. 5,334,979, 5,337,006, 5,128,629, 5,603,106, 5,303,268, 5,126,688, 5,182,527 and EP 0369135 describe adjusting output power by varying the single carrier signal at an RF frequency using controllable attenuators or variable gain amplifiers. WO 9302505 and U.S. Pat. No. 5,193,223 perform the adjustment of a single carrier signal at an intermediate frequency. U.S. Pat. No. 5,293,407 describes a digital adjustment of the power level.
A preferred approach for increasing the number of channels in a cell, is to use a multi-carrier broad band transmitter to implement parallel multiple access.
FIG. 1
illustrates a transmitter in which first, second and third digital signals
2
,
4
and
6
are respectively input to first, second and third modulators
10
,
12
and
14
to modulate carriers having frequencies F
1
, F
2
and F
3
and produce respective first, second and third digital modulated signals
16
,
18
and
20
. Each of the first, second and third digital signals
2
,
4
and
6
is a stream of data bits be transmitted. Each stream of data bits controls a modulator to produce a digital modulated signal which itself is composed of a stream of digital words.
Each one of the digital modulated signals
16
,
18
and
20
is a digital representation of an analogue carrier having respectively frequencies F
1
, F
2
and F
3
modulated by respective ones of the first, second and third digital signals
2
,
4
and
6
. The modulated signals
16
,
18
and
20
are input to an adder
22
which combines the signals to create a digital multi-carrier signal
24
. The digital multi-carrier signal
24
is input to the first intermediate frequency (IF) block
26
, comprising a digital to analogue converter
28
, a band pass or low pass filter
30
and an amplifier
32
in series to produce a multi-carrier analogue signal, first IF signal
34
. This signal is continuous in time and amplitude in comparison to the digital multi-carrier signal which is discrete in time and amplitude.
This signal is passed to the second IF block
36
, comprising a mixer
38
, a band pass filter
42
and amplifier
44
in series and a local oscillator
40
, to create a second intermediate frequency (IF) signal
45
. The second IF signal
45
is supplied to a radio frequency block
46
, comprising a mixer
48
and a band pass filter
52
in series and a local oscillator
50
. The output of the radio frequency block
46
, a radio frequency signal
53
, passes in series through a linear power amplifier and a band pass filter
56
to produce a power amplified radio frequency signal
57
which is then transmitted by an antenna
58
. As an example, the radio frequency signal has a carrier with a frequency range of 925-960 MHz. The multiple signals are combined in digital format, before conversion to analogue. In a TDMA system the slots and frames of the different carriers are synchronised.
The multi-carrier transmitter therefore operates in parallel and does not have separate transmitter components for each carrier wave, which allows wide band multi-carrier transceivers to be of reduced cost and size.
It is an aim of embodiments the present invention to provide power control in a multi-carrier radio transmitter.
According to one aspect of the present invention there is provided A multi-carrier radio transmitter comprising combination means for receiving and combining a plurality of carriers including a first modulated carrier for transmission in a first channel and a second modulated carrier for transmission in a second channel, to create a multi-carrier signal; and open loop power control means arranged to individually vary the power of each of the plurality of carriers before said combination and closed loop power control means arranged to vary the output power of the transmitter, the closed loop power control means being configured to operate on the multi-carrier signal after the combination means.
According to another aspect of the present invention there is provided a method of power compensation in a multi-carrier radio transmitter, wherein a plurality of carriers are combined to create a multi-carrier signal, said plurality of carriers including a first modulated carrier for transmission in a first channel and a second modulated carrier for transmission in a second channel, the method comprising the steps of:
(a) determining the transmit power level required in each carrier;
(b) varying the power level of each carrier to the determined levels using open loop power control;
(c) combining the carriers to form the multi-carrier signal; and
(d) compensating for changes in the power level of said multi-carrier signal using closed loop power control, by:
detecting said multi-carrier signal; and
adjusting the power of said multi-carrier signal in dependence upon said detection.
Preferably in both aspects, the open loop power control is configured to effect relatively fast power variations and the closed loop power control is configured to effect relatively slow power variations.
Power control is particularly i
Dekker Andre
Maatta Juha
Posti Harri
Nguyen Lee
Nokia Corporation
Persino Raymond
Squire Sanders & Dempsey L.L.P.
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