This study analyzes the performance of a downlink beamformer with partitioned vector quantization under optimized feedback budget allocation. A multiuser multiple-input single-output downlink precoding system with perfect channel state information at mobile stations is considered. The number of feedback bits allocated to the channel quality indicator (CQI) and the channel direction indicator (CDI) corresponding to each partition are optimized by exploiting the quantization mean square error. In addition, the effects of equal and unequal partitioning on codebook memory and system capacity are studied and elucidated through simulations. The results show that with optimized CQI-CDI allocation, the feedback budget distributions of equal or unequal partitions are proportional to the size ratios of the partitioned subvectors. Furthermore, it is observed that for large-sized partitions, the ratio of optimal CDI to CQI is much higher than that for small-sized partitions.

This paper presents the best transmit diversity schemes for three types of common/shared control signals from the viewpoint of the block error rate (BLER) performance in the Evolved UTRA downlink employing OFDM radio access. This paper also presents the coverage performance of the common/shared control signals using transmit diversity with respect to the outage probability that satisfies the required BLER performance, which is a major factor determining the cell configuration. Simulation results clarify that Space-Frequency Block Code (SFBC) and the combination of SFBC and Frequency Switched Transmit Diversity (FSTD) are the best transmit diversity schemes among the open-loop type transmit diversity candidates for two-antenna and four-antenna transmission cases, respectively. Furthermore, we show through system-level simulations that SFBC is very effective in reducing the outage probability at the required BLER for the physical broadcast channel (PBCH), for the common control signal with resource block (RB)-level assignment such as the dynamic broadcast channel (D-BCH) and paging channel (PCH), and in increasing the number of accommodated L1/L2 control signals over one transmission time interval duration, using mini-control channel element (CCE)-level assignment.

With the purpose of improving the performance of next generation wireless networks, cooperative relaying (CoR) and network coding (NC) are promising techniques. The number of time slots required for NC in bidirectional transmission is less than that required for CoR, and hence, NC can achieve higher throughput performance than CoR. However, the disadvantage of NC is that asymmetric traffic ratio conditions might cause a significant decrease in the bidirectional throughput. In contrast, CoR is robust to asymmetric traffic ratio conditions. In this paper, in order to improve the throughput of NC even under asymmetric traffic ratio conditions, we propose an opportunistic scheduling scheme for hybrid NC and CoR. In the proposed scheduling scheme, the transmission protocol with best throughput performance can be adaptively selected based on instantaneous channel state information. Computer simulation results reveal that the proposed scheduling scheme not only achieve higher throughput than the conventional scheduling scheme but is also robust against asymmetric traffic ratio conditions. By adjusting the scheduler's parameter, the proposed scheduling scheme can provide a tradeoff between the throughput and the traffic ratio. Moreover, in certain cases, maximizing the throughput of NC and guaranteeing the offered traffic ratio can be achieved at the same time.

In existing systems of mobile routers, the frequency band is shared in uplinks from wireless terminals to mobile routers, and carrier sense multiple access with collision avoidance (CSMA/CA) is generally used as the medium access control protocol. To use the frequency band effectively, adaptive control is one promising approach. In this paper, a decentralized access control protocol in which mobile routers adaptively select the minimum contention window size is proposed. However, because of their mobility, which is one of the main difference between mobile routers and fixed access points, individual local area networks (LANs) consisting of the mobile routers and wireless terminals randomly interact with each other, and such random interactions can cause instability. To analyze the stability of the proposed control, evolutionary game theory is introduced because a system with random interactions between numerous decision-making entities can be analyzed by using evolutionary game theory. Using evolutionary game theory, the condition for existence of a convergence point is obtained. In addition, to implement the decentralized access control, a learning rule is proposed. In the proposed learning rule, each mobile router selects a strategy based on the result of past trials. From the simulation result, it is confirmed that the decentralized access control converges to a point closed to the stable state derived through evolutionary game theory.

