ALOHA Scheme Research Articles

Irregular Repetition Slotted ALOHA Scheme With Short Packets Under Rayleigh Fading Channels

Irregular Repetition Slotted ALOHA Scheme With Short Packets Under Rayleigh Fading Channels

Multichannel Slotted ALOHA Simulator Design for Massive Machine-Type Communication (mMTC) on 5G Network

Massive Machine-type Communication (mMTC) is one of the main service scenarios in 5G. At the time of initializing the connection to the base station, the MTC machines will make a connection request via the random access procedure. One of the schemes of random access procedure for handling this connection request is similar to how multichannel slotted ALOHA works. Multichannel slotted ALOHA itself is a development of the slotted ALOHA scheme which originally has only a single channel. At the initial state of mMTC, there will be an explosion of the number of demands to the available channels. Given the number of machines that will be connected, the likelihood of a collision on the same channel increases. As a result, the probability of failure also increases. The system's configuration has an impact on the likelihood of success and the time it takes to achieve it. The number of channels influences the likelihood of collisions, the backoff window influences the transmission distribution in each slot, and the maximum transmission limits the ability of device retransmission. These three arrangements have an impact on one another. The simulator build in this research is expected to make it easier for researchers to optimize multichannel slotted ALOHA configurations in 5G to handle the surge in access demands from mMTC devices.

Coded Slotted ALOHA Scheme With Multi-Packet Reception Under Erasure Channels

Coded Slotted ALOHA Scheme With Multi-Packet Reception Under Erasure Channels

Polar-Slotted ALOHA Over Slot Erasure Channel

To reduce the throughput loss caused by the slot erasure channel (SEC), we propose a polar slotted ALOHA (PSA) framework where the access procedure is decomposed into two-stage and jointly optimized under the slot polarization idea. In the first stage, guided by the slot polarization, a slot subset is constructed at each active user side and the receiver side. With an irregular degree distribution, each active user randomly selects slots from the slot subset to transmit the packet replicas. Subsequently, in the second stage, by using the packet-based polarization transform, the slotted packets are encoded by using a packet-level polar code. Correspondingly, at the receiver side, a packet-oriented successive cancellation (pSC) or pSC list decoding algorithm is performed to overcome the corruption caused by the SEC. And then, the success interference cancellation procedure is executed to recover the packet. Furthermore, for a given average transmission rate, the irregular degree distribution is optimized by searching the maximum within all feasible traffic load thresholds. Then, an upper bound of the polar-code rate for the PSA scheme is derived. Simulation results indicate that the proposed PSA scheme can achieve an improved throughput over the irregular repetition slotted ALOHA scheme for the SEC.

Cognitive Energy-Aware Spectrum Sensing With Improved Throughput for Medical Sensor Networks

Internet of Things (IoT) based medical devices equipped with biosensors are installed at the patient's location to collect sensitive information, such as body temperature, heart rate, blood pressure, and saturated oxygen levels. With the rapid escalation in the number of wearable devices and other applications, the radio spectrum which was once plentiful is now overcrowded and became scarce. Data security, packet loss, and throughput are the common hurdles in these networks. Identification of spectrum holes in cognitive radio networks is done using spectrum sensing, and this process consumes time and power. This letter proposes a cooperative spectrum sensing using a slotted ALOHA scheme for medical sensor networks with the goal to improve the overall throughput. The channel is divided into slots to achieve efficient spectrum sensing. The modeled network reduces interference with primary users and substantially increases throughput up to 70% with increasing secondary users. Comparative analysis with the existing similar models shows that the proposed model is superior in terms of false detection probability, average network throughput, and energy efficiency.

Multi-Satellite Cooperative Beamforming ALOHA for LEO Satellite IoT Networks

In this paper, we proposed a cooperative beamforming ALOHA (CBA) scheme based on linearly constrained minimum variance criterion for low Earth orbit satellite (LEO) IoT networks to solve the problem of ‘deadlock’ in multi-satellite scenario. In multi-satellite overlapping coverage areas, packets can be received by multiple satellite receivers by sending them only once, which forms the concept of spatial diversity. The cooperative beamforming collision resolution technique combined with successive interference cancellation scheme is design to efficiently resolve packet collision by iteration way at the gateway station. The performance of cooperative beamforming ALOHA scheme is evaluated via mathematical analysis and simulations. Simulation results show that the proposed CBA scheme can effectively solve the problem of ‘deadlock’ and improve the performances of random access compared with benchmark problems.

