Soft-decision Viterbi decoding with diversity combining for multi-beam mobile satellite communication systems

A multi-beam mobile satellite communications system is proposed. This system has been investigated for maritime and land mobile satellite communications services. The dominant characteristics of the system are as follows: 1 S-band (2.6/2.5GHz) is adopted, which is the most favorable frequency band under 10GHz judging from propagation characteristics. 2 An optimized weight budget design method of satellite is proposed, maximizing channel capacity of system. 3 A new transponder configuration method is adopted, which is tolerant of traffic variation.

We calculate the availability of circuit service to a user in a mobile satellite communication system. The availability, i.e., the percentage of time the user can expect to communicate reliably using the communication system is a function of the power available to the user and the channel (Rician or Rayleigh fading) encountered by the user. In a mobile satellite communication system, the channel is a function of user position, the number of satellites visible to the user, and their positions. Using a simulation of the constellation orbits and an associated channel model, we calculate the availability provided by various proposed mobile satellite communication systems that use LEO and MEO satellites. A conclusion of this paper is that the visibility of multiple satellites is imperative for high availability.

In order to realize a higher-code-gain forward error correction scheme in mobile satellite communication systems, a novel concatenated coding scheme employing soft decision decoding for not only inner codes but also outer codes (double soft decision, or DSD, concatenated forward error correction scheme) is proposed. Soft-decision outer decoding can improve the bit error probability of inner decoded data. In this scheme, likelihood information from an inner Viterbi decoder is used in the decoding of outer codes. A technique using the path memory circuit status 1.0 ratio for likelihood information is proposed, and is shown to be the most reliable even though it requires the simplest hardware among the alternative methods. A computer simulation clarifies that the DSD scheme improves Pe performance to one-third of that of the conventional hard-decision outer decoding. Moreover, to reduce the interleaving delay time in fading channels or inner decoded data of concatenated codes, a parallel forward error correction scheme is proposed. >

Based on the characteristic that received signals of different beam cells are sent to the same gateway station in the multi-beam satellite system, this paper introduces a technique of multi-beam joint detection combination for TD-SCDMA compatible mobile satellite communication system. The proposed technique adopts Adjacent Beam Assisted Single-beam Joint Detection (ABA-SB-JD) technique to get the detection signals of users in each target-beam cell and adjacent beam cells from the interference signals of users in adjacent beam cells, and detects the signal of the same user in each beam cell according to the maximal ratio combining principle. The simulation results show that this technique gets a good system bit-error rate performance, significantly reduces the SNR threshold of the system, and greatly improves multi-user detection performance of the multi-beam satellite communication system.

In this paper, we describe the development of a GSM-derived regional mobile satellite communication system. We first discuss the market needs of a regional mobile communication system, and stress the technical requirements for such a system to be successful in the commercial world. We then point out the advantages of deriving such a system from the popular GSM standard and discuss the similarities and differences between the two systems. We then describe a system designed by Lockheed Martin Corp., known as ACeS, which serves the telecommunication needs of Asia. The ACeS system works in both the cellular and satellite environments and is designed to make optimal use of the similarities and differences to the GSM system. We end the paper by discussing some challenges in the evolving area of mobile satellite communication systems.

Multi-beam satellite communication systems can improve the resource utilization and system capacity effectively. However, the inter-beam interference, especially for the satellite system with full frequency reuse, will degrade the system performance greatly due to the characteristics of multi-beam satellite antennas. In this article, the user scheduling and resource allocation of a multi-beam satellite system with full frequency reuse are jointly studied, in which all beams can use the full bandwidth. With the strong inter-beam interference, we aim to minimize the system latency experienced by the users during the process of data downloading. To solve this problem, deep reinforcement learning is used to schedule users and allocate bandwidth and power resources to mitigate the inter-beam interference. The simulation results are compared with other reference algorithms to verify the effectiveness of the proposed algorithm.

