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Research on wireless sensor network (WSN) has increased tremendously throughout the years. In WSN, sensor nodes are deployed to operate autonomously in remote environments. Depending on the network orientation, WSN can be of two types: flat network and hierarchical or cluster-based network. Various advantages of cluster-based WSN are energy efficiency, better network communication, efficient topology management, minimized delay, and so forth. Consequently, clustering has become a key research area in WSN. Different approaches for WSN, using cluster concepts, have been proposed. The objective of this paper is to review and analyze the latest prominent cluster-based WSN algorithms using various measurement parameters. In this paper, unique performance metrics are designed which efficiently evaluate prominent clustering schemes. Moreover, we also develop taxonomy for the classification of the clustering schemes. Based on performance metrics, quantitative and qualitative analyses are performed to compare the advantages and disadvantages of the algorithms. Finally, we also put forward open research issues in the development of low cost, scalable, robust clustering schemes.

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This paper proposes a new mobile image transmission system based on the hierarchical modulation scheme for achieving a high quality and high speed digital image transmission in a bandlimited fading channel. The proposed system uses a hierarchical QAM (quadrature amplitude modulation) scheme t o give unequal transmission reliability depending on the importance of DCT (discrete cosine transform)-based compressed images. Numerical analysis shows that the proposed system is an effective high-quality and high-speed image transmission technique in a fading channel.