Method of accessing transmission channels of an information transmission system

The invention relates to a method for accessing the transmission channels of a communication system having at least one central device, with at least one duplex transmission channel for the transmission of signaling and a plurality of independent subscriber stations, in which the subscriber stations have access to the duplex transmission channel for a multiple access method and on the duplex transmission channel a plurality of subscriber stations with the central device can perform an exchange of information.

As an example of such a messaging system is referred to a system for transmitting messages over radio links. From DE-OS 2,537,683 a radio transmission system with fixed radio stations and mobile subscriber stations is known. Here each stationary radio station (central device) is assigned a set of duplex transmission channels. One (the service channel) is used to transmit control information for the operation and the other (the voice channels) are used for voice transmission. Next, the transmission direction from the subscriber stations to the central facility as forward direction, the reverse direction of transmission is called back direction. The operation and various channel access methods are described in DE-OS 2,537,683.

At the beginning of each transmission from a subscriber station to the central facility (duplex transmission channel) in forward direction is first sent its own vehicle ID (identification) on the service channel. Send two or more subscriber stations their respective identification simultaneously received on the service channel, as can be seen in the central facility, none of these identifications, except one of the identifications is with significantly higher performance than any other.

With an increasing number of subscriber stations, the probability that a plurality of subscriber stations wish to simultaneously access the service channel increases. Since the service channel must be shared by all subscriber stations, the probability of simultaneous accesses to them and thus the destruction probability is particularly great.

A further increase in the destruction probability is due to the repetition of accesses due to unrecognized identifications. For each access destroying the transmission channel is not usable at least for the duration of an identification, ie blocked. The proportion of time spent blocking the service channel by accessing destructions additionally increases with the length of the identification, ie the number of admitted throughout the messaging system subscriber stations.

With frequent and short transmissions is used only to a small extent due to the aforementioned effects, the capacity of the duplex transmission channel.

From US Patent No. 3458664 another access method for accessing a duplex transmission channel in a radio transmission system is known. Will a subscriber station to access the transmission channel, so this sends a special character, which is referred to as connect tone. A prerequisite for the transfer of a connect tone, that the transmission channel is free. Receives the central facility such connect tone via the transmission channel, so this takes a certain character, as idle tone designated by the communication channel away. The removal of this idle tone is the criterion for to find another transmission channel which transmits the idle tone for all subscriber stations. The central facility sends later called seize tone, which indicates in the subscriber station that the central device has the connect tone received and is now ready, the signaling characters (identification) to receive the subscriber station.

The subscriber stations are not characterized by the transmitted connect tone when the access method known from US Pat 3,458,664th Send therefore two different subscriber stations in each overlapping periods to connect tone, so for these subscriber stations, the removal of the idle tone by the central device will not be prompted for it to leave the transmission channel. So Sends the central facility to seize tone and takes this from the transmission channel away again, so both subscriber stations will begin transmitting the complete identification and is thus an access destruction before.

The object of the invention is a method of accessing transmission channels of a communication system of the aforementioned type such that the usability of a duplex transmission channel is increased.

This object is achieved in that the subscriber stations to initiate the proceeding from them transfers occupy the duplex transmission channel with signaling symbols and that subsequently the central device that successively prompts through the signaling Abbreviation subscriber stations marked for the complete identification and thus an information transfer initiates from and to the subscriber stations.

The method according to the invention has the advantage that the free access of a subscriber station does not take place on the duplex transmission channel with a complete identification, but with a much shorter signal. This signaling Abbreviation informs the central device that a transmission request is made by a subscriber station. The complete and unambiguous identification of these subscriber station can then, as well as, where appropriate, the transfer of further payload, under coordination by the central facility such. B. queuing at a later date on the same or a different transmission channel occur.

The dependent claims 2 to 4 indicate embodiments of the method in terms of the way as the central facility after receiving a signaling token's calling on the concerned subscriber station to complete identification. Given a both the central facility and the subscriber station known indicator of signaling short-label must be used. This indicator is used in the central device for distinguishing between the subscriber stations that have actually accessed for a given period with signaling symbols and thus want a message transmission. The risk of destruction access and thus one time share, for the duplex transmission channel is only slightly used is reduced by shortening the duration of the individual access. Thus, the potential utility of the transmission channel is increased significantly with payload.

After the sub-claims 2 or 3 can be used to partially identify the temporal position or the information content of the signaling mark or both. The impact of still occurring simultaneous accesses or existing on the transmission channel and access spoofing interference can be reduced (dependent claim 3). The subscriber stations can each select one of several signaling abbreviation. The central facility is in the request for identification of the type of signaling abbreviations used by the subscriber station in accessing.

