FI103308B - Synchronization Procedure - Google Patents

Description

1, 103308

synchronization method

Scope of the Invention

The invention relates to a synchronization method in a communication system, preferably in a cellular radio system.

Background of the Invention

The transmission capacity required for data transmission is constantly increasing, especially in cellular radio systems. For example, in addition to the current data rates of 9.6 10 kbit / s and 4.8 kbit / s in the pan-European GSM mobile communication system, there is also a need for higher data rates, for example 14.4 kbit / s, mm. PSTN data services such as modems and G3 fax machines.

Figure 1 of the accompanying drawings is a simplified block diagram of a pan-European GSM mobile communication system. The Network Subsystem NSS comprises a Mobile Switching Center MSC that communicates with other mobile switching centers and directly or through a Gateway Mobile Services Switching Center (GMSC) system interface, the mobile network connects to other networks, such as a public switched telephone network (PSTN). Switched Telephone 20 Network), Integrated Services Digital Network (ISDN), Other Public Land Mobile Network (PLMN) networks, and PSPDN for packet switched data networks and CSPDN for circuit switched data networks. The MSC has a Network Interworking Functions (IWF) for adapting the GSM network to other networks. The Network Adaptation IWF comprises an echo cancellation section, modems for modulating a signal from a cellular network in a desired manner before transmitting it over the system interface to other networks and a signal from other networks, respectively; to demodulate to a PCM signal. The network adaptation IWF further comprises a rate adaptation to adapt the transmission rate to other networks and to adapt the signaling rate from other networks to the GSM network, respectively. Through the A interface, the network subsystem NSS is connected to a base station subsystem BSS, which comprises base station controllers BSC, each controlling the associated base stations BTS. The interface between the base station controller BSC and the base stations BTS connected to it is the Abis interface.

103308 2

The base stations BTS, in turn, are in radio communication with the mobile stations MS via the radio interface.

The Transcoder / Rate Adapter Unit (TRAU) is part of the base station system BSS and may be located in connection with the base station controller BSC, as shown in Figure 1, or also with the mobile services switching center MSC. Transcoders convert speech from one digital format to another, for example, converting a 64 kbit / s PCM from a mobile switching center MSC into data to be exported to a base station, and vice versa. One 64 kbit / s PCM channel can accommodate four voice / data connections, whereby creating one voice / data channel at this interval is 16 kbit / s.

Between the mobile station MS and the data terminal 12, here PC, is shown in Fig. 1 a block TAF (Terminal Adaptation Function) which is designed to perform the matching between the data terminal 12 and the radio parts of the telephone to match the bit stream from the terminal. The mobile station MS connected to the data terminal 12 transmits user data over the radio interface on a radio channel at a standard rate of 9.6 kbit / s or 4.8 kbit / s. The base station BTS receives the traffic channel data and transmits it to the 64 kbit / s slot of the PCM cable. Three other traffic channels of the same carrier are also placed in the same time slot, i.e. the channel, so that the transmission rate per connection is 16 to 20 kbit / s. In the base station controller BSC, the transcoder / rate adjustment unit TRAU converts the encoded 16 kbit / s digital information into a 64 kbit / s channel and transmits the data to the IWF unit in the mobile services switching center MSC, which then performs the necessary modulation and conversion; Thus, user data is transmitted in fixed uplink from base station BTS to base station controller BSC and mobile switching center MSC and respectively to mobile station MS, transmitted downlink from mobile switching center MSC via base station controller BSC to base station BTS and further over the radio path. Base Station Channel Codec Unit:; 30 performs the conversion of the signal received on the radio channel to the channel of the interconnector over the Abis interface 7 * 'and the signal received over the Abis interface * to the radio channel.

The transcoder unit TRAU performs conversion operations over the A interface. for transferable signals.

; - 35 User data is transferred over the Abis interface from the base station BTS to the transcoding unit TRAU in a standard TRAU frame. The TRAU frame comprises 40 octets numbered 0, ..., 39 and thus has a total length of 320 bits and an I IP · 3 103308 duration of 20 ms. Figure 2 is a bit diagram showing a TRAU data frame for transmitting a data rate of 9.6 kbit / s or 4.8 kbit / s. The synchronization bits indicated in FIG. 2 as "0" and "Ί" are used to synchronize the transmitting and receiving units of the TRAU frame. The "0" bits in the two en-5 first octets of the TRAU data frame performs actual synchronization, and the "1" bits in the first bit position of the first, second, and fourth octets ensure that there are no other two octets per synchronization period appearing elsewhere in the data frame. Ό '' - bit sequence. The TRAU frame of Figure 2 is marked with control bits C1 through C1510 and X with user data bits. In control bit C6, data rate such as 8 kbit / s or 16 kbit / s is transmitted. The octet comprising user data is separated by dashed lines in the figure into 63 data bit sections having synchronization bits including a total of 72 bits. The unused data bits are set to "1" mode, for example during data transmission pauses.

