Showing papers in "HKIE Transactions in 1998"
TL;DR: In this article, the daily closing values of major stock market indices in Asia, Europe and America are predicted using information contained in articles pubilshed on the Web. And the forecasts are available real-time via www.cs.ust.hk/~beat/Predict dally at 7:45 am Hong Kong time.
Abstract: We predict stock markets using information contained in articles pubilshed on the Web. Mostly textual artictes appearing in the leading and the most influential financial newspapers are taken as input. From those articles the daily closing values of major stock market indices In Asia, Europe and America are predicted. Textual statements contain not only the effect (e.g., stocks down) but also the possible causes of the event (e.g., stocks down because of weakness in the dollar and consequently a weakening of the treasury bonds). Exploiting textual information therefore increases the quality of the input.The forecasts are available real-time via www.cs.ust.hk/~beat/Predict dally at 7:45 am Hong Kong time. Hence all predictions are available before the major Asian markets, Tokyo, Hong Kong and Singapore, start trading. Several techniques, such as rule-based, k-NN algorithm and neural net have been employed to produce the forecast. Those techniques are compared with one another. A trading strategy based on t...
29 citations
TL;DR: In this article, a high bandwidth efficiency variable rate adaptive channel coding scheme, ATC-QAM, is proposed, where known pilot symbols are transmitted periodically to aid demodulation.
Abstract: A high bandwidth efficiency variable rate adaptive channel coding scheme, ATC-QAM, is proposed. Known pilot symbols are transmitted periodically to aid demodulation. Past channel states are fed back to the transmitter with delay. Current channel state is then predicted at the transmitter to decide on the appropriate modulation mode for the current symbol. At good channel state, high level modulation is used to boost up the average throughput. At bad channel state, how level modulation is used to increase error protection. By matching the variable modulation level with a variable rate channel coder, the physical bandwidth is maintained constant. Design issues for the ATCQAM are considered. Pradicol schmes to maintain transmitter-receiver synchranization, namely the quasi-Closed loop control and the closed-loop control, are discussed. The effects offinite feedback delay, finite interleaving depth and mobile speed are Investigated. Keywords: Adaptive Channel Coding
25 citations
TL;DR: In this paper, an energy audit has been conducted for a commercial office building in Hong Kong, which is equipped with a large number of electricity sub-meters, and a survey of the energy end-use of tenants was conducted to obtain information about the lighting and equipment loads in various premises in the building.
Abstract: An energy audit has been conducted for a commercial office building in Hong Kong. This building is equipped with a large number of electricity sub,meters which greatly facilitated the audit study. In addition, a survey of the energy end-use of tenants has been conducted to obtain information about the lighting and equipment loads in various premises in the building. Besides the audit and survey results, comparisons with consumption of typical buildings in Hong Kong and with computer simulation results for an energy efficient building are presented. From the comparison, the most promising energy efficiency improvement measures have been identified for further in-depth studies.
20 citations
TL;DR: In this paper, a detailed investigation and statistical tests on the completeness of the earthquake catalogue and the regional variation of the seismicity have been carried out, and it has been found that in the catalogue compiled in this study the historical records on land since 1895 are likely to be complete for surface-wave magnitude M = 4 % or greater.
Abstract: The seismicity model, the Gutenberg-Richter magnitude-frequency relationship. has been developed for Hong Kong region. Detailed investigation and statistical tests on the completeness of the earthquake catalogue and the regional variation of the seismicity have been carried out. It has been found that in the catalogue compiled in this study the historical records on land since 1895 are likely to be complete for surface-wave magnitude M = 4 % or greater. and that there is no record before 1920 in offshore area about 100 km from coastal lines. Almost all historical records before 1894 are on land. indicating that the historical records may be complete only on land. The earthquake spatial distribution is not uniform on land. The number of earthquakes with M = 6 or greater per year in the last 100 years is much larger than that in the previous historical time (1500–1894). It has also been found that the regional variation of the seismicity is a significant factor likely to affect the seismic hazard in Hong Ko...
16 citations
TL;DR: In this paper, a survey has been conducted on certified contractors to collect objective and representative evidence of the practicability of applying ISO 9000 to the construction industry and reveal their motivation for and experience in impiementing a quality management system to ISO 9000.
