FR2864383A1 - Information processing method for general packet radio service system, involves effectuating processing on certain information based on read indications, where processing comprises determination of variable associated to mobile station - Google Patents

Abstract

The method involves reading certain indications transmitted by a packet control unit (22), at a base station (20). A processing is effectuated at the base station on certain information transmitted on a shared channel, based on the read indications. The effectuated processing comprises determination of a variable associated to a mobile station (10), based on information transmitted over the channel. An independent claim is also included for a base station comprising unit for receiving information transmitted from terminals.

Description

METHOD FOR PROCESSING INFORMATION TRANSMITTED ON A

  SHARED CHANNEL AND BASE STATION FOR THE IMPLEMENTATION OF

PROCESS

  The present invention relates to the processing of information transmitted on a shared channel. It relates in particular to the adaptive processing of information transmitted on a shared channel.

  Adaptive processing is understood to mean any processing of information aimed at determining a smoothed quantity over time, that is to say taking into account the values taken by this quantity in the past.

  By way of example, mention may be made of the sounding of a transmission channel, that is to say the estimation of the impulse response of this channel. Such a survey is taken into account to estimate the information transmitted on the channel. Channel probing methods are known.

  In particular, WO 98/47239 discloses a time-weighted poll of a transmission channel, wherein a channel statistic is acquired, then an estimate of the impulse response of the channel is established, this impulse response being weighted by said statistic.

  Furthermore, WO 98/47240 discloses a spatially weighted sounding of a multi-channel transmission path, in which a spatial statistics of the transmission path is acquired, and then the impulse response of the channels of the previously estimated transmission path is corrected by weighting using spatial statistics and an estimate of the additive noise of the channels.

  In the two cases mentioned above, the acquired statistic corresponds to a value of the impulse response prior to the acquisition of the received signal. The final estimate of the impulse response thus takes into account the past, which improves the reliability of the estimate and the additive noise resistance.

  When dealing with a communication system where a base station receives information undifferentiated from a set of terminals on a shared channel, under the control of a control unit, adaptive processing by the base station may prove difficult.

  In this case, in fact, only the control unit has the control of the speech time dynamically allocated to each terminal. The base station can not evaluate a magnitude relative to a transmission performed on the shared channel by a terminal among all the terminals. A fortiori, the base station can estimate a smoothed magnitude on a set of transmissions from such a terminal.

  Using the example above, a poll can not be performed efficiently for the part of the shared channel corresponding to a given terminal. The reliability of the estimation of the information transmitted on the shared o channel is thus limited.

  An object of the present invention is to overcome the aforementioned drawbacks, to achieve a processing of information transmitted on a shared channel, individually for terminals.

  Another object of the present invention is to achieve adaptive processing of information transmitted on a shared channel.

  The invention thus proposes a method of processing information transmitted to a base station from terminals in respective time slots on a shared channel, under the control of a control unit, in which the control unit is arranged. for transmitting to the terminals, via the base station, an indication of the terminal authorized to transmit information on the shared channel over at least one determined future time interval. The method comprises the following steps: - read, at the base station, at least some indications transmitted by the control unit; and perform a processing, at the base station, on at least some of the information transmitted on the shared channel, taking into account the read indications.

  We thus regularly acquainted with the base station, terminals that will transmit on the shared channel. This knowledge makes it possible to deal individually with the transmissions made by the different terminals, although these transmissions are carried out on the same communication channel.

  The processing carried out may for example comprise the determination of a quantity associated with a given terminal. In the context of the treatment, this magnitude can be advantageously smoothed to take into account the values obtained in the past.

  An example of a magnitude determined during the adaptive processing is an estimate of the impulse response of the shared channel. This gives an estimate with a good level of reliability.

  The invention also proposes a base station comprising means for receiving information transmitted from terminals in respective time slots on a shared channel, under the control of a control unit, and means for relaying from the control unit. control to the terminals an indication of the terminal authorized to transmit information on the shared channel over at least one determined future time interval. The base station further comprises: means for reading at least some of the indications to be relayed from the control unit; and means for processing at least some of the information transmitted on the shared channel, taking into account the indications read by the means for reading at least some of the indications to be relayed from the control unit.

  Other features and advantages of the present invention will appear in the following description of nonlimiting exemplary embodiments, with reference to the appended drawings, in which: FIG. 1 is a diagram of a GPRS type network to which invention can apply; and FIG. 2 is a block diagram of a control unit of such a network adapted to the implementation of the invention.

