Joint 3GPP TSG-RAN WG1 & WG2 Meeting on LTE
`Athens, Greece
`27 - 31 March 2006
`
`Agenda item:
`Source:
`Title:
`Document for:
`
`3.7
`Nokia
`Functions of the Physical Layer
`Approval
`
`R2-060824
`
`Introduction
`1
`Although the details of the physical layer for LTE still have to be decided in RAN1, existing agreements around some
`basic principles already allow giving a high level description of the functions of the layer 1. Based on existing text in
`25.302 [2] and 44.004 [3], this contribution proposes such a high level description for inclusion in 25.813 [1], and is an
`update of an earlier contribution [4].
`
`New Functions compared to WCDMA
`2
`In E-UTRAN, because the physical layer is not based on FDD WCDMA, but on OFDMA in downlink and SC-FDMA
`in uplink, both modifications to existing functions and some new functions are required when compared to UTRAN.
`
`In E-UTRAN, the physical layer performs the following main functions:
`- FEC encoding/decoding, rate matching and interleaving/deinterleaving of transport channels: physical
`layer functions, which operate in the binary domain. The functions take binary information divided into Protocol
`Data Units, add an appropriate amount of redundancy according to the Physical Resource Unit size allocated for
`transmission of the Protocol Data Unit, and interleave the bits. In the receiver, the Forward error correction
`decoding, rate dematching and deinterleaving functions perform the inverse operation. Performance and
`complexity requirements for FEC may change due to the increased peak data rate.
`- Error detection on transport channels: error detection on transport channels is the physical layer function
`which allows the detection of transmission errors by means of a CRC.
`- Support for Hybrid ARQ: the physical layer decodes associated control signalling, performs soft combining of
`data channels and signals ACK/NACK.
`- Power weighting of physical resources: the physical layer weighs the power of different physical resources.
`This may include power weighing of physical channels for data, control and reference symbols differently, but
`also power weighting of resource blocks for interference coordination purposes.
`- Modulation and demodulation of physical channels: modulation is a physical layer function, which takes
`binary information of physical channels, performs QAM-constellation mapping, creates a time domain base band
`signal based on the multiple access method, adds a cyclic prefix and constructs a modulated Radio Frequency
`signal. In uplink, the multiple access method is Single Carrier Frequency Division Multiple Access (SC-FDMA).
`In downlink, the multiple access method is Orthogonal Frequency Division Multiple Access (OFDMA).
`- Frequency and time (bit, slot, frame) synchronisation
`- Measurements and indication to higher layers: measurements measures and monitors various L1 related
`resource parameters, which are needed by higher layers. These might include current utilisation of the radio
`resources (spectral efficiency on a per-user level as well as total efficiency), as well as interference power
`measurements for different frequency resource blocks. Measurements should be available in both uplink and
`downlink. Some measurements such as direct measures of the channel quality will not be available to upper
`layers.
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`- RF processing
`- Power control: power control is a physical layer function which adapts the uplink transmission power according
`to the average channel attenuation.
`- Handover execution: in E-UTRAN, there are no soft handovers.
`- Support for timing advance of uplink channels: the timing advance is a signal derived from the time
`synchronisation of the UL sequence and sent by the eNB to the UE which the UE uses to advance its timings of
`transmissions to the eNB so as to compensate for propagation delay and thus time align the transmissions from
`different UEs with the receiver window of the eNB. By avoiding the overlapping of uplink transmissions, timing
`advance allows time domain multiplexing in the uplink.
`- Physical layer mapping: the mapping allows for multiplexing different users in the time domain as well as in
`the frequency domain.
`- Multiplexing of physical channels: multiplexing of physical channels is the physical layer function, which
`allows time and/or frequency multiplexing of separate physical channels. Time multiplexing of physical
`channels may happen in OFDM symbol resolution, in sub-frame resolution or in frame resolution and frequency
`multiplexing of physical channels may happen in sub-carrier resolution or in resource block resolution. The
`physical channels to be multiplexed in downlink include at least a Synchronization Channel, the downlink
`reference symbols, a downlink shared Control Channel, a downlink Shared data Channel (carries Transport
`Blocks of any Transport Channel). The physical channels to be multiplexed in uplink include at least uplink
`reference symbols, a Random Access Channel, an uplink Shared Control Channel (carries L1 and/or L2 data-
`associated control information), and a Shared data Channel (carries Transport Blocks of any Transport Channel).
`- Link adaptation and adaptive transmission bandwidth (ATB): link adaptation is the physical layer function,
`which allows the modulation and/or channel coding rate changes for a radio link in the time and frequency
`dimensions for units of resource blocks. For multi-antenna transmission, an additional spatial dimension may be
`added as an extension to link adaptation. Adaptive Transmission Bandwidth (ATB) is the physical layer
`function, which allows changes of the modulated bandwidth inside the defined system bandwidth for a radio
`link, in defined units of time. ATB techniques are expected to improve the coverage of radio links. ATB
`techniques are further expected to provide multi-user scheduling and multiplexing gains.
`- Diversity and multi-stream transmission and reception: diversity and multi-stream transmission and
`reception are physical layer functions that utilize possible multiple antennas in transmitters and receivers to
`improve transmission reliability and capacity of the physical channels.
`
`Text Proposal for 25.813
`4
`Services and functions
`5.2.1
`The physical layer offers information transfer services to MAC and higher layers. The physical layer transport services
`are described by how and with what characteristics data are transferred over the radio interface. An adequate term for
`this is “Transport Channel”.
`
`NOTE:
`
`This should be clearly separated from the classification of what is transported, which relates to the
`concept of logical channels at MAC layer.
`
`The physical layer performs the following main functions:
`
`- FEC encoding/decoding, rate matching and interleaving/deinterleaving of transport channels;
`
`- Error detection on transport channels;
`
`- Support for Hybrid ARQ;
`
`- Power weighting of physical resource;
`
`- Modulation and demodulation of physical channels;
`
`- Frequency and time (bit, slot, frame) synchronisation;
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`- Measurements and indication to higher layers;
`
`- RF processing;
`
`- Power control;
`
`- Handover execution;
`
`- Support for timing advance of uplink channels;
`
`- Physical layer mapping;
`
`- Multiplexing of physical channels;
`
`- Link adaptation and adaptive transmission bandwidth (ATB);
`
`- Diversity and multi-stream transmission and reception.
`
`Conclusions
`5
`It is proposed to agree the text in section 4 and include it in TR 25.813 [1].
`
`References
`[1] 3GPP TS 25.813, Evolved Universal Terrestrial Radio Access (UTRA) and Universal Terrestrial Radio Access
`Network (UTRAN);Radio interface protocol aspects
`
`[2] 3GPP TS 25.302, Services provided by the Physical Layer
`
`[3] 3GPP TS 44.004, Layer 1; General requirements
`
`[4] R2-060047, Physical Layer Functions, Nokia
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