We have succeeded in developing three techniques, a precise lens-alignment technique, low-loss built-in Spatial Multiplexing optics and a well-matched electrical connection for high-frequency signals, which are indispensable for realizing compact high-performance TOSAs and ROSAs employing hybrid integration technology. The lens position was controlled to within ±0.3 µm by high-power laser irradiation. All components comprising the multiplexing optics are bonded to a prism, enabling the insertion loss to be held down to 0.8 dB due to the dimensional accuracy of the prism. The addition of an FPC layer reduced the impedance mismatch at the junction between the FPC and PCB. We demonstrated a compact integrated four-lane 25 Gb/s TOSA (15.1 mm × 6.5 mm × 5.6 mm) and ROSA (17.0 mm × 12.0 mm × 7.0 mm) using the built-in spatial Mux/Demux optics with good transmission performance for 100 Gb/s Ethernet. These are respectively suitable for the QSFP28 and CFP2 form factors.

Nuclear power plants (NPPs) must be maintained periodically. Their maintenance efficiency must be improved and human error must be reduced simultaneously to improve NPPs' competitive capability in electricity markets. Although Augmented Reality (AR) offers great possibilities to support NPP maintenance work, some difficulties exist for application of AR to actual work support because current AR systems cannot be implemented in NPP environments without technical improvement. There are several kinds of problems such as recognition distance, tracking accuracy, and a complex working environment when applying AR to NPP field work support. Considerable extension of tracking distance and improvement of accuracy are particularly desired because NPPs are large-scale indoor environments. This study designed a linecode marker, a new type of paper-based marker, along with recognition and tracking algorithms for it to resolve these problems. In contrast to conventional paper-based markers, such as square markers and circle markers, the linecode marker is not merely easier to set up in complex industrial environments: it also enables the use of AR in industrial plants because of its considerable tracking-performance improvement. To evaluate tracking accuracy, the trackable distance, and the tracking speed of the proposed tracking method, an evaluation experiment was conducted in a large room. The experiment results show that the tracking distance is extended extremely over that of the traditional marker-based tracking method: tracking accuracy improved to 20 cm over a 10 m distance. The running speed of the tracking can be as fast as 15 frames per second using a laptop PC.

The spectral efficiency of cooperative relaying in interference-limited environments in which a given channel is spatially reused is investigated. Cooperative relaying is a promising technique that uses neighboring stations to forward the data toward the destination in order to achieve spatial diversity gain. It has been reported that by introducing cooperative relaying into communication between an isolated source-destination pair, the error rate or spectral efficiency is generally improved. However, it is not intuitively clear whether cooperative relaying can improve the performance in interference-limited environments because the simultaneous transmission of multiple stations increases the number of interference signals. Assuming the most fundamental cooperative relaying arrangement, which consists of only one relay station, numerical results reveal that cooperative relaying is not always superior to non-cooperative single-hop and two-hop transmissions in terms of spectral efficiency.

An automatic-repeat-request (ARQ) scheme for improving the system throughput efficiency is evaluated in coded multiple-input multiple-output (MIMO) transmissions. Supplementary trellis-coded modulation (TCM) code has been proposed for hybrid ARQ schemes. The free distance of the TCM after code combining can be increased by employing different TCM codes for retransmissions. The MIMO scheme offers additional flexibility in preventing successive frame errors by changing the connections between transmitters and transmit antennas upon retransmission. In this paper, an ARQ strategy employing both TCM reassignment and antenna permutation technique is investigated. It is shown through computer simulations that this ARQ scheme achieves high throughput even in severe conditions of low signal-to-noise ratio and high Rician factor over spatially and temporally correlated Nakagami-Rice fading MIMO channels.

In the phase locked loop (PLL) frequency synthesizer which is used in a higher frequency region, the prescaler method is employed in order to increase the operating frequency of the programmable divider. However, since the fixed divider whose division ratio is same as the prescaler is installed at the following stage of the reference divider, the reference frequency is decreased and the performance of the PLL frequency synthesizer is degraded. The prescaler PLL frequency synthesizer using multi-programmable divider is one of the counter measures answering the request. In this paper we propose the reduction of the number of programmable dividers by using the (N+1/2) programmable divider. The effectiveness of the proposed method is confirmed by experimental results.

