WO1996038013A1

WO1996038013A1 - Dynamic allocation of capacity in a telecommunications system

Info

Publication number: WO1996038013A1
Application number: PCT/IB1996/000328
Authority: WO
Inventors: John Richardson Bell
Original assignee: Philips Electronics N.V.; Philips Norden Ab
Priority date: 1995-05-25
Filing date: 1996-04-15
Publication date: 1996-11-28
Also published as: GB9510619D0

Abstract

A telecommunications system comprises a system controller (SC) and a plurality of primary stations (PS1A... PS3C) defining cells, one or more of which constitute a zone (Z1, Z2, Z3). The primary stations comprise means for transmitting signals. A plurality of secondary stations (SS1, SS2) are provided at least one of which (SS2) is capable of roaming in said zones. The system controller dynamically allocates the capacity of the system between the zones in order to match the capacity to the current usage of the system. The dynamic allocation may be done on a number of bases for example time division, frequency division, a combination of time division and frequency division, regrouping of the cells to change the geographical sizes of the zones or a code division multiple access basis.

Description

DESCRIPTION

Dynamic allocation of capacity in a telecommunications system

Technical Field

The present invention relates to a telecommunications system and particularly, but not exclusively, to a high rate data message transmission system for use in sending relatively long messages such as telescript.

Background Art

Paging systems such as POCSAG (or CCIR Radiopaging Code No. 1 ) or ERMES (a standard issued by the European Telecommunications Standards Institute (ETSI)) are capable of transmitting messages at relatively low data rates which makes them unsuited to the transmission of telescript. At the date of this patent application, the Applicants have proposed a POCSAG compatible paging standard called APOC which is capable of operating at any one of several rates up to 6400 bps (bits per second).

However even the highest rate may be too low for the efficient transmission of telescript. Another factor influencing the establishment of a radio-based telecommunications system is one of spectrum. As is known from cellular telephone systems, frequency reuse schemes are possible by the creation of cells to which sets of say 20 of say 140 frequency channels are allocated, with no adjacent cells having the same sets. Additionally and/or alternatively time division operation may be practised on one or each of a plurality of frequency channels. Rigidly assigning sets of frequency or time division channels to cells has disadvantages when it comes to matching demand to system capacity.

As is well recognised city centre areas have a very high level of telecommunications traffic compared to rural areas during business days whereas the demands change out of business hours. Furthermore, in a relatively large geographical area movements of people, say to a major sporting function, may swamp the capacity of cellular infrastructure in some areas, whilst similar equipment elsewhere is underused.

Disclosure of Invention It is an object of the present invention to match demand with capacity in a telecommunication system.

According to one aspect of the present invention there is provided a telecommunications system comprising a system controller, a plurality of primary stations, each of the primary stations comprising means for transmitting signals, each primary station defining a cell, a plurality of zones, each zone comprising a variable number of n cells, where n is an integer, and at least one secondary station, wherein the system controller dynamically allocates the capacity of the system in order to match the capacity to the current usage. If desired the dynamic allocation may be done on one or more of the following bases: regrouping of cells, time division, frequency division and/or code division.

If desired the sizes of the zones may be dynamically configured or reconfigured so that if the capacity of a zone is temporarily overloaded the size of the zone is reduced by some of its primary stations being re-allocated to adjacent, less heavily used zones thus making the busy zone smaller geographically and the neighbouring ones larger. Additionally and/or alternatively additional capacity, more time slots and/or additional frequency channels may be made available. According to a second aspect of the present invention there is provided a system controller for use in the telecommunications system in accordance with the present invention, the system controller comprising a controller, a secondary station location register for storing details of a cell in which the or each secondary station was last registered, means for receiving and encoding a message to be relayed to a secondary station and means for relaying the encoded message to the primary station(s) constituting the cell(s) in which the secondary station was last registered. If desired the system controller may have means for establishing a history of the cells in which a secondary station has become registered together with temporal information relating to each said registration and the controller may be programmed to take the history into account when trying to locate a secondary station.

According to a third aspect of the present invention there is provided a secondary station for use in the telecommunications system in accordance with the present invention, the secondary station comprising receiving means, decoding means, a location register for storing details of the zone in which the secondary station was last registered, a controller having means responsive to the zone identifier for energising the receiving means for the duration of said zone.

Optionally the secondary station may have transmitting means for transmitting signals to the or at least one primary station in its currently allocated zone.

