WO2007045779A1

WO2007045779A1 - Method of planning the allocation of carriers in a cellular radio communication network

Info

Publication number: WO2007045779A1
Application number: PCT/FR2006/050965
Authority: WO
Inventors: Guillaume Lebrun; Olivier Seller
Original assignee: France Telecom
Priority date: 2005-10-06
Filing date: 2006-09-29
Publication date: 2007-04-26
Also published as: FR2891977A1

Abstract

The invention relates to a method of planning the allocation of carriers in a cellular radio communication network. A cellular radio communication network (RR) is equipped with propagation channels which are split into time intervals and which are each associated with several carriers. In order to plan the allocation of carriers in the network, for each time interval and for each pair of network cells, when transmission in one cell from the pair creates an intercellular interference level that is greater than a pre-determined threshold in the other cell from the pair, a planning module (MP) allocates the cells with respectively-different opportunistic carriers and partially-shared diversity carriers. A database (BD) stores a global planned allocation strategy for all of the network cells as a function of the carrier allocations in a digital strategy file (FS) which can be accessed from base stations (BS) located respectively in the cells of the network.

Description

Carrier allocation planning in a cellular radio network

The present invention relates to carrier allocation planning in a cellular radio network. More specifically, it relates to a combination of carrier allocations opportunistically and in diversity.

In a cellular radio network, the geographical distribution of the access points, such as base stations, allows a user to remain connected to the network by changing the access point during his travels. Access points typically transmit multiple carriers in separate frequency bands to limit interference in the border areas of multiple cells.

In multi-carrier type networks, transmission opportunities are distributed between user mobiles, a transmission opportunity corresponding to the use of a carrier during a symbol time. In a multicellular network of multi-carrier type, the multiple access is at the network level to distribute these transmission opportunities between the cells and the mobile user and within a cell to distribute these opportunities of transmission between the mobile user. Radio communications are multipath, causing fading due to alternating constructive and destructive interference. SFN single frequency networks ("Single Frequency Network") transmit on the same transmission frequency in all cells and suffer from intercellular interference. Transmission opportunity allocation techniques are designed to limit the effects of fading and intercellular interference on network performance.

A first allocation technique, called the diversity strategy, relies on statistical methods that reduce cell edge interference by, for example, using carrier allocations to user mobiles respectively, the carrier frequencies being distributed. in the frequency band used by the network. The interference may be averaged by coding for Coded Orthogonal Frequency Division Multiplexing (COFDM) coded orthogonal frequency multiplexing transmission, by allocation of quasi-disjoint transmission opportunity sets for any pair of mobiles. for OFDMA (Orthogonal Frequency Division Multiple Access) orthogonal frequency division multiplex transmission, by frequency hopping spread spectrum for orthogonal frequency division multiplexed access FH-OFDMA ("Frequency Orthogonal Frequency Division Multiple Access ("in English"), or by a direct sequence spread spectrum for multiplexed multiplex access transmission of MC-CDMA encoded carriers ("Multi Carrier Coded Multiple Division Access"). The diversity strategy does not require knowledge of propagation channels, i.e. channel fading and interference power for each antenna and mobile. However the diversity strategy is not optimal since a transmission opportunity experiencing a strong fading can be allocated to the communication between a base station and a mobile, which generates a loss of symbol and an unnecessary consumption of energy.

A second allocation technique, called an opportunistic strategy, requires the knowledge of the propagation conditions in order to transmit data on a propagation channel when the conditions of the propagation channel are favorable, ie when the carrier does not undergo not a strong fainting and when the interference on the opportunity of transmission is low. The opportunistic strategy has the disadvantage of a permanent need for knowledge on propagation channels. In addition, when a user's traveling speed is high, permanent knowledge of the propagation channel is impossible and the opportunistic strategy is therefore inapplicable. In a multicellular network, the interference power in one cell varies according to the allocations in another neighboring cell. As a result, the opportunistic strategy suffers from instability when applied to a multicell network.

The aim of the invention is to plan carrier allocations by combining a diversity allocation strategy and an opportunistic allocation strategy, in order to overcome the aforementioned drawbacks and to benefit from the advantages of the two carrier allocation strategies.

