WO2002082846A1

WO2002082846A1 - Procedure and system for determination of parameters in radio communication networks

Info

Publication number: WO2002082846A1
Application number: PCT/SE2002/000654
Authority: WO
Inventors: Rolf Hermansson; Thomas Lindqvist
Original assignee: Telia Ab (Publ)
Priority date: 2001-04-03
Filing date: 2002-04-02
Publication date: 2002-10-17
Also published as: SE0101206L; SE0101206D0; SE523614C2

Abstract

In a link budget calculation for a radio cell an interference and fading margin which correspoonds to the traffic in the cell is included. The size of this interference and fading margin depends on teh total load in the cell, the cell load, which in its turn includes traffic which is generated by all teh services (types of services) which exist in the cell. The traffic from all service tpyes are mathematically weighed together, andinterference and fading margin is then calculated via a statistical evaluaiton of hte, form all service types combined, distributions of the fading and capacity varioations within the cell. The expected cell radius then is calculated by knowledge of max power of the radio tranmitters which shall be utilized for traffic within the cell.

Description

PROCEDURE AND SYSTEM FOR DETERMINATION OF PARAMETERS IN RADIO COMMUNICATION NETWORKS

Technical field The present invention relates to a procedure and a system for calculation of cell dimensions in cellular radio communication networks. More particularly does the invention relate to tools for nominal cell planning.

Prior art

An initial planning of the resource requirement at establishing of new radio communication networks, for instance mobile telephone networks, includes calculation of radio coverage and capacity. Radio coverage is a measure of an area within which a satisfactory signal level can be maintained, and capacity is a measure of how large amount of information that can be transmitted per time unit within a radio coverage area. The general terminology used is radio network cells, or only cells, and the traffic load in the cell, or the cell load.

At the planning of previous generations of mobile communication networks, for instance the well known GSM which operates according to the principle time sharing where the communication is made in time slots, radio coverage and capacity are handled independent of each other. New types of mobile communication systems which operate according to the principle code sharing, for instance CDMA-systems such as WCDMA, however, has the feature that the coverage area of a radio cell is strongly depending on the amount of radio traffic going on within the cell, or in other words there is a strong connection between cell size and cell load.

The known technology within the field to plan radio networks has the disadvantage not to take this dependence between cell area and cell load into consideration, so the methods will not produce a reliable result if they are used for planning of radio networks of, for instance, type WCDMA.

Description of the invention One aim of the present invention therefore is to provide a solution of a problem to calculate the dimensions of radio network cells in a radio communication network of, for instance, type WCDMA.

A solution, according to the invention, of a problem is a procedure and a system to facilitate cell planning in cellular radio communication networks. The procedure includes to calculate a link budget for a cell, at which the link budget includes an interference and fading margin the size of which depends on the total traffic from a plurality of service types which are utilized within the cell, and where the total traffic is calculated by a combination of the distribution of traffic of/for the different service types, and where the interference and fading margin is determined by said combination. In a link budget calculation for a radio cell which is made according to the invention, an interference and fading margin which corresponds to the traffic in the cell consequently is included. The size of this interference and fading margin depends on the total load in the cell, the cell load, which in its turn includes traffic which is generated by all the services (types of services) which exist in the cell.

The procedure and system according to the invention weighs mathematically together the traffic from all service types and then calculates interference and fading margin via a statistical analysis of the, from all service types combined, distributions of the fading and capacity variations within the cell. The expected cell radius then is calculated by knowledge of maximal power of the radio transmitters which shall be utilized for traffic within the cell . One advantage with/of the present invention is that, in comparison with normally used complicated simulation technology, discrete faltung is utilized at weighing together of traffic load and radio behavior. This implies the advantage that a calculation tool according to the invention is very simple to realize and by that very cheap.

Brief description of figures

The Figures 1-9 illustrate diagrams over results from calculations according to the invention.

Preferred embodiments

The invention now will be described in form of mathematical calculation algorithms and a number of results which are achieved at use of these algorithms. The calculations are preferably made in one with software equipped computer or computer system, where the software is adapted to operate according to the mathematical expressions and algorithms which will be described below. The calculations are shown separately for uplink respective downlink, that is, separately for the case communication from a mobile terminal (MS) to a base station (BTS), respective from BTS to MS. The algorithms are described in a symbolic way in form of the well known and widespread programming tool Visual Basic.

