Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
  • H04W16/24—Cell structures
  • H04W16/32—Hierarchical cell structures
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/04—Reselecting a cell layer in multi-layered cells

Definitions

• the present invention relates to the field of cellular radiotelephony. More specifically, the invention relates to the transmission of data, in particular at high bit rates, in a radiotelephony system.
• the third generation radio systems take or will take into account many services and applications supposing the transmission of data at very high data rates.
• the resources allocated to data transfers (for example files containing sound and / or still or moving images), in particular via the Internet or similar networks, will represent a preponderant part of the available resource and will probably be higher, in the long term.
• resources allocated to voice communications which should remain substantially constant.
• the total throughput available to users of radiotelephony equipment is limited. In order to allow sufficient availability of resources, we have traditionally used, in particular, a densification of cells in a given territory.
• micro-cells which are relatively small cells (corresponding, for example, to that of an urban district) or even “pico-cells”, which are large cells. even smaller (corresponding, for example, to a street or a building).
• a disadvantage of this technique is that it requires a multiplication of fixed stations (base station or BS from the English "Base Station”), which are relatively complex and expensive elements.
• base station or BS base station from the English "Base Station”
• the possible data rate although high, is not optimal.
• the more cells, and therefore the fixed stations the more complex the management.
• the third generation UMTS networks (from the English “Universal Mobile Telecommunications System” or “Universal Mobile Telecommunications System”) have a capacity limited by the power used by broadcast channels.
• broadcast channel describes the point-to-multi-point type channels, for example of the BCH (“Broadcast Channel”) or PCH (“Paging Channel”) type.
• pico-cells small cells which are intended for high speed transmission for mobile terminals with geographically reduced mobility (a few hundred meters for example).
• a first objective of the invention is to increase the overall capacity of a cellular network comprising cells of different sizes and in particular the overall throughput of cells of small sizes (pico-cells or micro-cells), by providing a minimum of modifications to the mobile terminals used.
• the invention also aims to enable the implementation of equipment intended for third generation mobile communications networks, by requiring little or no modification of the current standards in force and in particular the UMTS FDD (“Frequency Division Duplex”) standard. ) (in particular the 25 series of this standard) defined and distributed by the 3GPP committee (or “Third generation partnership project” from the English “3 rd Generation Partnership Project”).
• the invention provides a cellular communication network comprising at least a first cell, called a large cell, associated with a first base station and geographically including at least a second cell, called a small cell, associated with it.
• a network terminal can be in particular in communication mode, when communication is established between the terminal and a remote terminal, and in standby mode, when the terminal is not in communication mode but present and available for communication, in one of the cells of the network, remarkable in that the first base station manages the mode standby for the terminals present in the small cell, the second base station being able to take over the communication mode and implementing a common pilot channel.
• the cellular network is remarkable in that the first base station manages the opening of a communication for a terminal present in the small cell, then the network transfers the management of the communication to the second station basic.
• the invention allows in particular a transfer of the management of the communication or "hand- fast "over (ie without listening to the SCH channel) between the large and the small cell even if the frequencies are different (this is a real problem in UMTS to make a hand-over when the frequencies are different) .
• An advantage of the fast hand-over is that it makes it possible to reduce the duration of use of the compressed mode defined by the 3GPP standard when a fast handover is desired. In this mode, a base station and / or a terminal starts transmitting at relatively high power at a first frequency, which makes it possible to create a vacuum which is used to transmit at a second different frequency. This mode therefore creates annoying interference for the network.
• the cellular network is remarkable that after the end of the communication, the terminal goes into standby mode and is managed by the first base station.
• the cellular network is remarkable that the second base station comprises means for synchronization on a synchronization signal emitted by the first base station, by hertzian way (SCH).
• SCH hertzian way
• the cellular network is remarkable that the second base station comprises means for synchronization on a synchronization signal transmitted by the first base station, by wire link. According to a particular characteristic, the cellular network is remarkable that the terminal deduces its synchronization on the second base station from that on the first base station.
• the cellular network is remarkable that the synchronization of the terminal on the second base station is a pseudosynchronization, tolerating synchronization errors of the order of 5 to 30 ⁇ s.
• the invention allows the use of hardware means usually dedicated to the determination of multiple paths and which are here advantageously used to perform fine and rapid synchronization.
• the invention allows a simple implementation of the synchronization means not only in the base stations but also in the user terminals.
