Scalable feedback control for distributed beamforming in sensor networks

Abstract — Recent work has shown that large gains in communication capacity are achievable by distributed beamforming in sensor networks. The principal challenge in realizing these gains in practice, is in synchronizing the carrier signal of individual sensors in such a way that they combine coherently at the intended receiver. In this paper, we provide a scalable mechanism for achieving phase synchronization in completely distributed fashion, based only on feedback regarding the power of the net received signal. Insight into the workings of the protocol is obtained from a simple theoretical model that provides accurate performance estimates. I

Distributed transmit beamforming using feedback control

A simple feedback control algorithm is presented for distributed beamforming in a wireless network. A network of wireless sensors that seek to cooperatively transmit a common message signal to a Base Station (BS) is considered. In this case, it is well-known that substantial energy efficiencies are possible by using distributed beamforming. The feedback algorithm is shown to achieve the carrier phase coherence required for beamforming in a scalable and distributed manner. In the proposed algorithm, each sensor independently makes a random adjustment to its carrier phase. Assuming that the BS is able to broadcast one bit of feedback each timeslot about the change in received signal to noise ratio (SNR), the sensors are able to keep the favorable phase adjustments and discard the unfavorable ones, asymptotically achieving perfect phase coherence. A novel analytical model is derived that accurately predicts the convergence rate. The analytical model is used to optimize the algorithm for fast convergence and to establish the scalability of the algorithm. Index Terms Distributed beamforming, synchronization, wireless networks, sensor networks, space-time commu-nication

Datacollection in Event-Driven Wireless Sensor Networks with Mobile Sinks

We present a two-tier distributed hash table-based scheme for data-collection in event-driven wireless sensor networks. The proposed method leverages mobile sinks to significantly extend the lifetime of the sensor network. We propose localized algorithms using a distributed geographic hash-table mechanism that adds load balancing capabilities to the data-collection process. We address the hotspot problem by rehashing the locations of the mobile sinks periodically. The proposed mobility model moves the sink node only upon the occurrence of an event according to the evolution of current events, so as to minimize the energy consumption incurred by the multihop transmission of the event-data. Data is collected via single-hop routing between the sensor node and the mobile sink. Simulation results demonstrate significant gains in energy savings, while keeping the latency and the communication overhead at low levels for a variety of parameter values. © 2010 Harshavardhan Sabbineni and Krishnendu Chakrabarty