Clock synchronization is essential for a large number of applications ranging from performance measurements in wired networks to data fusion in sensor networks. Existing techniques are either limited to undesirable accuracy or rely on specific hardware characteristics that may not be available in certain applications. In this paper, we examine the clock synchronization problem in networks where nodes lack the high-accuracy oscillators or programmable network interfaces some previous protocols depend on. This paper derives a general model for clock offset and skew and demonstrates its application to real clock oscillators. We design an efficient algorithm based on this model to achieve high synchronization accuracy. This algorithm applies the Kalman filter to track the clock offset and skew. We demonstrate the performance advantages of our schemes through extensive simulations and real clock oscillator measurements.

Wireless communication systems are increasingly adopting orthogonal frequency division multiplexing (OFDM) to enable efficient high-data rate transmissions. Such systems often employ pilot symbols to estimate wireless channels, and null subcarriers on band edges to reduce adjacent channel interference. Recent work has focused on designing the pilot sequence to improve channel estimation performance. In this paper, we present a new pilot design for OFDM systems based on a arbitrary-order polynomial parameterization of the pilot subcarrier indices. We show our design achieves better performance than existing methods. Theoretical models and simulated performance demonstrate the increased accuracy of our design.

Clock synchronization across a network is essential for a large number of applications ranging from wired network measurements to data fusion in sensor networks. Earlier techniques are either limited to undesirable accuracy or rely on specific hardware characteristics that may not be available for certain systems. In this work, we examine the clock synchronization problem in resource-constrained networks such as wireless sensor networks where nodes have limited energy and bandwidth, and also lack the high accuracy oscillators or programmable network interfaces some previous protocols depend on. This paper derives a general model for clock offset and skew and demonstrates its applicability. We design efficient algorithms based on this model to achieve high synchronization accuracy given limited resources. These algorithms apply the Kalman filter to track the clock offset and skew, and adaptively adjust the synchronization interval so that the desired error bounds are achieved. We demonstrate the performance advantages of our schemes through extensive simulations obeying real-world constraints.

Routing in wireless networks confronts more diverse and more rapidly varying characteristics associated with wireless links. Several recent protocols have tried to exploit cooperative diversity to deal with these channel characteristics, but they suffer from large overhead costs due to the need for collaboration among candidate nodes of next hop. We propose a novel routing protocol that is able to realize cooperative diversity without exchanging information among candidate nodes. Our protocol divides the routing decision between the transmitter and the receivers: the transmitter decides the direction and an angle spread to broadcast the packet; each receiver, without communicating each other, decides whether to start a timer whose duration depends on the strength of the channel state information. The node with shortest timer transmits first and thus becomes the transmitter for the next hop. Thus, a multi-hop route is found in a noncooperative way where the communication overhead is minimal, and we show that cooperative diversity is collected. The performance characteristics and design parameters of this protocol are first theoretically analyzed, and then examined in a realistic network setting through simulations.