To achieve this goal, a method for scheduling carrier allocations in a network cellular radio communication system having propagation channels shared in time intervals and each associated with several carriers, is characterized in that it comprises, for at least one time slot and for at least two cells of the network comprising opportunistic carriers and carriers of diversity, an allocation of opportunistic carriers respectively distinct cells.

According to another characteristic of the invention, the method furthermore comprises a planning of a global allocation strategy for all the cells of the network as a function of the allocated carriers in a digital strategy file accessible from base stations situated respectively in the cells of the network.

According to the invention, the cellular radiocommunication network enjoys advantages due to the coexistence of opportunistic carrier allocations and diversity. The network is optimized, for example, for low mobile motion speeds according to opportunistic carrier allocations and for high mobile motion speeds according to diversity carrier allocations.

Furthermore, the invention facilitates the distribution of traffic in the network. For example, if downlink transmission from a base station to a mobile requires high throughput, then opportunistic carriers are allocated to that downlink.

In addition, when the transmission in one of the cells creates an intercellular interference power greater than a predetermined threshold in another of the cells, or when the cells are adjacent, the allocation of opportunist carriers respectively distinct to the cells can be performed. According to another characteristic of the invention, the method further comprises an analysis of measured quantities, including interference powers, relating to propagation channels between the base stations and receivers distributed in the network in order to allocate from carriers to cells.

According to another characteristic of the invention, the method further comprises a modification of parameters relating to opportunistic carriers for the entire network. The base stations according to the invention can assign opportunistic carriers to mobiles based on mobile-related characteristics and opportunistic carriers available according to the overall planned allocation strategy. On the other hand, opportunistic carriers may have powers greater than the carrier powers of diversity and may also carry signaling symbols.

According to another characteristic of the invention, common opportunistic carriers can be allocated to cells, when the transmission between these cells creates an intercell interference power lower than the predetermined threshold.

According to another characteristic of the invention, opportunistic carriers allocated to a cell during a given time interval can be exclusively distinct from the opportunistic carriers allocated to the same cell for a period of time consecutive to the given time interval. According to another characteristic of the invention, the method further comprises an introduction of an additional base station associated with an additional cell, said additional base station performing one of the following operations of estimating the propagation conditions respectively with neighboring cells and consider the opportunistic carriers allocated to the neighboring cells in order to allocate opportunistic carriers to said additional base station.

The invention also relates to a device for scheduling carrier allocations in a cellular radio network having propagation channels shared in time intervals and each associated with several carriers. The device is characterized in that it comprises: for at least one time interval and for at least two cells of the network comprising opportunistic carriers and diversity carriers, a means for allocating the respective opportunistic carriers to the cells respectively.

The device further comprises means for scheduling a global allocation strategy for all the cells of the network according to the allocated carriers in a digital strategy file accessible from base stations located respectively in the cells of the network.

Finally, the invention relates to a computer program capable of being implemented in a device for scheduling carrier allocations in a cellular radio network having propagation channels. shared in time intervals and each associated with several carriers, said program comprising instructions which, when the program is loaded and executed on said device perform the steps according to the method of the invention.

Other features and advantages of the present invention will emerge more clearly on reading the following description of several preferred embodiments of the invention, given by way of non-limiting examples, with reference to the corresponding appended drawings in which:

FIG. 1 is a diagram of a digital cellular radio network model according to the invention;

FIG. 2 is an algorithm of a planning method according to the invention;

FIG. 3 is a time representation of carrier allocation; FIG. 4 is a time-allocation representation of carriers with limited power for diversity carriers;

FIG. 5 is a time representation of carrier allocation with transmission of signaling symbols on opportunistic carriers; and

FIG. 6 is a temporal representation of dynamic carrier allocation.

With reference to FIG. 1, the cellular digital radiocommunication network RR comprises cells C _c at the heart of the network and cells C _b at the edge of the network. The RR network is connected to a DP planning device via a network of RT telecommunications which can be the internet or include specialized lines for example.