Abstract: Quality assurance has been widely adopted by the construction sectors in Hong Kong since the introduction of ISO 9000 quality standards in 1987. Over 100 building and Civil engineering contractors have successfully achieved ISO 9000 certification in Hong Kong but a vigorous debate still continues on how appropriate ISO 9000 is to the construction Industry. The ISO 9000 was initially developed with the manufacturing industry in mind and may not be totally suitable for the construction Industry. A survey has been conducted on certified contractors to collect objective and representative evidence of the practicability of applying ISO 9000. This paper reveals their motivation for and experience in impiementing a quality management system to ISO 9000. The benefits of the ISO 9000 quality system on construction companies and the inter-relationship between quality, cost and time are also discussed.
10 citations
TL;DR: An air conditioning system simulation program BECON has been developed for predicting energy consumption for airconditioning in buildings as discussed by the authors, which relies on a buiiding heat transfer simulation pragram HTB2 to provide the input of hourly space cooling loads of a building.
Abstract: An air-conditioning system simulation program BECON has been developed for predicting energy consumption for airconditioning in buildings. BECON relies on a buiiding heat transfer simulation pragram HTB2 to provide the input of hourly space cooling loads of a building. The two programs are adapted as the computing tool in HK-BEAM, the Hong Kong Building Environmental Assessment Method, launched in December 1996. in the paper, the range of system and equipment models included in BECON, the methods it uses to model the performance of air-conditioning systems, and the functions of its front-end program are described.
9 citations
TL;DR: In this article, a new approach is proposed for evaluating the performance of vertical drains, which involves comparing the minimum discharge capacity qw(min) of a vertical drain installation required for negligible well resistance with the discharge capacity mobilized in the field.
Abstract: A new approach is proposed for evaluating the fieid performance of vertical drains. This method involves comparing the minimum discharge capacity qw(min) of a vertical drain installation required for negligible well resistance with the discharge capacity mobilized in the field, qw(mob). A procedure has been developed for the estimation of qw(min), which has a typical value in the range Of 2 to 100 m3/yr, depending on the horizontal permeability of the soil and the maximum drainage length Of the vertical drain. A computer program, ILLICON, was developed for settlement analysis of embankments on soft ground and was used to back-calculate qw(min) from field observations of settlement and pore water pressure. The drain performance at four vertical drain installation schemes was evaluated using the proposed method. It was found that the magnitude of the compressive strain undergone by soil during preloading is a critical factor to the proper functioning of vertical drains.
6 citations
TL;DR: In this article, the authors used the Nakamura's ratio to assess seismic ampiification of sou sites in Hong Kong and found that the ratio takes a value of unity at a wide frequency range when the site has no large topographical effect.
Abstract: Microtremor records have been used to assess seismic ampiification of sou sites in Hong Kong. The method is based on ratios of horizontal and vertical camponents of microtremor (ambient noise) recards, and the ratios are aften referred to as Nakamura’s ratios. The peakfrequency of the Nakamura’s ratio carrelates well with thefundamental modal frequency estimated from the site shear wave velocities which were derived by a vertical seismic profiling method or were converted from SPT data. The amplitudes of the ratios are very stable and the standard deviation of the ratios derived from a series of measurements is reasonably small. Results from rock sites show that the ratios take a value of unity at a wide frequency range when the site has no large topographical effect. The ratios are generally larger than unity if the site has topographical effect but no dominant peak appears in the ratios. Results from sou sites show that a dominant peak appears at the fundamental frequency of the site and the amplitudes ...
6 citations
TL;DR: To examine the reliability of the travel time functions, the calibrated functions were validated by independent observed data and incorporated into a pedestrian simulation package for evaluation and could be used as a basis for the development of pedestrian simulation models for the underground stations in Hong Kong.
Abstract: This paper reports an investigation on the pedestrian travel timefundions for various pedestrian facilities in the Hong Kong Mass Transit Raifwoy (MTR) stations. As the pedestrian walking behavior con be influenced by the physical properties of the walking facilities, different pedestrian facilities are classified for analysis. Surveys were conduded in the Hong Kong MTR stations and the data collected were used to develop fifteen sets of pedestrian travel time function for the classified pedestrian facilities. The data colleded were also compared with the previous research findings for London underground stations. Further more, to examine the reliability of the travel time functions, the calibrated functions were validated by independent observed data and incorporated into a pedestrian simulation package for evaluation. The calibrated functions could be used as a basis for the development of pedestrian simulation models for the underground stations in Hong Kong.
