Docstoc

908

Document Sample
908 Powered By Docstoc
					                  INTERNATIONAL TELECOMMUNICATION UNION

                  RADIOCOMMUNICATION                                  Document 8F/908-E
                  STUDY GROUPS                                        27 March 2003
                                                                      English only
                  10TH MEETING OF WORKING PARTY 8F
                  PORTO SEGURO, 26 MARCH – 3 APRIL 2003
Source:    Documents 6S/317, 6S/320, 6S/337
                                                                                   SPECTRUM



                                     Working Party 6S

                  LIAISON STATEMENT TO WP 8F FROM WP 6S

   PDNR “PROBABILISTIC METHODOLOGY FOR THE ASSESSMENT OF
 INTERFERENCE FROM NON-GSO BSS (SOUND) INTO TERRESTRIAL IMT-
                             2000
                 IN THE BAND AROUND 2.6 GHz”

The attached PDNR “Probabilistic methodology for the assessment of interference from non-GSO
BSS (sound) into terrestrial IMT-2000 in the band around 2.6 GHz” has been reviewed by WP 6S.
Within the discussions of WP 6S and also JRG 6S-8F (See Document 6S/337), several areas of
concern were identified as well as areas where further work is necessary on this PDNR. These
concerns and areas for further work are summarized in the attached PDNR. WP 8F is invited to
review the contents of this PDNR and forward any comments to WP 6S in an effort to progress the
work on this methodology. WP 6S notes that this PDNR should be developed jointly with WP 8F.



Attachment 1: Document 6S/TEMP/176 (edited)




C:\DOCSTOC\WORKING\PDF\B2C5A9B4-C26A-4416-877C-E59BB6C5C62F.DOC                           16.08.12   16.08.12
                                                  -2-
                                                8F/908-E

                                             Attachment

Source:      Document 6S/TEMP/176


           PRELIMINARY DRAFT NEW RECOMMENDATION ITU-R BO.

Probabilistic methodology for the assessment of interference from non-GSO BSS
 (sound) systems into terrestrial IMT-2000 systems in the band around 2.6 GHz
The PDNR in Attachment 2 contains a methodology for the assessment of interference from non-
GSO BSS (sound) systems into terrestrial IMT-2000 systems in the frequency band around 2.6
GHz. It is noted that WP 6S and WP 8F have jointly developed a PDNR that contains another
methodology that addresses this same topic. The methodology in the attached PDNR takes a more
probabilistic approach to the assessment of interference than that methodology. During the WP 6S
meeting, several concerns and areas for further work were identified related to the attached PDNR
and these are included as Attachment 1.



                                            Attachment 1

      Comments on PDNR “Probabilistic methodology for the assessment of
                             interference from
        non-GSO BSS (sound) systems into terrestrial IMT-2000 systems
                       in the band around 2.6 GHz”
The statistical approaches proposed in the PDNR in Attachment 2 are basically averages of
“interference levels” received at IMT-2000 stations located evenly on Earth, and suffering
aggregate interference from an assumed constellation of non-GSO BSS (sound) satellites/systems.
The “statistics of interference” calculated at an IMT-2000 station are proposed to be evaluated in
terms of Isat/Nth statistics, or in terms of “availability loss” statistics using the methodology
contained in 6S/238, attachment 11: “working document towards a PDNR on the methodology for
determining the availability loss of terrestrial mobile base stations due to satellite interference” (see
6S-8F/22, sections 3.1.2 and 3.1.3).

1         Isat/Nth statistics
The Isat/Nth statistics using “Approach A” could be labelled “risk assessment method”: it is a
geographical averaging of Isat/Nth levels obtained with 6S-8F/22’ Approach A in section 3.1.1 on
each IMT-2000 station, hence including averaging over the IMT-2000 station orientations, latitudes
and longitudes. Hence the records obtained with this approach could be interpreted as the “risk” an
IMT-2000 station may receive a given Isat/Nth level… Several input documents to WP 6S and to
the JRG 6S-8F show that the BSS (sound) systems’ need for high power levels on their service area
will necessitate the use high performance directive antennas on board BSS (sound) space-stations.
These documents show then that the areas on Earth receiving the most important levels of
interference and seen with high elevation angles by the satellites will be distributed on a “belt” of
several tens or thousands of kilometres around the BSS (sound) service area (the belt’s wideness
depending on the antenna roll-off performance). This means that the “risk” would certainly not be



C:\DOCSTOC\WORKING\PDF\B2C5A9B4-C26A-4416-877C-E59BB6C5C62F.DOC                                    16.08.12   16.08.12
                                                 -3-
                                               8F/908-E

equally distributed over the Earth, and the averaging technique as proposed is therefore likely to
hidden evident very high risks of interference in potential victim countries whishing to implement
IMT-2000 stations and situated in the vicinity of a potential BSS (sound) service area. Therefore it
is anticipated that the results produced by this averaging technique would provide very poor
information or even misleading information that could be used in the context of specific co-
frequency interference situations assessment involving BSS (sound) and IMT-2000 systems.

