This paper discusses key technologies for intelligent radio transmissions and intelligent network constitution techniques for advanced wireless communication systems. In the former part, this paper discusses the intelligent radio transmission techniques, in which the adaptive modulation techniques are mainly introduced because it is very effective to intelligently assign radio resources to each terminals as well as to intelligently control radio transmission parameters under dynamically changing traffic, required quality of services (QOS), and channel conditions. In the latter part, this paper discusses intelligent networking techniques, in which autonomous radio networking techniques and IP address control techniques for mobile host in the Internet are introduced to obtain suggestions for future intelligent and robust networking technologies.

This paper overviews fiber-oriented wireless communication systems, particularly in the area of microcell systems. The benefits of fiber-oriented wireless systems are discussed focusing on an application board scheme to facilitate new service deployment in light of intelligent networks. Dynamic range improvement technologies to remove interference are highlighted. Overall system performance is calculated for an economical FP-LD. Furthermore, effective modem use and a potential diversity technique are introduced. This strategy will play a role in realizing flexible fiber-optic subscriber networks.

This paper reviews Dynamic Channel Allocation (DCA) in TDMA cellular systems. The emphasis is on distributed DCA, which features decentralized control and adaptability to interference. Performance measures are discussed not only from a theoretical viewpoint but also from a practical viewpoint. Major techniques to enhance the capacity of cellular systems are channel segregation, reuse-partitioning, and transmitter power control. In addition to the performance of conventional cellular systems, differing performance in microcellular systems and multi-layer cellular systems is also discussed.

This paper presents a method of employing a priority scheme in a random access environment. A prioritized nonblocked stack collision resolution algorithm with binary feedback is developed and tested using simulations. The algorithm accommodates an n-level priority scheme which makes it attractive in mobile data systems. The effectiveness of the algorithm is described on its ability to first, reject the lowest priority class when the system load is near or on the maximum value and second, minimize the delay spread of the higher class users. The performance of the algorithm is characterized using the throughput/delay and cumulative delay for each class of users.

This paper proposed a method of slot allocation in a multislot TDMA system when multiple service priorities are supported. The algorithm is tested both in Variable Rate Reservation Access (VRRA) and Advanced TDMA protocols. We exploit the multislot reservation capability to achieve the delay requirements of each priority level. The channel allocation algorithm assumed that all data terminals are capable of multislot reservation. In this case the delay variance can be controlled based on the packet length information and the accumulated delay of each data user. The performance of the system is evaluated using the cumulative delay distribution and mean overall delays for the different user types.

Multiple TDMA bursts assignment between a base station and a personal terminal will be required for multimedia communications that offers high speed signal transmission such as voice and data simultaneous transmission. This paper proposes a reliable packet transmission method for TDMA based wireless multimedia communications. The proposed method employs an adaptive transmission rate control according to the packet length and a burst diversity technique is applied to improve the frame error rate of a packet. The frame error rate performance has been approximated theoretically by using fade- and infade-duration statistics of a Rayleigh fading channel and a computer simulation has been carried out for two control channels, FACCH/SACCH (Fast/Slow Associated Control CHannel) in the PHS as well as GSM. Both results indicate that the frame error rate is dramatically improved, about one order, when two bursts have different frequency and improved by about 25% when the two bursts have the same frequency.

A new transmit permission control scheme applicable in multi-cell communication systems is proposed. In this scheme, by prohibiting the transmissions from the users with relatively high propagation loss to their connecting hub stations, level of multiple access interference is decreased, and hence throughput characteristics are improved. Moreover, we continue our discussion to propose two adaptive forms of the transmit permission control scheme, in which the prohibition condition becomes more intelligent by considering the level of the offered traffic loads to hub stations. These methods are utilized in a slotted Aloha random transmission of the spread spectrum packets, and on the uplinks of a low earth orbit satellite communication system as an example of the multi-cell systems. It is shown that the adaptive schemes exhibits significantly improved characteristics at all offered traffic loads in these systems.

