First, we see that the fractionally spaced STE
performed better than the symbol spaced STE. Next we see that the rank of the symbol-spaced STE
covariance matrix is equal to 5, while the rank of the fractionally spaced covariance matrix is equal
to 3. This is due to the fact as the taps become closer together in time, the matrix becomes more coherent,
and the rank now becomes dependent on the channel conditions rather than the STE architecture
chosen. It can be easily shown that the rank for the symbol-spaced covariance matrix is equal to the
number of taps on each antenna. However; for the fractionally spaced STE, the overall channel
response dictates the covariance matrix rank, which in this case is 3 due to the overall pulse-shaping
and flat-fading channel model investigated.
We have decided to plot the BER performance versus the covariance matrix rank for the purposes
of studying the possibility of reduced rank signal processing. The curves show the covariance matrix
rank is less than full and hence reduced rank opportunities exist.
6.2.2 Frequency Selective Fading Environment
In this next section, we introduce a two-ray channel model to address the presence of delay spread.
The received signals at both antennas are given as
(6.
Pages:
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512