What is DL: Adaptive OFDM in LTE?

Question

Not able to understand it. Is there an expert who can explain it in better way ?

Answer 1

If I understood your query correctly. You are asking about the adaptive modulation and coding techniques.
As I work only in lte technology. I would like to put some points here.
Lte network has capability to change modulation and coding schemes dynamically based on UE measurement report.
Coding rate and modulation both are generic term but I would like to explain little bit.
Coding rate is the ratio between actual amount of data is being transmitted/ Total physical bits can be transmitted.
Total physical bits can be calculated.

Modulation is nothing but how many bits are being transmitted on one resource element. In Lte, it can 2, 4 or 6 based on QPSK, 16 QAM and 64 QAM modulation scheme.
A CQI mapping table has defined. which has details like once eNodeB receives a particular CQI value from UE then which Modulation scheme would have to be used and transport block size per TTI.

Comments

Thanks for your valuable input, but my concern is why there is (adaptive) term has been used for downlink.

Answer 2

I am agreed with below answer and on ur comment. This is the meaning of adaptive that according to the scenarios the downlink layer can adapt. It is flexible. Like the Downlink in LTE depends on QoS, it means that the throughput in DL depends of the service that you are using (video call, Multimedia transaction, Consulting web pages, etc) if you are using a high priority service like video call, the system is going to assign you more subcarriers in the OFDMA in order to achieve a successful transaction. If you are using a low priority service, the system is going to allow you less subcarriers, but if in the Cell there are no more UEs that use a priority cell, the system could allow you the max throughput possible while the system could.