Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
  • H04W88/18—Service support devices; Network management devices
  • H04W88/181—Transcoding devices; Rate adaptation devices
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
  • H04L1/0006—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission format
  • H04L1/0007—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission format by modifying the frame length
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
  • H04L1/0014—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the source coding
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
  • H04L1/0015—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the adaptation strategy
  • H04L1/0022—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the adaptation strategy in which mode-switching is influenced by the user
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
  • H04L1/0023—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the signalling
  • H04L1/0026—Transmission of channel quality indication
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
  • H04L1/0009—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the channel coding

Definitions

• the invention relates to cellular mobile telephone systems using time division multiple access, and specifically to the enhancement of speech quality of a connection in such a cellular mobile telephone system.
• a more costly solution is to install an additional base station in the area of low signal strength.
• the interference resulting from tight frequency reuse is conventionally combated in a number of ways.
• the most obvious way is to build new sites in the high interference area.
• this is not only costly but also assumes that there are frequencies available for new cells to use. If the spectrum is limited, it may be difficult to find a frequency that can be used in that area but will not lead to interference problems in other areas. Then the only viable solution is to redraft the frequency plan.
• BSC base station controller
• the base station controller is configured to cause a mobile station experiencing interference to perform hand-off to another base station early, that is, before the signal strength between the mobile and the new base station has reached an optimum level. While this method mav Dermit the interference to be bypassed, it is very likely that the user will continue experiencing inferior speech quality as a result of the low signal strength.
• SUBSTfTUTE SHEET (RULE 26) control coding.
• the provision of better coding over the air interface between a mobile station and base station will clearly reduce the bit error rate of the radio connection.
• Error control coding is essentially the calculated use of redundancy.
• a strong error control code will in general be longer than a weak one. Accordingly in a TDMA connection there is a trade-off between the level of error control, i.e. the number of coding bits, and the amount of traffic information transmitted. Increasing the error-control will reduce the number of information bits that can be transmitted in each burst. However, the transmission of fewer speech bits per burst in turn results in inferior speech quality.
• a cellular telephone communication system based on TDMA by providing means in a mobile station and/or a base station for allocating at least one additional time slot for a particular connection.
• the mobile station may be provided with manually operable means, possibly in the form of a key, with which the end user can operate to request the allocation of one or more additional time slots from the network when the speech quality of a connection is perceived to be inferior.
• the request can be activated during a call, or the mobile telephone may be configured prior to a call to launch a request when the quality of the connection, i.e. the BER, falls below a predetermined level automatically.
• the network may be configured to automatically allocate at least one additional time slot to a communication with a specific mobile station when the level of interference is found to exceed a predetermined level.
• the invention further resides in a mobile station comprising manually operable means for requesting the allocation of at least one additional time slot for a particular connection.
• a method is further proposed whereby the speech quality of a connection may be improved by allocating at least one additional time slot to a connection.
• the additional time slot or slots may be used to increase the amount of error control coding transmitted with each fixed amount of user or speech information.
• the additional time slot is used to transmit an improved and expanded speech coding scheme to provide enhanced speech quality.
• the additional time slots are preferably allocated on request from the user. The request may occur during the call or an equivalent function be enabled prior to a call to allow the mobile telephone to issue a request when the quality of the connection warrants the use of an additional slot.
• the additional time slots may be allocated by the base station equipment when the bit error rate of a connection for an end user reaches a predetermined level and when the end user has registered a request with the network requesting the enhancement of speech quality.
