WO2008095541A1

WO2008095541A1 - Method and radio transmitter controlling device for reducing interference in a communication network

Info

Publication number: WO2008095541A1
Application number: PCT/EP2007/051292
Authority: WO
Inventors: Harald Kallin
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2007-02-09
Filing date: 2007-02-09
Publication date: 2008-08-14
Anticipated expiration: 2009-08-09

Abstract

The present invention relates to a method and an arrangement for controlling interference between cells in a communication network comprising a radio transmitter transmitting data to one or more receiver(s) over a radio interface. A power utilization profile is provided for determining how much time said transmitter is allowed to operate on different power levels over a period of time.

Description

METHOD AND RADIO TRANSMITTER CONTROLLING DEVICE FOR REDUCING INTERFERENCE IN A COMMUNICATION NETWORK

TECHNICAL FIELD The present invention relates to a method and an arrangement in a communication network, and particularly, to a radio transmitter controlling device and an arrangement allowing for controlling interference between cells in a communication network as well as a method for such control. The invention also relates to a radio base station and a user equipment provided with the radio transmitter controlling device for controlling interference between cells in a communication network. The invention further relates to a computer- readable medium containing computer program for controlling interference between cells in a communication network.

BACKGROUND OF THE INVENTION Wireless communication systems typically provide services to a subscriber coverage area based on a division of the coverage area into areas referred to as cells. Because the number of available frequencies is limited, efficient frequency utilization is an important consideration in wireless network layout. Cell layout is generally selected based on providing acceptable communication throughout the coverage area while avoiding interference between signals associated with the same frequency but produced in different (neighbouring) cells. In recent years, several techniques have been proposed for controlling this interference. First there was frequency planning when each cell was given a set of frequencies to operate on. Over time, this has evolved into allowing the use of all available frequencies in all cells, which requires a certain communication between the radio base stations located in the cells.

In GSM, fractional loading is used to allow a one-cell reuse of frequencies by introducing frequency hopping and not allowing the frequencies to be used all the time. By putting restrictions on their use, communication can still be maintained, even though the interference levels from other cells can be very high occasionally.

The primary use of this invention is in orthogonal frequency-division multiplexing (OFDM) systems where transmission of data is made in small blocks that are sent at a combination of time (frame) and frequency. The usage of time and frequency may change rapidly between transmissions.

One prior art approach is shown in US Patent 6757542, which discloses a method for providing a high capacity radio communication network. The network employs fractional loading as reuse technique between cells. Using the radio resource too much may cause interference, and this information is used for controlling the admission of new users into the network, i.e. new calls may be blocked.

This prior art approach, however, is circuit switched oriented, making simple yes/no binary decisions allowing a call or not, and does not exploit the bursty nature of data traffic.

Numerous attempts are also made in to introduce clever allocation of the resources so that clashes due to simultaneous use of the same resources in neighbouring cells are avoided. However, such schemes require planning and coordination, or a lot of signalling in the network between base stations, or between the base stations and a coordinating node.

SUMMARY OF THE INVENTION Accordingly, it is an objective with the present invention to provide an improved method for controlling interference between cells in a communication network comprising a transmitter transmitting data to a receiver over a radio interface.

According to a first aspect of the present invention this objective is achieved through a method as defined in the characterising portion of claim 1 , which specifies that interference between cells in a communication network is controlled by providing a power utilization profile determining how much time said transmitter is allowed to operate on different power levels over a period of time.

Another objective with the present invention is to provide an improved radio transmitter controlling device for controlling interference between cells in a communication network comprising a transmitter transmitting data to a receiver over a radio interface.

According to a second aspect of the present invention this other objective is achieved through a radio transmitter controlling device as defined in the characterising portion of claim 10, which specifies that interference between cells in a communication network is controlled by a radio transmitter controlling device comprising a power utilization profile arranged to determine how much time said transmitter is allowed to operate on different power levels over a period of time.

A further objective with the present invention is to provide an improved radio base station for controlling interference between cells in a communication network, said radio base station comprising a radio transmitter transmitting data to one or more user equipments over a radio interface.

According to a third aspect of the present invention this further objective is achieved through a radio base station as defined in claim 19, which specifies that interference between cells in a communication network is controlled by a radio base station comprising a radio transmitter controlling device comprising a power utilization profile arranged to determine how much time said transmitter is allowed to operate on different power levels over a period of time.

