Telefonaktiebolaget Lm Ericsson (publ)

Ericsson Gmbh

Roozbeh Atarius

Kjell Berthold Gustafsson

Torgny Palenius

Torsten John Carlsson

Christer Östberg

Ali S Khayrallah

Essam Abdelfattah Sourour

Håkan B Eriksson

H&aring;kan Eriksson

Christer &Ouml;stberg

Paul Wilkinson Dent

Gregory Edward Bottomley

Rajaram Ramesh

Wail Refai

Hakan B Eriksson

Murali Narasimha

Stuart Baker Sanders

Erik Dahlbäck

Erik Dahlb&auml;ck

H&aring;kan Henningsson

Code division multiple access signals received through at least one multipath propagation channel are processed to produce at least one relative frequency error estimate. This involves receiving and processing the signals using a local frequency reference oscillator to obtain representative complex numerical samples for processing. The complex numerical samples are correlated with shifts of a locally generated despreading code and a number of complex channel estimates are produced, each corresponding to a different delayed ray of the at least one multipath propagation channel. A frequency error estimate is computed for each ray based on successive values of a respective one of the channel estimates, and a weighted summation of the frequency error estimates is performed to provide at least one relative frequency error estimate.

Method and apparatus for automatic frequency control in a CDMA receiver

A searcher uses an input signal, and for example, a matched filter to generate a first set of candidate paths. A selector uses the input signal and the first set of candidate paths to generate a second set of paths. The second set of paths is used to configure the fingers of a RAKE receiver. According to one aspect of the invention, the first set of candidate paths contains M paths, and the second stage uses M correlators to generate a set of M correlation values. The second stage uses the M correlation values to select N paths that are used to configure the N fingers of the RAKE receiver. According to another aspect of the invention, the first set of candidate paths contains M paths, and the second stage uses a multiple of M correlators to track the M paths and generate a set of M estimates. The second stage uses the M estimates to select N paths that are used to configure the N fingers of the RAKE receiver. According to another aspect of the invention, the selector can generate new sets of N paths while the searcher is either active or inactive. The receiver can use a quality signal or a counter to notify the searcher and/or the selector to generate new sets of paths. The selector decreases the need to continuously run the matched filter. The receiver can re-configure the fingers without having to search for new paths. The receiver can also find paths that are uncorrelated and less susceptible to fading.

Method and apparatus for configuring a RAKE receiver

Method and apparatus for configuring a rake receiver

A CDMA communication system uses a set of quasi-orthogonal codes to supplement the standard set of Walsh codes used in conventional systems. Users are assigned a code selected from the set of Walsh codes, if available. If the number of users exceeds the number of available Walsh codes, selected users are assigned to quasi-orthogonal codes. The users assigned quasi-orthogonal codes are chosen based on user mobility.

CDMA system using quasi-orthogonal codes

A method and system enables matched filters of a CDMA system to be simplified using a two stage search. A course stage and a fine stage jointly produce the location(s) of received signal path-rays. In a first stage, an oversampled digital signal is decimated, and the decimated signal is applied to a matched filter to eventually produce an approximate location. In a second stage, the oversampled signal is shifted based on the determined approximate location and then correlated to a generated code, and a more-exact location is selected from the outputs of the correlations. Alternatively, a shifted version of the generated code is correlated to the oversampled signal, and the more-exact location is selected from the outputs of those correlations.

Searching for signals in a communications system

Methods, receivers, transmitters, and systems are provided for performing a soft hand-over of a mobile terminal between base station transceivers that communicate using different communication channels. A mobile terminal may be configured to receive and demodulate signals on a plurality of different communication channels concurrently and to modulate and transmit signals on a plurality of different communication channels concurrently. This allows, for example, multiple communication connections to be concurrently established between the mobile terminal and a plurality of different base station transceivers that use the different communication channels to communicate. The mobile terminal and cooperating base station transceivers may perform a soft hand-over by allowing the mobile terminal to establish communication connections with one or more new base station transceivers to decide which base station transceiver should be given control before terminating any pre-existing communication connection with a current base station transceiver.

Methods, receivers, transmitters, and systems for performing a soft hand-over of a mobile terminal between base stations that communicate using different communication channels

Locations of path rays in a multi-path channel receiver having multiple time references are detected, e.g., when the receiver switches time references. Locations of received path rays are searched for and determined. The locations are tracked for a predetermined amount of time. If the locations are lost after a predetermined amount of time, a new search for the locations of the received path rays is initiated. The searching may include determining a probable location of a most significant path ray, shifting the location within a predetermined interval, analyzing each shifted location to determine whether the shifted location corresponds to the actual location of the received path ray, and depending on the analysis results, completing the search or determining a probable location of a next most significant ray. The analysis may be performed by correlating each shifted location with a pilot sequence and determining if the correlation results exceed a predetermined threshold. If the correlation results do not exceed the threshold, a determination is made whether all the most significant path rays have been analyzed, and if so, a complete search for the path ray location is initiated. When switching from a time reference of low accuracy to a time reference of high accuracy, the low accuracy time reference may be calibrated to the high accuracy time reference based on averaged measurements of the ratio of clock cycles of the time reference of high accuracy to the clock cycles of the time reference of low accuracy.

