Terrestrial Microwave Link Design


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Terrestrial Microwave Link Design

  1. 1. Terrestrial Microwave Link Design ‗Abdulrahman1, Ong Sin Yee2, Nurul Shafikah3, Mohamud Mire mohamud 4 Radar Communication Laboratory, Faculty of Electrical Engineering Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia 1 abdurrahman3@live.utm.my 2 ongsinyee@hotmail.com 3 nshafikah91@yahoo.com 3 mire.2007@hotmail.com Abstract—Microwave links provide the bulk of the interconnectivity between sites in telecommunications networks (especially mobile voice and data networks) because they are rapidly deployable, relatively small and require less infrastructure outlay than technologies such as fibre transmission. Typical applications of microwave link includes mobile backhaul links - between 2G/3G base stations and WiMAX/LTE backhaul links. The basic components required for operating a radio link are the transmitter, towers, antennas, and receiver. To achieve point-to-point radio links, antennas are placed on a tower or other tall structure at sufficient height to provide a direct, unobstructed line-of-sight (LOS) path between the transmitter and receiver sites. Before a microwave link can be installed, an analysis and calculation of the microwave link must be made first. The analysis should take place before the site survey itself to get a clear idea about the dimensions of the antennas. Our analysis consists in this paper consists of Free space loss calculation and Link budget calculation. Keywords— transmitter design, receiver design, point-to-point microwave link, frequency of 9, 15 and 18 GHz, system level. I. INTRODUCTION A microwave link fundamentally consists of a transmitter and a receiver. The transmitter and the receiver are each connected to an antenna. This is typically a parabolic dish antenna connected to the transmitter, and also typically a dish antenna on the receiver. Based on operating 3G point-to-point microwave link system which functioning frequency 9, 15 and 18 GHz only. The receiver always needs to be typically within the range of kilometres of the transmitter, but the distance is very much dependent on the path between the transmitter and receiver, as in [1]. Before we discuss the different types of antennas, this is the objectives as follows:  To understand the project and problem statement given.  To design a terrestrial microwave link system.  To analysis and discuss on the performance of the designed system.  To determine the appropriate operating frequency to be engaged in this microwave link system.  To do analysis on actual overall costing for the microwave link design. We should have a quick look at the subject of polarization, as it is relevant to antennas used in terrestrial microwave communications. Signals transmitted in any frequency band have a property termed polarization, and this relates to the geometric plane in which the electromagnetic waves are transmitted or received. Hence polarization describes the orientation of the electric field radiated from the antenna, as in [2]. There is little fundamental difference between transmitting antennas and receiving antennas, since the same antenna is often used for both purposes. While some antennas can be as simple as a wire thrown out of a window, for the best performance the right type of antenna needs to be used. The most important properties of an antenna are its radiation pattern and its gain (the magnitude of the signal), whether it is being used at the transmitter or receiver. In the case of a transmitting antenna, the radiation pattern is a plot of the power strength radiated by the antenna in different directions. As a consequence of its radiation pattern, power radiated by an antenna may be concentrated in a particular direction, and this directivity is expressed in terms of power gain, as in [3]. In order to design terrestrial point-to-point link system, there are several technical choices that we considered for instance the microwave LOS link , the link budget , free space path loss and its accuracy on the link analyses. The choice of the transmission media is one the most important actions we took, always at the first stages of the design of a communication system. This section describes briefly the different choices for establishing a link between two locations, and the different advantages and drawbacks of each alternative. II. POINT TO POINT MICROWAVE LINKS Point-to-Point (PTP) Microwave technology provides dedicated, point-to-point connectivity using directional antennas. A microwave link is a communications system that uses a beam of radio waves in the microwave frequency range to transmit video, audio, or data between two locations, which can be from just a few meters to several kilometres apart. PTP links typically require clear Line of Sight (LOS) between the transmitting antennas. A. Microwave Line-of-Sight Systems Microwave frequencies range from 300 MHz to 30 GHz, corresponding to wavelengths of 1 meter to 1 cm. These
