WO2000057659A1 - Method for building up a connection in a radio communication system - Google Patents

Abstract

The invention relates to the building up of a connection between a subscriber station and a base station in a radio communication system which uses a TDMA multiple acess method, whereby RACH bursts are transmitted from the subscriber station in the initial access sequence with a partial length of a RACH time slot. According to the invention, a base station (B1, B2, B3) presets the initial access to the RACH time slot for the subscriber station (MS1, MS2, MS3).

Description

description

Method for establishing a connection within a radio communication system

The invention relates to a method for connection establishment ^¬ acquisition between a subscriber station and a base station within a radio communication system, in particular a cellular mobile radio system, which are separated signals to be transmitted with the help of a TDMA Vielfachzugriffsver- driving, and to a corresponding radio communication system.

In future universal mobile telecommunications systems, such as the UTMS system (Universal Mobile Telecommunication System), which is intended to serve to illustrate the technical background of the invention below, without restricting the generality of its use, broadband is to be used for information transmission via the air interface - TDMA / CDMA methods are provided which implement multiple access by combining a broadband TDMA / FDMA system with a CDMA system by additionally providing multiple access according to the CDMA method in m specific time slots. Two modes are provided for flexible upward and downward transmission of the signals between the stations, frequency division duplex (FDD) and time division duplex (TDD). The FDD mode is a broadband CDMA, characterized by the degrees of freedom frequency and spreading code, and the TDD mode is a TD / CDMA method, characterized by the degrees of freedom frequency, time slot and spreading code.

A number of logical channels are defined for each frequency-, time- or spread-code-selective so-called physical traffic channel. The logical channels are identified by the respective specific parameter group. User information (e.g. language, data) is see useful channels (TCH) and control signals transmitted via logical control channels (CCH). Furthermore, the control channels, namely the Broadcast Control Channel (BCCH), are down radiates on the radio network specific organizational information from the base station to the subscriber stations out ^¬ and in particular the Common Control Channel (CCCH) caring, about whose Aufwartsstrecke, the so-called random access channel ( RÄCH), a subscriber station in random multiple access establishes a connection to the base station.

Accordingly, the first access of a subscriber station for the purpose of establishing a connection takes place via its own logical channel.

The information to be transmitted, such as signaling, is transmitted in TDD mode during the time slots in blocks with a predetermined structure, so-called bursts. There are different types of bursts.

A burst type is the access burst. It consists of data bits on which the logical channels are mapped and transmitted, a predefined and thus known training sequence which, together with front and rear tail bits, is used for bit-precise synchronization of the burst and for channel estimation, and a protection period during which no bits are transmitted. The protection period ensures that signals arriving at the base station from subscriber stations of different distances arrive in the correct time relationship despite their transit time differences, so that bursts of honorary subscriber stations do not overlap in time. To the disadvantage of the data bits, the access burst has an extremely long protection period in order to keep the probability of collisions during random multiple access, which occur on the RACH time slot because of subscriber stations that are not time-synchronized, as low as possible. The access burst is the first signal sent from a subscriber station to the base station when a connection request is notified and is transmitted on the RACH time slot used and therefore also referred to as RÄCH burst.

In the UMTS system, the RÄCH burst is defined for all radio cells in such a way that two RÄCH bursts can be sent in a RACH time slot reserved for this purpose, ie one Räch burst e half slot of a full slot. Thus, according to the current state, using the 16 spreading codes in TDD mode from UMTS up to a radio cell size of approx. 2 km, a RÄCH burst can be sent simultaneously by 2 x 16 = 32 subscribers on a RACH time slot without any the participants disturb each other. However, a multiple division of the RACH time slot is also conceivable.

In the UMTS system, dynamic resource allocation between logically linked radio cells, called clusters, is also provided. The RACH time slot is the same in all radio cells of a cluster. The access of the subscriber stations to a half slot is arbitrary. If several subscriber stations of different radio cells transmit in a half-slot at the same time, the RÄCH bursts overlap and are therefore undetectable at the receiving base stations. After a collision, the affected subscriber stations try again to send a RÄCH burst. The more often the first access has to be repeated, the longer the waiting time and the more the effectiveness of this access method drops.

The object of the invention is to provide a method according to which the initial access in terms of the number of subscribers can be increased significantly compared to the existing RACH concept without the subscribers significantly interfering with one another when establishing a connection.

This object is achieved with a method according to claim 1 and with a radio communication system according to claim 10. Advantageous embodiments and further developments of the invention are subject of the dependent claims ^¬ Ge.

