JP2002541690A - Method and apparatus for synchronizing devices of an ATM-based base station subsystem using a special virtual channel connection - Google Patents

Abstract

SUMMARY A method and apparatus for a synchronization device in an ATM-based base station subsystem using a special ATM virtual channel connection is disclosed. The present invention provides a high constant bit rate connection with a BTS via an ATM cloud that exists primarily for synchronization. The method according to the present invention includes the steps of establishing a high constant bit rate virtual channel connection from a transmitting device to each of a plurality of remote devices, and processing by the plurality of remote devices to infer a target clock frequency to be synchronized. Broadcasting the data cell to perform to a plurality of remote devices. These remote units have a base transceiver station (BTS). The transmitting device (1210) is a functional device for interconnection, but this device may be a transcoder. The method includes determining the available capacity of the buffer by outputting a synchronous residual time stamp through analysis that infers the arrival of the data cell, and determining a plurality of remote capacities in response to the available buffer capacity. By performing clock adjustment of the device, clock synchronization is enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to a method and apparatus for synchronizing between network devices, and more particularly to a method and apparatus for a synchronous device in an ATM-based base station subsystem that uses a special virtual channel connection.

[0002]

[Prior art]

Demand for mobile communications by consumers around the world is growing at a rapid pace and will continue for at least the next decade. By the end of 1995, more than 100 million people had used mobile communication services. This number is expected to increase to 300 million by 2000. Several factors contribute to this exciting growth in the telecommunications industry. For example, the combination of technology and competition is bringing more value to consumers. Phones are smaller and lighter, have longer battery life, and are now available in large quantities. Operators offer excellent sound quality, innovative services and roaming nationally and worldwide. Most importantly, the cost of mobile communications is no longer expensive, and many people are using mobile communications. In the United States and around the world, governments are granting additional frequency allocations for new carriers and competing with traditional cellular carriers. Competition brings consumers innovation, new services and lower prices.

[0003] Personal wireless communication networks (PCN) based on digital technology have emerged as an important area of communication activity. This is mainly due to the success of mobile phones, pagers and notebook computers. However, the age of being able to send and receive e-mail, fax and other types of data using a simple portable device is rapidly approaching.

In a cellular system, each geographic cell is served by an individual base station, which provides wireless communication services to a set of mobile stations located within the cell. However, transmission and reception by the base station need to be synchronized with each other and also with the transcoder. Today, this is also the case for pulse code modulation (PCM) networks widely used in cellular networks. In the future, these systems will be connected via ATM networks.

When using ATM for transmission in a cellular network, synchronization of network elements may be a problem. Transcoder (TC)
Or, more generally, the interconnection function (IWF) between ATM and PCM
It inherits a common network clock from the STN or MSC. However, transfer of this clock to the base transceiver station (BTS) can be problematic. This is especially true when public ATM networks are used. Nevertheless, even within private networks, some ATM switches lack the ability to lock on the physical transmit clock. Therefore, all the BTSs belonging to the network need to be synchronized.

[0006] The clock (oscillator) in the BTS is very accurate. This means that the oscillator can operate freely without synchronization for a very long period of time (eg one week). AT
There are synchronization techniques that can synchronize the two end elements via M. For example, in an ATM-based cellular network, a plurality of BTSs exist at the edge of the ATM cloud. Since synchronization is missing at the physical level, B
The TS must be synchronized by some other method.

Typically, the synchronization techniques are based on examining time stamps, the average arrival rate of incoming ATM cells, or examining the buffer fill level for incoming ATM cells. Nevertheless, all of these synchronization techniques
It is based on scanning the cell rate of the channel. However, the use of traffic channels raises certain problems. This is because cell rates or bit rates for voice traffic channels are much lower, and are now getting lower, and in the future traffic flows will be variable rather than fixed. Thus, inferring a clock from a low variable bit rate traffic channel is difficult and time consuming. One contributing factor is the elimination of CDVs (cell transfer delay fluctuations), which take a long time, but the duration of a single cell is usually not enough to do this. Synchronization may even be impossible due to the variable bit rate connection.

It can be seen that there is a need for a method and apparatus for synchronizing with a BTS at the edge of an ATM cloud.

[0009]

[Problems to be solved by the invention]

To solve, or at least reduce, the limitations in the prior art described above,
Further, to solve or at least mitigate other limitations that will become apparent upon reading and understanding this specification, the present invention provides a synchronization device in an ATM-based base station subsystem that uses a special ATM virtual channel connection. And a method and apparatus for the same.

