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.
Adaptive Equalizer With Enhanced Error Quantization
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.
Reduced Complexity Equalizer For Multi Mode Signaling
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.
Equalizer Method And Apparatus Using Constant Modulus Algorithm Blind Equalization And Partial Decoding
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
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.
Thomas J Endres - Pipersville PA, US Samir N Hulyalkar - Plainsboro NJ, US Christopher H Strolle - Glenside PA, US Troy A Schaffer - Langhorne PA, US Anand M Shah - Yardley PA, US
Assignee:
ATI Technologies Inc. - Ontario
International Classification:
H03H 21/00
US Classification:
375233, 375229, 375232, 708322, 708323
Abstract:
An equalizer for use in a communication receiver includes an infinite impulse response (IIR) feedback filter operated in acquisition and tracking feedback modes on a sample by sample basis to form a hybrid Decision Feedback Equalizer (DFE) architecture. In acquisition mode, soft decision samples from the filtered received signal are input to the IIR filter. In the tracking mode, hard decision samples from a slicer are input to the IIR filter. Acquisition and tracking operating modes are selected in accordance with a set of decision rules on a sample by sample basis based on the quality of the current hard decision. If the current hard decision is low quality, then the soft decision sample (acquisition mode) is used. If the current hard decision is high quality, then the hard decision sample (tracking mode) is used. In such manner, the DFE is operated in a hybrid mode, i. e.
Troy Schaffer (1984-1988), Jeremy Same (1987-1991), Serge Rolston (1974-1978), Kim Jones (1965-1966), Joan Turner (1972-1974), Crystal Coull (1979-1979)