Digital Cellular Telephone Research Articles

Influence of D-net (EUROPEAN GSM-standard) cellular telephones on implanted pacemakers in children.

This study was designed to evaluate possible interactions between digital cellular telephones and implanted pacemakers in children. The study comprised 95 patients (53 males and 42 females) with a mean age of 11.5 +/- 4.6 years (range 1-22 years). The average time from pacemaker implantation was 2.5 years (range 1 month-12 years). Fourteen (15%) devices were dual chamber and the remaining were single chamber pacemakers. The following companies manufactured the pacemakers tested: Medtronic (n = 42), Telectronics (n = 9), Vitatron (n = 16), Pacesetter (n = 19), CPI (n = 8), and Biotronik (n = 1). All the patients were tested in the supine position during continuous ECG monitoring. After completion of the routine pacemaker check, the effects of the European Global system for mobile communication (GSM) was tested using two cellular telephone models (Ericsson GA 628 and Siemens S 25, 2-W power). For this purpose, atrial and ventricular sensitivity settings were programmed to the most sensitive values, and the tests were carried out in the unipolar and bipolar sensing modes. The evaluation was performed during ringing, switching on/off, and conversation phase with the cellular telephone positioned over the pulse generator and around the pacemaker pocket. A malfunction of the pacemaker was not observed in any patient. Only 1 (1%) of 95 patients showed a brief oversensing problem during calls with the cellular telephone. In this case, an AAIR pacemaker was implanted transvenously in a subcutaneous pocket and the sensing defect occurred only with the unipolar sensing mode and was not reproducible. Once the source of interference was removed, no sensing defect was detected and the patient remained asymptomatic. No symptoms were experienced in this study. The authors believe that pacemaker dependent patients with nonprotected pulse generators manufactured at the beginning of 1990s may be tested by their physicians for possible interferences before they use a digital cellular telephone.

Investigation for a global AVL system

Real-time reporting systems are now becoming widely available, in order to aid emergency dispatch assistance and traffic control management as being an important part of intelligent transportation systems (ITS). Based on the fact that the global system mobile (GSM) standard is widely accepted as being the most comprehensively deployed of all the various second generation digital cellular telephony standards, studies have been focused on using it as a communication link for real-time application reporting. This paper introduces a study made on an integrated system incorporating a global positioning system (GPS) receiver, a control area network (CAN) and the short message service (SMS) of GSM as the transmission media. The goal of the research study conducted, is to measure the end to end delays experienced, and consequently its practicality, when using a CAN bus and the GSM-SMS bearer service for position reporting for use in an ITS environment. The paper initially presents the previous research that has been carried out relevant to this study. Following it outlines the system architecture of the integrated system studied together with its functionality in an ITS environment. The results obtained from the various simulation scenarios are presented as well as an estimation algorithm that aims to diminish the positioning error incorporated from the transmission delays occurred. Concluding this paper discusses the advantages of using this integrated system as a solution for position reporting in ITS as well as proposing further research to be conducted.

A 2.4-kbps variable-bit-rate ADP-CELP speech coder

Based on ADP-CELP (Adaptive Density Pulse Code Excited Linear Prediction), in which the sound source is expressed in terms of an adaptive density pulse train model, a variable-rate ADP-CELP system is proposed in which one mode out of four, with different bit rate depending on the nature of the short section speech signal, is selected for each frame. The coding method in each mode is designed to be adapted to the nonspeech section, nonsound section, steady speech section, and nonsteady speech section. The bit rates are 0.53, 2.67, 3.17, and 4.1 kbps. In the variable-rate ADP-CELP system, the variation of the spectral envelope is used as a guideline so that a high sound quality and low bit rate are attempted by means of the speech/nonspeech classification method to accurately distinguish the speech section and nonspeech section even under a background noise environment and of the interpolation vector quantization method that can reduce the coding volume for the pitch period to one-half without degrading the quality. In the variable-rate ADP-CELP system, the average rate is less than 2.4 kbps in the case of sound rate of 60% and the corresponding quality is more than the half-rate standard system (3.45 kbps) of domestic digital cellular telephones. © 2000 Scripta Technica, Electron Comm Jpn Pt 3, 83(7): 32–41, 2000

