2.4.
EP 525 met de titel “Radio Communication System”, is verleend op 9 mei 2012 op een aanvraag van 15 oktober 2002, met een beroep op prioriteitsdata 19 oktober 2001 (GB 0125175) en 5 november 2001 (GB 0126421). EP 525 kent 15 conclusies die in de oorspronkelijke Engelse taal als volgt luiden:
1.A radio communication system having a communication channel for the transmission of data packets from a primary station (100) to a secondary station (110) the secondary station having receiving means for receiving a data packet (202) and acknowledgement means for transmitting a signal to the primary station to indicate the status of a received data packet, which signal is selected from a set of at least two available signal types (204,206) wherein the acknowledgement means is arranged to select the power level at which the signal is transmitted depending on its type and in dependence on an indication of the power level at which each type of signal is transmitted, the indication being signaled from the primary station to the secondary station.
2.A system as claimed in claim 1, characterized in that the available signal types include signals indicating positive and negative acknowledgements.
3.A system as claimed in claim 2, characterized in that the available signal types further include a revert signal indicating a request for retransmission of a packet received before the packet just received.
4.A system as claimed in claim 3, characterized in that the revert signal is identical to the negative acknowledgement signal but is transmitted at a higher power.
5.A primary station (100) for use in a radio communication system having a communication channel for the transmission of data packets from the primary station to a secondary station (110), wherein means are provided for transmitting a data packet to the secondary station and for receiving a signal from the secondary station to indicate the status of a received data packet (202), which signal is selected from a set of at least two available signal types and is transmitted with a power level selected depending on its type (204,206), and wherein means are provided for signaling to the secondary station an indication on how the power level at which the secondary station transmits each type of signal depends on the type of the signal.
6.A primary station as claimed in claim 5, characterized in that means are provided for determining the type of the received signal depending on its received power level.
7.A primary station as claimed in claim 5 or 6, characterized in that the indication comprises an instruction to the secondary station to transmit at least two types of signals at different powers.
8.A primary station as claimed in claim 5 or 6, characterized in that the indication informs the secondary station of the transmission power that it should use for at least one of the available signal types.
9.A primary station as claimed in claim 5, 6 or 8, characterized in that the indication informs the secondary station of a required power difference between two different types of signals.
10.A secondary station (110) for use in a radio communication system having a communication channel for the transmission of data packets from a primary station (100) to the secondary station, wherein receiving means are provided for receiving a data packet (202) from the primary station and acknowledgement means are provided for transmitting a signal to the primary station (204, 206) to indicate the status of a received data packet, which signal is selected from a set of at least two available signal types, wherein the acknowledgement means is arranged to select the power level at which the signal is transmitted depending on its type and in dependence on an indication of the power level at which each type of signal is transmitted, the indication being signaled from the primary station to the secondary station.
11.A secondary station as claimed in claim 10, characterized in that the signal types include signals indicating positive and negative acknowledgements and in that the acknowledgement means transmits negative acknowledgements at a higher power than positive acknowledgements.
12.A secondary station as claimed in claim 11, characterized in that the acknowledgement means only transmits negative acknowledgements at a higher power than positive acknowledgements if a time-averaged ratio of positive acknowledgements to negative acknowledgements is greater than a predetermined value.
13.A secondary station as claimed in claim 10 or 11, characterized in that the available signal types include signals conveying information relating to prevailing radio conditions other that the status of the received data packet.
14.A secondary station as claimed in claim 10, characterized in that the indication informs of an offset value of the power level at which the signal is transmitted.
15.A method of operating a radio communication system having a communication channel for the transmission of data packets from a primary station (100) to a secondary station (110) the method comprising the secondary station receiving a data packet (202) and transmitting an acknowledgement signal (204,206) to the primary station to indicate the status of a received data packet, which signal is selected from a set of at least two available signal types, the method comprising selecting the power level at which the signal is transmitted depending on its type and in dependence on an indication of the power level at which each type of signal is transmitted, the indication being signaled from the primary station to the secondary station.