This paper proposes an adaptive selection algorithm for the surviving symbol replica candidates (ASESS) based on the maximum reliability in maximum likelihood detection with QR decomposition and the M-algorithm (QRM-MLD) for Orthogonal Frequency Division Multiplexing (OFDM) multiple-input multiple-output (MIMO) multiplexing. In the proposed algorithm, symbol replica candidates newly-added at each stage are ranked for each surviving symbol replica from the previous stage using multiple quadrant detection. Then, branch metrics are calculated only for the minimum number of symbol replica candidates with a high level of reliability using an iterative loop based on symbol ranking results. Computer simulation results show that the computational complexity of the QRM-MLD employing the proposed ASESS algorithm is reduced to approximately 1/4 and 1/1200 compared to that of the original QRM-MLD and that of the conventional MLD with squared Euclidian distance calculations for all symbol replica candidates, respectively, assuming the identical achievable average packet error rate (PER) performance in 4-by-4 MIMO multiplexing with 16QAM data modulation. The results also show that 1-Gbps throughput is achieved at the average received signal energy per bit-to-noise power spectrum density ratio (Eb/N0) per receiver antenna of approximately 9 dB using the ASESS algorithm in QRM-MLD associated with 16QAM modulation and Turbo coding with the coding rate of 8/9 assuming a 100-MHz bandwidth for a 12-path Rayleigh fading channel (root mean square (r.m.s.) delay spread of 0.26 µs and maximum Doppler frequency of 20 Hz).

This paper discusses a communication system with a multiple-access channel where two users simultaneously send complex-valued signals in the same frequency-band. In this channel, ambiguity in decoding occurs when receiver trying to estimate each users' signal. In order to solve the ambiguity problem, a family of uniquely decodable code is derived in this paper. The uniquely decodable code is designed by using trellis-coded modulation (TCM) pair where the trellis structure of one TCM is a transformation of the other in the pair. It is theoretically proved that, with the proposed coding scheme, the composite received signal can be uniquely decomposed into the two constituent signals for any power ratio and any phase difference between the received two users' signals. Improvement of BER performance over non-uniquely decodable code is illustrated by computer simulation.

In this paper, the performance of dynamic channel assignment for cellular systems with an array antenna is evaluated assuming realistic beamformer. A new dynamic channel assignment algorithm is proposed to improve the performance by forming a directional beam pattern to cancel stronger co-channel interference with higher priority. Performance comparison is carried out by computer simulations. Conventional algorithm shows 2.7 fold capacity increase compared with an omni antenna system, whereas proposed algorithm shows around 3.3 fold capacity increase, at the point of 3 percent blocking probability. The simulation results also denote that a shorter reuse distance can be achieved by the proposed algorithm, which indicates a more efficient utilization of channel resource.

This paper presents frequency diversity effects of localized transmission, clustered transmission, and intra-subframe frequency hopping (FH) using a frequency domain equalizer (FDE) for discrete Fourier transform (DFT)-precoded Orthogonal Frequency Division Multiple Access (OFDMA). In the evaluations, we employ the normalized frequency mean square covariance (NFMSV) as a measure of the frequency diversity effect, i.e., randomization level of the frequency domain interleaving associated with turbo coding. Link-level computer simulation results show that frequency diversity is very effective in decreasing the required average received signal-to-noise power ratio (SNR) at the target average block error rate (BLER) using a linear minimum mean-square error (LMMSE) based FDE according to the increase in the entire transmission bandwidth for DFT-precoded OFDMA. Moreover, we show that the NFMSV is an accurate measure of the frequency diversity effect for the 3 transmission schemes for DFT-precoded OFDMA. We also clarify the frequency diversity effects of the 3 transmission schemes from the viewpoint of the required average received SNR satisfying the target average BLER for the various key radio parameters for DFT-precoded OFDMA in frequency-selective Rayleigh fading channels.