• the terminal comprises:
• the analysis means implementing a step of determining at least one path corresponding to the predetermined signal supplying the synchronization means, the path or one of the paths corresponding to the predetermined signal, called the first path, being considered as the basis for synchronization.
• the cellular network is remarkable that the synchronization means take account only of the determination of at least one path corresponding to the predetermined signal transmitted by the second base station, the determination being implemented by the means of multipath analysis.
• the cellular network is remarkable that the predetermined signal is a signal (CPICH) dedicated to the processing of multiple paths and transmitted by the second base station. According to a particular characteristic, the cellular network is remarkable that at least certain cells composing it function asynchronously.
• CPICH signal
• the cellular network is remarkable that at least certain cells composing it operate synchronously, with a tolerance for synchronization error between them less than 5 ⁇ s.
• the small cell comprises means for transmitting a synchronization signal (SCH) allowing the terminal to synchronize with the second base station with a lower error tolerance at 5 ⁇ s.
• SCH synchronization signal
• the small cell does not need to synchronize with the large cell but has the drawback of not allowing a rapid "hand-over" and of consuming bandwidth.
• the invention also relates to a base station, remarkable in that, in a cellular network, the base station, called the first base station, is intended to be associated with a cell called the small cell which is itself intended to be geographically included in a cell, known as a large cell, itself associated with a second base station and geographically encompassing at least a second cell, a network terminal being able to be in particular in communication mode, when a communication is established between the terminal and a remote terminal, and in standby mode, when the terminal is not in communication mode but present and available for communication, in one of the cells of the network, and in that the second base station associated with the large cell manages the standby mode for the terminals present in the small cell, the first base station being able to support com mode munication and implementing a common pilot channel.
• the base station is remarkable in that it is suitable for high-speed communications.
• the invention also relates to a terminal intended to cooperate with at least one base station as previously described, remarkable in that the terminal comprises:
• CPICH predetermined signal
• the terminal is remarkable in that the first synchronization tolerates synchronization errors of the order of 5 to 30 ⁇ s.
• the terminal is remarkable in that the second synchronization tolerates synchronization errors of less than 5 ⁇ s.
• the invention relates to a cellular network management method comprising at least a first cell, called large cell, associated with a first base station and geographically including at least a second cell, called small cell, associated itself at a second base station, a network terminal being able to be in particular in communication mode, when a communication is established between the terminal and a remote terminal, and in standby mode, when the terminal is not in communication mode but present and available for communication, in one of the cells of the network, remarkable in that it comprises the following steps: management of a standby mode by the first base station for the terminals present in the small cell; and support for the communication mode and implementation of a pilot common channel by the second base station.
• the advantages of the terminal, the base station and the management method are the same as those of the telecommunications network, they are not described in more detail.
• - Figure 1 shows a network diagram according to the invention according to a particular embodiment
• - Figure 2 illustrates the network of Figure 1 after establishing communication between a terminal and a base station associated with a micro-cell;
• - Figure 3 describes a "micro-cell" base station of the network illustrated in Figures 1 and 2; and - Figure 4 illustrates a communication protocol between different network elements allowing the transition from a situation illustrated with reference to Figure 1 to a situation illustrated with respect to Figure 2.
• a network comprising large cells (for example, macrocells), some of these cells comprising smaller cells (for example micro- or pico-cells).
• the general principle of the invention is based in particular on a pseudosynchronization of each of the small cells on a macro-cell which encompasses it and on the implementation in small cells of dedicated channel management (transmission of data), but not (or to a limited extent) of the management of common channels (that is to say corresponding to point-to-multipoint links), user terminals (or user equipment also denoted UE of l 'English' User Equipments') being attached to the macro-cell encompassing these small cells, when the user equipment is in standby state.
• the user terminals are in particular mobile or fixed wireless terminals (for example mobile telephones or any other device (in particular portable computers) comprising a wireless communication system).
• a user equipment does not connect directly to a pico-cell: in standby mode, if it is present in a pico-cell itself included in a macro-cell, the equipment user is managed by this macro-cell, on which it depends. In particular, it receives the signals transmitted on BCH and PCH channels by a base station of the macro-cell. The picocell is then only accessible to the terminal by a “hand-over”, that is to say by a cell transfer managed and decided by the network.
• the start of a communication that is to say the opening of the dedicated channel, is done on the macro-cell. Only then does the terminal switch to the pico-cell. The terminal thus does not need the system information normally broadcast by a BCH channel (or “Broadcast Channel”) or equivalent which would be specific to the pico-cell.
