MXPA00000478A - Automatic gain control for a receiver and method therefor - Google Patents

Abstract

A receiver automatic gain control includes a variable gain receiver having a control input and responsive to a gain control signal for adjusting the output level of the receiver. A controller is coupled to the variable gain receiver. The controller monitors a received signal quality and a received signal power level. The controller generates a control signal for controlling the gain of the variable gain receiver as a function of the signal quality and the power level. The controller controls the gain as function of the receiver signal power level and selectively controls the gain as a function of the signal quality.

Description

AUTOMATIC CONTROL OF GAIN OF A RECEIVER AND METHOD FOR THE SAME FIELD OF THE INVENTION The present invention relates to automatic gain controls, and more particularly to the automatic gain control of a receiver, and to the allocation of a channel.

BACKGROUND OF THE INVENTION A variety of devices including transceivers used in communication with other compatible devices are known. Examples of these devices include wireless communication devices such as radiotelephones, which may be wireless, bi-directional radios, base stations, paging devices, and communication devices by cable or wireline such as modems, data terminals or the like. These devices typically include circuitry for controlling the gain in the transmission and reception path, such that the reception signals are transferred at a somewhat uniform signal level. In particular, it is difficult for wireless communication systems to provide power control, as is the environment, due to its very dynamic nature. The distance between P10 0 / 00MX mobile devices, or a mobile device and a base station, undergoes constant change. Additionally, the transmission path may change as the obstructions move in the transmission path between the mobile device and another device. For example, constructions, hills, and other obstructions enter and exit the transmission path of a cell phone as it moves. These obstructions will negatively impact the level of the signal received by the base station and the mobile device during a communication exchange. Therefore, systems such as the Global System for Mobile Communications (GSM), require a power control of radio frequency (RF). The objective of this power control is to achieve the minimum amount of power necessary for an adequate quality of wireless communication. By limiting the level of the communicated signals, the average amount of RF spectral energy detected by mobile stations and surrounding bases is reduced. This has the effect of reducing the interference, since the level of interference in an RF channel is the sum of the contributions of all RF sources. The purpose of the RF power control is, therefore, to reduce the amount of interference of the channel present in each channel. This P1020 / OOMX increases link reliability and channel capacity. For example, the GSM standard for circuit-switched voice telephony specifies that the interval over which the RF power of the base station subsystem is to be controlled (BSS) extends from the maximum of the station to 30 dB below the maximum. The standard specifies similar requirements for the mobile station, depending on the type of power output of the mobile device. However, for the Radio Service of Packages, General (GPRS), power control is significantly more difficult to achieve. This is due to the varying length of the data packets and variations in the time period between the transmission of the data packets between the base station and the mobile station in the GPRS mode. The control method specified for the transmissions from the base station to the mobile station in the GSM GPRS example, requires that the BTS must transmit the four bursts that comprise an individual data block at the same power level. However, this standard also allows control of the base transceiver station (BTS) on a block-by-block basis, based on the Channel Quality Reports. The degree of power control in the P1020 / 00MX transmission of the data blocks in accordance with this example standard can be extended from the value of the output power transmitted by the base transceiver station on the broadcast control channel (BCCH) to a level of 30 dB per below the BCCH carrier. Additionally, a mobile GPRS apparatus may be required to receive downlink data blocks in more than one time slot. For example, the amplitude of two intervals of four bursts comprising a data block may differ. These factors combine to present difficulties in the implementation of the effective AGC function for mobile stations. One purpose that has been made is to provide data in a transmission indicating the amount of attenuation, relative to the RF power level of the BCCH bearer, at which the next data block of the base transceiver station will be transmitted. However, their problems are associated with the acceptance of this type of information. For example, it is difficult to achieve an initial acquisition of automatic gain control (AGC). There are problems associated with processing actions for adjusting the AGC level in the absence of a decodable signal, such as intermittent decoding errors distributed over a downlink transfer. They will be presented P1020 / 00 X additional problems when trying to decode the data in more than one time interval. However, something more problematic is the achievement of the allocation of the dynamic time slot for mobile transmissions, where the mobile device is required to inspect all time intervals, some of which can be directed to other mobile devices, in order to receive an assignment of which uplink time interval is the one to be transmitted. Accordingly, there is a need for an improved method for providing automatic gain control in a receiver for a dynamic system.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic circuit in the form of a block diagram illustrating a communication system. Figure 2 is a schematic circuit in the form of a block diagram illustrating a transmitter and a processor. Figure 3 is a schematic diagram in the form of a block diagram illustrating a receiver and a processor. Figure 4 is a schematic diagram illustrating a mobile radiotelephone system. Figure 5 is a schematic diagram that P1020 / 00MX represents GPRS data. Figure 6 is a schematic diagram representing a data transfer sequence. Figure 7 is a schematic diagram representing the allocation of multiple mobile data frames. Figure 8 illustrates the mobile reception amplitude as a function of distance. Figure 9 illustrates data packets. Figure 10 represents a PDCH carrier relative to a BCCH bearer. Figure 11 represents a zone channel assignment for a base station.

