Cooperative synchronization and channel estimation in wireless sensor networks

Abstract

A critical issue in applications involving networks of wireless sensors is their ability to synchronize, and mitigate the fading propagation channel effects. Especially when distributed "slave" sensors (nodes) reach-back to communicate with the "master" sensor (gateway), low power cooperative schemes are well motivated. Viewing each node as an antenna element in a multi-input multioutput (MIMO) multi-antenna system, we design pilot patterns to estimate the multiple carrier frequency offsets (CFO), and the multiple channels corresponding to each node-gateway link. Our novel pilot scheme consists of non-zero pilot symbols along with zeros, which separate nodes in a time division multiple access (TDMA) fashion, and lead to low complexity schemes because CFO and channel estimators per node are decoupled. The resulting training algorithm is not only suitable for wireless sensor networks, but also for synchronization and channel estimation of single-and multicarrier MIMO systems. We investigate the performance of our estimators analytically, and with simulations.

Timing and frequency synchronization for OFDM based cooperative systems

“…The N ch part of the CP is dedicated to accommodating the channel delay spreads, and the N dl part of the CP and the PP, whose length is denoted by N pp , are inserted to accommodate the different propagation delays among relay nodes. It is worth pointing out that the proposed training sequences introduce a lower overhead than TDM training sequences adopted in [4], since long guard time intervals are required by each TDM training sequence. The structure of the proposed training sequence is shown in Figure 2.b.…”

“…Unlike [4] which uses a TDM training sequence to avoid the multidimensional search, we adopt a frequency-domain multiplexing for our training design in order to obtain low overhead.…”

“…To avoid the multidimensional search required by maximumlikelihood (ML) synchronization, a time division multiplexing (TDM) training based synchronization algorithm was proposed in [4]. However, although the resulting algorithms are computationally attractive, the overhead is extremely high since long guard time intervals may be required to avoid overlap of different relay node's signals, especially in mobile networks where the assignment of relay nodes can be highly dynamic.…”

Blind Timing and Carrier Synchronization in Decode and Forward Cooperative Systems

“…Multiple carrier offset estimation using pilots or training sequences has been considered in the context of general MIMO systems [4], MIMO-OFDM systems [5]- [7], sensor networks [8] and Decode and Forward (DF) and Amplify and Forward (AF) cooperative networks [9]. Multiple timing offset estimation has been considered in the context of DF cooperative systems [10], using pilots to design a resynchronization filter to align asynchronous signals at the destination.…”

Carrier Frequency Offset in Coordinated Multibase MIMO Narrowband Systems

“…Therefore, our second topic in this paper is a method for estimation of the several CFOs by each mobile subscriber (MS). Unlike existing methods [4], [5], [6] our method copes with loss of orthogonality of training sequences and requires much less peak power from the expensive radio power amplifiers.…”