This paper presents a VLSI design of a Tomlinson-Harashima (TH) precoder for multi-user MIMO (MU-MIMO) systems. The TH precoder consists of LQ decomposition (LQD), interference cancellation (IC), and weight coefficient multiplication (WCM) units. The LQ decomposition unit is based on an application specific instruction-set processor (ASIP) architecture with floating-point arithmetic for high accuracy operations. In the IC and WCM units with fixed-point arithmetic, the proposed architecture uses an arrayed pipeline structure to shorten a circuit critical path delay. The implementation result shows that the proposed architecture reduces circuit area and power consumption by 11% and 15%, respectively.

The implementation and experimental evaluations of distributed zero-forcing beamforming (DZFBF) for downlink multi-user multiple-input multiple-output (DL MU-MIMO) systems are presented. In DZFBF, multiple access points (APs) transmit to own desired stations (STAs) at the same time and using the same frequency channel while mitigating inter-cell interference. To clarify the performance and feasibility of DZFBF, we develop a real-time transmission testbed that includes two APs and four STAs; all are implemented using field programmable gate array. For real-time transmission, we also implement a simple weight generation process based on ZF weight using channel state information which is fed back from STAs; it is an extension of the weight generation approach used in DL MU-MIMO systems. By using our testbed, we demonstrate the real-time transmission performance in actual indoor multi-cell environments. These results indicate that DL DZFBF is more effective than DL MU-MIMO with time division multiple access.

This paper proposes an opportunistic feedback and user selection method for a multiuser two-way relay channel (MU-TWRC) in a time-varying environments where a base station (BS) and a selected mobile station (MS), one of K moving MSs, exchange messages during two time slots via an amplify-and-forward relay station. Specifically, under the assumption of perfect channel reciprocity, we analyze the outage probabilities of several channel feedback scenarios, including the proposed scheme. Based on the analysis, the transmission rates are optimized and the optimal user selection method is proposed to maximize the expected sum throughput. The simulation results indicate that, with opportunistic feedback, the performance can be significantly improved compared to that without feedback. Moreover, the performance is nearly identical to that with full feedback, and close to the case of perfect channel state information at BS for low mobility MSs.

In the recently developed Flexible Wireless System (FWS), the same platform needs to deal with different wireless systems. This increases nonlinear distortion in its wideband power amplifier (PA) because the PA needs to concurrently amplify multi-band signals. By taking higher harmonics as well as inter- and cross-modulation distortion into consideration, we have developed a method to analytically evaluate the adjacent channel leakage power ratio (ACPR) and error vector magnitude (EVM) on the basis of the PA's nonlinear characteristics. We devise a novel method for modeling the PA amplifying dual-band signals. The method makes it possible to model it merely by performing a one-tone test, making use of the Volterra series expansion and the general Wiener model. We then use the Mehler formula to derive the closed-form expressions of the PA's output power spectral density (PSD), ACPR, and EVM. The derivations are based on the assumption that the transmitted signals are complex Gaussian distributed in orthogonal frequency division multiplexing (OFDM) transmission systems. We validate the method by comparing measurement and simulation results and confirm it can appropriately predict the ACPR and EVM performance of the nonlinear PA output with OFDM inputs. In short, the method enables correct modeling of a wideband PA that amplifies dual-band signals merely by conducting a one-tone test.

Histogram sequences represent high-dimensional time-series converted from images by space filling curves (SFCs). To overcome the high-dimensionality nature of histogram sequences (e.g., 106 dimensions for a 1024×1024 image), we often use lower-dimensional transformations, but the tightness of their lower-bounds is highly affected by the types of SFCs. In this paper we attack a challenging problem of evaluating which SFC shows the better performance when we apply the lower-dimensional transformation to histogram sequences. For this, we first present a concept of spatial locality and propose spatial locality preservation metric (SLPM in short). We then evaluate five well-known SFCs from the perspective of SLPM and verify that the evaluation result concurs with the actual transformation performance. Finally, we empirically validate the accuracy of SLPM by providing that the Hilbert-order with the highest SLPM also shows the best performance in k-NN (k-nearest neighbors) search.

We evaluated the behavior of a multi-user multiple-input multiple-output (MIMO) system in time-varying channels using measured data. A base station for downlink or broadcast transmission requires downlink channel state information (CSI), which is outdated in time-varying environments and we encounter degraded performance due to interference. One of the countermeasures against time-variant environments is predicting channels with an autoregressive (AR) model-based method. We modified the AR prediction for a time division duplex system. We conducted measurement campaigns in indoor environments to verify the performance of the scheme of channel prediction in an actual environment and measured channel data. We obtained the bit-error rate (BER) using these data. The AR-model-based technique of prediction assuming the Jakes' model was found to reduce BER. Also, the optimum AR-model order was investigated by using the channel data we measured.

