Interference-based DL Calculations

Interference-based calculations include all the calculations that involve the calculation of interference received from interfering transmitters in addition to the signal level received from the server.

3.2.1 DL Carrier-to-Interference Ratio Calculation

MSA (Mobile Station Allocation) Definition

In order to understand the difference between each frequency hopping mode from the point of view of a mobile, it is inter-esting to consider the Mobile Station Allocation. MSA is characterised by the pair (Channel list, MAIO). In the following, we will use this notion to characterise the interference and resources set of a mobile.

For non-hopping (NH) mode, the channel list is 1 channel. For base-band hopping (BBH) or synthesized frequency hopping (SFH), the channel list corresponds to the mobile allocation list (MAL).

For BBH, channels of MAL belong to the same TRX type.

Examples:

• Non-hopping (NH): An MSA is the channel assigned to a TRX used by a mobile.

• Baseband hopping (BBH): An MSA is the Mobile Allocation List (MAL) and the TRX index.

• Synthesised frequency hopping (SFH): An MSA is the Mobile Allocation List (MAL) and the Mobile Allocation Index Offset (MAIO).

Therefore, from the point of view of a mobile station, BBH and SFH work in the same way. An MSA will be attached to each mobile considered during the simulation and the level of interference will be evaluated on this MSA.

Notations and Assumptions In the following description:

• v is a victim transmitter,

• MSAS(v) is the set of MSAs (Mobile Station Allocations) associated to v,

The number of MSAS(v) depends on TRX types to be analysed. You may study a given TRX type tt (there will be as many MSA(v) as TRXs allocated to the subcell (v,tt)) or all the TRX types (the number of MSA(v) will correspond to the number of TRXs allocated to v).

Several MSAs, m, are related to a transmitter. Therefore, Atoll calculates the DL C/I for each victim transmitter v with MSA m (m  MSAS(v)).

TRX index Channel list MAIO MSA

1 53 - (53,-)

2 54 - (54,-)

TRX index Channel list MAIO MSA

1 53 * ([53,54,55],0)

2 54 * ([53,54,55],1)

3 55 * ([53,54,55],2)

TRX index Channel list MAIO MSA

1 53 54 55 56 2 ([53,54,55,56],2)

2 53 54 55 56 3 ([53,54,55,56],3)

C^v m I^v m

--- 

 

 

Atoll considers the most interfered MSA, therefore, the displayed C/I or C/(I+N) are or

, respectively. If the Detailed Results check box is selected, the C/I values for all MSAs are displayed.

• i is any potential interfering transmitter (TBC transmitters whose calculation areas intersect the service area of v),

• MSAS(i) is the set of MSAs related to potential interferers i,

• INT(v) is the set of transmitters that interfere v,

• is the carrier power level received from v on m,

• corresponds to the interference received from interfering transmitters i on m,

• used in the C/I calculation is based on the C/I standard deviation.

Calculations

The carrier power level is the power received from the victim transmitter at the terminal.

If the interference conditions are based on C/(I+N), Atoll takes the total noise into account. The total noise is the sum of the thermal noise (-121 dBm by default or user-defined), the terminal noise figure , and the

inter-technology downlink noise rise .

Interference can be received from interfering transmitters i on co-channel and adjacent channels. Interference may also be received from the transmitters of another technology.

Therefore,

is the average power control gain defined for the interfering transmitter i and is the diversity gain defined for the considered subcell.

Each interference component is explained below.

Co- and Adjacent Channel Interference:

is the interference received at v on m on co-channel, given by:

is the interference received at v on m on adjacent channels, given by:

Here, is the carrier power level received from i on n.

T_i(n) is occupancy of the MSA n:

is the traffic load defined for the MSA n or i. It can be set to 100% in the coverage prediction properties.

The C/I shadowing margin is applied on the carrier power level. The interference levels are not changed.

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is the activity factor defined for the MSA n of i. If the subcell (i,tt) supports DTX, the value specified in the coverage prediction properties is used. Otherwise, the activity factor is 1.

is the probability of having a co- or adjacent channel collision between MSAs n and m, depending on the used frequency hopping mode.

• Collision Probability for Non Hopping Mode:

• Collision Probability for BBH and SFH Modes:

MSA m of v can be defined as the pair ([f₁,f₂,….f_n], MAIO) and MSA n of i as the pair ([f’₁,f’₂,….f’_n], MAIO’) ( f and f’ are channels).