• the speech quality of a connection can be improved by increasing the redundancy of a time slot or burst by spreading the user or speech data over two or more time slots instead of one, and utilising the additional capacity for an improved error control code. Furthermore, by utilising the additional time slots to accommodate an improved, and therefore longer, speech coding scheme (codec) the overall perceived quality of speech may be increased. Since the additional time slots can be allocated upon request by the end user, for example during periods of high interference, the additional cost of the connection can be passed onto the user directly by the operator. The end user need not request the improved speech quality if he or she is unwilling to pay, and the operator is not obliged to make costly additional resources generally available.
• Fig. 1 schematically depicts a cellular mobile telephone system
• Fig. 2 illustrates the conventional allocation of time slots for a connection
• Fig. 3 illustrates the allocation of time slots for a connection according to the present invention
• Fig. 4. shows a procedure for boosting speech quality initiated by a user
• Fig. 5 shows a procedure for boosting speech quality based on a registered user request.
• the cellular telephone system comprises a network including several base transceiver stations (BTS) 20, generally located in the centre of a cell, base station controllers (BSC) 30, each of which typically controls a plurality of base transceiver stations 20, and mobile services switching centres (MSC) 40, which are responsible for setting up, managing and clearing connections as well as routing calls to the proper cell.
• BTS base transceiver stations
• BSC base station controllers
• MSC mobile services switching centres
• MSC's also provide interfaces to the fixed telephone system (PSTN or ISDN) as well as provisions for charging and accounting services.
• PSTN or ISDN fixed telephone system
• MS mobile stations
• the mobile station 10 is provided with a control key or keys, schematically illustrated by a rectangle 11.
• the control key or keys 11 serve to allow the user to request an enhancement of the speech quality from the network, as will be described in more detail below.
• a mobile station 10 In the air interface between a mobile station 10 and a base transceiver station 20, user traffic is transferred by means of a combination of frequency division multiplexing and time division multiple access techniques. Up to eight mobile stations 10 are assigned to a communications channel of fixed bandwidth of, typically, 200 kHz.
• the user traffic between each mobile station 10 and the network is divided into fixed lengths bursts or time slots. These bursts or time slots are multiplexed into 8-slot TDMA frames which are sent across the channel bv modulatine- the RF carrier. The frames may further be multiplexed together for sending in a fixed time period.
• Fig. 2 shows the operation of a voice connection to and from a mobile station 10.
• the allocation of time slots is illustrated for one carrier frequency channel utilised for the downlink.
• Eight time slots, numbered from 0 to 7 in the figure, make up a TDMA frame and generally one time slot in every eight is allocated to user traffic from a specific mobile station 10. This is illustrated by the shaded areas.
• the user traffic transmitted in each time slot comprises digitised voice information as well as synchronisation and control bits.
• the conversion of an analogue voice signal to a digital signal is performed using a speech coding scheme (codec) conventionally designed for a fixed number of bits.
• codec speech coding scheme
• the resulting digital signal is then coded to render the signal less sensitive to transmission errors.
• Error control coding introduces redundancy into the digitised speech signal. Generally, an increased redundancy, i.e. an increased number of error control bits, indicates a more robust connection.
• the quality of a voice connection is enhanced by utilising a more powerful error correction scheme and therefore increasing the redundancy in the error control coding of the digitised voice signal.
• the same amount of voice information is transmitted spread over two time slots. The additional capacity provided by this second time slot is then available to substantially increase the error control coding redundancy.
• Fig. 3 This increased allocation of time slots per connection is illustrated in Fig. 3.
• two consecutive time slots per frame are allocated to a single mobile station 10. If the BER is particularly high, more than one supplementary time slot per frame could be allocated to a single connection.
• the consecutive arrangement of slots allocated to a single mobile station 10 is given by way of example only.
• the slots may be also distributed in another manner through the TDMA frame.
• the improved error control coding may be implemented by replacing the normally used coding with a superior scheme for those time slots allocated to a connection.
• a further option would be to pre-code the digitised speech, for example on an application level, and subsequently subject the pre-coded signal to the normal error control coding process. This latter procedure has the advantage that the existing functions, which in some cases may be imposed by a standard, can be retained.
• the mobile station 10 is equipped with one or more control keys 11, which may be dedicated function keys, or be a specified combination of keys already present on the keypad.
• control keys 11 which may be dedicated function keys, or be a specified combination of keys already present on the keypad.
• the request issued by the user may result in one additional time slot being allocated, in which case several requests must be issued to obtain a connection wherein several time slots per frame are allocated.
• the number of time slots required for the connection (up to a maximum of 8) may be specified in a single request.
• Fig. 3 illustrates the procedure for this user initiated boost of speech quality.
