(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(19) World Intellectual Property
`Organization
`International Bureau
`
`I lllll llllllll II llllll lllll lllll lllll llll I II Ill lllll lllll lllll 111111111111111111111111111111111
`
`( 43) International Publication Date
`1July2004 (01.07.2004)
`
`PCT
`
`(10) International Publication Number
`WO 2004/056145 A2
`
`(51) International Patent Classification7:
`
`H04Q 7/36
`
`(21) International Application Number:
`PCT/EP2003/050950
`
`(22) International Filing Date: 5 December 2003 (05.12.2003)
`
`(25) Filing Language:
`
`(26) Publication Language:
`
`English
`
`English
`
`(30) Priority Data:
`0229390.0
`
`18 December 2002 (18.12.2002) GB
`
`(71) Applicant (for all designated States except US): MO(cid:173)
`TOROLA INC [US/US]; 1303 E. Algonquin Road,
`Schaumburg, IL 60196 (US).
`
`(74) Agent: LITCHFIELD, Laura; Motorola European Intel(cid:173)
`lectual Property Operations, Midpoint, Alencon Link, Bas(cid:173)
`ingstoke, Hampshire RG21 7PL (GB).
`
`(81) Designated States (national): AE, AG, AL, AM, AT, AU,
`AZ, BA, BB, BG, BR, BY, BZ, CA, CH, CN, CO, CR, CU,
`CZ, DE, DK, DM, DZ, EC, EE, EG, ES, Fl, GB, GD, GE,
`GH, GM, HR, HU, ID, IL, IN, IS, JP, KE, KG, KP, KR,
`KZ, LC, LK, LR, LS, LT, LU, LV, MA, MD, MG, MK,
`MN, MW, MX, MZ, NI, NO, NZ, OM, PG, PH, PL, PT,
`RO, RU, SC, SD, SE, SG, SK, SL, SY, TJ, TM, TN, TR,
`TT, TZ, UA, UG, US, UZ, VC, VN, YU, ZA, ZM, ZW.
`
`(84) Designated States (regional): ARIPO patent (BW, GH,
`GM, KE, LS, MW, MZ, SD, SL, SZ, TZ, UG, ZM, ZW),
`Eurasian patent (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM),
`European patent (AT, BE, BG, CH, CY, CZ, DE, DK, EE,
`ES, Fl, FR, GB, GR, HU, IE, IT, LU, MC, NL, PT, RO, SE,
`SI, SK, TR), OAPI patent (BF, BJ, CF, CG, CI, CM, GA,
`GN, GQ, GW, ML, MR, NE, SN, TD, TG).
`
`(72) Inventors; and
`RATFORD,
`(75) Inventors/Applicants (for US only):
`Michael [GB/GB]; Ground Floor Flat, 10 Pulteney Street,
`Bath, Somerset BA2 4BR (GB). BRUSCH, Simon
`[GB/GB]; 1 Sandview, Faringdon, Oxfordshire SN7 7UT
`(GB). WILLIAMS, Olatunde [GB/GB]; Flat B, Avon
`House, Tithe Barn Crescent, Swindon SNl 4NP (GB).
`
`Published:
`without international search report and to be republished
`upon receipt of that report
`
`For two-letter codes and other abbreviations, refer to the "Guid(cid:173)
`ance Notes on Codes and Abbreviations" appearing at the begin(cid:173)
`ning of each regular issue of the PCT Gazette.
`
`iiiiiiii
`
`!!!!!!!!
`iiiiiiii ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
`(54) Title: METHOD AND APPARATUS FOR DETERMINING AN INTERFERENCE RELATIONSHIP BETWEEN CELLS
`OF A CELLULAR COMMUNICATION SYSTEM
`
`---iiiiiiii
`iiiiiiii ---
`-iiiiiiii
`--
`--
`
`SELECT f!RST AND SECOND CELL
`
`OETER~INE EVALUATION INTERVAL
`
`DIVIDE INTO SUB-INTERVALS
`
`201
`
`203
`
`205
`
`207
`
`209
`
`211
`
`- !
`
`!!!!!!!
`iiiiiiii
`
`iiiiiiii ----
`
`215
`
`217
`
`ln
`~
`,....i
`\0
`ln
`~ (57) Abstract: The invention relates to a system for determining an interference relationship between cells of a cellular communi(cid:173)
`~ cation system comprising at least a first cell and a second cell. A method comprises the step of dividing (205) an evaluation interval
`0
`into a plurality of sub-intervals. For each sub interval, the method proceeds to determine (209) a sub-interval simultaneous occu(cid:173)
`~ pancy related to the correlation between communication in the first and second cell. The sub-interval simultaneous occupancy is
`determined from an occupancy of each of the first cell and the second cell. A sub-interval potential interference is then determined
`0 (209) in response to the interference characteristics in each sub-interval. An interference relationship is subsequently determined
`> from the sub-interval potential interferences and the sub-interval simultaneous occupancies. The interference relationship provides
`~ a measure of the impact of interference between the first and second cell suitable for frequency planning.
`
`Ericsson v. IV II LLC
`Ex. 1022 / Page 1 of 26
`
`

