Radio transmission system with a variable time slot duration in a time division multiplex frame.

p0001The invention relates to a digital radio communication system according to the preamble of claim 1.

p0002For transmitting messages via a jointly used by a plurality of subscribers transmission medium (eg. B. line, transmission path) are three basic methods are known, namely, the code division multiplex process, the frequency division multiplexing method and the time division multiplex method.

p0003When code division multiplexing the various guided via a common transmission medium messages, for example, by basic modulation modulates a carrier and the resultant compared to the channel bandwidth narrowband signal will spread by multiplex modulation using a receiver characterizing codeword on the channel bandwidth spectrally.

p0004The detection of the signal is not by time or frequency terms selection, but on the basis of spectral coding. The superimposed in the code division channel variety of spektralcodierten messages are selected in the receiver on the basis of this associated codeword.

p0005In frequency division multiplexing the time available for message transmission total bandwidth is divided into narrow frequency bands, each corresponding to a communication channel. For the duration of the radio transmission to the subscriber is such a narrow frequency band.

p0006When time-division multiplex method each participant, the entire range of a single radio channel available, which the participant may use but only for short periods of time. The characters or strings of different participants are interleaved and transmitted in accordance with the higher bit rate in the single radio channel, said one participant at a time assigned channel is repeated periodically with the frame period.

p0007From DE-OS 25 37 683 a radio transmission system with fixed radio stations and mobile radio stations is known, in which various channel access method uses asynchronous time division multiplexing, code division and frequency-division multiplexing.

p0008Combinations of the above processes and their application in a digital radio transmission system are known. For example, "38 (1984), No. 7, pages 264-268 Telecommunications, Electronics + Telematic" a digital radio transmission system is described in, wherein the time-division multiplex method is used in combination with interleaving, but no separation of different subscribers using the code division multiple access takes place. In the time channels for voice and / or data transmission (communication channel TCH) one after the other a bit sequence for determining the bit clock (synchronous), a frame synchronization word (opening) and the bit sequence of the message be transmitted itself. The time slots for message transmission (3 x 20 TCH) are msec with control channels (CCH 3) to a time-division multiplex frame with the duration of 31.5. arranged. Should the message the voice signal to be transmitted, can be used for analog / digital conversion, the adaptive delta modulation. The resulting message characters (bits) are superimposed in the transmitter with a code. It has proven to be advantageous to four bits each to combine the individual message character in blocks together, and to spread the blocks thus formed with an orthogonal alphabet. The spreading factor used for this is a compromise to keep up with the demand for spectrum efficiency to combine the advantages of spread spectrum each.

p0009As is apparent from the foregoing, it is known in radio transmission systems to transmit a plurality of communication channels in time multiplex. Here, the TDMA frame is divided into a fixed time frame and the mobile station is received from the base radio station, can in which time slot receive and transmit the mobile radio station information. Such a time-division multiplexing is advantageous if all participants need the same channel bandwidth for message transmission in the transmission system. Are participants with unterschieldlichem bandwidth requirement in the transmission system vorhande, then (a subscriber available) is not fully utilized with low bandwidth requirements channel capacity of participants. This is in particular in the transmission of the message via a radio link from a disadvantage, since in a radio transmission system, the system bandwidth is limited anyway. Such participants with varying bandwidth requirements occur during data transfer for various services such as fax, teletext, etc. Rechnerkommunkation on. It can be expected that less bandwidth for voice transmission, in particular for analog-digital conversion, are required due to the progress of technology in the future. The later a company introduces such new generation of mobile radio stations with a lesser bandwidth requirement is only possible at a division of the time division frame in a fixed grid.

p0010From DE-PS 31 05 199, a method for transmitting data packets of several extensions it is known to a main body via a common channel, in which the allocation of the time slots is dynamsich to the extensions or subscribers. Dynamic allocation means that a subscriber for access as many time slots are allocated, as this requires the transmission of information, the number of time slots is changed from access to access and from subscriber to subscriber.

p0011Such a method is suitable for the transmission of messages and not time-critical packet data, because the time between two successful accesses can not be determined, that it may not have a fixed data transmission rate can be guaranteed. However, such a process can not be used for the transmission of voice, since would have done the procedure described in DE-PS 31 05 199, a new access to the common transmission channel with a transmission of a speech signal during the conversation only, in accordance with. Whether or not such access is successful or not, it depends on the transport services, so that this method for the transmission of messages and time-critical data can not be used with different sizes but a constant data rate.

