GB2424343A - Prioritising access to a shared communication resource - Google Patents

Abstract

In a network infrastructure 101, 102 of a communication system 100, a resource allocation processor 108, 118 allocates access of mobile stations 109-111, 119-121 to a shared communication resource, such as a packet data channel (PDCH), on a prioritised basis. A priority of access is assigned based upon the size of an information packet to be communicated by each mobile station 109-11, 119-121. For example, if the size of the information packet to be communicated is less than a first threshold, the request for communication is of higher priority. Thus, communications of shorter length, in terms of a number of time slots, are prioritised over communications of greater length.

Description

TITLE: COMMUNICATION SYSTEM AND PROCESSOR AND METHOD FOR

USE THEREIN

FIELD OF THE INVENTION

The present invention relates to a communication system and a processor and a method for use therein. In particular, it relates to a system having a processor which allocates wireless communication resources, e.g. use of a shared channel for data communication, to mobile stations on a prioritised basis.

BACKGROUND OF THE INVENTION

Mobile wireless communication systems, for example cellular telephony or private mobile radio communication systems, typically provide for radio telecommunication links to be arranged between a plurality of user or subscriber terminals, often termed mobile stations' MSs, via a system infrastructure including one or more base transceiver stations (BTSs) . Methods for communicating information simultaneously in such systems exist wherein communication resources are shared by a number of users. Such methods are termed multiple access' techniques. A number of multiple access techniques exist, whereby a finite communication resource is divided into a number of physical parameters.

Within such multiple access techniques, different duplex (two-way communication) paths are arranged.

Such paths can be arranged in a frequency division duplex (FDD) configuration, whereby a frequency is dedicated for uplink communication, i.e. from a MS to its serving ETS, and a second frequency is dedicated for downlink communication, i.e. from a serving BTS to one or more MS5. Alternatively, the paths can be arranged in a time division duplex (TDD) configuration, whereby a first time period is dedicated for up-link communication and a second time period is dedicated for downlink communication.

An example of a zone/cell-based wireless communication system is a TETRA (TErrestrial Trunked Radio) system, which is a system operating according to TETRA standards or protocols as defined by the European Telecommunications Standards Institute (ETSI) . A primary focus for a TETRA system is use by the emergency services, as TETRA provides dispatch and control services. The system infrastructure in a TETRA system is generally referred to as a switching and management infrastructure (SwMI), which contains substantially all of the communication elements apart from the MSs.

The communication system may provide radio communications between the infrastructure and MSs (or between MS5 via the infrastructure) of information in any of the known forms in which such communications are possible. In particular, information may represent speech, sound, data, picture or video information. Data information is usually digital information representing written words, numbers etc, i.e. the type of user information processed in a personal computer, often referred to in relation to communication in a network as text' information or packet data' information. In addition, control signalling messages are communicated.

These are messages relating to the communication system itself, e.g. to control the manner in which user information is communicated in compliance with the selected industry protocol such as TETRA. Different channels may be used for communication of the different forms of information. In particular, for transmission of packet data information from a MS. packet data services, PDS, are requested and communication is by a packet data channel, PDCH.

In TETRA systems and in some other cellular systems, when a user needs to make a new request to access to a particular resource of the system, for example to access a particular channel, e.g. the PDCH, this request is made using a method known as a Random Access Procedure. The method is also known as Reservation ALOHA. In this procedure, the user's MS sends a request message to a processor of the infrastructure, known as the BRC or Base Radio Controller', indicating the resource required, e.g. capacity in a particular communication channel such as the PDCH, to which access is required. The request may be successful or unsuccessful depending on whether it is chosen or not by the Random Access procedure. If it is successful, the BRC may grant the request in whole or in part by reserving all or some of the capacity requested.

TETRA systems use TDMA operating protocols.

In such protocols, some slots in the timing procedure of the control signalling channel may be reserved for the Random Access requests or such slots may be allocated by the system infrastructure on a dynamic basis. The infrastructure informs the MS5 of users through its downlink transmission that the next say N slots are to be devoted to the Random Access Procedure. These slots are available for the MS5 which require access to a system resource to have opportunities to request the infrastructure to allow or reserve access to the resource. A MS will use a Random Access opportunity in one of the designated slots to make a Random Access request. If the request is successful, the infrastructure will reserve or grant access to the appropriate resource to the MS as described earlier. The resource when granted may be defined in terms of a number of identified slots made available.