• a BCH channel or “Broadcast Channel”
• the functionality of the pico-cell is restricted, which in particular does not support a terminal in the standby mode.
• This restriction of functionality of the pico-cell is not a drawback, because the small cells are mainly intended to manage channels reserved for high speed data transmissions more than for the management of mobiles in standby state, but an advantage, the base station of the picocell being greatly simplified.
• the terminal At the end of a communication on the pico-cell, the terminal returns to standby mode on the macro-cell.
• the SCH synchronization channels are not necessary for the “hand-over” from the macro-cell to the pico-cell because, on the one hand, the hand-over is pseudo-synchronous and, on the other hand , the destination cell is a pico-cell therefore of very small size.
• This “hand-over” can therefore be done directly, for example by looking for echoes on the pilot pico-cell channel (CPICH), the temporal uncertainty being very low.
• CPICH pilot pico-cell channel
• the synchronization between the pico-cells and the macro-cell does not need, according to the approach of the invention, significant precision.
• the channel SCH (“Synchronization Channel”) of the macro-cell to which it is attached.
• the pico-cell may be pseudo-synchronized on a macro-cell by a wire link between the base stations of each of the two cells.
• a pico-cell is pseudo synchronized on a macro-cell, a synchronization error of a few “chips” (a “chip” has a duration equal to 0.26 micro-seconds in the UMTS standard) on the synchronization of the terminal on the macro -cell does not pose a problem at the terminal to synchronize on the pico-cell.
• a pico-cell can implement its own SCH channel which allows asynchronous operation of the pcio-cell with respect to a macro-cell which includes it.
• the disadvantage of this embodiment is that it involves an asynchronous "hand-over” for the transition from the macro-cell to the pico-cell, that is to say a “hand-over” between two asynchronous cells ".
• an asynchronous "hand-over” is a procedure that takes time especially when it is a "handover” with frequency change as is the case here.
• the pilot channel is the only common channel that is essential, it allows the mobile when it is not connected to the pico-cell to see that it is in the coverage area. It also makes it possible to “hand-over” the macrocell to the pico-cell.
• the invention does not require adapting all the pico-cells of the UMTS networks.
• certain pico-cells can operate according to the mechanism of the invention, other pico-cells having all the broadcasting channels as proposed by the UMTS standard today in force.
• the network is for example a network compatible with the standard
• UMTS Universal Mobile Telecommunication System
• the network includes a large cell 100 (or “macro-cell”) which is managed by a baselOl station (BS).
• This cell 100 includes two smaller cells 110 and 120
• Each of the cells 110 and 120 respectively comprises a base station respectively 111 and 121 capable of managing the communications inside the corresponding cell. It is noted that by way of illustration, several terminals (UE) are present in the cell 100. Some of these terminals are also present in one of the small cells 110 and 120.
• UE terminals
• the terminal 112 is inside the cell 110 and can therefore receive or transmit signals from or to the base stations 101 and 111.
• the terminals 122 and 123 are inside 120 and can therefore receive or transmit signals from or to the base stations 101 and 121.
• the terminals 102 and 103 present in the cell 100 but not in one of the cells 110 and 120 can or transmit signals coming from or bound for the base station 101 but not from the base stations 111 or 121.
• the links between the various elements of cell 100 have been shown, at a given time: - in fine dotted lines for the links between base stations; in broad dashed lines for the links between the base station 101 and the terminals in standby state (the terminals 112, 122, 123 and 102 according to the example in FIG. 1); and
• certain terminals are in standby mode, that is to say in a mode where the terminals are not in communication mode but present and available for communication in one of the cells 100, 110 or 120.
• These terminals including listening to signals emitted by the base station 101 belonging to the macro-cell 100. These signals are emitted on: common transport channels corresponding to the services offered to the upper layers of the communication protocol, in particular on BCH (or “broadcast channel” from English “Broadcast CHannel”) and PCH (or “mobile search channel” from English “Paging CHannel”); and
• the terminals are not listening to the dedicated channels.
• the terminal 103 is not in standby mode since it is in communication with the base station 101 on a dedicated channel DCH (from the English “Dedicated CHannel”) which is both up and down.
