Edgewater Wireless Systems Inc.

Edgewater Computer Systems, Inc.

Manish Bhardwaj

Garret Shih

Kanu Chadha

Maneesh Soni

Jian Cui

Automatic Gain Control (AGC) system for multi-channel signals attenuates an incoming multi-channel signal by providing a gain. The system further adjusts each individual channel, of the multi-channel signal, by supplying a second gain if needed. The AGC system is designed to ensure a received signal power is at an optimal level for analog to digital conversion or any other form of signal processing. The system also enables elimination of mid-packet gain adjustments.

Automatic gain control (AGC) for multichannel/wideband communications system

Gain variations during a packet can lead to significant performance degradation in communications systems that use high order quadrature amplitude modulation (QAM). A method and the associated apparatus track such variations in an OFDM system and completely eliminate any performance degradation. Gain estimation and compensation is employed with the use of pilot subcarriers in the payload of an OFDM data packet. Estimated pilot magnitude ratios are averaged, throughout the processing life of a packet, to yield accurate gain estimations. A gain compensation factor is used to adjust data carriers. An exclusion method is also employed to eliminate pilot carriers which contribute to noise.

Method and apparatus to track gain variation in orthogonal frequency division multiplexing (OFDM) systems

The invention relates to a novel methodology and apparatus for clock-offset compensation and common-phase offset correction in Frequency Division Multiplexing based wireless local area network (WLAN) environment, such as an Orthogonal Frequency Division Multiplexing (OFDM) environment. A curve fit, such as a threshold-based, least mean squares (LMS) fit of phase of the pilot sub-carriers in each OFDM symbol is used to estimate and counteract the rotation of the data sub-carriers due to residual frequency offset, low frequency phase noise, and clock offset. The invention is particularly well suited to wireless channels with multipath where pilots typically undergo frequency-selective fading. The thresholding LMS is implemented in a hardware-efficient manner, offering cost advantages over a weighted-LMS alternative. Additionally, the invention uses a unique phase-feedback architecture to eliminate the effects of phase wrapping, and avoid the need to refine channel estimates during packet reception.

Receiver architecture for pilot based OFDM systems

The present invention allows multi-channel communications equipment to detect and eliminate a false interpretation of interference as a valid signal. The solution is based on the observation that the simultaneous arrival of energy on two independent channels is an impossible event. So, when such an event happens, it is a reliable signature of confusing out-of-band energy for a valid signal.

Detecting and eliminating spurious energy in communications systems via multi-channel processing

Upon a triggering event, a delay chain shifts data out at a higher rate than incoming packets and a processor controls bypassing circuitry to reduce the latency of hardware implementations of, for example, 802.11a OFDM receivers, with long delay chains. The signal processing algorithms used to recover symbol timing need a large number of samples stored in a delay chain, often consisting of pipelined registers. Such a delay chain introduces a large lag between the time samples have been acquired by the data converters and the time they are processed. This delay makes it difficult for higher level network layer implementations to meet the deadlines of 802.11a WLAN protocol. The proposed scheme implements dynamic reduction in the depth of the delay chain once timing recovery has been performed. A multi-step scheme achieves exponential reduction in the number of elements in the delay chain in every step.

Method and system for dynamically reducing length of a delay chain

Using a combination of auto-correlation and cross-correlation techniques provides a symbol timing recovery in a Wireless Local Area Network (WLAN) environment that is extremely robust to wireless channel impairments such as noise, multi-path and carrier frequency offset. An auto-correlator provides an estimate for a symbol boundary, and a cross-correlator is subsequently used to more precisely identify the symbol boundary. Peak processing of the cross-correlation results provides further refinement in symbol boundary detection. In receiving a packet conforming to the IEEE 802.11a standard, the method requires a minimum of only three short symbols of the 802.11a short preamble to determine timing, and guarantees timing lock within the duration of the 802.11a short preamble. This method and system can be easily applied to any other preamble based system such as 802.11g and High Performance Radio LAN/2 (HIPERLAN/2).

Method and system for fast timing recovery for preamble based transmission systems

In a multi-user radio receiver, a method and apparatus for reducing the effects of non-linear distortion due to adjacent channel interference (ACI) includes receiving and processing a multi-user information signal to provide a plurality of multi-user information values and then detecting, from the plurality of multi-user information values, at least a first information value having a signal strength which is relatively high compared with the signal strengths of the other plurality of multi-user information values. The apparatus then utilizes the plurality of multi-user information values, the first information value and a spectral representation of the first information value to generate a plurality of second information values having significantly reduced adjacent channel interference with respect to the first information value. The method and apparatus can thus increase the system capacity by increasing the frequency reuse factor in the a receiver system (e.g. a wideband receiver system) for wireless LAN applications.

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Cambridge, MA, United States of America

Manish Bhardwaj