Yeong Min Jang

Call admission control based on adaptive bandwidth allocation for wireless networks

Provisioning of quality of service (QoS) is a key issue in any multi-media system. However, in wireless systems, supporting QoS requirements of different traffic types is a more challenging problem due to the need to simultaneously minimize two performance metrics - the probability of dropping a handover call and the probability of blocking a new call. Since QoS requirements are not as stringent for non-real-time traffic, as opposed to real-time traffic, more calls can be accommodated by releasing some bandwidth from the already admitted non-real-time traffic calls. If the released bandwidth that is used to handle handover calls is larger than the released bandwidth that is used for new calls, then the resulting probability of dropping a handover call is smaller than the probability of blocking a new call. In this paper, we propose an efficient call admission control algorithm that relies on adaptive multi-level bandwidth-allocation scheme for non-realtime calls. The scheme allows reduction of the call dropping probability, along with an increase in the bandwidth utilization. The numerical results show that the proposed scheme is capable of attaining negligible handover call dropping probability without sacrificing bandwidth utilization.

Cost-Effective Frequency Planning for Capacity Enhancement of Femtocellular Networks

The femto-access-point, a low-cost and small-size cellular base-station, is envisioned to be widely deployed in subscribers homes, as to provide high data-rate communications with improved quality of service. As femtocellular networks will co-exist with macrocellular networks, mitigation of the interference between these two network types is a key challenge for successful integration of these two technologies. In particular, there are several interference mechanisms between the femtocellular and the macrocellular networks, and the effects of the resulting interference depend on the density of femtocells and the overlaid macrocells in a particular coverage area. While improper interference management can cause a significant reduction in the system capacity and can increase the outage probability, effective and efficient frequency allocation among femtocells and macrocells can result in a successful co-existence of these two technologies. Furthermore, highly dense femtocellular deployments—the ultimate goal of the femtocellular technology—will require significant degree of self-organization in lieu of manual configuration. In this paper, we present various femtocellular network deployment scenarios, and we propose a number of frequency-allocation schemes to mitigate the interference and to increase the spectral efficiency of the integrated network. These schemes include: shared frequency band, dedicated frequency band, sub-frequency band, static frequency-reuse, and dynamic frequency-reuse. We derive an analytical model, which allows us to analyze in details the users outage probability, and we compare the performance of the proposed schemes using numerical analysis.

Handover management in high-dense femtocellular networks

Femtocell technology is envisioned to be widely deployed in subscribers’ homes to provide high data rate communications with quality of service. Dense deployment of femtocells will offload large amounts of traffic from the macrocellular network to the femtocellular network by the successful integration of macrocellular and femtocellular networks. Efficient handling of handover calls is the key for successful femtocell/macrocell integration. For dense femtocells, intelligent integrated femtocell/macrocell network architecture, a neighbor cell list with a minimum number of femtocells, effective call admission control (CAC), and handover processes with proper signaling are the open research issues. An appropriate traffic model for the integrated femtocell/macrocell network is also not yet developed. In this article, we present the major issues of mobility management for the integrated femtocell/macrocell network. We propose a novel algorithm to create a neighbor cell list with a minimum, but appropriate, number of cells for handover. We also propose detailed handover procedures and a novel traffic model for the integrated femtocell/macrocell network. The proposed CAC effectively handles various calls. The numerical and simulation results show the importance of the integrated femtocell/macrocell network and the performance improvement of the proposed schemes. Our proposed schemes for dense femtocells will be very effective for those in research and industry to implement.

Service quality improvement of mobile users in vehicular environment by mobile femtocell network deployment

The femto-access-point (FAP), a low power small cellular base station provides better signal quality for the indoor users. The mobile users in the vehicular environment suffer for the low quality signal from the outside wireless networks. The deployment of femtocells in the vehicular environment can solve the low level signal-to-noise plus interference problem. In this paper, we propose new application of the femtocell technology. The femtocells are deployed in the vehicular environment. Short distance between the user and the FAP provides better signal quality. The inside FAPs are connected to the core network through the outside macrocellular networks or the satellite networks. One stronger transceiver is installed at outside the vehicle. This transceiver is connected to FAPs using wired connection and to macrocellular or the satellite access networks through wireless link. The capacity and the outage probability are analyzed. The simulation results show that the proposed mobile femtocell deployment significantly enhances the service quality of mobile users in the vehicular environment.

