PDH: Plesynchronous Digital Hierarchy SDH: Synchronous Digital Hierarchy
The non homogeneity of the atmosphere influences the waves propagation 1°) Path curvature ： 2°) Reflecting, diverging, focusing intermittent events ：
Sunshine worse than sunless: The received signal on cloudy and rainy days, foggy days, and windy days is more stable than the received signal on sunny days and quiet days. Fast fading always occurs when it clear up after rain stops or fog disperses
Mw presentation 1
MW Basic Knowledge• Microwave Microwave is kind of electromagnetic wave. In a broad sense, the microwave frequency range is from 300MHz to 300GHz. But in microwave communication, the frequency range is generally from 3GHz to 30GHz. According to the characteristics of microwave propagation, microwave can be considered as plane wave. The plane wave has no electric field and magnetic field longitudinal components along the propagation direction. The electric field and magnetic field components are vertical to the propagation direction. Therefore, it is called transverse electromagnetic wave and TEM wave for short
MW Basic Knowledge Microwave Radio Link Hop Hop Hop NO.1 NO.2 No.n Or TX/Rx TX/Rx TX/Rx TX/Rx Terminal Relay station Relay station Terminal Station (Active) (Passive) StationCable Radio Link Cable Distance between the transmitter and the receiver, a few km < D < 100km Availability and quality depends on the distance recommended by ITU-R.
MW Basic Knowledge Radio Wave Propagation （ 1 ）The radio link propagation follows the line of sight: it requires a perfect clearing betweentransmitting and receiving antennas. The propagation medium is made of the lower layersof the atmosphere (a few meters to a few hundred of meters above ground) The non homogeneity of the atmosphere influences the waves propagation: 1. Path curvature 2. Reflecting, diverging, focusing intermittent events Free space loss (Lfs)=92.4+20×log(f×d) (dB) f:GHz, d:km
MW Basic KnowledgeRadio Wave Propagation （ 2 ） Atmosphere influence Refraction Partial reflection Absorption Diffusion Diffusion Gaz and water vapor volume n2 n2 i.2 Freq. < 15GHz : insignificant 20 GHz : 0.1 dB / km Rain i.1 n1 Freq. > 10GHz n1 500kmn1×sin i.1 = n2×sin i.2 Almost horizontal
MW Basic KnowledgeRadio Wave Propagation（ 3 influenceGround ） Diffraction ReflectionDiffraction on a ridge Spherical diffraction
MW Basic KnowledgeRadio Wave Propagation（ 4） Air refraction index at sea level: n = 1.000 315 N N = 315 N unitsh Standard atmosphere ∆ N = - 39 N kmh Ro K = R/Ro = 4/3 R Real Earth Imaginary Earth ∆ N : Gradient of air refraction index ∆ N may reach more extreme values than + 250 or - 350, during short percentage of time An imaginary earth with the radius of 8500km, allows to simplify analysis on Refraction propagation of radio wave.
MW Basic Knowledge• Microwave Transmission Characteristic• —Loss Characteristic The Rules of Loss changing: A: Higher Frequency; Longer Distance; Worse Loss. B: Day better than Night; Winter better than Summer; C: Cloudy, Windy more stable than Sunny day D: Over water is worse than Over land; E: Over Hill/Mountain is better than Over Plain;The reason is the reflection index of electric wave is changing with different time, location and height
MW Basic Knowledge• Microwave Transmission Characteristic When there is loss in the link, not only with worse SNR (Signal Noise Ratio), but also the deep loss will break off the link; To get a better performance and reliability in MW transmission, we need to consider some methods to avoid the loss, such as Diversity. Diversity has the following types: Space diversity, Frequency diversity, Polarization diversity, Angle diversity and Multiply diversity.
MW Basic Knowledge• Microwave Transmission Characteristic —Overcome Loss 1. Space Diversity Signals have different multi-path effect over different paths and thus have different fading characteristics. Accordingly, two or more suites of antennas at different altitude levels to receive the signals at the same frequency which are composed or selected. This work mode is called space diversity. If there are n pairs of antennas, it is called n-fold diversity. Advantages: The frequency resources are saved; Disadvantages: The equipments is complicated, as two or more suites of antennas are required; Antenna distance: As per experience, the distance between the diversity antennas is 100 to 200 times the wavelength in the frequency used frequency bands, and normally we choose 5/10 meters, also we can calculation by;
MW Basic Knowledge• Microwave Transmission Characteristic —Overcome Loss 1. Space Diversity d= (100~200)λ= (100~200)ν/F Where v=3*108
MW Basic Knowledge• Microwave Transmission Characteristic —Overcome Loss 2. Frequency Diversity Signals at different frequencies have different fading characteristics. Accordingly two and more microwave frequencies with certain frequency spacing to transmit and receive the same information which is then selected or composed, to reduce the influence of fading. This work mode called frequency diversity Advantages: The effort is obvious. Only one antenna is required; Disadvantages: The utilization ratio of frequency bands is low;
MW Basic Knowledge• Microwave Transmission Characteristic —Overcome Loss 3. Polarization Diversity When using polarization diversity, utilizing the same aerial on different polarizations and scrambling polynomials have to be different for both signals send the same signal. 4. Angle Diversity The efficiency of angle diversity is based on the antennas uncorrelated radiation pattern (resultant signals are different).One antenna and two feedersTwo antennas (are located close to each other, space diversity effect is achieved if antennas are far a way from each other) and the other antenna has been tilted
MW Basic Knowledge• Microwave Transmission Characteristic Advantage: 1. Can be rapidly installed; 2. Can use the existing network infrastructure repeatedly (digital radio uses the infrastructure of the analogue radio) 3. Can cross complicated terrains (rivers, lakes and mountains) 4. Can use point-to-point radio transmission structure in the remote mountains 5. Can rapidly restore the communication after the natural disasters 6. Can protect hybrid multiple transmission mediaThose advantages not only apply to the fixed nodes or temporary nodes and feeder routes in the urban areas, but also apply to very long long- distance routes.
MW Basic Knowledge• Microwave Transmission Characteristic Disadvantage: 1. Line of sight transmission conditions should be ensured; 2. Transmission distance between two stations should be not too long; 3. Frequencies need to be applied for; 4. Communication quality is greatly affected by the environment; 5. Communication capacity is limited.
Application/SolutionPoint to Point Digital Microwave transmission system Coaxial cable Microwave link MUX MUX Satellite Fiber optic cable
Mobile Network Application SDH SDH ..... PDH BTS MSC PDH PDH BTS BTS PDH BTS BTS BTS PDH BTS BTS BTS BTS BTS PSTN MSC BSC SDH SDH BTS BSC BTS SDHPSTN: Public Switched BSC BTS SDH Telephone NetworkMSC: Mobile Switching Center BTS BTS BSCBSC: Base Station Controller PDH BTSBTS: Base Transceiver Station PDH BTS BTS PDH BTS PDH SDH SDH Microwave BTS BTS BTSPDH PDH Microwave
Cellular Network Application （1）UMTS: Universal MobileTelecommunication System
Difficult Areas for Microwave Links• In areas with lots of rain, use the lowest frequency band allowed for the project.• Microwave hops over or in the vicinity of the large water surfaces and flat land areas can cause severe multipath fading. Reflections may be avoided by selecting sites that are shielded from the reflected rays.• Hot and humid coastal areas 21