In high speed rail wireless networks, handover between evolved Node Bs(eNBs) occurs frequently, and the probability of handover failure is dramatically increased, thus seriously degrading the users' experience. To tackle this issue, this paper proposes a network-assisted mobile relay (MR)- controlled fast handover scheme. Under this scheme, the serving eNB provides, in advance, the network assistance information about the available resources of the target eNB, to MR. The MR then makes the handover decision based on continual measurements. Different from the conventional handover scheme, in the proposed scheme, the handover decision is made by the MR instead of eNB. Simulation results show that this scheme can effectively improve handover performance, in terms of handover failure and communication interruption probabilities.

Long Term Evolution uses a new location update (LU) scheme, called a tracking area list (TAL)-based scheme, to overcome the defects of the LU scheme used in 2G and 3G cellular networks. Under the TAL-based LU scheme, each time a user equipment (UE) performs an LU, it is allocated a group of tracking areas, referred to as a TAL, within which the UE can move freely without any LU. The UE performs an LU when moving out of the TAL. The performance of the TAL-based LU scheme depends on the allocated TAL. In this paper we develop a mathematical model to analyze the signaling overhead of the TAL-based LU scheme for local UEs whose mobility exhibits strong regularity. We derive formulas for the LU cost and the paging cost of a TAL allocation strategy. With these formulas we can find an optimal TAL allocation strategy to minimize the signaling cost of the TAL-based LU scheme.

In this paper, switch-and-stay combining (SSC) is considered in two-way relay systems with amplify-and-forward (AF) relays, among which one is activated to assist the information exchange between two sources. We assume that the two-way relay system operates in the analog network coding (ANC) protocol where the communication can only be achieved through the active relay without the direct link. The outage probability and the average bit error rate (BER) for Rayleigh fading channels are studied. In particular, we derive closed-form lower bounds for the outage probability and the average BER, which is tight for different fading conditions. Moreover, we present asymptotic analysis for both the outage probability and the average BER at high signal-to-noise ratio (SNR) region. It is shown that SSC can achieve the full diversity order in two-way relay systems with proper switching thresholds. Numerical and simulation results are also provided to verify the theoretical study.

The security and privacy preservation issues are prerequisites for vehicular ad hoc networks. Recently, secure and privacy enhancing communication schemes (SPECS) was proposed and focused on intervehicle communications. SPECS provided a software-based solution to satisfy the privacy requirement and gave lower message overhead and higher successful rate than previous solutions in the message verification phase. SPECS also presented the first group communication protocol to allow vehicles to authenticate and securely communicate with others in a group of known vehicles. Unfortunately, we find out that SPECS is vulnerable to impersonation attack. SPECS has a flow such that a malicious vehicle can force arbitrary vehicles to broadcast fake messages to other vehicles or even a malicious vehicle in the group can counterfeit another group member to send fake messages securely among themselves. In this paper, we provide a secure scheme that can achieve the security and privacy requirements, and overcome the weaknesses of SPECS. Moreover, we show the efficiency merits of our scheme through performance evaluations in terms of verification delay and transmission overhead.

Relay is one of the key technologies used by both the Third Generation Partnership Project (3GPP) Long Term Evolution-Advanced (LTE-Advanced) and IEEE 802.16m to ameliorate cell edge throughput. Despite the throughput enhancement achieved by deploying relay stations (RSs), wireless systems supporting relay are vulnerable to frequent handoffs, which deteriorate the dropping performance of realtime communications. This paper proposes a mathematical model to appraise the dropping performance of the eNB-first channel access policy in LTE-Advanced relay networks. The eNB-first policy prefers an eNB-channel over a RS-channel when determining an access channel for a new and a handoff call. Closed-form analytical result is obtained for the dropping probability of the eNB-first policy and based on the result a numerical study is conducted to evaluate the influences of various parameters on the dropping performance. The result developed in this paper can be used to adjust the call admission control strategies to get acceptable dropping performance in LTE-Advanced relay networks.

A call admission control scheme named thinning scheme, which smoothly throttles the admission rates of calls according to their priorities and aims to provide multiple prioritized traffic with a desired quality of service, is investigated under more general conditions. Using the theory of multidimensional Markov birth-death process, analytical formulas for call blocking probabilities are derived.