Overhead and Spectral Efficiency of Pilot-Assisted Interference Alignment in Time-Selective Fading Channels

Abstract

Abstract-The spectral efficiency achievable by IA (interference alignment) in a K-user MIMO (multiple-input multipleoutput) interference channel is studied in the face of timeselective continuous fading explicitly estimated through pilotsymbol observations. The robustness of IA in such operationally relevant conditions is assessed through a joint optimization of the pilot overhead and the IA update interval, which are characterized-in high-power conditions-as solutions of a fixedpoint equation. Variations of the formulation are given for both FDD (frequency-division duplexing) and TDD (time-division duplexing), the former requiring explicit feedback of the fading estimates and the latter relying on fading reciprocity. For the FDD variation, analog feedback is considered. In addition to arbitrary numbers of users and antennas, and arbitrary temporal fading correlation functions, the derivations accommodate forward and reverse links with asymmetric power levels.Index Terms-Interference alignment, time-selective fading, pilot-assisted transmission, spectral efficiency, pilot overhead, precoder update interval.

On Analytical Achievable Rate for MIMO Linear Interference Alignment with Imperfect CSI

“…Substitute the closed form analytical lower bound (19) into the upper bound (12), the analytical upper bound for i.i.d. uncorrelated Rayleigh fading channels can be obtained.…”

“…However, it is worth noting that there exists a trade-off between the overhead paid for CSI improvement and effective data transmit [19].…”

“…The analysis therein is based on a channel model with only transmit correlation, while the impact of receive correlation is omitted in consideration of its difficulty in analyzing. Other work on IA with imperfect CSI can be found in [17][18][19][20][21][22][23][24][25][26][27], including trade-off on overhead and spectrum efficiency, CSI sharing with limited feedback link and robust IA schemes conquering CSI imperfection, etc.…”

Optimal overhead selection for interference alignment in time-varying two-user MIMO X channel

“…Estimation algorithms are therefore required [12] that involve an exchange of information among transmitting and receiving nodes. This inevitably implies an increase of the associated overhead with a consequent decrease on the overall information rate [8]- [10]. Studies were conducted for IA in block fading channel [11] and continuous fading channel [8], [10].…”

“…This inevitably implies an increase of the associated overhead with a consequent decrease on the overall information rate [8]- [10]. Studies were conducted for IA in block fading channel [11] and continuous fading channel [8], [10]. The optimum pilot overhead and IA update interval for K-user interference channel in continuous fading have been obtained analytically in [8].…”