Abstract
Channel estimation scheme for OFDM modulated transmissions usually combines an initial block-pilot-assisted stage with a tracking one based on comb or scattered pilots distributed among user data in the signal frame. The channel reconstruction accuracy in the former stage has a significant impact on tracking efficiency of the channel variations and the overall transmission quality. The paper presents a new block-pilot-assisted channel reconstruction procedure based on the DFT-based approach and the Least Square impulse response estimation. The proposed method takes into account a compressibility feature of the channel impulse response and restores its coefficients in groups of automatically controlled size. The proposition is analytically explained and tested in a OFDM simulation environment. The popular DFT-based methods including compressed sensing oriented one were used as references for comparison purposes. The obtained results show a quality improvement in terms of Bit Error Rate and Mean Square Error measures in low and mid ranges of signal-to-noise ratio without significant computational complexity growth in comparison to the classical DFT-based solutions. Moreover, additional multiplication operations can be eliminated, compared to the competitive, in terms of estimation quality, compressed sensing reconstruction method based on greedy approach.
Highlights
OFDM (Orthogonal Frequency Division Multiplexing) has become the primary modulation for physical layer design in many modern digital transmission systems since the beginning of the century
When the modulation parameters such as the subchannel spacing, guard interval, and symbol lengths are well matched to the occupied frequency band, channel characteristics, and system mobility, the subchannels are orthogonal, and the transmission within them is mutually independent in consecutive OFDM symbols [1]
The simulation results show that coefficient clustering mechanism during impulse response reconstruction has a generally positive influence on the transmission quality
Summary
OFDM (Orthogonal Frequency Division Multiplexing) has become the primary modulation for physical layer design in many modern digital transmission systems since the beginning of the century. When the modulation parameters such as the subchannel spacing, guard interval, and symbol lengths are well matched to the occupied frequency band, channel characteristics, and system mobility, the subchannels are orthogonal, and the transmission within them is mutually independent in consecutive OFDM symbols [1]. The subchannel orthogonality as a result of FFT makes data decoding in the individual subchannels straightforward with ZF (Zero Forcing) approach, provided that the channel frequency characteristic is known at the time when the OFDM symbols are received. The CSI (Channel State Information) is acquired prior to data reception by means of pilots, i.e., training complex symbols (e.g., belonging to QPSK constellation) known to the receiver and defined in the frequency domain. It is worth mentioning that estimation precision of CSI is crucial for high data reception quality and for effective users management in multiuser MIMO-OFDM systems [4]
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