The problem is solved erfmdungsgemaß by αen participants merstationen the radio cells is signaled may be sent if and m wel ^¬ chen RACH sub slots. For a division of the RACH timeslot (which can also be referred to as a "pinch timeslot") into half-slots, this means that it is signaled whether transmission is only in the first half-slot, only in the second half-slot, m two half-slots or in none of the half-slots In this way, in a further development of the invention, an RACH time slot can be dynamically divided over several radio cells of a cluster (RACH time slot clustering), which considerably reduces interference in the RACH time slot, such as collisions with neighboring radio cells In a further embodiment of the invention, system information about, for example, the BCCH, can be used to inform the subscriber stations on which half-slot the RÄCH burst may be sent on first access also the second ha lb slot for the RACH burst. In addition, it can be provided according to the invention that a radio cell of the cluster blocks the first half-slot or the second half-slot of the RÄCH for RÄCH bursts, for example in the case of low traffic. Likewise, in the event of an overload, both half slots can be blocked for access. This procedure leads to an extremely dynamic locking and unlocking of RACH-

Resources within a cluster or between clusters of a network system.

In a further embodiment of the invention, the access measurements and the decisions about the administration of the

Rach time slot are carried out independently in a base station. Of this, the continuation of the invention thanking a superordinate entity, such as the Ba sisstationssteuerung (BSC) or the operation and maintenance ^¬ center (OMC), are informed. According to another Ausprä ^¬ the invention, the supply traffic measurements m of uber- parent instance performed and broadcast decisions on the management of the RACH time slot on the BCCH or another CCH.

It goes without saying that the principle of the invention is not limited to the application at RÄCH, but can always be used when the length of a time slot is a multiple of the length of the burst to be transmitted on this resource

The invention will be explained in more detail using an exemplary embodiment. 1: A mobile radio communication system,

2 shows a schematic representation of the frame structure of a TDD transmission method,

Fig. 3: A schematic representation of a RÄCH burst

Fig. 4: An example of a RÄCH burst separation

5: A schematic representation of different transmission times for RACH bursts,

Fig. 6: An example of an information element in a mobile radio communication system m and

Fig. 7: Possible parameter values for the availability of half-slots within a RÄCH.

The mobile radio system shown in FIG. 1 as an example of a radio communication system consists of a large number of mobile switching centers MSC which are networked with one another or which provide access to a fixed network PSTN and only one of which is shown as an example. They are at least a base station controller BSC is connected to _j each case for distributing radio resources and with an operation and maintenance system OMC which Organisationsinsm- formations transmits for the mobile radio system or for parts. Each base station controller BSC enables a connection to another one or more base stations BS1, BS2, BS3. Each base station BS1, BS2, BS3 can via an air interface ^¬ a connection to subscriber stations MSI, MS2, MS3, for example, Mobi stations, build. At least one radio cell ZI, Z2, Z3 is formed by each base station B1, B2, B3. The radio cells ZI, Z2, Z3, for example, form a logical group of cells (clusters) within the cellular mobile radio network. In the case of sectoring or hierarchical cell structures, several radio cells are also supplied per base station BS. 1 shows, by way of example, connections VI, V2 for the transmission of useful information and signaling information between the subscriber stations MSI, MS2 and a base station BS1, a request for resource allocation in a half-slot of the RACH timeslot (uplink in the CCH) by a further subscriber Stations MS3 and the transmission path for system information from the base station BS1 to the subscriber stations are shown in the BCCH. The functionality of this structure can be transferred to other radio communication systems, in which the invention can be used.

The frame structure of the radio transmission can be seen from FIG. According to a TDMA component, a broadband frequency band B1, for example of the bandwidth B1 = 5 MHz, m is divided into a plurality of time slots of the same duration, for example 16 time slots 1 to 16. Some of the time slots are used in the downward direction DL and some of the time slots in the upward direction UL. In between there is a variable switchover point SP. In this TDD transmission method, the frequency band for the downward direction DL corresponds to the frequency band for the upward direction UL. Within a broadband frequency range Bl, the successive time slots are divided 1 to 16 according to a frame structure ^¬ by 16 time slots are combined into a time-slot frames frs.

Information of a plurality of connections VI, V2 is transmitted within a time slot, in that each time slot is once again spread individually for each connection with a subscriber code c corresponding to the CDMA component m UMTS, as a result of which 16 access resources per time slot (fill slot) can be separated on the receiving side.