A still further objective with the present invention is to provide an improved user equipment for controlling interference between cells in a communication network, said user equipment comprising a radio transmitter transmitting data to a radio base station over a radio interface.

According to a fourth aspect of the present invention this still further objective is achieved through a user equipment as defined in claim 20, which specifies that interference between cells in a communication network is controlled by a user equipment comprising a radio transmitter controlling device comprising a power utilization profile arranged to determine how much time said transmitter is allowed to operate on different power levels over a period of time.

A yet further objective with the present invention is to provide an improved computer- readable medium containing computer program for controlling interference between cells in a communication network comprising a radio transmitter transmitting data to a receiver over a radio interface. According to a fifth aspect of the present invention this objective is achieved through a computer-readable medium as defined in the characterising portion of claim 21 , which specifies that interference between cells in a communication network is controlled by a computer program which provide a power utilization profile determining how much time said transmitter is allowed to operate on different power levels over a period of time.

Further embodiments are listed in the dependent claims.

Thanks to the provision of a method and an arrangement, which reduce the operation on the highest power levels, the surrounding cells are given an opportunity for successful communication between radio base stations and user equipments. The present invention provides a courtesy rule that increases chances of communication by e.g. avoiding resource overload (breakdown). The inventive method requires no coordination at all, or very limited coordination, between cells or radio base stations.

Still other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, wherein like reference characters denote similar elements throughout the several views:

Figure 1 shows the communication network architecture according to the present invention;

Figure 2 shows an inventive power is profile for one cell;

Figure 3a shows how the allowed power is ramped in a discrete fashion according to one embodiment of the present invention; Figure 3b shows how the allowed power is ramped in a discrete fashion according to another embodiment of the present invention;

Figure 4 is a block diagram showing a user equipment and a radio base station provided with the inventive arrangement;

Figure 5 shows how the power is ramped over time in a generalized fashion;

Figure 6 shows a computer-readable medium.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 depicts a communication system, such as a OFDM system, including a Radio Access Network (RAN), such as the UMTS Terrestrial Radio Access Network (UTRAN) architecture, comprising at least one Radio Base Station (RBS) (or Node B) 15, two are shown in fig. 1 , connected to one or more Radio Network Controllers (RNCs) 10. The RAN is connected to a Core network (CN) 12. The RAN and the CN 12 provide communication and control for a plurality of user equipments (UE) 18. The UEs 18 each uses downlink (DL) channels (i.e. base-to-user or forward) and uplink (UL) channels (i.e. user-to-base or reverse) to communicate with at least one RBS 15 over a radio interface. On the downlink channel, the RBS 15 transmits data to each user equipment 18 at respective power level. On the uplink channel, the user equipments 18 transmit data to the RBS 15 at respective power level. According to a preferred embodiment of the present invention, the communication system is herein described as a OFDM communication system. The skilled person, however, realizes that the inventive method and arrangement works very well on all communications system. The user equipments 18 may be mobile stations such as mobile telephones ("cellular" telephones) and laptops with mobile termination and thus can be, for example, portable, pocket, hand-held, computer-included or car-mounted mobile devices which communicate voice and/or data with the RAN.

According to the preferred embodiment of the present invention, a "code of conduct" is introduced that stipulates how much transmit power the base station or user equipment is allowed to use. Just because the base station, or the equipments, is capable of transmitting at some power does not mean it is advisable to do so, due to the interference any transmission may cause. A simple realisation is to translate the code of conduct into a "power utilization profile" that determines what power levels are allowed during a specific time segment.

More specifically, according to the present invention a method is provided for controlling interference between cells in a communication network comprising a transmitter transmitting data to one or more receiver(s) over a radio interface, wherein the method comprises the step of providing a power utilization profile determining how much time said transmitter is allowed to operate on different power levels over a period of time.

The code of conduct, or power utilization profile, may change based on radio measurements such as the cell or system load and/or the quality experienced, or change over time. Based on these radio measurements, the power profile may be dynamically adopted to reflect the actual conditions in the actual environment. Instead of measurements, or in combination with, it is also possible to change the power profile based on predefined rules that also may change e.g. over the time of day, based on experienced quality or cell or system load. In particular, the power profile may increase gently at start-up of new base stations, in order to reduce the impact on the existing radio network when adding a new base station.

