WO1997023072A1

WO1997023072A1 - High-speed data transmission in a mobile telephone network

Info

Publication number: WO1997023072A1
Application number: PCT/FI1996/000666
Authority: WO
Inventors: Mikko Kanerva; Marko Valo; Juha Räsänen; Harri Jokinen; Jari HÄMÄLÄINEN
Original assignee: Nokia Telecommunications Oy
Current assignee: Nokia Oyj
Priority date: 1995-12-18
Filing date: 1996-12-17
Publication date: 1997-06-26
Anticipated expiration: 1998-06-18
Also published as: FI956088A7; FI956088L; AU1099197A; FI956088A0

Abstract

Data transmission is often asymmetric to a great extent, i.e. actual data is transmitted only in one direction, whereas only negotiation messages controlling the data stream or other similar messages and possibly small amounts of data are transmitted in the other direction. Only the mobile station knows on which sub-channels of a traffic channel - such as time slots (0 to 7) of a TDMA system - it can, or it is advantageous for it, to receive data. The mobile station must therefore inform the network on which TCH/Ss the network should transmit. The mobile station can do this, for example, by means of a bit map on one sub-channel or separately on each sub-channel.

Description

HIGH-SPEED DATA TRANSMISSION IN A MOBILE TELEPHONE NETWORK

BACKGROUND OF THE INVENTION

The invention relates to a method for transmitting data over a radio path in a mobile telephone system which is based on time division multiple access (TDMA) and in which a plurality of time slots in a frame can be as¬ signed to a mobile station for data transmission.

The Applicant's Finnish Patent Application No. 951 971 discloses a data transmission method in which time slots are assigned symmetrically but used asymmetrically. Said Patent Application "971 was not available to the public at the priority date of the present application.

The Finnish Patent Application '971 does not give a detailed de¬ scription of a situation where a mobile station should receive data in a smaller number of channels than it uses for transmission. According to the solution disclosed therein, asymmetric use is not signalled to the mobile telephone network, either.

Figure 1 illustrates a possible situation in high-speed data transmis¬ sion where sub-channels have been allocated symmetrically. Numbers 0 to 7 in Figure 1 correspond to time slots in a TDMA system. Three time slots in each frame of eight time slots are used for both transmission and reception; these time slots are indicated by Tx and Rx, respectively. There are two prob¬ lems are associated with this situation. First, a mobile station MS has very little time to monitor neighbouring base stations for any handover. For this reason, the mobile station should be provided with more complex radio parts, such as faster frequency synthesizers or separate modules for transmission and re- ception. Second, on account of timing advance, the radio part of the mobile station would have to start transmission before the reception has ended; even for this reason, the mobile station should be provided with more complex radio parts.

BRIEF SUMMARY OF THE INVENTION It is a first object of the invention to provide a method which allows a mobile station to negotiate the asymmetry it uses with the mobile telephone network or to inform the network about it at the beginning of a connection. It is a second object of the invention to provide this method without unnecessarily increasing the load of network elements, particularly an interworking function IWF. It is a third object of the invention to provide a method by which the de- gree and direction of asymmetry can be changed during a connection. The objects of the invention are achieved with a method which is characterized by what is disclosed in claim 1. Preferred embodiments are disclosed in the de¬ pendent claims. The invention is based on the realization that, in practice, data transmission is often asymmetric to a great extent: actual data is transmitted in only one direction, and only negotiation messages controlling the data stream or similar messages and possibly small amounts of data are transmitted in the other direction. In addition, the invention is based on the fact that only the mo- bile station usually knows on which sub-channels of a traffic channel it can - or it is advantageous for it - to receive data. It is also conceivable that data on the abilities of different mobile stations could be stored in an equipment register, which could be provided in connection with the subscriber registers HLR and/or VLR of the network or apart from them. The problem with this solution is at least that the mobile station consists of two portions: the actual mobile equipment (ME) and a subscriber identity module (SIM). Subscriber registers store information on the location of SIMs, whereas the abilities of the mobile station depend on those of the ME. It is therefore preferred that the mobile station informs the network of its abilities by a negotiation procedure, for ex- ample.

