AU5363599A

AU5363599A - Method of packet mode communication in a cell with distributed antennas

Info

Publication number: AU5363599A
Application number: AU53635/99A
Authority: AU
Inventors: Luc Dartois
Original assignee: Alcatel CIT SA; Alcatel SA
Current assignee: Alcatel Lucent SAS
Priority date: 1998-10-12
Filing date: 1999-10-12
Publication date: 2000-04-13
Also published as: EP0994633A1; CA2282887A1; FR2784536B1; FR2784536A1

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention title: Method of packet mode communication in a cell with distributed antennas The following statement is a full description of this invention, including the best method of performing it known to us:

SPECIFICATION

Method of packet mode communication in a cell with distributed antennas The present invention concerns the field of communications in cellular mobile radio systems or mobile telecommunication networks. It is more particularly concerned with packet mode communications in a cell comprising a plurality of radiating points or antennas.

Conventionally, such networks are formed of cells each comprising a base transceiver station providing communications with mobile stations in the cell. Various standards have already been drawn up for terrestrial telecommunication systems using mobile terminals, in particular the GSM 900 and DCS 1800 standards. Such standards provide for a plurality of layers; for example, the upper layers in the GSM standard are referred to as the call control (CC) and mobility management (MM) layers. In accordance with the GSM standard, each base transceiver station (BTS) *...transmits in a cell in which it is identified by a broadcast control channel (BCCH).

S 15 The invention is more particularly concerned with transmitting packet data in cells having a plurality of antennas or radiating points. Such cells, also referred to as distributed antenna cells or picocells, comprise a large number of antennas *00. distributed in a small area, for example a campus or a group of buildings, and S* connected to a radio controller implementing the functions of a high capacity logical 20 base transceiver station. A cell of this kind with distributed antennas can typically ooo* serve more than 1 000 mobile stations with a usage rate of The invention is described hereinafter with particular reference to the GSM mobile network and the general packet radio service (GPRS). However, it is not limited to this particular example.

For cells of the above kind having a plurality of distributed antennas, the problem arises of optimizing the transmission of data, and particularly in the case of the GSM, the transmission of data in packet mode. The aim of such optimization is to maximize the bit rate and to minimize the routing delay, statistically.

The following solution to this problem is proposed in GSM Recommendations ETR 03.60, 03.64 and 04.60 of the ETSI (European Telecommunications Standards Institute): in the downlink direction, from the base transceiver station to the mobile stations, the packets are sent serially and are broadcast throughout the cell, independently of its architecture and the number of antennas it includes, and in the uplink direction, from a mobile station to the base transceiver station, a protocol manages the speech time of the mobile station to prevent any collision of packets, and again this is at the cost of strict serialization of the packets from all the mobile stations of the cell.

This solution has the following drawbacks. The bit rate is limited. The capacity is limited to one carrier; in the case of the GSM, the capacity is limited to eight time slots for the whole cell and therefore supports transmission of 8*9.6 kbit/s or 8*14.4 kbit/s, depending on the nature of the call (data or voice). Also, this solution is therefore ill-suited to serving a large number of mobile stations, which is typically the case for a cell with distributed antennas. The proposed prior art solution therefore leads to statistically high-routing delays. Finallythese problems are all the more acute in that the use of such picocells in office buildings or on a campus generates traffic with a high proportion of data services; the bit rate required for such S. services is high, and the routing delays must be short.

US patent application Serial No. 09/297,773 filed 08 September 1998 15 proposes, in a cell with a plurality of relay stations, selectively assigning each uplink or downlink call a set of at least two relay stations. The above application proposes that the relay stations assigned to a call be chosen on the basis of information relating to the quality of the uplink call from a mobile station; the information for the call can include the carrier to interference ratio, the signal to noise ratio, the power received by the relay station, the raw or decoded bit error rate, the frame loss rate or a geographical position indication.

oooe The invention proposes a solution for transmission of data in a cell with distributed antennas which statistically increases the bit rate and reduces the routing :delay. It applies in particular to transmission of packet data. The invention addresses 25 the problem of increasing the bit rate of downlink and uplink packets; it therefore addresses the problem of increasing the number of mobile stations sending or receiving packet mode traffic simultaneously, or of increasing the bit rate and therefore reducing the average transmission time per mobile station. The invention is particularly advantageous in the downlink direction to provide access to servers at a higher bit rate. Finally, the invention can be implemented at the level of the cell with distributed antennas in a manner that is transparent for the remainder of the mobile network- According to a first aspect of the present invention there is provided a method of communication between a base transceiver station and at least one mobile station in a cell comprising a plurality of radiating points, the method comprising: assigning a radiating point to a mobile station, and transmitting calls to the mobile station from the radiating point.

The call is advantageously a packet mode call.

