Channel estimation and equalization for CE-OFDM in multipath fading channels

In OFDM, the orthogonal subcarriers can be assumed to undergo flat fading in a frequency selective channel permitting operation without an equalizer especially when differential data encoding is used. However, in CE-OFDM, the data symbols are no longer confined to orthogonal subcarriers and, therefore, an equalizer is required for operation in frequency selective channels. A frequency domain equalizer (FDE) is known to perform well for OFDM as well as CE-OFDM [3]. In this paper, we study the performance of CE-OFDM in multipath fading channels while employing a FDE. The quality of the channel estimate which is obtained using a training signal directly affects the performance of the equalizer. We investigate channel estimation using both the least squares (LS) as well as the linear minimum mean square error (LMMSE) techniques and compare the equalizer performance for both these cases. It is desirable to have a training signal that has a low PAPR in time domain while also having a flat power spectrum in the frequency domain. While CE-OFDM has a constant envelope, it does not have a flat spectrum in the frequency domain. Therefore, we also investigate various training signals for channel estimation and compare their performance in the presence of an amplifier.

[1]  Elena Costa,et al.  Impact of amplifier nonlinearities on OFDM transmission system performance , 1999, IEEE Communications Letters.

[2]  R. C. North,et al.  Scattering functions from the naval communication channels dataset , 1999, MILCOM 1999. IEEE Military Communications. Conference Proceedings (Cat. No.99CH36341).

[3]  V. K. Jones,et al.  Channel estimation for wireless OFDM systems , 1998, IEEE GLOBECOM 1998 (Cat. NO. 98CH36250).

[4]  S.C. Thompson,et al.  Constant Envelope OFDM with Channel Coding , 2006, MILCOM 2006 - 2006 IEEE Military Communications conference.

[5]  James R. Zeidler,et al.  Threshold Extending Receiver Structures for CE-OFDM , 2007, MILCOM 2007 - IEEE Military Communications Conference.

[6]  Hikmet Sari,et al.  Frequency-domain equalization of mobile radio and terrestrial broadcast channels , 1994, 1994 IEEE GLOBECOM. Communications: The Global Bridge.

[7]  Adel A. M. Saleh,et al.  Frequency-Independent and Frequency-Dependent Nonlinear Models of TWT Amplifiers , 1981, IEEE Trans. Commun..

[8]  Sergio Barbarossa,et al.  Estimation of time-varying multipath channel parameters using chirp signals , 2001, Proceedings. 2001 IEEE International Symposium on Information Theory (IEEE Cat. No.01CH37252).

[9]  Y. Tsai,et al.  Orthogonal frequency division multiplexing with phase modulation and constant envelope design , 2005, MILCOM 2005 - 2005 IEEE Military Communications Conference.

[10]  R.W. Brodersen,et al.  Constant envelope multicarrier modulation: performance evaluation AWGN and fading channels , 2005, MILCOM 2005 - 2005 IEEE Military Communications Conference.

[11]  Per Ola Börjesson,et al.  OFDM channel estimation by singular value decomposition , 1996, Proceedings of Vehicular Technology Conference - VTC.

[12]  J. Zeidler,et al.  Constant envelope OFDM phase modulation: spectral containment, signal space properties and performance , 2004, IEEE MILCOM 2004. Military Communications Conference, 2004..

[13]  Chong Eng Tan,et al.  Near-optimum training sequences for OFDM systems , 2003, 9th Asia-Pacific Conference on Communications (IEEE Cat. No.03EX732).

[14]  David V. Roderick.  A Coded Orthogonal Frequency Division Multiplexing Simulation of a High Data Rate, Line-Of-Sight, Digital Radio for Mobile Maritime Communications. , 1997 .

[15]  James R. Zeidler,et al.  Constant Envelope OFDM , 2008, IEEE Transactions on Communications.

[16]  P. H. Moose,et al.  A COFDM-based radio for HDR LOS networked communications , 1999, 1999 IEEE International Conference on Communications (Cat. No. 99CH36311).

[17]  F. Raab,et al.  Power amplifiers and transmitters for RF and microwave , 2002 .

[18]  Xiaohu You,et al.  Efficient Channel Estimation for MIMO Single-Carrier Block Transmission With Dual Cyclic Timeslot Structure , 2007, IEEE Transactions on Communications.

[19]  Ramjee Prasad,et al.  OFDM for Wireless Multimedia Communications , 1999 .

[20]  Dimitrios Hatzinakos,et al.  Error Rate Analysis of Phase-Modulated OFDM (OFDM-PM) in Awgn Channels , 2006, 2006 IEEE International Conference on Acoustics Speech and Signal Processing Proceedings.

[21]  J. Zeidler,et al.  Constant envelope binary OFDM phase modulation , 2003, IEEE Military Communications Conference, 2003. MILCOM 2003..