Signaling Basis with High Inter-symbol Interference Rejection Pilots in Doubly Dispersive Channels

In pilot aided transmissions over doubly dispersive channels, channel estimation is impaired due to contamination of pilot symbols by leakage from neighboring data symbols in rectangular window based block transmissions; no overlap in time between pulses corresponding to neighboring symbols. Block transmissions can be viewed as a basis consisting of time-frequency shifts of a prototype window shape, commonly known as Gabor bases, where the window shape controls the time-frequency confinement; better confinement is obtained when non-rectangular window shapes are used, however at the loss of orthogonality. In this work, a non-Gabor basis comprised of discrete prolate spheroidal sequences is considered for signaling due to the resilience of its high order sequences to time-frequency spread; beyond a certain sequence order, the higher the order the better the resilience. By using such high order sequences as pilots, the pilot energy relative to data symbol energy needed to overcome interference from data leakage can be lowered while maintaining good channel estimation accuracy.