Reliable Random Access for Decentralized UAV Networks Based on Raptor Codes

In this paper, we propose the Raptor coded random access (RCRA) scheme to enable reliable transmission in the decentralized unmanned aerial vehicle (UAV) network. The considered network is composed of several overlapped random access systems with interference nodes, and the proposed RCRA scheme reduces bit-error ratio (BER) of the random access systems by three steps. First, we choose the number of slots based on a derived lower bound, which is necessary for reliable random access. Second, error-correcting codes are incorporated as the precode before random access, and then the access probability is optimized to achieve the minimum BER. Third, by correlating two consecutive slots, an idle-slot-filling approach is designed to further improve the efficiency of the random access systems. Numerical results show the proposed RCRA scheme reduces significantly both block-error ratio (BLER) and BER at moderate-and high-signal-to-noise ratio (SNR) region. With Es/N0 equal to 0 dB, the RCRA scheme saves 20% slots, compared with the existing frameless ALOHA scheme, to achieve a target BER of 10-4.

A Tag-Correlation-Based Approach to Fast Identification of Group Tags

Tag identification is a critical operation in large-scale RFID applications. Typically, in the RFID-enabled warehouse, the reader needs to execute tag identifications to obtain the inventory information of numerous tagged items. The existing schemes usually divide the time frame into multiple slots and map each tag to one of them for replying its identity. This imposes serious tag collisions because two or more tags may be mapped to the same slot and their responses corrupt with each other. When tag collision happens, all the collided tags cannot be identified by the reader, which significantly increases the identification delay. To overcome the collision problem in the identification process, this paper proposes a Group Tag Identification (GTI) framework to identify grouped tags in both singleton and collision slots. The key novelty of GTI is in leveraging tag-correlation to identify grouped tags in the collision slots without any extra transmission overhead. The main challenge of this work is to overcome the communication and architectural limitations of RFID systems in the context of building ID and slot-correlation between tags. Extensive simulations show that GTI significantly reduces the identification delay by up to 40 percent when compared with the state-of-the-art dynamical frame slotted aloha schemes.

Delay-Constrained Topology-Transparent Distributed Scheduling for MANETs

Transparent topology is common in many mobile ad hoc networks (MANETs) such as vehicle ad hoc networks (VANETs), unmanned aerial vehicle (UAV) ad hoc networks, and wireless sensor networks due to their decentralization and mobility nature. There are many existing works on distributed scheduling scheme design for topology-transparent MANETs. Most of them focus on delay-unconstrained settings. However, with the proliferation of real-time applications over wireless communications, it becomes more and more important to support delay-constrained traffic in MANETs. In such applications, each packet has a given hard deadline: if it is not delivered before its deadline, its validity will expire and it will be removed from the system. This feature is fundamentally different from the traditional delay-unconstrained one. In this article, we for the first time investigate distributed scheduling schemes for a topology-transparent MANET to support delay-constrained traffic. We analyze and compare probabilistic ALOHA scheme and deterministic sequence schemes, including the conventional time division multiple access (TDMA), the Galois field (GF) sequence scheme proposed by Chlamtac and Farago and the combination sequence scheme that we propose for a special type of sparse network topology. We use both theoretical analysis and empirical simulations to compare all these schemes and summarize the conditions under which different individual schemes perform best.

A Hybrid Multi-Class MAC Protocol for IoT-Enabled WBAN Systems

This study proposes a hybrid MAC protocol that can efficiently and effectively optimize the communication channel access of a WBAN multi-class system. The proposed protocol consists of two major processes that include the contention phase (CP) and the transmission phase (TP). In the CP, only the biomedical devices that have health packets to transmit randomly contend with equal probabilities using a slotted ALOHA scheme for transmission opportunities and the successful biomedical devices are allocated a transmission time-slot by employing a reservation-based time division multiple access (TDMA) scheme in the transmission phase. A multi-objective optimization problem was formulated to maximize the system sum-throughput, packet success-access-ratio, as well as the reservation ratio, and solved by the controller (i.e., access point) to determine the optimal length of the CP and the number of biomedical devices that can transmit in the TP. Monte Carlo simulation was performed and the optimization solution improved the proposed protocol’s performances. For validation purposes, the simulated results in MATLAB revealed that the proposed protocol performs better than the contemporary system in the context of the system sum-throughput, reservation ratio, and the average health packet delay with performance gains of about 9.2%, 9.5%, and 9.6% respectively.