2       Availability loss using Annex 2 of PDNR
The “availability loss” methodology contained in Annex 2 of the PDNR aims to be applied in any
case involving terrestrial cellular systems in the Mobile Service and satellite interferers, special
considerations being made regarding terrestrial cellular CDMA systems. Working Party 6S has
received several liaisons statements making observations on this document, at its September 02
meeting in Geneva (see 6S/253, 6S/256). The observations mainly address concerns about the
limitation of this document’s considerations to the outage of one single link, and its subsequent lack
of accuracy to meaningfully address the “availability loss” (or capacity loss) of terrestrial cellular
mobile systems, and in particular in CDMA IMT-2000 systems.
In summary, the outage of one single link is expressed as a signal availability, which is calculated in
absence, and in presence, of satellite external interference. The loss of availability of this link is
then calculated from the difference between the two signal availability results: this approach is akin
to an approach in terms of “C/N+I” degradation for the link into consideration. The methodology
then proposes averaging methods to assess a “loss of availability” on a terrestrial cellular deployed
network. Basically, the document considers that a cell in a cellular network is a set of several single
links, each of which is living independently in a given environment (characterised by a level of
noise rise, determined through parametrical equations taking into consideration a “cell load” factor
and an other factor standing for “perfect, or imperfect, power control”). This assumption is the main
reason why the proposed methodology does not reflect the specificities of a terrestrial CDMA
cellular systems, and in particular the necessary power control associated with this technology. A
cell and its load or number of users, is not to be considered as a set of independent links, but rather
as a set of links which are dependant to each other and monitored through power control algorithms
to optimise the overall CDMA system performance, which is compound of three interlinked
parameters (cell capacity or cell load, quality of service offered to the users, and the coverage of the
cells). Document 6S/238 attachment 11 concludes in particular that the “loss of availability” due to
satellite interference over a cell is independent of its load, whereas it has been shown in other
studies that the effect of satellite interference over heavily loaded cells (which are capacity limited)
is lower in terms of capacity loss than over lightly loaded cells (which are coverage limited), all
other parameters being fixed (cell range and quality of service). This shows that this “signal
availability loss”-derived methodology is unproper to assess the global impact of satellite
interference into cellular systems, that is : on an overall network of cells, each cell containing a
number of users whose individual quality of service, distance from the base stations, and transmit
power are monitored globally by the base stations, with dedicated power control algorithms.
In addition to that, documents 6S/253 and 6S/256 (section 4) also underlines that the working
document in 6S/238 Attachment 11 conveys some erroneous ideas about terrestrial CDMA cellular
systems.
Furthermore, it is unclear in the proposed methodology how the results in terms of “availability
loss” are meant to be presented, but would the intent be to further average again the results over
location and orientation of the IMT-2000 base stations, then the comments concerning the “risk
availability approach” would apply in addition to the ones presented here.




C:\DOCSTOC\WORKING\PDF\B2C5A9B4-C26A-4416-877C-E59BB6C5C62F.DOC                                  16.08.12   16.08.12
                                                 -4-
                                               8F/908-E

                                          Attachment 2

           PRELIMINARY DRAFT NEW RECOMMENDATION ITU-R BO.
Probabilistic methodology for the assessment of interference from non-GSO BSS
(sound) systems into terrestrial IMT-2000 systems in the band around 2.6 GHz1
                               (QUESTIONS ITU-R 204-1/10 AND 229/8)

The ITU Radiocommunication Assembly,
         considering
a)    that a methodology is required to assess the aggregate interference to IMT-2000 from non-
GSO BSS (sound) for the technical study as invited in Resolution 539 (WRC-2000),
         recognizing
a)      that as far as space services are concerned, the band 2 535-2 655 MHz is allocated on a
primary basis to BSS (sound) and complementary terrestrial broadcasting service under RR No.
5.418;
b)      that BSS (sound) systems under RR No. 5.418 are subject to RR Resolution 528 (WARC-
92) and that these systems are not subject to the pfd limits in RR Table 21-4;
c)       that WRC-2000 adopted Resolution 539 which, inter alia, contains provisional pfd
threshold levels for non-GSO BSS (sound) systems under RR No. 5.418 and invited ITU-R to
conduct the necessary technical and regulatory studies in time for WRC-03 relating to frequency
sharing in the band 2535-2655 MHz with a view to avoiding placing undue constraints on either
service (see Res. 539);
d)     that the band 2 500-2 690 MHz band is also identified in RR No. 5.384A for use by
Administrations wishing to implement IMT-2000 in accordance to Resolution 223 (WRC-2000);
e) that RR No. 5.384A states this identification does not preclude the use of these bands by any
application of the service to which they are allocated and does not establish priority in the Radio
Regulations;
         further considering
        that the preliminary draft new recommendation “A methodology to assess interference from
BSS (sound) into terrestrial IMT-2000 systems intending to use the band 2 630-2 655 MHz” can
also be used to assess interference from, and possible impact of, BSS (sound) on terrestrial IMT-
2000 systems intending to use the band 2 630 - 2 655 MHz in the context of co-frequency operation
through the development of pfd masks,
         recommends
1      that the methodology described in Annex 1 of this Recommendation could be used for the
assessment of interference from non-GSO BSS (sound) systems into terrestrial IMT-2000 systems.

____________________
1   It should be noted that, in accordance with Resolution 528 (WARC-92), broadcasting-satellite
    service (sound) systems may only be introduced within the upper 25 MHz of the band 2 535-2
    655 MHz.


C:\DOCSTOC\WORKING\PDF\B2C5A9B4-C26A-4416-877C-E59BB6C5C62F.DOC                                 16.08.12   16.08.12
                                                 -5-
                                               8F/908-E

                                              Annex 1

    Probabilistic methodology for assessing the potential interference from non-
                GSO BSS (sound) systems into terrestrial IMT-2000

1        Input data and scenarios
1.1      Characteristics of the systems
A given scenario will consist of non-GSO BSS (sound) systems interfering into IMT-2000 systems
(base and/or mobile stations).

1.1.1    IMT-2000 stations2
•        Receiver characteristics:
         – thermal noise level (dBW/MHz);
         – noise factor (dB);
•        Antenna characteristics:
         – maximum gain (dBi);
         – polarization;
         – feed loss;
         – 3 dB beamwidth3;
         – vertical and azimuthal antenna radiation patterns over a range of elevation angles2;
         – downtilt of the antenna2;
         – site sectorization2;
•        Location of the receivers (for example, an area bounded by latitude(s) and longitude(s)
         data).

