WO1995009496A1

WO1995009496A1 - Method for digital semi-duplex transmission

Info

Publication number: WO1995009496A1
Application number: PCT/FI1994/000430
Authority: WO
Inventors: Kimmo MÄKELÄINEN
Original assignee: Nokia Telecommunications Oy
Priority date: 1993-09-27
Filing date: 1994-09-26
Publication date: 1995-04-06
Also published as: FI94696B; FI934230A; AU7700194A; FI94696C; FI934230A0

Abstract

The invention relates to a method for digital semi-duplex transmission between two radio units. To transmit reverse information, the method comprises the steps of transmitting a selected number (N-1) of speech or data blocks during a time period shorter than the original total duration (T) of the speech or data blocks from a radio unit having the transmitting permission to a radio unit having the receiving permission; and utilizing the time difference between the original total duration of the blocks and the actual transmission period for transmitting reverse information (203) and time synchronization information (202) from the radio unit having the receiving permission to the radio unit having the transmitting permission.

Description

Method for digital semi-duplex transmission

Field of the Invention

The invention relates to a method for digital semi-duplex transmission between two radio units.

Background of the Invention

In semi-duplex mobile radio systems and particu¬ larly in FDMA radio systems, information, such as speech or data messages, is transmitted from one radio unit to another. Such traffic typically takes place when a subscriber station in a mobile radio system, i.e. a mobile radioraand a base station of the mobile radio system transmit speech or other information be¬ tween them.

A problem with prior art data transmission methods is that, unlike full-duplex FDMA and TE A mobile radio systems, a semi-duplex FDMA mobile radio system does not allow a mobile radio to receive during its transmission. A mobile station having the per¬ mission to receive is not able to transmit any kind of information to a mobile station having the permission to transmit. The receiving mobile station cannot interrupt the transmission of the transmitting mobile station. In the prior art, attempts have been made to solve the problem by providing short listening periods e.g. in connection with the change of the transmitting permission, i.e. when the transmitting permission changes from one subscriber station to another in the mobile radio system In the prior art solutions, the subscriber stations xisten to the transmission of the base station for a short period of time at the change of the transmitting permission. If the subscriber stations listen to the signalling only at the change of the transmitting permission, one problem is that the successful transmission of reverse signalling cannot be ensured in a predetermined maximum time period. If the monitoring of reverse transmission is based on a very short listening period, another problem is the poor reliability of signalling trans¬ mitted on the reverse signalling channel on a radio channel of inferior quality.

Disclosure of the Invention

The object of the invention is to solve the above problem, i.e. how to interrupt the transmission of a semi-duplex radio unit during its transmission and transmit reverse signalling to the concerned sub¬ scriber station without interrupting or interfering with the speech or data transmission of the subscriber station having the transmitting permission. This new method for digital semi-duplex trans¬ mission between two radio units is achieved by a method according to the invention, which is character¬ ized in that the method comprises the steps of trans¬ mitting a selected number of speech or data blocks during a time period shorter than the original total duration of the speech or data blocks from a radio unit having the permission to transmit to a radio unit having the permission to receive; and utilizing the time difference between the original total duration of the blocks and the actual transmission period for transmitting reverse information and time synchron¬ ization information from the radio unit having the receiving permission to the radio unit having the transmitting permission. The idea of the invention can be presented in the following way. As speech or data information to be transmitted consists of blocks of fixed duration, a selected number of successive blocks are gathered up and transmitted over the radio path during a period of time shorter than their original duration. A period corresponding to the differen^ce between the original duration of the blocks and the transmission period can thus be used for transmitting reverse information and timing synchronization information from a radio unit having the receiving permission to a radio unit having the transmitting permission.

An advantage of this kind of method for digital semi-duplex transmission between two radio units is that the invention Hows reverse information to be transmitted from a iio having the receiving permis¬ sion to a radio un__<_ having the transmitting permis¬ sion without causing a break to occur in the informa¬ tion transmitted from the mobile station having the permission to transmit. This is an important feature especially in the transmission of speech information and in long-duration data transmissions with a low resistance to errors.

Another advantage of the invention is that the regular frame structure used in the reverse signalling channel establishment according to the invention en¬ sures the successful transmission of reverse signalling during a guaranteed maximum period. The use of a relatively long frame in reverse signalling reduces the possibility of an interpretation error caused by a short:-duration radio channel interference.

Brief Description of the Drawings

In the following the invention will be described more fully with reference to the attached drawings, where

Figure 1 shows a frame structure illustrating the rate change of speech or data information accord¬ ing to the invention; Figure 2 shows the structure of a multiframe according to the invention.

