Mitsubishi Electric Research Laboratories, Inc.

Princeton University

Lucent Technologies Inc.

Stmicroelectronics S.r.l.

Hisashi Kobayashi

Andreas F Molisch

Sinan Gezici

H Vincent Poor

Jay Bao

Shun Zheng Yu

Jinyun Zhang

Ivan P Kaminow

Piero Castoldi

Daqing Gu

Giuseppe Avellone

Luca Fanucci

Stuart C Schwartz

Pei Chen

Warren S Warren

Andrea Concil

Lorena Simoni

Duanyi Wang

Jan Bajcsy

June-Koo Rhee

Riccardo Grasso

Xiaoqiang Ma

A receiver for receiving digital signals exposed to intersymbol interference as well as multiple access interference the method including linearly detecting said signals by combating said intersymbol interference by equalizing said received digital signals as well as mitigating said multiple access interference by detecting said digital signals using sliding window detection.

Low complexity detection in digital receivers

In a time-hopped impulse radio system, each symbol is transmitted over a channel having different multipath components as a set of Nframes. Each frame includes one pulse. All frames of a received signal corresponding to the symbol are sampled to generate N&#xd7;L samples, where L is the number of samples for each frame. Then, the N&#xd7;L samples are combined according to a minimum mean square error criterion to obtain a decision variable corresponding to the symbol.

Linear receivers for time-hopping impulse radio systems

A method and system acquire a received impulse radio signal by first searching, with respect to time, a region of the impulse radio signal using a first template signal to locate a block including a signal cell, and second searching, with respect to time, the block using a second template signal to locate the signal cell to acquire the received impulse radio signal.

Method and system for acquiring ultra-wide-bandwidth communications signals using sequential block searches

The present invention relates to a method and system for providing Web content from pull and push based services running on Web content providers to mobile users. A proxy gateway connects the mobile users to the Web content providers. A prefetching module is used at the proxy gateway to optimize performance of the pull services by reducing average access latency. The average access latency can be reduced by using at least three factors: one related to the frequency of access to the pull content; second, the update cycle of the pull content determined by the Web content providers; and third, the response delay for fetching pull content from the content provider to the proxy gateway. Pull content, such as documents, having the greatest average access latency are sorted and a predetermined number of the documents are prefetched into the cache. Push services are optimized by iteratively estimating a state of each of the mobile users to determine relevant push content to be forward to the mobile user.

System for wireless push and pull based services

A method and system acquire a received impulse radio signal by correlating a region, including a plurality of cells, of the received impulse radio signal using multiple time-shifted template signals, each template signal having a different delay to obtain a correlation value for each template signal. The correlation values are averages, and a particular delay associated with a particular template signal having a substantial increase in successive averages to locate a signal cell in the region.

Method and system for acquiring ultra-wide-bandwidth communications signals using average block searches

A system and method detect symbols of a modulated signal received via a plurality of channels of a wireless communications system. A symbol transmitted via the channels is initially estimated based on the channel estimate from either pilot symbol or previously estimated symbol, and then channel estimate is updated. The next estimate of the symbol is computed by using updated channel information and maximizing the expectation of the log likelihood function. The next estimate is then quantized according to the signal constellation. The quantized estimate of the symbol is compared with the previous estimate of the symbol to determine if the previous estimate of the symbol and the quantized next estimate of the symbol have converged. Otherwise, the quantized next estimate of the symbol is made as the input for the next iteration, and the updating, optimizing, quantizing, and comparing are repeated until the estimate converges.

Expectation-maximization-based channel estimation and signal detection for wireless communications systems

In orthogonal frequency division multiplexing systems, iterative maximum likelihood channel estimation and signal detection is preformed. The channel estimation gives the maximum likelihood estimates of time domain channel parameters. A cost function is defined. An iterative process estimates a joint channel impulse response and a transmitted signal that minimize the cost function, and thus solves the channel estimation and signal detection problem jointly without having specific knowledge of the channel.

Iterative maximum likelihood channel estimation and signal detection for OFDM systems

A matrix transform method and circuit provides for MAP decoding of turbo codes. The method begins by initializing a forward recursion probability function vector &agr; , and a backward recursion probability function vector &bgr; . Then, transition probability matrices &Ggr;(R ) and &Ggr; (R ) are determined according to each received symbol of the sequence R . And then, values of &agr; , corresponding to the received R are determined according to &Ggr;(R ). At the same time of determining &agr; , a plurality of multiplacation on &Ggr;(R ) and &Ggr; (R ) are accomplished in parallel. By making use of the results of the matrix multiplications, after receiving the complete symbol sequence R , values of all of the backward recursion probability vector &bgr; , where k&equals;1, 2, . . . , N&minus;1, are determined in parallel, and the log likelihood ratio for every decoded bit d , k&equals;1, 2, . . . , N, are also determined in parallel. The circuit performs successive decoding procedures in parallel using a set of regular matrix operations. These operations substantially accelerate the decoding speed and reduce the computational complexity, and are particularly suited for implementation in special-purpose parallel processing VLSI hardware architectures. Using shift registers, the VLSI implementation effectively reduces memory requirements and simplifies complicated data accesses and transfers.

MAP decoding for turbo codes by parallel matrix processing

A received signal is first converted into a digital sequence that may contain 'erasures' (or ambiguity symbols) as well as errors. Then iterative decoding is applied in order to eliminate or reduce the erasures. This decoding procedure works effectively with the associated transmitter that adopts a concatenation of an outer coder, a permutation and an inner coder. The principal of the invention is also applicable to a system in which the inner coder is replaced by a 'digital modulator' that introduces some constraint, or a channel that introduces some memory such as partial response signaling, intersymbol interference or multipath propagation. The invention can be applied to many existing systems while maintaining 'backward compatibility' in the sense that the transmitter side need not be modified.

System and method for error correcting a received data stream in a

A DPSK communication system employs an optical signal which comprises plural, coherent, optical frequencies, each optical frequency positioned within a range of frequencies (i.e., a 'frequency slot'). The optical signal comprises plural frequency slots, with the wavefront in each time segment of each frequency slot being phase modulated in accordance with data signals. Plural frequency slots are transmitted 'in parallel', in each of a plurality of succeeding time segments. A demodulator includes first and second optical paths, the first component of the optical signal directed onto the first optical path and a second component directed onto the second optical path. A modulator is positioned in at least one of the optical paths and is responsive, during a time segment, to a first applied control signal, to alter the phase, and thus the frequency, of the first component by approximately one frequency slot. At the output of the first and second optical paths, an optical coupler interferes the first component and the second component so as to enable constructive and destructive interference therebetween in accordance with respective phase modulations thereof.

Apparatus for spectral encoding and decoding of femtosecond optical

A combined wavelength router and switch apparatus for use in an optical communication system is disclosed. The apparatus includes arrays of optical signal demultiplexers, wavelength division switches, space division switches and multiplexers, arranged in a manner that can increase the connectivity of an optical system using wavelength division multiplexed (WDM) signals. In several embodiments, time-multiplexed wavelength division switches and time-multiplexed space division switches may be used to increase further the degree of connectivity of the system or to reduce the number of wavelength division switches and space division switches required. Additional arrays of wavelength division switches or time-multiplexed wavelength division switches may be included to allow carrier frequencies to be shifted to meet the channel ordering requirements of the optical system.

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Princeton, NJ, United States of America

Hisashi Kobayashi