GPRS/EDGE calculations include coding scheme selection and throughput calculation. Coding schemes may be selected using ideal link adaptation or without it. Once coding schemes have been selected, throughputs corresponding to these coding schemes are readily determined from the look-up tables.
The following sections describe the two categories of calculations, i.e., with and without ideal link adaptations. Ideal link adaptation implies that the selected coding scheme corresponds to the highest available throughput under the given radio conditions.
GPRS/EDGE calculations may be based on signal levels (C) alone, on C/I, or on C/(I+N). For calculating the noise, either the noise figure defined for the calculations or that of the selected terminal type is used.
Different GPRS/EDGE configurations may be defined for transmitter and terminals. In this case, Atoll only selects the coding schemes that are common in the two, and gives priority to the thresholds defined in the terminal configuration. If no terminal type is defined for the calculation, or if the terminal type does not have any GPRS/EDGE configuration assigned to it, Atoll only uses the GPRS/EDGE configuration of the transmitter. If the transmitter does not have any GPRS/EDGE configuration assigned to it, no coding scheme selection and throughput calculation is carried out.
In the following calculations, we assume that:
• is the signal level received from the selected TRX type (tt) or on all the TRXs of Txi on each pixel of the Txi coverage area,
• is the Power Backoff defined for the subcell for 8PSK, 16QAM, or 32QAM modulations,
• CS is the set of all available coding schemes,
• are the values of reception thresholds for the coding schemes available in the GPRS/EDGE configuration,
• are the values of C/I thresholds for the coding schemes available in the GPRS/EDGE configuration,
• are the values of C/(I+N) thresholds for the coding schemes available in the GPRS/EDGE configuration,
• The priorities of the coding scheme lists are as follows: DBS > DAS > MCS > CS.
When the calculations are based on C/I and C/(I+N):
• Atoll calculates the carrier-to-interference ratio for all the GPRS/EDGE TBC transmitters but takes into account all the TBC transmitters (GSM and GPRS/EDGE) to evaluate the interference.
• The reception thresholds given for signal level C are internally converted to C/N thresholds ( N is the thermal noise defined in the document database at -121 dBm by default) in order to be indexed by C/(I+N) values. C/I thresholds are also indexed by the C/(I+N) value.
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For more information on interference (I) calculation, see "DL Carrier-to-Interference Ratio Calculation" on page 131.
3.3.1 Coding Scheme Selection and Throughput Calculation Without Ideal Link Adaptation
3.3.1.1 Calculations Based on C
Coding Scheme Selection
Atoll selects a coding scheme, cs, from among the coding schemes available in the GPRS/EDGE configuration, such that:
For each TRX type, tt,
The selected coding scheme, cs, is the coding scheme with the lowest coding scheme number from the lowest priority coding scheme list.
Throughput Calculation
Once the coding scheme cs is selected, Atoll reads the corresponding throughput value for the received signal level from the Throughput=f(C) graph associated with cs.
3.3.1.2 Calculations Based on C/I
Coding Scheme Selection
Atoll selects two coding schemes from among the coding schemes available in the GPRS/EDGE configuration, such that:
For each TRX type, tt,
And,
csC is the coding scheme determined from the signal level, and csC/I is the coding scheme determined from the C/I level. Both coding schemes are the coding schemes with the lowest coding scheme number from the lowest priority coding scheme list.
The selected coding scheme, cs, is the coding scheme with the lower coding scheme number among csC and csC/I: .
Throughput Calculation Based on the Worst Case Between C and C/I
For the coding scheme csC determined above, a throughput value, TPC, corresponding to the signal level is determined from the TP = f(C) graph.
For the coding scheme csC/I determined above, a throughput value, TPC/I, corresponding to the C/I is determined from the TP
= f(C/I) graph.
The resulting throughput TP is the lower of the two values, TPC and TPC/I: .
3.3.1.3 Calculations Based on C/(I+N)
Coding Scheme Selection
Atoll selects two coding schemes from among the coding schemes available in the GPRS/EDGE configuration, such that:
The selection of coding schemes is mainly based on the radio conditions mentionned above. Nevertheless, you can optionally define some specific coding scheme graphs accoding to a specific hopping mode, mobility type, frequency band and MAL. As an example, you can model the gain due to longer MALs in coding scheme selection.
cs Lowest CS
For each TRX type, tt,
And,
csC/N is the coding scheme determined from the C/N, and csC/(I+N) is the coding scheme determined from the C/(I+N) level.
Both coding schemes are the coding schemes with the lowest coding scheme numbers from the lowest priority coding scheme list.
The selected coding scheme, cs, is the coding scheme with the higher coding scheme number among csC/N and csC/(I+N): .
Throughput Calculation Based on Interpolation Between C/N and C/(I+N)
For the coding scheme csC/N determined above, the TP = f(C) graph is internally converted to TP = f(C/N) graph. A throughput value, TPC/N, corresponding to the C/(I+N) is determined from the TP = f(C/N) graph.
For the coding scheme csC/(I+N) determined above, the TP = f(C/I) graph is internally converted to TP = f(C/(I+N)) graph. A throughput value, TPC/(I+N), corresponding to the C/(I+N) is determined from the TP = f(C/(I+N)) graph.
