It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

On the capacity of a cellular CDMA system

Contention resolution diversity slotted ALOHA (CRDSA) is a simple but effective improvement of slotted ALOHA. CRDSA relies on MAC bursts repetition and on interference cancellation (IC), achieving a peak throughput T ≅ 0.55, whereas for slotted ALOHA T ≅ 0.37. In this paper we show that the IC process of CRDSA can be conveniently described by a bipartite graph, establishing a bridge between the IC process and the iterative erasure decoding of graph-based codes. Exploiting this analogy, we show how a high throughput can be achieved by selecting variable burst repetition rates according to given probability distributions, leading to irregular graphs. A framework for the probability distribution optimization is provided. Based on that, we propose a novel scheme, named irregular repetition slotted ALOHA, that can achieve a throughput T ≅ 0.97 for large frames and near to T ≅ 0.8 in practical implementations, resulting in a gain of ~ 45% w.r.t. CRDSA. An analysis of the normalized efficiency is introduced, allowing performance comparisons under the constraint of equal average transmission power. Simulation results, including an IC mechanism described in the paper, substantiate the validity of the analysis and confirm the high efficiency of the proposed approach down to a signal-to-noise ratio as a low as Eb/N0=2 dB.

Graph-Based Analysis and Optimization of Contention Resolution Diversity Slotted ALOHA

Satellite communications (SatComs) have recently entered a period of renewed interest motivated by technological advances and nurtured through private investment and ventures. The present survey aims at capturing the state of the art in SatComs, while highlighting the most promising open research topics. Firstly, the main innovation drivers are motivated, such as new constellation types, on-board processing capabilities, non-terrestrial networks and space-based data collection/processing. Secondly, the most promising applications are described, i.e., 5G integration, space communications, Earth observation, aeronautical and maritime tracking and communication. Subsequently, an in-depth literature review is provided across five axes: i) system aspects, ii) air interface, iii) medium access, iv) networking, v) testbeds & prototyping. Finally, a number of future challenges and the respective open research topics are described.

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Satellite Communications in the New Space Era: A Survey and Future Challenges

Adaptive linear and decision feedback receiver structures for coherent demodulation in asynchronous code division multiple access (CDMA) systems are considered. It is assumed that the adaptive receiver has no knowledge of the signature waveforms and timing of other users. The receiver is trained by a known training sequence prior to data transmission and continuously adjusted by an adaptive algorithm during data transmission. The proposed linear receiver is as simple as a standard single-user detector receiver consisting of a matched filter with constant coefficients, but achieves essential advantages with respect to timing recovery, multiple access interference elimination, near/far effect, narrowband and frequency-selective fading interference suppression, and user privacy

Adaptive receiver structures for asynchronous CDMA systems

In this paper, a random access scheme is introduced which relies on the combination of packet erasure correcting codes and successive interference cancellation (SIC). The scheme is named coded slotted ALOHA. A bipartite graph representation of the SIC process, resembling iterative decoding of generalized low-density parity-check codes over the erasure channel, is exploited to optimize the selection probabilities of the component erasure correcting codes via density evolution analysis. The capacity (in packets per slot) of the scheme is then analyzed in the context of the collision channel without feedback. Moreover, a capacity bound is developed and component code distributions tightly approaching the bound are derived.

Coded Slotted ALOHA: A Graph-Based Method for Uncoordinated Multiple Access

A key requirement for the future multi-beam broadband satellite design is the provision of flexibility to adapt to different traffic demands by re-assigning capacity to beams in accordance with changing traffic distributions. Such flexibility would enable the best match to be maintained between the system resources and traffic demands over the satellite lifetime, thereby greatly enhancing the system utilisation and competitiveness. The current paper examines the use of beam hopping to provide such flexibility. It investigates the advantages of beam hopping and compares the performance and capacity capabilities of a beam hopped with that of equivalent non-hopped systems also designed to provide flexibility.

