Abstract—Space-frequency (SF) coded orthogonal fre-quency division multiplexing (OFDM) systems have been recentlyproposedfor cooperative communicationsto achieve both full cooperative and full multipath diversities without thetime synchronizationrequirement.In this paper,weshow that the fulldiversityproperty still holdsfora familyofSF codes (rotation-based SF codes) when there are multiple carrier frequency offsets (CFOs) from relay nodes under the condition that the absolute values of the normalized CFOs are less than 0.5.We then prove that this full diversity property can be preserved if we seek to reduce the receiver complexityby usinga zeroforcing (ZF) method to equalize the multiple CFOs, before applying maximum likelihood (ML) decoding. Furthermore, by exploiting the properties of SF codes, we show that a specific permuted version of this family of SF codes can still achieve full diversity even when the inter-carrier interference (ICI) matrix is singular. This is possible as long as the maximum absolute value of the normalized CFOs is not less than 0.5. However, in this case the ZF method cannot be directly used to reduce the decoding complexity. To avoid the necessity of jointly considering all the subcarriers, two suboptimal detection methods are proposed in which full diversity is achieved even for singular ICI matrix. All these imply that the SF coded OFDM system is robust to both timing errors and frequency offsets.

Index Terms—Cooperative communications, diversity, ICI, multiple CFOs, OFDM, space-frequency codes

Cite: K. Vinodh, N. Prakash, V. Lalitha and P. Vijay Kumar, "High Speed Data Routing in Vehicular Sensor Networks," Journal of Communications, vol. 5, no. 4, pp.317-331 , 2010. Doi: 10.4304/jcm.5.4.317-331