• 3GPP networks are well known to those skilled in the art of mobile networks and are in particular specified in the standard “3 rd Generation Partnership Project; Technical Specification Group Radio Access Network; Physical Channels and mapping of transport channels onto physical channels (FDD) release 1999 ”reference 3GPP TS25.211 and distributed by the 3GPP publications office. These channels will therefore not be described more fully.
• FIG. 2 represents the network of FIG. 1 when a certain time has elapsed and in particular after an establishment of a communication between the terminal 123 and the base station 121 inside the micro-cell 120.
• the terminal 123 is directly connected to the base station 121 via a dedicated DCH up or down channel allowing the transport of the channel and / or the data exchanged.
• FIG. 3 schematically illustrates the base station 121 as illustrated with reference to FIGS. 1 and 2.
• the base station 121 comprises, interconnected by an address and data bus 307:
• wired network interface 300 allowing a link to a fixed infrastructure of the mobile network or to other networks;
• a reception radio interface 301 making it possible to receive the signals transmitted by the terminals in communication with the base station 121 on dedicated uplink channels and signals transmitted by the base station 101 in particular on the synchronization channel SCH (from the English “CHannel synchronization”) (note that the current UMTS standards do not provide that the SCH channel is listened to only by user equipment and not by a base station);
• a transmission radio interface 302 making it possible to transmit signals on dedicated downlink channels and on common transport channels corresponding to the physical layer (and not to the upper layers of the communication protocol) (in particular the CPICH channel); and
• the RAM 306 stores data, variables 309 and intermediate processing results.
• the non-volatile memory 305 stores in registers which, for convenience, have the same names as the data they store, in particular:
• the parameters 311 for configuring the base station 121 are the parameters 311 for configuring the base station 121.
• the base station 121 is implemented in a simpler manner than the base station 101 and in particular includes a simpler operating program than that of the base station 101 since it does not include the functionality of common channels that the base station 121 does not have to manage.
• the base station 121 does not synchronize on the SCH channel of the base station
• the radio reception interface 301 therefore makes it possible to receive the signals transmitted by the terminals in communication with the base station 121 on dedicated uplink channels and does not receive signals transmitted by the base station 101 in particular on the SCH synchronization channel (from “Synchronization CHannel”).
• the wired network interface 300 allowing a link to a fixed infrastructure of the mobile network or to other networks receives a synchronization signal emitted by the base station 101 on the wired network or on a dedicated link connecting the stations of base 101 and 121.
• the synchronization signal is implemented according to techniques known to those skilled in the art (for example, pulse according to a certain rhythm or particular bit sequence on which the base station 121 sets its own synchronization). This synchronization signal will therefore not be described further.
• wired synchronization requires a wired link. However, wired synchronization saves bandwidth on the radio medium and is very reliable by not being subject to radio interference.
• a terminal not shown, comprises interconnected by an address and data bus: - a processor;
• a reception radio interface making it possible to synchronize in standby mode on a SCH type signal sent by the base station 101 then, in communication mode, on a CPICH type signal sent by the base station 121 and to receive generally the signals transmitted by the base stations 101 and 121 on dedicated downlink channels;
• - a transmission radio interface making it possible to transmit signals on dedicated uplink channels and on uplink common transport channels; and - a man / machine interface allowing dialogue with the machine for control and maintenance.
• FIG. 4 illustrates a communication protocol between the base stations 101 and 121 and the terminal 123 during the transition from the situation illustrated with regard to FIG. 1 where the terminal 123 is in standby mode to a situation illustrated with regard to the figure 2 where the terminal 123 is in communication with the base station 121.
• the base station 101 transmits a signal 400 on the downlink SCH intended for the base stations and the terminals present in the macro-cell 100 and in particular of the base station 121 and of the terminal 123.
• the station of base 121 and the terminal 123 (which is, according to FIG. 1, in standby mode) are synchronized on the SCH channel of the base station 101.
• this signal SCH is transmitted regularly by the base station 101 and that as soon as the pseudo-synchronization of the base station 121 degrades beyond a certain predetermined threshold, the base station 121 resynchronizes on the station basic 101.
• this delay being for example equal to the propagation time of the signal SCH between the base stations 101 and 121;
• a “hand-over” signal (signal 405 detailed below) transmitted to the terminal 123 and conveying information indicating the position of the synchronization.
• the base station 101 also transmits a signal 401 on the BCH channel.
• This downlink signal indicates to terminal 123 which PCH channel it should listen to. Thus, after reception of this signal, the terminal 123 listens to the PCH channel indicated by the signal 401.
• the base station 101 transmits a signal to the terminal 123 on the PCH channel indicated by the signal 401, this signal making it possible to detect an incoming call.
• the terminal 123 transmits a signal 403 on the RACH channel (from the English “Random
• this signal 403 indicating to the base station 101 that the terminal 103 requests the establishment of a communication. Then, the base station 101 transmits a communication channel allocation signal 404 on the FACH channel (from the English “Fast Access CHannel” which is also a common channel corresponding to a high layer service).
• the hand-over allowing the passage of a communication from the terminal 123 to the base station 121 is made by decision of the network (in particular of the RNC or "Radio Network Controller" connected to the base stations 101 and 121) in function multiple criteria, in particular the speed, the quality of the communication and the specifics of the base station 121 (in particular the fact that it is well suited to handle high-speed communications).
• the terminal 123 listens to the pilot channel 406 CPICH which according to the invention makes it possible to refine the synchronization of the terminal 123.
• the cell 120 is small and that the base station 121 is pseudo-synchronized (by pseudo-synchronization, here is understood a synchronization with an accuracy of less than 50 ⁇ s and preferably less than or equal to 30 ⁇ s) on station 101 (c ' that is to say if the synchronization between the cells 120 and 100 is rough and not perfect, the synchronization error being less than approximately 50 ⁇ s and preferably 30 ⁇ s then in synchronized networks, known per se, the error on the synchronization is less than 5 ⁇ s, the resulting synchronization error between the terminal 123 and the base station 121 can be compensated for by using the signal 406.
• the terminal 123 comprises means s making it possible to take advantage of the multiple paths affecting a signal transmitted by a base station (This phenomenon of multiple paths is well known to those skilled in the art and is in particular the consequence of reflections on obstacles of a signal transmitted in several directions , the different signals received from the same transmitted signal but having followed different paths are generally of different amplitudes and out of phase). It should be noted that in particular a “rake” type receiver makes it possible to determine the different delays affecting a multi-path signal. Thus, if the delay is not too great (that is to say less than 20 ⁇ s within the framework of the 3GPP standard), the terminal 123 is able to synchronize on the CPICH channel.
• the receiver of the terminal 123 stalling on this hypothetical path searches for at least one path corresponding to a signal transmitted on the CPICH channel of the base station with the means also used for determining the multiple paths in a signal transmitted on a CPICH channel. This is possible because the synchronization differences between the terminal 123 and each of the base stations 101 and 121 are small. The path or one of the determined paths is then used as the synchronization base for the terminal 123 on the base station 121.
• the CPICH makes it possible to process multi-paths with a delay of 20 ⁇ s, which makes it possible to compensate for an error when the small cell has a radius less than or equal to approximately 6 km (ie the equal delay of the order here of 20 ⁇ s multiplied by the speed of the light). It is also noted that when it is synchronized with the base station 121, the terminal 123 maintains a servo-control on this synchronization via the CPICH channel managed by the base station 121.
• the terminal 123 and the base station 121 exchange data on dedicated channels DPCH via several signals 407 to 409 of which a small part has been shown.
• the terminal 123 and / or the base station 121 indicate via the signal 409 that the communication ends.
• the network imposes on the terminal a "hand-over" to the base station 101. It is noted that this "hand-over" can be carried out quickly with synchronization on the CPICH signal emitted by the base station 101 since the terminal is synchronized with the base station 121 which is itself pseudo-synchronized with the base station 101.
• the terminal 123 therefore returns to a standby mode and the situation then becomes that which is illustrated with reference to FIG. 1.
• the base station 101 then transmits signals 410, 411 and 412 respectively on the SCH, BCH and PCH channels, these signals being similar to the signals 400, 401 and 402 respectively described above.
• the base station of the small cell can transmit a SCH type signal, the terminals then synchronizing on this signal when they are in communication with this base station.
• the invention is not limited to UMTS or 3GPP networks but extends to any cellular network in which large cells includes smaller cells.
• the invention is not limited to a purely material installation but that it can also be implemented in the form of a sequence of instructions of a computer program or any form mixing a material part and a part software.
• the corresponding sequence of instructions may be stored in a removable storage means (such as for example a floppy disk, a CD-ROM or a DVD-ROM) or no, this storage means being partially or totally readable by a computer or a microprocessor.

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  • 2001-11-28 FR FR0115470A patent/FR2832896B1/fr not_active Expired - Lifetime
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