The present invention solves the above-mentioned problem by providing a high fixed bit rate connection with the BTS via an ATM cloud that exists primarily for synchronization.

A method in accordance with the principles of the present invention includes the steps of establishing a high constant bit rate virtual channel connection from a transmitting device to each of a plurality of remote devices, and providing a plurality of inferring target clock frequencies to be synchronized. Broadcasting data cells to the plurality of remote devices for processing by the remote devices.

[0012] Other embodiments of certain methods in accordance with the principles of the present invention may include alternative or optional additional aspects. One such aspect of the invention is that the remote device has a base transceiver station.

Another aspect of the present invention is that the transmitting device is a functional device for interconnection.

Another aspect of the present invention is that the functional device for interconnection has a transcoder.

Another aspect of the invention is that the transmitting device and the remote device are connected via an asynchronous connection, which prevents the transmitting device's clock from being physically transmitted.

In another aspect of the invention, a synchronization residual time stamp is provided in a data cell to enable a plurality of remote devices to infer the transmitter's clock and synchronize with the transmitter's clock. Is output.

In another aspect of the invention, a method includes analyzing at a plurality of remote devices to infer the arrival time of a data cell and calculating a difference between the expected arrival time of the cell and its arrival time. And adjusting the clocks of the plurality of remote devices according to the calculated difference to synchronize the clocks of the plurality of remote devices with the transmitting device.

[0018] In another aspect of the invention, a method includes storing a calculated difference for N cells, deriving an average arrival time for N cells, Adjusting the clocks of the plurality of remote devices in response to the average arrival time for the N cells to synchronize the clocks with the transmitting device.

According to another aspect of the present invention, analyzing the buffers in the plurality of remote devices to determine a filling level of the buffers, and synchronizing the clocks of the plurality of remote devices with the transmitting device. Adjusting the clocks of the plurality of remote devices according to the filling level of the buffer for the remote device.

As another aspect of the present invention, a cellular communication system includes a plurality of base transceiver stations, the plurality of base transceiver stations connected to an ATM network, wherein the plurality of base transceiver stations are an ATM network and Connected to an interconnecting device having a transcoder, and further connected to an ATM network providing an interconnecting function between the ATM network and the communication system. In this case, the interconnection device establishes a high constant bit rate virtual channel connection with each of the plurality of base transceiver stations, and then establishes a high constant bit rate virtual channel connection with the plurality of base transceiver stations. Broadcasts the data cell to the remote device via the, thereby enabling multiple base transceiver stations to infer the target clock frequency of the interconnect device for synchronization.

For a better understanding of the invention, its advantages and objects attained by its use, reference is made to the drawings which form a further part of this specification, and Reference will be made to the accompanying description in which specific embodiments of the device are illustrated and described. In the reference drawings, like reference numerals designate corresponding parts throughout the drawings.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION

In the following description of the exemplary embodiments, reference is made to the accompanying drawings that form a part hereof. The drawings show specific embodiments in which the invention can be implemented. It should be understood that other embodiments may be utilized as structural modifications without departing from the scope of the invention.

The present invention provides a method and apparatus for synchronizing devices in an ATM-based base station subsystem using a special virtual channel. According to the present invention, a high constant bit rate connection with the BTS is made via an ATM cloud that exists primarily for synchronization.

FIG. 1 illustrates the physical layer 100 of the Open Systems Interconnection (OSI). Modern networks need to handle multiple types of traffic, such as video 110, audio 112, data files 114, and interactive data 116. AT
The M adaptation layer 120 is a group of standardized protocols that provide services to higher layers by adapting user traffic to a cell format. The AAL 120 has a convergence sublayer (CS) and a cell division / assembly (
SAR) sublayer (not shown). The ATM layer 130 is the second layer of the ATM protocol stack model 100 that performs the configuration and processing of the ATM cell. A
The functions of the TM layer 130 include support for usage parameter control (UPC) and quality of service (QoS) classes. Finally, the physical layer 140 is the lowest layer of the ATM protocol reference model 100. The physical layer 140 is subdivided into two sublayers, a transmission convergence (TC) sublayer and a physical medium (PM) sublayer (not shown). The physical layer 140
AT transmitted over a physical interface interconnecting ATM devices
Provide M cells.

