Multiple Access Interference Mitigation in OFDMA Uplink via static assignment of Guard Bands and Guard Intervals

In the uplink of OFDMA-based systems, Multiple Access Interference (MAI), caused by synchronization offsets, can cause considerable degradation in the performance of the User Terminals (UTs). The conventional approach to deal with MAI is based on the usage of Cyclic Prefix (CP) also known as Guard Intervals (GI) in time domain. The time and frequency offsets of UTs signals arriving at BS are estimated and then these estimations are used to subtract the offsets and to re-build orthogonality among subcarriers. However the large overhead, caused by long CP and pilot subcarriers, and imposed by this approach, is considered as a main drawback of this approach. Another way of mitigating MAI is by inserting frequency Guard Bands (GB) to reduce the MAI on adjacent subcarriers. In this report, we examine the feasibility of using GB together with CP instead of only CP using a simple standard model. We consider a scenario where a fixed-width CP is used with fixed-width GB to mitigate MAI and improve UT throughput. Various combinations of CP and GB lengths are evaluated under different time and frequency offset profiles. It is shown that short CP together with GBs can bring significant improvement in throughput compared to the mere usage of long CP. Particularly, using GBs with short CP achieves the best performance in presence of both frequency and time offset.