DE19740838A1 - System with discrete variable slot width in TDM / TDMA systems - Google Patents

Abstract

A system protocol for a communication system having a number of time frames (402), each of the number of time frames having a predetermined period of time divided into a number of discrete multiple time slots (452) wherein a total width of all of the number of discrete multiple time slots is equal to the predetermined period of time, a given number of the number of discrete multiple time slots are aggregated (aggregated time slots) (440), and a preamble (450) is provided at a beginning of the aggregated time slots and is not replicated anywhere else in the aggregated time slots.

Description

Field of the Invention

The present invention relates generally to broadband RF communications communication protocols and in particular to a protocol in which the time slot most be combined within a TDM / TDMA system to transfer signals with multiple bit rates and / or analog digitally encoded signals enable.

State of the art

In digital TDM / TDMA communication systems (TDM = time division multi plexing, time division multiplex; TDMA = time division multiple access, time division multiplex access), N _max time slots, which are organized in frame structures at a constant rate, are assigned to each set of FDD carriers (FDD = frequency division duplex, frequency duplex) modulated or divided (multiplexed onto). Each time slot represents a direction of a basic two-way channel with a constant rate. A two-way channel (or carrier) consists of a transmitter-side channel and a receiver-side channel and is assigned a protocol suitable for a TDM / TDMA system.

A group of bits (referred to as a burst) that are transmitted according to a protocol of a TDM / TDMA system are then transmitted in each time slot of a time frame within a given frequency range (or carrier). The time frames are repeated with a fixed duration T _f . Each burst in a conventional TDM / TDMA protocol is divided into two sections, a general part and a payload part. The number of bits in the payload or payload part divided by the frame rate T _f represents the bit rate B _{c of} each channel with full bit rate.

In general, TDM / TDMA systems have N _max channels with full bit rate, which are time-division multiplexed onto each pair of two-way channels. For applications that require higher bit rates than B _c , two or more of the N _max time slots are assigned to the same user in each time frame. In these cases, the data for transmission into the multiple payloads (in which the time slots each have a general part and a payload part) are fragmented and reassembled at the receiving end of the connection. This process is referred to as shift keying multiplexing or as a method with several time slots. The time slots within a multiple time slot assignment do not have to follow one another within a frame since the payload is fragmented in every case.

Each of the inversely multiplex modulated time slots in a multiple time slot Assignment or the combined time slots contains, as already stated, so probably a general part as well as a payload part. The retained general However, bits in each of the combined time slots are redundant because of the function each of the common bits is duplicated within each one. For everyone together a quantified time slot, an assigned general (overhead) part is provided, in which the information within each bit in the general part for everyone summarized time slot are identical. Accordingly, the then summarized payload or payload with multiple slot allocation total P = N x ((total bits / burst) - (general part bits / burst)). How to get out of it is the multi-slot approach with significant waste connected by bits.

BRIEF DESCRIPTION OF THE DRAWING

Fig. 1 is a block diagram showing a communication system in which a system of the invention protocol is used;

Fig. 2 shows a graphical representation of a receiver-side signal current structure;

Fig. 3 is a graph showing a transmission-side signal current structure;

Fig. 4 is a graphical representation of a signal current structure in a preferred embodiment of the present invention;

Fig. 5 is a graphical representation of a signal stream structure according to a second embodiment of the present invention, and

Fig. 6 shows a graphical representation for several examples of how the second embodiment of the present invention can be implemented with different summarized time slot groups.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, TDM / TDMA time slots become like this summarized that redundancy is avoided, which is inherent with the conventional len solution with multiple slots for combining TDM / TDMA time slots zen is connected. In practicing the present invention Bits within combined TDM / TDMA time slots are used, which otherwise would be wasted by redundancy so as to increase the number of bits in the payload increase, which makes it easier to transmit more information per burst and / or an error correction, e.g. B. in the form of a forward correction, within a Bursts becomes possible.

Fig. 1 shows a communication system 110 in which a TDM / TDMA-Sys can be used dung temprotokoll according to a preferred embodiment of the present OF INVENTION. The most important elements of the communication system 110 are the central control point 120 and the user interface devices 150 . User interface devices 150 are generally permanently installed in a user's room, as shown in FIG. 1. The user interface devices 150 are connected to a coax cable 152 , and the coax cable 152 is connected to a fiber node 140 , which is connected to the central control point 120 via a fiber cable 142 .