As already mentioned, the code of conduct can be translated into a power profile that determines how much time a transmitter is allowed to operate on different power levels over a period of time. An example of this is seen in figure 2, which shows that the transmitter is allowed to transmit with:

^π Maximum power 30 % of the time, π Maximum power minus 5 dB for no more than 60 % of the time, π Maximum power minus 1 O dB for no more than 90 % of the time.

By integrating the power usage over time, it is possible to create a power (resource) utilization factor, π. In a more generalized form:

∑pt π e [o..i]

P max T t and 7 is a time measure, wheras P_max and p is power that may be measured in Watts directly, or in decibels or some other transformation of the physical representation that may be appropriate.

All the time, the power output of the transmitter is measured by the base station, e.g. by incrementing histogram counters. The scheduler that decides on the actual use of the time and frequency, needs to observe the used (wanted) power and compares it with the allowed usage. If the power need is higher than what is allowed, the output power of the upcoming transmissions must be reduced, or delayed/postponed to a later occasion.

In order to fulfil the power utilization profile without having to correct it afterwards, it is possible to schedule users known having a large power utilization (needing maximum power) in advance and interpose users in need of less power in between these large power consumers.

The power profile can be applied both for downlink transmissions (base station transmitter) and uplink transmissions (user equipment transmitters). For the latter, the base station would decide on the user equipment's transmit power and the allocation of time slots. That is, observing the power profile in the decision process of granting the mobiles' permission to transmit and at what power. If an individual mobile's power is not decided by the base station, the base station can either judge this from the reports from the user equipment, or assume the output power based on the transmit power the base station uses when communicating with the user equipment.

According to a second preferred embodiment of the present invention, there is more than one power profile in operation in one cell, ruling the power usage over different periods of time. For example, there can be one power profile for every OFDM frame (e.g. 10 milliseconds) and another profile for every second, or even longer intervals. The short term power profile may be more relaxed to temporary use of high power (for example to minimize delays), whereas the longer term power profile will guarantee the performance over longer periods of time.

According to a third preferred embodiment of the present invention, the inventive power profile is used to allow a smooth introduction of new base stations into an existing radio network. When initially starting a new base station, the surrounding - already existing - base stations may be impacted in an unfavourable way, even making communication more or less impossible in some geographical spots. By gradually (gently) increasing the power profile for a new base station, the existing base stations are given an opportunity to adapt to the new base station; either by self-optimizing algorithms, or by raising alarms for manual intervention, or simply by statistical collection and processing of the base station performance for further manual actions. Also, by gently increasing the power profile for the new base station, the new base station is given an opportunity to adapt to the surrounding base stations.

In this case, the ramping of the power profile may take hours or days and can either be ramped in time usage, ramped in maximum power allowed or an increasing π_aιι_owed. (The first method is less desirable since it is more prone of introducing congestion problems, pretending it is capable of offering traffic that is distant from the base station, when it actually cannot).

Figure 3a shows how the allowed power utilization profile is ramped in time usage in a discrete fashion over time according to one embodiment of the present invention. At t-i the transmitter is allowed to transmit with: π Maximum power 10 % of the time, π Maximum power minus 5 dB for no more than 20 % of the time, π Maximum power minus 10 dB for no more than 30 % of the time.

And, at t₂ the transmitter is allowed to transmit with: π Maximum power 20 % of the time, π Maximum power minus 5 dB for no more than 40 % of the time, π Maximum power minus 1 O dB for no more than 60 % of the time.

At t₃ the allowed power utilization profile is fully ramped and the transmitter is allowed to transmit with: π Maximum power 30 % of the time, π Maximum power minus 5 dB for no more than 60 % of the time, π Maximum power minus 1 O dB for no more than 90 % of the time.

Figure 3b shows another preferred embodiment of the present invention of how to ramp the allowed power utilization profile over time. At ti the transmitter is allowed to transmit with maximum power minus 1 O dB for no more than 90 % of the time. And, at t₂ the transmitter is allowed to transmit with: π Maximum power minus 5 dB for no more than 60 % of the time, π Maximum power minus 10 dB for no more than 90 % of the time.

