On pilot design for interference limited OFDM systems

Modern cellular networks are inherently interference limited, and therefore, pilot design is extremely important to the overall system performance. The pilots have to be carefully arranged and modulated to track the fading channel as well as to suppress the interference efficiently. 4G wireless systems based on OFDMA use pilot design strategies that can be classified as `Data on Pilot´ and `Pilot on Pilot´. In this paper, a `Null on Pilot´ scheme that uses null tones and pilot tones to avoid most of the interference on the pilots is considered. Various design aspects of these three pilot schemes are discussed in detail. The channel estimation, interference covariance estimation, link performance with different interference profiles, and system throughput are analyzed and compared with these pilot schemes. It is shown that the popular approach of `Data on Pilot´ scheme is inferior to the other two approaches in exploiting the post-processing SNR gain of MMSE interference suppression receivers. The performances of `Null on Pilot´ and `Pilot on Pilot´ are quite similar.