Radio Network Forensic with mmWave Using the Dominant Path Algorithm

higher constraint for implementing and deploying higher losses, low diﬀractions, and low signal penetrations for the mentioned two bands. For outdoor, a MATLAB built-in 3D ray tracing algorithm is used while for an indoor oﬃce environment, an in-house algorithmic simulator built using MATLAB is used to analyze the channel characteristics.


Introduction
Present research work in the field of network forensic is on traditional networks. Because of the emergence of cellular or radio networks, radio network forensic provides the platform to investigate, capture, and detect faults, illegal activities, and cybercrimes [1]. Figure 1 illustrates the investigation process for digital forensic.
e DFRWS model begins from identifying the crime. is identification is further divided to different tasks, for example, signature resolving, system monitoring, analysis, profile detection, complaints, and anomalous detection. e next step is the preservations. In preservations, we need to set up case management, management of the technology, insurance of custody chain, and synchronizing the time element. In the third step, data are collected by following the approved methodology. Examination is the fourth stage in DFWS. In examination, data are examined. en, the data are analyzed, and tracing of evidences, validation of data, and filtering of data begin. In the presentation stage, we document the evidence, and final decision is taken. Frequencies greater than sub-6 GHz are not properly utilized in digital forensics due to which mmWave provides much greater bandwidth than the existing ones. On the one hand, higher-frequency bands (e.g., mmWave bands) are not heavily utilized and, thus, offer larger bandwidths for wireless communication systems. Hence, determinations are focused upon the discovery of advanced frequencies as an alternate to the sub-6 GHz band [2]. On the other hand, the performance of the wireless communication system (WCS) is affected by multipath fading. As a matter of fact, the mobile device and the router for WCS have to cope up multipath manifestations which in other words demand deep knowledge of the propagation channel [3]. e designers of radio coverage make use of path loss prediction models and other channel parameters to deploy and install access points in an environment for the sake of better coverage and through put [4]. is work deals with extensive measurements, modeling, ray tracing, and simulations of channel characteristics in open outdoor as well as in narrow corridor and institution room environment. e frequency bands considered for the WCS modeling are 28 GHz and 60 GHz. We rationally premeditated received signal strength (RSS) by the principle of the "five rays" and "two rays" receiving power model. To associate proposed model systematic results, simulations and measurements were performed at e University of Faisalabad, Faisalabad, Pakistan. e experimental campaign is shown in Figure 2(a). e outdoor scenario is shown in Figure 2(b). e transmitter indicated in red is roughly 250 m apart from the receiver shown in blue. e remaining part of the article is described as follows. A summary of the recent related work and the contribution are discussed in Section 2. Section 3 deals with the path loss modeling for both outdoor as well as indoor environment. Section 4 deals with the ray tracing modeling. Section 5 analyzes the detailed simulations and algorithm for the smart ray tracing algorithm. Finally in Section 6, we draw conclusion.

Recent Studies and Contributions
Numerous tactics are suggested in the literature to control the extraordinary attenuation issue on mmWave frequency bands [6,7]. In [8,9], the authors indicated that increment in the directivity or gain of the concerned antennas can be beneficial in high attenuation problems. Table 1 illustrates the recent findings in the field of mmWave. e model used, geometry, scenario, carrier frequency, and separation between the transmitter and receiver are mentioned against each reference. Another aspect is the material characteristics of the environment [32]. e need for ray tracing comes here as the indoor and outdoor environment difference in geometry so is the LoS and NLoS for numerous frequency bands. Ray tracing is used to model the propagation characteristics [33][34][35][36].
A separate ray source is presented in this article for endto-end penetration. We considered five rays for indoor and five for outdoor. In indoor, we analyzed one ray for LoS and the rest of four for the wall, ground, and ceiling of the room. All the five rays considered to be contributing in received and illustrated with different colors. ese remain because of the small separation between transmitter and receiver antennas. e reflected rays are excluded by Rx because of the directivity pattern. e high fresnel reflection coefficients are organised with reference to the radio links. An escalation in the RSS was spotted as compared to outdoors. e path loss for the outdoor open environment has greater slope than that for indoor.
Normally, two ray models are deliberated for outdoors because of their nature of modeling P r in an unavailability scenario of 1 st order reflections.
us, no concrete solid evidence of the difference is found between PL slopes. At last, the calculated modeling is compared with experimental parameters and RT simulations. We also prepared a reasonable investigation of the measurements with 5-ray and 2ray investigative models, and RT simulations with 5 rays are delivered for the indoor office environment.
In Figure 3(a), the probability of dipole antenna for the proposed model is marginal with the theoretical values. is indicates that the probability of dipole decreases with the increase in path loss. Additionally, the probability for closein and 3GPP models deviates from the theoretical model.  reactance and resistance are opposite to each other. e above recent literature when compared with our proposed work points out the following differences: (i) Five dominant rays for indoor and two dominant rays for outdoor were adequate considering this work.
(ii) e distance of rays was considered to be resolvable when compared with LoS. Smaller is the distance of resolution and the rays superimposed on one another. (iii) At 28 GHz and 60 GHz, a polarized dependent variable was utilized.  (iv) e close deployment of Tx and Rx is very common in indoor scenarios nowadays. is scenario with a typical classroom environment is focused here.
(v) Antenna gains for Tx and Rx are closely monitored with the help of MATLAB simulations using antenna radiation patterns.  Figure 4 is taken from the recent studies conducted by authors to ray trace the path loss in a different environment with heatmap techniques using MATLAB Simulink. e close-in (CI) free-space path loss model is utilized to adjust the path loss from the result of simulations. e supremacy of CI is that its parameters are dependent on the operating frequency. e relationship of PL with frequency for CI is as follows [37]:

Path Loss Modeling
represents the free-space path loss in dB and is given by where d 0 is the Tx-Rx separation at 1 m reference; f stands for the frequency of the carrier radio wave; c denotes the light speed, and n is the path loss exponent (PLE). In [38], WINNER II and 3GPP are illustrated with the help of floating intercept (FI). According to [38], FI is expressed as follows: where σ SF of Y FI σ SF is the Gaussian SF. Multifrequency path loss models are used for a variety of mmWaves. For this aspect, the famous alpha-beta-gamma (ABG) model with a 1 m reference distance and 1 GHz referred frequency is considered here as follows [39]: In the above equation, α and c denote constant coefficients. β denotes the offset, and X ABG σ is a Gaussian random variable. In literature [40], ABG is solved with the help of MMSE to minimize error.
Another derived model from CI and FSPL which is widely used for path loss analysis is CIF (Close in free space) [38]: where m and g are the distance dependent and linear frequency dependent factors, respectively.

RT Modeling
Ray tracing involves two patterns. (a) ray launch and (b) the image theory. In the first line of attack, rays commencing Tx are launched with even angular departure and then traced. After tracing the rays, the received field will be calculated to find the power [41][42][43]. is approach has faster computational time but has less accuracy when the separation increases. An alternate approach as mentioned is the image method, in which the route is first defined of image points from Tx or Rx [41,43]. is method of images has a drawback of high computational time and involves complex algorithms. e interaction mechanism implements propagation's theory; nonetheless, the deviation through different RT tools occurs due to the dissimilar method of modeling the similar phenomena (e.g., diffraction, diffusion, scattering, and reflection). Other deviations follow in the antenna design, pattern, sources, frequencies, and models. e constitutive material aspects, e.g., the magnetic permeability (μ), electrical permittivity (ϵ), and the conductivity (ρ), are essentials for accomplishing accurate channel estimations in RT [44]. Undeniably, Maxwell's electromagnetic wave equations for diverse edges are fighting fit for constitutive parameters.
is directly affects the wave's phase and amplitude, therefore, eventually governs the influence of discrete multipath constituents. e influence of "material properties" on the RT estimations precision depends on the dominant propagation.
Accordingly, in situations wherever the LoS dominates, material properties can affect very little on the accuracy of the prediction algorithm. e modeling of diffused scatterings is usually carried out with the help of severe roughness models as proposed in literature [45]. Because the model is not dependent on the Maxwell equation, it solves the issue of diffused component's power. Besides, the roughness model is not dependent on the material properties; it can predict a diffuse scattered field. Fresnel's equation works on smooth surfaces for the analysis of reflection coefficients and transmission coefficients. e reflection coefficient for the smooth surface is given by [32] In the above equation, e i ⊥ denotes the incident electric fields, θ i represents the incident angles, e r ⊥ expresses the reflected electric fields, η is the wave impedance, and θ r declares the transmission's angle. e transmission coefficients are denoted by e constitutive parameters of the used materials will determine the impedance of the wave (η) and the also the angle of transmission θ t : Security and Communication Networks where Ω stands for the angular frequency and p denotes the wave number for that frequency.
More accurate results for diffracted wedges can be obtained by using the "Uniform eory of Diffraction" (UTD). For UTD, the details of material constitutive parameter are necessary to be determined. Considering Figure 5, the diffraction coefficient can be obtained by [46] where where Ψ ' is the incidence angle and Ψ is the diffraction angle; the Fresnel integral Y(v) can be expressed as follows:  Security and Communication Networks L is defined as follows: Figure 5 explains that n represents the wedge's factor, and s and s ′ are the distances. a ± is defined as follows: Finally, M ± are the integers of the following equations: e information of material properties is hence crucial to precisely model the diffraction. Figure 6 indicates the properties of different materials and diffraction loss occuring due to different material constitutes.

