Zaw Htike

HER-MAC: A Hybrid Efficient and Reliable MAC for Vehicular Ad Hoc Networks

Vehicular Ad hoc Networks (VANETs) should provide the vehicles with reliable safety message broadcasts and efficient non-safety message transmissions. The IEEE 1609.4 MAC is designed for VANETs to support multi-channel operations, but the safety message broadcast is not much reliable and the Service Channel (SCH) resources are not fully utilized. In this paper, we propose a new multi-channel MAC for VANETs, named HER-MAC, which supports both TDMA and CSMA multiple access schemes. The HER-MAC allows vehicle nodes to send safety messages without collision on the Control Channel (CCH) within their reserved time slots and to utilize the SCH resources during the control channel interval (CCHI) for the non-safety message transmissions. Compared to the current IEEE 1609.4, the proposed HER-MAC protocol is more reliable in the safety message broadcast, efficient in the service channel utilization.

The Life Cycle of the Rendezvous Problem of Cognitive Radio Ad Hoc Networks: A Survey

In cognitive radio or dynamic spectrum access networks, a rendezvous represents meeting two or more users on a common channel, and negotiating to establish data communication. The rendezvous problem is one of the most challenging tasks in cognitive radio ad hoc networks. Generally, this problem is simplified by using two well-known mechanisms: the first uses a predefined common control channel, while the second employs a channel hopping procedure. Yet, these two mechanisms form a life cycle, when they simplify the rendezvous problem in cognitive radio networks. The main purpose of this paper is to point out how and why this cycle forms.

Broadcasting in multichannel cognitive radio ad hoc networks

Cognitive radio network technology is regarded as a new way to improve the spectral efficiency of wireless networks. It has been well studied for more than a decade and numerous precious works have been proposed. However, very few existing works consider how to broadcast messages in cognitive radio networks that operate in multichannel environments and none of these provides a full broadcast mechanism. Therefore, in this paper, we propose a broadcasting mechanism for multichannel cognitive radio ad hoc networks. Then, we analyze the mechanism regarding the speed of message dissemination, number of transmissions, portion of the users that receive the broadcast message and so forth.

A MAC protocol for cognitive radio networks with reliable control channels assignment

In cognitive radio network, control information dissemination is critical. Secondary users need to exchange control information for utilizing the available channels efficiently, to maintain connectivity, to negotiate for data communication such as sender-receiver handshakes, for neighbor discovery etc. In currently proposed MAC protocols for cognitive radio networks, control information are disseminated among users by using two famous mechanisms. The first one is the use of common control channel (CCC) and the second one is using channel hopping. However, both methods have their own drawbacks. The use of CCC may not be feasible in cognitive radio networks as the available channels, including control channel, are dynamically changing according to primary users activities. Channel hopping approaches cause significant amount of channel access delay which is known as time to rendezvous (TTR). In this paper, we propose a hybrid protocol of these two mechanisms. This hybrid protocol can maintain connectivity among secondary users by using multiple control channels. The use of multiple control channels guarantees the secondary users to be able to exchange control information in dynamic environment. Channel hopping is performed only for control channels, so it provides relatively small amount of channel access delay.

Neighbor discovery for cognitive radio ad hoc networks

Neighbor discovery is a critical task in cognitive radio ad hoc networks since the secondary users operate on available channels which are dynamically changing according to the primary users activities. In this paper, we propose a neighbors discovery mechanism that provides how a secondary user could find its neighbor in cognitive radio ad hoc networks without any collaboration. In this mechanism, no prior knowledge of neighboring users is required. In the cognitive radio networks, the available channel sets are varying and users choose neighbor discovery strategies according to the number of available channels they observed. In other words, neighbor discovery strategies are adaptively changing in a dynamic environment. The strategies are simple and totally distributed, but these provide minimum time to rendezvous (TTR).