Reliable communication is a vital issue for safety- and mission-critical wireless sensor network environments such as industrial monitoring, medical care, and battlefield surveillance. These networks require highly accurate and delay-intolerant wireless communications. Under such critical conditions, the chip sequences used in these networks become vulnerable because of channel impairments and other interferences, thereby significantly decreasing overall system performance. In this paper, polyphase sequences are employed at the physical layer of IEEE Standard 802.15.4 to enhance the communication reliability of wireless sensor networks. Through an extensive simulation, it is found that upon applying polyphase sequences, the chip errors are reduced to $2.94\times {10}^{-6}$ in comparison to $1.18\times {10}^{-5}$ of conventional binary sequences (PN sequences).