tailieunhanh - Advanced wireless networks 4g technologies phần 10

Hình 19,17 Tác giả của mã hóa mạng. Như trong Chương 7, chúng tôi xác định một mạng lưới giao thông như một cặp (G, S), trong đó G là một đạo hữu hạn multigraph và S (source) là nút duy nhất trong G mà không có bất kỳ cạnh đến. Một cạnh đạo diễn trong G được gọi là một kênh trong mạng lưới giao thông (G, S). | NETWORK CODING 771 Figure End-to-end delay vs number of nodes in the network. Figure Illustration ofnetworkcoding. As in Chapter 7 we define a communication network as a pair G 5 where G is a finite directed multigraph and S source is the unique node in G without any incoming edges. A directed edge in G is called a channel in the communication network G S . A channel in graph G represents a noiseless communication link on which one unit of information . a bit can be transmitted per unit time. The multiplicity of the channels from a node X to another node Y represents the oapacityoí dứect transmission from X to Y. We assume that every single channel has unit capacity. At the source s information is generated and multicast to other nodes on the network in the multihop fashion where every node can pass on any of its received data to other nodes. At each nonsource node which serves as a sink the complete information generated recovered. Nowlhe question isliow fast each sink node can receive the complete information. As an example consider the multicast of two data bits bl and ỉ 2 from the source o inaherommumcation networkdepietedbyFigure a as bothn uliS Y one z. One sclueignii tain t theuiiannele er n na d wz caraytlio bit aanl nt iiez tstsirol intUlt ehamo eb intcmiadiatr nodcieiidi gifia dwtnbiioelyie in i eensi thctamceiio omaaotbci aode T aedeivaafiid bit otidtnnds uoopy cn each cf thelwochaamelsOTmd art. SmtihoevAha aodeer receivesllirhe n and tendsa cqsveiii reiolt oftiia twochanids GIT andGZiWe estumelhat tholmttn lpl occs maiielay at the intermediate nodes. 772 NETWORK INFORMATION THEORY Unlike a conserved physical commodity information can be replicated or coded. The notion of network coding refers to coding at the intermediate nodes when information is multicast in a network. Let US now illustrate network coding by considering the communication network depicted in Figure .