391 results about "Delay spread" patented technology

A wireless communications adapts its mode of operation between spatial multiplexing and non-spatial multiplexing in response to transmission-specific variables. An embodiment of a wireless communications system for transmitting information between a base transceiver station and a subscriber unit includes mode determination logic. The mode determination logic is in communication with the base transceiver station and the subscriber unit. The mode determination logic determines, in response to a received signal, if a subscriber datastream should be transmitted between the base transceiver station and the subscriber unit utilizing spatial multiplexing or non-spatial multiplexing. In an embodiment, the mode determination logic has an input for receiving a measure of a transmission characteristic related to the received signal. In an embodiment, the mode determination logic includes logic for comparing the measured transmission characteristic to a transmission characteristic threshold and for selecting one of spatial multiplexing and non-spatial multiplexing in response to the comparison of the measured transmission characteristic to the transmission characteristic threshold. In an embodiment, the transmission characteristic includes at least one of delay spread, post-processing signal-to-noise ratio, cyclical redundancy check (CRC) failure, residual inter-symbol interference, mean square error, coherence time, and path loss. By adapting the mode of operation in response to transmission-specific variables, the use of spatial multiplexing can be discontinued in unfavorable conditions. Additionally, because the wireless communications system can adapt its mode of operation between spatial multiplexing and non-spatial multiplexing, the communications system is compatible with both subscriber units that support spatial multiplexing and subscriber units that do not support spatial multiplexing.

A gain control circuit adjusts the signal level of a received signal responsive to the bandwidth a received signal and / or the delay spread of the channel in which the signal has propagated. The bandwidth and delay spread are evaluated to estimate the amount of signal variation that is expected due to fast fading. Adjustments to the signal level are then made to avoid clipping while at the same time ensuring that the dynamic range of a receiver component is efficiently utilized.

A method and apparatus for adaptive beam-steering are disclosed. In one embodiment, the method comprises performing adaptive beam steering using multiple transmit and receive antennas, including iteratively performing a pair of training sequences, wherein the pair of training sequences includes estimating a transmitter antenna-array weight vector and a receiver antenna-array weight vector.

An embodiment of the present invention uses estimates of delay spreads of transmissions from user equipments (UEs) to a NodeB to determine a set of transmission parameters for the UEs reference signals. In an exemplary embodiment, the transmission parameters for reference signals include cyclic shifts. Thus, embodiments include a set of allocated cyclic shift values that are tailored to the delay spreads. The set of allocated cyclic shift values are used by a corresponding set of UE being served by a NodeB to form references signals. Each UE uses the allocated cyclic shift to form its reference signal by applying the cyclic shift to a modified reference sequence. The modified reference sequence can be generated from a Constant-Amplitude-Zero-Auto Correlation (CAZAC) sequence. The set of allocated cyclic shift values can be updated periodically to account for changes of delay spreads, which can be caused by physical movements of the set of UEs.

An OFDM system uses a normal mode which has a symbol length T, a guard time TG and a set of N sub-carriers, which are orthogonal over the time T, and one or more fallback modes which have symbol lengths KT and guard times KTG where K is an integer greater than unity. The same set of N sub-carriers is used for the fallback modes as for the normal mode. Since the same set of sub-carriers is used, the overall bandwidth is substantially constant, so alias filtering does not need to be adaptive. The Fourier transform operations are the same as for the normal mode. Thus fallback modes are provided with little hardware cost. In the fallback modes the increased guard time provides better delay spread tolerance and the increased symbol length provides improved signal to noise performance, and thus increased range, at the cost of reduced data rate.

A method for establishing a cyclic shift sequence to provide against the frequency offset is disclosed. The method calculates a distance between a channel response position of the sequence and an alias channel response position caused by a frequency offset, calculates the number of cyclic shifts per group according to the calculated distance, and establishes the cyclic shift (CS)-applying interval. This method easily establishes a cyclic shift (CS) interval at a specific location having no overlapping by considering a channel response of a reception (Rx) sequence and an alias location of this reception (Rx) sequence, although a reception (Rx) signal is shifted by a channel delay spreading or a propagation delay irrespective of categories of a domain generating a sequence, so that it can greatly reduce the number of the detection errors and the false alarm rate. And, if a sequence of the cyclic shift (CS) is allocated to a cell having a frequency offset of more than a predetermined level, the present invention can minimize the influence of a frequency offset on a high-mobility cell.

There is provided a hybrid rake / equalizer receiver for correlating a delay spread in a spread spectrum system. The hybrid rake / equalizer receiver includes a plurality of adaptive equalizers, each for filtering different regions of the delay spread that have an energy level above a pre-specified threshold to respectively provide equalized-descrambled chip sequences for correlation. Equalizer coefficients respectively corresponding to the plurality of adaptive equalizers are updated individually.

A method and apparatus for the signal synchronization of an OFDM system are proposed including a delay conjugate multiplication module, a phase processor and an edge detector. It provides estimates for the boundaries of ISI-free region by utilizing the characteristics of the guard interval and combining the techniques of the delay conjugate multiplication module, phase differential operation, symbol-by-symbol average operation, and edge detection. This method provides an improved performance in a multi-path fading channel with large delay spread, and can be utilized in a broadcasting system, such as the DAB and DVB-T systems. This invention is easy to determine a fixed optimal threshold that can directly separate the ISI region in any mobile environment, thereby most symbol information with ISI-free version can be obtained.

An exemplary fast Fourier transform (FFT) numerology for an orthogonal frequency division multiple access (OFDMA) downlink transmission system is described. The exemplary FFT numerology reduces the FFT sampling rate for a given transmission bandwidth, thereby increasing the battery life of a UE. The FFT numerology increases robustness against Doppler spread, phase noise, and frequency offset, enabling operation in channels with high delay spread, such as occurs in mountainous regions. The described numerology might provide the following without altering standard sub-frame duration: increased intercarrier spacing; reduced FFT sampling frequency across the transmission bandwidths; reduced FFT size across all transmission bandwidths; increased number of OFDM symbols per sub-frame; and / or increased cyclic prefix length choices.

An embodiment of the present invention uses estimates of delay spreads of transmissions from user equipments (UEs) to a NodeB to determine a set of transmission parameters for the UEs reference signals. In an exemplary embodiment, the transmission parameters for reference signals include cyclic shifts. Thus, embodiments include a set of allocated cyclic shift values that are tailored to the delay spreads. The set of allocated cyclic shift values are used by a corresponding set of UE being served by a NodeB to form references signals. Each UE uses the allocated cyclic shift to form its reference signal by applying the cyclic shift to a modified reference sequence. The modified reference sequence can be generated from a Constant-Amplitude-Zero-Auto Correlation (CAZAC) sequence. The set of allocated cyclic shift values can be updated periodically to account for changes of delay spreads, which can be caused by physical movements of the set of UEs.