  The present invention finds an application in particular within the framework of the GPRS system ("General Packet Radio Service"). The GPRS system has been developed to allow the transmission of packet data in GSM cellular networks (Global System for Mobile Communications). In particular, uplink packet transmission, i.e., mobile stations to the network infrastructure, will be considered. We are hereinafter in this context, without however limiting the scope of the invention.

  The GPRS network illustrated in FIG. 1 is built on a GSM infrastructure, and conventionally divided into a core network, also called network and switching subsystem or NSS (Network and Switching Subsystem), and a radio access network also called Subsystem subsystem or BSS (Base Station Subsystem).

  For the packet service, the NSS switches are called GPRS Support Nodes or GSN (GPRS Support Node). There are the SGSNs (Serving GSN) 5 which are connected to the BSS via an interface called Gb, and the GGSNs (Gateway GSN, not shown) which serve as gateway with external packet transmission networks, such as for example the Internet network.

  A general description of the radio interface, called Um, between the mobile terminals (MS) 10 and the base stations (BTS) 20 of the BSS is provided in the technical specification ETSI TS 101 350, Digital cellular telecommunications system (Phase 2+); General Packet Radio Service (GPRS); Overall description of the GPRS radio interface; Stage 2 (GSM 03.64, version 8.5.0, Release 1999), published by the ETSI (European Telecommunications Standards Institute) in August 2000.

  Each base station 20 is supervised by a base station controller (BSC) 21 through an interface called Abis. To handle GPRS packet transmission, the BSS further includes a packet control unit (PCU) 22. The location of the PCU within the BSS is not standardized. In the example shown in FIG. 1, the PCU 22 is located between the BSC 21, with which it communicates through an interface called Agprs, and the NSS, with which it communicates through the interface Gb.

  FIG. 2 illustrates a possible structure of a PCU 22 located between an SGSN 5 and a BSC 21, as in the example of FIG. 1. The reference 40 designates the interface controller Gb for the connection with the SGSN 5.

  The interface Gb is of asynchronous type. It is based on the Frame Relay (FR) protocol and a protocol called BSSGPRS (BSSGP Protocol) that carries routing and quality of service information between the BSS and the SGSN. The Gb 40 interface controller provides the physical link with the SGSN 5, as well as the procedures specific to the FR and BSSGP protocols.

  The links between the PCU 22 and the BTS 20 through the Agprs interface are of the synchronous type. As a result, the data manipulated by the PCU 22 between the Gb interface controller 40 and the Agprs interface controller 42 passes through a buffer 41 where packet queues are recorded.

  Between the PCU 22 and the BTS 20, the information is carried by frames of type TRAU (Transcoder / Rate Adapter Unit) of 320 bits. These TRAU frames are shaped and processed by a module 44 and transmitted via synchronous interface circuits 45 which perform PCM sub-channels at 16 kbit / s with the BTS 20. In GSM systems, the channels at 64 kbit / s (DSO) are usually subdivided into four sub-channels each dedicated to a physical channel on the radio. Several channels (sub-channels) at 16 kbit / s are multiplexed over time on the Agprs interface and switched by the BSC 21 for routing to the BTS.

  A module 46 of the Agprs interface controller 42 implements the radio protocols of the layer 2 of the ISO model, namely the RLC / MAC (Radio Link Control / Medium Access Control) protocols described in the European standard ETSI EN 301 349, Digital cellular telecommunications system (Phase 2+); General Packet Radio Service (GPRS); Mobile Station (MS) Base Station System (BSS) interface; Radio Link Control / Medium Access Control (RLCIMAC) protocol (GSM 04.60, version 8.3.1, Release 1999), published by ETSI in October 2000.

  The RLC sublayer interfaces with the higher layer protocol, called LLC (Logical Link Control). It provides segmentation and reassembly of the LLC protocol data units (LLC-PDUs), which are exchanged asynchronously on the Gb interface. It produces RLC data blocks to which the MAC sublayer adds a one-byte MAC header.