The TRAU frame of Figure 2 is not suitable for transmitting signals at a data rate of 14.4 kbit / s as 288 data bits should be placed in one frame. An extended TRAU data frame, the structure of which is shown in Figure 3, has been proposed for use in this data transmission. The extended TRAU data frame is also suitable for transmitting 7.2 kbit / s data rate signals. In FIG. 20, 3 user data bits D3 to D286 are denoted by X for simplicity. The 288 bits of the 14.4 kbit / s signal are thus placed in user data bits D1 to D288. The synchronization bits of the first bit position of the octets 4-39 of the normal TRAU data frame are thus replaced by user data bits in the extended TRAU data frame and bits S1 and S2 are replaced by control bits C14 and C15. For non-transparent data, the S1 bit conveys information about the half-number of the multi-frame transmission, and the S2 bit for discontinuous transmission DTX, and for transparent data the S-bits indicate multi-frame numbering. Because the extended TRAU data frame has had to reduce the synchronization bits, a synchronization frame formed from the normal TRAU data set in FIG. In the synchronization procedure, the channel unit CCU of the base station BTS transmits to the TRAU a transmission of 7.2 or 14.4 kbit / s, initially with a synchronization frame according to Fig. 4, whose control bits indicate the type of frame used, such as extended 14.4 kbit / s or extended 7.2 kbit / s The transcoder TRAU responds with a similar synchronization frame, 4 103308, after which the channel unit CCU initiates the actual transmission by transmitting an extended TRAU data frame. The transmission of synchronization frames is also performed as described above when the traffic channel data rate 5 changes from another data rate of 7.2 or 14.4 kbit / s during transmission.

, Successful communication requires the sending and receiving units to be in sync. When transmitting TRAU frames, the transcoder unit TRAU receives synchronization from the base station BTS. If the synchronization is lost during 10 data transmissions, the transcoder TRAU transmits the information to the base station BTS in the following transmitting TRAU frame with the Uplink Frame Error or UFE parameter. The UFE parameter is shown for placement in the extended TRAU data frame to the control bit C6, which is in "1" mode during normal synchronization and in "0" mode when uplink synchronization is lost. The base station channel unit 15 CCU responds to the arrival of the UFE parameter by sending the TRAU a synchronization frame which is acknowledged by the TRAU with the corresponding synchronization frame. If the channel unit CCU detects a loss of synchronization in the downlink direction, it initiates the corresponding synchronization procedure.

On the transmission line between the network switching unit IWF of the mobile switching center MSC and the TRAU unit in the base station system BSS, data rates of 9.6 kbit / s and 4.8 kbit / s are normally transmitted in an 80 bit V.110 frame according to ITU-T recommendation V.110. 5. The frame comprises 10 octets, numbered 0, ..., 9. At a transmission rate of 16 j kbit / s, the frame duration is 5 ms. The bits of the first octet and the en- The J / 25 digest bits are synchronization bits. The "0" bits of the first octet are | female frame synchronization and, similarly, as in the TRAU frame, in the "T" state of the first bit of the other octets, there are no eight consecutive "0" bits in the frame that could be understood as frame synchronization. The idle 30V shown in FIG. 110 data frame with all data bits set to "1." The D1 and X bits shown in Figure 5 are data bits that can fit into one V.110 frame 63. Thus, four V.110 bits are required to transfer bits of a normal TRAU data frame. frame.

Over the Abis interface in an extended TRAU data frame, the 4 * 72 bits transmitted in 14.4 kbit / s user data cannot fit into the four V.110 frames shown in FIG. Therefore, the proposed proposals also propose the transfer of the TRAU frame on the 64 kbit / s channel over the A interface. If n

'T'H

However, 103308 uses 16 kbit / s V.110 frames for data transmission on this 64 kbit / s channel, there is a problem that the expanded V.110 frame cannot be formed in the same way as the extended TRAU data frame by changing the synchronization bit of the first bit of the frame octets to data bit , because the low synchronization bits of the V.110 frame would no longer be sufficient to ensure unambiguous synchronization. Further, according to the synchronization frame used in the extended TRAU data frame, the synchronization frame formed analogously to the imaginary extended V.110 frame would be exactly the same as the idle V.HO frame shown in Figure 6, since the V.110 frames 10 do not contain any control bits expressing information data. -peuden. In this case, the frame receiving unit would not be able to distinguish the synchronization of the extended V.110 frame from the standard V.110 idle transmission.

