WO2007057517A1

WO2007057517A1 - Communications network

Info

Publication number: WO2007057517A1
Application number: PCT/FI2006/050498
Authority: WO
Inventors: Aarne Hummelholm
Original assignee: Tellog Ag
Priority date: 2005-11-16
Filing date: 2006-11-15
Publication date: 2007-05-24
Also published as: FI20051170A0; FI20051170L; EP1961248A1; EP1961248A4

Abstract

The present invention concerns a novel mobile communication network and network topology, and a method for designing and optimizing the network. According to the invention, instead of one directional antenna, the coverage and services of a plurality of directional antennas, and/or instead of one base station, the coverage and services of a plurality of base stations, are provided for the user terminal.

Description

Communications network

The present invention concerns a novel mobile communication network and network topology and a method for designing and optimizing said network.

The traditional network topology in mobile communication systems is the so called cellular system. There each transmitter that is called base station, covers a certain area, in other words cell. The radius of the cell can range from a couple of meters in a building and couple of hundreds of meters in towns to tens of kilometers in the countryside. The form of the cell is never a perfect circle or hexagon, but it depends on the environment (buildings, mountains, valleys, etc.), the weather conditions and sometimes even on the load of the system. Examples of this kind of systems include telecommunication systems (GSM, TETRA, UMTS etc.), in which the mobile station communicates within the area of the cell with the base station, and vice versa.

Also radio stations can be understood to operate with a cellular principle. In case of radio stations the cells are big and the transmitters are efficient. Cells used by telecommunication systems, however, are notably smaller. Traditionally, one base station provides the service option connections for the mobile station located in their respective cell area.

The meaning of the smaller cells used by the telecommunication systems is to provide a bigger capacity for the system. By means of small cells it is possible to reuse frequencies. If a transmitter is far from another, for example outside the interference area, it can reuse the same frequencies. Because the most of the mobile phone systems assign frequencies to predetermined users, those frequencies are excluded from other users. The amount of frequencies is, however, not unlimited, and therefore the amount of simultaneous users of one cell is strictly limited. Multiple users are not enabled even by big cells. On the contrary, their number of users per square kilometer is smaller. This is also a reason why very small cells are used in cities, because there the number of mobile phone users is bigger.

One advantage of small cells is also the decreasing of transmission power. Even though power considerations are not the biggest problem for base stations, they are a problem for mobile stations. A receiver located far from the base station needs much transmission power. In addition, small cells reduce local interference. If the distance between the transmitter and the receiver is long, even bigger interference problems occur. In small cells the mobile stations and base stations only need to deal with local interferences. J

And further, small cells have the advantage of having spread and single components. Spread in this way they are not as easily damaged. If one antenna is damaged, it has effects on the connections only within a small area.

) Not even the small cells are, however, perfect. Small cells require very careful frequency planning. To avoid interference between transmitters using the same frequencies, the frequencies must be very carefully divided. On one hand, interferences should be avoided, but, only a small set of frequencies is available.

! Traditionally, the first approach has been the grouping of the cells. Grouping means that the cells located next to each other do not operate with the same frequency, but between two cells operating on the same frequency there is always at least one cell using a different frequency. Traditionally one base station forms a service complex for its respective cell.

> Another approach has been the use of sectorized antennas. As described by its definition, the antennas are not non-directional, but they are divided in different sectors. A cell can be sectorized for example into three or six sectors, whereby the reuse of frequencies is enabled. A sectorized antenna is in practice a set of directional antennas connected to one point.

There are, however, still disadvantages connected with these cellular network systems of the prior art. Because the worst possible case is that some area remains uncovered - which in practice means that any mobile station roamed onto that area looses the network - the cellular network is constructed so that usually the coverage areas of adjacent cells are widely overlapping. Even directional antennas are not able to provide such a precise directioning, that the whole area would be covered without overlappings. Then this kind of an overlapping always causes interference due to the other users. Another big disadvantage is the earlier mentioned damaging of the antenna of a base station or a base station. When one base station is damaged, it leaves a gap of the size of the respective base station coverage area, and the surrounding base stations, even though they have the sectorized antennas, are not able to immediately fill up this gap. At least redirectioning of the

• surrounding antennas is required. The worst case is that this broken base station is the only one to connect two important areas, and in case of damaging, separates these areas from each other.

The purpose of the present invention is to provide a network topology comprising the benefits ⁾ of the networks of the prior art but having the complexity of the present networks and the resulted disadvantages of design and implementation removed. A covering network with backupping can be constructed without unnecessary overlappings (the user can use the stronger base station only), in other words, with as fiew interferences as possible and so that it can be easily designed and optimized. This preferably quadratic cross-coverage area replaces i the traditional coverage area formed by the traditional one or a plurality of base station cells (i.a. micro- and picocells).