The programming tool calculates a maximal cell radius based on presented/indicated link budget parameters and the distribution of load between four service types. The service types which this model takes into consideration can be divided into four classes: Speech, that is traditional speech service, Circui t Swi tch (CS) , that is circuit switched data communication service, Packet Swi tch (PS) , that is packet switched data communication without delay, Packet Swi tch Best Effort (PS BE) , that is packet switched data communication with delay. Input parameters which are required for the calculation in uplink are according to the following

(indicated for each of the four service types):

Pτχ-_max - Maximal output power from the mobile terminal (MS) per physical channel.

L_Tx - Losses in the transmission antenna system of the mobile terminal.

G _X - Transmission antenna amplification in the mobile terminal . F_n ~ Noise factor in the receiver of the base station

(BTS) .

No - The thermal noise level.

R_b - Data rate for the service in the uplink direction.

Factor (Service informa tion ra te/User informa tion ra te) - Factor (0-1) for calculation of reduction of the data rate

User information rate - Service information ra te (R±) .

Ej/ (No+Io) ~ Required bit energy for respective service

(SIR) .

G_Rx - Antenna amplification for the receiver in BTS. L_Rx - Losses in the antenna system in BTS, that is cabling, connection devices and combiners (At use of LNA about 0 dB)

L_B - Radiation losses due to influence of the human body.

Cl utter a ttenua tion - Radiation losses (gains) due to terrain features . W - Bandwidth per carrier.

Kmax ~ Maximal number of users per service:

At uplink applies

W *R, *SIR K„,_v = -

R. *S/R[l+/]

At downlink applies

The value of f depends on a lot of factors, network structure and selection of antenna system. The value in the example is 0,9 and corresponds to networks with "three sector structure" and antennas with defined 65° angle of aperture. In addition are in the formula above the orthogonality factor, m extreme value 0 no orthogonality and 1 perfect orthogonality.

Percent of average simultaneous users wi thin Busy Hour -

Corresponds to Erlang/service during busy hour in the uplink direction.

G_H0 - Radiation gain due to soft handover (HO) .

Lpc - Radiation loss due to deficiencies at power control of mobile at the edge of the cell.

Lmax - Total tolerable radiation attenuation in the uplink direction calculated according to the parameters above for respective service. Interference and fading marginal not included.

Input parameters which are required for the calculation in downlink are as follows (indicated in the same way as above, for each of the four service types) :

Pτx-maχ ~ The maximal power per physical channel which is transmitted by BTS that the system allows (for use in link budget calculation) .

Pτx-_mm - The lowest power per physical channel which is transmitted by BTS for use in the link budget calculation for avoiding exorbitant demands on dynamics in power amplifiers .

L_Tx - Losses in the antenna system in BTS, that is in cabling and connection devices. G_Tx - Losses in the transmission antenna system in BTS.

BTS power max - Maximal output power for BTS, summed up over all services per carrier and cell.

Max average power - Maximal output power for BTS summed up over all carriers per cell. Pilot Power - Total power requirement BTS for signaling channels (20% of Max Power DL) .

F_n - Noise factor for the receiver in MS.

N₀ - Thermal noise level. R_b - Data rate for service in the downlink direction.

Fa ctor (Servi ce informa tion ra te/User informa tion ra te) -

Factor (0-1) for calculation of reduction of the data rate.

User informa tion ra te - Servi ce informa tion ra te (R±)

E±/ (No+Io) ~ Required bit energy for respective service (SIR) .

G_Rx - Antenna amplification for the receiver antenna in MS.

L_Rx - Losses in cables, connection devices and combiners in

MS antenna systems .

L_B ~ Radiation losses due to the influence of the human body.

Clutter a ttenua tion - Radiation losses (gains) due to terrain features. α - Orthogonality factor which is used to indicate how interference from intra and intercell interference influence the receiver of the mobile terminal. A value of

1 corresponds to influence according to "white noise"

(unsynchronized codes) , and a value of 0 corresponds to no influence (perfect orthogonal codes) .

