Periodic reservation allows periodic and random packets to share the same satellite random access channel efficiently. The periodic reservation protocol is particularly suitable for mobile satellite position reporting services, where some of the information messages, such as dispatch function, are classified as "periodic" and others, such as signaling, are classified as "random." When a new mobile terminal logs on to the system, Network Management Center (NMC) reserves subsequent time slots for transmitting periodic packets without contention. A mobile terminal recognizes each time slot as "reserved" or "unreserved (available)" according to the broadcast message received from NMC. Other random packets use the slotted ALOHA protocol to contend with other mobile terminals for an unreserved time slot. The performance results suggest that the use of the periodic reservation protocol can be regarded as a viable solution for mobile satellite position reporting services such as automatic dependent surveillance (ADS).

In a conventional client-server system using the satellite communications, the responsibility of the system to the client user is considerably degraded by the long transmission time between the satellite and the ground terminal as well as the relatively low data transmission rate in comparison with the ground transmission line as the Ethernet. In this paper, a new client-server control, VEEC, is proposed to solve the problem. As a result of the experimental performance studies, it is clarified that the responsibility in the client is remarkably improved when the pre-fetching mechanism of VEEC works efficiently.

The link properties of double-layered constellation composed of inclined orbits for an advanced global satellite communications network connected by optical inter-satellite links (ISLs) have been evaluated. The constellation consists of lower layer satellites for mobile and personal satellite communications, and upper layer satellites for large-capacity fixed satellite communications and feeder links. Optical inter-satellite links, which can perform high-capacity communications with small terminals, are used for all inter-satellite data transmission. Although a satellite constellation using polar orbits in both layers offers the merit of simplicity in network configurations, it has disadvantages caused by the satellite consentration above high latitudes. The inclined orbit constellation offers the potential for reducing the required number of satellites improving ling properties, and enhancing the coverage in middle and low latitudes, by selecting the optimum orbital inclinations. The link properties between the satellites and terminals on the ground, optical ISL properties, and required number of satellites were evaluated for constellations using inclined orbits, and compared with those of a polar orbit constellation. Three kinds of inclined orbit constellations achieving continuous double coverage, which is a minimum requirement for future advanced satellite communications applying satellite diversity, were assumed for each layer.

This paper evaluate the performance of a PN (pseudonoise) code acquisition for a direct-sequence/code-division-multiple-access (DS/CDMA) system in a mobile satellite environment. The acquisition scheme considered consists of a parallel matched-filter and a FFT processor. The uplink of mobile satellite channel is modeled as shadowed Rayleigh fading channel. The effects of power control error and shadowing are considered in the analysis of acquisition performance. It is shown that the power control error causes acquisition to be slower than the case of perfect power control, and for high SNR/chip, the effect of power control error becomes less significant. It is also shown that the case with heavy shadowing takes longer time to achieve acquisition than that with light shadowing. For the subinterval-based PN code search, the parallel MF scheme is thought to be more appropriate than the serial MF scheme at the cost of complexity. The analysis in the paper can be applied to the uplink of a DS/CDMA system for packet-type services in a mobile satellite channel.

Recently, computer communications, especially Internet services, have become popular and as a result, high-speed network access circuits are now desired. NTT has developed an economical and high-speed multimedia computer network, combining satellite and terrestrial circuits. The satellite circuit transmission rate is approximately 30-Mbit/s. To select IP packets from such high-speed satellite circuits, this system employs the asynchronous transfer mode (ATM) in the satellite section and we have developed a new economical satellite circuit receive adapter (SRA) for the satellite section. This paper describes the system configurations and the key network control technologies for multi-link routing, high speed processing and broadcasting.

As the demand for communications via satellite is rapidly increasing, techniques that produce large traffic capacity are becoming more and more appreciated. We present a class of block coded modulation (BCM) and multiple block coded modulation (MBCM) schemes in this paper. While the BCM scheme is directly derived from our previous work, the MBCM schemes are newly developed using a technique of multiple symbol transmission via a single trellis branch. This class of BCM and MBCM schemes is both power and bandwidth efficient. They also have an advantage in holding both a trellis and a block structure. Code structures, decoding trellises and the corresponding branch variables of these BCM and MBCM schemes are all derived. Their applications to satellite communications are discussed. Computer simulations are performed to verify coding gain performance.

Key aspects and technologies of future satellite communications are discussed toward multimedia era. Onboard processing called the switchboard in the sky and networking taking full advantage of features peculiar to satellite communications are pointed out as essential technologies to overcome a variety of big challenges for realizing future satellite communications. Several experimental and commercial systems are introduced as the first step toward multimedia era.

