Spread ALOHA Research Articles

Is Satellite Ahead of Terrestrial in Deploying NOMA for Massive Machine-Type Communications?

Non-orthogonal multiple access (NOMA) technologies are considered key technologies for terrestrial 5G massive machine-type communications (mMTC) applications. It is less known that NOMA techniques were pioneered about ten years ago in the satellite domain to match the growing demand for mMTC services. This paper presents the key features of the first NOMA-based satellite network, presenting not only the underlying technical solutions and measured performance but also the related deployment over the Eutelsat satellite fleet. In particular, we describe the specific ground segment developments for the user terminals and the gateway station. It is shown that the developed solution, based on an Enhanced Spread ALOHA random access technique, achieves an unprecedented throughput, scalability and service cost and is well matched to several mMTC satellite use cases. The ongoing R&D lines covering both the ground segment capabilities enhancement and the extension to satellite on-board packet demodulation are also outlined. These pioneering NOMA satellite technology developments and in-the-field deployments open up the possibility of developing and exploiting 5G mMTC satellite- and terrestrial-based systems in a synergic and interoperable architecture.

Nonorthogonal CSK/SS ALOHA system under MANET environment

Spread ALOHA systems that combine the spread spectrum techniques with the ALOHA system (a simple random access protocol without carrier sensing function) have been investigated as Mobile Ad-hoc Network (MANET) protocols. This paper presents the effect of the nonorthogonal Code Shift Keying Spread Spectrum (CSK/SS) ALOHA system on improving the throughput and delay performances of the spread ALOHA system under the MANET environment. The nonorthogonal CSK/SS system, which uses systematically-constructed nonorthogonal sequences, is one of the multilevel modulation systems for the spread spectrum technique with increasing the number of bits per frame. Optimum parameters can be used to obtain the best system performance; thus, this paper gives analytical expressions of the data transmission efficiency and delay property of the proposed scheme as a function of the system parameters under the assumption of no power control. Numerical results show that the nonorthogonal CSK/SS ALOHA system is useful in the MANET environment, compared with the conventional spread ALOHA systems.

On the Optimum Packet Power Distribution for Spread Aloha Packet Detectors With Iterative Successive Interference Cancelation

Recent work has been stimulated by the need to enhance the satellite networks' Random Access (RA) performance. Results have shown that large performance improvement is possible by exploiting Iterative Successive Interference Cancelation (I-SIC) at the demodulator side. Coded spread spectrum Aloha (SSA) is a particularly suitable access technique for RA satellite networks due to its inherent asynchronous access nature and its high multiple access Achievable Sum Rate (ASR). Moreover, the adoption of I-SIC allows further boosting of the SSA sum rate and its robustness to the packet power unbalance. In this paper, we derive an analytical approach to the optimal packet power distribution that maximizes the performance of SSA RA exploiting I-SIC at the demodulator. The proposed approach takes into account the physical layer coding and modulation together with the number of demodulator iterations and the non-ideal cancelation effects. The analytical findings are successfully compared with the simulation and measurement results. Finally, a practical algorithm that approximates the optimum incoming power packet distribution in a realistic multi-beam satellite broadband network with open-loop power control is proposed and validated in a study case.

Enhanced spread Aloha physical layer design and performance

SUMMARYThis paper describes the key design and performance aspects of the Enhanced Spread Spectrum Aloha (E‐SSA) physical layer, which represents an essential component of the S‐band Mobile Interactive Multimedia European Telecommunication Institute standard. Thanks to advanced signal processing at the gateway side, the E‐SSA random access protocol allows to achieve unprecedented spectral efficiency in a pure asynchronous random access mode with high robustness against received packets power unbalance. The E‐SSA physical layer is closely derived from the Third Generation Partnership Wideband Code Division Multiple Access random access channel physical layer with some adaptation to best operate in the Land Mobile Satellite channels. Particular emphasis is devoted to the E‐SSA physical layer system design drivers as well to the packet transmission control policies, which are of high relevance for S‐band Mobile Interactive Multimedia. The demodulator architectural design is also illustrated jointly with some of the key detection performance. Finally, the E‐SSA random access protocol performance are reported for Additive White Gaussian Noise and satellite mobile channels. Copyright © 2014 John Wiley & Sons, Ltd.

Development of a CDMA intervehicle communications system for driving safety support

Driving safety support is one of the most attractive applications of an intervehicle communications system. Real-time and reliable packet exchange among vehicles is key to offering timely warnings to drivers in order to avoid fatal accidents. In this article we introduce multicarrier multicode spread Aloha (MM-SA) system, an intervehicle communications system developed to satisfy challenging requirements for supporting driving safety. MM-SA is based on code-division multiple access technology, and has inherent robustness to the increase of node density as well as the hidden terminal problem. We present an overview of MM-SA system including protocol design and prototyping as well as the GUI tool, which are all developed for avoiding intersection collisions. We also present performance comparison between the MM-SA system and a CSMA-based system under a realistic accident scenario. Our evaluation results show that the MM-SA system has superior performance to the CSMA-based system, and achieves the communication performance required for driving safety support.

