WO2001074021A1

WO2001074021A1 - Method for signaling the start of a logical channel in a jointly used physical transmission channel of a radio communications system

Info

Publication number: WO2001074021A1
Application number: PCT/DE2001/001171
Authority: WO
Inventors: Stefan Bahrenburg; Volker Franz
Original assignee: Siemens Aktiengesellschaft
Priority date: 2000-03-27
Filing date: 2001-03-27
Publication date: 2001-10-04
Also published as: DE10015041C2; KR100524537B1; DE10015041A1; KR20020088407A; CN1419770A; CN1163040C

Abstract

The invention relates to a method for signaling the start of a logical channel in a jointly used physical transmission channel of a radio communications system according to which the start is signaled by means of a phase relation between the logical channel and another transmission channel.

Description

description

Method for signaling the start of a logical channel in a shared physical transmission channel of a radio communication system

The invention relates to a method for signaling the start of a logical channel in a shared physical transmission channel of a radio communication system.

In radio communication systems, for example the second-generation European mobile radio system GSM (Global System for Mobile Communications), information (for example voice, image information or other data) is transmitted with the aid of electromagnetic waves via a radio interface. The radio interface relates to a connection between a base station and subscriber stations, the subscriber stations being, for example, mobile stations or fixed radio stations. The electromagnetic waves are emitted at carrier frequencies that lie in a frequency band provided for the respective system. For future radio communication systems, for example the UMTS (Universal Mobile Telecommunication System) or other 3rd generation systems, frequencies in the frequency band of approx. 2000 MHz are planned. Two modes are provided for the third mobile radio generation, one mode denoting FDD operation (frequency division duplex) and the other mode denoting TDD operation (time division duplex). These modes are used in different frequency bands. Both modes support a so-called CDMA subscriber separation procedure (Code Division Multiple Access). A proposal for a third generation mobile radio system according to “TD-SCDMA Radio Transmission Technology for IMT-2000 N Draft V.0.4, the CATT from September 1998, is based on the described TDD mode with the support of a CDMA subscriber separation method. By using the CDMA subscriber separation method, transmission blocks, which generally consist of a data part and a known training sequence, can be processed in parallel by a base station from a number of subscriber stations in a time slot. For this purpose, it must be ensured that the transmission blocks and in particular the training sequences arrive at the base station location within a certain time window in order to ensure reliable detection and separation of the different signals. This problem of the synchronization of the signal transmission in the upward direction occurs in the same way in known CDMA-based radio communication systems.

The described TD-SCDMA system and the TDD mode of the

UMTS mobile radio systems have shared physical transmission channels, so-called P-CCPCH (Primary Common Control Physical Channel), in which, for example, both a general signaling channel BCCH (Broadcast Control Channel) with organizational information and a so-called paging channel PCH (Pagmg Channel) can be sent separately as logical channels. The logical channels are additionally nested over a certain number of time frames (mterleaved) within the m time frames (frames) and superordinate so-called superframe structured radio interface. In the following, the term interleaving frame is also used for the number of interleaved time frames for a logical channel. For the BCCH and the nesting depth corresponds to the PCH, for example, four time frames.

If a subscriber station receiving the logical channels is not aware of which time frame of the nested logical channel is currently being received, the following disadvantages result. First, the subscriber station must use a so-called try and error technique to determine the start of an interleaving frame. If the so-called CRC check fails during the demodulation, the subscriber station must assume a further start of an interleaving frame or a poorly received start of an interleaving frame. This disadvantageously reduces the reliability and the speed of the detection of the logical channel. Furthermore, the subscriber station often has to detect time frames that belong to an incomplete nesting frame and then reject them. This disadvantageously increases energy consumption as well as the time until a complete nesting frame is received.

To avoid the disadvantages described, the following points are desirable from the point of view of the subscriber station:

the subscriber station can detect the start of an interleaving frame, the subscriber station can determine the position of the currently received time frame within an interleaving frame, and the subscriber station can detect the position of the interleaving frame within a superframe. At the second point, with a nesting depth of four and an exemplary detection of a second time frame, the subscriber station could refrain from further detection of the missing time frames.

