The capacity of a cellular direct sequence code division multiple access system is investigated in situations with and without power control for both the reverse link (from mobile to base station) and the forward link (from base station to mobile). The capacity is defined as the number of simultaneous users per cell with a prespecified performance. A theoretical analysis of the effect of imperfect power control on the reverse link capacity is presented using an analytical model. To investigate the reverse link capacity without any form of power control, a general spatial user distribution is developed which is very suitable for analytical study of any multiple access system with the near-far effect problem. The performance of the reverse link of a CDMA system is also evaluated considering the users located in surrounding cells. Finally, the forward link capacity is studied considering multiple cells. Two possible forward power control schemes, namely carrier-to-interference ratio driven and distance driven systems, are discussed.

A group-based random access communication system which consists of two groups of many users is considered. The two different groups share a common random multiple access channel. Users from a group are allocated a high transmitting power level and have a high probability of correct reception among overlapping packets. We set a threshold, θ, which is such that the group with the high power level will occupy the channel if less than or equal to θ packets are transmitted from the group with the low power level. We obtain a two-dimensional Markovian model by tracing the number of backlogged users in the two groups. The two-dimensional Markov chain is shown to be not ergodic and thus the system is not stable. A two-dimensional retransmission algorithm is developed to stabilize the system and the retransmission control parameters are chosen so as to maximize the channel throughput. An equilibrium point analysis is performed by studying the drift functions of the system backlog and it is shown that there is a unique global equilibrium point. The channel capacity for the system is found to be in the range from 0.47 up to 0.53, which is a remarkable increase compared to the conventional slotted ALOHA system.

A new redundancy technique especially suitable for ultra-high-speed static RAMs (SRAMs) has been developed. This technique is based on a decoding-method that uses two kinds of fuses without introducing any additional delay time. One fuse is initially ON and can be turned OFF afterwards, if necessary, by a cutting process using a focused ion beam (FIB). The other is initially OFF and can be turned ON afterwards by a connecting process using laser chemical vapor deposition (L-CVD). This technique is applied to a 64 kbit SRAM having a 1.5-ns access time. The experimental results obtained through an SRAM chip repaired using this redundancy technique show that this technique does not introduce any increase in the access time and does not reduce the operational margin of the SRAM.

In this paper, a general theory on multiple-valued static random-access-memory (RAM) is investigated. A criterion for a stable and an unstable modes is proved with a strict mathematical method and expressed with a diagrammatic representation. Based on the theory, an NMOS 6-transistor ternary and a quaternary static RAM (SRAM) cells are proposed and simulated with PSPICE. The detail circuit design and realization are analyzed. A 10-valued CMOS current-mode static RAM cell is also presented and fabricated with standard 5-µm CMOS technology. A family of multiple-valued flip-flops is presented and they show to have desirable properties for use in multiple-valued sequential circuits. Both PSPICE simulations and experiments indicate that the general theory presented are very useful and effective tools in the optimum design and circuit realization of multiple-valued static RAMs and flip-flops.

We propose a direct-sequence spread-spectrum multi-access (DS/SSMA) receiver that incorporates multipath diversity combining and multistage co-channel interference (CCI) cancellation. This receiver structure which is more resistant to the near/far problem essentially removes more and more of the CCI with each successive cancellation stage. With the assumption that perfect channel estimates have been obtained, we analyze the bit error rate (BER) performance of this system when received powers are unequal. Results show that the BER can approach that of a single-user case as the number of CCI cancellation stages increases.

The security problems of object-oriented database system are investigated and security level assignment constraints and an access control mechanism based on the multilevel access control security policy are proposed. The proposed mechanism uses the Trusted Computing Base. A unique feature of the mechanism is that security levels are assigned not only to data items (objects), but also to methods and methods are not shown to the users whose security level is lower than that of the methods. And we distinguish between the security level of a variable in a class and that in an instance and distinguish between the level of an object when it is taken by itself and it is taken as a variable or an element of another complex object. All of this realizes the policy of multilevel access control.

A system is constructed for the processing of question-answer dialogue as a subsystem of the speech response device. In order to increase the adaptability to dialogue topics, rules for dialogue processing are classified into three groups; universal rules, topic-dependent rules and task-dependent rules, and example-based description is adopted for the second group. The system is disigned to operate only with information on the content words of the user input. As for speech synthesis, a function is included in the system to control the focal position. Introduction and guidance of ski areas are adopted as the dialogue domain, and a prototype system is realized on a computer. The dialogue example performed with the prototype indicates the propriety of our method for dialogue processing.

