# WLAN Aware Cognitive Medium Access Control Protocol for IoT Applications
## 2 Related Work  
Several ideas have been proposed to improve the communication and energy efficiency in IoT wireless sensor devices. In Reference [17], the authors minimize the idle listening time by turning off the radio of the sensor nodes when they are idle and not transmitting. This technique is implemented by using wake-up radios and an adaptive duty cycle control algorithm. In Reference [18; 19], wireless sensor nodes tune to the best available communication band in a multi-channel network based on cross-network interference. The authors in [20] propose techniques, such as frame aggregation and back-up channel availability, to improve the energy efficiency of the network. When both the sender and the receiver of a packet are the same, frame aggregation is performed at the MAC layer, where ten data frames are combined. Using this approach, packet overhead is reduced since packet headers are only attached once with the aggregated frame. To improve network reliability, backup channel availability is used in which, at any instant, if a primary user needs to access a channel when secondary users may be engaged in a communication, then without any transmission break-up, the secondary users move over to the available backup channel. Authors in [21] propose a multi-channel MAC protocol in which secondary users reserve data channels using information exchange on a separate control channel. Nodes share information, such as channel sensing and destination node address, in the form of short preamble packets sent in series, rather than an extended preamble. Rather than being awake for the extended preamble, nodes that are not the destination for a packet go to sleep mode whenever the first short preamble is heard. Reference [22] proposed a MAC protocol that improves channel utilization and energy efficiency. In a cognitive network where periodic spectrum sensing is performed, the transmission interval that is available for secondary users is often narrow which results in contention and reduced energy efficiency. The proposed scheme grants access to a single secondary user to transmit data packets before the start of the next spectrum sensing interval. Within this period, all other nodes go into their sleep mode, hence conserving the energy. In Reference [23], authors propose a MAC protocol that mitigates WLAN interference experienced by the Zigbee devices using payload and header redundancy. WLAN transmissions can uniformly alter any of the bits in a Zigbee packet, thereby losing the whole frame. In the case of collisions, the header is generally the part that is altered. The proposed MAC protocol sends frames with multiple headers, allowing numerous opportunities to detect the packets. Having multiple headers increases network overhead, but it minimizes data loss, thereby reducing packet re-transmission, increasing network delivery rate, and improving energy consumption. Authors in [24] propose a MAC protocol in which wireless sensors nodes (with packets to transmit) force WLAN to back off by sending a high powered jamming signal at the Distributed Interframe Spacing (DIFS) interval. The transmit power value of the jamming signal is set to the maximum WLAN power measured during the sensing period. The proposed MAC protocol reduces collision faced by the sensor nodes and results in a high packet delivery ratio. However, due to the use of jamming signals, the energy consumption of the network is increased. A multi-hop cognitive MAC protocol is proposed in Reference [25] to reduce energy consumption caused by hidden WLAN terminals. Using continuous spectrum sensing, nodes decide about the available transmission opportunities. The next-hop distance for multi-hop communication is optimized based on the WLAN channel occupancy statistics. Results show an increased data throughput and reduced packet error rate. A coexistence model between IEEE 802.15.4 and IEEE 802.11b/g is proposed by authors in [10]. The model uses factors, such as transmit power and transmission time, to establish co-existence ranges.