MXPA99003937A - Method for propagation delay control - Google Patents

Abstract

A method for maintaining synchronization between a base transceiver station (BTS) (30) and an interworking function (IWF) (40) within a cellular communications network (45) is disclosed. The method utilizes a synchronization procedure between the IWF (40) and the BTS (30) that makes the IWF (40) aware of propagation delays (36) between the IWF (40) and BTS (30). The IWF (40) utilizes this information to adapt to the delays (30) such that the correct sequence is unpacked uplink when obtained from the base transceiver station (30). The IWF (40) also uses synchronization data to control transmissions from the IWF (40) to the BTS (30) such that frame numbers and timeslots (20) are received at the BTS (30) in the correct sequence.

Description

"METHOD FOR CONTROL OF PROPAGATION DELAY" RELATED REQUESTS This application claims the benefit ^ of the Previous North American Provisional Application, filed and co-pending Serial Number 60 / 030,015, called "Control of Synchronization of Multiple Squares", pre-set on November 1, 1996 (Touch of Attorney Number 27946-199L, Inventors: Peter Galyas, Stefan Jung, Martin Bakhuizer, Caisa Carneheisu, Per-Olof Anderson, and Lars Malm).

BACKGROUND OF THE INVENTION TECHNICAL FIELD OF THE INVENTION The present invention relates to propagation delay within transport networks of telecommunication systems and, more particularly, to a method for controlling propagation delays in a transport network by synchronizing an external node with a synchronous air interface.

DESCRIPTION OF THE RELATED TECHNIQUE In a cellular communication network, the synchronized air interface and an external network node such as PLMN, PSTN, ISDN or the Packet Data Network are interconnected through a separate node such as an interaction function (IWF) or a packet control unit (PCU) and a base transceiver station (BTS) through an associated transport network. However, the separation between the IWF and the base station of the transceiver invites propagation delays through the transport network between these devices. The delays create problems with the re-assembled data transmitted through the transport network. For transport networks that use only a single traffic channel for calls, these delays should be reduced to a minimum. For transport networks that use more than one traffic channel, the delays must be minimized and the variations of independent delay within the system must be determined in order to recreate the transmitted data stream. A solution to combat the independent time delay in the different sub-channels in a fixed cellular network Involves the use of a terminal adaptation function (TAF) in the mobile station, and the use in the IWF of a multiple-frame structure together with a sub-channel memory. A band signal is generated using bits of redundant control in the CCITT.V.110 tables. One bit is used for each multiple frame structure and three bits are used for the sub-channel numbering. This sequence resolves a delay variation up to (n-l) / 2 (where n = number of bits used in the sequence) V.110 frames. However, this solution has several inconveniences. The maximum sub-channel delay variation can not be determined from only the algorithmic delays. Significant delay variations can arise within the transport networks where the sub-channels can be routed independently. In addition, the sending of signals in bands is transferred through the air_interface where the bit error rates can be very high. The error rate, the air interface and the length of the frame structure cause prolonged synchronization and re-synchronization winds. There is also a risk of false detection. In addition, each of these proposed solutions have been generated with respect to the use of data, switched in high-speed circuits and do not provide solutions for other types of implementations such as GPRS. Therefore, alternative solutions are necessary.

COMPENDIUM OF THE INVENTION The present invention overcomes the above problems and others with a method for maintaining synchronization between a first node, preferably comprising a transceiver base station (BTS) and a second node, preferably comprising either an interaction function ( IWF) or a packet control unit (PCU) within a cellular communications network. Initially, an uplink synchronization frame is transmitted from the base station of the transceiver to an interaction function. This causes the IWF to transmit a link synchronization box ~ down to the BTS. The downlink synchronization box contains downlink synchronization data useful for synchronizing the connection between the BTS and the I F. Upon receipt of the downlink synchronization data (SeqD) by the BTS, the BTS marks the received SeqD with the falling package of the associated adjusted frame number (aFNd), and a time margin between the downlink synchronization frames and the air interface can be determined. The SeqD marked with aFNd, the time frame and other data from uplink synchronization are transmitted to the interaction function within an uplink synchronization frame. The receipt of the uplink synchronization data in the interaction function initiates a determination of the unpacking sequence for the frames transmitted to the IWF. The determination of the unpacking sequence consists of determining the phase of the frames of their different channels that have the same uplink of the adjusted frame number (aFNu) and the sequence number of the uplink. The determined phases provide the unpacking sequence. Once the interaction function receives downlink synchronization information from the uplink synchronization frames, the _jt_etards_in can be determined. the downlink direction for each individual sub-channel. The delays are used to place the transmission in the downlink direction of. such that frame numbers and time slots are received in the order of the downlink sequence number that increases in the BTS. The communication link between the base station of the transceiver and the interaction function can be monitored to determine whether synchronization is maintained in both uplink and downlink directions. If the synchronization is lost in the downlink direction, the synchronization procedures discussed above may be re-initiated to recover synchronization.

