Contention Resolution Diversity Slotted ALOHA Research Articles

Coherent Contention Resolution Diversity Slotted ALOHA: An Improved Multiple Access Method for Satellite IoT System

For Beyond 5G/6G system, satellite communication systems become an effective component of the space and terrestrial integrated network. Among typical applications, massive Machine Type of Communication (mMTC) is a promising and challenging application. The demands of low power consumption and light signaling make random access methods as the potential solution. Up to now, contention resolution-based ALOHA methods, such as contention resolution diversity slotted ALOHA (CRDSA), improve the throughput significantly. However, its throughput will meet the inflection point soon with the normalized load increasing since collisionless packets are hardly existing. In fact, the diversity of transmitting packets is not utilized totally. In this paper, an improved random access method, named coherent CRDSA method (C-CRDSA), is proposed. It accumulates replicated packets coherently at receiver and further improve the throughput over CRDSA. Detailed derivations and simulations are given. Simulation results corroborate the effectiveness of the proposed method.

Energy-Constrained Design of Joint NOMA-Diversity Schemes with Imperfect Interference Cancellation.

This study proposes a set of novel random access protocols combining Packet Repetition (PR) schemes, such as Contention Resolution Diversity Slotted Aloha (CRDSA) and Irregular Repetition SA (IRSA), with Non Orthogonal Multiple Access (NOMA). Differently from previous NOMA/CRDSA and NOMA/IRSA proposals, this work analytically derives the energy levels considering two realistic elements: the residual interference due to imperfect Interference Cancellation (IC), and the presence of requirements on the power spent for the transmission. More precisely, the energy-limited scenario is based on the relationship between the average available energy and the selected code modulation pair, thus being of specific interest for the implementation of the Internet of Things (IoT) technology in forthcoming fifth-generation (5G) systems. Moreover, a theoretical model based on the density evolution method is developed and numerically validated by extensive simulations to evaluate the limiting throughput and to explore the actual performance of different NOMA/PR schemes in energy-constrained scenarios.

An Intelligent Load Control-Based Random Access Scheme for Space-Based Internet of Things.

Random access is one of the most competitive multiple access schemes for future space-based Internet of Things (S-IoT) due to its support for massive connections and grant-free transmission, as well as its ease of implementation. However, firstly, existing random access schemes are highly sensitive to load: once the load exceeds a certain critical value, the throughput will drop sharply due to the increased probability of data collision. Moreover, due to variable satellite coverage and bursty traffic, the network load of S-IoT changes dynamically; therefore, when existing random access schemes are applied directly to the S-IoT environment, the actual throughput is far below the theoretical maximum. Accordingly, this paper proposes an intelligent load control-based random access scheme based on CRDSA++, which is an enhanced version of the contention resolution diversity slotted ALOHA (CRDSA) and extends the CRDSA concept to more than two replicas. The proposed scheme is dubbed load control-based three-replica contention resolution diversity slotted ALOHA (LC-CRDSA3). LC-CRDSA3 actively controls network load. When the load threatens to exceed the critical value, only certain nodes are allowed to send data, and the load is controlled to be near the critical value, thereby effectively improving the throughput. In order to accurately carry out load control, we innovatively propose a maximum likelihood estimation (MLE)-based load estimation algorithm, which estimates the load value of each received frame by making full use of the number of time slots in different states. On this basis, LC-CRDSA3 adopts computational intelligence-based time series forecasting technology to predict the load values of future frames using the historical load values. We evaluated the performance of LC-CRDSA3 through a series of simulation experiments and compared it with CRDSA++. Our experimental results demonstrate that in S-IoT contexts where the load changes dynamically, LC-CRDSA3 can obtain network throughput that is close to the theoretical maximum across a wide load range through accurate load control.

Complexity analysis for recent ALOHA random access techniques in satellite communications