ATM (Asynchronous Transfer Mode) has been advocated as an important technology for wide area interconnection of heterogeneous networks. In an ATM network, data is divided into small fixed-length units called cells. FIG. 2 illustrates an ATM cell 200. Cell 200 has 53 bytes. Each cell includes a 5-byte header 210 consisting of an identifier, control priority, and route selection information. The remaining 48 bytes are the actual data 220. ATM does not perform error detection operations on the user payload in cell 200 and does not provide retransmission services. Only a few operations are performed on small headers.

The ATM switch supports two types of interfaces: a user network interface (UNI) and a network node interface (NNI). UNI connects an ATM termination system (host, router, etc.) to an ATM switch, but UNI may be incorrectly defined as an interface for connecting two ATM switches together. The ITU-T recommends that an ATM connection be identified by a connection identifier assigned for each user connection in an ATM network.

At the UNI, two values in the cell header, the virtual path identifier (
The connection is identified by the VPI) and the virtual channel identifier (VCI). FIG. 3 illustrates the operation 300 of VPI and VCI. The VPI and VCI are used by switches in an ATM network to determine how cells are routed through the network. For example, a video session 310 connection:
Associated with VPI = 4 (312) / VCI = 10 (314) at the first UNI 320 and VPI = 20 (330) / VCI = 3 at the other UNI 340
3 (332). The way in which the VP / VCI values are established and processed is left to the administrator network. In this example, the VPI / VCI values have local significance at each UNI. Of course, the network needs to ensure that these local VPI / VCI values at each UNI are mapped together over the network.

Both VPI and VCI are combined together to form a virtual circuit identifier. There are two basic types of ATM connections: fixed connection virtual connections (PVC) and switched connection virtual connections (SVC). PVC is a connection setup by an external mechanism (generally network management),
A set of switches between the ATM source and the destination ATM system must have the appropriate VPI / V
It is programmed using the CI value. PVC always requires some manual configuration. SVC is a connection that is automatically set by a signal protocol. S
VCs do not require the manual interaction required to set up a PVC. Therefore, they tend to be more widely used. All upper layer protocols operating over ATM primarily use SVC.

As shown in FIG. 1, the ATM adaptation layer (AAL) 120 provides a mechanism to support a transport protocol via ATM cells.
AAL1 and AAL2 are AAL3 / 4 for data transport without connection for support services of fixed bit rate and variable bit rate respectively.
And is defined by the ITU-T for wide area use. However, AAL5 has been proposed for all types of computer-oriented multi-service traffic, especially for local areas. AAL5 has low payload overhead per cell and relies on quality of service and statistical mechanisms to provide multi-service capability.

FIG. 4 illustrates a communication system 400 in accordance with the present invention, comprising an ATM 420 and a PC.
The transcoder 410 is used as an interconnection function between the M networks 430 and 432. When using ATM for transmission in a cellular network, problems can occur with the synchronization of network elements. Transcoder (TC) 410 or more generally ATM 420 and PCM 430,4
The interworking function (IWF) to and from PSTN 32 inherits a common network clock from PSTN 432 or MSC 430. At this time, the problem is the transfer of this clock to the BTS 440. This is especially true if a public ATM network is used. Even in private networks, some ATM switches lack the ability to lock on the physical transmit clock.

In FIG. 4, a base transceiver station (BTS) 440 is connected to a communication network via an ATM connection. Transcoder (TC) 410 is essentially an ATM 420 and PCM
An interconnection function (IWF) between 430 and 432. IWF410 is an ATM
Adaptation of the rate between the PCM 420 and the PCMs 430 and 432 and data conversion are performed. PC
The world of M is in response to the evolutionary stages of ATM-based networks,
2 or MSC30. The transcoder rate adapter unit (TRAU) frame is a one-to-one mapping, ie, AAL0
, AAL1, or AAL2.

The transmission clock of the _BTS 440 operates at the frequency f _BTS , and the reception clock of the _TC 410 operates at the frequency f _TC . At this time, since the transmission is asynchronous, TC4
10 cannot know the exact frequency of the BTS transmitter 440. If f _BTS is slightly higher than f _TC and DTX (discontinuous transmission) is not used in ATM 420, the buffer of receiving TC 410 will overflow at some moment. PCM when TRAU frame is discarded due to buffer overflow
An audible click sounds on the phone connected to 430,432. The same occurs in the opposite direction as well.