1.1.2    Non-GSO BSS (sound) systems
Although the orbital simulation approach (including time variation of the satellite) requires more
complex simulation tools, this approach will produce more accurate results and is recommended for
the accurate pfd assessment. The following orbital elements and characteristics are required.
•       Orbital elements (Inclination angle, altitude of apogee, altitude of perigee, argument of
        perigee, longitude of the ascending node)
•       Orbital characteristics (the number of active satellites in the active arc, start of active arc,
        and end of active arc etc.)
•       The respective positions of non-GSO satellites are defined by longitude, latitude and height
        which can be determined from orbital elements and characteristics.
Information on the polarization used by the satellite transmitters would be required to assess
polarization discrimination if needed (see factor Pi in equations 1 in section 3.1.1).
The following example models could be used in the analysis:
____________________
2   Additional system specific input parameters for IMT-2000 stations would be required for usage
    of methods in section 3.1.3.
3   Only applies to base station receivers.


C:\DOCSTOC\WORKING\PDF\B2C5A9B4-C26A-4416-877C-E59BB6C5C62F.DOC                                  16.08.12   16.08.12
                                                                              -6-
                                                                            8F/908-E

–           Model 1 : A number of equally spaced non-GSO systems with synchronization: All have
            their “active arc” located in the northern hemisphere. The orbital parameters are identical to
            those given in the above table with the constellations separated synchronously.
–           Model 2 : A number of equally spaced non-GSO systems without synchronization: All have
            their “active arc” located in the northern hemisphere. The orbital parameters are identical to
            those given in the above table with the constellations separated non-synchronously.
Model 1 is easier one to perform calculations and not far from the realistic situation because the size
of the “active arcs” of the each non-GSO BSS (sound) systems are small to have the minimum
elevation angles of not less than 40 deg over their service areas and the difference between the
results of Model 1 and those of Model 2 is expected to be small.
Model 2 is expected to bring the most realistic results.

2           Results
Presentation of the results
The results are expressed as statistics of Isat/Nth received at IMT-2000 stations.
The results are also expressed as statistics of the reduction in the signal availability (see Annex 2).

3           Method of calculation and production of the results
3.1         Assessment of the interference into an IMT-2000 base station
In the analysis for the pfd assessment, IMT-2000 base stations at latitudes varying in 10
increments from XoN to YoN are evaluated (X and Y can be determined from the visible surface
area of the Earth from the non-GSO BSS (sound) satellite). At each latitude, it is assumed that there
is an IMT-2000 base station located at every 1 of longitude. Each base station antenna azimuth is
also varied from 0 to 360 in 10 steps.

3.1.1       Aggregation of the interference from multiple satellites into a given IMT-2000 base
            station receiver
The calculation steps for the aggregation of the satellites interference are summarized below:
–           considering a set of non-GSO satellites distributed on the 360° longitude around Earth;
–           considering given pfd threshold values applicable to non-GSO satellite;
–           considering an IMT-2000 base station with sectoral antenna, characterized by its latitude,
            longitude and orientation;
–           the azimuth and elevation, hence the gain of the antenna depends on the location of the base
            station (latitude, longitude) with regard to the satellite under consideration;
–           calculation of the aggregate interference at the receiver entrance from all co-frequency
            visible satellites (whose elevation is positive) and the subsequent Isat/Nth IMT-2000 base
            station receiver (sector) at a given latitude and longitude (lat, long), and pointing in a given
            direction (orientation, tilt angle) from all co-frequency visible satellites and the subsequent
            Isat/Nth is given by the following formula:
                                                      
                                                        pfd ( elevation _ ti ( t )) G ( azimuth _ oi ( t ),elevation _ ti ( t ))10 log  
                                                                                                                                           2               
                                                                                                                                                   FL  Pi       
                                            1 n _ sat                                                                                                        / 10 
Isat
     lat, long, orientation, t   10 log       10
                                                                                                                                            4 
                                                            i
                                                                                                                                                          
                                                                                                                                                                   
                                                                                                                                                                      (1)
Nth                                         Nth i 1                                                                                                        
                                                                                                                                                                    
                                                                                                                                                                   




C:\DOCSTOC\WORKING\PDF\B2C5A9B4-C26A-4416-877C-E59BB6C5C62F.DOC                                                                                              16.08.12       16.08.12
                                                       -7-
                                                     8F/908-E

where:
Isat
       Nth
             lat, long, orientation, t  (dB)   is the resulting aggregate Isat
                                                                                Nth
                                                                                    from all co-frequency
                                                 satellites at the IMT-2000 receiver;
         Isat          The appropriate approach to calculate Isat/Nth should relate to the appropriate
                Nth
                                                 criterion of Isat/Nth for the co-primary sharing. Isat/Nth is
                                                 calculated at a given base station location as a result of the
                                                 transmissions of multiple non-GSO BSS (sound) systems ;

pfdi(elevation) (dBW/m2/MHz) is the pfd at the IMT-2000 station from visible BSS (sound) satellite
                                          i;
G(azimuth_oi ,elevation_ti) (dBi)is the gain of the IMT-2000 base station antenna for the off-axis
                                          angle towards the satellite i;
Elevation_ti (°) is the absolute elevation together with the tilt angle from the base station to the
                                          satellite i; it is the elevation angle (the angle of arrival of
                                          the satellite i incident wave to the IMT-2000 station,
                                          above the horizontal plane), plus the tilt angle (a downtilt
                                          angle is a negative value);
 Azimuth_oi (°) is determined by the longitude and latitude of the base station together with its
                                          orientation relative to the satellite i; it is the azimuth angle
                                          (North pole, IMT-2000 station, satellite i), plus the
                                          orientation of the IMT-2000 station with regard to the
                                          North direction on Earth;
               (m) is the wavelength;
      FL (dB) is the IMT-2000 receiver feeder loss;
       Pi (dB) is the expected averaged polarization discrimination between transmitting antenna
                                        of satellite i and the IMT-2000 base station receiving
                                        antenna;
         n_sat is the number of satellites ;
 Nth (W/MHz) is the IMT-2000 station receiver thermal noise.