A subarray signal processing scheme is described for a large-scale two-dimensional analog-digital hybrid beamformer to be used in quasi-millimeter-wave-band mobile communication systems. Multiple analog phased arrays direct their respective beams to multiple users, enabling space-division multiple access (SDMA). An iterative soft-input soft-output (SISO) multi-user detector recovers multi-user signals from subarray output signals corrupted by inter-user interference (IUI). In addition, a phased-array directivity control algorithm is derived based on inter-subarray signal phase-difference estimation from inter-beam-interference (IBI)-cancelled subarray output signals. Simulation results demonstrate that our proposed scheme achieves reduced hardware complexity, IUI-resistant multi-user signal detection, and IBI-resistant multi-user-tracking phased-array directivity control.

As a network evolves following initial deployment, its service functions remain diversified through the openness of the network functions. This indicates that appropriate simplification of the service functions is essential if the evolving network is to achieve the required scalability of service processing and service management. While the screening of service functions is basically performed by network users and the market, several service functions will be automatically simplified based on the growth of the evolving network. This paper verifies the simplification of service functions resulting from the evolution of the network itself. First, the principles that serve as the basis for simplifying the service functions are explained using several practical examples. Next, a simulation model is proposed to verify the simplification of service functions in terms of the priority control function for path routing and load balancing among multiple paths. From the results of the simulation, this study clarifies that the anticipated simplification of service functions is actually realizable and the service performance requirements can be reduced as the network evolves after deployment. When the simplification of service functions can improve network quality, it accelerates the evolution of the network and increases the operator's revenue.

In this paper, we present a real-time hand pose recognition method to provide an intuitive user interface through hand poses or gestures without a keyboard and a mouse. For this, the areas of right and left hands are segmented from the depth camera image, and noise compensation is performed. Then, the rotation angle and the centroid point of each hand area are calculated. Subsequently, joint points and end points of a finger are detected by expanding a circle at regular intervals from a centroid point of the hand. Lastly, the hand pose is recognized by matching between the current hand information and the hand model of previous frame and the hand model is updated for the next frame. This method enables users to predict the hidden fingers through the hand model information of the previous frame using temporal coherence in consecutive frames. As a result of the experiment on various hand poses with the hidden fingers using both hands, the accuracy showed over 95% and the performance indicated over 32fps. The proposed method can be used as a contactless input interface in presentation, advertisement, education, and game applications.

This letter proposes a new delivery format in order to realize unified transmissions of stereoscopic video contents over a dynamic adaptive streaming scheme. With the proposed delivery format, various forms of stereoscopic video contents regardless of their encoding and composition types can be delivered over the current dynamic adaptive streaming scheme. In addition, the proposed delivery format supports dynamic and efficient switching between 2D and 3D sequences in an interoperable manner for both 2D and 3D digital devices, regardless of their capabilities. This letter describes the designed delivery format and shows dynamic interoperable applications for 2D and 3D mixed contents with the implemented system in order to verify its features and efficiency.

We experimentally investigate and analyze faults in optical fiber connections with refractive index matching material that have incorrectly cleaved fiber ends. We explain that incorrectly cleaved fiber ends, which are not ideal because they are uneven and not perpendicular to the fiber axis, are caused by defective optical fiber cleavers. We discover that the optical performance of field installable connections using incorrectly cleaved fiber ends might change greatly. We also infer that the significant change in insertion and return losses might be attributed to partially air-filled gaps by using scatter diagrams of measured insertion and return losses. Our experiment results reveal that the optical performance might deteriorate to more than 40dB in terms of insertion loss and less than 30dB in terms of return loss.

As mobile multimedia services expand, user behavior will become more diverse and the control of service quality from the user's perspective will become more important in service design. The quality of the network is one of the critical factors determining mobile service quality. However, this has mainly been evaluated in objective physical terms, such as delay reduction and bandwidth expansion. It is less common to use a human-centered design viewpoint when improving network performance. In this paper, we discuss ways to improve the quality of web services using time-fillers that actively address the human factors to improve the subjective quality of a mobile network. A field experiment was conducted, using a prototype. The results of the field experiment show that time-fillers can significantly decrease user dissatisfaction with waiting, but that this effect is strongly influenced by user preferences concerning content. Based on these results, we discuss the design requirements for effective use of time-fillers.

A complete 4-level pulse amplitude modulation (4-PAM) serial link transceiver including a wide frequency range clock generator and clock data recovery (CDR) is proposed in this paper. A dual-loop architecture, consisting of a frequency locked loop (FLL) and a phase locked loop (PLL), is employed for the wide frequency range clocks. The generated clocks from the FLL (clock generator) and the PLL (CDR) are utilized for a transmitter clock and a receiver clock, respectively. Both FLL and PLL employ the identical voltage controlled oscillators consisting of ring-type delay-cells. To improve the frequency tuning range of the VCO, deep triode PMOS loads are utilized for each delay-cell, since the turn-on resistance of the deep triode PMOS varies substantially by the gate-voltage. As a result, fabricated in a 0.13-µm CMOS process, the proposed 4-PAM transceiver operates from 1.5 Gb/s to 9.7 Gb/s with a bit error rate of 10-12. At the maximum data-rate, the entire power dissipation of the transceiver is 254 mW, and the measured jitter of the recovered clock is 1.61 psrms.