SummaryIn this paper, we study the the complexity of packet localization at reception, for recent synchronous Random Access (RA) techniques based on the protocol ALOHA for satellite communications. The promising CRDSA (Contention Resolution Diversity Slotted ALOHA) offers better throughput, in comparison to the traditional slotted ALOHA protocols, thanks to the use of Successive Interference Cancellation (SIC) along with multireplica transmission. MARSALA (Multi‐replicA decoding using corRelation baSed locALizAtion) is one of the many variants and enhancement schemes of CRDSA that have been proposed in the literature. It is applied to CRDSA each time a decoding deadlock situation is reached (when no packets can be retrieved by CRDSA). MARSALA first localizes the replicas of collided packets on a chosen reference time slot using correlations. Then it performs coherent signal combination of packet replicas prior to decoding. However, despite the good performance offered by MARSALA, its localization process adds a significant complexity to the receiver in terms of correlation operations. R‐SPOTiT (Random Shared POsition Technique for Interfered random Transmissions) mitigates this complexity by introducing a shared information between the receiver and each of the transmitters, about all potential packets' locations on the frame, without any additional signaling overhead. We focus in this paper on the analysis of the total number of correlations which are needed to localize packets' replicas for both MARSALA and R‐SPOTiT, with a single or with multiple Gold preambles. This should include preamble detection operations that are performed at CRDSA with a coarse and fine tracking. The results show that the most suitable system to use is the multi‐preamble R‐SPOTiT with two preambles.

Nanosatellite-5G Integration in the Millimeter Wave Domain: A Full Top-Down Approach

This paper presents a novel network architecture for an integrated nanosatellite (nSAT)-5G system operating in the millimeter-wave (mmWave) domain. The architecture is realized adopting a delay/disruption tolerant networking (DTN) approach allowing end users to adopt standard devices. A buffer aware contact graph routing algorithm is designed to account for the buffer occupancy of the nSATs and for the connection planning derived from their visibility periods. At the terrestrial uplink, a coded random access is employed to realize a high-capacity interface for the typically irregular traffic of 5G users, while, at the space uplink, the DTN architecture is combined with the contention resolution diversity slotted Aloha protocol to match the recent update of the DVB-RCS2 standard. To achieve a reliable testing of the introduced functionalities, an accurate analysis of the statistic of the signal to interference-plus-noise ratio and of the capture probability at each mmWave link is developed by including interference, shadowing, fading, and noise. The application of the designed architecture to data transfer services in conjunction with possible delay reduction strategies, and an extension to inter-satellite communication, are finally presented by estimating the resulting loss/delay performance through a discrete-time discrete-event platform based on the integration of Matlab with Network Simulator 3.

A Novel Random Access Algorithm for Very High Frequency Data Exchange (VDE)

VHF Data Exchange System (VDES) is considered as an important component of the future maritime communication system by the International Maritime Organization (IMO). On the basis of the existing Automatic Identification System (AIS), VDES adds the other two higher capacity subsystems: Application Specific Message (ASM) and VHF Data Exchange (VDE). The Random Access Channel (RACH) of VDE was first introduced in the International Telecommunication Union (ITU) Recommendation M.2092-0. As the slot planning principle of RACH in VDE is by interval, which is significantly different from the continuous slot map for access algorithms in AIS, the existing slot access algorithms cannot meet the requirements of VDE. The simulation results show that the VDE slot map can reduce the normalized throughput of the existing algorithm by 39%. A novel random access algorithm called Adaptive Traffic Load Contention Resolution Diversity Slotted ALOHA (ATL-CRDSA) is proposed in this paper. The algorithm combines the load control strategy and contention resolution scheme to overcome the challenges of the new RACH of VDE. Simulation results show that ATL-CRDSA has remarkable improvement on RACH, making it very efficient and providing low latency of the packets. The insights gained from this study may be of assistance to the Media Access Control (MAC) layer design for upcoming versions of VDES standard.

Randomly Pre-Coded Packets Based Random Access Scheme for IoT-Oriented Satellite Networks

In this article, a novel random pre-coding (RPC) based random access (RA) scheme is proposed to improve the system performance in the Internet of Things-oriented satellite networks. In this scheme, each device randomly selects a non-orthogonal multi-level complex sequence from a pre-defined pre-coding sequence set to pre-code the transmitted packets in a sub-frame, by which multiple superimposed packets in the sub-frame can be successfully decoded by using the minimum mean squared error (MMSE) based successive interference cancellation (SIC) detection algorithm. Besides, by combining the proposed RPC with the existing contention resolution diversity slotted ALOHA (CRDSA) scheme, which the RPC-CRDSA scheme is generated. The SIC processing should be carried out across sub-frames to remove the received signals that are already recovered, which can further significantly improve the system throughput. The performance of the RPC-RA scheme is evaluated via both theoretical analysis and computer simulation. The collision probabilities of both preamble and pre-coding sequences and an upper bound of throughput are derived, respectively. Simulation results show that the peak normalized throughput of RPC-CRDSA with the pre-coding sequence length $L = 8$ can reach 1.87 bits/symbol, which largely outperforms traditional schemes.