Kmax ~ Maximal number of users per service. Calculated by: At uplink

W*R, *SIR

R, * S/R[l+/]

At downlink

Percen t of average simul taneous user wi thin Busy Hour - Corresponds to Erlang/service during rush hour in the downlink direction.

G_H0 - Radiation gain due to soft handover- functionality. L-_na-]?τ_x (interference & fade margin not included, P_rx=0dBm) - Total tolerable radiation attenuation Downlink calculated according to the parameters above for respective service .

Common parameters for calculations in both uplink and downlink are the following:

Number of carriers - Number of "equipped" carriers.

Frequency - RF frequency for use in prediction model.

H_roof ~ The average value of the height of buildings

(according to Waifisch-Ikegami) . H_base - The height of the antenna on BTS.

Hmo_bii_e ~ The height of the antenna of the mobile terminal .

W - Width of street (according to Waifisch-Ikegami) .

B - Distance between buildings (according to Walfisch-

Ikega i) . J - Angle, in degrees, between street direction and propagation direction of/for radio waves (according to

Waifish-Ikegami) .

Metropoli tan center - Built up urban areas type, 1 = metropolitan, 0 = other. E - Probability of detection on the cell edge.

Log-normal fading standard deviation ~ Standard deviation on lognormal fading.

Used prediction model - Selection of prediction model, 1 ■=

Waifisch-Ikegami .

Uplink calculations

Below follows a presentation of the uplink calculations, at which the calls to the services Speech , CS and PS are supposed to be poisson-distributed and independent of each other.

The data flow via the PS BE- service is queued by the present communication system depending on the momentary system load, that is depending on the delay sensitive services .

The program tool calculates the the maximal cell radius from 0-100% cell load in steps of 2%, that is for 50 data points. In a first moment, the services are combined to cell load, at which the following parameters shall be specified/indicated per service:

Percent of average simul taneous user wi thin Busy Hour - Corresponds to Erlang/service during rush hour in the uplink direction

Kmax - Maximal number of users per service, which is calculated according to: At uplink

W* R, * SIR

A„,_v = -

R_t *SIR[l + f]

At downlink

Load_f ^'actor - which is a constant, is calculated according to: load__f actor = 2 / (percent_users_speech / maxusers_speech + percent_users__CS / maxusers__CS + percent_users_PS / maxusers__PS + percent_users_BE / maxusers_BE) / resolution radi us where resolution_radius corresponds to the number of steps in cell load that is wanted, which in this embodiment is 50.

In each data point of the fifty cases, then the average number of simultaneous users per service (Erlang) can be calculated according to the algorithm:

For da ta_point = 0 To resolution_radius mean__users__speech - da ta_point * load__f a ctor * percent_users_speech mean_users_CS __= da ta_point * load_f actor * percent_users__CS mean_users_PS - da ta_point * load_f actor * percent_users_PS mean_users_BE = data_point * load_f actor * percent_users_BE Next da ta_poin t

For conversion of Poisson-distributed call intensity to share cell load per service is utilized:

cell load = ( 1 i

K„

where K_max is calculated according to formula At uplink applies

W* R *SIR ^{max _} R, *S/R[l+/]

At downlink applies

(2) Where W is the bandwidth of the channel, R± is service information rate, and SIR is the value Eb/ (I₀+N₀) which is required for the type of service. For combination of the services (in addition to PS BE) is utilized for discrete faltung the expression:

By use of expression (3) the data services CS and PS are first combined:

data[n] = CS[k] ■ PS[n -k] ( ; i=-∞

where da ta [n] is the probability that the system has the data load n and k is allowed to vary where substantial values exist (in this example 0%-200%}. The step length will be determined by PS according to the algorithm:

For no_users = 0 To (maxusers__PS * 2) cell_load_speech (no_users) = 0 cell__load_CS (no_users) = 0 Next no__users

no_users_speech = 0 no_users_^_CS = 0

For no_users_PS = 0 To maxusers__PS * 2 cell_load_PS (no_users_PS) = pois_PS (no__users_PS) Do Until ( (no_users__PS + 0. 5) / maxusers_PS < no_users_speech / maxusers_speech) Or no__users_speech > maxusers_speech * 2 cell_load__speech (no_users_PS) = cell_load_speech (no_users__PS) + pois__speech (no_ users_speech) no__users_speech = no_users_speech + 1 Loop Do Until ( (no_users_PS + 0. 5) / maxusers_PS < no_users_CS / maxusers_CS) Or no_users_CS > maxusers_CS * 3 cell_load__CS (no_users_PS) = cell__load_CS (no_users_PS) + pois__CS (no_users__CS) no users CS = no users CS + 1 Loop Next no users PS

After faltung of the data services, the result with the speech-service is falted according to the same principle:

P{cell load(%)} = P{ data(%)} * P{speech(%)} ^{( 5 }}

The result of this process of faltung is shown in Figure 1.

For calculation of total distribution of cell load inclusive "PS BE" the following procedure is executed:

- Distribution of total cell load "Speech", CS and PS within interval {0%-100%}, is reflected. - The reflected distribution is after that shifted downwards (towards 0) until mathematical expectation for distribution corresponds to wanted average number of simultaneous users (Erlang) for the service PS BE during rush hour, regarding data point (0-50), according to: min_cell_l oad = maxusers_PS Do mean_load_BE = 0

For no_users_PS = 0 To maxusers_PS mean_load_BE ~ mean_l oad_BE + no_users_PS / maxusers_PS * cell__l oad_BE (no__users_PS)

Next no_users__PS

If mean_load_BE > mean__users_BE / maxusers_BE Then cell_load_BE (0) = cell__load__BE (0) + cell_load_BE (l ) For no__users_PS = 1 To maxusers_PS - 1 cell_load_BE (no_users_PS) = cell_load__BE (no_users_PS + 1) Next no_users__PS cell_load_BE (maxusers_PS) = 0 iτiin_ce22_load = min_cell_load - 1

Else

Exi t Do End If Loop Summed up probability for PS BE now is added to the. cell load point (1-number of steps) which corresponds to the modified reflection point according to:

For no_users_PS = 1 To min_cell_load Cell_load (min_cell_load) = Cell_load (min_cell_load) + Cell_load (min_cell_load - no__users_PS) Cell_load (min_cell__load - no_users_PS) = 0 Next no_users_PS

By this algorithm that value of cell load is found which least has to be occupied by the system to make it possible to transmit/transport data amount according to PS BE. If 100% cell load is not sufficient for transmission/ transport, that traffic (average number of simultaneous users) which is managed during rush hour is specified according to:

If min_cell_load = maxusers_PS Then mean__users_BE •= mean_load_BE * maxusers_PS End If

Then a moment follows to calculate the combined interference and fading margin. From the total distribution of cell load, distribution of interference margin is calculated according to formula:

/_marg = 10 -log₁₀(l - _Ce /θΩi- ) ⁽⁶⁾

The distribution is grouped in whole 1 dB steps according to :

For dB = 0 To inte ference__margin_ max interference_margin_dB (dB) = 0

Next dB no_users_PS = 0

For dB = 0 To inter ference_ argin_max Do Until (dB + 0. 5) < interference margin load (no users PS) interference_ margin_dB (dB) = inter f erence_margin_dB (dB) + Cell_load (no_users_PS) no__users_PS = no_users___PS + 1 If no__users_PS > maxusers_PS - 1 Then

Exi t Do End If Loop

If no__users__PS > maxusers_PS - 1 Then Exit For

End If Next dB

After that, distribution interference margin is falted by/with log normal distribution (indicated standard divergence, 1 dB steps) :

P{FI(dB)} = P {Interference^)} * P{Fαding(dB)} ( 7 )

Result is obtained according to Figure 2. In order to determine at which total fading/interference margin (Flmarg) at which "outage" occurs at selected edge probability, this is searched for in the cumulative distribution according to:

Cum(FI) = Edge probability ( 8 )

Next moment is to calculate cell radius. These calculations are made with support of the specified link budget parameters and with consideration to calculated fading/interference margin.