BRIEF DESCRIPTION OF THE DRAWINGS_ For a more complete understanding of the present invention, reference is made to. the following detailed description which is taken in conjunction with the accompanying drawings, wherein: Figure 1 is a diagram illustrating the separation of a data stream into a plurality of sub-channels; Figure 2 - SS an illustration of the delays generated within a GPRS system; Figure 3 is an illustration of the transport network; Figure 4 is a diagram of the synchronization signals and procedures for obtaining the synchronization of the signal between the base station of the transceiver and the interaction function; Figure 5 is an illustration of an uplink synchronization frame V.11CT; Figure 6 is an illustration of a downlink synchronization frame V.110; Figure 7 is a flow diagram of the synchronization procedures carried out in the base station of the transceiver; Figure 8 is a flowchart of the synchronization procedures carried out in the interaction function; and Figure 9 is a flow chart of the re-synchronization procedures. . _ DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, and more particularly to Figure 1, the transmission of a single data stream 10 through a plurality of data sub-channels 35 is illustrated. The stream 10 of a single data originates in a mobile station _15. The data stream 10 is divided into a plurality of time slots 20 which are transmitted through the synchronized air interface 25 to the base station of the transceiver 30. The data stream 10 is received on the. station, the base of the transceiver (BTS) 30 and sent to an interaction function (IWF) 40, through a plurality of separate sub-channels 35. Each of the plurality of separate sub-channels 35 includes an independent delay 36 which affects the transmission of the time slots 20 through the transport network 45. The interaction function 40 repackages the plurality of time slots 20 to the original data stream 10 that was transmitted from a mobile station. Unfortunately, this repackaging process is complicated by the time delays 36 that occur through the network 45 of. _Transportation. The delays in the transport network 45 arise from the different routing paths that can be followed by the individual time intervals 20 between the base station of the transceiver 30 and the interaction function 40. Referring now to Figure 2, an alternative environment in which the present invention is used is illustrated. A data packet is transmitted from a packet control unit (PCU) 46 to a base station of the transceiver 30 through a transport network 45 in a single sub-channel 35. As before, the single sub-channel 35 induces a quantity. delay 36 specifies through the sub-channel interconnecting the PCU 46 with the BTS 30. The data packet is transmitted from the BTS 30 each of the mobile stations 10 through the synchronized air interface 25 within a single time interval 20.