p0012The invention is based on the object in a digital radio transmission system, are summarized in the transmitted in shared radio transmission channel di ezu messages after the time division multiplexing, optimum use of the channel capacity of the radio transmission channel.

p0013This object is achieved in a digital radio transmission system having the features of claim 1.

p0014The inventive digital radio transmission system with variable time slot period of the time slots in the time-division multiplex frame has the advantage that the channel capacity of the radio transmission channel is used for subscriber optimally with unterschieldichem bandwidth requirements. Since the usable channel capacity of the time-division multiplex frame can be divided into any steps in accordance with the requirements of the participants, the possibility of adjustment is added for future system expansions.

p0015The inventive digital radio transmission system with reference to the drawings shown embodiments described and illustrated. It shows:<ul><li>Fig. 1 shows the division of the time-division multiplex frame,</li><li>Fig. 2 shows the multiplexing within a radio cell,</li><li>Fig. 3 shows the block diagram of the transmitting part of the stationary radio station and</li><li>Fig. 4 shows the block diagram of the receiving section in the mobile radio station.</li></ul>

p0016The Zeitmultiplexrahem illustrated in FIG. 1 includes a central control channel and can example, be occupied by three data and two voice channels (1st line) or by three voice channels (Line 2). The central organization channel, through which the Zeitzutei ment is communicated by the base radio station BS the mobile stations MS can also be located in a different channel on another carrier frequency. The receiver in the mobile radio station MS requires only the frame and bit synchronization and the information on the first and last bit of this mobile station MS the allocated time slot.

p0017With reference to FIGS. 2-4, an embodiment of a digital radio transmission system will be described in more detail and illustrated, different combinations of multiplex methods are used in the bundling of the message channels. The message to be sent is inserted in the transmission direction from the stationary radio station BS to the mobile station MS in the news channels using the combination of code division multiple access, time division multiplexing and frequency division multiplexing. For the transmission direction from the mobile station MS to the base station BS, for example, the communication can be carried out in separate, narrow-band frequency channels.

p0018In the digital radio transmission system fixed radio stations BS arranged for a cellular system spatially. Each base radio station BS associated with a number of radio transmission channels are transmitted via which messages to mobile station MS.

p0019In the two transmission directions different combinations of multiplexing methods are used for the bundling of communications channels. In the Übertragunsrichtung from the stationary radio station BS to the mobile stations MS, the message to be transmitted (voice or data) is inserted into the news channels under appli cation of code division multiple access, time division multiplexing and frequency division multiplexing. For this purpose, inter alia a TDM multiplexer 3, codeword generator 5 and a synthesizer are in the stationary radio station BS disposed 9 (see. Fig. 3). In the mobile station MS, the separation of the news channel of the received digital signal is provided using the code division multiple access, time division multiplexing and frequency division multiplexing. For this purpose, in the mobile radio station MS, among other things, a synthesizer 19, correlators 24 and 25, and a TDM demultiplexer 31 (see. Fig. 4). For the transmission direction from the mobile stations MS to the base station BS, the message transmission takes place in mutually separated, narrow-band frequency channels. In the following the multiplexing for the transmission direction from the stationary radio station BS to the mobile stations MS is described and explained in more detail.

p0020A base radio station BS has, for example, at least one channel set, consisting of 32 news channels on. The individual communication channels for the various mobile radio stations MS in a channel set are separated by different Spreizcodewörter (CDMA) and / or different time slots (TDMA). In Fig. 2, three such sets of channels are shown, in the example shown channel sets 1 and 2 at the same radio cell and channel set 3 belong to a neighboring radio cell. The identification of individual communication channels (channel identifier) ​​is in fig. 2 illustrates the sequence of numbers with three digits. The first digit represents the number of the time slot, the second digit the codeword used in each case and the dritë point the respective number of the carrier frequency used. The pooling of news channels in the transmission direction from the stationary Funksta station BS to the mobile stations MS is carried out by the succession of time division, code division, and finally frequency division multiplexing. This preferred sequence facilitates the realization of the transmitting and receiving devices of the digital Funküberträgungssystems.