3.1.2    Evaluation using Isat/Nth Statistics
This approach determines the probability that an IMT-2000 base station will experience different
Isat/Nth levels (see Section 3.1.1).
For the analysis, simulations are performed to calculate the interference into an individual base
station. The simulation takes into account each satellite that is visible to the base station and is
located within its “active arc”. For a given latitude, longitude and azimuth combination for the
IMT-2000 base station, the orbital positions of each satellite (in all of the constellations) is updated
for each time increment. At each time increment, the point angles (azimuth and elevation) from the
base station location to the active satellite in each constellation are calculated. For each satellite that
is visible to the base station location, the azimuth and elevation off-pointing angles (i.e., the angles
between the direction the base station is pointing and the direction to the satellite) are calculated.
The gain of the base station antenna in the direction of each visible active satellite is then
calculated. The satellite power-flux density is determined from the power-flux density mask that is



C:\DOCSTOC\WORKING\PDF\B2C5A9B4-C26A-4416-877C-E59BB6C5C62F.DOC                                         16.08.12   16.08.12
                                                   -8-
                                                 8F/908-E

assumed in the analysis and the elevation angle from the base station location to the satellite. The
interfering signal power received by the base station from each visible satellite is calculated. The
aggregate interfering signal power received by the base station from all visible active satellites is
then calculated, as is the Isat/Nth due to the interference from all visible active satellites. This process
is repeated for each azimuth at a given latitude and longitude location. This process is repeated for
each longitude at a given latitude in accordance with the approach described in Section 3.1.1. The
maximum and average Isat/Nth levels received for all base stations at a given latitude are also
calculated.
The percentage of base stations where Isat/Nth exceeds at the interest level should be compared to the
appropriate criterion for the co-primary sharing. Further study will be required to establish the
appropriate criterion for the co-primary sharing.

3.1.3   Evaluation using signal availability
After Isat/Nth level is obtained at the point of interest, the methodology in the Annex 2 should be
taken for the signal availability evaluation.
The reduction of signal availability with respect to the design value should be compared to the
appropriate criterion for the co-primary sharing. Further study will be required to establish the
appropriate criterion for the co-primary sharing.

3.2 Assessment of the interference into an IMT-2000 mobile station
In the analysis for the pfd assessment, IMT-2000 mobile stations at latitudes varying in 10
increments from XoN to YoN are evaluated (X and Y can be determined from the visible surface
area of the Earth from the non-GSO BSS (sound) satellite). At each latitude, it is assumed that there
is an IMT-2000 mobile station located at every 1 of longitude.
For the I/N evaluation, the calculation methodology in 3.1.1 and 3.1.2 could be used. The
evaluation methodology for the signal availability of mobile stations should be further studied.

                                                Annex 2

    Methodology for determining the availability loss of terrestrial mobile base
                      stations due to satellite interference


1       Introduction
This contribution presents a methodology for estimating the effect of potential satellite interference,
Isat, from either GSO or non-GSO satellites on the performance of cellular systems. The
methodology is demonstrated for the case of cellular uplinks (mobile to base station) using CDMA
signalling, but has application to the downlink (base to mobile) as well as to other signalling
techniques. In the analysis presented, the effect of Isat (interference power from satellites) is
measured in terms of reduced cellular system signal availability as a function of the ratio of satellite
interference to system thermal noise Isat/Nth. It is demonstrated that the reduction in signal
availability due to Isat is the most appropriate measure of loss in cellular system.
The analysis presented shows that the effect on signal availability is small for Isat/Nth < 0 and that
for future cellular systems economic measures are available to offset the potential effect of Isat.
The low impact of Isat is due, in large part, to the margin required in the design of the cellular
system to address the statistical nature of the propagation medium. The typical design goal of 95%



C:\DOCSTOC\WORKING\PDF\B2C5A9B4-C26A-4416-877C-E59BB6C5C62F.DOC                                      16.08.12   16.08.12
                                                  -9-
                                                8F/908-E

availability at the edge of coverage requires that the cellular system be designed to accommodate
statistical variations of greater than 30 dB. This is very large relative to a possible increase of 1 dB
in overall system noise plus interference (N+I).
Precedence exists for using an acceptable reduction in system performance as the basis for
determining acceptable levels of Isat with specific examples being:
1)      In establishing pfd limits in the band 3 700-4 200 MHz for satellite systems, the effect of
        potential interference into the terrestrial fixed point to point microwave stations was
        evaluated on the basis of allowing a certain level of interference for a given percentage of
        time.
2)      In considering the introduction of the Skybridge system in sharing with BSS systems in the
        12.2 to 12.7 GHz band, the allowable levels of interference from Skybridge into existing
        BSS systems was based on an increase in BSS outage time as contained in
        Recommendation ITU-R BO.1444.
These two cases dealt with the accommodation of new technologies within the ITU frequency plan.
Basing allowable levels of interference on a performance basis is appropriate for the analysis of
sharing between co-primary services.

2       Basic approach
First, the performance of a cell at edge of coverage is considered. A basic design parameter for the
cell is the signal availability at the edge of coverage, Ase, which is the probability that a typical user
can achieve service with the minimum required Eb/No. A typical design value for Ase is 95%.
In order to analyse cellular system performance it is helpful determine the required mean signal at
the base station receiver for a user transmitting at full power from the edge of coverage. This can be
determined from Ase, the required Eb/No, the noise and interference levels at the base station
receiver and the statistical variation of the desired signal. The availability at edge of coverage when
Isat is present and not present can then be determined. Figure 1 illustrates the process for
determining the impact of Isat at the edge of coverage as the difference in system availability with
and without Isat. The reduction in signal availability is illustrated as the darkened portion of the
signal statistical distribution at the edge of coverage.
The propagation model then provides the means for extending this basic approach to the analysis of
performance at any distance from the base station.
The cellular system performance measures used in evaluating the impact of Isat are:
Ase = Signal availability at the edge of the cell in %.
Asa = Signal availability averaged over the entire cell in %.

