Codebook Selection Strategies in Long-range Sub-1 GHz WLANs

The new long-range WLANs will enable a simple and cost-efficient setup of wireless ambient systems, including smart city and smart grid communication networks. The emerging IEEE 802.11ah WLAN standard utilizes carrier frequencies at 900 MHz in the ISM-band and facilitates multi-antenna MIMO-OFDM. In order to further increase the wireless coverage, precoding selection strategies are proposed and analyzed. The Grassmannian and the Kerdock manifold are in the focus of this study due to their simplicity and effectiveness. Whereas the Grassmannian manifold may provide an optimal codeword distance, the Kerdock man- ifold has been found to be more effective due to its reduced quantized codewords combined with an increased SNR. Simulation studies as well as real-world evaluation results indicate a 2-3 dB increase of precoding gains when the proposed Kerdock manifold is applied, thus increasing the coverage. The codebooks have been evaluated in a SDR-based IEEE 802.11ah WLAN prototype.