The RR radio network is a cellular network having shared propagation channels in time intervals each associated with several carriers. Base stations in the network cells are synchronized in frequency. For example, the cellular network RR is of the OFDM orthogonal frequency multiplexing type with multiple frequency access FDMA ("Frequency Division Multiple Access"). According to other examples, the cellular network RR is of the quadrature amplitude modulation type with OQAM offset ("Offset Quadrature Amplitude Modulation" in English), also known by the acronym OFDM / OQAM, or of the MC-CDMA type.

Each cell of the RR network extends around a respective base station BS. M mobiles and RE receivers are located under the coverage of the BS network stations of the RR network. The arrangement of cells in the array corresponds for example to deploy a network on a city mostly covered by cells C _c and the surrounding countryside mostly covered by cell C _b -

In FIG. 1, the outline of the cells of the network is schematized in a conventional manner by juxtaposed hexagons. For the sake of simplification, the border cells C _b have a shape close to that of a rhombus and only three C _c cells and nine C _b cells are represented. Moreover, in order not to overload FIG. 1, a single mobile M, a single receiver RE and a single base station BS are represented. The planning device DP is for example a server associated with a database BD.

The DP device mainly comprises a central processing unit UC, an estimation module ME and an planning module MP.

The central processing unit UC is equipped with a microprocessor μP and a memory M containing, for example, instructions from a computer program Pg for scheduling carrier allocations.

The estimation module ME executes predefined algorithms for estimating propagation conditions of different propagation channels between base stations BS of the RR network and mobiles M and receivers RE.

The planning module MP analyzes the results of the execution of the predefined algorithms in order to plan carrier allocation strategies relating to the different cells of the network.

The database BD is linked to the planning device DP, that is to say it is either integrated in the planning device DP, or incorporated into a database management server and connected to the planning device by a local or remote link. The database BD includes information on carrier allocation strategies, measured GM values for propagation channels and FS strategy files.

The carrier allocation strategies of the invention are composed of opportunistic allocation strategies and diversity allocation strategies. Each strategy consists of allocating a set of carriers to mobiles by a base station in a cell of the RR cellular radio network.

According to the opportunistic allocation, an algorithm allocates a so-called "opportunistic carrier" carrier to a mobile based on information on the propagation channel used by the base station. For example, the opportunistic allocation depends on a signal-to-noise ratio or a signal to interference ratio, and / or the speed of movement of the mobile and / or the position of the mobile, and carriers are preferably allocated mobiles with the best propagation conditions on these carriers. In this case, the base station uses characteristic magnitudes of the propagation channel in combination with a multi-antenna technique to adapt the signal transmission to the propagation channel.

According to the diversity allocation, an algorithm allocates a carrier called "diversity carrier" to a mobile independently of information on the propagation channel used by the base station. Generally, the base station of a cell allocates respectively to mobiles of the carriers distributed in the frequency band relative to the cell by using various spread spectrum techniques.

Most often in the heart of the network, mobiles move slowly and require a large bandwidth, for example for video signals. In this case, opportunistic carriers are bestowed on mobiles.

At the edge of the network, mobiles move faster but require a smaller bandwidth, for example for voice signals. In In this case, carriers of diversity are bestowed on mobiles.

Therefore, cells C _v located in the heart of the network usually have more opportunistic carriers that C _B cells at the edge of the network.

With reference to FIG. 2, the planning method according to a preferred embodiment of the invention comprises steps E1 to E6, executed for example before the putting into service of the RR network or during the deployment of the RR network. Steps E2 to E6 succeeding the preliminary step E1 are executed by the planning device DP. The RR cellular radio network has propagation channels shared in time intervals and each associated with several carriers to be assigned to several mobiles M.

In step El, receivers RE distributed in the cells of the network RR receive signals transmitted by the base stations BS located respectively in the cells. Receivers are devices intended to perform measurements and may be mobiles. Each receiver RE performs measurements based on a received signal in order to extract various measured variables GM relating to the propagation channel between a given base station BS transmitting the received signal and the receiver. The magnitudes measured are, for example, a signal-interference ratio CIR ("Carrier-to-Interference Ratio"), that is to say the ratio of the power received in the channel of propagation by the receiver on the power of d interference received by the receiver, or signal-to-noise ratio (SNR) English). The interference power received by the receiver RE is due to the propagation channels relating to other receivers having active downlinks with the given station BS and to the base stations other than the given base station BS.

In step E2, all the receivers RE transmit the GM measured quantities of the propagation channels to the planning device DP via the telecommunications network RT.

In step E3, the estimating module ME of the planning device DP collects and analyzes all the measured quantities received GM, including interference powers. The module ME executes predefined algorithms in order to estimate propagation conditions of the different propagation channels between base stations BS of the network RR and receivers RE distributed on different points of the network and thus to subsequently allocate carriers to the cells. . In particular, for each pair of cells of the network, the module ME estimates an intercellular interference power created by the transmission of a cell to another cell and compares the estimated interference powers to a predetermined threshold. For example, the ME module calculates an average of the estimated interference powers for each cell, compares the averages calculated to distinguish appropriate cells from the opportunistic allocations, and a greater number of opportunistic carriers can be allocated to the appropriate cells. If the averages calculated are substantially equal, no distinction is made and the same number of opportunistic carriers is allocated to all the cells. Other quantities measured corresponding to characteristics of a mobile such as the speed of movement and the position of the mobile in a cell are analyzed in particular with respect to the other cells of the network.

Alternatively, steps E1 to E3 are optional.

In step E4, the scheduling module MP defines a total number N of available carriers for the cells having shared propagation channels in time slots. According to the compared interference powers of each pair of cells for example, the module MP allocates an integer number k of opportunistic carriers and an integer number N - k of diversity carriers of the N carriers available in each cell, for each interval. of time. The integer can be variable from one time interval to the next and the cells are for example adjacent. When the transmission in a first cell creates intercellular interference power greater than a predetermined power threshold in a second cell, the MP module allocates, for each time slot and for the pair of the first cell and the second cell of the second cell. RR network, a first group of opportunistic carriers to the first cell and a second group of opportunistic carriers to the second cell, as well as diversity carriers partially common to both cells. At each time interval, the carriers of the first group are distinct from the carriers of the second group. In addition, some or all of the opportunistic carriers allocated to a cell during a given time interval may be exclusively distinct from the set of opportunistic carriers allocated to the same cell for a period of time consecutive to the given time interval. In addition, opportunistic carriers allocated to the first cell during a time interval may be the same as those allocated to the second cell for a consecutive time interval. The opportunistic carriers allocated to distinct cells are thus temporally confounded. When the transmission between cells creates an intercell interference power lower than the predetermined power threshold, common opportunistic carriers can be allocated to these cells. The integer number k of opportunistic carriers allocated to each cell is variable according to the other cells of the network, especially nearby cells creating interference. In general, the number N - k is greater than the number k. For example, when the network RR has a regular pattern of m cells of the same type, the number k of opportunistic carriers is equal to the integer part of the ratio of the number N of available carriers to the number m of cells of the same type, with N > m. For example, with reference to the tables of FIG. 3 in which the abscissa represents time and consecutive time intervals and the ordinate axis represents the frequency corresponding to carrier indices, the RR network comprises m = 3 types. cells A, B and C distributed uniformly in the network and has N = 12 carriers available for the cells. At each time interval, each cell has k = 4 opportunistic carriers designated by OPP and N - k = 8 diversity carriers designated by DIV, all having the same power of emission P. The opportunistic carriers of the cell being distinct from the opportunistic carriers in cells neighboring said cell, while the diversity carriers are partially common to the cells.

Alternatively, the MP module allocates a number k of opportunistic carriers and a number N - k of diversity carriers to each cell for all time slots.

For example, with reference to FIG. 1, the RR network comprises three C _c cells and nine frequency-synchronized C _b cells and has N = 9 different carrier frequencies for the cells. Each cell C _c is allocated k _c = 3 different opportunistic carriers of the N - k _c = 6 opportunistic carriers allocated to the two other C _c cells, and each cell C _b is allocated k _f c, = 1 opportunistic carrier different from the N - k _b = 8 opportunistic carriers in the other cells C _b , the allocations being valid and definitive for all time intervals.

