LTE

1. Long Term Evolution
LTE
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2. Physical protocol layers overview
Layer 2 protocol architecture
Mobility Management
Scheduling and Rate Control
ARQ
HARQ
Table of contents
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3. Physical protocol layers overview
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Figure 1: LTE protocol layers

4. Layer 2 protocol architecture
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Segm.
ARQ
Multiplexing UE1
Segm.
ARQ
...
HARQ
Multiplexing UEn
HARQ
BCCH PCCH
Scheduling / Priority Handling
Logical Channels
Transport Channels
MAC
RLC
Segm.
ARQ
Segm.
ARQ
PDCP
ROHC ROHC ROHC ROHC
Radio Bearers
Security Security Security Security
...
Figure 4: Layer 2 structure at the eNode B

5. Mobility Management
• Mobility control in RRC_IDLE is UE controlled
• Mobility in RRC_connected is controlled by E-
UTRAN (handover)
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Figure 1: Handover within LTE

6. Scheduling
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Figure 2: Dynamic scheduling in DL
Figure 3: Semi-persistant and dynamic scheduling in DL

7. ARQ
• Re-transmits RLC PDUs; retransmissions are
based on RLC status reports.
• Polling of RLC status report is used when needed
by RLC.
• Status reports are triggered by upper layers.
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8. HARQ
• N-process Stop and Wait
• Transmits and retransmits transport blocks
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Downlink Uplink
Asynchronous adaptive HARQ Synchronous HARQ
Uplink ACK/NACK in response to
downlink (re)transmissions sent on
PUCCH/PUSCH
Maximum number of retransmissions
configured per UE and not per radio
bearer.
PDCCH signals HARQ process number Downlink ACK/NACK on PHICH
Retransmissions are always scheduled
through PDCCH
Uplink HARQ in Table 2
TABLE 1: HARQ PROCESS AT E-UTRAN

9. HARQ
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TABLE 2: UL HARQ OPERATION
HARQ Feedback seen
By the UE
PDCCH seen by the UE UE Behaviour
ACK or NACK New Transmission New transmission
according to PDCCH
ACK or NACK Retransmission Retransmission according
to PDCCH (adaptive
retransmission)
ACK None No (re)transmission, keep
data in HARQ buffer and a
PDCCH is required to
resume retransmissions
NACK None Non-adaptive
retransmission

10. HARQ
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Figure 3: DL scheduling with HARQ

11. Thank you
Questions?
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