An occurence refers to the event when a channel f of m encounters a channel f’ of n during hopping. A collision occurs when f and f’ are co- or adjacent channels:

such that

The probability of collision is the ratio of the number of collisions to the number of occurences:

The probibility of collision depends on the correlation between m and n. There can be two cases:

i. MSAs m and n are correlated

m and n must have identical HSN and synchronisation. The number of occurrences depends on the MAL length, MAIO, and MAIO’.

Example:

Here, the number of occurrences is 3, the number of co-channel collisions is 1, and the number of adjacent channel collisions is 1. Therefore,

and

ii. MSAs m and n are not correlated

m and n do not have identical HSN and synchronisation. The probability of collision is the same for all the channels.

Example:

Here, the number of occurrences is 9, the number of co-channel collisions is 1, and the number of adjacent channel collisions is 3. Therefore,

BCCH TRXs are always on. Therefore, DTX and traffic loads do not impact the interference

from BCCH. In other words, and for the BCCH TRXs of the

interferers.

Schematic view of hopping sequences MSA m of v

([34 37 39], MAIO=0) 34 37 39

MSA n of i

([38 36 34], MAIO’=2) 38 36 34

Schematic view of hopping sequences MSA m of v

([34 37 39], MAIO=0) 34 37 39

MSA n of i

([38 36 34], MAIO’=2) 38 36 34

f_actⁱ  n

f_actⁱ  n = 1 L_trafficⁱ  n = 1

p_{m n}^{v i}_

p_{m n}^{v i}_ = 1

OCCUR f _m^vf'_nⁱ

Collision = OCCUR f _m^vf'_nⁱ f_m^v –f'_nⁱ = 0 or 1

p_{m n}^{v i}_ n_collision n_occurence

---=

p_{m n}^{v i}_

 _co 1

3

---= p_{m n}^{v i}_ _adj 1 3

---=

and Diversity gain:

is the diversity gain defined for the victim subcell.

Two types of diversity modes can be defined. In Tx Diversity, the signal is transmitted as many times that there are antennas. In, the signal is successively transmitted on the various antennas.

For Tx Diversity mode, the diversity gain is defined as:

is the additional transmit diversity gain defined for the clutter class on which is located m.

For Antenna Hopping mode, the diversity gain is defined as:

is the antenna hopping gain defined for the clutter class on which is located m.

Inter-technology Downlink Interference:

is the total inter-technology interference level on m due to transmitters in a linked Atoll document.

The interference from a transmitter Tx in a linked Atoll document is given as:

is the frequency used by the transmitter Tx within its list of frequencies, is the total transmitted Tx power on , are the total losses between the transmitter Tx and the terminal, and is the inter-technology channel protection between the frequencies used by the transmitter Tx and the victim transmitter v.

3.2.2 Point Analysis

Analysis provided in the Interference tab is based on path loss matrices. Therefore, it is possible to display the interference levels received from TBC transmitters for which path loss matrices have been calculated over their calculation areas.

Atoll displays the following at the terminal:

• The carrier power level received from the victim transmitter v on the most interfered MAS m,

• Co-channel, adjacent channel, or both co- and adjacent channel interference received from interfering transmitters i on MAS m (for further information about noise calculation, please refer to Signal to noise calculation: noise calculation part),

Interferers are sorted in the order of descending carrier power levels.

• In case of frequency hopping, the ICP value is weighted according to the fractional load.

• In the ICP, the frequency gap is based on the defined base frequency for each technology (e.g., 935 MHz in GSM 900)

p_{m n}^{v i}_

 _co 1

9

---= p_{m n}^{v i}_ _adj 1 3

---=

G_Div^v

G_Div^v = 3dB+G_clutter^Tx_Div G_clutter^Tx_Div

G_Div^v = G_clutter^Ant_Div G_clutter^Ant_Div

I_inter^DL _{–technology}

I_inter^DL _{–technology} PTransmitted Tx  ic_i L_total^Tx ICP_ic

if

 Tx

---ni



=

ic_i i^th PTransmitted

Tx  ic_i

ic_i L_total^Tx ICP_ic

if Tx

• Neither DTX nor traffic load of TRXs are taken into account to evaluate interference

levels. Therefore, we have .

• The C/I shadowing margin is applied on the carrier power level. The interference levels are not changed.