`

`WO 2004/056145
`
`PCT /EP2003/050950
`
`1
`
`METHOD AND APPARATUS FOR DETERMINING AN INTERFERENCE
`RELATIONSHIP BETWEEN CELLS OF A CELLULAR COMMUNICATION
`SYSTEM
`
`5
`
`Field of the invention
`
`The invention relates to a method and apparatus for determining an
`interference relationship between cells of a cellular communication system and
`
`10 in particular for determining an interference relationship suitable for
`
`frequency planning.
`
`Background of the Invention
`
`15
`
`FIG. 1 illustrates the principle of a conventional cellular communication
`system 100 in accordance with prior art. A geographical region is divided into
`
`a number of cells 101, 103, 105, 107 each of which is served by base station
`
`109, 111, 113, 115. The base stations are interconnected by a fixed network
`
`20 which can communicate data between the base stations 109, 111, 113, 115. A
`mobile station is served via a radio communication link by the base station of
`the cell within which the mobile station is situated. In the example of FIG. 1,
`mobile station 117 is served by base station 109 over radio link 119, mobile
`station 121 is served by base station 111 over radio link 123 and so on.
`
`25
`
`As a mobile station moves, it may move from the coverage of one base station
`
`to the coverage of another, i.e. from one cell to another. For example mobile
`station 125 is initially served,by base station 113 over radio link 127. As it
`moves towards base station 115 it enters a region of overlapping coverage of
`
`30 the two base stations 113 and 115 and within this overlap region it changes to
`
`be supported by base station 115 over radio link 129. As the mobile station 125
`
`Ex. 1022 / Page 2 of 26
`
`

`

`WO 2004/056145
`
`PCT /EP2003/050950
`
`2
`
`moves further into cell 107, it continues to be supported by base station 115.
`
`This is known as a handover or handoff of a mobile station between cells.
`
`A typical cellular communication system extends coverage over typically an
`
`5 entire country and comprises hundreds or even thousands of cells supporting
`
`thousands or even millions of mobile stations. Communication from a mobile
`
`station to a base station is known as uplink, and communication from a base
`
`station to a mobile station is known as downlink.
`
`10 The fixed network interconnecting the base stations is operable to route data
`
`between any two base stations, thereby enabling a mobile station in a cell to
`
`communicate with a mobile station in any other cell. In addition the fixed
`
`network comprises gateway functions for interconnecting to external networks
`such as the Public Switched Telephone Network (PSTN), thereby allowing
`
`15 mobile stations to communicate with landline telephones and other
`
`communication terminals connected by a landline. Furthermore, the fixed
`
`network comprises much of the functionality required for managing a
`
`conventional cellular communication network including functionality for
`
`routing data, admission control, resource allocation, subscriber billing, mobile
`
`20 station authentication etc.
`
`Currently, the most ubiquitous cellular communication system is the 2nd
`
`generation communication system known as the Global System for Mobile
`
`communication (GSM). GSM uses a technology known as Time Division
`
`25 Multiple Access (TDMA) wherein user separation is achieved by dividing
`
`frequency caniers into 8 discrete time slots, which individually can be
`allocated to a user. A base station may be allocated a single carrier or a
`multiple of carriers. One carrier is used for a pilot signal which further
`
`contains broadcast information. This carrier is used by mobile stations for
`
`30 measuring of the signal level of transmissions from different base stations, and
`
`the obtained information is used for determining a suitable serving cell during
`
`Ex. 1022 / Page 3 of 26
`
`

