With COVID-19 as an initiation, the stage for human socioeconomic activities is rapidly shifting from physical space to cyberspace. Mobile networks have evolved as essential communication networks for connecting individuals and things to the cloud. Further evolution of mobile networks is essential to realize Digital Twin. In particular, low latency and guaranteed QoS using network slicing are extremely challenging requirements that legacy mobile networks until 4G have not been able to meet. In addition, the chronic shortage of spectrum accompanying the shift to broadband continues to encourage the use of small cells, which naturally make xHaul11xHaul referred in this paper denotes a term that expresses either fronthaul, midhaul or backhaul. problem be more serious. The author has worked on this xHaul problem in both academia and industry for 20 years, developing a unique WLAN mesh protocol for backhaul. In order to bring the results of this research to practical use, PicoCELA Inc. as a vehicle for commercialization of the fruits, was incorporated. The edge device brought by PicoCELA with the WLAN mesh capability are linked to a cloud server and are serving various applications as a general-purpose platform to facilitate the introduction of Digital Twin. This paper reviews the history of WLAN mesh technology to date, identifies the technical issues that arise when using it in an enterprise scenario, and then provides an overview of how PicoCELA’ s WLAN mesh addresses these issues. The PicoCELA solution as an edge platform is overviewed, followed by some real-world use cases. Finally, the outlook for mobile communications in the future is summarized.

In this paper, we investigate the dynamic small cell (SC) clustering strategy and their precoding design problem for interference coordination in two-tier heterogeneous networks (HetNets) with massive MIMO (mMIMO). To reduce interference among different SCs, an interference graph-based dynamic SC clustering scheme is proposed. Based on this, we formulate an optimization problem as design precoding weights at macro base station (MBS) and clustered SCs for maximizing the downlink sum rate of SC users (SUs) subject to the power constraint of each SC BS (SBS), while mitigating inter-cluster, eliminating inter-tier, intra-cluster and multi-macro user (MU) interference. To eliminate the inter-tier and multi-MU interference simultaneously, we propose a clustered SC block diagonalization precoding scheme for the MBS. Next, each SU's precoding vector at clustered SCs is designed as the product of the following two parts. The first part is designed with singular value decomposition to remove the intra-cluster interference. The second part is designed to coordinate the inter-cluster interference for maximizing the downlink sum rate of SUs, which is a non-convex optimization problem and difficult to solve directly. A non-cooperative game-based distributed algorithm is proposed to obtain a suboptimal solution. Meanwhile, we prove the existence and uniqueness of Nash equilibrium for the formed game. Finally, simulation results verify the effectiveness of our proposed schemes.

Pilot contamination due to the pilot reuse in adjacent cells is a serious problem in time-division duplex (TDD) massive multi-input multiple-output (MIMO) system. Therefore, the pilot allocation is significant for improving the performance of the system. In this paper, we formulate the pilot allocation optimization problem for maximizing uplink sum rate of the system. To reduce the required complexity for finding the optimum pilot allocation, we propose a low-complexity pilot allocation algorithm, where the formulated problem is decoupled into multiple subproblems; in each subproblem, the pilot allocation at a given cell is optimized while fixing the pilot allocation in other cells. This process is continued until the achievable sum rate converges. Through multiple iterations, the optimum pilot allocation is found. In addition, to improve users' fairness, we formulate a fairness aware pilot allocation as maximization problem of sum of user's logarithmic rate and solve the formulated problem using a similar algorithm. Simulation results show that the proposed algorithms obtain good performance comparable to the exhaustive search algorithm, meanwhile the users' fairness is improved.

Although accurate positioning systems are important to provide location-aware services, solutions that are applicable in high-rise areas and inside buildings have not yet been realized. We propose an accurate positioning system that utilizes widely and densely placed Wi-Fi access points. The proposed system utilizes probe request signals broadcast by mobile devices to estimate their positions. The positioning algorithm is based on proximity detection using received signal strength indication. In addition, the proposed method employs a computation time reduction strategy and error reduction techniques. The proposed system can also show pedestrian flow, which is valuable information for developing shop branching plans, street improvement, and so on. The experimental results show that the proposed positioning system achieved an accuracy of 5.36 m. The system can also visualize pedestrian flow trends in a given Wi-Fi coverage area based on the position estimates.

