WO1997036382A1 - Cdma power control - Google Patents
Cdma power control Download PDFInfo
- Publication number
- WO1997036382A1 WO1997036382A1 PCT/GB1997/000864 GB9700864W WO9736382A1 WO 1997036382 A1 WO1997036382 A1 WO 1997036382A1 GB 9700864 W GB9700864 W GB 9700864W WO 9736382 A1 WO9736382 A1 WO 9736382A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- signal
- power control
- generating
- agc
- rssi
- Prior art date
Links
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03G—CONTROL OF AMPLIFICATION
- H03G3/00—Gain control in amplifiers or frequency changers without distortion of the input signal
- H03G3/20—Automatic control
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/02—Power saving arrangements
- H04W52/0209—Power saving arrangements in terminal devices
- H04W52/0225—Power saving arrangements in terminal devices using monitoring of external events, e.g. the presence of a signal
- H04W52/0245—Power saving arrangements in terminal devices using monitoring of external events, e.g. the presence of a signal according to signal strength
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/52—TPC using AGC [Automatic Gain Control] circuits or amplifiers
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
Definitions
- This invention relates to power control in a spread spectrum code division multiple access cellular telephone system (TIA:IS-95) .
- TIA spread spectrum code division multiple access cellular telephone system
- Such systems normally employ so-called “open loop” and “closed loop” power control.
- Open loop power control requires that the automatic gain control stages in the receiver and transmitter of the mobile should track, i.e. for every ldB increase in the receiver input level, the transmitter output level should decrease by ldB and vice versa. Since the dynamic range of the AGC system is some 80dB, this is quite difficult to achieve, especially over a range of temperatures.
- Closed loop power control requires the mobile transmitter to increment or decrement the output level in ldB steps in response to commands from the base station.
- Normally open and closed loop AGC systems are implemented either by relatively simple variable gain/attenuation devices in the RX and TX chains which require extensive calibration, or sophisticated temperature compensated variable gain MMICs which still require (simpler) calibration.
- the present invention seeks to provide a power control system which can utilise readily available and cheap analogue cellular components and which is inherently self calibrating.
- the present invention provides a power control system for a CDMA cellular telephone system comprising means for generating a first signal representing received signal strength; means for generating a second signal representing transmitted signal strength; comparator means for generating an error signal from the difference of the first and second signals; and gain control means for adjusting the transmitted signal strength in accordance with the error signal until the first and second signals are equal.
- gain control means are provided for the received signal input, by comparing the output of the means for generating the first signal, with a reference level, and adjusting the gain until they are equal.
- the output from the second signal generating means is also modified by a closed loop power control signal, before it is supplied to the comparator.
- a preferred form of the present invention therefore provides a power control system for a CDMA cellular telephone system comprising means for supplying the received (RX) CDMA signal to the input of a RX-AGC circuit which is arranged to provide a constant level input for RX-A/D converters by setting the gain to be inversely proportional to the received signal level; means for tapping off the RX- AGC output, and means for filtering the tapped-off signal to reject possible interfering signals and to generate a first received signal strength voltage (RSSI 1) ; means for supplying the received CDMA signal to the input of a transmit (TX) AGC; means for generating a second received signal strength voltage (RSSI 2) from the output of the TX- AGC; means for comparing the first and second RSSI voltages and producing a difference signal which is used to adjust the TX-AGC until the RSSI voltages are equal.
- RX received
- RX-AGC circuit which is arranged to provide a constant level input for RX-A/D converter
- the second RSSI voltage is also summed with a closed loop power control signal so as to increment or decrement the TX output in response to commands from a base station.
- Figure 1 is a block diagram of the overall arrangement of the circuitry
- Figure 2 is a schematic diagram of an AGC amplifier.
- the received CDMA signal (2) is downconverted to an IF and passes through an RX-AGC amplifier (4) .
- the gain of the amplifier is adjusted by the AGC system to ensure that the receive A to D converters (6, 8) are driven at a constant level i.e. the gain is inversely proportional to the received power level.
- the AGC amplifier may for example be a simple circuit using dual gate FETs, the second gate being used for gain control, in a well-known manner. For example, as shown in Figure 2, a dual gate FET 30 is driven by the input signal (32) at gate g2, while an AGC signal (34) is applied at gate gl to provide an output (36) .
- the CDMA cellular system has to coexist with conventional analogue cellular systems which in practice means that there could be strong interfering signals as close as 900 kHz from the wanted CDMA signal which could cause false RX power measurements if there is insufficient filtering.