This paper proposes a new AFC (automatic frequency control) circuit employing a double-product type frequency discriminator to enable fast acquisition in very-low CNR (carrier to noise power ratio) environments. The frequency step responses of the proposed AFC circuit are theoretically analyzed. In addition this paper evaluates the performance of the proposed AFC circuit by computer simulation in very-low CNR environments. The simulation results confirm that click noise at the frequency discriminator causes large frequency tracking error and that this error can be improved by increasing the delay time of the double-product type frequency discriminator. The frequency error can be also reduced by introducing the proposed frequency discriminator to modify the frequency error detection performance. The acquisition time of the proposed AFC circuit can be reduced by about 100 symbols compared to the conventional cross-product type AFC circuit.

This paper presents fully digital high speed (17.6Mb/s) burst modem for Offset Quadrature Phase Shift Keying (OQPSK), which employs novel digital modem VLSICs. The modulator VLSIC directly generates modulated intermediate frequency (IF) signals in a fully digitalized manner. A newly proposed digital reverse-modulation and pre-filtered carrier filter-limiter scheme realizes low power consumption and stable operation in a low Eb/No condition. The demodulator VLSIC also achieves fast bit-timing acquisition in burst mode. Moreover, it supports stable initial burst acquisition by a novel automatic frequency control (AFC) acquisition detector and a digital burst detector. A digital burst automatic gain control (AGC) compensates burst-to-burst level differences without analog circutits. Performance evaluation results show that the new modem achieves satisfactory bit-error-rate performance in severe environments. The developed modem has been employed in a commercial portable earth station for ISDN services and reduces the hardware size to one third that of the conventional one.

This paper examines the performance of a direct sequence, spread spectrum (DSSS) multiple access (MA) system used over two typical, frequency-selective, fading satellite channels. In an attempt to increase the system efficiency, an adaptive receiver described by Rapajic and Vucetic [1] has been implemented. This system has been combined with soft-decision convolutional coding in order to improve the system performance under the fading conditions relative to the uncoded system and to allow as many simultaneous users as possible. Various code rates have been examined and the results are given. This paper specifically focuses on DSSS-MA systems with low spreading ratios. The satellite channels used in this paper were produced by models developed as a result of experimental measurements of fading satellite channels for rural and urban environments.

In the envisaged Universal Mobile Telecommunications System (UMTS), the satellite component will have to provide services to mobile or, in some cases, hand held terminals with a required grade of user co-operation and link availability in various communication environments. This may require the capability of the satellite link to cope with more severe multipath environments than those for which mobile satellite links are most frequently designed (maritime or open rural applications); unfortunately, when the mobile radio channel is affected by multipath and a coherent demodulation is chosen, the phase synchronisation can be a critical issue. To satisfactorily deal with the arising difficulties, a dual channel demodulation is a viable and efficient strategy for the forward link, since only one common pilot channel is needed in this case. If the same dual channel demodulation is considered for the return link, an unacceptable capacity reduction may result. In this paper, some synchronisation strategies are analysed and an efficient dual channel demodulation scheme is proposed for the return link of a satellite DS-CDMA mobile communication system; furthermore, the impact on the overall system performance or capacity is analysed.

This paper proposes a novel Doppler frequency shift compensation technique to achieve terrestrial and low earth orbit (LEO) satellite dual mode DS/CDMA terminals robust to high Doppler shift and multipath fading. In order to satisfy the requirements of wide dynamic range and high accuracy simultaneously, the proposed scheme employs two stage compensation scheme, i.e., coarse compensation to keep dynamic range of about 100 kHz and fine compensation to satisfy its resolution of about 30 Hz, using block demodulation technique. Computer simulation results show that the proposed scheme can sufficiently compensate for the offset frequency up to the range of about 100 kHz at the terrestrial and LEO satellite combined mobile communication systems.

This paper presents a configuration of circularly polarized annular-ring microstrip antenna (ARMSA) and its design method to obtain high gain and low axial ratio including the analysis of finite ground plane effect using G.T.D. for personal satellite communication use. The ARMSA excited at TM21 mode through co-planar branch-line hybrid coupler for circular polarization produces a conical pattern which has high gain in low elevation angle. The relation of gain and axial ratio versus the dielectric constant of substrate are shown and the existence of the dielectric constant which satisfies two requirements, that is, high gain and low axial ratio are clarified. For car-top application, experimental results in the L-band showed satisfactory characteristics for vehicle antenna.

In this paper, coded modulation techniques suitable for satellite broadcasting of digital high-definition TV are studied. An overview of current approaches to satellite broadcasting is presented. New constructions of coded modulation schemes for unequal error protection (UEP), based on both block and trellis codes, are introduced in this paper. The proposed schemes can achieve both better overall performance and enhanced graceful degradation of the received signal, in comparison with existing digital satellite broadcasting approaches.