2.5.
In de onbestreden Nederlandse vertaling luiden deze conclusies:
1. Radiocommunicatiesysteem met een communicatiekanaal voor de overdracht van gegevenspakketten van een primair station (100) naar een secundair station (110), waarbij het secundaire station ontvangmiddelen heeft voor het ontvangen van een gegevenspakket (202) en bevestigingsmiddelen voor het overdragen van een signaal naar het primaire station om de status van een ontvangen gegevenspakket aan te duiden, waarbij het signaal is gekozen uit een reeks van ten minste twee beschikbare signaaltypes (204, 206), waarbij het bevestigingsmiddel is ingericht om het vermogensniveau te kiezen waarbij het signaal wordt overgedragen afhankelijk van zijn type en afhankelijk van een aanduiding van het vermogensniveau waarbij elk type signaal wordt overgedragen, waarbij de aanduiding uit het primaire station naar het secundaire station wordt overgeseind.
2. Systeem volgens conclusie 1, met het kenmerk, dat de beschikbare signaaltypes signalen omvatten die positieve en negatieve bevestigingen omvatten.
3. Systeem volgens conclusie 2, met het kenmerk, dat de beschikbare signaaltypes verder een teruggekeerd signaal omvatten dat een vraag aanduidt voor heroverdracht van een pakket ontvangen vóór het pakket dat net werd ontvangen.
4. Systeem volgens conclusie 3, met het kenmerk, dat het teruggekeerde signaal identiek is aan het negatieve bevestigingssignaal, maar bij een hoger vermogen wordt overgedragen.
5. Primair station (100) voor gebruik in een radiocommunicatiesysteem met een communicatiekanaal voor de overdracht van gegevenspakketten uit het primaire station naar een secundair station (110), waarbij middelen worden voorzien voor het overdragen van een gegevenspakket naar het secundaire station en voor het ontvangen van een signaal
uit het secundaire station om de status van een ontvangen gegevenspakket (202) aan te duiden, waarbij het signaal is gekozen uit een reeks van ten minste twee beschikbare signaaltypes en wordt overgedragen met een vermogensniveau gekozen afhankelijk van zijn type (204, 206), en waarbij middelen worden voorzien voor het overseinen naar het secundaire station van een aanduiding over hoe het vermogensniveau waarbij het secundaire station elk type signaal overdraagt, van het type van het signaal afhangt.
6. Primair station volgens conclusie 5, met het kenmerk, dat middelen worden voorzien voor het bepalen van het type van het ontvangen signaal afhankelijk van zijn ontvangen vermogensniveau.
7. Primair station volgens conclusie 5 of 6, met het kenmerk, dat de aanduiding een instructie voor het secundaire station omvat voor het overdragen van ten minste twee types signalen bij verschillende vermogens.
8. Primair station volgens conclusie 5 of 6, met het kenmerk, dat de aanduiding het secundaire station op de hoogte stelt van het overdrachtsvermogen dat het zou moeten gebruiken voor ten minste één van de beschikbare signaaltypes.
9. Primair station volgens conclusie 5, 6 of 8, met het kenmerk, dat de aanduiding het secundaire station op de hoogte stelt van een vereist vermogensverschil tussen twee verschillende types signalen.
10. Secundair station (110) voor gebruik in een radiocommunicatiesysteem met een communicatiekanaal voor de overdracht van gegevenspakketten uit een primair station (100) naar het secundaire station, waarbij ontvangstmiddelen worden voorzien voor het ontvangen van een gegevenspakket (202) uit het primaire station en bevestigingsmiddelen worden voorzien voor het overdragen van een signaal naar het primaire station (204, 206) om de status van een ontvangen gegevenspakket aan te duiden, waarbij het signaal is gekozen uit een reeks van ten minste twee beschikbare signaaltypes, waarbij het bevestigingsmiddel wordt ingericht voor het kiezen van het vermogensniveau waarbij het signaal wordt overgedragen afhankelijk van zijn type en afhankelijk van een aanduiding van het vermogensniveau waarbij elk type signaal wordt overgedragen, waarbij de aanduiding van het primaire station naar het secundaire station wordt overgeseind.