These Random Access opportunities are available to all legitimate MS5 operating within a given cell. This may include, for example, all MS5 within the cell or all MSs in a given user class within the cell as specified by the infrastructure. Collisions may occur in the sending of requests. When this happens, each MS concerned will not receive any feedback from the infrastructure as to the success of its request and may need to try, after some delay, to repeat the request procedure.

In currently available TETRA systems, the only mechanism employed for the BRC to prioritise the grant of resources to different users who are to share the same data communication channel, the PDCH, is to give priority to users who are already involved in a communication and request further channel access time.

Such a request is made by a procedure known as a Reserved Access Procedure and is in contrast to the procedure for other users who make a new request for access time by the Random Access Procedure described earlier. The BRC gives priority to requests made via the Reserved Access Procedure. This is a design feature rather than an essential feature defined in the TETRA standard. In consequence, where one user has a large amount of data to send on the PDCH, that user could occupy all available resources on the channel, blocking any other users from sharing the PDCH resources. The inventors have appreciated that this is a serious problem for those users who have only a small amount of data to send.

SU1ARY OF THE INVENTION According to the present invention in a first aspect there is provided a processor for use in an infrastructure of a communication system, the processor being as defined in claim 1 of the accompanying claims.

According to the present invention in a second aspect there is provided a communication system, the system being as defined in claim 13 of the accompanying claims.

According to the present invention in a third aspect there is provided a method of operation in a communication system, the method being as defined in claim 15 of the accompanying claims.

The processor of the invention, which may for example comprise a Base Radio Controller, BRC, operates in an infrastructure to prioritise the grant of resources on a channel of interest, particularly a data channel such as a PDCH in a TETRA system, in a new manner. Grant of resources is prioritised based upon a length of time information, e.g. a packet data package, to be sent will occupy the channel. In order to simplify the prioritisation, so that it may be implemented easily and inexpensively, a length of time, e.g. a number of required time slots, of the intended package indicated in a request may be compared with a threshold, or in stages with two or more thresholds increasing in size at each stage. A significant benefit obtained using the processor of the invention is for resources to be granted more readily to those users who have only a small information package to send, e.g. less frequently.

In this way, users will be treated more fairly overall and a greater proportion of users will have a chance to access the same channel. An illustration of these benefits is given later.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block schematic diagram of a mobile communication system embodying the present invention.

FIG. 2 is a flowsheet of a procedure operated by an infrastructure processor in the system illustrated in FIG. 1.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 shows a communication system 100 operating in accordance with an embodiment of the invention. The system 100 may be a TETRA system. The system 100 includes a first network infrastructure 101 and a second network infrastructure 102. The network infrastructure 101 includes as known main components (together with other components) (i) a BTS (base transceiver station) 103 which includes one or more transceivers providing radio communication with mobile stations within range of the BTS 103; (ii) a router 104 for routing communications into and out of the network infrastructure 101, e. g. via a PSTN (public switched telephone network) 105, and within the network infrastructure 101 and to the mobile stations served thereby; (iii) an authentication processor 106 which carries out authentication functions of the network infrastructure 101 and a memory 107 which stores data and programs needed in operation by processors of the network infrastructure 101. The network infrastructure 101 also includes a resource allocation processor 108, e.g. a Base Radio Controller, which controls allocation of communication resources available to mobile stations served by the network infrastructure 101.

The system 100 also includes a plurality of MSs (mobile stations) served by the network infrastructure 101, particularly by the BTS 103, three of which, MSs 109, 110 and 111 are shown.

The network infrastructure 102 includes as known main components (together with other components) (i) a BTS (base transceiver station) 113 which includes one or more transceivers providing radio communication with mobile stations within range of the BTS 113; (ii) a router 114 for routing communications into and out of the network infrastructure 102, e. g. via a PSTN (public switched telephone network) 115, and within the network infrastructure 102 and to the mobile stations served thereby; (iii) an authentication processor 116 which carries out authentication functions of the network infrastructure 102 and a memory 117 which stores data and programs needed in operation by processors of the network infrastructure 102. The network infrastructure 101 also includes a resource allocation processor 118 which controls allocation of communication resources available to mobile stations served by the network infrastructure 102.