  2. 2. frequencies are useful for terrestrial and communication systems, both fixed and mobile. satellite important to realize that ITU-R recommendations are usually adopted on a worldwide basis. "Line-of-sight" is a term used in radio system design to describe a condition in which radio device antennas can actually see each other. High frequency radios, such as those used in Spread Spectrum Radio require line-of-sight between antennas, as shown in Fig. 1, as in [4]. So, in our case, which is specifies the minimum performance parameters for terrestrial fixed service digital radio communications equipment‘s operating in the 13 GHz, 15 GHz and 18 GHz frequency bands. Systems considered are able to respect ITU-R national or international grade performance objectives, i.e. ITU-R Recommendations F.1189 for national, F.1092 for international and ITU-R Recommendation G.826. We also respect to the ITU-R P.53012 – Propagation data and prediction methods required for the design of terrestrial line-of-sight systems. ATPC power level definitions and limits are shown in Table 1. In the case of point-to-point radio links, antennas are placed on a tower or other tall structure at sufficient height to provide a direct, unobstructed line-of-sight (LOS) path between the transmitter and receiver sites, as in [5]. We also make use of the Automatic Transmit Power Control (ATPC) range in our project. ATPC is defined as the power interval from the maximum (including tolerances) output power level to the lowest transmitter output power level. If implemented, the ATPC range shall not be less than 10 dB. ATPC set manually to a fixed value for system performance. Other than that, ATPC also set at maximum provide power for Transmit (TX) performance. TABLE 2 VALUE OF LINK BUDGET Fig. 1 Line of sight of point-to-point application B. Standards Each country has a varying requirement for the licensing of microwave radio links. In most cases this license only addresses the transmitter, but in the same instance, it offers regulatory protection to any interference that may affect the microwave receiver. In the United States, radio channel assignments are controlled by the Federal Communications Commission (FCC) for commercial carriers and by the National C. Microwave Link Structure Telecommunications and Information Administration (NTIA) The basic components required for operating a radio link for government systems. are the transmitter, towers, antennas, and receiver. Transmitter The FCC's regulations for use of spectrum establish functions typically include multiplexing, encoding, eligibility rules, permissible use rules, and technical modulation, up-conversion from baseband or intermediate specifications. FCC regulatory specifications are intended to frequency (IF) to radio frequency (RF), power amplification, protect against interference and to promote spectral efficiency. and filtering for spectrum control. Receiver functions include Equipment type acceptance regulations include transmitter RF filtering, down-conversion from RF to IF, amplification at power limits, frequency stability, out-of-channel emission IF, equalization, demodulation, decoding, and demultiplexing. To achieve point-to-point radio links, antennas are placed on a limits, and antenna directivity. tower or other tall structure at sufficient height to provide a The International Telecommunications Union Radio direct, unobstructed line-of-sight (LOS) path between the Committee (ITU-R) issues recommendations on radio channel transmitter and receiver sites, as shown in Fig. 2, as in [6]. assignments for use by national frequency allocation agencies. Although the ITU-R itself has no regulatory power, it is Radio transmitters are described in terms of power output expressed in watts. The power output may also be expressed
