CN1189072A - Method of reverting to tanden operation between transcoders of communication system - Google Patents

Abstract

To facilitate the reversion of a communication to tandem operation (200), a first transcoder (20), having previously changed back to tandem operation (206), inverts bits of a double-encoded frame format that correspond to synchronisation bits in a non-tandem, single-encoded frame format to generate errors, in relation to the synchronisation bits, at a second transcoder (34). Upon detection (210) of a predetermined number of errors in the synchronisation bits during a predetermined time, the second transcoder (34) reverts to tandem operation, as shown in the flow diagram of FIG 2.

Description

Turn back to the method for cascade operation mode in the communication system between all permuters

A kind of communication system that is arranged to implement escape work of relate generally to of the present invention especially, but is not uniquely, is applicable to be arranged to provide the method for non-cascade speech coding working method and relevant signaling schemes in a cellular communications networks.

In general, in telephone system, in order to guarantee significant and distinguishable communication, voice quality should remain on the level of an adaptation.Really, in mobile communications network, for example in global system for mobile communications (GSM), improve voice quality to satisfy the market penetration power of users, becoming the thing that becomes more and more important to this system's requirement (particularly being related to the calling between mobile unit and the mobile unit) and support and these systems of improvement.

In mobile communication system, current a kind of dual coding processing procedure appearred.Specifically, a mobile unit will at first be encoded to voice, so that for example, be transferred to the base station by a radio frequency link.Subsequently, this fixing infrastructure will further be encoded and will be transferred to this system this signal, to guarantee effective with sane the communicating by letter of air interface (typically towards another mobile unit) of passing through.

For example, with regard to GSM, a mobile unit is encoded to general voice call according to the speed of 16 kbps, comprising the sampling of 13 kbps and the supplementary of coded voice information and 3 kbps, for example parity check bit, corrected transposition (like that) and synchronizing information; They are put into a frame the inside that is called permuter Rate Adapter Unit (TRAU).The voice messaging of this 16 kbps is through multiplexed, enter a time slot that contains other 3 road audio calls, so that produce the channel of one 64 kbps on a road communicating line, and this channel communicates by a base station controller (BSC) (in a down link) and at least one fixing base transceiver subsystem (BTS).To understand that later on base transceiver subsystem is served a unit, the latter typically is divided into different all zones, and each zone is managed by independent transmitter-receiver, and a base station controller is then served a group unit.A permuter (encoding scheme that it receives base transceiver subsystem provides code position to change) carries out multichannel to this channel and decomposes, then each road voice communication is encoded to the pulse code modulation (pcm) form of 64 kbps, so that be transferred to one second permuter and carry out the PCM decoding by one first mobile switching centre (MSC), second mobile switching centre with the order leading thread pellucidly, be transferred to a base station controller, base transceiver subsystem forward and finally may arrive another subscriber unit by route then.

Pay particular attention to this gsm system coding work of (it is used for illustration purpose individually), the trau frame of an information has the duration of 20 milliseconds (ms), and voice are then sampled with the speed of 8000 samples of per second.Therefore, per 20 milliseconds voice section contains 160 eight samples.Subsequently, by the permuter operation, these 160 samples respectively are encoded to one eight pcm word, with the PCM information (being equivalent to 64 kbps) that 1280 of every frames are provided.To understand that below the structure of this PCM frame of eight is in order to represent a kind of signal level, in the reconstruct of coded message, compare that least significant bit (LSB) has relatively less importance with each relative importance in succession.Ground worthy of the name, highest significant position (MSB) has maximum influence in the reconstruct of coded message, because its place value is compared with the place value of least significant bit, have bigger importance.

