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As demand for high quality transmission increases increase of spectrum efficiency and an improvement of error performance in wireless communication systems are important. One of the promising approaches to 4G is adaptive OFDM (AOFDM). Fixed modulation systems uses only one type of modulation scheme (or order), so that either performance or capacity should(More)
As the demand of high quality service in next generation wireless communication systems increases, a high performance of data transmission requires an increase of spectrum efficiency and an improvement of error performance in wireless communication systems. One of the promising approaches to 4G is adaptive OFDM (AOFDM). In AOFDM, adaptive transmission(More)
Data rate is important in telecommunication because it is directly proportional to the cost of transmitting the signal. Saving bits is the same as saving money. In this paper we propose new digital companding scheme for OFDM system based on using different constellation orderings (QAM modulator) , depending on the data to be transmitted. Depending on the(More)
The data rate is important in telecommunication because it is directly proportional to the cost of transmitting the signal. Saving bits is the same as saving money. In this paper we propose new digital companding scheme based on using different constellation orderings (QAM modulator), depending on the data to be transmitted. The proposed scheme was(More)
To achieve high bit rate in transmission over wireless channels frequency reuse is an encouraging concept. Rather than dividing allocated frequency spectrum into narrow band width channels , one for each user information is transmitted over a very wide frequency spectrum using the same carrier frequency within same frequency band. In this paper we propose(More)
The Indian mathematician Brahmagupta made valuable contributions to mathematics and astronomy. He used Pythagorean triangles to construct general Heron triangles and cyclic quadrilaterals having integer sides, diagonals, and area, i.e., Brahmagupta quadrilaterals. In this paper we describe a new numerical construction to generate an infinite family of(More)
Reducing error in a communication system is important to increase its performance. This paper shows how custom ordering in Quadrature Amplitude Modulation (QAM) can be used in an effective manner for voice transmission purposes in a soft radio to give better quality results. This would be compared to the M-ary Gray Coded Mapping Scheme and binary coded(More)
In orthogonal frequency-division multiplexing (OFDM) systems, synchronization issues are of great importance since synchronization errors might destroy the orthogonality among all subcarriers and, therefore, introduce intercarrier interference (ICI) and intersymbol interference (ISI). Several schemes of frequency offset estimation in OFDM systems have been(More)
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