Troy F Schaffer

US Patent:

6337878, Jan 8, 2002

Filed:

Mar 3, 1999

Appl. No.:

09/261843

Inventors:

Thomas J Endres - Pipersville PA
Samir N Hulyalkar - Plainsboro NJ
Christopher H Strolle - Glenside PA
Troy A Schaffer - Langhorne PA

Assignee:

Nxt Wave Communications - Langhorne PA

International Classification:

H03H 740

US Classification:

375229, 375232, 375346, 375350, 708322, 708323

Abstract:

An adaptive equalizer for use in blind equalization systems to compensate for transmission channel distortion and noise in a digital communication system quantizes the input signal samples to generate a quantized implementation of the Constant Modulus Algorithm (CMA). To quantize the input signal samples, a nearest-element decision device (a slicer), that is typically present in a digital receiver, is used to pre-compute the quantized CMA error function. The number of unique values for the CMA error term is thereby reduced, and the reduced number of CMA error term values are stored in a lookup table. By greatly reducing the number of received signal values used in the CMA error calculation a relatively small lookup table can be used to compute the CMA error function. Passband implementation is accommodated by incorporating the signal de-rotation factor into the lookup table entries. In one embodiment the CMA multiply operation is replaced with shifts and adders.

US Patent:

6418164, Jul 9, 2002

Filed:

Jan 14, 1999

Appl. No.:

09/231888

Inventors:

Thomas J Endres - Perkasie PA
Samir N Hulyalkar - Plainsboro NJ
Christopher H Strolle - Glenside PA
Troy A Schaffer - Langhorne PA

Assignee:

Nxtwave Communications, Inc. - Langhorne PA

International Classification:

H03H 2100

US Classification:

375232, 375233, 375235, 375243, 375285, 708323, 455204, 348607

Abstract:

An adaptive equalizer for use in blind equalization systems to compensate for transmission channel distortion and noise in a digital communication system uses multiple quantization levels for implementation of the Constant Modulus Algorithm (CMA). Different quantization levels are used in different regions of the CMA error function for both passband and baseband equalizers. In one embodiment, a quantizer with a step rise having logarithmic scale is used to digitize the CMA error function. In particular, a quantizer with a step rise in which each level of the quantizer step rise is a power of 2 is used to digitize the CMA error function. In another embodiment, a quantizer with a step rise in which each level of the quantizer step rise is the sum of two or more logarithmic scales is used to digitize the CMA error function. In particular, a quantizer with a step rise wherein each level of the quantizer step rise is the sum of two or more numbers each of which is a power of 2 is used to digitize the CMA error function. The use of logarithmic scales, the sum of logarithmic scales, powers of 2, or the sum of powers of 2 for the quantizer step rise size to digitize the CMA error function make efficient use of shift and add operations to achieve multiplication in the adaptation process.

US Patent:

6426972, Jul 30, 2002

Filed:

Jun 19, 1998

Appl. No.:

09/100705

Inventors:

Thomas J. Endres - Perkasie PA
Samir N. Hulyalkar - Bensalem PA
Troy A. Schaffer - Langhorne PA
Christopher H. Strolle - Glenside PA

Assignee:

NxtWave Communications - Langhorne PA

International Classification:

H03H 730

US Classification:

375229, 375233

Abstract:

A transmission channel equalizer system may be used to process either signals that have been modulated according to quadrature amplitude modulation (QAM) or vestigial sideband modulation (VSB) to convey digital symbols. The equalizer system includes a sparse digital filter having coefficients which are adaptively updated. The filter system includes a finite impulse response (FIR) filter which processes modulated pass-band RF signals and an infinite impulse response (IIR) filter which processes demodulated base-band signals. At least one of the FIR and IIR filters is implemented as a sparse filter. The filter system is responsive to a control signal to switch between processing QAM and VSB signals. The update algorithm for the equalizer employs a constant modulus algorithm (CMA) to acquire the digital signal and a decision directed (DD) algorithm to track the digital signal. The CMA algorithm used when VSB signals are processed is a single axis CMA (SACMA) algorithm.

US Patent:

6560299, May 6, 2003

Filed:

Jul 30, 1999

Appl. No.:

09/363813

Inventors:

Christopher H Strolle - Glenside PA 19038
Anand M Shah - Pendel PA 19047
Thomas J Endres - Pipersville PA 18947
Samir N Hulyalkar - Plainsboro NJ 08536
Troy A Schaffer - Newtown PA 18940

International Classification:

H04B 710

US Classification:

375347, 375232, 375233

Abstract:

A diversity receiver is coupled to a composite antenna having first and second antennas physically configured to provide one or more forms of diversity reception. The multiple channel diversity receiver includes first and second RF channels with joint signal processing. First and second RF signals are processed jointly in the multiple channel diversity receiver with respect to tuning, automatic gain control (AGC), baud clock recovery, RF carrier recovery and forward equalization. The multiple channels of the diversity receiver are linked or cross coupled to each other through respective joint processing circuitry. In particular, first and second RF tuners share a common local oscillator and a common AGC feedback loop. First and second front ends share a common baud timing loop and a common pilot carrier recovery loop. Finally, first and second diversity receiver channels share a common sparse equalization filter.