In practice, the mobile station thus has to inform the network of the TCH/S sub-channels on which the network should transmit. The mobile station can also inform the network of the TCH/S sub-channels on which it intends to transmit. The abbreviation TCH/S will be used herein for a traffic channel sub- channel. The term "sub-channel" is used of a channel (e.g. a time slot of a TDMA system) which is part of a high-speed data channel TCH/HSD consist¬ ing of several sub-channels. The sub-channel may be identical or almost iden¬ tical with a conventional data channel of the GSM system. There may be dif¬ ferences in the signalling channels associated with the channels; signalling channels are not necessarily associated with each sub-channel but possibly only with one of them.

It is an advantage of the method of the invention that it provides a flexible solution for asymmetric data transmission. According to a preferred embodiment of the invention, the degree and direction of asymmetry can be flexibly changed during a connection such that the downlink direction is fa¬ voured instead of the uplink direction or vice versa. A further advantage of the invention is that it improves the invention disclosed in Patent Application '971 by reducing the load of the interworking function IWF. Over the air interface, time slots are still allocated in symmetric pairs.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING In the following, the invention will be described in greater detail by means of preferred embodiments, with reference to the accompanying draw¬ ings, in which

Figure 1 illustrates, by way of example, allocation of sub-channels at the beginning of signalling, when sub-channels are allocated symmetrically; and

Figure 2 illustrates, by way of example, a situation where the mobile station has indicated that it will release those sub-channels of reception which it will not need.

DETAILED DESCRIPTION OF THE INVENTION Figure 2 illustrates, by way of example, an asymmetric connection of the invention, on which the mobile station MS uses three time slots for transmission (Tx, time slots 1 to 3) and one for reception (Rx, time slot 2). The neighbouring base stations can be monitored, for example, during time slot 0 of the reception, and the preceding and following time slot. Increasing the number of TCH/Ss used on a TCH/HSD channel leads finally to a situation where the neighbouring base stations cannot be as easily monitored during each frame, if the mobile station comprises simple radio parts. However, the monitoring can be performed during an idle frame of the multiframe, as dis¬ closed in said Finnish Patent Application "971. According to a first embodiment of the invention, the mobile station

MS informs the mobile services switching center MSC and/or the interworking function IWF connected to it, during an RLP XID negotiation period (Radio Link Protocol exchange IDentification), about the TCH/Ss on which the MS wishes to transmit and receive data. The negotiation can be conducted either jointly on one or more of the TCH/Ss used on the transmission path or, alter¬ natively, separately on each TCH/S.

The negotiation can be conducted inclusively (by indicating the sub¬ channels that are used) or exclusively (by indicating the sub-channels that are not used) or by using both methods simultaneously. The TCH/Ss have preferably sub-channel-specific default values which determine whether the channel in question is used unless otherwise negotiated. The default values may be the same or different in the uplink and downlink directions. If one or more of the TCH/Ss is a primary TCH/S, its de- fault values may be different from those of the other sub-channels. If the ne¬ gotiation is conducted on one TCH/S, this sub-channel may be a certain pre¬ determined (e.g. the above-mentioned primary) TCH/S, a TCH/S negotiated during the connection or any TCH/S.

The MS may send the network a bit map containing a proposal made by the MS for the TCH/Ss the network should use. Since a TDMA frame is divided into eight time slots, it is sensible to use an 8-bit bit map. It is also conceivable that the highest possible transmission capacity of a TCH/HSD channel could be eight time slots. Bit '0' in a bit map may indicate, for exam¬ ple, that the TCH/S in question is not used according to the proposal made by the MS, and bit '1' may indicate that the TCH/S is used. Bit map '00001000', for example, would indicate that time slot number 4 is used, whereas the other time slots are idle.