  In the downstream direction, from the PCU to the MSs, the MAC header of each RLC / MAC block includes: - a Uplink State Flag (USF) field, to indicate which mobile station is allowed to use one or a plurality of upstream resources corresponding to the downstream resource on which the RLC / MAC block is transmitted; a three-bit acknowledgment control field, including a sub-field of a SIP (Supplementary / Polling) bit indicating whether the acknowledgment control field is active (SIP = 1) or inactive (S / P = 0) and a two-bit Relative Reserved Block Period (RRBP) subfield which uniquely specifies an uplink block in which the destination mobile station is to transmit an acknowledgment message; a two-bit Payload Type field specifying the next RLC block type (data, control, ...).

  We are interested here in the transmission of RLC data blocks. Each of these blocks has an RLC header following the MAC header byte. This RLC header includes the following information: - temporary flow identity TFI (Temporary Flow Identity), consisting of five bits identifying the temporary block flow (TBF, Temporary Block Flow) from which the RLC data block. A TBF is a connection supporting unidirectional transfer of LLC-PDUs on physical data channels. A TBF is temporary, that is, it is maintained only during the data transfer; a sequence number of the BSN Block Sequence Number (BSN), which contains the sequence number of the RLC / MAC block in the TBF, modulo 2SNS SNS being a predefined number.

  The MAC sublayer also manages the multiplexing of the blocks belonging to the different active TBFs on the available physical channels, by arbitrating between the different mobile users by a scheduling mechanism.

  Moreover, a variable level of protection against transmission errors on the radio can be selected block by block within a TBF, by the choice of a coding scheme CS (Coding Scheme) among four CS-schemes. 1 to CS-4 specified in European standard ETSI EN 300 909, Digital cellular telecommunications system (Phase 2+); Channel coding (GSM 05.03, version 8.5.1, Release 1999), published by ETSI in November 2000.

  CS-4 does not use error-correcting coding, that is, the coding efficiency is 1: only a block check sequence (BCS) is attached to the data blocks . Schemes CS-1 to CS-3 use a 1/2 convolutional code after the addition of the BCS sequence. No punching is done in CS-1 (which offers the highest level of protection), while punching is applied in CS-2 and CS-3 schemes to give coding efficiencies. overall values of about 2/3 and about 3/4, respectively.

  CS-i channel coding (1 i 4) is applied at the physical layer protocol level, that is, in the BTS for the downlinks and at the MS for the uplinks. Each BTS has at least one transmitting / receiving unit (TRX) processing eight multiplexed physical channels. The multiplexing of these eight physical channels is TDMA (Time-Division Multiple Access) time division, with successive frames of 4.615 ms each broken down into eight time slots. A physical channel corresponds to time slots of corresponding rank in the frame structure. The transmission frequency on such a channel may be fixed, or variable from one frame to another if a frequency hopping method is applied. Each RLC / MAC block gives rise to a radio block which, after the channel coding in a TRX unit, consists of 456 bits transmitted in corresponding time intervals of four consecutive TDMA frames. The 114 bits of coded information of each time slot are modulated to be transmitted on the radio interface according to a Gaussian Minimum Shift Keying (GMSK) type two-phase phase shift keying.

  For a physical data channel (PDCH), a multiframe lasts 240 ms and consists of 52 TDMA frames, four of which are inactive or used to transmit control information. There are thus twelve radio blocks by multiframe, ie a radio block every 20 ms.

  In a uplink data transmission, on a PDCH shared physical channel, the BTS demodulates each unit of data, contained within a time interval, as soon as it has received it. The BTS is generally unaware at this stage of the identity of the MS that transmitted the unit of data in question. Indeed, it is necessary to wait for the BTS to have received the data contained in the four time intervals making it possible to reconstitute an RLC block, for the decoding of the latter to be possible. When an RLC block is decoded, the TFI temporary stream identity it contains is then available at the BTS, which allows the latter to find the identity of the MS at the origin of the transmission.

  Such demodulation leads to an unreliable estimate of the information transmitted. Indeed, the estimation of the information transmitted by a given MS is obtained from the estimate of the impulse response for the portion of the PDCH channel carrying the information in question. However, the estimation of the impulse response is then largely affected by additive noise, as indicated in the introduction, since it is based only on a single transmission time interval, without taking into account the previous transmissions since the same time. MS.

