North American Digital Cellular Research Articles

A Voltage-Translinear Based CMOS Signal Component Separator Chip for Linear LINC Transmitters

The LINC transmitter is an architecture that provides linear amplification using nonlinear but power efficient amplifiers. One crucial signal processing function of LINC is the signal component separator (SCS) which forms two constant-amplitude phase-modulated signals from the source signal. This paper presents an analog SCS chip implemented in a 0.35 μm CMOS process using a novel design based on the so-called voltage-translinear circuit principle. An experimental LINC transmitter was built with the SCS chip, nonlinear amplifiers and a power combiner. Test results showed that all output spurious levels some -55{\rm dBc} and -48 dBc could be obtained with a North American Digital Cellular (NADC) signal and an IS-95 signal, respectively. This implies a high degree of linearity.

A 3.3 V Power Feedback Chip for Linearization of RF Power Amplifiers

The power feedback technique is a simple and low cost linearization scheme suitable for consumer products such as hand sets. This paper presents a custom chip for linearization of RF power amplifiers using power feedback. The chip, implemented in a standard double-metal double-poly 0.6 μm CMOS process, operates with 3.3 V supply voltage and consumes 62 mW. When it was used to linearize a commercially available high efficiency RF power amplifier at 850 MHz, experimental results showed that out-of-band power at 30 kHz offset was reduced some 10 dB for a π/4-shifted DQPSK modulated North American digital cellular (NADC) signal. For the same level of adjacent channel interference (ACI), the efficiency was increased from 35% to 48%.

A 200-MHz IF BiCMOS signal component separator for linear LINC transmitters

The linear amplification with nonlinear components (LINC) transmitter is an architecture that provides linear amplification using nonlinear but power efficient amplifiers. The signal component separator (SCS) is a crucial signal processing function of LINC. It forms two constant-amplitude phase-modulated signal components from the input signal. Due to the nonlinear signal processing involved, digital signal processing (DSP) implementation of the SCS at baseband has so far been assumed to be the best choice although it suffers from matching, bandwidth and power consumption problems. In this paper a new SCS architecture based on analog integrated circuit techniques is presented to avoid the disadvantages in a DSP based realization. A 200-MHz IF SCS chip using the proposed architecture was designed and fabricated in a 0.8 /spl mu/m BiCMOS process. An experimental LINC transmitter was built with the SCS chip, nonlinear amplifiers and a power combiner. Test results showed that spurious levels around -50 dBc could be obtained with a /spl pi//4-shifted DQPSK modulated North American Digital Cellular (NADC) signal. This implies a high degree of linearity in the implemented LINC transmitter.

Spontaneous and Nitrosourea-Induced Primary Tumors of the Central Nervous System in Fischer 344 Rats Chronically Exposed to 836 MHz Modulated Microwaves

We have tested an 836.55 MHz field with North American Digital Cellular (NADC) modulation in a 2-year animal bioassay that included fetal exposure. In offspring of pregnant Fischer 344 rats, we tested both spontaneous tumorigenicity and the incidence of induced central nervous system (CNS) tumors after a single dose of the carcinogen ethylnitrosourea (ENU) in utero, followed by intermittent digital-phone field exposure for 24 months. Far-field exposures began on gestational day 19 and continued until weaning at age 21 days. Near-field exposures began at 35 days and continued for the next 22 months, 4 consecutive days weekly, 2 h/day. SAR levels simulated localized peak brain exposures of a cell phone user. Of the 236 original rats, 182 (77%) survived to the termination of the whole experiment and were sacrificed at age 709-712 days. The 54 rats (23%) that died during the study ("preterm rats") formed a separate group for some statistical analyses. There was no evidence of tumorigenic effects in the CNS from exposure to the TDMA field. However, some evidence of tumor-inhibiting effects of TDMA exposure was apparent. Overall, the TDMA field-exposed animals exhibited trends toward a reduced incidence of spontaneous CNS tumors (P < 0. 16, two-tailed) and ENU-induced CNS tumors (P < 0.16, two-tailed). In preterm rats, where primary neural tumors were determined to be the cause of death, fields decreased the incidence of ENU-induced tumors (P < 0.03, two-tailed). We discuss a possible approach to evaluating with greater certainty the possible inhibitory effects of TDMA-field exposure on tumorigenesis in the CNS.

An IC for linearizing RF power amplifiers using envelope elimination and restoration

This paper presents a monolithic CMOS implementation of an envelope elimination and restoration linearization system that improves the linearity of efficient radio-frequency power amplifiers. The linearization IC, which occupies 4.3 mm/sup 2/ when implemented in a 0.8-/spl mu/m CMOS technology, consists of a limiter, envelope detectors, and delta-modulated switching power supply. This circuit was used to linearize advanced mobile phone system cellular power amplifiers transmitting North American digital cellular (NADC) waveforms. Measurements show that the linearized outputs meet the spectral mask and phase distortion requirements of NADC. The linearization system can improve the overall efficiency from 36 to 49%, while increasing the maximum linear output power from 26.5 to 29.5 dBm.