It is also possible to use eight bits for indicating the maximum ca¬ pacity of a TCH/HSD channel. Bit pattern '01000000', for example, would indi- cate that the first time slot assigned to the mobile station is 'idle', the second one is 'used', etc. If, for instance, three sub-channels are used on a TCH/HSD channel, only the three first bits are significant. In other words, in cases where the maximum capacity of a TCH/HSD channel is less than eight sub-channels, the extra bits can be used for signalling or for transmitting other information during a data connection. It should be noted that there is no connection be¬ tween TDMA time slot numbers and TCH/S numbers.

According to the Finnish Patent Application 951 971 , only the mo¬ bile station knows which time slots will be used in the uplink direction. Accord¬ ing to the present invention, it is suggested alternatively that the mobile station may use XID frames for negotiating and informing the network of the time slots it intends to use in the uplink direction. An advantage of this embodiment is that it reduces the amount of processing needed in the MSC and/or the IWF by reducing the number of RLP dummy frames or by informing the MSC and/or the IWF of the channels on which RLP dummy frames should not be used for transmission. Bit pattern 'Downlink 00001000, Uplink 00001110' would indicate that time slot 4 is used in the downlink direction, and time slots 4, 5 and 6 in the uplink direction. The other time slots are idle in both direc¬ tions. This example is based on the first bit pattern notation. Other notations would produce a different but corresponding bit pattern.

It should be noted that an IWF of the prior art is not aware of the meaning of the bits in a bit pattem and of the correlation between them and what the IWF transmits. In order that the bit map technique might be used, the unit that sends packets, i.e. the IWF of the invention, must have this informa¬ tion. In the case of a channel-specific negotiation, an IWF of the prior art is not able to recognize the channel pairs of the uplink and downlink direction when a multichannel connection is used. To allow an asymmetric connection to be established by a channel-specific negotiation, the IWF should be able to rec¬ ognize the channel pairs of the uplink and downlink direction.

Data transmission between the MSC/IWF and the base station BTS is transparent, and the present invention does not affect the operation of other network elements, such as the base station controller BSC and the TRAU (Transcoder and Rate Adaptor Unit).

The parameters used in an RLP negotiation will be dealt with in the following. When a call is being established, a symmetric time slot combination is allocated to a high-speed channel TCH/HSD; i.e. the same number of time slots are allocated in both the uplink and the downlink direction. If transmission is limited in one direction to only some of the allocated time slots, the mobile station MS is allowed to use a larger number of time slots in the other direction than is possible when the TCH/HSD is used symmetrically as conventional. This can be easily implemented in cases where more capacity is needed in the downlink direction than in the uplink direction, since the MS can freely decide in which time slots it wishes to transmit. This is possible, because the IWF lis¬ tens to all TCH/Ss and simply discards idle frames. Unless the mobile station transmits on certain TCH/Ss, idle frames are generated between the base sta¬ tion BTS and the IWF. This may be wasting of resources but does not weaken the connection, which may be maintained as normal.

The situation is more complex when higher transmission capacity is required in the uplink direction, since the MS does not perhaps have the ca¬ pacity to listen to all TCH/Ss; instead, the mobile station must know exactly on which TCH/Ss the IWF transmits towards the MS. The IWF and the MS may use an RLP XID negotiation to agree on the TCH/Ss on which data will be transmitted over the TCH/HSD channel. It is possible to include a new parameter in the existing XID parameters for this purpose, as appears from Table 1 below. The table is taken from ETSI stan¬ dard GSM 04.22; however, the parameters that are valid from version 1 or later are taken from standard proposals which are likely to be accepted. The compression parameters are based partly on ITU Recommendation V.42 bis and partly on mutual agreements between equipment manufacturers.

TABLE 1

Value 'OObbbbbb' is multiplied by 8.

