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The VLF transmitting system in Cutler, ME currently broadcasts at one frequency through a two-element antenna system. This study investigates simultaneous operation at 24.0 and 17.8 kHz. Detailed nonlinear PSPICE models were generated for the system including the amplifier triodes, saturable dynamic-tuning reactors, and the closely-coupled antenna elements. The predicted behavior is in close agreement with available observations. Upper limits are placed on harmonic content, < -59.8 dBc, and intermodulation distortion, < -78 dBc.

Byline: Americo Correia (1) Keywords: transmit diversity; multi-path fading; estimation errors; multiple access interference Abstract: Previous work on transmitter antenna diversity has shown that the use of multiple transmitter antennas at the base station results in improved performance due to increase of diversity (path diversity). This happens with no bandwidth cost, even when the signal quality along several paths is poor, but the receiver estimates the channel with accuracy. This paper evaluates the effects of channel estimation errors in the performance of the schemes designated as Space-Time Transmitter Diversity (STTD) and Selective Transmitter Diversity (STD). We consider low to medium signal to noise ratios characteristic of Wideband Code Division Multiple Access (WCDMA) networks. Different fading channel models are considered for comparison between the two schemes. The improvement due to convolutional coding associated with these techniques is also evaluated. Author Affiliation: (1) Instituto de TelecomunicacAues, Lisbon, Portugal Article History: Registration Date: 11/10/2004

Byline: Jeongseok Ha (1), Apurva N. Mody (1), Joon H. Sung (1), John R. Barry (1), Steven W. McLaughlin (1), Gordon L. Stuber (1) Keywords: orthogonal frequency division multiplexing; singular-value decomposition; Alamouti diversity scheme; low-density parity-check codes Abstract: Two transmit two receive space-time processingwith LDPC coding is evaluated for OFDM transmission.The two methodsfor space-time processing are Alamouti's combining and the SVD technique.The channel estimates are calculated and provided tothe diversity combiner, the SVD filters and LDPC decoder.Noise variance estimates areprovided to the LDPC decoder. Using the proposed schemewe can obtain a BER of 10.sup.-5 at an SNR of 2.6 dB withspectral efficiency of0.4 bits/sec/Hz and 14.5 dB with a spectral efficiency of 4.2 bits/sec/Hz. Author Affiliation: (1) School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA, 30332, U.S.A Article History: Registration Date: 13/10/2004

Recent developments in RF power transistor technology makes solid state transmitters economically attractive for UHF DTV terrestrial transmissions. These transmitters will probably use silicon bipolar, MOS or silicon carbide SIT transistors in the RF power amplifiers. This paper examines these RF transistor technologies. In addition, this paper provides an overview of a typical DTV solid state transmitter. The authors have conducted DTV transmission tests and demonstrations using a silicon carbide, solid state transmitter. This paper provides a brief description of these tests.

Radiocollars, which commonly are used to study mammals, might increase the mortality of the animals studied. We used Cormack-Jolly-Seber modeling on data of root voles (Microtus oeconomus), to test whether an increase in mortality due to radiocollars occurred. Higher mortality was not detected in animals wearing collars compared with animals that did not wear collars. Key words: Microtus oeconomus, Cormack-Jolly-Seber model, radiocollars, root voles, survival

The Cartesian loop transmitter is now a well-known linear transmitter architecture and is finding application in a number of mobile radio systems employing linear modulation technologies. In particular, systems utilizing [Pi]/4 DQPSK require a linear transmitter, and many emerging standards [e.g., trans-European trunked radio (TETRA)] provide applications for the Cartesian feedback linearization (CFL) technique. One problem with the CFL transmitter is that its output-noise performance is no longer dominated by that of the RF power module employed within it (as is the case in more conventional transmitter architectures). The use of significant degrees of attenuation, followed by a high level of gain, within the loop, means that the noise performance of the loop is significantly poorer than that of a conventional transmitter. There are a number of tradeoffs that are available to the designer of a CFL transmitter to aid in the optimization of the output-noise performance. This paper presents a derivation of the noise performance of a Cartesian loop transmitter and highlights the design methods that may be employed in order to optimize its noise performance. It also provides a comparison of the theoretically derived behavior with that of a practical transmitter operating in the TETRA band. Index Terms - Amplifier linearization, noise, noise measurement, power amplifiers, transmitters.

This paper investigates the effect of chip waveform shaping on the error performance, bandwidth confinement, phase continuity, and envelope uniformity in direct-sequence code-division multiple-access communication systems employing offset quadrature modulation formats. An optimal design methodology is developed for the problem of minimizing the multiple-access interference power under various desirable signal constraints, including limited 99% and 99.9% power bandwidth occupancies, continuous signal phase, and near-constant envelope. The methodology is based on the use of prolate spheroidal wave functions to obtain a reduced-dimension discrete constrained optimization problem formulation. Numerous design examples are discussed to compare the performance achieved by the optimally-designed chip waveforms with other conventional schemes, such as offset quadrature phase-shift keying, minimum-shift keying (MSK), sinusoidal frequency-shift keying (SFSK), and time-domain raised-cosine pulses. In general, it is found that while the optimized chip pulses achieved substantial gains when no envelope constraints were imposed, these gains vanish when a low envelope fluctuation constraint was introduced. In particular, it is also shown that MSK is quasi-optimal with regard to the 99% bandwidth measure, while the raised-cosine pulse is equally good with both the 99% and 99.9% measures, but at the expense of some envelope variation. On the other hand, SFSK is quasi-optimal with regard to the 99.9% bandwidth occupancy, among the class of constant-to-low envelope variation pulses. Index Terms-- Chip waveform optimization, direct-sequence CDMA, envelope uniformity, multiple-access interference, phase continuity.

We investigate the effects of fading correlations in multielement antenna (MEA) communication systems. Pioneering studies showed that if the fades connecting pairs of transmit and receive antenna elements are independently, identically distributed, MEA's offer a large increase in capacity compared to single-antenna systems. An MEA system can be described in terms of spatial eigenmodes, which are single-input single-output subchannels. The channel capacity of an MEA is the sum of capacities of these subchannels. We will show that the fading correlation affects the MEA capacity by modifying the distributions of the gains of these subchannels. The fading correlation depends on the physical parameters of MEA and the scatterer characteristics. In this paper, to characterize the fading correlation, we employ an abstract model which is appropriate for modeling narrow-band Rayleigh fading in fixed wireless systems.