RADIO SYSTEMS – ETI 051 Contents 4 • Why do we need channel models? Lecture no: • Narrowband models – Review of properties – Okumura’s measurements – Okumura-Hata model – COST 231-Walfish-Ikegami model Channel models • Wideband models – Review of properties – COST 207 model for GSM and antennas – ITU-R model for 3G • Antennas – Efficiency and bandwidth – Mobile station antennas – Base station antennas – Dipole and parabolic antennas Ove Edfors, Department of Electrical and Information Technology Ove.Edfors@eit.lth.se 2008-11-06 Ove Edfors - ETI 051 1 2010-03-25 Ove Edfors - ETI 051 2 Why do we need channel models? During system design, testing and type approval: Simple models reflecting the important properties of important channels (best, average, worst case) Models used to make sure that the system design WHY DO WE NEED behaves well in typical situations. CHANNEL MODELS? During network design: More detailed models appropriate for certain geographical areas Models used to obtain an efficient network in terms of base station locations and other parameters 2010-03-25 Ove Edfors - ETI 051 3 2010-03-25 Ove Edfors - ETI 051 4
Narrowband models Review of properties Narrowband models contain ”only one” attenuation, which is modeled as a propagation loss, plus large- and small-scale fading. Path loss: Often proportional to 1/ d n , where n is the propagation exponent. (n may be different at different distances) Large-scale fading: Log-normal distribution (normal distr. in dB scale) NARROWBAND Small-scale fading: Rayleig, Rice, Nakagami distributions ... ( not in dB-scale) MODELS NOTE: Several of these models are found in an on-line appendix of the textbook which can be downloaded from the course web site (click on “ App. 7 ” in the schedule). Printed copies of textbook appendices are allowed during Part B of the written exam. 2010-03-25 Ove Edfors - ETI 051 5 2010-03-25 Ove Edfors - ETI 051 6 Okumura’s measurements Okumura’s measurements Background How to calculate the prop. loss 1. We start by calculating the free-space attenuation Extensive measurement campaign in Japan in the 1960’s. 2. Apply a frequency and distance dependent correction 3. Apply a BS-height and distance dependent correction Parameters varied during measurements: 4. Apply a MS-height, frequency and environment dependent correction Free space Frequency 100 – 3000 MHz L attenuation Oku Distance 1 – 100 km Mobile station height 1 – 10 m Base station height 20 – 1000 m Environment medium-size city, large city, etc. Propagation loss is given as a median value (50% of the time and 50% of the area). Results from these measurements are displayed in figures 7.12 – 7.14. Fig. 7.12 Fig. 7.13 Fig. 7.14 2010-03-25 Ove Edfors - ETI 051 7 2010-03-25 Ove Edfors - ETI 051 8
Okumura’s measurements Okumura’s measurements Example 1. Calculate free-space loss Attenuation between two Propagation at 900 MHz in medium-size city isotropic antennas in free with 40 m base station antenna height and space is (free-space loss): 1.5 m mobile station antenna height. L free ∣ dB d = 20log 4 d Use Okumura’s curves to calculate the propagation loss at a distance of 30 km between base station and mobile station. The obtained value does not depend on antenna heights. 900 MHz and 30 km distance => 121 dB 2010-03-25 Ove Edfors - ETI 051 9 2010-03-25 Ove Edfors - ETI 051 10 Okumura’s measurements Okumura’s measurements 2. Apply correction for excess loss 3. Apply correction of BS height FIGURE 7.13 FIGURE 7.12 Distance [km] ] B ] d m [ ] k r B [ o d e t [ c c a s n s f These curves a o n Note : Lower base t are only for l s o station means s i i D h b =200 m and t s INCREASING c e h m =3 m e attenuation => c r x subtract this number. r E o C 40 m BS and 900 MHz and 30 km distance 30 km distance BS height [m] => - 16 dB Frequency [MHz] => 36.5 dB 2010-03-25 Ove Edfors - ETI 051 11 2010-03-25 Ove Edfors - ETI 051 12