DETAILED DESCRIPTION OF THE DRAWINGS An automatic gain control of the receiver includes a variable gain receiver having a control input and is responsive to a gain control signal for adjusting the output level of the receiver. A controller coupled to the variable gain receiver. The controller inspects the quality of the received signal and the power level of the received signal. The controller controls the gain of the variable gain receiver as a function of the signal quality and the power level of the carrier. The controller selectively controls the gain as a function of the signal power level P1020 / OO X received and the quality of the received signal. The gain control ensures the operation in the linear portion of the amplifiers of the receiver. As a result, an appropriately decodable signal is produced by the receiver for the data blocks directed to the remote receiver. A communication system 100 (Figure 1) includes a local transceiver 102 and a remote transceiver 104 connected to a communication link 106. The local transceiver 102 may be in any communication device such as a modem, a base station, a terminal data, or similar. The remote transceiver 104 may be in any communication device such as a portable telephone, a modem, a satellite telephone, a data terminal or the like. The communication link 106 may be a cable line, a cable, a wireless air link, or any other means of transmission. The remote transceiver 104 illustrated includes a microphone 110 and a loudspeaker 112 coupled to a processor 114. The transceiver 104 includes a transmitter 116 and a receiver 118 connected to an antenna 120. The remote transceiver is coupled to a transmitter 132, a receiver 134, and a switch 136. The "switch" can be any communication device such as a router, a switch or a signal source that communicates signals to and from P1020 / 00 X from the processor 130. The transmitter 132 and the receiver 134 are connected to an antenna 138. The transmitter 132 of the local transceiver 102 illustrated includes a variable gain amplifier 202 (FIG. 2) controlled by the processor 130. The amplifier 202 is responsive to the control signals of the processor 103 to control the amplitude of the signal emitted from the local transceiver 102 for communication to the remote transceiver 104. The receiver 118 of the remote transceiver 104 operates under the control of a processor 114. The processors or controllers 114130, each can be implemented using a digital signal processor (DSP), a microprocessor, a microcontroller, a programmable logic unit (PLU), a logic circuitry or a combination thereof. The remote receiver 118 includes a mixer 302 (FIG. 3), a variable gain amplifier 304, a mixer 306, a variable gain amplifier 308, a filter 310, and a variable gain amplifier 312. The mixers 302 and 304 are provided to demodulate and lower the frequency of the bearer signal, desired (for example, the communication channel in a cellular system, down to an intermediate frequency). The variable gain amplifiers 304, 308 and 312 are sensitive to gain control signals P1020 / 00MX from the processor 114 to control the gain of the received signal, such that the signal transfer at 314 is at a desired amplitude to ensure the linear operation of the amplifications on the transceiver that processes the received signal. The filter 310 removes the signals outside the frequency band of the received, desired signal. The automatic gain control of the system operates by the local transceiver 102 when determining first where to adjust the power level of the transmitter 132 for the packet data channel (PDCH) in relation to the broadcast carrier channel (BCCH). The decision is made in the processor 130 based on a measurement of the signal quality received from the remote station 104 and the BCCH bearer in the received bearer power, reported by the remote transceiver 104 back to the local transceiver 102. In In particular, there is a certain level of power in which increases in the transmission power of the local station 102 will not produce increases in the quality of the signal received from the remote transceiver 104. This is because all the data that is transmitted is demodulate and recover exactly by the remote receiver 118 the transmission power of the transmitter 132. The processor 130 determines how low the transmission power of the transmitter can be reduced.

