Yasushi Yamao

Overlay cognitive radio OFDM system for 4G cellular networks

In this study, we integrate overlay cognitive radio technology into 4G cellular networks for the sharing of TV spectrum. On one hand, OFDM is a promising technique for high-speed data transmission over multipath fading channels and has been considered to be the best candidate for 4G mobile networks. On another hand, the overlay cognitive radio model makes it possible to have two concurrent transmissions in a given interference region, where conventionally only one communication takes place at a given time. We investigate different service provision scenarios and propose both time domain and frequency domain overlay cognitive radio OFDM systems for next generation cellular networks. Numerical results show our proposed schemes can achieve satisfying performance in different use cases.

Radio access network design concept for the fourth generation mobile communication system

The growth in mobile multimedia services will accelerate over the next decade. This paper discusses service aspects and system requirements for the fourth generation mobile communication (4G) system that will allow us to provide higher-speed communications and deal with user demand in the next decade. This paper also proposes a new radio access network (RAN) structure suited to the 4G system. The principles of the proposed cluster-cellular RAN are localized handover processing and horizontal structure. The advantages of the proposed RAN are also discussed.

Wideband Digital Predistortion Using Spectral Extrapolation of Band-Limited Feedback Signal

With the ever increasing demands for higher data rate, wider bandwidth is required for improving the throughput. This trend, however, imposes design challenges for the digital predistortion (DPD) in many aspects. In order to sample the broadband power amplifier (PA) output signal, it requires the use of high-speed analog-to-digital converters (ADCs), which tend to be the most expensive components in a transmitter with DPD. The sampling speed of the ADC for conventional DPD has to be several times of the original signal bandwidth in order to cover the out-of-band intermodulation components caused by nonlinear PA. In this paper, a novel technique, which allows the use of low-speed ADCs by introducing spectral extrapolation to the band-limited feedback signal, is proposed. This allows efficient implementation of DPD for very wideband signals. Experimental results demonstrate that the bandwidth of the acquisition path can be even less than the bandwidth of original signal applying the proposed technique. In addition, satisfactory linearization performance has been achieved employing wideband signals up to 160 MHz bandwidth.

Vehicle-roadside-vehicle relay communication network employing multiple frequencies and routing function

Vehicle to vehicle (V2V) communication is regarded as an essential means for enabling vehicle safety communications (VSC) to avoid traffic accidents. However, reliability of the communications severely suffers from wireless propagation on the road, such as deep fading due to multi-path and shadowing by surrounding buildings and vehicles. In this paper, a new vehicle-roadside-vehicle relay communication network employing multiple frequency bands is proposed to achieve more reliable V2V communications. By assigning lower frequencies such as 700 MHz for relay transmission, and higher frequencies of 5.8 GHz for direct communication, remarkable improvement can be obtained. In order to confirm the performance of the proposed relay network, computer simulations using QualNet network simulator assuming 200 vehicles at an intersection were conducted. The simulation results show that the packet delivery rate is remarkably improved by the proposed relay network.

FPGA Implementation of Adaptive Digital Predistorter With Fast Convergence Rate and Low Complexity for Multi-Channel Transmitters

This paper reports an adaptive digital predistorter (DPD) with fast convergence rate and low complexity for multi-channel transmitters, which is fully implemented in a field programmable gate array. The design methodology and practical implementation issues are discussed, with concerns about the impact caused by carrier power shutdown and transmission power control. The proposed DPD is composed of multiple adaptive lookup table (LUT) units of uniform structures, allowing configurability for desired memory depth. A simplified multiplier-free normalized least mean square algorithm for fast adapting the LUT is introduced. The proposed DPD is also experimentally exploited to linearize a Doherty amplifier. The adjacent channel leakage ratio reaches -60 dB for both lower and upper bands in the test applying a long-term evolution signal. It is also demonstrated in this paper that the proposed DPD shows high robustness when a multi-channel global system for mobile communications signal with occasional carrier power shutdown is applied.