In the preferred embodiment of the present invention, many user interface devices 150 are connected to the coax cable 152 . Each of the user interface devices 150 includes a cable transceiver designed to operate in accordance with the system protocol, which in the preferred embodiment includes a modified version of the legal successor's CACS (Cable Access Control System) protocol to the present invention. Each of the user interface devices 150 can be designed either for a symmetrical basic protocol or for an asymmetrical protocol extension. In both cases, the user interface devices 150 form the end point of a cable feed in the communication system 110 , and are designed as a compact unit for permanent installation in the user's rooms. The user interface devices 150 are also equipped with one or more interfaces to support various technical systems in the user's premises, such as standard wired telephones, cable television (CATV), on set or accessories, PCs and the like.

The fiber optic node 140 , via which the coax cable 152 is connected to the central control point 120 , performs the bidirectional conversion between the optical area of the fiber optic network and the electrical area of the coax cable 152 .

The central control point 120 is a device, which is often referred to as an input stage, which transmits image signals according to the CATV, MPEG-1, MPEG-2, HDTV standard, satellite broadcasts, television programs in local networks, and other television programs as well Receives image or video information, which are designated as image sources in FIG. 1. The central control point 120 also communicates with various data sources ( 170 ) and telephone networks ( 180 ), e.g. B. in PSTN and ISDN technology. The central control point 120 can thus deliver data, voice telephone signals and video telephone signals with the user interface devices 150 on the receiver side of television signals and on the transmitter side and on the receiver side.

Communication between any number of connected users in the communication system 110 is possible via the central control point 120 and the user interface device 150 , regardless of whether they are connected directly to the communication system 110 via the coax cable 152 or via the EO switch 122 described below.

Telephone networks 180 are in communication with the central control point 120 via the user device (EO) 122 . The EO device 122 supports standardized digital subscriber loop carrier systems as described, for example, in the Bellcore documents TR-NWT-000303 ( 124 ) and TR-NWT-001203 ( 126 ). The EO device 122 represents a digital telephone switch which is connected to a digitally switched network (not shown here).

The data sources 170 are in communication with the central control point 120 via a data switch 128 . The data switch 128 is a packet switching processor which establishes the connection between channels for supplying the user interface devices 150 and various public or private data networks and servers. The data switch 128 is in communication with a cable control unit (CCU, cable control unit) 130 and with various transmitters / receivers (transceivers) 138 , 136 and 134 via data connections for operation with corresponding local network protocols (LAN protocols).

The cable control unit 130 carries out all functions which are necessary to support the system protocol (for example the CACS protocol in the form modified according to the invention). The CCU 130 is the end point for all display and control messages to and from the user interfaces 150 and does all RF channel assignments, handovers, etc. The CCU 130 also serves as a connection interface to subscriber loop devices from the EO Unit 122 off, modulates / demodulates the data traffic and the reporting channels at these devices, and forms the conclusion of all control messages to and from the EO device 122 . The CCU unit 130 performs logic functions to control the transmission of information in the system, the alarm, access, authentication and encryption processes via the system protocol, in which the subscriber connection identity with a corresponding subscriber line message in the EO unit 122 or a data network address in the data switch 128 are correlated.

The RF combiner 132 combines receiver-side signals from multiple transmitters and switches through transmitter-side signals to multiple receivers. The RF combiner 132 is coupled to the CCU 130 through the CPX (cable port tranceiver) 134 , each CPX 134 consisting of a digital transceiver that is the destination of the central control point (front end ) for a symmetrical TDM / TDMA / FDD carrier pair (time division multiplex / time division multiplex access / frequency duplex). The RF combiner 132 is also connected to the CCU 130 via the cable port receiver 136 (CPR) 136 , each CPR 136 consisting of a digital receiver which is the destination of the central control point (input stage) for one of the transmitter end Carries a TDMA / FDD carrier group. A broadband cable transmitter 138 (BCT) is connected between the CCU unit 130 and the RF combiner 132 , and each BCT unit 138 consists of a digital transmitter which is the destination point of the central control point (input stage) for the receiver-side 30 Mb / s - Carrier from the TDMA / FDD carrier group.

