Then the sensor proxy delivers the data to
the query processor. Thus, the sensor proxy shields the sensor from having to
deliver data to hundreds of interested end-users. In addition, the sensor proxy
directs sensors to perform certain local computations to aggregate samples in
a predefined way. Moreover, the sensor proxy actively monitors sensors, evaluates
user needs and current power conditions, and appropriately programs
and controls sensors??™ sampling rate and delivery rate to achieve acceptable
290
Chapter 12 Data Management in Sensor Networks
Fig. 1. Architecture of Fjord [13].
sensor battery lifetime and performance.
(2) Cougar
Cougar is a sensor database project developed at Cornell University [7, 4].
The basic idea of this project is to push as much computation as possible into
the sensor network to reduce the communication between sensor nodes and
front-end server(s). In this model, the query workload determines the data that
should be extracted from sensors. The approach is thus flexible and e?±cient
since only relevant data are extracted from the sensor network. Di?®erent from
Fjord, sensors in Cougar not only performs local computation over its own
sampling data, it also communicates with nearby sensors to perform certain
aggregations, labelled as ???in-network aggregation??? in Figure 2.
Fig. 2. Architecture of Cougar [22].
291
Jinbao Li, Zhipeng Cai, and Jianzhong Li
2.3 Distributed Model
In this model, each sensor is assumed to have high storage, computation and
communication capabilities.
Pages:
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470