Abstract: Techniques are described for carrier frequency offset (CFO) and channel estimation of orthogonal frequency division multiplexing (OFDM) transmissions over multiple-input multiple-output (MIMO) frequency-selective fading channels. A wireless transmitter forms blocks of symbols by inserting training symbols within two or more blocks of information-bearing symbols. The transmitter applies a hopping code to each of the blocks of symbols to insert a null subcarrier at a different position within each of the blocks of symbols, and a modulator outputs a wireless signal in accordance with the blocks of symbols. A receiver receives the wireless signal and estimates the CFO, and outputs a stream of estimated symbols based on the estimated CFO.

Abstract: A semidefinite (SDR) programming formulation for state estimation (SE) of nonlinear AC power systems is described. The techniques make use of convex semidefinite relaxation of the original problem to render the process efficiently solvable. In addition, robust techniques are described that are resilient to outlying measurements and/or adversarial cyber-attacks. Further, techniques for SDR-based SE are described in which local control areas solve the centralized SDP-based SE problem in a distributed fashion.

Abstract: Techniques are described for carrier frequency offset (CFO) and channel estimation of orthogonal frequency division multiplexing (OFDM) transmissions over multiple-input multiple-output (MIMO) frequency-selective fading channels. A wireless transmitter forms blocks of symbols by inserting training symbols within two or more blocks of information-bearing symbols. The transmitter applies a hopping code to each of the blocks of symbols to insert a null subcarrier at a different position within each of the blocks of symbols, and a modulator outputs a wireless signal in accordance with the blocks of symbols. A receiver receives the wireless signal and estimates the CFO, and outputs a stream of estimated symbols based on the estimated CFO.

Abstract: Techniques are described for carrier frequency offset (CFO) and channel estimation of orthogonal frequency division multiplexing (OFDM) transmissions over multiple-input multiple-output (MIMO) frequency-selective fading channels. A wireless transmitter forms blocks of symbols by inserting training symbols within two or more blocks of information-bearing symbols. The transmitter applies a hopping code to each of the blocks of symbols to insert a null subcarrier at a different position within each of the blocks of symbols, and a modulator outputs a wireless signal in accordance with the blocks of symbols. A receiver receives the wireless signal and estimates the CFO, and outputs a stream of estimated symbols based on the estimated CFO.

Abstract: Techniques are described for carrier frequency offset (CFO) and channel estimation of orthogonal frequency division multiplexing (OFDM) transmissions over multiple-input multiple-output (MIMO) frequency-selective fading channels. A wireless transmitter forms blocks of symbols by inserting training symbols within two or more blocks of information-bearing symbols. The transmitter applies a hopping code to each of the blocks of symbols to insert a null subcarrier at a different position within each of the blocks of symbols, and a modulator outputs a wireless signal in accordance with the blocks of symbols. A receiver receives the wireless signal and estimates the CFO, and outputs a stream of estimated symbols based on the estimated CFO.

Abstract: Techniques are described that provide inter-symbol interference—(ISI) and multi-user interference—(MUI) resilient blind timing synchronization and low complexity demodulation in wireless communication systems. A nonzero mean symbol is transmitted with a predetermined period in a stream of zero mean symbols during a synchronization phase. Only zero mean symbols are transmitted outside of the synchronization phase. Blind or non-data aided synchronization is performed at the receiver while bypassing channel estimation. The techniques enable timing synchronization via energy detection and low-complexity demodulation by matching the received waveform to a synchronized aggregate template (SAT). The SAT is recovered by averaging samples of the received waveform during the synchronization phase.

Abstract: Techniques are described that provide noncoherent demodulation via correlating “dirty” templates in wireless communication systems. In particular, the described techniques cross-correlate dirty templates that are adjacent symbol-long segments of the received noisy waveform. Unlike transmitted reference (TR) and differential templates that are noisy, i.e., propagate through the wireless communication channel, these dirty templates are both noisy and offset in time and, thus, are dirty. As a result, the described techniques enable noncoherent demodulation without timing synchronization and channel estimation. Symbol demodulation may be performed utilizing a maximum likelihood (ML) sequence detector or, alternatively, conditional ML demodulation may be performed to reduce receiver complexity. The described techniques may also be applied to a TR scheme to improve performance in the presence of mistiming.