BRIEF DESCRIPTION OF THE INVENTION The object of the present invention is to provide a simple and secure synchronization method for transmitting data rates higher than those currently available in data frames with relatively few synchronization bits.

This new type of synchronization is achieved by the method of the invention in a communication system comprising a transmitting unit, a receiving unit, and a transmission link between them. The information to be transmitted in the telecommunication system is transmitted from the transmitting unit to the receiving unit in a data frame comprising an information part and a synchronization part. The bits of the synchronization section in each successive data frame are always in the same state as in the previous data frame and the synchronization section 25 consists of at least one synchronization bit in the selected logical state. The method synchronizes the transmitting and receiving units of the data frame with synchronization bits. The method according to the invention is characterized in that it provides a synchronization frame comprising at least as many synchronization bits as the data frame, and each synchronization frame containing bits in the same logical state of the data frame in the selected logical state with up to a maximum number of bits the number of synchronization bits of the data frame minus one, wherein the other bits of the synchronization frame are in a selected logical state in the complementary state, and transmitting said synchronization frame over the transmission link to synchronize between the transmitting and receiving units.

6, 103308

The invention is based on the idea that a transmission line carries data frames with a low proportion of synchronization bits, and by a separate synchronization procedure a synchronization frame which contains bits that are essentially in the same state. The synchronization frame according to the invention comprises at least as many bits as the data frame. In addition to the information section, the data frame comprises a synchronization section comprising at least one synchronization bit. The bits to be placed in the synchronization frame are selected such that the synchronization frame comprises only bits in the same logical state only or bits in the selected logical state up to 10 corresponding to the number of bits in the synchronization part of the data frame minus one. This form of synchronization frame ensures that the data frame does not resemble a synchronization frame for any user data content. In particular, the present invention can be used to transfer 14.4. kbit / s user data on a 16 kbit / s channel 15 using extended V. 110 frames and a synchronization frame according to the invention.

The advantage of such a synchronization method is that it is simple and requires only minor changes to known synchronization procedures.

A further advantage of the synchronization method according to the invention is that the setting of the synchronization of the extended V.110 frame is unambiguous and J also secure in various transmission change situations.

A further advantage of the synchronization method according to the invention is that the synchronization frame transmitted over the j link is easily identifiable, since>. 25 it always stands out from the data frame.

List of figures

The invention will now be described in more detail in connection with preferred embodiments with reference to the examples of Figures 7 to 11c in the accompanying drawings, in which: Figure 1 shows the essential parts of the mobile network for the invention, Figure 2 shows the structure of a TRAU data frame;

Figure 3 shows the structure of an extended TRAU data frame,

Figure 4 shows the structure of the synchronization frame used for transmission of the extended TRAU data frame, Ι έ 35 Figure 5 shows the structure of the V.110 recommendation frame,

Figure 6 shows the structure of an idle frame according to V.110 recommendation, ί 23 7 103308

Figure 7 shows a preferred embodiment of the structure of an expanded V.110 frame formed from a V.110 recommendation frame,

Fig. 8 shows a preferred embodiment of the structure of the synchronization frame according to the invention for transmission of an extended V.110 frame,

Figure 9 shows a secondary embodiment of the structure of an expanded V.110 frame formed from a V.110 recommendation frame,

Fig. 10 shows a secondary embodiment of the structure of a synchronization frame according to the invention used for transmitting an extended V.110 frame, and

Figures 11a-11c illustrate a resynchronization procedure between a trans encoder TRAU and a network adaptation IWF.

DETAILED DESCRIPTION OF THE INVENTION

The present invention can be applied to any telecommunication system, preferably a cellular radio system. In the following, the invention will be described in more detail by way of example primarily in the context of a pan-European digital GSM mobile communication system. Figure 1 shows a simplified structure of the GSM network as described above. For a more detailed description of the GSM system, reference is made to the GSM Recommendations and to "The GSM System for Mobile Communications", M. Mouly & M. Pautet, Palaiseau, France, 1992, ISBN: 2-9507190-0-7.

