Abstract: Orthogonal frequency division multiplexing (OFDM) receiver embodiments of the invention provide data demodulator synchronization by finding the end of the short preamble in an IEEE-802.11a burst transmission. This method exploits the fact that there are certain symmetries in the long-preamble that can be used to determine synchronization. The long-preamble sequence is composed of a guard interval (GI) and two long-preamble symbols; the GI is the last 32 samples of the long-preamble symbol. The 32nd sample of the long-preamble acts as a “pilot” or “anchor” sample in that the previous N and subsequent N samples are complex conjugates, or conjugate “mirror” vectors. Due to the periodicities of the long-preamble, this property repeats every 32 samples. No other samples in the long preamble exhibit this property. Coherent combining is used in one embodiment for robustness.

Abstract: The present invention relates to a radar detector and a radar detecting method for WLAN systems according to 802.11 wireless communication standards, and particularly concerns the radar detection for 802.1 l h dynamic frequency selection mechanism. The essence of the innovation consists in projecting the received phase vector on the signal subspace orthogonal to the expected radar pulse subspace and taking the norm of the resulting vector. The closer the norm is to zero, the more likely the received signal is to be a radar pulse. The invention is able to detect both, sinusoidal radar signals and chirp-like radar signals.

Abstract: Many communications protocols involve a collection of communication channels collectively forming the dimensions of a finite dimensional vector space, of which at any point in time, only a subset of those channels or dimensions must be received. Messages on these channels are time progressions in at least the actively used dimensions of the vector space which have been linearly transformed to create a sample list transported across at least one physical transport layer to a receiver. The linear transform may further include an estimation of the effects of the transport of the sample list across the one or more physical layers to the receiver. This invention uses at least portions of pseudo-inverses of the linear transform in various ways within receivers and receiver portions of transceivers.

Abstract: Orthogonal frequency division multiplexing (OFDM) receiver embodiments of the invention provide timing misalignment estimation by calculating the intra-baud timing differential. The preferred method exploits the spectral structure of the short-preamble in that a time delay in the time-domain is manifest as a phase rotation in the frequency-domain. The timing misalignment is determined by special processing the spectral peaks of the modified short-preamble. An alternative embodiment linearly combines the two long-preamble symbols to construct a single “best estimate” long-preamble symbol. A normalized dot product of the “best estimate” long-preamble symbol and the ideal on-baud symbol is computed to obtain the magnitude of the timing misalignment. A dot product between the “best estimate” long-preamble symbol and the time derivative of the ideal on-baud sampled sequence is computed to obtain the sign of the timing misalignment.

Abstract: Orthogonal frequency division multiplexing (OFDM) receiver embodiments of the invention demodulate quadrature amplitude modulated (QAM) signals transmitted in the five GHz frequency band and digitally correct for frequency offset errors in their digital signal processing (DSP) units. A method comprises a step in which an OFDM transmission is I/Q sampled and a portion of the received packet is selected. It is assumed that the coarse frequency offset has been estimated and that the remaining frequency offset after coarse frequency offset compensation does not exceed ±10 kHz (valid for 802.11a PHY implementation only). It is also assumed that a timing reference has been determined. A cost function is used to determine a fine-frequency offset. Once the fine frequency offset is determined, the estimate is used in the downstream digital signal processing.

Abstract: Many communications protocols involve a collection of communication channels collectively forming the dimensions of a finite dimensional vector space, of which at any point in time, only a subset of those channels or dimensions must be received. Messages on these channels are time progressions in at least the actively used dimensions of the vector space which have been linearly transformed to create a sample list transported across at least one physical transport layer to a receiver. The linear transform may further include an estimation of the effects of the transport of the sample list across the one or more physical layers to the receiver. This invention uses at least portions of pseudo-inverses of the linear transform in various ways within receivers and receiver portions of transceivers.

Abstract: An orthogonal frequency division multiplexing (OFDM) receiver which digitally estimates and corrects for frequency offset and demodulates quadrature amplitude modulated (QAM) signals transmitted in the 5 GHz frequency band embodies the current invention. Possible modulation types include binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), 16-QAM, 64-QAM, (and 256-QAM in future standard enhancements). During the so-called short-preamble, the first few basic constituents are deliberately skipped. Then every 2.4 &mgr;s, a 1.6 &mgr;s duration sequence is collected until three such sequences are collected. Because the same waveform can be safely assumed to being repeated during all three sequences, any differences amongst the sequences are directly related to the frequency-offset error. The solution is set-up as a simultaneous-equation mathematical problem with a single unknown variable, a pseudo-rank of one.

