1 WP 2.2 Propagation and Diversity: Topology and Mobility Effects on Links Candida Spillard Budapest, November 2004

2 Topology and Mobility Effects Basic link margins Link outage durations Rain Clouds Tunnels Short-term variations Scintillation A channel model, for modulation and coding simulations Polarisation Multipath From terrain From buildings and other structures Doppler Effects

3 Basic Link Margins From ITU-R P Frequency 28 GHz, elevation angle 30 o, Location Torino

4 Event Servicing: Variability of Margins To deliver 99.99% availability, the link must tolerate: in an average year, rain rate up to 24mm/hr in , rain rate up to 40 mm/hr (plot taken from S. Ventouras, C. L. Wrench, and S. A. Callaghan, "New thinking required to offset limitations imposed by V-band propagation," AIAA International Communications Satellite Systems Conference, 2001)

5 Link outage durations and characteristics Rain: ITU-R P.1623 Power-law for short outages, log-normal for long outages No dependence on climatic zones: this is under review Cloud edges (excessive scintillation) May disrupt higher-order modulation signals Tunnels, cuttings, other structures Tunnel lengths in the UK have a log-normal distribution Cuttings obstruct LOS at up to 60 o elevation angle Signal gantries: knife-edge diffraction Power supply cable supports: knife-edge diffraction with predictable periodic occurrence Trees Rayleigh-like distributions of signal fading

6 Scintillation Phase Variations are Gaussian in I and Q Amplitude

7 Amplitude variations Standard deviations of signal amplitude variation as a function of meteorological parameters (ITU-R P.618-7) citymonthtime temperatureHumidity% N wet  (dB) RomeAugust13: RomeDecember13: RomeAugust07: RomeDecember07: GibraltarAugust14: NicosiaAugust14:

8 Phase variations Standard deviation of phase as a function of three atmospheric parameters C n 2 (m –2/3 ) L (m) (m/sec)  ( o ) air over sea  heavy rain warm front  edge of Cu cloud BER = 2 erfc (  /2  )  Phase difference between 2 points in constellation (eg 8 o for 256QAM)  Standard deviation of scintillating phase variations

9 Model for short-term variations Based on time-series generator Developed by Fiebig

10 Time-series generator developed by Fiebig Time-series generator output r(t) Each time segment is: Almost constant (C), Monotonically decreasing (D) or Monotonically increasing (U) Attenuation at a certain instant depends only on the attenuation  t seconds before and on the type of signal segment (C, D or U). Measured PDFs of the likelihood P(y/x) for the segments C, D and U has a Gaussian-like shape

11 Typical output

12 Multipath For specular-type reflection, roughness height must not exceed h c, where: h c = /(8 sin  ) Terrain is generally rougher than  = 0.2 cm! Narrow antenna beams preclude multipath from buildings

13 Depolarisation Depolarisation exceeded for a given percentage of the time, 28 GHz, 30 o elevation angle, Torino. ITU-R P.618_7, section 4.1

14 Doppler Effects Frequency shift effect: Symbol timing effect: N c ratio between the symbol and the carrier periods f d (t) Doppler frequency shift f c carrier frequency

15 Effect on QPSK Without DopplerWith Doppler (Oscilloscope traces of superpositions of all possible demodulated wave forms) Eye patterns of QPSK signals (Trapezoidal pulse)

16 Effect on GMSK Without Doppler With sinusoidally-varying Doppler, f d (max) = 0.2f c, f r = f c, Bit Rate = 3000 Eye patterns of GPSK signals (BT = 0.5)

17 Effect on GMSK Without Doppler Eye patterns of GPSK signals (BT = 0.25) With sinusoidally-varying Doppler, f d (max) = 0.2f c, f r = f c, Bit Rate = 3000

18 Document Properties