Multi-Mode OFDM Communication System Using the Multiple Constellations

Abstract

We like to propose a multi-mode OFDM (orthogonal frequency division multiplexing) system of the multiple constellations that has a new mapping scheme to improve the OFDM system efficiency. As an example, the multi-mode OFDM system can use different modes of multiple constellations that have different shapes and are not overlapped. Furthermore, by using the additional index bits, modulation types and each mode is identified to determine by the combination method which mode symbol is to be mapped to each subcarrier. In the receiver, the log likelihood ratio (LLR) algorithm can be used to find and demodulate the arrangement of subcarriers. For the performance comparison with the conventional OFDM system, we investigate the bit error rate (BER) performance and peak-to-average power ratio(PAPR) performance using the same constellation form as the overall constellation form of the multi-mode OFDM system using the non-overlapping four-mode constellation diagram. In the high signal-to-noise ratio (SNR) region, the proposed multimode OFDM system shows some BER performance improvement than the conventional OFDM system. In addition, the multi-mode OFDM system has more flexible because it forms the overall constellation by combining several types of nonoverlapping constellation diagrams, which makes it possible to use a constellation shape suitable for the environment.