## 1 Introduction  
Multi-channel MAC protocols have recently obtained considerable attention in wireless sensor networks (WSNs) because they help increase the network performance. Operating on multiple channels can ensure robustness against internal and external interference and allow collision free parallel communications. Most existing MAC protocols proposed for WSNs use a single channel for data transmission. This is essentially due to the fact that energy efficiency is considered to be the most important issue in WSNs. On the other hand, in dense deployment of sensor networks, a single channel utilization generates a high level of interference and limit the use of the bandwidth. This is especially the case when a large burst of packets is generated simultaneously in different nodes due to a change in the monitored conditions, or when running multiple applications and accumulating the traffic of each application leads to higher packet density in the network. In these cases, the use of multiple channel can help optimize the bandwidth usage as it has been shown in the literature. The hardware of most popular platforms and those compliant with the IEEE 802.15.4 and Zigbee standards provides a radio chip capable of switching its communication channel, and is therefore not limited to a single channel operation. In the literature, several surveys on multi-channel MAC protocols with different objectives have been proposed for WSNs [1; 2; 3]. These surveys classify multi-channel MAC protocols according to several criteria: periodicity of channel assignment, centralized or distributed manner for channel assignment, schedule-based or contention based MAC protocols. In a multi-hop topology, packets must be transmitted several times in order to reach the final destination. This overloads the radio channel and induces interference. It also increases the risk of collision due to the hidden terminal problem for example [4], which results in degrading the medium access protocol performance. The use of multiple channels helps mitigate the effect of interference and enhances the network performance under high traffic load. The availability of multiple channels increases the number of simultaneous transmissions between nodes which leads to an increase in the global network throughput. HMC-MAC was first proposed in [5], a Hybrid Multi-Channel MAC protocol that uses a combination between TDMA (Time Division Multiple Access), CSMA (Carrier Sense Multiple Access) and FDMA (Frequency Division Multiple Access) techniques. It is based on CSMA/CA which has the advantage of being a distributed and a lightweight algorithm that does not require a strict synchronization to exchange data frames and which enables the network to be easily scalable. Simulation results using NS2 simulator showed that HMC-MAC provides a smaller interference level compared to other allocation methods based on random choice and 2-hop neighborhood information. In this paper, we extend the state of the art, we give more details about the algorithms of our contribution and we evaluate additional network metrics. We consider high data rates and burst traffic in multi-hop WSNs where a large burst of packets needs to be transported to the final destination. We consider one single destination also known as sink. We are interested in evaluating the performance of HMC-MAC and compare it to other channel allocation schemes and MAC protocols. We introduce a multi-interface sink in order to further enhance the network throughput when all the traffic is destined to the sink. In order to optimize the reception of the sink, we modified the channel allocation method in order to keep the interfaces of the sink in reception mode and at least one neighbor of each interface in transmission mode. Thus, the channel allocation scheme allows the sink to continuously receive data frames. The paper is organized as follows. In Section 2, we give a quick survey of the different techniques used in multi-channel MAC protocols for WSNs.