Channel equalization with staggered modulation formats

The channel equalization problem for staggered (or offset) modulation formats is considered. It is shown that, due to the relative time offset of the in-phase and quadrature components, the received signal must be sampled at twice the baud rate of the corresponding non-staggered signal. This suggests that perfect zero-forcing equalization may be achievable as in standard fractionally sampled systems. To explore this feature, the MMSE linear equalizer (LE), which turns out to be a periodically time-varying filter, is obtained. It is shown that the MMSE LE can be implemented with an LTI (linear time invariant) filter and a set of periodic switches and modulators. Using this, necessary conditions for zero-forcing equalization with FIR filters are derived.

[1]  S. Gronemeyer,et al.  MSK and Offset QPSK Modulation , 1976, IEEE Trans. Commun..

[2]  Petros G. Voulgaris,et al.  On optimal ℓ∞ to ℓ∞ filtering , 1995, Autom..

[3]  J. W. Craig.  Equalization for unbalanced QPSK and for staggered QPSK , 1993, Proceedings of GLOBECOM '93. IEEE Global Telecommunications Conference.

[4]  Raul A. Casas,et al.  Global convergence of a single-axis constant modulus algorithm , 2000, Proceedings of the Tenth IEEE Workshop on Statistical Signal and Array Processing (Cat. No.00TH8496).

[5]  J. C. Tu.  Optimum MMSE equalization for staggered modulation , 1993, Proceedings of 27th Asilomar Conference on Signals, Systems and Computers.

[6]  Sergio Benedetto,et al.  Principles of digital transmission , 1999 .

[7]  Phillip A. Bello,et al.  Adaptive Equalization for SQPSK and SQPR Over Frequency Selective Microwave LOS Channels , 1984, IEEE Trans. Commun..

[8]  Bernard Mulgrew,et al.  An adaptive Kalman equalizer: Structure and performance , 1987, IEEE Trans. Acoust. Speech Signal Process..

[9]  Constantinos B. Papadias,et al.  Fractionally spaced equalization of linear polyphase channels and related blind techniques based on multichannel linear prediction , 1999, IEEE Trans. Signal Process..

[10]  C. Zheng,et al.  ; 0 ; , 1951 .