Irregular Repetition Slotted ALOHA With Energy Harvesting Nodes

We propose an irregular repetition slotted ALOHA (IRSA) based uncoordinated random access scheme for energy harvesting (EH) nodes. Specifically, we consider the case in which each user has a battery that is recharged with harvested energy from the environment in a probabilistic manner. We analyze this scheme starting with a unit-sized battery at the nodes and extend the analysis to the case of a finite-sized battery. For both scenarios, we derive the asymptotic throughput expressions and obtain the optimized probability distributions for the number of packet replicas of the users. We demonstrate that for the case of IRSA with EH nodes, these optimized distributions perform considerably better than the alternatives, including slotted ALOHA (SA), contention resolution diversity slotted ALOHA (CRDSA), and IRSA, which do not take into account the EH process for both asymptotic and finite frame length scenarios.

Multisatellite Cooperative Random Access Scheme in Low Earth Orbit Satellite Networks

Multisatellite cooperative random access (MSC-RA) scheme is proposed in low earth orbit (LEO) satellite networks. In the scheme, a packet structure based on single carrier interleaved frequency division multiple access (SC-IFDMA) is designed to overcome the effect of users’ propagation delays on the received signals at satellite nodes, which ensures the synchronization of received signals. The transmission model from multiple terminals to multiple satellite nodes in a slot can be equivalent to a virtual multi-input multioutput model, and MSC detection is employed to decode multiple collided packets. The MSC detection can be applied to slotted ALOHA (SA), contention resolution diversity slotted ALOHA (CRDSA), CRDSA-3, and irregular repetition slotted ALOHA (IRSA) protocols, which are dubbed MSC-SA, MSC-CRDSA, MSC-CRDSA-3, and MSC-IRSA, respectively. At the gateway station, the MSC detection and iterative interference cancellation processing are alternately conducted for multiple collided packets at satellite nodes. The performance of these MSC-RA schemes is evaluated via mathematical analysis and computer simulation in terms of throughput, stability and energy efficiency. Simulation results show that MSC-SA, MSC-CRDSA, MSC-CRDSA-3, and MSC-IRSA schemes significantly outperform conventional ones, and the MSC-CRDSA scheme is superior to MSC-SA, MSC-CRDSA-3 and MSC-IRSA schemes.

Random Pattern Multiplexing for Random Access in IoT-Oriented Satellite Networks

In this paper, random pattern multiplexing (RPM) for random access (RA) is proposed to improve the throughput in Internet of Things-oriented satellite networks. The pattern is defined as the mapping scheme of packet onto a resource block (RB) that consists of multiple resource elements (REs). The patterns are randomly selected by active satellite machine-type-communication terminals (SMTs) from a set of available patterns, and are employed to differentiate signals of different SMTs sharing a RB. Message passing detection algorithm is employed to decode multiple superimposed packets, which enables multiple packet reception capability in the RA scheme. The proposed RPM can be combined with contention resolution diversity slotted ALOHA (CRDSA), which generates RPM–CRDSA protocol. In this protocol, the interference cancellation technique can be carried out across RBs to remove the received signals that are already decoded, which further improves the throughput. The performance of RPM–CRDSA is evaluated via mathematical analysis and computer simulation. The probability of preamble collision and an upper bound of throughput are derived, respectively. Simulation results show that the peak normalized throughput of RPM–CRDSA with $N = 4$ REs can reach 2.03 b/symbol, which largely outperforms traditional protocols.

임의 접속 위성망의 CRDSA 성능 향상을 위한 NOMA 응용

CRDSA (Contention Resolution Diversity Slotted ALOHA) 기술의 등장은 위성 네트워크 환경에서 임의 접속기법을 사용자 트래픽 전송에 사용하는 계기를 마련해주었다. 이후 많은 연구에서 CRDSA의 성능을 향상시키기 위한 연구가 계속 되었다. 하지만, 현재까지의 CRDSA 성능 향상을 위한 기술들은 복제 패킷의 개수를 늘리는 형태를 사용하기 때문에 CRDSA 보다 패킷 전송율은 향상되지만 복제 패킷 수량 증가로 인해 전력 효율이 감소한다. 위성 단말들이 소형, 이동형으로 개발되면서 효율적인 임의접속 기술은 매우 중요하다. 본 논문에서는 전력 효율을 CRDSA와 동일하게 유지하면서 패킷 전송율을 향상시키기 위해 NOMA (Non-Orthogonal Multiple Access) 기술을 CRDSA에 적용할 것을 제안한다. 위성 네트워크에 NOMA를 적용하기 위한 방안을 제시하고, NOMA-CRDSA의 성능을 모의실험을 통해 확인한다.