IntroductionThe popularity of mobile communication systems has increased remarkably during the last decade and the market demand still continues to increase.As a fundamental part of these systems, antenna is one of the most important design issues in modern mobile communication units.Although there are several similar definitions, an antenna can be mainly described as a device, which transforms the electromagnetic waves in an antenna to radiating waves in an unbounded medium such as air in transmitting mode and vice versa in receiving mode.Because antennas are dependent on frequency, they are designed to operate for certain frequency bands.The rapid growth of mobile communication systems has forced to the use of novel antennas for base and mobile station applications (mobile phone, notebook computer, personal digital assistants (PDA), etc.).Earlier, mobile systems were designed to operate for one of the frequency bands of 2G (second generation) systems, which are Digital Cellular System (DCS), Personal Communications Service (PCS) and Global System for Mobile Communications (GSM) networks.Currently, many mobile communication systems use several frequency bands such as GSM 900/1800/1900 bands (890-960 MHz and 1710-1990 MHz); Universal Mobile Telecommunication Systems (UMTS) and UMTS 3G expansion bands (1900-2200 MHz and 2500-2700 MHz); and Wi-Fi (Wireless Fidelity)/Wireless Local Area Networks (WLAN) bands (2400-2500 MHz and 5100-5800 MHz) where the list of frequently used frequency bands is given in Table 1 ( Best, 2008).Conventionally, because a single antenna can not operate at all of these frequency bands of mobile communication, multiple different antennas covering these bands separately should be used.However, usage of many antennas is usually limited by the volume and cost constraints of the applications.Therefore, multiband and wideband antennas are essential to provide multifunctional operations for mobile communication.A multiband antenna in a mobile communication system can be defined as the antenna operating at distinct frequency bands, but not at the intermediate frequencies between bands.For example, a triple band antenna for GSM 900/1800/1900 bands can cover the frequency bands 890-960 MHz and 1710-1990 MHz (Ali et al., 2003); however, it does not operate properly at the frequencies such as 1200 MHz or 2500 MHz.On the other hand, a wideband antenna operates at every frequency points within a given frequency band.For example, a wideband antenna covering UMTS, extended UMTS and WLAN 2400 bands functions at every frequency points www.intechopen.com

In this paper we investigate the effect of an adaptive fuzzy closed-loop power control (CLPC) scheme on the performance of the DS/CDMA-based mobile satellite communication systems with a low earth orbit (LEO) satellite constellation in which the long round trip delay (RTD) and fading effect according to elevation angle should be considered. Since the RTD between mobile terminals (MT) and earth station (ES) via satellite in LEO is on the order of 10-20 ns and fading is more severe, a conventional closed-loop power control with fixed step size is much less effective than it is on a terrestrial channel. In order to cope with this performance degradation, we propose a closed-loop power control scheme by adaptive fuzzy rule-based step size decision method which is based on fuzzy logic control (FLC). So, in this paper, we compare the performance of the adaptive fuzzy closed-loop power control with that of the conventional fixed step closed-loop power control, we show that the proposed method makes better performance.

[Abstract] This paper proposes dynamic bandwidth/channel access technique using FFT based block signal transmission for future broadband mobile satellite communication systems, which is to supplement next generation terrestrial mobile networks. One of the key issues for next generation mobile satellite communication systems is flexible and scalable access technique in terms of data rate and traffic type, to accommodate various satellite users. OFDMA is a technique to meet the above-mentioned requirements, however it needs large output backoff at HPA. To solve this problem, this paper proposes a new bandwidth/channel access technique using FFT based block signal transmission. The proposed technique uses single carrier modulation suitable for small output backoff operation in HPA, keeping flexibility and scalability as OFDMA has. This paper describes basic principle of the proposed dynamic bandwidth/channel access technique and preliminary performance evaluation results by computer simulation.

Two models for nonstationary traffic analysis of mobile satellite communications systems are developed. First, a cell associated with a satellite footprint is modeled as the M/M/c/c loss system. The corresponding birth-and-death equations yield a differential equation for the system state dynamic evolution in time. Examining the channel holding times distribution in more detail shows that its exponential feature is very doubtful. A more general model following the M/G/c/c system is proposed. In order to match the mean and variance of the actual service time we adopt a method of stages consisting in decomposing the service time distribution into a collection of distributions provided by exponential servers in series. Both proposed models are validated by means of extensive simulations.