This paper proposes a novel mobile communications system of integrating microcell and macrocell for future land mobile communications which allows the user to enjoy mobile communications services by using one terminal regardless of his terminal speed. Current and developing digital land mobile communications systems are classified into two categories according to their differences in cell size, operating environments, service requirements and terminal speeds. One is a microcell system offering cordless telephone services for the user moving at low speeds and the other is a macrocell system offering vehicle telephone services for the user moving at high speeds. In order to access these two systems, the user needs to have two different terminals and to use an appropriate one according to the operating environments, service requirements and terminal speeds. In this paper, we propose a land mobile communications system in which the user can place a call without any of the inconvenienced described above. The proposed system consists of multi layered composite microcell system with no handover areas, each layer being composed of a number of microcells. This paper presents the detailed structure of this system and evaluates the performances of the channel capacity and the frequency of handovers during a call based on computer simulation results.

A new dynamic channel allocation algorithm which is integrated with transmitting power control is proposed. By introducing a new threshold, referred to as TPC threshold (Transmitting Power Control threshold), which is added some margin to the threshold of channel allocation, the subsequent transmitting power control can be performed effectively. This DCA algorithm can achieve a cellular system with both high traffic capacity and high service quality such as interference frequency performance simultaneously. The computer simulation shows that this DCA algorithm improves blocking probability performance 4 times better than that of DECT system at 14 Erlang, while keeping the same interference frequency and forced termination performances.

The dynamic channel assignment (DCA) strategy proposed here uses information on the mobile station speed and direction of motion to reduce the number of forced call terminations and channel changes in micro cellular systems. This SMD (speed and moving direction) strategy is compared with the main DCA strategies by simulating a one-dimensional service area covering a road on which there are high-speed mobile stations (HSMSs) and low-speed mobile stations (LSMSs).The simulation results show that the SMD strategy has the best performance in terms of forced call termination and channel change. The performance difference between the SMD strategy and the other DCA strategies increases as cell size decreases and as HSMS speed increases. While the SMD strategy does not yield the best total call blocking rate, its total carried load is the best when cells are small and HSMS speed is high. Also, the SMD performance improves when the HSMS offered load is small and the LSMS offered load is large. Although the SMD strategy requires information on the speed and direction of each mobile station and it increases call blockings somewhat, it reduces the number of forced call terminations and channel changes considerably, which is important in micro cellular systems.

This paper proposes a new digitized group modulator and demodulator (a group modem) for adaptive frequency hopping and multi-carrier (AFHMC) radio systems. The group modem can flexibly vary the number of carriers handled simultaneously, especially employing a time division multiplexing technique in the demodulator. We discuss the operational principle of the modem. The required operational clock frequency in the group demodulator is also examined and clarified taking into consideration the frequency characteristics of the baseband filter. The basic performance of the proposed configuration is measured experimentally by constructing a π/4-shift QPSK group modulator and a π/4-shift QPSK group demodulator. First, by measuring the output spectrum of the significant parts in the demodulator, we confirm that the basic operational performance conforms to the design specifications. Secondly, investigating the relationship between the number of multiplexed low-pass filter taps and the required CNR when multiple carriers are simultaneously input confirms that more than 40 taps are enough to obtain the best BER performance in this experiment. Next, examining the relationship between the number of carriers simultaneously input, the required CNR, and the input level of these carriers confirm that the required CNR is roughly constant and there is no significant difference among the cases when D/U is more than 0 dB. Finally, an experiment shows that the required number of quantization bits for A/D input in the demodulator is more than 6, which is enough to obtain the best BER even if simultaneous handled carriers are 4.

A new matched-filter (MF) acquisition scheme with adaptive threshold is proposed for a frequency-hopped/spread-spectrum multiple-access (FH/SSMA) system. Detection and false alarm probabilities are derived for combined interference environments. The combined interference consists of partialband noise jamming or tone jamming, multiple access interference (MAI), multipath interference, and thermal noise. We use Gaussian approximation for modeling the MAI and multipath interference. Equal power assumption of the users is employed which is typically used in the SSMA system analysis. In the proposed scheme, MF output is compared to an adaptive threshold determined by the number of jammed frequency slots. It is shown that the proposed adaptive-threshold acquisition scheme achieves higher detection probability and lower false alarm probability than a conventional fixed-threshold scheme for each jammed fractional bandwidth, JSR, the number of multipaths, and the number of users. It is also shown that adaptive threshold achieves faster acquisition and higher packet throughput than fixed threshold in application to FH/SSMA packet radio system.