Before transmission of user data, however, a connection must first be established from a subscriber station MS3 to a base station BS1, BS2, BS3. For this purpose, the subscriber station MS3 receives the signals of the organization channels BCCH of one or more base stations BS1, BS2, BS3 and measures the interference of the organization channels. The radio cell ZI, Z2, Z3 with the most powerful organization channel BCCH within the cluster is selected. The subscriber station MS3 then sends a RÄCH burst RB in the upward direction UL in a half slot of the RÄCH, which at least contains the identifier of the subscriber station MS3, for the purpose of a corresponding request for the allocation of radio resources. This identifier can be supplemented by further information about the base station BS1, BS2, BS3 or via physical channels. In the upward direction UL, all base stations Bsl, BS2, BS3 receive the RÄCH burst in the same RACH time slot, for example in the first time slot 11 after the switchover point SP that can be administered by the organization and maintenance center OMC. One of the base stations BS1, BS2, BS3 decodes the transmitted RACH and assigns the subscriber station MS3 a transmission resource, that is to say a frequency band B1, B2, a time slot 1 to 10 and a subscriber code c. A RÄCH burst RB is shown in more detail in FIG. 3. It consists of two sections with data d, m which the receiving end be ^¬ known training sequences are embedded tseq. Furthermore, a comparatively large guard time is gp for compensating different signal propagation tents of the compounds being ^¬ depends.

The separation of the RACH is determined by two parameters. The first parameter is the spread code c, in the TTD mode of UMTS 16 spread codes are provided. The second parameter is the send time of the R CH burst. For this purpose, two times are provided in the UMTS system, the start of a time slot tO and the middle of a time slot tl. A multiple division of the time slot is also conceivable. If the subscriber stations MSI, MS2, Ms3 are not more than 2 km away from their base station BS1, BS2, BS3, according to the definition, if the RACH is divided, m half-slots within this radio cell radius can simultaneously have up to 32 subscribers on the RACH time slot 11 without collision access danger because one RÄCH burst RB is received per half slot.

The RACH time slot 11 is the same in all radio cells ZI, Z2, Z3 of the cluster. In order to reduce interference on the RACH time slot 11 between adjacent radio cells ZI, Z2, Z3, the invention signals at what time the RÄCH burst RB may be sent by the subscriber stations MSI, MS2, MS3. In one radio cell ZI, for example, the RÄCH burst RB is always sent at time tO and in an adjacent radio cell Z2 the RÄCH burst RB is always sent at time t1 (FIG. 4). The interference on the RACH time slot 11 between the two radio cells ZI, Z2 is thus decoupled. One speaks of the fact that the RACH accesses are temporally orthogonal to each other. In a third neighboring radio cell Z3, which is supplied with brisk radio traffic by a base station BS3, all two half-slots of the RACH time slot 11 can be used for the RÄCH Burst RB must be approved. The interference within this radio cell Z3, caused by the subscribers of the base stations BS1, BS2, is greatly reduced, since the RACH time slot 11 for the base station BS3 m in the first half of the RACH time slot 11 only by the subscribers in the base station BS1 and m second half of the RACH time slot 11 is only affected by subscribers of the base station BS2 and not simultaneously by the subscribers of the radio cells BS1 and BS2.

Participants from up to three radio cells can send their RÄCH burst RB in the same physical channel, that is to say in the same RACH time slot 11, with the Räch bursts RB with a reduced risk of collision with regard to the data components d m. The RACH bursts RB can be evaluated more reliably by the base stations BS1, BS2, BS3 of the cells ZI, Z2, Z3 and the subscriber stations MSI, MS2, MS3 can be assigned one or more channels without delay. The radio traffic is channeled through the allocation according to the invention of the half-slot to be used in the R CH 11.

There is also the possibility that when the radio traffic m, for example the radio cell ZI, increases due to frequent access to the RACH time slot 11, the base station BS1 autonomously signals that the mobile stations MSI, MS2, MS3 are also allowed to access the second half slot of the RACH 11. Conversely, there is the possibility that, for example, the radio cell Z3 blocks the first or the second half-slot of the RACHs TsO for RÄCH bursts RB, for example due to low traffic volume.

The individual distinction is made in TDD mode by the spreading code c. The subscriber stations MSI, MS2, MS3 are informed of system information, for example via the BCCH, that when the RÄCH burst RB is accessed for the first time either at time tO, at time tl, at both times tO, tl or at none of the times of the RACH Time slot zes 11 may be sent, so that the RACH time slot 11 is distributed over several cells ZI, Z2, Z3 to avoid interference (RÄCH time slot clustering).

The measurements of the accesses to the RACH time slot 11 can be carried out independently by each base station BS1, BS2, BS3, as can the decisions for the allocation of one or more resources. If a decision is made, the higher-level authority BSC and the OMC can be informed. On the other hand, there is also the possibility that the traffic measurements of the higher-level entity BSC are carried out and the latter makes the appropriate decisions. The decisions and the configurations with regard to the RACH time slot 11 can be carried out dynamically and, for example, can be broadcast on the BCCH or another control channel.