In the conv / comb unit (CATV converter / combiner) 139 , the signals coming from image sources 160 and from RF combiner 132 are converted and used to modulate an optical carrier for forwarding on the receiver side via optical fiber cable 142 to optical fiber node 140 . The transmitter (s) optical carrier (s) from the fiber node 140 are demodulated, converted into the corresponding RF frequencies and forwarded by the conv / comb unit 139 to the RF combiner 132 .

Fig. 2 and 3 each show two receiver-side time frames (201 and 202) and two transmitter-side time frames (301 and 302) of a signal stream is defi ned as used in the cable communication system 110 of FIG. 1 system log. The receiver-side protocol comprises a number of continuous time frames that are transmitted serially. These structures are also conventional TDM / TDMA protocol structures, as they are used today in communication systems in the cable telephone service. As shown in FIG. 2, the receiver-side signal current is transmitted essentially in the range between 50 and 750 MHz, while the receiver-side signal current is generally transmitted in the range between 5 and 30 MHz.

The receiver side signal current in FIG. 2 is designed so that it carries Sy stemsteuersignale, digital image signals as well as telephony signals in digital format. The sender-side signal current shown in FIG. 3 performs telephony signals, Control panel ersignale and image signals, all in digital format. According to the formats for conventional cable communication systems, e.g. B. CACS, the time frame has a length per frame or frame in the transmitter and receiver signal streams, which corresponds to a predetermined period of 2.5 milliseconds (ms). Each frame is divided into a number of discrete multiple time slots in which the total width (defined in time) of all discrete multiple time slots is equal to the duration of the time frame. The carrier spacing signal currents are 600 kHz, with QAM modulation (quadrature amplitude modulation) of 2 bits / symbol and a symbol rate of a total of 384 K-sym / sec. The gross bit rate is 768 Kb / s with a payload of N × 64 kb / s, where N is at most 8 with a maximum of 512 Kb / s per carrier. In each burst structure there are 240 bits per time slot on the receiver side. A certain pair of carrier frequencies are assigned a certain frame and a certain time slot sequence. Frame and time slot synchronization is required for all receiver-side carriers in a cable communication system, and the transmitter-side transmissions are synchronized with receiver-side transmissions and dynamically aligned in time for correct reception in the input stage.

Each time slot in a receiver side signal stream in the TDM / TDMA protocol structure of a conventional cable communication system comprises the elements of a receiver side burst 203 according to FIG. 2, the illustration in FIG. 2 being representative of the time slot "0" of the time frame 202 . Likewise, each time slot in a transmitter-side signal stream in the TDM / TDMA protocol structure of a conventional cable communication system comprises the elements of the transmitter-side burst 303 shown in FIG. 3, the image in FIG. 3 being representative of the time slot "0" of the time frame 302 . The elements of the receiver-side burst 203 and the transmitter-side burst 303 are shown in Table 1 below for better understanding.

Table 1

As can be seen in particular from FIG. 2, the elements SYG, GG and SG of the receiver-side burst 203 comprise a receiver-side burst attachment 204 , and the element ECC comprises a receiver-side burst postamble 205 . The fast channel FC of the receiver-side burst 203 represents the payload or payload 206 . Similarly, in Figure 3, the GC-element, the elements DE, SYC, CC and SC, a transmitter-side burst postamble comprise FIG. At the beginning of the transmitter-end burst 303, a transmitter-side header 304 and the elements ECC and C at the end of the transmitter-side bursts 303,305 . Element FC of transmitter-side burst 303 re presents payload 306 .

Of Fig. 4 now, results that are summarized a series of six multi-slot channels in the 402nd As shown, each of the combined multi-slot channels has an attachment, the payload and a postamble according to the above definition. In this particular example, it does not matter whether the multi-slot channels are in the transmitter-side or receiver-side signal stream, since the header and the postamble or a supplementary note or an attachment are not defined in detail. What can be clearly seen from Figure 4 is the fact that although the prefixes 404 , 406 , 408 , 410 , 412 and 414 all contain the same information as before in connection with the combination of the time slots, they are all duplicated and record value bits within the time frame. In the same way, all postambles 416 , 418 , 420 , 422 , 424 and 426 contain the same or similar information and are duplicated, as a result of which bits are wasted which would otherwise be available in the time frame.