  3. 3. in terms of decibels of gain (dB). Radio receivers are rated in terms of sensitivity (ability to receive a minimal signal). The rating is listed in terms of milliwatts (mW), or decibels of gain (dB). Antenna cable is rated in terms of signal loss per foot and expressed as dB of loss per foot. The antenna is rated in terms of gain (dB). There are a number of software programs that will calculate path loss by frequency and use the specifications of the system hardware to help determine the overall system feasibility. Fig. 2 Point-to-point microwave link structure III. MICROWAVE LINK DESIGN A block diagram of a transmitter base station is shown in Fig. 3. The transmitter base station of digitalization and encoding, WCDMA Generation (modulator), and transmitter. A block diagram of a receiver base station is shown in Fig. 4. The transmitter base station of receiver, demodulator, and digitalization and encoding. to analogue. Encoding using orthogonal coding, spreading, and correlation that W-CDMA uses a variable length code. The length of spreading code is also known as the spreading factor. Base station that receives a transmitted data sequence and attempts to demodulate it using the ―wrong‖ orthogonal code, would interpret the information as noise. 2) Transmitter: The transmitter produces a microwave signal that carries the information to be communicated. The transmitter has two fundamental functions: generating microwave energy at the required frequency and power level, and modulating it with the input signal so that it conveys meaningful information. Modulation is accomplished by varying some characteristic of the energy in response to the transmitter‘s input. 3) Transmission Line: The transmission line carries the signal from the transmitter to the antenna and, at the receiving end of the link, from the antenna to the receiver. At microwave frequencies, coaxial cables and, especially, hollow pipes called waveguides are used as transmission lines. 4) W-CDMA Generation (Modulator): The access technology, W-CDMA (Wideband Code Division Multiple Access), is termed UTRA (UMTS Terrestrial Radio Access). The information that was modulated onto the carrier from the carrier itself. It could be audio and/or video information, or other data. The modulator accomplished by puts the information or intelligence onto a carrier wave at the transmitter input. 5) Receiver: The receiver extracts information from the microwave signal and makes it available in its original form. To accomplish this, the receiver must demodulate the signal to separate the information from the microwave energy that carries it. The receiver must be capable of detecting very small amounts of microwave energy, because the signal loses much of its strength on its journey. Fig. 3 Transmitter base station block diagram Fig. 4 Receiver base station block diagram D. Description of the Purpose and Operation of All the Major Components of Base Stations 1) Digitalization and Encoding: using ADC at transmitter to convert the information from analogue to digital and it using DAC at receiver to convert the information from digital 6) Demodulator: Demodulator is a circuit used in AM (amplitude modulation) and FM (frequency modulation) receivers to separate the information that was modulated onto the carrier from the carrier itself. It could be audio and/or video information, or other data. A demodulator is the analogue of the modulator. The demodulator pulls it off so it can be processed and used on the other end. E. Brief Description of the Basic Operation of Transmitter and Receiver A block diagram of a transmitter is shown in Fig. 5. The transmitter of mixer with local oscillator, band pass filter, RF amplifier, cable and antenna. A block diagram of a receiver is shown in Fig. 6. The transmitter of antenna, cable, receiver, lower noise amplifier, band pass filter and mixer with local oscillator.