p0021The structure of a channel set is, for example characterized in that a plurality of time slots, each of which contains the information for a respective subscriber, can be combined to form a time-division multiplex frame. In FIG. 2, the time-division multiplex frame comprises four time slots, such as news channel 1.1.1 to 4.1.1. The time division multiplex frame for example consists of 800 symbols and has a period of 20 msec. Of 20 synchronization symbols are distributed at regular intervals over the frame. The synchronization bits are not shown in FIG. 1. For a common control channel, a number of icons, preferably arranged, provided on the frame beginning. Typically, the time-division multiplex frame with four voice channels is occupied with 16 kbits usable bit rate and 3 kbits redundancy. The only requirements that must be met in the digital radio transmission system for the formation of the time-division multiplex frame, the frame length and the position of the control channel in the TDMA frame.

p0022Subsequently, the information of such time-division multiplex frame is spread with suitably chosen Godewörtern, which make it possible to transmit a plurality of time division multiplex frames at the same time and with the same carrier frequency. The spreading of each of these TDMA frame is done by assigning a password, which is assigned to this specific TDMA frame in this channel set. This means firstly that within a channel set any time-division frame for the spread contains a specific for him and different from the other TDMA frame codeword and, secondly, that the information is spread in the time slots of a time division multiplex frame with the same code word.

p0023In the embodiment shown in FIG. 2, eight different codewords per channel set dg be used, a channel set contains eight TDMA frame with four Zeitkänalen, ie together 32 Nachrcihtenkanäle per channel set.

p0024By assigning selected code symbols for spreading such as psuedozufällige, orthogonal or quasi-orthogonal code words, the simultaneous transmission of news in the code division multiple access is possible. The eight individual spreading codes have a spread of 31, ie a length of 31 chips on. It all code division channels are transmitted synchronously by the transmitter of the base radio station BS with the same power and. By using four symbols in each code division channel (the four symbols can be for example by two antipodal codewords represent) can be two bits of the useful signal to summarize a symbol. Thus, the symbol rate is reduced compared to the bit rate of the base band by half. For the coding of the baseband signal and the synchronization are six different symbols available, two of which are used exclusively for synchronization. If eight individual Spreizcodeebenen formed with four staggered channels, so 32 news channels / s can be transmitted, for example, 16 kbit which are modulated a common RF carrier after interleaving. When using a 4-phase modulation is obtained for the transmission of 32 message channels, for example, a bandwidth of 1.25 MHz. The time scale and hence the number of communication channels per Spreizcodeebene depends on the bit rate required for each communication channel.

p0025Due to the assembly of two bits each to one of four possible symbols remains one hand the symbol duration of 25 us long enough to inter-symbol interference caused by multipath reception to avoid, and the other part of the effort in the receiving devices for the correlators is low. The innherhalb a stationary funct station BS used to separate the code levels 16 spreading codes are for example orthogonal in pairs, while in various fixed radio stations BS with the same carrier, the different synchronizing symbols should have the smallest possible cross-correlation products, at any time shifts.

p0026For example, the spreading Gold codes may be used. A change of the spreading code has only gerigen influence on the receiving device, as these programmable correlators comprises, which are adjusted from connection to connection on the instructions of the base radio station BS new. For the transfer of such setting information and for separating the individual time channels (news channels) in time-division multiplex frame, a control channel may be provided.

p0027As already mentioned, the time-division multiplex frames of a channel set are superimposed in the transmitter of the stationary radio station BSeinander together amplified and radiated onto an RF carrier via an antenna. In the receiver of the mobile station MS, the received digital signal is mixed into the baseband. Then, in the mobile radio station that assigned at connection time slot information by correlation with the use ended for this news channel code word, which is also communicated to the mobile station when establishing a connection, recovered. In the receiver of the mobile station MS thus the separation of the message channels of the received digital signal in the reverse sequence, ie demultiplexing with respect to frequency, code, and time, as in the bundling of the message channels in the stationary radio station BS. With a frame length of 20 ms, for example, for the time-division multiplex frame, a symbol duration of Spreizcodeworts of 25 microseconds and a spread of 31, the chip duration is 0.806 ns, and the chip rate of 1.24 Mcps. This means that the chip duration is small enough to allow a sufficient resolution and utilization of the multipath and to avoid fading influences largely.

