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A sensor network consists of a large number of small, low-cost devices with sensing, processing and transmitting capabilities. The sensor nodes have limited battery power; therefore energy efficiency is a critical design issue. In this paper we propose to move the sink node, called Base Station (BS) so as to decrease the energy consumption of the whole network. We present two possible strategies to move the BS: the first one minimizes the average consumed energy, while the other one minimizes the maximum transmission energy for every active sensor. To evaluate the performance of the two strategies, we compare these with the case, when the BS is deployed in a fixed position. Simulation results show that the proposed processes can reduce energy consun~ption. thereby significantly extending the lifetime of the entire sensor network.

Due to the evolution of mobile technology and the emergence of terminals like smart phones, Internet based applications mostly accessed over the Transmission Control Protocol (TCP) have become dominant on mobile platforms. However, since the TCP flow control mechanisms were designed for wired environments, short-term degradations on the air interface of radio access systems may lead to unnecessary performance drops. TCP freeze is a possible solution to improve such situations by triggering the persist mode of the TCP sender, preventing TCP timeouts and rate reductions during poor radio conditions. This paper investigates a network element based implementation of the TCP freeze mechanism, which has the advantage that it can accurately follow the radio conditions of the User Equipments (UE) while being completely transparent to the TCP sender and receiver. The possible performance gain of the solution was investigated by simulating a network with coverage holes. Results indicate that the network side freeze can considerably reduce the time the TCP connections spend in outage and thus it can increase the responsivity and data throughput provided by the system.