Irregular Repetition Slotted ALOHA Research Articles

Throughput Analysis for Parallel Decoding of Irregular Repetition Slotted ALOHA With Noise

Throughput Analysis for Parallel Decoding of Irregular Repetition Slotted ALOHA With Noise

Irregular repetition slotted Aloha with multiuser detection: A density evolution analysis

Irregular repetition slotted Aloha (IRSA) has shown significant advantages as a modern technique for uncoordinated random access with massive number of users due to its capability of achieving theoretically a throughput of 1 packet per slot. When the receiver has also the multi-packet reception of multi-user (MUD) detection property, by applying successive interference cancellation, IRSA also obtains very low packet loss probabilities at low traffic loads, but is unable in general to achieve a normalized throughput close to 1. In this paper, we reconsider the case of IRSA with k-MUD receivers and derive the general density evolution equations for the non-asymptotic analysis of the packet loss rate, for arbitrary frame lengths and two operational variants: frame-structured and frameless transmissions. The first one defers transmission attempts until the beginning of the next frame of slots, while the second allows transmission immediately after a packet arrival. Next, using the potential function, we give new capacity bounds on the capacity of the system, showing the threshold arrival rate for zero decoding error probability. Our numerical results illustrate performance in terms of throughput and average delay for k-MUD IRSA with finite memory at the receiver, and also with bounded maximum delay.

G-SC-IRSA: Graph-Based Spatially Coupled IRSA for Age-Critical Grant-Free Massive Access

In this paper, we focus on a grant-free massive access setup and analyze its age of information (AoI), where a large number of user equipments (UEs) are randomly activated and attempt transmitting status update packets to a base station (BS) over a common shared channel. To support this age-critical grant-free massive access, we propose a graph-based spatially coupled irregular repetition slotted ALOHA (G-SC-IRSA) random access protocol, which utilizes the pseudo-random access pattern (PRAP), coupled frames, and sliding window decoder (SWD) to improve the packet loss rate (PLR) and AoI performance. Specifically, we derive the approximate expressions to the normalized average AoI (AAoI) as a function of the PRAP and system load. Then, we establish the problem of minimizing the AAoI under the G-SC-IRSA protocol. Furthermore, we utilize the density evolution (DE) with a bipartite graph to evaluate the system load threshold of G-SC-IRSA in asymptotic regime, and achieve an optimal degree distribution via the differential evolution algorithm, and finally obtain the optimal PRAP with PEG algorithm. Simulation results validate the accuracy of our theoretical derivations, and show the G-SC-IRSA can achieve the minimum AAoI with the optimal PRAP, and outperforms the existing benchmark schemes in terms of PLR and AAoI.

Raptor-IRSA Grant-free Random Access protocol for smart grids applications

This paper deals with the reliability of random access (RA) protocols for massive wireless smart grid communication (m-SGC). We propose and analyze an improved grant-free RA (GF-RA) protocol for critical SG applications under strict QoS m-SGC requirements. At first, we discuss the main features of the SG neighborhood area network (NAN) architecture. We explore the main features of low-rate machine-type wireless networks, and also we describe a technology characterization of wireless neighborhood area networks (WNAN) in medium-range coverage applications. We propose a new-improved irregular repetition slotted ALOHA, combining Raptor codes and irregular ALOHA, namely RapIRSA random access protocol, to better respond to critical high-reliability QoS requirements under a 5G network perspective. Then, we compare and comprehensively analyze the proposed RapIRSA protocol with two existing RA protocols, the IRSA protocol, and the classical Slotted Aloha. Finally, We summarize the potential challenges in implementing the proposed RA protocol for SG critical applications considering a massive number of smart sensors (SS).

