Degrees-of-Freedom Based on Interference Alignment with Imperfect Channel Knowledge

Won-Yong SHIN
Muryong KIM
Hyoseok YI
Ajung KIM
Bang Chul JUNG

IEICE TRANSACTIONS on Communications   Vol.E94-B    No.12    pp.3579-3582
Publication Date: 2011/12/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E94.B.3579
Print ISSN: 0916-8516
Type of Manuscript: LETTER
Category: Fundamental Theories for Communications
channel state information (CSI),  degrees-of-freedom (DoFs),  error variance,  interference alignment (IA),  signal-to-noise ratio (SNR),  

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The impact and benefits of channel state information (CSI) are analyzed in terms of degrees-of-freedom (DoFs) in a K-user interference network operating over time-selective channels, where the error variance of CSI estimation is assumed to scale with an exponent of the received signal-to-noise ratio (SNR). The original interference alignment (IA) scheme is used with a slight modification in the network. Then, it is shown that the DoFs promised by the original IA can be fully achieved under the condition that the CSI quality order, represented as a function of the error variance and the SNR, is greater than or equal to 1. Our result is extended to the case where the number of communication pairs, K, scales with the SNR, i.e., infinite K scenario, by introducing the user scaling order. As a result, this letter provides vital information to the system designer in terms of allocating training resources for channel estimation in practical cellular environments using IA.