Satellite diversity in mobile satellite CDMA systems (original) (raw)
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On the satellite diversity in CDMA based mobile satellite systems
2000
With non-GEO constellations the primary means of counteracting the shadowing and the blockage effects is through the use of the satellite diversity, i.e. multiple satellites in the constellation are simultaneously visible to user. The probability system availability is improved by increasing the probability at least one satellite is in clear line of sight. In the selection diversity (SD) scheme the user is served by one satellite selected on the basis of the better signal to noise ratio. In CDMA systems the spatial diversity provided by the satellite diversity can be more effectively exploited by combining signal replica coming from satellites in view with the aim at increasing the system capacity. Actually, the performance of signal combining/selection diversity schemes depend on the specific propagation scenario and it is not always effective to combine signal replica. In this paper hybrid selection/combining diversity schemes are proposed and a performance comparison in terms of system availability and capacity enhancement is carried out. Furthermore, an analytical methodology of the downlink of DS-CDMA systems which takes into account the power constraints of a satellite environment is described and applied for the capacity assessment of the proposed satellite diversity schemes
Satellite Diversity Gain Over The LEOS Channel , Based CDMA Systems
2000
There is a trend for mobile satellite system architectures aimed at the deployment of multi-satellite constellations in Non-Geostationary Earth Orbits (NGEOs). This allows the user terminals to be small size, low cost and having low power demand. In present and next generation satellite systems, CDMA has been proposed as the multiple access technique for a number of mobile satellite communication systems. To enhance the coverage and quality of service, Low Earth Orbiting (LEO) constellations are usually selected. In this paper, we analyze the performance of the downlink of a LEO satellite channel. The provision of such a service requires that the user have sufficient link quality for the duration of service. To have sufficient link quality, the user must have an adequate power to overcome the path loss and other physical impairments to provide acceptable communication and improve the performance of the system. This paper addresses satellite diversity with the effect of both power co...
Path diversity performance of DS-CDMA systems in a mobile satellite channel
IEEE Transactions on Vehicular Technology, 2000
We derive easy to compute semianalytical expressions for the bit error rate performance of coherent and differentially coherent binary phase-shift keying direct-sequence code-division multiple-access systems operating in a mobile satellite channel. The channel is modeled as frequency nonselective with diversity gain obtained through path diversity. This is the scenario when a signal is transmitted to all satellites in view, and
Comparison of CDMA and FDMA/TDMA in non-GEO Satellite Systems
4bstract--We compare CDMA and FDMA (or TDMA) schemes in multi-beam non-geostationary satellite systems, taking the effects of antenna patterns on inter-cell interference into consideration. The maximum acceptable number of users per cell in uplink is employed as a measure of the system capacity. We have found that in FDMA (or TDMA) systems the maximum acceptable number of users varies according to the altitude of the satellites, while the performance is insensitive to the altitude in CDMA systems. For this reason, the altitude of the satellites is found to be an important factor for selecting multiple access schemes in non-geostationary satellite systems.
IEEE Communications Letters, 2000
To mitigate the main impairments due to the mobile satellite channel, satellite systems adopting code-division multiple access (CDMA) can exploit diversity. Each signal can flow through more than one paths, increasing link availability or improving signal-to-noise ratio (SNR). This letter presents a general mobile satellite channel model for an arbitrary diversity order assuming that all the links are statistically independent. A diversity availability improvement upper bound is calculated.
International Conference on Aerospace Sciences and Aviation Technology
In this paper, we analyse the performance of the downlink of a Non-Geostationary Earth Orbits (NGEO) mobile satellite channel based on Direct Sequence-Code Division Multiple Access (DS-CDMA) in the presence of shadowing, fading and interference from other satellites visible at the same time. In particular, the performance of QPSK convolutionally coded DS-CDMA over a Rice-Lognormal channel is analysed in depth. The provision of such a service requires that the user must have sufficient link quality for the duration of call. To have sufficient link quality, the user must have an adequate power to overcome the path loss and other physical impairments and maintain the performance of the system. The most important factor in determining the performance is the probability of signal shadowing which depends both on the user environment and on the constellation. The paper addresses the exploitation of satellite diversity in the Rician-Lognormal channel. In particular, we focus on the impact of satellite diversity on service availability, path blockage, call dropping and system capacity, considering the effects of imperfect power control, shadowing and voice activity. Concatenated codes are used to provide different bit error probabilities for different services. We show that satellite diversity is an essential in providing service availability especially in urban and suburban areas. Also we show the impact of satellite diversity on the system capacity under different environments, which is related to elevation angle, latitude and the nature of the user terminal environment.
Improvement of QoS of Land Mobile Satellite Systems Using Diversity Techniques
2014
In order to enhance the availability and the offered Quality of Service (QoS), Land Mobile Satellite Systems (LMSS) will have the option to use simultaneous transmission via two or more satellite as diversity. In this paper the performance of a TDMA and CDMA single user return link employing such a diversity reception is investigated by means of computer simulation using a multi state mobile satellite channel model. System capacity and availability have been theoretically evaluated under different operating conditions. The obtained results have shown that by using signal combining techniques improvement of the balance between service availability and system capacity is feasible.
Design study for a CDMA-based LEO satellite network: downlink system level parameters
IEEE Journal on Selected Areas in Communications, 1996
The performance analysis of a new concept of a code-division multiple-access (CDMA) based low earth orbit (LEO) satellite network for mobile satellite communications is presented and discussed. The starting point was to analyze the feasibility of implementing multisatellite and multipath diversity reception in a CDMA network for LEO satellites. The results will be used to specify the design parameters for a system experimental test bed. Due to the extremely high Doppler, which is characteristic of LEO satellites, code acquisition is significantly simplified by using a continuous wave (CW) pilot carrier for Doppler estimation and compensation. The basic elements for the analysis presented in this paper are: the channel model, the pilot carrier frequency estimation for Doppler compensation, and multipath and multisatellite diversity combining.
IEEE Personal Communications, 2001
This article presents a comparison study of the uplink performance of two well-known transmission schemes, W-CDMA and OFDM, for mobile multimedia communications via LEO satellites. In order to provide a framework for a fair comparison we have considered for both schemes common parameters, including identical channel bandwidth, coding/decoding algorithms and similar net data rate. The values of these parameters have been appropriately selected in accordance with the corresponding UMTS system specifications. For W-CDMA, we propose a receiver structure that eliminates ISI for both channel estimation and equalization at the LEO satellite. For OFDM, we propose a system the design of which is based upon the parameters of W-CDMA for UMTS. For both schemes appropriate transceiver structures are proposed and analyzed and their performance is evaluated in terms of computer simulation. The design of these transceiver structures effectively takes into account the statistical characteristics of the LEO satellite channel, so that the overall system performance is improved. The simulation results evaluating the uplink BER performance for a single user indicate that, although the BER performance of W-CDMA is slightly better than that of OFDM, the performance differences are rather small. Furthermore, these differences in performance become even smaller when channel coding is applied and when LOS conditions between the mobile terminal and the LEO satellite exist. Since these results have not shown a clear-cut winner, further comparative studies are required in order to identify the most appropriate transmission scheme for applications supporting global mobile multimedia communication via LEO satellite networks. Such studies should include determination of the downlink BER performance as well as spectrum efficiency and capacity performance evaluations for both up and down satellite communication links.