Brief Description of Drawings

The present invention will now be described, by way of example, with reference to the accompanying drawings, wherein: Figure 1 is a block schematic diagram of a telecommunications system made in accordance with the present invention,

Figure 2 is a block schematic diagram of the system controller, Figure 3 is a flow chart of the steps by which the system controller locates a mobile secondary station, Figure 4 is a block schematic diagram of a secondary station,

Figure 5 is a diagram of the cycle/batch structure, Figure 6 is a diagram of a time division allocation of a single frequency between 3 zones, and

Figures 7A and 7B illustrate two allocations of frequency channels. In the drawings the same reference numerals have been used to identify corresponding features. Modes for Carrying Out the Invention

Referring to Figure 1 , the telecommunications system comprises a plurality of geographically distributed primary or base station transceivers PS1 A, PS1 B, PS2A, PS2B, PS2C, PS3A, PS3B and PS3C coupled by respective landlines to a system controller SC. The primary stations PS1 A to PS3C respectively define cells, the geographical size and shape of which depend upon the transmitter output power and topographical features which affect signal propagation. One or more cells form dynamically created zones Z1 , Z2, Z3. For convenience of illustration the boundaries of the zones are shown as continuous lines and those between cells of the same zone as broken lines.

The system controller SC comprises a suitably programmed control computer, means for receiving and formatting long data messages to be relayed to the primary stations constituting a respective zone under the control of the control computer, and means for processing signals received by the primary stations. The system controller SC will be described in greater detail later with respect to F gure 2.

Figure 1 shows two secondary stations, a relatively fixed or transportable secondary station SS1 and a portable secondary station SS2 which is able to roam between the zones.

The system controller shown in Figure 2 comprises a stage 10 which has an input 1 2 to which is applied messages to be relayed to a secondary station. Message data, such as telescript, together with details of the addressee are received in block 10 which formats the message, appends the addressee's address code word read-out from an address code word store 1 l and if required adds a checksum. The complete message is held in store 1 3. The central computer 20 checks with a secondary station location store 22 to see in which cell or zone the addressed secondary station was last recorded as being located and assuming an entry is found, the stored complete message is routed by a switch 1 51 , controlled by the central computer 20, to the appropriate queue 14, 1 6, 18 of messages to be transmitted at the relevant time to secondary stations in the coverage area of the associated cell or zone. Depending on the mode of operation of the system, for example time division multiple access, the transmission of the queue of messages by the primary station(s) in a particular cell or zone is determined by the central computer 20. Control messages are exchanged between the central computer 20 and the primary stations comprising the system in order to determine the transmitter turn-on and turn-off times, which may vary as a result of measures to optimise the usage of the system capacity. The control messages are sent and received by lines 1 5, 17, 1 9 coupled to terminals 24, 26, 28, respectively. When the transmitters or transmitting sections of the primary stations forming a zone are turned on then the queue of messages for secondary stations believed to be in that zone are read-out under the control of the central computer and relayed to the primary stations via the terminal 24, 26 or 28. If a time division protocol is being operated then only one of said terminals will be active at any one time. It may occur that a formatted message for a roaming secondary station whose location is not known for certain, is sent to other zones in which case that formatted message is placed in two or more queues 14, 1 6, 1 8.

The terminals 24, 26, 28, also act as inputs for low bit rate signals, for example registration signals, acknowledgements and simple responses to the messages transmitted, which are received by the primary stations from secondary stations. A receive message store 30, 32, 34, is connected respectively to the terminals 24, 26 and 28. In the event of the signals being in the form of spread spectrum signals then the outputs of the stores 30, 32, 34, are supplied to respective multipliers 36, 38, 40, to each of which is connected a generator 37, 39, 41 of pseudo random bit sequences. The message applied to the multiplier is multiplied by each sequence in turn until an intelligible signal is recovered, for example by correlation, and is held in another store 42, 44, 46, respectively. Each of the stores is coupled to a single pole three way switch 47 which, under the control of the central computer 20, couples the store concerned to an output terminal 48. In the event of the signals being read out comprising registration or re-registration signals these are detected by a detector 50 and used to update the relevant entry in the location register 22.

Figure 3 is a flow chart relating to the steps involved when the system controller builds up a history of the cells/zones in which a secondary station has been or is registered in relation to time of day and day of the week. In step 100 the system controller sends what is termed an "ahoy" signai to the secondary station by way of the primary station in its last registered cell/zone. If the secondary station is still in range then at a suitable moment, it sends an answerback signal in the form of say a spread spectrum signal. The system controller in block 102 checks to see if the secondary station has replied and if it has (Y) then at the next opportunity it transmits the message, block 104.

If the answer to block 102 is No (N), then a check is made to see if the system controller has built-up a location history for the secondary station concerned, block 106. If a history exists (Y), then in block 108 the system controller arranges to send an "ahoy" message to that or those cells/zones which the history indicates that the secondary station has been in at that time of day. At the appropriate opportunity the system controller in block 1 10 checks to see if it has received an answerback from the secondary station and from which cell/zone it was received. If an answer is received (Y) then in block 1 1 2 the message is transmitted.