Accordingly, in a preferred embodiment, the present ing invention the unnecessary duplication of bits in the header and in the postamble not provided so that a larger portion of the bits are used in the payload can, increasing the amount of information transmitted in a single burst becomes.

In a preferred embodiment of the present invention A header begins at the beginning of a certain number of time slots or a preamble is provided, the header in the receiver burst Synchronization channel, the control channel and the slow channel contains. In the transmitter side The burst contains the safety channel, the differential coding, the syn chronization channel, the control channel and the slow channel. The resolution is at the beginning of the first time slot. The resolution is the same as the resolution for everyone other summarized multi-slot time slots and is therefore not for everyone the following summarized time slots repeated. In the same way it is Postamble provided at the end of the combined time slots. Because the postamble is just like the postamble of the previous combined time slots, it will not reappear anywhere else in the combined time slots get. Therefore, all bursts of the combined time slots are consecutively between between the end of the combined time slots and the postamble coupled together at the end of the combined time slots without the front sentence and the postamble in between are repeated again. With the preferred In the exemplary embodiment, only the synchronization channel is repeated for each payload.

Fig. 4 shows examples of different numbers summarized time slots in the serial slots 430-444. For example, serial slot 430 shows only one time slot. In this case the structure of the burst would be identical to a time slot in a multi-slot structure with a header, a payload and a postamble. However, if one considers the serial slot 440 with six time slots, which are to be summarized like multi-slot time slots 402 , only an attachment 450 and a postamble 452 are provided there. The payloads and synchronization channels for each of the combined time slots are coupled between header 450 and postamble 452 in the order SYC and FC, which is repeated for all combined time slots. Correspondingly, in the serial slot 440, the order of prefix 450 (which in this example contains the SYC element of the first combined time slot), element FC 452 , element SYC 454 , element FC 456 , element SYC 458 , element FC 460 , element SYC 462 , Element FC 464 , element SYC 466 , element FC 468 , element SYC 470 , element FC 472 , and postamble 452 .

It should be noted that by including the synchronization channel (SYC) for each of the payloads (FC), the present invention can be implemented in current cable communication systems, such as a cable communication system 110 , without changes in hardware. Only changes in the software or in the built-in standard programs (firmware) would have to be made.

By combining time slots according to the preferred execution Example of the present invention are additional bits for the information about opened up. Table 2 shows the multiplication of the bandwidth when using the preferred embodiment of the present invention in Compared to conventional multi-slot solutions for summarizing time slits result.

Table 2

As can be seen from Table 2, the profit is in any case on the transmission side higher than on the receiver side, where more than one time slot is combined. Of the  The reason for this is that the transmitter-side signal stream SAC contains only 14 bits On the other hand, the signal stream SYC on the receiver side is 25 bits.

In Fig. 5, a second embodiment of the present invention is Darge. As in FIG. 4, the multi-slot solution for summarizing six time slots is indicated at 502 , each of the combined time slots containing a header, a payload and a postamble. In the second exemplary embodiment of the present invention according to FIG. 5, no synchronization channel is assigned to each of the payloads to be combined, and the payloads for each of the combined time slots are successively coupled between the header and the postamble. The synchronization channel is included in the header of the summarized time slots. Fig. 6 shows examples of how channel assignments to sammengefaßten time slots to the second embodiment of the present invention may be made of the invention.

In the second exemplary embodiment of the present invention, changes in the hardware as well as in the software and in the existing cable communication system, for example the cable communication system 110 (but not with the basic structure shown in FIG. 1 but with the detailed implementation of some of the elements shown) firmware required. Since the second embodiment contains a SYC element only in the header, even more information can be transmitted in the combined time slots. In addition, a meaningful forward error correction can be used to improve the transmission performance of the cable communication system by opening further bits through the previously repeated SYC element. Table 3 shows a comparison between the second embodiment and the multi-slot solution.

