Title of Invention	AN APPARATUS FOR LIMITING TRANSMIT POWER OF A RADIO OPERATING IN A CELLULAR ENVIRQMENT
Abstract	The process and apparatus of the present invention limits the output power of a radiotelephone, operating in a cellular system in the preferred esnbodiment. This ensures the transmits sidebands and synthesizer phase noise remains within a certain specification. This is accomplished by power detection and a correction accumulator that together generate a gain control signal by limiting the gain adjustment to a maximum value, even when the cell site communicating with the tadiotelepbone. This process includes dynemically correcting the output level of the transmitter due to gain variations in the transmitter stages or gain control elements. PRICE : THIRTY RUPEES

Title of Invention

AN APPARATUS FOR LIMITING TRANSMIT POWER OF A RADIO OPERATING IN A CELLULAR ENVIRQMENT

Abstract

The process and apparatus of the present invention limits the output power of a radiotelephone, operating in a cellular system in the preferred esnbodiment. This ensures the transmits sidebands and synthesizer phase noise remains within a certain specification. This is accomplished by power detection and a correction accumulator that together generate a gain control signal by limiting the gain adjustment to a maximum value, even when the cell site communicating with the tadiotelepbone. This process includes dynemically correcting the output level of the transmitter due to gain variations in the transmitter stages or gain control elements. PRICE : THIRTY RUPEES