`

`WO 2004/056145
`
`PCT /EP2003/050950
`
`3
`
`initial access or hand overs. Further description of the GSM TD:MA
`
`communication system can be found in 'The GSM System for Mobile
`
`Communications' by Michel Mouly and Marie Bernadette Pautet, Bay Foreign
`
`Language Books, 1992, ISBN 2950719007.
`
`5
`
`Currently, 3rd generation systems are being rolled out to further enhance the
`communication services provided to mobile users. The most widely adopted 3rd
`generation communication systems are based on Code Division Multiple
`Access (CDMA) wherein user separation is obtained by allocating different
`
`10 spreading and scrambling codes to different users on the same carrier
`
`frequency. The transmissions are spread by multiplication with the allocated
`
`codes thereby causing the signal to be spread over a wide bandwidth. At the
`
`receiver, the codes are used to de·spread the received signal thereby
`regenerating the original signal. Each base station has a code dedicated for a
`
`15 pilot and broadcast signal, and as for GSM this is used for measurements of
`multiple cells in order to determine a serving cell. An example of a
`communication system using this principle is the Universal Mobile
`
`Telecommunication System (UMTS), which is currently being deployed.
`
`Further description of CDMA and specifically of the Wideband CDMA
`
`20 (WCDMA) mode ofUMTS can be found in 'WCDMA for UMTS', Harri Halma
`(editor), Antti Toskala (Editor), Wiley & Sons, 2001, ISBN 0471486876.
`
`In order to optimise the capacity of a cellular communication system, it is
`
`important to minimise the impact of interference caused by or to other mobile
`25 stations. Thus, it is important to minimise the interference caused by the
`
`communication to or from a mobile station, and consequently it is important to
`
`use the lowest possible transmit power. As the required transmit power
`
`depends on the instantaneous propagation conditions, it is necessary to
`
`dynamically control transmit powers to closely match the conditions. For this
`
`30 purpose, the base stations and mobile stations operate power control loops,
`
`where the receiving end reports information on the receive quality back to the
`
`Ex. 1022 / Page 4 of 26
`
`

`

`WO 2004/056145
`
`PCT /EP2003/050950
`
`4
`
`transmitting end, which in response adjusts it's transmit power. This ensures
`
`that the minimum transmit power necessary to ensure a given quality is used,
`
`and thus that interference caused by communication with each mobile station
`
`is minimised.
`
`5
`
`An important advantage of cellular communication systems is that, due to the
`
`radio signal attenuation with distance, the interference caused by
`
`communication within one cell is negligible in a cell sufficiently far removed,
`
`and therefore the resource can be reused in this cell. In GSM systems, carrier
`
`10 frequencies are therefore reused in other cells in accordance with a frequency
`
`plan. Frequency planning is one of the most important optimisation operations
`
`for a cellular communication system in order to maximise the communication
`
`capacity of the system. The frequency planning typically considers a vast
`
`number of parameters including propagation characteristics, traffic profiles
`
`15 and communication equipment capabilities.
`
`Specifically, known frequency planning methods rely heavily on interference
`
`estimations between different cells. Automatic frequency planning methods
`
`have been developed wherein potential cross-interference and resulting carrier
`
`20 to interference ratios are determined for different possible frequency
`
`allocations. Typically, an interference level is determined as the interference
`
`caused to a communication between a mobile station and a base station in one
`
`cell by a potential communication between a mobile station and base station in
`
`a different cell. Conventionally, the interference is determined from
`
`25 propagation predictions based on calculated and measured propagation
`
`characteristics.
`
`However, these interference values and carrier to interference ratios do not
`
`reflect the true impact on the performance of the communication system as
`
`30 they do not consider the relationship between the caused interference and the
`
`quality of service parameters provided by the communication system.
`
`Ex. 1022 / Page 5 of 26
`
`