DSP-based architectures for mobile communications: past, present and future

Programmable DSPs are pervasive in the wireless handset market for digital cellular telephony. We present the argument that DSPs will continue to play a dominant, and in fact increasing, role in wireless communications devices by looking at the history of DSP use in digital telephony, examining the DSP-based solution options for today's standards, and looking at future trends in low-power DSPs.

Method and apparatus for reducing audio interference from cellular telephone transmissions

Apparatus and method for reducing the interference of digital cellular telephones with hearing aids. A digital cellular phone (3) is provided with a second antenna (2) that transmits a local, low-power signal which fills in the gaps in the transmitted switched information carrier. This prevents the hearing aid (4) from demodulating the low frequency switched carrier components of the digital cellular phone (3). Alternatively, the main antenna (1) can transmit on a garbage frequency between time slots, or the hearing aid (4) can detect and cancel the interfering signal.

Hearing aid measurement and consumer counseling

The relationship between digital cellular telephones and hearing aid devices requires specific measurement techniques to determine system compatibility between the two technologies. The ANSI C63.19 working group has developed such measurement techniques related to the actual usage of a digital phone while wearing a hearing aid—known as ‘‘near field’’ or ‘‘user’’ condition. The hearing aid rf near-field immunity test requirements involve hearing aid orientation and bias as well as rf near-field simulated test conditions. The testing is performed in both the audio and telephone-coil modes. The measurement figure of merit is defined as IRIL (input referred interference level) which normalizes the hearing aid acoustic gain. It can be shown that hearing aids will be required to withstand digital phone E-field emission levels greater than 50 dB V/m and H-field emission levels greater than −2 dB A/m. By characterizing the simulated phone antenna properly this test enables hearing aid immunity testing within a controlled rf laboratory. The outcome of these measurements will be used to classify hearing aids for compatibility with categorized digital phones. This classification process will assist the hearing aid dispenser in patient counseling.

Mid‐entry technology strategy: the Korean experience with CDMA

Mid‐entry strategy is an R&D strategy designed for an efficient utilisation of scientific and technological resources across the nations. It chooses the entry point of R&D projects in the mid‐stage of technical development. The technological situation of developing countries compels them to choose the mid‐entry strategies tailored to specific technologies. The development of the CDMA (Code Division Multiple Access) based digital cellular mobile communication system by ETRI, Korea’s government‐sponsored research institute, is an example showing the application of this strategy. ETRI utilised scientific resources owned by US based Qualcomm Ltd and co‐operated with local companies for the development. In the first half of 1996 the successful commercialisation of the CDMA digital cellular telephone service was launched in Korea, ahead of all other countries. Two Korean mobile communications providers have adopted the system.

Development of hearing-aid near-field EMI testing

With the introduction of digital cellular telephone technology, cellular telephone interference to hearing aids is now a noticeable problem for both hearing-impaired digital cellular phone users and bystanders. Previously, bystander hearing-aid immunity levels (far field) were defined by the IEC committee and are contained in the current IEC 118-13 hearing-aid electromagnetic immunity standard. With the realization that an up-scaled far-field test would be insufficient to provide an accurate correlation of digital cellular telephone usability, the ANSI C63.19 working group developed a near-field test procedure using calibrated dipole antennas. This paper discusses the development of near-field testing, broken down in the following topics: (1) digital cellular phone interference and spectral properties; (2) rf interference coupling into the hearing aid; (3) far-field testing and rationalization behind the use of 1-kHz 80% AM modulation to quantitatively determine hearing-aid immunity characteristics; (4) near-field simulation using dipoles and antenna calibration; (5) near-field repeatability testing; and (6) preliminary results of near-field hearing-aid interference measurements. The result of these developments has led directly to the formulation of the near-field test procedure described in Sec. 5 of the currently developing ANSI C63.19 standard.

