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By using continuous-phase frequency shift keying (CPFSK) in a direct-sequence code-division multiple-access (DSCDMA) system, and by partitioning the spreading sequence so that differing patterns of plus and minus chips are multiplied onto successive data bits, the net phase change will differ from bit to bit, giving an apparent variation in modulation index similar to multi-h CPFSK. This gives similar coding gain effects as multi-h CPFSK when maximum-likelihood sequence detection is used. Improved probability of error performance in terms of increased minimum distance has been demonstrated when the spreading sequence of a CDMA system is properly overlaid on outgoing data bits in the CPFSK modulation scheme. At the best modulation index observed, h = 5/7, a computer search shows [approximately]1.4-dB advantage over binary phase shift keying, and a ~0.6-dB advantage over the best fixed-h CPFSK. Index Terms - Continuous-phase frequency shift keying, code division multiple access, spread spectrum.

The worldwide installed analog broadcast networks suffer from problems in quality, power consumption, and waste of frequency spectrum. They will be replaced by digital networks in the next century. For analog networks, the planning parameters for frequency, power, and site assignment are well known. For digital audio broadcasting (DAB) networks, the research of the relevant criteria has just started. This paper presents the derivation of protection ratios and field strength levels under worst case conditions for Eureka 147 orthogonal frequency division multiplex (OFDM)-based digital audio broadcast systems from the bit error rate (BER) of the unprotected propagation channel. The channel is characterized by a three-dimensional (3-D) ray optical wave-propagation model. The peculiarities of the resulting multipath field strength delay spectra in single-frequency networks (SFN's) for the calculation of the signal-to-noise ratio (SNR) and the BER at the receiver are discussed. Different terrain types and frequencies are considered. A statistical analysis of the relationship between the SNR and BER leads to the determination of the cochannel protection ratio. An expansion thereof results in the adjacent-channel protection ratios. The minimum required field strength is derived from the protection ratios and the BER's. The influence of different spatial and temporal probabilities is investigated. Examples are shown for verification at 230 and 1472 MHz. Index Terms - Bit error rate, channel characterization, digital audio broadcasting, protection ratio.

A drift-diffusion model for silane and a three-moment model for chlorine were used to study the step response of typical electronegative process gases. Three types of transients were found for silane. The step response of chlorine discharges was characterized by a smooth transition from one steady state to the next. Results suggested that the temporary extinction of the discharge and natural pulsed steady state is the effect of how the voltage is divided between the gap and blocking capacitor during the transient.

Lower bounding techniques were employed to address a frequency assignment problem. The techniques, which perform better than direct heuristic application, are specifically proven effective in assignment problems that result from practice since they are often able to achieve good bounds from such kind of constraints. Lower bounding techniques involve identification of best lower bounds from the complete problem's subproblem.

The channel-assignment problem is important in mobile telephone communication. Since the usable range of the frequency spectrum is limited, the optimal channel-assignment problem has become increasingly important. In this paper, a new channel-assignment algorithm using a modified Hopfield neural network is proposed. The channel-assignment problem is formulated as an energy-minimization problem that is implemented by a modified discrete Hopfield network. Also, a new technique to escape local minima is introduced. In this algorithm, an energy function is derived, and the appropriate interconnection weights between the neurons are specified. The interconnection weights between the neurons are designed in such a way that each neuron receives inhibitory support if the constraint conditions are violated and receives excitatory support if the constraint conditions are satisfied. To escape the local minima, if the number of assigned channels are less than the required channel numbers (RCN's), one or more channels are assigned in addition to already assigned channels such that the total number of assigned channels is the same as the required number of channels in the cell even though energy is increased. Various initialization techniques, which use the specific characteristics of frequency-assignment problems in cellular radio networks, such as cosite constraint (CSC), adjacent channel constraint (ACC), and cochannel constraint (CCC), and updating methods are investigated. In the previously proposed neural-network approach, some frequencies are fixed to accelerate the convergence time. In our algorithms, no frequency is fixed before the frequency-assignment procedure. This new algorithm, together with the proposed initialization and updating techniques and without fixing frequencies in any cells, has better performance results than the results reported previously utilizing fixed frequencies in certain cells. Index Terms - Cellular mobile network, channel assignment, neural network, wireless communication.