6 citations
TL;DR: In this article, a survey of 30 central chiller plants in Hong Kong was conducted to obtain a general picture about the provision of instrumentation in chiller systems in general, and the survey results indicated that instrumentation provision was in general inadequate.
Abstract: A survey of 30 central chiller plants has been conducted to obtain a general picture about the provision of instrumentation in chiller plants in Hong Kong. The survey results, summarized in this paper, indicate that instrumentation provision was in general inadequate. Equipment performance calculated from readings measured by inaccurate instruments will have unacceptably high uncertainties. The relationship between the uncertainties in the measurements and in the calculated equipment performance is analysed in this paper. The analysis includes the relative impacts of different measurements and covers instruments that range from those which comply with the recommendations given in ASHRAE Standard 114–1986 to poorer ones that can be found in chiller plants in Hong Kong. Greater attention to instrumentation provision for chiller plants is found to be very much needed.
6 citations
TL;DR: In this paper, a fully coupled effective stress 1-D finite element code formulated on the basis of vectored motion and generalized material stiffness was adopted for the anaiysis.
Abstract: Seismic response analysis was carried out to examine the liquefaction potential of hydraulic sand-fills for land reclamation works in Hong Kong. A fully coupled effective stress 1-D finite element code formulated on the basis of vectored motion and generalized material stiffness was adopted for the anaiysis. The selection of model parameters for the finite element code was described, results from in-situ field testing and laboratory static and cyclic triaxial tests were used to define model parameters. Ground motions, pore water pressure response and ground settlement at the Tseung Kwan O reciamation site induced by an earthquake loading up to M = 7.0 on the Richter scale were described. Analysis on a scale-down ground motions by adjusting the maximum horizontal ground surface acceleration to 0.07 g was also conducted. Results of the analysis indicated that liquefaction at the site is not likely to occur under the original and scaled-down earthquake loading.
TL;DR: A link-based alternative to Bell’s logit assignment method is proposed with making use of the volume successive average algorithm and the absence of any efficiency constraint on the set offeasible paths makes the algorithm attractive for use in stochastic user equilibrium assignment.
Abstract: A Bell’s logit assignment method was recently proposed as an alternative to Dial’s algorithm. While retaining the absence of a need for path enumeration, Bell’s method dispenses with either a forward or a backward pass. It therefore does not require minimum node-to-node cast information beforehand. The aniy constraint on the set of feasibie paths imposed is that there are no loops and/or cycles. However, it is difficult to avoid loaps in real networks. In order to minimize the cycle problems, a link-based alternative to Bell’s logit assignment method is proposed with making use of the volume successive average algorithm. The absence of any efficiency constraint on the set offeasible paths makes the algorithm attractive for use in stochastic user equilibrium assignment. Extensions of the proposed method to limit the number and type of cycles permitted in the feasible path set are also discussed. Numerical examples are given to illustrate the applications of the proposed method and to compare the results wi...
TL;DR: A simple second order IIR filter is employed for interference suppression in a direct sequence spread spectrum system which is overlaid on a narrow-band BPSK system.
Abstract: The use of FIR filters in anti-jam and interference rejection of spread spectrum systems has been studied extensively. However, little work have been donefor cases of IIR filters. This paper employs a simple second order IIR filter for interference suppression in a direct sequence spread spectrum system which is overlaid on a narrow-band BPSK system. The bit error rate expression of such a DS SS system is derived and numerical results are presented.
TL;DR: In this article, the effect of zeolite on the strength of concrete was investigated and it was found that at higher water to total cementitious materials ratios (W/(C+P)>O.38), the direct partial replacement of cement by zeolites resulted in the decrease of compressive strength, especially the early strength and tensile splitting strength.
Abstract: Zeolite, a type of natural pozzolanic material, is abundantly deposited in China and is easy to quarry. It is widely used in producing blended cement and concrete structural elements. This paper reports the study of effect of zeolite on the strength of concrete. It was found that at higher water to total cementitious materials ratios(W/(C+P)>O.38), the direct partial replacement of cement by zeolite resulted in the decrease of compressive strength, especially the early strength and tensile splitting strength. Silli fume was incorporated to enhance the strength performance of zeolite. It was found that the ternary blended cement (zeolite plus silica fume and cement) concrete performed better than the binary biended cement (zeolite and cement) concrete. Within the W/(C+P) ratios from 0.26 to 0.44 tested, it was found that as compared with the control concrete, the partial replacement of cement by a combined admixture camprising of zeolite and silica fume (zeolite: silicafume = 60:40) at a level of 70% could...
