This paper focuses a single cell system employing sectorization using nonorthogonal-multiple access (NOMA) and employing cooperative relaying to forward signal to the cell-edge users. In a conventional fixed sectorization, if the density of cellular users has to be variable throughout the cell, the region with the higher density of users experiences poor service. This conventional fixed sector approach is inefficient in distributing the transmitter power efficiently to all the users. To address this issue, we propose an adaptive sectorization approach, aiming to provide all the users fair services, irrespective of their position in the cell. In the adaptive sectorization, the sector-angle and the transmission power of each sector antenna is adaptively chosen according to the density of the users in the cell. The paper also proposes the angle selection scheme for finding the coverage range of the relay equipment and adaptive NOMA technique. In adaptive NOMA scheme, the downlink system adaptively changes its working modes based on the relay equipment power, for optimizing system energy efficiency and reducing power consumption of the cell-edge users. Our simulation results validate the effectiveness of the proposed scheme, and show that the adaptive sectorization scheme can achieve a higher energy efficiency performance than fixed sector approach, in the considered network.