室内覆盖设计.doc

1.1. Indoor Coverage
Why should indoor solutions be used?
· cellular competition moves indoors
· subscribers expect continuous coverage and quality
· outdoor cells do not provide sufficient coverage indoors
The benefits of indoor solutions are pointed out in the following picture:

1.1.1. Building Losses
Mobile networks are increasingly expected to provide coverage also within buildings. This, however, can rarely be modelled with a prediction tool, since a prediction would require a very detailed database of buildings. This would include locations, window orientations, building materials etc.
Therefore signal levels in buildings are estimated by applying an empirically measured “building penetration loss” margin. Typical values are 15..25 dB. This varies from country to country with typical architecture and building materials used.
Signal levels within the same building are not constant. There are big differences between locations near an outside window and “deep indoor” situations, e.g. in hallways.

1.1.2. Building Penetration Loss
Signal levels in buildings are estimated by applying a “building penetration loss” margin. Big differences between rooms with windows and “deep indoor” exist (10 ..15 dB).
Signal losses for building penetration vary greatly with building materials used, e.g.:
mean value sigma
reinforced concrete wall, windows 17 dB 9
concrete wall, no windows 30 dB 9
concrete wall within building 10 dB 7
brick wall 9 dB 6
armed glass 8 dB 6
wood or plaster wall 6 dB 6
window glass 2 dB 6

No major differences exist for 900 and 1800 MHz.
Total building loss =
add median values
superimpose standard deviations
add (lognormal) margin for higher probabilities
1.1.3. Incident Angle
Penetration loss depends heavily on incident angle of the radio wave. E.g. measured values for armed glass at 1800 MHz (typical facade of office building):

1.1.4. In-building Path Loss

1.1.5. Indoor Coverage Solutions
Indoor coverage solutions include the following features:
· Small BTS
mini BTS
PrimeSite
· Repeaters
active, passive
optical
· Antennas
distributed antennas
radiating cable
· Signal distribution
power splitters
optical fiber

1.1.6. Summary of Indoor Solutions

1.1.7. Radiating Cable
· Coaxial cable with perforated leads ==> “energy leak”
· Radiating losses 10 ..40 dB per 100m
· Coupling loss typically 55 dB (at 1m reference distance)
· Produces constant field strengths along cable runs
· Operates in wide frequency range
· Radiating losses become higher with frequency
· Very large bending radii
· Bending disturbs field distribution
· Formerly often used for tunnel coverage
· VERY EXPENSIVE
1.1.8. Indoor Coverage Examples
· With repeater
relay outdoor signal into target building
needs “donor” cell; adds coverage, no capacity
· With indoor BTS and distributed antennas
heavy losses by power splitting and cabling

1.1.9. Optical Repeater
· Signal from in-building BTS
· Fiberoptic distribution system
very low cabling losses (2 dB/ 1000m)
>50 remote antennas possible
signal amplification and distribution at remote end
easy cabling (very thin fibers)
· Application examples
multi-level offices, shops
airport halls (large distances!)
industrial plants

1.1.10. Repeater
· Passive repeater
needs strong external signal
useful only with very short cables
seldomly used
· Active repeater
amplifies and re-transmits all received signals
· Wideband or narrowband repeater
· Application examples
places with coverage need and little traffic
remote valleys
tunnels
underground coverage (e.g. garages)

1.1.11. The “Lightbulb Principle”

1.1.12. The “Newspaper Principle”

1.2. Tunnel Coverage
1.2.1. Wave Propagation in Tunnels
· Ideal antenna position: centre of cross-section
· Distance to walls: min. 2 l
· Tunnel cross-section shape unimportant, if > 10 l
· Time dispersion decreases with distance ==> constant
· Tunnel bends and curves negligible ( >> l )
· Mount antenna ~50..100m before tunnel entrance
· Good signal coupling between successive tunnels
· Tunnels are very friendly environment for radio wave propagation
1.2.2. Tunnel Cross-sections
· Radio wave propagation possible if cross-section > ~ 7 l
· “Filling factor” determines propagation conditions
· Typical ranges for filling factors
high speed trains (Germany) ICE: 13% (aerodynamics)
road tunnels: 10% (exhaust fumes, ventilation...)
underground: 60..90%