A novel link switching scheme using pre-scanning and RSS prediction in visible light communication networks

Visible light communication (VLC) is gaining increasing attention and is considered as a promising technology for future wireless indoor communications. Because movable users expect a seamless connectivity experience when switching among transmitters (i.e., VLC access points) in the VLC system, fast link switching operations must be supported by the networks. This paper presents a novel hard link switching scheme for VLC networks with the use of pre-scanning and received signal strength (RSS) prediction. Our proposed scheme achieves the advantages of both conventional hard and soft link switching schemes without changing device hardware or the IEEE 802.15.7 medium access control (MAC) protocol. To help compare our proposed scheme with conventional hard and soft link switching schemes, the signal-to-interference-plus-noise ratio (SINR), the outage probability regarding the link switching situation, and the queuing models for link switching schemes are taken into account. Simulation and numerical results validate that our proposed scheme outperforms conventional hard and soft link switching schemes.

Interference mitigation using dynamic frequency re-use for dense femtocell network architectures

The next generation network aims to efficiently deploy low cost and low power cellular base station in the subscribers home environment. For the femtocell deployment, frequency allocation among femtocells and macrocell is big concern to mitigate the interference, and to ensure the best use of the expensive spectrum. There are many sources of interference in integrated femtocell/macrocell networks. Lagging in proper management of interference reduces the system capacity, increases the outage probability, and finally users feel bad quality of experience (QoE). The cost effective interference management technique depends on the size of femtocells deployment. In this paper, firstly we present deployable various possible femtocell network scenarios. We propose the dynamic frequency re-use scheme to mitigate interference for femtocell deployment. For highly dense femtocells, we propose the functionalities of self organizing network (SON) based femtocell network architecture. The outage probability of a femtocell user is analyzed in details. The performances of the proposed schemes for various femtocell deployments are performed using numerical analysis.

Neighbor cell list optimization for femtocell-to-femtocell Handover in dense femtocellular networks

Dense femtocells are the ultimate goal of the femtocellular network deployment. Among three types of handovers: femtocell-to-macrocell, macrocell-to-femtocell, and femtocell-to-femtocell, the latter two are the main concern for the dense femtocellular network deployment. For these handover cases, minimum as well appropriate neighbor cell list is the key element for the successful handover. In this paper, we propose an algorithm to make minimum but appropriate number of neighbor femtocell list for the femtocell-to-femtocell handover. Our algorithm considers received signal level from femto APs (FAPs); open and close access cases; and detected frequency from the neighbor femtocells. The simulation results show that the proposed scheme is able to attain minimum but optimal number of neighbor femtocell list for the possible femtocell-to-femtocell handover.

Mitigation Technique for Receiver Performance Variation of Multi-Color Channels in Visible Light Communication

“Green” and energy-efficient wireless communication schemes have recently experienced rapid development and garnered much interest. One such scheme is visible light communication (VLC) which is being touted as one of the next generation wireless communication systems. VLC allows communication using multi-color channels that provide high data rates and illumination simultaneously. Even though VLC has many advantageous features compared with RF technologies, including visibility, ubiquitousness, high speed, high security, harmlessness for the human body and freedom of RF interference, it suffers from some problems on the receiver side, one of them being photo sensitivity dissimilarity of the receiver. The photo sensitivity characteristics of a VLC receiver such as Si photo-detector depend on the wavelength variation. The performance of the VLC receiver is not uniform towards all channel colors, but it is desirable for receivers to have the same performance on each color channel. In this paper, we propose a mitigation technique for reducing the performance variation of the receiver on multi-color channels. We show received power, SNR, BER, output current, and outage probability in our simulation for different color channels. Simulation results show that, the proposed scheme can reduce the performance variation of the VLC receiver on multi-color channels.

Asynchronous scheme for optical camera communication-based infrastructure-to-vehicle communication

This paper introduces infrastructure-to-vehicle (I2V) communication based on asynchronous optical camera communication (OCC), the transmitter of which can be an LED traffic light or electronic display, with the receiver being the existing front vehicle camera. In asynchronous OCC-based I2V communication, the key technique is an asynchronous scheme. An asynchronous scheme not only takes advantage of simplicity owing to the lack of an uplink or synchronization requirement, but is also the most feasible solution for communication to/from moving vehicles where synchronization is difficult to achieve within a short time. An asynchronous scheme for OCC-based I2V communication is proposed, and a performance evaluation shows its feasibility for use in a number of promising OCC-based wireless communication applications and services in a vehicular environment.

Group handover management in mobile femtocellular network deployment

The mobile femtocell is the new paradigm for the femtocellular network deployment. It can enhance the service quality for the users inside the vehicles. The deployment of mobile femtocells generates lot of handover calls. Also, number of group handover scenarios are found in mobile femtocellular network deployment. In this paper, we focus on the resource management for the group handover in mobile femtocellular network deployment. We discuss a number of group handover scenarios. We propose a resource management scheme that contains bandwidth adaptation policy and dynamic bandwidth reservation policy. The simulation results show that the proposed bandwidth management scheme significantly reduces the handover call dropping probability without reducing the bandwidth utilization.