In this paper, we propose using different quantization values, including 1-bit compressed sensing for perceptual audio signal compression in perceptual systems[1], in order to clarify the effect of the quantization process on the achievable quality of audio signal. Simulations results show that reasonable performance is achieved for different quantization CS compared to quantized classical CS.

The innovative concept of Compressed Sensing (CS) presents a breakthrough that enables the acquisition of sparse signals at much lower sampling rates compared to the conventional Nyquist rate. The scope of CS is not limited only to sparse signal but it is also applicable to compressible signals, such as multimedia signals including audio signals. Representing the random samples from CS process using finite-precision is a crucial problem in communication systems. In this paper, we focus on 1-bit quantized CS. We propose to take into account the perceptual CS model for audio compression, where the perceptual properties are taken into account. We propose two models, the first applies perceptual effect at the transmitter side. In the other model, a modified Binary Iterative Hard Thresholding (BIHT) is proposed to improve the performance of 1-bit compressed sensing by taking the perceptual properties of the received audio signal into account. The Mean Opinion Score (MOS) is used to compare the perceptual quality of the received signal for the proposed 1-bit perceptual CS algorithms. Simulation results show that a better performance is achieved using the proposed algorithms.

In this paper, we apply an efficient scaling strategy on layered scaled min-sum LDPC decoder. In addition, we propose a joint optimization strategy for the quantization and scaling parameters of layered scaled min-sum LDPC decoder. The study of our optimization results, for DVB-S2 LDPC codes with different constellation sizes and code rates, shows that each constellation size code rate pair has different optimal scaling and quantization parameters. In order to maximize the achievable performance, we propose using the different scaling and quantization parameters for each constellation size code rate pair. The simulation results show the performance improvement of separately using optimal scaling parameters or optimal quantization parameters, and the overall performance enhancement of using both optimal scaling and quantization parameters.

Analog-to-digital (A/D) converter (ADC) and related analog hardware designs are important factors to simplify the transceiver circuits in wireless communication systems. In order to mitigate the nonlinearity of a low-resolution ADC that reduces the required analog hardware complexity, we have investigated two nonlinearity mitigation techniques for A/D conversion, i.e., the dither-ADC and the hysteresis-ADC. In this paper, we evaluate the effect of the nonlinearity mitigated A/D conversion techniques on the achievable performance in single carrier offset-quadrature-amplitude-modulation (OQAM)and QAM systems, where the receiver adopts either the dither-ADC or the hysteresis-ADC. Simulation results prove that both the dither-ADC and the hysteresis-ADC are effective in improving BER performance of both OQAM and QAM systems affected by the nonlinearity of ADC, while the transmitter employs a selected mapping technique that achieves a low peak-to-average power ratio (PAPR).

Interference alignment (IA) emerged on the communication scene as a solution to the interference problem in all interference-limited networks, including heterogeneous cellular systems. However, the performance of IA is greatly related to the accuracy of the channel state information at transmitters (CSIT), namely the number of feedback bits. Accordingly, in order to improve the performance of IA, it would be useful to analyze the number of feedback bits with respect to the sum rate loss. Motivated by that, this paper studies a limited feedback-based IA scheme suitable for two tier macrocell-femtocell heterogeneous networks. First, an approximate analytical expression for the upper bound on the total sum rate loss due to limited feedback in the studied IA system, is derived. Then, a simulation based evaluation of the sum-rate loss due to the implementation of limited feedback IA in heterogeneous networks is obtained. Simulation results confirmed the severe effect of quantization of CSI on the interference alignment performance.

In MIMO space division multiplexing (SDM) systems, the peak power of the transmit signal at each antenna element is increased by the precoder and hence it causes the power efficiency degradation and/or nonlinear distortion at the power amplifier. To solve this problem, this paper present a peak power aware precoding scheme for MIMO-SDM systems, where the precoder is designed to mitigate the peak output power at each antenna element so that peak amplitude of the transmit signal at each antenna is reduced while minimizing the performance degradation caused by the peak power restriction. The proposed system employs an alternative iterative optimization algorithm that determines the precoding matrix so that the precoding and virtual post-coding matrices are alternatively optimized under the constraint of peak output at each antenna element. Simulation results show that the proposed method is effective in restricting the peak transmission power at each antenna within a permissible level while mitigating performance degradation in bit error rate (BER) performance of the precoded SDM systems.

