Before revision:  A sensing-based protocol is designed to support the unlicensed channel access for both LTE users and D2D pairs, based on which we investigate the subchannel allocation problem to maximize the sum rate of LTE users and D2D pairs while taking into account their interference to the existing Wi-Fi systems.
After revision:  A sensing-based protocol is designed to support the unlicensed channel access for both LTE users and D2D users. We further investigate the subchannel allocation problem to maximize the sum rate of LTE users and D2D pairs while taking into account their interference to the existing Wi-Fi systems.