At the third point, the subscriber station was able to specifically detect a specific logical channel, for example. In the TD-SCDMA system described, a superframe consists of 48 time frames. Inside this superframe are, for example, two nesting frames, each with four

BCCH timeframe arranged. In the event that the subscriber station only wanted to detect the BCCH, it could specifically suppress the detection of the PCHs sent in the further time frame.

The object of the invention is to provide a method which enables reliable signaling of the start of a logical channel. This object is achieved by the method having the features of patent claim 1 and by the base station system of patent claim 17. Advantageous developments of the invention can be found in the dependent claims.

Exemplary embodiments of the invention are explained in more detail with reference to the accompanying drawings.

Show

1 shows a block diagram of a radio communication system. 2 shows a schematic representation of the frame structure of a radio interface with a TD-SCDMA subscriber separation method,

3 shows a section of the frame structure from FIG. 3, and 4 shows a schematic representation of the coding of a

Radio blocks. FIG 5 table 1 FIG 6 table 2 FIG 7 table 3

1 shows part of a mobile radio system as an example of the structure of a radio communication system. A mobile radio system consists in each case of a multiplicity of mobile switching centers MSC (Mobile Switchmg Center), which belong to a switching network (SSS - Switchmg Subsystem) and are networked with one another or provide access to a fixed network, and each with one or more Mobile switching centers MSC connected base station systems BSS (Base Station Subsystem). A base station system BSS in turn has at least one device RNC (Radio Network Controller) for assigning radio resources and at least one base station NB (node B) connected to it.

A base station NB can establish and maintain connections to subscriber stations UE (user equipment) via a radio interface. At least one radio cell Z is formed by each base station NB. The size of the radio cell Z is generally determined by the range of a general signaling channel BCCH (Broadcast Control Channel), which is sent by the base stations NB with a constant transmission power. Other logical signaling channels, such as a Pagmg channel PCH (Pag g channel), a notification channel (NCH - Notification Channel) or an access confirmation channel (AGCH - Access Grant Channel) are timed together with the signaling channel BCCH separated in a physical transmission channel P-CCPCH sent. Furthermore, a pilot channel pilot sends synchronization sequences from the base station NB, which are used to synchronize the subscriber station UE with the time base of the base station NB.

In the case of sectorization or hierarchical cell structures, a plurality of radio cells Z can also be supplied per base station NB. The functional act of this structure can be transferred to other radio communication systems in which the invention can be used.

The example in FIG. 1 shows a subscriber station UE which is located in the radio cell Z of a base station NB. The subscriber station UE has set up a communication link to the base station NB, on the upward UL and downward direction DL, a signal transmission of a selected service takes place. The communication connection is separated by one or more spreading codes assigned to the subscriber station UE from communication connections established in parallel in the radio cell Z, the subscriber station UE in each case providing part or all of the spreading codes currently assigned to the radio cell Z for receiving the signals of the own communication connection in accordance with the Known Jo t detection method uses.

The frame structure of the radio transmission of the TD-SCDMA mobile radio system can be seen from FIG. The radio interface is a broadband radio interface with a frequency band B = 1.6 MHz (thus three frequency bands per 5 MHz), with a time frame duration of 5 ms (thus two time frames for each UTRA time frame), with 7 time slots ts of a respective length of 675 us for traffic channels, as well as with CDMA Participant separation using 16 different spreading codes cO to cl5.

In the TDD transmission method shown, the frequency band B for the upward direction UL corresponds to the frequency band B for the downward direction DL. The same is repeated for further carrier frequencies. Due to the variable assignment of the tent slots ts for the upward or downward direction UL, DL, a variety of asymmetrical resource allocations can be made. Part of the time slots tdO .-. Tdn is used accordingly for the signal transmission in the downward direction DL (Downlmk) and the other time slots tuO ... turn for the signal transmission in the upward direction UL (Upl k). The parameters n, m and thus the switchover point SP (Switchmg Point) can be individually adapted to a current requirement, the relationship n + m + 2 = 7 in each case. Following the first time slot tdO for the downward direction DL, there is a guard time for separating the transmission lines DL and UL, which represents the switchover point SP.

