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High data rate at high mobile speed will still be an essential requirement for the future 5G mobile cellular system. High frequency bands above 6 GHz are particularly promising for the 5G system because of large signal bandwidths such high frequencies can offer. By using high gain beamforming antennas, the problem of high propagation loss at high frequencies can be overcome. However, the use of beamforming antennas at such high frequencies requires a significant change in the design of a cellular system. In particular, it requires a significant change in key functions such as cell search, random access, measurement of beams for fast beam adaptation, and various physical control and data channels. In this paper, we propose a new radio frame structure for the future mobile cellular communications system at millimeter wave frequency that addresses such challenges. A testbed was built at Samsung Electronics, Korea, based on the proposed frame structure at 28 GHz with bandwidth of 800 MHz. It attained the downlink (DL) data rate of 7.5 Gbps by delivering four streams of 64 QAM data with code rate of 3/4 to two mobile stations (MSs) located in a close distance to the base station antennas at fixed positions. It also achieved the DL data rate of 1.2 Gbps by delivering single stream of 16 QAM data with code rate of 3/4 to an MS moving at 110 km/h in a single cell of up to 800 m in a line-of-sight environment. Finally, it implemented handover and achieved an average handover interruption time of 21 ms in a three-cell environment, and demonstrated feasibility of mobile cellular communications at millimeter wave frequency.

The ever growing traffic explosion in mobile communications has recently drawn increased attention to the large amount of underutilized spectrum in the millimeter-wave frequency bands as a potentially viable solution for achieving tens to hundreds of times more capacity compared to current 4G cellular networks. Historically, mmWave bands were ruled out for cellular usage mainly due to concerns regarding short-range and non-line-of-sight coverage issues. In this article, we present recent results from channel measurement campaigns and the development of advanced algorithms and a prototype, which clearly demonstrate that the mmWave band may indeed be a worthy candidate for next generation (5G) cellular systems. The results of channel measurements carried out in both the United States and Korea are summarized along with the actual free space propagation measurements in an anechoic chamber. Then a novel hybrid beamforming scheme and its link- and system-level simulation results are presented. Finally, recent results from our mmWave prototyping efforts along with indoor and outdoor test results are described to assert the feasibility of mmWave bands for cellular usage.

The paper proposes a new duplexing scheme, which is called the hybrid division duplex (HDD), that is suitable for fourth-generation mobile communication systems. The proposed mobile communication system is much more flexible and efficient in providing asymmetric data service and managing intercell interference by exploiting the advantages of both time division duplex (TDD) and frequency division duplex (FDD) schemes. The HDD scheme has a pair of frequency bands such as the FDD, performing a TDD operation using one of the bands in such a manner that allows for simultaneous FDD and TDD operations. Considering the properties of the HDD system architecture, frequency hopping orthogonal frequency division multiple (OFDM) access is adopted in one band for the TDD operation and code division multiple access (CDMA) in the other band for the FDD uplink operation. The important advantage of the HDD scheme is the robustness against cross time slot interference that is inherent to the TDD system, which is caused by the asynchronous downlink/uplink switching boundaries among all neighbor cells. From the simulation results, the proposed system can achieve approximately 7% and 30% improvement with regard to the downlink and uplink throughput, respectively, as compared to the conventional TDD system under cell-independent downlink/uplink traffic asymmetries. It demonstrates that the HDD scheme is a viable solution for future communication systems that are projected to have a cell-independent asymmetric-traffic-supported hierarchical cell structure.

We have demonstrated a broadband radio-over-fiber communication system transmitting wireless signals at the millimeter-wave bands. The system incorporated 25 km of an optical intermediate frequency feeder. 60 GHz orthogonal frequency division multiplexing (OFDM) signal transmission at 155 Mbps with a bit error rate (BER) of less than 10/sup -6/ was achieved within the system cell of a radius of 2.6 m under the channel condition of line-of-sight with choke horn antennas. SNR enhancement of 6 dB for a BER level of 10/sup -6/ was achieved with the forward error correction code, simultaneous synchronization, and channel estimation algorithm.

