This paper proposes a graph-theory-based Euler number computing algorithm. According to the graph theory and the analysis of a mask's configuration, the Euler number of a binary image in our algorithm is calculated by counting four patterns of the mask. Unlike most conventional Euler number computing algorithms, we do not need to do any processing of the background pixels. Experimental results demonstrated that our algorithm is much more efficient than conventional Euler number computing algorithms.

This paper proposes applying our inter-cell interference (ICI) cancellation method to fractional frequency reuse (FFR) and evaluates the resulting spectral efficiency improvement. With our ICI cancellation method based on base station cooperation, the control station generates ICI replica signals by simple linear processing. Moreover, FFR effectively utilizes frequency resources by both allowing users in the cell-center region to access all available sub-channels and increasing the transmission power to users in the cell-edge region. FFR provides the conditions under which the ICI cancellation method works effectively. Computer simulations show that the average spectral efficiency of the proposed method is comparable to that of cooperative MU-MIMO, which can completely remove ICI.

Many distributed systems use a replication mechanism for reliability and availability. On the other hand, application developers have to consider minimum consistency requirement for each application. Therefore, a replication protocol that supports multiple consistency models is required. Multi-Consistency Data Replication (McRep) is a proxy-based replication protocol and can support multiple consistency models. However, McRep has a potential problem in that a replicator relaying all request and reply messages between clients and replicas can be a performance bottleneck and a Single-Point-of-Failure (SPoF). In this paper, we introduce the multi-consistency support mechanism of McRep to a combined state-machine and deferred-update replication protocol to eliminate the performance bottleneck and SPoF. The state-machine and deferred-update protocols are well-established approaches for fault-tolerant data management systems. But each method can ensure only a specific consistency model. Thus, we adaptively select a replication method from the two replication bases. In our protocol, the functionality of the McRep's replicator is realized by clients and replicas. Each replica has new roles in serialization of all transactions and managing all views of the database, and each client has a new role in managing status of its transactions. We have implemented and evaluated the proposed protocol and compared to McRep. The evaluation results show that the proposed protocol achieved comparable throughput of transactions to McRep. Especially the proposed protocol improved the throughput up to 16% at a read-heavy workload in One-Copy. Finally, we demonstrated the proposed failover mechanism. As a result, a failure of a leader replica did not affect continuity of the entire replication system unlike McRep.

Petri nets are a kind of formal language that are widely applied in concurrent systems associated with resource allocation due to their abilities of the natural description on resource allocation and the precise characterization on deadlock. Weighted System of Simple Sequential Processes with Resources (WS3PR) is an important subclass of Petri nets that can model many resource allocation systems in which 1) multiple processes may run in parallel and 2) each execution step of each process may use multiple units from a single resource type but cannot use multiple resource types. We first prove that the liveness problem of WS3PR is co-NP-hard on the basis of the partition problem. Furthermore, we present a necessary and sufficient condition for the liveness of WS3PR based on two new concepts called Structurally Circular Wait (SCW) and Blocking Marking (BM), i.e., a WS3PR is live iff each SCW has no BM. A sufficient condition is also proposed to guarantee that an SCW has no BM. Additionally, we show some advantages of using SCW to analyze the deadlock problem compared to other siphon-based ones, and discuss the relation between SCW and siphon. These results are valuable to the further research on the deadlock prevention or avoidance for WS3PR.

This paper proposes a new antenna array design of Massive MIMO for capacity enhancement in line of sight (LOS) environments. Massive MIMO has two key problems: the heavy overhead of feeding back the channel state information (CSI) for very large number of transmission and reception antenna element pairs and the huge computation complexity imposed by the very large scale matrixes. We have already proposed a practical application of Massive MIMO, that is, Massive Antenna Systems for Wireless Entrance links (MAS-WE), which can clearly solve the two key problems of Massive MIMO. However, the conventional antenna array arrangements; e.g. uniform planar array (UPA) or uniform circular array (UCA) degrade the system capacity of MAS-WE due to the channel spatial correlation created by the inter-element spacing. When the LOS component dominates the propagation channel, the antenna array can be designed to minimize the inter-user channel correlation. We propose an antenna array arrangement to control the grating-lobe positions and achieve very low channel spatial correlation. Simulation results show that the proposed arrangement can reduce the spatial correlation at CDF=50% value by 80% compared to UCA and 75% compared to UPA.