P1020 / 00 X local transceiver 132, before appreciable degradation occurs in the quality of the received signal, measured in the receiver 118 by the processor 114. This determination is made based on the measurement of the signal quality, elaborated by the processor 114 of transceiver 104, measurement of signal quality which for example may be the bit error rate measured by the remote receiver. The bit error rate indicates whether the amount of data received by the receiver 118 is being decoded accurately. If this is the case, then the gain of the transceiver 132 can be decreased until the bit error rates decline. The critical threshold occurs when the reductions in transmission power produce increases in the bit error rate reported by the remote transceiver 104 back to the local transceiver 102. Based on these criteria, the local transceiver can adjust its power level of transmission for the data packets sent in the DPCH. The receiver 118 of the remote station 104 provides additional automatic gain control when the transmitter 132 can no longer reduce its gain, but the receiver is transferring the signal above the optimum threshold at which the additional gain will not result. Increases in transceiver performance P1020 / 00MX 104. This automatic gain control of the receiver is provided to ensure that the level of the received signal transferred in 314 is not as great as that of the receiver amplifiers (shown and not shown) are not operating in their linear range , thereby causing the distortion of the reception data, resulting in bit errors. The automatic gain control of the receiver uses measurements of the quality of the reception signal, for example by monitoring the bit error rate and the magnitude of the received carrier signal, or other signal indicative of the interference level for the receiver link. communication 106. These measurements can advantageously be the same measurements reported back to the local receiver as described above. In particular, if the reported ratio of the signal strength of the carrier to the bit error rate measurement is less than or equal to an optimum threshold level (the level at which the increase in the power level is not produces an increase in signal quality as measured by the remote transceiver 104) no additional power control is applied to the receiver. However, if the ratio of the carrier signal to the bit error rate is above the optimum threshold level then the gain of the receiver is attenuated to its maximum attenuation level, by P1020 / 00MX example, in steps. It is further contemplated that the remote transceiver 118 may follow the value of the BCCH bearer's broadcast over the local site. The BCCH bearer is a continuously transmitted signal having a pre-determined fixed level when it is transmitted by the local transceiver 102. Due to the fixed transmission level, the magnitude of the BCCH bearer when it is received at the remote station 104 is indicative of the loss of signal in the communication channel. By adjusting the receiver gain inversely to the magnitude of the received carrier signal, the gain of the receiver is increased when the remote transceiver is receiving a weaker signal. If the quality of the reported signal, measured on the remote transceiver 104 is greater than the optimum threshold level and the difference between the reported and optimum signal level is less than or equal to the maximum amount of power reduction that the transmitter 132 can apply to the transmission, then power control is applied to the remote receiver 104 to maintain the threshold power level transferred by the gain controls 304, 308, 312 of the receiver, under the control of the processor 114. In this way , a control system P1020 / OO X gain can extend the gain control of both the local transceiver 102 and the remote transceiver 104. The automatic gain control follows the value of the BCCH bearer level from the local transceiver If the measured signal from C to I is reported is greater than the optimal signal level, and the difference between the measurement of the quality of the reported and optimal signal is greater than the maximum amount of power reduction, a base station can not apply to a downlink transmission, then the power control is applied to the receiver 118. The automatic gain control (AGC) in the receiver will subsequently follow the value of the BCCH bearer level of the local transmitter to provide automatic gain control in the receiver. The carrier signal is measured by detecting at the remote receiver 104 the level of the desired carrier signal broadcast from the desired local transceiver 134. It is contemplated that the desired carrier signal will be coded such that it is identifiable. In this way, the remote transceiver can identify and measure the carrier signal from the desired source. The interference can result from a variety of different sources. In Figure 4 a similar system 400 is illustrated. The local transceiver 102 is in a base station. The remote transceiver P1020 / 00MX 104 is on a portable radiotelephone. The interference may result from transmissions from the base stations 402 different from the desired local transceiver. In a time-division system, interference can be caused by transmissions from other portable cellular phones 404-408 that communicate at the same frequency, but at other time intervals. Interference can also result from other devices operating at other frequencies. It is contemplated that the interference can be measured by the bit error rate. It is known that the GSM system, for example, is used to measure the interference for an assisted, mobile non-manual control, known as the ratio of C to I. This relationship is a measurement of the carrier to interference. The characteristics of the GPRS data transfer for the GSM system make automatic gain control particularly problematic. Data transfer is provided by packet switching. Instead of a dedicated time slot, each data transfer from the local transistor to the remote transistor is achieved by using packets that have an adjusted sequence, data, and a chill sequence as depicted in Figure 5. The duration of the periods of time between the data packets is P1020 / 00MX can be used to service other remote devices that operate on the same carrier frequency. In this GPRS system, there is no guarantee that a signal will be provided for the cellular radiotelephone, represented by the remote transceiver 104, at any particular time. The transmission of GPRS data is illustrated in Figure 6. The period of time between the packets is separated by intervals which can be separations in seconds or hours, depending on the demands of data transfers of the mobile application or other needs of the mobile device.

