This document defines and explains key symbols and concepts related to UMTS networks. It discusses: 1) Symbols such as Ec, Eb, Io, No, and their meanings in relation to energy, power, interference, and noise. 2) The concept of pilot pollution which occurs when there are too many strong pilot signals within coverage but none is dominant, negatively impacting network performance. 3) Causes of pilot pollution including unreasonable cell layout, antennas being too high, improper antenna azimuth or tilt, and ambient environmental effects. 4) Ways to reduce pilot pollution such as optimizing the network plan, proper site selection, and adjusting antenna parameters and transmit powers.

1. Basic UMTS Understanding

2. Symbol Explanation
• Ec
– Average energy per Chip
– Not considered individually, but used for Ec/Io
– Pilot Ec is measured by the UE (for HO) or the Pilot
scanner, in the form of Received Signal Code
Power (RSCP)
– For CPICH Ec:
• Depends on power and path loss.
• Constant for a given power and path loss. Ec is not
dependent on load
– For DPCH Ec:
• Depends on power and path loss

3. Symbol Explanation
• Eb
– Average energy per information bit for the PCCPCH,
SCCPCH, and DPCH, at the UE antenna connector.
– Typically not considered individually, but used for Eb/Nt
– Depends on channel power (can be variable), path loss, and
spreading gain (Gp)
– Constant for a given bit rate, channel power, and path loss
– Can be estimated form Ec and processing gain
• Speech 12.2kbps example
• Ec = -80 dBm
• 12.2kbps data rate => Processing gain = 24.98 dB
• Eb~ -80 + 24.98 = -55.02 dBm

4. Symbol Explanation
• Io
– The total received power spectral density, including signal and
interference, as measured at the UE antenna connector.
– Similar to UTRA carrier Receive Strength Signal Indicator
(RSSI), at least for practical consideration (SC scanner)
• RSSI in W or dBm
• Io in W/Hz or dBm/Hz
– Measured by the UE (for HO) or Pilot scanner in the form of
RSSI
– Depends on All channel power, All cells, and path loss
– Depends on same-cell and other cell loading
– Depends on external interferences

5. Symbol Explanation
• No common RF definition
– Thermal noise density
– Typically not considered individually, but used for Eb/No
– Can be calculated
• No = KT
– K is the Bolzman constant, 1.38*10^-23
– T is the temperature, 290 K
• No = 174 dBm/Hz under typical conditions
– Typically the bandwidth noise and the receiver noise figure are
also considered
• No = KTBNF, where NF is noise figure
– To avoid confusion, NF should be used when referring to thermal
noise

6. Symbol Explanation
• No for WCDMA system
– Total one-sided noise power spectral density
due to all noise sources
– Typically not considered individually, but used
for Eb/No
– Defined this way, No and Io are substituted
for one another:
• On the uplink the substitution is valid
• On the downlink, differentiating between Noise and
Interference is more challenging

7. Symbol Explanation
• RTWP
– Received Total Wide Bandwidth power
– To describe uplink interference level
– When uplink load increase 50%, RTWP value
will increase 3dB
• RSSI
– Received Signal Strength Indicator
– To describe downlink interference level at UE
side

8. Symbol Explanation
• RSCP
– Revived Signal Code Power (Ec)
– Ec/Io = RSCP/RSSI, to describe downlink
CPICH quality
• ISCP
– Interference Signal Code Power; can be
estimated by:
• ISCP = RSSI – RSCP

9. Concept of Pilot Pollution
• Concept of pilot pollution
– Pilot pollution means that
there are too many strong
pilots within the coverage, but
none of the pilots is dominant
• Criteria of pilot pollution
– There are more than 3 pilots
with Ec > -95 dBm
– The level difference between
the strongest pilot and the
fourth strongest pilot is < 5 dB

10. Effect of Pilot Pollution
• Pilot pollution is specific to the CDMA
system CDMA and greatly affects the
network performance
• Effect of pilot pollution
– High BLER
– Low system capacity
– High call drop rate due to frequent handover
– Low access success rate due to no dominant
cell

11. Causes of Pilot Pollution
• The causes of the pilot pollution includes:
– Unreasonable cell layout
– Too high site or antenna
– Unreasonable azimuth or tilt angle of an
antenna
– Effect of the back lobe of an antenna
– Effect of the ambient environment of the
coverage

12. Unreasonable cell layout
• The distances among the Site A, B and C are not
balanced, and the location relation between the Sites
is distinctly different from an equilateral triangle
Site A
Site C
Site B

13. Too high site or antenna
• The antennas of A and C are too high, so it is hard to
control overshooting
Pilot pollution

14. Unreasonable azimuth of an
antenna
• The antenna azimuth of the sector with scramble of
100 is unreasonable

15. Unreasonable tilt angle of an
antenna
• The too small antenna tilt angle results in
overshooting

16. Effect of the back lobe of an
antenna
• Front-to-back ratio of the antenna does not
meet the requirement, so the signal of the back
lobe leaks

17. The Ways to Reduce Pilot
Pollution
• An area with pilot Pollution can be
predicted in the planning simulation
– Optimize the planned scheme to avoid the
pilot Pollution
• Optimal solution – excellent system design
– Proper site
– Proper azimuth and tilt angle of antennas
– Proper transmit power and power ratio of sites