GB1562963A

GB1562963A - Radio information transmission

Info

Publication number: GB1562963A
Application number: GB54065/77A
Authority: GB
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1976-12-30
Filing date: 1977-12-29
Publication date: 1980-03-19
Also published as: JPS5828975B2; IT1089196B; NL176824B; FR2376571A1; NL7714547A; BE862543A; ATA939077A; AT365025B; DK147534B; DE2659569B1; NL176824C; FR2376571B1; JPS5384604A; DK585477A; DE2659569C2; CH625091A5; DK147534C

Abstract

The radio network has stationary and mobile subscriber stations (T1, T2) and comprises a plurality of base stations (1, 2, ... 7) in a physical arrangement with overlapping radio areas. A frequency distribution plan for the base stations largely eliminates co-channel interference in the respective radio area, including an extended peripheral zone. Each mobile subscriber station (T1, T2) decides semi-automatically or fully automatically from its reception situation, taking into account the traffic load of the network base stations which can be received by it, on the radio area (1, 2, ... 7) to which it will assign itself and when it will change radio areas. As a result, subscribers abandon an overloaded base station and transfer to an adjacent, less heavily loaded base station. <IMAGE>

Description

(54) RADIO INFORMATION TRANSMISSION (71) We, SIEMENS AKTIENGESELL SCHAFT, a German Company, of Berlin and Munich, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a method and system for information transmission for stationary and mobile subscriber stations in the area of a radio network composed of a plurality of radio concentrators mutually spatially arranged in the manner of a cellular system having overlapping radio zones, for example employing a frequency distribution plan for the radio concentrators which eliminates like channel disturbances in the relevant radio zone and including an extended border zone.

Attention is drawn to our co-pending U.K. Patent Application No. 54066/77 (Serial No. 1,562,964) which is also concerned with radio systems of this type.

A whole series of radio networks of different structures is in existence for mobile, public and private radio services. Here it is necessary to differentiate between the public mobile ground radio and the private mobile ground radio. The public mobile ground radio comprises the mobile telephone subscribers who can be connected via radio connections to the automatic exchanges of the public telephone network.

The subscriber groups of the private mobile ground radio system include public safety bodies such as the Police, Fire Brigade, emergency services and catastrophe protection, and services such as taxi and transport undertakings, industry radio, commercial radio, contracting firms and the like.

For the major part of the subscribers to the private ground radio who are uninterested in long distance traffic, the local radio concentrators are adequate for the information transmission. These groups of subscribers thus are not conducted across the radio telephone exchange but are switched through in an internal switching network. In addition to these mobile radio services, radio services also exist for stationary subscribers which, however, are restricted to thinly populated areas.

In addition to the transmission of speech information, information transmission in the form of texts and stationary images may also be required. A further form of radio service can consist in the transmission of a call, for example a personal call or an emergency call.

The various radio services, and the various subscriber groups, and the resultant large number of different radio services result in a decidedly poor frequency economy.

Furthermore the cost outlay for the technical equipment is in part extremely high as the radio concentrators must in each case be designed for the likely peak load within the relevant radio range. Further development of radio services within the private mobile ground radio system is impeded in particular by this in sufficient frequency economy, and in the public mobile ground radio system is impeded by extremely high capital outlay costs.

According to the present invention there is provided a method of information transmission for stationary and mobile subscriber stations in the area of a radio network composed of a plurality of radio concentrators mutually spatially arranged in the manner of a cellular system having overlapping radio ranges, and operating on different frequencies, wherein each mobile subscriber station decides semi automatically or fully automatically, on the basis of its own radiotechnical situation and taking into account the radio range related load of the network, which radio range it will be assigned and when it will change a radio range.

In another aspect the invention provides a radio system comprising a plurality of radio concentrators, distributed over an area and having overlapping ranges and operating on different frequencies, and a plurality of mobile radio stations, for communication with the concentrators, each of which stations includes means responsive to its own radio technical situation and the load carried by the concentrators to effect, at least partially automatically, changes from one concentrator to another.

By radio-technical situation we mean factors upon which the possibility or otherwise of satisfactory radio communication depends. These may include, inter alia, received signal strength and signal-to-noise ratio and available transmitter power.

By "semi-automatic" is meant that the establishment of communication with a particular radio concentrator may be carried out in part manually. For example the mobile equipment may provide an indication to the operator of those concentrators which are available and with which a satisfactory link is obtainable, the actual frequency selection being effected manually.