Study of Coded ALOHA with Multi-User Detection under Heavy-Tailed and Correlated Arrivals

In this paper, we study via simulation the performance of irregular repetition slotted ALOHA under multi-packet detection and different patterns of the load process. On the one hand, we model the arrival process with a version of the M/G/∞ process able to exhibit a correlation structure decaying slowly in time. Given the independence among frames in frame-synchronous coded-slotted ALOHA (CSA), this variation should only take effect on frame-asynchronous CSA. On the other hand, we vary the marginal distribution of the arrival process using discrete versions of the Lognormal and Pareto distributions, with the objective of investigating the influence of the right tail. In this case, both techniques should be affected by the change, albeit to a different degree. Our results confirm these hypotheses and show that these factors must be taken into account when designing and analyzing these systems. In frameless operations, both the shape of the packet arrivals tail distribution and the existence of short-range and long-range correlations strongly impact the packet loss ratio and the average delay. Nevertheless, these effects emerge only weakly in the case of frame-aligned operations, because this enforces the system to introduce a delay in the newly arrived packets (until the beginning of the next frame), and implies that the backlog of accumulated packets is the key quantity for calculating the performance.

Irregular Repetition Slotted ALOHA Over Rayleigh Block Fading Channels: Bounds and Threshold Saturation via Spatial Coupling

Irregular Repetition Slotted ALOHA Over Rayleigh Block Fading Channels: Bounds and Threshold Saturation via Spatial Coupling

Distributed Scheduling for Status Update with Heterogeneous Services under the IRSA Protocol

The peak age-of-information (AoI) performance in irregular repetition slotted ALOHA (IRSA) is revisited in this paper with a particular focus on heterogeneous networks, where types of users may have different numbers of users, active probabilities, and sensitivities to AoI. A distributed scheduling framework that is both conceptually and practically simple is proposed. A series of analyses and approximations are conducted, which lead to a closed-form approximation of the best scheduling policy within the proposed framework. Extensive simulations are provided to confirm that in spite of being extremely low complex, the proposed policy can significantly reduce the weighted average peak AoI, especially for heavily overloaded scenarios.

Analytic Distribution Design for Irregular Repetition Slotted ALOHA With Multi-Packet Reception

Associated with multi-packet reception at the access point, irregular repetition slotted ALOHA (IRSA) holds a great potential in improving the access capacity of massive machine type communication systems. This work investigates the packet repetition of the users in an IRSA-based random access system where the access point can simultaneously retrieve multiple packets in a slot. Specifically, we propose an analytical transmission probability distribution for IRSA with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dual-packet reception capability</i> . In addition, the energy efficiency optimization in terms of the maximum number of replica is also presented. Numerical results show that using the proposed transmission distribution for the replica can achieve a significant higher throughput than the existing benchmark distributions. With optimized repetition rate, the energy efficiency of users can be also improved remarkably.

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.

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

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

Joint Intra/Inter-Slot Code Design for Unsourced Multiple Access in 6G Internet of Things

Unsourced multiple access (UMA) is the technology for massive, low-power, and uncoordinated Internet-of-Things in the 6G wireless system, improving connectivity and energy efficiency on guaranteed reliability. The multi-user coding scheme design is a critical problem for UMA. This paper proposes a UMA coding scheme based on the T-Fold IRSA (irregular repetition slotted Aloha) paradigm by using joint Intra/inter-slot code design and optimization. Our scheme adopts interleave-division multiple access (IDMA) to enhance the intra-slot coding gain and the low-complexity joint intra/inter-slot SIC (successive interference cancellation) decoder structure to recover multi-user payloads. Based on the error event decomposition and density evolution analysis, we build a joint intra/inter-slot coding parameter optimization algorithm to minimize the SNR (signal-to-noise ratio) requirement at an expected system packet loss rate. Numerical results indicate that the proposed scheme achieves energy efficiency gain by balancing the intra/inter-slot coding gain while maintaining relatively low implementation complexity.

Optimal Probabilistic Repetition for Massive MIMO-Aided Grant-Free Short-Packet Transmissions

In this letter, we propose a novel probabilistic repetition scheme for the uplink massive MIMO system with grant-free access. Compared with canonical K-repetition, the proposed scheme is more flexible and covers the K-repetition as a special case. With the consideration of multiple practical factors, including the sporadic arrivals, the short-packet transmissions, probabilistic repetition, and channel estimation error, the reliability and throughput of the proposed probabilistic repetition assisted grant-free access scheme are theoretically analyzed. It is also proved that the optimal transmission probability for reliability maximization exists and can be found through gradient descent method. Simulation results validate the accuracy of our theoretical analysis, and also show that the proposed Optimal Probabilistic Repetition assisted grant-free Access scheme (OPRA) is superior to the popular modern grant-free random access with repetition transmission, that is, irregular repetition slotted ALOHA (IRSA).

