Peter Christian Gunreben

Equalization concepts for Alamouti's space-time block code

In this paper, we develop receiver concepts for transmission with space-time block codes (STBCs) over frequency-selective fading channels. The focus lies on Alamoutis space-time block-coding scheme, but the results may be generalized to other STBCs as well. We show that a straightforward combination of conventional equalizers and a space-time block decoder is only possible if at least as many receive antennas as transmit antennas are employed, but not for the practically interesting case of pure transmit diversity, for which space-time coding had been originally developed. This restriction is circumvented by our approach. Here, the structural properties of the transmit signal of space-time block coding, which is shown to be improper (rotationally variant), are fully used. For this, equalizers with widely linear (WL) processing are designed, such as a WL equalizer, a decision-feedback equalizer with WL feedforward and feedback filtering, and a delayed decision-feedback sequence estimator with WL prefiltering. Simulation results demonstrate that the proposed concepts may be successfully employed in an enhanced data rates for GSM evolution (EDGE) receiver, especially for pure transmit diversity. Here, significant gains can be observed, compared with a conventional single-input single-output transmission.

Widely linear equalization for space-time block-coded transmission over fading ISI channels

We develop receivers for transmission with space-time block codes (STBCs) over fading intersymbol interference (ISI) channels. The focus lies on Alamoutis STBC, but the results may be generalized to related codes. It turns out that a straightforward combination of conventional equalizers and a space-time block decoder is only possible if at least as many receive antennas as transmit antennas are employed, but not for the practically interesting case of pure transmit diversity. This restriction is circumvented by our approach. Equalizers with widely linear (WL) processing are designed, exploiting the structure of Alamoutis STBC, which is shown to produce an improper (rotationally variant) transmit signal. The presented receivers are especially well suited for high-level modulated signals, which are used in third-generation time-division multiple access (TDMA) mobile communications standards such as EDGE (enhanced data rates for GSM evolution). In contrast to block-based STBCs which have recently been proposed for ISI channels, our approach of combining a symbol-based STBC and equalization can be easily accommodated to channels with time-variant behaviour inside a transmission burst. Furthermore, for our scheme, the present burst structure of the EDGE system can be retained.

Symbol-by-symbol and trellis-based equalization with widely linear processing for space-time block-coded transmission over frequency-selective fading channels

In this paper, we develop receiver concepts for transmission with space-time block codes (STBC) over frequency-selective fading channels. The focus lies on Alamoutis STBC, but the results may be generalized to related STBC. We show that a straightforward combination of conventional equalizers and a space-time block decoder is only possible if at least as many receive antennas as transmit antennas are employed, but not for the practically interesting case of pure transmit diversity. This restriction is circumvented by our approach. Equalizers with widely linear (WL) processing are designed, utilizing the structural properties of the transmit signal of space-time block coding, which is shown to be improper (rotationally variant). These schemes are especially suited for equalization of high-level modulated signals, which are used in third-generation time-division multiple access mobile communications standards such as EDGE (Enhanced Data Rates for GSM Evolution).