Confirm,, can improve the voice calls quality of whole mobile-to-mobile calls significantly by using a kind of avoid between all permuters, the carrying out what is called " non-cascade " of pcm encoder or the operation of " speech coder is close to the road ".At this on the one hand, signaling schemes between all mobile switching centres has been proposed, but these schemes have all run into tangible signaling latency issue, and can not determine when all callings are sent out (therefore failing in this example) through external voice compress wind network.A kind of mechanism of accommodation relates to signaling or the control character exchange that all lowest orders that utilize this 64 kbps PCM circuit in band send the voice messaging of coding and do not need to add, but this mechanism is not being optimized aspect system's control and the signaling as yet effectively.Another kind of recommended mechanism relates to a kind of use of in-band signalling scheme, but this can only use in call setup, and can not handle the variation in the communication that the calling route that may cause when Additional Services or handover brought.

Also can cause non-cascade operation mode such as the mechanism described in patent WO 96/23297, in this patent, all lowest orders of a chosen frame in the sound circuit of for example one 64 kbps send a predetermined data model in band.If one second permuter of this communication path detects the data channel of this embedding, then cause non-cascade (permuter is close to the road) working method, and directly utilize two of this 64 kbps circuit to transmit by each frame of permuter Rate Adapter Unit (TRAU) (in the special case of GSM) of 16 kbps coding.Be appreciated that (data channel of embedding) coding obviously is undetectable in such band concerning normal audio call.The purpose of this data model is to confirm type, form and the compatibility of employed permuter (for example the machine of a special manufacturer production has a kind of specific PCM frame format) in cataloged procedure.Therefore, this predetermined data model is specified according to the type of permuter, and therefore is retained in this permuter for use in coding and identifying purpose.Particularly, if might remove to discern the permuter that this is being encoded, so, just might be by changing the working method of this permuter of encoding, perhaps preferably reach the purpose that speech coder is close to road (being non-cascade system work) by eliminating the demand that permuter is carried out encoding and decoding fully.Will eliminate the demand of permuter being carried out encoding and decoding fully, the condition that should satisfy is: all permuters of this interconnection structurally identical and they therefore can be only support on the speech coding aspect that direct data transmit.

Fig. 1 is the block diagram that portion contains the prior art communication system 10 of all permuters that are useful on the speech coding work of implementing non-cascade.This communication system 10 shows with the form of simplifying and in order to the calling routing mechanism of explanation between the inner all subscriber units of this communication system.All subscriber units can be all mobile units, can be the terminals of all fixed positions, and they can be arranged at by a public base station transceiver subsystem coverage area of service or different the insides, all unit are provided.One first subscriber unit 12 is by a communication link, and for example a radio-frequency channel or an optical fiber link are sent to one first base transceiver subsystem 14 with data 16 (passing through up link).This first base transceiver subsystem 14 is connected to one first base station controller 18, and this first base station controller 18 is connected to one first permuter (XCDR ₁) 20.So data 16 sequentially are sent to this first permuter 20 from first subscriber unit 12.This first permuter 20 is connected to this first mobile switching centre 22 by a communication channel resources 24 and a control channel resource 26.This control channel resource be twocouese and mainly be arranged between this first permuter 20 and this first mobile switching centre 22 and transmit the control information that is used for system management.One is positioned second mobile switching centre 28 at a distance via a communication channel resources 30 and a control channel resource 32, is connected to this first mobile switching centre 22, and one second permuter (XCDR ₂) 34 items via a communication channel resources 36 and a control channel resource 38, is connected to this second mobile switching centre 28.In a down link, this second permuter 34 is connected to one second base station controller 40, and the latter is connected to one second base transceiver subsystem 42 again.At last, this second base transceiver subsystem BTS is arranged by suitable communication media 46 this initial data 16 to be relayed to one second subscriber unit 44.

For the purpose of brief, only infrastructure and the subscriber equipment with limited quantity carries out graphic extension and narration to this communication equipment 10, yet people will understand that this system can hold, for example, and many subscriber units and many permuters.

