Table 1 Comparison of routing protocols for CRAHNs

SORP [13] and DORP [14]

• Suitable for delay-sensitive application

• Does not include PU avoidance

• Simulation result: lower cumulative delay

WHAT routing [15]

• Multiple consideration on metric calculation

• Uses manually defined parameter

• Simulation result: enhances throughput

Connectivity-based routing [17]

• Observes connectivity of SUs’ network by considering PUs’ activity

• Discovers all possible paths during route discovery, which might result in high resource consumption

• Includes PUs’ activity and channel switching in the routing metric

CAODV [18]

• Considers spectrum diversity, which provides adaptability to PUs’ activity

• Discovers multi-path or multi-channel routes, which might result in high resource consumption

D²CARP [19]

• Considers spectrum diversity, which provides adaptability to PUs’ activity

• Discovers multi-path and multi-channel routes and broadcasts RREP packets, which might result in high resource consumption

MSCRP [16]

• Solves the deafness problem

• Adds node networking tasks

• Simulation result: significantly improves throughput

Local coordination-based routing [20]

• Provides load balancing

• Adds control packet exchanges

• Simulation result: incurs fairly lower cumulative delay

SPEAR [21]

• Provides channel reservation

• Uses traditional routing metric

• Simulation result: achieves significant throughput improvement

• Uses manually defined parameter

BCCCS [22]

• Provides backup channel

• Adds list and table keeping

• Simulation result: shows almost 100% connectivity

TACR [23]

• Includes learning capability

• Uses manually defined parameter

• Simulation result: reduces end-to-end delay and packet loss rate

• Adds complexity

CRM-IC [24]

• Maximum capacity route selection

• Uses single routing metric

• Simulation result: larger end-to-end throughput and better transmission completion time

AiSorp [25]

• Defines route maintenance procedure modification

• Uses manually defined parameters

• Simulation result: longer routing lifetime

Anti-intermittence routing [26]

• Defines route maintenance procedure modification

• Uses manually defined parameters

• Simulation result: longer routing lifetime

STOD-RP [27]

• Provides proactive route via tree-based routing

• Lacks analysis of gateway node activity (e.g., energy consumption)

• Simulation result: reduces end-to-end delay and control overhead