TL;DR: In this paper, a modal test carried out on an existing prestressed concrete bridge was then used to update an analytical model for the bridge, which was constructed from a beam model with the best mas$ model investigated.
Abstract: Modal tests are useful to study the structural health of an existing bridge. However, conducting a test on 'on existing bridge with heavy traffic conditions in a city such as Hong Kong is difficult and rare. This paper presents results from a modal test carried out on an existing prestressed concrete bridge. The results from the modal test were then used to update an analytical model for the bridge. The analytical model was constructed from a beam model with the best mas$ model investigated. Besides the modal parameters, the dynamic elastic modulus and creep factor of the test brIdge were also determined from the modal test. In addition, calibration factors for the bridge deck in the experimental model were obtained from a static system calibration. Bridges in Hong Kong are designed to BS5400 with certain parts replaced by the Structures Design Manual. Discrepancies of the elastic moduli between the experimental and Structures Design Manual values were 27.54% and 12.62% for the static and dynamic moduli respectively. When comparing with the values specified in BS5400, the corresponding differences were only 2.0% and 1.04%. It was shown that when the elastic modulus specified in BS5400 was consistently used, the experimental and the codes specified creep factors would have a difference of 4.53%.
TL;DR: In this article, a twa-dimensional inverse method for the volute profile design of centrifugal compressors was proposed and further modified and simplified for the calculation of incompressible flow.
Abstract: Recently, a twa-dimensional inverse methodfor the volute profile design of centrifugal compressors was proposed by Qi et al. The method has been applied to the redesign of the original volute profiles of two centrifugal fans and has been shown experimentally to be effetive in improving the performance. In this paper, the method is further modified and simplified for the calculation of incompressible flow in order that it can be diretly and conveniently applied to the volute profile design for centrifugal fans. Additionally, It is indicated that when the original methad is applied to fans, the accuracy of the estimation of the losses is lowered and some improved proposals ore suggested. The calculated results show that this Improved version of the method is simple, pradical and valid.
TL;DR: In this paper, a two-dimensional inverse method is proposed to design forward-swept radial and backwardswept blade profiles by specifying the distribution of angular momentum CuR along the mean streamline m on the stream surface of revolution of the impeller (CuR-m distribution).
Abstract: A two-dimensional inverse method is proposed in this paper. The method can be used to design forward-swept radial and backward-swept blade profiles by means of specifying the distribution of angular momentum CuR along the mean streamline m on the stream surface of revolution of the impeller (CuR-m distribution). At the same time, the distribution of relative velocity W along the mean streamline is calculated and is used as a reference point to evaluate the quality of design. Far the impeller with backward-swept blades, the blade profiles can also be designed directly by specifying the distribution of relative velocity W along the mean streamline m (W-m distribution). Three calculated examples are presented and some advice on the choice of suitable CUR-m and W-m distributions are suggested. Results show that this design method is simple and practical, and can conveniently be combined with the designers’ experience to obtain an impeller with good performance characteristics.
TL;DR: In this article, a multilayer feed-forward neural network is proposed to predict the fire resistance of concrete expressed as a loss in compressive strength, and the model is based on a modified back propagation (BP) learning algorithm.
Abstract: This paper describes a study of the feasibility of predicting the fire resistance of concrete using artificial neural networks. The factors influencing the fire resistance of concrete in terms of strength loss are first analyzed and a multilayer feedfarward neural network is proposed to predict the fire resistance of concrete expressed as a loss in compressive strength. The model is based on a modified back propagation (BP) learning algorithm. It had an adaptive learning rate and a momentum was also applied to speed up the learning process. Twenty - five cases of experimental data were assembled for the purpose of training the neural network. When the training was completed, three further sets of data were inputted into the model and the predicted outputs were compared with the actual experimental resuits. The prediction accuracy was found to be satisfactory with an error of less than ± 10%.
TL;DR: In this paper, the authors assess whether seismic detailing is necessary for reinforced concrete buildings in Hong Kong and present a study of the earthquake force demand and yield capacity of a generic building.