Electromagnetic interference of external pacemakers by walkie-talkies and digital cellular phones: experimental study.

A number of experimental and clinical studies have documented the risk potential of interference with implanted pacemakers by various types of cellular phones. Radiofrequency susceptibility of external medical equipment has also been reported in experimental studies. The purpose of this experimental study was to evaluate electromagnetic interference of external pacemakers by walkie-talkies and digital cellular telephones. External bipolar pacing was monitored using a digital oscilloscope to record pacemaker pulses and electromagnetic interference separately. Tests with the walkie-talkie, Private Mobile Radio (PMR) (160 MHz, 2.5 W) were conducted during the calling phase. Tests with the cellular phones, global system for mobile communications (GSM) (900 MHz, 2 W) and Digital Cellular System (DCS) (1,800 MHz, 1 W) were conducted in the test mode. Nine widely used external pacemakers from four manufacturers were tested. Various disturbances including pacing inhibition and asynchronous pacing were observed in eight pacemakers by the PMR, in four by the GSM phone, and in two by the DCS phone. The maximum distance that interference persisted ranged from 10-200 cm. This experimental study shows a potential risk of interference of external pacemakers by walkie-talkies and cellular digital phones. Appropriate warnings should be issued against the potentially serious risks of using communication devices in the vicinity of acutely ill patients treated with temporary transvenous cardiac pacemakers.

The 1.5 GHz electromagnetic near-field used for cellular phones does not promote rat liver carcinogenesis in a medium-term liver bioassay.

We have recently established that local exposure to a 929.2 MHz electromagnetic near‐field, used for cellular phones, does not promote rat liver carcinogenesis in a medium‐term bioassay system. In the present study, a 1.439 GHz electromagnetic near‐field (EMF), another microwave band employed for cellular phones in Japan, was similarly investigated. Time division multiple access (TDMA) signals for the Personal Digital Cellular (PDC) Japanese cellular telephone standard system were directed to rats through a quarter‐wavelength monopole antenna. Numerical dosimetry showed that the peak SARs within the liver were 1.91–0.937 W/kg, while the whole‐body average specific absorption rates (SARs) were 0.680–0.453 W/kg, when the time‐averaged antenna radiation power was 0.33 W. Exposure was for 90 min a day, 5 days a week, over 6 weeks, to male F344 rats given a single dose of diethylnitrosamine (200 mg/kg, i.p.) 2 weeks previously. At week 3, all rats were subjected to a two‐thirds partial hepatectomy. At week 8, the experiment was terminated and the animals were killed. Carcinogenic potential was scored by comparing the numbers and areas of the induced glutathione S‐transferase placental form (GST‐P)‐positive foci in the livers of exposed (48) and sham‐exposed rats (48). Despite increased serum levels of corticosterone, adrenocorticotropic hormone (ACTH) and melatonin, the numbers and the areas of GST‐P‐positive foci were not significantly altered by the exposure. These findings clearly indicated that local body exposure to a 1.439 GHz EMF, as in the case of a 929.2 MHz field, has no promoting effect on rat liver carcinogenesis in the present model.

Mobile Digital Assistants for Community Support

We applied mobile computing to community support and explored mobile computing with a large number of terminals. This article reports on the Second International Conference on Multiagent Systems (ICMAS'96) Mobile Assistant Project that was conducted at an actual international conference for multiagent systems using 100 personal digital assistants (PDAs) and cellular telephones. We supported three types of service: (1) communication services such as e-mail and net news; (2) information services such as conference, personal, and tourist information; and (3) community support services such as forum and meeting arrangements. After the conference, we analyzed a large amount of log data and obtained the following results: It appears that people continuously used PDAs in their hotel rooms after dinner; e-mail services were used independently of the conference structure, but the load on information services reflected the schedule of the conference. Postquestionnaire data showed that our trial was considered interesting, although people were not fully satisfied with the PDAs and services provided. Participants showed a deep interest in mobile computing for community support.