In radio systems, quality of service is achieved by assigning channels with reference to a set of protection ratios, which in a simplified setting may be replaced with frequency-distance bounds. This paper considers the assignment problem on a lattice of hexagonal cells, with the allowed assignments generated by regular tilings of a single polyhex. The main aim is to investigate the interplay between the cochannel and adjacent channel separations without restricting the assignments unnecessarily. The outcome is a unified framework in which all previous results appear as particular cases. The possible cochannel lattices are carefully classified, and then an algorithm is developed, which assigns channels on any cochannel lattice so that the adjacent channel separation is maximized. In this way, a library of the best assignments can be compiled. The results are of relevance to a range of applications, including both broadcast and mobile systems. Index Terms - Radio channel assignment, regular networks, spectrum planning.

An innovative hierarchical microcell/macrocell architecture is presented. By applying the concept of cluster planning, the proposed sectoring arrangement can provide good shielding between microcells and macrocells. As a result, underlaid microcells can reuse the same frequencies as overlaying macrocells without decreasing the macrocell system capacity. With the proposed method, microcells not only can be gradually deployed, but they can be extensively installed to provide complete coverage and increase capacity throughout the service area. With these flexibilities, the proposed method allows existing macrocellular systems to evolve smoothly into a hierarchical microcell/macrocell architecture. Index Terms - Cluster planning, hierarchical cellular architecture, macrocell/microcell overlaying system.

To achieve a high spectrum efficiency in cellular radio systems, the radio resource allocation algorithms have to be adaptive to the actual traffic and interference situation. The focus of the paper is on performance bounds of a cellular radio system using Dynamic Channel Assignment (DCA) combined with Power Control (PC). A trivial upper bound on the performance is identified. The bound is given by the performance of a hypothetical system which is able to use all channels simultaneously in all cells. A lower bound on the performance is derived from a theoretical PC supported DCA-algorithm. For a highway micro cellular system and a deterministic propagation model, numerical results show that the lower and upper bounds are tight. That is, the results indicate that it is possible to use all channels in all cells simultaneously and still provide an acceptable signal-to-interference ratio in all assigned communication links.

This paper deals with an efficient Dynamic Channel Allocation (DCA) technique applicable to terrestrial mobile cellular networks. A channel (or resource) is a fixed frequency bandwidth (FDMA), a specific time-slot within a frame (TDMA), or a particular code (CDMA), depending on the multiple access technique used. A cost function has been defined by which the optimum channel to be assigned on demand can be selected. In addition, a suitable mobility model has been derived to determine the effects of handovers on network performance. The performance of the proposed DCA technique has been derived by computer simulations in terms of call blocking and handover failure probabilities. Comparisons with the classical Fixed Channel Allocation (FCA) technique and other dynamic allocation algorithms recently proposed in the literature have been carried out to validate the proposed technique.

We investigate algorithms based on simulated annealing to solve the channel assignment problem for cellular radio networks. The blocking probability of a network is chosen as the optimization criterion. In order to check the quality of the solutions obtained by simulated annealing, we examine some special types of networks which allow an effective calculation of optimal solutions by tailored algorithms. Our investigations show that simulated annealing is a very powerful tool for solving channel assignment problems.

For wireless cellular communication systems, one seeks a simple effective means of power control of signals associated with randomly dispersed users that are reusing a single channel in different cells. By effecting the lowest interference environment, in meeting a required minimum signal-to-interference ratio of Rho per user, channel reuse is maximized. Distributed procedures for doing this are of special interest, since the centrally administered alternative requires added infrastructure, latency, and network vulnerability. Successful distributed powering entails guiding the evolution of the transmitted power level of each of the signals, using only local measurements, so that eventually all users meet the Rho requirement. The local per channel power measurements include that of the intended signal as well as the undesired interference from other users (plus receiver noise). For a certain simple distributed type of algorithm, whenever power settings exist for which all users meet the Rho requirement, we demonstrate exponentially fast convergence to these settings.