The purpose of the invention can be implemented by means of a cross-coverage method (RPMe). This means that unlike in traditional systems, the coverage and services of a plurality

> of directional antennas are directed to the terminal device or the mobile station instead of those provided by one directional antenna, and/or the coverage and services of a plurality of base stations are directed to the terminal device or the mobile station instead of those provided by one base station. The terminal device of the user uses and gets the service from the base station or through the base station offering the best connection in terms of quality, or

' eventually simultaneously through a plurality of antennas or from or through a plurality of base stations. In a network in accordance with the cross-coverage method, the adjacent base stations can be connected with each other by means of narrow beam directional antennas, and by means of other directional antennas the base stations serve the users of the mobile stations. Adjacent base stations can also be connected with each other for example by means of wired

• connections. From the network in accordance with the cross-coverage method, the user gets the service through a coverage complex formed by a plurality of base stations. Preferably the coverage complex is formed by four base stations. Preferably a network topology in accordance with this cross-coverage method can be considered as a grid viewed from above. Accoding to the invention, a corner of each square comprises a base station. Preferably this kind of a single base stations comprises transmitters (narrow beam directional antennas) being in connection with adjacent base statiosand i transmitters (directional antennas of about 90 degrees) being directed for example inside the square formed by four base stations in order to provide the frequencies required by the mobile stations. Preferably these sevice squares required by the mobile stations can be directed to any direction. Also for example upwards and downwards, whereby for example the air traffic and the direction downwards from the base station can be served. For each direction, a respected

I radio transmitter can be provided. So, at the simpliest, the invention can be a square or a parallelogram. According to a preferred embodiment, the network according to the cross- coverage method can also be formed of cubes or irregular cubes, that further can form grids, hi one preferred embodiment, the communication network in accordance with the invention can move, be in motion or move partially.

An advantage of the network according to the cross-coverage method in accordance with the present invention is that a vide coverage can be provided for the network with as few interferences as possible. Another advantage is that in case one radio transmitter of the network in accordance with the cross-coverage method fails, the area covered by this failed I radio transmitter still remains within the netword. In case a whole base station fails, the coverage of the adjacent base stations compensates the failed base station, and above all, no one of the base stations can be located in that way in a critical place, that its failure would prevent the operation of the network.

! hi an even network topology in accordance with the the cross-coverage method of the invention, the user terminal in each square is connected to that base station, that can give the best possible sevice in terms of quality. Thus, in case some of the base stations is not able to serve, the user according to the cross-coverage method automatically utilizes another service of the base station directed to the area. Cross-coverage areas (squares) can operate

) independently as their own respective complex with their respective services, and by connecting them with each other, wider network entities can be constructed, with all their services. This does not restrict the costructional size of the network in accordance with the topology. In a topology in accordance with the cross-coverage method, the users are able to utilize the total capacity offered by the coverage complex.

Design of a network in accordance with the invention is simple, because the path attenuation of the radio wave is known in different circumstances and because it is not necessary to take the overlappings of different channels into consideration. Thus, the size of a square of the network in accordance with the cross-coverage method can be easily calculated. A square- related equation, modified based on the Erlang equation can be used for calculating the minimum capacity needed by the users. The needed network capacity can be calculated in a i simple way, because for example a total communication capacity of 200 Mb/s for interfaces in simultaneous use will be offered to each square. According to the quality, the terminal of the user selects, based on the quality and usability, the base station from the square that offers the best service. Thus, the total capacity provided for the square can be filled. The construction of the network enables the corresponding capacity for the uniform trunk traffic amount.

The cross-coverage method also serves the communication between the base stations. Thus, the network in accordance with the cross-coverage method operates with a multiple backup. The capacity per square can be increased by increasing the use of frequency resources with allowed blocking. When allowing blocking (by weakening the service quality), the amount of • simultaneous users can be increased. This network topology also provides an easy dynamic management and allocation of frequency ressources according to the needs of the users. In the network in accordance with the cross-coverage method, the frequencies can be selected according to the situation and coverage requirements among a plurality of frequency bands, that can be used at the same time or separately to form the coverage areas according to the cross-coverage method. This method provides a flexible management and control of base stations and user devices related to base station, coverage area or network. The connections out depend on the amount of communication, f.ex. if a connection of 1 Gb can manage 5 squares of 200 Mb/s each, no blocking occurs.

i As an example, e.g. a big square formed house having a base station at each corner, whereby a radio transmitter of one sector, respectively, is directed to the inside the house. When moving inside the hose, you are always in the coverage area of at least one of the transmitters, and all the refelctions are strongly oblique, whereby there is the most efficient multipath propagation. The user is served by the base station having the best connection in terms of quality. A network in accordance with the cross-coverage method can also act as operator of the communications between the base stations. This guarantees the multiple back-up for the communications between the base stations.

More precicely, the cross-coverage method and the network topology in accordance with the invention will be evident from the enclosed drawing. Figure 1 shows one preferred embodiment of the cross-coverage method in accordance with the invention, in this case a square.

Figure 1 shows at numeral 1 a base station point, that is a cross-coverage point, comprising directional antennas for the communication from one base station to another and the antennas for connecting the users. Reference numeral 2 shows the beams of the antennas meant for connecting the user terminals to the communication network. Reference numeral 3 shows the beams operating in the communication between the base stations.