For mobile/personal satellite systems, an ARQ protocol with low transmitter/receiver complexity as well as high throughput performance in a long Round-Trip-Delay (RTD) and even in a bad channel condition is required. In this paper, a new Selective-Repeat (SR) ARQ with multicopy retransmission is proposed and a performance on an AWGN channel is analyzed. The proposed scheme can be viewed as a modified version for SR + Stutter (ST) Scheme 2 [6]. The basic idea of the strategy is to repeat only erroneous blocks stored in the vN block transmitter buffer multiple times, when v consecutive retransmissions in SR mode are received in error, where N denotes RTD in blocks. Numerical analysis and simuration results in the case of N block transmitter/receiver buffer show that the proposed scheme presents better performance than SR + ST scheme 2 of 2N block buffer, especially that the robustness in the high BER region is remarkable.

In this paper, authors propose a linear array antenna using two bifilar helical antenna elements placed along the helix axis to reduce beam direction movement according to frequency change. The beam direction movement of this proposed array antenna is smaller than that of a conventional bifilar helical antenna. Also, the gain of this proposed array antenna is higher than that of the conventional helical antenna for a cross point angle of radiation patterns at the different transmit and receive(Tx and Rx) frequencies. The conventional helical antenna is suitable for vehicle antennas in mobile satellite communication systems such as the MSAT system because it owns circularly polarized omni-directional radiation pattern and its thin pole form. However, this antenna has a disadvantage that the beam direction in an elevation plane moves according to frequency change. In the proposed array antenna, the beam direction movement is about 9 smaller than that of the conventional bifilar helical antenna on condition that antenna total length is 4.83 λ0, antenna diameter is 0.12 λ0, and frequency change is from 0.957f0 to 1.043f0(f0 is center frequency and λ0 is free space wavelength at f0). Also, the Tx and Rx gains of this proposed array antenna at the cross point angle between Tx and Rx beams are about 2 dB higher than that of the conventional bifilar helical antenna on the same condition.

The main propagation effect on interference between adjacent earth-space paths is considered to be the differential rain attenuation. In the present paper, a unified method for the prediction of rain differential attenuation statistics, valid for both single/dual polarization systems, which is based on the two-dimensional gamma distribution, in proposed. The method is particularly oriented for application to earth-space paths located in Japan and other locations with similar climatic conditions. From another point of view, the present work is considered to be the complementary aspect of the present work is considered to be the complementary aspect of the predictive analysis which uses the lognormal assumption. Numerical results are presented referring to communication systems suffering from differential rain attenuation under the hypothesis of using both single and dual polarization.

This paper proposes an integrated interference suppression scheme which realizes interference-resistant satellite digital signal transmission systems. It employs a notch filter in the receiving side to suppress the co-channel interference (CCI) signal. Moreover, the proposed scheme employs an adaptive equalizer combined with a forward error correction (FEC) scheme to improve the Pe (probability of error) performance degradation due to the inter-symbol interference caused by notch filtering of the desired signal. In the typical frequency modulation (FM) CCI environment with a BWi/FN of 2.3 (BWi: interference signal required bandwidth, fN: one half the Nyquist bandwidth of the desired signal), a Δf / fN of 1.05 (Δf: interference frequency offset) and a D/U of 3 dB (desired to undesired (interference) signal power ratio), the proposed scheme improves the required Eb/NO by 1.5 dB at a Pe of 10-4 compared to that without an adaptive equalizer.

An analytical framework to study the nonuniformity in geographical distribution of the traffic load in low earth orbit satellite communication systems is presented. The model is then used to evaluate the throughput performance of the system with direct-sequence packet spread-slotted ALOHA multiple-access technique. As the result, it is shown that nonuniformity in traffic makes the characteristics of the system significantly different from the results of uniform traffic case and that the performance of each user varies according to its location. Moreover, the interference reached from users of adjacent satellites is shown to be one of the main factors that limit the performance of system.

This paper proposes a novel phase ambiguity resolver with combining a very low power Viterbi decoder employing a scarce state transition scheme to realize cost effective receivers for the PCM sound broadcasting satellite service. The theoretical analyses on phase decision performance show that the proposed resolver achieves the symbol-by-symbol phase detection and decides correctly phases of the demodulated data even if the bit error probability of 710-2. The resolver also reduces the phase decision time to below 1/1000 of that of the conventional resolver. Furthermore, experimental results of the power consumption estimate that the prototype Viterbi decoder consumes only 60mW at the data rate of 24.576Mbit/s.