Those skilled in the art will recognize that interconnect device 410 may not include a transcoder as shown in FIG. Therefore, if you are skilled in the art,
If a transcoder is not included as part of the interconnect, a synchronous virtual channel connection is required either between the interconnect and the BTS or between the transcoder and the BTS, depending on the transcoder's location Recognize that

FIG. 5 illustrates a more detailed block diagram 500 of BTS 540 and IWF 540 in accordance with the present invention. In FIG. 5, the BTS 540 includes an ATM IF 542 and a synchronization unit 544. Similarly, the IWF 510 includes an ATM IF 512 and a synchronization unit 514. Therefore, the synchronization unit 514 of the IW 510
It is necessary to synchronize with the synchronization unit 544 of 0. If this synchronization does not occur, the clock must be desynchronized in some other way to prevent overflow.

Clock synchronization may be performed by physically transmitting the clock from the PSTN 532 to the BTS 540, or by inferring the clock frequency in some other way. For example, it is possible to utilize the physical transmission of a clock via an Independent Synchronous Digital Hierarchy (PDH) or Synchronous Digital Hierarchy (SDH) frame. If all transmitters, or ATM switches, support this type of clock locking, the clock will be transmitted from PSTN 530,532 to BTS5
It can propagate up to 40. This is the simplest way to ensure synchronization.

Alternatively, the clock frequency of the transmitter can be inferred using either a time stamp, a check of the average arrival rate of incoming ATM cells, or a check of the buffer filling level for the incoming ATM cells. it can.

The method used in AAL1 is Synchronous Residual Time Stamping (SRTS). FIG. 6 illustrates an AAL1-PDU 600. The 4-bit field 600 is
It is provided in AAL1-PDU that can be used for SRTS. This processing is IT
It is defined in U Recommendation 1.363. The ATM network clock is selected and divided by 2k, where k = 0, 1,... K is the service
It is selected to generate frequencies close to the bit rate (greater than the service bit rate and less than twice the service bit rate). A difference between the service bit rate and the network-related frequency is generated, and the 4 lsb (least significant bit) of this difference is calculated using the 4 CSI bits in the SN field 610 for eight consecutive ATMs.
Sent from cell. These four bits contain the SRTS. Both the transmitting device and the receiving device can perform this process and synchronize the local clock with the remote clock by comparing the locally generated SRTS with the received far-end SRTS. Become.

As a result of the above, the SRTS outputs a residual clock between the source and the network clock, which is sent to the other end. Therefore, connection to a master clock source is required. Using this method, it is possible to propagate the clock over the entire network. If AAL1 is not in use, this type of method can be used with AAL0, AAL2, AAL5. In the case of AAL0 (ie, for one-to-one mapping), there is room for an absolute timestamp field, so that the absolute timestamp field may be added to the cell.

FIG. 7 illustrates a diagram of system equipment 700, which may provide an alternative method for inferring clock frequency. Device 700 includes a receive buffer 710 for incoming cells 720. Processor 730 includes buffer 710
Monitor and control the transmission of cells in the buffer 710. The measured value of the filling level of the buffer for incoming cells 710 may be used. The purpose of measuring the filling level of the incoming cell buffer 710 is to keep the filling level of the incoming cell buffer 710 at a certain level. If the buffer 710 is full, the clock frequency is increased slightly until the fill level of the buffer 710 is again at the predetermined level. If the buffer 710 is underflowing, the buffer 710
The clock frequency is reduced until the filling level of the clock signal reaches the predetermined level again.

Yet another method involves the principle of investigating the average arrival rate of arriving cells, which requires information about when cells arrive. For example, one end A
Device 700 transmits a cell every t _A , and processor 730 of device 700 at the other end B knows that the cell arrives at time t _B. The processor calculates the time difference t _B -t _A and uses this time difference to adjust the clock. In an ATM network, cell transfer delay fluctuation (CDV) can be reduced by using, for example, a median value when 10 cells arrive. This method is particularly suitable for ATM-based GSM systems where one-to-one mapping is used. This method is more fully illustrated with reference to FIGS.

When the transmission / reception clocks at one end are locked with respect to each other, it is desirable that the other end be a master clock. This other end detects the incoming cell rate and adjusts its clock frequency as appropriate.

