Abstract-Ad hoc network mostly finds its application in military, emergency services, wireless mesh networks, sensor networks, and collaborative computing due to its simplicity, mobility and ease of deployment.Ad hoc networks mostly use free unlicensed bandwidth therefore they have to have intelligent MAC protocols for reserving frequency for establishing wireless ad hoc communications. Efficient use of provided limited bandwidth is vital to overcome any sort of problems that reduces performance of the network. Thus, division of the provided bandwidth into multiple channels takes place for best use of the bandwidth.

 

Principal behind the Ad Hoc Networking came to live back in ancient era in 500 B.C. Darius I, the king of Persia invented a new form of communication which is 25 times faster than ordinary messenger available at that time What he did is to put a line of men on tall structures in the controlled provinces to bring news to the capital by means of shouting. This principal brought to live in the second half of the last century as the result of PRNET project in the U.S. in 1970s. PRNET project initially aimed to bring a portable, mobile wireless networks for military applications. As the result of the project, the feasibility of the infrastructure-less networks was proven and the project was extended, which then called as DARPA. Eventually, Mobile ad hoc networks (MANET) working team was established to make standard protocols and functional specifications for Ad Hoc Wireless Networks.  Ad Hoc Wireless Networks are infrastructure-less form of networks, which enable operations anywhere because of their independence on base stations. Most popular form of ad hoc network is Bluetooth, used for small area connection with a range of up to 10 meters. Bluetooth became very popular due to its less power consumption and low cost for communication between mobile phones and other forms of technologies as well as for its simplicity for establishing small temporal network.

Wireless Ad Hoc Networks are widely used modern day form of wireless communication in military, public and private places by individuals or any size of organizations. Today any laptop computers include devices for establishing wireless ad hoc networks that use free unlicensed frequency band for wireless network connections. Also, modern time demand for portable gadgets that use wireless ad hoc connections increasing, hence, the need for high quality communication is essential. However, there is no restriction for using free unlicensed band, which leads to conflicts when the capacity of the bandwidth is exceeded. Hence, conflicts in using free frequency band causes interference of the signals deteriorating the wireless connection and degrading the quality of  the receiving signals. Deterioration of quality of the receiving signals in wireless ad hoc network communications and wireless network connection failures require detailed study of techniques and algorithms that can enhance the overall performance and reliability of ad hoc wireless networks.

This project is involved in the studying the existing techniques used in wireless ad hoc networks and improving the overall performance as well as studying cause of interference in ad hoc wireless networks. Severe interference can cause wireless communication failure as the probability of error in the system increases as well as interference power. Another important thing is to illustrate the throughput and spectral efficiency of the wireless ad hoc networks. These four factors will demonstrate the overall performance in the ad hoc wireless network communications. Moreover, it is vital to study the effect of multiple accesses to the shared bandwidth, initially assuming that there is only single channel hopping and then multi — channel hopping. There are two widely used methods for multiple channel access of which are Frequency Hopping (FH) and Adaptive Frequency Hopping (AFH). FH and AFH will be explained in details later in this report. Therefore, this project is mainly focuses on the performance evaluation of AFH wireless ad hoc networks when capacity of bandwidth is exceeded and interferences occur. 

There are many layers in the ad hoc wireless networks but here in this project only MAC and Physical layers were interested as these are responsible for identifying the communicating nodes, doing channel choice, dealing with interferences, doing node coordination, utilizing available bandwidth, handling encoding – decoding and modulation of signals.

Performance evaluation has been carried out using Matlab software environment by making various software models and simulations. Many functions that carry out drawing graphs and mathematical calculations of average Signal-To-Interference-plus-Noise Ratio (SiNR), Average Spectral Efficiency (SE), Average Bit Error Rate (BER), Average Throughput, distances of two or many nodes as well as generating special random numbers for various uses in desired dimensions were designed for simplicity of the codes and ease to understand. Monte Carlo technique was used to work out approximate average of performance evaluation. How the Monte Carlo technique was applied and used will also be explained in details later in the report. 

Ad hoc networks provide freedom and flexibility for establishing network for various purposes because no base stations and fixed infrastructure required. Small networks for establishing communication at any place and location for sharing data between two or many nodes without need of centralized router and licensed frequency band makes it quickly deployable and economically profitable. Therefore, ad hoc wireless networks are applicable in many areas such as in military, computing, emergency operations, wireless mesh networks, wireless sensor networks and hybrid network architectures.

The outcome of the simulation results are presented and analyzed. Previously explained intelligent algorithms such as Frequency Hopping (FH) and Adaptive Frequency

Hopping (AFH) were simulated and graphs were plotted. Performance presentation was done taking into account the four factors: Signal – to – interference- plus noise ratio (SiNR), Probability of Error (PE), Throughput, and Spectral Efficiency. 

In order to present performance improvements in the newly developed AFH the comparisons between AFH-1 and AFH-2 equal and unequal conditions were given and how they perform was demonstrated as can be seen later in this chapter. 

In the real world a number of available channels may be already engaged therefore it is important to see how the wireless systems would respond in such circumstances. In the below simulation results illustrated in the Figures starting at 5.1 to 5.4, “n” refers to the number of channels and “ni” refers to the already occupied number of channels in this case there are 20 channels for FH, AFH-1 and AFH-2.

A lot have been told about FH and AFH algorithms and why AFH offers better performance than FH in theory. In this section it is possible to observe the graphical representation of their performances in terms of SiNR illustrated in the Figure.
































Figure Signal – to – interference – plus noise ratio (SiNR) comparisons of FH, AFH-1 and AFH-2. n= number of channels, ni = number of initially engaged channels

 

Overall the project completion was done in three periods: Research on the project and Matlab software, building software models for performance evaluation and writing simulation program, and finally making the simulations, comparing the results and testing for validity of the outcomes. 

The MAC protocol design of the ad hoc wireless networks is the one the challenging bit because the network performance dependant to the MAC protocol as it is responsible for the intelligent management of the resources. AFH is one of the mechanisms in the MAC layer used for efficient use of the accessible bandwidth. 

Targeted FH and AFH performance evaluation was carried out and the comparison of their performance and behaviors under real world conditions was tested.   Performance evaluation was achieved by determining four factors such as SiNR, PE, SE and Throughput.Involving Monte Carlo Technique. 

Maximum use of the features of the Matlab software environment was done, encapsulating some confusing calculation procedures into functions and naming functions according their operations eased the readability and reusability of the codes and instead of using huge loops the vectors was used. Overall,  the most loops used for carrying out some calculations were avoided by intelligent use of provided vectors that boosted the simulation speed as well as codes became highly cohesive and easy for maintain, modify and extend in the future.  Furthermore, two version of the AFH technique AFH-1 and AFH-2 were offered, it was proven that AFH-2 overwhelming the AFH-1 as the result of the simulations in terms of performance. How much of performance lost by using FH was illustrated comparing it with the AFH. 

To make the simulations more realistic the locations of potentially interfering nodes were made in 3 dimensions (3D) and the distance from the interfered node was worked out to compute the SiNR value.