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.

Towards the implementation of advanced random access schemes for satellite IoT

SummaryMachine‐to‐machine (M2M) communications being pivotal for internet of things (IoT) networks are characterized by low‐cost, low complexity, and often energy constrained terminals with low traffic duty cycle. Satellite networks provide an attractive low‐cost solution for such application, in particular when the terminals (both fixed and mobile) are distributed over a wide geographical area not well served by terrestrial infrastructure. An ALOHA random access (RA) scheme is a natural candidate for M2M communications since it is well matched to sporadic traffic, and it requires little terminals coordination. However, the classical ALOHA scheme suffers from a low throughput when operated in a load region requiring low probability of packet loss. To overcome this intrinsic ALOHA limitation, in the last decade, a lot of effort has been devoted to the investigation of evolutions of the ALOHA scheme reducing the probability of destructive packet collisions thus making it more attractive for satellite IoT. In such context, the Contention Resolution Diversity ALOHA (CRDSA) scheme and the Asynchronous Contention Resolution Diversity ALOHA (ACRDA) have emerged as promising solutions thanks to their high spectral efficiency achievable with low packet loss probability. The results reported in literature are however assuming ideal demodulator performance. This paper investigates the design and optimization of RA burst demodulator algorithms for single‐frequency and multifrequency CRDSA and ACRDA. It evaluates the performance of such algorithms in a number of system scenarios of practical interest and studies the impact of relevant system parameters on several performance metrics.

Decentralised resource allocation of position‐based and full‐duplex‐based all‐to‐all broadcasting

The broadcasting services of vehicles in both vehicular networks and unmanned aerial vehicle (UAV) networks can be seen as the typical applications of all-to-all (A2A) scenario. In order to achieve efficient information broadcasting in A2A scenarios, this study proposes a two-stage resource allocation scheme. In the first stage, to improve the frequency spectrum reusability, the communication area is divided into as many non-overlapping square regions as possible based on the reliability requirements and power constraints of the vehicles, where the nonadjacent square regions share the same frequency spectrum. In the second stage, the vehicles belonging to the same region broadcast information with distributed time division multiplexing, and an improved coded slotted ALOHA scheme is proposed based on full-duplex, where each vehicle can detect whether its broadcasted information is successful. Thus, the number of retransmissions and collision probability can be reduced and therefore the system energy can be saved. Results indicate that the two-stage resource allocation scheme significantly improves the resource reusability while guaranteeing the communication reliability.

Hybrid ORA and NORA schemes for machine‐to‐machine communication in long‐term evolution networks

Massive machine-type communication (MTC) devices will be deployed in the fifth-generation wireless communication networks, which will inevitably result in access collision problems. To alleviate this issue, the authors propose a hybrid orthogonal random access (ORA) and non-orthogonal random access (NORA) scheme to improve the throughput. In the proposed scheme, an expanded physical random access channel is employed to transmit preambles and MTC devices identity information simultaneously, which can help the base station (BS) to determine whether the MTC device can successfully transmit preamble. Subsequently, the MTC devices whose transmitted preambles are detected successfully by BS are statistically grouped, and then the devices in the same group transmit their data messages in a non-orthogonal multiple access manner. Meanwhile, to further improve the access throughput, the MTC devices that did not pass access class barring check are permitted to compete for the remained unscheduled resources with orthogonal multiple access manner. They also analyse the access throughput of the proposed scheme. Simulation results show that to serve all MTC devices distributed in a cell, their proposed scheme outperforms the traditional multichannel ALOHA and two-stage random access scheme in terms of access throughput and required number of random access slots.