The system also includes a plurality of MS5 (mobile stations) served by the network infrastructure 102, particularly the BTS 113, three of which, MSs 119, 120 and 121 are shown.

A link 122 exists between the network infrastructure 101 and the network infrastructure 102.

The link 122 may be formed in one of the ways known in the prior art. The link 122 may for example be provided by radio or microwave communication, hard wired electrical or optical communication, or the internet.

If, say, the MS 109 is to communicate with another mobile station the MS 109 first registers with the network infrastructure 101 by a known procedure which includes sending radio messages between the MS 109 and the BTS 103 and the messages being passed between the BTS 103 and the authentication processor 108. The authentication processor 108 verifies that the MS is to be served by the network infrastructure 101. When registration has been established, a communication set up request radio signal is received from the MS 109 at the BTS 103 and is passed to the resource allocation processor 108. The processor 108 allocates a resource for a communication in a manner to be described later.

When the resource is available, the router 104 routes the communication appropriately. For example, if the communication is to be directed to the MS 119, the router 104 routes the communication via the link 122 via the network infrastructure 102, particularly the router 114 and the BTS 113. Alternatively, if the communication is to be sent to another terminal (not shown) in a remote location the router 104 may route this via the PSTN 105.

Operation of the resource allocation processor 108 will now be described in more detail. The resource allocation processor 118 operates in a similar manner.

The operation is described in terms of allocation of access to a packet data channel (PDCH) in compliance with the TETRA standard. This is for illustration purposes only. Operation is not necessarily limited to this particular form of operation. The packet data channel is used for communication to and from mobile stations of packet data, i.e. packets of data comprising text information, e.g. alphanumeric characters etc, e.g. entered by a user at a user terminal using a keyboard or the like.

The user of each mobile station served by the network infrastructure 101 wishing to send a packet data communication initially requests packet data services (e.g. by selection from a menu displayed on a display of the mobile station) and is thereby connected via the BTS 103 to the resource allocation processor 108. Next, the user enters a resource reservation request to send a packet data communication (e.g. again by selection from a menu) . The request is sent from the mobile station, say MS 109, to the BTS 103 and is passed by the BTS 103 to the processor 108. The request includes an indication of the size (length of time) of the data package to be sent. In practice, the request is sent in a resource request data message (PDU') in which there is a field indicating how many slots are required. The layer 2 addressing software of the mobile station automatically calculates this size. The processor 108 receives a number of resource reservation requests on an ongoing basis. Some of the requests received are made by the Reserved Access Procedure referred to earlier and some are made by the Random Access procedure referred to earlier. An example of a random access procedure is described in Applicants' WO-A-2004/086797. The resource allocation processor 108 allocates access to the packet data channel on a prioritised basis in the manner illustrated in FIG. 2.

Firstly, in the method 200 depicted in FIG. 2, a packet data resource allocation request is received in a step 201. The processor 108 determines in a step 202 whether the request has been received by the Reserved Access Procedure, i.e. is a RES' request, or by the Random Access Procedure, i.e. is a RAN' request. RAN requests are deemed to be of higher priority (in contrast to the prioritisation in the known system) and are passed to a step 203. RES requests are deemed to be of lower priority and are passed to a step 204. In each of steps 203 and 204 the size 5, indicated in the request, of the data package to be communicated is compared with a first pre-determined size threshold stored in the memory 107. If the size S of the data package to be communicated in step 203 is less than the first threshold Ti, the request is of higher priority and is passed to a step 205. If the size S of the data package to be communicated is determined in step 203 to be equal to or greater than the first threshold Ti, the request is of lower priority and is passed to a step 206.

If the size S of the data package to be communicated is determined in step 204 to be less than the first threshold Ti, the request is of higher priority and is passed to the step 206, and if the size S of the data package to be communicated is determined in step 204 to be equal to or greater than the first threshold Ti, the request is of lower priority and is passed to a step 207.

In each of steps 205, 206 and 207 the size 5, indicated in the request, of the data package to be communicated is compared with a second predetermined size threshold T2 the value of which is stored in the memory 107. The second threshold T2 may for example be double that of the first threshold Ti. In practice, there may be a design parameter incorporated in the processor 108, or in the memory 107 for use in conjunction with the processor 108. This design parameter defines the thresholds Ti and T2. The design parameter may be the Maximum Number of Slots per Grant that is used by the processor 108 to determine how many time slots in a TDMA timing structure the processor 108 may grant to an MS at a time. Typically, Ti may be a length of time equivalent to half of the Maximum Number of Slots per Grant, while T2 may be a length of time equivalent to the Maximum Number of Slots per Grant.