Full Text	The present invention relates to an apparatus for limiting transmit power of a radio operating in a cellular environment. The Federal Communications Commission (FCC) governs the use of the radio frequency (RF) spectrum. The FCC allocates certain band-widths within the RF spectrum tor specific uses. A user of an allocated bandwidth of the RF spectrum must take measures to ensure that the radiated emissions inside and outside of that bandwidth are maintained within acceptable levels to avoid interfering with other users operating in the same and or other band widths. These levels are governed by both the FCC and the particular user groups of said bandwidth. The 800 MHz cellular telephone system operates its forward link, the cell to radiotelephone transmission, in the bandwidth of 869.01 MHz to 893.97 MHz and the reverse link, the radiotelephone to cell transmission in the bandwidth of 824.01 MHz to 848.97 MHz. The forward and reverse link bandwidths are split up into channels each of which occupies a 30 kHz bandwidth. A particular user of the cellular system may operate on one or several of these channels at a time. All users of the system must ensure that they are compliant with the level of radiated emissions allowable inside and outside of the channel or channels that they have been assigned. There are several different techniques of modulation that can be used in the cellular telephone system. Two examples of modulation techniques are frequency division multiple access (FDMA) and code division multiple access (CDMA). The FDMA modulation technique generates signals that occupy one channel at a time while the CDMA modulation technique generates signals that occupy several channels. Both of these techniques must control their return link radiated emissions to with in the acceptable limits inside and outside of the assigned channel or channels. For maximum system performance, users of the CDMA technique must carefully control the level of radiated power inside the channels in which they are operating. FIG. 1 shows a typical prior cellular radiotelephone. In both an FDMA and a CDMA based radiotelephone, there exists the possibility of driving the power amplifier (101) in the transmitter beyond a point where acceptable out of channel radiated emissions are maintained. This is primarily due to the increased distortion output levels of the power amplifier (101) at high output powers. Also, driving the power amplifier (101) beyond a certain point can cause interference internal to the radio. For example, PA puncturing in CDMA affects synthesizer phase noise due to large current transitions. Both of these issues cause unacceptable radio performance. Maintaining the proper on-channel output power can be difficult due to several undesirable effects in the radiotelephone hardware. For example, the CDMA based radio must implement a power control system that operates over a very wide dynamic range, 80dB to 90dB, such that the transmitted output power is linearly related to the received input power. Closed loop and open loop power control together determine the return link transmit energy, as disclosed in U.S. Patent No. 5,056,109 to Gilhousen et al. and assigned to Qualcomm, Incorporated. Therefore, the linear and nonlinear errors produced in both the receiver (103) and transmitter (102) RF sections can cause unacceptable power control performance. Also, both the FDMA and CDMA based radios must operate on different channels while maintaining acceptable output power levels. Variation in output power level and input power detection versus frequency can cause an unacceptable amoimt of error in the amount of return link transmitted energy. These issues present significant problems to the designer of both FDMA and CDMA based radiotelephones. There is a resulting need for an effective, cost efficient means of correcting these problems. Accordingly the present invention provides an apparatus tor limiting transmit power of a radio operating in a cellular environment the cellular environment comprising a plurality of cells that transmit power control commands to the radio, the radio comprising a variable gain amplifier and a power limiting accumulator, the apparatus comprising : a receiver for receiving a signal from at least one of the plurality of cells; measuring means for determining a power value of the signal; control means for determining a closed loop power control value in response to the signal; generating means for generating a limiting gain control setting in response to the closed loop power control value and the power value, the limiting gain control signal being within a predetermined range; combining means for combining the closed loop power control value and the power value and the limiting gain control setting to generate a gain contol setting; and means for adjusting the variable gain amplifier in response to the gain control setting. With reference to the accompanying drawings, in which : FIG.l shows a block diagram of a typical prior art radiotelephone frequency section for use in a radiotelephone system. FIG.2 shows a block diagram of the preferred embodiment power control correction implementation. FIG.3 shows a block diagram of the power limiting control section as related to FIG.2. FIG.4 shows a block diagram of the closed loop power control section as related to FIG.2. FIG.5 shows a block diagram of the PA limit threshold control section as related to FIG.2. FIG.6 shows an alternate embodiment of the present invention that employs a power Umiting control system based on accumulator feedback control. FIG. 7 shows an alternate embodiment of the present invention that employs a power limting control system based on the closed loop power control accumulator. FIG.8 shows an alternate embodiment of the present invention that employs a power limiting control system based on integral feedback control. FIG. 9 shows an alternate embodiment of the present invention that employs a power limiting control sy.stem based on a measure of receive power and the closed loop power control setting to estimate output power. The process of the present invention provides power control correction for a mobile radiotelephone as well as maintaining acceptable in and out of band maximum emission levels. This is accomplished by realtime compensation utilizing a set of correction tables that are generated during the production testing of each radiotelephone. FIG. 2 shows a block diagram of a CDMA radiotelephone with the preferred embodiment power control correction implementation. FIGs. 3, 4, and 5 detail specific blocks of FIG. 2. The radiotelephone is comprised of a receive linearization section, transmit linearization section, power amplifier bias control section, and power limiting control section. The receive linearization section includes an automatic gain control (AGO section. The signal input to the AGO section is received on the forward link and amplified by a low noise amplifier (LNA) (211). The output of the LNA (211) is input to a variable gain amplifier (212). The variable gain amplifier (212) produces a signal that is converted to a digital signal using an analog to digital converter (ADC) (213). The power of the digitized received signal is next computed by a digital power detector (214). The power detector (214) includes an integrator that integrates the detected power with respect to a reference voltage. In the preferred embodiment, this reference voltage is provided by the radio's demodulator to indicate the nominal value at which the demodulator requires the loop to lock in order to hold the power level constant. The demodulator reqmres this value for optimum performance since a power level too far out of the optimum range will degrade the performance of the demodulator. The power detector (214) performs the integration, thus generating an AGC setpoint. The setpoint and a receive frequency index are input to a receiver linearizing table (216). The AGC setpoint and the frequency index are used to address the linearizer (216), thus accessing the proper calibration value. This calibration value is then output to a digital to analog converter (215) that generates the analog representation of the receive AGC setting. The analog value adjusts the biasing of the variable gain amplifier (212). The control of the variable gain amplifier (212) forces the receive AGC loop to close such that the input to the receiver linearizing table (216) follows a predetermined straight line with respect to RF input power. This linearization removes the undesired linear and non-linear errors in addition to variations versus fi'equency that would otherwise be apparent at the input to the receiver linearizing table (216) in the receiver. These errors and variations would contribute to errors in the transmitter. In order to reduce the error in the receive and transmit chains versus frequency, the receive and transmit linearizers utilize the frequency index that specifies the current center frequency on which the receive and transmit chains are operating. During factory calibration of the radiotelephone, the linearizers are loaded with values, in addition to the previously mentioned calibration values, that are indexed by frequency to correct the errors related to operating center frequency. The AGC setpoint is the open loop power control signal for the radio. In the preferred embodiment, this is the power control performed by the radio by itself without control input from the cells. As the power of the signal received from the cell increases, the radio decreases its transmit power. This output power control is accomplished by the AGC setpoint that is filtered by a low pass filter (217). The transmit section includes a digital summer (210) that combines the AGC setpoint and a closed loop power control setting (206). The output of the summer (210) is fed into a power control limiting section (205). The operation of the power control limiting section (205) and the closed loop power control section (206), illustrated in FIGs. 3 and 4 respectively, will be discussed subsequently in greater detail. The output of the power control limiting section (205), along with the transmit frequency index, are used to address values stored in a transmitter linearizing table (204). The transmitter linearizing table (204) contains values determined from production testing of the radiotelephone. The selected value is input to a digital to analog converter (203) whose output, an analog representation of the digital value input, controls a variable gain amplifier (202). The biasing of the variable gain amplifier (202) is adjusted by the analog calibration value to a point such that the input to the transmitter linearizing table (204) follows a predetermined straight line with respect to transmitted RF output power. This linearization removes the undesired linear and non-linear errors along with variations versus frequency in the transmitter. This, combined with the previously mentioned