Blind and Semiblind Channel Estimation - Nonlinear Signal and Image Processing: Theory, Methods and Applications - page 259

In this chapter we present the principles of blind channel estimation. Var-
ious statistical and structural signal properties used in blind channel equal-
ization and identification are described. Impairment caused by the channel
and channel models are also considered. Algorithms for single-user receivers
are briefly reviewed. The problem of blind equalization in MIMO systems is
considered in more detail. Widely used blind equalization and channel esti-
mation methods for wireless systems such as GSM, DS-CDMA, and OFDM
are reviewed. Finally, semiblind methods are considered briefly.
Because it is impossible to cover all the research by the many different
researchers in the area of blind receiver structures, we refer readers to the
several recent topics and papers for more detailed information. 1-6

8.2 Time-Varying Channel Model
Fundamentally, mobile radio communication channels are time-varying mul-
tipath channels. As the performance of digital radio communication sys-
tems is strongly affected by impairment caused by scattering, reflection, and
diffraction, channel models are of great interest. 7-15
A time-varying radio channel (TVC) may be represented by a two-
dimensional channel impulse response h ; Figure 8.1 presents an example.

Multipath propagation results in time dispersion of the transmitted signal,
which is visible on the

( t, τ)

plot. Time variations of the channel are
given on the t axis, where T is the symbol duration.

τ axis of h ( t, τ)

1

0.8

0.6

0.4

0.2

0

20

15

2000

1500

10

1000

τ

5

500

t/T

0 0

FIGURE 8.1
COST-207 “Hilly Terrain” channel, receiver speed of 90 km/h.