Exploiting capture and interference cancellation for uplink random multiple access in 5G millimeter-wave networks

The forthcoming 5G technology aims to provide massive device connectivity and ultra-high capacity with reduced latency and costs. These features will be enabled by increasing the density of the base stations, using millimeter-wave (mmWave) bands, massive multiple-input multiple-output systems, and non-orthogonal multiple access techniques. The ability to support a large number of terminals in a small area is in fact a great challenge to guarantee massive access. In this context, this paper proposes a new receiver model for the uplink of 5G mmWave cellular networks. The receiver, called Iterative Decoding and Interference Cancellation (IDIC), is based on the Slotted Aloha (SA) protocol and exploits the capture effect alongside the successive IC process to resolve packet collisions. A 5G propagation scenario, modeled according to recent mmWave channel measurements, is used to compare IDIC with the widely adopted Contention Resolution Diversity SA (CRDSA) scheme to show the performance gain of IDIC, when elements of practical relevance, like imperfect cancellation and receive power diversity, are considered. The impact of packet and power diversity is also investigated to derive the preferable uplink random access strategy that maximizes the system throughput according to the offered channel load.

TCP-Based M2M Traffic via Random-Access Satellite Links: Throughput Estimation

Machine-to-machine services are witnessing an unprecedented diffusion, which is expected to result in an ever-increasing data traffic load. In this context, satellite technology is playing a pivotal role, since it enables a widespread provisioning of machine-to-machine services. In particular, oil industry, maritime communications, as well as remote monitoring are sectors where the use of satellite communications is expected to dramatically explode within the next few years. In the light of this sudden increase of machine-to-machine data transported over satellite, a more thorough understanding of machine-to-machine service implementation over satellite is required, especially focusing on the interaction between transport and MAC layers of the protocol stack. Starting from these observations, this paper thoroughly analyses the interaction between TCP and the Contention Resolution Diversity Slotted Aloha access scheme defined in the DVB-RCS2 standard, assuming the use of an MQTT-like protocol to distribute machine-to-machine services. A novel TCP model is developed and validated through extensive simulation campaigns, which also shed important lights on the design choices enabling the efficient transport of machine-to-machine data via satellite.

Pre-Weighting Based Contention Resolution Diversity Slotted ALOHA Scheme for Geostationary Earth Orbit Satellite Networks

Pre-Weighting Based Contention Resolution Diversity Slotted ALOHA Scheme for Geostationary Earth Orbit Satellite Networks

Enhancing CRDSA With Transmit Power Diversity for Machine-Type Communication

Contention resolution diversity slotted ALOHA (CRDSA) is a promising solution to meet the challenge of designing efficient random access in future wireless networks. In this paper, we consider CRDSA with transmit power diversity where each packet copy from a device is transmitted at a randomly selected power level. This results in interslot received power diversity, which is exploited by employing a signal-to-interference-plus-noise ratio based successive interference cancellation (SIC) receiver. Leveraging edge-weighted bipartite graph representation, we propose a novel graph-based message passing algorithm to model the SIC decoding. We derive an expression to characterize the recovery-error probability of the scheme. We also formulate and solve an optimization problem to determine the optimal transmit power distribution. The results show that by enhancing the capture effect, the optimal transmit power distribution leads to considerable performance improvement.

On the Modeling and Performance Assessment of Random Access With SIC

In this paper, we review the key figures of merit to assess the performance of advanced random access (RA) schemes exploiting physical layer coding, repetitions, and collision resolution techniques. We then investigate RA modeling aspects and their impact on the figures of merit for the exemplary advanced RA schemes: contention resolution diversity slotted ALOHA (CRDSA), irregular repetition slotted ALOHA (IRSA), coded slotted ALOHA (CSA) and enhanced spread-spectrum ALOHA (E-SSA). We show that the typical simplifications of the reception model when used to optimize RA schemes lead to inaccurate findings, both in terms of parameter optimization and figures of merit, such as the packet loss ratio (PLR) and throughput. We also derive a generic RA energy efficiency model able to compare the schemes in terms of the energy required to transmit a packet. The combination of achievable RA throughput at the target PLR and energy efficiency, for the same average user power investment per frame and occupied bandwidth, shows that E-SSA, which is an unslotted scheme, provides the best overall performance, while, in terms of the slotted schemes, CRDSA outperforms the more elaborated IRSA and CSA. This surprising results are due to the fact that the IRSA and CSA optimization has so far been performed using RA channel models that are not accurately reflecting the physical layer receiver behavior. We conclude by providing insights on how to include more accurate reception models in the IRSA and CSA design and optimization.

