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Maritime networks establish wireless multi-hop networks to provide wireless broadband service at sea, connecting various kinds of ships, maritime buoys, and beacons. The maritime networks possess two distinguishing characteristics highly affected by maneuver at sea-dynamic link quality and bandwidth constrained, and dynamic network topology-that warrant specific attention. Unlike land vehicles, maneuver at sea is affected by sea surface movement and wave occlusions, which can cause unstable environment with a high rate of link breakages caused by low link stability, as well as low and highly variable bandwidth. In spite of the need to achieve performance close to high-speed terrestrial wireless broadband service on land, there is only a perfunctory effort to investigate maritime networks. There is an urgent need to refresh the interest to investigate, as well as to further enhance, maritime networks. This paper presents a review of the limited research works of this topic, which revolve around the networking issues in the link, network, and upper layers, in the literature. The objective is to establish a foundation in order to motivate a new research interest in maritime networks. Open issues are also presented to foster new research initiatives in this burgeoning and exciting area. INDEX TERMS Maritime network, ship ad hoc network, wireless network.

Cognitive Radio (CR) is a dynamic spectrum access approach, in which unlicensed users (or secondary users, SUs) exploit the underutilized channels (or white spaces) owned by the licensed users (or primary users, PUs). Traditionally, SUs are oblivious to PUs, and therefore the acquisition of white spaces is not guaranteed. Hence, a SU must vacate its channel whenever a PU reappears on it in an unpredictable manner, which may affect the SUs' network performance. Spectrum leasing has been proposed to tackle the aforementioned problem through negotiation between the PU and SU networks, which allows the SUs to acquire white spaces for a guaranteed period of time. Through spectrum leasing, the PUs and SUs enhance their network performances, and additionally PUs maximize their respective monetary gains.

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