Femtocells, despite their name, pose a potentially large disruption to the carefully planned cellular networks that now connect a majority of the planet's citizens to the Internet and with each other. Femtocells - which by the end of 2010 already outnumbered traditional base stations and at the time of publication are being deployed at a rate of about five million a year - both enhance and interfere with this network in ways that are not yet well understood. Will femtocells be crucial for offloading data and video from the creaking traditional network? Or will femtocells prove more trouble than they are worth, undermining decades of careful base station deployment with unpredictable interference while delivering only limited gains? Or possibly neither: are femtocells just a "flash in the pan"; an exciting but short-lived stage of network evolution that will be rendered obsolete by improved WiFi offloading, new backhaul regulations and/or pricing, or other unforeseen technological developments? This tutorial article overviews the history of femtocells, demystifies their key aspects, and provides a preview of the next few years, which the authors believe will see a rapid acceleration towards small cell technology. In the course of the article, we also position and introduce the articles that headline this special issue.

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Femtocells: Past, Present, and Future

Support of femtocells is an integral part of the Long Term Evolution - Advanced (LTE-A) system and a key enabler for its wide adoption in a broad scale. Femtocells are short-range, low-power and low-cost cellular stations which are installed by the consumers in an unplanned manner. Even though current literature includes various studies towards understanding the main challenges of interference management in the presence of femtocells, little light has been shed on the open issues of mobility management (MM) in the two-tier macrocell-femtocell network. In this paper, we provide a comprehensive discussion on the key aspects and research challenges of MM support in the presence of femtocells, with the emphasis given on the phases of a) cell identification, b) access control, c) cell search, d) cell selection/reselection, e) handover (HO) decision, and f) HO execution. A detailed overview of the respective MM procedures in the LTE-A system is also provided to better comprehend the solutions and open issues posed in real-life systems. Based on the discussion for the HO decision phase, we subsequently survey and classify existing HO decision algorithms for the two-tier macrocell-femtocell network, depending on the primary HO decision criterion used. For each class, we overview up to three representative algorithms and provide detailed flowcharts to describe their fundamental operation. A comparative summary of the main decision parameters and key features of selected HO decision algorithms concludes this work, providing insights for future algorithmic design and standardization activities.

Mobility Management for Femtocells in LTE-Advanced: Key Aspects and Survey of Handover Decision Algorithms

A method to provide an optimized intra-HeNB GW handover operation that reduces signaling to and from an LTE MME (Mobility Management Entity) function of the 3GPP E-UTRAN Evolved Packet core (EPC). In operation, an HeNB Gateway (GW) intercepts handover requests from a source HeNB to a target HeNB and processes these requests locally, with minimal interaction from the MME. Where possible, messaging to and from the MME is minimized and/or reduced, irrespective of the 3GPP requirement that the GW relay all handover-related messages to the MME.

Optimized Home Evolved NodeB (eNB) Handover in an LTE Network

This paper provides an overview of the use of small cells (e.g., femtocells) in the Internet of Things (IoT) environments. As a result of rapid increase in the number of mobile connected devices such as smart-phones and tablets, the demand for data traffic is exponentially increasing. In order to satisfy mobile users’ requests and meet the requirements of high data traffic, mobile operators have to increase the network capacities dramatically. One of the promising solutions for the network operators to improve coverage and capacity, and provide high data rate services in a less costly manner is the deployment of femtocells related technologies. Femtocells will help mobile operators to provide a basis for the next generation of services which are a combination of voice, video, and data services to mobile users. Moreover, proper traffic modelling and deployment strategies of femtocells will improve the overall performance of the femtocell network. Therefore, in this survey paper, we overview modelling traffic and deployment strategies in femtocells and provide a review for the use of femtocells and their applications in the IoT environments. In addition, we present open research issues associated with IoT-femtocell based applications.

Small Cells in the Forthcoming 5G/IoT: Traffic Modelling and Deployment Overview

In this paper a survey of the research effort invested in the analysis of multicasting over wireless access networks from the late nineties onwards is presented. The analysis is dedicated although not limited to video multicasting both of live events and pre-stored video streaming. This investigation was not limited to a particular access network but focused on infrastructure topologies, including ad-hoc networks only when the latter was used to aid the former, which is a method frequently used in cooperative networking. We were interested in proposals aiming to decrease the packet error rate, in order to overcome the bursty error-prone wireless medium, since multicasting cannot simply receive feedback from the users as these will reply simultaneously causing a collision at the source. Hence, in this survey a review is presented showing how researchers proposed to solve this constraint using both modified unicast data transmission and also error correction techniques at various levels of the network protocol stack. However, a survey of multicasting over IEEE 802.16 and 3G radio access networks shows that reliability and resilience was not the only interest in which researchers have shown. There was in fact significant work dedicated to resource allocation as shall also be presented hereafter.

