Space time coding has by now been well documented as an attractive means of achieving high data rate transmissions with diversity and coding gains, provided that the underlying propagation channels can be accounted for. In this paper, we rely on redundant linear precoding to develop a (semi-)blind channel estimation algorithm for space time (ST) orthogonal frequency division multiplexing (OFDM) transmissions with Alamouti's block code applied on each subcarrier. We establish that multichannel identifiability is guaranteed up to one or two scalar ambiguities, regardless of the channel zero locations and the underlying signal constellations, when distinct or identical precoders are employed for even and odd indexed symbol blocks. With known pilots inserted either before or after precoding, we resolve the residual scalar ambiguities and show that distinct precoders require half the number of pilots than identical precoders to achieve the same channel estimation accuracy. Simulation results confirm our theoretical analysis and illustrate that the proposed semi-blind algorithm is capable of tracking slow channel variations and improving the overall system performance relative to competing differential ST alternatives.
Bibliographical noteFunding Information:
Manuscript received February 12, 2001; revised January 28, 2002. This work was supported by the NSF Wireless Initiative under Grant 99-79443, NSF Grant 0105612, and by the ARL/CTA under Grant DAAD19-01-2-011. This work was presented in part at the 34th Asilomar Conference on Signals and Systems, Pacific Grove, CA, October 29–November 1, 2000, and at the 11th IEEE Workshop on Statistical Signal Processing, Singapore, August 6–8, 2001. The associate editor coordinating the review of this paper and approving it for publication was Dr. Helmut Bölcskei.
- Block precoded transmissions
- Space-time coding
- Subspace based channel estimation