Title of Invention: Method for adaptively controlling amplifier linearization devices
Abstract: A method for linearizing amplifiers by measuring the intermodulation products at the output of the linearized amplifier using minimum additional hardware without the performance problems associated with pilot tones. In one embodiment, the amplifiers are adaptively linearized using performance monitoring radios. Specifically, the performance monitoring radios are used to measure the signal levels of the intermodulation products in unused communication channels. Such measurements are then used to adaptively linearize the amplifiers and reduce the levels of intermodulation products.
Detailed Description: Part PAC: DETAILED DESCRIPTION
Part PAR: FIG. 1 shows a wireless communication 10 used in accordance with the present invention. Wireless communication system 10 comprises a mobile switching center (MSC) 12 and base stations 14, 16, 18. Each of the base stations 14, 16, 18 are connected via T1 lines 22, 24, 26 to MSC 12, which is connected to a public switching telephone network (PSTN) 28. Base stations 14, 16, 18 provide wireless communication services to mobile-telephones 46 within geographic coverage areas referred to as cells 34, 36, 38. Associated with each of the base stations 14, 16, 18 are sets of communication channels for communicating voice and/or data messages to and from mobile-telephones within the geographic coverage areas, wherein the communication channels have associated frequencies. MSC 12 is operable to connect mobile-telephones to PSTN 28 via base stations 14, 16, 18, and to manage the resources of base stations 14, 16, 18 including assigning and unassigning the communication channels belonging to base stations 14, 16, 18. In order to assign and unassign communication channels, MSC 12 should have a priori knowledge or be operable to determine whether a communication channel is currently assigned to or used by one or more mobile-telephones. Alternately, base stations 14, 16, 18 should be operable to manage its own resources.
Part PAR_2: Each of the base stations 14, 16, 18 are equipped with cellular radio and/or Personal Communication System (PCS) transceivers 40, 42, 44 having performance monitoring radios, amplifiers and linearizers, all of which are well-known in the art. The performance monitoring radios being operable to receive and demodulate signals and to measure signal strength on a per communication channel basis; the amplifiers being operable to amplify the desired signals; and the linearizers being operable to linearize the amplifiers. The performance monitoring radios will have channel bandwidths corresponding to the standard in use, i.e., 30 kHz for IS-136 or 1.25 MHz for IS-95. The performance monitoring radios are utilized by the present invention to measure the signal level of the intermodulation products for purposes of tracking the characteristics and enhancing the linearization of the amplifiers, as will be described herein.
Part PAR_3: When signals are to be transmitted by one of the base stations 14, 16, 18, the signals are first amplified by the cellular radio/PCS transceivers 40, 42, 44. Amplification of the signals may create intermodulation products that will impair transmission or exceed some acceptable threshold or standard. Whether or not such intermodulation products are present depend on the frequencies of the signals. If these intermodulation products are present, the level of the intermodulation products are reduced using the linearizers and performance monitoring radios. Specifically, the present invention utilizes the performance monitoring radios to measure the levels of the intermodulation products falling on unused communication channels, and the linearizers to adaptively reduce the level of the measured intermodulation products.
Part PAR_4: The performance monitoring radios are used to measure the levels of the intermodulation products falling on unused communication channels (i.e., communication channels over which none of the amplified signals will be transmitted). Since the communication channels over which the signals are being transmitted are known, then the frequencies associated with such communication channels are also known. Based on these known frequencies, it is possible to calculate the frequencies at which the intermodulation products will fall or be created, as is well-known in the art. For example, for two signals: wagnerdouglas@example.org and the wagnerdouglas@example.org, a third-order non-linearity will produce intermodulation wagnerdouglas@example.org -F.sub.2 and 2F.sub.2 -F.sub.1. For three signals: wagnerdouglas@example.org, wagnerdouglas@example.org, and the other wagnerdouglas@example.org, the intermodulation products will wagnerdouglas@example.org +F.sub.2 -F.sub.3, F.sub.1 +F.sub.3 -F.sub.2, etc. Therefore, given the knowledge of the frequencies of the signals and whether a communication channel is currently assigned or used, as mentioned earlier, it is possible to determine 1) the frequencies at which the intermodulation products will fall, and 2) whether those frequencies fall on unused communications channels where the level of the intermodulation products can be measured directly. Such information allows the performance monitoring radios to be tuned to unused communication channels where the intermodulation products are present and measure the corresponding signal levels. Adaptive means can then be used to adjust the linearizer to reduce the level of the intermodulation products falling on the unused communication channels.
