Packet detection for wireless networking with multiple packet reception

A blueprint for an experimental low-power communications device (wireless mote) suitable for ad-hoc and networking applications is presented. The proposed device implements a random access packet-based communications protocol that exploits a special packet structure which is composed of separate header and payload portions. To enable robust packet detection, the headers consist of a preassigned spreading sequence which acts as a system access "key". The payload portion, on the other hand, utilizes a unique, packet-specific long spreading sequence to enable multi-packet reception (MPR), among other features. The packet header consists of W repetitions of a fixed spreading sequence, which are differentially encoded to provide immunity to unknown carrier frequency drifts. The receiver despreads the header and estimates the packet start time by differential coherent correlation before performing a threshold-based detection decision. Fixed-point simulation and FPGA measured results are provided for this the packet header detector and compared with the analytical packet-loss and miss probabilities. Near-far power loss experiments and analyses are discussed to demonstrate the feasibility of this receiver operating in wireless environments with large receive power variations.