Simulations with the Dominant 3D Ray Tracing
In mmWaves (high frequencies), the concept of ray optics is considered. Maxwell equations are solved asymptotically. e wave length of the electromagnetic wave plays a key role in obtaining attractive and accurate results. Greater the size of the wavelength, the more accurate the results from an RT stimulation [47,48]. Reliant on the electrogeometrical appearances available in digital maps, a ray undergoes diffuse scattering, diffraction, penetration, reflection, or attenuation. e penetration of rays joints upon accurate geometric and materialistic characteristics. e simulation setup is shown in Table 2. We have considered a three-floored building. e path loss model we used for simulations is Close in. Two mmWave frequencies (28 GHz and 60 GHz are discussed for the complex layout of LoS and NLoS. e length and width of the wall are 2.8 m and 0.1 m, respectively. e rest of the parameters of the Base station and User terminal are mentioned in Table 2. RT tool complications increase with the order of interaction mechanism. Nevertheless, with high order interaction, the expansions in relation to prediction precision are frequently negligible but even so acquire major computations overhead [49].

Simulations for Outdoor.
e simulations performed in this campaign are based on the intelligent 3D ray tracer built-in MATLAB. is tool is different from other 3D RT tools as it is capable of performing full 3D ray tracing in terms of path loss and received power. Other ray-tracing tools can find many paths, but the mentioned tool is used to find the dominant paths. e 3D map of the concerned scenario is shown in Figure 7.
In this section, received signal strength (RSS) is the main parameter in designing the simulator. e antenna designed for outdoor simulations is an omni-directional circular dipole antenna with a transmitting frequency of 28 GHz and 60 GHz. Figure 8(a) shows the current distribution of the antenna. e current at the center (circular) is greater than that at the bottom and top of the antenna. is is because of the feed which is at the center of the antenna. Figure 8(b) shows the 3D radiation pattern. e maximum radiation is 1.71 dBi and minimum is 13.2 dBi (Algorithm 1). e height of the receiver (user with mobile phone) is 1.6 m. e user is standing still on the location mentioned in Table 2. Figure 7 indicates the RSS in dBm. Figure 7 reveal that the RSS level has a mean difference of around 8 dBm-10 dBm between 28 GHz and 60 GHz. is is due to the fact that the huge gap between mmWave frequencies does not affect much power of the signal in small cell environments. On the other hand, this is the sign of low penetration, low signal diffraction, and very high free-space losses.

Simulations for Indoor.
e indoor floor map of the simulation environment is shown in Figure 9.
ere are three transmitters in the facility. To understand the complex scenario for ray tracing, we choose the nearby transmitter, (in the corridor) (i.e., Tx2). Rx is in the office. Figure 10 illustrates the typical classroom where measurements were performed, and simulations were carried out. It consists of plywood, concrete tiles, plastic, brick work, plaster, and metal. Figure 6 shows the path loss of different material obstacles in the path of rays against a range of frequencies. It is evident that the loss due to bricks is constant throughout the range of mmWave frequencies (Algorithm 2). Figures 11(a) and Figure 11  Security and Communication Networks dominant rays are considered here to decrease computational time and make the algorithm less complex. In Figure 11(a), the color of two LoS rays is dark blue showing that the path loss is near to 80 dB. e other rays colored red and yellow are indicating path loss of 90 and 95 + respectively.
is is due to the NLoS, reflection and diffraction of metal and brick walls. More detailed analyses of the rays and pattern of the path loss are explained in Table 3.

Conclusion
In this paper, the outdoor to outdoor and indoor to indoor characteristics of the path loss with increasing the mmWave frequencies considering the network forensic with the help of the dominant path algorithm are studied. In the first approach, a conventional approach of the empirical and statistical analysis of path loss is adopted. ree different models including ABG, CI, and FI are discussed. e conclusion of the models is done that close in is better for indoor as well as outdoor scenarios. In the second approach, a software-based method is applied. Raytracing simulations indicate that the outdoor RSS level has a mean difference of around 8 dBm-10 dBm between 28 GHz and 60 GHz. is is due to the fact that, on the one hand, the huge gap between mmWave frequencies does not affect the power of the signal in small cell environments. On the other hand, this is the sign of low penetration, low signal diffraction, and very high free-space losses. Similarly, in indoor environment, the difference between the path loss is due to the two different transmitting frequencies which is promising in a way that increasing the frequency in indoor environment results in an increase in the path loss by 5 dB for every 10 GHz. In the future, we would like to investigate radio network forensic for artificial intelligence-aided wireless systems.

Data Availability
No data were used to support this study.

Conflicts of Interest
e authors declare that they have no conflicts of interest.