Time-division Multiple-access Signals Research Articles

Short‐term exposure to a 1439‐MHz TDMA signal exerts no estrogenic effect in rats

The aim of this study was to elucidate the possible effects of short-term exposure to a 1439-MHz electromagnetic field (EMF) employing time division multiple access (TDMA), which is the basis of the Japanese Personal Digital Cellular system, on estrogenic activity in rats. Sixty-four ovariectomized female Sprague-Dawley rats were divided into four groups: EMF exposure (EM), sham exposure, cage control, and 17 beta-estradiol injected (E2). The EM group was exposed, for 4 h per day on three consecutive days, to the 1439-MHz TDMA signal that produced 5.5-6.1 and 0.88-0.99 W/kg average specific absorption rates in the brain and the whole body, respectively. The uterine wet mass and serum estradiol level significantly increased in the E2 group, while there were no differences among the other three groups. Although negative effects of long-term EMF exposure must be thoroughly investigated before a final conclusion can be reached, our results do not support the assumption that the high frequency EMF used in cellular phones exerts estrogenic activity.

Application of Multirate Filter Bank to Group Demodulation of Frequency‐Multiplexed TDMA Signals

AbstractAs a method to obtain the baseband signal from each of several time division multiple access (TDMA) signals that are frequency‐multiplexed in the uplink in wireless communication, this paper proposes a method of group demodulation using a multirate filter bank. The proposed method allows demodulation when the TDMA signals are asynchronously received in the uplink. Further, it can be applied to the case in which TDMA signals with different bandwidths are frequency‐multiplexed, if the multiple resolution capability of the multirate filter bank is used. Hence, this method is useful in the situation where several different types of signals coexist in such environments as software radio. In the systems discussed in this paper, it is necessary to realize a sharp amplitude response and a linear phase response in the filters of the multirate filter bank with a small computational effort. This is accomplished in this paper by using an infinite impulse response (IIR) filter with approximately linear phase response. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 85(4): 44–52, 2002

Time-transfer performance in burst-mode communication systems

This paper studies the performance of the clock transfer scheme for burst-mode communication systems for which data are received during short, equally spaced intervals. Its main focus is on satellite-based time-division multiple-access (TDMA) communication systems with data regeneration and switching onboard the satellite, although the results apply to other TDMA systems as well. The system reference clock is generated onboard from an incoming, very stable ground source, based on a burst-mode demodulator that extracts the clock from a discontinuous modulated carrier due to the bursty nature of TDMA signals. If good enough, this onboard regenerated clock avoids the use of bulky and expensive clocks in the satellite payload and can act as the master clock of the TDMA system.

A constrained least-squares algorithm with data-adaptive beamforming and equalization for cochannel TDMA signals

Cochannel signals in a time-division multiple-access (TDMA) cellular network interfere with each other in an asynchronous manner. In order to demodulate one of these signals, the receiver must be able to separate the cochannel interferers for a variety of burst overlap scenarios. In this paper, we present an adaptive beamforming and equalization algorithm that separates cochannel TDMA signals using the known synchronization sequences. It is based on a least-squares formulation with soft constraints, and the antenna data are processed in two sequential passes. In this way, the data are accurately beamformed within a burst even when the cochannel scenario changes during the burst. A data-adaptive version of the algorithm for fast-fading channels is also presented. It employs the synchronization sequences to generate estimates of the multipath channels between the cochannel sources and the base station.

Joint receiver for DS-CDMA/TDMA signals using complex multirate filter bank

This paper discusses the problem of coexistence of DS-CDMA (direct sequence code division multiplex access) and TDMA (time division multiple access) systems where their signals are transmitted in the same frequency band. The DS-CDMA signal is robust against narrowband interference, but there is a limit to its immunity against interference. This paper proposes, from such a viewpoint, a method using a complex multirate filter bank, as a way to reject TDMA signals, which act as narrowband interference to the DS-CDMA signal, in the coexistence system. By the proposed method, a notch filter can be composed with an arbitrary frequency resolution at an arbitrary frequency, by constructing the complex version of the conventional multirate filter bank. It is shown that, by eliminating the TDMA signal by the proposed method, the bit error rate of the DS-CDMA signal is improved, indicating that the proposed system is useful in the coexistence problem. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 82(5): 34–41, 1999