The invention will now be described in more detail in the light of the preferred embodiment of the invention with reference to Figures 7 and 8. Fig. 7 shows an extended V.110 frame suitable for data transmission of 14.4 kbit / s, for example for data transmission between a transceiver TRAU and an IWF unit. The expanded V.110 frame comprises two 36 data bit sections D1 to D36 and DT to D36 ', i.e. a total of 72 data bits, control bits H and M, in the downlink direction of the UFE parameter and the corresponding bit position in the "1" bit uplink, and five synchronization bits . Four such V.110 extended frames 1 '30 can accommodate 14.4 kbit / s user data of the extended TRAU frame. The UFE parameter reports the loss of uplink synchronization, as described in the prior art description of the TRAU frame. The H bit is set to "1" mode in every fourth expanded V.110 frame to indicate the first expanded V.110 frame of the four expanded V. 110 frames formed from the expanded TRAU data frame. The S1 bit is set to the M bit when the H bit is in the "T" state and the 8 103308 S2 bit is the H bit in the "'" state. The S bits denote the multi-frame numbering for transparent data and non-transparent data for the half-frame and DTX information of the multi-frame transmission, as described above in connection with the prior art description.

Of the synchronization bits shown in Figure 7, four are placed at the beginning of the first octet and the fifth at the first bit of the second octet. Synchronization bits can also be placed in a frame in other ways, since it is only essential for frame synchronization that the synchronization bits are located in successive frames at the same point in the frame. In other possible embodiments, the number of synchronization bits 10 to 10 is set to fit within the frame so that the synchronization part comprises at least one synchronization bit. In the case shown in Fig. 7, one of the synchronization bits is in the "1" state and the other in the "0" state. In the example case shown in Fig. 7, a bit in the "1" state of the synchronization section is selected as a character bit, which determines the structure of the synchronization frame according to the present invention.

FIG. 8 shows a synchronization frame according to the present invention used to synchronize transmission of the extended V.110 frame of FIG. 7 in a separate synchronization procedure. The synchronization frame according to the invention comprises up to a number of bits in the same logical state selected from the synchronization section 20 of the extended V.110 frame, corresponding to the number of synchronization bits in the same logical state minus the character bits in the synchronization section j of the extended V.110 frame. In the case of Figure 7, in the same "1" mode as the selected mer kibit, there are no other synchronization bits in the synchronization section of the expanded 25 V.110 frame, so the synchronization frame cannot have any bits in "1" mode, but all bits in the synchronization frame are "0" mode. The synchronization frame according to the invention comprises at least as many bits as the extended V.110 frame, preferably the synchronization frame has the same number of bits as the extended V.110 frame, so that the synchronization frame never looks like an expanded V.110 frame or a normal one. V.110 frame, but these frames are always different. The long synchronization frame thus formed ensures a secure synchronization of the connection, since the sequence of 80 "0" bits in Fig. 8 can never appear in the extended V. 110 frame or in the normal V.110 frame 35. For example, when the TRAU or IWF receives 80 consecutive "0" bits, this is obviously the synchronization frame of FIG. 8.

9 103308

Fig. 9 shows an expanded V.110 frame according to a secondary embodiment of the invention, which corresponds to the extended V.110 expanded frame according to the preferred embodiment, described above in connection with the description of Fig. 7. The synchronization section 5 of the extended V.110 frame of Figure 9 comprises one synchronization bit in "0" mode and four synchronization bits in "1" mode. In the example of Fig. 9, the only "0" bit in the synchronization partition is selected as the character bit, which means that the synchronization frame of Fig. 10 cannot have any bits in the "0" state but all bits in the synchronization frame are in the "1" state. Again, the synchronization frame and the extended 10.1 V.110 frame as well as the normal V.110 frame can always be readily identified by the bit structure.

In other embodiments of the invention, the synchronization section of the extended V.110 frame may be implemented, for example, by setting more than one of the synchronization bits to a "1" mode selected as a character bit mode. If two of the 15 synchronization bits are set to "1", the synchronization frame according to the invention is formed by placing one of the bits in the "1" state and the other bits in the "0" state or by setting all bits in the "0" state. If the synchronization bit in the "0" mode is selected as the character bit, for example, two bits of the synchronization section of the extended V.110 frame may be set to "0", whereby one of the bits in the "0" mode and the other bits are formed. "Γ mode or by setting all bits to" Γ mode. The synchronization bits in the synchronization part of the extended V.110 frame can also all be in the same logical state.

The synchronization of the transmission link is performed at the beginning of the connection with the synchronization frame according to the invention according to the prior art by transmitting the synchronization frame according to the invention to a network receiving unit, e.g. the IWF unit of the mobile switching center. The synchronization frame receiving unit sends the synchronization frame of similar form back to the master unit 30 to acknowledge the synchronization, after which the master unit transmits an extended V.110 frame containing user data. The transport link transmits these extended V.110 frames until one of the units involved in the transmission detects a loss of connection synchronization, for example, when a handover of the mobile system is performed, after which connection resynchronization is performed. In the synchronization method according to the invention, the resynchronization can be initiated, for example, by transmitting a synchronization frame according to the invention or by setting the UFE parameter in the downlink state to "0".