receive linearization, greatly reduces the open and closed loop power control errors due to RF performance imperfections. The power amplifier (PA) bias control section (218) controls the bias point, of the transmit PA (201) based on the transmit gain setting such that the transmit sidebands for the given gain setting are optimized versus PA (201) current consimiption. This allows a battery powered telephone to maximize talk time by reducing PA (201) current consumotion at lower output powers while still maintaining acceptable sideband levels at higher output power levels. The power control limiting section (205) is illustrated in FIG. 3. The power control limiting section (205) controls the closed loop power control and transmit gain settings when the output of the transmit gain summer (210) corresponds to a transmit output power level which is equal to or greater than the intended maximum output power. The maximum gain setting is determined by the PA limit threshold control section (209). The threshold control section (209) determines the maximimi gain setting based on a nominal value that is modified by a real-time measurement of the transmitted output power. The measurement is accompUshed by an analog power detector (207) whose output transformed into a digital signal by an analog to digital converter (208). The digitized power value is then input to the threshold control section (209). The threshold control section, detailed in FIG. 5, operates by the high power detector (HDET) linearizer (501) scaling the input digitized power value in order to match the numerology of the digital transmit gain control section. The scaled output from the linearizer (501) is subtracted (502) from the nominal maximun gain setting. This maximum gain setting can be hard coded into the radio during assembly or input during manufacturing and testing of the radio. The difference of the maximum gain setting and the scaled output power is then added to the maximum gain setting. The sum of these signals is then used as the corrected maximum gain setting. This realtime modification of the detected power helps mitigate the errors introduced by temperature variations and aging of the transmitter PAs. In other words, if the difference between the maximum gain setting and the real-time measured power value is 0, then no correction is necessary. If there is a difference between the two, the difference is used to correct the maximum gain setting. Referring to FIG. 3, a digital comparator (301) detects when the output of the transmit gain summer (210) equals or exceeds the maximum gain setting. The comparator (301) controls a 2:1 multiplexer (302) that outputs the maximum allowable setting when the output of the summer (210) exceeds the maximum allowable setting. When the output of the summer (210) is less than the maximum allowable setting, the multiplexer (302) outputs the direct output of the summer (210). This prohibits the transmitter from exceeding its maximum operating point. The closed loop power control section (206), illustrated in FIG. 4, accumulates the power control commands sent on the forward link by the controlling radiotelephone cell site and outputs a gain adjust signal. The power control commands are collected in an accumulator (401). The operation of the accumulator (401) is controlled by the power control limiting section (205) when the transmit power amplifier (201) is outputting the maximum allowable power. When the output of the summner (210) changes from being less than to equal or greater than the maximum allowable setting, the output of the closed loop power control accumulator (401) is latched into a flip-flop (402). While the output of the summer (210) is equal to or greater than the maximum allowable setting, an AND gate (405) masks off any closed loop power control up commands that would force the accumulator (401) above the flip-flop's (402) latched value. This prevents the accunulator from saturating during power limiting yet allows the closed loop power control setting to change anywhere below the latched value. An alternate embodiment of the process of the present invention is illustrated in FIG. 6. In this embodiment, a power limiting control system is employed based on accumulator feedback control. The system operates by first measuring the output power of the power amplifier (609) using a power detector (610). The detected power is then digitized by an ADC (611) and compared to a maximum allowable setting by the comparator (601). If the output power is greater than the maximum setting, the power limiting accumulator (602) begins turning power down by reducing the gain of the variable gain amplifier (608). If the output power is less than the maximum setting the power limiting accimiulator (602) returns to a OdB correction value. In this embodiment, a closed loop power control limiting function, similar to the preferred embodiment, is employed. However, the trigger for the closed loop power control limiting function is a comparator (603) that detects when the power limiting accumulator (602) is limiting the output power by comparing the accumaulator (602) output to OdB with the comparator (603). The linearizing compensation tables, similar to the tables in the preferred embodiment, are added into the transmit gain control using a summer (606). In another alternate embodiment, illustrated in FIG. 7, a power limiting control system is employed that is based on the closed loop power control accumulator (702). The system operates by first measuring the output power of the power amplifier (705) using a power detector (706). The detected power is digitized (707) and compared to a maximum allowable setting by the comparator (701). If the output power is greater than the maximum setting, the closed loop power control acctunulator (702) is modified to turn the amplifier (704) power down by one step each 1.25 ms until the output power is less than the maximum setting. If the output power is less than the maximum setting, the closed loop power control accumulator is not modified. The linearizing compensation tables, similar to the preferred embodiment, are added into the transmit gain control using a summer (703). In yet another embodiment, illustrated in FIG. 8, a power limiting control system is employed that is based on integral feedback control. The system operates by first measuring the output power of the power amplifier (808) using a power detector (809). The detected power is digitized (810) and input to an integrator (801) that follows the equation: The integrator (801), generating a gain control signal, saturates at OdB and -63dB of correction. The gain control signal is thus limited within a range. If the output power is greater than the setpoint the integrator turns down the output power of the amplifier (807) at a rate based on the integration constant K until the setpoint is reached. The integrator is allowed to turn power down by as much as 63dB. If the output power is less than the setpoint, the output of the integrator (801) will be forced to zero, thus not adjusting output power. In this embodiment, a closed loop power control limiting function, similar to the preferred embodiment, is employed. The trigger for the closed loop power control limiting function, however, is a comparator (802) that detects when the power limiting integrator (801) is limiting the output power. The linearizing compensation tables, similar to the preferred embodiment, are added into the transmit gain control using a summer (805). In still another embodiment, illustrated in FIG. 9, a power limiting control system is employed that is based only on a measure of receive power and the closed loop power control setting as opposed to actual output power. The transmit power limiting and closed loop power control limiting function (901) can be implemented with either the preferred or one of the alternate embodiments. However, only the receive power and closed loop power control setting are used to estimate transmit output power. In summary, the process of the present invention ensures that the transmitted sidebands and synthesizer phase noise of a radio transmitter remains within a predetermined specification by limiting the maximum output power. This power limitation is accomplished by a control loop including a calibration look-up table. Therefore, a radiotelephone using the process of the present invention would not exceed it's nominal maximum power level due to the cell issuing too many power turn-up commands. The radiotelephone limits the power output even when the cell erroneously decides the radiotelephone power should be increased. WE CLAIM: 1. An apparatus for limiting transmit power of a radio operating in a cellular environment, the cellular environment comprising a plurality of cells that transmit power control commands to the radio, the radio comprising a variable gain amplifier and a power limiting accumulator, the apparatus comprising : a receiver for receiving a signal from at least one of the plurality of cells; measuring means for determining a power value of the signal; control means for determining a closed loop power control value in response to the signal; generating means for generating a limiting gain control setting in response to the closed loop power control value and the power value, the limiting gain control signal being within a predetermined range; combining means for combining the closed loop power control value and the power value and the limiting gain control setting to generate a gain contol setting; and means for adjusting the variable gain amplifier in response to the gain control setting. 2. The apparatus as claimed in claim 1 comprising means for correcting transmit power of a radio device having a plurality of predetermined calibration values, a reference voltage signal and capable of transmitting and receiving on a plurality of frequencies, each frequency having a frequency index; a receiver for receiving a first signal having a first gain, a first frequency of the plurality of frequencies, and the first frequency's associated frequency index; measuring means for determining a receive power value of the first signal; generating means for generating an automatic gain control setpoint in response to the receive power value and the reference voltage signal; selection means for selecting a first predetennined calibration value in response to the automatic gain control setpoint and the first frequency index; means for adjusting the first gain in response to the first calibration value; transmitter means for transmitting a second signal having a second gain and a second frequency of the plurality of frequencies, the second fi-equency having a second fi-equency index; measuring means for determining a transmit power value of the second signal; generating means for generating a second calibration value in response to the automatic gain control setpoint, the second fi*equency index; and the transmit power value; and means for adjusting the second gain in response to the second calibration value. 