Evaluación del rendimiento de protocolos Frame Slotted-ALOHA basados en técnicas de cancelación de interferencias para redes M2M

Performance Evaluation of Frame Slotted-ALOHA protocols based on interference cancellation techniques for M2M networks. Since the technologies related to the Internet of Things (IoT) have spread across the world, M2M networks have become more popular. M2M networks allow devices to communicate between each other remotely and without human intervention, through wired or wireless communication channels. These devices have three basic functions: collect, store and transmit information. M2M communications is not different from any other communication process. The devices involved in the transmission form what is called a M2M area network, which is connected to the communication network through the gateway. The gateway manages the data packets and sends the information to a final server, where it subsequently reaches the M2M applications and the end-user. In this project we considered a M2M network used for data collection. It is composed of several devices that send their data packets to the gateway periodically and under request. Once one device has succeed it switches into a low-power mode. Due to the fact that M2M networks include lots of devices, efficiency and protocols optimization are required in order to guarantee low energy consumption and avoiding delays in data transmission. As a first approach, protocols based in ALOHA offer low complexity and easy implementation. However, its performance decreases drastically when the data-traffic-load increases or with a large number of devices. Lots of protocols based in ALOHA have been developed in the search for energy efficiency, such as Slotted-ALOHA (SA) or Frame Slotted-ALOHA (FSA). Previous works evaluated the performance of the Successive Interference Cancellation (SIC) techniques on FSA. In these protocols, the devices send a copy of its data packets in different time slots. Each copy includes the reference to the slots in which the remaining replicas were transmitted. In order to decode data packets, the gateway identifies the slots free of collisions. With the decoded packets, it is able to solve the collisions in other slots where this packet has been sent. This process is known as Successive Interference Cancellation. In this work we evaluate the performance of Intra-frame SIC and Inter-frame SIC. Intra-frame SIC uses the decoded data packets to solve collisions inside a transmission frame. On the other hand, Inter-frame SIC performs the interference cancellation outside the current frame, i.e, packets decoded in current frame are used to solve collisions from past frames, which have been previously stored by the coordinator. In addition, we study the effect of Diversity in FSA, by evaluating some probability density functions (PDF) in the selection of the number of replicas. Therefore, the devices could select a fixed number of replicas or a random number of replicas with uniform PDF or irregular PDF. By means of simulation codes developed in Matlab we evaluate delay and energy consumption using Intra-frame and Inter-frame SIC-FSA. The results were compared against FSA protocol. It was proved that Intra-frame SIC-FSA can reduce average delay and the coordinator's energy consumption in 78%, while Inter-frame SIC-FSA reaches 94% of reduction in delay and energy consumed by the coordinator. In addition, the average energy consumption per device can be reduced by around 18% by using Intra-frame SIC-FSA, while Inter-frame SIC-FSA outperforms FSA protocol by decreasing the energy of the devices in 22%

Characterization of Coded Random Access with Compressive Sensing based Multi-User Detection

The emergence of Machine-to-Machine (M2M) communication requires new Medium Access Control (MAC) schemes and physical (PHY) layer concepts to support a massive number of access requests. The concept of coded random access, introduced recently, greatly outperforms other random access methods and is inherently capable to take advantage of the capture effect from the PHY layer. Furthermore, at the PHY layer, compressive sensing based multi-user detection (CS-MUD) is a novel technique that exploits sparsity in multi-user detection to achieve a joint activity and data detection. In this paper, we combine coded random access with CS-MUD on the PHY layer and show very promising results for the resulting protocol.Comment: Submitted to Globecom 201

Modern Random Access for Satellite Communications

The present PhD dissertation focuses on modern random access (RA) techniques. In the first part an slot- and frame-asynchronous RA scheme adopting replicas, successive interference cancellation and combining techniques is presented and its performance analysed. The comparison of both slot-synchronous and asynchronous RA at higher layer, follows. Next, the optimization procedure, for slot-synchronous RA with irregular repetitions, is extended to the Rayleigh block fading channel. Finally, random access with multiple receivers is considered.Comment: PhD Thesis, 196 page

Near-Far Effect on Coded Slotted ALOHA

International audienceMotivated by scenario requirements for 5G cellular networks, we study one of the candidate protocols for massive random access: the family of random access methods known as Coded Slotted ALOHA (CSA). A recent trend in research has explored aspects of such methods in various contexts, but one aspect has not been fully taken into account: the impact of path loss, which is a major design constraint in long-range wireless networks. In this article, we explore the behavior of CSA, by focusing on the path loss component correlated to the distance to the base station. Path loss provides opportunities for capture, improving the performance of CSA. We revise methods for estimating CSA behavior, provide bounds of performance, and then, focusing on the achievable throughput, we extensively explore the key parameters, and their associated gain (experimentally). Our results shed light on the behavior of the optimal distribution of repetitions in actual wireless networks