Abstract: The invention provides an ultra-wideband (UWB) transmitter and various techniques for generating digitally filtered UWB pulses that substantially maximize power and bandwidth in one or more frequency bands while allowing narrow-band interference (NBI) to be avoided, e.g. interference to and from wireless local area networks (WLANs). In particular, the UWB transmitter utilizes a digital filter to generate digitally filtered UWB pulses to substantially maximize power and bandwidth in the Federal Communications Commission (FCC) spectral mask for UWB communications. In one embodiment, the invention provides a method comprising generating digitally filtered ultra-wide band (UWB) pulses to substantially maximize power in one or more frequency bands of a UWB spectrum and to substantially reduce power in one or more NBI frequency bands of the UWB spectrum. The invention may be implemented without modifying the analog components of existing UWB transmitters.

Abstract: A wireless communication system is described that generates FDFR transmissions with any number of transmit and receive antennas through flat-fading channels and frequency- or time-selective channels. In particular, the system utilizes layer-specific linear complex-field (LCF) coding with a circular form of layered space-time (ST) multiplexing to achieve FDFR wireless communications with any number of transmit and receive antennas through flat-fading and frequency- or time-selective channels. Additionally, the described techniques provide flexibility for desirable tradeoffs among performance, rate, and complexity.

Abstract: Techniques are described for multicarrier multiple access wireless transmission, e.g. orthogonal frequency-division multiple access (OFDMA) transmissions, over frequency selective fading channels. The techniques are designed to maintain constant modulus transmissions for uplink while effectively mitigating intersymbol interference. Specifically, the techniques utilize non-redundant unitary precoding across OFDMA subcarriers to maintain constant modulus transmissions for uplink communications. For example, the techniques involve precoding a block of information symbols and assigning a different subcarrier for each symbol of the block. The subcarriers are selected to be equi-spaced and may be selected, for example, from a phase-shift keying constellation. The number of symbols per block is equal to the number of subcarriers assigned per user. Importantly, even with multiple subcarriers per user, the techniques enable constant modulus transmissions for uplink.

Abstract: Techniques are described for space-time block coding for single-carrier block transmissions over frequency selective multipath fading channels. Techniques are described that achieve a maximum diversity of order NtNr (L+1) in rich scattering environments, where Nt (Nr) is the number of transmit (receive) antennas, and L is the order of the finite impulse response (FIR) channels. The techniques may include parsing a stream of information-bearing symbols to form blocks of K symbols, precoding the symbols to form blocks having J symbols, and collecting consecutive Ns blocks. The techniques may further include applying a permutation matrix to the Ns blocks, generating a space-time block coded matrix having Nt rows that are communicated through a wireless communication medium. The receiver complexity is comparable to single antenna transmissions, and the exact Viterbi's algorithm can be applied for maximum-likelihood (ML) optimal decoding.

Abstract: Techniques are described for channel estimation of block transmissions over time- and frequency-selective wireless fading channels. A wireless transmitter forms blocks of symbols that include at least two blocks of training symbols separated by at least one information-bearing symbol. Each block of training symbols comprises a first block of zero symbols and a second block of zero symbols separated by at least one training symbol. Each block of training symbols is equally long and equally spaced between information-bearing symbols. The training and information-bearing symbols are transmitted with equal power, respectively. A wireless receiver receives a wireless transmission signal formed according to the blocks of symbols and forms an estimate of a wireless communication channel based on the training symbols within the received signal.

Abstract: Techniques are described for generating digital carrier multi-band user codes for a baseband ultra-wideband (UWB) signal. The digital carrier multi-band user codes comprise spreading codes that enable multiple access in a UWB system. The user codes are digital, lead to baseband operation, and provide flexibility in handling narrow band interference (NBI) within the UWB system. In one embodiment, the invention provides a method comprising generating digital carrier multi-band user codes for a baseband ultra-wideband (UWB) signal of a user in an UWB system.

Abstract: The invention is directed to techniques for space-time coding in a wireless communication system in which the transmitter makes use of multiple transmit antennas. The transmitter uses channel information estimated by a receiving device and returned to the transmitter, e.g., as feedback. In one exemplary embodiment, the transmitter receives a mean feedback information that defines a mean channel value associated with the different channels of the different antennas. In another exemplary embodiment, the transmitter receives covariance feedback, e.g., statistical values associated with each of the different channels.