3. The apparatus as claimed in claim 2 wherein a digitizing means is provided for digitizing the received power value before generating the automatic gain control setpoint and a converting means is provided for converting the first predetermined calibration value to an analog value before adjusting the first gain. 4. The apparatus as claimed in claim 1 wherein a radio having a transmit power calibration capability is provided for transmitting and receiving signals having a plurality of frequencies, each frequency having a frequency index, the radio transmitting signals through a variable gain, transmit amplifier having a control input and receiving signals through a variable gain receive amplifier having a control input, the said radio comprising: a power detector, coupled to the receive amplifier, for generating a first power value from a received signal having a first frequency; an integrator, coupled to the power detector, tor generating an automatic gain control setpoint from the power value; a receive linearizer, coupled to the integrator and the receive amplifier, for generating a receive calibration value in response to theautomatic gain control setpoint and a first frequency index corresponding to the frequency of the received signal, the receive calibration value being coupled to the receive amplifier control input and adjusting the gain of the receive amplifier; a second power detector, coupled to the transmit amplifier for generating a second power value from a transmitted signal having a second frequency; and a transmit linearizer for generating a transmit calibration value in response to the automatic gain control setpoint, the second power value, and a frequency index corresponding to the second fi-equency; the transmit calibration value being coupled to the control input of the transmit amplifier and adjusting the gain of the transmit amplifier. 5. The apparatus as claimed in claim 1 wherein a radio having a transmit power calibration capability, is provided for transmitting and receiving signals having a plurality of frequencies, each fi-equency having a fi-equency index, the radio transmitting signal, having a first fi-equency, through a variable gain transmit amplifier having a control input and receiving a signal, having a second frequency, through a variable gain receive amplifier having a control input, the said radio comprising : a first analog to digital converter, coupled to the receive amplifier, for generating a digital signal from the received signal; a power detector, coupled to the first analog to digital converter, for generating a power value from the digital signal; an integrator, coupled to the power detector, for generating an automatic gain control setpoint from the power value; a receive linearizer, coupled to the integrator, for generating a receive calibration value in response to the automatic gain control point and a first frequency index corresponding to the second frequency; a first digital to analog converter, coupled to the receive linearizer, for generating an analog, receive calibration value from the receive calibration value, the analog calibration value coupled to the receive amplifier control input and varying the gain of the receive amplifier; a second power detector, coupled to the transmit amplifier, for generating an analog power value from the transmitted signal; a second analog to digital converter, coupled to the second power detector, for generating a digital power value from the analog power value; a transmit linearizer, coupled to the integrator, for generating a transmit calibration value in response to the automatic gain control setpoint the digital power value, and the frequency index corresponding to the first frequency; and a second digital to analog converter, coupled to the second control input, for generating an anlog, transmit calibration value, from the transmit calibration value, the analog, transmit calibration value adjusting the gain of the transmit amplifier. 6. The apparatus as claimed in claim 1 wherein limiting means is provided for limiting transmit power of a radio operating in a radio communications system, the radio communications environment comprising at lease one base station that transmits signals to the radio having power control commands, the radio comprising a variable gain amplifier and a maximum gain setting, and said apparatus comprising: means for determining an open loop power control value in response to a signal received from the at least one base station; means for determining a gain adjust signal in response to the transmit power control commands; means for combining the open loop power control value and the gain adjust signal to produce a summation signal; means for comparing the maximum gain setting to the summation signal; means for, if the summation signal is greater than or equal to the maximun gain setting, adjusting the variable gain amplifier in response to the maximum gain setting; and means for, if the summation signal is less than the maximum gain setting, adjusting the Variable gain amplifier in response to the summation signal. 7. The apparatus as claimed in claim 6 wherein a gain setting means is provided for adjusting the maximum gain setting in response to a temperature of the variable gain amplifier. 8. The apparatus as claimed in claim 1 wherein the said gain setting means for adjusting the maximum gain setting comprises transmitter means for transmitting a signal with the variable gain amplifier; detector means for detecting a power value of the transmitted signal; scaling means for scaling the power value to produce a scaled power signal; subtracting means for subtracting the maximum gain setting from the scaled power signal to produce a difference signal; and adding means for adding the difference signal to the maximum gain setting. 9. The apparatus as claimed in claim 1 wherein limiting means is provided tor limiting transmit power of a radio operating in a cellular environment, the cellular enivronment comprising a plurality of cells that transmit power control commands to the radio, the radio comprising a variable gain amplifier and a maximum gain .setting, the said apparatus comprising means tor determining an open loop power control value in respon.se to a signal received from at least one cell; means for determining a gain adjust signal in response to the transmit power control commands; means for combining the open loop power control value and the gain adjust singal to produce a summation signal; means for adjusting the maximum gain setting in response to a temperature of the variable gain amplifier; means for comparing the adjusted maximum gain setting to the summation signal; means for, if the summation signal is greater than or equal to the maximum gain setting, prohibiting the gain adjust signal from changing in response to the transmit power commands; means for, if the summation signal is greater than or equal to the maximum gain setting, adjusting the variable gain amplifier in response to the maximum gain setting; and means tor, if the summation signal is less than the maximum gain setting, adjusting the variable gain amplifier in response to the summation signal. 10. The apparatus as claimed in claim 1 wherein limiting means is provided for limiting transmit power of a radio operating in a cellular enviomment, the cellular environment comprising a plurality of cells that transmit power control commands to the radio, the radio comprising a variable gain amplifier, a maximum gain setting, and a power limiting accumulator, the said apparatus comprising tramsitter means for transmitting a signal with the variable gain amplifier; measuring means for determining a gain adjust signal in response to the transmit power control commands; detector means tor detecting a power value of the transmitted signal; digitizing means for digitizing the power value; comparing means for comparing the digitized power value to the maximum gain setting; means for, if the digitized power value is greater than the maximum gain setting, decreasing the gain of the variable gain amplifier; and means for, if the digitized power value is greater than the maximum gain setting, prohibiting the gain adjust signal from changing in response to the transmit power commands. 11. The apparatus as claimed in claim 1 wherein limiting means is provided for limiting transmit power of a radio operating in a cellular environment, the cellular environment comprising a plurality of cells that transmit power control commands to the radio, the radio comprising a variable gain amplifier, a maximum gain setting, and a power control command accumulator that generates a gain adjust signal, the said apparatus comprising : transmitter means for transmitting a signal with the variable gain amplifier; measuring means for determining a gain adjust signal in response to the transmit power control commands; detector means for detecting a power value of the transmitted signal; digitizing means for digitizing the power value; comparing means for comparing the digitized power value to the maximum gain setting; means for, if the digitized power value is greater than the maximum gain setting, decreasing the gain adjust signal by a predetermined amount of every predetermined unit of time until the gain adjust signal is less than the maximum gain setting; and means for, if the digitized power value is less than or equal to the maximum gain setting, varying the gain of the variable gain amplifier in response to the gain adjust signal. 12. The apparatus as claimed in claim 1 wherein limiting means is provided for limiting transmit power of a radio operating in a cellular environment, the cellular environment comprising a plurality of cells that transmit power control commands to the radio, the radio comprising a variable gain amplifier, a maximum gain setting, and a power limiting accumulator, the .said apparatus comprising transmitter means for transmitting a signal with the variable gain amplifier, measuring means for determining a gain adjust signal in response to the transmit power control commands; detector means for detecting a power value of the transmitted signal; digitizing means for digitizing the power value; comparing means for determining a difference between the digitized power value and the maximum gain setting; means for integrating the difference to generate a gain control signal, tlie gain control signal being limited to a predetermined range; means for adjusting the variable gain amplifier with the gain control signal; means for, if the gain control signal is less than a predetermined value, prohibiting the gain adjust signal from changing the variable gain amplifier in response to the transmit power commands. 13, An apparatus for limiting transmit power of a radio operating in a cellular environment, substantially as herein described with reference to the accompanying drawings.