Similarly, in the course of an existing telephone conversation or other communication the mobile equipment may indicate that the contact can be maintained only if a change of concentrator is made, the actual switch over being initiated manually.

The invention is based upon the known fact that when the radio concentrators are mutually spatially arranged in the manner of a cellular system it is possible to manage with a relatively small number of transmitting and receiving frequencies if the radio concentrators which possess the same transmitting and receiving frequencies possess a distance from one another sufficient to eliminate same-channel interference in the region of a radio concentrator. For example the "Jahrbuch des elektrischen Fernmeldewesens", 21st edition, 1970, published by Verlag fur Wissenschaft und Leben, Georg Heidecker, Bad Windsheim, pages 305 to 311, in particular page 380 Figure 1, discloses a cellular system which operates with seven frequency groups and in which the frequency distribution between the individual radio concentrators takes place in accordance with a so-called diamond movement plane.

The invention also is based upon the recognition that the number of transmittingreceiving frequencies to be made available by a radio concentrator, which number is dependent upon the likely peak traffic load, can be reduced in that the mobile subscriber stations retain the freedom to themselves decide, in accordance with predetermined criteria, to which radio concentrator they wish to apply, and in fact with a predetermined minimum number of favourable channels established on the basis of its own radio-technical situation, and offered as free bv the radio concentrator.In this respect the radio-range-related traffic load criterion acquires particular significance inasmuch as the subscriber stations are thus able to avoid threatened overloads of a radio concentrator and thus the blockage thereof in order to switch further channels by employing adjacent radio concentrators. The effects of this behaviour of the mobile subscriber station can be described as a traffic-load dependent breathing of the radio ranges.

If the traffic load of a radio range increases to peak load, it contracts, as it were, whereas the adjusted radio ranges expand into their extended border zone. The reverse procedure takes place if the traffic load in a radio range falls to lower values and the free channels are required to relieve the load of adjacent radio ranges. For example, every mobile subscriber station monitors the radio-range-related traffic load of the network by establishing the number of free channels of the radio range which it is or can be assigned.

In this respect it is preferable for every mobile subscriber station in the unseized state to constantly monitor the traffic load of the free channels made available in the assigned radio range by the relevant radio concentrator, on the establishment of a reduction below a predetermined limit value to check the possibility of a change of range to a different radio range with a number of free channels exceeding this limit value, and in the event of a positive result to carry out this change when its own radio-technical situation ensures an information transmission of adequate quality in respect of the other radio range.

In principle the possibility exists for the subscriber stations to establish the free channels in the assigned radio range by interrogating all the channels of the radio concentrator in accordance with a predetermined timing. However, this takes a substantial time. For this reason it is preferable for each mobile subscriber station to monitor the information concerning the traffic load in the relevant assigned radio range by interrogating a central organisation channel specifically assigned to the radio range and in which this information is constantly transmitted.

The traffic information transmitted in such a central organisation channel may consist merely in a statement as to whether the load on the radio concentrator liies below or above a predetermined, critical threshold.

In a preferred embodiment of the invention, the information transmission is effected in digital fashion, preferably in binary frequency modulation. As is known, binary signals can be regenerated extremely well so that the signal to noise ratio required for the satisfactory reception of such a binary signal can be reduced to less than 10 dB. This means a deepening of the extended border zone of a radio range and thus an increase in the mutually overlap ping areas of radio ranges which are adjacent to one another, in which a mobile subscriber station can optionally decide between two or more radio ranges for the execution of an information transmission.

The transmission of the information signals in digital form also has the great advantage of being able to protect the information from unauthorised listening in both simply, reliably and economically by means of digital coding.

Digital transmission also offers the very great advantage of standardising such a radio network for many different radio services, and in fact since the transmission of different items of information, such as speech, text, stationary image, personal call, emergency call etc. may be carried out with a standard bit rate via individual radio devices.

Expediently the standard bit rate amounts to approximately 5 kbit/s, to which the relatively wide-band items of information, such as speech, can be adapted prior to their actual transmission by the use of redundancy-reducing processes.

The high flexibility of a radio network operating by the process in accordance with the invention in respect of fluctuations in the radio-range-related traffic load enables the radio concentrators to be designed in respect of their transmitter/receiver radio equipment for an average traffic load, which not only is economical in respect of frequencies, but also results in a considerable reduction in the technical outlay.