* Negotiation procedure in accordance with ITU Recommendation V.42 bis

The new parameter could be, for example, as follows:

Channel usage 9 1 OOOOabcd MS decides ≥2

Bit 'a' indicates whether the MS and the IWF transmit on all the TCH/Ss allocated to the connection or whether the status of the TCH/Ss allo¬ cated to the connection is negotiated channel-specifically as follows: when 'a'=1 , both transmit on all available TCH/Ss; and when 'a'=0, the status of each sub-channel is negotiated separately. Bit 'b' indicates the status of the uplink part of a TCH/S of a circuit-switched TCH/HSD connection as follows: when 'b'=1 , the MS transmits only on this sub-channel unless bit 'b' is negotiated to be 1 on other sub-channels; and when 'b'=0, the MS transmits on all allocated sub-channels or only on the sub-channels on which bit 'b' is negotiated to be 1. Bit 'c' indicates the status of the downlink part of a TCH/S of a circuit- switched TCH/HSD connection as follows: when 'c'=1 , the MS receives only on this sub-channel unless bit 'c' is negotiated to be 1 on other sub-channels; and when 'c'=0, the MS receives on all allocated sub-channels or only on the sub¬ channels on which bit 'c' is negotiated to be 1.

Bit 'd' is used when a new TCH/S is allocated to an existing TCH/HSD high-speed channel. When 'd'=1 , bits 'b' and 'c' are used for negoti- ating the status of the new sub-channel as follows. When 'b -1 , the MS trans¬ mits on this sub-channel as well as on the ones used in the preceding configu¬ ration; and when 'b'=0, the MS does not transmit on the newly added sub¬ channel. When 'c'=1 , the MS receives on this sub-channel and on the ones used in the preceding configuration; and when 'c'=0, the MS does not receive on the newly added sub-channel. If 'd'=0, it has no effect on the negotiation procedure defined in the preceding paragraph. The status of an added sub¬ channel can be negotiated over any active sub-channel of the TCH/HSD con¬ nection.

This new parameter is used in the HSD operation, and it must be negotiated over at least one sub-channel that is in use. Both the IWF and the MS may initiate the negotiation process, but it is the MS that decides on which sub-channels it wishes to receive and on which to transmit. Although the IWF is able to listen to all sub-channels, the MS indicates which sub-channels it will use for transmission. This arrangement reduces the amount of processing performed by the IWF.

If desired, the right of decision of the mobile station can be limited in such a manner that the channels offered in the uplink and downlink directions are limited to those indicated by the XID message which initiates the negotia¬ tion. The mobile station will, however, decide on the physical positioning of the sub-channels in time slots.

Table 2 shows the values of the XID parameters: TABLE 2

Name Value range Default value Recommended value

Version N 0 - 2 0 1 k MS → IWF for N = 0/1 0 - 61 61 61 k MS → IWF for N = 2 0 - 480 480 480 k MS → IWF for N = 0/1 0 - 61 61 61 k MS → IWF for N = 2 0 - 480 480 480

T1 > 380 ms 480 ms (full rate) 480 ms (full rate)

> 600 ms 780 ms (half rate) 780 ms (half rate)

T2 <80 ms (full rate) <80 ms (full rate) <80 ms (half rate) <80 ms (half rate)

N2 > 0 6 6

T4 > 25 ms 30 ms 30 ms

T2 < T1 - T4 - (2 ^* propagation delay)

Channel usage 0 - 8 8 8

The default value for the parameter 'channel usage' is 8

(00001000), i.e. the mobile station both transmits and receives on all sub¬ channels allocated to the connection.

According to a second embodiment of the invention, N time slots of a TCH/HSD connection are allocated as symmetric time slot pairs, i.e. as TCH/Ss. The default value is that the switching centre MSC and the IWF can transmit on all sub-channels. According to the second embodiment, the MS signals on each TCH/S it uses: "I transmit on this channel." Asymmetric serv¬ ice is possible even without such signalling, but the signalling simplifies the task of the IWF, since it does not have to listen to sub-channels on which the MS does not transmit, in addition, the MS signals on each TCH/S on which it does not wish to receive: "do not transmit on this channel."

