Since the first use of mobile satellite communications in 1976 by MARISAT, a number of studies have been carried out to expand their application from international to regional, and to domestic services. By employing the conventional satellites for fixed satellite communications, domestic mobile satellite data communication services have been in commercial use since 1989. Moreover, domestic mobile satellite communication systems employing dedicated satellites to mobile satellite communication are scheduled for commercial operation in Australia, Canada and the USA. Prior to this operation, preliminary mobile satellite communications services employing the MARISAT and MARECS B-2 satellites for data transmission started in Canada and the USA in 1990. Furthermore, more sophisticated and advanced mobile satellite communication systems such as personal communication systems are under development in various countries. This paper reviews the current and future mobile satellite communication systems and related technologies.

With the rapid advance in satellite communications technologies, development of mobile satellite communications systems has been carried out in various countries. In a technical aspect to construct high-capacity and high-reliable mobile satellite communication networks, there are two main barriers to get over, i.e., bandwidth limitation and power limitation. In addition, another barrier associated with mobile motion is fading and shadowing. Digital modulation/demodulation and coding techniques, which are key technologies to get over these barriers, have been developed in fusion of advanced satellite communication techniques and specific techniques having grown in terrestrial mobile communication systems. This paper summarizes the mobile satellite channel characteristics and describes a trend of modulation/demodulation and coding techniques for mobile satellite communications systems.

We explore the implications of deviating from the PSK transmit constellations on using differential detection. By introducing subset dilation, the free distance of the shortest error paths is increased. Analysis based on asymptotic coding gains and simulation results indicate that by exploiting the trellis structure, moderate bit error rate improvements are possible without increasing the receiver complexity.

This paper analyzes performances of trellis coded(TC) 8PSK modulation in Rician fading channels to optimize parameters of Viterbi decoders. The computer simulation clarifies that when carrier power to multipath power ratio (C/M) equals 10dB, P_e performance with reasonable length interleaving depends on free Euclidean distance (d_free) but not on effective code length(ECL) in a practical range of bit error probability (P_e= 10^-3-10^-4). In the case of C/M=5dB, the effect of ECL appears in the range of bit energy to noise power density ratio (E_b/N_o)C/M (=5dB). Therefore, for domestic mobile satellite communication systems for non-high latitude countries, only d_free must be considered for TC8PSK Viterbi decoder design. Moreover, to improve P_e performance in slow fading environment, pre-Viterbi-decoding maximal ratio combining is proposed. The proposed diversity scheme improves required E_b/N_o to achieve P_e=10^-4 by more than 6dB compared with no interleaving and more than 2.5 dB compared with interleaving.

In this paper a new 16-ary Differentially Encoded Quadrature Amplitude (16-DEQAM) demodulator for medium and high bit rate (from 2 MBit/s to 100 MBit/s) Land Mobile Satellite Communications is proposed and its performance is evaluated. The synchronization and detection digital techniques employed in this system are described. The hardware speed limitations have been overcome effectively with extensive use of look-up tables and concurrent digital signal processing on polar signal representation. The acquisition and Bit Error Rate(BER) performances are evaluated by computer simulation over Additive White Gaussian Noise (AWGN) and Rician fading channel.

A new modulation technique, π/4-Controlled Transition PSK (π/4-CTPSK), suitable for non-linearly amplified digital mobile satellite communications systems is introduced. This technique is derived from π/4-QPSK, the modulation scheme adopted as the new U.S. and Japanese digital cellular standard. The π/4-CTPSK modulated carrier is shown to undergo significantly less spectral regeneration after non-linear amplification compared to π/4-QPSK, leading to more efficiant utilization of the available power and spectrum. A principal application of π/4-CTPSK is for systems which may require differential or discriminator detection, such an low bit-rate satellite and land mobile radio communications.

An improvement is made on the previously proposed preambleless demodulation method based on FFT(Fast Fourier Transform) technique⁽¹⁾, in order to cope with a short-term frequency variation caused by an acceleration of a vehicle in mobile communications. The major modification to the previous method is an introduction of a novel phase synchronizer which can synchronize to a signal having a short-term frequency variation. In the mobile communications, the carrier frequency of the received carrier may vary in a short-term because of an acceleration of a vehicle, a rolling of a ship and the like. A carrier synchronization for a burst signal under such an environment would be quite involved and a countermeasure is imperative for the short-term frequency variation. In order to cope with the short-term frequency variation within a received burst, this paper proposes a novel phase synchronizer based on iterative use of a PLL. The phase synchronizer repeats a carrier pull-in process back and forth consecutively along the buffered burst signal. After a forward or backward pull-in process, a value of short-term frequency variation is calculated from a change in an internal state of the PLL. Then this value is used as a new initial state for the next pull-in process which proceeds to the reverse direction to correct the short-term frequency variation is in the burst. By executing this sequence several times, the PLL can complete carrier synchronization regardless of the amount of frequency variation in a burst. The parameter design of the improved preambleless demodulation method incorporating the newly proposed phase synchronizer is performed for the INMARSAT-C signalling channel as a good example of the burst mode channel which suffers a short-term frequency variation. The preambleless demodulation method with the designed parameters shows a good performance under an anticipated operating environment.

This paper describes the implementation and evaluation of the switching network equipment of a 620-Mb/s circuit-switching system, which will economically provide both 4-MHz bandwidth television and high-definition television services. A bit-synchronization LSI capable of handling 52-Mb/s, 155-Mb/s, and 620-Mb/s input signals was developed for this equipment. This LSI together with a 1.5-Gb/s space-division switch LSI and high-speed physical design technology were used in constructing a prototype. A feature of this prototype is that it is designed with multiple printed circit boards which plug into a back panel. Although a switching board that can deal with over 620 Mb/s has previouly been developed, such an implementation is new. Evaluation of the prototype shows that it satisfies the system objectives.

A new algorithm for acoustic echo cancellation called frequency bin adaptive filtering (FBAF) is derived. The FBAF algorithm is based on decomposition of the BLMS algorithm. The FBAF achieves the same cancellation performance as the conventional frequency domain adaptive filtering (FDAF). Both computational complexity and annoying transmission delay are reduced in the FBAF structure as compared with the time domain adaptive filtering and the FDAF, respectively. For input correlated signal, an efficient method for normalizing the step size in the FBAF algorithm is introduced to speed up the convergence rate. The unconstrained FBAF is presented with even fewer FFT operations and consequently less computational load with the price of lowering speed of convergence. A hybrid structure for trading off between system complexity and convergence speed is also presented.

A definition of flexibility in PCM multiplexing architectures is given based on the concept of information entropy. New architectures and coding arrangements are proposed based on the idea of flexibility. Binary terms are created to allow for a better description of system parameters.