US Patent:

6668014, Dec 23, 2003

Filed:

Dec 9, 1999

Appl. No.:

09/457496

Inventors:

Thomas J Endres - Pipersville PA
Samir N Hulyalkar - Plainsboro NJ
Christopher H Strolle - Glenside PA
Troy A Schaffer - Langhorne PA
Raul A Casas - Doylestown PA
Stephen L Biracree - Jamison PA
Anand M Shah - Pendel PA

Assignee:

ATI Technologies Inc. - Ontario

International Classification:

H03K 5159

US Classification:

375232, 375341, 375287, 375224, 375265, 375229, 375346, 375350, 375233, 375340, 714796, 714786, 714792, 714794, 714795, 708322, 708323

Abstract:

A digital communication receiver includes a blind equalizer using the Constant Modulus Algorithm (CMA) to compensate for channel transmission distortion in digital communication systems. Improved CMA performance is obtained by using a partial trellis decoder to predict 1 bit or 2 bits of the corresponding 3-bit transmitted symbol. The predicted bits from the partial trellis decoder are used to reduce the effective number of symbols in the source alphabet, which reduces steady state jitter of the CMA algorithm. Specifically, the received input signal to the CMA error calculation is shifted up or down by a computed delta (), in accordance with the predicted bit(s). In addition, a different constant gamma (), for the CMA error calculation is selected in accordance with the predicted bit(s). The disclosed technique is applicable to trellis and non-trellis codes in which at least one bit of the present symbol can be predicted in advance and used to reduce the effective number of symbols in the source alphabet.

US Patent:

6870892, Mar 22, 2005

Filed:

Apr 9, 2003

Appl. No.:

10/409371

Inventors:

Christopher H Strolle - Glenside PA, US
Anand M Shah - Pendel PA, US
Thomas J Endres - Pipersville PA, US
Samir N Hulyalkar - Plainsboro NJ, US
Troy A Schaffer - Newtown PA, US

Assignee:

ATI Technologies, Inc. - Markam

International Classification:

H04B007/10
H04L001/02

US Classification:

375347, 375349, 375327, 375326, 375344, 4552761, 455132, 455139

Abstract:

First and second RF signals in the respective first and second channels of a multiple channel diversity receiver are processed jointly in a joint timing loop filter for baud clock recovery. The channel with the stronger signal determines the frequency of the baud clock for the channel with the weaker signal, leaving the respective PLL's to make individual phase adjustments for each channel. The first and second channels also share a skew corrector for baud clock recovery when the multipath delay between the first and second RF signals is greater than one whole baud clock period. The whole baud skew corrector computes the correlation between the first and second received signals, and if the correlation is low, shifts the first and second signals by one whole baud and recomputes the correlation. The process of shifting the first and second received signals and computing the correlation function is repeated for various whole baud shifts in accordance with a search strategy to find the best (highest) correlation.

US Patent:

6937677, Aug 30, 2005

Filed:

Apr 9, 2003

Appl. No.:

10/408881

Inventors:

Christopher H Strolle - Glenside PA, US
Anand M Shah - Pendel PA, US
Thomas J Endres - Pipersville PA, US
Samir N Hulyalkar - Plainsboro NJ, US
Troy A Schaffer - Newtown PA, US

Assignee:

ATI Technologies Inc. - Ontario

International Classification:

H04B007/10
H04L001/02

US Classification:

375347, 455137, 455132

Abstract:

Original RF carriers are recovered for first and second channels in a diversity receiver and used to de-rotate (demodulate) each of the first and second received signals. The pilot loop filters of each channel are cross coupled to create a joint pilot loop between both channels. The channel with the stronger signal provides a dominant influence on the frequency of the synthesized recovered RF carrier in the channel with the weaker signal. The phase locked pilot loops in both channels will tend to be frequency locked to the frequency of the stronger signal, leaving the respective phase locked pilot loops to make an individual phase adjustment for each channel.

US Patent:

6970523, Nov 29, 2005

Filed:

Mar 7, 2003

Appl. No.:

10/384048

Inventors:

Christopher H Strolle - Glenside PA, US
Anand M Shah - Pendel PA, US
Thomas J Endres - Pipersville PA, US
Samir N Hulyalkar - Plainsboro NJ, US
Troy A Schaffer - Newtown PA, US

Assignee:

ATI Technologies, Inc. - Ontario

International Classification:

H04L027/08

US Classification:

375345, 375347, 375267, 455136

Abstract:

A multiple channel diversity receiver includes joint automatic gain control (AGC) signal processing wherein the first and second channels of the multiple channel diversity receiver share at least one joint AGC loop. The maximum difference between the AGC feedback signal in the control loop for the first channel and the AGC feedback control signal in the control loop for the second channel is limited to a selectable maximum differential. The AGC control loop with the stronger first RF signal thus limits the maximum amount that the weaker signal is amplified in the AGC control loop with the weaker second RF signal. By limiting the AGC feedback signal in the control loop of the second channel to a maximum differential with respect to the AGC feedback signal in the control loop of the first channel, the weaker signal is not overly amplified thereby avoiding the undue amplification of noise in the second channel.