If the size S of the data package to be communicated in step 205 is determined to be less than the second threshold T2, the request is of higher priority and is passed to a step 208. If the size of the data package to be communicated is determined in step 205 to be equal to or greater than the second threshold T2, the request is of lower priority and is passed to a step 209.

If the size S of the data package to be communicated is determined in step 206 to be less than the second threshold T2, the request is of higher priority and is passed to the step 209. If the size of the data package to be communicated is determined in step 206 to be equal to or greater than the second threshold T2, the request is of lower priority and is passed to a step 210.

If the size S of the data package to be communicated is determined in step 207 to be less than the second threshold T2, the request is of higher priority and is passed to the step 210. If the size S of the data package to be communicated is determined in step 207 to be equal to or greater than the second threshold T2, the request is of lower priority and is passed to a step 211.

The four steps 208, 209, 210 and 211 assign output priority levels of the various requests. Thus requests that reach step 211 are of lowest priority, say priority level 1, PR1. Requests that reach step 210 are of the next to lowest priority, say priority level 2, PR2.

Requests that reach step 209 are of the next higher priority, say priority level 3, PR3. Requests that reach step 208 are of highest priority, say priority level 4, PR4.

Finally, in a step 212 the requests given a priority level in each of steps 208 to 211 are sorted in a priority level order. The processor 108 grants access to the packet data channel for the requests in the order formed in step 212.

In practice, if communication by the system 100 uses a TDMA timing structure, as in a TETRA system, the length of time required for communication of a data package is defined in terms of a number of time slots required and the resource granted is specified in terms of a number of particular defined slots made available.

MS5 which are granted access are notified of the particular slots which have been made available to them and operate to send data during these slots only. Each MS will not know anything about the order in which the available slots have been selected.

In the event that a MS has requested more slots than the Maximum Number of Slots per Grant the number of slots made available is limited to that Maximum Number.

A further request is needed by the MS to complete the communication of the data packet. The MS can calculate and specify how many more slots are needed to complete the communication of the whole data package.

In order to compare the behaviour of the known prioritisation algorithm used by a currently available BRC with a prioritisation algorithm embodying the invention operating in the manner described with reference to FIG. 2, a communication traffic profile has been defined and used in a simulation model. The traffic profile is composed of the following. (1) There are five mobile stations MS-i, MS-2, MS-3, MS-4 and MS-5 which have to use the same PDCH having a Maximum Number of Slots per Grant of 68. (2) MS-i, MS-2, and MS-3 have data packages of i50 bytes, i60 bytes, and i70 bytes respectively, to send every 36 seconds, while MS-4 and MS-5 have data packages of i472 bytes and 1440 bytes respectively to send every 2.5 seconds; (3) Under unloaded-channel situations, MS-i, MS-2, and MS3 will need less than 0.5 seconds to finish a transaction, while MS-4 and MS-5 will need more than 3 seconds to finish a transaction. (4) The PDCH will therefore be very heavily loaded by MS-4, MS-5 and MS-i, MS-2, and MS-3 will have the risk of being totally blocked from sharing the PDCH.

Results from using both algorithms are summarised in the following tables: Table 1: Results from using the currently implemented known algorithm.

Performance MS-i MS-2 MS- MS-4 MS-5 Result Items 3 for all MSs Message reject 99.8 100. 99. 67.02 50.02 62.39 rate (%) _____ 0 8 _______ Mean 0. 07 0.0 1553.4 2302.4 3855.9 Throughput (bps 8 0 9 Mean Delay 20.1 - 1.7 368.11 356.72 361.13 (seconds) 5 ______ 2 The throughput is the total amount of data (in bps) successfully received on the SwMI side.

Table 2: Results from using the new algorithm embodying the invention.