Okumura’s measurements Okumura’s measurements 4. Apply correction of MS height Summary of example FIGURE 7.14 Frequency [MHz] ] B Propagation loss (between isotropic antennas) using d [ Okumura’s measurements: r o t c a = + − − − − = L 121 36.5 ( 16) ( 3) 176.5 dB f Note : Lower mobile Oku dB | n station means o INCREASING i t c attenuation => e Calc. step: 1 2 3 4 subtract this number. r r o C 1.5 m MS and 900 MHz in medium-size city MS height [m] => -3 dB 2010-03-25 Ove Edfors - ETI 051 13 2010-03-25 Ove Edfors - ETI 051 14 The Okumura-Hata model The Okumura-Hata model Background How to calculate prop. loss ( ) = + + h b and h m L A B log d C In 1980 Hata published a parameterized model, based on Okumura’s O H − | km in meter measurements. ( ) ( ) ( ) = + − − A 69.55 26.16log f 13.82log h a h 0| MHz b m ( ) = − B 44.9 6.55log h The parameterized model has a smaller range of validity than b the measurements by Okumura: ( ) = a h C = m 8.29 log 1.54 h m 2 − 1.1 Metropolitan for f 0 200MHz Frequency 150 – 1500 MHz 0 areas 3.2 log 11.75 h m 2 − 4.97 for f 0 400MHz Distance 1 – 20 km Mobile station height 1 – 10 m Small/medium- Base station height 30 – 200 m 0 size cities ( ) ( ) − − 1.1log f 0.7 h Suburban 0| MHz m − 2 log f 0 ∣ MHz / 28 2 − 5.4 ( ) ( ) environments − 1.56log f 0.8 0| MHz − 4.78 log f 0 ∣ MHz 2 18.33log f 0 ∣ MHz − 40.94 Rural areas 2010-03-25 Ove Edfors - ETI 051 15 2010-03-25 Ove Edfors - ETI 051 16
COST 231-Walfish-Ikegami model COST 231-Walfish-Ikegami model Background How to calculate prop. loss The Okumura-Hata model is not suitable for micro cells or small = + + L L L L macro cells, due to its restrictions on distance ( d > 1 km). 0 msd rts The COST 231-Walfish-Ikegami model covers much smaller Free Building Roof-top distances and is better suited for calculations on small cells. space multiscreen to street Frequency 800 – 2000 MHz Distance 0.02 – 5 km BS Mobile station height 1 – 3 m MS Base station height 4 – 50 m d Details about calculations can be found in Appendix 7.B. 2010-03-25 Ove Edfors - ETI 051 17 2010-03-25 Ove Edfors - ETI 051 18 Wideband models Review of properties Let’s assume the tapped delay-line model N h t , = ∑ i t exp j i t − i i = 1 WIDEBAND The power-delay profile tells us how much energy the channel has MODELS at a certain delay τ (essentially the rms values of the α i ( t )’s). The Doppler spectrum tells us how fast the channel changes in time (essentially how fast the α i ( t )’s and θ i ( t )’s change). There can be one Doppler spectrum for each delay. 2010-03-25 Ove Edfors - ETI 051 19 2010-03-25 Ove Edfors - ETI 051 20
Wideband models Wideband models COST 207 model for GSM COST 207 model for GSM Four specified power-delay profiles The COST 207 model specifies: P dB [ ] P dB [ ] 0 0 TYPICAL URBAN RURAL AREA FOUR power-delay profiles for different − − 10 10 environments. − − 20 20 − − 30 30 τ µ τ µ [ s ] [ s ] FOUR Doppler spectra used for different 0 1 2 3 4 5 6 7 0 1 delays. P dB [ ] P dB [ ] IT DOES NOT SPECIFY PROAGATION LOSSES FOR THE 0 0 HILLY TERRAIN BAD URBAN DIFFERENT ENVIRONMENTS! − − 10 10 − − 20 20 − − 30 30 τ µ τ µ [ s ] [ s ] 0 5 10 0 10 20 2010-03-25 Ove Edfors - ETI 051 21 2010-03-25 Ove Edfors - ETI 051 22 Wideband models Wideband models COST 207 model for GSM COST 207 model for GSM Four specified Doppler spectra Doppler spectra: CLASS GAUS1 GAUS2 ( ) ( ) P ν τ P ν τ , , s i s i P dB [ ] RURAL AREA P dB [ ] TYPICAL URBAN 0 0 CLASS GAUS1 First tap − − 0.5 s i ≤ 2 s 10 10 i ≤ 0.5 s RICE − − 20 20 here − − 30 30 τ µ τ µ [ s ] [ s ] − ν + ν − ν + ν 0 1 2 3 4 5 6 7 0 1 0 0 max max max max ( ) ( ) P ν τ P ν τ , , s i s i BAD URBAN HILLY TERRAIN P dB [ ] P dB [ ] 0 0 GAUS2 RICE − − 10 10 Shortest i 2 s path in − − 20 20 rural areas − − 30 30 τ µ τ µ [ s ] [ s ] − ν + ν − ν + ν 0 5 10 0 10 20 0 0 max max max max 2010-03-25 Ove Edfors - ETI 051 23 2010-03-25 Ove Edfors - ETI 051 24
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