3GPP TSG-RAN WG1 Rel-6 Ah Hoc
`Cannes, France
`June 21 – 24, 2004
`
`
`Agenda item: 5 FDD Enhanced Uplink – RAN1/RAN2 Joint Session
`
` R1-04-0746
`(R1-04-0532)
`
`Source:
`
`Nokia
`
`Title:
`
` Requirements for UL Signalling
`
`Document for: Discussion
`
`1
`
`Introduction
`
`RAN plenary meeting #23 in March 2004 concluded the E-DCH Study Item and approved the SI TR [1] as well as
`initiated a FDD Enhanced Uplink Work Item as proposed in [2]. This document discusses different possibilities on how
`the uplink signalling could be designed to meet the needs of the features under specification.
`
`2
`
`Discussion
`
`The WI scope is as recommended in the SI TR [1]. Node B controlled scheduling, hybrid ARQ, and shorter TTI are
`parts of the work item. Adoption of Node B controlled scheduling, hybrid ARQ or both will set new requirements to
`uplink signalling. Additionally, adoption of a shorter (than 10 ms) TTI can be considered as such being a new
`requirement to uplink physical layer structure which has a direct impact on how the signalling can be introduced in the
`physical layer.
`
`The requirements for the uplink signalling agreed during the study item are captured in 7.5.2.1 of the SI TR [1]:
`
`----- Start of a quotation from [1] -----
`
`There are some requirements for the physical channel structure for L1 signalling on uplink:
`
`- The L1 signalling in uplink should be independent from HS-DSCH operation: UE should not be required to
`support HS-DSCH operation at the same time with E-DCH in uplink, but it should be possible to have E-DCH in
`uplink and HS-DSCH in downlink at the same time.
`
`- Delays should be kept low.
`
`- Signalling should be possible also when the UE's DCH is in SHO. The support of E-DCH in SHO is FFS.
`
`- The effect of PAR needs to be taken into consideration when designing signalling channel for the uplink.
`
`- The relative power offsets between various uplink channels needs to be set appropriately so as to achieve
`reliable signalling while at the same time optimising peak and average power requirements at the UE.
`
`- Signalling reliability should be balanced with minimizing overhead.
`
`- Signalling channel can be sent time aligned or not time-aligned with the enhanced uplink DCH. The effect of
`time aligned or not time aligned control channel on Node-B decoding time, sector throughputs etc. should be
`considered.
`
`----- End of a quotation from [1] -----
`
`2.1
`
`Node B Controlled Scheduling
`
`Assuming that the Node B controlled scheduling requires new dedicated uplink signalling, the design of the uplink
`channel structures should enable conveying required scheduling related information with a sufficient reliability and
`frequency and with sufficiently low latency. (With some scheduling approaches the uplink scheduling signalling could
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`be eliminated completely, see e.g. [4]) Introducing new signalling brings also certain penalties, and thus the chosen
`uplink physical layer design should
`
`- Minimize the instantaneous Tx power required for the signalling to minimize the impact to the uplink coverage
`
`- Minimize the average Tx power required for the signalling to minimize the impact to the uplink capacity
`
`Parameters that are to be considered with the above points are at least:
`
`- How many (uncoded) bits per uplink message needs to be transmitted (size of a single message)
`
`- How reliably the message needs to be transmitted (affects the ECR and required power)
`
`- How long signalling latency can be accepted (affects the instantaneous power requirement)
`
`- How often the message needs to be transmitted (affects the average power requirement)
`
`Thus the signalling penalty would be minimized, if the
`
`-
`
`Size of the (uncoded) uplink scheduling message transmitted in the uplink would be as small as possible
`
`- The uplink scheduling message would be transmitted as seldom as possible (e.g. only when needed)
`
`- The uplink scheduling message would be relatively error-tolerant (omit the need for CRC, reduce the required
`amount of redundancy and/or transmitted power)
`
`- The coded uplink scheduling message bits would be spread over the longest sensible time period (Reduces the
`peak power requirement and thus increases the coverage)
`
`2.2
`
`Hybrid ARQ
`
`----- Start of a quotation from [1] -----
`
`The necessary information needed by the Node B to operate the hybrid ARQ mechanism can be grouped into two
`different categories: information required prior to soft combining/decoding (outband signaling), and information
`required after successful decoding (inband signaling). Depending on the scheme considered, parts of the information
`might either be explicitly signaled or implicitly deduced, e.g., from CFN or SFN.