  According to the invention, an identification of the MS transmitting data up to the BTS on a PDCH is made possible for any time interval on the radio channel. This identification results from the knowledge, by the BTS, of an indication allowing to find the identity of an MS. This indication may be for example the USF field, presented above, which is transmitted by the PCU 22 to a set of MS, via the BTS 20, according to the notations of Figure 1. This field allows indeed to indicate which MS is allowed to use one or more upstream resources corresponding to the downstream resource on which the RLC / MAC block is transmitted. Thus, a USF value is assigned to each MS. When the USF transmitted in the MAC header of a downlink RLC / MAC block targets a given MS, for example the MS 10, it means that this MS will be able to transmit upstream data in one or more future radio blocks. Typically, the MS 10 will then be authorized to transmit data, 60 ms after the reception of the USF by the MS 10, and this, on a radio block or on four successive radio blocks.

  The BTS 20 reading, for example via the read function module 23, the USF field of the descendant RLC / MAC blocks, can then deduce the identity of the MS transmitting data rising at each time interval. It can thus store certain information contained or deduced from the uplink data units that pass through it, while associating them with the MS which is at the origin of the transmission of these data units.

  The BTS 20 can then perform a processing on these uplink data units, through its processing functional module 24. It can for example estimate the impulse response of the part of the PDCH channel carrying the traffic of a given MS. It is then able to refine this estimate by performing a smoothing of the impulse response of this part of the PDCH channel, taking into account certain estimates made in the past, for example on the previous time intervals within the same radio block. As an illustration, an estimate of the impulse response for such a portion of the PDCH channel can be carried out by the BTS 20, according to one of the methods referred to in the introduction, that is to say by weighting performed after constitution of a spatial or temporal statistics. Such a poll of the shared channel then has the reliability advantages indicated in the introduction.

  The example of weighted sampling of a part of the PDCH channel relating to a given MS has been taken above as an advantageous application of the present invention. However, as indicated in the introduction, many other adaptive treatments can be performed by the BTS 20 when it has acquired the knowledge of the MS transmitting at each time slot on the shared channel. In particular, the BTS 20 can estimate and smooth over time other quantities, such as a doppler arrival time.

Claims (8)

  A method of processing information transmitted to a base station (20) from terminals (10) in respective time slots on a shared channel, under control of a control unit (22), wherein control unit is arranged to transmit to the terminals, through the base station, an indication of the terminal authorized to transmit information on the shared channel over at least one determined future time interval, the method comprising the following steps: read , at the base station, at least some of the indications transmitted by the control unit; and perform a processing, at the base station, on at least some of the information transmitted on the shared channel, taking into account the read indications.   The method according to claim 1, wherein the processing performed at the base station (20) comprises determining a magnitude associated with a terminal (10), based on information transmitted on the shared channel in at least one a time interval over which said terminal was authorized to transmit, according to at least one indication read to the base station.   The method of claim 2, wherein determining a magnitude associated with a terminal (10) is performed based on information transmitted on the shared channel in a plurality of time slots on which said terminal was allowed to transmit, according to at least one indication read to the base station, and wherein the processing performed at the base station further comprises a smoothing of the magnitude over said time intervals.   The method of claim 2 or 3, wherein the determined magnitude is an estimate of an impulse response of the shared channel.   - 12 - Base station (20) comprising means for receiving information transmitted from terminals (10) in respective time slots on a shared channel, under the control of a control unit (22), and means for relaying from the control unit to the terminals an indication of the terminal authorized to transmit information on the shared channel over at least one determined future time interval, the base station further comprising: means for reading at least some of the indications to be relayed from the control unit; and means for processing at least some of the information transmitted on the shared channel, taking into account the indications read by the means for reading at least some of the indications to be relayed from the control unit.   The base station (20) according to claim 5, wherein the means for performing processing on at least some of the information transmitted on the shared channel comprises means for determining a magnitude associated with a terminal (10), based on of information transmitted on the shared channel in at least one time interval on which said terminal was authorized to transmit, according to at least one indication read by the means for reading at least some indications to be relayed from the control unit.   The base station (20) according to claim 6, wherein the means for determining a magnitude associated with a terminal (10) is implemented on the basis of information transmitted on the shared channel in a plurality of time slots on which said terminal was authorized to transmit, according to at least one indication read to the base station, and wherein the means for performing processing on at least some of the information transmitted on the shared channel further comprise means for smoothing the magnitude on said intervals time.   The base station (20) of claim 6 or 7, wherein the magnitude determined by the means for determining a magnitude associated with a terminal (10) is an estimate of an impulse response of the shared channel.