CHANNEL MODEL for INFOSTATIONS Can this be the
CHANNEL MODEL for INFOSTATIONS Can this be the model for outdoors? Andrej Domazetovic, WINLAB – February, 23
OBJECTIVE Assuming that the channel is Ricean and using the measurements by Feuerstein, Rappaport et. al. in San Francisco (2 -ray model) try to develop the channel model proposal described as the behavior of Ricean K-factor with respect to transmitter-receiver distance.
INITIAL ASSUMPTIONS ¨ Low transmitter antenna heights (3, 4 and 5 m) ¨ Receiver antenna height 1. 7 m ¨ Clear line of sight path - no shadowing ¨ Carrier frequency 5. 1 GHz ¨ Channel bandwidth 100 MHz ¨ Omnidirectional antennas ¨ No mobility (yet)
OUTLINE ¨ Brief overview of standard 2 -ray propagation model ¨ Brief overview of Propagation over the earth ¨ Closer look into propagation issues ¨ Modified model ¨ Link to Ricean K-factor ¨ Real antenna pattern ¨ Conclusions/Questions
Standard 2 -ray propagation model Friis free space equation: Relation between power and electric field: Where: EIRP - effective isotropic radiated power, E - magnitude of radiating portion of electric field in the far field, Rfs - free space intrinsic impedance and Ae - antenna effective aperture Source: [] Rappaport - Wireless Communications
Standard 2 -ray propagation model The electric field at receiver: assuming: large distance from the transmitter, Taylor series approximations, perfect ground reflection. . . Source: [] Rappaport - Wireless Communications
Standard 2 -ray propagation model In measurements performed in San Francisco, it was shown that 2 -ray model is fairly good model for microcellular urban environment It was also shown that the path loss within first Fresnel zone clearance is purely due to spherical spreading of the wave front: decreases as d-2 and not d-4 (10 m being the minimum T-R distance) Source: [] Feuerstein, Rappaport et. al. - Path loss, Delay spread and Outage models as Functions of Antenna Height for Microcellular System Design - TVEH, Aug, 1994
Standard 2 -ray propagation model Source: [] Feuerstein, Rappaport et. al. - Path loss, Delay spread and Outage models as Functions of Antenna Height for Microcellular System Design - TVEH, Aug, 1994
Standard 2 -ray propagation model Fresnel zone clearance Source: [] Feuerstein, Rappaport et. al. - Path loss, Delay spread and Outage models as Functions of Antenna Height for Microcellular System Design - TVEH, Aug, 1994
Propagation over a plane earth Propagation over smooth, conducting, flat earth Bullington: Where: first term - direct wave second term - reflected wave third term - surface wave rest - induction field and ground secondary effects - phase difference between reflected and direct paths Source: [] W. C. Jakes - Microwave Mobile Communications
ASSUMTIONS Friis free space equation: • The formula is a valid predictor for Pr for d which are in the far-field of the transmitting antenna - Fraunhofer region i. e. when inductive and electrostatic fields become negligible and only radiation field remains df=2 D 2/ , df>>D and df>> • For fc = 5. 1 GHz and the antenna size D = 10 cm df=33. 9 cm , df>>10 cm and df>>5. 9 cm • If D (largest linear dimension of antenna) and fc increase, so does df - attention must be paid Source: [] Rappaport - Wireless Communications
ASSUMTIONS First Fresnel zone distance: Antenna height: fd: 3 m 70. 47 m 4 m 118. 29 m 5 m 179. 6 m for fc=5. 1 GHz Mobile height: 1. 7 m Since wavelength=5. 9 cm, the Bullington equation also holds (surface wave can be neglected) Source: [] Feuerstein, Rappaport et. al. - Path loss, Delay spread and Outage models as Functions of Antenna Height for Microcellular System Design - TVEH, Aug, 1994 [] W. C. Jakes - Microwave Mobile Communications
Ricean K-factor Source: [] Rappaport - Wireless Communications [] Steele - Mobile Radio Communications
Propagation Mechanisms Source: [] Rappaport - Wireless Communications
Propagation Mechanisms Reflection coefficient (Fresnel) depends on material properties, frequency, incident angle… It is often related to relative permittivity value: (for lossy dielectric) - some energy absorbed Type of surface (S/m) Poor ground Average ground Good ground Sea water Fresh water Brick Limestone Glass at 10 GHz 0. 001 0. 005 0. 02 5 0. 01 0. 028 0. 005 4 15 25 81 81 4. 44 7. 51 4 If material is good conductor (f< / r 0) - not sensitive to f For lossy dielectrics: - 0, r - const. with f but may be sensitive Source: [] Rappaport - Wireless Communications [] W. C. Jakes - Microwave Mobile Communications
Propagation Mechanisms From Maxwell’s equations and Snell’s Law: When the first medium is free space and Source: [] Rappaport - Wireless Communications
Reflection coefficient
Ricean K-factor
Ricean K-factor
Reflection coefficient
Reflection coefficient
Ricean K-factor
Ricean K-factor
Ricean K-factor
Ricean K-factor
Real antenna issues
Ricean K-factor - antenna
Ricean K-factor - antenna
Close scatters – practical issue Assuming 100 MHz bandwidth 200 Msamples/second 1. 5 m path distance in order to detect another path wave
Some hints that look promising Source: [] Bolcskei et. al, “Fixed Broadband Wireless Access: State of the Art, Challenges, and Future Directions“, IEEE Communication magazine, Jan 2001.
Conclusions/Questions 1. 2. What do you think IMW or JFAI? What to pursuit? - If this idea holds, how to prove it? - If not, should COSTs/ITUs/etc. be investigated better and picked one of those models? If the channel is really that good why OFDM? - Simplicity for Downlink (no PAPR headache, implementable on Winlab hardware) - DS-CDMA (no near-far, fully orthogonal code set, multiple access…)
- Slides: 31