Full Text

The present invention relates to an apparatus for limiting transmit power of a radio operating in a cellular environment.
The Federal Communications Commission (FCC) governs the use of the radio frequency (RF) spectrum. The FCC allocates certain band-widths within the RF spectrum tor specific uses. A user of an allocated bandwidth of the RF spectrum must take measures to ensure that the radiated emissions inside and outside of that bandwidth are maintained within acceptable levels to avoid interfering with other users operating in the same and or other band widths. These levels are governed by both the FCC and the particular user groups of said bandwidth.
The 800 MHz cellular telephone system operates its forward link, the cell to radiotelephone transmission, in the bandwidth of 869.01 MHz to 893.97 MHz and the reverse link, the radiotelephone to cell transmission in the bandwidth of 824.01 MHz to 848.97 MHz. The forward and reverse link bandwidths are split up into channels each of which occupies a 30 kHz bandwidth. A particular user of the cellular system may operate on one or several of these channels at a time. All users of the system must ensure that they are compliant with the level of radiated emissions allowable inside and outside of the channel or channels that they have been assigned.
There are several different techniques of modulation that can be used in the cellular telephone system. Two examples of modulation techniques are frequency division multiple access (FDMA) and code division multiple access (CDMA).
The FDMA modulation technique generates signals that occupy one channel at a time while the CDMA modulation technique generates signals that occupy several channels. Both of these techniques must control their return link radiated emissions to with in the acceptable limits

inside and outside of the assigned channel or channels. For maximum system performance, users of the CDMA technique must carefully control the level of radiated power inside the channels in which they are operating.
FIG. 1 shows a typical prior cellular radiotelephone. In both an FDMA and a CDMA based radiotelephone, there exists the possibility of driving the power amplifier (101) in the transmitter beyond a point where acceptable out of channel radiated emissions are maintained. This is primarily due to the increased distortion output levels of the power amplifier (101) at high output powers. Also, driving the power amplifier (101) beyond a certain point can cause interference internal to the radio. For example, PA puncturing in CDMA affects synthesizer phase noise due to large current transitions. Both of these issues cause unacceptable radio performance.
Maintaining the proper on-channel output power can be difficult due to several undesirable effects in the radiotelephone hardware. For example, the CDMA based radio must implement a power control system that operates over a very wide dynamic range, 80dB to 90dB, such that the transmitted output power is linearly related to the received input power.
Closed loop and open loop power control together determine the return link transmit energy, as disclosed in U.S. Patent No. 5,056,109 to Gilhousen et al. and assigned to Qualcomm, Incorporated. Therefore, the linear and nonlinear errors produced in both the receiver (103) and transmitter (102) RF sections can cause unacceptable power control performance. Also, both the FDMA and CDMA based radios must operate on different channels while maintaining acceptable output power levels. Variation in output power level and input power detection versus frequency can cause an unacceptable amoimt of error in the amount of return link transmitted energy.
These issues present significant problems to the designer of both FDMA and CDMA based radiotelephones. There is a resulting need for an effective, cost efficient means of correcting these problems.

Accordingly the present invention provides an apparatus tor limiting transmit power of a radio operating in a cellular environment the cellular environment comprising a plurality of cells that transmit power control commands to the radio, the radio comprising a variable gain amplifier and a power limiting accumulator, the apparatus comprising : a receiver for receiving a signal from at least one of the plurality of cells; measuring means for determining a power value of the signal; control means for determining a closed loop power control value in response to the signal; generating means for generating a limiting gain control setting in response to the closed loop power control value and the power value, the limiting gain control signal being within a predetermined range; combining means for combining the closed loop power control value and the power value and the limiting gain control setting to generate a gain contol setting; and means for adjusting the variable gain amplifier in response to the gain control setting.
With reference to the accompanying drawings, in which :
FIG.l shows a block diagram of a typical prior art radiotelephone frequency section for use in a radiotelephone system.
FIG.2 shows a block diagram of the preferred embodiment power control correction implementation.
FIG.3 shows a block diagram of the power limiting control section as related to FIG.2.
FIG.4 shows a block diagram of the closed loop power control section as related to FIG.2.

FIG.5 shows a block diagram of the PA limit threshold control section as related to FIG.2.
FIG.6 shows an alternate embodiment of the present invention that employs a power Umiting control system based on accumulator feedback control.
FIG. 7 shows an alternate embodiment of the present invention that employs a power limting control system based on the closed loop power control accumulator.
FIG.8 shows an alternate embodiment of the present invention that employs a power limiting control system based on integral feedback control.
FIG. 9 shows an alternate embodiment of the present invention that employs a power limiting control sy.stem based on a measure of receive power and the closed loop power control setting to estimate output power.

The process of the present invention provides power control correction for a mobile radiotelephone as well as maintaining acceptable in and out of band maximum emission levels. This is accomplished by realtime compensation utilizing a set of correction tables that are generated during the production testing of each radiotelephone.
FIG. 2 shows a block diagram of a CDMA radiotelephone with the preferred embodiment power control correction implementation. FIGs. 3, 4, and 5 detail specific blocks of FIG. 2. The radiotelephone is comprised of a receive linearization section, transmit linearization section, power amplifier bias control section, and power limiting control section.
The receive linearization section includes an automatic gain control (AGO section. The signal input to the AGO section is received on the forward link and amplified by a low noise amplifier (LNA) (211). The output of the LNA (211) is input to a variable gain amplifier (212). The variable gain amplifier (212) produces a signal that is converted to a digital signal using an analog to digital converter (ADC) (213).
The power of the digitized received signal is next computed by a digital power detector (214). The power detector (214) includes an integrator that integrates the detected power with respect to a reference voltage. In the preferred embodiment, this reference voltage is provided by the radio's demodulator to indicate the nominal value at which the demodulator requires the loop to lock in order to hold the power level constant. The demodulator reqmres this value for optimum performance since a power level too far out of the optimum range will degrade the performance of the demodulator. The power detector (214) performs the integration, thus generating an AGC setpoint. The setpoint and a receive frequency index are input to a receiver linearizing table (216).
The AGC setpoint and the frequency index are used to address the linearizer (216), thus accessing the proper calibration value. This calibration value is then output to a digital to analog converter (215) that generates the analog representation of the receive AGC setting.
The analog value adjusts the biasing of the variable gain amplifier (212). The control of the variable gain amplifier (212) forces the receive AGC loop to close such that the input to the receiver linearizing table (216) follows a predetermined straight line with respect to RF input power. This linearization removes the undesired linear and non-linear errors in addition to variations versus fi'equency that would otherwise be apparent at the input to the receiver linearizing table (216) in the receiver. These errors and variations would contribute to errors in the transmitter.

