Comparison of CDMA and FDMA/TDMA in non-GEO Satellite Systems (original) (raw)
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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...
European Transactions on Telecommunications, 1991
The project to interconnect, in the C.N.R. environment, local area networks via satellite links at high speed, presents the problem of an efficient utilization of the transmit capacity of the satellite channel, as well as problems related to the terminal design. In particular, referring to satellite access schemes in FDMA and/or TDMA, the optimization of the transmission capacity utilization, according to the traffic requirements, is analyzed. Two systems, based on hybrid MF-TDMA. are presented and synchronization problems are analyzed.
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.
Satellite diversity in mobile satellite CDMA systems
IEEE Journal on Selected Areas in Communications, 2001
The paper addresses the exploitation of satellite diversity in a satellite mobile network. In particular, we focus on the impact of diversity on service availability and on system capacity, considering the forward link of a CDMA system with a multisatellite and multibeam architecture. The analysis includes the effects of path blockage, intrabeam and interbeam interference, imperfect power control, and fading correlation in the time domain due to nonideal interleaving. A closed-form solution is given for the estimation of system capacity. We show that satellite diversity is essential in providing service availability in urban and suburban areas, while the impact of satellite diversity on system capacity may be positive or negative, mainly depending on the fading channel characteristics. In particular, diversity becomes more and more beneficial for increasing fading time-domain correlation (i.e., for low mobile speed and/or limited interleaving depth). The analytical results have been validated by means of Monte Carlo simulation.
International Journal of Satellite Communications, 1992
This paper analyses and compares possible access schemes to be used in satellite networks with a large number of small earth-stations. Basically, frequency division (FDMA), time division (TDMA), and spread spectrum multiple access (SSMA) are considered. For TDMA, one single carrier originated in one particular earth-station is transmitted in each sub-band and therefore a single-channel-percarrier system results (SCPUFDMA). For TDMA and SSMA, it is assumed that groups of earthstations using either of these access schemes share the full available band in FDMA. The corresponding systems are thus TDMA/FDMA and SSMA/FDMA. Moreover, for SCPCIFDMA and TDMAIFDMA individual carriers may be spread to the extent that the available bandwidth is always fully occupied. Spectral efficiencies for these three access modes (Spread SCPCIFDMA, Spread TDMAIFDMA and SSMA/FDMA) are computed and compared for transmission through a non-linear satellite channel and optimum operating points for the non-linear amplifier are also determined. Comparisons are also performed for the situation in which transmitting earth-stations are bounded to obey an off-axis emission constraint.
A Comparison between RSMA, SDMA, and OMA in Multibeam LEO Satellite Systems
arXiv (Cornell University), 2023
Low Earth orbit (LEO) satellite systems enable close to global coverage and are therefore expected to become important pillars of future communication standards. However, a particular challenge faced by LEO satellites is the high orbital velocities due to which a precise channel estimation is difficult. We model this influence as an erroneous angle of departure (AoD), which corresponds to imperfect channel state information (CSI) at the transmitter (CSIT). Poor CSIT and non-orthogonal user channels degrade the performance of space-division multiple access (SDMA) precoding by increasing inter-user interference (IUI). In contrast to SDMA, there is no IUI in orthogonal multiple access (OMA), but it requires orthogonal time or frequency resources for each user. Rate-splitting multiple access (RSMA), unifying SDMA, OMA, and non-orthogonal multiple access (NOMA), has recently been proven to be a flexible approach for robust interference management considering imperfect CSIT. In this paper, we investigate RSMA as a promising strategy to manage IUI in LEO satellite downlink systems caused by non-orthogonal user channels as well as imperfect CSIT. We evaluate the optimal configuration of RSMA depending on the geometrical constellation between the satellite and users. Index Terms Low Earth orbit (LEO), Rate-Splitting Multiple Access, multiuser beamforming, MIMO satellite communications, beamspace MIMO, angle division multiple access, 3D networks I. INTRODUCTION Mobile networks are currently evolving from being focused on low-altitude and ground-based devices towards three-dimensional (3D) networks. Incorporating air-and spaceborne terminals into the sixth generation (6G) of mobile networks is expected to lead to ubiquitous global connectivity, a reduced carbon footprint of information This article is presented in part at the 2023 International ITG 26th Workshop on Smart Antennas and 13th Conference on Systems, Communications, and Coding.
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
CDMA2000 for a satellite environment
2003
Abstroci-CDMA2000 is the American telecommunication standard for 3G. It is a wideband spread spectrum radio interface designed to provide high data rates and multimedia services to the wireless user. It has two modes of operation, 1X (DS-CDMA) and 3X (MC-CDMA). In this paper, we compare the forward link performance of the two modes for a satellite environment. In order to focus our comparison on the transmission technolugy (DS-CDMA, MC-CDMA), two services with similar data rates and the same coding scheme, are studied.
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.