Enhancing the Performance of Random Access Networks with Random Packet CDMA and Joint Detection

Random packet CDMA (RP-CDMA) is a recently proposed random transmission scheme which has been designed from the beginning as a cross-layer method to overcome the restrictive nature of the Aloha protocol. Herein, we more precisely model its performance and investigate throughput and network stability. In contrast to previous works, we adopt the spread Aloha model for header transmission, and the performance of different joint detection methods for the payload data is investigated. Furthermore, we introduce performance measures for multiple access systems based on the diagonal elements of a modified multipacket reception matrix, and show that our measures describe the upper limit of the vector of stable arrival rates for a finite number of users. Finally, we simulate queue sizes and throughput characteristics of RP-CDMA with various receiver structures and compare them to spread Aloha.

A novel random wireless packet multiple access method using CDMA

Random packet CDMA, a novel packet-based multiple access scheme for connectionless, uncoordinated random channel access is proposed. Random packet CDMA, or RP-CDMA, utilizes a novel packet format which consists of a short header and a data portion. Each header is spread with a unique spreading code which is identical for all users and packets, while the data portion of each packet is spread by a randomly chosen spreading sequence. The receiver operates in two stages: header detection and data detection. For header detection a conventional spread spectrum receiver is sufficient. Headers are spread with a large enough processing gain to allow detection even in severe interference. The data portion is decoded with a sophisticated receiver, such as a multiuser detector, which allows for successful decoding of overlapping active packets. It is shown that the RP-CDMA system is detector capability limited and that it can significantly outperform spread ALOHA systems whose performance is limited by the channel collision mechanism. RP-CDMA also experiences a much smaller packet retransmission rate than conventional or spread ALOHA, and provides better spectral efficiencies

Advances in ALOHA random multiple access techniques

Since the 1970s random multiple access techniques have made big progress and found a wide application in modern communication systems. In this paper we review the evolution of ALOHA random multiple access techniques: from pure ALOHA to Spread ALOHA. We introduce the principle of Spread ALOHA, investigate the relationship between spread-spectrum CDMA and Spread ALOHA, and discuss the prospective applications of Spread ALOHA. Copyright © 2000 John Wiley & Sons, Ltd.

Performance of slotted asynchronous CDMA using controlled time of arrival

A slotted asynchronous (SA) code-division multiple-access communication scheme controlling the time of arrival is proposed for distributed spread-spectrum packet radio networks where the transmission range is limited as in an indoor wireless system. In this scheme, each terminal can send its packet randomly at any one of N/sub w/, possible time instants, equally spaced over one period of direct-sequence spread-spectrum signals. Such transmissions initiated at different time instants can be resolved because of the high time resolution of wide-band signals if the channel delays associated with multipath are small due to limited transmission range. Quasi-synchronous distributed networks are considered to allow timing drift among terminals and also reflect wireless multiple-access channels, in which common-transmitter-based (C-T) and receiver-transmitter-based (R-T) spreading code assignments are adopted to permit a contention mode only for the header portion. The throughput is evaluated under the spread ALOHA assumption on collision events and also by reflecting the effect of the MAI in the header detection process. Theoretical results show that the combination of the SA scheme with C-T assignment results in more significant improvement than the case of R-T assignment, and also the former provides the benefit of the efficient usage of spreading codes in a code-limited environment.

Wideband random access for the last mile

Data network access options available today employ either some variant of a narrowband connectionless ALOHA channel or a connection-oriented network architecture ill suited to the traffic characteristics of many data applications. But first-generation ALOHA is difficult to implement in networks operating at more than a few lens of kilobits. When connectionless access with aggregate data rates in the megabits are required it is possible to combine conventional ALOHA with the wide-bandwidth operation of spread spectrum to provide the high data rates required for today's applications. This combination is called spread ALOHA multiple access (SAMA).

Transmit permission control on spread ALOHA packets in LEO satellite systems

A transmit permission control method for improving the throughput characteristics of a low Earth orbit (LEO) satellite communication system employing spread-slotted ALOHA multiple-access scheme is proposed. Both nonfading and fading satellite links are considered. The basic idea of the proposed scheme is to decrease the level of interference at each satellite and, hence, to increase the probability of packet success, by prohibiting the packet transmission from the users with relatively high propagation loss to their connecting satellites. It is shown that the method has the ability to improve the throughput performance in heavy traffic loads and the peak value of the throughput, significantly. It is also shown that the average delay performance of the system employing the proposed scheme is superior to that of the conventional system at heavy traffic loads.

