Disclosed are a method and device for estimating a channel in a multiple-receiving antenna system. The network interface device includes a processor and a DMA controller. The apparatus also includes a strap disposed at the second end of the at least one line for detachably securing the at least one line to a stationary object. The vector modulator means is arranged to operate at low power levels, where it can operate more efficiently. The identifying symbol may be a shape, and the symbol may further include an identifying color.