- the filtering is normally provided by a SAW filter at the IF and a steep rolloff low pass filter at baseband. Due to the wideband nature of CDMA(+/- 630kHz), significant rejection at 900kHz is difficult to achieve both technically and cheaply.
- the CDMA signal is also tapped off and filtered first by a conventional FM IF filter (10) .
- Most FM cellular receivers employ a second Intermediate Frequency of 450 or 455 khz which means that the first IF filter must provide approximately 70db of rejection at +/- 900kHz (the "image" frequency) .
- the signal then passes into an FM IF chip, converted down to a second IF of say 450kHz, filtered further (12) and a receiver signal strength voltage (14) generated which is compared to a reference (15) in a comparator (16) to produce a gain control voltage for the receiver AGC amplifier.
- the RX CDMA signal prior to amplification, is also fed into the TX AGC amplifier (18) (similar circuit to the RX circuit) and the output level measured in a similar FM IF chip producing a second RSSI voltage (20) .
- a closed loop power control voltage is also added (22) to the second RSSI voltage at a summer (23) to increment or decrement the power level in response to commands from the base station.
- the gain of the TX AGC amplifier is adjusted (21) using the difference signal (25) of the two RSSI voltages. For a closed loop control voltage (22) input of zero, the gains of the RX and TX AGC stages are equal.
- a gain offset is normally required because the TX IF signal level at the input of the TX AGC amplifier (18) is substantially higher than the RX-IF input level to the RX AGC amplifier 4 and thus gain is provided by an amplifier (26) .
- a filter (24) is required at the output of the TX AGC amplifier (18) to prevent the RX IF signal being retransmitted.
- RSSI-1 and RSSI-2 should have identical characteristics (i.e. slope, intercept and temperature coefficient) .
- Toshiba offer a suitable device, TA31138FN "Dual Mixer and IF Amplifier for Diversity Reception" for a Japanese Digital Cellular system, employing spatial diversity and therefore requiring two matched IF chains, as shown in the data sheet attached hereto as Appendix A.
- FM IF chips have a highly linear RSSI characteristic. This can be exploited for closed loop power control by adding an adjustment voltage to the output of RSSI-2.
- the RSSI sensitivity (mV per dB) can be easily measured during manufacture of the telephone.
- the preferred form of the invention has a number of advantages.
- the 900kHz filtering function is performed by cheap, readily available components.
- the FM SAW filter, IF amplifier-1 and one of the second IF filters (12) can be used for FM demodulation.
- the "turn around" performance of the open loop power control or the ability of the RX and TX AGC circuits to track is a direct function of only how well the two FM IF circuits match (the Toshiba device should achieve +/- ldB over temperature) .
- Closed loop power control accuracy is a function of the linearity of the FM IF chip circuit only.
Abstract
A power control system for a CDMA cellular telephone system comprising means for generating a first signal (14) representing received signal strength; means for generating a second signal (20) representing transmitted signal strength; comparator means (21) for generating an error signal (25) from the difference of the first and second signals; and gain control means (18) for adjusting the transmitted signal strength in accordance with the error signal until the first and second signals are equal.
Description
"CDMA Power Control"
This invention relates to power control in a spread spectrum code division multiple access cellular telephone system (TIA:IS-95) . Such systems normally employ so-called "open loop" and "closed loop" power control.
Open loop power control requires that the automatic gain control stages in the receiver and transmitter of the mobile should track, i.e. for every ldB increase in the receiver input level, the transmitter output level should decrease by ldB and vice versa. Since the dynamic range of the AGC system is some 80dB, this is quite difficult to achieve, especially over a range of temperatures.
Closed loop power control requires the mobile transmitter to increment or decrement the output level in ldB steps in response to commands from the base station.
Normally open and closed loop AGC systems are implemented either by relatively simple variable gain/attenuation devices in the RX and TX chains which require extensive calibration, or sophisticated temperature compensated variable gain MMICs which still require (simpler) calibration.
The present invention seeks to provide a power control system which can utilise readily available and cheap analogue cellular components and which is inherently self
calibrating.
Accordingly the present invention provides a power control system for a CDMA cellular telephone system comprising means for generating a first signal representing received signal strength; means for generating a second signal representing transmitted signal strength; comparator means for generating an error signal from the difference of the first and second signals; and gain control means for adjusting the transmitted signal strength in accordance with the error signal until the first and second signals are equal.
Preferably, gain control means are provided for the received signal input, by comparing the output of the means for generating the first signal, with a reference level, and adjusting the gain until they are equal.
Preferably, the output from the second signal generating means is also modified by a closed loop power control signal, before it is supplied to the comparator.