The protection time consists of a downward pilot time slot DPTS (downlmk pilot time slot) with a length of 75 us for sending synchronization sequences differentiated by a set of so-called gold codes, and a protection time GP (guard period) with a length of 75 us for the switching process between sending and receiving m of the base station NB, and from an upward pilot time slot UPTS (Upl k Pilot Time Slot) with a length of 125 us for sending a synchronization sequence when a connection attempt is made by a subscriber station UE with a subsequent signal on the channel for random access RÄCH. For sub- Divorce of several subscriber stations UE in this access procedure a set of gold codes is used again.

Information of several connections radio blocks are transmitted within the time slots ts. The data d are spread individually with a fine structure, a spreading code cO, cl ... cn, so that, for example, n connections can be separated on the receiving side by this CDMA component. The spreading of individual symbols of the data d has the effect that Q chips of the duration Tc are transmitted within the symbol duration T _sym . The Q chips form the connection-specific spreading code c. A channel measurement sequence tseq for a channel estimation at the receiving end is also embedded in the radio blocks. A radio block is completed with a protection time gp.

The parameters of the radio interface used for the described TD-SCDMA system are advantageously: Chip rate: 1.28 Mchip / s frame duration: 5 ms

Number of time slots: 7

Duration of a time slot: 675 μs spreading factor: 1 to 16

Bandwidth: 1.6 MHz

These parameters enable the best possible harmonization with the UTRA TDD and FDD mode (FDD frequency division duplex) as well as the well-known GSM mobile radio system.

The method according to the invention for signaling the start of a time frame within an interleaving frame, for signaling the position of a time frame within an interleaving frame or for signaling the position sition of the nesting frame within a superframe is based on a modulation of the phase of the pilot channel pilot in the waiting pilot time slot DPTS. For this purpose, the midamble, also referred to as the training sequence tseq, of the shared physical transmission channel P-CCPCH is used as a reference value for determining the phase difference. Using this channel as a reference value has the advantage that it is sent every time frame for and the midamble always corresponds to the first derivative of the midamble basic code used in the radio cell. This is known per se to the subscriber station UE. Furthermore, as shown in FIGS. 2 and 3, the P-CCPCH is always sent to the last time slot tdO for the downward direction DL, so that there is a minimum distance a between the center of the midamble tseqO and the center of the synchronization sequence sync of the pilot channel pilot , The distance a between the midamble tseqO and the synchronization sequence sync in the TD-SCDMA system is, for example, 393.75 us or 31.5 symbols, and determines the effects of the time variation and frequency offset on the detection algorithm used.

Various algorithms can be used to detect the modulation of the pilot channel Pilot, the algorithms presented below differing in complexity and reliability.

In a first algorithm, the midamble of the P-CCPCH and the region around the DPTS are detected. A channel estimation is then carried out in the channel treasure window for the P-CCPCH. The strongest channel impulse taps are evaluated using a channel impulse response post processing algorithm used for a known jomt detection process. Subsequently, the contents of DPTS means of a sogenann ^¬ th matched filter is detected (convolutionally encoded with the Ka nalimpulsantwort) and the output signal of the matched filter demodulated.

In the case of further algorithms, for example: the frequency offset is determined by means of the α mid-range tseqO and / or the synchronization sequence sync, the information of the frequency tracking algorithm is used for the removal of the frequency offset, this can be used for a double check during the detection of the P - CCPCH are carried out, an adaptive equalization is used to update the channel impulse response, the channel impulse response at the end of the P-CCPCH radio block being taken into account as a reference for determining the modulation of the pilot channel pilot, and a channel estimation using the last detected symbol of the P-CCPCH performed.

Different signaling strategies according to the invention are described below.