In the system of Fig. 1, on basis as described below, can cause non-cascade operation mode.As in UK Patent Application UK9616734.1, being narrated, permuter XCDR ₁Receive the voice signal (the multichannel synthetic speech signals of 16 kbps of for example, in GSM, using) of one section coding.Determine whether to enter non-cascade operation mode then.If cannot, the voice signal of this coding carries out again coding by a kind of PCM process (or like that).Carry out after the dual coding permuter XCDR with PCM ₁In all pcm words of a selected frame, occupy its lowest order, and with representing this permuter XCDR ₁A kind of data model of type replaces these lowest orders (therefore having revised the information content of this sample).In this example, after inserting this data model, this pcm encoder information is by relaying (or transmission) 62 to XCDR ₂Subsequently, this second permuter is decoded to the pcm encoder signal that receives.If this XCDR ₁There is (the permuter type compatibility of acknowledged in or be complementary to this permuter type that receives this PCM signal) in (embedding) data model, then set up a kind of working method of speech coder bypass, thereafter the information that is received is contemplated to the voice messaging of coding, and directly do not need by the route of this permuter therefore to take the PCM decoding.Typically, permuter XCDR ₂By this signaling channel (promptly by a control channel resource) to the permuter that sends this calling, i.e. XCDR ₁Send identification or confirmation signal, can and be ready to receive the information of only carrying out speech coding to show it.In the non-cascade operation mode between the inbound branch road of an ongoing communication and departures branch road (wherein each bar branch road can be believed to comprise all users and between one move or fixed subscriber unit and mobile switching centre between infrastructure), one typically the frame structure 60 of voice signal of coding comprise an initial synchronizing sequence 62, follow thereafter be control information 64.In the content of frame 60, being positioned at after the control information 64 mainly is data 66-72 (may take the form of all eight bit bytes of adjacency).Yet in order to guarantee to keep synchronously in interior quite long data transfer cycle at frame 60, additional all sync bit 74-76 are periodically spread in these eight bit bytes to be gone.Typically, in per two eight bit bytes, a sync bit is just arranged.At last, this frame 60 usually with an additional control information piece 78 as ending up.

An important requirement to so non-cascade operation mode is exactly to detect demand that turns back to PCM (cascade) work and the ability that turns back to PCM work apace.When the transmission path between two branch roads becomes opaque, promptly when worsening appearred in reception in information (for example Bian Ma voice signal), such ability was absolutely necessary.And on a direction of this link between two branch roads, when the voice signal of this coding had been replaced by a PCM signal, the requirement that turns back to the cascade operation mode just became vital thing.Really,, will cause the remarkable reduction of voice quality, so fast detecting also switches to the PCM load mode and is absolutely necessary because if this PCM signal or the encoding speech signal that seriously worsened are interpreted as legal encoding speech signal.In fact, will worsen or PCM signal (by means of infrastructure) be interpreted as legal encoding speech signal during this period of time in, its final result may can't be understood fully.

In UK Patent Application UK9616734.1, switch to the PCM mode and depend on (in the special case of GSM): by the channel of this 64 kbps, with the voice signal of this coding together, sends a low level and have the PCM signal (taking a kind of fixing known PCM model) of noise at higher some.Under nearly all situation, error code in this model or deliberate change can both be detected and allow to switch to the PCM mode soon in the time of inferior millisecond.Regrettably, after carrying out such switching, have one inevitable period, this low level and PCM (promptly should the fixing model) signal that has a noise are encoded and are sent to this mobile radio station therein.For fear of such time-delay, the scheme of flexible no cascade work follows the voice signal of this coding to send together this original PCM signal (replacing this fixing model), but owing to have a model at random, carrying information (rather than a predetermined bit sequence) in the higher some positions of this channel, this just means can not switch to the PCM mode apace.Therefore, these flexible schemes depend in the framing procedure of encoding speech signal the identification to all error codes.

In addition, some causes this code signal to worsen or replaces the incident of encoding speech signal with PCM, only influences in this calling a direction of the signal transfer mechanisms between two branch roads.For example, be inserted into external network (promptly, such as between two mobile switching centres, or the infrastructure between a mobile switching centre and routing node or private telephone exchange) a double-tone multifrequency (DTMF) signal or dialing tone can only send along a direction frequently.This folk prescription to the signal degradation that forms only appear at receive this dtmf signal branch road (for example, contain the #1 branch road of base transceiver subsystem 14 to mobile switching centre 22) in, this branch road will switch to the PCM mode subsequently, so that with the signal interpretation that arrives is PCM signal (being in rightabout with regard to it leads to regard to the transmission path of another branch road), and send the PCM signal to replace rock sign indicating number voice signal with beginning.This process is introduced one section time-delay inevitably, thereby causes (voice of deterioration or PCM) signal of this reception to be interpreted as legal encoding speech signal.

