Radio Propagation

S/N ratio should be above a certain threshold (a function of modulation scheme). Signal power should be above the sensitivity threshold. Predict received signal strength when the transmitter and receiver have a clear line-of-sight path between them.
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Radio Propagation Chapter 2: RADIO PROPAGATION Đặng Lê KhoaEmail: dlkhoa@fetel.hcmuns.edu.vn Facuty of Electronics & Telecommunications, HCMUS 1Understanding RF Propagation Goals 1. Estimate radio coverage area 2. Estimate link performance 3. Estimate network design parameters 1. Transmitters and their location 2. Transmit power 3. Antenna type Conditions for correct receptionPt sensitivity threshold Noise C power A B S/N ratio should be above a certain threshold (a function of modulation scheme) Signal power should be above the sensitivity thresholdWhat will happen if noise level increases?What will happen in presence of another transmitter?Interesting Scenarios At which locations will correct reception take place? Antenna Basics Pdirectional G= Pisotropic High gain DipoleIsotropic directional 0 dBi 2.2 dBi 14 dBi Free Space Propagation Model PT Isotropic power 2 PDi = PR W / m density 4πd 2 d PT PT GT Power density along PD = the direction of 4πd 2 maximum radiation Power received by PR = PD Aeff Antenna λ2 PT GT Aeff = PR = Aeff 4π G 4πd 2Predict received signalstrength when the transmitterand receiver have a clear 2 Also known λline-of-sight path between them PR = PT GT GR  as Friis free   4πd  space formula Near Field and Far Field 2 λ PR PR = PT GT GR    4πd  Pt Good predictor when 2D 2 Largest physical df receiver is in far field df = dimension of antenna (the region beyond df) λnear fieldExampleFind the near field distance for an antenna with max dimension of 1mAnd operating frequency of 900 MhzAnswerλ at 900 Mhz = 33 cm 2(1) 2df = = 6m 0.33 Path Loss (relative measure) 2 λ PR PR = GT GR    4πd  PTPt 0.57 *10 −3 f is in MHz PR = GT GR d is in Km (df ) 2 PT  PR    = (GT ) dB + (GR ) dB − (32.5 + 20 log10 d + 20 log10 f ) P   T  dB Path Loss represents signal attenuation (measured on dB) between the effective transmitted power and the receive power (excluding antenna gains) Path Loss (Example) Assume that antennas are isotropic. PR Calculate receive power (in dBm) at free space distance of 100m from the antenna. What is PR at 10Km? Pt  PR  50 W   = (GT ) dB + (GR ) dB − (32.5 + 20 log10 d + 20 log10 f ) P = 47 dBm  T  dB  PR  59   = 0 + 0 − (32.5 + 20 log10 0.1 + 20 log10 900) P   T  dB 20 (for d = 10) -20 (for d = 0.1)  PR   PR    = −111.5dB   = −71.5dB P  P   T  dB  T  dB ( PR ) dBm = 47 − 111.5 = −64.5dBm ...