The BER performance results assume the CPICH transmit power is 10% of the total transmitted
power. Recall the following closed-form BER expressions were presented previously and are rewritten
and slightly modified for sake of reference [1]:
AWGN:
(7.89)
Flat fading:
; (7.90)
Two-ray, equal power fading:
(7.91)
Two CE algorithms were compared to each other under various channel conditions. The first technique
used the CPICH channel (common pilot, CP), where an MA filter of 5 symbols in length was
used and the channel estimate was updated every 256 chips. Recall the CPICH is transmitted in parallel,
so the estimate can be updated faster. The second technique used the dedicated pilot (DP) bits
of DPCCH, where the channel estimate from time slot k is used for the duration of time slot k 1.
Since we need to use gated pilot bits to estimate the channel, this technique assumes the channel is
relatively constant over the time slot. The user data rate is 384 kbps, which corresponds to an SF of 8.
The particular time slot format chosen had eight pilot symbols in the DPCCH. Both of these techniques
are based on causal signal processing. Fig. 7.71 represents the uncoded BER versus Eb/No for
a flat fading channel with a Doppler spread of 20 Hz.
Pages:
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659