This paper proposes a null-space expansion scheme for multiuser massive MIMO transmission in order to suppress inter-user interference (IUI) triggered by the temporal variation of the channel. The downlink multiuser MIMO channel capacity of time varying channels is severely degraded since IUI must be suppressed at the transmitter side by using past estimated channel state information at the transmitter side (CSIT). Massive MIMO has emerged as one of the most promising technologies for further capacity enhancement by increasing the number of base station (BS) antenna elements. Exploiting the excess degrees of freedom (DoFs) inherent in massive MIMO, a BS with the proposed IUI suppression scheme performs multiple null-steering for each UE (User Equipment) antenna element, which expands the null-space dimension. Computer simulations show that the proposed scheme has superior IUI suppression performance to the existing channel prediction scheme in time varying channels.

This paper experimentally verifies the potential of higher order space division multiplexing in line-of-sight (LOS) channels for multiuser massive MIMO. We previously proposed an inter-user interference (IUI) cancellation scheme and a simplified user scheduling method for Massive Antenna Systems for Wireless Entrance (MAS-WE). In order to verify the effectiveness of the proposed techniques, channel state information (CSI) for a 1×32 SIMO channel is measured in a real propagation environment with simplified test equipment. Evaluations of the measured CSI data confirm the effectiveness of our proposals; they offer good equal gain transmission (EGT) performance, reduced spatial correlation with enlarged angular gap between users, and quite small channel state fluctuation. Link level simulations elucidate that the simple IUI cancellation method is stable in practical conditions. The degradation in symbol error rate with the measured CSI, relative to that yielded by the output of the theoretical LOS channel model, is insignificant.

This paper presents a reduced-complexity maximum likelihood detection (MLD) scheme for orthogonal frequency division multiplexing with space division multiplexing (OFDM-SDM) systems. Original MLD is known to be an optimal scheme for detecting the spatially multiplexed signals. However, MLD suffers from an exponentially computational complexity because it involves an exhaustive search for the optimal result. In this paper, we propose a novel detection scheme, which drastically reduce the complexity of MLD while keeping performance losses small. The proposed scheme decouples the spatially multiplexed signals in two stages. In stage one, the estimated symbols obtained from zero-forcing (ZF) are used to limit the candidate symbol vectors. In stage two, to form a final estimate of the transmitted symbol vector, the Euclidean or original defined likelihood metric is examined over all symbol vectors obtained from stage 1. Both the bit error rate (BER) and packet error rate (PER) performances are evaluated over a temporally and spatially uncorrelated frequency selective channel through the computer simulations. For a four-transmit and four-receive OFDM-SDM system transmitting data at 144 Mbit/s and 216 Mbit/ss i.e., employing 16 Quadrature Amplitude Modulation (16QAM) and 64QAM subcarrier modulation over 16.6 MHz bandwidth channel, the degradation in required SNR from MLD for PER = 1% are about 0.6 dB and 1.5 dB, respectively. However, the complexity of MLD is reduced to 0.51000% and 0.01562%.

This paper describes the experimental performance of eigenbeam multi-input multi-output with orthogonal frequency division multiplexing (MIMO-OFDM) systems as measured in a testbed implemented with field programmable gate arrays (FPGAs). The FPGA-testbed, characterized by the software-defined radio (SDR) technique, offers 1/5-scale real time signal processing. Extensive experiments on the testbed confirm the basic operation and performance of eigenbeam MIMO-OFDM with quadrature phase-shift keying (QPSK) and 16 quadrature amplitude modulation (QAM). From the packet error rate (PER) performance, we confirm that the eigenbeam 16QAM/MIMO-OFDM scheme with permutation matrix and three transmit antennas (Mt=3) drastically improves the required carrier-to-noise power ratio (CNR) by approximately 5.6 dB over the scheme without eigenbeam with Mt=2. Furthermore, to determine the impact of Doppler frequency fd, we focus on the transmission interval between the MIMO channel estimation and data transmission. To suppress the required CNR degradation to within 1.5 dB, it is found that the eigenbeam 16QAM/MIMO-OFDM scheme with permutation matrix and Mt=3 permits a transmission interval of approximately 68.5 ms when fd=1 Hz for a 1/5-scale model.

Multiple input multiple output (MIMO) systems represent a very attractive candidate for future high data rate wireless access systems to increase the channel capacity. To obtain a further increase in the channel capacity, a distributed wireless communication system that has multiple access points (APs) and an access controller (AC), was proposed. This system increases not only the peak transmission rate but also the overall transmission rate in the service area. In this paper, we consider a cooperative multiple AP system where APs are synchronized in terms of time, but not in terms of phase. We propose a transmission method for the cooperative multiple AP system that enables the mobile station to obtain a high achievable bit rate regardless of decoding algorithms. The performance of the multiple AP systems is evaluated in comparison to the conventional single AP system. To evaluate the effectiveness of the proposed method in the cooperative multiple AP system, computer simulations are performed using the i.i.d. channel in Rayleigh and Ricean fading environments. Furthermore, we evaluate the performance of the cooperative multiple AP system using the channel measured in an actual indoor environment.