Cell radius is calculated for the services "Speech", CS and PS. The calculations are executed automatically for the 50 data points corresponding cell load 0-100% (in steps of 2%) and the following data is generated.

- Cell load 0-100%.

- Number of simultaneous users (Erlang) for "speech" - Number of simultaneous users (Erlang) for CS

- Number of simultaneous users (Erlang) for PS

- Max cell radius "speech"

- Max cell radius CS

- Max cell radius PS

- Summed up probability distribution total cell load (control value)

- Number of simultaneous users (Erlang) for PSE BE.

Downlink calculations

Below follows a presentation of the downlink calculations, at which the calls to the services Speech , CS and PS are assumed to be poisson-distributed and independent of each other. The data flow via the PS BE-service is queued by the current communication system depending on the momentary system laod, that is depending on the delay sensitive services .

The program tool calculates the maximal cell radius from 0-100% cell load, in steps of 2%, that is for 50 data points .

For calculation of the maximal cell radius also power calculations are executed in each point.

Combination of services to cell load is performed in corresponding way as for the uplink, but with the difference that the calculation of max number of users per service is made by means of: At uplink applies

W * * SIR

K_m«„ =

R, *SIRll + f]

At downlink applies

( 8 )

Where a is the orthogonality factor which modifies the influence of the interference.

Calculation of combined interference and fading margin is made in corresponding way as for the uplink, but with specific downlink parameters .

Calculation of power, "Outage", is made with consideration to two cases:

1. Max. output power for physical channel is not sufficient at link budget calculation.

2. Max. output power from BTS is not sufficient for the users in the cell. Max cell radius for "outage" according to case 1 above is calculated for respective service: "speech", CS and PS.

At the calculation, calculated fading/interference margin is taken into consideration.

For analysis of "outage" according to case 2 above, analysis zone is selected according to:

r_DL = min[max(r_ψ∞cA),max(r_cs),max(7 _s)] ( 9. Within calculated analysis zone is assumed that the users are uniformly distributed with uniform call intensity. Probability for call at respective "path loss"- distance then can be calculated according to (resolution 50 increments) : radius_prob (0) - 0

For radius = 1 To resolution_radius_prob radius_prob (radius) = (radius ^Λ 2) / (resolution__radius_prob ^Λ 2) - ((radius - 1) ^Λ 2) / (resolution_radius_prob ^Λ 2) radius_loss (radius) =

Walfish_Ikigama__C0ST231_loss(cell_radius_DL * (radius - 0.5) / resolution_radius_prob, Frequency, Hroof , Hbase, Hmobile, w, b, j, metro) Next radius

After that, "path loss"-values are grouped in 3 dB steps according to:

For dB = 0 To ( (max_radius_loss - min__radius_loss) / 3) radius_loss_3dB (dB) = 0 Next dB radius = 0

For dB = 0 To ( (max_radius_loss - min_radius_loss) / 3) Do Until (dB * 3 + min_radius_loss + 1.5) < radius_loss (radius) radius_loss_3dB (dB) = radius_loss_3dB (dB) + radius_prob (radius) radius = radius + 1

If radius > resolution_radius__prob Then Exit Do End If

Loop If radius > resolution_radius_prob Then

Exit For End If Next dB

The result of this calculation is shown in Figure 3, where the "path loss"-distribution is shown. This distribution, however, does not take into consideration variations due to fading or load. In order to handle this, the "path loss"-distribution is falted by/with distribution fading/interference, grouped in 3 dB steps, according to the expression:

P{L_DL(dB)} = P{L_r(dB)} * P{FI(dB)} ( 10 )

The result of this calculation is shown in Figure 4.

The power from BTS now can be summed up for each service by means of the expression:

LrDL ⁺F/m arg

P_sarvi∞ = ∑max[PTx_mia ,min(PTx_ιmx ,PTx(L_DL) - P{L_Dl } - K)] U D i ^UD_nL, =~ min where "path loss" and L_DL, are stepped in 3 dB steps and where K is average number of simultaneous users per service and rush hour, L_rDL is "path loss" in dB at r_DL, and FI_marg is fading/interference margin at selected edge probability.