Enhancing the Physical Layer of Contention Resolution Diversity Slotted ALOHA

There is an urgent need for substantially enhancing random access schemes to be able to support native massive machine-to-machine communications in the next generation wireless systems. Lately, contention resolution diversity slotted ALOHA (CRDSA) and its variants have contributed to a drastic improvement in throughput compared with the traditional slotted ALOHA protocols. In this paper, we further enhance the CRDSA flexibility and performance along different physical layer dimensions. Based on simulation results, we show that there is still room for improvement in terms of throughput and, using heuristic methods, we find an optimized distribution of the packets power that is entering the demodulator for an additive white Gaussian noise channel. Applying this power distribution, which is easy to implement at the terminal in open loop and in a decentralized manner, is shown to achieve significantly enhanced performance. By introducing multi-frequency CRDSA, a drastic reduction in the terminal’s peak power requirement is attained. Furthermore, we investigate spread spectrum CRDSA, which improves the robustness of the scheme against irresolvable packet collisions allowing for enhanced energy efficiency. To support the work presented herein, we have developed a computationally efficient yet accurate methodology for estimating CRDSA performance, a novel approximate centrally coordinated CRDSA achievable sum rate analysis accounting for modulation and forward error correction constraints, as well as a more accurate loop probability analysis.

Polarized MIMO Slotted ALOHA Random Access Scheme in Satellite Network

The massive number of the machine type communication terminals accessing the satellite network brings a new challenge for the random access (RA) system. To meet the challenge, by using the polarization transmission structure in the satellite uplink, we propose a new RA scheme dubbed polarized multiple input multiple output slotted ALOHA (PMSA). In PMSA, in one slot, one packet and two overlapped packets can be decoded successfully with the polarized MIMO detection algorithms, and some of three overlapped packets may be decoded successfully in consideration of the capture effect at the satellite node. For the new features of the proposed scheme in physical layer, the protocol of medium access control (MAC) is modified based on the slotted ALOHA (SA). Simulation results show that the normalized throughput of the PMSA can reach 0.84 and is consistent with the theoretical throughput. Moreover, it is also shown that the throughput of PMSA is about 2.3 times as large as that of the SA and 1.5 times as large as that of the contention resolution diversity slotted ALOHA (CRDSA), without the need for additional transmitted power and time slots to transmit the replicas of the packets. The received packets in the proposed PMSA are processed slot by slot, not as that processed frame by frame in the CRDSA with a large additional frame delay.

위성 채널에서 데이터 트래픽의 신속한 전송을 위한 다중 슬롯 예약 기법

In this paper, we propose a multiple slot reservation scheme to transmit data rapidly in the satellite random access channel. In the R-CRDSA (Reservation scheme with Contention Resolution Diversity Slotted ALOHA), each satellite terminal can use only one slot in a frame. Therefore, many slots are wasting in the low traffic load and the satellite terminals which have large date needs many frame to transmit their data although there are unused slots. In the multiple slot reservation scheme, each satellite terminal transmits a packet with their data size and reserves many slots in the light of data size and slot reservation status. Therefore, each satellite terminal transmits their data faster than R-CRDSA. This is because they can reserve many slots in a frame. Furthermore, we simulate proposed scheme and validate the performance of proposed scheme.

Asynchronous Contention Resolution Diversity ALOHA: Making CRDSA Truly Asynchronous

Following the introduction of contention resolution diversity slotted ALOHA (CRDSA), a number of variants of the scheme have been proposed in literature. A major drawback of these slotted random access (RA) schemes is related to the need to keep slot synchronization among all transmitters. The volume of signaling generated to maintain transmitters' slot synchronization is impractical for large networks. In this paper, we describe in detail asynchronous contention resolution diversity ALOHA (ACRDA), which represents the evolution of the CRDSA RA scheme. ACRDA provides better throughput performance with reduced demodulator complexity and lower transmission latency than its predecessor while allowing truly asynchronous access to the shared medium. The performance of the ACRDA protocol is evaluated via mathematical analysis and computer simulations and is compared with that of CRDSA.