Impact of Segmentation and Capture on Slotted Aloha Systems Exploiting Interference Cancellation

The performance of the widely adopted slotted Aloha (SA) scheme has been recently improved thanks to the introduction of novel mechanisms, including interference cancellation (IC), packet segmentation, and slot slicing. The combined effect of these mechanisms in the presence of capture has however not yet deeply investigated, even if the resulting impact on the network behavior is determinant for properly quantifying the achievable throughput. To deal with this issue, this paper analyzes the influence of capture on a framed SA (FSA) system adopting IC, segmentation, and slicing, by considering a reliable decoding criterion that accounts for the actually experienced signal to interference-plus-noise ratio. A theoretical model is developed to evaluate the capture probability in fast and slow Rayleigh fading conditions, deriving closed-form expressions for the interference-limited case. The IC-based FSA throughput is then estimated adopting a Markov chain approach validated by Monte Carlo simulations. Finally, the performance of an actual system using a quadrature phase-shift keying modulation in conjunction with a turbo encoder is compared with that estimated by adopting the considered decoding criterion, in order to check its applicability to practical communication networks.

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

Design of Coded ALOHA With ZigZag Decoder

In this study, we investigated the effects of combining a zigzag decoder (ZD) with a coded ALOHA using the successive interference cancellation (SIC) technique to retrieve packets from collisions. We proposed zigzag decodable coded slotted ALOHA (ZDCSA) and enhanced-ZDCSA (E-ZDCSA) as a scheme which applies ZD before and after SIC, respectively. Furthermore, we derived the asymptotic analysis for the throughput and packet loss rate (PLR) performances of E-ZDCSA and validated its accuracy with the Monte Carlo simulations. Through numerical and asymptotic analyses, we showed that E-ZDCSA outperforms ZDCSA and the conventional coded ALOHA schemes in terms of throughput and PLR performances in most of the offered load regime. Moreover, we demonstrated that our proposed schemes outperform the conventional protocol in a practical scenario in which ZD cannot resolve all the collisions.

Enhancing Contention Resolution ALOHA Using Combining Techniques

Recently, random access protocols have acquired a new wave of interest, not only from the satellite communication community, but also from researchers active in fields like Internet of Things and machine-to-machine. Asynchronous (slot- and frame-wise) ALOHA-like random access protocols, are very attractive for such applications, enabling low complexity transmitters and avoiding time synchronization requirements. Evolutions of ALOHA employ time diversity through proactive replication of packets, but the time diversity is not fully exploited at the receiver. Combining techniques, as selection combining and maximal-ratio combining, are beneficial and are adopted in the enhanced contention resolution ALOHA (ECRA) scheme, presented here. A tight approximation of the packet loss rate for asynchronous random access, including ECRA, well suited for the low channel load region is derived. Finally, ECRA is evaluated in terms of spectral efficiency, throughput and packet loss rate in comparison with recent protocols, showing that it is able to largely outperform both slotted synchronous and asynchronous schemes.

Asymptotic Performance of Coded Slotted ALOHA With Multipacket Reception

In this letter, we develop a converse bound on the asymptotic load threshold of coded slotted ALOHA (CSA) schemes with $K$ -multipacket reception capabilities at the receiver. Density evolution is used to track the average probability of packet segment loss and an area matching condition is applied to obtain the converse. For any given CSA rate, the converse normalized to $K$ increases with $K$ , which is in contrast with the results obtained so far for slotted ALOHA schemes based on successive interference cancellation. We show how the derived bound can be approached using spatially coupled CSA.

Coded Slotted ALOHA for Erasure Channels: Design and Throughput Analysis

In this paper, we investigate the design and analysis of coded slotted ALOHA (CSA) schemes in the presence of channel erasure. We design the code probability distributions for CSA schemes with repetition codes and maximum distance separable codes to maximize the expected traffic load, under both packet erasure channels and slot erasure channels. We derive the extrinsic information transfer (EXIT) functions of CSA schemes over erasure channels. By optimizing the convergence behavior of the derived EXIT functions, the code probability distributions to achieve the maximum expected traffic load are obtained. Then, we derive the asymptotic throughput of CSA schemes over erasure channels. In addition, we validate that the asymptotic throughput can give a good approximation to the throughput of CSA schemes over erasure channels.