In one embodiment of the invention, assigning a radiating point to a mobile station comprises the steps of: monitoring the various mobile stations at all the radiating points, 10 comparing the intensities of the signals received by the various radiating points, and assigning a mobile station the radiating point for which the intensity of the signals transmitted by the mobile station is highest.

In one embodiment of the invention, the assignment is performed at the start of the call 15 at the time of the access request.

o In another embodiment of the invention, each radiating point comprises at least one frequency-agile single carrier receiver and the step of monitoring the mobile stations includes sweeping all possible carrier frequencies.

In a further embodiment of the invention, each radiating point comprises a broadband a a° digital receiver and the monitoring step includes spectrum analysis of the received signals.

a In both cases, the monitoring step and the assignment step are preferably repeated during a call.

The method advantageously further comprises the reception of calls from the mobile station by the radiating point.

In one embodiment of the invention, the method comprises reception by a radiating point of serialized packets from mobile stations to which the radiating point is assigned and assembly of packets received by the radiating points.

Freehills Patent Attorneys SYDCA\99285001.7 12 October 1999 According to a second aspect of the present invention there is provided a base transceiver station for a telecommunication network cell, the cell comprising a plurality of radiating points and means for assigning one of the radiating points to a mobile station located in the cell for calls to the mobile station.

The calls are advantageously packet mode calls.

In one embodiment of the invention, the assigning means comprise: means for monitoring the various mobile stations at all the radiating points, and means for comparing the intensities of the signals received by the various radiating points in order to assign to a mobile station the radiating point for which 9*

S

Freehills Patent Attorneys SYDCA\99285001.7 12 October 1999 the intensity of the signals transmitted by the mobile station is highest.

The base transceiver station advantageously comprises means for demultiplexing packets received from the telecommunication network and dynamically routing the packets intended for a mobile station to the radiating point assigned to that mobile station.

The base transceiver station preferably further comprises a plurality of radiating point control means managing and assigning radio resources for the calls of each radiating point and receiving the packets from the demultiplexing means.

In one embodiment of the invention the base transceiver station comprises means for multiplexing packets received from the radiating points before transmitting them to the telecommunication network.

q The multiplexing means preferably receive the packets from the control means of the radiating point.

Other features and advantages of the invention will become apparent on 15 reading the following description of embodiments of the invention given by way of example and with reference to the accompanying drawings, in which Figure 1 is a diagrammatic representation of a cell with distributed antennas, and Figure 2 is a more detailed diagrammatic representation of the cell from figure 1.

°Figure 1 is a diagrammatic representation of a cell with distributed antennas; the cell has a radio controller 1 and S remote or distributed antennas or radiating points 21 through 2S, S being an integer; the value of S is typically in the .range from 2 to 30. The radiating points provide quasi-uniform radio coverage of the S 25 cell, for example in the building(s) constituting the cell. Each radiating point 2i can implement some of the radio functions and is capable of transmitting and receiving several carriers simultaneously, using the frequency hopping technique. The division of functions between the radio controller 1 and the remote antenna 2 i is typically effected at the level of GSM layer 1 and its exact implementation has no effect on the invention. In the example of the GSM, all the radiating points transmit synchronously; they transmit simultaneously and monitor the BCCH carrier. The radiating points can have a traffic capacity of at least one frequency hopping carrier.

Figure 1 also shows mobile stations 31 through 3 n in the cell with distributed antennas and, in dashed outline, the coverage of each radiating point.

The invention proposes to identify the best radiating point for at least some In one embodiment of the invention, the assigning means comprise: means for monitoring the various mobile stations at all the radiating points, and means for comparing the intensities of the signals received by the various radiating points in order to assign to a mobile station the radiating point for which the intensity of the signals transmitted by the mobile station is highest.

In one embodiment of the invention the base transceiver station comprises means for S multiplexing packets received from the radiating points before transmitting them to the telecommunication network.

The multiplexing means preferably receive the packets from the control means of the radiating point.

I

Other features and advantages of the invention will become apparent on reading the following description of embodiments of the invention given by way of example and with 44.e reference to the accompanying drawings, in which @44444 Figure 1 is a diagrammatic representation of a cell with distributed antennas, and Figure 2 is a more detailed diagrammatic representation of the cell from figure 1.

Figure 1 is a diagrammatic representation of a cell with distributed antennas; the cell has a radio controller 1 and S remote or distributed antennas or radiating points 21 through S being an integer; the value of S is typically in the range from 2 to 30. The radiating points provide quasi-uniform radio coverage of the cell, for example in the building(s) constituting the cell. Each radiating point 2i can implement some of the radio functions and is capable of transmitting and receiving several carriers simultaneously, using the frequency hopping technique. The division of functions between the radio controller 1 and the remote antenna 2i is typically effected at the level of GSM layer 1 and its extract implementation has no effect on the invention. In the example of the GSM, all the radiating points transmit synchronously; they Freehills Patent Attorneys SYDCA\99285008.8 transmit simultaneously and monitor the BCCH carrier. The radiating points can have a traffic capacity of at least one frequency hopping carrier.