Air interfaces of the future mobile communication are widely spreading, because of the multimedia service demands, technology trends and radio propagation conditions. Radio-Highway Networks are expected to realize the universal, seamless and multi-air-interface capability for mobile access networks, and play an important role in the future multimedia radio communications. For the radio-highway networks, this paper newly proposes natural bandpass sampling - asynchronous time division multiple access (NBS-ATDMA) method, where radio signals are natural bandpass sampled at the radio base station and are asynchronously multiplexed on the optic fiber bus link and intelligently transmitted to its desired radio control station. We theoretically analyze the loss probability of the radio signal due to collision in the network and the carrier-to-noise power ratio of received radio signals at the radio control station. Moreover, in order to reduce the loss probability, two access control methods, carrier sense and pulse width control, are proposed, and it is clarified that these improve the number of base station connected to radio highway networks.

This paper describes a variable multi-level QAM modem applied to a wireless ATM transport network with the aim of effectively offering ATM network services over a terrestrial digital radio system. The concept of the wireless ATM transport network based on a Virtual Path (VP) capacity control system which optimizes both the number of channels and the multi-level QAM scheme for existing traffic variation is discussed. To achieve a hitless switch as a technical requirement of this network, we propose a modem configuration and a modulation scheme control (MSC) signal transmission. In this modem configuration, a multi-level control logic circuit in the modulator is used as the signal formatter. A modulated signal for the modulation scheme is maintained at a constant average power. Decision data and error signal selection for the received signal is carried out in the multi-level control logic circuit in the demodulator. The fluctuation of the demodulator loops due to modulation scheme switch can be reduced by using a fully digitized AGC loop and by converting the received signal to the condition of decision level constant. The MSC signal inserted into the first path data signal is transmitted without error by arranging the maximum amplitude of the signal point set. In this way, switching between the modulator and the demodulator is possible frame by frame. Finally, we present experimental results for a variable multi-level QAM modem employing four modulation schemes: QPSK, 16 QAM, 64 QAM, and 256 QAM. Through experiments, we prove that the modulation scheme is switched without fluctuation of the demodulator control loops by maintaining the signal condition of the decision level constant. The achievement of a hitless switch for multi-level QAM is also confirmed by experiments.

This paper proposes an adaptive modulation system with a punctured convolutional code for land mobile communications to achieve high quality, high bit rate, and high spectral efficient data transmission in multipath fading environments. The proposed system adaptively controls the coding rate of the punctured convolutional code, symbol rate, and modulation level according to the instantaneous fading channel conditions. During good channel conditions, the modulation parameters are selected to increase the transmission rate as much as possible with satisfying a certain transmission quality. As channel conditions become worse, lower rate modulation parameters are applied or transmission is stopped. The performances in fading environments are evaluated theoretically and by computer simulations. The results show that the proposed system can realize higher quality transmission without the degradation in average bit rate compared to conventional adaptive modulation systems.

This paper proposes a directive antenna diversity reception scheme for an adaptive modulation/time division multiple access (TDMA)/time division duplex (TDD) system to achieve high quality, high bit rate and high spectral efficient data transmission in high mobility land mobile communication environments. In mobile stations, a directive antenna is applied to equivalently reduce the observed variation speed of the fading channel. At each branch, the offset frequency (f_off) and f_off-canceled fading variation are estimated to improve accuracy of the propagation path characteristics estimation even in high maximum Doppler frequency (f_d) environments. Computer simulation confirms that the proposed scheme can achieve successful variable rate transmission in fast fading environments.

