3GPP TSG RAN WG1 Meeting #52
`Shenzhen, China, 31 March – 4 April, 2008
`
`R1-081456
`
`Agenda item:
`Source:
`Title:
`
`Document for:
`
`6.1.4
`Nokia Siemens Networks, Nokia
`DTX detection in case of simultaneous transmission of SR and
`ACK/NACK
`Discussion and Decision
`
`1 Introduction
`In the Sorrento meeting it was agreed that if ACK/NACK and SR need to be transmitted simultaneously, ACK/NACK
`is transmitted using SR resource. In this contribution our focus is DTX detection issue related to simultaneous
`transmission of SR and ACK/NACK.
`DTX situation relates to the failure of DL resource allocation grant. When DL resource allocation fails the
`ACK/NACK(s) associated with the PDCCH is missing from the given UL sub-frame (this is DTX from ACK/NACK
`point of view) because the UE has missed the DL allocation and therefore has no reason to include an ACK/NACK.
`However, the Node B cannot know the ACK/NACK is not present and may therefore interpret the reception incorrectly.
`DL ACK/NACK DTX detector can be used to solve the problem, i.e., to identify whether the DL ACK/NACK is
`present or not. However, when ACK/NACK DTX detector fails then it is possible that two types of errors occur:
`
` Misdetection, DTX ->ACK/NACK: DL resource allocation grant fails but eNode-B cannot detect it
`
`
`
`False alarm, ACK/NACK->DTX: eNode-B considers that the DL allocation grant has failed although it has been
`correctly received by the UE
`
`In the context of this study, DTX corresponds to signalling of SR instead of combination ACK/NACK+SR. DTX to
`ACK means the error, when eNB detects ACK even though ACK was not sent, but only scheduling request. The
`combination of DL scheduling information miss detection and DTX to ACK error (for DL-SCH) has an impact on
`higher layer protocols, i.e. it leads to a higher layer error. Interpreting SR as ACK is a severe error situation from DL
`point of view since a transmission is erroneously assumed to be OK and higher layers will have to detect this and
`provide means to recover (significantly slower recovery than L1 recovery and much more overhead). Such error cases
`should only happen with an extremely low probability.
`
`2 DTX detection methods
`In this chapter two different methods are considered in order to solve the DTX to ACK problem in the case when SR is
`transmitted simultaneously with ACK/NACK:
`
` The SR (+DTX) is transmitted by using the same constellation point than NACK´
`
` The ACK/NACK constellations are arranged in such a way that SR+DTX and SR+ACK/NACK can be
`separated in the complex domain.
`
`We think that DTX to NACK detection is not needed in the case of simultaneous transmission of SR and ACK/NACK,
`so we think that method 1 below should be used i.e. Euclidean distance of SR and ACK should be maximized.
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`2.1 Method 1: Positive SR transmitted as NACK
`If Method 1 is used then SR (+DTX) can be transmitted by using the same constellation point than NACK. The goal is
`to get maximum separation between ACK and SR signal. The agreed constellation mapping of 1-bit ACK/NACK is
`presented in the figure 1 below. In this case we propose that SR uses the same constellation point than NACK.
`
`ACK
`
`1
`
`1
`
`0
`
`0
`
`-1
`
`-1
`
`NACK
`
`Figure 1 Mapping of 1 bit ACK/NACK constellations according to Method 1.
`
`In this case mapping of the constellation points is made according to Table 1.
`
`Table 1 Constellation mapping for 1 bit ACK/NACK according to method 1
`I
`Q
`-1/ √2
`-1/ √2
`1/ √2
`1/ √2
`-1/ √2
`-1/ √2
`
`NACK
`ACK
`SR
`
`Constellation arrangement in the case of 2-bit ACK/NACK is depicted in Figure 2.
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`NACK ACK
`
`NACK NACK
`SR
`
`-1
`
`1
`
`0
`
`0
`
`-1
`
`ACK ACK
`
`1
`
`NACK NACK
`NACK ACK
`ACK NACK
`ACK ACK
`SR
`
`ACK NACK
`
`Figure 2 Mapping of 2 bits ACK/NACK constellations according to Method 1
`
`In 2-bit case mapping of constellation points is made according to Table 2.
`
`Table 2 mapping for 2 bit ACK/NACK according to method 1
`
`NACK NACK
`NACK ACK
`ACK NACK
`ACK ACK
`SR
`
`I
`
`-1/ √2
`-1/ √2
`1/ √2
`1/ √2
`-1/ √2
`
`Q
`
`-1/ √2
`1/ √2
`-1/ √2
`1/ √2
`-1/ √2
`
`When UE sends only SR (+DTX), it uses constellation point (-1/ √2, -1/ √2) reserved for NACK (1-bit case) or
`NACK/NACK (2-bit case).
`
`2.2 Method 2: SR and ACK/NACK separated in complex domain
`Constellation mapping for ACK/NACK and SR can also be made so that SR signal and ACK/NACK signal are
`separated in the complex domain. Furthermore, in the case of 2-bit ACK/NACK we propose to apply constellation re-
`arrangement between two slots. This will provide maximum separation between ACK(s) and SR signals. Figure 3 and
`Figure 4 show the constellation mapping in the case of 1-bit and 2-bit ACK/NACK signaling.
