Telecommunication System Engineering: Basics, PSTN, Digital Microwave Radio Systems

System Engineering

Discuss about the Telecommunication System Engineering.

Basics of the system engineering utilizes system thinking to organize whole knowledge. Some critical issues like requirements engineering, coordination among team members, logistics, testing, reliability, maintainability and many such disciplines are necessary for system design, development, and implementation [1]. System engineering defines work processes to optimize the methods. It provides risk management strategies and tools for projects. System engineering might overlap with human centered disciplines like manufacturing engineering, project management, industrial engineering, control engineering or software engineering. System engineering is not a manufacturing process, it is more likely a discovery process to deploy efficient methods. A manufacturing process is mainly focused on repetitive activities to achieve high quality products with minimum resources. Whereas system engineering process starts with discovering real problems which needs to be resolved and identifies impact of failures to cause loss. System engineering helps to identify problem and then provides solutions for those problems.

System efficiency and reliability are important aspects of any software system in the organization. Organization depends on these aspects for continuous delivery of the services. There are many effective ways to make this happen. These are:

Clean data: Data is required for most of the applications. Insufficient and incorrect data will create trouble instead of generating outputs. Wrong data may result in wrong interpretation or wrong information. Clean data will give accurate and reliable results.

Defines Processes: Software might have fixed processes which needs to be repeat for different purposes. Defining these processes according to the requirement of the system is required. All the process will not fir the system. These processes need to be modified whenever required[2].

Security: System security is most important concern for any organization. Communication over internet may be a risky affair for a content sensitive company. If company wants to keep its information confidential, it must secure the system with latest updates software or firewalls.

Information access: Information should be easily accessible to the authorized users. It should not be a complex process to get any relevant information from the system.

Maintenance and Adaptation: Regular maintenance of the system is required to repair any loss of system capability or information. It can be done through documentation or through automatic software checkers.

PSTN is used to meet requirements of offices, organizations or individuals to transmit telephone messages all across country. It can also be provided international access. System will be provided interconnection of private networks and access to PSTN which will be according to present requirements. PSTN supports the data transmission, e-mail and messages to cross point switches when corresponding equipment is used at terminal [3].  PSTN is designed to enable two way voice communication. Enabling a connection between two points was as simple as placing a normal wire between the two points. Cost of this connection depended on the distance between the locations and the distance of end users from each other. With increase in distance, cost increases and accessibility decreases. Telephony network developed with the time and now more users can be connected through each other. Earlier only one user could be connected to a single user with the point-to-point connections over telephone network architecture. Network engineers developed a network to interconnect large number of devices by placing switching equipment at central locations. This was called Public Switched Telephone Network (PSTN).

System Efficiency and Reliability

It is focused on circuits used in network. It is a connection oriented system for delivering only one service which is voice. In this system, each network user require to set up a “call-setup” to both the points which needs to be connected. It reserves the resources along the path for two way communication. This allows the network operator to route and bill the calls by identifying every step of call path and it also manages the switching system network. PSTN arranges the network offices in hierarchical stages according to the function they perform and employ trunk lines between network switches. It can scale up the tele-communication network to accommodate many end users. By doing this, it can manage the traffic between switch offices depending on which switch needs to be connected. It identifies the traffic as local traffic, international traffic or long distance traffic. PSTN operates on a link to link basis. Each switch forwards the traffic in a hierarchy towards link or hop to next PSTN based on call setups [4]. 

Microwave transmission is information or energy transmission by electromagnetic waves. Wavelength of these waves is measure in centimeters. Range of wavelength is from 1 Gigahertz to 300Gigahertz. These waves are used for point to point communication. Small wavelength is used conveniently for small sized antennas to direct it in narrow beams which can easily be pointed out to receiving antenna. Therefore nearby microwaves can use same frequencies without interfering with other devices or communications. This is the problem with lower frequency radio waves. Another big advantage of this is that high frequency waves give band large information carrying capacity without distortion [6]. This has the bandwidth 30times of all other radio spectrums. But there is limitation too and which constraints it to line of sight propagation only. These waves can’t be passed across the hills or mountains but lower frequency waves can be easily passed through these obstacles.

Microwave transmission is mostly used for point to point communication on the plane surface of earth, in space radio communication or also in satellite communication. It is also used for radio navigations, radio astronomy, radars and sensory systems. There is a higher part of radio electromagnetic spectrum which is above 30 GHz and below 100GHz, these are called millimeter waves.  These radio waves in this band limit can be highly attenuated by atmosphere and particles at earth.at wider frequency band, radio waves are attenuated by atmospheric molecular oxygen. Electronic technologies used in millimeter band are difficult to utilize than microwave band [7]. There are two types information transmission:

• One-way or two way transmission through communication satellite
• Terrestrial microwave telecommunication 

Public Switched Telephone Network (pstn)

Digital radio transmitter takes baseband waves and translates them into a waveform which can be effectively transmitted by channel. Before this transmission to radio frequency from baseband, waveform is digitized to gain the advantages of digital modulation. Coding is also used to efficiently use the available bandwidth by minimizing the interference and noise introduced by the channel. This coded signal is filtered and changed to analog waveform which is then converted to desired frequency transmission [8]. At last, RF signal is amplified after filtration and then transmitted from antenna.