Typically, a base station subsystem (BSS) 2 in a cellular network
The two elements are connected using a synchronous PCM connection. As mentioned above, one of these devices is selected as the master and this master clock is
Synchronize with PCM frames sent over the connection. Second device (slave)
Synchronizes its own clock with this master. However, if two PCM devices are connected using an asynchronous ATM connection that does not transfer synchronization at the physical level, this synchronization is lost. FIG. 8 is a diagram illustrating a system 800 that uses an ATM connection. In FIG. 8, which requires clock synchronization, a TC 810 that transmits data 812 to a BTS 820 is illustrated. TC810 is _f t 830
Clock frequency. BTS820 has a clock frequency of _f r 832.
As illustrated in FIG. 8, when the two clocks 830 and 832 have exactly the same frequency, no problem occurs because the transmitting end and the receiving end operate at the same speed.

Unfortunately, however, there is no exact clock, so there is no synchronization and one of the clocks is probably faster than the other. For example, the clock of the transmission device 810, if the clock frequency _f t 830 faster than the clock frequency _f r 832 of the receiving apparatus 820, the buffer of the receiving device is filled gradually. This can result in data loss, and for time-sensitive applications such as GSM voice, can lead to accumulated delays that can quickly irritate people.

To solve this problem, a method based on the expected arrival of cells and the averaging process is used to remove the effects of cell transfer delay fluctuation (CDV). The method can be used whenever the time interval between transmitted ATM cells is a known constant. For example, the system can pack one GSM full rate TRAU frame inside one ATM cell. 20m for TRAU-frame
s encoded speech. Therefore, the ATM cell has a cell rate r _t
= 20 cells / sec, transmitted at intervals of 20 ms. The clock frequency f is
f _k = Rr _k (the case of where the receiving device, k = r, when the transmitting device, k = t, R is a constant)
From the cell rate r. For simplicity of explanation, as follows, the clock of the device has the same frequency as the cell rate _{(f k = r k),} R
Suppose = 1.

FIG. 9 illustrates the arrival of two neighboring cells 910, 912 at the connected receiving end as shown using the clock of the receiving device. The time interval between cells is Δt _r 920 =
1 _/ r r is expected to be 20 ms, _also, r r = 50 cells / sec is expected rate of the incoming cell. However, cell i 910 arrives after interval Δt _t 930 according to the clock of the receiving device. This means that the receiving device thinks that the transmitting device is transmitting at some cell rate slightly different from 50 cells / second. This is due to the difference in clock frequency. Therefore, the new corrected clock frequency of the receiving device should be:

However, what we usually want to know is the frequency difference represented by the following equation:

[0047] Here, it is assumed that the difference Δt _r -Δt _t is to be due only to the difference between the clock.
The time interval Δt _r 920 is constant from the perspective of the receiving device, and is denoted by C here to emphasize that. At the receiving end, this difference must be added to the clock frequency so that the clock starts running at the frequency of the transmitting device. Therefore, the expression
From (2) the following equation is obtained: Here, the suffix corr indicates the corrected frequency of the receiving device.

However, there is one additional part to the time interval Δt _t 930 as seen by the receiving device. That is, ATM cells carrying TRAU frames have some cell transfer delay fluctuation (CDV) caused by the ATM network. Thus, the time interval is actually the sum of the CDV at this point and the difference between the clock frequencies,

Therefore, N cells can be observed by a certain realization device before adjusting the clock of the receiving device.

FIG. 10 illustrates a flow chart 1000 for this device, where N cells are observed before clock adjustment. When the first cell arrives, the receiving device to start the timer 1010, and stops at time Delta] t _t where the next cell arrives (1020). Then, a time difference Delta] t _r -.DELTA.t _t is calculated as C-Δt _t (103
0). Then, C-Delta] t _t is stored (1040), the timer is started (105
0). Thereafter, i is incremented and a check is made to determine if i is equal to N (1060). This process is repeated N times (1070). Then, the average value of the measured values Delta] t _t is calculated (1080). Next, the clock of the receiving device is corrected using equation (5). Therefore, Becomes However, when N → ∞, the first sum approaches zero.

The receiver of the frequency f _r as is illustrated in Figure 11 the phase-locked loop (P
LL) 1100. This time difference calculator (subtractor) is a PLL 11
00 can be considered as a phase detector (PD) 1110. If the result of the subtraction is positive, a positive pulse is generated by integrator 1120. If the result of the subtraction is negative, a negative pulse is generated by integrator 1120. Using these pulses, the PLL
A voltage controlled oscillator (VCO) 1130 of 1100 is controlled. This example demonstrates that only requires time difference Δt _r -Δtt to perform frequency correction of the receiver.