The key technical elements in designing digital mobile satellite communication systems are identified, and tradeoff studies on the transmission parameters of the satellite link, which were based on experience with an experimental system and the results of field trials, on digital maritime and aeronautical satellite communication systems, are described. The future evolution of the various new communication services to be offered in the digital mobile communication systems are discussed. In the digital mobile satellite communication systems which will be operated under the condition of low C/N and with a signal-level fluctuation due to multipath fading etc., it has been found that the most important requirement is to establish the frame synchronization quickly and maintain it stably in addition to the stable carrier/clock tracking, under this severe link condition. >

In order to increase the capacity and to suppress co-channel interference in digital communication systems such as mobile cellular and mobile satellite communication systems, the employment of array beamforming techniques has been proposed. However, conventional beamforming methods are not suitable for such cases since these methods were mainly developed for signal detection and direction-of-arrival (DOA) estimation in radar and sonar. In this paper, utilizing the cyclostationary properties of communication signals, we propose three blind cyclic adaptive beamforming (CAB) algorithms and their fast implementation schemes. Several numerical examples are included. These results demonstrate that the CAB algorithms are good candidates for spatial reuse of frequency spectrum in digital mobile communication systems of the next generation.

The subject of research in this article is the process of building a mobile communication system that operates under electronic countermeasures. The aim is to develop recommendations for building a wireless mobile communication system that operates effectively in a complex interfering electromagnetic environment. The strategy for building a mobile wireless communication system is based on the use of a grouping of low-altitude UAVs with ultra-wideband signal technology circulating in control and communication channels, with the integration of artificial intelligence elements into its structure. The objective of this study is to ensure the stable and secure operation of a wireless mobile communication system despite electronic countermeasures. The methods of analytical, temporal positional pulse coding, and fuzzy logical inference were used to make decisions on the transfer of service in the network. The following results were obtained. A strategy for building a wireless mobile communication system despite electronic countermeasures has been developed. It is shown that in order to obtain high noise immunity of control and communication channels and to protect information from interception, wireless ultra-wideband communication technology should be used. This will provide large volumes and speeds of information transmission. A technical solution for the design of an ultra-wideband transceiver antenna system is proposed. Moreover, it is recommended to use the results of data processing in a fuzzy decision-making system for the transfer of service between mobile network nodes in conditions of interference. Conclusions. The scientific novelty of the obtained results is as follows. The use of ultra-wideband channels makes it possible to increase the number of control and communication channels in a wireless mobile system almost unlimitedly. The preliminary distribution of orthogonal codes between the channels realizes the process of control and communication without the interception of information and mutual interference. The use of the time-position-pulse coding method prevents the occurrence of intercharacter distortions of the encoding ultrashort pulses. This also reduces the level of distortion of information signals caused by multipath propagation, which guarantees the security of information in the system. The use of a fuzzy decision-making system for the transfer of services between mobile network nodes allows dynamically changing the network topology in real time and maintaining high quality of service under electronic countermeasures.

This paper addresses coding and modulation techniques for handheld mobile satellite communication systems such as ICO, Iridium, and ACeS. The design of modulation and coding for such systems is different than terrestrial systems, and usually different from satellite systems used in fixed services. The differences are due to the fact that traffic channels in mobile satellite systems have to operate in Rician fading channels with typical Rician factors between 7 dB and 14 dB; the control channels for these systems have to operate reliably in a slow Raleigh fading environment. Results on coherent detection for QPSK and GMSK are presented, and a robust error control coding approach is presented and evaluated.

This paper presents a new study in an attempt to apply Fast Euclidean Direction Search (FEDS) algorithm on adaptive smart antennas. The novelty in this work is the use of FEDS algorithm in a smart antenna system for mobile communications because up to our knowledge this algorithm is not applied on smart antenna so far. In order to properly evaluate the performance of smart antenna for mobile communication systems, an Additive White Gaussian Noise (AWGN) channel model is required that each received signal at each element in the array includes only an additive, zero mean, Gaussian noise . The ability of the FEDS algorithm to operate in a fast changing signal environment is examined by subjecting the input signal to Rayleigh fading with a Jakes power spectral density which is a popular choice for land mobile communications systems. Through simulation results of smart antennas for AWGN channel, the RLS and FEDS start to converge from the initial iteration and 10 respectively, whereas, the LMS and NLMS start to converge after 50 and 10 iterations respectively. In the presence of the Rayleigh fading channel, the LMS, and NLMS algorithms converge after 60 and 25 iterations respectively, while the RLS convergence from the initial iteration and FEDS converge from the iteration number 25. On the other hands, the FEDS algorithm shows better tracking and estimation of the desired input signal compared with both LMS and NLMS algorithms and comparable with RLS algorithm. The comparison of linear plot of array factor using FEDS and RLS , both algorithms generates the same deeper null for undesired signals of about í30 dB towards the interferer using an AWGN channel, while it generates deeper null of about -23 dB and -30 dB respectively using the Rayleigh fading channel.