If a negative answer (N) is given by the blocks 106 and 1 10, then in block 1 14 an all-zone "ahoy" message is transmitted by all the primary stations. In block 1 1 6 a check is made to see if the addressed secondary has replied. If the answer is No (N) then in block 1 1 8 either the message is stored and the cycle is repeated later, just in case the secondary station was temporarily unable to receive the "ahoy" signal, or the message is aborted. If a response is received (Y) then in block 1 20 the identity of the relevant cell/zone is stored in the location register and in block 122 the message is transmitted at the relevant opportunity. Block 124 denotes the end of the flow chart.

Figure 4 is a block schematic diagram of a secondary station. The secondary station comprises an antenna 52 which is coupled to a receiver 54 in which it is frequency down converted using a frequency provided by a local oscillator 56. The intermediate frequency signal is applied to a decoder 58 which in turn is coupled to a processor 60 which operates in accordance with a program stored in a program store 62. The processor 60 includes means for identifying the address in a received signal and if the signal is not addressed to that secondary station the processor switches off the receiver 54 for a determined time period. Optionally a location register 64 may be coupled to the processor 60 in order to store information regarding the zone in which the secondary station is located or currently located in the case of a transportable secondary station. In the event of a message being addressed to the secondary station then the decoded message itself is stored in a random access memory 66 in readiness for subsequent use. A display device such as a LCD panel 68, is coupled by way of appropriate drivers 70 to an associated output of the processor. A keypad 72 is coupled to the processor 60 and constitutes a man/machine interface. Annunciating devices comprising one or more of an acoustic device 74, a LED 76 and a vibrator 78, are coupled to the processor 60. A user actuating the keypad 72 can cause an acknowledgement, registration or simple response signal to be generated as a spread spectrum sequence which is applied to a modulator 80 which provides a modulated signal to a transmitter 89, which is coupled to the antenna 52. The oscillator signal for the transmitter is derived from the local oscillator 56.

In the event of the secondary station being operated in accordance with a time division protocol then for predetermined periods the secondary station will be de-energised apart from the processor and associated circuitry but at other times the receiver or the transmitter will be energised as will be discussed later. In an alternative mode of operation where the system operates in accordance with a frequency division protocol or a combined frequency division/time division protocol, it is necessary for both the receiver and the transmitter to be able to select the appropriate frequency. Accordingly the local oscillator 56, is a tunable oscillator in response to a frequency select signal provided by a frequency select stage 84 controlled by the processor 60.

Figure 5 shows a suitable signal structure which may be used in the transmission system made in accordance with the present invention. The structure is based on a repetitive period termed a cycle and in the example being described a cycle has a duration of 6.8 seconds. Each cycle commences with a cycle information field 86 which contains the following items of information: zone identification, if the cycle is an answerback cycle, the bit rate being used to send the message proper, channel information and system messages. The bit rate has an influence on the number of cells constituting a zone and as a general rule higher bit rate signals can only be used in zones comprising a single cell having a single base station whereas lower bit rate signals may be used in zones comprising a plurality of cells having primary stations operating in a quasi-synchronous mode. The bit rate is chosen by the system controller accord ing to the coverage/capacity/performance required in a given zone. The secondary stations have the ability to decode signals at any of the predetermined bit rates used. Figure 5 also indicates the presence of a message M commencing with an address code word ACW which is concatenated with a plurality of data code words DCW1 , DCW2 ... DCWn, where n is an integer.