In the following the invention will be explained by way of example, making reference to the drawing, in which: Figure 1 schematically illustrates a radio network constructed in the manner of a cellular system; Figure 2 schematically illustrates the mode of functioning of the process in accordance with the invention in the cellular system shown in Figure 1; and Figure 3 illustrates the curve of the radio field strength over the range of a radio network as illustrated in Figure 1 and 2.

Figure 1 is the fundamental diagram of an extendable mobile radio network, in which radio concentrators are spatially arranged in the manner of a cellular system.

The average radius of a radio range which is referenced R in Figure 1 amounts to approximately 15 km. The radio network operates, for example, with frequency duplex in the UHF range at approximately 450 MHz. The transmitting band and receiving band possess a frequency spacing of approximately 10 MHz as required for 100%, electromaenetic compatibility. Transmitting and receiving bands organised so as to be uniform in respect of their frequency as signment.

As can be seen in detail from Figure 1, the radio network is divided into frequency assignment ranges which each possess seven radio concentrators provided with the numerals 1 to 7. Figure 1 emphasises three differently shaded frequency assignment ranges. The radio concentrator designated 1 is provided with a cross to disttinguish it from the other radio concentrators: this to indicate that these radio concentrators are extended to form exchanges for connection to the automatic exchanges of the public telephone network. The frequency assignment ranges, with their seven radio concentrators, are all of identical construction and possess the same frequency distribution plan. The numbers 1 to 7 of the radio concentrators simultaneously designate the radio range numbers.

In order to ensure a gap-free accessibility of the mobile subscribers, the radio ranges of the radio concentrators 1 to 7 possess a mutual overlap. Furthermore, the least possible like channel disturbance is to occur in the overlap range.

It is possible for same-channel interference to occur in further removed radio concentrators, taking into account a minimum channel signal to noise ratio, which is dependent upon the type of modulation, at the reception location of a mobile subscriber station. This fact must be taken into consideration in the frequency distribution plan within a frequency assignment range, taking into account the superordinate spatial plan of the frequency assignment ranges which are adjacent to one another, The frequency assignment to the individual radio concentrators is carried out in such manner that the radio concentrators which possess the same range numbers and which operate with the same radio frequencies, possess a mutual minimum spacing of approximately 80 km in the exemplary embodiment, so that no appreciable samechannel interferences can occur in directly adjacent radio ranges.If, for example, the transmitting and receiving band is divided into 120 channel groups each comprising seven radio channels, expediently each radio range is assigned one channel per channel group, where the position of a channel, belonging to a specific radio range, within the channel group remains the same. Thus, for example, the first channel of a channel group is assigned to the radio range 1, the second channel to the radio range 6, the third channel to the radio range 4 etc. With an arrangement of this type it is achieved that the radio channels employed in each radio range always possess a mutual frequency spacing of six channels, so that the channels of each radio range are separated from one another by a sufficient distance to safely avoid adjacent channel interference of the transmitters in the various ranges.

In Figure 3 the attenuation of the transmitting level given at 0 dBm is plotted over the distance range, in kilometres, for the radio ranges FB1, FB2 and FB5 of a frequency assignment range and of the radio range FB1 of an adjacent further frequency assignment range. In order to simplify the drawing. Figure 3 does not show the actually existing scatter zone of these attenuation curves.

Half the average distance between two directly adjacent radio ranges of a frequency assignment range is referenced R' and, relative to Figure 1 with a radius R of 15 km, amounts to approximately 13.5 km.

This difference takes into account the mutual overlap of the radio ranges which adjoin one another. In accordance with the frequency distribution plan, the radio ranges FB1, relative to a radio channel, operate with the frequency distribution plan, the radio ranges FB1, relative to a radio channel, operate with the frequency fl and the radio ranges FB2 and EBBS, again relative to a radio channel, operate with the frequencies f2 and f5. The like channel signal to noise ratio at the point of transition from the radio range FB1 to the radio range FB2 with the spacing R1 amounts to approximately 35 dB. The signal to noise ratio of 6 dB, which is critical for digital transmission is not reached until approximately 32 km.These values apply to the middle-European area with an average rideau of 50 m level difference and an assumed antenna height of 75 m for the radio concentrators.