A further improvement in channel utilization is obtained by sub-claim 4, when the central device only sends an identification request when a signaling Abbreviation been identified with sufficient reception quality. This recognition of access or destruction -vortäuschungen and accesses with slow performance no periods of duplex transmission channel to be kept free for any case unsuccessful identifications.

Further increases the usability of access blocked periods (periods during which the free access is blocked for other subscriber stations) when the set called for identifying subscriber station uses her this time available as well as possible. A subscriber station requires a certain reaction time, for. Example, to evaluate the identification request before they can send their identification. According to dependent claim 5 or lower to claim 6 is a set by the system or a case by case basis to be determined by the central device delay between transmissions in reverse direction (z. B. Call for complete identification) and the related transfers in forward direction (z. B. identification) used to view the said response time for other purposes.

The dependent claims 7 to 9 indicate possible designs for the coordination to the concentration of Nutzverkehrs. In a method according to claim 7 and 8 under a transmission channel is used for both accesses the subscriber stations during the allowed for free access periods, as well as for transmitting user information during closed to free access periods. Destruction of the payload through free access other subscriber stations is thereby in accordance with a method according to claim 15 under largely, in a method according to any one of the dependent claims 7 to 9, completely avoided.

The likelihood of mutual destruction of signaling abbreviation is less when carried as evenly as possible during the time allowed for access, the number of hits. According to dependent claim 10 accesses a subscriber station after recognizing the permission to free access not necessarily immediately. The exact date for sending the signaling short character is selected z. B. randomly.

A simple implementation of the processes in the subscriber station is obtained when is divided into time slots of equal length according to dependent claim 13 of the duplex transmission channel in return direction. Each allowed for free access time slot is divided into a number of short so-called Rufschlitzen according to dependent claim 12, wherein the time duration of a Rufschlitzes at least, the same for all subscriber stations, duration of a signaling short character (sub-claims 11 to 13).

According to dependent claim 14, there is the possibility, in some or all of the transmissions of the central facility, in particular those of a particular (already fully identified) subscriber station to provide a period of time. This can be used for an identification request to another subscriber station, which had access to a signaling abbreviation. Instead of such identification request to the extent provided in a notification period also enable tag or a lock-label can be entered. 8

The invention will be described below with reference to FIGS. 1 to 4 for application to a radio telephone service in more detail and explained. It shows<ul><li>Fig. 1 shows the organization of a channel,</li><li>Fig. 2 shows the sequence of access to the service channel,</li><li>Fig. 3a, 3b, 3c, the dialogues between subscriber station and a central device during call setup, in the presence of communication and with new registrations and</li><li>Fig. 4 of a period of the service channel with different dialogs according to the invention.</li></ul>

In a radio telephone service fixed radio stations (the central institutions) ordered by a cellular system spatially. A furnished by a radio station geographic area is also called a radio zone. Each radio station (and therefore each radio zone) is a number of duplex transmission channels, also called radio channels assigned. Of these, at least one channel, the service channel used for signaling to control system functions. This includes, for. Example, the transmission of election information in the development of conversations to and from mobile subscriber stations and residence relating to the mobile subscriber stations to indicate their availability. This service channel, the inventive method is applied in order to serve the largest possible number of mobile subscriber stations without providing further service channels, thereby saving radio channels and to contribute to the frequency economy.

As shown in FIG. 1, each service channel is divided in each transmission direction in a sequence of equally long time slots. Each time slot ZS in rear direction RR (from the stationary radio station to the mobile subscriber stations) of the next-time slot in forward direction HR is permanently assigned (by the mobile subscriber stations to the base radio station). This is indicated in Fig. 1 by arrowed lines. A similar association between outward direction HR and rear direction RR is not made. The base radio station sends in the rear direction RR from continuously Mld messages with a fixed period of time which corresponds to a time slot ZS. Any notification Mld the rear direction RR a mark Mk is available about the intended use of the assigned time slot ZS the forward direction HR information. The marking Mk can have one of three meanings:<ul><li>He = permission for free access from mobile subscriber stations by signaling symbol in assigned time slot</li><li>Sp = lock the assigned time slot ZS Free Hits</li><li>XY = request for a full identification of the assigned time slot ZS for that mobile subscriber station, which had access to the marked by XY signaling abbreviation. For all other mobile subscriber stations, this corresponds to a share lock.</li></ul>

Everyone for free hits allowed time slot ZS is divided by setting the system in a certain number of z. B. eight Rufschlitzen. Also by system down a uniform duration of signaling abbreviation SK is agreed for all mobile subscriber stations.