2.1     Signal, noise and interference at edge of coverage
Table 1 presents computations of the basic signal, noise and interference levels for a typical cellular
system. The computation of N+I is shown on lines 1-24 for the cases of "without Isat" and "with
Isat". The impact of Isat on overall N+I is given on line 25. The determination of mean signal at
edge of coverage, based on a specified Ase, is given in lines 26-31. In a cellular, spread spectrum
system, interference is contributed from other users. The internally generated interference or
interference resulting from other users, relative to the sum of thermal noise plus Isat at the base
station receiver as given on line 20 is given by:

                                          Ii = 10 log (L/(1L))                                        (1)




C:\DOCSTOC\WORKING\PDF\B2C5A9B4-C26A-4416-877C-E59BB6C5C62F.DOC                                    16.08.12   16.08.12
                                                 - 10 -
                                               8F/908-E

Where L is the normalized loading relative to the theoretical maximum, or pole capacity. In
selecting the appropriate value for L, allowance is made for interference from users in adjacent
cells. The cellular system will be operating with power control so that all user signals arrive at the
base station with the same signal level. The user transmitter levels are set so that the received
signals are the minimum level to maintain the required Eb/No for all users. However, to represent
realistic conditions in which the other user signals can exceed the desired value since power control
is not perfect, an allowance for power control error of 1 dB is made. The noise from other users is
modelled as being 1 dB higher than that for the case of all user signal arriving at the base station
receiver with equal level.
The signal variation, in location, from any distance to the base station is modelled as a lognormal
distribution with 8-10 dB standard deviation [See References 1 and 2]. The mean required signal
level to provide the desired Ase, can then be determined as given in line 31.
The first column of Table 1 presents the basic signal, noise and interference parameters for the case
where Isat is not present with the second column presenting the values for the parameters, which
change due to the presence of Isat. Isat is specified in terms of the system thermal noise level as
shown in row 13. The net effect of the presence of Isat relative to the overall N+I, is shown on
line 25.

2.2      Signal, noise and interference at any point in the cell
The noise and interference levels at the base station receiver are independent of user location within
the cell. The internal interference, Ii (Equation 1) is only dependent upon the number of users
within the cell as specified by the loading ratio, L.
The propagation model is illustrated in Figure 1 with the mean signal received at the base station
receiver, for points not close to the base station, Pr, given by:

                                             Pr  k / D b                                             (2)

Where:
            D=    distance of the user from the base station,
             b=   power law coefficient.
            k=    a constant including mobile power and antenna heights and gain
            Pr=   mean signal level at the base station receiver
For the Hata and CCIR propagation models, 3.52 <b<3.84. The signal variation in location, for any
distance to the base station is modelled as a lognormal distribution with an 8 to 10 dB standard
deviation [Reference 1 page 247, Section 2.2.3]. In the sample computations presented below, the
propagation model is based on a power law coefficient of 3.84 and a standard deviation of 8 dB.
From the basic propagation model given in Equation 2, the mean signal at any distance from the
base station can be determined from:

                                            Pr  Pe( Rd )b                                            (3)

Where:
           Pe = Mean signal level at edge of cell coverage
           Rd = (De/Ds) is the distance ratio
           De = distance to the edge of coverage



C:\DOCSTOC\WORKING\PDF\B2C5A9B4-C26A-4416-877C-E59BB6C5C62F.DOC                                 16.08.12    16.08.12
                                                 - 11 -
                                               8F/908-E

           Ds = distance to the point of interest

3       Signal availability with uniform traffic density
For convenience in computing the impact of Isat, the cell is divided into rings with the impact of
Isat computed for each ring. Figure 2 presents the procedure for dividing the cell area into a number
of rings. The width of each ring is determined such that little variation in system performance
occurs throughout the ring. Equation 3 provides the basic method for performing the analysis on a
normalized basis independently of the actual cell size. The radii of each ring need only be specified
relative to De. The performance within each ring is represented as the performance at the average
radius of the ring.
The mean signal levels at the center of each ring can be determined from Equation 3 since the signal
level at edge of coverage has been determined. The statistical distribution of the received signal at a
point removed from the edge of coverage is illustrated in Figure 1.
The widths of the outer rings are smaller than the width of the inner rings since the impact of Isat on
the performance in the outer rings is suggesting a higher degree of resolution. The performances
within each ring are weighted by the area of the ring relative to the total cell area and summed to
determine the impact on signal availability due to the presence of Isat. Weighting signal availability
by the area of the ring is consistent with an assumption of uniform traffic, or user, density.

3.1     CDMA system operation and user available power margin
In a CDMA spread spectrum cellular system, power control of the mobile transmitters is used to
equalize the signal received at the base station receiver for all users, with the mobile or user
transmitter power being set to the minimum required to achieve the desired Eb/No at the base
station receiver. The user available margin, shown on Figure 1, is the difference between the signal
at the base station for maximum user transmitter power available to a mobile and the signal at the
base station necessary to achieve the required Eb/No at the base station receiver.
If the user has available power margin greater than the noise increase due to Isat, the transmitted
power is increased to overcome the effect of Isat. In the analysis to follow the impact of Isat is
measured in terms of the reduction in signal availability at the edge of the cell, Ase, and the
reduction in signal availability averaged over the entire cell, Asa. Both parameters are determined
based on the assumption that the mobile transmitter is free to transmit at full power if required.