Bit-error rate of TDMA links under cochannel interference in overlaid cellular networks

This paper presents a series of numerical experiments conducted to investigate the error performance of a simulated digital time-division multiple-access (TDMA) radio link between a portable handset and the base station serving it, subject to interference coming from other portable handsets. The experiments take radio channel impairments such as fading, shadowing, and distance loss into account. Analytical expressions for the bit-error probability in uncoded digital radio transmission bursts under interference from nearby analog FM or digital minimum-shift keying (MSK) transmitters are reviewed. Numerical methods are used to extend analytical estimates of symbol error probability of a link with a single interferer, without channel impairments, to the case where the interference is due to a random distribution of transmitters whose signals are subject to fading, shadowing, and distance power loss. Specifically, three links, each based on one of three different modulation methods, MSK, quadrature phase-shift keying (QPSK) (proposed in the North American Digital Cellular Standard IS-54), and Gaussian MSK (GMSK) [used in the Global Standard for Mobile communications (GSM)] are simulated, and the bit-error rate (BER) results reported. The BER results generated thus indicate the sensitivity of the digital radio link to the user density for a given radio frequency (RF) bandwidth and, where applicable, to fading depth and postmodulation intersymbol interference (ISI) removal method. Possible extensions and applications of the simulation model to the problem of resource sharing between coexisting networks are suggested.

Performance evaluation of non-linear transmit power amplifiers for North American digital cellular portables

This paper discusses the system performance degradation resulting from using a non-linear transmit power amplifier (PA) in a North American digital cellular (NADC) portable radio. The NADC portables require a linear power amplifier for the spectrally efficient linear modulation scheme, /spl pi//4-DQPSK. It is well known that these PA's can exhibit non-linear characteristics that degrade system performance. System degradation is measured using bit error rate (BER) as the figure of merit. The PA is modeled by its AM-AM and AM-PM characteristics; the receiver architecture contains the simple, yet robust, differential detector. Simulation results are presented for additive white Gaussian noise (AWGN), Rayleigh fading, and frequency selective fading environments, and compared to results for a truly linear PA. In addition, PA spectral regrowth is discussed as well as the potential use of a linearization technique to compensate for the PA effects.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Adaptive two-stage maximum likelihood estimation for cellular radio

The problem of optimal detection over nonselective fading channels for cellular radio is treated from the viewpoint of adaptive two-stage maximum likelihood estimation (MLE). Data for transmission are divided into blocks, each preceded by one or more reference symbols. For selective fading, the receiver consists of an adaptive filter (AF) and a two-stage maximum likelihood estimator (TSMLE). For nonselective fading, TSMLE is preceded by a fixed filter. For quadrature modulation, the complex output of the filter contains two sets of unknowns, the quadrature data symbols (QDS) and the quadrature gains (QG) between transmitter and filter output. Stage I generates MLE estimates of the QG during the reference period and Stage II generates QDS estimates during the data intervals. AF coefficients are adjusted using a QR-decomposition least squares (QRD-LS) algorithm. A likelihood ratio test is performed to produce noise-free data estimates which Stage I in turn can use, in a decision aided manner, to update its gain estimates for the next interval. The quadrature gain estimates can be used to further correct reference carrier phase errors. Nonrecursive and recursive estimation procedures are developed. Bit error rate (BER) expressions are presented for 4-PSK and pi /4-DQPSK. Numerical results show that the scheme meets the North American Digital Cellular (NADC) system performance specifications (IS-54) with a margin. The BER floor is an order of magnitude lower than those of other schemes reported in the literature. For nonselective fading the BER floor is practically eliminated. This, and results reported elsewhere (Haeb and Meyr, 1989), lead us to conclude that schemes performing quadrature gain estimation can be used to lower error probabilities, attractively.

Evolution of wireless information networks

Consumer and business demands for cellular mobile telephones and residential cordless phones are growing rapidly throughout the world. Both are relatively new and still function with their original, first generation technologies. In response to various pressures second generation systems and services are scheduled for introduction over the next three years. Meanwhile researches are formulating a vision of the third generation, when cordless, cellular, and other wireless networks will merge in a unified means of wireless access to advanced information services. This paper traces the evolution of wireless information networks by examining goals, network architecture, transmission technologies, and control channels. In each instance, we describe, in a general way, first generation systems. We then discuss details of four different second generation systems: Pan-European Digital Cellular (GSM), North American Digital Cellular (IS-54), Second Generation Cordless Telecommunications (CT2), and Digital European Cordless Telecommunications (DECT). Finally, we provide a glimpse into the future by presenting work in progress on third generation technology, based on packet transmission and switching.