Co-channel interference is a major factor limiting spectral efficiency of a cellular radio system. The trellis-coded co-channel interference canceller (TCC) leading to the significant increase of traffic capacity of a cellular system has been proposed. In this scheme, a maximum-likelihood sequence estimation implemented with the Viterbi algorithm is extended to estimate both desired signal and co-channel interference, and combined with trellis-coded modulation to enhance the co-channel interference cancelling capability. The complexity of TCC grows exponentially with the channel memory and the constraint length of the trellis encoder. In this paper, two reduced-state sequence estimation algorithms, namely, the delayed decision feedback sequence estimation and the M-algorithm, are applied to TCC and their performance is compared. In addition, effective trellis coded modulation schemes to reduce the computational complexity are proposed. The performance of these schemes is examined through simulations, and compared to that of a conventional interference canceller.

This paper describes a CDMA cellular system based on adaptive interference cancellation (CDMA-AIC) with a large capacity. In the CDMA-AIC, each base station employs a single-user type adaptive interference canceller (AIC), which consists of a fractionally chip-spaced code-orthogonalizing filter (COF) and a coherent detector. The AIC adaptively removes power-dominant multiple-access interferences (MAIs) in the cellular system, regardless of whether they are intra-cell interferences or inter-cell interferences, without any information about them, such as spreading codes, signal received timings and channel parameters. Evaluation under the multiple-cell environment demonstrates that the reverse link capacity of the CDMA-AIC with QPSK modulation is 3.6 times as large as the capacity of the CDMA without MAI cancellation. Further, the capacity is less sensitive to transmission power control errors than that of the conventional CDMA systems.

Several papers have been shown equalization in the reception side. However, equalization in transmission side that is partial response signaling (PRS) or precoding is also possible in a two-way interactive communication such as time or frequency division duplex (TDD of FDD). This paper proposes and investigates a system which includes a transmission equalization and reception equalization based on an array antenna. This system is the extension in spatial and temporal domains. The channel capacity can be improved in the super channel which includes the transmitter and receiver array antenna.

This paper compares two techniques in recovering the capacity degradation caused by sectorization in a cellular system. They are the Directed Retry and Load Sharing in sector cells. Since both techniques requires an overlapping area between adjacent sectors, the values of the overlapping area are chosen such that the Carrier to Interference Ratio (CIR) is satisfied.

As the most applicable interference canceller, an Extraction and Reinjection-type Interference Canceller (ERIC) has been proposed, which extracts interference signals from received signals and cancels interference using these extracted signals. However, it is not yet clarified as to how this canceller's performance level for interference cancellation can be obtained when fading occurs. In this letter, a theoretical evaluation is performed using an ERIC by dividing it into an interference extraction part and an interference cancellation part. The performance of the interference extraction for transmission is estimated, and that of the improvement factor is derived. It is confirmed that theoretical estimations agree closely with experimental results. In addition, through simulations, we estimate the degree of improvement in the interference cancellation using this canceller in a fading environment. The results clarify that this canceller is the most valid when the average received-signal power rate, D/U, is 20 dB, and the maximum improvement using this canceller is 7.5 times better than without using the canceller.

In order to pave the way to B-ISDN, one of the most important issues for network providers is to identify the most efficient B-ISDN introduction strategy. This paper focuses on the costs of introducing ATM transmission systems into backbone transport networks which must provide highly reliable broad band transmission capability. In this context, the main rival to ATM is Synchronous Transfer Mode (STM); recent Synchronous Digital Hierarchy (SDH) equipment supports the establishment of advanced STM-based high speed transport networks. This paper offers a cost comparison of ATM and STM based backbone transport networks. A digital path network in STM has a hierarchical structure determined by the hierarchical multiplexing scheme employed. The minimum cost STM path network can only be determined by developing a path design method that considers all hierarchical path levels and yields the optimum balance of link cost and node cost. Virtual paths have desirable features such as non-deterministic path bandwidth and non-hierarchical and direct multiplexing capability into high speed optical transmission links. These features make it possible to implement a non-hierarchical VP network with ATM cross connect systems which can handle any bandwidth VP with a universal cell switching function. This paper shows that the non-hierarchical VP routing, which strongly minimizes link cost, can be implemented without significantly increasing node cost. Network design simulations show that the virtual path scheme, possible only in an ATM network, yields the most cost effective path network configuration.