In FIG. 2, the flow of access is displayed on the service channel. Will a mobile subscriber station to access the service channel, it first waits for a release permit it to free access to, the release permission He assigned (by arrowed line indicated) time slot of the forward direction HR. This time slot is denoted by X and is divided by agreement z. B. in eight call slots. Of these Rufschlitzen the mobile subscriber station randomly selects one, designated hereafter by Y, paging slot and sends in their signaling abbreviation. This is z. B. from a unitary to all mobile subscriber stations bit pattern and therefore offers no possibility of distinguishing. The direction indicated by the pair of values ​​XY timing of the signaling short character is thus both the mobile subscriber station and the base radio station known. The call for complete identification now exists in the indication of XY as a marker with the already explained meaning. The marking of these dedicated over next time slot is only the invited mobile subscriber station available to send in a message ID (XY) their complete identification and the nature of the desired of their dialogue with the stationary radio station.

In Fig. 3a, 3b and 3c different types of dialogue are presented. . As dialog types eg are provided:<ul><li>1. Establishing a call from a mobile subscriber station to a fixed subscriber of the telephone network (Fig. 3a),</li><li>2. Presence Communication at operational readiness of the mobile subscriber station (Fig. 3b) and</li><li>3. re-registration when changing from one service area to another (Fig. 3c).</li></ul>

Each of these dialogues consists of at least two messages and may be constructed as described below.

1. call origination

Upon receipt of the identification request sends, in Fig. 3a designated by IDG, the mobi le subscriber station in the forward direction HR their full identification and an indication that it wants to establish a conversation. After a while the base radio station acknowledges the identification and calls, described in Fig. 3a with WAF, the mobile subscriber station for transmitting dialing information on. Then take the mobile subscriber station in the next time slot before the transmission of a dialing information WÜT. The base radio station acknowledges this with a dial acknowledgment WLQ and begins to build up the desired compound. After the called party answers, references the base radio station with a channel command CBF on an intended for talking speech channel.

2. Presence Notification

By switching on or at regular intervals during the operational readiness informs the mobile subscriber station of the stationary radio station that it is accessible in the radio zone for calls. After successful access to the service channel and the call for full identification, the mobile subscriber station transmits a presence message IDA, which contains the complete identification. This announcement IDA is confirmed by the stationary radio station by a receipt AMQ, so the dialogue is completed.

3. Ummeldung

Substituted a mobile subscriber station, the radio zone, so it shall be that fixed radio station in whose service area it goes, the radio zone change be notified so that it remains accessible for calls. The necessary dialogue corresponds to the presence of a message (2) wherein the messages are IDA Duch reregister with identification IDU and AMO replaced Duch Ummeldequittung UMQ. In the messages IDG, IDA and IDU accepts because of the large number of admitted in the whole system mobile subscriber stations to identify the most part a. In comparison, the information falls to distinguish the kinds of dialogue negligible. In addition to these messages WAF, WLQ, KBF, AMO and UMQ there in rear direction RR additional messages for other system functions. This system functions should not be two different levels here and in the figures (Fig. 1 and 4) indicated by Msg.

In FIG. 4 is a time section of the service channel is shown with different dialogues. The various dialogues are conducted with a plurality of mobile subscriber stations Tln interleaved in time. With^* Timeslots marked represent bits of dialogue that were started before the beginning of the time period shown in Fig. 4. The numbering of the time slots is performed cyclically with the digits 0 to. 9 Therefore, the XY prompt for the complete identification consists of two digits. The first digit indicates the number of X Rufschlitzes (in the time slot X), in which the signaling Abbreviation been sent. When implementing it, in contrast to this simplified representation be cheaper to specify the number X, the number of years passed since the transmission of the signaling Abbreviation timeslots. From Fig. 4 it is seen that<ul><li>- The locked Free access time can be fully utilized for the transmission of useful information (messages)</li><li>- Only a relatively small part of the capacity of the service channel for free access must be made available,</li><li>- But only a small portion of the available paging slots is occupied by signaling Abbreviation, resulting in a low probability of destruction follows, and thus,</li><li>- Total by the present process a high usability (payloading) of the service channel is achieved with a low probability of access destructions.</li></ul>

The inventive method also offers a number of advantages for the implementation of particular control procedures in the mobile subscriber station.