It can be implemented in many ways with certain components in all receivers. It should be able to extract RF signal in presence of potential interference. There is a pre-selector filter which is most important part of the receiver. It attenuates signals which are out of band while receiving from antenna. Low noise amplifier is used to boost desired signals while ignoring noise of radio signal. A mixer is installed to down covert RF signal to intermediate frequency by collaborating local oscillator with RF signal. Unwanted components of the frequency are attenuated using IF filter. All the variations at the receiver are manifested by themselves at receiver. 

Link design start with link budget analysis. Radio system has a gain which depends on radio design and used modulation. Gain at each antenna are supplementary to this gain. Higher gains are possible from large antennas. Free space loss is subtracted from system when radio signal travels over the air. Loss is higher with longer links. This energy can be absorbed by rain or other environmental factors. Rain can cause outage if sufficient energy is absorbed which cause receiver to lose the signal. Radio link engineering to accommodate these rain attenuated effects is based on global rain models. These models are derived from attenuation combined with meteorological observations. The resulted fade margins are calculated. Anything in this margin can be overcome by the radio signal, if margin exceeds then the link will go down.

It is a graphical representation of path of the radio waves between two end point links. It determines height of antenna and its location at each link end. It tries to get link free of obstructions like hills and multipath reflections. Link endpoints should have unobstructed line of sight radio waves. Frequency of microwave is lower than visible light, because of this it behave differently in environmental conditions. It require more clear way than line of sight way to accommodate microwave signal characteristics. Electromagnetic waves do not travel on straight path. It spreads as it propagates. Individual signal does not travel at same velocity. A French scientist divided the wave paths in different zones according to their speed and phase of wave propagation. Sizes of these Fresnel zones vary according to radio signal frequency and path length [5]. Fresnel zone size increases with decrease in frequency and increase in path length. Radius of Fresnel zone is maximum when signal is at mid of path. Therefore, midpoint needs most clearance in path than any other point. 

Digital Microwave Radio Systems

It is the expected attenuation in a signal while its travel away from transmitting device. Signal spread over larger distance while radiating from an antenna. Power density decreases with increasing area covered which deteriorates the radio signal.

FSL = 32.44 + 20lgF + 20lgD

F is frequency in MHz and D is distance between endpoints of link in Km. 

It is the difference between receiver sensitivity threshold and un-faded receive signal. Every link should have enough fade margin to keep it secure from path fading which deteriorates radio signals.  Fade margin works as an insurance against system outages. It is related to link availability which is calculated as percentage of time when link was functional. This percentage increases with increase in fade margin. A link will have fewer system outages with larger fade margins. Link which have no fade margin or little fade margin might experience interrupted outages because of path fading phenomena.

Path fading increases in worse climatic conditions like flat or humid environment, dry or rough location. Link in flat or humid areas need larger fade margin to achieve better link availability. Climatic conditions like maritime temperature, coastal or humid temperature, sub-tropic climate, high dry mountains climate should be taken into considerations while calculating link availability performance [9].

Cost and operations of the telecom system depends on the requirements of the company. Cost can be adjusted based on the quality requirements and the distance between communicating devices. Maintenance cost is negligible in this system, although installation cost can be very high depending on geographical and environmental conditions.

[1]  P. . Fontolliet, “Telecommunication system engineering,” Signal Processing, vol. 23, no. 1, p. 107, Apr. 2011.

[2 J. M. Griffiths, “Telecommunication system engineering,” Electronics and Power, vol. 26, no. 9, p. 750, 2010.

[3]  H. J. Kim, “Suitability of IP telephony in the public switched telephone network (PSTN),” International Journal of Business Data Communications and Networking, vol. 3, no. 3, pp. 39–56, 2007.

[4]  R. Frieden, “The mixed blessing of a Deregulatory Endpoint for the public switched telephone network,” SSRN Electronic Journal, vol. 2, 2008.

[5] M. C. S. Young and P. M. Grant, “Reduction of multipath propagation effects in microwave digital radio communication systems,” Electronics & Communications Engineering Journal, vol. 2, no. 1, p. 4, 1990.

[6]  L. J. Stagg, “High-capacity digital microwave radio systems,” IEE Journal on Microwaves, Optics and Acoustics, vol. 1, no. 1, p. 1, 2006.

[7] K. Watanabe, S. Uwano, and H. Matsue, “Pre-interference canceller for digital microwave radio systems,” Electronics and Communications in Japan (Part I: Communications), vol. 78, no. 6, pp. 103–114, Jun. 2005.

[8] I. Flood and D. Bacon, “Towards more spectrally efficient frequency assignment for microwave fixed links,” International Journal of Mobile Network Design and Innovation, vol. 1, no. 2, p. 147, 2006.

[9] A. D. Sarma, M. V. S. N. Prasad, and B. Balakrishna, “Significance of rain induced Attenuation and Multipath in the design of digital microwave links,” IETE Technical Review, vol. 12, no. 5-6, pp. 359–373, Sep. 1995.