Assuming digital information transmission, a radio concentrator can in practice extend its radio range limit far into the directly adjacent radio ranges, should this be necessary in order to support an adjacent radio range and it is able to do so as a result of its own situation as regards the traffic load. In other words, in this way it is advantageously possible to counter overloads of a radio range which threaten to occur indirectly via the subscribe stations, so that the radio concentrators can be designed for an average traffic load even taking into account brief peak loads.

This function of neighbouring assistance between adjacent radio ranges will be described in more detail making reference to Figure 2 which shows the two frequency assignment ranges of the radio network from Figure 1. In the left-hand part of the drawing, the mobile traffic subscriber T1 is shown within the radio range 1 in the region of the outer edge. At an earlier point of time, as . result of its local situation, it approachec the radio concentrator of the radio range 1.

but since that time has remained in the unseized state. In this state it continuously interrogates the control organisation channel of the radio concentrator from which it receives information including informatiton as to the number of free channels available in the radio concentrator. At a specific point of time the subscriber station T1 establishes that the traffic load of the radio concentrator exceeds a critical threshold value and in this way the subscriber station is warned of the danger of an overload. The subscriber station T1 subsequently automatically checks whether, on the basis of its radio technical situation it can participate in a serviceable connection to one of the adjacent radio ranges 3 and 4, taking into account also the traffic load of one of these ranges.If this check has a positive outcome, the subscriber station T1 withdraws from the radio concentrator of the radio range 1 and approaches the corresponding adjacent radio range 3 or 4. This means that in the event of a threatened overload.

the radio concentrator of the radio range contracts, as it were, to the sub zone A and the remaining zone Al of annular shape, is tatken over, by way of neighbouring assistance, by the adjacent radio ranges for the mobile subscriber stations contained therein. In Figure 2 this is indicated by arrows pointing from the ranges 2 to 7 in the direction of the radio range 1.

The opposite situation is illustrated in the case of the radio range on the right-hand side of Figure 2. As a result of a threatened overload indicated by the radio concentrator of the radio range 2, the subscriber station T2 contained therein approaches the radio range 1 which has a sufficient number of free channels and, furthermore, has been recognised as suitable for a connection for the subscriber station T2 on account of its radio technical situation. Here the radio range 1 expands its range of influence as it were in a ring shape into an extended boundary zone B which also covers the subscriber station T2 in the radio range 2.

WHAT WE CLAIM IS:- 1. A method of information transmission for stationary and mobile subscriber stations in the area of a radio network which comprises a plurality of radio concentrators mutually spatially arranged in the manner of a cellular system having overlapping radio ranges and operating on different frequencies in which each subscriber station decides semi-automatically or fully automatically, on the basis of its own radio technical situation and taking into account the radio-range-related traffic load of the network, to which radio range it will be assigned and when it will change a radio range. 2. A method as claimed in Claim 1, in which each mobile subscriber station moni

