1108 results about "Intersymbol interference" 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.

Disclosed is a method and system that adapts coefficients of taps of a Finite Impulse Response (FIR) filter to increase elimination of Inter-Symbol Interference (ISI) introduced into a digital communications signal due to distortion characteristics caused by a real-world communications channel. In the communications system there is a Finite Impulse Response (FIR) filter. The FIR filter has at least one pre and / or post cursor tap that removes pre and / or post cursor ISI from the signal, respectively. The pre / post cursor taps each have pre / post cursor coefficients, respectively, that adjusts the effect of the pre / post cursor portion of the FIR filter. The FIR filtered signal is transmitted over the channel which distorts the signal due to the changing and / or static distortion characteristics of the channel. The channel distorted signal is received at a receiver that may pass the channel distorted signal through a quantifier / decision system (e.g., a slicer) as the quantifier input signal to quantify the quantifier input signal to one of multiple digital values. The channel distorted signal may be further adjusted by summing the channel distorted signal with the output of a Decision Feedback Equalizer (DFE) filter to create a DFE corrected signal which then becomes the quantifier input signal. An error signal is determined by finding the difference between the scaled quantifier decision and the quantifier input signal. The pre / post cursor coefficient values that adjust the effects of the pre / post cursor taps of the FIR filter are updated as a function of the error signal and at least two quantifier decision values, and update coefficient values, may be sent over a communications back-channel to the FIR filter.

A symbol sequence contained in a received signal comprising a cyclic convolution of a Walsh code multiplexed signal and a channel impulse response of a multipath channel is detected using Walsh Hadamard domain equalization techniques. The method comprises converting the received signal and the channel impulse response of the multipath channel from the time domain to the WHT domain, and determining the symbol sequence based on equalizing the received signal in the WHT domain using WHT spectra of the channel impulse response to remove inter-symbol interference from the received signal due to cross-correlation between Walsh codes.

A wireless Internet access system and method supports the transmission and reception of multiple types of traffic between mobile subscriber units and existing networks. A frame structure is used that can support the transmission of multiple types of traffic and adapt to changes in the traffic types needed and the amount of data for a particular traffic type. In addition, data transmission is performed using orthogonal frequency division multiplexing and differential phase shift keying to avoid inter-symbol interference. Receiving units in the mobile subscriber units and existing works include antenna arrays to provide a multipath transmission.