`
`The information required prior to soft combining consists of:
`
`- Hybrid ARQ process number.
`
`- New data indicator. The new data indicator is used to control when the soft combining buffer should be cleared
`in the same way as for the HS-DSCH.
`
`- Redundancy version. If multiple redundancy versions are supported, the redundancy version needs to be known
`to the Node B. The potential gains with explicit support of multiple redundancy versions should be carefully
`weighted against the increase in overhead due to the required signaling. Note that, unlike the HS-DSCH, the
`number of users simultaneously transmitting data in the uplink using hybrid ARQ may be significant.
`
`- Rate matching parameters (number of physical channel bits, transport block size). This information is required
`for successful decoding. In R99/4/5, there is a one-to-one mapping between the number of physical channel bits
`and the transport block size, given by the TFCI and attributes set by higher layer signaling. This assumption
`does not hold for hybrid ARQ schemes if the number of available channel bits varies between (re)transmissions,
`e.g., due to multiplexing with other transport channels. Hence, individual knowledge of these two quantities is
`required in the Node B.
`
`The information required after successful decoding can be sent as a MAC header. The content is similar to the MAC-hs
`header, e.g., information for reordering, de-multiplexing of MAC-d PDUs, etc.
`
`----- End of a quotation from [1] -----
`
`The uplink physical layer design is affected by the information required to be signalled prior to decoding (i.e. the
`HARQ outband information). The physical layer should enable conveying the required HARQ outband information
`with a sufficient reliability and with sufficiently low latency. The parameters that are to be optimized are at least
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`- How many (uncoded) outband information bits per data packet needs to be transmitted
`
`- How the sufficient reliability level is reached (e.g. CRC, channel coding, Tx Power)
`
`- How long signalling latency can be accepted (affects the instantaneous power requirement and thus the
`coverage)
`
`2.3
`
`Shorter TTI
`
`If a new, shorter TTI is introduced for data transmission, at least the HARQ outband signalling frequency has to be
`increased to meet the increased TTI frequency. Additionally signalling a new E-TFCI may be required. It is probably
`safe to assume that regardless of the TTI length, the same signalling needs to be transmitted in a TTI, thus with a shorter
`TTI more power is required to transmit the same signalling with a same reliability than with the existing TTI.
`
`Thus introducing a shorter TTI will make the uplink physical layer design more challenging, e.g. in terms of signalling
`coverage, number of bits that can feasibly be transmitted and penalty in the capacity.
`
`3
`
`Possible Uplink Channel Structures
`
`The general approaches for the coding, multiplexing and mapping of the uplink signalling are captured in 7.5.2.2 of the
`SI TR [1]:
`
`- Mapping on (E-)DPDCH
`
`- Mapping on DPCCH
`
`- Mapping on E-DPCCH
`
`These approaches should be reviewed against the above mentioned requirements before making the final decisions.
`
`4
`
`Conclusions
`
`In order to maximize the coverage of the FDD Enhanced Uplink, the required instantaneous transmit power for the new
`uplink signalling should be minimized. In order to minimize the capacity penalty from the new signalling and thus
`maximize the capacity benefits of the features, the long term average power of the uplink signalling should also be
`minimized.
`
`- The instantaneous transmit power of the signalling is minimized, when the number of transmitted information
`bits is minimized, the energy of the bits is spread over as long a time period as possible and the reliability
`requirements for the signalled information can be made loose.
`
`-
`
`In addition to the above list, the long term average power of the uplink signalling is minimized when the
`frequency of the signalling is kept as low as possible.
`
`Thus when making the FDD Enhanced Uplink design choices the above points should be kept in mind. It is worth
`noting that introducing a shorter TTI length would increase both the instantaneous and average required uplink
`signalling power.
`
`References
`
`[1] TR25.896, Feasibility Study for Enhanced Uplink for UTRA FDD, v6.0.0, March 2004
`
`[2] RP-040081, Proposed Work Item on FDD Enhanced Uplink, Ericsson
`
`[3] R1-030670, Impact of DL Support Channels on E-DPDCH, Qualcomm
`
`[4] R1-040535, Signalling aspects of the rate scheduling, Nokia
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