The multiple access broadcast (MABC) is an effective two phases transmission (2P) ANC protocol for the half-duplex (HD) communication mode. However, MABC does not make use of channel gain of the direct link (DL) no matter how strong it is. On the other hand, the time division broadcast (TDBC) is known as a three phases transmission (3P) protocol which enables transceivers to utilize DL and thus offers the possibility to achieve higher performance compared with the MABC at the expense of a reduced spectral efficiency due to the one extra transmission phase. In this paper, we investigate a joint single relay selection and power allocation schemes for energy-efficient wireless communication systems with analog network coding (ANC) for TDBC, where two-way relay channel with two end nodes and N parallel relay nodes is considered under an assumption of perfect channel-state information (CSI). Our objective is to minimize the total system transmit power consumption under quality-of-service (QoS) constraints for TDBC protocol with joint single relay selection and nodes power allocation. In addition, a zero-forcing based relay signal combining technique that combines the signals received at the 1st and 2nd transmission phases, also known as zero-forcing relay power allocation (ZF-RPA), is also investigated. Numerical simulation shows that the traditional VG-RPA is more energy-efficient than the ZF-RPA scheme for TDBC in cases with and without utilizing DL.

In this paper, cooperative compressive spectrum sensing is considered to enable accurate sensing of the wide-band spectrum. The proposed algorithm is based on compressive sensing theory and aims to reduce the hardware complexity of the cognitive radio receiver by distributing the sensing work among groups of sensing nodes. The proposed algorithm classifies the cooperated sensing nodes into different sensing groups depending on the quality of the reporting channel between the sensing node and the fusion center (FC). To sense the wide- band analog signal and take a global decision about spectrum occupancy, each node uses its local sensing matrix, which is assigned to its sensing group and a part of a global sensing matrix at the FC. The size of the local sensing matrix of each sensing node,and consequently the contribution of this node in the overall measurement vector, depends on its sensing group. The FC classifies and rearranges the compressed data to formulate one global measurement vector which is used with a global sensing matrix to estimate the wide-band signal spectrum. The receiver operation characteristics (ROC) of the overall spectrum sensing system show that the proposed receiver provides more protection to primary users (higher detection probability) at the same secondary user throughput (probability of false alarm).

Underlay cognitive radio (CR) permits unlicensed secondary users (SUs) to transmit their own data over the licensed spectrum unless the interference from the SUs on the licensed primary user (PU) exceeds an acceptable level. This paper proposes two interference alignment (IA)-based distributed optimization designs for multiple secondary transceivers in underlay cognitive radio case with channel uncertainty. The precoding and power allocation matrices for each SU are either independently or jointly optimized for imperfect channel knowledge to maximize the secondary rates and to control the secondary interference on the primary receiver to be below the acceptable limit that is determined by the primary receiver. Numerical results prove the ability of the proposed methods to support significant secondary rates and to protect the PU from extra interference, within the acceptable primary range, even in presence of channel uncertainty case. In addition, joint optimization design has higher secondary performance than the independent optimization design.

Fractional Frequency Reuse (FFR) is an efficient method to mitigate Inter Cell Interference in multicellular Orthogonal Frequency Division Multiple Access (OFDMA) systems. In this paper, we analyze the downlink worst case Signal to Interference Ratio for FFR schemes. A closed form expression is derived analytically for the worst SIR, outage probability, and Spectral Efficiency (SE). The proposed analytical technique is used to configure a FFR solution for the downlink of OFDMA cellular system. The analysis is performed using two-tiers cellular network with uniform user density and for three different cases of FFR, namely, Frequency Reuse Factor (FRF) = 3, FRF=4 and sectored FFR. The inner radius configuration depends on equalizing the worst SIR for both inner and outer edges of the cell. Numerical results show that sectored FFR yields the highest SE and low outage probability. Sectored FFR highly balances the needs of interference reduction and resource efficiency.