Abstract: To assess whether seismic detailing is necessary for reinforced concrete buildings in Hong Kong, a study of the earthquake force demand and yield capacity of a generic building is presented. Seismic provisions of the New Zealand and the American concrete design codes are reviewed. Their relevance for Hong Kong design practice is discussed.
TL;DR: In this paper, a set of unified equations of motion for the building-damper system under wind-Induced vibration control of tall buildings are presented and the effect of water dampers on the suppression of building response is then demonstrated through establishing an equivalent damping ratio for the water dampeners.
Abstract: The purpose of this paper is to establish some simple and useful water damper design formulas for wind-Induced vibration control of tall buildings. A total of four different types of water dampers (CTLD, RTLD, TLCD and LCVA) are considered in this study. These four types of water dampers represent a stream of reliable and effective passive control devices which are well studied and ready to be used on flexible buildings and structures. A set of unified equations of motion for the building-damper system under wind-Induced excitation are presented. First the along-wind and the cross-wind responses for a tall building are revisited and derived. The effect of water dampers on the suppression of building response is then demonstrated through establishing an equivalent damping ratio for the water dampers. It is seen that the addition of water dampers would increase the damping ratio of the building and thus reduce its wind-induced vibration. A set of formulas for the optimal properties and the optimal equivalen...
TL;DR: In this paper, the authors describe studies of the above parameters and recommend reasonable values of unsupported lengths of deck adjacent to end supports, taking into account the practical prablems of construction.
Abstract: In most modern cable-stayed bridges, the bridge deck is supported by closely spaced cables. in single tower cable-stayed bridges in particular, the lengths of ‘unsupported’ deck adjacent to the end supports are important parameters affecting the internal forces and deflections of the deck and the tower. This paper describes studies of the above parameters and recommends reasonable values of unsupported lengths of deck adjacent to end supports, taking into account the practical prablems of construction.
TL;DR: In this article, the authors present a feasibility study for a codified treatment of wind-induced dynamic response of tall buildings in Hong Kong and evaluate alongwind and crosswind responses of three typical tall buildings under Hong Kong wind conditions.
Abstract: This paper presents a feasibility study for a codified treatment of wind-induced dynamic response of tall buildings in Hong Kong. The most up-to-date code-based dynamic approach is used to evaluate alongwind and crosswind responses of three typical tall buildings under Hong Kong wind conditions. The results from this dynamic approach are then compared with those determined by the quasi-steady approach of the Code of Practice on Wind Effects Hong Kong–1983 (the Hong Kong wind loading code, thereafter). The serviceability performances are finally discussed in terms of human comfort criteria associated with acceleration response.
TL;DR: In this article, a three-dimensional numerical simulation of wind flows around and pressures on building surfaces for different wind directions is presented. The computational procedure includes solving the problem of wind flow simulation.
Abstract: This paper presents three-dimensional numerical simulation of wind flows around and pressures on building surfaces for different wind directions. The computational procedure includes solving the ti...
TL;DR: In this article, the authors investigated the methanogenic activity and toxicity resistance of the thermophilic sucrose-degrading granules developed in lab-scaled VASB reactars kept at 55°C, under the effect of five selected heavy metals: cadmium, chromium, copper, nickel and zinc.
Abstract: Industrial wastewater produced from industrial parks may be complex in nature. It may contain effluent discharged at elevated temperature from dyeing industries, high content of organic matter from food processing industries, heavy metals from electroplating industries, etc. This study aimed at further investigating into the application of upfloW anaerobic sludge blanket (VASB) technology which has a great potential to be applied to treat industrial effluents in Hong Kong. This study was conducted to investigate the methanogenic activity and toxicity resistance of the thermophilic sucrose-degrading granules developed in lab-scaled VASB reactars kept at 55°C, under the effect of 5 selected heavy metals: cadmium, chromium, copper, nickel and zinc which can be commonly found in electroplating effluents. The toxicity of the heavy metals on the thermophilic sucrose-degrading granules was found to be in the following order: zinc (most tOxic) >nickel> copper> chromium >cadmium (least toxic). At high concentratio...
TL;DR: In this article, the authors present the results of the vibrocompaction and discuss some of the factors encountered during the compaction that can lead to apparent no-no conditions.