Additionally, the periods for each transmission (marked "D") are not uniform, although the adjustment and abatement for each package will be substantially uniform. This makes it difficult to adjust the gain of the local receiver in time to receive and decode the packet data component. In Figure 7, the frame allocation to the mobile devices (radiotelephones) 104, 404, 405 is illustrated. In the GPRS, there are times when the mobile radiotelephones 104, 404, 405 may need to be aware of all the blocks of communication. Downlink data to decode the address fields, which is the method by which a mobile device determines if a data block was proposed for it. The main purpose of control of P1020 / OOMX power is to reduce the amount of average RF energy radiated around the antenna 138 of a base station incorporating the local transceiver 102, thereby reducing the amount of co-channel interference to the mobile apparatuses 104, 404, and 405 that share the same channel. The smaller the co-channel interference from the perspective of a set of mobile radiotelephones, the greater the number of mobile radiotelephones that a base station can serve in an environment such as a cellular environment where downlink power control is used on the server's co-channel base station sites. The more the downlink power levels of the base stations are reduced, the lower the co-channel interference to the mobile apparatuses 104, 404, 405 in the margin areas of the cells covered by other base stations. The base stations reduce their level of downlink power to the mobile devices based on how the signals of the base station are receiving the mobile stations, as determined from the measurement of the signal quality of the mobile station, analyzed before. The longer the communication link 106 between a local transceiver 102 of the base station and a mobile remote station 104, the greater the attenuation of the signal along the route P1020 / 00MX 106. As shown, the closer the mobile remote station 104 is to the local transceiver 102 of the base station, the more the base station will apply the power control, thereby reducing the amount of power distributed to the remote transceiver 102 mobile and other radiotelephones. Figure 8 illustrates the plane for power control for a mobile device in a somewhat dense environment, such as an urban cell environment. The upper curve represents the level of the desired signal received by the mobile remote transceiver 104 if the local transceiver 102 of the base station transmits at full power. The power level decreases as the distance increases. The lower curve represents the signal level of the desired signal received by the mobile remote transceiver 104 with the local transceiver 102 transmitting to its maximum attenuation level. The signal received by the mobile remote transceiver 104 is illustrated in Figure 9 when the local transceiver 102 of the base station has power control. Because the BCCH bearer is transmitted at a constant amplitude, the level of the BCCH detected by a mobile apparatus will increase as the mobile apparatus moves closer to the base station. Prior to the point Tl, the level of the PDCH bearer sent is identical to the BCCH bearer. The power control in the P1020 / 00MX mobile device is not used at this point since the level of the received signal is at the threshold level where the decreases in signal level result in a degradation of the ratio of C to I to an unacceptable level . The level measurements from C to I are reported in the interference report to the base station as an indication of the bit error rate and the level of the bearer signal received. During interval 2, the base station communicates the data in the PDCH to another mobile apparatus 404 that is closer to the antenna 138. In the interval 3, the transmitter 132 of the local transceiver 102 attenuates the transmitted PDCH to the mobile remote transceiver 104 since the ratio of C to I will tolerate a lower transmission level without affecting the decoding of the data. In this way, the power level of the PDCH is reduced using a variable gain control 202 of the transmitter such that the received signal is at an acceptable quality level. During interval 4, the base station transmits to mobile radiotelephone 404. During subsequent intervals 5, the base station transmits to mobile remote transceiver 104 with additional attenuation. An additional algorithm is provided to significantly improve the performance of the system. The additional algorithm is AGC performed in the P1020 / 00MX receiver 118 of the mobile remote transceiver 104. The receiver 118 uses the bearer-to-interference ratio used to adjust the gain of the transmitter 132 of the local station, to periodically adjust the gain of the receiver, which helps to ensure the operation of the amplifiers of the receiver in the linear region of its transfer curve. This, in turn, ensures proper decoding of the proposed demodulated data for the remote, mobile transceiver 104. The GSM GPRS specification requires, for example, that radio telephones 104, 404, 405 repetitively signal mentions and communicate this information to the base station. In particular, it is contemplated that the base station will reduce the power of the downlink bearer in the PCDH relative to the power of the BCCH bearer if the ratio of the bearer signal to the bit error rate reported by the mobile apparatus to the base station is sufficient to support this power control. Additionally, it is contemplated that if the level of the BCCH bearer reported by the mobile apparatus to the base station is above a certain threshold at which the reduction of the transmitted power will still result in an appropriately decoded signal in the mobile apparatus. Now the power control will be described P1020 / 00MX in the receiver with respect to the following: C is a measurement of the BCCH bearer, I is an interference measurement which is preferably the bit error rate of the received data; Vb is the value of the