And, at this rightabout (promptly, be not subjected to this folk prescription to worsening and not having notified another branch road that leads to this infrastructure that changes the cascade operation mode over to), the voice signal of coding will be considered to legal encoding speech signal, up to #2 branch road (that is, comprising mobile switching centre 28 that branch road) to base transceiver subsystem 42 confirm the #1 branch road switched to the cascade operation mode and thereby send the PCM signal this constantly till.Therefore, inevitable and unacceptable time-delay has appearred in the handoff procedure of #2 branch road, within this section time-delay, because the voice signal that the PCM signal that arrives is interpreted as encoding causes service quality to reduce.Similar with the #1 branch road, the identification of all error codes during this detection speed (turning back to relaying work thus) depends in the encoding speech signal of this framing sync bit.

Therefore, there is demand, is intended to turn back to the cascade operation mode, so that in two permuters, rebulid the PCM working method apace from a kind of mode of walking around speech coder to a kind of effective mechanism.

According to a first aspect of the invention, provide a kind of in a communication system that contains many permuters, from non-cascade operation mode (therein, information communicates by single encoded frame format) switch to the cascade operation mode (therein, information communicates by the dual coding frame format) method, this method comprises following all steps: in one first permuter: switch to the cascade operation mode; And this is inverted the some positions corresponding to all sync bits in this list encoded frame format in the encoded frame format; Non-cascade operation mode and being connected in second permuter of this first encoder in originally one worked: this dual coding frame format that will receive is treated as a kind of single encoded frame format; From all sync bits (as all corresponding results who is squeezed this dual coding frame format) of this list encoded frame format, detect some mistakes; And, after from all sync bits, detecting some mistakes, in response, switch to the cascade operation mode.

In order to guarantee to turn back to the cascade operation mode apace, all sync bits should intersperse among each position in the frame.And, in order to guarantee in return course not drop-out, the present invention plans the information that receives from this second permuter is carried out buffer-stored, and, after switching to this cascade operation mode, in response, this buffer-stored information is handled for being used as a kind of dual coding frame format, and this buffer-stored information is carried out suitable decoding.

Referring now to all accompanying drawings, an exemplary embodiment of the present invention is illustrated.

Fig. 1 is the block diagram that adopts the communication system of prior art, and this system has arranged all permuters, in order to implement a kind of speech coding work of non-relaying, also shows a kind of typical frame format of using among the figure in communication process.

Fig. 2 is a a kind of flow chart that turns back to the mechanism of relaying work that illustrates according to a preferred embodiment of the present invention.

Fig. 3 is the block diagram of operable a kind of permuter in the method for the invention.

According to a preferred embodiment of the present invention, by the equipment in the #1 branch road (in case it is switched to the PCM mode) the PCM signal of preparing to be sent to the #2 branch road is carried out preliminary treatment, the testing process that makes it whether the suitable receiver in the #2 branch road is switched to the PCM mode can be quickened significantly.Because the infrastructure in the #1 branch road possesses the abundant knowledge of frame structure that is sent to the encoding speech signal of #2 branch road about it, particularly about all synchronous bit position and knowledge regularly in this frame structure the inside, so the #1 branch road knows that in this PCM signal those several specific positions will be interpreted as all sync bits in (and corresponding to) #2 branch road.Therefore, in a kind of frame format of speech coding, by allowing the #1 branch road influence in the PCM signal those positions selectively corresponding to sync bit, make the #2 branch road by means of the appearance of the timing error of repeatability, just can detect the signal interpretation that whether needs arrival is the PCM signal.Therefore, a legal vocoder frames the inside, along with #1 branch road switch operating mode, occupy and change all PCM position, in response corresponding to all sync bits, the #2 branch road can promptly change its working method, changes the cascade operation mode over to from the speech coder bypass.