The accuracy depends on the value of N. If the frequency difference in equation (2) is very small, the method can make the situation worse, even if N is too small. Thus, if physical synchronization is not available, this synchronization method can also be used as a second option.

Thus, several synchronization techniques are available for synchronizing two end elements via ATM. The technique described above uses time stamps and incoming ATM
It is a technique based on examining the average cell arrival rate and examining the buffer level for incoming ATM cells.

However, all of the various types of adaptive methods described above are based on scanning the cell rate of a traffic channel. One problem is raised by the use of traffic channels due to the fact that the cell rate or bit rate of voice traffic channels is much lower and even lower. Further, in the future, traffic flows will be variable rather than constant. Thus, inferring a clock from a low variable bit rate traffic channel is difficult and time consuming. This is why CDV (cell transfer delay fluctuation) takes time. The duration of a single cell is usually not sufficient for this CDV. Synchronization may not even be possible due to the variable bit rate connection.

FIG. 12 illustrates the use of T to deduce the clock frequency in the BTS, in accordance with the present invention.
FIG. 5 illustrates the use of ATM multicasting 1200 to transmit a cell stream from C or IWF to a BTS. In FIG. 12, a plurality of BTSs 1240
It is connected to PCM 1230 via C 1210 and ATM 1220. A high constant bit rate virtual channel 1260-70 is set up for each of the BTSs 1240 for synchronization. The TC transmits the cell stream to the BTS 1240 using the broadcast virtual channel 1260 to 1270.

Using any of the methods described above in connection with the present invention, the clock frequency in the BTS can be inferred using the synchronous virtual channels 1260-1270. For example, the setting of the synchronous virtual channels 1260 to 1270 can be performed during the night time when the traffic load is low. The cell rate of each of the synchronous virtual channels 1260-1270 is selected to be sufficiently high. When using a public carrier, a high cell rate can be expensive, but the synchronization process according to the invention does not require a long time due to the high constant bit rate. In addition, synchronization only needs to be done once a day, thereby minimizing costs.

For example, a method for removing CDV has been introduced as described above. It was previously assumed that CDVs were distributed randomly in a Gaussian distribution. This assumption is not always true, but is still valid in this case. It has previously been shown that CDV can be removed by measuring a sufficient amount of cells (N cells) and thereby averaging the CDV. However, we did not define how large N would be desirable. Still, if N = 105, a single GSM
Traffic channel and AAL5 are used, cell rate The connection with follows. Sync time is And this time is longer than 30 minutes. However, this duration is too long compared to the normal call duration of a mobile phone.

In accordance with the present invention, this problem is solved using a high cell rate. For example, if a 155 Mbit / sec line is used, Is used. Time to synchronize To a fairly significant improvement.

Because of the problem with variable cell rates for traffic channels, a constant bit rate (CBR) connection is used for synchronous virtual channels 1260-1270. In addition to the synchronization data, the synchronization cells can include software updates.

In summary, the present invention describes a method for using a special virtual channel for synchronization in an ATM-based BSS. By using a special virtual channel for synchronization, the problems of tie-up traffic channels for adaptive synchronization are reduced. Therefore, a dedicated high fixed cell rate connection is used for synchronization.

The foregoing description of the exemplary embodiment of the invention has been presented for purposes of illustration and description. The above description is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention not be limited by the above detailed description, but rather by the claims appended hereto.

[Brief description of the drawings]

FIG. 1 illustrates the physical layer of Open Systems Interconnection (OSI).

FIG. 2 illustrates an ATM cell.

FIG. 3 illustrates the operation of VPI and VCI.

FIG. 4 illustrates a communication system in which a transcoder is used as an interconnecting function between an ATM cloud and a PCM network according to the present invention.

FIG. 5 illustrates a more detailed block diagram of a BTS and IWF in accordance with the present invention.

FIG. 6 illustrates AAL1-PDU.

FIG. 7 illustrates a diagram of system equipment illustrating an alternative method of inferring a clock frequency.

FIG. 8 illustrates a system that uses an ATM connection that requires clock synchronization.

FIG. 9 illustrates the arrival of two neighboring cells to the connected receiving end as shown, utilizing the clock of the receiving device.

FIG. 10 illustrates an implementation flowchart in which N cells are observed before clock adjustment.

FIG. 11 illustrates a phase locked loop for correcting frequency f.

