A new spatial modulation scheme exploiting linear frequency modulation

Abstract

In forthcoming 6 G wireless networks, spatial modulation (SM) has established itself as a technique in massive MIMO setups. In this letter, a novel SM architecture embedding linear frequency modulation (LFM) principle is proposed. In the resulting SM-LFM scheme, the data block is split into the signal and the antenna index parts, and prior to its transmission, distinctly assigns a different LFM chirp (up or down) to be mixed up with the SM block, depending on the index of the antenna to be activated. When the antenna index is even, the associated chirp is up, while the down chirp is retained otherwise. Similarly, the proposed SM-LFM receiver part consists of two main parts: the LFM chirp recognizer and the tuned SM detector. In the former, the received signal is fed to the two up and down LFM chirp-correlators, and the chirp selected at the transmitter is retrieved by an energy comparator. The target behind the incorporation of the LFM chirps, between each adjacent antennas-pair, is to mitigate the miss-estimation of the antenna indices at the receiver side. Depending upon the detected chirp, in the tuned SM detector, only the signals (indices and symbols) emanating from even- or odd-indexed antennas are processed. The performance of the resulting scheme is investigated by adopting a channel model, which considers the effects of estimation errors and antenna correlation. Two modified detectors which adapt to the LFM signaling are investigated, namely the iterative maximum ratio combining (i-MRC) and the maximum likelihood (ML) detectors. The improvement provided, by adopting LFM concept in SM, is shown in terms of data reliability and complexity reduction.