Licensed Assisted Access

RFmx Waveform Creator 19.1 Help

Edition Date: October 2019

Part Number: 377064G-01

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Licensed assisted access (LAA) is introduced in release 13 of 3GPP specification to enable the operation of an LTE system in an unlicensed band. It combines an LTE carrier in the unlicensed spectrum with an LTE carrier in the licensed band using carrier aggregation. Frame structure type 3 is the new type of frame structure defined by 3GPP specification for LAA.

Frame structure Type 3

Frame structure type 3 is applicable to LAA unlicensed carrier with normal cyclic prefix only. Each radio frame is 10 ms long and consists of 10 subframes of length 1 ms. Any of these 10 subframes can be used for uplink/downlink transmission or can be empty. LAA transmission can start and end at any subframe and can consist of one or more consecutive subframes in the burst.

Partial Subframes

Partial subframes are introduced by 3GPP specification, as a part of frame structure type 3, to cater to the needs of Listen Before Talk (LBT) principles and for efficient use of unlicensed spectrum by LAA.

Partial subframes in uplink

  • LAA uplink burst gets transmitted either from the start of the 0th symbol or from the start of the 1st symbol in a subframe. The transmission can also start between the 0th and the 1st symbol, as defined in section 5.6 of 3GPP 36.211 specification. Thus, the 0th symbol in the first subframe of an LAA uplink burst can be partially filled, completely filled, or completely empty.
  • LAA uplink transmission can end either at the 12th or 13th OFDM symbol in a subframe as mentioned in sections 5.3.3.1.1A and 5.3.3.1.1B of 3GPP 36.212 specification. Therefore, the last subframe in an LAA uplink transmission can be completely filled with 14 OFDM symbols or can be partially filled with 13 OFDM symbols.

Partial subframes in downlink

  • LAA downlink transmission can start from 0th OFDM symbol (Subframe boundary) or from 7th OFDM symbol (Second Slot Starting Position) of a subframe. Refer to section 13A of 3GPP 36.213 specification for more information.
  • LAA downlink transmission can either end at the subframe boundary or at any of the DwPTS symbols. Therefore, the last subframe can be completely occupied with 14 OFDM symbols or can consist of any of DwPTS duration symbols i.e. 3, 6, 9, 10, 11, or 12 OFDM symbols. Refer to section 4.3 of 3GPP 36.211 specification for more information.

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