In order to reduce the error in the receive and transmit chains versus frequency, the receive and transmit linearizers utilize the frequency index that specifies the current center frequency on which the receive and transmit chains are operating. During factory calibration of the radiotelephone, the linearizers are loaded with values, in addition to the previously mentioned calibration values, that are indexed by frequency to correct the errors related to operating center frequency.
The AGC setpoint is the open loop power control signal for the radio. In the preferred embodiment, this is the power control performed by the radio by itself without control input from the cells. As the power of the signal received from the cell increases, the radio decreases its transmit power. This output power control is accomplished by the AGC setpoint that is filtered by a low pass filter (217).
The transmit section includes a digital summer (210) that combines the AGC setpoint and a closed loop power control setting (206). The output of the summer (210) is fed into a power control limiting section (205). The operation of the power control limiting section (205) and the closed loop power control section (206), illustrated in FIGs. 3 and 4 respectively, will be discussed subsequently in greater detail.
The output of the power control limiting section (205), along with the transmit frequency index, are used to address values stored in a transmitter linearizing table (204). The transmitter linearizing table (204) contains values determined from production testing of the radiotelephone. The selected value is input to a digital to analog converter (203) whose output, an analog representation of the digital value input, controls a variable gain amplifier (202).
The biasing of the variable gain amplifier (202) is adjusted by the analog calibration value to a point such that the input to the transmitter linearizing table (204) follows a predetermined straight line with respect to transmitted RF output power. This linearization removes the undesired linear and non-linear errors along with variations versus frequency in the transmitter. This, combined with the previously mentioned receive linearization, greatly reduces the open and closed loop power control errors due to RF performance imperfections.
The power amplifier (PA) bias control section (218) controls the bias point, of the transmit PA (201) based on the transmit gain setting such that the transmit sidebands for the given gain setting are optimized versus PA (201) current consimiption. This allows a battery powered telephone to maximize talk time by reducing PA (201) current consumotion at lower

output powers while still maintaining acceptable sideband levels at higher output power levels.
The power control limiting section (205) is illustrated in FIG. 3. The power control limiting section (205) controls the closed loop power control and transmit gain settings when the output of the transmit gain summer (210) corresponds to a transmit output power level which is equal to or greater than the intended maximum output power. The maximum gain setting is determined by the PA limit threshold control section (209).
The threshold control section (209) determines the maximimi gain setting based on a nominal value that is modified by a real-time measurement of the transmitted output power. The measurement is accompUshed by an analog power detector (207) whose output transformed into a digital signal by an analog to digital converter (208). The digitized power value is then input to the threshold control section (209).
The threshold control section, detailed in FIG. 5, operates by the high power detector (HDET) linearizer (501) scaling the input digitized power value in order to match the numerology of the digital transmit gain control section. The scaled output from the linearizer (501) is subtracted (502) from the nominal maximun gain setting. This maximum gain setting can be hard coded into the radio during assembly or input during manufacturing and testing of the radio.
The difference of the maximum gain setting and the scaled output power is then added to the maximum gain setting. The sum of these signals is then used as the corrected maximum gain setting. This realtime modification of the detected power helps mitigate the errors introduced by temperature variations and aging of the transmitter PAs. In other words, if the difference between the maximum gain setting and the real-time measured power value is 0, then no correction is necessary. If there is a difference between the two, the difference is used to correct the maximum gain setting.
Referring to FIG. 3, a digital comparator (301) detects when the output of the transmit gain summer (210) equals or exceeds the maximum gain setting. The comparator (301) controls a 2:1 multiplexer (302) that outputs the maximum allowable setting when the output of the summer (210) exceeds the maximum allowable setting. When the output of the summer (210) is less than the maximum allowable setting, the multiplexer (302) outputs the direct output of the summer (210). This prohibits the transmitter from exceeding its maximum operating point.

The closed loop power control section (206), illustrated in FIG. 4, accumulates the power control commands sent on the forward link by the controlling radiotelephone cell site and outputs a gain adjust signal. The power control commands are collected in an accumulator (401). The operation of the accumulator (401) is controlled by the power control limiting section (205) when the transmit power amplifier (201) is outputting the maximum allowable power.
When the output of the summner (210) changes from being less than to equal or greater than the maximum allowable setting, the output of the closed loop power control accumulator (401) is latched into a flip-flop (402). While the output of the summer (210) is equal to or greater than the maximum allowable setting, an AND gate (405) masks off any closed loop power control up commands that would force the accumulator (401) above the flip-flop's (402) latched value. This prevents the accunulator from saturating during power limiting yet allows the closed loop power control setting to change anywhere below the latched value.
An alternate embodiment of the process of the present invention is illustrated in FIG. 6. In this embodiment, a power limiting control system is employed based on accumulator feedback control. The system operates by first measuring the output power of the power amplifier (609) using a power detector (610). The detected power is then digitized by an ADC (611) and compared to a maximum allowable setting by the comparator (601). If the output power is greater than the maximum setting, the power limiting accumulator (602) begins turning power down by reducing the gain of the variable gain amplifier (608). If the output power is less than the maximum setting the power limiting accimiulator (602) returns to a OdB correction value.
In this embodiment, a closed loop power control limiting function, similar to the preferred embodiment, is employed. However, the trigger for the closed loop power control limiting function is a comparator (603) that detects when the power limiting accumulator (602) is limiting the output power by comparing the accumaulator (602) output to OdB with the comparator (603). The linearizing compensation tables, similar to the tables in the preferred embodiment, are added into the transmit gain control using a summer (606).
In another alternate embodiment, illustrated in FIG. 7, a power limiting control system is employed that is based on the closed loop power control accumulator (702). The system operates by first measuring the output power of the power amplifier (705) using a power detector (706). The

detected power is digitized (707) and compared to a maximum allowable setting by the comparator (701). If the output power is greater than the maximum setting, the closed loop power control acctunulator (702) is modified to turn the amplifier (704) power down by one step each 1.25 ms until the output power is less than the maximum setting. If the output power is less than the maximum setting, the closed loop power control accumulator is not modified. The linearizing compensation tables, similar to the preferred embodiment, are added into the transmit gain control using a summer (703).
In yet another embodiment, illustrated in FIG. 8, a power limiting control system is employed that is based on integral feedback control. The system operates by first measuring the output power of the power amplifier (808) using a power detector (809). The detected power is digitized (810) and input to an integrator (801) that follows the equation:

The integrator (801), generating a gain control signal, saturates at OdB and -63dB of correction. The gain control signal is thus limited within a range. If the output power is greater than the setpoint the integrator turns down the output power of the amplifier (807) at a rate based on the integration constant K until the setpoint is reached. The integrator is allowed to turn power down by as much as 63dB. If the output power is less than the setpoint, the output of the integrator (801) will be forced to zero, thus not adjusting output power.
In this embodiment, a closed loop power control limiting function, similar to the preferred embodiment, is employed. The trigger for the closed loop power control limiting function, however, is a comparator (802) that detects when the power limiting integrator (801) is limiting the output power. The linearizing compensation tables, similar to the preferred embodiment, are added into the transmit gain control using a summer (805).
In still another embodiment, illustrated in FIG. 9, a power limiting control system is employed that is based only on a measure of receive power and the closed loop power control setting as opposed to actual output power. The transmit power limiting and closed loop power control limiting function (901) can be implemented with either the preferred or one of the alternate embodiments. However, only the receive power and

closed loop power control setting are used to estimate transmit output power.
In summary, the process of the present invention ensures that the transmitted sidebands and synthesizer phase noise of a radio transmitter remains within a predetermined specification by limiting the maximum output power. This power limitation is accomplished by a control loop including a calibration look-up table. Therefore, a radiotelephone using the process of the present invention would not exceed it's nominal maximum power level due to the cell issuing too many power turn-up commands. The radiotelephone limits the power output even when the cell erroneously decides the radiotelephone power should be increased.

WE CLAIM:
1. An apparatus for limiting transmit power of a radio operating in a cellular environment, the cellular environment comprising a plurality of cells that transmit power control commands to the radio, the radio comprising a variable gain amplifier and a power limiting accumulator, the apparatus comprising : a receiver for receiving a signal from at least one of the plurality of cells; measuring means for determining a power value of the signal; control means for determining a closed loop power control value in response to the signal; generating means for generating a limiting gain control setting in response to the closed loop power control value and the power value, the limiting gain control signal being within a predetermined range; combining means for combining the closed loop power control value and the power value and the limiting gain control setting to generate a gain contol setting; and means for adjusting the variable gain amplifier in response to the gain control setting.
2. The apparatus as claimed in claim 1 comprising means for correcting transmit power of a radio device having a plurality of predetermined calibration values, a reference voltage signal and capable of transmitting and receiving on a plurality of frequencies, each frequency having a frequency index; a receiver for receiving a first signal having a first gain, a first frequency of the plurality of frequencies, and the first frequency's associated frequency index; measuring means for determining a receive power value of the first signal; generating means for generating an automatic gain control setpoint in response to the receive power value and the reference voltage signal; selection means for selecting a first

predetennined calibration value in response to the automatic gain control setpoint and the first frequency index; means for adjusting the first gain in response to the first calibration value; transmitter means for transmitting a second signal having a second gain and a second frequency of the plurality of frequencies, the second fi-equency having a second fi-equency index; measuring means for determining a transmit power value of the second signal; generating means for generating a second calibration value in response to the automatic gain control setpoint, the second fi*equency index; and the transmit power value; and means for adjusting the second gain in response to the second calibration value.
3. The apparatus as claimed in claim 2 wherein a digitizing means is provided for digitizing the received power value before generating the automatic gain control setpoint and a converting means is provided for converting the first predetermined calibration value to an analog value before adjusting the first gain.
4. The apparatus as claimed in claim 1 wherein a radio having a transmit power calibration capability is provided for transmitting and receiving signals having a plurality of frequencies, each frequency having a frequency index, the radio transmitting signals through a variable gain, transmit amplifier having a control input and receiving signals through a variable gain receive amplifier having a control input, the said radio comprising: a power detector, coupled to the receive amplifier, for generating a first power value from a received signal having a first frequency; an integrator, coupled to the power detector, tor generating an automatic gain control setpoint from the power value; a receive linearizer, coupled to the integrator and the

receive amplifier, for generating a receive calibration value in response to theautomatic gain control setpoint and a first frequency index corresponding to the frequency of the received signal, the receive calibration value being coupled to the receive amplifier control input and adjusting the gain of the receive amplifier; a second power detector, coupled to the transmit amplifier for generating a second power value from a transmitted signal having a second frequency; and a transmit linearizer for generating a transmit calibration value in response to the automatic gain control setpoint, the second power value, and a frequency index corresponding to the second fi-equency; the transmit calibration value being coupled to the control input of the transmit amplifier and adjusting the gain of the transmit amplifier.
5. The apparatus as claimed in claim 1 wherein a radio having a transmit power calibration capability, is provided for transmitting and receiving signals having a plurality of frequencies, each fi-equency having a fi-equency index, the radio transmitting signal, having a first fi-equency, through a variable gain transmit amplifier having a control input and receiving a signal, having a second frequency, through a variable gain receive amplifier having a control input, the said radio comprising : a first analog to digital converter, coupled to the receive amplifier, for generating a digital signal from the received signal; a power detector, coupled to the first analog to digital converter, for generating a power value from the digital signal; an integrator, coupled to the power detector, for generating an automatic gain control setpoint from the power value; a receive linearizer, coupled to the integrator, for generating a receive calibration value in response to the automatic gain control point and a first frequency index corresponding to the second frequency; a first digital to analog converter, coupled to the receive

