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WSNs (wireless sensor networks) are networks that hundreds or thousands of nodes poured in a field and nodes try to send sensed event to base station (BS). In many cases, the BS isn't in the field and is so far away from nodes. Energy efficiency is one of the major concerns in wireless sensor networks since it impacts the network lifetime. So instead of transmitting directly to BS, in hierarchical network, we choose a cluster head (CH) to send aggregated data from neighbors to BS. In this paper we investigate a new threshold assignment for LEACH and xLEACH that improves energy consumption. We insert the distances of nodes from BS in threshold assignment in order to unbalance the CH selection to reduce energy consumption in the network.

Analysis and design of multi-element antenna systems in mobile fading channels require a model for the space-time cross-correlation among the links of the underlying multipleinput multiple-output (MIMO) Mobile-to-Mobile (M-to-M) communication channel. In this paper, we propose a MIMO channel reference model for M-to-M communication systems that we call it as the modified geometrical two-ring model. This model is based on the extension of single-bounce two-ring scattering model for flat fading channel under the assumption that the transmitter and the receiver are moving. Assuming an isotropic and singlebounce scattering model, a closed-form expression for the spacetime cross-correlation function (CCF) between any two sub channels is derived. The proposed model provides an important framework in M-to-M system design, where includes many existing correlation models as special cases. Some numerical results are presented as special cases of the derived CCF.

Analysis and design of multielement antenna systems in mobile fading channels require a model for the space-time cross-correlation among the links of the underlying multipleinput multiple-output (MIMO) Mobile-to-Mobile (M-to-M) communication channels. In this paper, we propose the modified geometrical two-ring model, a MIMO channel reference model for M-to-M communication systems. This model is based on the extension of single-bounce two-ring scattering model for flat fading channel under the assumption that the transmitter and the receiver are moving. Assuming single-bounce scattering model in both isotropic and nonisotropic environment, a closed-form expression for the space-time cross-correlation function (CCF) between any two subchannels is derived. The proposed model provides an important framework in M-to-M system design, where includes many existing correlation models as special cases. Also, two realizable statistical simulation models are proposed for simulating both isotropic and nonisotropic reference model. The realizable simulation models are based onSum-of-Sinusoids (SoS)simulation model. Finally, the correctness of the proposed simulation models is shown via different simulation scenarios.

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