Arraycomm, Inc.

Proxim Corporation

Alcatel

Proxim Wireless Corporation

Alain M Chiodini

David M Parish

Mitchell D Trott

Paul Petrus

Michael Youssefmir

Dov Rosenfeld

Craig H Barratt

John Terrence Reagan

Kamaraj Karuppiah

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 32sample 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 &#x201c;mirror&#x201d; 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. Once this &#x201c;pilot&#x201d; or &#x201c;anchor&#x201d; sample is located, the end of the short-preamble is declared to have occurred 32 samples earlier, thus establishing a time reference.

OFDM data demodulators synchronization

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.

Method and apparatus using pseudo-inverses of linear transformations in multi-carrier modulation receivers and transceivers

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 &#x201c;best estimate&#x201d; long-preamble symbol and the time derivative of the ideal on-baud sampled sequence is computed to obtain the sign of the timing misalignment.

Timing misalignment estimation

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 &#xb1;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.

Fine-frequency offset estimation

A method for generating a reference signal from a modulated signal transmitted to a communications station that includes an array of antenna elements and spatial processing means including: separating from the signals received at the antenna elements a copy signal corresponding to the signal transmitted by a particular remote station using an initial spatial weight vector corresponding to the particular remote station; determining from the terminal copy signal a reference signal having substantially the same frequency offset and time alignment as the received antenna signals; and computing a new spatial weight vector by optimizing a cost function, the cost function using the received antenna signals and the reference signal. For demodulation, the method further includes extracting the symbols of the modulated signal.

Method for reference signal generation in the presence of frequency offsets in a communications station with spatial processing

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.

Method of spatial location of a mobile station in a cell of a communication network and corresponding base station, mobile station and signaling packet

A method and apparatus for estimating the parameters of a wireless communication system which includes at least one base station and at least one remote terminal, each of the base stations having m antenna elements, the parameters being one or more of: the time alignment; the frequency offset; and the weight vector for spatial processing. At any stage, some of the parameters may already be estimated. A signal of known characteristics is transmitted and received as m received signals at the antenna elements. A cost function that is related to the at least one or more parameters of the second set is determined using a copy signal determined from samples of the received signals, estimates of one or more parameters, if available, known characteristics of transmitted first signal. The estimate of the parameters to be determined is obtained by minimizing the cost function.

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Mountain View, CA, United States of America

Alain M Chiodini