One base station offers four separate beams 2a, 2b, 2c, 2d to the users. The figure shows four base stations 1, forming in the middle a square-formed coverage complex. From these base stations, one directional antenna of each, respectively, is directed inside the coverage area complex. When interpreting the figure, it must be noticed, that each base station in principle corresponds to all the base stations. That is to say, that from each base station beam 2a, 2b, 2c, 2d is provided. In this Figure, however, only one beam is shown coming from each base station, with the exception of 2a. In the Figure, the reference numerals of the beams 2a, 2b, 2c, 2d meant for the user terminals, are shown so that their numeral is marked at the boundary of the coverage area of the respective directional antenna of 90 degrees, directed inside the square. Reference numeral 2a is meant for better understanding of the coverage area of each beam, as it is repeated both in the first square left, and in the adjacent square on the right. This kind of a square of the cross-coverage method is covered as a whole so that in the middle of the square there is the coverage area of the beam of each base station in the corners. Preferably this middle area is designed so that there is the highest demand of services, and thus also the best offer of services. In the coverage area complex of the cross-coverage method, the user terminal always has a connection at least with two directional antennas anywere inside the square. Reference numerals 4arespresent these kinds of coverage areas of two directional antennas. Reference numerals 4b show areas, where the coverage area of three directional antennas is extended. Reference numerals 4c then represent the area of the highest service demand, where the coverage area of four directional antennas is directed to.

According to a preferred embodiment, the network topology can be formed so, that each base station point 1 is in connection with all the nearest base stations. In that way, a simple grid can • be formed, wherein the users are served with antennas of the base station points 1 of corners, said antennas being directed inside the respective square.

In an another preferred embodiment, the base stations 1 are not in connection with all the adjacent base stations, but the cross-coverage method can act so that the nearest base stations i in certain corners are in connection with each other by means of beams 3. Base stations in certain other corners, in turn, are not necessarily in connection with adjacent base stations. At an advantageous location, and suitable for the respective environment, the networks formed in this way superposed can be connected with each other.

) Furhter, according to a preferred embodiment, the cross-coverage method can be implemented so that antennas directed upwards and downwards are added for communication between the base stations. Thus, the coverage area of the network can be expanded towards a matrix model. Also the directional antennas meant for serving mobile users can be directed upwards and downwards, whereby an even more diversified coverage area of the communication

> network can be provided.

According to a preferred embodiment, the cross-coverage method can also be a so-called matrix model. There, two network topologies are connected with each other superposed by means of networks directed upwards and downwards, hi that way a network covering a very ) large area can be constructed to any direction so that a failure of a single base station point or a radio transmitter comprising a base station point is not critical.

Claims

1. A communication network, characterized in that it comprises at least two directional antennas forming from different directions a coverage area complex being at least partly overlapping, whereby the user terminal receives from said coverage area complex contact to the service equally through said at least two directional antennas

2. A communication network in accordance with claim 1, characterized in that the user terminal gets a contact to the service simultaneously through the both directional antennas.

•

3. A communication network in accordance with claim 1 or 2, characterized in that the directional antennas are connected to at least one base station.

4. A communication network in accordance with any of the claims from 1 to 3, characterized in that there are at least two different coverage area complexes on the service area of the directional antennas of the base station.

5. A communication network in accordance with any of the claims from 1 to 4, characterized in that on the service area of the directional antennas of the base station there is a coverage of at least two base stations.

6. A communication network in accordance with any of the claims from 1 to 5, characterized in that one base station comprises from 1 to n antennas.

7. A communication network in accordance with any of the claims from 1 to 6, characterized in that the base stations use the same frequencies.

8. A communication network in accordance with any of the claims from 1 to 6, characterized in that the base stations use different frequencies.

9. A communication network in accordance with any of the preceding claims, characterized in that each base station has a wireless connection to at least one adjacent base station.

5 10. A communication network in accordance with any of the preceding claims, characterized in that each base station has a wired connection to at least one adjacent base station.

11. A communication network in accordance with any of the preceding claims, 3 characterized in that the communication network has a connection to other communication networks.

12. A communication network in accordance with any of the preceding claims, characterized in that the base stations are located so that they form substantially

5 squares, a coverage area complex offering the service being formed inside a sigle square.

13. A communication network in accordance with any of the preceding claims, characterized in that the base stations are located so that they form cubical prisms.

)

14. A communication network in accordance with any of the preceding claims, characterized in that the base stations are located so that they form irregular prisms.

15. A communication network in accordance with any of the preceding claims, 5 characterized in that the base stations are located so that they form a multidimensional grid structure.

16. A communication network in accordance with any of the preceding claims, characterized in that the management and control service of the network is

) implemented base-station-related.

17. A communication network in accordance with any of the preceding claims, characterized in that the management and control service of the network is implemented coverage-area-related.

18. A communication network in accordance with any of the preceding claims, characterized in that the management and control service of the network is implemented communication-network-related.

19. A communication network in accordance with any of the preceding claims, characterized in that the communication network is a multiservice network.

20. A method for providing service for users of a communication network comprising base stations, characterized in that the method comprises:

- communication between the base station and the terminal device at least with two directional antennas simultaneously.