3.2     Computation of Signal Availability
Table 2 presents sample computations for the % of users not served within each ring with each
column corresponding to a ring. Lines 34-42 and 43-51 show computations of availability loss with
and without Isat, respectively. The difference is the availability loss due to Isat as given on line 52.
The maximum radius of each ring is presented in both lines 34 and 43 on a normalized basis relative
to the cell radius. The percent of the total cell area within each ring is given on lines 36 and 45.
The mean signal level at edge of coverage is given in line 31 of Table 1 and Equation 2 provide the
basis for computing the mean signal at the average radius of each ring as given in rows 38 and 47 of
Table 2. Basically, the user not served does not have sufficient power to overcome N+I and an
unfavorable propagation condition.
As the radius of the rings decrease the users have additional power margin and the probability of
not being served is reduced. The probability (in %) within the ring of not being served is given in
lines 40 and 49. The probability of no service within the ring is weighted by the normalized area to
give the percentage of the total cell subscribers not being served as shown in lines 41 and 50. The
percentage of unserved users within each ring can then be summed to obtain the average



C:\DOCSTOC\WORKING\PDF\B2C5A9B4-C26A-4416-877C-E59BB6C5C62F.DOC                                  16.08.12   16.08.12
                                                   - 12 -
                                                 8F/908-E

unavailability within the cell as given in lines 42 and 51. The difference is the overall reduction in
signal availability due to the presence of Isat, as shown on line 52. Figure 3 presents the reduction
in Asa due to Isat as a function of Isat/Nth and Ase. Figure 4 presents results for different
propagation model parameters illustrating that availability loss due to Isat is not sensitive to power
law coefficient and signal standard deviation over the range of accepted value.
The reduction in signal availability is independent of the design value for cell loading when the cell
is operating at design cell loading. When the cell is operating with less loading than the design
value, the reduction in availability due to Isat is less than that when operating at design loading.
Accordingly, the reduction in availability presented in Figures 3 and 4 is the upper bound on
availability loss for a given Ase and Isat/Nth. For a given Ase, the loss in availability is also found to
be independent of the system thermal noise level and the required Eb/No. Both, however, are
factors in determining Ase.
As can be seen from Figures 3 and 4, the reductions in overall signal availability is small, especially
for systems designed with high Ase. Typically, Ase  95% in cellular system design. Table 3 presents
a summary of the reduction in both Asa and Ase for Ase = 95% and Isat/Nth = 6 and 10 dB.
Figure 5 shows the variation of availability with loading expressed relative to the design loading.
The reduction in loading leads to an increase in both Ase and Asa.

3.3     Considerations in cellular system design
Although the impact of Isat on cellular system performance is small, it can be taken into account in
the design of new systems with a corresponding increase in the design value of Ase. Methods for
achieving this include reduction in base station receiver noise, increase in mobile transmitter power
and with slight increases in base station antenna gain and height. The overall effect on receiver
N + I for Isat/Nth = 6 dB is 0.97 dB.
From the standard propagation models summarized in Reference 1, signal level increases
approximately in proportion to the square of the receiving antenna height so that n increase of 5%
would overcome a 1 dB increase in N+I. Other means include reduction in cell size and in the
loading for each cell in accordance with Figure 5 which presented the variation of availability with
system loading. It would be necessary to reduce the loading by approximately 25% in order to
maintain Ase at 95%. Similarly a reduction in cell area of approximately 8% would be required to
offset a 1 dB increase in N+I. It is concluded that compensating for Isat with a reduction in either
cell loading or cell size should not be considered in estimating the economic impact of Isat as far
more economic measures are available.

4       Effect of non-uniform or random traffic density on availability loss
The results presented in Figures 3 and 4 are based on the assumption of geographically uniform user
distribution over the cell coverage area. Additional analysis has been performed to investigate the
effect that random user distributions throughout the cell would have on loss of signal availability in
order to determine the sufficiency of the uniform user distribution assumption. Availability loss
computations were performed for 50 and 20 users respectively with 50 trials being performed for
each case. For each trial, random user locations were generated for each user. The ratio of the
number of users in each ring to the total number of users was used in place of the normalized area
on line numbers 36 and 45 in Table 2, and used to weigh the "Unavailability" in lines 40 and 49 to
determine the percent of the total cell subscribers not being served within the ring.
Table 4 presents the variation in availability loss results for the random user distribution trials. As
seen in the results, the standard deviation and statistical range of signal availability loss for different
percentiles is quite small. The variance of the results is slightly greater for the case of 20 randomly



C:\DOCSTOC\WORKING\PDF\B2C5A9B4-C26A-4416-877C-E59BB6C5C62F.DOC                                     16.08.12   16.08.12
                                                 - 13 -
                                               8F/908-E

positioned users. It is concluded that additional investigation of availability loss can be made with
the "uniform user distribution model".

5       Summary and conclusions
A method has been presented for determining the impact of satellite interference into cellular
systems. The method is based on the use of edge of coverage signal availability, which allows for
analysis to be performed on a normalized cell with results independent of actual cell dimensions.
This method can be used in sharing studies since it presents a direct measure of the reduction in
signal availability within a cell as a result of potential satellite interference.
The results presented are based on uniform geographic user, or load, distribution over the cell
service area under consideration. It has been demonstrated through a combination of statistical
analysis and simulation techniques that random load distribution does not alter the results to any
significant degree. Further the results are not sensitive to the power law coefficient and standard
deviation of the lognormal distribution used to characterize the propagation model.
For a given signal availability at edge of coverage, the loss in availability due to satellite
interference is found to be independent of cellular loading, required Eb/No and system thermal
noise level when the system is operating at design loading. For system loading less than the design
value, the Availability loss due to Isat is always less than for the case when operating at design
loading. The overall availability loss in the cell for Isat/Nth = 6 dB is less than 0.5 %, with the
overall increase in N+I being 0.97 dB.
The impact on cellular system design is small with several economic design measures available to
compensate for Isat/Nth = 6 dB. It is concluded that compensating for Isat with a reduction in either
cell loading or cell size should not be considered in estimating the economic impact of Isat on
cellular operation, as far more economic measures for compensating for Isat are available. Methods
for achieving this include reduction in base station receiver noise, increase in mobile transmitter
power and with slight increases in base station antenna gain and height. The overall effect on
receiver N + I for Isat/Nth = 6 dB is 0.97 dB.