`

`WO 2004/056145
`
`PCT /EP2003/050950
`
`5
`
`Accordingly, the frequency planning may become flawed, and sub-optimal
`
`frequency plans may be determined.
`
`Hence, an improved system for determining an interference relationship
`
`5 between cells of a cellular communication system would be advantageous and
`
`in particular a system for determining an interference relationship suitable for
`
`frequency planning would be advantageous.
`
`10 Summary of the Invention
`
`Accordingly, the Invention seeks to mitigate, alleviate or eliminate one or more
`
`of the above mentioned disadvantages singly or in any combination.
`
`15 According to a first aspect of the invention there is provided a method of
`
`determining an interference relationship between cells of a cellular
`
`communication system comprising at least a first cell and a second cell; the
`
`method comprising the step of. determining an interference relationship
`
`between the first cell and the second cell in response to a potential interference
`
`20 relationship between the first and the second cell and a simultaneous
`
`occupancy of the first cell and the second cell.
`
`The Inventors of the current invention have realised that a more reliable
`
`measurement of the impact of interference on the performance of a cellular
`
`25 communication system can be achieved by considering a simultaneous
`
`occupancy between different cells. The simultaneous occupancy is a measure of
`
`the time correlation between communications of the first cell and second cell.
`It may specifically be determined as a probability of communications for the
`
`first and second cell being simultaneous and thus interfering with each other.
`
`30 Preferably, the simultaneous occupancy may be determined as the average
`
`Ex. 1022 / Page 6 of 26
`
`

`

`WO 2004/056145
`
`PCT /EP2003/050950
`
`6
`
`probability of a resource unit in a first cell and the corresponding resource unit
`
`of the second cell being occupied at the same time.
`
`The method allows for the interference relationship to reflect not only a level
`
`5 of potential interference but also the probability that such an interference will
`
`cause interference to a communicating unit. As such it provides a significantly
`
`more accurate reflection of the impact of the interference caused and thus a
`
`much improved interference relationship is provided. The improved
`
`interference relationship allows for much more accurate performance
`
`10 prediction of a cellular communication system. It allows for improved
`
`frequency planning and may accordingly significantly increase the capacity of
`
`the communication system.
`
`According to a feature of the invention, the method further comprises the steps
`
`15 of. dividing an evaluation interval into sub·intervals; for each sub·interval
`determining a sub-interval potential interference in response to the
`interference characteristics in each sub·interval; and determining the
`
`potential interference relationship for the evaluation interval in response to
`
`the sub-interval potential interferences.
`
`20
`
`An improved accuracy of the determined interference relationship may be
`
`achieved by the consideration of the conditions in individual sub-intervals.
`
`Division into sub·intervals is furthermore suitable for practical
`
`implementations and may allow for a simple and low complexity
`
`25 implementation. Determining sub·interval potential interference provides a
`
`suitable method for talcing into account the variation in interference with time
`
`thereby improving the reliability and/or accuracy of the determined
`interference relationship.
`
`30 According to another feature of the invention, the step of determining a
`
`simultaneous occupancy comprises the steps of. dividing an evaluation interval
`
`Ex. 1022 / Page 7 of 26
`
`

`

`WO 2004/056145
`
`PCT /EP2003/050950
`
`7
`
`into sub-intervals; for each sub-interval, determining a sub-interval
`
`simultaneous occupancy by determining an occupancy of each of the first cell
`
`and the second cell; and determining the simultaneous occupancy for the
`
`evaluation interval in response to the sub-interval simultaneous occupancies.
`
`5
`
`An improved accuracy of the determined interference relationship may be
`achieved by the consideration of the conditions in individual sub·intervals.
`
`Division into sub-intervals is furthermore suitable for practical
`
`implementations and may allow for a simple and low complexity
`
`10 implementation. Determining sub·interval simultaneous occupancy provides a
`
`suitable method for taking into account the variation of occupancy with time
`
`thereby improving the reliability and/or accuracy of the determined
`
`interference relationship.
`
`15 According to another feature of the invention, the method further comprises
`
`the step of. dividing an evaluation interval into a plurality of sub-intervals; for
`
`each sub interval performing the steps of. determining a sub-interval
`
`simultaneous occupancy by determining an occupancy of each of the first cell
`
`and the second cell, determining a sub·interval potential interference in
`20 response to the interference characteristics in each sub·interval, and
`determining a sub-interval interference relationship in response to the sub(cid:173)
`
`interval simultaneous occupancies and the sub-interval potential
`
`interferences; and wherein the interference relationship is determined in
`
`response to the sub-interval interference relationships.
`
`25
`
`An improved accuracy of the determined interference relationship may be
`
`achieved by the consideration of the conditions in individual sub-intervals.
`
`Division into sub·intervals is furthermore suitable for practical
`
`implementations and may allow for a simple and low complexity
`
`30 implementation. Determining sub-interval simultaneous occupancy and
`
`potential interference provides a suitable method for taking into account the
`
`Ex. 1022 / Page 8 of 26
`
`