Particularly, in one predetermined (but very short) period, the preferred embodiment of the present invention can guarantee, all have all numerical value of negating that is equivalent to all numerical value of this sync bit corresponding to these of all sync bits (with regard to the #2 branch road) in this PCM signal.Generally speaking, the occupying and reverse and be limited in (that is, a predetermined number) in one limited period of position, so that reduce the total deterioration degree of this PCM signal.And in the preferred embodiment, in (PCM) signal that this eight bit byte that transmits between two branch roads is arranged, the position of the encoding speech signal of framing is arranged like this, makes it always occupy the position of lowest order (being LSB), if possible.Therefore, the potential deterioration of the position that a few in being sent to this PCM signal of #2 branch road is lower is for the intelligibility of this received PCM signal of #2 branch road and do not make significant difference.

The preferred embodiment of the present invention is considered further, an independent encoded speech frames the inside, only needs to detect the mistake of two sync bits in the #2 branch road, is the such working method of PCM with regard to being enough to make the #2 branch road switch to the signal interpretation that will arrive.This numeral is a kind of random selection, although in order to guarantee that will get back to relaying is operated in an independent frame the inside, can detect the more timing error of multidigit, this will be illustrated below.

Now, GSM is considered as a special case, contain the sequence of paired eight bit byte at the mid portion of the encoded speech frames (being so-called trau frame) of GSM, in all eight bit bytes, except a sync bit, all everybody all be the voice signal of sign indicating number.(through the preliminary treatment in the #1 branch road) guarantees that all these synchronous bit positions all make a mistake, and just can guarantee in the receiving cycle of all eight bit bytes of encoded voice of 4 frames the #2 branch road to be switched to the PCM mode.In GSM, this cycle is 2 milliseconds.In fact, if in the #2 branch road, have at least the encoded voice of 4 eight bit bytes to cushion (being sent to before this second mobile radio station 44), so, do not wait until that the #2 branch road is legal encoding speech signal with the PCM signal interpretation of any arrival improperly, the operation that switches to PCM just might take place.Particularly, in order to receive at least two sync bits, the #2 branch road just must receive 4 eight bit bytes, and along with the buffering of these 4 eight bit bytes, allows under cascade system this coded message to be carried out follow-up processing (in the #2 branch road).

Fig. 2 is the flow chart that a explanation according to a preferred embodiment of the present invention turns back to the mechanism of cascade operation mode.This system initially worked in PCM mode 200 before making the decision that enters non-cascade (changing speech coder over to) working method according to the positive branch of differentiating frame 202.Enter after the non-cascade operation mode, numerous permuters is shared a communication repeating encoding speech signal 204 that carries out work mutually.In the positive branch of differentiating frame 206, () influence recovers original PCM working method to one first permuter perhaps in addition, otherwise just (in negative branch) keeps non-cascade operation mode owing to being subjected to external network.At square frame 208, this first permuter has returned to the PCM working method, and in the voice transfer signal of the coding of this framing, occupies and be inverted all PCM position corresponding to all sync bits.The situation that the PCM signal is transferred to this second permuter is appearring in communication now.At square frame 210, this second permuter detects inverted (thereby being wrong) all sync bits of necessary number in the encoded speech frames of expection, confirm that thus the PCM working method restarts, and received frame should be decoded according to the PCM signal in (rather than bypass).Then, this system turns back to square frame 200, is carrying out PCM working method completely there.

Though the present invention is applicable to all sync bits and appears at the situation of an independent position within the frame,, the employed all sync bits of mechanism according to the present invention preferably embed (distribution) among the data flow of independent many adjacency that Frame comprised.

