Multihop Wireless Networks: Opportunistic Routing

7.5 CodeOn: a Cooperative Popular Content Broadcast Scheme for VANETs Based on SLNC

In this section, we study the cooperative broadcast of popular contents in VANETs. Next we introduce specific design requirements of such MCD service. After that, the main design will be given, followed by detailed simulation and performance evaluation results.

7.5.1 Design Objectives

For any popular content distributed by the MCD service, the primary objective is to achieve low average downloading delay, which is equivalent to high average downloading rate. For each vehicle in an AoI, its downloading delay is defined as the elapsed time from downloading start to 100% completion. Meanwhile, it is desirable to achieve a high degree of fairness, i.e., the variation of downloading delays among different vehicles should be small. Finally, high-rate content distribution cannot come at the cost of incurring too much protocol overhead and data traffic, otherwise the MCD service would be less compatible with other possible services in the service channel. Thus it is also important to maintain high protocol efficiency.

We first define the main notations used in this chapter in Table. 7.1.

Table 7.1 Frequently used notations

Notation	Definition
F	The file to be distributed
N	Data packet size (bytes)
L	File length (number of generations)
K	Generation size (number of pieces)
J	Piece size (bytes)
M	Number of symbols in a packet
Gi	Generation i
The Galois field used in network coding
U(v)	The utility ...