Exploiting Capture Effect in Frameless ALOHA for Massive Wireless Random Access

The analogies between successive interference cancellation (SIC) in slotted ALOHA framework and iterative belief-propagation erasure-decoding, established recently, enabled the application of the erasure-coding theory and tools to design random access schemes. This approach leads to throughput substantially higher than the one offered by the traditional slotted ALOHA. In the simplest setting, SIC progresses when a successful decoding occurs for a single user transmission. In this paper we consider a more general setting of a channel with capture and explore how such physical model affects the design of the coded random access protocol. Specifically, we assess the impact of capture effect in Rayleigh fading scenario on the design of SIC-enabled slotted ALOHA schemes. We provide analytical treatment of frameless ALOHA, which is a special case of SIC-enabled ALOHA scheme. We demonstrate both through analytical and simulation results that the capture effect can be very beneficial in terms of achieved throughput.Comment: Accepted for presentation at IEEE WCNC'14 Track 2 (MAC and Cross-Layer Design

Multiple Access for Massive Machine Type Communications

The internet we have known thus far has been an internet of people, as it has connected people with one another. However, these connections are forecasted to occupy only a minuscule of future communications. The internet of tomorrow is indeed: the internet of things. The Internet of Things (IoT) promises to improve all aspects of life by connecting everything to everything. An enormous amount of effort is being exerted to turn these visions into a reality. Sensors and actuators will communicate and operate in an automated fashion with no or minimal human intervention. In the current literature, these sensors and actuators are referred to as machines, and the communication amongst these machines is referred to as Machine to Machine (M2M) communication or Machine-Type Communication (MTC). As IoT requires a seamless mode of communication that is available anywhere and anytime, wireless communications will be one of the key enabling technologies for IoT. In existing wireless cellular networks, users with data to transmit first need to request channel access. All access requests are processed by a central unit that in return either grants or denies the access request. Once granted access, users' data transmissions are non-overlapping and interference free. However, as the number of IoT devices is forecasted to be in the order of hundreds of millions, if not billions, in the near future, the access channels of existing cellular networks are predicted to suffer from severe congestion and, thus, incur unpredictable latencies in the system. On the other hand, in random access, users with data to transmit will access the channel in an uncoordinated and probabilistic fashion, thus, requiring little or no signalling overhead. However, this reduction in overhead is at the expense of reliability and efficiency due to the interference caused by contending users. In most existing random access schemes, packets are lost when they experience interference from other packets transmitted over the same resources. Moreover, most existing random access schemes are best-effort schemes with almost no Quality of Service (QoS) guarantees. In this thesis, we investigate the performance of different random access schemes in different settings to resolve the problem of the massive access of IoT devices with diverse QoS guarantees. First, we take a step towards re-designing existing random access protocols such that they are more practical and more efficient. For many years, researchers have adopted the collision channel model in random access schemes: a collision is the event of two or more users transmitting over the same time-frequency resources. In the event of a collision, all the involved data is lost, and users need to retransmit their information. However, in practice, data can be recovered even in the presence of interference provided that the power of the signal is sufficiently larger than the power of the noise and the power of the interference. Based on this, we re-define the event of collision as the event of the interference power exceeding a pre-determined threshold. We propose a new analytical framework to compute the probability of packet recovery failure inspired by error control codes on graph. We optimize the random access parameters based on evolution strategies. Our results show a significant improvement in performance in terms of reliability and efficiency. Next, we focus on supporting the heterogeneous IoT applications and accommodating their diverse latency and reliability requirements in a unified access scheme. We propose a multi-stage approach where each group of applications transmits in different stages with different probabilities. We propose a new analytical framework to compute the probability of packet recovery failure for each group in each stage. We also optimize the random access parameters using evolution strategies. Our results show that our proposed scheme can outperform coordinated access schemes of existing cellular networks when the number of users is very large. Finally, we investigate random non-orthogonal multiple access schemes that are known to achieve a higher spectrum efficiency and are known to support higher loads. In our proposed scheme, user detection and channel estimation are carried out via pilot sequences that are transmitted simultaneously with the user's data. Here, a collision event is defined as the event of two or more users selecting the same pilot sequence. All collisions are regarded as interference to the remaining users. We first study the distribution of the interference power and derive its expression. Then, we use this expression to derive simple yet accurate analytical bounds on the throughput and outage probability of the proposed scheme. We consider both joint decoding as well as successive interference cancellation. We show that the proposed scheme is especially useful in the case of short packet transmission