Radio Network Dimensioning

Posted by wireless on Sunday, August 23, 2009

Radio Network Dimensioning


• Dimensioning is the main part of the pre-planning phase. In addition
to the dimensioning parameters the priority of the parameters also
needs to be agreed.
• It is imperative to agree the network layout, usage of three sector
sites or a combination of three sector and omni sites with the
operator.
• One important planning issue is also whether only macro cells are
used in the beginning or a combination of macro, micro and pico
cells.
• The macro cells are used in rural and suburban areas to cover large
areas. The macro cell has a cell range of 1–35 km and is
characterized by an outdoor antenna, which covers a large area.
Antennas are above rooftops.
• Micro cells are used in city areas to cover areas close by and
antennas are on the walls. The micro cell has a cell range of less
than 1 km and is for outdoor coverage. The antennas are typically
mounted on walls and below the average rooftop level.
• The pico cells are used to cover either very specific hot spot in an
outdoor area or to give indoor coverage. The pico cell has a cell
range less than 500 m and is characterized by antennas mounted
low on the walls, clearly below the rooftop level. They are used for
both indoor and outdoor coverage

Link Budget Calculations


• The radio link budget aims to calculate the cell coverage
area.
• One of the required parameters is radio wave
propagation to estimate the propagation loss between
the transmitter and the receiver. The other required
parameters are the transmission power, antenna gain,
cable losses, receiver sensitivity and margins.


  • When defining the cell coverage area, the aim is to balance the uplink and downlink powers.
  • The links are calculated separately and are different from the transmission powers.
  • The BTS transmission power is higher than the MS transmission power and therefore the reception of the BTS needs to have high sensitivity.
  • The radio signal experiences the same path loss when travelling from the BTS to the MS as from the MS to the BTS.
  • The GSM link budget parameters are:
BTS sensitivity
– MS sensitivity
– MS and BTS powers
– Antenna gains
– Diversity gain
– Cable and connector losses
– Other equipment loss factors
– Mast head amplifier (MHA) and booster
– The interference degradation margin

• BTS sensitivity
– Specified on the ETSI GSM recommendation 05.05 and the recommended value
is −106 dBm. This is a general recommendation and therefore when preparing a
link budget with a certain manufacturer’s equipment this vendor’s
recommendations can be used.
• MS sensitivity
– is also specified in the ETSI recommendation 05.05, where the receiver
sensitivity value is separate for each MS class.
– MS class 4, which means GSM 900, the recommended value is −102 dBm.
– MS class 1, GSM 1800, the value is −100 dBm.
• The MS sensitivity can also be calculated using the information of receiver
noise F and minimum Eb/N0.
• The value for the noise is 10 dB and the minimum Eb/N0 is 8 dB, as defined
in the ETSI recommendation 03.30. The receiver sensitivity Si is solved
from the following equation, where the input noise power Ni is the product of
three parameters: the Boltzman constant k, temperature T0 = 290K and
bandwidth W = 271 kHz (54 dB):

• MS and BTS powers
– MS TX (transmission) power is defined by the MS class in ETSI specifications.
For MS class 4 (GSM 900) the maximum TX power is 2Wand for class 1 (GSM
1800) 1W.
– BTS TX power depends on the BTS type and vendor. The TX power is
adjustable, which enables the link budget to be balanced.
• Antenna gains
– The BTS antenna gain is dependent on the antenna type and whether the
antenna is omnidirectional or directional. The gain of a directional BTS antenna is
dependent on the horizontal and vertical half power beam widths. It is also
dependent on the physical size of the antenna which in turn has an impact on the
frequency range.
– Also frequency range is inversely proportional to the size of the antenna, which is
then connected to the radiating aperture of the antenna.
– The antenna gain is around 16–20 dBi when there is a widely used antenna with
60–65◦ horizontal half power beam width and 5–10 vertical half power beam
width.
– In the link budget calculations for the MS antenna the gain is generally 0 dBi. The
actual MS antenna gain is complicated to estimate, because the gain is highly
dependent on the mobile user’s relative location towards the base station when
the amount of body loss varies.
• Diversity gain
– can be used for correcting unbalance between the uplink and downlink. The
typical way to arrange diversity is to have it in the BTS reception. One basic
method is to separate receiver antennas vertically or horizontally; the method

• Cable and connector losses
– are case specific and need to be measured or calculated separately. An
individual connector gives a loss of around 0.1 dB, but depending on the
cable installations there can be several in one antenna line.
• Other equipment loss factors
– consist of isolator, combiner and filter losses.
• Two other gain factors, which need to be considered in the link budget if
used, are the mast head amplifier (MHA) and booster.
– The MHA, which is located close to the antenna in BTS reception, is
used to amplify the received signal. This decreases the unbalance
between the uplink and downlink by giving extra gain in the uplink the
direction. The booster can be used to amplify the BTS transmission
power.
• The interference degradation margin
– describes the loss due to frequency reuse.

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