Each cell C _b has an opportunistic carrier in common with one of the cells C _c so that the intracellular transmission of the cell C _b creates an interference power lower than a predetermined threshold in the cell C _c , for example when the cells are far enough apart, for the duration of network activity or until a new allocation schedule.

In step E5, the planning module MP plans a global carrier allocation strategy for all the cells of the RR network. function of previously allocated carriers. For each time slot, all the cells of the RR network have a particular carrier allocation adapted to the different propagation conditions respectively in the cells of the network. The module MP stores the global carrier allocation strategy for example in a digital strategy file FS in the database BD. The global allocation strategy is accessible from the base stations BS located respectively in the cells of the network RR via the telecommunications network RT so that each base station reads the frequencies of the carriers that have been allocated to it. Alternatively, lists of carrier frequencies included in the strategy file and allocated to the base stations are transmitted via the telecommunications network RT to all base stations BS of the network which stores them.

In step E6, the planning module MP optionally modifies parameters relating to the opportunistic carriers for the entire RR network. The FS policy file including the modified parameters is then stored again in the database BD. For example, opportunistic carriers have powers greater than carrier powers of diversity, to minimize intercellular interference to opportunistic carriers. With reference to the tables in FIG. 4 similar to the tables in FIG. 3, the opportunistic carriers designated by OPP have a power P four times greater than the power P / 4 of diversity carriers designated DIV. Thus, a mobile can detect the type of cell in which it is thanks to the opportunistic carriers transmitted with a high power.

In another example, opportunistic carriers carry signaling symbols such as pilot sequences. Referring to the tables of FIG. 5 similar to the tables of FIG. 4, the opportunistic carriers designated by OPP carry signaling symbols schematized by black blocks in FIG. 5. Indeed, the opportunistic carriers are less sensitive to intercellular interference than the carriers. diversity carriers that are more interfering carriers.

Alternatively, step E6 is executed before step E5 or after deployment of the RR network.

At the end of step E6, the cellular radiocommunication network RR is configured and planned according to a global allocation strategy. Each base station BS has a set of antennas adaptable to the carrier allocation strategies used. For example, base stations transmit opportunistic carriers from a directional antenna and diversity carriers from an omnidirectional antenna. When the network is active, the base stations allocate opportunistic carriers to mobiles based on mobile-related characteristics and opportunistic carriers available according to the overall planned allocation strategy. The characteristics relating to a mobile are, for example, the propagation channel between the base station and the mobile, the speed of movement of the mobile, the position of the mobile, the type of data traffic (voice, video) generated and / or undergone. speak mobile, the technical capabilities of the modem relating to the mobile or the type of subscription of the mobile user.

If an additional base station associated with an additional cell is to be introduced into the RR network, the additional base station estimates the propagation conditions respectively with neighboring cells and / or considers the opportunistic carriers allocated to the neighboring cells in order to allocate opportunistic carriers to said additional base station according to inter-cell interference powers for example. The global allocation strategy thus allows dynamic allocations when using the network.

With reference to the tables of FIG. 6 similar to the tables of FIG. 4, the network RR dynamically allocates opportunistic carriers designated by OPP. For example, each cell has a set of identical opportunistic carriers for several time slots, the carrier indices in each set being consecutive. When a new cell C is introduced into the RR network, part of a dashed-line time slot for cell C is dedicated to the interference power measurement to allocate opportunistic carriers to cell C according to intercellular interference powers relating to the transmissions in the active cells A and B of the RR network.

The invention described herein relates to a method and a device for scheduling carriers in a RR cellular radio network having shared propagation channels at time intervals and each associated with a plurality of carriers. According to a preferred implementation, the steps of the method of the invention are determined by the instructions of a computer program, such as the program Pg, incorporated in a computing device such as the device DP. The program comprises program instructions which, when said program is loaded and executed in the computing device whose operation is then controlled by the execution of the program, perform the steps of the method according to the invention. Accordingly, the invention also applies to a computer program, including a computer program on or in an information carrier, adapted to implement the invention. This program can use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code such as in a partially compiled form, or in any other form desirable to implement the method according to the invention.