Short-Packet Transmission in Irregular Repetition Slotted ALOHA System Over the Rayleigh Fading Channel

Random access systems are potential for Internet of Things in the future wireless communication network for its operational simplicity. Irregular repetition slotted ALOHA (IRSA) system is one of the high-efficiency random access systems. In this paper, performance analysis of the irregular repetition slotted ALOHA systems with short-packet, i.e. finite-blocklength, transmission for the quasi-static Rayleigh fading channel is given. A cumulative distribution function of signal-to-interference power ratio (SIR) is derived and thus a closed-form expression of an average packet error probability (PEP) at the SIR with short packets for the Rayleigh fading channel is given. The closed-form expression makes it possible to optimize the degree distributions at a specific blocklength in the sense that the systems give the maximum system load.

Fast Finite Frame Length IRSA Optimization Based on Bayesian Optimization

Simplified packet reception models such as collision model are usually adopted for optimizing irregular repetition slotted ALOHA (IRSA), which may lead to performance penalty due to its poor accuracy. In this letter, we consider the problem of online IRSA optimization in the finite frame length regime using a more accurate reception model. In order to allow a fast optimization of IRSA, we present a new method based on Bayesian optimization with Gaussian processes. Our method finds the optimal user degree distribution minimizing packet loss rate (PLR) in an iterative way. At each iteration, a surrogate is built to model the unknown IRSA PLR performance function using Gaussian process (GP) regression, and then an acquisition function defined from the surrogate is utilized to choose the next degree distribution, whose PLR is evaluated by the more accurate model. The proposed method is able to infer the PLR of an untested degree distribution, thus converging quickly within only tens of iterations. Simulation results show that IRSA schemes optimized using our method can achieve lower PLR compared with those optimized based on the collision model.

Energy Efficiency Optimization for Irregular Repetition Slotted ALOHA-Based Massive Access

Irregular repetition slotted ALOHA (IRSA) is a promising mechanism to support massive access in Internet of Things (IoT). As IoT devices are usually battery capacity-limited, the energy efficiency (EE) should be paid close attention to when operating the IRSA scheme. This letter improves the EE of devices by adjusting the transmit power and maximum number of packet replicas based on two high-throughput transmission probability distributions of IRSA scheme. Specifically, the optimal transmit power and the optimal packet replica number are found explicitly following individual parameter optimizations. Based on the obtained individual optimums, an iterative algorithm is proposed for finding the global optimum quickly. Numerical results show that the EE of devices can be enhanced significantly by using the found optimums.

Enhanced Irregular Repetition Slotted ALOHA Under SIC Limitation

Uncoordinated multiple access has been proposed as a modern technique to provide massive connectivity. Among many proposals, irregular repetition slotted ALOHA (IRSA) was shown to achieve a close-to-optimum throughput by irregular packet repetition and successive interference cancellation (SIC). However, most of the previous works are based on certain ideal assumptions. In this paper, we tackle one of such ideal assumptions, where a decoded packet can always be used to cancel out <i>all</i> its replicas transmitted in other slots. In reality, the random nature of IRSA results in a large dynamic range of the received power that cannot be recovered under a practical quantizer. A SIC limit that dictates the number of recoverable collided packets at a slot should exist. To resolve this issue, we propose a novel protocol, named IRSA with frame partitioning (IRSA-FP), which partitions a frame into several subframes. A feedback mechanism is enforced to inform those users, whose packets have been successfully decoded, to cease their transmissions. We then propose a novel density-evolution-type analysis for IRSA-FP. Simulation results show the performance of the proposed IRSA-FP can be accurately predicted by our analysis and the proposed IRSA-FP outperforms the traditional IRSA when practical SIC limit is introduced.

