Frameless ALOHA Research Articles

On the Average and Distribution of Age of Information for Frameless ALOHA

On the Average and Distribution of Age of Information for Frameless ALOHA

Age of Information Minimization for Frameless ALOHA in Grant-Free Massive Access

In this paper, we focus on the optimal problem of average age of information (AAoI) in grant-free massive access, and propose an age-critical frameless ALOHA (ACFA) random access protocol, where the AAoI is implicitly reduced by banning the transmission of activated user equipments (UEs) recovered successfully in the last frame. In particular, we analyze the dense and sparse access models according to the activation probability, and present these scenarios with time-stamped sampling either at the beginning of the frame or in the first slot transmitting the packet. In order to qualify the AAoI of proposed protocol, we define two virtual rates and establish an iterative framework to analyze the access successful probability (ASP) of the protocol in asymptotic regime, and derive the closed-form expressions of AAoI as a function of ASP and virtual rate in all cases. Further, we formulate the optimal problems of normalized AAoI in all cases, and obtain the selection of access parameters by asymptotic analysis and simulations, respectively. Finally, we compare our protocol with state-of-the-art schemes, and the simulation results show that the ACFA random access protocol outperforms these benchmark schemes, and has great potential of access-banned policy in minimizing AAoI for frame-based protocols.

The Dynamic Behavior of Frameless ALOHA: Drift Analysis, Throughput, and Age of Information

The Dynamic Behavior of Frameless ALOHA: Drift Analysis, Throughput, and Age of Information

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.

Reliability-Latency Performance of Frameless ALOHA With and Without Feedback

This paper presents a finite length analysis of multi-slot type frameless ALOHA based on a dynamic programming approach. The analysis is exact, but its evaluation is only feasible for moderate number of users due to the computational complexity. The analysis is then extended to derive continuous approximations of its key parameters, which, apart from providing an insight into the decoding process, make it possible to estimate the packet error rate with very low computational complexity. Finally, a feedback scheme is presented in which the slot access scheme is dynamically adapted according to the approximate analysis in order to minimize the packet error rate. The results indicate that the introduction of feedback can substantially improve the performance of frameless ALOHA.

Application of ZigZag Decoding in Frameless ALOHA

As ZigZag decoding (ZD) can resolve a collision between two packets, the combination of ZD and successive interference cancellation (SIC) is expected to provide a lower packet loss rate (PLR) and higher average throughput than the conventional frameless ALOHA. Therefore, in this paper, we considered applying ZD in frameless ALOHA. A straightforward implementation is first considered while deriving the exact theoretical expression for the PLR, and implementation results show higher PLR and lower throughput performance than in the conventional scheme. In addition, we propose a sophisticated implementation called enhanced ZigZag decodable frameless ALOHA (E-ZDFA), where the transmission probability is dynamically increased to improve the throughput by enhancing the chances for unretrieved users to transmit. The computer simulations revealed that E-ZDFA achieves higher throughput performance than the original frameless ALOHA and the state-of-the-art irregular-repetition-slotted ALOHA. Moreover, E-ZDFA achieves a lower error floor than frameless ALOHA, enabling the prevention of user silence, i.e., no transmission of the packet during the protocol.

Optimized Frameless ALOHA for Cooperative Base Stations With Overlapped Coverage Areas

Herein, we consider the problem of cooperative multi-access in the presence of overlapped coverage areas. Assuming a frameless ALOHA transmission scheme, we derive exact analytical throughput expressions for throughput in the aforementioned scenarios as a function of the frame length of the system and for arbitrary average numbers of users transmitting in each slot (target degree). After obtaining these original expressions, we then formulate a utility function whose maximization (obtained, e.g., through genetic algorithms) yields unequal and optimum target degrees to be employed by users in each group in order to maximize the peak throughput of the whole system while satisfying a given prescribed outage. A comparison of the resulting cooperative multiple base station (BS) multi-access scheme against optimized single-BS frameless ALOHA systems—which presume the perfect isolation of users at each BS and an equal optimum target degree for all users—indicates a significant gain in overall throughput, thereby revealing that a “multi-access diversity gain” can be reaped by allowing groups of users from different BSs to overlap.

Enhanced frameless slotted ALOHA protocol with Markov chains analysis

In this paper, we propose a novel approach to enhance the performance of frameless slotted ALOHA (SA) protocol. We employ signature codes to help the receiver identify the packets contained in collisions, and use successive interference cancellation (SIC) for packet recovery. We model the proposed scheme as a two-state Markov model represented by a uni-partite graph. We evaluate the throughput, expected delay and average memory size of the proposed scheme, and optimize the proposed scheme to maximize the throughput. We show that the theoretical analysis matches well with simulation results. The throughput and expected delay of the proposed protocol outperform the conventional slotted ALOHA protocol significantly.

Finite-Length Analysis of Frameless ALOHA With Multi-User Detection

In this letter, we present a finite-length analysis of frameless ALOHA for a $ k$ multi-user detection scenario, i.e., assuming the receiver can resolve collisions of size $ k$ or smaller. The analysis is obtained via a dynamical programming approach, and employed to optimize the scheme’s performance. We also assess the optimized performance as a function of $k$ . Finally, we verify the presented results through Monte Carlo simulations.

An energy-efficient adaptive frameless ALOHA protocol

Random access protocols are a key feature of a family of emerging communication networks such as machine-to-machine, radio frequency identification (RFID), and sensor networks. To accommodate the needs of such networks with a massive number of uncoordinated devices, new random multiple access (MAC) protocols have been proposed that aim to improve the system efficiency by resolving collisions in the received signal. In this work, we consider one of such protocols, called frameless ALOHA, and propose two techniques to improve its energy efficiency without sacrificing the network throughput. More specifically, we propose mechanisms to adaptively control the access probability at the users. The proposed mechanisms are local and like the original frameless ALOHA, no coordination between the users is needed. Our simulation results verify the improvement achieved in the energy efficiency by the proposed techniques.