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. of the transmitters in the various ranges. In Figure 3 the attenuation of the transmitting level given at 0 dBm is plotted over the distance range, in kilometres, for the radio ranges FB1, FB2 and FB5 of a frequency assignment range and of the radio range FB1 of an adjacent further frequency assignment range. In order to simplify the drawing. Figure 3 does not show the actually existing scatter zone of these attenuation curves. Half the average distance between two directly adjacent radio ranges of a frequency assignment range is referenced R' and, relative to Figure 1 with a radius R of 15 km, amounts to approximately 13.5 km. This difference takes into account the mutual overlap of the radio ranges which adjoin one another. In accordance with the frequency distribution plan, the radio ranges FB1, relative to a radio channel, operate with the frequency distribution plan, the radio ranges FB1, relative to a radio channel, operate with the frequency fl and the radio ranges FB2 and EBBS, again relative to a radio channel, operate with the frequencies f2 and f5. The like channel signal to noise ratio at the point of transition from the radio range FB1 to the radio range FB2 with the spacing R1 amounts to approximately 35 dB. The signal to noise ratio of 6 dB, which is critical for digital transmission is not reached until approximately 32 km.These values apply to the middle-European area with an average rideau of 50 m level difference and an assumed antenna height of 75 m for the radio concentrators. Assuming digital information transmission, a radio concentrator can in practice extend its radio range limit far into the directly adjacent radio ranges, should this be necessary in order to support an adjacent radio range and it is able to do so as a result of its own situation as regards the traffic load. In other words, in this way it is advantageously possible to counter overloads of a radio range which threaten to occur indirectly via the subscribe stations, so that the radio concentrators can be designed for an average traffic load even taking into account brief peak loads. This function of neighbouring assistance between adjacent radio ranges will be described in more detail making reference to Figure 2 which shows the two frequency assignment ranges of the radio network from Figure 1. In the left-hand part of the drawing, the mobile traffic subscriber T1 is shown within the radio range 1 in the region of the outer edge. At an earlier point of time, as . result of its local situation, it approachec the radio concentrator of the radio range 1. but since that time has remained in the unseized state. In this state it continuously interrogates the control organisation channel of the radio concentrator from which it receives information including informatiton as to the number of free channels available in the radio concentrator. At a specific point of time the subscriber station T1 establishes that the traffic load of the radio concentrator exceeds a critical threshold value and in this way the subscriber station is warned of the danger of an overload. The subscriber station T1 subsequently automatically checks whether, on the basis of its radio technical situation it can participate in a serviceable connection to one of the adjacent radio ranges 3 and 4, taking into account also the traffic load of one of these ranges.If this check has a positive outcome, the subscriber station T1 withdraws from the radio concentrator of the radio range 1 and approaches the corresponding adjacent radio range 3 or 4. This means that in the event of a threatened overload. the radio concentrator of the radio range contracts, as it were, to the sub zone A and the remaining zone Al of annular shape, is tatken over, by way of neighbouring assistance, by the adjacent radio ranges for the mobile subscriber stations contained therein. In Figure 2 this is indicated by arrows pointing from the ranges 2 to 7 in the direction of the radio range 1. The opposite situation is illustrated in the case of the radio range on the right-hand side of Figure 2. As a result of a threatened overload indicated by the radio concentrator of the radio range 2, the subscriber station T2 contained therein approaches the radio range 1 which has a sufficient number of free channels and, furthermore, has been recognised as suitable for a connection for the subscriber station T2 on account of its radio technical situation. Here the radio range 1 expands its range of influence as it were in a ring shape into an extended boundary zone B which also covers the subscriber station T2 in the radio range 2. WHAT WE CLAIM IS:-

1. A method of information transmission for stationary and mobile subscriber stations in the area of a radio network which comprises a plurality of radio concentrators mutually spatially arranged in the manner of a cellular system having overlapping radio ranges and operating on different frequencies in which each subscriber station decides semi-automatically or fully automatically, on the basis of its own radio technical situation and taking into account the radio-range-related traffic load of the network, to which radio range it will be assigned and when it will change a radio range.

2. A method as claimed in Claim 1, in which each mobile subscriber station moni

tors the radio-range-related traffic load of the network.

3. A method as claimed in Claim 1 or 2, in which, in the unseized state each mobile subscriber station constantly monitors the traffic load of the free channels made available in the assigned radio range by the relevant radio concentrator, on the establishment of a drop below a predetermined limit value checks on the possibility of a change to a different radio range having a number of free channels exceeding this limit value, and in the event of a positive result carries out this change only when its own radio technical situation relative to the other radio range likewise permits an information transmission of adequate quality

4.A method as claimed in any one of the preceding claims, in which each mobile subscriber station monitors the information regarding the traffic load in the particular assigned radio range by interrogating a central organisation channel specifically assigned to the radio range, in which this information is constantly additionally transmitted.

5. A method as claimed in Claim 4, in which the traffic information transmitted in the central organisation channel consists merely of an indication as to whether the load of the radio concentrator lies below or above a predetermined, critical threshold.

6. A method as claimed in any one of the preceding claims, in which the information transmission is carried out in digital fashion.

7. A method as claimed in Claim 6, in which the transmission of different items of information is carried out with a standard bit rate for standard radio devices.

8. A method as claimed in Claim 7, in which the standard bit rate amounts to approximately 5 kbit/s, to which relatively wide-band items of information, such as speech, are matched prior to their actual reducing procedures.

9. A method of information transmission substantially as herein described with reference to the accompanying drawings.

10. A radio system comprising a plurality of radio concentrators, distributed over an area and having overlapping ranges and operating on different frequencies, and a plurality of mobile radio stations, for communication with the concentrators each of which stations includes means responsive to its own radio technical situation and the load carried by the concentrators to effect.

at least partially automatically, changes from one concentrator to another.

11. A system as claimed in Claim 10 in which each radio concentrator includes means for transmitting, on a separate channel, information as to its traffic load and the mobile stations include means for receiving said information.

12. A radio system substantially as herein described with reference to the accompanying drawings.