In a spectrum sharing system, lower-priority users are allowed to spatially reuse the spectrum allocated to higher-priority users as long as they do not disrupt communications of the latter. Therefore, to improve spectrum utilization, an important requirement for the former users is to manage the interference and ensure that the latter users can maintain reliable communications. In the present paper, a game theoretic framework of joint channel selection and power allocation for spectrum sharing in distributed cognitive radio networks is proposed. First, a utility function that captures the cooperative behavior to manage the interference and the satisfaction level to improve the throughput of the lower-priority users is defined. Next, based on the defined utility function, the proposed framework can be formulated as a potential game; thus, it is guaranteed to converge to a Nash equilibrium when the best response dynamic is performed. Simulation results show the convergence of the proposed potential game and reveal that performance improvements in terms of network throughput of the lower-priority users and outage probability of the higher-priority users can be achieved by the introduction of an adaptive coefficient adjustment scheme in the proposed utility function at the expense of the convergence to the Nash equilibrium.

This paper describes a new method to determine the 3-D position coordinates of a Lambertian surface from four shaded images acquired with an actively controlled, nearby moving point light source. The method treats both the case when the initial position of the light source is known and the case when it is unknown.

A context-sensitive method to predict linguistic expressions in the next utterance in inquiry dialogues is proposed. First, information of the next utterance, the utterance type, the main action and the discourse entities, can be grasped using a dialogue interpretation model. Secondly, focusing in particular on dialogue situations in context, a domain-dependent knowledge-base for literal usage of both noun phrases and verb phrases is developed. Finally, a strategy to make a set of linguistic expressions which are derived from semantic concepts consisting of appropriate expressions can be used to select the correct candidate from the speech recognition output. In this paper, some of the processes are particularly examined in which sets of polite expressions, vocatives, compound nominal phrases, verbal phrases, and intention expressions, which are common in telephone inquiry dialogue, are created.

This paper experimentally investigates the effect of frequency error compensation provided by demodulation automatic frequency control (AFC) using the Synchronization Channel (SCH) in downlink OFDM radio access. The implemented OFDM receiver compensates for the frequency error caused by the difference in frequency between a base station (BS) and a user equipment (UE) using a time-division multiplexed SCH signal and that caused by the Doppler shift generated by the mobility of a user using reference signals with staggered multiplexing. Experimental results show that even when the standard oscillator frequency of the UE cannot be made to track the more accurate frequency of a BS, demodulation AFC can suppress the residual frequency error to a sufficiently low level, i.e., within 0.3 ppm, using the SCH so that the degradation in the block error rate of the physical broadcast channel control signals is slight, i.e., within approximately 0.1 dB, with respect to the case without frequency error for speeds greater than 350 km/h.

This letter reports laboratory experiments of trellis-coded multiple-antenna systems. We evaluate the effect of spatial interleaving for the vector Viterbi algorithm under several conditions such as line-of-sight (LOS), non-LOS propagation, frequency-flat and frequency-selective channels.

This paper considers coordinated linear precoding for rate optimization in downlink multicell, multiuser orthogonal frequency-division multiple access networks. We focus on two different design criteria. In the first, the weighted sum-rate is maximized under transmit power constraints per base station. In the second, we minimize the total transmit power satisfying the signal-to-interference-plus-noise-ratio constraints of the subcarriers per cell. Both problems are solved using standard conic optimization packages. A less complex, fast, and provably convergent algorithm that maximizes the weighted sum-rate with per-cell transmit power constraints is formulated. We approximate the non-convex weighted sum-rate maximization (WSRM) problem with a solvable convex form by means of a sequential parametric convex approximation approach. The second-order cone formulations of an objective function and the constraints of the optimization problem are derived through a proper change of variables, first-order linear approximation, and hyperbolic constraints transformation. This algorithm converges to the suboptimal solution while taking fewer iterations in comparison to other known iterative WSRM algorithms. Numerical results are presented to demonstrate the effectiveness and superiority of the proposed algorithm.

In this paper, we propose a probabilistic approach to derive an approximate polyhedral description from range data. We first compare several least-squares-based methods for estimation of local normal vectors and select the most robust one based on a reasonable noise model of the range data. Second, we extract the stable planar regions from the range data by examining the distributions of the local normal vectors together with their spatial information in the 2D range image. Instead of segmenting the range data completely, we use only the geometries of the extracted stable planar regions to derive a polyhedral description of the range data. The curved surfaces in the range data are approximated by their extracted plane patches. With a probabilistic approach, the proposed method can be expected to be robust against the noise. Experimental results on real range data from different sources show the effectiveness of the proposed method.