received BCCH bearer; Co is the value of the ratio of C to I when it is optimal; Cr is the ratio of C to I, measured, real that the remote transceiver reported; Rm is the maximum allowable value of the downlink power reduction that the local transceiver can apply (e.g., 30dB on the transmitter 132); Copt, indicates that the ratio of C to I reported is optimal; Cm indicates that the ratio of C to I is maximum (it is at a point over which the increase in the power of the received signal does not result in a non-attainable benefit); P is the power control level applied by the local transceiver 102; and Pm indicates that the power control is applied at a maximum allowable level (Vb-Rm). The power control is provided as follows: If Cr is less than Co, then C a l is not Optimal P1020 / 00MX power control is not applied to receiver 118 here, and AGC follows the value of the BCCH bearer level associated with local transceiver 102. If Cr is greater than Co, Cr-Co is lower what Rm, then the power control is applied to the receiver 118 of the remote transceiver to maintain Co in such a way that the AGC in the receiver follows the value of Vb- (Cr-Co). If Cr is greater than Co, and (Cr-Co) is greater than Rm, the power control in the receiver is applied to the maximum allowable degree, and in such a way that the AGC function follows the level of the BCCH carrier of the service cell minus the maximum allowable power level of the power control in the receiver . As the mobile station reaches the base station with the time going through the base of Figure 10, the level of the BCCH bearer is increased. The levels of the PDCH and BCCH bearers are equal (in region 1) until the signal quality as determined by the ratio of the ratio of C to I as reported and the level of the BCCH bearer are sufficient to guarantee the power control in the uplink PDCH. The power level of the PDCH is reduced in the transmitter to the mobile station to maintain the optimum C to I ratio with the power level P1020 / 00MX maximum transmitted, thereby minimizing interference and maximizing cell occupancy. Once the mobile device is not near the transmit antenna of the base station so that the maximum power control range has been reached, the level of the PDCH carrier will be equal to the level of the BCCH carrier minus 30 dB (represented by region 3). At this point in the operation of the system, the signal level of the receiver can cause the receiver to operate in the non-linear region. It is at this point that the receiver's automatic gain control provides additional attenuation at the receiver to remove this distortion. It is further contemplated that the dynamic allocation of channels will be provided in the base station associated with the local transceiver 104 in such a way that the mobile devices having a common distance (losses in the signal path) are in a common channel . In this way, the mobile devices will be placed in a channel based on their distance from the antenna 138. In particular, the mobile devices in the cell of the base station will be assigned to the respective zones of the cell. All mobile devices in the same area, in this way in different similar distances, are placed in a common channel. This allows a further improvement in the P1020 / 00 X system performance. In particular, the base local transceiver serving a plurality of remote devices 104, 404, 405 can group radiotelephones at common distances in common areas. Figure 10 shows zones 1, 2, 3 and 4. A first channel will be assigned to those mobile devices that share zone 1. The power control provided to the packets transmitted to the radiotelephones in zone 1 in this way may be at similar levels. This facilitates the ability of the base station to provide a signal to all mobile devices in its area with a comparable attenuation of the base station, reducing the amount of change required for transmissions to different mobile devices and allowing service to more mobile devices in areas that have better performance, and providing reduced co-channel interference. Accordingly, it can be seen that an improved gain control system is described. The system provides a significant improvement in systems such as cellular systems, where gain control for packet transmissions is particularly challenging.

P1020 / 00MX

Claims (5)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following CLAIMS is claimed as property 1. An automatic gain control of a receiver, characterized by: a variable gain receiver which has a control input and is responsive to a gain control signal to adjust the output level of the receiver; and a controller coupled to the variable gain receiver, the controller that inspects the quality of the received signal and a level of the received signal power, the controller that generates a control signal to control the variable gain receiver signal as a function of the signal quality and the power level, the controller that controls the gain as a function of the power level of the received signal that selectively controls the gain as a function of the quality of the signal. 2. The automatic gain control of a receiver according to claim 1, wherein the controller controls the variable gain receiver as a function of the signal quality measurement when the signal quality measurement exceeds a predetermined threshold
2. P1020 / 00 X
3. 3. The automatic gain control of a receiver according to claim 2, wherein the measurement of the signal quality is generated as a function of the signal interference.
4. 4. The automatic gain control of a receiver according to claim 3, wherein the measurement of the signal quality is a function of the ratio of the level of the received signal to the signal interference.
5. 5. A method for providing channel allocation to remote transceivers, characterized by the step of: determining the gain control zone for a plurality of remote transceivers; and assigning a channel to those mobile devices in a common area of gain control. P1020 / 00MX