Optimal Non-Coherent M-Ary Energy Shift Keying For Cooperative Transmission In Sensor Networks

Cooperative transmission follows the idea to achieve better reception quality for wireless communication systems by exploiting spatial diversity. We discuss the case where a group of sensor nodes transmit cooperatively and simultaneously identical symbols to a far destination. Doing so, they achieve a higher total transmit power. This is useful to reach destinations when no intermediate relays are able to act as repeater. We discuss this situation under the constraints of low power and low cost hardware and derive an optimal symbol constellation for a M-ary modulation scheme to minimize the symbol error. For this, we assume neither phase nor carrier synchronization between cooperatively transmitting nodes or the receiver yielding an easy to implement system with very low requirements for the participating wireless sensor nodes. Transmitted signals superimpose non-coherently in the receiver which uses only the amplitude information to decode symbols acting as an energy detector. We therefore name this modulation Energy Shift Keying (ESK).