                                          REFERENCES
[1]     CDMA Systems Engineering Handbook, Lee and Miller, Artech House, 1998.
[2]     Recommendation ITU-R M.1225, Guidelines for Evaluation of Radio Transmission
        Technologies for IMT-2000, (Question ITU-R 39/8) and 2)).




C:\DOCSTOC\WORKING\PDF\B2C5A9B4-C26A-4416-877C-E59BB6C5C62F.DOC                                 16.08.12   16.08.12
                                                   - 14 -
                                                 8F/908-E

                                            TABLE 1
                          System Signal, Thermal Noise and Interference
                          System Thermal Noise
                            at Receiver Input
                                                                   No Isat    w/Isat
              1    Rec Noise Figure                          dB         4
              2    Feeder Loss                               dB         2
              3    Ant Temp                                  deg      290
                                                              K
              4    Portion of Energy not absorbed by                  0.63
                   feeder
              5    Portion of Energy Absorbed by Feeder               0.37
              6    Room Temp                                 K      290.00
              7    Rec temp                                  K      438.45
              8    Feeder Loss Temp                          K      107.02
              9    Ant Temp @ Rec                            K      182.98
              10   System Temp, Nth                          K      728.45
              11   System Noise Figure                       dB       5.46
                   Noise + Interference
              12   Sys Thermal Noise /MHz                    dBW   139.98   139.98
              13   Isat/Nth                                  dB                6.00
              14   Isat                                      dBW             145.98
              15   Isat+Nth                                  dBW   139.98   139.00
              16   Cell Loading in %                         %       50.00     50.00
              17   Voice/Data Average Activity               %       75.00     75.00
              18   Increase in Load from other Cells         %       33.00     33.00
              19   Overall Loading                           %       49.88     49.88
              20   Noise due to cell loading re:(Isat+Nth)   dB      0.02     0.02
              21   Power Control Error                       dB       1.00      1.00
              22   Noise due to cell loading w/o PCE         dBW   140.00   139.02
              23   Noise due to cell loading with PCE        dBW   139.00   138.02
              24   (N+I) total                               dB    136.45   135.48
              25   Impact of Isat to tot Noise               dB       0.97
                   Required Signal
              26   Eb/No Required                            dB       5.00      5.00
              27   Required Signal                           dBW   131.45   130.48
              28   Signal Availability at Edge of Coverage   %         95        95
              29   Signal Standard Deviation                 dB         8
              30   Standard Deviations Required                       1.64
              31   Mean Signal at edge of coverage           dBW   118.29




C:\DOCSTOC\WORKING\PDF\B2C5A9B4-C26A-4416-877C-E59BB6C5C62F.DOC                        16.08.12   16.08.12
                                                                      - 15 -
                                                                    8F/908-E

                                                                 TABLE 2
                                                     Reduction in Signal Availability
      % Not Served With Isat
34    Max Ring Range/Max Cell Range                              1.00         0.95      0.90       0.85      0.80      0.70       0.50     0.30
35    Center of Ring/Max Cell Range                              0.98         0.93      0.88       0.83      0.75      0.60       0.40     0.15
36    % Total Area in Ring                            %          9.75         9.25      8.75       8.25     15.00     24.00     16.00      9.00
37    Acum Normalized Area(Users)                                9.75        19.00     27.75      36.00     51.00     75.00     91.00    100.00
38    Mean signal in range                            dBW     117.87      116.99   116.06    115.08   113.49   109.77   103.01    86.65
39    Std Dev above req Signal                                   1.58         2.31      2.43       2.55      2.75      3.21       4.06     6.10
40    Unavailability                                  %         5.752        4.592     3.581      2.716     1.688     0.483     0.030     0.000
41    Percent of Tot Users not served                 %         0.561        0.425     0.313      0.224     0.253     0.116     0.005     0.000
42    Percent Reduction in Availability               %         1.897


      % Not Served Without Isat
43    Max Ring Range/Max Cell Range                              1.00         0.95      0.90       0.85      0.80      0.70       0.50     0.30
44    Center of Ring/Max Cell Range                              0.98         0.93      0.88       0.83      0.75      0.60       0.40     0.15
45    % Total Area in Ring                            %          9.75         9.25      8.75       8.25     15.00     24.00     16.00      9.00
46    Acum Normalized Area(Users)                                9.75        19.00     27.75      36.00     51.00     75.00     91.00    100.00
47    Mean signal in range                            dBW     117.87      116.99   116.06    115.08   113.49   109.77   103.01    86.65
48    Std Dev above req Signal                                  1.698        1.807     1.923      2.046     2.245     2.710     3.555     5.600
49    Unavailability                                  %         4.479        3.535     2.723      2.038     1.240     0.337     0.019     0.000
50    Percent of Tot Users not served                 %         0.437        0.327     0.238      0.168     0.186     0.081     0.003     0.000
51    Total Users in Cell not served                  %         1.440


