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This correspondence presents a design of 3780-point IFFT Processor for TDS-OFDM terrestrial DTV transmitter using FPGA. It demonstrates the algorithm design and error analysis of the processor, which can achieve a throughput of 7.56M complex IFFT operations per second. This design meets the signal-to-quantization noise ratio requirement of the TDS-OFDM system. It consists of two FPGA and one dual-port RAM. The data stream pipeline algorithm is implemented. Index Terms--Circuit optimization, FFT, HDTV, pipeline processing, signal processing.

Single Rhodamine 6G (R6G) molecules in levitated glycerol microdroplets have been detected with signal-to-noise ratios of >40 using CW laser-induced fluorescence. The fluorescence signal from single R6G molecules was identified by the magnitude of the fluorescence signal and by the unique time dependence of the fluorescence count rate before photobleaching. This high sensitivity allows single molecules to be counted by use of a digital detection approach offering significantly lower detection limits than those possible with conventional detection methods.

The analysis of spectral autocorrelation (SAC) function for scatterer configurations, a function of the regularity of the interspacing distances between scatterers, facilitates the detection of localized flaws in grain noise. The analysis is conducted for two cases of maximum likelihood estimator for backscattered energy, pertaining to coherent reflectors found within the media of microstructure scatterers. The uniformity of microscatterer distribution results in the enhancement of SAC terms between different frequencies. The characterization of SAC facilitates the improvement of signal to noise ratio in the coherent scatterer echo intensities of estimators.

We consider the computational cutoff rate and its implications on signal design for the complex quasi-static Rayleigh flat-fading spatio-temporal channel under a peak-power constraint where neither transmitter nor receiver know the channel matrix. The cutoff rate has an integral representation which is an increasing function of the distance between pairs of complex signal matrices. When the analysis is restricted to finite-dimensional sets of signals, interesting characterizations of the optimal rate-achieving signal constellation can be obtained. For an arbitrary finite dimension, the rate-optimal constellation must admit an equalizer distribution, i.e., a positive set of signal probabilities which equalizes the average distance between signal matrices in the constellation. When the number N of receive antennas is large, the distance-optimal constellation is nearly rate-optimal. When the number of matrices in the constellation is less than the ratio of the number of time samples to the number of transmit antennas, the rate-optimal cutoff rate attaining constellation is a set of equiprobable mutually orthogonal unitary matrices. When the signal-to-noise ratio (SNR) is below a specified threshold, the matrices in the constellation are rank one and the cutoff rate is achieved by applying all transmit power to a single antenna and using orthogonal signaling. Finally, we derive recursive necessary conditions and sufficient conditions for a constellation to lie in the feasible set. Index Terms--Flat Rayleigh fading, minimal-distance codes, optimal signal design, peak-power constraints, space--time coding, spatial diversity, unitary constellations.

A pressure-measurement system based on surface-acoustic-wave (SAW) sensors is presented in this paper. Since SAW sensors are powered by the energy of the RF field, no battery is required, which is a major drawback of conventional microcontroller-based telemetry systems. A successful combination of a SAW reflective delay line with a high-Q capacitive pressure sensor is shown. With a new way of matching the sensor impedance to the SAW reflector impedance, both a high signal-to-noise ratio and a high signal dynamic are achieved, which supports accurate signal evaluation. As an example of realization, the prototype of a tire pressure sensor unit is presented. Index Terms--Pressure measurement, surface-acoustic-wave delay lines, telemetry.

The signal-to-interference ratio (SIR) has been highlighted in the literature to be an efficient criterion for several radio resource management algorithms such as power control and handoff. In this paper we address the problem on how to obtain fast and accurate measurements of this quantity in a practical context. We develop a general SIR estimation technique for code division multiple access (CDMA) cellular systems, that is based on a signal subspace approach using the sample covariance matrix of the received signal. Analysis and simulation results for an IS-95 like system show that the SIR can be estimated to within 80% of the actual SIR after less than seven frames, or within 90% of the actual SIR after less than 15 frames. We also study a computationally less expensive SIR tracking algorithm based on updating the signal subspace. We show that the algorithm works well in the context of a rapidly time varying channel. Index Terms--code division multiple access (CDMA), signal-to-interference ratio (SIR), subspace algorithms.

Described is a decorrelating filter that separates signals in a multiuser environment by relying on the relative delays to be sufficiently distinct. The input signal is fractionally sampled to allow for the differentiation of the user delays. Both zero-forcing and minimum mean-square-error versions of this filter are derived and probability of error expressions are given. The algorithm successfully separates unknown digital signals by using the known received pulse shapes and the symbol rate. A delay-division multiple-access (DDMA) scheme based on this signal decorrelator is proposed that will allow signals to be transmitted without spreading the signal spectrum. It is shown that in a noisy environment the signal-to-noise ratio penalty for DDMA can be severe yet the bandwidth advantage is very pronounced compared to spread-spectrum systems and is similar to other bandwidth efficient schemes. The performance of a code-division multiple-access (CDMA) system using this signal decorrelator is also given. The decorrelator can be used as a blind multiuser detector or as a preprocessor to enhance the performance of a CDMA system. Index Terms--Code-division multiaccess, decorrelation, multiuser channels.

The problem of noncoherent multiuser detection for multipulse modulation over the Gaussian multiuser channel is studied. It is assumed that neither the energies nor the carrier phases of the signals of any of the users are available at the receiver. Recently, a post-decorrelative generalized likelihood ratio test (GLRT) based detector was proposed as a solution to this problem. In this paper, we introduce the concept of noncoherent decision feedback (DF) that forms the basis for an improved solution to the same problem. The users are detected sequentially in some fixed order, and the decision for a particular user takes advantage of the reduction of uncertainty associated with the signal space resulting from decisions already made for previous users. In contrast to coherent DF, therefore, the feedforward and feedback transformations in the noncoherent case are themselves functions of the matched filter outputs. An efficient implementation of the noncoherent DF detector for M-ary modulation and [Rho]-dimensional signal space requires O(M[Rho]) computational complexity per user. Upper and lower bounds on its symbol error probability are obtained. It is shown that significant improvements over the post-decorrelative GLRT-based detector are often possible. Sufficient conditions are obtained which guarantee, without ignoring error-propagation effects, that the high signal-to-noise performance of the DF strategy can be as good as its genie-aided version in which perfect past users' decisions are used. Index Terms--Code-division multiple access, differentially coherent decision feedback, multiuser channels, noncoherent decision feedback, noncoherent detection, multipulse modulation.

A new look-ahead (LA) scheme, distributed look-ahead (DLA), is proposed for pipelined implementation of recursive digital filters. It is established that, in the case of many recursive filters, DLA can provide equivalent and stable implementation with reduced multiplication and latch complexities, higher area-efficiency. It also produces outputs with reduced delays, when compared with some existing LA schemes. Stability regions for the proposed scheme are also well defined. Next, a time-domain approximation method is proposed for direct design of pipelined recursive filters that can achieve superior match with reduced pipelined filter orders. Index Terms--Filter approximation, IIR filters, look-ahead approach, optimal filters, pipelining.