LTE INTER SYMBOL INTERFERENCE
When Interference occurs between two symbols because of straight path and reflected path it’s called ISI.
ISI STRAIGHT VS REFLECTED WAVE:
ISI SOLUTIONS:
** ISI OLD SOLUTIONS:
(1) Rake Receiver:
It’s a Multi Finger antenna which is capable for receiving and separating multi directional waves.
Advantages:
· No ISI any more.
· Due to Multipath reception diversity increases the signal decoding success rate.
Disadvantage:
· Expensive due to use of Rake receiver
· High Power consumption required for multi signal processing.
(2) ISI FACTORS
· Delay Time: If delay time increase than ISI will increase and vice versa.
· Bandwidth: If Bandwidth increase than ISI will increase and vice versa.
** ISI NEW SOLUTIONS:
(1) Sub Carrier Techniques:
In this techniques each sub-carrier size should be 15 kHz Bandwidth because if lower the bandwidth so ISI also less.
LTE Sub-carrier: Scalable Bandwidth in below table:
LTE Cyclic Prefix Method:
Add a waste piece at a start of a symbol so that it can absorb the shock of the impact.
· Short CP: 14000 symbols per second per sub carrier and remaining 1000 symbols are used as a cyclic prefix.
· Long CP: 12000 Symbols per second per sub-carrier.