This paper investigates a preprocessing technique for a multiuser MIMO downlink system. An efficient joint precoder design with adaptive power allocation is proposed by adopting the channel-diagonalization technique and the minimum mean square error (MMSE) criterion. By exploiting an MMSE-based decoder, we propose an iterative algorithm to design the precoder with further derived closed-form solutions for implementing adaptive power allocation. Simulation results verify the effectiveness of our proposed approach. Compared with conventional benchmark schemes, they show that our proposal matches the performance but with reduced computational complexity.

This paper presents a proposed NMOS-centered 6T SRAM cell layout that reduces a neutron-induced multiple-cell-upset (MCU) SER on a same wordline. We implemented an 1-Mb SRAM macro in a 65-nm CMOS process and irradiated neutrons as a neutron-accelerated test to evaluate the MCU SER. The proposed 6T SRAM macro improves the horizontal MCU SER by 67–98% compared with a general macro that has PMOS-centered 6T SRAM cells.

We propose a motor speed ripple elimination method using a state dependent disturbance observer (SDDOB). The SDDOB eliminates the state dependent disturbance in the system regardless of the operation frequency, input time delay and output time delay. The SDDOB and a main proportional integral (PI) controller constitute a robust motor speed controller. Experimental results show the effectiveness of the proposed method.

We have investigated the operational performance of an optical serial-to-parallel conversion scheme using a phase-shifted preamble handling optical packets formatted by differential phase shift keying (DPSK) for integrated optical serial-to-parallel converter (OSPC). The same architecture for on-off keyed signals, based on a transmitter-side preamble at the top of the packet and phase-shifted by π/2, which is then -π/2 phase-biased with a Mach-Zehnder delay interferometer (MZDI), is available for binary and differential PSK signals. The delay length of these signals is determined by the relative timing positions of the gated bit and a balanced receiver-side photodetector. We simulated the operational performance of this scheme and its tolerance against the degree of modulation and optical chirp, with our results showing that a phase shift of more than 0.94π is required in order to attain a suppression ratio in the OSPC output consistent with a bit error rate of less than 10-9 (based on the ratio of intensity of the extracted bit to the maximum peak intensity of the cancelled bits using a single-arm phase modulator). However, by using a Mach-Zehnder phase modulator, the modulation angle can be relaxed to about 0.36π. Experimental investigation of the OSPC showed that its functional tolerance with respect to the modulation angle agreed well with the simulated values. Finally, we performed optical label processing using the OSPC in conjunction with an address table, and our results confirmed the potential of the OSPC for use in label recognition.

By using impedance (Z) matching circuits in a low-cost transistor outline (TO) CAN package for a 10 Gb/s transmitter, we achieve a cost-effective and small bidirectional optical subassembly (BOSA) with excellent optical transmission waveforms and a > 40% mask margin over a wide temperature range (-10 to 85). We describe a design for Z matching circuits and simulation results, and discuss the advantage of the cost-effective compensation technique.

Overlay networking makes it easy for users add new network functionalities while keeping existing Internet connectivity intact. This paper introduces SCONE (Service-COmposable InterNEt) as a networking service to facilitate the management of service overlay networking. By looking into the structure of programmable overlay nodes, SCONE provides programmable IP service gateways (PSGs) that ensure high-speed per-flow packet processing for overlay networking. In order to meet the data-rate requirements of various host applications, each PSG is accelerated by hardware packet processing for its data plane. It also leverages the space-efficient pattern matching of entity cloning and provides localized (i.e., de-centralized) services to assist the scalable support for software-defined networking (SDN). An experiment result shows that the proposed PSGs can support high-fidelity overlay networking from both performance and scalability perspectives.

Multi-view video consists of multiple video sequences which are captured by multiple closely spaced cameras from different angles and positions. It enables each user to freely switch viewpoints by playing different video sequences. However, the transmission of multi-view video requires more bandwidth than conventional multimedia. To reduce the bandwidth, UDMVT (User Dependent Multi-view Video Transmission) based on MVC (Multi-view Video Coding) for a single user has been proposed. In UDMVT, the same frames are encoded into different versions for different users, which increases the redundant transmission. To overcome this problem and extend UDMVT to multiple users' environment, this paper proposes UMSM (User dependent Multi-view video Streaming for Multi-users). UMSM calculates the overlapping and un-overlapping frame area for multiple users from all frames based on feedback information at a server. Proposed UMSM exploits the combination of multicasting overlapping area to multiple users and unicasting un-overlapping area to each user. By means of this concept, UMSM only transmits required frames for each user. To achieve further reduction of the traffic, UMSM combines other two features with this concept. The first one is that offset of the requests from multiple users is aligned periodically to maximize the overlapping frame area. The second one is that the SP-frames standardized in H.264/AVC are exploited as the anchor frame of overlapping frame area to prevent redundant transmissions of overlapping frames. The combination of these three techniques achieves substantial reduction of the transmission bitrate for multiple users in multi-view video streaming. Simulation results using benchmark test sequences provided by MERL show that UMSM decreases the transmission bit-rate 47.2% on average for 4 users are watching the same multi-view video compared to UDMVT.