67 Uplink noncausal CE overview.
Data
Pilot Cntrl
Data
Pilot Cntrl
Data
Pilot Cntrl
Data
Pilot Cntrl
Data
Pilot Cntrl
DCH
CCH
hk(t) hk+1(t) hk+2(t) hk+3(t) hk+4(t)
Time
Time Slot
Using the three sets of points available to us, namely, (3, h1), (13, h2), and (23, h3), one can easily
show the interpolation coefficients are given as follows, where x is used to indicate time in terms of
bit duration increments:
(7.84)
If we wish to determine the interpolated channel estimate at bit time x 17, then we have the following
operation to perform:
(7.85)
In a fast fading environment, the channel will change more rapidly than a slow fading environment.
In an effort to track these rapid changes, the interpolation coefficients should be time varying.
This way the channel estimate is updated during the bit times between the pilot fields. Other types of
interpolation techniques exist such as linear, and cubic splines [27]. Depending on the pilot field separation,
the number of pilot bits, the SNR of the pilot bits, fading channel parameters, and so forth,
some techniques will work better than others.
A general NodeB receiver block diagram is given in Fig. 7.69 for a RAKE. We have assumed the
multipath searcher has found K distinct paths and sent their respective timing information to each finger.
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