# Dynamic Cooperative MAC Protocol for Navigation Carrier Ad Hoc Networks: A DiffServ-Based Approach
## 2 Related Works  
Although extensive recent papers delve specifically into QoS-aware MAC problems, the literature pertaining to QoS MAC for high-dynamic ad hoc networks is extremely limited, and that addressing NC-NET remains almost non-existent, in spite of being described as an open issue at the link layer in reference [1]. In this section, we analyze the related works on typical QoS-aware MAC protocols for wireless networks. Directional antennas can offer clear advantages in terms of improving the signaling range without extra power (as opposed to omni-directional antennas), especially for long-range transmission. Previous research has incorporated directional antennas in the design of MAC protocols. DMAC [5] is one of the earliest of these. This protocol is based on a modified 802.11 MAC protocol [6], and uses a per-sector blocking mechanism to block a sector once it senses a request-to-send (RTS) or clear-to-send (CTS) packet, whereas the data packets are transmitted through directional beams. This kind of mechanism is beneficial for spatial reuse, end-to-end transmission delay, and power consumption in data transmission [7]. Unfortunately, some problems also arise from the use of directional antennas, such as the deafness problem [8], the new hidden terminal problem [8; 9], and the head-of-line (HOL) blocking problem [10]. Previous directional MAC protocols have already defined several techniques to handle these problems [8; 9; 10; 11; 12]. However, they mainly focus on some specific aspects; for example, augmentation of the busy-tone channel [10; 11], attachment of a start-of-frame [8; 9], or multi-channel diversity [12; 13]. Nevertheless, the question of how to combine these techniques in a large-scale mobile wireless network and maximize the advantages of directional antennas in a multi-service environment is still an open issue, motivating the research in this study. Furthermore, in view of the complex communication challenges in NC-NET, in this research, the usage of directional antennas is combined with other techniques, i.e., differentiated services and cooperative communication. Differentiated services (DiffServ) is a widely known and utilized technique for QoS provision in networks with multiple traffic services [14], which are differentiated and prioritized based on one or more criteria and formed into several traffic classes. In the literature [14; 15; 16; 17; 18], the majority of DiffServ mechanisms are proposed for wireless multimedia sensor networks (WMSN), and can be classified according to various types of criteria, such as drive-mode-aware criteria, QoS-aware criteria, and other criteria. In references [15; 16], the services are differentiated based on drive modes,whereby the cyclically occurring services are classified as a time-driven class, whereas stochastic services are classified as an event-driven class. Thereby, the medium access of the two classes is realized based on schedule-based MAC and contention-based MAC, respectively, or hybrid solutions including TDMA/CSMA, CDMA/CSMA, FDMA/CSMA, etc. In references [17; 18], multiple services are classified based on QoS-aware criteria such as delay sensitivity and packet loss sensitivity. [PERSON] et al. [17] proposed a CSMA/CA approach, classifying the co-existing packets into two categories, i.e., streaming multimedia (over UDP) packets and Best Effort FTP (over TCP) packets. Moreover, Diff-MAC [18] is designed with the key features of service differentiation and QoS guarantee for heterogeneous traffic (e.g., video, voice and periodic scalar data), which is differentiated into three classes, i.e., real-time (RT) multimedia traffic, non-real-time (NRT) traffic and best effort (BE) traffic. Note that these DiffServ mechanisms are mainly proposed with one of or a hybrid of the following features: (i) adaptive contention window (CW) adjustment, (ii) dynamic duty cycling (changing active time), (iii) fragmentation and message passing for long packets, and (iv) intra-node and intra-queue prioritization [18].