FIG. 12 shows TC or I to deduce the clock frequency in the BTS according to the present invention.
4 illustrates ATM multicasting transmitting a cell stream from a WF to a BTS.

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SL, SZ, TZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CR, CU, CZ, DE, DK, DM, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID , IL, IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, TZ, UA, UG, US, UZ, VN, YU, ZA, ZW

Claims (17)

[Claims] 1. A method for synchronizing a clock of a transmitting device with a clock for a plurality of remote devices, comprising: establishing a high constant bit rate virtual channel connection from the transmitting device to each of the plurality of remote devices. Broadcasting data cells to the plurality of remote devices for processing by the plurality of remote devices to infer a target clock frequency to be synchronized. 2. The method of claim 1, wherein said remote device comprises a base transceiver station. 3. The method according to claim 1, wherein the transmitting device is a functional device for interconnection. 4. The method according to claim 3, wherein the functional device for interconnection comprises a transcoder. 5. The method of claim 1, wherein said transmitting device and said remote device are connected via an asynchronous connection, said asynchronous connection preventing physical transmission of said transmitting device's clock. Features method. 6. The method of claim 1, wherein the plurality of remote units infer a clock of the transmitter and synchronize residual time stamps to enable synchronization with the clock of the transmitter. The data cell outputs 7. The method of claim 1, wherein analyzing at the plurality of remote devices to infer an arrival time of the data cell, and between the expected arrival time of the cell and its arrival time. Calculating the difference between the plurality of remote devices, and adjusting the clocks of the plurality of remote devices according to the calculated difference to synchronize the clocks of the plurality of remote devices with the transmitting device. how to. 8. The method of claim 7, further comprising: storing the calculated differences for the N cells; deriving an average arrival time for the N cells; To synchronize a clock with the transmitting device,
Adjusting the clocks of the plurality of remote devices in response to the average arrival time for N cells. 9. The method of claim 1, further comprising: analyzing a buffer in the plurality of remote devices to determine a fill level of the buffer; and transmitting the clocks of the plurality of remote devices to the transmitting device. Adjusting the clocks of the plurality of remote devices according to a filling level of a buffer for the plurality of remote devices for synchronizing. 10. A cellular communication system, comprising: a plurality of base transceiver stations, wherein the plurality of base transceiver stations are connected to an ATM network; and an interconnect function between the ATM network and the communication system. ,
A cellular communication system having an interconnecting device connected to said ATM network, wherein said interconnecting device is connected to each of said plurality of base transceiver stations with a high fixed bit rate.
Configured to establish a virtual channel connection, and further configured to broadcast data cells to the plurality of remote devices via the high constant bit rate virtual channel connection with the plurality of base transceiver stations. A cellular communication system configured to allow said plurality of base transceiver stations to infer a target clock frequency of said transcoder to be synchronized. 11. The cellular communication system according to claim 10, further comprising a pulse-coded modulation communication system. 12. The cellular communication system according to claim 11, wherein said pulse coded modulation system comprises a mobile communication service switching center. 13. The cellular communication system according to claim 11, wherein said pulse-coded modulation system comprises a public switched telephone network. 14. The cellular communication system according to claim 10, wherein said plurality of base transceiver stations infers a clock of said transcoder and synchronizes with said clock to enable synchronization. A cellular communication system wherein the data cell provides a stamp. 15. The cellular communication system of claim 10, wherein each of the plurality of base transceiver stations is configured to analyze the data cell to infer an arrival time of the data cell; Configured to calculate a difference between a cell arrival and an expected arrival, wherein the plurality of base stations are responsive to the calculated difference to synchronize the clocks of the plurality of base transceiver stations with the transcoder. A cellular communication system configured to adjust a clock at each of the transmitting and receiving stations. 16. The cellular communication system of claim 15, wherein each of the plurality of base transceiver stations is configured to store the calculated difference for N cells, and for N cells. At each of the plurality of base transceiver stations according to the average arrival time for N cells to synchronize the clocks of the plurality of base transceiver stations with the transcoder. A cellular communication system characterized by adjusting 17. The cellular communication system of claim 10, wherein each of the plurality of base transceiver stations is configured to analyze a buffer in the plurality of base transceiver stations to determine a filling level of the buffer. Further, in order to synchronize the clocks of the plurality of base transceiver stations with the interconnect device, the clocks of the plurality of base transceiver stations are adjusted according to a filling level of a buffer for the plurality of base transceiver stations. A cellular communication system comprising: