Design of a Microwave Path Profiling Link - Coursework Example

Design of a Microwave Path Profiling Link Introduction In this research paper,the main aim is to make a comprehensive study of the design of a microwave path profiling link and budget calculator for various designs and applications. The software that will be designed should be capable of defining the application, entry of the relevant parameters of a particular radio link, calculation of the expected transmission loss in the system and if time will allow, it should be able to calculate the transmission loss links and the statistics related to time and space variations. An appropriate design process for the system will be formulated and the particular details of the applicability of the same analyzed. By comparing the performance of the systems to its failures, it will be possible to justify the applicability of the microwave path profiling link and budget calculator. Background A microwave communication system makes use of radio frequencies that have a span of between 2 and 60 GHz. The nature of the electromagnetic wave that will be used is dependent on the intended use and application of the system. The electromagnetic waves normally occur in the form of energy waves that are composed of both an electric and magnetic field (Freeman, 2008). Unlike mechanical waves, these are capable of transmitting energy across vacuums. These waves are normally classified according to their frequencies as illustrated below. Figure 1: Electromagnetic spectrum Compared to radio waves, microwaves have a shorter wavelength. They are used in cooking of food, transmission of information and the prediction of weather. Microwaves are appropriate for use in weather analysis and transmission of communication signals due to its ability to penetrate tough clouds, smoke and other forms of interference. Microwave links have several factors that make them appropriate for use in fixed media networks (Seybold, 2005). These waves have less exposure to accidental damages; and make use of single point installations. They are cost effective since they can be deployed quickly. However, it is also crucial to point out that this technology is limited to capacity, in certain areas where the terrain is unfriendly, there may be need for pylons to be erected and the relay stations must be located over long distances making it unsuitable for short distances communications (Jimenez, 1999). Discussion In order to understand the operations of the microwave path profiling link and budget calculator. The following have to be analyzed. a. Antenna gain This is determined by the number of wavelengths in its area of signal capture. It occurs in two positions where the frequency of the system may rise or the size of the signal capture area may give up (Jimenez, 1999). Most of the point to point microwaves systems make use of parabolic antennas so that they are able to achieve the necessary gain and the interference that has been reduced from the system. A formula for the parabolic gain is given as: 7.5 + 20 Log (F) + 20 Log (D) Where F = Frequency in GHz and D = Diameter in Feet b. The antenna beam width The antenna beam width is related to the forward gain of the antenna. Antennae gains result from the redirection of available radiated energy within a particular direction and if the gain is higher on the forward direction, it reduces in magnitude on the other directions. This is the reason why large antennas normally have higher gains that are more directional (ITU-R recommendations: Online). The beam-width of a parabolic antenna is given by the formula: 70/F x D Where: F = Frequency in GHz and D = Parabola diameter in feet c. The Fresnel zones These are concentric areas that surround the direct path of the signal beam between the two antennas. In order to determine the RF line-of-sight, it is important to clear about 60% of the first Fresnel zone boundary from the signal beam centerline outwards across the entire signal path (Rankstel: Online). Every succeeding Fresnel zone has a ½ wavelength relationship to the previous zone and the distance that separates the Fresnel zones reduces as the number of zones increases. The boundaries in the Fresnel zones can be computed with the formula: Where: F1 = First Fresnel zone radius in feet d1 = Distance from one end of path to reflection point in miles d2 = Distance from reflection point to opposite end of path in miles D = Total length of path in miles f = Frequency in GHz d. Multi-path reflections These occur when the point of reflection of a particular path has a reflective surface that is visible to both antennas. The multipath reflected signals result into problems that are experienced in wireless systems and are normally implemented through proper path engineering. This is done by field engineers who scrutinize the documents describing the antenna coordinates, the obstacles on the signal path and the characteristics of the surface (Seybold, 2005). The final report they present will contain important information that will be required by the systems engineers to perform reflection activities, establish links and analyze the design of the system. e. The reflected signal Point to point terrestrial lines of sight microwave systems normally cause most of the reflected signals to occur at angles that are small as a result of the high ratio of path to the height of the antenna that is above a specific point of reflection. This usually has a number of negative effects to the system which include: a) The primary beam width of the antenna is normally broad enough to cause illuminations on the points of reflection using the full signal power of the primary beam of the antenna. b) The reflections that occur at angles that are small usually result into an inversion of the signal. f. Atmospheric refraction The differences that occur in the propagation of waves and the velocity result from the refraction of the