  4. 4. conversion, also referred to as heterodyning, produces the sum and difference frequencies of the frequency of the local oscillator and frequency of the input signal of interest. These are the beat frequencies. Normally, the beat frequency is associated with the lower sideband, the difference between the two. Fig. 5 Transmitter block diagram Fig. 6 Receiver block diagram 1) Lower Noise Amplifire (LNA): LNA is an electronic amplifier used to amplify possibly very weak signals (for example, captured by an antenna). It is usually located very close to the detection device to reduce losses in the feedline. An LNA is a key component which is placed at the frontend of a radio receiver circuit. Per Friss‘ formula, the overall noise figure (NF) of the receiver‘s front-end is dominated by the first few stages. A good LNA has a low NF (e.g. 1 dB), a very large enough gain (e.g. 20 dB) and should have large enough intermodulation and compression point. The gain of the LNA is 22 dB and the NF is 2.5 dB. 2) RF Amplifier: RF Amplifier (power amplifier) is a type of electronic amplifier used to convert a low-power radiofrequency signal into a larger signal of significant power, typically for driving the antenna of a transmitter. It is usually optimized to have a high efficiency, high output power compression, good return loss on the input and output, good gain and optimum heat dissipation. 3) Band Pass Filter (BPS): Band Pass Filter is a device that passes frequencies within a certain range and rejects frequencies outside that range. An ideal band pass filter would have a completely flat passband (e.g. with no gain/attenuation throughout) and would completely attenuate all frequencies outside the passband. Additionally, the transition out of the passband would be instantaneous in frequency. In practice, no bandpass filter is ideal. The filter does not attenuate all frequencies outside the desired frequency range completely; in particular, there is a region just outside the intended passband where frequencies are attenuated, but not rejected. This is known as the filter roll-off, and it is usually expressed in dB of attenuation per octave or decade of frequency. 4) Local Oscillator: To generate a signal normally for the purpose of converting a signal of interest to a different frequency using a mixer. This process of frequency 5) Cable: The cable is to provide power from a power source to some piece of equipment or tool. The basic and sole purpose of a power cable is to transport electrical energy from the source of the electricity to the device. 6) Antenna: The last part of the microwave system is the antennas. On the transmitting end, the antenna emits the microwave signal from the transmission line into free space. At the receiver site, an antenna pointed toward the transmitting station collects the signal energy and feeds it into the transmission line for processing by the receiver. Antennas used in microwave links are highly directional, which means they tightly focus the transmitted energy, and receive energy mainly from one specific direction. By concentrating the received signal, this characteristic of microwave antennas allows communication over long distances using small amounts of power. 7) Microwave tower: A microwave tower is a structure built to enhance wireless communication. For them to work, they have to cover large areas using an interconnecting pattern and they can be located anywhere. Most of them are located close to where people habit and to power supply areas. F. Signal spreading in W-CDMA transmitter and receiver The process start with IF input 350 MHz then convert to 9 GHz or 15 GHz or 18 GHz. The data is then "spread‖ using a code which is running at either 9 GHz or 15 GHz or 18 GHz code rate. The resulting spread bits are called chips and the resulting transmitted spread rate is expressed as either 9 GHz or 15 GHz or 18 GHz. The distance is fixed to 10km. The receiver of base station will see this spread signal together with noise, interference, and messages on other code channels in the same RF frequency slot. The interference can come from other signal. The base station‘s demodulator then reapplies the code and recovers the original data signal. The signal spreading as shown in Fig. 7. Fig. 7 Signal spreading in W-CDMA transmitter and receiver