Figure 1 also shows mobile stations 31 through 3, in the cell with distributed antennas and, in dashed outline, the coverage of each radiating point.

The invention proposes to identify the best radiating point for at least some of the mobile stations so that the various radiating points can be used to send different packets to different mobile stations at different radiating points simultaneously. In this way the invention statistically increases the transmission capacity of the packets, exploiting the parallel nature of the transmission; it is preferably used in the downlink direction, but can also be used in the uplink direction. The statistical improvement can be proportional to the number of radiating points, typically in the case of mobile stations also distributed in the cell.

To this end the invention proposes to provide in the cell with distributed antennas means for assigning antennas to the mobile stations, so as to be able to send and/or receive different packets to/from different mobile stations at different antennas simultaneously. One solution to the problem of assigning an antenna to the mobile station is to identify the distributed antenna yielding the best transmission quality to or from a mobile station. This "best antenna" can be chosen at the beginning of an incoming or outgoing call, for example, on the basis of the access request, as explained below. The "best antenna" can also be determined during a call.

o*• °In figure 1, for example, the best radiating point for the mobile station 31 is the point 23 o'20 in whose immediate vicinity it is located. The assigning means could therefore assign the 0:000.

radiating point 23 to the mobile station 31 or assign the mobile station 31 to the radiating point 23.

:In the figure 1 embodiment, the assigning means 4 are shown in the radio controller 1.

The assigning means can operate by monitoring and tracking mobile stations. In the embodiment in which the access request is used to assign an antenna to the mobile station, the access packets are transmitted by the mobile stations at a fixed frequency on the BCCH carrier; in this case, the BCCH receive of the cell may be sufficient to analyse the access packets received at the various radiating points and the assigning means can use information from the BCCH receiver to identify the best radiating point; this can be as a function of the intensity of the signal received at each radiating point, for example, or using either of the methods proposed in the previously mentioned US patent application Serial No. 09/297,773.

Freehills Patent Attorneys SYDCA\99285008.8 In the embodiments in which the best antenna is determined during a call, the radiating points can monitor the mobile stations in various ways, depending on the radio technology employed; only two examples are given here. if a radiating point comprises a limited number of frequency-agile single-carrier receives, a time slot of one of the receivers can be used as a monitoring unit; in this case, that receiver can be used to sweep all the frequencies used in the cell in succession. In this way access packets transmitted by the various mobile stations from the various radiating points are monitored. The various carriers are monitored in a number of time slots equal to the number of carriers. In a typical case, m 4 to 63 frequencies can be used within the cell with distributed antennas.

On the other hand, if each radiating point comprises a broadband receiver covering all the frequencies simultaneously, a field measurement can be performed simultaneously with each packet at all the frequencies in the band. This solution is particularly advantageous in the case of packet mode transmission; in this mode, the mobile stations send packets during short S time periods and at unpredictable times. A broadband receiver avoids the need to predict the .4 5 packet transmission time, or to be more precise allows the packets to be received regardless of the time at which the packets are transmitted and their duration.

The principles of spectrum analysis can be used for this purpose; one embodiment of the invention proposes to use a digital filter bank to provide a measurement of the intensity of the signal at the various carrier frequencies which the mobile stations can use. A different embodiment of the invention proposes to apply a Fourier transform to the signals received at the various radiating points. It is then a simple matter to determine the intensity of the signal received by each of the radiating points at the various carrier frequencies that can be used in the 9*9.

cell. In the case of broadband receives, it is then possible to measure at the packet timing rate S° the signals received from the mobile stations by the various radiating points. The measurement, whether by digital filters or by the Fourier transform, can be effected without any dedicated receiver, which avoids occupying a time slot or losing receive capacity.

In all embodiments, monitoring the various mobile stations from the radiating points provides measurements of the field received at all the radiating points. The assigning means can therefore establish a collection of the various signals received and choose the radiating point with the maximum intensity for a given frequency, i.e. for a given mobile station. It is therefore possible to determine, for each mobile station, the radiating point receiving the signal with the highest intensity. In this way each mobile station can be assigned a "best antenna", which is the Freehills Patent Attorneys SYDCA\99285008.8 8 includes antenna control means which manage and assign radio resources for the various carriers used by each antenna at each antenna or radiating point. The antenna control means receive the packets to be transmitted by each antenna and intended for the mobile stations in the coverage of the antenna; for each antenna or radiating point, the packets can be multiplexed locally in accordance with the GPRS protocol mentioned above. This assures that the priority rules are also respected in the cell where the invention is implemented: in a time slot, the packets are transmitted simultaneously to the various radiating points of the cell and the priority rules are respected at a given radiating point.

