UK SG3
CP85rev1
INTERNATIONAL TELECOMMUNICATION UNION
RADIOCOMMUNICATION
STUDY GROUPS
Document 3K/UK15-E
22 March 2002
English only
United Kingdom
PROPOSED REVISION TO RECOMMENDATION ITU-R P. 1411-1
DEPENDENCE OF RMS DELAY SPREAD ON SHADOWING
1. Introduction
Bit error rates are related to the second central moment (rms delay spread) of the power
delay profile. Hence, the rms delay spread tends to be one of the main parameters
determined from wideband measurements. Also, several researchers have attempted to
determine suitable fits to rms delay spread as a function of distance or as a function of
path loss. In the measurements carried out in Manchester for the characterisation of the
two frequency bands of UMTS, the rms delay spread was observed to be more correlated
with shadowing i.e. path loss than with range. Also, the frequency dependence of rms
delay spread was found to be dependent on shadowing.
2. Measurement results
Wideband measurements over the two UMTS frequency division duplex bands were
carried out with a dual frequency chirp sounder designed and implemented in the UK [1].
The measurements were carried out either with a trolley over ten different routes within
1.6 km from the transmitter and each route covered a range of a few hundred meters or
with a van within a 5 km radius. The transmit antenna was located on top of a 46-m
building and the receive antenna was either at 1.7 m for the trolley measurements or 2.5
m for the van measurements. Both antennas were vertically polarised and omnidirectional and the effective radiated power was 34 dBm. The overall number of
locations surveyed was 581.
Measurements over the two 60 MHz bands were analysed first on small-scale i.e. a
distance of a few wavelengths. Figure 1 shows three power delay profiles obtained at
three different locations for both the uplink and the downlink [2]. The figure shows
while the multipath structure at the two frequency bands is similar, the different
components exhibited different strengths and certain components, which were present in
one frequency band were not present in the other. The data were also processed for third
generation systems by dividing each frequency band into 5-MHz sections. Figure 2
shows examples of power delay profile variations as a function of frequency at two
locations, one with line-of-sight and another in a non line of sight location. The figure
shows that for the LOS situation of figure 2a the variations across each frequency band
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and between the two bands were considerably lower than those for the NLOS location of
figure 2b where the variations were fairly pronounced [3].
Also, the extent of multipath was generally found to increase in shadowed locations as
seen from figure 3, which displays the peak power level versus location (a-b), and rms
delay spread versus location (c-d) for two different routes (a and c for a route with mainly
LOS components and b and d for a route with mixed LOS and NLOS locations) [4]. The
figure shows the relationship between the received power and the rms delay spread where
low power levels are associated with larger delay spreads. Also, for locations 40-62 of
figure 3.d, where the rms delay spread is seen to increase, the values at the two frequency
bands are different.
The variations as a function of frequency for route 2 (mixed LOS and NLOS) across the
two bands are shown in figure 4 for the twelve frequency sections (60 MHz divided by 5
MHz) [3]. The figure demonstrates that for 70% of the locations, the frequency
differences are small whereas for the rest of the locations the differences across each
band and between the two bands can be significant.
To verify the relationship between rms delay spread and range or received power, scatter
plots of rms delay spread versus range (figure 5) and versus path loss (figure 6) were
obtained for all the trolley data. Figure 5 shows that for nearby shadowed locations, the
rms delay spread was greater than for LOS locations farther away from the transmitter
[4]. To verify the range dependence of the rms delay spread, the relationship of
Greenstein et. al [5] which relates the median of the rms delay spread of an area to
distance as a power law was used. For dense urban areas the relationship is of the form,
0.5
where T1 is the median delay spread at 1 km. This relationship
 med (area )  0.76T1d max
was found not to fit the measurements in Manchester city centre although Greenstein et.al
claim that they have applied it to numerous measurements which they scaled from
published results. The correlation coefficient between rms delay spread and range was
found to be only 0.38.
Relationships between the rms delay spread and path loss have also been studied and a
correlation coefficient of 0.62 was found to be suitable for the Manchester measurements.