A preferred form of the present invention therefore provides a power control system for a CDMA cellular telephone system comprising means for supplying the received (RX) CDMA signal to the input of a RX-AGC circuit which is arranged to provide a constant level input for RX-A/D converters by setting the gain to be inversely proportional to the received signal level; means for tapping off the RX- AGC output, and means for filtering the tapped-off signal to reject possible interfering signals and to generate a first
received signal strength voltage (RSSI 1) ; means for supplying the received CDMA signal to the input of a transmit (TX) AGC; means for generating a second received signal strength voltage (RSSI 2) from the output of the TX- AGC; means for comparing the first and second RSSI voltages and producing a difference signal which is used to adjust the TX-AGC until the RSSI voltages are equal.
Preferably, the second RSSI voltage is also summed with a closed loop power control signal so as to increment or decrement the TX output in response to commands from a base station.
One embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:
Figure 1 is a block diagram of the overall arrangement of the circuitry;
Figure 2 is a schematic diagram of an AGC amplifier.
The received CDMA signal (2) is downconverted to an IF and passes through an RX-AGC amplifier (4) . The gain of the amplifier is adjusted by the AGC system to ensure that the receive A to D converters (6, 8) are driven at a constant level i.e. the gain is inversely proportional to the received power level. The AGC amplifier may for example be a simple circuit using dual gate FETs, the second gate being used for gain control, in a well-known manner. For example, as shown in Figure 2, a dual gate FET 30 is driven by the input signal (32) at gate g2, while an AGC signal
(34) is applied at gate gl to provide an output (36) .
The CDMA cellular system has to coexist with conventional analogue cellular systems which in practice means that there could be strong interfering signals as close as 900 kHz from the wanted CDMA signal which could cause false RX power measurements if there is insufficient filtering. The filtering is normally provided by a SAW filter at the IF and a steep rolloff low pass filter at baseband. Due to the wideband nature of CDMA(+/- 630kHz), significant rejection at 900kHz is difficult to achieve both technically and cheaply.
The CDMA signal is also tapped off and filtered first by a conventional FM IF filter (10) . Most FM cellular receivers employ a second Intermediate Frequency of 450 or 455 khz which means that the first IF filter must provide approximately 70db of rejection at +/- 900kHz (the "image" frequency) . The signal then passes into an FM IF chip, converted down to a second IF of say 450kHz, filtered further (12) and a receiver signal strength voltage (14) generated which is compared to a reference (15) in a comparator (16) to produce a gain control voltage for the receiver AGC amplifier.
The RX CDMA signal, prior to amplification, is also fed into the TX AGC amplifier (18) (similar circuit to the RX circuit) and the output level measured in a similar FM IF chip producing a second RSSI voltage (20) . A closed loop power control voltage is also added (22) to the second RSSI
voltage at a summer (23) to increment or decrement the power level in response to commands from the base station. The gain of the TX AGC amplifier is adjusted (21) using the difference signal (25) of the two RSSI voltages. For a closed loop control voltage (22) input of zero, the gains of the RX and TX AGC stages are equal. In practice, a gain offset is normally required because the TX IF signal level at the input of the TX AGC amplifier (18) is substantially higher than the RX-IF input level to the RX AGC amplifier 4 and thus gain is provided by an amplifier (26) . A filter (24) is required at the output of the TX AGC amplifier (18) to prevent the RX IF signal being retransmitted.
Various easily available components may be utilised to construct the circuitry. Many manufacturers offer FM IF receiver devices with an RSSI characteristic which is very stable over temperature. Ideally RSSI-1 and RSSI-2 should have identical characteristics (i.e. slope, intercept and temperature coefficient) . Toshiba offer a suitable device, TA31138FN "Dual Mixer and IF Amplifier for Diversity Reception" for a Japanese Digital Cellular system, employing spatial diversity and therefore requiring two matched IF chains, as shown in the data sheet attached hereto as Appendix A.
Many FM IF chips have a highly linear RSSI characteristic. This can be exploited for closed loop power control by adding an adjustment voltage to the output of RSSI-2. The RSSI sensitivity (mV per dB) can be easily
measured during manufacture of the telephone.
The preferred form of the invention has a number of advantages. The 900kHz filtering function is performed by cheap, readily available components.
In dual mode applications (CMDA/AMPS or CDMA/ETACS) , the FM SAW filter, IF amplifier-1 and one of the second IF filters (12) can be used for FM demodulation.
The "turn around" performance of the open loop power control or the ability of the RX and TX AGC circuits to track is a direct function of only how well the two FM IF circuits match (the Toshiba device should achieve +/- ldB over temperature) .