Part PAR_5: Note that the intermodulation products falling on used communication channels are not being measured and used for adaptively adjusting the linearizer. The reason being because other signals are also present on those communication channels (e.g., voice and/or data traffic being transmitted between mobile-telephones and base stations). Thus, the signal levels of the intermodulation products falling on used communication channels cannot be measured directly by the performance monitoring radios. By contrast, the intermodulation products falling on the unused communication channels can be measured directly by the performance monitoring radios because only the intermodulation products should be present on those communication channels or frequencies.
Part PAR_6: FIG. 2 illustrates a schematic diagram of one possible cellular radio/PCS transceiver 60 having an amplifier linearization device 62 used in accordance with the present invention. As shown in FIG. 2, the amplifier linearization device 62 comprises an amplifier 64, a performance monitoring radio 66 and a linearizer, wherein the linearizer includes directional couplers 70, 74, 84, gain and phase adjusters 72, 78, delays 75, 81, cancellation circuits 76, 82, correction amplifier 80 and controller 86. In this example, controller 86 receives information (from a base station or a mobile-switching center) indicating which communication channels are used or unused. Based on this information and the frequencies of the signals, the controller 86 instructs the performance monitoring radio 66 on which unused communication channels to measure signal levels for the intermodulation products created by the signals.
Part PAR_7: The performance monitoring radio 66 will measure the signal levels of such intermodulation products in the unused communication channels and relay these measurements to the controller 86. The controller 86 will use the measurements from the performance monitoring radio 66 (and/or the output signal from the cancellation circuit 76) to adaptively control the gain and phase adjusters 72 and/or 78 to reduce the level of the intermodulation products in the output of the feed-forward amplifier 62. Specifically, the gain and phase adjusters 72 and/or 78 are adjusted to modify the amplitude and phase of signals entering them such that the signal level of the intermodulation products are reduced at the output of the amplifier linearization device 62.
Part PAR_8: Note that when certain types of linearizers are adjusted, gain is affected as well as linearity. This is undesirable since the goal is generally to reduce the levels of the intermodulation product levels without affecting the signal levels of the signals. If only the intermodulation product levels are measured, an adaptive system might result in the linearizer simply reducing the gain and hence output signal level of the system. For this reason, it is desirable to hold the output power of the system constant while adjusting the linearizer. This can be done by measuring the signal level of a signal with the performance monitoring radio, and adjusting the output accordingly. Measurements of the signal power, intermodulation power, and their ratio will yield enough information to correctly adjust the linearizer.
Part PAR_9: If, for whatever reason, a performance monitoring radio is not available, a simple radio could be added to the linearized amplifier system to perform the function of a performance monitoring radio. This would of course add to the cost, but at least the difficulties associated with pilot tones would be avoided.
Part PAR_10: Although the present invention has been described in considerable detail with reference to certain embodiments, other versions are possible. Therefore, the spirit and scope of the present invention should not be limited to the description of the embodiments contained herein.


{'bibliographic_information': "{'Patent Number': '06160996&', 'Series Code': '9', 'Application Number': '0528331', 'Application Type': '1', 'Art unit': '275', 'Application Filing Date': '19980331', 'Title of Invention': 'Method for adaptively controlling amplifier linearization devices', 'Issue Date': '20001212', 'Number of Claims': '7', 'Exemplary Claim Number(s)': '1', 'Assistant Examiner': 'Kincaid; Lester G', 'Primary Examiner': 'Eisenzopf; Reinhard J.', 'Number of Drawing Sheets': '2', 'Number of figures': '2'}", 'source_file': './grant/2000/pftaps20001212_wk50.txt', 'source_data': 'USPTO-Grant'}