Abstract: Techniques are described for maintaining the orthogonality of waveforms transmitted in ultra wideband (UWB) multi-user wireless communication systems. The multi-stage block-spreading (MS-BS) techniques described herein deterministically eliminate multiple user interference (MUI) in the presence of frequency-selective fading channels. A transmitter includes a block-spreading unit to generate a stream of frames from a block of information bearing symbols by applying an orthogonal set of spreading codes, such as direct sequence cod& division multiple access (CDMA) codes or digital carrier frequency multiple access codes, such that the frames corresponding to different blocks of the symbols are interleaved. The transmitter further includes a time-hopping spreading unit to generate a stream of chips from the stream of frames by applying an orthogonal set of time-hopping (TH) spreading codes such that chips corresponding to different frames are interleaved.

Abstract: Techniques are described for space-time-frequency (STF) coding of multi-carrier transmissions over frequency-selective fading channels. In particular, techniques for STF coding of MIMO-OFDM systems are described that provide maximum diversity, high coding gains, and low decoding complexity are described. A set of generally correlated OFDM subcarriers are divided into groups of subcarriers creating a set of group STF (GSTF) subsystems, within which STF coding is applied to each GSTF subsystem. Subcarrier grouping preserves maximum diversity gains and simplifies both the code construction within each GSTF and decoding complexity. ST coding techniques are used in designing STF block (STFB) and STF trellis (STFT) codes which are applied within GSTF subsystems.

Abstract: Techniques are described for performing block equalization on a received wireless communication signal formed according to interleaved chips generated from sub-blocks of symbols. For example, a one-step block equalization process is described which produces estimates of the information-bearing symbols from a wireless communication signal received from two or more transmitters in a soft handoff environment. The techniques provide improved performance in high load, soft handoff environments with low complexity, highly flexible equalization. The wireless communication signal may be a CIBS-CDMA signal in which a symbol block is divided into sub-blocks and spread by a user-specific block-spreading matrix. The CIBS signal is received through M subchannels and a de-spreading matrix is applied to produce a multi-user interference (MUI) free sub-block output for the mth channel.

Abstract: Techniques are described for synchronizing the timing of the receiver with the received waveform in ultra wideband (UWB) communication systems. The described techniques correlate the received waveform with dirty templates, i.e. segments of the received waveform, with the received waveform to estimate the timing offset. The described techniques include receiving an ultra wideband (UWB) waveform through a wireless communication channel, wherein the received UWB waveform comprises bursts of information-bearing symbols. A template is selected to be used for estimating the timing offset of a burst of the received UWB waveform, wherein the template comprises a segment of a burst of the received UWB waveform, and the template is correlated with a segment of a burst of the received waveform so as to form an estimate of the timing offset of the received UWB waveform. A stream of symbol estimates is output in accordance with the estimated timing offset.

Abstract: Space-time (ST) coding techniques are described for multi-antenna transmissions in ultra-wideband (UWB) communication systems. The ST coding schemes may, therefore, be tailored for dense multipath channels. The techniques may be applied with linear and nonlinear modulation, coherent and noncoherent reception, and block interleaving of symbols. An UWB communication system is described that includes an ST encoder at the transmitter, multiple transmit and receive antennas, and two-step maximum ratio combining (MRC) at the receiver. The two-step MRC enables the receiver to collect full spatial and multipath diversity from a transmission. Two coding schemes for an UWB system with two transmit antennas and one receive antenna are described. Multiple antenna transmissions of ST encoded symbols increase the amount of diversity a receiver is able to collect without increasing the complexity of the receiver.

Abstract: In general, linear complex-field encoding techniques are proposed For example, transmitter of a wireless communication system includes an encoder and a modulator. The encoder linearly encodes a data stream to produce an encoded data stream. The modulator to produce an output waveform in accordance with the encoded data stream for transmission through a wireless channel. The modulator generates the output waveform as a multicarrier waveform having a set of subcarriers, e.g., an Orthogonal Frequency Division Multiplexing (OFDM) waveform. The encoder linearly encodes the data stream so that the subcarriers carry different linear combinations of information symbols of the data stream.