Referring now to Figure 3, the transport network 45 between the mobile station 10, the base station of the transceiver 30 and the interaction function 40 or _PCU 46 is illustrated in more detail. With the further development of user applications within a public land mobile network (PLMN), a number of high capacity non-speech data services has been introduced. These services include all circuit switched data services. As defined in TSGSM02.02 and TSGSM02.03, as well as other GSM 2+ phase services, including facsimile transmission of data connected in high-speed circuit (HSCSD) ), high-speed modem connections, and general packet radio services (GPRS). As a result, a telecommunications module known as an interaction function (I F) 40 has been developed to allow transmission and adaptation of the protocol from a telecommunications network such as a PSTN 50 connected to the service PLMN. The IWF 40 can co-locate within a specific mobile switching center (MSC) that serves a designated geographic area or can be implemented as a separate telecommunication node. The I F 40 is connected to a transcoder / rate adapter unit (TRAU) 55. The TRAU 55 is also connected to a number of base stations of the transceiver (BTS) 30 that provide radio coverage for the mobile stations 15 placed within the coverage area of the service MSC. A communication link 70 established between the IWF 40 and the TRAU 55 is known as an "A-interface" within the overall system for the mobile communication system (GSM) and uses tables prepared in format (CCIIT) V.110 and the committee international telegraph and telephone consultation to prepare the data format of the. user among them. The communication link 70 is capable of transporting the data of 16 Kbps per channel, while communicating the CCITT V.110 frames of 5 ms carrying the user's cost-effective data load of 9.6 Kbps. The remaining bandwidth is used for synchronization and transport of control data to facilitate communication. the user's cost-effective 9.6 Kbps load between the service IWF 40 and the TRAU 55. A communication link 75 established between the TRAU 55 and the service BTS 30 is referred to as the "A-BIS" interface within of the GSM specification. In accordance with the _ GSM 08.60 specification, which specifies the speech and data frames prepared in format between the BTS 30 and the TRAU 55, when the TRAU 55 is placed remote from the BTS, the A-BIS 75 interface provides a data rate of 16 Kbps, while transports the 20 ms data boxes prepared in GSM 08.60 format. The data is transferred between a channel encoder-decoder unit (CCU) 80 within the BTS 30 * and the TRAU 55 using the "TRAU frames" prepared in accordance with the GSM 08.60 specification. Within these boxes, the voice / data, the synchronization pattern and the control data associated with TRAU are included and transmitted. As a result, of the 16 Kbps of data, only 13.5 Kbps are used to transport the user data and the rest of the bandwidth is used to communicate between them, the synchronization and the control data. The TRAU 55 performs the necessary transcoding and regime adaptation to facilitate the communication of the user data between the IF 40 and the BTS 30. Referring now to Figure 4, where a diagram illustrating the different signals is presented and methods used for synchronization of an external node (IWF or PCU) to a synchronous air interface in the BTS 30. For purposes of the following description, the procedure between an IF 40 and a BTS 30 will be described. However, the procedures are equally applicable between a PCU and a BTS for a general packet radio (GPRS) system. The method relies on the fact that the air interface is synchronized and solves the problem of variable independent delays introducing synchronization procedures between the IWF 40 and the BTS 30. The method makes the IWF 40 aware of the propagation delays between the IF and the BTS 30. This information is used by the IF 40 to adapt to the delays in such a way that a correct data stream stream is the unpacked uplink when it has the BTS 30. When a call is being established and no data is received, the BTS 30 transmits the TRAU frames with the data busy to IWF 40. These frames are identified as uplink synchronization frames V.110 and are illustrated in Figure 5. All E, S, X and data bits (85, 90, 95, 100 ) within one of the CCITT V.110 frames are set to a binary in the direction of the uplink. In IF 40 this is interpreted as a busy data since in the transport mode the data rate indicated in the bits El, E2 and E3 of the V.110 tables have not been defined and in the non-transport mode, the Protocol box of a radio link (RLP) is not found. This fact is used to define a signal sending path between the BTS 30 and the IWF 40. In each unoccupied CCITT V.110 frame, the uplink of the set frame number (aFNu) 105 is adjusted to the burst received last on the the block of coding of the corresponding channel, module 104 and the time interval information (TS) 107 is included. All CCITT V.llO frames belonging to the same channel coding block are also marked with a sequence number (SeqU) 115 in the direction of the uplink in