52    Reduction in Capacity                           %         0.457




                                                                 TABLE 3
                                       Change in Signal Availability due to Isat, Ase = 95%,
                                                    Operating at Design Load
                                              Signal Availability Edge                  Average Signal Availability
                                                  of Coverage (%)                             over Cell (%)
                 Isat/N (dB)              w/o Isat    Reduction         with Isat    w/o Isat      Reduction        with Isat
                                                      Due to Isat                                   Due to
                                                                                                     Isat
                              6            95.00            1.38          93.62        98.56              0.46           98.10
                             10            95.00            0.56          94.44        98.56              0.18           98.38




     C:\DOCSTOC\WORKING\PDF\B2C5A9B4-C26A-4416-877C-E59BB6C5C62F.DOC                                                                16.08.12      16.08.12
                                                  - 16 -
                                                8F/908-E

                                                TABLE 4
                          Distribution of Isat Availability Loss with
                        Random User Location, I/N =6 dB, Ase = 95%
                               50 Users, Operating at design Loading
        Percentile               0.05     0.1      0.3      0.5    0.7    0.9   0.95   0.99
        Availability Loss(%)     0.35    0.37     0.41     0.44   0.50   0.53   0.54   0.60
                                 Std    Mean
                                 Dev
                                 0.68   0.446


                               20 Users, Operating at design Loading
        Percentile               0.05     0.1      0.3      0.5    0.7    0.9   0.95   0.99
        Availability Loss        0.31    0.33     0.40     0.42   0.49   0.54   0.56   0.62
        (%)
                                 Std    Mean
                                 Dev
                                 0.88   0.443




C:\DOCSTOC\WORKING\PDF\B2C5A9B4-C26A-4416-877C-E59BB6C5C62F.DOC                               16.08.12   16.08.12
                                                           - 17 -
                                                         8F/908-E




                               Mean Signal                        Distribution of Received Signal with
                                                                  Max Mobile Transmitter Power.
                                                                  Power law coefficient =3.8
                                                                  Lognormal Distribution with 8 dB Std. Dev .
        Desired Signal
        System Noise




                                                                                                         Edge of Coverage Availability
                                                                  Typical Mobile
        and Interference                                          Situation
        At the Base
        Station Receiver
              (dB)




                                                                                                         Typically 95%
                                                                  Available Power
        Required Signal                                           Margin
        With Isat

        Required Signal
        Without Isat

        Due to                        Eb /No            Loss of Signal Availability due to Isat
        Isat
        Interference due
        to other Users

        System Thermal
        Noise
                                  Distance from Base Station
                                                                                            Edge of Coverage




                                                        FIGURE 1
                                    Effect of Isat on CDMA Performance



                                                                                   Edge of Coverage

                                                                                   Max Radius Ring i
                                                                                   Min Radius Ring i

                                                                                   Av Radius Ring i



                                                                                   Cell Radius




                                                        FIGURE 2
                           Dividing the Cell Into Rings of Uniform Performance



C:\DOCSTOC\WORKING\PDF\B2C5A9B4-C26A-4416-877C-E59BB6C5C62F.DOC                                                                          16.08.12   16.08.12
                                                                                                                                                - 18 -
                                                                                                                                              8F/908-E




                                                                                                     3.6


                                                                                                     3.2
           Reduction in Signal r Availability, Asa (%)




                                                                                                     2.8

                                                                                                     2.4
                                                                                                                                       Parameter: Signal Availability at
                                                                                                                                       Edge of CoverageWithout Isat
                                                                                                     2.0                               85 %
                                                                                                                                       90%
                                                                                                                                       95%
                                                                                                     1.6                               98%

                                                                                                     1.2


                                                                                                     0.8


                                                                                                     0.4

                                                                                                     0

                                                                                                               - 20            - 15                        - 10             -5   0
                                                                                                                                                       Isat /N (dB)




                                                                                                                                            FIGURE 3
                                                                                                      Reduction in UpLink Availability Due to Isat, Cellular system
                                                                                                                      Operating at Design Load




                                                                                                         3.6


                                                                                                         3.2
                                                         Reduction in Signal Availability, Asa (%)




                                                                                                                       Parameter: Power Law Coefficient
                                                                                                                       and Standard Deviation
                                                                                                         2.8           b            Std Dev
                                                                                                                       3.52         8
                                                                                                         2.4           3.52         10
                                                                                                                       3.84         8
                                                                                                                       3.84         10
                                                                                                         2.0


                                                                                                         1.6

                                                                                                         1.2


                                                                                                         0.8


                                                                                                         0.4

                                                                                                         0

                                                                                                                 -20            -15                      -10               -5        0
                                                                                                                                                      Isat /N (dB)




                                                                                                                                            FIGURE 4
                                                                                                      Reduction in UpLink Availability Due to Isat, Cellular system
                                                                                                                 Operating at Design Load, Ase = 95%




C:\DOCSTOC\WORKING\PDF\B2C5A9B4-C26A-4416-877C-E59BB6C5C62F.DOC                                                                                                                          16.08.12   16.08.12
                                                                                             - 19 -
                                                                                           8F/908-E


                                                      100

        Signal Availability at Edge of Coverage (%)
                                                      99

                                                      98
                                                                                                       Average Availability throughout cell

                                                      97                                               Availability at Edge of Coverage


                                                      96
                                                                 Key:
                                                                 Ase = 95%
                                                      95
                                                                 Isat /N= -6.0 dB
                                                                 Without Isat
                                                                 With Isat
                                                      94


                                                      93
                                                            0              0.25                   0.50                 0.75                   1.00
                                                                                    Load Re: Maximum D esign Load




                                                                                          FIGURE 5
                                                      Signal Availability at Edge of Coverage Vs. Loading Re: Design Load


                                                                                      ______________




C:\DOCSTOC\WORKING\PDF\B2C5A9B4-C26A-4416-877C-E59BB6C5C62F.DOC                                                                                      16.08.12   16.08.12

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:3
posted:8/16/2012
language:Unknown
pages:19