The invention allows the implementation of asymmetric traffic in which the primary direction of information, i.e. the direction of higher capacity, is either the uplink or the downlink direction. The direction of higher capacity can be flexibly changed during a connection as many times as required.

If TCH/Ss are added to or removed from a TCH/HSD connection, the same rules apply to the use of all sub-channels: the IWF is allowed to transmit on all sub-channels unless it is specifically forbidden to do so, and the MS must signal on the added sub-channels if it wishes to transmit on them. It will be obvious to one skilled in the art that the basic idea of the invention can be implemented in many different ways. As an alternative to the embodiments described above, it is conceivable that the mobile station could inform the network of its ability to support multichannel operation, for instance by sending a 'classmark change' message. It would also be conceivable that the mobile station could inform that it is only capable of establishing an asym¬ metric connection. In this case, the default values of some sub-channels can be different. The invention and its embodiments are thus not limited to the ex¬ amples described above but may be modified within the scope of the ap¬ pended claims.

Claims

1. A method for high-speed data transmission in a mobile telephone system based on time division multiple access (TDMA), characterized in that data transmission channels in uplink and downlink directions are asymmetric in such a manner that sub-channels are used in both directions according to the transmission rate required in the direction in question and/or according to the properties of a mobile station; and that the mobile station (MS) informs the mobile telephone network (MSC, IWF) of the sub-channels on which data will be transmitted.

2. A method according to claim 1, characterized in that the mobile station (MS) indicates the sub-channels that are in use during an RLP XID negotiation period.

3. A method according to claim 1 or 2, characterized in that the mobile station (MS) indicates the sub-channels that are in use jointly on a sub-channel used in the uplink direction.

4. A method according to any one of claims 1 to 3, characterized in that the mobile station (MS) sends the network a bit map containing a proposal made by the mobile station for the sub-channels to be used in the downlink and/or uplink direction.

5. A method according to any one of claims 1 to 4, characterized in that the mobile station (MS) indicates the sub¬ channels that are in use.

6. A method according to any one of claims 1 to 4, characterized in that the mobile station (MS) indicates the sub- channels that are not in use.

7. A method according to any one of claims 1 to 6, characterized in that the sub-channels have channel-specific default values which determine which channels are used, unless negotiated other¬ wise.

8. A method according to claim 7, c h a r a c t e r i z e d in that the channel-specific default values are the same in the uplink and downlink direc¬ tions.

9. A method according to claim 7, characterized in that the channel-specific default values are different in the uplink and downlink direc- tions.

10. A method according to any one of claims 7 to 9, characterized in that sub-channels are classified in at least two classes, such as primary and ordinary sub-channels; and that the channel- specific default values depend on the class ofthe sub-channel in question.

11. A method according to claim 1 or 2, characterized in that the mobile station (MS) sends the network a bit map containing a proposal made by the mobile station for the maximum capacity of the high-speed data channel.

12. A method according to claim ^characterized in that the mobile station (MS) indicates the sub-channels it wishes to use separately on each sub-channel.

13. A method according to claim 12, characterized in that the mobile station (MS) indicates on each sub-channel if it transmits on said sub-channel.

14. A method according to claim 12, c h a r a c t e r i z e d in that the mobile station (MS) indicates on each sub-channel if it does not transmit on said sub-channel.

15. A method according to claim ^characterized in that the mobile station (MS) informs the network of its ability to negotiate the transmis- sion capacities of an asymmetric connection.

16. A method according to claim 15, characterized in that the mobile station (MS) informs the network of its ability to negotiate the transmission capacities of an asymmetric connection by sending a classmark change message.