And, at t₃ the allowed power utilization profile is fully ramped and the transmitter is allowed to transmit with: π Maximum power 30 % of the time, π Maximum power minus 5 dB for no more than 60 % of the time, π Maximum power minus 10 dB for no more than 90 % of the time.

Figure 4 is a block diagram showing a user equipment 18 and a radio base station 15 provided with the inventive arrangement. Thus, the RBS 15 comprises a radio transmitter 42 and a receiver 41. The transmitter 42 is transmitting data to a receiver 47 of the user equipment 18 over a radio interface. The transmitter 42 is controlled by a radio transmitter controlling device 43 which determines how much time the transmitter 42 is allowed to operate on different power levels over a period of time by means of the power utilization profile discussed above. The RBS 15 also comprises a scheduler 45, which decides which data packets to send when, and means for measuring 44 output power of the transmitter 42.

The user equipment 18 comprises a radio transmitter 46 arranged to transmit data to the receiver 41 of the RBS 15 and a receiver 47 arranged to receive data transmitted from the RBS 15. Also the user equipment 18 comprises a radio transmitter controlling device 48 which determines how much time the transmitter 46 is allowed to operate on different power levels over a period of time by means of the power utilization profile. Figure 4 is just an illustrative block diagram showing different functions in a user equipment and a RBS respectively.

Figure 5 shows alternative methods of increasing the power over time when the power utilization profile is in a generalized fashion (or a discrete fashion with a large number of discrete steps). The examples show increase of π_aιι_owed in a logarithmic way (shown with a dashed line), a linear way (shown with a solid line) and an exponential way (shown with a dash dotted line). It will be appreciated that at least some of the procedures described above are carried out repetitively as necessary to respond to the time-varying characteristics of the channel between the transmitter and the receiver. To facilitate understanding, many aspects of the invention are described in terms of sequences of actions to be performed by, for example, elements of a programmable computer system. It will be recognized that the various actions could be performed by specialized circuits (e.g. discrete logic gates interconnected to perform a specialized function or application-specific integrated circuits), by program instructions executed by one or more processors, or a combination of both.

Moreover, the invention can additionally be considered to be embodied entirely within any form of computer-readable storage medium, an example of which is shown in fig. 6 and denoted 60, having stored therein an appropriate set of instructions for use by or in connection with an instruction-execution system, apparatus or device, such as computer- based system, processor-containing system, or other system that can fetch instructions from a medium and execute the instructions. As used here, a "computer-readable medium" 60 can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction-execution system, apparatus or device. The computer-readable medium 60 can be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device or propagation medium. More specific examples (a non- exhaustive list) of the computer-readable medium include an electrical connection having one or more wires, a portable computer diskette, a random access memory (RAM), a read only memory (ROM), an erasable programmable read only memory (EPROM or Flash memory), an optical fibre, and a portable compact disc read only memory (CD-ROM).

Thus, a computer-readable medium containing computer program according to a preferred embodiment of the present invention for controlling interference between cells in a communication network comprising a transmitter transmitting data to one or more receiver(s) over a radio interface, is provided wherein the computer program performs the step of providing a power utilization profile determining how much time said transmitter is allowed to operate on different power levels over a period of time..

Modifications to embodiments of the invention described in the foregoing are possible without departing from the scope of the invention as defined by the accompanying claims. Expressions such as "including", "comprising", "incorporating", "consisting of", "have", "is" used to describe and claim the present invention are intended to be construed in a nonexclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural and vice versa.

Numerals included within parentheses in the accompanying claims are intended to assist understanding of the claims and should not be construed in any way to limit subject matter claimed by these claims.

Claims

1. A method for controlling interference between cells in a communication network comprising a radio transmitter transmitting data to one or more receiver(s) over a radio interface, characterized in that the method comprises the step of determining how much time said transmitter is allowed to operate on different power levels over a period of time by means of a power utilization profile in a radio transmitter controlling device.

2. A method according to claim 1 , characterized in that the method further comprises the step of dynamically adopting said power utilization profile based on radio measurements.

3. A method according to claim 1 , characterized in that the method further comprises the step of changing said power utilization profile based on pre-defined rules.

4. A method according to claim 3, characterized in that said pre-defined rules are based on at least one of the following: what time of the day it is, experienced quality, cell load, or system load.