  5. 5. G. Signal spreading in W-CDMA transmitter and receiver The typical technical characteristics of microwave point to point transmission links as follows:  Range: microwave point to point links use 10 km. Microwave radio communication requires clear line-ofsight (LOS) between the respective endpoints. Increase in range typically requires higher antenna heights to account for the ―earth bulge‖.  Data Rate: Microwave PTP systems can support up to Gigabit speeds.  Frequency Bands: Microwave PTP links operate in Licensed and Unlicensed frequency bands  Licensed frequency bands require expensive license. However there are multiple benefits associated with using licensed frequencies including  High system availability  Secure as compared to unlicensed band  Optimum system performance due to lack of interference  Lower long term operational cost  Considerations with licensed band H. Applications Microwave PTP can be used for a very wide range of applications. Currently mostly PTP Microwave systems are used for cellular backhaul application, for example Mobile backhaul links between 2G/3G base stations. Cellular companies utilize PTP microwave links for their equipment connectivity. Enterprise networks utilize microwave PTP system for Internet/Intranet access, corporate voice, File transfers, Videoconferencing. PTP systems are commonly used for last mile access to the PSTN and other voice and data networks. PTP microwave system are widely used for increasing rural telephony and network extensions. IV. LINK ANALYSIS AND BUDGET A. Free space loss path calculation The Free Space Path Loss (FSPL) measures the power loss in free space without any obstacles. So for end-users, it is important to know the approximate frequency between the transmitter and receiver while maintaining a certain link quality at different data transfer rates. FSPL depends on two parameters:  Frequency of radio signals  Wireless transmission distance In our task, we choose to fix the parameter distance and varied the frequency. The following formula can reflect the relationship between them as follows: ( ) ( ) () d = distance (10 km) f = frequency (9 GHz, 15 GHz, 18 GHz) (1) K= constant that depends on the units used for d and f If d is measured in kilometres, f in MHz, the formula is: ( ) ( ) () (2) 1) FSPL (dB) of 9 GHz ( ( ) ) ( ) ( ) 2) FSPL (dB) of 15GHz ( ( ) ) ( ) ( ) ( ) 3) FSPL (dB) of 18 GHz ( ( ) ) ( ) B. Link Budget Calculation A wireless link budget for a point-to-point radio link accounts for all the gains and losses from the transmitter, through cables, antennas and free space to the receiver. The link budget values are shown in Table 2. Estimating the value of the "power" in the different parts of the radio link is necessary to be able to make the best design and the most adequate choice of equipment. The equation of link budget as follow: Link Budget = Tx power (dBm) + Tx Antenna Gain (dBi) + Rx Antenna Gain (dBi) – Tx Cable losses (dB) – Rx Cable Losses (dB) –FSPL (3) TABLE 2 VALUE OF LINK BUDGET Frequency Tx Power (dBm) Tx/Rx Tx/ Rx FSPL Antenna Cable (dB) Gain Losses (dBi) (dB) 9 GHz 18 34.0 22.1 131.52 15 GHz 18 32.1 23.1 135.96 18 GHz 18 38.6 27.3 137.55 *For Tx Power is assumed to be equal to 18dBm for all the frequency. For others, the value is taken from the data sheet. 1) Link Budget (dB) of 9 GHz
  6. 6. ( ) ( ) 4 Low Noise Amplifier 22 2.5 1 RM141.60 2 RM2,298.00 2) Link Budget (dB) of 15 GHz AMMP-6220 6-20 GHz 5 ( ) ( Antenna 3) Link Budget (dB) of 18 GHz HPD2-10 High-Performance Dual Polarized 9-10 GHz 6 ( 34 ) ) ( Cable ) 7 *For Rx sensitivity (minimum received signal) to be assumed = 110 dB 4m RM218.04 984ft RM91,069.20 RG405 U Cable Coax 0.5-20 GHz Cable 1.17 EW85, HELIAX® Standard Elliptical Waveguide 8.5–9.8 GHz 8 Microwave Microwave tower Communication tower 295m Total The performance of any communication link depends on the quality of the equipment being use. The receive power or 2 RM6,379.00 the link budget is determined by transmit power, transmitting antenna gain, receiving antenna gain and some losses. With that value, we have to minus with Free Space Path Loss of the RM101,764.28 link path and make a comparison with the receiver sensitivity. The difference between the minimum received signal level and the actual received power is called the link margin. The B. Cost Budget for Transmitter and Receiver using 15 GHz link margin must be positive, and should be maximized. No Component Name and Picture Gain NF Quantity Total Price 1 Based on the calculation on the Free Space Path Loss and Link Budget Calculation the frequency of 9 GHz is the most appropriate frequency compare to 15 GHz and 18 GHz because of the lowest value of losses (131.52 dB) and it receive the highest power (based on link budget). Moreover, the link margin for 9 GHz is 20.28 dB which the link margin should be maximized for reliable link. Mixer with Local Oscillator A. Cost Budget for Transmitter and Receiver using 9 GHz 2 3 Total Price RM143.49 4 1 3.1 3.1 Bandpass Filter 2 RF Amplifier 6 P35-4150-000-200 2-18 GHz 7.5 RM1,654.90 1 7.5 1 RM274.95 22 Low Noise Amplifier RM1,240.00 2.5 1 RM141.60 2 RM2,862.00 AMMP-6220 6-20 GHz 5 RF Amplifier 2 6 Antenna 32.1 K&L S/N 1 9SB107000/T4000-O/O 5-9 GHz 3 RM143.49 P35-4150-000-200 2-18 GHz HMC144 GaAs MMic Triple-Balanced 5-20 GHz 1 2 AFL05158 12-18 GHz No Component Name and Picture Gain NF Quantity 1 Mixer with 10 10 2 Local Oscillator Bandpass Filter 10 HMC144 GaAs MMic Triple-Balanced 5-20 GHz V. COST BUDGET 2 10 RM274.95 HSX6-144-B4A/A HSX High Performance, Super High XPD Parabolic Shielded Antenna, dual
