In this work, the AOMDV is optimized using a heuristic method to find the optimal route. The proposed technique is based on Hybrid BAT optimization. To find the optimal route, the link quality, BER, node velocity and neighbouring node queuing delay are considered. In this section methods like link availability and Hybrid BAT Harmony Search Algorithm are presented.
3.2 Enhanced AOMDV Routing with Hybrid Bat
Sonar echoes are utilized by bats for obstacle detection. Short, loud sound pulses (with pulse rates of 0 to 20 times/second) are emitted by the bats during their flight. Upon hitting the obstacles, the sound pulses undergo transformation into a frequency. These are then reflected upon hitting any object. The bats use the delay between the emission and reflection for navigation. Bats will convert their pulses into useful information to assess the distance from their prey. Wavelengths with a range of 0.7 to 17 mm or inbound frequencies of 20-500 kHz are utilized by the bats [26].
Harmony Search (HS) is developed on the basis of natural musical performance processes that take place when an optimal harmony state is sought by the musician. Operators that are used for specifying the HS algorithm optimization are: bandwidth of pitch adjustment (bw), rate of pitch adjustment (PAR), rate of harmony memory consideration (HMCR), Harmony Memory (HM) and the harmony memory size (HMS) - it shows the solution vector stored in the HM.
HS was motivated by the improvisation of Jazz musicians who individually refine their individual improvisation through a piece of music variation resulting in musical variations that produce aesthetic harmony. Stages of HS protocol are:
Begin
HM initialized and fitness evaluated.
do
for 1-D in d do
Compare rand and HMCR // memory
assign 𝑥𝑎 to 𝑥new of (𝑑)
Compare rand and PAR // pitch adjustment
𝑥new (𝑑) = 𝑥old (𝑑) + 𝑏𝑤 × (2 × rand − 1)
end
𝑥new(𝑑) = 𝑥min,𝑑+ rand × (𝑥max,𝑑− 𝑥min −𝑑)
end
end for d
Updating HM as 𝑥𝑤 = 𝑥new, if (𝑥new) < (𝑥𝑤) (minimization objective)
Updating best harmony vector
Step 4. end
End
The steps of the protocol are detailed below:
Stage 1. Setting up of the optimization issue as well as algorithm variables
In the initial stage, the optimization issue is given by
Min (or Max ) \(f(\underset{\_}{x)}\)subject to\({x}_{i}ϵ{X}_{i}, i =\text{1,2},....,N.\)
The solution is obtained by either maximizing or minimizing as required. In this work, for a specified source to destination, several paths are identified through the link measure in AOMDV by modifying path discovery procedure. For maintaining a balance between network loads as well as QoS, the aim is the minimization of packet loss rate, estimated load, and the delay in route.
F(i) are scalar objective functions to be optimized Xi refers to the range of values of all continuous decision variables xi.
Additionally, the control variables of HS are also given in this particular stage. The variables are the HMS that is the quantity of solution vectors (Chakraborty et al., 2009 and Amiri et al., 2010).
Stage 2. HM initialization
Every member of every matrix in the concurrent population of HM that is the extent of HMS is assigned a random integer that is equitably spread between upper and lower bounds at this phase.
The following equation is used to achieve this for the i-th element of the j-th solution vector:
$$[{L}^{{x}_{i}},{U}^{{x}_{i}}], 1\le i\le N$$
$${x}_{i}^{j}={L}^{{x}_{i}}+rand\left(\text{0,1}\right).({U}^{{x}_{i}}-{L}^{{x}_{i}})$$
Stage 3. New Harmony improvisation:
A Harmony vector \(\underset{\_}{x }=({x}_{1}^{\text{'}},{x}_{2}^{\text{'}},....{x}_{N}^{\text{'}})\) is created on the based on
(1) Memory,
(2) Pitch adjustments, and
(3) Arbitrary selection.
Creating a novel harmony known as ‘improvisation’ helps to explore the solution space for better solutions.
Stage 5. Check terminating criteria: Last stage is to check the criterion for continuing the process the terminating criteria (maximal NI) is fulfilled, computations are stopped. Else, stages 3 and 4 are iterated.
Although the Bat Algorithm is effective in exploitation (local search), it does fall into the local optima sometimes. As a result, it loses its capability to carry out proper global search. As BAT relies on random walks for searching, it is unable to ensure rapid convergence. By hybridizing BAT with HS by maximizing BAT’s population diversity, the issue of falling into the local optima can be avoided. Addition of pitch adjustment in HS is an enhancement which acts as a mutation operator for making convergence faster so as to extend the approach’s feasibility for even more practical applications whilst ensuring that the basic BAT’s attractive characteristics are preserved.
A hybrid metaheuristic approach that incorporates pitch adjustment in HS as an evolutionary algorithm into the BAT allows for benchmark function optimization. The distinction between HS/BAT and BAT is that the mutation operator improves the original BAT, resulting in a unique solution for each bat [26]. As a result, this strategy will use HS algorithms to seek out new search space, as well as BAT to leverage population information in order to avoid falling into the local optima in BAT [25, 27].
The BAT-HS critical operator is a hybrid harmony search mutation operator that improvises harmony in HS with BA. Following considerations form the basis behind this new hybrid mutation operator: the new search space’s exploration is enhanced by the mutation operator. Thus, there is full development of the BAT’s exploitation capabilities as well as the strong exploration capabilities of the original HS.
Bat Algorithm (BAT) is unable to ensure rapid convergence as the search wholly depends on random walks. BAT can be enhanced by the addition of the mutation operator which also includes three minor enhancements for speeding up convergence so as to make the method feasible for practical applications whilst retaining the attractive feature of the original method.