Vehicular networks are the subject of active research in the field of networks as well as transport. The potential for vehicular networks to provide services such as traffic information in real time or accident makes this technology a very important research domain. These networks may support vehicle-to-vehicle communications (V2V), vehicle-to-infrastructure (V2I), or a combination of both. The IEEE 1609.4 is the specification of multichannel operations for IEEE802 .11p/WAVE vehicular networks (VANETs). It uses seven channels; one being a control channel (CCH) which is listened periodically by the vehicles and the other six channels are used as service channels (SCH). It also defines a time division between alternating CCH and SCH intervals. The purpose of this thesis is to evaluate the performance of VANETs in the case of vehicular communications without infrastructure, and at the lower layers of IEEE 802.11p standard. In the first part, we propose an opportunistic multichannel MAC allocation in an environment without infrastructure. This approach is consistent with the standard IEEE1609.4 -2010/WAVE for a multi-channel operation, and it is designed for data services applications (non-urgent), while ensuring the transmission of road safety messages and control packets. To maintain the quality of service of the two types of messages (urgent and non-urgent) by exploiting the channel capacity, two solutions are proposed. In the second part, when the vehicle selects its channel and controls its temporal alternation between CCH and SCH, it starts transmitting its packets, particularly on the CCH, which have an expiration time. We present an approach to minimize collisions between transmitters while avoiding contention at the beginning of CCH interval, especially in a context of high vehicular density. Although the mechanisms proposed above reduce the collision rate, it is not possible to completely remove these collisions. In the third part, we address the problem of collisions between broadcast packets on the CCH, especially when the load of transmitted messages exceeds the channel capacity. For this purpose, we propose a new analog network coding mechanism adapted to QPSK modulation for broadcast messages on the CCH. In this approach, known symbols are sent before sending the packets to estimate the channel parameters and an explicit solution is used to reverse the system of the superposition of two packets