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`1
`
`0
`
`0
`
`-1
`
`ACK
`
`ACK
`NACK
`SR
`
`1
`
`SR
`
`-1
`
`NACK
`
`Figure 3 Mapping of 1 bit ACK/NACK constellation
`
`The constellation points are defined in Table 3.
`
`Table 3 mapping for 1 bit ACK/NACK according to method 2
`I
`Q
`-1/ √2
`-1/ √2
`1/ √2
`1/ √2
`1/ √2
`-1/ √2
`
`NACK
`ACK
`SR
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`SR
`
`-1
`
`NACK ACK
`
`NACK NACK
`
`1
`
`0
`
`0
`
`-1
`
`ACK ACK
`
`NACK ACK
`
`1
`
`-1
`
`ACK NACK
`
`NACK NACK
`
`1
`
`0
`
`0
`
`SR
`
`-1
`
`ACK ACK
`
`1
`
`NACK NACK
`NACK ACK
`ACK NACK
`ACK ACK
`SR
`
`ACK NACK
`
`Figure 4 Constellation re-arrangement between two slots in case of 2-bit ACK/NACK
`
`The constellation points are defined in Table 4.
`
`Table 4 mapping for 2 bit ACK/NACK according to method 2
`
`NACK NACK
`NACK ACK
`ACK NACK
`ACK ACK
`SR
`
`SLOT #1
`
`SLOT #2
`
`I
`-1/ √2
`-1/ √2
`1/ √2
`1/ √2
`-1
`
`Q
`-1/ √2
`1/ √2
`-1/ √2
`1/ √2
`0
`
`I
`-1/ √2
`-1/ √2
`1/ √2
`1/ √2
`0
`
`Q
`-1/ √2
`1/ √2
`-1/ √2
`1/ √2
`-1
`
`3 Simulations
`In this chapter we evaluate the performance of ACK/NACK signalling against the error requirements given in Table 1.
`
`Table 5 Approved error requirements for downlink ACK/NACK signalling
`Event
`Target quality
`ACK miss detection (for DL-SCH)
`(1e-2)
`DTX to ACK error (for DL-SCH)
`(1e-2)
`NACK to ACK error (for DL-SCH)
`(1e-4)
`
`Simulations assume that ACK/NACK transmission is made using the SR resource. In the simulations DTX to ACK
`error is considered in the case where eNB detects ACK even though ACK was not sent, but only the scheduling request.
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`IPR2017-1581
`Huawei v. NSN
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`NSN 2002 Page 5
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`Table 6 summarizes the main parameters used in the link simulations. The results have been obtained assuming
`practical receiver and realistic channel estimation algorithms. Slot-based frequency hopping and TU channel with UE
`speed of 3 km/h were assumed.
`
`Table 6 Simulation parameters
`Number of information bits
`ACK/NACK: 2 bit
`Channel
`TU (3 km/h)
`Number of RS blocks
`3
`Receiver
`MRC
`Modulation
`QPSK
`System bandwidth
`5 MHz
`
`Two different threshold values are used in the simulations The first threshold (Threshold_1) is common for both of the
`methods with equal value and it is targeting to detect DTX. The operation is such that eNB detects the DTX if the signal
`power is below Threshold_1. The second threshold (Threshold_2) is targeting to optimize NACK to ACK error rate
`requirement. The operation is such that eNB detects ACK only if the ACK decision variable is Threshold_2 times
`higher than NACK decision variable. Note that in Method 1, the SR to ACK (DTX to ACK) error rate requirement is
`guaranteed by Threshold_2 because the NACK to ACK has lower error rate requirement.
`
`1
`
`0.1
`
`0.01
`
`0.001
`
`0.0001
`
`-16
`
`-15
`
`-14
`
`-13
`
`-12
`
`-11
`
`-10
`
`-9
`
`-8
`SNR [dB]
`
`-7
`
`-6
`
`-5
`
`-4
`
`-3
`
`-2
`
`-1
`
`0
`
`

`

`4 Summary
`In this contribution we have analyzed two methods to solve the DTX to ACK problem in the case when ACK/NACK is
`transmitted with SR:
`
`1. The SR (+DTX) is transmitted by using the same constellation point than NACK
`
`2. The ACK/NACK constellations are arranged in such a way that SR (+DTX) signal and SR+ACK/NACK can
`be separated in the complex domain.
`
`Results show that the SR to DTX problem can be solved with both methods. The performance of method 2 is about 1
`dB worse than method 1. The drawback of method 1 is that DTX to NACK can not be detected at the eNB. We think
`DTX to NACK detection is not necessary in this special case so we propose that method 1 is selected.
`
`5 References
`[1] R1-080932, “Simultaneous transmission of ACK/NACK and SR”, Nokia Siemens Networks, Nokia
`
`IPR2017-1581
`Huawei v. NSN
`
`NSN 2002 Page 7
`
`