On the minimization of overhead in channel impulse response measurement

This paper presents a new method for channel impulse response measurement with a suitably designed binary sounding sequence. This method minimizes the system overhead and results in ideal channel estimation using three correlators instead of one. This system complexity can be easily overcome by the present technologies. The class of sounding sequences used in this method is the training sequence for channel impulse response measurement with the zero values of the autocorrelation function at all shifts except zero and middle shifts in European digital cellular mobile telephone systems based on the global system for mobile communication (GSM). Computer searches are carried out to find the suitable sounding sequences.

Digital cellular telephone interaction with implantable cardioverter-defibrillators.

This study sought to determine, in vivo, whether electromagnetic interference (EMI), generated by North American Digital Communications (NADC)/Time Division Multiple Access-50-Hz (TDMA-50) mobile cellular digital telephone model AT&T 6650, disturbs normal implantable cardioverter-defibrillator (ICD) operation and to verify these observations in vitro by testing a selection of telephones representing worldwide systems. The effects of cellular phone interference on the operation of various models of market-released ICDs from a single manufacturer, Medtronic, Inc., were tested. The in vivo clinical test was undertaken in 41 patients using the AT&T 6650 digital telephone with the NADC/TDMA-50 technology. The in vitro component of the study was examined twofold: 1) antenna generated far field; and 2) analog/digital cellular telephone near field. None of the ICDs tested in 41 patients were affected by oversensing of the EMI field of the cellular telephones during the in vivo study. Therefore, the binomial upper 95% confidence limit for the failure rate of 0% is 7%. The in vitro antenna-generated field testing showed that telephone modulation frequencies used in the international Global System Mobile and TDMA-50 cellular telephone technologies did not result in ICD sensing interference at the predicted electric field intensity. The in vitro near field tests were performed using both analog and digital cellular telephones in service, or in the test mode, and indicated no interaction with normal operation. However, the static magnetic field generated by the cellular telephone placed over the ICD at a distance < or = 0.5 cm will activate the internal reed switch, resulting in temporary suspension of ventricular tachycardia and fibrillation detection. We conclude that TDMA-50 cellular telephones did not interfere with these types of ICDs. However, we recommend that the patient not carry or place the digital cellular telephone within 15 cm (6 in.) of the ICD.

Measurement of low frequency magnetic fields from digital cellular telephones

Digital cellular telephones using the GSM (Global System for Mobile Communication) transmit information in bursts of microwaves. This pulsed transmitting mode causes the battery current and currents in the electronics of the apparatus to be pulsed. These pulsed currents produce corresponding pulsed magnetic fields near the phones. A study to determine the magnitude of these fields involved two models of digital telephones. The highest value of the magnetic flux density was 1.8 microT (rms).

Measurement of low frequency magnetic fields from digital cellular telephones

Measurement of low frequency magnetic fields from digital cellular telephones

Measurement of low frequency magnetic fields from digital cellular telephones

Measurement of low frequency magnetic fields from digital cellular telephones

Incorporating cost modeling in embedded-system design

The emergence of multimedia and wireless applications as growth leaders has created an increased demand for embedded systems. Examples of such applications range from digital cellular telephones to high-performance avionics systems. Along with the increased market share of these products, however, has come an increase in system complexity and cost. For example, the complexity of embedded avionics systems has quickly grown from millions to billions of operations per second. These systems, formerly implemented in hardwired or uniprocessor architectures, now must consist of programmable-multiprocessor arrays to meet performance requirements. Time-to-market and life-cycle costs are key factors in the success of these products in the competitive electronics marketplace. These costs, therefore, should have a dominant influence on the design of embedded microelectronic systems. In addition, these systems must meet rigid form factor (such as size, power, and weight) constraints, which further complicate the design task. For designers of high-end embedded microsystems or large-volume consumer products, rapidly prototyping cost-effective implementations that meet stringent performance, functional, timing, and physical requirements is a formidable challenge.

