Packet acquisition for low-complexity frequency-hop receivers

The diversity provided by frequency-hop (FH) signaling can protect against jamming and multiple access interference (MAI). A FH transmission consists of two parts — an acquisition preamble and a data payload. The acquisition preamble allows the receiver to detect and synchronize with an incoming packet. Acquisition must be at least as robust as demodulation and decoding. If acquisition fails, the receiver is unable to process the payload. Once acquisition has occurred, a receiver can simply tune a narrowband demodulator to the current hopping channel. However, during the acquisition stage, the lack of timing information makes it impossible to know what the current channel is. Instead, the optimal receiver must make an acquisition decision by simultaneously processing all channels over which the preamble is spread. If the preamble uses M channels, the receiver must have resources to tune to all M. Thus, it is desirable that M be small to keep the receiver’s complexity low. However, if M is small, the preamble lacks frequency diversity and may be vulnerable to jamming and MAI. We consider FH acquisition for cases where the preamble has limited frequency diversity and explore the trade-offs that must be made for robust performance in the presence of interference.