Novel Band-Reconfigurable High Efficiency Power Amplifier Employing RF-MEMS Switches

A novel scheme for a multi-band power amplifier (PA) that employs a low-loss reconfigurable matching network is presented and discussed. The matching network basically consists of a cascade of single-stub tuning circuits, in which each stub is connected to a transmission line via a Single-Pole-Single-Throw (SPST) switch. By controlling the on/off status of each switch, the matching network works as a band-switchable matching network. Based on a detailed analysis of the influence of non-ideal switches in the matching network, we conceived a new design perspective for the reconfigurable matching network that achieves low loss. A 900/1900-MHz dual-band, 1 W class PA is newly designed following the new design perspective, and fabricated with microelectro mechanical system (MEMS) SPST switches. Owing to the new design and sufficient characteristics of the MEMS switches, the dual-band PA achieves over 60% of the maximum power-added efficiency with an output power for each band exceeding 30dBm. These results are comparable to the estimated results for a single-band PA. This shows that the proposed scheme provides a band-switchable highly efficient PA that has superior performance compared to the conventional multi-band PA that has a complex structure.

GaAs Monolithic Low-Power Amplifiers with RC Parallel Feedback (Short Paper)

GaAs monolithic broad-band low-power-dissipated amplifiers with inductive/resistive load and RC parallel feedback circuits have been developed. An inductive load amplifier provides a gain of 8 dB, a 3-dB bandwidth of 2.5 GHz, and a noise figure of 2.7 dB at 1 GHz with less than + 1-V supply voltage and very low-power dissipation of 20 mW. A resistive load two-stage amplifier provides a gain of 15 dB and a 3-dB bandwidth of 2 GHz. Input and output reflection coefficients at 1 GHz are -13 dB and -21 dB, respectively.

Multi-Hop Transmission Performance of Cognitive Temporary Bypassing for Wireless Ad Hoc Networks

In wireless ad hoc networks, the link SNR varies due to fading and this causes a temporary link error and blocks the multi-hop packet transmission. The cognitive temporary bypassing method was proposed to improve the transmission quality. In this paper, the proposed protocol is improved by adding acknowledgement and anti-collision functions necessary to achieve reliable multi-hop transmission. Packet success probability with the improved method has been analyzed for Rayleigh faded wireless links as functions of hop count. Simulation results using a modified QualNet simulator validate that packet success probability is remarkably improved with the method for maximum Doppler frequencies up to 30Hz.

The Future Generations of Mobile Communications Based on Broadband Access Methods

The forthcoming mobile communication systems are expected to provide much variety of services from high quality voice to high definition videos through high data rate wireless channels at anywhere in the world. High data rate requires broad frequency bands, and sufficient broadband can be achieved in higher frequency bands such as microwave, Ka-band and millimeter-wave. Broadband wireless channels have to be connected to broadband fixed networks such as the Internet and local area networks. The future generation systems will include not only cellular phones, but also many new types of communication systems such as broadband wireless access systems, millimeter-wave LAN, intelligent transport systems (ITS) and high altitude stratospheric platform station (HAPS) systems. The key words in the future generations of mobile communications are “multimedia communications”, “wireless access to broadband fixed networks” and “seamless roaming among different systems”. This article discusses the future generations mobile communication systems.

Performance of broadcast transmission from multiple vehicles in vehicle-roadside-vehicle relay network

Vehicle to vehicle (V2V) communication is regarded as an essential means to avoid traffic accidents and increase vehicle safety. However, reliability of the communications severely suffers from wireless propagation on the road. A vehicle-roadside-vehicle relay communication scheme has been proposed to improve the reliability of the V2V communications. The packet broadcast transmission performance of the proposed scheme with large number of transmitting vehicle stations around intersection is evaluated by computer simulations that assume fading, corner loss attenuation and carrier sense range. The combinations of two frequency bands, 700 MHz and 5.9 GHz, are also compared for the direct and relay transmissions. Simulated results show that the average packet reception ratio is remarkably improved with the proposed scheme regardless of number of the vehicle stations. The frequency combination of 700 MHz as vehicular station transmission and 5.9 GHz as relay station retransmission shows better performance.