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AssigneeCingular Wireless II, LLC
InventorsJari M. Heinonen, Michael R. Hirano, Hongliang Zhang
Estimating the term…
Automatic gain control (AGC) methods and apparatus suitable for use in orthogonal frequency division multiplexing (OFDM) receivers are described. One AGC method includes the steps of repeatedly performing a first AGC process which adjusts amplifier gain based on determining that a signal level of multiple time sample values is outside a limit set by a first predefined threshold; and repeatedly performing a second AGC process which adjusts the amplifier gain based on determining that a signal level of multiple frequency sample values associated with a plurality of pilot tones is outside a limit set by a second predefined threshold. Preferably, the first AGC process is performed repeatedly at a first rate and the second AGC process is performed repeatedly at a second rate that is less than the first rate.
An automatic gain control (AGC) method for use in an OFDM receiver, the AGC method comprising:
An automatic gain control (AGC) method for use in a wireless OFDM receiver, the AGC method comprising:
Automatic gain control (AGC) circuitry for an OFDM receiver, comprising:
An automatic gain control (AGC) method for use in a wireless OFDM receiver, the AGC method comprising:
A wireless OFDM receiver having an automatic gain control (AGC), comprising:
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Multicarrier modulation systems: arrangements specific to the receiver only
Gain control in amplifiers or frequency changers: digital control of analog signals
In amplifiers having semiconductor devices: control of digital or coded signals
Digital communication
Term end not estimated
1. Field of the Invention
The present invention relates generally to the fields of automatic gain control (AGC) in orthogonal frequency division multiplexing (OFDM) communication receivers.
2. Description of the Related Art
FIG. 1 is a diagram of a wireless communication system, such as a fixed wireless system utilizing orthogonal frequency division multiplexing (OFDM) communication techniques, which includes one or more base units and one or more receiver units;
FIG. 2 is a block diagram of electronic components of a receiver unit in the wireless communication system of FIG. 1;
FIG. 3 is a block diagram of more specific electronic components of the receiver unit of FIGS. 1 and 2, which is more closely related to the automatic gain control (AGC) of the present invention;
Automatic gain control (AGC) methods and apparatus suitable for use in orthogonal frequency division multiplexing (OFDM) receivers are described. One AGC method includes the steps of repeatedly performing a first AGC process which adjusts amplifier gain based on determining that a signal level of multiple time sample values is outside a limit set by a first predefined threshold; and repeatedly performing a second AGC process which adjusts the amplifier gain based on determining that a signal level of multiple frequency sample values associated with a plurality of pilot tones is outside a limit set by a second predefined threshold. Preferably, the first AGC process is performed repeatedly at a first rate and the second AGC process is performed repeatedly at a second rate that is less than the first rate.
FIG. 1 is an illustrative representation of a wireless communication system 100 which utilizes orthogonal frequency division multiplexing (OFDM) or OFDM-like communication methodologies. Wireless communication system 100 includes at least one base unit 106 having one or more antennas 108, and a plurality of remote units 102 (“RUs” or “receiver units”), such as remote unit 104. Base unit 106 and remote units 102 communicate via radio frequency (RF) signals, such as RF signals 110 between base unit 106 and remote unit 104. Wireless communication system 100 can make use of a number of different communication techniques, such as frequency division multiple access (FDMA), time division multiple access (TDMA), or time division duplex (TDD). Preferably, wireless communication system 100 is a fixed wireless system (FWS), where base unit 106 provides telephone and high-speed data communication to each one of a number of fixed-location subscribers equipped with an RU. Also, the RF OFDM communications signals are modulated using 16 quadrature amplitude modulation (QAM), but could be modulated using quadrature phase shift keying (QPSK).
FIG. 2 is a block diagram of electronic components 200 of receiver unit 104 in wireless communication system 100 of FIG. 1. As shown, electronic components 200 include diversity antennas 204 and 206 coupled to an airlink physical interface 202, a field programmable gate array (FPGA) 208, two Fast Fourier Transform (FFT) application-specific integrated circuits (ASICs) 210, an airlink digital signal processor (DSP) 212, a time generator FPGA 214, an audio coder DSP 216, a controller 220, a telco interface 999, and power supply circuitry 224. Airlink physical interface 202 has a two-branch RF receiver with two analog-to-digital (A/D) converters, and a single branch RF transmitter with a digital-to-analog (D/A) converter. FFT ASICs 210 and FPGA 208 provide a time-frequency domain translation engine for OFDM waveforms. Airlink DSP 212 performs airlink physical layer processing and audio coder DSP 216 performs the OFDM waveform coding and decoding functions. Time generation FPGA 214 provides a serial time division multiplex (TDM) interface along with hardware support for RF control. Telco interface 222 has a subscriber link interface circuit to provide an interface to a customer's telephone wiring. Controller 220 provides control for most of these devices, and power supply circuitry 224 provides electrical power for operation of the devices. Preferably, airlink and audio coder DSPs 212 and 216 utilize DSPs provided by Texas Instruments and controller 220 utilizes an MC68360 Quad Integrated Communications Controller (QUICC) CPU provided by Motorola, Inc.