11. Secundair station volgens conclusie 10, met het kenmerk, dat de signaaltypes signalen omvatten die positieve en negatieve bevestigingen aanduiden en dat het bevestigingsmiddel negatieve bevestigingen bij een hoger vermogen dan positieve bevestigingen overdraagt.
12. Secundair station volgens conclusie 11, met het kenmerk, dat het bevestigingsmiddel enkel negatieve bevestigingen bij een hoger vermogen dan positieve bevestigingen overdraagt, indien een tijdgemiddelde verhouding van positieve bevestigingen tot negatieve bevestigingen groter is dan een vooraf bepaalde waarde.
13. Secundair station volgens conclusie 10 of 11, met het kenmerk, dat de beschikbare signaaltypes transportinformatie met betrekking tot geldende radiovoorwaarden verschillend van de status van het ontvangen gegevenspakket omvatten.
14. Secundair station volgens conclusie 10, met het kenmerk, dat de aanduiding op de hoogte stelt van een offsetwaarde van het vermogensniveau waarbij het signaal wordt overgedragen.
15. Werkwijze voor het laten werken van een radiocommunicatiesysteem met een communicatiekanaal voor de overdracht van gegevenspakketten uit een primair station (100) naar een secundair station (110), waarbij de werkwijze omvat dat het secundaire station een gegevenspakket (202) ontvangt en een bevestigings-signaal (204, 206) naar het primaire station overdraagt om de status van een ontvangen gegevenspakket aan te duiden, waarbij het signaal is gekozen uit een reeks van ten minste twee beschikbare signaaltypes, waarbij de werkwijze het kiezen omvat van het vermogensniveau waarbij het signaal wordt overgedragen afhankelijk van zijn type en afhankelijk van een aanduiding van het vermogensniveau waarbij elk type signaal wordt overgedragen, waarbij de aanduiding van het primaire station naar het secundaire station wordt overgeseind.
2.6.
In de beschrijving van EP 525 is onder meer opgenomen:
[0001] The present invention relates to a radio communication system and further relates to primary and secondary stations for use in such a system and to a method of operating such a system. While the present specification describes a system with particular reference to the Universal Mobile Telecommunication System (UMTS), it is to be understood that such techniques are equally applicable to use in other mobile radio systems.
[0002] There is a growing demand in the mobile communication area for a system having the ability to download large blocks of data to a Mobile Station (MS) on demand at a reasonable rate. Such data could for example be web pages from the Internet, possibly including video clips or similar. Typically a particular MS will only require such data intermittently, so fixed bandwidth dedicated links are not appropriate. To meet this requirement in UMTS, a High-Speed Downlink Packet Access (HSDPA) scheme is being developed which may facilitate transfer of packet data to a mobile station at up to 4Mbps.
[0003] A conventional component of a packet data transmission system is an ARQ (Automatic Repeat reQuest) process, for handling data packets received in error. For example, consider downlink packet transmission from a Base Station (BS) to a Mobile Station (MS) in HSDPA. When the MS receives a data packet it determines whether the packet has been corrupted, for example using Cyclic Redundancy Check (CRC) information. It then transmits a codeword to the BS, with a first codeword used as an acknowledgement (ACK), to indicate that the packet was successfully received, and a second codeword used as a negative acknowledgement (NACK), to indicate that the packet was received but corrupted. Since packet transmission is typically intermittent, discontinuous transmission (DTX) is normally employed, so that nothing is transmitted by the MS unless a data packet has been received.
[0004] A problem with such an ARQ scheme is that the consequences of errors in the ACK and NACK are significantly different. Normally the BS would re-transmit a packet if a NACK were received. If the BS receives a NACK when a ACK was sent, then the packet is re-transmitted anyway, which only wastes a little system resource. If a NACK is sent, but received as a ACK, then no re-transmission is made. Without special physical layer mechanisms, this situation can only be recovered from by using higher layer processes, which adds delay and is a significant waste of system resources. Hence, the cost of an error in a NACK is much more serious than the cost of an error in a ACK.
