Rakesh Shrestha

LTE in the Unlicensed Spectrum: A Survey

ABSTRACT Fueled by the increasing popularity of handheld mobile devices with powerful data processing capabilities, the wireless industry is witnessing an avalanche of mobile traffic. This unprecedented escalation has imposed significant challenges due to the limited licensed spectrum for cellular networks. Any effort to achieve capacity growth through network densification will face the challenge of severe inter-cell interference. Among the most effective solutions to this issue is to make the best use of all spectrum types through matured technology. Long-term evolution (LTE) access to unlicensed spectrum is considered one of the latest groundbreaking innovations to provide high-performance and a seamless user experience under a unified radio technology by extending LTE to the readily available unlicensed spectrum. In this article, we introduce the dawn of LTE access to unlicensed spectrum as a boon to the spectrum scarcity problem. Then, we explore deployment scenarios for LTE in unlicensed spectrum. We further identify key issues in bringing LTE unlicensed spectrum access to reality, together with other technologies for accessing unlicensed spectrum, specifically Wi-Fi. Finally, we discuss some existing coexistence mechanisms for successful, harmonious deployment of LTE and Wi-Fi in the same unlicensed band.

Challenges of Future VANET and Cloud-Based Approaches

Vehicular ad hoc networks (VANETs) have been studied intensively due to their wide variety of applications and services, such as passenger safety, enhanced traffic efficiency, and infotainment. With the evolution of technology and sudden growth in the number of smart vehicles, traditional VANETs face several technical challenges in deployment and management due to less flexibility, scalability, poor connectivity, and inadequate intelligence. Cloud computing is considered a way to satisfy these requirements in VANETs. However, next-generation VANETs will have special requirements of autonomous vehicles with high mobility, low latency, real-time applications, and connectivity, which may not be resolved by conventional cloud computing. Hence, merging of fog computing with the conventional cloud for VANETs is discussed as a potential solution for several issues in current and future VANETs. In addition, fog computing can be enhanced by integrating Software-Defined Network (SDN), which provides flexibility, programmability, and global knowledge of the network. We present two example scenarios for timely dissemination of safety messages in future VANETs based on fog and a combination of fog and SDN. We also explained the issues that need to be resolved for the deployment of three different cloud-based approaches.

LTE or LAA: Choosing Network Mode for My Mobile Phone in 5G Network

Long Term Evolution (LTE) in unlicensed spectrum, Licensed Assisted Access (LAA), has been considered as an effective complement in offloading growing traffic. The LAA is expected to be deployed initially through the small cell integrated under LTE macro cell. Therefore, LTE users under the coverage of LAA small cell must decide to connect one of the co-located networks either LTE or LAA to maximize their performance. In this scenario, we model a network selection game for LTE users using mixed strategy game theoretic approach. Afterwards, we formulate behavior of strategic users toward network selection as a function of the number of nearby users. The simulation results show that increasing number of nearby users make a user less likely to switch to LAA small cell. Additionally, more users nearby make it less likely that LAA resources is being utilized.

Trustworthy Event-Information Dissemination in Vehicular Ad Hoc Networks

In vehicular networks, trustworthiness of exchanged messages is very important since a fake message might incur catastrophic accidents on the road. In this paper, we propose a new scheme to disseminate trustworthy event information while mitigating message modification attack and fake message generation attack. Our scheme attempts to suppress those attacks by exchanging the trust level information of adjacent vehicles and using a two-step procedure. In the first step, each vehicle attempts to determine the trust level, which is referred to as truth-telling probability, of adjacent vehicles. The truth-telling probability is estimated based on the average of opinions of adjacent vehicles, and we apply a new clustering technique to mitigate the effect of malicious vehicles on this estimation by removing their opinions as outliers. Once the truth-telling probability is determined, the trustworthiness of a given message is determined in the second step by applying a modified threshold random walk (TRW) to the opinions of the majority group obtained in the first step. We compare our scheme with other schemes using simulation for several scenarios. The simulation results show that our proposed scheme has a low false decision probability and can efficiently disseminate trustworthy event information to neighboring vehicles in VANET.

Sybil attack detection in vehicular network based on received signal strength

Vehicular networks are vulnerable to many security threats. One of the security threats is Sybil attack, and traditional security solutions which are based on cryptography and centralized authority are insufficient to protect vehicular network from Sybil attacks. We present a lightweight solution for Sybil attacks based on received signal strength. Our scheme is lightweight enough to be used by independent vehicles without using centralized trusted third party and additional hardware like GPS. We show through the experiments that it is possible to detect Sybil attacks by using received signal strength of the neighboring vehicles.

Access point selection mechanism to circumvent rogue access points using voting-based query procedure

One of the challenging issues in wireless network is rogue access point (RAP) detection and mitigation. The authors propose a new access point (AP) selection mechanism to keep wireless users from RAPs. A centralised server called AP registration centre (APRC) maintains a list of authorised APs, and a wireless user can check if a specific AP is legitimate by querying APRC about its legitimacy in a secure way using the concept of voting and signal strength-based authentication. The authors compare their scheme with a timing-based scheme and the experiment results show that our scheme detects RAPs accurately with lower false positives and false negatives.