Review on Cross Layer Design for Cognitive Ad-hoc and Sensor Network

Chetna Singhal, Rajesh A
2020 IET Communications  
Most of the ad-hoc networks including wireless sensor network operates in unlicensed spectrum bands (e.g. 2.4 GHz ISM band), which is shared by other wireless technologies. This leads to coexistent interference and degrades the performance of ad-hoc sensor network (AHSN). Introducing cognitive radio (CR) concept in AHSN, the unutilised licensed spectrum (white spaces) can be used opportunistically without disturbing licensed holders. Conventional TCP/IP layered architecture for CR network lacks
more » ... in mobility, data transfer performance, energy efficiency, quality of service and so on. Coupling of some of the layers allows coordination, interaction and joint optimisation of protocols to achieve significant performance improvements for CR-AHSN. Of late, many researches are going on different approaches of using CR for reusing unused spectrum and enhancing total system capacity. This study presents a comprehensive review of various cross-layer design approaches in CR sensor network. Introduction Recently, ad-hoc sensor networks (AHSNs) have found wide range of applications including military, disaster recovery, medical, smart home and intelligent information systems due to their infrastructure less prompt set-up, self-organising/healing capability and no stringent requirement of licensed frequency band. However, due to increasing usage by varieties of user profiles, the unlicensed ISM frequency band gets congested creating adverse interference effect on AHSN communication. Hence, such sensors can benefit by exploiting the underutilised licensed spectrum as secondary users (SUs), when not in use by the primary or licensed users (PUs). This interesting field of research gave birth to the cognitive radio (CR) model for sensors to improve spectrum efficiency without additional deployment cost. However, there exists lot of potential challenges for CR-AHSN like distributed multi-hop structure, varying network topology, availability of spectrum and many other factors which are discussed briefly as follows: Challenge 1: spectrum availability; the channel that each sensor node operates is not fixed and mostly varies with time based on PUs activity. It is important here not to harm the PUs communication by any means. Challenge 2: topology management; as the SU nodes operate over a wide range of spectrum bands which often keeps changing, gathering network connectivity information about all the neighbours is quite difficult for any sensor node. This leaves the nodes having incomplete topology information of the network leading to probability of more collision interference among SUs and even in PU network. Challenge 3: spectrum handover [1]; due to dynamic changes in the spectrum from one frequency channel to another, there exist good chances of wireless communication adversities like latency, path loss, interference, packet drop, retransmission and many more which are undesirable. Challenge 4: multihop routing; typical ad-hoc network consists of multi-hop architecture. End-to-end data transmission for CR-AHSN by appropriate route establishment across multiple hops and diverse set of spectrum is quite challenging. Challenge 5: sensing node mobility; the node mobility in any adhoc network is realised when the node does not reply with periodic hello or beacon message to all the surrounding neighbours due to movement from the previous location and eventually gets disconnected from the connectivity list of neighbouring nodes. However, in CR-AHSN, a node might not reply immediately because of sudden appearance of PU in a node's current operating frequency channel. This can very well create misconception about CR node's mobility here. In this regard, node location mobility is also very relevant since users in the real-time scenarios will be deployed randomly either in a homogeneous or heterogeneous network with or without any infrastructure. All these factors greatly influence the received signal strength, interference, channel occupancy and distance between nodes, which in turn impact the performance of CR-AHSN. Challenge 6: spectrum sharing; the CR-AHSN nodes share the spectrum after sensing the vacant frequency band in a cooperative manner, i.e. each sensor share their spectrum sensing information with each other and take combined decision while accessing the spectrum. This creates large overhead and also probability of false detection arises. Challenge 7: energy efficiency; the ad-hoc sensor nodes are battery powered and limited in energy resource. The phenomena of frequent spectrum sensing, multi-channel transmission and spectrum handover are pretty much energy consuming leading to shorter lifetime of CR-AHSN nodes. Challenge 8: scalability; managing network with increasing number of secondary sensor nodes, bring probability of higher collision and interference with the presence of PUs. Hence having scalable network for such CR nodes is tough. Challenge 9: network coverage; because of link failure and PU's activity, the CR-AHSN nodes might face frequent disconnection. Hence maintaining good network coverage is difficult here. Challenge 10: security; as the SUs operate in the unlicensed band, any malicious agent can launch security attacks like jamming, eavesdropping, masquerading of cognitive messages, adverse interference to PUs and many more. Challenge 11: quality of service (QoS); because of all the abovementioned challenges, the CR-AHSN is always QoS demanding. All these unique and critical challenges call for new approach known as cross-layer design techniques that simultaneously handle broad range of communication issues involving several layers of the protocol stack inside the cognitive sensor nodes. This new paradigm exploits the interdependence of protocol layers to achieve performance improvement and different from conventional Fig. 12 SU data rate with variation of distance [48] IET
doi:10.1049/iet-com.2019.0636 fatcat:7fduwpktgjhjpishypcxttqke4