Various fits were also applied to the data and these are given here as an upper bound fit
(equation 1) and a logarithmic fit (equation 2) [4].
 rms  exp 0.038PL (dB)  3.567 ns
log(  rms )  1.583  0.017 P(dBm )
(1)
(2)
In equation 1 the rms delay spread is related to the path loss referenced to 1 m and in
equation 2 it is related to the received power. Equation 1 is similar to that proposed by
Feurstein et. al [5] with the addition of the constant and equation 2 has the same form as
that proposed by Devasivartham [6].
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Also, the different cumulative distribution functions were fitted to the rms delay spread
and the Kolomogrov-Simirnov goodness of fit was used to identify the best fit. It was
found that the best fit was a log-normal distribution which was also observed by
Greenstein et. al. [7].
References
1. S. Salous and H. Gokalp, “Dual frequency sounder for UMTS frequency division
duplex channels,” in press IEE Proceedings-Communications.
2. S. Salous, W-CDMA measurements for 3G Systems, 4es Journees d’etudes
propagation electromagnetique dans l’atmosphere du decametrique a l’angstrom,
Rennes, March 2002, pp 1-8.
3. S. Salous and H. Gokalp, Characterisation of W-CDMA channels in FDD UMTS bands,
IEEE Conference on Vehicular Technology, VTC2001, New York, October 200, pp 11011105.
4. S. Salous and H. Gokalp, Medium and large-scale characterisation of UMTS allocated
frequency division duplex channels, submitted to the IEEE Transaction on Vehicular
Technology.
5. D. M. J. Devasivartham, “Radio propagation studies in a small city for universal
portable communications,” in Proc. 38th IEEE Veh. Technol. Conf., 1998, pp
100104.
6. M. Feuerstein, et al., “Path loss, delay spread and outage models as functions of
antenna height for microcellular system design”, IEEE Trans. Veh. Technol., vol. 43,
no. 3, pp 487497, Aug. 1994.
7. L. J. Greenstein, et al., “A new path-gain/delay-spread propagation model for digital
cellular channels,” IEEE Trans. Veh. Technol., vol. 46, no. 2, pp 477485, May 1997.
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Figure 1. Power delay profiles at three different locations for both the uplink (left) and
downlink (right).
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(a)
(b)
Figure 2. PDP as a function of frequency for the uplink (left column) and the downlink
(right column).
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Figure 3. Received power and rms delay spread as a function of location for two routes,
route one (a and c) and route 2 b and d. Solid line: uplink and dashed line is downlink.
Figure 4. Range of values of CDF’s for the twelve frequency sections for uplink (left)
and downlink (right) bands for a single route.
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Figure 5. Scatter plot of rms delay spread as a function of range.
Figure 6. Scatter plot of rms delay spread as a function of path loss
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ANNEX
Proposed Revision to Recommendation ITU-R P.1411-1
Section 6, Multipath models
Add at the end of the section
“Characteristics of multipath delay spread in an urban high-rise environment for small
macro-cells (as defined in Table 3), have been found to be strongly related to shadowing.
In general shadowing increases the delay spread of multipath and hence results in larger
rms delay spread values. It also results in significant variations of the multipath delay
spread as a function of frequency. For mixed LOS and NLOS routes, the effect of
shadowing on the rms delay spread appears to be more significant than range The
measurements showed that the correlation coefficient between rms delay spread and
range was only 0.38; whereas it was 0.62 between path loss and rms delay spread. Two
possible relationships between rms delay spread and path loss, PL (dB) or received power,
P (dBm) are of the following form:
 rms  exp  A.PL  B 
ns
log(  rms )  C  D.P
(35)
(36)
where A, B, C, and D are constants determined from the best fit to the scatter plot of rms
delay spread versus path loss, or received power. For the frequency range between 1.92.1 GHz, the values for the constants were evaluated to be
A = 0.038, B = 3.57 when PL was referenced to path loss at 1 m.
C = 1.583, D = 0.0167.
From the same measurements, the distribution of rms delay spread for a point to area was
found to fit a log-normal distribution.”