For the connection request procedure in mobile communication systems, a previous study had shown that the 3-channel systems provide the haighest maximum of stable per channel throughput. In this paper, we propose and study a new algorithm, called the Parallel Collision Resolution Algorithm, which can be implemented in a Q-channel connection request environment, where Q3. For the implementation, the channels are arranged in R groups, where R is a positive integer. The collision resolution scheme distributes the collided messages over all the groups so that throughput and delay measures can be improved. At any point in time, there can be a maximum of R collision resolution schemes operational irrespective of the channel or the group number over which collisions occurred. The performance measures are estimated by computer simulation. Under the new algorithm, almost the same level of the perchannel stable throughput measure of a 3-channel network can be achieved in networks for which Q3. This feature allows freedom to the network designer to employ a higher number of connection request channels without forfeiting high channel utilization rates. When Q is an integral multiple of 3, the maximum stable per channel throughput level achieved can be the same as that achieved by the 3 channel system, if the grouping of channels is such that each group consists of 3 channels. When Q is not an integral multiple of 3, the intuitive strategy of organizing the channels in such a way that Q/3 groups consist of 3 channels each and one group consists of (Q mod 3) channels, may result in much degraded performance. It is found that, if the channels are so organised that no group is composed of (Q mod 3) channels, the performance levels can be substantially enhanced. Also, under the new algorithm, the delay measure is significantly improved, particularly in schemes like the mobile satellite systems with high propagation delays. We conclude that the new scheme presents a promising collision resolution methodology for connection request procedures.

Modeling and performance analysis have played an important role in the economical design and efficient operation of switching systems, and is currently becoming more important because the switching systems should handle a wide range of traffic characteristics, meeting the grade of service requirements of each traffic type. Without these techniques we could no longer achieve economy and efficiency of the switching systems in complex traffic characteristic environments. From the beginning of research on electronic switching systems offering circuit-switched applications, Stored Program Control (SPC) technology has posed challenges in the area of modeling and performance analysis as well as queueing structure, efficient scheduling, and overload control strategy design. Not only teletraffic engineers and performance analysts, but also queueing theorists have been attracted to this new field, and intensive research activities, both in theory and in practice, have continued over the past two decades, now evolving to even a broader technical field including traditional performance analysis. This article reviews a number of important issues that have been raised and solved, and whose solutions have been reflected in the design of SPC switching systems. It first discusses traffic problems for centralized control systems. It next discusses traffic problems inherent in distributed switching systems.

This paper describes a perspective on Personal Communicatoins Services (PCS) and technological trends. It takes into consideration rules pertaining to the use of PCS for mobile radio communication and countermeasures to cope with the huge increase in PCS subscribers. In this paper, PCS network structures, inter-regional roaming, microcell structure, radio access and channel access methods are also covered as PCS technologies. Furthermore, trends in domestic and international standards are also described. Although these technologies present many difficulties, we believe that they will be overcome and PCS services will be introduced in the near future.

An improved array architecture to realize fast access, low power dissipation, and wide operating margin, for the 16 Mbit DRAM is proposed. A high speed access is obtained by the fully embedded sense drive scheme for the RAS access time (tRAC), and the special page mode with the hierarchical I/O data bus lines and multi-purpose-register (MPR) for the column address access time (tCAA). A low power dissipation and wide operating margin are obtained by the improved twisted-bit-line (TBL) architecture with double dummy canceling. The 16 Mb DRAM using these architectures has 38 ns tRAC, 14 ns tCAA and 75 mA power dissipation at the typical condition.

The essential functions of the passive double star (PDS) system are clarified by comparing them to the functions of the single star (SS) and the active double star (ADS) system. A layered structure describing the functional characteristics of the PDS system is proposed for flexible transport capability. The functions of the optical network unit (ONU) on the customer premises are systematically partitioned into four layers. The functions of the optical subscriber unit (OSU) in the central office are described using five layers. Call by call activation and deactivation techniques are described on the basis of a layered architecture. The reduction of ONU power consumption by adopting activation and deactivation control is also discussed.

Fading is unavoidable in many communication systems such as urban and mobile radio systems. Fading, in principle, results in increased error in data communications. However, the random variation of received signal envelope due to natural fading divides the received signals into many different power level, a method known to improved utilization of ALOHA network due to capture effects. In this paper, we consider Nakagami fading model for the radio channel. We derive the exact form of capture probabilities and show that the probabilities can be modeled as semi-exponential model. Thus we can determine the channel capacity of ALOHA system with capture channel.

It is known that the uniquely decodable code pairs (C1, C2) for the two-user binary adder channel relates to the maximum independent set of a graph associated with a binary code. This paper formulates the independence number of a class of graphs associated with binary linear codes, and presents an algorithm of the maximum independent set for those graphs. Uniquely decodable code pairs (C1, C2)'s are produced, where C1 is a linear code and C2 is a maximum independent set of the graph associated with C1. For the given C1, the transmission rate of C2 is higher than that by Khachatrian, which is known as the best result as so far. This is not rather surprising because the code C2 is a maximum independent set in this paper but not be Khachatrian's.