Exposure of nerve growth factor-treated PC12 rat pheochromocytoma cells to a modulated radiofrequency field at 836.55 MHz: effects on c-jun and c-fos expression.

Rat PC12 pheochromocytoma cells have been treated with nerve growth factor and then exposed to athermal levels of a packet-modulated radiofrequency field at 836.55 MHz. This signal was produced by a prototype time-domain multiple-access (TDMA) transmitter that conforms to the North American digital cellular telephone standard. Three slot average power densities were used: 0.09, 0.9, and 9 mW/cm2. Exposures were for 20, 40, and 60 min and included an intermittent exposure regimen (20 min on/20 min off), resulting in total incubation times of 20, 60, and 100 min, respectively. Concurrent controls were sham exposed. After extracting total cellular RNA, Northern blot analysis was used to assess the expression of the immediate early genes, c-fos and c-jun, in all cell populations. No change in c-fos transcript levels were detected after 20 min exposure at each field intensity (20 min was the only time period at which c-fos message could be detected consistently). Transcript levels for c-jun were altered only after 20 min exposure to 9 mW/cm2 (average 38% decrease).

Role of modulation on the effect of microwaves on ornithine decarboxylase activity in L929 cells.

The effect of 835 MHz microwaves on the activity of ornithine decarboxylase (ODC) in L929 murine cell was investigated at an SAR of approximately 2.5 W/kg. The results depended upon the type of modulation employed. AM frequencies of 16 Hz and 60 Hz produced a transient increase in ODC activity that reached a peak at 8 h of exposure and returned to control levels after 24 h of exposure. In this case, ODC was increased by a maximum of 90% relative to control levels. A 40% increase in ODC activity was also observed after 8 h of exposure with a typical signal from a TDMA digital cellular telephone operating in the middle of its transmission frequency range (approximately 840 MHz). This signal was burst modulated at 50 Hz, with approximately 30% duty cycle. By contrast, 8 h exposure with 835 MHz microwaves amplitude modulated with speech produced no significant change in ODC activity. Further investigations, with 8 h of exposure to AM microwaves, as a function of modulation frequency, revealed that the response is frequency dependent, decreasing sharply at 6 Hz an 600 Hz. Exposure with 835 MHz microwaves, frequency modulated with a 60 Hz sinusoid, yielded no significant enhancement in ODC activity for exposure times ranging between 2 and 24 h. Similarly, exposure with a typical signal from an AMPS analog cellular telephone, which uses a form of frequency modulation, produced no significant enhancement in ODC activity. Exposure with 835 MHz continuous wave microwaves produced no effects for exposure times between 2 and 24 h, except for a small but statistically significant enhancement in ODC activity after 6 h of exposure. Comparison of these results suggests that effects are much more robust when the modulation causes low-frequency periodic changes in the amplitude of the microwave carrier.

An efficient transport service for slow wireless telephone links

Modern digital cellular telephones and portable computers have created a new platform for distributed information processing. However, the characteristics of wireless telephone links are different from those of wireline links. With standard TCP/IP protocols, this can lead to severe performance problems; some are related to the control of the wireless link, some to the cooperation of the wireless link and the fixed network. One possible solution is to split the end-to-end communication path into two parts, and to establish a separate control for each part. The Mowgli communication architecture is a sophisticated elaboration of this basic idea covering several data communication layers. One of its main components is the Mowgli data channel service (MDCS), which transparently replaces the standard TCP/IP core protocols over the slow wireless link. We discuss how the Mowgli approach, using the MDCS, alleviates the problems encountered with TCP/IP protocols over slow wireless links. The results of our performance tests indicate the merits of the Mowgli approach. The transfer times and the response times become more stable, transfer times for multiple parallel bidirectional transfers are substantially reduced, and response times in interactive work can be kept at a low and predictable level, even when there is other traffic on the wireless link.