Transmission efficiency of spread ALOHA system using unified spread‐spectrum code

AbstractThis paper considers the direct‐spread ALOHA system using the same spread‐spectrum code where the individual packet signals are separated using the time compression of the output signal from the matched filter in the demodulator. A method is shown to derive theoretically the transmission efficiency of the system and then the performance of the spread ALOHA system of the spread code length of seven chips is shown as an example. The transmission efficiency (channel traffic performance and the throughput) of the system is compared to that of the conventional slotted ALOHA system and discussed quantitatively. It is shown that the spread ALOHA system can realize a good performance with a low peak transmitted power.

Multiple access in wireless digital networks

General principles for the design of a multiple-access system for large numbers of terminals transmitting to a single hub station are discussed. The importance of understanding the nature of the traffic to be carried by the network is emphasized. After some discussion of multiple access options for steady traffic and for slowly varying traffic, the use of random-access protocols for rapidly varying traffic is explained. Two general random-access protocols have been used in a variety of data networks, ALOHA and CDMA. Although these two techniques have different origins and are generally thought of as separate, they are in fact but different ways of looking at the same basic signals. The author shows that the use of multiple spreading codes in a CDMA network is not necessary in order to achieve multiple access capability. A single code can greatly reduce the complexity of a CDMA system. He introduces a spread-spectrum version of an ALOHA channel (spread ALOHA) which is equivalent to a CDMA channel with a common spreading code for all users. The equivalence the author demonstrates opens the door to a variety of techniques commonly used in ALOHA channels which can significantly increase both the throughput and the efficiency of the spread-spectrum channel.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A rural messaging network using spread ALOHA access with VSAT satellite terminals

This paper underlines the characteristics of a proposed mesh network for messaging applications in C-band using spread ALOHA protocol. A simulation program has been developed for studying the behaviour of large networks employing ALOHA access or its variants. It is a simulation for a large population network consisting of thin traffic small messaging terminals (SMTs), and models an infinite user population which employs fixed length data packets. The program is general and allows for the study of either the mesh or the star connected networks. Certain variations of the classical ALOHA schemes, such as slotted ALOHA (with user selectable slot length) and spread ALOHA, have been studied for network operation. In the case of spread ALOHA access, the program can be run with Barker, pseudorandom, Ping Fai Li or any other spreading sequence. The results of the simulation have confirmed the utility of spread ALOHA as an access protocol for MESCOMNET. It has identified an operating point on the throughput-traffic curve at which spread advantage is available for power reduction of SMTs.

Fundamentals of packet multiple access for satellite networks

The fundamental objectives which guide the design of a packet multiple-access technique for satellite networks with large numbers of earth stations are explained. Among these objectives are low peak power in the transmitters, low average power from the satellite transponder, high channel capacity, and low complexity of the multiple-access receiver. The author reviews the fundamentals of satellite packet multiple access and relates these fundamentals to the objectives listed. Code division multiple-access (CDMA) and ALOHA multiple access are described in terms of these fundamentals. A simple linear transformation of conventional ALOHA access, called spread ALOHA, is described. For the case of a low signal-to-noise ratio in the receiver and a low duty cycle of individual and identical transmitters, it is not possible to find a multiple-access method at the same average power and are the same bandwidth which is more efficient than spread ALOHA. >

VSAT data networks

The use of satellite channels for very small-aperture terminal (VSAT) data networks such as spread spectrum and ALOHA is reviewed. Certain basic aspects of the architecture of VSAT data networks are discussed. Although spread spectrum and ALOHA have different origins and are sometimes represented as competing technologies, they can in fact be characterized as different ways of viewing the same low-dimensional signals in a high-dimensional signal space. After a brief introduction to the architecture of VSAT networks, it is shown how a simple linear transformation of conventional ALOHA packets called spread ALOHA leads to signals identical in all respects to the most common form of spread-spectrum signals. Two practical consequences of this theoretical result are discussed. First, for the case of small earth stations it is not possible to find an Access technique with a higher throughput than spread ALOHA. Second, the use of different spreading sequences for different users in a packet network using spread spectrum is not necessary for user separation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Low Cost VSAT Satellite Mesh Network and Proposed Transputer Realisation of Synchronisation Circuits

Spread ALOHA is an access scheme for use by VSATs in a Satellite Network. In this paper a link design for a mesh network using Satellite has been given. The need for synchronisation in the digital satellite communications is also discussed. The paper then gives an outline of a Software Locked Loop (SLL) for implementing the synchronisation and other baseband circuits for a Spread ALOHA access VSAT.