Channel allocation is one of the fundamental problems faced by designers of the portable communication systems. A Distributed Dynamic Channel Allocation (DDCA) algorithm is proposed. The DDCA combines the advantages of both the fixed and the dynamic channel allocation algorithms in an effective way. Initialization is easy and it is adaptive to slowly changing environments. It is flexible. A port can utilize all the channels available to the system. It is adaptive to slowly changing environments so that the port can adjust the channel allocation automatically when ports are added or removed from the system. It is stable, simple and fully distributed. Simulation shows that it has 25% improvement over the U.K. DECT testbed DCA and 16% improvement over the Channel Segregation DCA, in terms of system capacity with one percent of grade of service.

In this paper, we consider the problem of dynamic channel allocation in cellular networks. Each cell can use any channel, subject to the interference constraints. Channel allocation algorithms are executed by the network switch in a centralized way. We show how to design and use objective functions aimed at proper channel allocation and improvement of network performance. As a figure of merit of network performance, we consider the blocking probability in the network as a whole, and the maximum blocking probability in any particular cell of the network ('hot-spot' in the network). We designed three specific channel allocation policies, based on three different objective functions. Compared with two other benchmark policies, our approach shows significant improvement. Performance analysis of various channel allocation policies is virtually impossible without simulations, which are prohibitively time-consuming in the case of small blocking probabilities. We propose an original approximate method based on a short simulation and an analytic approximation. The method exhibits good accuracy and significant improvement in efficiency.

In this paper, a hardware device called Channel Allocator is proposed to speed up channel allocation and to select the appropriate channel allocation algorithm according to the current traffic requirements and/or interference conditions. The main advantage of Channel Allocator is its high efficiency in allocation of available radio channels (order of nanoseconds). Channel Allocator belongs to the architecture of the network switch. Several channel allocation algorithms can be incorporated within Channel Allocator at the same time. If the traffic and/or interference conditions change, Channel Allocator selects the channel allocation algorithm (among the available) which provides a desired performance for the new conditions.

The paper extends the evaluation of packet reservation multiple access (PRMA) from a single cell case, investigated in several previous papers, to a cellular environment characterized by user mobility and by the interference from other cells. The analysis will be based on a comparison of PRMA performances with those of classical circuit switching schemes. The work is structured in two parts: firstly the comparison methodology is defined, subsequently the comparison is performed by means of a simulation program based on a dynamic traffic model. Finally the paper deals with the possibility of using PRMA together with dynamic channel allocation.

The channel assignment problem (CAP), i.e., the task to assign the channels to the radio base stations in a spectrum efficient way, is an NP-complete optimization problem occurring during design of cellular radio systems. So far, this problem has been solved by graph coloring algorithms. An alternative approach is presented in this paper. The problem is solved using simulated annealing, which is a general approach to combinatorial optimization. The algorithm has been successfully applied to practical radio network planning situations. One major benefit of the approach consists in the enhanced flexibility it gives to the engineer.

This paper describes a new multi-correlation process for reducing the rms error between the field strength values predicted by the use of the method laid down in Report 894.2 (1) and the values of Databank.D1. We use three functions. The first function has 1080 coefficients describing 10 distance ranges, 4 solar activity ranges and 27 frequency to MUF ratio (f/MUF) ranges. The second function covers 10 distance ranges and 24 local time data in the mid path with a total of 240 coefficients. The third function has 720 coefficients covering 10 distance ranges, 6 modified dip angle values, and 12 months. With the use of these new functions, the final rms error is 7.69 dB for the whole set of circuits of Databank.D1 database and 7.29 dB for short paths. The Report 894.2 method has a rms error of 10.1 dB. Four plots are included to compare that method with the improved method (2).

An ordered dynamic channel assignment with reassignment (ODCAR) scheme is proposed, and its performance is studied in a highway microcellular radio environment. Channels are assigned in an ordered basis in conjunction with a minimax algorithm under co-channel interference constraints, to provide high capacity and to alleviate worst case channel congestion in each microcell. Simulation results show significant performance improvements in terms of channel utilization and probability of call failure, at the expense of an increase in complexity and call switching requirements.

Sprites are upper atmospheric optical phenomena associated with lightning (1, 2). They have been implicated in electrochemical processes in the upper atmosphere (3) and transfer large amounts of charge between [...]