This paper describes a fully digitized modem designed for variable baud rate transmission systems with the aim of efficiently providing multimedia services over a wireless communication network. The concept of a variable baud rate wireless communication system is discussed focusing on the access scheme and channel allocation from the viewpoint of frequency utilization efficiency. For easy system construction, we propose a fully digitized variable baud rate modem based on multirate digital signal processing, taking into account the need for even performance and easy clock control for all transmission rates. We also discuss the operational principle of modulation, the degradation factor in the A/D converter, and the configuration of the clock recovery circuit. Steady modulation performance can be kept by generating the same frequency system clock for all transmission rates and using the sampling rate conversion technique without selecting the channel filter for each transmission rate. It is proved by the analysis of the degradation factor in the A/D converter that only the bandwidth of the channel filter in demodulator should be changed for the transmission rate. A double loop clock recovery configuration capable of both tank-limit type and baseband estimation type clock recovery is shown to be suitable for this system. The tank-limit clock recovery circuits can be constructed easily by employing a tank circuit array. Finally, we present experimental results for a modem having transmission rates of 1.544Mbps and 6.312Mbps for the digital hierarchy and information speed of video signals such as MPEG-1 and MPEG-2. The measured basic performance of the proposed modem shows it delivers superior performance without the need for precise adjustment when a QPSK modulation scheme is employed.

An ultra-wideband (UWB) system usually occupies a large frequency band, which may overlap with the spectrum of a narrow band system. The latter is referred to as a victim system. To effectively use frequency, a UWB system may create a notch in its spectrum to accommodate the victim signal for interference avoidance. Parameters of the notch such as the depth and the width of a notch need to be decided in accordance to victim systems. In this paper, we investigate the effective UWB avoidance by examining the suitable notch based on experimental evaluation. In the experiments, 3GPP LTE, Mobile WiMAX, as well as an IMT Advanced Test-bed are respectively employed to represent different types of victim systems. The UWB system is set up based on WiMedia specifications and operates at the UWB low band of 3.1–4.8 GHz. A notch is fabricated by nullifying the related subcarriers of the UWB signal. In addition, a filter or a window function is formed and employed to further smooth the notch. Bit error rate (BER) or packet error rate (PER) performances of victim systems are measured and used to evaluate the UWB interference. Our results show that when a notch is properly formed, the interference level introduced by UWB can be below the permitted level by regulations.

The paper presents capability of signal detection for realizing coexistence between broadband wireless access (BWA) systems and ultra wideband (UWB) devices. The capability is experimentally evaluated for baseband signals of downlink (DL) in both mobile WiMAX and 3GPP LTE. An UWB receiver based on fast Fourier transform (FFT) compliant with MB-OFDM standard is implemented as a detector of the BWA signals. The capability is evaluated in terms of elapsed time required to achieve signal detection with probability of 99% by the implemented FFT-based UWB receiver at different conditions of the receiver. Decisions on the signal detection are made by the simplest method which is by setting a threshold which is determined by noise floor of the receiver as reference. The experiments have been conducted though baseband signals for both AWGN and multipath fading channels without any synchronization between the DL signals and UWB receiver. In AWGN environment, results show that the elapsed time depends on the duty ratio of the DL signal to be detected, however, the correlation between the required time and duty ratio is not linear since their envelopes of the DL signals are not constant. In multipath fading environments based on channel models commonly employed as mobile radio environments, the required time for the signal detection becomes as 17 times longer than that in AWGN due to its signal attenuation. For robust signal detection in multipath fading environments, it has been revealed that the number of quantization bits at ADC is crucial through the experiments.

A precise measurement of Cosmic Microwave Background (CMB) provides us rich information about the universe. In particular, its asymmetric polarization patterns, $B$-modes, are smoking gun signature of inflationary universe. Magnitude of the $B$-modes is order of 10,nK. Its measurement requires a high sensitive millimeter-wave telescope with a large number of superconducting detectors on its focal plane. Microwave Kinetic Inductance Detector (MKID) is appropriate detector for this purpose. MKID camera has been developed in cooperation of National Astronomical Observatory of Japan (NAOJ), Institute of Physical and Chemical Research (RIKEN), High Energy Accelerator Research Organization (KEK), and Okayama University. Our developments of MKID include: fabrication of high-quality superconducting film; optical components for a camera use; and readout electronics. For performance evaluation of total integrated system of our MKID camera, a calibration system was also developed. The system was incorporated in a 0.1 K dilution refrigerator with modulated polarization source. These developed technologies are applicable to other types of detectors.

A SuperHTM embedded processor core implemented in a 130-nm CMOS process running at 400 MHz achieved 720 MIPS and 2.8 GFLOPS at a power of 250 mW in worst-case conditions. It has a dual-issue seven-stage pipeline architecture but maintains the 1.8 MIPS/MHz of the previous five-stage processor. The processor meets the requirements of a wide range of applications, and is suitable for digital appliances aimed at the consumer market, such as cellular phones, digital still/video cameras, and car navigation systems.

This paper describes a variable multi-level QAM modem applied to a wireless ATM transport network with the aim of effectively offering ATM network services over a terrestrial digital radio system. The concept of the wireless ATM transport network based on a Virtual Path (VP) capacity control system which optimizes both the number of channels and the multi-level QAM scheme for existing traffic variation is discussed. To achieve a hitless switch as a technical requirement of this network, we propose a modem configuration and a modulation scheme control (MSC) signal transmission. In this modem configuration, a multi-level control logic circuit in the modulator is used as the signal formatter. A modulated signal for the modulation scheme is maintained at a constant average power. Decision data and error signal selection for the received signal is carried out in the multi-level control logic circuit in the demodulator. The fluctuation of the demodulator loops due to modulation scheme switch can be reduced by using a fully digitized AGC loop and by converting the received signal to the condition of decision level constant. The MSC signal inserted into the first path data signal is transmitted without error by arranging the maximum amplitude of the signal point set. In this way, switching between the modulator and the demodulator is possible frame by frame. Finally, we present experimental results for a variable multi-level QAM modem employing four modulation schemes: QPSK, 16 QAM, 64 QAM, and 256 QAM. Through experiments, we prove that the modulation scheme is switched without fluctuation of the demodulator control loops by maintaining the signal condition of the decision level constant. The achievement of a hitless switch for multi-level QAM is also confirmed by experiments.

An all digital 256 QAM modulator including the carrier signal of nearly 10 MHz, was constructed. In order to achieve, the very high-speed operation of nearly 100 MHz is required. In this experiment, the very high-speed digital devices such as digital multiplier with delay time of 4.3 ns was employed. Excellent modulation performance was achieved with no adjustment. Roll-off spectal shaping filter using a new BTF circuits was constructed. The excellent transmission performance was obtained and the transmission capacity of nearly 20 Mbit/s was achieved. The results provide prospects for an all digital LSI-based high-speed 256 QAM modem for high-capacity Digital Microwave Radio.