Bandpass sampling algorithm is effectively adopted to obtain the digital signal with significantly reduced sampling rate for a single radio frequency(RF) signal. In order to apply the concept to multiple RF signals, we propose bandpass sampling algorithms with the normal and the inverse placements since we are interested in uniform order of the spectrum in digital domain after bandpass sampling. In addition, we verify the propose algorithms with generalized equation forms for the multiple RF signals.

A B S T R A C TThe challenges faced in underwater communication systems are limited bandwidth, Energy consumption rate, larger propagation delay time, End-End Delay (E-ED), 3D topology, media access control, routing, resource utilization and power constraints. These issues and challenges are solved by means of deploying the energy efficient protocol. The protocol can either be localization-based protocol or localization free protocol. In this paper, review of localization free protocols were discussed and reviewed with reference to environmental factors, data transmission rate, transmission efficiency, energy consumption rate, E-ED and propagation delay. The review analysis gives the pros and cons to give rise to the new directions of research for future improvements in Underwater Wireless Sensor Networks (UWSNs). This manuscript propose a survey on localization free protocol according to the problem addressed or the major parameter considered during routing in UWSNs. Unlike the existing survey, the present survey focuses on present state and art of routing protocols, in terms of routing strategy issues addressed. The solutions of energy efficient protocol is arrived by highlighting the pros of each protocols. The description of routing strategy for each protocol is presented to understand its operation in an understandable form. The cons of each protocol is taken into consideration for further investigation and to arrive the best protocol. The presented routing strategy, pros and cons provide open challenges and research directions for future investigation.

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We investigate the performance of cellular CDMA systems through adopting two types of array antennas, switched beam forming (SBF) and tracking beam forming (TBF) in the base station. Also, in order to enhance the system performance, we optimize a beam shape using side-lobeto-main-beam-energy ratio (SMER) defined by the energy ratio of side lobe region and main beam region. As a result, it is observed that the TBF method gives about 30% capacity improvement over the SBF method under 1% outage probability requirement. In addition, an optimized beam shape using SMER provides maximally 8% and 14% more capacity increment comparing conventional non-optimized beam shapes under 1% outage probability requirement when we use 5 and 7 beams per sector with SBF method, respectively.