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How Data Transmission in UL in LTE?

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In UL, the UE has no dedicated resources to transmit directly when new data arrived in the buffer from higher layer. 
It requests resources to transmit them. 
It receives radio resources. 
It transmits them.

The scheduling request is sent on the Physical Uplink Control Channel (PUCCH). 

This channel carries radio signaling in uplink: 

  • Scheduling Request to grant resources in UL 
  • Radio measurement report from the UEs 
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Radio retransmission ack or nack 

The UE can know from the SIB how to use the PUCCH. 

The response, the UL grant, is sent on the PDCCH.

The Physical Uplink Share Channel (PUSCH) carries: 

  • User data 
  • User Signaling 
  • The resources are dynamically assigned in time and frequency. 
  • The PUSCH supports the H-ARQ.

When the UE transmits in UL, it transmits also UL reference signals. 

  • Data demodulation reference signal (DM-RS) 
  • Sent with each packet transmission in order to demodulate data 
  • Occupies center SC-FDMA symbol of the slot, only sent over bandwidth allocated for data transmission

Sounding reference signal (SRS) 

  • Used to sound uplink channel to support frequency selective scheduling 
  • SRS parameters are UE specific and configured semi-statically 
  • 1 symbol in subframe used for SRS 
  • Periodicity: {2, 5, 10, 20, 40, 80, 160, 320} ms 
  • Bandwidth: typically transmitted over the entire PUSCH
    bandwidth (does not include PUCCH region) 
  • SRS is not sent when there is a scheduling request (SR) or CQI to be sent on PUCCH (to avoid multicarrier transmission)
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