Excessive capture power in at-speed scan testing may cause yield loss due to timing failures. Although reducing the number of clock domains that capture test responses simultaneously is a practical and scalable solution for reducing capture power, no available capture-safety checking metric can assess its effect in an accurate-enough manner, especially when multiple clock domains capture test responses in a short period of time. This paper proposes a novel CLEAR (CLock-Edge-Arrival-Relation-based) capture-safety checking method that, for the first time, takes clock edge arrival times for different clock domains into consideration. The accuracy and usefulness of the proposed method have been clearly demonstrated by simulation-based evaluation with the largest ITC'99 benchmark circuit as well as real-chip-based evaluation with an industrial chip embedded with on-chip delay measurement circuitry.

Excessive capture power in at-speed scan testing may cause timing failures, resulting in test-induced yield loss. This has made capture-safety checking mandatory for test vectors. This paper presents a novel metric, called the TTR (Transition-Time-Relation-based) metric, which takes transition time relations into consideration in capture-safety checking. Capture-safety checking with the TTR metric greatly improves the accuracy of test vector sign-off and low-capture-power test generation.

The Remotely Keyed Encryption Schemes (RKESs) are greatly useful in solving the vital problem of how to do bulk encryption/decryption for high-bandwidth applications (like multimedia data encryption) in a way that takes advantage of both the superior power of the host and the superior security of the smart card. Accordingly, we propose two novel RKESs, a Length Preserving (LP) RKES and a Length Increasing (LI) RKES. The proposed LPRKES is based on a general view of the well known Feistel-Network (FN) in which we only use two rounds in an efficient and secure way, employing data-dependent cipher-keys. In the LIRKES, an extra ciphertext block is used, encrypting the one-time random cipher-key based on a signature of the whole ciphertext. The security of the presented schemes are theoretically proven and, compared to the state-of-the-art RKESs, the savings in the required computational complexity, run-time, bandwidth, and storage space are emphasized.

The authors have proposed Multi-Input Multi-Output (MIMO)-Constant Envelope Modulation, (MIMO-CEM), as power and complexity efficient alternative to MIMO-OFDM, suitable for wireless backhaul network in which relay nodes are fixed in their positions. One of the major problems to withstand real application of MIMO-CEM is to estimate MIMO channel characteristics. The MIMO-CEM is based upon two contrary schemes; one is the nonlinear CEM modified Maximum Likelihood Sequence Estimator (MLSE) proposed by the authors, which needs accurate channel information to replicate the received signal passing through channel. The other is low resolution analog-to-digital converter (ADC), i.e., 1-bit in the default operation and 2 or 3 bits in the optional operations, which means that the received channel amplitude information may be completely or partially destroyed. These two contrary demands make MIMO-CEM channel estimation a big challenge; how we can accurately estimate the channel in these severe low ADC resolution conditions. We consider this issue through designing an efficient MIMO-CEM channel estimator based upon a block based adaptive filter. In addition, in order to speed up the parameter convergence rate in the proposed adaptive estimator, we design a correlator estimator as initial channel state estimation used in the adaptive estimator. We prove the effectiveness of the proposed MIMO-CEM channel estimation under different channel scenarios and different low ADC resolutions such as 1, 2 and 3-bit.

This paper presents a new at-speed logic built-in self-test (BIST) architecture supporting two launch-on-capture schemes, namely aligned double-capture and staggered double-capture, for testing multi-frequency synchronous and asynchronous clock domains in a scan-based BIST design. The proposed architecture also includes BIST debug and diagnosis circuitry to help locate BIST failures. The aligned scheme detects and allows diagnosis of structural and delay faults among all synchronous clock domains, whereas the staggered scheme detects and allows diagnosis of structural and delay faults among all asynchronous clock domains. Both schemes solve the long-standing problem of using the conventional one-hot scheme, which requires testing each clock domain one at a time, or the simultaneous scheme, which requires adding isolation logic to normal functional paths across interacting clock domains. Physical implementation is easily achieved by the proposed solution due to the use of a slow-speed, global scan enable signal and reduced timing-critical design requirements. Application results for industrial designs demonstrate the effectiveness of the proposed architecture.

Reducing excessive launch switching activity (LSA) is now mandatory in at-speed scan testing for avoiding test-induced yield loss, and test set modification is preferable for this purpose. However, previous low-LSA test set modification methods may be ineffective since they are not targeted at reducing launch switching activity in the areas around long sensitized paths, which are spatially and temporally critical for test-induced yield loss. This paper proposes a novel CAT (Critical-Area-Targeted) low-LSA test modification scheme, which uses long sensitized paths to guide launch-safety checking, test relaxation, and X-filling. As a result, launch switching activity is reduced in a pinpoint manner, which is more effective for avoiding test-induced yield loss. Experimental results on industrial circuits demonstrate the advantage of the CAT scheme for reducing launch switching activity in at-speed scan testing.

Power-aware X-filling is a preferable approach to avoiding IR-drop-induced yield loss in at-speed scan testing. However, the quality of previous X-filling methods for reducing launch switching activity may be unsatisfactory, due to low effect (insufficient and global-only reduction) and/or low scalability (long CPU time). This paper addresses this quality problem with a novel, GA (Genetic Algorithm) based X-filling method, called GA-fill. Its goals are (1) to achieve both effectiveness and scalability in a more balanced manner, and (2) to make the reduction effect of launch switching activity more concentrated on critical areas that have higher impact on IR-drop-induced yield loss.Evaluation experiments are being conducted on benchmark and industrial circuits, and initial results have demonstrated the usefulness of GA-fill.

At-speed scan testing is susceptible to yield loss risk due to power supply noise caused by excessive launch switching activity. This paper proposes a novel two-stage scheme, namely CTX (Clock-Gating-Based Test Relaxation and X-Filling), for reducing switching activity when test stimulus is launched. Test relaxation and X-filling are conducted (1) to make as many FFs inactive as possible by disabling corresponding clock-control signals of clock-gating circuitry in Stage-1 (Clock-Disabling), and (2) to make as many remaining active FFs as possible to have equal input and output values in Stage-2 (FF-Silencing). CTX effectively reduces launch switching activity, thus yield loss risk, even with a small number of donpsilat care (X) bits as in test compression, without any impact on test data volume, fault coverage, performance, and circuit design.

TurboBIST-Logic (TBL) is a software tool suite for incorporating logic built-in self-test (BIST) technology into digital Integrated Circuits and has been used by a variety of industrial designs globally since 2002. This abstract describes major features of TBL, and uses three industrial cases to show practical issues encountered and solved over the years. It also discusses an important new trend in going "hybrid," a flexible combination of capture-clocking schemes, with the goal to achieve an ever more optimal result over stand-alone schemes. Each of the three cases had its unique requirements for logic BIST, some needing to customize an existing solution, but all were set to achieve common BIST goals of at-speed testing, simple test interface to/from ATE, low test cost, high product reliability, and repeat testability investment reuse from IC, board, system, to in-field diagnosis.

Capture-safety, defined as the avoidance of any timing error due to unduly high launch switching activity in capture mode during at-speed scan testing, is critical for avoiding test- induced yield loss. Although point techniques are available for reducing capture IR-drop, there is a lack of complete capture-safe test generation flows. The paper addresses this problem by proposing a novel and practical capture-safe test generation scheme, featuring (1) reliable capture-safety checking and (2) effective capture-safety improvement by combining X-bit identification & X-filling with low launch- switching-activity test generation. This scheme is compatible with existing ATPG flows, and achieves capture-safety with no changes in the circuit-under-test or the clocking scheme.

Test data modification based on test relaxation and X-filling is the preferable approach for reducing excessive IR-drop in at-speed scan testing to avoid test-induced yield loss. However, none of the existing test relaxation methods can control the distribution of identified don’t care bits (X-bits), thus adversely affecting the effectiveness of IR-drop reduction. In this paper, we propose a novel test relaxation method, called Distribution-Controlling X-Identification (DC-XID), which controls the distribution of X-bits identified from a set of fully-specified test vectors for the purpose of effectively reducing IR-drop. Experimental results on large industrial circuits demonstrate the effectiveness and practicality of the proposed method in reducing IR-drop, without any impact on fault coverage, test data volume, or test circuit size.

This paper deals with a new class of equalizations for multiple codes-code division multiplexing (MC-CDM) signals. Criterion of the equalization is to equalize a distorted modulation block so as to be one proportional to the original waveform of the source signal block during its limited time span. A key idea is that the criterion is only applied to during the source signal span and no attention is paid to for any time space else other than the span, which is discriminated from the traditional inverse filter in which the same criterion is applied for infinite time space. This paper also proposes an inter-modulation block interference (IBI) canceller for further improvement of the equalizer. Simulation results ensure improved BER performances by combination of the proposed equalizer and the IBI canceller in comparison with OFDM.

Intermittent Periodic Transmit (IPT forwarding) is known as a packet forwarding scheme that achieves highly efficient packet relays in wireless multihop networks. In the method, a source node sends source packets intermittently and periodically with some transmit period, by which co-transmission space of forwarding packets, that is defined as space between multihop nodes in packet transmission, can be controlled in accordance with the given transmit period. If the transmit period is greater than a certain limit, packet collisions due to interference are eliminated and thus packet forwarding is maximized in its efficiency. However, the IPT forwarding needs elaborations on network topology for a given node layout because the principle of the scheme relies on string topology of node layout. This paper proposes a technique to enable the IPT forwarding in any network topologies. In the proposed scheme, a source node reserves a packet forwarding path to make the relay nodes on the path devote themselves to forward the packets originated by the source node. In addition, neighboring nodes close to the forwarding path are made to set their NAV (Network Allocation Vector) to prevent them from giving interference to the nodes on the reserved path. The proposed scheme can be combined with a conventional routing algorithm such as tree type ones or mesh type ones. Simulation results ensure that the combination of the IPT forwarding with the proposed path reservation achieves higher throughput and lower average packet delay compared with a conventional packet forwarding method.

The quality of at-speed testing is being severely challenged by the problem that an inter-clock logic block existing between two synchronous clocks is not efficiently tested or totally ignored due to complex test control. This paper addresses the problem with a novel inter-clock at-speed test control scheme, featuring a compact and robust on-chip inter-clock enable generator design. The new scheme can generate inter-clock at-speed test clocks from PLLs, and is feasible for both ATE-based scan testing and logic BIST. Successful applications to industrial circuits have proven its effectiveness in improving the quality of at-speed testing

Three experiments and a computational analysis were conducted to investigate the effects of a delegation-type interface on human supervision of simulated multiple unmanned vehicles. Participants supervised up to eight robots using automated behaviors ("plays"), manual (waypoint) control, or both to capture the flag of an opponent with an equal number of robots, using a simple form of a delegation-type interface, Playbook. Experiment 1 showed that the delegation interface increased mission success rate and reduced mission completion time when the opponent "posture" was unpredictably offensive or defensive. Experiment 2 showed that performance was superior when operators could flexibly use both automated behaviors and manual control, although there was a small increase in subjective workload. Experiment 3 investigated additional dimensions of flexibility by comparing delegation interfaces to restricted interfaces. Eight interfaces were tested, varying in the level of abstraction at which robot behavior could be tasked and the level of aggregation (single or multiple robots) to which plays could be assigned. Performance was superior with flexible interfaces for four robots, but this benefit was eliminated when eight robots had to be supervised. Finally, a computational analysis using task-network modeling and Monte Carlo simulation gave results that closely paralleled the empirical data on changes in workload across interface type. The results provide initial empirical evidence for the efficacy of delegation-type interfaces in human supervision of a team of multiple autonomous robots.

This work describes the VirtualScan technology for scan test cost reduction. Scan chains in a VirtualScan circuit are split into shorter ones and the gap between external scan ports and internal scan chains are bridged with a broadcaster and a compactor. Test patterns for a VirtualScan circuit are generated directly by one-pass VirtualScan ATPG, in which multi-capture clocking and maximum test compaction are supported. In addition, VirtualScan ATPG avoids unknown-value and aliasing effects algorithmically without adding any additional circuitry. The VirtualScan technology has achieved successful tape-outs of industrial chips and has been proven to be an efficient and easy-to-implement solution for scan test cost reduction.

This paper presents results of an experimental study on mode awareness in an adaptive cruise control system with two operational modes. Two cognitive experiments were conducted using a low-fidelity driving simulator. First, the understandability of the system behaviors was investigated in a situation in which the system lost sight of a target vehicle. The simulated driving under suppression on the system state information shows that some participants exhibited difficulty in predicting the system behavior in complicated situations. Through an analysis of participants' behaviors and understanding, valuable information that may improve their mode awareness was identified. The second experiment examined and compared design alternatives for the activatable and operational speed ranges in terms of the convenience and understandability. The results suggest that it may be possible to emphasize the convenience in the use of the ACC system without leading greater confusions in drivers' mode awareness.