A Survey of Multicasting over Wireless Access Networks

Femtocell, a small cellular base station in home and small business environment, is an attractive solution for operators to improve indoor coverage and network capacity in 3G networks. However, there are technical problems due to its mass deployment. The paper presents a femtocell architecture for LTE and investigates different handover scenarios. Two mobility management schemes at radio network layer (RNL) are proposed and their signaling cost, complexity, standard impact and application scenarios are also discussed.

Mobility Management Schemes at Radio Network Layer for LTE Femtocells

In this paper, we propose a MAC layer multicast protocol for 802.11n WLAN for the first time. In IEEE 802.11n, new feature at MAC layer, such as frame aggregation and more flexible link adaptation are defined to increase the effective throughput. Recently, several multicast protocols at MAC layer have been proposed for WLAN. However, these protocols don't consider the new features defined in 802.11n, and cannot satisfy the requirement of fast speed transmission. In our proposed multicast protocol, "Double Piggyback Mode Multicast Protocol (DPMM)", we use new features (frame aggregation and link adaptation) in 802.11n to improve the multicast throughput. With DPMM, ACK packets are eliminated and collisions of control frames are avoided. A CHs (Cluster Heads) selection mechanism using Success Threshold is also developed to further improve upon DPMM. Simulation results, using the OPNET, confirm that the improvements are encouraging.

Supporting MAC Layer Multicast in IEEE 802.11n: Issues and Solutions

In this paper, we study reliable multicast at the MAC layer for IEEE 802.11 wireless LANs. In IEEE 802.11, multicast protocol is based on the basic access procedure of carrier sense multiple access with collision avoidance (CSMA/CA). This protocol does not provide any recovery mechanism for multicast frames. As a result, transmitted multicast frames may be lost due to collisions or errors. Recently, several reliable multicast protocols at MAC layer have been proposed for 802.11, and they can be classified into two categories: one is based on negative feedback (NFB-based) and the other is based on positive feedback (PFB-based). We first analyze the problems with existing reliable multicast MAC protocols and then propose a novel PFB-based scheme: "Extended Implicit MAC Acknowledgment (EIA)". With EIA, ACK packets are eliminated and collisions of CTS frames are avoided. Since ACK packets account for nearly one-third of the total control overhead, we argue that such a scheme can be beneficial. Simulation results, using the OPNET, confirm that the improvements are encouraging.

Reliable Multicast Mechanism in WLAN with Extended Implicit MAC Acknowledgment

The invention provides a real world living broadcast system, comprising a plurality of living broadcast content collecting devices and each living broadcast device collects the living broadcast information at current position and updates the collected living broadcast information to a content server, a plurality of content servers which are used for collecting the living broadcast information collected in-situ by the living broadcast content collecting devices, caches the living broadcast information, manages the living broadcast information and controls the access-in of the living broadcast content collecting devices on the content servers, a distribution server which is used for processing the service request of the terminal subscriber and transferring the living broadcast information to the terminal subscriber from the content servers, and a connecting network which is used for connecting the content servers with the distribution server so as to transmit the information between thecontent servers and the distribution server and distribute the living broadcast information to the terminal subscriber to the network.

Real world broadcasting system and method

In IEEE 802.11, multicast protocol is based on the basic access procedure of Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). This protocol does not provide any recovery mechanism for multicast frames. As a result, transmitted multicast frames may be lost due to collisions or errors. Recently, several reliable multicast protocols at MAC layer have been proposed for 802.11. They can be classified into two categories: one is based on negative feedback (NFB-based) and the other is based on positive feedback (PFB-based). After analyzing the problems with existing reliable multicast MAC protocols, we propose a novel PFB-based multicast protocol, namely DPMM (Double Piggyback Mode Multicast). The protocol piggybacks the ACK in the CTS frame and piggybacks the priority information in the DATA frames. With DPMM, ACK packets are eliminated and collisions of control frames are avoided. A grouping algorithm using RSS (Received signal strength) measurement is also developed to further improve upon DPMM. Simulation results, using the OPNET, confirm that the improvements are encouraging.

A Reliable and Efficient MAC Layer Multicast Protocol in Wireless LANs

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