Abstract: Orthogonal frequency division multiplexing (OFDM) receiver embodiments of the invention provide timing misalignment estimation by calculating the intra-baud timing differential. The preferred method exploits the spectral structure of the short-preamble in that a time delay in the time-domain is manifest as a phase rotation in the frequency-domain. The timing misalignment is determined by special processing the spectral peaks of the modified short-preamble. An alternative embodiment linearly combines the two long-preamble symbols to construct a single “best estimate” long-preamble symbol. A normalized dot product of the “best estimate” long-preamble symbol and the ideal on-baud symbol is computed to obtain the magnitude of the timing misalignment. A dot product between the “best estimate” long-preamble symbol and the time derivative of the ideal on-baud sampled sequence is computed to obtain the sign of the timing misalignment.

Abstract: Orthogonal frequency division multiplexing (OFDM) receiver embodiments of the invention demodulate quadrature amplitude modulated (QAM) signals transmitted in the five GHz frequency band and digitally correct for frequency offset errors in their digital signal processing (DSP) units. A method comprises a step in which an OFDM transmission is I/Q sampled and a portion of the received packet is selected. It is assumed that the coarse frequency offset has been estimated and that the remaining frequency offset after coarse frequency offset compensation does not exceed ±10 kHz (valid for 802.11a PHY implementation only). It is also assumed that a timing reference has been determined. A cost function is used to determine a fine-frequency offset. Once the fine frequency offset is determined, the estimate is used in the downstream digital signal processing.

Abstract: Orthogonal frequency division multiplexing (OFDM) receiver embodiments of the invention provide data demodulator synchronization by finding the end of the short preamble in an IEEE-802.11a burst transmission. This method exploits the fact that there are certain symmetries in the long-preamble that can be used to determine synchronization. The long-preamble sequence is composed of a guard interval (GI) and two long-preamble symbols; the GI is the last 32 samples of the long-preamble symbol. The 32nd sample of the long-preamble acts as a “pilot” or “anchor” sample in that the previous N and subsequent N samples are complex conjugates, or conjugate “mirror” vectors. Due to the periodicities of the long-preamble, this property repeats every 32 samples. No other samples in the long preamble exhibit this property. Coherent combining is used in one embodiment for robustness.

Abstract: In a method for spatially locating a mobile station in a cell of a mobile radio network, the cell being of the type controlled by a base station with an omnidirectional antenna and divided into a plurality of angular sectors centered on the base station, a separate location signal element is allocated to each angular sector. The mobile station sends a signaling packet carrying all the location signal elements. For each angular sector the base station modifies the signaling packet sent by the mobile station before it is received by the omnidirectional antenna, the modification being specific to the angular sector. The base station determines the modification that has been made from the signaling packet received by the omnidirectional antenna and deduces from it the angular sector in which the mobile station is located. A corresponding base station with an omnidirectional antenna, mobile station and signaling packet are also disclosed.

Abstract: The invention relates to a control signal for receivers, said control signal being formed by juxtaposing two signal elements of equal duration, and time symmetrical. For example, the signal comprises at least one first pseudo-random noise digital sequence s(N.sub.s -1) to s(0) and, periodically, at least one second digital sequence s(N.sub.s -1) to s(0), corresponding to the inverse, obtained by time symmetry, of said first sequence. The signal may be used in particular for performing time and frequency synchronization on receivers and/or for equalizing signals received by said receivers. The invention also relates to methods and apparatuses that use said signal.

Abstract: A signalling packet for a communication system has a reference signal to support time and frequency synchronization. The reference signal is modulated so that it varies with time according to a predetermined modulation law. The variation is with respect to both the I and Q channels. Because of the variation with time, receivers can synchronize in frequency and in time with a base station in a simplified manner. Doppler shift can be determined and compensated.

Abstract: For recognizing information conveyed by a received signal, represented by convention by possible elementary forms of the signal to be transmitted, a device includes a correlator for establishing a correlation between the received signal and various possible forms of signal, in accordance with the convention. A neural network using correlation coefficients obtained from the correlator is trained by application to its input of correlation coefficients corresponding to a received signal conveying given information whilst imposing the given information at its output. The network supplies recognized information.

Abstract: A sectorized cell of a mobile radio network forms a first set which comprises a nucleus and a plurality of sectors disposed around the nucleus, the coverage of the cell being provided by transceiver units forming a second set, the first and second sets being associated on a one-to-one basis. Each sector comprising a core, at least one separation section being provided between the cores of two adjacent sectors, and the control station comprises an allocation unit capable of allocating the same resource to the cores of two adjacent sectors.

Abstract: A positioning method for a mobile station in the radio coverage area of a satellite entails determining the instantaneous distance between the satellite and the mobile station. The instantaneous elevation angle .phi. of the satellite is then calculated from the instantaneous distance, the altitude of the satellite and the radius of the Earth. The Doppler shift .delta. is then determined, after which the angle .theta. between the projections onto the surface of the Earth of the track of the satellite and a straight line segment passing through the satellite and the mobile station is calculated from the Doppler shift .delta. and the instantaneous elevation angle .phi.. The location of the mobile station is then determined from the instantaneous distance, the instantaneous elevation angle .phi. and the angle .theta..