T_i n = L_trafficⁱ   fn  _actⁱ  n = 1

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3.2.3 Interference-based DL Coverage Predictions

Two interference-based DL coverage predictions are available:

• Coverage by C/I Level (DL): Provides a global analysis of the network quality.

Atoll calculates the C/I on each pixel within the service area of studied transmitters, determines the pixels where the calculated C/I exceeds the defined minimum threshold, and colours these pixels depending on C/I value.

• Interfered Zones: Shows the areas a transmitter is interfered.

Atoll calculates the C/I on each pixel within the service area of studied transmitters, determines the pixels where the calculated C/I is lower than the defined maximum threshold, and colours these pixels depending on colour of the interfered transmitter.

For each TBC transmitter, Txi, Atoll calculates the selected parameter on each pixel inside the Txi calculation area. In other words, each pixel inside the Txi calculation area is considered a probe (non-interfering) receiver.

Coverage prediction parameters to be set are:

• The coverage conditions in order to determine the service area of each TBC transmitter,

• The interference conditions to meet for a pixel to be covered, and

• The display settings to select the displayed parameter and its shading levels.

The thermal noise (N = -121 dBm, by default) is used in the calculations if the coverage prediction is based on C/(I+N). This value can be modified by the user.

3.2.3.1 Service Area Determination

Atoll uses parameters entered in the Condition tab of the coverage prediction properties dialogue to determine the areas coverage will be displayed. Service areas are determined in the same manner as for signal level-based coverage predictions.

See "DL Service Area Determination" on page 126 for more information.

3.2.3.2 Coverage Area Determination

For each victim transmitter v, coverage area corresponds to pixels where DL or is between the lower and upper thresholds defined in the coverage prediction properties.

The two options defining the thresholds are explained below.

3.2.3.2.1 Interference Condition Satisfied by At Least One TRX

In this case, the coverage area of a transmitter Txi corresponds to the pixels :

or

, TRX_j is any TRX belonging to Txi.

3.2.3.2.2 Interference Condition Satisfied by The Worst TRX

In this case, the coverage area of a transmitter Txi corresponds to the pixels :

or

, TRX_j is the TRX (belonging to Txi) with the worst C/I or C/(I+N) at the pixel.

3.2.3.3 Coverage Display

3.2.3.3.1 Coverage Resolution

The resolution of the coverage prediction does not depend on the resolutions of the path loss matrices or the geographic data and can be defined separately for each coverage prediction. Coverage predictions are generated using a bilinear interpolation method from multi-resolution path loss matrices (similar to the one used to calculate site altitudes, see "Path Loss Calculation Prerequisites" on page 57 for more information).

3.2.3.3.2 Display Types

It is possible to display the coverage predictions with colours depending on any transmitter attribute or other criteria such as:

C

C/I Level

Each pixel of the transmitter coverage area is coloured if the calculated DL C/I (or C/(I+N)) level is greater than or equal to the specified minimum thresholds (pixel colour depends on DL C/I (or C/(I+N)) level). Coverage consists of several independent layers whose visibility in the workspace can be managed. There are as many layers as transmitter coverage areas. Each layer shows the different DL C/I levels available in the transmitter coverage area.

Max C/I Level

Atoll compares calculated DL C/I (or C/(I+N)) levels received from transmitters on each pixel of each transmitter coverage area coverage areas overlap the studied one and chooses the highest value. A pixel of a coverage area is coloured if the DL C/I (or C/(I+N)) level is greater than or equal to the specified thresholds (the pixel colour depends on the DL C/I (or C/(I+N)) level).

Coverage consists of several independent layers whose visibility in the workspace can be managed. There are as many layers as defined thresholds. Each layer corresponds to an area the highest received DL C/I level exceeds a defined minimum threshold.

Min C/I Level

Atoll compares DL C/I (or C/(I+N)) levels received from transmitters on each pixel of each transmitter coverage area the coverage areas overlap the studied one and chooses the lowest value. A pixel of a coverage area is coloured if the DL C/I (or C/(I+N)) level is greater than or equal to the specified thresholds (the pixel colour depends on the DL C/I (or C/(I+N)) level).

Coverage consists of several independent layers whose visibility in the workspace can be managed. There are as many layers as defined thresholds. Each layer corresponds to an area the lowest received DL C/I level exceeds a defined minimum threshold.

In document Atoll 3.3.0 Technical Reference Guide.pdf (Page 131-136)