Abstract: The new Hong Kong airport at Chek Lap Kok is being constructed on a 1248 hectare site of which 928 hectares is reclaimed land. Part of the reclamation consists of marine sand fill. Site investigation, including the CPT and shear wave velocity testing, indicated that the sand was in a relatively loose state state below the water table, with relative densities in the order of 20 to 40%. Vibrocompaction was carried out at three different areas of the reclamation in order to increase the reiative density of sand fill, thereby increasing its’ stiffness and strength, and creating an improved and more uniform material for follow on construction. The method for acceptance testing for the vibrocompaction was based on the use of the CPT, with the acceptance criterion set as a tip resistance value of either 8 MPa or 15 MPa, depending on required degree of compaction. This paper presents the results of the vibrocompaction and discusses some of the factors encountered during the compaction that can lead to apparent no...
TL;DR: An analytical expression based on linear wave theory for determining the wave height due to the combined effect of refraction, shoaling and friction was proposed in this article, using the computer package MathCAD.
Abstract: An analytical expression based on linear wave theory for determining the wave height due to the combined effect of refraction, shoaling and friction A simple computer program for evaluating the analytical expression is developed using the computer package MathCAD The accuracy of the proposed expression has been verified by comparing the solutions obtained from the program and the exact solutions obtained from design charts available in the Shore Protection Manual and BS6349
TL;DR: The concept of a solution of the global minimum, an orthogonol searching technique and associated computer programs are presented to overcome the non-unique solution issue and to obtain user Independent results in backcalculatian of moduli.
Abstract: Extensive studies have been done on backcalculation of moduli associated with the Falling Weight Deflectometer (FWD) evaluation of road and airport pavements. A review of the recent international developments in backcalculation of moduli reveals that the backcalculated values of moduli are software and user dependent. This non-unique solution Issue has caused practitioners and pavement designers to lose their confidence in the backcalculated modulus values and become skeptical about the blackcalculation practice This issue is the topic that this paper is intended to address. Based on a current layered elastic pavement theory, the concept of a solution of the global minimum, an orthogonol searching technique and associated computer programs are presented to overcome the non-unique solution issue and to obtain user Independent results in backcalculatian of moduli. Numerical examples are given to clearly illustrate the non-unique solution Issue associated with the most current backcalculation computer progra...
TL;DR: In this paper, an application of hybrid dynamic programming-artificial neural network algorithm (ANN-DP) appraach to Unit Commitment is presented and comparison of the algorithm with conventional DP approach is given.
Abstract: In this paper, an application of hybrid dynamic programming-artificial neural network algorithm (ANN-DP) appraach to Unit Commitment is presented. Artificial neural network (ANN) is used to generate a pre-schedule according to the input load profile. Then a dynamic search is performed at those stages where the commitment states of some of the units are not certain. Comparison of the algorithm with conventional DP approach is given on several cases.
TL;DR: The results show that the proposed scheme constitutes a high efficiency parallel transmissian method for high-bit-rate COMA systems.
Abstract: This paper presents the evaluatian of a residue number system (RNS) based direct-sequence, code division multiple-access communication system with respect to bit error rote (BER), when the channel is modeled as a multipath Rayleigh fading and noncoherent square-law detection with equal gain combining (EGC) is emplayed. Bath the uncoded system and the well-known concatenated coded system with nonbinary Reed-Solomon (RS) codes as the outer codes and the so-coiled residue number system product codes (RNS-PC) as the Inner codes are concerned. Expressions of BER for both uncoded and concatenated coded systems are presented. Our results show that the proposed scheme constitutes a high efficiency parallel transmissian method for high-bit-rate COMA systems.
TL;DR: In this article, the authors proposed two arrival control schemes which attempt to schedule the packet arrivals among many mobile radios to the base station for enhancing channel efficiency in a centralized slotted common code spread-spectrum packet radio network.
Abstract: In this paper, we stUdy twa arrival control schemes which attempt to schedule the packet arrivals among many mobile radios to the base station for enhancing channel efficiency in a centralized slotted common code spread-spectrum packet radio network. We assume the base station has a receiver with multiple capture capability, i.e. if two or more packets using the same spreading sequence arrive at the receiver with sufficient time of/sets, these packets can be successfully decoded. Both simulation and analytical results are given for some examples. It is shawn that the use of the scheduled arrival scheme results in a higher channel efficiency compared with the random arrival scheme.