A novel distributed scheduling scheme for OFDMA uplink using channel information and probabilistic transmission

Distributed uplink scheduling in OFDMA systems is considered. In the proposed model, mobile terminals have the responsibility of making their own transmission decisions. The proposed scheme is based on two dimensional reservation in time and frequency. Terminals use channel state information in order to favor transmissions over certain subchannels, and transmission is done in a probabilistic manner. The proposed approach provides more autonomy to mobile devices in making transmission decisions. Furthermore, it allows avoiding collisions during transmission since it leads to collision detection during the resource reservation phase. The proposed approach is compared to other random access methods and shown to be superior in terms of increasing sum-rate, reducing the number of users in outage, and reducing the collision probability in the reservation phase.     

Using fractional delay to control the magnitudes and phases of integrators and differentiators

The use of fractional delay to control the magnitudes and phases of integrators and differentiators has been addressed. Integrators and differentiators are the basic building blocks of many systems. Often applications in controls, wave-shaping, oscillators and communications require a constant 90deg phase for differentiators and -90deg phase for integrators. When the design neglects the phase, a phase equaliser is often needed to compensate for the phase error or a phase lock loop should be added. Applications to the first-order, Al-Alaoui integrator and differentiator are presented. A fractional delay is added to the integrator leading to an almost constant phase response of -90deg. Doubling the sampling rate improves the magnitude response. Combining the two actions improves both the magnitude and phase responses. The same approach is applied to the differentiator, with a fractional sample advance leading to an almost constant phase response of 90deg. The advance is, in fact, realised as the ratio of two delays. Filters approximating the fractional delay, the finite impulse response (FIR) Lagrange interpolator filters and the Thiran allpass infinite impulse response (IIR) filters are employed. Additionally, a new hybrid filter, a combination of the FIR Lagrange interpolator filter and the Thiran allpass IIR filter, is proposed. Methods to reduce the approximation error are discussed.     

A state variable approach to designing a resistive input, lownoise, noninverting differentiator

A state variable approach to designing a resistive input noninverting differentiator is presented. The differentiator consists of an active integrator and a summer. The upper break frequency where differentiation ceases is tunable by trimming a single resistance. The lower corner frequency where differentiation starts is tunable by varying the RC product of an integrator. The differentiation of high-frequency noise is avoided by switching to amplifier action at high frequencies. The integrator de-emphasizes high-frequency noise     

Comments on “FSK demodulation using an adaptive recursivedigital filter”

In a recent paper by Werter (see ibid., vol.44, p.1822-5, July 1996), an unjustified normal frequency distribution is assumed, and then, the resulting error probability is compared with that of the traditional noncoherent frequency shift keying (FSK). However, the traditional FSK demodulators were developed because such a distribution could not be justified. This work presents a more appropriate error probability expression     

Novel approach to designing digital differentiators

A novel approach to designing recursive stable digital differentiators is introduced. A four-step design procedure is presented. The procedure consists of obtaining or designing an integrator and then modifying its transfer function appropriately to obtain a stable differentiator. As an example a second order recursive differentiator is developed.<>     

An enhanced first-order sigma-delta modulator with a controllable signal-to-noise ratio

This paper presents an enhanced first-order sigma-delta modulator. The proposed modulator, derived using the Al-Alaoui operator, outperforms the conventional modulator. A comparison is drawn showing that the conventional sigma-delta modulator is a special case of the enhanced sigma-delta modulator. The paper includes an analytical derivation as well as extensive simulations revealing the superiority of the proposed modulator reaching optimal performance.     

A novel differential differentiator

A novel differentiator with differential inputs is described. It is characterized by a resistive input impedance and a single RC network which controls the differentiation action of the circuit. The differentiation of high-frequency noise is avoided by a transition to amplifier and integrator action at high frequencies. The common mode rejection ratio (CMRR) is more controllable in the new differentiator than in the traditional differential differentiator. Simulation and experimental results support the theoretical derivation     

Application of constrained generalized inverse to pattern classification

A constrained MSE procedure in the generalized inverse setting is presented. The procedure is motivated by Fisher's linear discriminant. The procedure is adaptive and tries to classify the means of the classes correctly and then vary the margin of this classification to achieve the least possible errors on the design set. The procedure was carried out on an example with very favorable results.     

Novel Approach to Analog-to-Digital Transforms

A novel approach to analog-to-digital transforms, s-to-z transforms, is presented. The approach applies the Boxer-Thaler expansion to a leaky differentiator or to a leaky integrator instead of an ideal differentiator or integrator. The bilinear (Tustin) and the matched pole-zero (MPZ) transformation are special realizations of the new transforms, with an additional built-in prewarping and additional built-in zero placement, respectively. Examples are presented that demonstrate the viability of the approach where the proposed method is compared with the least-squares, bilinear (Tustin), and MPZ transformations     

A stable differentiator with a controllable signal-to-noise ratio

The feedback properties of operational amplifiers are used in the construction of the differentiator. The basic concept, however is device-independent. Utilizing the tracking properties of feedback and using an integrator for a plant, the resulting error signal will approximate the derivative of the input. The system is stable for positive values of the gain. The signal-to-noise ratio (S/N) is controllable and is inversely proportional to the cubic power of the unity-gain bandwidth. The differentiator can have a higher frequency range of operation than is possible with other methods of design