In the case of a 4PSK modulation for the DPTS, two bits per time frame can be signaled. These two bits are sufficient for signaling, for example, the position of the current time frame within an interleaving frame. More than one time frame is necessary to signal further information.

According to a first implementation of the invention

The position of the current time frame within a nesting frame is signaled every time frame. This corresponds to the example table 1 m FIG. 5 assigns the respective time frame number to a specific phase difference in comparison to a previously determined phase. The phase difference is determined, for example, in every time frame.

The minimum number of time frames to be detected, in order to determine the position within the nesting frame, is one in this embodiment. For example, to determine a BCCH time frame within a super frame of 43 time frames, at least 4 time frames must be detected.

In this method, the position of the time frame within an interleaving frame is advantageously coded directly; after only one detection of a DPTS, the position can be determined. For a double check while receiving a nesting frame, further steps can be carried out. In the case of a strong frequency offset, the first and third time frames of an interleaving frame are differently coded without possible ambiguity, and the second and fourth time frames smα are coded with double ambiguity.

According to a second embodiment of the method according to the invention, the start of an interleaving frame is signaled differently and the position within a superframe is signaled directly in the first and third time frames of an interleaving frame.

In the exemplary case that the start of the nesting frame is only signaled differentially, the direct signaling can be used to indicate, for example, the start of the next BCCH nesting frame the. For example, the P-CCPCH has two equidistant BCCH nesting frames within 12 nesting frames of a superframe. The following scheme, shown in Table 2 in FIG. 6, is used to signal the start of the next BCCH nesting frame. The phase for the first time frame is defined within the nesting frame according to the rule shown.

In this example, the phase for the third time frame within the nesting frame is 90 ° larger. The first time frame mnerhalo of the nesting frame is characterized by a phase difference of 0 or + 90 ° compared to the phase of the previous time frame. The third time frame within the nesting frame is accordingly characterized by a phase difference of -90 °. In the event that a phase offset of 225 ° or 315 ° is detected, the subscriber station can determine the first time frame of the nesting frame within two or four time frames and then determine whether this nesting frame is a BCCH or only one of the following nesting frames corresponds to the BCCH.

The minimum number of time frames to be detected for determining the position of the nesting frame is 2 to 3 in this method. The minimum number of time frames to be detected for determining the BCCH nesting frame is accordingly 2 to 3.

In addition to the mentioned advantages of the first described embodiment, the position of a Nesting frames are advantageously signaled with ambiguities.

According to a third embodiment of the method according to the invention, both the start of a nesting frame and its position within a superframe are signaled directly. In this embodiment, for example, the phase 45 ° is reserved for marking the start of a nesting frame. For the other time frames of the nesting frame, the respective phase 135 °, 225 ° and 315 ° is only used to determine the position within the super frame. To avoid detection errors between 45 ° symbols and the other symbols, the further phase quadruples have as many 225 ° symbols as possible. The 180 ° phase difference results in a clear assignment. The closer to the BCCH nesting frame, the more 225 ° symbols are used. These relationships are shown in Table 3 in FIG. 7.

To determine the position within the superframe, the four phases (phase quadruples) of an interleaving frame are evaluated. With a length of a superframe of 48 time frames, 12 nesting frames with 4 time frames each can be distinguished.

The minimum number of time frames to be detected for determining the position within a nesting frame is 1 to 3 in this embodiment. The minimum number of time frames to be detected for determining the BCCH and the super frame is 3 to 4.

This method according to the invention is advantageous in addition to the advantages of the preceding methods already mentioned. ren the beginning of a nesting frame advantageously encoded directly. Furthermore, the time structure of the superframe is only signaled by four time frames. The order and the phase quadruple used can be optimized in such a way that a differential decoding of four or five successive DPTSs also enables the position within the superframe to be detected with large frequency offsets. If detection is carried out under poor transmission conditions, this embodiment enables reliable detection of the superframe.