p0028As stated above, at least one control channel is provided for each channel set to the access the mobile radio stations MS to establish connections and through which the connection is established and a number of special services are handled. The mobile stations MS to know the frequency position of the possible channel rates, the corresponding timeslot and the code words for the assigned within the digital radio transmission system organization channels. With this knowledge, the mobile radio station MS can to search for these appropriate control channel, where all of the access (eg frequency of narrowband (re) direction of mobile radio station MS to the base station BS of the respective control channel) and for establishing the connection (eg timeslot as the frequency for the narrowband direction from the mobile station MS to the base radio station BS) required information received and code word for the direction from the stationary radio station BS to the mobile station MS. The usable channel capacity of a time-division multiplex frame of 76 kbit / s (there are eight such code levels on an RF carrier) can be in steps of beispeilsweise 100 bits / s arbitrary split between the two extremes of a participant to 76 kbit / s and 760 participants mti ever 100 bit / s.

p0029Whereas in a stationary radio station BS over 32 news channels are needed, multiple channel sets can be superimposed using the frequency division multiplexing today. The different sets of channels are radiated with unterschieldlichen RF carrier frequencies. In FIG. 2, the stationary radio station BS1 are assigned the channel sets 1 and 2. For both the stationary radio station BS1 zugerodneten channel sets may, because they are transmitted on different carrier frequencies, the same code words are used.

p0030The separation of the message channels of neighboring base radio stations BS is carried out either using the frequency division multiplexing (different RF carrier for the channel sets used in these stationary radio stations BS), using the code division multiplexing (different code word sets in the used channel sets) or by combinations of these two multiplexing methods. In the embodiment shown in FIG. 2, the channel set 3 of the stationary radio station BS2 different from the two channel sets 1 and 2 of the stationary radio station BS1 both in codeword set (2nd digit of the channel identifier), as well by the used RF carrier frequency (3rd digit the channel identifier). In sufficiently large spatial intervals (defined by on passing co-channel interference) from one cell to another, a inserted into this cell channel set (RF carrier and / or code word set) are repeated. It introduces the possibility of using the same RF carrier frequency in the remote radio cell and / or different codeword sets to use, to an additional flexibility and freedom in the reuse planning and facilitates the introduction of small cell structures.

p0031For the transmission direction from the mobile stations MS to the base radio station BS can for example be provided with frequency channels in 25 kHz increments a narrowband transmission. In the radio cells themselves, the frequency division is not fixed, but the frequencies of the fixed radio station BS be freely assigned.

p0032Fig. 3 shows the block diagram of the transmitting part of the stationary radio station BS. The transmitted baseband data / voice stream is composed as follows. The digitized speech of each channel is first recoded in a transcoder 1 from PCM to the required for radio transmission transmission method with correspondingly lower bit rate. At the interface BB a data source can be connected. In a connected to the data source or transcoder 1 channel encoder 2 a special channel coding is added to protect significant bits against transmission errors on the transmission channel. This channel coding may vary according to the transferring service. In a related channel encoder 2 multiplexer 3 connectionless signaling accompanying and resulting from a synchronizing circuit 4 Synchronisationsin formation is added to the data stream. The TDM signal (<u>T</u>ime <u>D</u>ivision <u>M</u>ultiplex signal) at the output of TDM multiplexer 3 so in the embodiment shown in FIG. 3 includes four voice / data channels, one accompanying the connection signaling channel (for a TDM-channel group) as well as the necessary data for Synchronisaiton in the mobile stations MS synchronization bits. The synchronization bits are inserted into the TDM signal, as is proposed in P 35 11 430.4.

p0033The TDM signal at the output of the multiplexer 3 is multiplied by the respective generated by Codegneratoren 5 codewords, whereby two bits are combined to a symbol and spread with the desired code. The code generator 5 is connected to a control device 15 and inserts the command of the controller 15 synchronizing symbols instead of data symbols in the appearing at the output of the multiplexer 3 a continuous data stream. On the spread signal a the characteristics of the radio transmission channel adapted modulation method is used, beispeilsweise the phase one was from an oscillator 6 carrier signal with the spread signal then keyed, thereby having the information and the code word linked at a low intermediate frequency modulated BPSK (Binary phase Shift keying) signal is produced. The modulated CDM signal is an adder 7 which has its output connected to a bandpass filter eighth Eight of these modulated CDM signals form after addition and a multi-stage band-pass filtering in the amplitude of the total signal which is finally converted to the final frequency.