Figure 6 illustrates an example of cycle allocation when a time division protocol is being followed. In Figure 6 the vertical broken lines indicate the boundaries between the cycles C1 ... C20. The activity within each of the zones Z1 , Z2 and Z3 is indicated by the relevant trace being high thus for example zone Z1 is active for the period represented by cycles C1 to C4 and C1 6 to C1 8. In the case of zone Z2 the cycles C5 to C7 and C1 9 and C20 are active. Lastly the zone Z3 is active for the period represented by the cycles C8 to C1 2. As is illustrated by these examples the activity periods of the zones is not equal from zone to zone and as will be explained the cycles are allocated dynamically to reflect the level of radio traffic in the respective zones. Cycles C1 3, C14 and C1 5 have been shown cross-hatched and represent those cycles indicated by the system controller in the cycle information field as being answerback cycles in which the secondary stations can transmit acknowledgements, registration signals and/or responses as low bit rate spread spectrum signals. As may be deduced from Figure 6 the time allocated to each zone is always an integral number of 6.8 second cycles. The allocation of cycles may be applied to a multiplicity of zones which are separated by at least the re-use factor of the system. Cells defined by primary stations are allocated dynamically to zones and cycles by the system controller. Zones are distinguished by a colour code, contained within the cycle information field 86 (Figure 5) and the colour codes may be reused in zones separated by at least the re-use factor. A secondary station need only listen to a single cell at any given time. In every cycle, the cycle information field gives the number of cycles remaining for which the cell will be active (including the current one) and the minimum number of cycles for which the cell will be inactive. This allows the secondary stations listening to a given cell to switch off for a large part of the inactive periods thus economising on battery power. If a system-wide quasi-synchronous telescript transmission is required at any time, a special colour code is used to indicate this mode. This is also useful for allocating a cycle consisting only of answerback opportunities in all cells simultaneously. The present invention requires the system controller to operate the system in a manner to maximise the capacity available and to match this with the demand as far as is practical having regard to the fact that it will not be distributed uniformly across the system. Referring back to Figure 1 each of the zones is constituted by one or a multiplicity of two or more cells operating in a quasi-synchronous mode. Quasi-synchronous operation automatically confirms that the bit rates used in the zones lie in the low to medium part of the range because, as indicated earlier, at higher bit rates each zone is constituted by a single cell. Thus for example, if zone Z2 becomes relatively busy then initially the system controller uses a higher bit rate when encoding the data messages which are to be transmitted by the primary stations PS2A, PS2B and PS2C this being indicated by the relevant field in the cycle information field. If the demand to relay messages cannot be fulfilled then in order to be able to operate at yet a higher bit rate it is necessary to subdivide the zone Z2 into three single cell zones Z2A, Z2B and Z2C. This not only enables the bit rate in the single cell zones to be increased but also for the number of cycles allocated to the zone Z2 to be reallocated to the newly created zones. If the demand in the single cell zones continues to increase then the system controller can relieve the zones Z1 and Z3 of cycle periods and allocate them as appropriate to the single cell zones. If the demand for capacity reduces in one of the single cell zones then initially it can reduce its bit rate however if the demand diminishes further then for example it may be able to relinquish a cycle period, or merge with the cells of another zone say in the case of the cell C6 that this merges into zone Z3 the bit rate in which may be increased and/or it being allocated more cycles.

These types of changes can be made at the option of the system controller.

In an alternative frequency division arrangement shown in Figures 7A and 7B a plurality of radio frequency channels F1 to F8 are allocated or re¬ allocated dynamically as indicated by the arrow, to the zones Z1 , Z2 and Z3 in accordance with their need. The other option is to use a combination of time division and frequency division allocation of capacity to zones. A further option is to dynamically allocate system capacity on a code division multiple access basis.

From the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which may already be known in the design, manufacture and use of telecommunications systems and the component parts thereof and which may be used in said of or in addition to features already described herein. Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present application also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. The applicants hereby give notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

Industrial Applicability

Cellular type of long data message telecommunications system.

Claims

1 . A telecommunications system comprising a system controller, a plurality of primary stations, each of the primary stations comprising means for transmitting signals, each primary station defining a cell, a plurality of zones, each zone comprising a variable number of n cells, where n is an integer, and at least one secondary station, wherein the system controller dynamically allocates the capacity of the system in order to match the capacity to the current usage.

2. A system as claimed in Claim 1 , characterised in that the dynamic allocation is done by changing the number of cells between at least 2 of said zones and/or the number of zones.

3. A system as claimed in claim 1 , characterised in that the dynamic allocation is done on at least a time division basis.

4. A system as claimed in claim 1 , characterised in that the dynamic allocation is done on at least a frequency division basis.

5. A system as claimed in Claim 1 , characterised in that the dynamic allocation is done on a code division multiple access basis.

6. A system as claimed in Claim 3, characterised in that the primary station(s) in adjacent zones is (or are) energised non- contemporaneously.

7. A system as claimed in claim 1 , wherein a zone comprises at least two cells, characterised in that the transmitting means of the primary stations constituting the at least two cells are operated in a quasi- synchronous mode.

8. A system as claimed in any one of Claims 1 to 7, characterised in that the bit rate of the transmitted signal is selected to have one of a plurality of alternative bit rates.

9. A system controller for use in the telecommunications system as claimed in any one of claims 1 to 8, comprising a controller, a secondary station location register for storing details of a cell in which the or each secondary station was last registered, means for receiving and encoding a message to be relayed to a secondary station and means for relaying the encoded message to the primary station(s) constituting the cell(s) in which the secondary station was last registered.

10. A secondary station for use in the telecommunications system as claimed in any one of claims 1 to 8, comprising receiving means, decoding means, a location register for storing details of the zone in which the secondary station was last registered, a controller having means responsive to the zone identifier for energising the receiving means for the duration of said zone.