In the case of poor transmission conditions, the situation can arise in which a subscriber station is not able to uniquely identify the BCCH or another logical channel, since several logical channels are mapped onto a shared physical transmission channel P-CCPCH. In the known GSM mobile radio system, the BCCH was therefore signaled by means of a synchronization channel SCH (synchronization channel). The described TD-SCDMA system is not provided with such a channel. This information is implicitly the phase difference.

In order to enable reliable detection of, for example, the BCCH in the event of poor transmission conditions, an uncoded radio block of the logical channel is added with a status indicator f (flag), which can consist of one or more bits or symbols for differentiating the different logical channels. The binary state of this status indicator f defines which logical channel it is.

Correct detection is achieved by the in-band signaling of the status indicator f described below in relation to FIG of the logical channel. The method described above using the phase difference can thus be used without hesitation, since the correct channel for determining the phase difference is always referenced in the detection.

4 shows the expansion of a radio block according to the invention by a status indicator f. In a first step 1, the encoder forms a radio block with, for example, 184 bits or data symbols d. In a second step 2, an additional bit for the status indicator f is added to this radio block. According to an exemplary third step 3, a CRC checksum (cyclic redundancy check) is added to the expanded radio block by block coding, and finally, in a fourth step 4, the radio block is convolutionally coded.

The status indicator f is thus protected twice for transmission via the radio interface and can be reliably detected. A binary state of the status indicator f of 1 can, for example, identify the BCCH, during which the other logical channels are identified by the binary state 0. When using several bits for the status indicator, it is also possible to differentiate between the other logical channels.

Claims

claims

1. Method for signaling the start of a logical channel (BCCH) a shared physical transmission channel (P-CCPCH) of a radio communication system,

the beginning is signaled by means of a phase relationship between the logical channel (BCCH) and a further transmission channel (pilot).

2. The method according to claim 1, in which a phase difference between symbols of the logical channel (BCCH) and symbols of the further transmission channel (pilot) signals the beginning.

3. The method according to any preceding claim, in which the beginning is signaled by a phase modulation of the symbols of the further transmission channel (pilot).

4. The method according to the preceding claim, wherein the phase of the logical channel (BCCH) serves as a reference for determining the phase difference.

5. Method according to a preceding claim, in which the logical channel (BCCH) is transmitted nested over several time frames (fr) within the shared physical transmission channel (P-CCPCH).

6. The method according to any preceding claim, in which m the shared physical transmission channel (P-CCPCH) is transmitted at least em another logical channel (PCH).

7. The method according to any preceding claim, wherein the logical channel (BCCH) a number of time frames (fr) is transmitted within a superframe consisting of several time frames (fr).

8. The method according to the preceding claim, wherein a position of the respective time frame (fr) within the nested time frame (fr) for the logical channel (BCCH) is defined by the phase relationship.

9. The method according to any one of claims 1 to 7, in which a position of the beginning of the nested time frame (fr) is signaled within a superframe by the phase relationship.

10. The method according to the preceding claim, wherein the position of the respective time frame (fr) within the nested time frame (fr) for the logical channel

(BCCH) is defined by a differential phase relationship.

11. The method according to any one of claims 1 to 7, wherein the position of the respective time frame (fr) within the nested time frame (fr) for the logical channel (BCCH) and the position of the start of the nested

Time frame (fr) is defined within a superframe by a respective constellation of several phase relationships.

12. The method according to any preceding claim, in which the logical channel (BCCH) can be distinguished by at least one further logical channel (PCH) by means of a status indicator (f)

13. The method as claimed in one of the preceding claims, in which an e physical transmission channel (P-CCPCH, pilot) is defined by at least e frequency band (B) and an expansion code (c) for each individual connection.

14. The method according to the preceding claim, in which a physical transmission channel (P-CCPCH, pilot) is additionally defined by a time slot (ts).

15. The method according to claim 6 or 7, wherein the radio interface of the radio communication system is organized according to a time-division duplex method.

16. The method according to any preceding claim, in which the signal transmission in a downward direction (DL) is carried out from a base station (NB) of the radio communication system to at least one subscriber station (UE).

17. Base station system (BSS) of a radio communication system for performing the method according to claim 1.