The power from BTS then will be according to:

PβTS = P_SP^ + PCS + P_PS + P_PSBE + P,_g ,,_ng ^ ) ( 12 !

The power from BTS, in addition to power for signaling, is now tested against BTS max power minus power signaling channels. If this power is exceeded, cell radius is reduced according to the algorithm:

If power_BTS > (max_power_average - pilot_power) * 1000

Then cell__radius_DL =

Walfish_Ikigama_COST231_distance (radius_loss (resolution_rad i us_prob - I) , Frequency, Hroof, Hbase, Hmobile, w, b, j , metro)

Else

Exi t Do

End If Loop The power calculation is repeated until the power condition is fulfilled.

Calculation of the area probability of/for a cell is executed by, for each data point (0-100% cell load) , calculating:

P_ar∞(P_adS = ∑ P{LDL) ⁽13⁾

L_D =mιn

Where path loss and L_DL, are stepped in 3 dB steps.

Output data for the downlink calculations are generated by calculations which are executed automatically for the 50 data points corresponding to cell load 0-100% (2% steps) , at which and the following data are generated:

- Number of simultaneous users (Erlang) for "speech"

- Number of simultaneous users (Erlang) for CS

- Number of simultaneous users (Erlang) for PS - Power per physical channel at cell edge for "speech"

- Power per physical channel at cell edge for CS

- Power per physical channel at cell edge for PS

- Cell radius downlink for weakest service ("speech", CS, PS) - Power from BTS

- Area probability as function of indicated edge probability

- Number of simultaneous users (Erlang) for PS BE

- Power per physical channel at cell edge for PS BE

In the Figures 5-9 are shown examples of after- processing of data from the calculations above. The calculations and the diagrams are examples of how the calculations from the program tool according to the invention can be utilized for network planning purposes at initial planning of mobile communication systems.

The values of the parameters, according to the description above, which have been used, are shown in the following table:

Figure 5 shows a diagram for the cell radius of the uplink and the number of simultaneous users/km² per service as a function of the cell load. The graph for "Selected radius" is the cell radius at which the user density has been calculated.

Figure 6 shows a diagram for the cell radius of the uplink and Gbyte/km² per service as a function of the cell load. The radio coded data density corresponds to the not radio based data density.

Figure 7 shows a diagram for the cell radius of the downlink and the number of simultaneous users/km² per service as a function of the cell load. The diagram shows the same information as for the uplink in Figure 5, besides that the graph for area probability is shown, and that max cell radius for downlink is only calculated for the weakest service . Figure 8 shows a diagram for the cell radius of the downlink and Gbyte/km² per service as a function of the cell load. The diagram shows the same information as for the uplink in Figure 6.

Figure 9, finally, shows the power of the downlink as a function of the cell load.

Claims

PATENT CLAIMS

1. Procedure to facilitate cell planning in cellular radio communication networks, including to calculate a link budget for a cell, at which the link budget includes a varying interference and fading margin the size of which ^■ depends on the total traffic from a plurality of service types which are utilized within the cell and where the total traffic is calculated by a combination of the distribution of traffic of/for the different service types and where said interference and fading margin is determined by said combination.

2. Procedure as claimed in patent claim 1, at which the combination of the distribution of traffic at least partially is made by means of faltung of distributions of traffic regarding at least two of the service types.

3. Procedure as claimed in patent claim 1 or 2, at which the service types include a speech service, a circuit switched data service, a first packet switched data service and a second packet switched data service the data flow of which varies depending on the data flow from/of the speech service, the circuit switched data service and the first packet switched data service.

4. Procedure as claimed in patent claim 3, at which the combination includes:

- faltung of the distributions of traffic of/for the circuit switched data service and the first packet switched data service, whereupon resulting distribution is subject to faltung by/with the distribution of traffic of the speech service, whereupon resulting distribution is combined with the second packet switched data service.

5. System to facilitate cell planning in cellular radio communication networks, including devices to execute a procedure according to any of the patent claims 1-4.

6. System as claimed in patent claim 5, including at least one computer.