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The frequency synthesizer is the heart of any frequency hopping system. Recently, the direct digital synthesizer is considered as one of the most important type due to the high resolution capability. The switching time of the conventional direct digital is mainly depending on the number of bits of the accumulator and the main clock of the reference frequency. In this paper, a proposed direct digital synthesizer is designed to reduce the time needed to change the required frequency. Computer simulation tests are used to examine the proposed system. The results of these tests show that the switching time is equal to the time interval of the main clock frequency.

: Recently, the technology has developed and the wireless sensor networks (WSNs) have received great interest and have attracted the attention of the entire world. Wireless sensor network is a large set of sensor nodes that work to move or follow different phenomena. These sensor nodes are specific resources (energy, memory, etc.). Once the power is completed or equipped with the sensor node, this causes the sensor node to lose permanently because the sensor node cannot be processed again if the power supply is finished. It is necessary to pay attention to it well as it is the biggest challenge in wireless sensor networks. Military and border surveillance WSNs are becoming an integral part of military command, control, communication and intelligence systems. So it is preferred to encrypt the data transmitted through these networks. In WSNs, due to relatively smaller size and low computation power, elliptic curve cryptography is very popular public key encryption technique. However, such encryption operation in turn consumes further energy. This paper suggests two approaches to enhance the energy consumption of the structure free WSNs with encrypted data. The first is based on spread spectrum technology, while the other approach deals with the mechanism of selecting the sensing and the next node of the routing path. The results show an improvement in energy consumption of 40% and 12% when the first and the second approaches are used respectively.

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