Closed loop power control accuracy is a function of the linearity of the FM IF chip circuit only.
Claims
1. A power control system for a CDMA cellular telephone system comprising means for generating a first signal (14) representing received signal strength; means for generating a second signal (20) representing transmitted signal strength; comparator means (21) for generating an error signal (25) from the difference of the first and second signals; and gain control means (18) for adjusting the transmitted signal strength in accordance with the error signal until the first and second signals are equal.
2. A power control system according to claim 1 further characterised by gain control means (16) for the received signal input, which is adapted to compare the output of the said means for generating the first signal, with a reference level (15), and to adjust the gain until they are equal.
3. A power control system according to claim 1 or claim 2 further characterised by means (23) for modifying the output from the second signal generating means in accordance with a closed loop power control system (22) , before it is supplied to the comparator (21) .
4. A power control system for a CDMA cellular telephone system comprising means for supplying the received (RX) CDMA signal to the input of a RX-AGC circuit (4) which is arranged to provide a constant level input for RX-A/D converters by setting the gain to be inversely proportional to the received signal level; means for tapping off the RX- AGC output, and means for filtering the tapped-off signal to reject possible interfering signals and to generate a first received signal strength voltage (RSSI 1) ; means for supplying the received CDMA signal to the input of a transmit (TX) AGC (18) ; means for generating a second received signal strength voltage (RSSI 2) from the output of the TX-AGC; and means (21) for comparing the first and second RSSI voltages and producing a difference signal (25) which is used to adjust the TX-AGC (18) until the RSSI voltages are equal.
5. A power control system according to claim 4 in which the second RSSI voltage (RSSI2) is also summed with a closed loop power control signal (22) so as to increment or decrement the TX output in response to commands from a base station.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GBGB9606269.0A GB9606269D0 (en) | 1996-03-26 | 1996-03-26 | CDMA Power control |
| GB9606269.0 | 1996-03-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| WO1997036382A1 true WO1997036382A1 (en) | 1997-10-02 |
Family
ID=10790987
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/GB1997/000864 WO1997036382A1 (en) | 1996-03-26 | 1997-03-26 | Cdma power control |
Country Status (2)
| Country | Link |
|---|---|
| GB (1) | GB9606269D0 (en) |
| WO (1) | WO1997036382A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2001033733A2 (en) * | 1999-11-03 | 2001-05-10 | Koninklijke Philips Electronics N.V. | Power control in a transmitting station of a communication system |
| FR2803705A1 (en) * | 2000-01-12 | 2001-07-13 | Mitsubishi Electric France | METHOD FOR GENERATING A BASEBAND SIGNAL REPRESENTATIVE OF THE TRANSMITTED RADIO FREQUENCY POWER, CORRESPONDING DEVICE AND TRANSMITTING STATION |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1993007702A1 (en) * | 1991-10-08 | 1993-04-15 | Qualcomm Incorporated | Transmitter power control system |
| WO1994006218A1 (en) * | 1992-09-04 | 1994-03-17 | Telefonaktiebolaget Lm Ericsson | A method and apparatus for regulating transmission power |
-
1996
- 1996-03-26 GB GBGB9606269.0A patent/GB9606269D0/en active Pending
-
1997
- 1997-03-26 WO PCT/GB1997/000864 patent/WO1997036382A1/en active Application Filing
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1993007702A1 (en) * | 1991-10-08 | 1993-04-15 | Qualcomm Incorporated | Transmitter power control system |
| WO1994006218A1 (en) * | 1992-09-04 | 1994-03-17 | Telefonaktiebolaget Lm Ericsson | A method and apparatus for regulating transmission power |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2001033733A2 (en) * | 1999-11-03 | 2001-05-10 | Koninklijke Philips Electronics N.V. | Power control in a transmitting station of a communication system |
| WO2001033733A3 (en) * | 1999-11-03 | 2001-09-27 | Koninkl Philips Electronics Nv | Power control in a transmitting station of a communication system |
| FR2803705A1 (en) * | 2000-01-12 | 2001-07-13 | Mitsubishi Electric France | METHOD FOR GENERATING A BASEBAND SIGNAL REPRESENTATIVE OF THE TRANSMITTED RADIO FREQUENCY POWER, CORRESPONDING DEVICE AND TRANSMITTING STATION |
| EP1117196A1 (en) * | 2000-01-12 | 2001-07-18 | Mitsubishi Electric Telecom Europe (S.A.) | Method for generating a base band signal representative of the transmitted radiofrequency power, corresponding device and transmitting station |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9606269D0 (en) | 1996-05-29 |
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