linearizer, for generating an analog, receive calibration value from the receive calibration value, the analog calibration value coupled to the receive amplifier control input and varying the gain of the receive amplifier; a second power detector, coupled to the transmit amplifier, for generating an analog power value from the transmitted signal; a second analog to digital converter, coupled to the second power detector, for generating a digital power value from the analog power value; a transmit linearizer, coupled to the integrator, for generating a transmit calibration value in response to the automatic gain control setpoint the digital power value, and the frequency index corresponding to the first frequency; and a second digital to analog converter, coupled to the second control input, for generating an anlog, transmit calibration value, from the transmit calibration value, the analog, transmit calibration value adjusting the gain of the transmit amplifier.
6. The apparatus as claimed in claim 1 wherein limiting means is provided for limiting transmit power of a radio operating in a radio communications system, the radio communications environment comprising at lease one base station that transmits signals to the radio having power control commands, the radio comprising a variable gain amplifier and a maximum gain setting, and said apparatus comprising: means for determining an open loop power control value in response to a signal received from the at least one base station; means for determining a gain adjust signal in response to the transmit power control commands; means for combining the open loop power control value and the gain adjust signal to produce a summation signal; means for comparing the maximum gain setting to the summation signal; means for, if the summation signal is greater than or equal to the maximun gain setting, adjusting the variable gain

amplifier in response to the maximum gain setting; and means for, if the summation signal is less than the maximum gain setting, adjusting the Variable gain amplifier in response to the summation signal.
7. The apparatus as claimed in claim 6 wherein a gain setting means is provided for adjusting the maximum gain setting in response to a temperature of the variable gain amplifier.
8. The apparatus as claimed in claim 1 wherein the said gain setting means for adjusting the maximum gain setting comprises transmitter means for transmitting a signal with the variable gain amplifier; detector means for detecting a power value of the transmitted signal; scaling means for scaling the power value to produce a scaled power signal; subtracting means for subtracting the maximum gain setting from the scaled power signal to produce a difference signal; and adding means for adding the difference signal to the maximum gain setting.
9. The apparatus as claimed in claim 1 wherein limiting means is provided tor limiting transmit power of a radio operating in a cellular environment, the cellular enivronment comprising a plurality of cells that transmit power control commands to the radio, the radio comprising a variable gain amplifier and a maximum gain .setting, the said apparatus comprising means tor determining an open loop power control value in respon.se to a signal received from at least one cell; means for determining a gain adjust signal in response to the transmit power control commands; means for combining the open loop power control value and the gain adjust singal to produce a summation signal; means for adjusting the maximum

gain setting in response to a temperature of the variable gain amplifier; means for comparing the adjusted maximum gain setting to the summation signal; means for, if the summation signal is greater than or equal to the maximum gain setting, prohibiting the gain adjust signal from changing in response to the transmit power commands; means for, if the summation signal is greater than or equal to the maximum gain setting, adjusting the variable gain amplifier in response to the maximum gain setting; and means tor, if the summation signal is less than the maximum gain setting, adjusting the variable gain amplifier in response to the summation signal.
10. The apparatus as claimed in claim 1 wherein limiting means is provided for limiting transmit power of a radio operating in a cellular enviomment, the cellular environment comprising a plurality of cells that transmit power control commands to the radio, the radio comprising a variable gain amplifier, a maximum gain setting, and a power limiting accumulator, the said apparatus comprising tramsitter means for transmitting a signal with the variable gain amplifier; measuring means for determining a gain adjust signal in response to the transmit power control commands; detector means tor detecting a power value of the transmitted signal; digitizing means for digitizing the power value; comparing means for comparing the digitized power value to the maximum gain setting; means for, if the digitized power value is greater than the maximum gain setting, decreasing the gain of the variable gain amplifier; and means for, if the digitized power value is greater than the maximum gain setting, prohibiting the gain adjust signal from changing in response to the transmit power commands.

11. The apparatus as claimed in claim 1 wherein limiting means is provided for limiting transmit power of a radio operating in a cellular environment, the cellular environment comprising a plurality of cells that transmit power control commands to the radio, the radio comprising a variable gain amplifier, a maximum gain setting, and a power control command accumulator that generates a gain adjust signal, the said apparatus comprising : transmitter means for transmitting a signal with the variable gain amplifier; measuring means for determining a gain adjust signal in response to the transmit power control commands; detector means for detecting a power value of the transmitted signal; digitizing means for digitizing the power value; comparing means for comparing the digitized power value to the maximum gain setting; means for, if the digitized power value is greater than the maximum gain setting, decreasing the gain adjust signal by a predetermined amount of every predetermined unit of time until the gain adjust signal is less than the maximum gain setting; and means for, if the digitized power value is less than or equal to the maximum gain setting, varying the gain of the variable gain amplifier in response to the gain adjust signal.
12. The apparatus as claimed in claim 1 wherein limiting means is provided for limiting transmit power of a radio operating in a cellular environment, the cellular environment comprising a plurality of cells that transmit power control commands to the radio, the radio comprising a variable gain amplifier, a maximum gain setting, and a power limiting accumulator, the .said apparatus comprising transmitter means for transmitting a signal with the variable gain amplifier, measuring means for

determining a gain adjust signal in response to the transmit power control commands; detector means for detecting a power value of the transmitted signal; digitizing means for digitizing the power value; comparing means for determining a difference between the digitized power value and the maximum gain setting; means for integrating the difference to generate a gain control signal, tlie gain control signal being limited to a predetermined range; means for adjusting the variable gain amplifier with the gain control signal; means for, if the gain control signal is less than a predetermined value, prohibiting the gain adjust signal from changing the variable gain amplifier in response to the transmit power commands.
13, An apparatus for limiting transmit power of a radio operating in a cellular environment, substantially as herein described with reference to the accompanying drawings.

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Patent Number

187616

Indian Patent Application Number

96/MAS/1995

PG Journal Number

30/2009

Publication Date

24-Jul-2009

Grant Date

29-Nov-2002

Date of Filing

30-Jan-1995

Name of Patentee

QUALCOMM INCORPORATED

Applicant Address

6455 LUSK BOULEVARD, SAN DIEGO, CALIFORNIA 92121

Inventors:

#	Inventor's Name	Inventor's Address
1	ANA L. WEILAND	2042 SHERIDAN ROAD, ENCINITAS CALIFORNIA 92024
2	RICHARD K. KORNFELD	12384 BRICKELLA DRIVE, SAN DIEGO, CALIFORNIA 92129
3	RICHARD J. KERR	3644 CAMINITO CIELO DEL MAR, SAN DIEGO, CALIFORNIA 92130
4	JOHN E MALONEY	10030-53 SCRIPPS VISTA WAY, SAN DIEGO, CALIFORNIA 92131
5	NATHANIEL B WILSON	11346-8 PORTOBELO, SAN DIEGO, CALIFORNIA 92124

PCT International Classification Number

H04B7/005

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA