US Patent 10200947 Asymmetrical hail timing

A method includes transmitting first hail messages from a first device at a first hailing rate, in which time between beginnings of each consecutive first hail message is a first period, each first hail message transmitted for a first length of time, and a first gap extends between an end of each first hail message and a start of a next first hail message; listening at the first device for a second hail message repeatedly transmitted at a second hailing rate, wherein a second time between beginnings of each consecutive second hail message is a second period, each second hail message transmitted for a second length of time, and a second gap extends between an end of each second hail message and a start of a next second hail message; and performing, at the first device, a channel activity detection of a preamble in the second hail message.