Physical layer metrics for vertical handover toward OFDM-based networks

Abstract

The emerging trend to provide users with ubiquitous seamless wireless access leads to the development of multimode terminals able to smartly switch between heterogeneous wireless networks. This switching process known as vertical handover requires the terminal to first measure various network metrics relevant to decide whether to trigger a vertical handover (VHO) or not. This paper focuses on current and next-generation networks that rely on an OFDM physical layer with either a CSMA/CA or an OFDMA multiple-access technique. Synthesis of several signal feature estimators is presented in a unified way in order to propose a set of complementary metrics (SNR, channel occupancy rate, collision rate) relevant as inputs of vertical handover decision algorithms. All the proposed estimators are "non-data aided" and only rely on a physical layer processing so that they do not require multimode terminals to be first connected to the handover candidate networks. Results based on a detailed performance study are presented to demonstrate the efficiency of the proposed algorithms. In addition, some experimental results have been performed on a RF platform to validate one of the proposed approaches on real signals.

Physical layer metrics estimation for CSMA/CA networks using a Markov modeling and source enumeration

“…We observe that even with this bad choice of the transition probabilities the proposed algorithm still has a good estimation capabilities of the channel occupancy rate. Figure 8 compares the performance of our algorithm to the ones proposed in [6], [4]. We observe that the proposed approach out performs both techniques based on Akaike Information Criterion (AIC) and Minimum Description Length (MDL).…”

“…The main drawback of this method is that it requires to be connected to the access point in order to obtain the NAV information from the header, this may increases the decision time if many standards or Access Point (AP) are detected. An alternative technique has been presented in [4], [5], [6] for the estimation of the channel occupancy rate. This technique relies on a physical layer sensing, but requires the knowledge of noise variance and does not give any information about the collision rate which is a complementary metric to the channel occupancy rate.…”

“…Thus, higher is the collision rate, lower is the available QoS. To the best of our knowledge, the only passive technique for collision detection has been studied in [4], [6]. Unfortunately, this method needs the knowledge of the edges of the frame (the start and end points) in order to apply information theoretic criterion to test if a collision is occurred.…”

“…In (6) the number of active sources is the number of eigenvalues of R(k) which are larger than σ 2 (k) and is in fact a function of the time k and needs to be determined. We propose the following a four steps soft enumeration algorithm to determine the probability of each hypothesis in (2), recurssively.…”

“…We observe that the proposed approach out performs both techniques based on Akaike Information Criterion (AIC) and Minimum Description Length (MDL). this mainly due to the fact that the estimation is done jointly in our approach, when in the other hand for [6], [4] we first need to estimate the number of frame using [5] than extract the ones suffering of a collision. Thus two independent sources of error are possible in that case : one in the numerator and one in the denominator.…”