Fig. 3 is the block diagram of operable in the method for the invention a kind of permuter 300.This permuter 300 contains the intelligent processor 302 of the work that can control its permuter 300.This intelligent processor 302 is connected to buffer storage 304, and the latter is receiving data stream originally, and is temporarily arranged to go the received data of this permuter of storage (for follow-up processing intent) 300.This intelligent processor 302 also is connected to a memory 306, has wherein stored the frame format of a vocoder frames.So, this intelligent processor 302 just can remove to visit this memory 306 respectively, and goes to revise or inquire about a data flow, so that insert an inverted sync bit respectively, determines that perhaps whether it exists.

If not adopting position of the present invention occupies and inversion techniques, then add the PCM needed sense cycle of working and to be prolonged significantly in order to return, because in " at random " of arrival PCM signal, the probability that receives a wrong numerical value on a synchronous bit position is about 0.5.Yet the present invention can guarantee that in one section prior official hour, it is incorrect being in the locational some positions of sync bit, thereby makes the probability that receives an incorrect sync bit approach 1.(because this is inverted the deterioration in the path of position between #1 branch road and #2 branch road, this probability may be slightly less than 1), and, the PCM signal of sending here from the #1 branch road, only need occupy and be inverted the position of minority, just can guarantee to be detected and turn back to the cascade operation mode by the #2 branch road.

Therefore, the present invention advantageously provide a kind of be used to turn back to the cascade operation mode fast and effective mechanism.And, technology of the present invention can be effectively applied to all current and GSM coder-decoders (the full rate form that comprises half rate, full rate and expansion) in the future, also can be applied to other telecommunications networks that in the different phase of call (within the scope of this infrastructure) uses speech coding and/or compression.

Certainly, people will understand, top explanation only provides as an example, can make the modification on the details within the scope of the invention, for example this General Principle is applied to data communication, particularly under the abundant again sane situation of the existing fully high quality of the communication resource between all permuters (all mobile switching centres).And, as people will understand, though all permuters shown in Figure 1 between mobile switching centre and base station controller (and, really, in many systems, usually near this mobile switching centre), but the present invention is not limited to this structure, therefore, can consider this permuter is positioned other positions, particularly a position between base transceiver subsystem and base station controller of illustrated infrastructure the inside.In addition, above detailed description provides with reference to the system that all therein mobile unit and base transceiver subsystem communicate specially, be appreciated that, the present invention is applicable to comparably that also those use fixedly connected system, for example PSTN (PSTN) or private branch exchange (PBX).

Claims (9)

1. in a communication system that contains many permuters, the non-cascade operation mode that communicates by single encoded frame format from information switches to a kind of method of the cascade operation mode that information communicates by the dual coding frame format, and this method comprises following all steps:

In one first permuter:

Switch to the cascade operation mode; And

Some positions corresponding to all sync bits in this list encoded frame format in this dual coding frame format are inverted;

Originally work in non-cascade operation mode and be connected in second permuter of this first permuter at one:

This dual coding frame format that receives is treated as a kind of single encoded frame format;

From all sync bits of this list encoded frame format, detect some conducts result's that all corresponding positions are squeezed in this dual coding frame format mistake; And

After from all sync bits, detecting some mistakes, in response, switch to the cascade operation mode.

2. in the described method of claim 1, all sync bits are spread to the diverse location within the frame.

3. in the described method of claim 1, some mistakes of all sync bits appear within the frame.

4. in the described method of claim 3,, then switch to the cascade operation mode if in same frame, detect two mistakes.

5. in the described method of claim 1, this first permuter will be inverted corresponding in succession some positions of predetermined number of all sync bits in this list encoded frame format in this dual coding frame format.

6. in the described method of claim 1, this list encoded frame format is the voice signal of coding.

7. in the described method of claim 6, the pulse code modulation product of the voice signal that this dual coding frame format is this coding.

8. the described method of claim 1 may further comprise the steps further:

The information stores that this second permuter is received is to buffer storage; And

Switch to after the cascade operation mode, in response, the information that is stored in the buffer storage the inside is used as the dual coding frame format handles, and it is carried out suitable decoding.

9. in the described method of claim 1, the switching of first permuter is that conduct is to putting on the response of the influence of this first permuter from an external network.

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