Automatic repeat request (ARQ) for wireless ATM (WATM) operating at 20 Mbit/s or higher is required to achieve high throughput performance as well as high transmission quality, i.e., low CLR (cell loss ratio). Selective Repeat (SR) and Go-Back-N (GBN) are typical ARQ schemes. Though SR-ARQ is superior to GBN-ARQ in throughput performance, the implementation complexity of SR-ARQ's control procedures is disadvantageous to its application to high-speed wireless systems. In addition, when PDU (protocol data unit) length on wireless link is short, the capacity for ARQ control messages can be significantly large. GBN-ARQ, on the other hand, cannot avoid serious throughput degradation due to fairly high BER caused by multipath fading and shadowing, though its implementation is simple. To solve the above-mentioned problems, this paper proposes a novel ARQ scheme named PRIME-ARQ (Partial selective Repeat superIMposEd on gbn ARQ). PRIME-ARQ achieves high throughput performance, almost equal to selective repeat ARQ, with a simple algorithm resulting in reduced implementation complexity for high speed operation. This paper describes the design, implementation, and performance of the proposed PRIME-ARQ. In addition, it shows the experimental results using an experimental PRIME-ARQ hardware processor and proto-type AWA equipment.

The Euler number of a binary image is an important topological property for pattern recognition, and can be calculated by counting certain bit-quads in the image. This paper proposes an efficient strategy for improving the bit-quad-based Euler number computing algorithm. By use of the information obtained when processing the previous bit quad, the number of times that pixels must be checked in processing a bit quad decreases from 4 to 2. Experiments demonstrate that an algorithm with our strategy significantly outperforms conventional Euler number computing algorithms.

This paper proposes a new scheme that can evaluate the cell throughput performance of wireless local area network (LAN) systems, which use carrier sense multiple access/collision avoidance (CSMA/CA) and multiple transmission bit-rates (multi-rate). We extend the interference model of the conventional scheme in order to deal with interference more accurately in multi-cell environments. Unlike the conventional scheme, the proposed scheme is able to handle multi-rate systems. We use the proposed scheme to evaluate the IEEE 802.11a system and systems whose signal-bandwidth is expanded from that of the IEEE 802.11a system. We find that a system with 35(75) MHz signal-bandwidth achieves about 1.3(1.25) times higher cell throughput than the IEEE 802.11a system. Furthermore, the system with 35(75) MHz signal-bandwidth is also shown to have the potential to achieve up to 1.5(1.8) times higher cell throughput performance than the IEEE 802.11a system if the transmission efficiency on the media access control (MAC) layer is assumed to be ideal. It is concluded that the proposed scheme confirms that the approach to expand the signal bandwidth of the IEEE 802.11a system is effective to improve the cell throughput performance. This result is virtually impossible to derive with the conventional scheme.

Silva et al. has suggested a criterion based on incidence matrix to verify if a given extended free choice net has a live and bounded marking. This paper shows that this criterion is a necessary and sufficient condition that a given net is a state machine allocatable (SMA) net. This result gives a polynomial algorithm to verify SMA net.

Petri net is a graphical and mathematical modeling tool for discrete event systems. This paper treats analysis problems for Petri nets under the earliest firing rule. Under this firing rule, transitions must fire as soon as they are enabled. Marked Petri nets under the earliest firing rule are called earliest firing systems, for short. First, some relations in analysis problems between the earliest and the normal firing systems are discussed. These problems include deadlock freedom, boundedness, persistency and liveness. Then, relations among three types of reachability are considered from the viewpoint of the earliest firing rule. Since earliest firing systems can simulate register machines, they have equivalent modeling powers to Turing machines. It suggests, however, that most of the analysis problems of earliest firing systems with general net structures are undecidable. In this paper, net structures are restricted to a subclass called dissynchronous choice (DC) nets. It is shown that the reachability problem from an initial marking to dead markings (markings where no transition can fire) in earliest firing DC systems is equivalent to the usual reachability problem of the same systems under the normal firing rule. Then, the result is applied to reachability problems of controlled DC systems in which some transitions in the net have external control input places. It is shown that for systems where every transition in the net has an external control input place, one type of reachability problem is decidable. Lastly, the liveness problem of earliest firing DC systems is considered and it is shown that this problem is equivalent to that of the underlying DC system under the normal firing rule. It is also shown that this liveness problem is decidable.