[0005] In order to optimise system performance, it is desirable to control the relative probabilities of errors in decoding ACKs and NACKs. In one UMTS embodiment this is done by setting different detection thresholds at the BS, which requires the MS to transmit the ACK/NACK codeword with a specific power level (e.g. relative to uplink pilot power). This power level and the detection threshold can therefore be chosen to balance costs of ACK/NACK errors, interference generated by the MS, and battery power used by the MS. With DTX, the situation is a little more complex. However, the BS, as the source of the packet, is aware of when a ACK/NACK should be sent by the MS and it should therefore not normally be necessary to specifically detect the DTX state.
[0006] In our co-pending German patent application DE10132577 a physical layer mechanism for recovering from the case where the BS misinterprets a NACK as an ACK is disclosed. This mechanism makes use of an additional codeword, REVERT, which informs the BS that the MS has received a transmission of a new packet when it was expecting retransmission of the previous packet. In a variation on this scheme two REVERT codewords are used, to provide in addition a NACK or an ACK in respect of the new packet.
[0007] US 4888767 discloses a radio communication system having a communication channel for the transmission of data packets from a primary station to a secondary station, the secondary station having receiving means for receiving a data packet and acknowledgement means for transmitting a signal to the primary station to indicate the status of a received data packet. In more details, the secondary station transmits a repeat request signal to indicate that the status of the data packet is erroneous, and does not transmit a signal if the status of the data packet is correct.
[0008] US 5517507 discloses subject matter similar to US 4888767. In more details, a NACK/ACK signal is transmitted, a NACK signal being represented by an energy burst and an ACK signal being no burst (which is equivalent, according to the examiner, to the transmission of a signal having a power level of zero).
[0009] An object of the present invention is to improve the efficiency of a packet data transmission system.
[0010] According to a first aspect of the present invention there is provided a radio communication system having a communication channel for the transmission of data packets from a primary station to a secondary station, the secondary station having receiving means for receiving a data packet and acknowledgement means for transmitting a signal to the primary station to indicate the status of a received data packet, which signal is selected from a set of at least two available signal types, wherein the acknowledgement means is arranged to select the power level at which the signal is transmitted depending on its type.
[0011] By transmitting different acknowledgement signals at different power levels, the probability of the primary station correctly interpreting signals of different types can be manipulated to improve total system throughput and capacity. In one embodiment negative acknowledgements are transmitted at a higher power level than positive acknowledgements to increase the probability of the primary station retransmitting a data packet when necessary. In another embodiment an additional revert signal type is provided, which requests the primary station to retransmit a data packet initially transmitted prior to the current data packet and which was not correctly received. The revert signal may be identical to the negative acknowledgement signal but transmitted at a higher power level.
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[0023] It is likely for most applications that DTX would be applied for most of the time, given the typically intermittent nature of packet data transmission. In addition, for a well configured system, NACKs 204 should be sent significantly less often than ACKs 206. Hence, in a system made in accordance with the present invention a NACK 204 is transmitted at a higher power level than an ACK 206. This power offset is advantageous because it reduces the error probability for the NACK 204 without increasing the power transmitted for the ACK 206. It is particularly advantageous if the probability of a MS 110 missing a packet is very small, so there is no need to consider optimum setting of BS detection thresholds to differentiate NACK from DTX. Hence, any given error performance targets could be achieved with minimum average power transmitted by the-MS 110.
[0024] It will be recognised that if a MS 110 is transmitting more NACKs 204 than ACKs 206, this proposed strategy would result in an increase in average uplink interference rather than the desired decrease. Therefore, in one embodiment of the present invention, the MS 110 is forbidden from applying the power offset unless it has previously positively acknowledged more than a certain proportion of packets (e.g. 50%). This prevents the power offset from causing an undue increase in uplink interference in poor downlink channel conditions.