According to the invention, an RACH time slot 11 transmitted RÄCH bursts RB differ in the temporal arrangement within the RACH time slot 11. Thus, according to FIG. 5 m, an RACH time slot 11 RÄCH bursts can consist of up to three radio cells with a considerably reduced risk of collision be sent. With regard to the orthogonal RÄCH bursts from the radio cells ZI and Z2, no mutual impairments are to be expected. Each RÄCH burst RB is, for example, prescribed the transmission time tO or tl. A third mobile station MS3 from the radio cell Z3 sends its RÄCH burst, for example, in both half-slots of the R CH. This distributes possible interference caused by subscriber stations of the radio cells ZI, Z2 to both RÄCH bursts and the probability is high that one of the transmitted RÄCH bursts will be recognized by the base stations without errors. Depending on the traffic, it can also be stipulated that it may currently only send a RÄCH burst only in one or due to overloading in none of the half-slots, so as not to disturb the connection of the subscribers of the radio cells ZI and Z2. It is within the scope of the invention that more than one time slot ^¬ a time slot frame as RACH Zeitscnlitz is available, for example, time slot 12, either by appropriate reservation or by variable Administration in the OMC.

Likewise, it is within the scope of the invention that the RACH burst RB in addition to the distribution part of the slots, so examples game as half-slots, slot even within a partial of the RACH time slot (11) to each other in time or ^¬ can be sent, orthogonal, that is that the data portion d is sent first and then its guard time gp from one RÄCH burst RB (FIG. 3) and the guard time gp and then the data portion d from another RÄCH burst.

In this way, the collisions that can possibly occur due to the transmission of two RACH bursts in the same partial slot can also be excluded.

6 is an example of an information element IE

R CH slot for broadcasting on the BCCH is displayed within a system information (System Information Message). The availability or non-availability of RACH time slots for the RÄCH burst indicates the subscriber stations of a radio cell m bits and bytes.

FIG. 7 shows which parameter values the information element IE RÄCH slot according to FIG. 6, printed bits and bytes, can assume, namely: Both half slots of an RACH time slot are available, only the first half slot is available, only the second half slot is available , no half slot of the RRACH time slot is available.

Claims

claims 1. A method for establishing a connection between a subscriber station (MSI, MS2, MS3) and a base station (BS1, BS2, BS3) within a radio communication system with TDMA subscriber separation, in which an access time ^slot (11) is divided into several part-time ^slots , Gesen in which from the subscriber stations access burst (RB) m- nerhalb of part-time slots of the access time slot ^¬ be det, characterized in that one of the subscriber stations (MSI, MS2, MS3) is signaled m, where the part-time slots to its inlet gπffsbursts (RB) may send out. 2. The method according to claim 1, characterized in that the subscriber station (Msl, MS2, MS3) is signaled whether their access bursts (RB) m the first stop (tO) of the access time slot (11), m the second half (tl), m both halves (tO, tl) or m none of the halves (tO, tl) of the train time slot (11) may be sent. 3. The method according to any one of the preceding claims, that the access time slot (11) is dynamically distributed over a plurality of radio cells (ZI, Z2, Z3). 4. The method according to any one of claims 1 to 5, characterized in that the message about the permissible part-time slots of the Zugπffszeitschlitzes (11) of the subscriber station (MSI, MS2, MS3) is signaled by one of the base stations (BSl, BS2, BS3). 5. The method according to claim 4, characterized in that the base station (BSl, BS2, BS3) independently manages the allocation of the part ^{¬ time} slots to the subscriber station. 6. The method of claim 5, d a d u r c h g e k e n n z e i c h n e t that the base station (BSl, BS2, BS3) communicates its decision to a higher authority. 7. The method according to any one of claims 1 to 4, d a d u r c h g e k e n n z e i c h n e t that one of the base stations (BSl, BS2, BS3) superordinate entity manages the allocation of the part-time slots to the subscriber station. 8. The method as claimed in one of the preceding claims, that the decision regarding the part-time slots to be signaled is made dynamically on the basis of the traffic volume. 9. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that more than em access time slot is used within a time slot frame. 10. Radio communication system with TDMA subscriber separation, in which an access time slot (11) is divided into several partial time slots, in which the subscriber stations have units for sending access bursts (RB) within the partial time slots of the access time slot by a unit for signaling which of the part-time slots one of the subscriber stations (MSI, MS2, MS3) is allowed to send out their access bursts (RB).