5. A method according to claim 1 , characterized in that the method further comprises the steps of:

- measuring a power output from said transmitter;

- comparing said measured output power with an allowed output power;

- if said measured output power is higher than said allowed output power, adjusting an output power of the next data transmission.

6. A method according to claim 1 , characterized in that the method further comprises the steps of:

- scheduling data transmissions of user equipments known having a large power utilization in advance;

- interposing user equipments in need of less power in between said user equipments having a large power utilization.

7. A method according to any of the preceding claims, characterized in that the method further comprises the step of providing two power utilization profiles, whereby a first power utilization profile is used over a first period of time and a second power utilization profile is used over a second period of time which is longer than said first period of time.

8. A method according to claim 1 when introducing a new radio base station in said communication network, characterized in that the method further comprises the step of gradually increasing said power utilization profile for said new radio base station, whereby existing radio base stations and said new radio base station are given an opportunity to adapt to each other.

9. A method according to claim 8, characterized in that said adaptation is done by using at least one of the following: self-optimizing algorithms, manual intervention after an alarm has been raised or statistical processing of radio base station performance for further manual actions.

10. A radio transmitter controlling device for controlling interference between cells in a communication network comprising a radio transmitter (42, 46) transmitting data to a receiver (41 , 47) over a radio interface, characterized in that said radio transmitter controlling device (43, 48) comprises a power utilization profile arranged to determine how much time said radio transmitter (42, 46) is allowed to operate on different power levels over a period of time.

1 1. A radio transmitter controlling device according to claim 10, characterized in that said radio transmitter controlling device (43, 48) is arranged to dynamically adopt said power utilization profile based on radio measurements.

12. A radio transmitter controlling device according to claim 10, characterized in that said radio transmitter controlling device (43, 48) is arranged to change said power utilization profile based on pre-defined rules.

13. A radio transmitter controlling device according to claim 12, characterized in that said pre-defined rules are based on at least one of the following: what time of the day it is, experienced quality, cell load, or system load.

14. A radio transmitter controlling device according to claim 10, characterized in that the radio transmitter controlling device (43, 48) comprises two power utilization profile, whereby a first power utilization profile is used over a first period of time and a second power utilization profile is used over a second period of time which is longer than said first period of time.

15. An arrangement for controlling interference between cells in a communication network comprising a radio transmitter (42, 46) transmitting data to a receiver (41 , 47) over a radio interface, characterized in that said arrangement comprises a transmitter controlling device (43, 48) according to any of claims 10 - 14.

16. An arrangement according to claim 15, characterized in that the arrangement further comprises:

- means (44) for measuring a power output from said radio transmitter; - means (44) for comparing said measured output power with an allowed output power;

- means (44) for adjusting an output power of the next data transmission if said measured output power is higher than said allowed output power.

17. An arrangement according to claim 15, characterized in that the arrangement further comprises a scheduler (45) arranged to schedule data transmissions of user equipments (18) known having a large power utilization in advance and to interpose user equipments (18) in need of less power in between said user equipments (18) having a large power utilization.

18. An arrangement according to any of claims 15 - 17 when introducing a new radio base station (15) in said communication network, characterized in that the arrangement further comprises means for gradually increasing said power utilization profile for said new radio base station (15), whereby existing radio base stations (15) and said new radio base station (15) are given an opportunity to adapt to each other by means of at least one of the following: self-optimizing algorithms, manual intervention after an alarm has been raised or statistical processing of radio base station performance for further manual actions.

19. A radio base station (15) for controlling interference between cells in a communication network, said radio base station (15) comprising a radio transmitter (42) transmitting data to one or more user equipments (18) over a radio interface characterized in that it further comprises an arrangement according to any of claims 15-18.

20. A user equipment (18) for controlling interference between cells in a communication network, said user equipment (18) comprising a radio transmitter (46) transmitting data to a radio base station (15) over a radio interface characterized in that it further comprises a radio transmitter controlling device (48) according to any of claims 10-14.

21. A computer-readable medium (60) containing computer program for controlling interference between cells in a communication network comprising a transmitter transmitting data to a receiver over a radio interface, characterised in that the computer program performs the step of determining how much time said transmitter is allowed to operate on different power levels over a period of time by means of a provided power utilization profile.