• the mobile station 10 notifies the network of the request to boost speech quality.
• This request is handled by the MSC 40 which issues an assignment request to the BSC 30 if the network can allow the modification.
• the BSC 30 After this there will follow a resource upgrading or downgrading procedure, during which the number of time slots allocated will be altered and the appropriate error coding scheme adapted to the increased capacity designated. Subsequently, the BSC 30 notifies the MSC 40 of the completion of this procedure in step 3, and in step 4 the modification is acknowledged by the
• the mobile telephone 10 may be provided with certain functions enabling it to monitor the line and indicate to the user when the connection would benefit from the use of an additional time slot. In the same way, the mobile station 10 could prompt the user to order the release of an additional time slot when the connection is good enough to provide acceptable speech quality with the standard error control coding provided in one time slot per frame.
• this latter arrangement is extended.
• the functionality of the manually operable control keys 11 is incorporated in the phone itself by the user changing the settings of the telephone 10 prior to a call.
• this function is enabled, the mobile telephone itself automatically requests an additional time slot when the BER becomes too high and subsequently releases an additional time slot when the BER drops again.
• the enabling of this function could be achieved using a dedicated control key 11 or by lodging the request with a specified key configuration through the normal key pad of the telephone.
• the user may not be required to manually request the boosting of speech quality but may instead register a permanent request with the network.
• the network continually monitors the signal level and quality of the channels so that any increase in the carrier to interference ratio (C/T) will be detected. If a request from the user is registered, the quality of a connection can be boosted automatically by the network by allocating additional time slots and utilising a more powerful error control coding.
• Such a request may be stored in a register in the network, for example together with identifying information about the user and other supplemental services provided to the user in the home location register (HLR).
• HLR home location register
• the network may reduce the number of time slots allocated when the BER of the connection returns to an acceptable, or at least less noticeable, level.
• Fig. 4 This procedure is illustrated in Fig. 4.
• the BSC 30 determines that the BER of a connection is such that the user would benefit from the allocation of an additional time slot, or the removal of an added time slot.
• the BSC 30 informs the BTS 20 which additional slots are to be allocated or released. This command is acknowledged in step 3.
• the MS 10 is then notified of the change in configuration in step 4, and this command is acknowledged in step 5.
• Steps 2 and 3 are performed as many times as needed depending on the BER of the connection and the strength of the utilised error control scheme.
• Figs. 4 and 5 may also be implemented, whereby a manual request will be processed only when this function is registered by the network for the user.
• the speech quality can be brought up to the ordinary speech quality of a connection that is subjected to little or negligible interference.
• the additional time slot or slots allocated on request to a user are used to accommodate an improved speech coding scheme (codec).
• codec improved speech coding scheme
• the resulting connection then has speech quality that, depending on the codec utilised, can be far superior to that of even a fixed line. For practical reasons it may be preferable to limit the number of time slots utilised to implement an improved codec.
• additional time slots could then be allocated to improve the error control of a connection.
• the enhanced speech quality attained through the allocation of supplementary time slots and utilising an improved error control coding or codec may be provided in only the downlink connection or in both the downlink and uplink connections.
• the user may request that the speech quality in an uplink connection be boosted when the network detects a deterioration.
• the boost in speech quality is initiated by the user, either by a request during a connection or by a previously registered function request, the cost of allocating the additional resources may be passed on directly to the user. The user in turn will only have to pay for those periods of increased time slots which he requested.

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• Engineering & Computer Science (AREA)
• Quality & Reliability (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Mobile Radio Communication Systems (AREA)
• Time-Division Multiplex Systems (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20413279

Family Applications (1)

Country Status (7)

Cited By (4)

Citations (3)

• 1998
  • 1998-11-13 SE SE9803886A patent/SE515700C2/sv not_active IP Right Cessation
• 1999
  • 1999-11-04 WO PCT/SE1999/001992 patent/WO2000030383A1/en not_active Application Discontinuation
  • 1999-11-04 JP JP2000583278A patent/JP2002530955A/ja active Pending
  • 1999-11-04 EP EP99972414A patent/EP1129589A1/en not_active Withdrawn
  • 1999-11-04 CN CN 99813248 patent/CN1326650A/zh active Pending
  • 1999-11-04 AU AU14349/00A patent/AU1434900A/en not_active Abandoned
• 2001
  • 2001-05-31 ZA ZA200104496A patent/ZA200104496B/en unknown

Patent Citations (3)

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