The information carrier may be any entity or device capable of storing the program. For example, the medium may comprise storage means or recording medium on which is stored the computer program according to the invention, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or a USB key, or a magnetic recording means, for example a floppy disk or a hard disk. On the other hand, the information medium may be a transmissible medium such as an electrical or optical signal, which may be conveyed via an electrical or optical cable, by radio or by other means. The program according to the invention can in particular be downloaded to an Internet type network.

Alternatively, the information carrier may be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in carrying out the method according to

The invention.

Claims

1 - Method for planning carrier allocations in a cellular radiocommunication network (RR) having propagation channels shared in time intervals and each associated with several carriers, characterized in that it comprises, for at least one interval of time and for at least two cells of the network comprising opportunistic carriers and diversity carriers, an allocation (E4) of opportunistic carriers respectively distinct to the cells.

2 - Method according to claim 1, comprising planning (E5) of a global allocation strategy for all the cells of the network according to the allocated carriers accessible from base stations (BS) located respectively in the cells of the network .

3 - Method according to claim 1 or 2, according to which, when the transmission in one of the cells creates an intercellular interference power greater than a predetermined threshold in another of the cells, the allocation of respectively distinct opportunistic carriers to the cells is carried out.

4 - Method according to any one of claims 1 to 3, according to which the allocation of respectively distinct opportunistic carriers to the cells is carried out when the cells are adjacent.

5 - Method according to any one of claims 1 to 4, comprising an analysis (E3) of measured quantities (GM), including interference powers, relating to propagation channels between the base stations (BS) and receptors (RE) distributed in the network (RR) in order to allocate carriers to the cells.

6 - Process according to any one of claims 1 to 5, comprising a modification

(E6) parameters relating to opportunistic carriers for the entire network (RR).

7 - Method according to any one of claims 2 to 6, according to which the base stations (BS) allocate opportunistic carriers to mobiles according to characteristics relating to the mobiles and available opportunistic carriers according to the overall allocation strategy planned.

8 - Method according to any one of claims 1 to 7, according to which opportunistic carriers have powers greater than the powers of the diversity carriers.

9 - Method according to any one of claims 1 to 8, according to which opportunistic carriers transport signaling symbols.

10 - Method according to any one of claims 3 to 9, according to which common opportunistic carriers are allocated to cells, when the transmission between these cells creates a intercellular interference power lower than the predetermined threshold.

11 - Method according to any one of claims 1 to 10, according to which opportunistic carriers allocated to a cell during a given time interval are exclusively distinct from opportunistic carriers allocated to the same cell during a time interval consecutive to the given time interval.

12 - Method according to any one of claims 1 to 11, comprising an introduction of an additional base station associated with an additional cell, said additional base station performing one of the following operations consisting of estimating the propagation conditions respectively with neighboring cells and consider the opportunistic carriers allocated to neighboring cells in order to allocate opportunistic carriers to said additional base station.

13 - Device (DP) for planning carrier allocations in a cellular radiocommunication network (RR) having propagation channels shared in time intervals and each associated with several carriers, characterized in that it comprises, for at least a time interval and for at least two cells of the network comprising opportunistic carriers and diversity carriers, a means (MP) for allocating respectively distinct opportunistic carriers to the cells. 14 - Device (DP) according to claim 13, further comprising means (MP) for planning a global allocation strategy for all the cells of the network (RR) according to the carriers allocated in a digital strategy file (FS ) accessible from base stations (BS) located respectively in the cells of the network.

15 - Computer program capable of being implemented in a device for planning carrier allocations in a cellular radiocommunication network (RR) having propagation channels shared in time intervals and each associated with several carriers, said program being characterized in that it comprises instructions which, when the program is loaded and executed in said device, carry out the steps of the method according to at least one of claims 1 to 12.

16 - Recording medium on which a computer program according to claim 15 is stored.