On the Impact of Channel Estimation on the Design and Analysis of IRSA Based Systems

Irregular repetition slotted aloha (IRSA) is a distributed grant-free random access protocol where users transmit multiple replicas of their packets to a base station (BS). The BS recovers the packets using successive interference cancellation. In this paper, we first derive channel estimates for IRSA, exploiting the sparsity structure of IRSA transmissions, when non-orthogonal pilots are employed across users to facilitate channel estimation at the BS. Allowing for the use of non-orthogonal pilots is important, as the length of orthogonal pilots scales linearly with the total number of devices, leading to prohibitive overhead as the number of devices increases. Next, we present a novel analysis of the throughput of IRSA under practical channel estimation errors, with the use of multiple antennas at the BS. Finally, we theoretically characterize the asymptotic throughput performance of IRSA using a density evolution based analysis. Simulation results underline the importance of accounting for channel estimation errors in analyzing IRSA, which can even lead to 70&#x0025; loss in performance in severely interference-limited regimes. We also provide novel insights on the effect of parameters such as pilot length, SNR, number of antennas at the BS, etc, on the system throughput.

User Activity Detection for Irregular Repetition Slotted Aloha Based MMTC

Irregular repetition slotted aloha (IRSA) is a grant-free random access protocol for massive machine-type communications, where a large number of users sporadically send their data packets to a base station (BS). IRSA is a completely distributed multiple access protocol: in any given frame, a small subset of the users, i.e., the active users, transmit replicas of their packet in randomly selected resource elements (REs). The first step in the decoding process at the BS is to detect which users are active in each frame. To this end, a novel Bayesian user activity detection (UAD) algorithm is developed, which exploits both the sparsity in user activity as well as the underlying structure of IRSA-based transmissions. Next, the Cramer-Rao bound (CRB) on the mean squared error in channel estimation is derived. It is empirically shown that the channel estimates obtained as a by-product of the proposed UAD algorithm achieves the CRB. Then, the signal to interference plus noise ratio achieved by the users is analyzed, accounting for UAD, channel estimation errors, and pilot contamination. The impact of these non-idealities on the throughput of IRSA is illustrated via Monte Carlo simulations. For example, in a system with 1500 users and 10% of the users being active per frame, a pilot length of as low as 20 symbols is sufficient for accurate user activity detection. In contrast, using classical compressed sensing approaches for UAD would require a pilot length of about 346 symbols. The results also reveal crucial insights into dependence of UAD errors and throughput on parameters such as the length of the pilot sequence, the number of antennas at the BS, the number of users, and the signal to noise ratio.

A Game Theoretic Approach to Irregular Repetition Slotted Aloha

Many technological enhancements are being developed worldwide to enable the &#x201C;Internet of Things&#x201D; (IoT). IoT networks largely rely on distributed access of billions of devices, but are still lagging in terms of combined reliability and low latency. To mend that shortcoming, it is paramount to adapt existing random access methods for the IoT setting. In this article, we shed light on one of the modern candidates for random access protocols fitted for IoT: the &#x201C;Irregular Repetition Slotted ALOHA&#x201D; (IRSA). As self-managing solutions are needed to overcome the challenges of IoT, we study the IRSA random access scheme in a distributed setting where groups of users, with fixed traffic loads, are competing for ALOHA-type channel access. To that aim, we adopt a distributed game-theoretic approach where two classes of IoT devices learn autonomously their optimal IRSA protocol parameters to optimize selfishly their own effective throughput. Through extensive simulations, we assess the notable efficiency of the game based distributed approach. We also show that our IRSA game attains the Nash equilibrium (NE) via the &#x201C;better reply&#x201D; strategy, and we quantify the price of anarchy in comparison with a centralized approach. Our results imply that user competition does not fundamentally impact the performance of the IRSA protocol.

Adaptive Traffic Load in IRSA-NOMA Prioritizing Emergency Devices for 6G Enabled Massive IoT

Irregular repetition slotted ALOHA (IRSA) based non-orthogonal multiple access (NOMA) with priority adaptive traffic load (ATL) (PATL-IRSA-NOMA) is proposed to prioritize the performance of emergency devices in 6G enabled massive Internet of Things. In PATL-IRSA-NOMA, emergency devices (ED) and regular devices (RD) are coexisting and differentiated by access probability before sending packets, where RD performing traffic load estimation and applying ATL to access the channel. Different from conventional ATL that is performed by all users/devices, priority ATL in PATL-IRSA-NOMA is only performed by RD and reduces the contention of RD in IRSA-NOMA channel. The superior of PATL-IRSA-NOMA over conventional IRSA-NOMA is shown in terms of packet loss rate and throughput for both ED and RD groups.