The final throughput is computed by interpolating between the throughput values obtained from these two graphs. The throughput interpolation method consists in interpolating TPC/N and TPC/(I+N) according to the respective weights of I and N values.
The resulting throughput TP is given by:
, pN is the thermal noise power (value in Watts), and p(I+N) is the interferences + thermal noise power (value in Watts).
3.3.2 Coding Scheme Selection and Throughput Calculation With Ideal Link Adaptation
3.3.2.1 Calculations Based on C
Throughput Calculation
For the received signal level, and coding schemes whose reception thresholds are lower than the received signal level, Atoll determines the highest throughput from the graphs available in the GPRS/EDGE configuration.
Coding Scheme Selection
The selected coding scheme, cs, is the one corresponding to the highest throughput calculated above.
If there are more than one coding schemes providing the highest throughput at the pixel, the selected coding scheme, cs, is the one with the lowest coding scheme number from the lowest priority coding scheme list.
3.3.2.2 Calculations Based on C/I
Throughput Calculation Based on Worst Case Between C and C/I
For the received signal level, and coding schemes whose reception thresholds are lower than the received signal level, Atoll determines the highest throughput from the graphs available in the GPRS/EDGE configuration.
csC N Lowest CS
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For the received C/I, and coding schemes whose C/I thresholds are lower than the received C/I, Atoll determines the highest throughput from the graphs available in the GPRS/EDGE configuration.
The resulting throughput TP is the lower of the two values, TPC and TPC/I.
Coding Scheme Selection
The selected coding scheme, cs, is the one corresponding to the lower of the two highest throughputs calculated above.
If there are more than one coding schemes providing the highest throughputs at the pixel, the selected coding scheme, cs, is the one with the lowest coding scheme number from the lowest priority coding scheme list.
3.3.2.3 Calculations Based on C/(I+N)
Throughput Calculation Based on Interpolation Between C/N and C/(I+N)
Atoll internally converts the TP = f(C) graphs into TP = f(C/N) graphs. For the received C/(I+N), and coding schemes whose C/
(I+N) thresholds are lower than the received C/(I+N), Atoll determines the highest throughput from the TP = f(C/N) graphs available in the GPRS/EDGE configuration.
Atoll internally converts the TP = f(C/I) graphs into TP = f(C/(I+N)) graphs. For the received C/(I+N), and coding schemes whose C/(I+N) thresholds are lower than the received C/(I+N), Atoll determines the highest throughput from the TP = f(C/(I+N)) graphs available in the GPRS/EDGE configuration.
The final throughput is computed by interpolating between the throughput values obtained from these two graphs. The throughput interpolation method consists in interpolating TPC/N and TPC/(I+N) according to the respective weights of I and N values.
The resulting throughput TP is given by:
, pN is the thermal noise power (value in Watts), and p(I+N) is the interferences + thermal noise power (value in Watts).
Coding Scheme Selection
The selected coding scheme, cs, is the one corresponding to the higher of the two highest throughputs calculated above.
If there are more than one coding schemes providing the highest throughputs at the pixel, the selected coding scheme, cs, is the one with the highest coding scheme number from the highest priority coding scheme list.
3.3.3 Application Throughput Calculation
Application throughput is calculated from the effective RLC throughput as follows:
TPC = Highest TP=f C =PrecTxiTRX P– BackoffTxi TRX CS
is the effective RLC throughput, and and are the throughput offset (kbps) and the throughput scaling factor (%) defined for the selected service.
3.3.4 BLER Calculation
Block error rate is calculated as follows:
TP is the throughput per timeslot calculated for a pixel and TPMAX is the maximum throughput per timeslot read from the GPRS/EDGE configuration used for the calculations.
3.3.5 GPRS/EDGE Coverage Predictions
Two GPRS/EDGE coverage predictions are available:
• Coverage by GPRS/EDGE Coding Scheme: Shows the areas various coding schemes are available.
• Packet Throughput and Quality Analysis: Shows the throughputs corresponding to the coding schemes available.
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.
3.3.5.1 Service Area Determination
Atoll uses parameters entered in the Condition tab of the coverage prediction properties dialog box to determine the areas coverage will be displayed.
We can distinguish eight cases as below. Let us assume that:
• Each transmitter, Txi, belongs to a Hierarchical Cell Structure (HCS) layer, k, with a defined priority and a defined reception threshold.
• Each transmitter, Txi, is GPRS/EDGE-capable.
• No max range is set.
3.3.5.1.1 All Servers
The service area of Txi corresponds to the pixels :
3.3.5.1.2 Best Signal Level and an Overlap Margin
The service area of Txi corresponds to the pixels :
And
M is the specified overlap margin (dB). The Best function considers the highest value from a list of values.
• If M = 0 dB, Atoll considers pixels the received signal level from Txi is the highest.
• If M = 2 dB, Atoll considers pixels the received signal level from Txi is either the highest or within a 2 dB margin from the highest.
• If M = -2 dB, Atoll considers pixels the received signal level from Txi is 2 dB higher than the signal levels from transmitters which are 2nd best servers.
TPRLC MAC TPOffset SF
BLER
TP TPMAX
--- If TP TP MAX 0 If TP TPMAX
=
SubcellReceptionThresholdPrecTxi tt
SubcellReceptionThresholdPrecTxi tt
PrecTxi tt Best
ji PrecTxj tt M–
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