propagated signals through the atmosphere (Olsen and Tjelta, 2013). At a normal atmosphere, the velocity of propagation is about 99.997% that of the free space. In normal circumstances, this density decreases in a linear manner with the altitude of the atmosphere. This result into a signal path that that has the tendency to follow the curvature of the earth but at a lesser degree (Rankstel:Online). In microwave engineering, the K factor is used to describe the type and amount of atmospheric refraction. A K factor of a value 1 describes a situation where there is no refraction at all and the signal propagates in a straight line (Deygout, 1996). A factor of K less than 1 describes an occurrence where the refracted path of the signal deviates from the straight line and arcs in the opposite direction of the curvature of the earth. A K factor that is greater than 1 is used to describe a condition whereby the refracted signal path is able to deviate away from the straight line and arc in the same direction as the curvature of the earth. g. The earth bulge The bulge describes the effect of the physical curvature of the earth along a direct path between two points on the surface of the earth. Figure 2: The earth bulge parameters The extent of the physical bulge of the earth can be described using the formula: Where h= Vertical distance from a horizontal line of reference in feet d1= Distance from the data point to point A in miles d2= Distance from the data point to point B in miles Design of the microwave link The technical part of the design of this system is through detailed design practices. The mode of design applied in this case must also be cost effective and within the limits of the budgetary allocation (Manning, 2009). The design of the microwave link will start by the study of the digital terrain maps in order to identify new points that will be allocated to the network. The DTM will be used with software that is capable of performing altitude analysis such as ERDAS in order to ensure that the site have a line of sight within the range of the terrain. a. The process of design Figure 3: The design process b. Generation of path profile Assuming that the points identified for the propagation of the signal are points A and B, the coordinates of point A will be identified using survey methods and the vertical, horizontal, azimuth and the altitude of the point must be obtained (Anderson, 2003). The same procedure is repeated at point B. The distance of separation between the transmitter and the receiver should also be defined and set to a given distance. c. The field survey works This will be conducted in order to verify the parameters and the obstacles that lie along the path and the feasibility of the link bases. Using the information obtained in the exercises above, the microwave link will be designed with specifications such as availability of 99.99%, a transmitted power f 35dBm and the antenna should have a parabolic dish that has a diameter of 1.2 m and an efficiency of 55%. d. The link budget of the system This is the combination of all the gains and losses to be incurred in the radio communication link. This link can be determined through the addition of the power of transmission and then subtracting the received levels of the signal (Goktas et al. 2014). The steps that will be followed in the in the determination of the link budget are as outlined in the sections below: (i) The Effective Isotropic Radiated Power (EIRP) This is the summation of the transmit power and the antenna gain less the other losses. The transmitted power is given by: (ii) The free Space Loss The free space model is given by the equation: (iii) Atmospheric absorption The total amount of absorption by atmospheric gases on a terrestrial radio link of length d is given the formula: (iv) Receiver gain The receiver gain is given by the total antenna gain less any random losses. It is given by the equation: (v) The Un-faded Receiver Signal Level (RSL): To determine the Unfaded Receiver Signal Level, the reciever antenna gain and path loss will be subtracted from the effective isotropic radiated power. Conclusion From the discussions carried out above, the design process for the microwave path profiling link and budget calculator has been well outlined. The factors that must be taken into consideration have been discussed in detail. The methodology and procedures that are needed in the design of this software have also been well discussed. The microwave path profiling link and budget calculator will be crucial in defining the application, entry of the relevant parameters of a particular radio link and the calculation of the expected transmission loss in the system. References A. Vigants, Space diversity engineering," Bell System Technical Journal, vol. 54, no. 1, pp. 103-142 (2005). Seybold J.S., Introduction to RF Propagation, John Wiley and Sons, pp. 79 (2005). H. R. Anderson, Fixed Broadband Wireless System Design, John Wiley & Sons Ltd., 2003. J. Frank Jimenez , Fundamentals of Radio Link Engineering, Path Engineering (1999). R. L. Olsen and T. Tjelta, Worldwide techniques for predicting the multipath fading distribution on terrestrial LOS links: Background and results of tests," IEEE Transactions on Antennas and Propagation, vol. 47, no. 1, pp. 157 (2013). P. Goktas, A. Altintas, S. Topcu and E. Karasan, The effect of terrain roughness in the microwave line-of-sight multipath fading estimation based on Rec. ITU-R P.530-15," in General Assembly and Scientific Symposium (URSI GASS), August 2014. T. Manning, Microwave Radio Transmission Design Guide. Artech House, 2009. J. Deygout, Multiple knife-edge di_raction of microwaves," IEEE Transactions on Antennas and Propagation, vol. 14, pp. 480-489 (1996). ITU-R recommendations, available on: http://www.itu.int/pub/R-REC . Accessed on 18th May 2015. Rankstel online, available on: www.rankstel.com. Accessed on 18th May 2015. Read More