DocumentCode :
86240
Title :
A Factor Graph Approach to Exploiting Cyclic Prefix for Equalization in OFDM Systems
Author :
Jindan Yang ; Qinghua Guo ; Huang, Defeng David ; Nordholm, Sven Erik
Author_Institution :
Sch. of Electr., Electron. & Comput. Eng., Univ. of Western Australia, Perth, WA, Australia
Volume :
61
Issue :
12
fYear :
2013
fDate :
Dec-13
Firstpage :
4972
Lastpage :
4983
Abstract :
In OFDM systems, cyclic prefix (CP) insertion and removal enables the use of a set of computationally efficient single-tap equalizers at the receiver. Due to the extra transmission time and energy, the CP causes a loss in both spectrum efficiency and power efficiency. On the other hand, as a repetition of part of the data, the CP brings extra information and can be exploited for detection. Therefore, instead of discarding the CP observation as in the conventional OFDM system, we utilize all the received signals in a soft-input soft-output equalizer of a turbo equalization OFDM system. First, the models for both the CP part and the non-CP part of observation are presented in a Forney-style factor graph (FFG). Then based on the computation rules of the FFG and the Gaussian message passing (GMP) technique, we develop an equalization algorithm. With proper approximation, the complexity of the proposed algorithm is reduced to changedmathcal O(2RNlog2N+4RGlog2G+2RG) per data block for R iterations, where N is the length of the data block and G is equal to P+L-1 with P the length of the CP and L the maximum delay spread of the channel. To justify the performance improvement, SNR analysis is provided. Simulation results show that the proposed approach achieves a significant gain over the conventional approach and the turbo equalization system converges within two iterations.
Keywords :
Gaussian processes; OFDM modulation; approximation theory; delays; equalisers; graph theory; iterative methods; message passing; radio spectrum management; CP insertion; FFG; Forney-style factor graph approach; GMP technique; Gaussian message passing technique; approximation theory; cyclic prefix insertion; data block length; iteration method; power efficiency; signal receiver; single-tap equalizer; soft-input soft-output equalizer; spectrum efficiency; turbo equalization OFDM system; Complexity theory; Convolution; Covariance matrices; Equalizers; OFDM; Receivers; Vectors; OFDM system; cyclic prefix; factor graph; iterative receiver;
fLanguage :
English
Journal_Title :
Communications, IEEE Transactions on
Publisher :
ieee
ISSN :
0090-6778
Type :
jour
DOI :
10.1109/TCOMM.2013.102713.130330
Filename :
6657833
Link To Document :
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