An efficient method is proposed for reconstructing speakerphone-mode cellular phone sound. The overall transfer function from digital PCM signals stored in a cellular phone to dummy head-recorded signals is modeled as a combination of a cellular phone transfer function (CPTF) and a cellular phone-to-listener transfer function (CPLTF). The CPTF represents the linear and nonlinear characteristics of a cellular phone and is modeled by the Volterra model. The CPLTF represents the effect of the path from a cellular phone to a dummy head and is measured. Listening tests show the effectiveness of the proposed method. An application scenario of the proposed method is also addressed for sound quality assessment of cellular phones in speakerphone mode.

This paper proposes the test phantom for the cochlear implant to estimate electromagnetic interference (EMI) from a cellular phone. This test phantom is constructed from a square tank filled with saline solution. The use of a flat phantom provides a level of consistency in duplicating the exposure conditions in the EMI tests. The measurement and calculation results show that there is no difference in the E-field strength near the surface of the phantom when comparing flat and head-shaped phantoms and that the flat phantom is sufficiently thick to disregard the influence of reflective waves near the surface of the phantom. The calculation results also indicate the appropriateness of using physiological saline (0.18 g/l) up to 3 GHz when comparing the E-field strength inside a phantom comprising physiological saline and in a 2/3 muscle model. The results of actual EMI testing of a cochlear implant show that there is no difference in the maximum interference distance when using either the flat or head-shaped phantom. Based on these results, this paper presents the validity of using the flat phantom in EMI tests from cellular phone for the cochlear implant.

We have developed an application processor optimized for 3G cellular phones. It provides high energy efficiency by using various low power techniques. For low active power consumption, we use a hierarchical clock gating technique with a static clock gating controlled by software and a two-level dynamic clock gating controlled by hardware. This technique reduces clock power consumption by 35%. And we also apply a pointer-based pipeline to in the CPU core, which reduces the pipeline latch power by 25%. This processor contains 256 kB of on-chip user RAM (URAM) to reduce the external memory access power. The URAM read buffer (URB) enables high-throughput, low latency access to the URAM while keeping the CPU clock frequency high because the URAM read data is transferred to the URB in 256-bit widths at half the frequency of the CPU. The average miss penalty is 3.5 cycles at the CPU clock frequency, hit rate is 89% and the energy used for URAM reads is 8% less that what it would be for URAM without a URB. These techniques reduce the power consumption of the CPU core, and achieve 4500 MIPS/W at 1.0 V power supply (Dhrystone 2.1). For the low leakage requirements, we use internal power switches, and provides resume-standby (R-standby) and ultra-standby (U-standby) modes. Signals across a power boundary are transmitted through µI/O circuits to prevent invalid signal transmission. In the R-standby mode, the power supply to almost all the CPU core area, except for the URAM is cut off and the URAM is set to a retention mode. In the U-standby mode, the power supply to the URAM is also turned off for less leakage current. The leakage currents in the R-standby and in the U-standby modes are respectively only 98 and 12 µA. For quick recovery from the R-standby mode, the boot address register (BAR) and control register contents needed immediately after wake-up are saved by hardware into backup latches. The other contents are saved by software into URAM. It takes 2.8 ms to fully recover from R-standby.

A frequency selection algorithm leveraging the capability of a handset to autonomously select idle channels of a public communication system for use in a private communication system was previously proposed, and its effectiveness was verified through experiments conducted in a metropolitan area. This paper describes the results of an experiment verifying the algorithm's effectiveness in rural areas with relatively low public communication system traffic.

This paper presents a system for reading comics on cellular phones. It is necessary for comic images to be divided into frames and the contents such as speech text to be displayed at a comfortable reading size, since it is difficult to display high-resolution images in a low resolution cellular phone environment. We have developed a scheme how to decompose comic images into constituent elements frames, speech text and drawings. We implemented a system on the internet for a cellular phone company in our country, that provides downloadable comic data and a program for reading.

The rapid spread of cellular phones in recent years has facilitated not only voice communication but also Internet access via the cellular phone system, and in addition, subscriber demand has led to a diversification in the services provided. One service in high demand is the seamless use of cellular phones in both public and private wireless network areas. In the data world, there is already such an application in the form of public and private use of wireless LAN. However, an increase in the number of users would require the realization of low-cost, easy-to-install very small base stations (VSBS) that use the frequency band efficiently in order to allow private use of ordinary cellular phones. To bring such VSBS into effect, a technology that autonomously selects frequencies which do not interfere with the public communication system from out of the publicly used frequency band is essential for turning such VSBS into reality. This paper proposes a frequency selection algorithm that actively uses cellular phone features such as frequency selection and received signal level measurement, and discusses the results of verification experiments.