The demultiplexing means can advantageously also control the dynamic tracking of mobile stations. In this case, they receive from the assigning means information relating to the best antenna for each mobile station and can transmit to the new antenna the items relating to the parameters and radio resources assigned to a mobile station if the antenna is changed for a given mobile station; the parameters 15 can be transmitted from the antenna control means of the previous antenna, or can :also be modified. This assures tracking of mobile stations using a packet mode downlink, enabling the mobile station to move around in the cell and to change radiating point.

This use of a single packet mode downlink antenna is well suited to conventional use of the call to access a server. In this case, the bit rate on the oooo downlink is generally much higher than the bit rate on the uplink. In accordance with the invention, the bit rate on the downlink can be increased in proportion to the number of radiating points in the cell.

The conventional GPRS techniques mentioned above can be used for the uplink; in this case, the mobile stations of the cell all transmit in the same time slot, and a packet is therefore received in each time slot through the cell. This solution cannot increase the capacity of the uplink; it is nevertheless well suited to access from terminals to servers, with a higher bit rate for the downlink than for the uplink, as indicated above.

Each mobile station can also be assigned a dedicated antenna or radiating point for the uplink. In this case, each radiating point receives packets transmitted by the mobile stations in its coverage and transmits them to the radio controller. The antenna control means can then demodulate and decode the packets received at each radiating point; the packets can then be transmitted to multiplexing means; the latter means assemble the packets and transmit them to the mobile network. In this Apart from the demultiplexing means, the radio controller advantageously includes antenna control means which manage and assign radio resources for the various carriers used by each antenna at each antenna or radiating point. The antenna control means receive the packets to be transmitted by each antenna and intended for the mobile stations in the coverage of the antenna; for each antenna or radiating point, the packets can be multiplexed locally in accordance with the GPRS protocol mentioned above. This assures that the priority rules are also respected in the cell where the invention is implemented: in a time slot, the packets are transmitted simultaneously to the various radiating points of the cell and the priority rules are respected at a given radiating point.

The demultiplexing means can advantageously also control the dynamic tracking of mobile stations. In this case, they receive from the assigning means information relating to the best antenna for each mobile station and can transmit to the new antenna the items relating to the parameters and radio resources assigned to a mobile station if the antenna is changed for a given mobile station; the parameters can be transmitted from the antenna control means of the :6 5 previous antenna, or can also be modified. This assures tracking of mobile stations using a ,r packet mode downlink, enabling the mobile station to move around in the cell and to change radiating point.

This use of a single packet mode downlink antenna is well suited to conventional use of the call to access a server. In this case, the bit rate on the downlink is generally much higher :'20 than the bit rate on the uplink. In accordance with the invention, the bit rate on the downlink can be increased in proportion to the number of radiating points in the cell.

0444 4 The conventional GPRS techniques mentioned above can be used for the uplink; in this case, the mobile stations of the cell all transmit in the same time slot, and a packet is therefore 444044 received in each time slot through the cell. This solution cannot increase the capacity of the uplink; it is nevertheless well suited to access from terminals to servers, with a higher bit rate for the downlink than for the uplink, as indicated above.

Each mobile station can also be assigned a dedicated antenna or radiating point for the uplink. In this case, each radiating point receives packets transmitted by the mobile stations in its coverage and transmits them to the radio controller. The antenna control means can then demodulate and decode the packets received at each radiating point; the packets can then be transmitted to multiplexing means; the latter means assemble the packets and transmit them to the mobile network. In this way the various packets received at the distributed radiating points Freehills Patent Attorneys SYDCA\99285008.8

Claims

13. A base transceiver station according to any one of claims 10 to 12 comprising means for demultiplexing packets received from the telecommunication network and dynamically routing packets intended for a mobile station to the radiating point assigned to the mobile station.

14. A base transceiver station according to claim 13 comprising a plurality of radiating point control means managing and assigning radio resources for the .calls of each radiating point and receiving the packets from the demultiplexing means.

15. A base transceiver station according to any one of claims 10 to 14 comprising S 15 means for multiplexing packets received from the radiating points before transmitting them to the telecommunication network.

16. A base transceiver station according to claims 14 and 15 wherein the multiplexing means receive the packets from the control means of the radiating point.

17. A method of communication between a base transceiver station and at least one mobile station in a cell comprising a plurality of radiating points station substantially as hereinbefore described with reference to the accompanying drawings.

18. A base transceiver station substantially as hereinbefore described with reference 6 25 to the accompanying drawings.