## 2 Related Work  
The MCRN was first proposed by [PERSON] _et al._[3]. The authors analyzed and presented the design requirements of the MCRN to enable cognitive operations and be suitable for the sea environment. Moreover, they investigated the possible available spectrum in the sea, the requirements that follow and the standards available. The challenges associated with MCRN, including movement on the sea surface and channel characterization, were addressed. A medium access control (MAC) protocol and a routing protocol were also presented to meet the challenges associated with MCRN. In [10], we presented performance analysis for spectrum sensing in MCRN. In which existing fusion rules for cooperative spectrum sensing were compared to highlight the need for a unique cooperative spectrum sensing scheme for MCRN. We investigated entropy-based spectrum sensing for local spectrum sensing in MCRN in [11]. However, a cooperative spectrum sensing scheme that is unique to MCRN is not discussed in [10, 11]. Recently, some new communication systems, particularly for maritime networks, have been proposed. In Singapore, WISE-PORT (Wireless-broadband-access for Seaport) provides IEEE802.16e-based wireless broadband access up to 5 Mbps, with a coverage distance of 15 km [12]. However, it still requires improvements. The first digital VHF network with a data rate of 21 and 133 kbps with a coverage range of 130 km was developed in Norway [13]. This system operates in the licensed VHF channel, which results in a narrow bandwidth and slow communication speed. To provide high speed and low cost ship-to-shore and ship-to-ship communication, the mesh/_ad hoc_ network based on IEEE 802.16d mesh technology was proposed in a project called TRITON [14]. The authors developed a prototype that operates at 2.3 and 5.8 GHz. Each ship is required to be capable of sensing the spectrum for MCRN. Moreover, the maritime environment has challenges, like the channel model, link quality, due to the sea movement, and so on. Television spectrum, cellular band and maritime spectrum holes are available at sea, which may range between tens of MHz to several GHz. Each ship in the MCRN needs to sense the spectrum according to its capability and change its operational frequency to achieve the best communication quality. Currently, the main focus of research in spectrum sensing for cognitive radio is divided into two main streams: (i) improving local sensing; and (ii) enhancing cooperative spectrum sensing for better data fusion results. The major local sensing techniques considered for cognitive radios are energy detection, matched filter detection and cyclostationary detection. Energy detection is the simplest technique, which has a short sensing time, but its performance is comparatively poor under low signal-to-noise ratio (SNR) conditions. Matched filter detection is another simple technique, but it requires prior knowledge about the waveform of the PU. Cyclostationary detection provides reliable spectrum sensing, but it is computationally complex and requires a long sensing time [4]. In cooperative spectrum sensing, all the local sensing observations made by SUs are reported to a fusion center, and a final decision about the presence or absence of the PU is conducted at the fusion center [7]. Based on the final decision received by the fusion center, each SU reconfigures its operating parameters. Spectrum sensing must produce a high probability of detection and a low probability of false alarms to achieve better network performance. The sea environment is divided into 10 different sea states, depending on the wave height, the average period of waves and the average wavelength of waves [15]. The higher probability of detection can be achieved by a longer sensing time [3]. Moreover, for relatively calm sea (e.g., sea state 3), the usual spectrum sensing schemes may be used. However, relatively advanced spectrum sensing schemes and cooperative fusion rules are required for higher sea states.