[0025] In another embodiment of the present invention, the relative power levels of ACKs 206 and NACKs 204 are modified depending on the proportion of ACKs and NACKs sent. For example, this adaptation could be controlled by a time-weighted average of the proportion of ACKs 206 sent. The detection threshold at the BS 100 could adapted in a similar way based on the proportion of ACKs 206 received. It is apparent that such processes would converge, even in the presence of errors.
[0026] In another embodiment of the present invention, instead of being predetermined the ACK/NACK power offset (or maximum offset) could be signalled by the BS 100 depending on the type of service being conveyed to the MS 110 via the data packets 202. For example, in a real-time streaming service with strict timing constraints, a packet which is lost due to a wrongly-detected NACK 204 may simply be ignored by the application if there were not enough time even for a physical layer retransmission. However, for a data service where correct receipt of packets was essential, an ACK/NACK power offset could be signalled. The offset might also be useful in streaming services with slightly less strict timing requirements, where there was insufficient time for a higher-layer retransmission, but a NACK power offset would increase the chance of an erroneous packet being rectified by means of fast physical layer retransmission. It would therefore be beneficial to allow a different offset value to be signalled for each downlink transport channel.
[0027] This approach can be further developed by assigning different offset values to the ACK/NACKs for different packets of the same transport channel. For example, in an MPEG stream it is very important to receive the I-frames correctly to avoid errors in subsequent frames. An ACK/NACK power offset could therefore be applied for acknowledgement of packets containing I-frame data while a smaller (or zero) offset is applied for acknowledgement of other packets. Some special signalling could be required, such as a physical layer tag or a particular sequence number on the packets 202, to indicate which packets contained the I-frame data.
[0028] In a further development of this approach, other information, such as channel quality, could be signalled by the use of different codewords in the data field reserved for ACK/NACK messages, as disclosed in our co-pending International patent application WO 02067618 (applicant's reference PHGB 010069). In general it is likely that there are different costs of errors in detecting the different information possibilities. Therefore, there could be different power levels applied to the transmission of different subsets of codewords. Furthermore, this approach could be combined with design of the codeword distances to reach specified performance targets. As an example, if NACK is 0000, then ACK might be 1110, and sending ACK together with an indication of high channel quality might be 1111.
[0029] In one preferred embodiment, particularly suitable for UMTS HSDPA, the ACK/NACK power offset used by the MS 110, as well as the ACK power level would be determined by higher layer signalling from the network. Alternatively, the offset could be signalled using a single information bit, signifying "no offset" (i.e. equal transmit power for ACK 206 and NACK 204) or "use offset", signifying the use of a pre-determined value of power offset. More signalling bits could be used to indicate a larger range of values of offset.
[0030] The BS 100 (knowing the power levels used by the MS 110) would use a detection threshold adjusted to optimise system performance (although the BS 100 would not necessarily have to know the power levels used by the MS 110, as a "neutral" threshold could be set based on the received uplink pilot information). An optimised threshold could be set by the Radio Network Controller (RNC) or other means.
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[0040] In the second embodiment, DTX and NACK sent with same (zero) - power, while REVERT sent as a different codeword to ACK but with the same power. (…)
[0048] In general, the power levels at which the ACK/NACK and/or REVERT commands are transmitted may be adjusted in order to achieve a required level of reliability. These power levels could be controlled by messages sent from the BS 100 to the MS 110. These could specify the power level relative to the pilot bits on the uplink dedicated control channel, or relative to the current power level for the channel quality metric. In the case of the dedicated control channels of one MS 110 being in soft handover with more than one BS 100 the power of the uplink dedicated control channel is not likely to be optimal for all the BSs 100 involved. Therefore, a different power level, preferably higher, may be used for sending the ACK/NACK and/or REVERT commands. This power difference could be fixed, or determined by a message from a BS 100. When the transmission of ACK/NACK and/or REVERT is directed to a particular BS 100, the power level may be further modified to take into account the quality of the radio channel for that transmission. For example, if the best radio link from the active set is being used, the power level may be lower than otherwise.
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