The human-centered automation concept claims two general requirements on situation awareness (SA) of human operators. One is the necessity of keeping the SA of an artifact, and the other is keeping the SA of automation. Nevertheless, the fundamental methods or techniques, especially quantitative ones, are not mature enough to be used as rational tools for human-machine design. An important approach for establishing the method must be identification of a proper "level of automation", where ten levels are proposed by T.B. Sheridan (1999). A goal of the research presented is to establish a theoretical framework for evaluating automation levels from a viewpoint of operator's situation awareness in real domains. A method using discrete event simulation is developed, and applied to a particular artifact: a nuclear power plant.

This paper proposes site selection diversity transmission power control (SSDT), an advanced form of transmission power control (TPC) for CDMA forward link, SSDT realizes site selection transmission diversity instead of full site transmission diversity used in conventional TPC during soft hand over (SHO) mode. The major intention of the site selection is to mitigate interference caused by multiple site transmission done at conventional TPC. Simulation results indicated that the higher the capacity gain of SSDT is in comparison to conventional TPC, the lower the mobile station (MS) speed is. Capacity gain of about 55% for a pedestrian MS is achieved by SSDT in case of MS reception diversity and 6 finger RAKE reception. This paper also presents the benefits of SSDT in terms of its high path capturing efficiency and the mitigation of power imbalance among active BSs due to TPC command reception error.

Channel segregation, a distributed dynamic channel assignment method is applied to small cell systems in order to avoid intermodulation interference (IMI). Computer simulation is made to investigate the channel selection pattern achieved with this scheme for the assumed systems affected by IMI. The obtained channel selection patterns are shown to be free from any possible IMIs caused by the 3rd order products of the selected channels.

Co-channel interference disturbs the spectral efficiency in cellular radio systems. A co-channel interference reduction method using a constant modulus algorithm (CMA) adaptive array antenna is proposed. When we apply an adaptive array antenna to reduce co-channel interference, a co-channel interference signal may be captured. In this method, the replica of the interference signal is generated and then eliminated from the received signal, and thus the desired signal can be obtained. Computer simulation results of GMSK modulation confirm that a CMA adaptive array antenna that uses this method can reduce co-channel interference more than a conventional CMA adaptive array antenna.

High spectrum efficiency is promised by reuse partitioning in a cellular system. We propose an improved algorithm for self-organized reuse partitioning (SORP), a distributed dynamic channel assignment scheme, in order to obviate the need for broadcasting transmit power level information of each mobile terminal. The concept of the improved scheme is simple: a mobile terminal with low transmit power uses a low numbered channel throughout the system. Reuse partitioning can be achieved owing to such a channel segmentation. The algorithm is designed to realize the channel segmentation without the broadcasting of the transmit power level. Computer simulation results show that a high capacity and short delay time in finding an appropriate channel can be obtained. Furthermore, a higher capacity can be obtained by introducing quality based power control into this algorithm.

The umbrella cell system, where the same radio system is used for microcells and overlaying macrocells, is the most promising strategy for deploying microcell service to cope with increased portable radio subscribers. A practical approach to implementing a microcell system overlaid with an existing macrocell system is proposed. There is no need to design the channel assignment and transmit power management for the microcell system by introducing the channel segregation, a self-organized dynamic channel assignment and the automatic transmit power control. The system channels are reused automatically between the macrocells and microcells. The interference from the macrocell to the microcell is compensated by slight increase of transmit power for the microcell system. It is shown by computer simulation that locally increased traffic is accommodated with the microcells laid under macrocells without any effort for channel management.>

A digital 384-kbps TDMA-TDD microcellular system using pi /4-shifted DQPSK modulation is under development in Japan. To simplify the demodulator's configuration using this system and to reduce its power consumption, the authors propose a pi /4-shifted DQPSK demodulator that includes what they call an arctangent differential detector (ATN-DD) and an arctangent automatic frequency controller (ATN-AFC) because they process the phase of the received signal rather than the quadrature components. They present the configuration and the principles of operation of the ATN-DD and the ATN-AFC and show the results of BER and AFC performance testing. In addition, they investigate the most suitable AFC structure. Their study enabled a differential detector and AFC circuit gate-count reduction of more than 60%.>