High-Speed Optical Time-Division Multiple-Access (OTDMA) Networks Using Optical Signal Processing

In this paper, we design high-speed optical fiber networks based on the time-division multiple-access (TDMA) technique. To achieve an ultrahigh throughput, optical signal processing should be used in the network. We present a feasible scheme to implement optical TDMA networks, with the emphasis on optical clock distribution, synchronization, and optical time demultiplexing. Since the proposed network uses two wavelengths to carry optical TDMA and clock signals respectively, at each TDMA receiver slot synchronization is feasibly achieved by using simple optical delay lines to process the separated optical clock and TDMA signals. This in turn allows us to build a large-scale distribution network which is attractive for future HDTV broadcasting applications. Using the proposed scheme also allows to implement a high-capacity broadcast and select optical TDMA network for real-time data communications.

Adaptive MAPSD algorithms for symbol and timing recovery of mobile radio TDMA signals

Dual-mode adaptive algorithms with rapid convergence properties are presented for the equalization of frequency selective fading channels and the recovery of time-division multiple access (TDMA) mobile radio signals. The dual-mode structure consists of an auxiliary adaptive filter that estimates the channel during the training cycle. The converged filter weights are used to initialize a parallel bank of filters that are adapted blindly during the data cycle. When the symbol timing is known, this filter bank generates error residuals that are used to perform approximate maximum a posteriori symbol detection (MAPSD) and provide reliable decisions of the transmitted signal. For channels with timing jitter, joint estimation of the channel parameters and the symbol timing using an extended Kalman filter algorithm is proposed. Various methods are described to reduce the computational complexity of the MAP detector, usually at the cost of some performance degradation. Also, a blind MAPSD algorithm for combining signals from spatially diverse receivers is derived. This diversity MAPSD (DMAPSD) algorithm, which can be easily modified for the dual-mode TDMA application, maintains a global set of MAP metrics even while blindly tracking the individual spatial channels using local error estimates. The performance of these single-channel and diversity MAPSD dual-mode algorithms are studied via computer simulations for various channel models, including a mobile radio channel simulator for the IS-54 digital cellular TDMA standard.

Dual wavelength optical fiber HDTV distribution networks using self-synchronization technique and multistar topology

A new optical fiber time-division multiple-access (TDMA) network is proposed for HDTV distributions. It uses two wavelengths to carry optical TDMA and clock signals through the common fibers to each subscriber. At the receiver, both signals are easily separated by using a wavelength division multiplexing (WDM) demultiplexer, and therefore, the frame and time-slot synchronizations are feasibly achieved by using optical fiber delay lines to independently process the separated clock and TDMA signals. This self-synchronization characteristic can be used to improve the network flexibility, which allows one to build a large-scale HDTV distribution network based on a multistar topology. Furthermore, a sensitivity analysis of optical TDMA receivers is carried out. It is shown that, compared with a point-to-point optical fiber digital system, the multi-user optical TDMA system requires a lower extinction ratio to alleviate the performance degradation. >

Calculation of the allan variances for the rain‐attenuated millimeter wave beacon from a geostationary satellite, and their application to the site‐diversity switching

AbstractWe calculated the Allan variance (the frequency stability measure in the time domain) of a rain‐attenuated 34.5 GHz beacon signal transmitted from a geostationary satellite. the obtained results showed that the rain‐attenuated signals basically had random‐process characteristics with fα (α < 0) types of power spectral densities‐typically with α = ‐2, i.e., a random walk process. Also calculated were the Allan variances of bit error rates (BER's) of time division multiple access (TDMA) signals which were attenuated by rain. Occasionally, the measurements showed that the variances were reduced to only a few seconds. We applied these results to sitediversity switching experiments and tried to determine optimum times to measure and compare the BER's of the TDMA signals to be switched (they came from both routes of the main and substations). Simulation experiment results showed that the measuring times to minimize the variances coincided almost with those to minimize switching errors. This was also proved by theoretical analysis.