At&t Wireless Services, Inc.

Cingular Wireless Ii, LLC

Radioframe Networks, Inc.

Jari Heinonen

Michael Hirano

Hongliang Zhang

Steven E McMeekin

Elliott Hoole

Mary Jesse

Mike Hirano

Greg Veintimilla

Brian Schladetzky

Louis Leung

Reijo Savola

William H Warner

An open loop power control system for an orthogonal frequency division modulation (OFDM)-based fixed/mobile wireless system. A preferred system and method comprise measuring signal strength of received interference-free pilot tones transmitted by a base station; determining pathloss according to received power level of pilot tones; and controlling transmit power level of the remote unit by adjusting transmitting channel attenuation according to the pathloss determined in the preceding step. The method may further comprise monitoring at the base station the received signal level of uplink pilot tones; checking if received signal level of uplink pilot tones is outside pre-set limits around the target level at the start of each call; and sending a command to the mobile station over the broadcast channel to increase or decrease the transmitting power level.

Transmit power control for an OFDM-based wireless communication system

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.

Automatic gain control methods and apparatus suitable for use in OFDM receivers

A method, apparatus and system detects a loss of synchronization between a transmitter and a receiver in a multiple-carrier communication system such as an OFDM system. A phase-frequency synchronization detector determines when the receiver has lost synchronization with the transmitter based on a phase-frequency relationship of plurality of pilot signals transmitted at different frequencies from the transmitter and received at the receiver. A loss of synchronization is detected when a slope of a line defined by the phase-frequency relationship exceeds a timing threshold more at a rate in excess of an occurrence threshold within a time period.

Apparatus and method for synchronization in a multiple-carrier communications system by observing a phase-frequency relationship of a plurality of pilot signals

A method, apparatus and system detects a loss of synchronization between a transmitter and a receiver in a multiple-carrier communication system such as an OFDM system. A plurality of synchronization indicators are observed to determine whether a loss of synchronization between a transmitter and a receiver in the wireless system has occurred. In one embodiment, the receiver is determined to have lost synchronization with the transmitter if two or more of the three synchronization indicators indicate a loss of synchronization. In such an embodiment, the three synchronization indicators include a timing error indicator, an energy guard band indicator and a phase-frequency slope indicator.

Apparatus and method for synchronization in a multiple-carrier communication system by observing a plurality of synchronization indicators

An orthogonal frequency division multiplexing (OFDM) communication system includes base units which simultaneously transmit pilot tones in a predetermined pilot tone pattern during one or more time slots of a message slot. OFDM signals are received within a time slot; an OFDM signal level is determined at each frequency of a plurality of pilot tone frequencies; the signal levels and the predetermined pilot tone pattern are correlated; and a pattern detection value based on performing the correlation is generated and stored. This process is repeated for each time slot of a plurality of time slots. This process may be repeated for a plurality of message frame durations to produce a plurality of averaged pattern detection values, following which the plurality of averaged pattern detection values and a predetermined message frame pattern may be correlated. Then, a boundary of a message slot may be detected based on the correlation.

Methods and apparatus for use in obtaining frame synchronization in an OFDM communication system

A distributed radio system with multiple transceivers for simulcasting and selective processing of received signals is provided. The distributed radio system includes a plurality of processing elements and radio frequency transmitter elements interconnected by an Ethernet network. The system designates a number of radio frequency transmitter elements to be elements of a radio frequency simulcast set. The system utilizes relatively few frequency channels, and transmits at very low power levels, and thus causes minimal interference with an existing macrocellular environment. When signals transmitted from a mobile unit are detected by multiple radio receivers, the system is able to select a desired radio receiver signal for processing. When selecting a received signal for processing, the system utilizes a distributed processing technique that performs the selection process throughout several levels. The distributed processing utilized by the selection process may be synchronized. A selection time window may be utilized for making the selection process for the upstream-received data traffic. The system utilizes a centralized data link layer. Transmissions are implemented by a two-level multicast technique. The data transmission traffic is bundled. Selective management of the Ethernet switches is performed by the system.

Distributed radio system with multiple transceivers for simulcasting and selective processing of received signals

A frequency correction process involves the steps of generating a plurality of tone values for a plurality of tone bins, where the plurality of tone bins includes a first set of tone bins assigned to a first frequency range and a second set of tone bins assigned to a second frequency range; performing complex conjugate multiplication between the tone values of the first and the second sets of tone bins; identifying a maximum value from results of the complex conjugate multiplication; and shifting receiver frequency based on a location of the maximum value relative to a predetermined pilot tone location. In this method, the first frequency range corresponds to a lower edge portion of a frequency band of interest, an upper edge portion of a lower adjacent frequency band, and a lower guard band in between the lower and the upper edge portions; and the second frequency range corresponds to an upper edge portion of the frequency band of interest, a lower edge portion of an upper adjacent frequency band, and an upper guard band in between the upper and lower edge portions.

Methods and apparatus for use in obtaining frequency synchronization in an OFDM communication system

An iterative method involves performing a coarse frequency correction process which adjusts receiver frequency so that a pilot tone signal is within a predetermined frequency range and, after performing the coarse frequency correction process, performing a fine frequency correction process which adjusts receiver frequency so that the pilot tone signal is substantially aligned with a pilot tone reference within the predetermined frequency range. By performing these processes, the receiver frequency may be adjusted so that the alias pilot tone signal is substantially aligned with the pilot tone reference and the pilot tone signal is undesirably shifted outside the predetermined frequency range. To eliminate this condition, the method further involves performing the coarse frequency correction process again and, after performing the coarse frequency correction process again, performing the fine frequency correction process again. By performing the coarse frequency correction process again, receiver frequency is adjusted so that the pilot tone signal is within both the predetermined frequency range and the Nyquist sampling frequency range. By performing the fine frequency correction process again, receiver frequency is adjusted so that the pilot tone signal is substantially aligned with the pilot tone reference.

A method, apparatus and system detects a loss of synchronization between a transmitter and a receiver in a multiple-carrier communication system such as an OFDM system. A guard band synchronization detector provides a synchronization indicator based on the energy detected within a guard band where a pilot tone is transmitted adjacent to the guard band. A timing error results in energy leakage into one or more guard bands. In one embodiment, a plurality of synchronization indicators are observed to determine whether a loss of synchronization between a transmitter and a receiver in the wireless system has occurred.

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Seattle, WA, United States of America

Jari Heinonen