Detailed Description of the Invention

Figure 1 shows a frame structure illustrating the rate change of speech or data information accord¬ ing to the invention. The figure illustrates a certain time period t, during which an information signal occurs. This signal may be a data signal, which is already in digital form, or a speech signal, whereby it has been necessary to sample and/or digitally en¬ code the audio signal. The time period t is divided into N-l transmission frames or time slots, one time slot being indicated with the reference numeral 100. A predetermined amount of digital information is insert¬ ed in each time slot. According to the invention, the transmission rate of information to be transmitted in each time slot 100 is changed so that it can be in¬ serted in a shorter time slot 101. The length of the original time slot can be indicated with T, and the length of the new time slot formed by changing the transmission rate e.g. by an equation ((N-1)/N)*T, if the duration of the original time period or multiframe is to be decreased by a single frame. Of course, the rate change could be greater, whereby the number 1 in the equation would be replaced with a greater number. In this way, a greater number of free frames could be obtained. In the solution described, the transmission rate is selected so that a speech block having duration T is transferred in a frame having a duration ((N-1)/N)*T, where each (N-l)th speech block will have a period of time of ((N-1)/N)*T which is not needed for the transmission of speech information. Such an extra frame 102 is thus available once in each time unit (N-1)*T, and it can be used for signalling. In practice, the duration of T should be equal to a speech coding basic block or its multiple. An approp¬ riate signalling capacity and maximum signalling delay can thereby be selected by varying the parameter N. Figure 2 shows the structure of a multiframe according to the invention. In the figure, a frame 102 has been left free, i.e. available for the transmis¬ sion of reverse information. In this case, the frame 102 is positioned in the 18th time slot or frame of the multiframe. During each normal, i.e. forward- direction time slot 1 to 17, forward information and signalling data 205 are transmitted. This is illus¬ trated by the time slot 5, which is shown in more detail in the frame 206. The reverse signalling chan- nel according to the invention, that is, the time slot 18, or frame 102, used in the transmission of the channel, will now be described more fully. It first comprises a guard period 201 in order that the mobile station that is to transmit will have time enough to switch off its transmitter and switch on its receiver. The reverse-direction frame then comprises synchron¬ ization information 202, which may be time synchron¬ ization information or frequency synchronization in¬ formation. Then the frame comprises a space reserved for reverse-direction information, i.e. for a reverse signalling channel 203. Finally, the frame again com¬ prises a guard period 204, during which the mobile station having the transmitting permission will have time enough to switch its transceiver back to the transmission mode. The signalling frame absolutely has to comprise some synchronization information (at least a training sequence of some kind) in order that reliable re¬ ception of the signalling frame would be possible. If there is sufficiently synchronization information available, it can be used for maintaining the mobile station in continuous frequency and timing synchron¬ ization with the base station.

The most important use of the actual signalling portion of the reverse signalling frame is the inter¬ ruption of the transmission of a mobile radio having the transmitting permission. However, thereby may also be other information so urgent that it has to be trans¬ mitted before the mobile radio terminates its speech mode. The need for reverse signalling is emphasized if the mobile radio is able to transmit not only speech but also data messages which may be very long in duration.

The greatest need for reverse signalling occurs when a mobile radio transmits to the base station. However, the solution described may equally well be used in the opposite direction to offer the mobile radio a possibility to interrupt the transmission of the base station. In semi-duplex traffic, it is of course fully possible that the speech mode and the transmitting party change during the N-l frames. As the transmission direction of the signalling frame is always reverse to the transmission direction used at the end of the preceding (N-l)th traffic frame, no problems will occur.

The drawings and the description related to them are only intended to illustrate the present invention. In its details, the method according to the invention for digital semi-duplex transmission between two radio units may vary within the scope of the claims. Even though the invention has been described above mainly in connection with semi-duplex FDMA systems, it can be applied in other kind of mobile radio systems as well.

Claims

Claims:

1. Method for digital semi-duplex transmission between two radio units, c h a r a c t e r i z e d in that it comprises the steps of transmitting a selected number (N-l) of speech or data blocks during a time period shorter than the original total duration (t) of the speech or data blocks from a radio unit having the permission to transmit to a radio unit having the permission to receive; and utilizing the time difference between the original total duration of the blocks and the actual transmission period for transmitting reverse informa- tion (203) and time synchronization information (202) from the radio unit having the receiving permission to the radio unit having the transmitting permission.

2. Method according to claim 1, c h a r a c¬ t e r i z e d in that said reverse information (203) contains a command for interrupting the transmission of the radio unit having the transmitting permission.

3. Method according to claim 1 or 2, c h a r¬ a c t e r i z e d by the following steps: the radio unit having the receiving permission transmits frequency synchronization information in addition to time synchronization information during the difference between the original total duration of the blocks and the transmission period; the radio unit having the transmitting permis- sion corrects the frequency of a local oscillator of its receiver and/or transmitter on the basis of said frequency synchronization information.