J. Rodriguez-Tellez

An efficient evolutionary algorithm for channel resource management in cellular mobile systems

Modern cellular mobile communications systems are characterized by a high degree of capacity. Consequently, they have to serve the maximum possible number of calls while the number of channels per cell is limited. The objective of channel allocation is to assign a required number of channels to each cell such that both efficient frequency spectrum utilization is provided and interference effects are minimized. Channel assignment is therefore an important operation of resource management and its efficient implementation increases the fidelity, capacity, and quality of service of cellular systems. Most channel allocation strategies are based on deterministic methods, however, which result in implementation complexity that is prohibitive for the traffic demand envisaged for the next generation of mobile systems. An efficient heuristic technique capable of handling channel allocation problems is introduced as an alternative. The method is called a combinatorial evolution strategy (CES) and belongs to the general heuristic optimization techniques known as evolutionary algorithms (EAs). Three alternative allocation schemes operating deterministically, namely the dynamic channel assignment (DCA), the hybrid channel assignment (HCA), and the borrowing channel assignment (BCA), are formulated as combinatorial optimization problems for which CES is applicable. Simulations for representative cellular models show the ability of this heuristic to yield sufficient solutions. These results will encourage the use of this method for the development of a heuristic channel allocation controller capable of coping with the traffic and spectrum management demands for the proper operation of the next generation of cellular systems.

Characterization of thermal and frequency-dispersion effects in GaAs MESFET devices

New simple and accurate measurement procedures that enable the dispersion and thermal effects in GaAs MESFETs to be observed independently are presented in this paper. The results indicate that the differences observed between the static and pulsed characteristics of the device are not solely due to thermal effects, as is sometimes thought. Electrical and thermal measurements also show the GaAs MESFET to take a relatively long time before the effect of self-heating manifests itself on the IV characteristics of the device.

Borrowing channel assignment strategies based on heuristic techniques for cellular systems

The demand for more efficient and fast channel allocation techniques in cellular systems increases day by day. Borrowing channel assignment (BCA) was introduced in the literature as a compromise between the classic fixed and dynamic channel allocation schemes. This paper examines the behavior of three heuristic BCA techniques based alternatively on a Hopfield neural network, an efficient evolutionary algorithm named combinatorial evolution strategy (CES) and a third heuristic which combines the basic advantages of the two above computational intelligence methods. By considering some specific assumptions that follows an ideal cellular mobile model, BCA is formulated as a combinatorial optimization problem. The above heuristics have been extensively applied to solve efficiently such problems in the past. Simulation results, derived for uniform and nonuniform traffic load conditions, are used to compare these BCA schemes each other as also with other well-established allocation techniques.

Performance of DVB-T OFDM based single frequency networks: effects of frame synchronisation, carrier frequency offset and non-synchronised sampling errors

The orthogonal frequency division multiplexed (OFDM) modulation scheme has been proposed by the digital video broadcasting (DVB) project to facilitate the implementation of single frequency networks (SFN). In this paper, the performance of the DVB-T (2k mode) based SFN system is analysed. The effects on performance due to timing offset errors, carrier frequency offsets and sampling frequency offsets due to the lack of synchronisation between the transmitter and the receiver clocks are considered.

Improved junction capacitance model for the GaAs MESFET

An empirical equation for simulating the bias dependency of the junction capacitances of the GaAs MESFET is presented and compared with existing techniques. It provides increased accuracy over a wide range of silicon and GaAs devices for microwave circuit design applications and up to 72% savings in CPU execution speed over existing techniques. >

Simulation of temperature and bias dependencies of beta and V/sub TO/ of GaAs MESFET devices

A DC and temperature-nonlinear GaAs MESFET device model is presented. It offers improved accuracy over existing models by simulating the bias dependency of the device transconductance ( beta ) and pinch-off point (V/sub TO/) parameters. The effect of these bias dependencies becomes more important as the temperature departs from room temperature. Expressions for simulating the temperature dependency of V/sub TO/ and beta are presented and provide improved accuracy over existing techniques. The model effectively couples the bias and temperature dependency of the devices. >

Optically controlled 2.4GHz MMIC amplifier

In this paper a 2.4GHz MMIC amplifier for mobile applications is used to demonstrate the significant control that can be achieved in the amplifiers performance using optical illumination. The results presented show a 15dB variation in the amplifiers S21 figure and a 6 to 10dB variation in the input and output return loss when the incident optical power is varied.

Comparison of joint coarse timing and fine carrier frequency estimation algorithms for DVB-T OFDM based single frequency networks

In this paper, a comparison of several time domain, non data aided (NDA) joint coarse timing offset and fine carrier frequency estimation algorithms for the DVB-T (2k mode) based SFN system are analyzed. The goal is to achieve a timing estimate that avoids intersymbol interference (ISI) in the receiver and a carrier frequency estimate with a small error and standard deviation compared to the subcarrier spacing so that the intercarrier interference (ICI) is negligible in the receiver. Simulations have been performed for four different SFN configurations for fixed and portable reception.

Borrowing channel assignment strategy using computational intelligence methods

Computational intelligence methods such as neural networks (NNs) and evolutionary algorithms (EAs) have found a wide use in the field of communications. This paper examines and compares two specific heuristic techniques: the Hopfield NN and the combinatorial evolution strategy (CES) concerning their application to a borrowing channel assignment (BCA) strategy in cellular networks. At first, a cellular mobile model is constructed. By considering specific assumptions, BCA becomes a combinatorial optimization problem and may be solved by these two specific methods. Simulation results, derived for uniform and nonuniform traffic distributions, are presented and show the ability of these heuristics to handle such problems.

Genetic inspired channel assignment schemes for cellular systems

Channel allocation schemes in a cellular network can be modeled as combinatorial optimization problems. Genetic algorithms (GAs) have been shown to be effective and robust tools in providing adequate solutions of such problems. This paper investigates the application of GAs to two common assignment strategies from the field of cellular communications: the dynamic (DCA) and the borrowing channel assignment (BCA). In both schemes, channel allocation is formulated as a discrete energy minimization problem and can be put in proper genetic representation. A computer simulation model examines the performance of the proposed GA-DCA and GA-BCA schemes for uniform and non-uniform traffic distributions under the effect of cochannel and adjacent channel interference constraints.