Abstract
This paper generalizes the technique of spatial power combining to modulated signals and applies it to effectively strengthen or deny communications and navigation services in desired area. The system and mathematical model of coherent combining for direct-sequence spread spectrum (DSSS) signals are established. By using the method of transmitting delay precompensation and coherent combination, the coherent energy level after de-spreading at the receiving scales is the square of the number of nodes rather than being additive. Thus, the energy coherence is proposed to analyze the interference and superposition effects in the focusing area rather than the commonly used performance metric of front-end energy analysis. Then, the influences of beam pointing error and clock phase error of the sparse array on coherent combining are studied by theoretical and numerical analysis. The results show that by controlling the array error within a certain allowable range, the proposed method can achieve a precise projection of coherent energy. More specifically, we demonstrate that with further improvements in synchronization and pointing accuracy, the actual distribution of the focal spot and effective interference spots can be precisely manipulated.
Highlights
The available transmitted power is constrained by the power limits of microwave devices, while spatial power combining obtains higher energy efficiency and is not subject to this constraint [1]
We focus on the spatial power combining of a pseudonoise (PN) spread spectrum signal, which is a class of spread spectrum modulations
Based on the principle of power combining by using sparse array, the coherent combining method of modulated signals is studied
Summary
The available transmitted power is constrained by the power limits of microwave devices, while spatial power combining obtains higher energy efficiency and is not subject to this constraint [1]. Each spread spectrum signal from the sparse array is transmitted separately and combined in spatial channel to project energy into the target region. In this paper, the spatial power combining technique is generalized to the case of modulated signals and utilized to combine direct sequence spread spectrum (DSSS) signals during propagation of electromagnetic waves after transmitting. It is necessary to remark here that for the receiving end of the DSSS system, a typical detector is based on the second order moment of the estimated correlation, (η) = |RP(η)|2 [19], [20] Inspired by this detector, we define the average value of the correlation function E Rp (η) 2 as the energy coherence at focal spot P. The ‘‘interference effect’’ of the energy coherence is presented in the focusing area, which will be simulated and analyzed in subsection II-C
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