`

`WO 2004/056145
`
`PCT /EP2003/050950
`
`8
`
`variation in both occupancy and interference with time as well as taking into
`
`account the correlation between these. This enables an improved reliability
`
`and/or accuracy of the determined interference relationship.
`
`5 According to another feature of the invention, the step of determining the
`
`simultaneous occupancy for the evaluation interval comprises determining the
`
`simultaneous occupancy as an average of the sub-interval simultaneous
`occupancies. An average simultaneous occupancy provides a suitable and
`
`advantageous measure of the simultaneous occupancy
`
`10
`
`According to another feature of the invention, the occupancy of at least one of
`
`the first cell and the second cell is determined from network statistics.
`This allows for the occupancy to be determined from statistics in the network.
`Typically, these statistics are also collected for other purposes and therefore
`
`15 the increased complexity is small. Hence, this allows for an implementation
`
`well suited for the characteristics of a cellular communication system.
`
`According to another feature of the invention, the network statistics comprise
`
`a measurement report quantity characteristic. An occupancy may specifically
`
`20 be determined by determining how many measurement reports are received in
`a sub-interval. The measurement reports provide an indication of the traffic
`
`level and thus the occupancy of the cell. Hence, this allows for a low
`
`complexity implementation while providing accurate measures of the
`occupancy.
`
`25
`
`According to another feature of the invention, the potential interference
`
`relationship is determined in response to a measurement of a signal level in
`
`the second cell associated with a transmission in the first cell. A reliable
`
`potential interference relationship may be determined from measurements of
`
`30 transmissions in the other cell. Specifically, a signal level measurement of a
`
`broadcast signal in the first cell may provide a reliable indication of the
`
`Ex. 1022 / Page 9 of 26
`
`

`

`WO 2004/056145
`
`PCT /EP2003/050950
`
`9
`
`potential interference that may be caused to communications in the second
`
`cell.
`
`According to another feature of the invention, the potential interference
`
`5 relationship is associated with assignment of co-channel carriers in the first
`
`and the second cell. The method of determining an interference relationship
`may specifically relate to co-channel interference thereby providing a low
`complexity, reliable and accurate method of determining the impact of
`
`allocating co-channel carriers in the first and second cell.
`
`10
`
`According to another feature of the invention, the potential interference
`relationship is associated with assignment of adjacent channel carriers in the
`
`first and the second cell. The method of determining an interference
`relationship may specifically relate to adjacent channel interference thereby
`
`15 providing a low complexity, reliable and accurate method of determining the
`
`impact of allocating adjacent channel carriers in the first and second cell.
`
`According to another feature of the invention, the potential interference
`relationship is in response to a ratio of communication units of the second cell
`20 for which an interference from the first cell will cause a quality level below a
`given threshold. Preferably the potential interference relationship is
`determined in relation to the ratio of communication units that cannot
`communicate with acceptable performance for the determined interference.
`
`This provides a very valuable measure of the degradation caused by the
`25 interference.
`
`According to a second aspect of the invention, there is provided a method of
`frequency planning for a plurality of cells in a cellular communication system,
`the method comprising the steps of. determining the interference relationship
`
`30 for each combination of two cells of the plurality of cells in accordance with the
`
`method described above; for each combination of two cells determining a
`
`Ex. 1022 / Page 10 of 26
`
`

