Читать книгу Wireless Connectivity - Petar Popovski - Страница 17

Back to the dark room analogy, we ask the question: how do two people, who have never met before, start to communicate when placed in a dark room? Reformulating this question in terms of wireless communication, we can ask: how do two wireless devices start to communicate? Who speaks first and who listens first? This is an important issue when the devices operate in a half-duplex manner, since a device cannot transmit and receive simultaneously. Before a packet from Zoya is sent to Yoshi, each of them needs to know that Zoya is about to transmit and Yoshi is about to receive. This may sound trivial and indeed it is, provided that we somehow let Zoya know in advance that she should take the transmitter role and Yoshi should take the role of a receiver. For example, if they have communicated in the past, then they may agree that, next time they are placed together in a dark room, Zoya takes the role of the one that starts to talk first. But, how do they know the roles if they have never communicated before? Let us explore this problem of first contact or rendezvous between two wireless nodes.