Variable Guard Interval Based on Maximum Delay Estimation for Adaptive OFDM Systems

Hideaki TANAKA
Yoshio ITOH

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E92-A    No.11    pp.2862-2865
Publication Date: 2009/11/01
Online ISSN: 1745-1337
DOI: 10.1587/transfun.E92.A.2862
Print ISSN: 0916-8508
Type of Manuscript: Special Section LETTER (Special Section on Smart Multimedia & Communication Systems)
Category: Communication Theory and Systems
OFDM,  guard interval,  multipath channel,  inter-symbol interference,  

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In orthogonal frequency division multiplexing (OFDM) system, a guard interval (GI) is used to remove the inter-symbol interference (ISI) due to a multipath channel. It is difficult to set an optimal GI length in the environment whose multipath varies. In this paper, we propose a variable guard interval based on the estimated maximum delay of a multipath channel. The maximum delay is estimated from a channel impulse response (CIR), which is estimated by a preamble symbol. However, since the estimated CIR includes the noise, it is difficult to decide the optimal GI. In order to solve the problem, we introduce the method which selects the path whose signal to noise ratio is high. Additionally, the information of the optimal GI length is required to be transmitted from a receiver to a transmitter. In this paper, we use an acknowledgment (ACK) frame for the feedback of the GI information.