Implementation of an improved clock frequency offset compensator for 4G OFDM System at ETRI

In the field of wireless mobile communications, various types of 4G(4th Generation) systems have been designed and developed over many countries. We also have been developing the HMm (High-Speed Multimedia Mobile) 4G testbed system with the specification of ECSUS(Enhanced Cellular System for Ubiquitous Service) that is designed at ETRI(Electronics and Telecommunications Research Institute). The HMm system is adopting OFDM (Orthogonal Frequency Division Multiplexing) modulation method, especially 2×2 MIMO (Multiple Input Multiple Output) OFDM. In the OFDM system, symbols are transmitted in parallel on several narrow-band subchannels, which are overlapping and orthogonal. Clock difference in sampling frequencies between an access system and a user equipment can lead to serious performance degradation due to the loss of orthogonality between the subcarriers. Therefore, the sampling frequency offset has to be estimated correctly and the error has to be compensated at the receiver. In this paper, we evaluated the performance of the HMm 4G MIMO OFDM testbed system according to the clock frequency offset values and proposed an improved algorithm to minimize the effect of clock frequency offsets.