Beam hopping in multi-beam broadband satellite systems: System simulation and performance comparison with non-hopped systems

This paper describes the main aspects relevant to the development of a third-generation radio transmission technology (RTT) concept identified as satellite wide-band CDMA (SW-CDMA), which has been accepted by the International Telecommunications Union (ITU) as one of the possible RTTs for the satellite component of International Mobile Telecommunications-2000 (IMT-2000). The main outcomes of the extensive system engineering effort that has led to the above ITU RTT are described. In particular, we address propagation channel characteristics, satellite diversity, power control, pilot channel, code acquisition, digital modulation and spreading format, interference mitigation, and resource allocation. Due to its similarity with respect to the terrestrial W-CDMA proposal from which it is derived, the SW-CDMA open air interface solution is described briefly, with emphasis only on the major adaptation required to best cope with the satellite environment. Quantitative results concerning the physical-layer performance over realistic channel conditions, for both forward and reverse link, are reported. A system capacity study case for a low-Earth-orbit constellation is also provided.

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Wide-band CDMA for the UMTS/IMT-2000 satellite component

Summary
In this survey paper, we review the random access (RA) techniques with particular emphasis on the issues and the possible solutions applicable to satellite networks. RA dates back to the 1970s when the ALOHA protocol was developed to solve the problem of interconnecting university computers located in different Hawaiian islands. Since then, several evolutions of the ALOHA protocol have been developed. In particular, solutions were devised to mitigate the problem of packet collisions severely degrading the RA protocols performance. The approach followed for many years has been to avoid the occurrence of collisions rather than solving them. More recently, techniques tackling the RA packet collision problem have appeared triggered by the need of improving RA performance in satellite and terrestrial wireless networks. In particular, satellite networks large propagation delay does not allow the adoption of enhanced terrestrial RA techniques based on channel sensing. Adopting conventional demand assignment multiple access protocols is not suitable for supporting a large number of sensors or devices transmitting small-size low duty cycle packets as required for machine-to-machine communications. This provided the stimulus to exploit successive interference cancelation schemes to solve packet collision issues. The use of successive interference cancelation in RA is relatively new and has opened up a promising research area. We provide an extensive review of recent high-performance RA techniques achieving more than three orders of magnitude throughput increase compared with the original ALOHA at low packet loss rate. In this survey, we cover both slotted and unslotted techniques. Finally, we review the use of RA in satellite systems and related standards including recent proposals for machine-to-machine applications. Copyright © 2016 John Wiley & Sons, Ltd.

Random access schemes for satellite networks, from VSAT to M2M: a survey

Point-to-point multibeam satellite systems based on the DVB-S standard are currently designed for link closure in the worst-case propagation and location conditions The DVB-S standard, conceived for broadcasting applications, considers a fixed coding rate and modulation format that are selected according to the assumed coverage and availability requirements This approach implies the occurrence of high margins in the majority of the cases, when interference and propagation conditions allow for higher signal-to-noise-plus-interference ratio The adaptive coding and modulation (ACM) introduction in the new DVB-S2 standard for the interactive service profile opens up a number of appealing opportunities for the design and development of satellite broadband networks In this article we show how the ACM introduction in the satellite downlink enables greatly enhanced system performance but also has a profound impact on the way the system and some of the key system components are designed

Adaptive Coding and Modulation for the DVB-S2 Standard Interactive Applications: Capacity Assessment and Key System Issues

A key requirement for the future multi-beam broadband satellite design is the provision of flexibility to adapt to different traffic demands by re-assigning capacity to beams in accordance with changing traffic distributions. Such flexibility would enable the best match to be maintained between the system resources and traffic demands over the satellite lifetime, thereby greatly enhancing the system utilisation and competitiveness. The current paper examines the use of beam hopping to provide such flexibility. It investigates the advantages of beam hopping and compares the performance and capacity capabilities of a beam hopped with that of equivalent non-hopped systems also designed to provide flexibility. (8 pages)

Gennaro Gallinaro

Papers

Beam hopping in multi-beam broadband satellite systems: System simulation and performance comparison with non-hopped systems

Wide-band CDMA for the UMTS/IMT-2000 satellite component

Random access schemes for satellite networks, from VSAT to M2M: a survey

Adaptive Coding and Modulation for the DVB-S2 Standard Interactive Applications: Capacity Assessment and Key System Issues

Beam hopping in multi-beam broadband satellite systems