PREAMBLE FOR LICENSED ASSISTED ACCESS USING FRACTIONAL OFDM SYMBOL FOR REDUCED OOB EMISSIONS

摘要

Context of invention is the release 13 of LTE and in particular the use of the unlicensed spectrum, on which WiFi (W-LAN) is currently deployed, ie so-called Licensed Assisted Access (LAA). LTE in unlicensed spectrum uses Clear Channel Assessment (CCA) like WiFi nodes before starting transmission to reserve resources for a given maximum duration. When transmission starts directly after CCA success, the first symbol is always a fractional OFDM symbol, ie having a time duration being a portion of a complete OFDM symbol. To minimize Out Of Band (OOB) emissions due to the fractional symbol, it is proposed here to send as the fractional symbol a cyclic extension of the adjacent OFDM symbol, or in other words filling up the gap before the next complete OFDM symbol by a cyclic extension of said following symbol thereby reducing OOB while providing an extended cyclic prefix and reserving the channel. The following complete OFDM symbol then may not need any further Cyclic Prefix.