Method and apparatus for fast detection of locations of path rays in a receiver having multiple time references

A method of forward link power control in a CDMA mobile communication system is adapted for diversity transmission. First and second diversity signals are transmitted from a base station to a mobile terminal. The mobile terminal derives first and second channel quality estimates associated with the first and second diversity signals respectively. The mobile terminal uses the channel quality estimates to derive first and second power control codes which it transmits to said base station. The base station adjusts the transmit power of first and second antennas associated with the base station based on the first and second power control codes, respectively.

Fast forward link power control for CDMA system

A method for synchronizing a local reference frequency in a mobile station includes measuring a current ambient condition of the mobile station and using stored data indicating variance of the local reference frequency with known ambient conditions to determine the method by which the local reference frequency is synchronized.

Method and apparatus for synchronizing a local reference frequency in a communication systems

A method and apparatus estimate an offset between a carrier frequency of a transmitter and a local reference frequency of a receiver. A received signal is separated into frequency synchronization signals and data, and a determination is made whether the frequency synchronization signals are adequate for estimating the frequency offset. This determination may be made based on, e.g., an estimated Doppler spread, an estimated signal to noise ratio, and/or an available amount of frequency offset estimation time. The frequency offset is estimated based on the determination results. If the frequency synchronization signals are adequate for estimating the frequency offset, the frequency synchronization signals are used for determining the frequency offset. Otherwise, the rate of the frequency synchronization signals is increased, e.g., by using the data as frequency synchronization signals, in which case the data is combined with the frequency synchronization signals to determine the frequency offset.

Method and apparatus for estimating a frequency offset by combining pilot symbols and data symbols

A receiver can identify the source of a signal from an unsynchronized source. The receiver has an antenna for receiving two signals. The receiver correlates the first signal with a code to find a first location in time, and correlates the second signal with the same code to find a second location in time. The receiver calculates a time difference between the first location in time and the second location in time and uses the time difference to identify the source of the two signals. A group of base stations or directional antennas use the same long code and synchronization codes. However, each source shifts the long code by a different amount so that for any two sources there is a unique difference between the shifts in the long code. Each source shifts a set of synchronization codes the same amount as the long code. The synchronization codes can be any short code that is relatively easy for the mobile station to detect. When the receiver receives the two signals, the receiver calculates the difference in the shifts. Because there is a unique difference for each pair of sources, the receiver can identify the source of a signal from an unsynchronized source without having to connect to the source to use a broadcast channel or control channel. The receiver can distinguish between different synchronized sources without any prior synchronization.

Method and apparatus for identifying the source of a digital signal

A receiver circuit allows extracting information from baseband components of a received signal. Means are disclosed for removing constant disturbance components from the baseband signal components.

Radio receiver

The present invention provides a system and method for reducing the power consumed by a RAKE receiver. In exemplary embodiments of the present invention, an environment variation estimator is implemented in a CDMA mobile station. The environment variation estimator is connected to the searcher of the RAKE receiver and provides an estimate of the rate at which the mobile station's environment is changing. By providing an estimate of the rate of change of the mobile station's environment, the duty cycle of the searcher can be optimized, thereby reducing the overall power consumed by the receiver. By also providing the estimate to the RAKE fingers, channel tracking can be improved.

Motion estimator for a CDMA mobile station

A method, apparatus, and system determine a location of a frequency synchronization signal in a frame of data transmitted from a transmitter and received by a receiver in a communication system including at least one transmitter and at least one receiver. A peak value representing a detected frequency synchronization signal transmitted from the transmitter to the receiver is calculated. A frequency offset between a carrier frequency of the transmitter and a frequency reference of the receiver is estimated, along with a quality factor for the estimated frequency offset. A determination is made whether the peak value is greater than or equal to a peak threshold and whether the quality factor is less than or equal to a quality threshold. When both of the predetermined threshold conditions are met, the peak value, frequency offset, and quality factor are stored. When either of the threshold conditions is not met, the location of the frequency synchronization signal corresponds to the location of a stored maximum peak value and a stored minimum quality factor.

Growing community of inventors

Cary, NC, United States of America

Roozbeh Atarius