Joint Source–Channel Communication for Distributed Estimation in Sensor Networks

Power and bandwidth are scarce resources in dense wireless sensor networks and it is widely recognized that joint optimization of the operations of sensing, processing and communication can result in significant savings in the use of network resources. In this paper, a distributed joint source-channel communication architecture is proposed for energy-efficient estimation of sensor field data at a distant destination and the corresponding relationships between power, distortion, and latency are analyzed as a function of number of sensor nodes. The approach is applicable to a broad class of sensed signal fields and is based on distributed computation of appropriately chosen projections of sensor data at the destination - phase-coherent transmissions from the sensor nodes enable exploitation of the distributed beamforming gain for energy efficiency. Random projections are used when little or no prior knowledge is available about the signal field. Distinct features of the proposed scheme include: (1) processing and communication are combined into one distributed projection operation; (2) it virtually eliminates the need for in-network processing and communication; (3) given sufficient prior knowledge about the sensed data, consistent estimation is possible with increasing sensor density even with vanishing total network power; and (4) consistent signal estimation is possible with power and latency requirements growing at most sublinearly with the number of sensor nodes even when little or no prior knowledge about the sensed data is assumed at the sensor nodes.     

Null synthesis with phase and amplitude controls at the subarray outputs

The generation of nulls in an antenna pattern by controlling the phase and amplitude of the subarray output signals is investigated. Although the nulls may be formed with any number of subarrays, the subarray configuration and desired null location have a major impact on the distortion in the far-field pattern that results. The distortion problem resulting from subarray nulling is well-known, but little theoretical analysis has been done to explain the cause of the distortion. A theoretical and graphical explanation of why the distortion occurs is offered.     

Reducing grating lobes due to subarray amplitude tapering

Subarray amplitude tapering is a simple, lower cost method to generate low sidelobes in an antenna's far-field pattern. Unfortunately, this simple technique also generates unwanted grating lobes. Placing the exact amplitude taper at the element outputs produces the desired far-field pattern, but the feed architecture is complicated and expensive. An alternative to these two techniques is described. A trade-off exists between sidelobe performance and simplicity of design. This trade-off consists of amplitude tapering the subarray outputs and the element outputs in such a way that the element amplitude tapers are identical for every subarray. In this way, the amplitude taper approximates the desired taper much better than subarray tapering alone, yet all the subarrays are identical. Thus, the feed design remains very simple.     

Nachweis von Kokosfett in Butter

Ohne ZusammenfassungMitteilung aus der Chemischen Untersuchungsanstalt der Stadt Leipzig.     

Methods for null control and their effects on the radiation pattern

Several methods for synthesis of array antenna patterns with prescribed nulls are reviewed. Methods based on full amplitude/phase control at each array element and methods with a restricted number of degrees of freedom are compared, with attention focused on the characteristic features of the resultant patterns. These features are largely independent of any algorithm for achieving the nulls, and therefore they also provide a perspective on the performance of adaptive antenna systems, which employ these various control architectures.     

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Ohne Zusammenfassung