Table 3

In addition to the advantages of the second embodiment mentioned above, Use of the same a twice summarized time slot user information transmitted at a rate of 160 Kb / s, which affects both the B channel and the D channel corresponds to an ISDN line clocked at the basic rate, whereby 16 Kb / s for others Purposes left, e.g. B. an extended SC or ECC element. In addition, in CACS protocol a 64 Kb / s DSO every 2.5 ms with 20 bytes. Consequently:

• - 2.5 DSOs can be transmitted in a 2X combined time slot
• - 4.0 DSOs can be transmitted in a 3X combined time slot
• - 5.5 DSOs can be transmitted in a 4X combined time slot
• - 7.0 DSOs can be transmitted in a 5X combined time slot
• - 8.5 DSOs can be transmitted in a 6X combined time slot
• - 10.0 DSOs can be transmitted in a 7X combined time slot
• - 11.5 DSOs can be transmitted in an 8X combined time slot.

Also, a user interface device 150 having two transceivers can accommodate 23 of the 24 channels in a full T1 line, while for the multi-slot three transceivers solution are required. Three transceivers in a user interface device 150 according to the second embodiment of the present invention can accommodate a full E1 line, while the multi-slot solution requires four transceivers for this.

Another advantage of the second embodiment of the present invention is the additional bandwidth thus made available, so that the Realisie an integrated packet channel protocol is possible and thus data traffic in the Trunk mode and in packet mode in different slot assignments single pair of carriers can be transmitted. Accordingly, the Da traffic in packet mode in the combined slots and the Trunk mode traffic in the other time slots of the time frame.

Claims (9)

1. Method in particular for determining a discretely variable slot width in a communication system, characterized by the following steps:
Subdivide a time frame with a predetermined duration of a time-based protocol for a communication system into a number of discrete multiple timeslots, wherein a (time-defined) total width of all timeslots in the number of discrete multiple timeslots is equal to the predetermined duration and a certain number from the Number of discrete multiple time slots are aggregated; and
Provide a preamble at the beginning of the combined time slots, the header being the same for all combined time slots and not repeated anywhere else in the combined time slots. 2. Device characterized by:
a transceiver that allows communication in a communication system between any number of users via the device, the transceiver operating with a system protocol; and
wherein the system protocol defines time frames, each of which has a predetermined time period, divided into a number of discrete multiple time slots, the total width of all time slots from the number of discrete multiple time slots being equal to the predetermined time period, and a certain number from the number of discrete multiple time slots are summarized (combined time slots), with a header being provided at the beginning of the combined time slots, which is not repeated anywhere else in the combined time slots. 3. Apparatus according to claim 2, in which at the end of the summarized Time slots a postamble and / or a postscript is provided that is nowhere is repeated differently in the combined time slots. 4. The apparatus of claim 3, wherein for each of the summarized Time slots a synchronization channel and a payload between the header and the Postamble and / or the postscript in a repeating sequence Synchronization channel payload are coupled.   5. The apparatus of claim 3, wherein for each of the summarized Time slots a payload between the header and the postamble and / or the Post is coupled, with the total payloads for each of the summarized time slots one after the other between the header and the postamble and / or the addendum are coupled. 6. System protocol for a communication system, characterized by a Number of time frames, each of which has a predetermined period of time, divided into a number of discrete multiple time slots, with a total width of all time slots the number of discrete multiple time slots is equal to the specified time period and a certain number from the number of discrete multiple time slots be summarized (combined time slots); and where a resolution at the beginning the combined time slots is provided, with the header nowhere else is repeated in the combined time slots. 7. System protocol for a communication system according to claim 6, in which chem a postamble and / or a at the end of the combined time slots Postscript is provided and nowhere else in the summarized time slots is repeated. 8. System protocol for a communication system according to claim 7, in which chem a synchronization channel and a payload for each of the combined times slits between the header and the postamble and / or the trailer in one repeating sequence of synchronization channel payload are coupled. 9. System protocol for a communication system according to claim 7, in which chem a payload for each of the combined time slots between the header and the postamble and / or the trailer is coupled, with all payloads for everyone the combined time slots one after the other between the header and the Postambel and / or the addendum are coupled.