order to achieve a resolution of a table. CCITT V.llO. The downlink information 109 is also included. Referring now again to FIG. 4, when a call set-up request 110 for any transparent or non-transparent data is transmitted from the BTS 30 to the? WF 40, the? WF 40 begins to transmit a synchronization pattern to the BTS 30 known as a downlink synchronization frame V.llO (Figure 6) in order to achieve synchronization between the IWF 40 and the air interface. The link synchronization frame 115, downward V.llO consists of all the data bits 116 of a V.llO frame set to a binary one and all the current state bits 117 are disconnected. A downstream 8-bit downlink sequence number 118 (SeqD) is further included with each downlink synchronization frame V.llO. Finally, the bits 119 El, E2 and E3 are set to a binary one. The downlink synchronization tables V.llO are prepared at interface A in order increased sub-channel as they are transmitted between the IWF 40 and the BTS 30. Once the BTS 30 receives the downlink synchronization frames 115. of the IWF 40, the process steps generally identified 118 illustrated more fully in Figure 1, they are carried out of course. The rad BTS 30 marks in step 117 the downlink sequence number 118 (SeqD) with the downlink of the number of associated frames (aFNd) and extracts in step 120, the downlink sequence number 118 (SeqD). ) of the first downlink synchronization frame V.llO within the TRAU 55. Using this information, the time margin (Td) between the air interface and the downlink synchronization frames 115 is calculated in step 125 and it is stored in step 130 with the adjusted frame number downlink (aFNd) associated with the downlink sequence number. The aFNd is defined as the number of the frame set to the first burst in the corresponding channel coding block that is transmitted. The aFNd acts as a sealed chrome for the downlink sequence number. This information is transmitted in the uplink direction in step 135 to the IWF 40 within t_n box 78 _ of uplink synchronization V.llO, such as downlink information 109. During receipt of the uplink synchronization frame 78, the IWF 40 performs several steps generally designated 136 and more fully described in Figure 8. In the transparent mode, when the IWF 40 receives the link information As shown in the above step (aFNu, SeqU and Td) in step 140, the unpacking sequence for the V.llO table can be calculated in step 45. This is accomplished by determining the phase of the tables of the different sub-channels that have the same aFNu and SeqU. Frames with larger phase difference are unpacked first. Once the phase is determined, the V.llO frames are unpacked in step 150 in increased order of time interval. When the IWF receives the. downlink information. (aFNd, SeqD, Td and TS) in step 135. This information is used to calculate the decrements in the downlink direction for each sub-channel in step 160. This is achieved by delaying each sub-channel for a number necessary such that for the same aFNd and TS in increased order to provide increased values for SeqD. This delay corresponds to the storage and memory delay between the IWF .40 and the BTS 30. By delaying the signals transmitted in step 161 for the IWF 40 to BTS 30 by this amount, the IWF can be synchronized with the air interface, whose signal is received by the BTS in increased TS order. In the synchronous transparent mode, Td is not used since the phase of the TRAU frames in the A-BIS interface can not be manipulated by the IWF 40 to achieve the resolution less than the block level. In a synchronous transparent mode, Td could be used to manipulate the TRAU frames. In the non-transparent mode, Td is used to adjust the phase of a RLP frame to minimize the buffer delay, of the downlink in the BTS 30 for up to 20 milliseconds. If the memory storage delay created for a subchannel in the IWF 40 exceeds 20 milliseconds. the delay can occur in steps of 20 milliseconds preparing the RLP frames in different TS order and counteracting the created buffer. Referring now to Figure 9, a flow chart describing the procedures in the case of a loss of synchronization is illustrated. The inquiry step 170 determines whether the synchronization is lost in the uplink or downlink direction. If synchronization is lost in the downlink direction, the BTS 30 begins to transmit uplink synchronization frames V.llO in step 175. The transmitted uplink synchronization frames 78 are detected by the IWF 40 in step 180, and the synchronization procedure is restarted in step 185 in the manner described above. if the synchronization in the uplink direction is lost, the IWF 40 informs the BTS 30 in step 190. The BTS 30 then restarts the synchronization procedure in step 175. Even though a preferred embodiment of the method and apparatus of the present invention in the accompanying drawings and described in the detailed description above, it will be understood that the invention is not limited to the modality disclosed, but is capable of numerous rearrangements, modifications and substitutions without deviate from the spirit of the invention, as stated and defined in the following claims.