`

`WO 2004/056145
`
`PCT /EP2003/050950
`
`10
`
`penalty associated with a corresponding frequency allocation in response to
`
`the interference relationship of that combination of two cells; and allocating
`
`carrier frequencies to the plurality of cells in response to the penalty values.
`
`5 The method of determining an interference relationship may preferably be
`
`used for frequency planning. The method may be automated. Accurate and
`
`reliable frequency plans with improved performance may thus be developed for
`the cellular communication resulting in improved performance and capacity of
`
`the cellular communication system.
`
`10
`
`According to another feature of the invention, the frequency allocation is such
`that the sum of penalty values is minimised. This allows for frequency plans to
`
`be determined that minimise a given penalty criterion.
`
`15 According to another feature of the invention, the cellular communication
`
`system is a GSM communication system. Hence, an improved method of
`
`determining an interference relationship between cells of a GSM
`communication system is provided allowing for improved frequency plans to be
`developed and accordingly fo1· increased performance of the GSM
`
`20 communication system.
`
`According to a third aspect of the invention, there is provided an apparatus for
`determining an interference relationship between cells of a cellular
`communication system comprising at least a first cell and a second cell; the
`25 apparatus comprising: means for determining an interference relationship
`between the first cell and the second cell in response to a potential interference
`relationship between the first and second cell and a simultaneous occupancy of
`the first and the second cell.
`
`30 These and other aspects and advantages of the invention will be apparent from
`
`and elucidated with reference to the embodiment(s) described hereinafter.
`
`Ex. 1022 / Page 11 of 26
`
`

`

`WO 2004/056145
`
`PCT /EP2003/050950
`
`11
`
`Brief Description of the Drawings
`
`5 An embodiment of the invention will be described, by way of example only,
`with reference to the drawings, in which
`
`FIG. 1 is an illustration of a cellular communication system in accordance with
`the prior art;
`
`10
`
`FIG. 2 illustrates a flow chart of a method of determining an interference
`relationship in accordance with a preferred embodiment of the invention.
`
`15 Detailed Description of a Preferred Embodiment of the Invention
`
`The following description focuses on an embodiment of the invention
`
`applicable to frequency planning for a GSM cellular communication system.
`
`However, it will be appreciated that the invention is not limited to this
`20 application but may be applied to many other applications and communication
`systems. Specifically, the invention will be described with reference to a
`communication systems such as that illustrated in FIG. 1.
`
`A method of frequency :planning for a GSM cellular communication system
`25 consist evaluating the potential interference that may be caused in one cell by
`transmission in another cell. Specifically, a carrier to interference ratio is
`determined for two cells under the assumption that they are allocated the
`same carriers.
`
`30 Conventionally, the carrier to interference ratio has been derived from
`propagation predictions. Traditionally, the interference has been determined
`
`Ex. 1022 / Page 12 of 26
`
`

`

`WO 2004/056145
`
`PCT /EP2003/050950
`
`12
`
`from transmit power assumptions and propagation predictions based on
`
`calculations or measurements. However carrier to interference ratios alone do
`not reflect the true impact of the interference caused by a frequency plan, as
`
`they do not take into account the amount of traffic suffering from interference
`
`5 or when that interference occurs. For example, one cell may cover a business
`
`park and a neighbouring cell may cover a football stadium. These cells may
`have high utilisation but the utilisation will tend to be at different times.
`Hence, although transmissions of one cell may result in high levels of
`interference in the other cell, this will not have significant impact on the
`
`10 performance of the communication system as one of the two cells will always
`
`have a very low loading. Specifically, the cells may be allocated the same
`carrier frequency. However, a conventional frequency planning will prevent
`
`this allocation leading to a sub-optimal frequency plan.
`
`15 In accordance with a preferred embodiment of the invention, a frequency
`planning method is provided wherein the frequency planning is in response to
`
`an interference relationship between cells. The interference relationship is
`determined in response to a simultaneous occupancy between the cells.
`
`20 FIG. 2 illustrates a flow chart of a method of determining an interference
`relationship in accordance with a preferred embodiment of the invention.
`
`In step 201 a first and second cell for which the interference relationship is to
`be determined is selected.
`
`25
`
`Step 201 is followed by step 203. In step 203, an evaluation interval is defined
`
`over which the interference relationship will be determined. The evaluation
`interval is preferably sufficiently long to allow for a statistically representative
`
`interference relationship to be determined. In the prefeiTed embodiment, the
`30 evaluation intenral preferably extends over several weeks thereby allowing the
`
`variations due to the daily and weekly traffic fluctuations to be included.
`
`Ex. 1022 / Page 13 of 26
`
`