Performance MS-i MS-2 MS-3 MS-4 MS-5 Result Items for all MSs Message 0. 41 0.20 0.30 61.58 60.36 55.29 Reject Rate (%) ________ ________ Mean 32.53 35.66 37.17 1809.91 1825.92 3741.19 Throughput _______ _______ Mean Delay 6.01 5.91 5.94 1112.21 1074.96 866. 44 It may easily be observed from Table 2 how the new algorithm has significantly improved the simulated channel performance compared with the currently implemented algorithm represented by Table 1. In particular: (1) Message Reject Rate (MRR) : For MS-i, MS-2 and MS-3 the results shown in Table 2 are very close to zero, whereas the results using the currently implemented algorithm shown in Table 1 are very close to 100% for these MSs. This is an MRR improvement of nearly 100%.

(2) Throughput: Nearly 100% of the offered load (data package to be transmitted) by the first 3 MS5, MS- 1, MS-2 and MS-3 has been transmitted using the new algorithm as illustrated in Table 2. In contrast, the amount transmitted from these MS5 using the currently implemented algorithm is close to zero. This is approaching a 100% improvement.

An objective in the described embodiment of the invention is to improve the performance of data communication for MS5 which are less frequent users, namely MS-i, MS-2, and MS-3. Therefore, the performance for the MS5 which are heavy users, namely MS-4 and MS-5, has been reduced slightly. However, as each of these two heavy users has each overloaded the channel in advance, the decrease in performance for them is less noticeable giving a more satisfactory overall performance for all users.

Claims (17)

1. A processor for use in a fixed infrastructure of a communication system including also a plurality of mobile stations, the processor being operable to allocate access of mobile stations to a shared communication resource on a prioritised basis, wherein the processor is operable to assign a priority of access to the resource which is related to a length of communication to be sent.

2. A processor according to claim 1 wherein the resource comprises a radio communication channel.

3. A processor according to claim 1 or claim 2 wherein the resource comprises a packet data communication channel.

4. A processor according to any one of claims 1 to 3 wherein the processor is operable to assign a priority level to a request from a mobile station to have access to the resource according to whether a size of information package to be communicated as indicated in the request is less than or greater than a predetermined size threshold.

5. A processor according to claim 4 wherein the processor is operable to assign a priority level also according to whether a size of information package to communicated as indicated in the request is less than or greater than a further predetermined size threshold.

6. A processor according to claim 5 wherein the processor is operable to assign a first priority level according to whether a size of package to be communicated as indicated in the request is less than or greater than a first predetermined size threshold and then to assign a second priority level according to whether a size of communication indicated in the request is less than or greater than a second predetermined size threshold greater than the first predetermined size threshold.

7. A processor according to any one of the preceding claims wherein the length of communication to be sent is defined in terms of a number of slots required in a time divided multiple access (TDMA) timing structure.

8. A processor according to any one of claims 4 to 7, which is operable to assign a priority level also according to a procedure of receiving the request by the processor.

9. A processor according to claim 8 wherein the procedure of receiving the request is either a reserved access procedure or a random access procedure and receiving by the random access procedure is given greater priority.

10. A processor according to any one of claims 1 to 3 which is operable to assign a priority level to a request from a mobile station to have access to the resource according to (i) whether a size of an information package to be communicated as indicated in the request is less than or greater than a predetermined first size threshold; and (ii) whether a size of information package to be communicated as indicated in the request is less than or greater than a second predetermined size threshold; and (iii) whether the request has been received by a reserved access procedure or a random access procedure.

11. A processor according to claim 10 which is operable to assign a priority level to a request wherein the priority level is one of at least four priority levels.

12. A processor according to any one of claims 4 to 11 which is operable to sort the requests and to grant access in a sorted order based on the assigned priority levels.

13. A communication system including an infrastructure and a plurality of mobile stations wherein the infrastructure includes a processor according to any one of the preceding claims.

14. A communication system according to claim 13 which is operable in accordance with TETRA standard procedures.

15. A method of operation to provide allocation of a shared resource in a communication system including a fixed infrastructure and a plurality of mobile stations, which method includes the mobile stations of the system sending requests for access to the resource to a processor of the infrastructure and the processor allocating access of mobile stations to the shared communication resource on a prioritised basis, wherein the processor assigns a priority of access to the resource which is related to a length of information package to be sent.

16. A method according to claim 15 and substantially as herein described with reference to the accompanying drawings.

17. A processor according to any one of claims 1 to 12 and substantially as herein with reference to the accompanying drawings.