The progress made in large-scale integration of the baseband circuits of digital cellular phones now makes it possible to implement a voice CODEC and its related functions in the baseband LSI rather than through a general-purpose digital signal processor. This paper describes an improved hardware solution that enables efficient application of the PSI-CELP CODEC-- the most complex CODEC for mobile systems--to the PDC half-rate system through its implementation as a DSP macro in a low-voltage, large-scale LSI. Specific circuit blocks are added as hardware engines to a general-purpose DSP-oriented core. These specific engines were implemented as peripheral circuits for a DSP macro that can be used as a single DSP with an added I/O circuit and is suitable for use in future highly integrated mobile baseband chips. With the assistance of these hardware engines and some additional ALU instructions to achieve efficient programming, the machine speed required for the CODEC can be relatively slow, thus allowing the same architecture to be repeatedly used without needing to set the transistor threshold voltage too low even when the use of deeper sub-micron technologies require a chip to run at a lower supply voltage. We evaluated this DSP-macro architecture using a 0.35 µm CMOS technology test chip. Then we developed a commercial base version using 0.25 µm technology and verified that it can operate at 1.2 V and that the PSI-CELP CODEC can be done at 40 MIPS with power consumption of 11 mW. We also verified that the circuit design can be applied up to 0.18 µm technology with a single threshold voltage of 0.3 V. Thus, the design of the DSP macro incorporating the hardware engines provides a great deal of flexibility that should allow its use in chips based on future technologies and the voice CODEC firmware can be effectively re-used. Although the DSP macro architecture was designed mainly through PSI-CELP application analysis, it can process other voice CODECs such as the AMR CODEC for third-generation mobile applications as well as some other mobile baseband functions such as channel CODECs. This approach can also be refined to permit its application to, for example, high-quality audio CODECs.

The three-dimensional chip-stacked CSP, which started with a flash/SRAM combination memory for cellular phones, was the forerunner from which 3D system packages realize full-scale capability. In the future, 3D package technology will act as a savior in achieving greater shrink of silicon processes--whose limits have come into sight. As SIP, it will surpass SOC, and, as the core technology of electronic equipment for our high-speed digital network society, it is expected to lead the way into the first period of the 21st century. Today, we are seeing the signs of this transition.

The third generation cellular system will provide high bandwidth data service and multimedia applications are proposed on the high-speed data link. On the other hand, cellular handsets are getting equipped with a short-range radio communication device that is mainly targeted to connect cellular handsets to computers. In this paper, we propose a percolating data delivery mechanism for a cellular-ad hoc integrated network utilizing multicast/broadcast communication, which is endorsed by data synchronization, and single-hop ad hoc networks for information shower/exchange services. The mechanism lessens data traffic in both the cellular and the ad hoc network for data delivery and tolerates unexpected disconnection in the ad hoc network. The mechanism also compensates data delivery in areas out of the cellular service. Our implementation of the data delivery mechanism utilizes Bluetooth for an ad hoc network configuration, and delivers data in the cellular network to the Bluetooth ad hoc network via the data synchronization mechanism. We evaluate communication traffic and delivery time on the prototype system and discuss about the efficiency of the mechanism.

We present a high performance AlGaAs/GaAs power HBT with very low thermal resistance for digital cellular phones. Device structure with emitter air-bridge is utilized and device layout is optimized to reduce thermal resistance based on three-dimensional thermal flow analysis, and in spite of a rather thick substrate (100 µm), which achieved a low thermal resistance of 23/W for a multi-finger (440 µm240 fingers) HBT. This 40 finger HBT achieved power added efficiency (PAE) of over 53%, 29.1 dBm output power (Pout) and high associated gain (Ga) of 13.5 dB with 50 kHz adjacent channel leakage power (Padj) of less than -48 dBc under a 948 MHz π/4-shifted QPSK modulation with 3.4 V emitter-collector voltage. We also investigated the difference of RF performance between two bias modes (constant base voltage and current), and found which mode is adequate for each stage in several stage power amplifier for the first time.

AlGaAs/GaAs power HBTs for digital cellular phones have been developed. A three-dimensional thermal analysis taking the local-temperature dependence of the collector current into account was applied to the thermal design of the HBTs. The HBTs were fabricated using the hetero-guardring fully selfaligned transistor technique. The HBT with 220µm2 60 emitters produced a 31.7 dBm CW-output power and 46% poweradded efficiency with an adjacent channel leakage power of -49 dBc at the 50kHz offset bands for a 948 MHz π/4-shifted QPSK modulated signal at a low collector-emitter voltage of 3V. Through comparison with the conventional GaAs power FETs, it has been shown that AlGaAs/GaAs power HBTs have a great advantage in reducing the chip size.