p0034For this purpose, a synthesizer 9 is provided as a mixing oscillator which can be switched within the frequency range of the digital radio transmission system with corresponding stages. The synthesizer 9 is only for the few possible frequencies FDM stage (<u>F</u>requency <u>D</u>ivision <u>M</u>ultiplex stage) designed. The mixture of the CDM signal with the corresponding frequency is supplied by the synthesizer 9 in eienr device 10 which is connected to a bandpass filter eleventh The output of the bandpass filter 11 is connected to a power amplifier 12 and the herausfgefilterte and amplified transmission signal passes through a transmitter coupler 13 to antenna 14 news transmission channels With smaller stationary radio stations BS with up to 32 accounts for the transmitter coupler 13 completely.

p0035The channel and code generator settings, the correct selection of the channel coding and the insertions of messages in the organization data stream by means of arranged in the stationary radio station BS controller 15. The selected radio transmission channel can a TDM channel in a CDM-level (cf.. P 35 11 430.4).

p0036Fig. 4 shows the block diagram of the receiving section of the mobile station MS. This from a common transmitting / receiving antenna 16 received signal passes through a receiving filter of a duplexer 17 to the input stage 18 of the receiver. The requirements on the receive filter of the duplexer 17 are relatively low, so that there is also for mobile radio stations MS with low service request, for example, simple data radio, a cost effective solution. In the input stage 18, the signal is mixed Enhancement and then a coming from a synthesizer 19 synthesizer frequency to an intermediate frequency.

p0037The intermediate frequency signal is an IF section 20 which is supplied, in which a further amplification and filtering of the signal is carried out. Also for the synthesizer 19 can be used as for the synthesizer 9 to the base radio station BS, a simple synthesizer that can be implemented inexpensively. In IF section 20 filters are arranged which serve the neighboring channel selection to distinguish it from adjacent broadband channels and to suppress mixing products. The actual noise filtering is done in correlators 23 to 25. The IF section 20 an amplitude control circuit 21 is connected, which raises the output of the IF section 20 to a sufficient level to drive the subsequent circuits, preventing a possible override these circuits. The amplitude control circuit 21 is similar among squinting diche radio field attenuation and level fluctuations due to shadowing, so that in the following bodies of the mobile radio station MS a linear processing can be performed. The control time constant of the amplitude control circuit 21 is essentially determined by these shadows.

p0038The regulated power in the IF signal at the output of the amplitude control circuit 21 is converted in a demodulator 22 connected thereto into the base band. This can be carried out according to the principle of a Costa loop, for example at application of BPSK modulation, so that frequency and phase are taken into account. Ambiguities by integer multiples of 180 ° can be detected and ausgegelichen accordingly based on the polarity of the received sync words (35 11 430.4, see. P).

p0039The demodulator 22 three correlators 23, 24 and 25 are connected, which are set by a control device 26 to the currently valid codes 1 and 2 and a force in the service area for the entire channel bundles synchronous code. By means of the control device 26 evaluates the received Organisation data stream by the data desired by the subscribers and the data for the Geräterat provided radio transmission channels are read, one is selecting the organization data stream as free ausgwiesener and also in switchable in the mobile radio station MS radio transmission channel and then an access signal on this selected radio transmission channel to the fixed radio station BS is transmitted.

p0040The output of the correlators 23 to 25 on the one hand used to derive symbol clock, frame clock and the bit clock on the other hand is used this to measure the instantaneous current multipath profile. Since a single synchronous code with correspondingly larger level is radiated in the entire channel bundles at the same time (see. P 35 11 430.4) produces a secure synchronization detection and Vermesung the multipath profile.

p0041The outputs of the correlators 24 and 25 are connected to sampling circuits 27, 28, which 24 and 25 sense the output signals of the correlators and perform the respective result of a decision stage 29th The results of the synchronously with the echoes of the multipath propagation running samples in the decision stage 29 proportional to the amplitude of the echoes are weighted (by means of a device 30). The decision stage 29 has the task to estimate the transmitted code and the Polaritätdes codes. The estimate thus allows dieAuswahl of the transmitted symbol with the highest probability. After the symbol-bit conversion in the decision stage 29, the output signal is fed to a connected to the decision stage 29 TDM demultiplexer 31st The demultiplexer 31 is connected to a channel decoder 32 at the output of the transmitted data stream is available again. In case of digital speech transmission the digital speech signal is decoded in a speech decoder 33, supplied to a D / A converter and a speaker connected thereto.

p0042If the mobile station MS, for example, the service type data service implemented, the data appearing at the output of the channel decoder Dieres 32 can be immediately displayed or printed, for example.