Claims (29)

1. R E I V I N D I C A C I O N S 1. A method for synchronizing the transmission of a data stream between a first node and a second node connected to an air interface of a transport network within a cellular communication system, comprising the steps of: a) transmitting from the second node to the first node the uplink synchronization frames containing uplink synchronization data; b) transmit from the first node to the second node downlink synchronization frames containing downlink synchronization data in response to the receipt of the uplink synchronization frames; c) determining an unpacking sequence for time intervals of the data stream transmitted from the uplink synchronization data; and d) unpacking the data stream according to the determined unpacking sequence.
2. 2. The method of claim 1, further comprising the steps of: receiving the downlink information in the first node within the uplink synchronization boxes; determine the delays for the sub-channels of the downlink information; and transmit on the sub-channels with respect to -determined delays.
3. 3. The method of claim 2, wherein the step of determining the delays for the sub-channels further comprises the step of retarding each sub-channel, such that the frame numbers and time intervals are received in a order of the number of downlink sequences increased in the second node. The method of claim 1, wherein the step of determining the unpacking sequence comprises the step of determining a frame phase of the different sub-channels having the same number-of uplink frame and sequence number uplink. The method of claim 1, further comprising the steps of: calculating a time margin between the second node and the air interface; and minimize the delays between the first node and the second node, using the time margin. 6. The method of claim 1, wherein the second node comprises a base station of the transceiver and a first node comprising an interaction function. The method of claim 1, wherein the second node comprises a base station of the transceiver and the first node comprises a packet control unit. The method of claim 1, wherein the step of transmitting from the second node to the first node further includes the step of adjusting the uplink of the adjusted frame number of each uplink synchronization frame to a burst received last in a corresponding channel coding block. The method of claim 1, wherein the step of transmitting from the second node to the first node further includes the step of adding an uplink sequence number to each uplink synchronization frame. The method of claim 1, wherein the step of transmitting from the second node to the first node further includes the step of fixing the downlink information to the uplink synchronization frame. 11. The method of claim 1, wherein the step of transmitting in the first node to the second node comprises the step of setting a downlink sequence number to the downlink synchronization frame. . 12. A method for synchronizing the transmission of a data stream between a first node and a second node connected to an air interface of a network of. transport within a cellular communication system, comprising the steps of: a) transmitting from the second node to the first node the uplink synchronization frames comprising frames V.llO containing the uplink synchronization data, the data uplink synchronization each contains an uplink of the adjusted frame number and an uplink sequence number; b) transmit from the first node to the second node, in response to the receipt of the uplink synchronization frames, downlink synchronization frame comprising the V.llO frames containing a downlink synchronization data, the frames of downlink synchronization each contains a downlink sequence number; c) comparing a phase of the frames of the different sub-channels with the same uplink of the frame number and number of the frame number sequence to determine an unpacking sequence for the transmitted data stream, and d) unpacking the stream of the transmitted data stream; data transmitted according to the determined unpacking sequence. The method of claim 12, further comprising the steps of: receiving the downlink information in the second node within the uplink synchronization frames; determine the delays for the sub-channels from the downlink information; and transmit on the sub-channels according to the determined delays. The method of claim 13, wherein the step of determining the delays for the sub-channels further comprises the step of retarding each sub-channel in such a way that the frame numbers and time intervals are received in the order of the downlink sequence number increased in the second node. 15. The method of claim 12, further comprising the steps of: calculate a time margin in which the second node of the air interface; and minimize the delays between the first node and the second node, using the time margin. The method of claim 12, wherein the second node comprises a transceiver base station and the first node comprises an interaction function. 17. The method of claim 12, wherein the second node comprises a base station of the transceiver and the first node comprises a packet control unit. The method of claim 12, wherein the step of transmitting from the second node to the first node further includes the step of adding an uplink sequence number to each frame of. uplink synchronization. 19. The method of claim 12, wherein the step of transmitting from the first node to the second node comprises the step of setting a downlink sequence number to the synchronization frame. of downlink. 20. A method for tuning the transmission of a data stream between a first node and a second node connected within an interface of a network of transport within the cellular communication system, comprising the steps of: initiating a synchronization request of the second node; a transmission means for determining a time delay from the first node to the second node in response to the request for synchronization - determining the time delay between the first and second nodes; and controlling the data stream__in the first node in response to the determined time delay. The method of claim 20, wherein the initiation step further comprises the step of transmitting the uplink synchronization frames from the second node to the first node. The method of claim 20, wherein the transmission step further includes the step of transmitting the downlink synchronization frames containing the downlink synchronization data. 23. The method of claim 20, wherein the determination step further includes the steps of: calculating the time delay in the second node of the determination medium; Y transmit the time delay back to the first node. The method of claim 23, further comprising the step of determining "an unpacking sequence for the time intervals of the transmitted data stream." The method of claim 24, wherein the step of controlling comprises the step of unpacking the data stream in accordance with the unpacking sequence 26. The method of claim 23, further comprising the step of determining the delays for a sub-channel from the time delay. claim 26, wherein the step of controlling comprises the step of transmitting the sub-channels in accordance with the determined delays. 28. The method of claim 20, wherein the second node comprises a base station of the transceiver and the first node comprises an interaction function. The method of claim 20, wherein the second node comprises a base station of the transceiver and the first node comprises a packet control unit,