In this paper, we study the performance of quality-based voice/data CDMA system where new and handoff traffic are considered. A call request for handoff data queues up if the signal-to-interference ratio exceeds a predefined threshold while priority is given to handoff voice calls by reserving some channels exclusively for them. The transmission rate of data users may vary according to measured SIR value. Important performance measures of the system such as blocking probability and system capacity for voice or data calls for proposed schemes are presented and compared.

Estimating the macroscopic demand for telephones is essential to long-term planning construction of telecommunication networks facilities. Although there are several useful forecast equations, they need some types and/or vast amounts of data that are sometimes unavailable, especially in developing countries. This paper presents a sophisticated telephone demand estimation technique that is based on the demands of residential and business users. It uses several parameters to estimate the increase in telephone demand. A simplified equation is also presented that is a function of only one parameter: normalized gross domestic product (GDP) per capita. This simplified equation is shown to be useful by using data for more than ten countries.

This paper reports experimental results of a media synchronization mechanism which was proposed by the authors, focusing on the graceful recovery scheme. The proposed method consists of intra-stream and inter-stream synchronization mechanisms. The inter-stream synchronization control is performed after the intra-stream synchronization control over each media unit (MU) such as a video frame. Then, whether the intra-stream synchronization is still maintained or not is checked. In the experimental system, video and voice stored in a source workstation are transferred to a destination workstation via an FDDI network, and then they are synchronized and outputted at the destination (i.e., lip-synch). At the transmission of each MU, we simulate network delay jitters by generating a pseudo-delay which is exponentially distributed. Using the system, we have confirmed the validity of the mechanism. We also clarify how to set the threshold and parameter values defined in the mechanism by evaluating mean square error and average MU rate or by subjective assessment. Furthermore, we demonstrate that the intra-stream synchronization control for each streams in addition to the inter-stream control is necessary for high quality synchronization.

Many ATM switching modules with high performance have been proposed and analyzed. A development of a large scale ATM switching system (e.g., used as a central switch) is the key to realization of the broadband ISDN. However, the dimension of ATM switching ICs is limited by the technological and physical constraints on VLSI. A multistage switching configuration is one of the promising configurations for a large scale ATM switch. In this paper, we treat a 3-stage switching configuration with no internal bufferes; i.e., bufferless switches are employed at the first and second stages, and output buffered switches at the third stage. A short-term cell loss probability is analyzed in order to examine the influence of bursty traffic on performance of the bufferless switch used at the first two stages. Furthermore, we propose a 4-stage switching configuration with traffic distributors added at the first stage. This switch provides more paths between a pair of input and output ports than the 3-stage switching configuration mentioned above. A few schemes to distribute cells are compared. It is shown that the distributor successfully reduces the deterioration of cell loss probability due to bursty traffic by splitting incoming cells into several switching modules.

Optical Feedering between Base Stations and Control Station is an effective technique for future microcellular mobile communication systems. The use of Laser Diode (LD) in such a system leads to the generation of intermodulation products, which consequently affect a system performance and ultimately restrain the maximum number of users that the system can serve. The problem becomes further intensified in case of CDMA system which is a candidate for future cellular mobile and personal communication systems. In this paper LD's Nonlinearity compensation technique for Direct Sequence spread spectrum CDMA signals in optical communication system is presented. This technique involves the implementation of a nonlinear block herein after called Post Nonlinearity Recovery Block (PNRB). This block is designed to exhibit the characteristics inverse to those of LD. The block is designed theoretically by deriving the complete expressions for Transfer functions. Some useful results of theoretical investigation of a proposed scheme have been presented, which form the basis for the experimental test system. The work is novel because, (i) Compensation analysis has been carried out for DS-CDMA signals for the first time, and (ii) Compensation has been proposed on the control station instead of base station, which is different from the conventional techniques and offers several additional advantages. Performance of the system with and without PNRB is evaluated by Intermodulation Distortion (IMD) and SNR Analysis. The results show that LDs' nonlinearity distortion level can be compensated to a remarkable extent.