  7. 7. polarized 14.4 – 15.35 GHz 6 Cable 4m RM218.04 984ft RM135,467.28 RG405 U Cable Coax 0.5-20 GHz 7 Cable 1.15 EW132-144, HELIAX® Standard Elliptical Waveguide 14.4–15.35 GHZ 8 Microwave Microwave tower Communication tower 295m Total 2 RM6,379.00 RM147,141.26 C. Cost Budget for Transmitter and Receiver using 18 GHz No Component Name and Picture Gain NF Quantity 1 Mixer with 10 10 2 Local Oscillator Total Price RM143.49 HMC144 GaAs MMic Triple-Balanced 5-20 GHz 2 Bandpass Filter 1 1 2 RM1,877.68 6 7.5 1 RM274.95 22 2.5 1 RM141.60 2 RM3,426.00 K-Band Filter 18-20 GHz 3 RF Amplifier P35-4150-000-200 2-18 GHz 4 Low Noise Amplifier AMMP-6220 6-20 GHz 5 Antenna 38.6 Based on the cost budget of 9 GHz is the most appropriate compare to 18 GHz and 15 GHz because of the lowest cost budget (RM101,764.28). VI. CONCLUSION Microwave link design is a specific sort of engineering in the broader field of communications. Most installers know that clear line of sight is required between two antennas, but there is a lot more to it than that. To have some certainty as to whether your wireless link will be reliable, an RF path analysis needs to be performed. Our main objective was to understand and design terrestrial microwave link system and also to analyse the performances of design system whether, Link budge, Free Space Loss and line of sight. Furthermore our designing link system to be operating these frequencies 9, 15 and 18GHz after analysis we were able to meet the needed appropriate operating frequency, lastly therefore we were able to make a terrestrial microwave link system. To get the good performance should use the 9 GHz because based on the calculation on the Free Space Path Loss and Link Budget Calculation the frequency of 9 GHz is lowest value of losses (131.52 dB) and lowest Cost Budget that is RM101,764.28. ACKNOWLEDGMENT We would like to express our deepest gratitude and appreciation to our laboratory instructor‘s Prof .Madya Dr .Mohamad Ngasri Bin Dimon and Dr. Kamaludin bin Mohd Yusof for their excellent guidance, caring, patience, suggestions and encouragement who helped usto coordinate our project especially to design the link. We would also like to acknowledge with much appreciation to all those who gave us the possibility to complete this project. A special thanks goes to the crucial role of the staff of the Radar communication Laboratory. Last but not least, again we would like to say many thanks go to our laboratory instructors, Prof .Madya Dr .Mohamad Ngasri Bin Dimon and Dr. Kamaludin bin Mohd Yusof, who are given as full effort guiding in our team to make the goal as well as the panels especially in our project presentation that has improved our presentation skills by their comment and tips. REFERENCES [1] HPLPD1-18 High-Performance Dual Polarized 17.7-19.7 GHz 6 [2] [3] Cable 4m RM218.04 984ft RM135,467.28 RG405 U Cable Coax 0.5-20 GHz 7 Cable EWP180-180, HELIAX® Premium Elliptical Waveguide 8 Microwave Microwave tower Communication tower 295m Total 1.09 [4] [5] [6] 2 RM90,311.52 RM104,992.28 (2010) Safari Books Online homepage. [Online] Available: http://my.safaribooksonline.com (2012) Diginet Terrestrial Link. [Online] Available: http://www.diginet.be/products/telecom/terrestrial-links/ (2011) Radio Waves, Inc. - The Leader in Microwave Antenna Innovation® [Online] Available: www.radiowavessinc.com (2013) Eogogics Inc Microwave Line-of-Sight Systems [Online] Available: http://www.eogogics.com/talkgogics/infocenter/microwaveline-of-sight-systems (2012) FM Video System Link Analysis [Online] Available: http://www.cobham.com/static/GMS%20Calc%20Files/calc_fm.asp (2011) IEEE Global History Network -Microwave Link Networks [Online] Available: http://www.ieeeghn.org/wiki/index.php/Microwave_Link_Networks