`

`WO 2004/056145
`
`PCT /EP2003/050950
`
`13
`
`Step 203 is followed by step 205. In step 205 the evaluation interval is divided
`
`into a plurality of sub-intervals. The sub-intervals are preferably sufficiently
`
`small for the parameters used in the frequency planning to be considered
`5 relatively constant. In the preferred embodiment, each sub-interval may for
`
`example have a duration of one hour. It will be -apparent, that the duration of
`
`the sub-interval will be a design parameter that can be selected by a person
`
`skilled in the art to meet the specific requirements and constraints of a specific
`
`embodiment.
`
`10
`
`15
`
`Step 205 is followed by step 207. In step 207, a sµb·interval potential
`interference is determined. In the preferred embodiment, the potential
`
`interference relates to the interference that may be received in the second cell
`
`by transmissions in the first cell.
`
`In the preferred embodiment, the potential interference is determined in
`
`response to the measurement reports received from the communication units
`of the second cell. In a GSM communication system, the communication units
`make measurements of the received signal level of the broadcast carriers
`
`20 (BCCH carriers) of neighbouring base stations. Hence, if the first cell is
`included in the neighbour list for the second cell, the communication units of
`
`the second cell make measurements of the broadcast signal transmitted from
`
`the base station in the first cell. These measurements are reported back to the
`
`base stations and are in the preferred embodiment collected and used by the
`
`25 method of FIG. 2. Specifically, an average measured receive level of the signal
`
`from the first cell in the second cell is used as the potential interference. This
`
`will correspond to the average interference that would be received in the
`
`second cell, if the base station of the first cell transmitted continuously and the
`
`two cells were allocated the same carrier.
`
`30
`
`Ex. 1022 / Page 14 of 26
`
`

`

`WO 2004/056145
`
`PCT /EP2003/050950
`
`14
`
`Hence, in the preferred embodiment, co-channel interference is specifically
`considered. Alternatively or additionally, adjacent interference associated with
`
`allocation of adjacent carriers to the first and second cell may be considered.
`
`The adjacent channel interference may specifically be determined similarly to
`5 the co-channel interference but further attenuated to reflect the reduction in
`interference in adjacent frequency bands.
`
`In the preferred embodiment, the sub·interval potential interference is
`
`determined in response to the interference characteristics in each sub·interval,
`10 such that only the operating conditions of the sub·interval for which the sub·
`
`interval potential interference relates to is taken into account. Specifically, the
`
`sub·interval potential interference is determined in response only to
`
`measurement reports of the specific sub-interval.
`
`15 Step 207 is followed by step 209. In step 209, a sub-interval simultaneous
`
`occupancy is determined for the sub·interval. In the preferred embodiment,
`
`the sub-interval simultaneous occupancy is determined from the individual
`
`occupancy of each of the first and second cell. Specifically, the ratio of utilised
`
`resource relative to the total available resource in the sub·interval is
`20 determined. For example, in GSM, a carrier comprises eight time slots. If the
`time slots of the first cell are used for an average of 30% of the duration of the
`
`sub·interval, the occupancy of the first cell is determined as 30%. The
`occupancy of the second cell is determined in the same way. A sub-interval
`simultaneous occupancy is then determined from the individual occupancies.
`25 Specifically, the sub·interval simultaneous occupancy Os is given by:
`
`Os = Ocell l · Ocell 2
`
`where Ocell l and Ocell 2 are the individual occupancies of the first and second
`30 cell respectively.
`
`Ex. 1022 / Page 15 of 26
`
`

`

`WO 2004/056145
`
`PCT /EP2003/050950
`
`15
`
`Hence, the sub-interval simultaneous occupancy is a measure of the
`
`probability that communication on equivalent time slots in the first and
`second cell will occur. It is thus a measm·e of the probability that interference
`caused by transmission in one cell will affect a communication in the other
`5 cell.
`
`The occupancy of the first and second cell is preferably determined from
`
`network statistics. Typically, in a cellular communication system, a large
`
`number of parameters are collected and used to determine statistics related to
`10 the operation of the cellular communication system. Specifically, traffic
`
`statistics are typically determined in an Operations and Maintenance Centre
`
`(OMC). These statistics typically include measures related to the loading of
`
`individual base stations. By relating these characteristics to each sub-interval,
`the occupancy in each sub-interval may be determined.
`
`15
`
`In one embodiment, the occupancy of a cell is determined from a measurement
`
`report quantity characteristic. S