Adaptive power permutation modulation: A novel transmission technique for increased spectral efficiency over fading channels

Abstract

SummaryIn this study, we propose a novel transmission technique for multiple‐input multiple‐output (MIMO) systems as a partial response to ever‐growing demand for the increased spectral efficiency. The introduced scheme, called adaptive power permutation modulation (APPM), relies on the distinct power allocations on the conventionally modulated symbols to convey a certain number of additional information bits. Unlike the traditional power allocation strategies which generally aim to combat the channel fading and entail some form of channel state information (CSI) at the transmit side, APPM utilizes different power levels to convey additional information and does not necessitate any kind of CSI at the transmitter. The proposed approach is applied to two well‐known MIMO configurations, Alamouti space‐time block coding and zero‐forcing beamforming, by embracing a general frequency‐selective fading scenario under digital phase modulation. Both the modulation order and the power allocation levels on the modulated symbols are adaptively determined based on a set of additional information bits. It is shown that in addition to the conventionally modulated symbols, an extra sequence of bits can be conveyed without any significant additional complexity where equals the number of subcarriers. Also, it is demonstrated that considerable transmit power savings can be attained when compared with the standard schemes under a certain target spectral efficiency.