A random beamforming technique for multiple-input multiple-output (MIMO) systems that simultaneously obtains downlink multiuser diversity gain, spatial multiplexing gain and array gain by feeding back only effective signal-to-noise ratios (SNRs) is described. In addition, power control using waterfilling is employed to improve the throughput of our method in correlated channels. In a slow fading channel, we prove that the throughput of the proposed method converges to that of eigen beamforming when many users are in a cell. The number of users required to achieve capacity bound increases with the number of antennas and SNR was determined. However, the capacity bound is achieved even with a small number of users, e.g., 16 users in a cell, when the SNR is low, e.g., 0 dB, and the number of transmit and receive antenna is small, e.g., two. We also find that the effect of waterfilling is more noticeable in correlated channels.

For the fast fading channels, e.g., fast mobile channels, non-coherent detection scheme is promising because the receiver does not require to measure the channel information, which results in reducing transmission overhead. In this paper, we compare the bit error rate of two non-coherent encoding/decoding schemes for multiple transmit antennas under fast fading environments when the number of antenna varies from two to three. The first approach is a unitary space-time modulation (USTM) that aims to achieve the non-coherent channel capacity. The second one is a differential space-time block code (DSTBC), which projects information symbols to a number of orthogonal bases that consist of the previously sent symbols. We exhibit the fact that the block length of both schemes affects the performance significantly rather than encoding/decoding methods when the channel varies fast. In addition, we present some problems of the DSTBC sending the complex symbols with more than two transmit antennas.

A Silicon Photo Multiplier (SiPM) is states of arts radiation detector, it is alternative to PM-Tube. But, availability research of SiPM is not entirely satisfactory. In this study, we suggest the radiation detector module coupled with the SiPM and the plastic scintillator, and then, evaluate the availability of detector module for Cs-137 dosimetry.

In wafer-scale CMOS image sensors, the 3-transistor structure suffers from its low speed. To overcome this limitation, we propose a digital pixel sensor which has a digital-pixel output instead of analog-pixel output as in a conventional 3-transistor pixel. The digital pixel sensor can provide a high frame because it eliminates analog-to-digital conversion time. In addition, it removes the noise from long analog-signal paths. As a prototype, we designed a 4.5mm × 4.0mm chip having 24 × 16 pixels of 100µm × 100µm using standard 0.18µm CMOS technology. With 2MHz clock, the readout time for each pixel was 6micro seconds. When 3000pixels are in each column of a full-wafer-size CMOS image sensor, 50fps can be achieved with the digital pixels based on pulse width modulation.

This paper presents a circuit of a digitized position decoder circuit for brain PET consisting of Silicon Photomultiplier (SiPM). Difference of proposed circuit and traditional circuit is the existence of analog-to-digital convertor (ADC). In this work, we conclude that the combination of ADC, field programmable gate array (FPGA) and digital data acquisition (DAQ) board can be substitute for an existing analog DAQ.

We present a multiple-input multiple-output (MIMO) relay system with hybrid automatic repeat request (HARQ) protocols which can achieve better outage behaviors than simple MIMO cooperative diversity schemes. Using repetition based and Alamouti based HARQ scheme, we can achieve better diversity gains without increasing additional transmit power. This system can be a practical solution for a new system which requires lower deployment costs and limited power in each nodes.

We investigate an adaptive modulation method for simultaneous voice and data transmission over fading channels. The proposed scheme applies a different switching threshold-carrier-to-noise ratio (CNR) boundary between different modulation indices-according to the required bit error rate (BER). Specifically, it starts to transmit voice with binary phase shift keying (BPSK) when the CNR allows BPSK transmission with the target BER for voice. When the CNR is improved to support M-ary quadrature amplitude modulation (QAM) with the target BER for data, it begins to transmit both data and voice with the same BER target. Compared with the adaptive hybrid BPSK/M-AM (amplitude modulation) scheme (see Mohamed-Slim Alouini et al., IEEE J. Select. Areas Commun., vol.17, p.837-50, 1999), the proposed method has the same P/sub out/ (outage probability) for voice, and slightly higher P/sub out/ for data. However, the spectral efficiency in high CNR is improved significantly. For example, in a Rayleigh fading channel with an average CNR of 30dB, the proposed scheme is able to transmit about 4.5 bits/s/Hz of data while adaptive hybrid BPSK/M-AM can send only 3.5 bits/s/Hz of data at a BER less than 10/sup -4/.