Figures 11a-11c illustrate various embodiments for performing re-sync synchronization on the link between the transcoder TRAU and the IWF unit. In the example of Fig. 11a, the IWF detects a loss of uplink synchronization and transmits to the TRAU at step 21 an extended V.110 frame with the UFE parameter set to 'O'. The TRAU responds to the notification received by sending the IWF of the synchronization frame according to the invention. to the acknowledged synchronization by transmitting a similar 10 synchronization frame to the TRAU at step 23. Thereafter, transmission may be continued with the extended V. 110 frames (steps 24 and 25).

In the example of Fig. 11b, the IWF detects a loss of uplink synchronization and transmits, in step 31, a synchronization frame according to the invention to the TRAU. In step 15, the TRAU responds to the notification received by transmitting the synchronization frame according to the invention to the IWF, after which transmission can be continued with the extended V.110 frames (paragraphs 33 and 34).

In the example of Figure 11c, the TRAU detects the loss of downlink synchronization and transmits to the IWF at point 41 the synchronization frame of the invention, which the IWF acknowledges by sending a similar sync 20 frame to the TRAU at step 42. Subsequently, transmission can be resumed with expanded V.110 frames. 43 and 44).

Resynchronization according to the invention with | the synchronization frame performs, for example, any of the above described processes, also when transmitting normal V.110 frames during a connection: to transmitting extended V. 110 frames, for example, when changing the user data rate from another rate to 14.4 kbit / s. The change from the transmission of extended V.110 frames to the transmission of standard V.110 frames is made, for example, when user data changes from 14.4 μ kbit / s to 9.6 kbit / s. In this case, the transcoder TRAU begins to transmit normal V.110 frames during the connection to which the IWF responds by setting the UFE parameter to "0" to indicate a loss of synchronization. The trans encoder TRAU forwards to the IWF standard V.110 frames. When the IWF detects normal V.110 frame synchronization, it starts sending V.110 frames back to the TRAUs. Thereafter, data transmission will be continued with standard 35 V. 110 frames.

The drawings and the description related thereto are only intended to illustrate the idea of the invention. The details of the dark 103308 cloning according to the invention may vary within the scope of the claims. Although the invention has been described above mainly in the context of data transmission between the transcoder TRAU and the network switching IWF of the mobile switching center, it can also be applied to other types of data transmission between two network units. The invention so-5 is also applicable to data rates other than 14.4 kbits / s for data transmission beyond the A-interface described in the above examples.

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Claims (10)

12 103308 A synchronization method in a communication system comprising a transmitting unit, a receiving unit and a transmission link between them, wherein the information to be transmitted in the communication system is transmitted from the transmitting unit 5 to the receiving unit in a data frame comprising an information part and a synchronization part with sequentially and the synchronization part comprising at least one synchronization bit in the selected logical state, wherein the method 10 synchronizes the transmitting and receiving unit of the data frame with one of the synchronization bits, characterized in that the method comprises generating a synchronization frame comprising at least data frame sync in mode up to the number of bits in the logical state in the same logon bit as corresponding to the number of synchronization bits of said data frame in the selected logical state minus one, wherein the other bits of the synchronization frame are in a selected logical state in a complementary transmitting frame. The method of claim 1, wherein the method transmits a synchronization frame as a source of synchronization from the competent unit at the beginning of the connection and from the loss detecting unit 25 upon synchronization loss, characterized in that the method transmits a synchronization frame between units only once for each data transmission unit involved. A method according to claim 1, characterized in that the information to be transmitted is transmitted in a data frame of 80 bits and a synchronization frame of 80 bits is formed. Method according to claim 1 or 3, characterized in that a synchronization frame is formed which contains mostly synchronization bits in logical "1" mode. Method according to claim 1 or 3, characterized in that a synchronization frame is formed which contains mostly synchronization bits in logical 'Ό' state. 13 103308 Method according to claim 1 or 3, characterized in that a synchronization frame is formed which contains only the synchronization bits in logical "1" state. A method according to claim 1 or 3, characterized in that a synchronization frame is formed which contains only the synchronization bits in the logical "0" state. A method according to claim 1, 2 or 3, characterized in that the data frame and said synchronization frame are transmitted to the GSM mobile communication system over a defined A interface. A method according to claim 1 or 8, characterized in that a data frame and said synchronization frame are transmitted between a transcoder / rate adaptation unit (TRAU) and a network adaptation unit (IWF). A method according to claim 1, 8 or 9, characterized by transmitting a data frame of 14.4 kbit / s at an information rate of 16 kbit / s on channel # 14 103308