Abstract: A system and method to provide antenna diversity by switching between antenna feeds to optimize signal quality. Antenna conditions are determined during an OFDM guard interval to minimize disruption of symbol transmission. When the signal quality assessment determines that an improved signal is available on an alternative antenna, an antenna change is performed to switch to the alternative antenna, also during a GI, again minimizing disruption in information transmission. Preferably, the process is continually applied, so that antenna conditions are monitored for changing conditions and the antenna experiencing the best signal is selected.

Abstract: A spur detection and spur cancellation apparatus in a multiple sub-carrier digital communication receiver includes a spur detection block that estimates, using one or more Fourier transforms, a frequency location of a narrowband interference spur in a received digital signal that includes a plurality of sub-carriers, and a spur cancellation block that attenuates the estimated narrowband interference spur. The spur detection block may use a fast Fourier transform (FFT) and/or a discrete Fourier transform (DFT) to locate a frequency and to measure a discrete power spectra of the narrowband interference spur. A channel state information block in the receiver may adjust a channel state information metric based on the located frequency and/or the measured discrete power spectra of the narrowband interference spur.

Abstract: This disclosure is directed to systems and methods that compensate for a phase change that results from a change in RF gain, a “phase glitch,” that would otherwise degrade the performance of a multiple sub-carrier communication system, such as OFDM. Pilot symbols are used to estimate the phase change, allowing the pilot and data symbols to be compensated by the estimated phase change. Preferably, the compensated pilots are used to per form a second iteration of phase change estimation that determines residual phase glitch. Thus, following the second estimation of phase change, data symbols can be compensated for the estimated residual phase change.

Abstract: A system and method are disclosed to synchronize adaptively a transform window in a multiple sub-carrier communication system based on analysis of a time domain channel impulse response. A set of frequency domain channel estimates, derived from received and one-dimensional Wiener filter interpolated channel estimates, are transformed into a time domain channel impulse response estimate containing multiple, repeated constituent responses. Each order of the constituent responses in the time domain channel impulse response estimate is associated with a two-dimensional Wiener interpolation filter. The set of two-dimensional Wiener interpolation filters generate interpolated channel estimates to compare with received channel estimates to determine a best channel impulse response order of the constituent responses. The transform window is adaptively updated using the best channel impulse response order.

Abstract: Scattered pilots are used to estimate the integer frequency offset and OFDM symbol index simultaneously. A cross-correlation between IFFT outputs of received samples with different spectral shift and OFDM symbol index is used to identify the channel impulse response. Upon determination of the channel impulse, the estimated integer frequency offset and OFDM symbol index can then be determined.

Abstract: This disclosure is directed to systems and methods for positioning a FFT window using the noise power that is related to ISI By selecting a FFT window position that minimizes the noise power, ISI is reduced or eliminated The techniques can be used in coherent and non-coherent systems Further, noise associated with the Doppler effect is compensated for, allowing the use of these system and methods in time-varying environments, such as mobile applications.

Abstract: An apparatus and method in a multiple sub-carrier digital communication receiver for reducing inter-channel interference (ICI) includes a channel estimation block for calculating channel estimates, an interpolation block for calculating interpolated channel estimates, and an ICI reduction block for calculating ICI reduced receive symbols. Channel estimates are calculated based on receive symbols or ICI reduced receive symbols using pre-determined transmit symbols. Interpolated channel estimates are calculated by Wiener filter interpolation of a set of channel estimates. ICI estimates are calculated based on a set of interpolated channel estimates and either receive symbols or ICI reduced receive symbols. ICI reduced receive symbols are generated by subtracting ICI estimates from receive symbols.

Abstract: A method and apparatus in a multiple sub-carrier digital communication receiver estimates a Doppler frequency bandwidth. The Doppler frequency bandwidth is estimated by comparing a first set of channel estimates to a second set of channel estimates generated by Wiener filter interpolation of the first set of channel estimates. The Wiener interpolation filter coefficients are generated for various Doppler frequency bandwidths. Pre-determined transmit pilot symbols may be used to generate the first set of channel estimates in an OFDM communication system. A set of Wiener filter interpolation errors may be generated at one or more sub-carrier frequencies, for each of the different Doppler frequency bandwidths, and averaged across time and/or frequency. The Doppler frequency estimation method and apparatus may select a Doppler frequency estimate based on the set of Wiener filter interpolation errors.

Abstract: A hybrid bit detection circuit for receiving bits from different global positioning systems, e.g. GPS and GLONASS, can include a frequency lock loop (FLL) for receiving the global positioning bits and removing Doppler frequency error and an integrate and dump (I&D) block coupled to an output of the FLL. A coherent detection circuit can be coupled to an output of the FLL and an output of the integrated and dump block. A differential detection circuit can be coupled to an output of the I&D block. Two parity check blocks can be coupled to outputs of the coherent and differential detection circuits.

Abstract: A method of determining a bit boundary of a GLONASS string is provided. In this method, a global position receiver can remove the meander sequence from bits of a GLONASS signal. After removing the meander sequence, time averages of bit energies for 20 possible (consecutive) bit boundary positions can be computed. At this point, the receiver can select a position from the 20 possible bit boundary positions that maximizes bit energy. A maximum accumulated value at this position as well as offset accumulated values at 5 ms and 15 ms offset from the position can be determined. Then, the receiver can determine whether a ratio of at least one of the offset accumulated values to the maximum accumulated value meets a predetermined condition. When the ratio meets the predetermined condition, the receiver can output the position as the bit boundary of the GLONASS string.

Abstract: A method and apparatus in a multiple sub-carrier digital communication receiver that estimates a communication channel. A second set of channel estimates are generated based on a Wiener filter interpolation of a first set of channel estimates. Pre-determined transmit pilot symbols may be used to generate the first set of channel estimates in an OFDM communication system. The coefficients of the Wiener interpolation filter are based on a channel impulse response estimate that includes two or more narrow regions of non-zero amplitude separated by one or more wide regions of essentially zero amplitude. The Wiener interpolation filter coefficients are also based on a Doppler frequency estimate. The Doppler frequency estimate may be determined from the first set of channel estimates, while the Wiener interpolation filter coefficients may be generated from a pre-determined set of channel impulse responses.