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Nowadays, low reuse factors are used in cellular systems because of high traffic demand, despite it produces high co-cell interference (CCI) levels. Consequently, soft-frequency-reuse (SFR) and sectorization are used to improve the spectral efficiency and to mitigate CCI. In addition, diversity techniques are necessary for a good system performance. Motivated by this scenario, for the uplink of orthogonal-frequency-division multiple access (OFDMA) systems, the bit error rate (BER) and the cellular spectral efficiency using multilevel-quadrature-amplitude-modulation (M-QAM) and maximalratio-combining (MRC) in Rician fading channels are analyzed, where diversity branches have different Rician K-factors (unbalanced diversity). SFR is used assuming non-ideal sectorized cells due to the irregular radiation pattern of base station antennas. An exact integral-form expression and a closed-form upper-bound to evaluate the BER are obtained. In addition, an algorithm, and an expression to calculate the cellular spectral efficiency are presented considering that a target BER must be guaranteed for all users in the cell. From the analysis, it is determined that the BER can be reduced and the spectral efficiency can be improved if some system operating parameters are selected in an adequate manner. Thus, it was noticed that the number of diversity branches, the sum of the K factors of these branches, and the antenna type, are decisive to guarantee the target BER and to maximize the cellular spectral efficiency.

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