## Capacity of Wideband Multipath Fading Channels

One of the well-known advantages of wideband CDMA systems is their
ability to exploit frequency-selective diversity by the resolution of
multipaths. However, we showed that, somewhat
surprisingly, the performance of CDMA will degrade instead when the
spreading bandwidth is too wide. In particular, we proved that the
information theoretic capacity of a very wideband CDMA system is
inversely proportional to the number of resolvable multipaths, and in
fact go to zero if the number of paths is too large! The limitation
comes from the fact that when there are many multipaths, it is very
difficult to track the channel. This result has
ramifications to the design of ultra wideband communication systems.

E. Telatar and D. Tse, "Capacity and
Mutual Information of Wideband Multipath Fading Channels", IEEE
Transactions on Information Theory, vol 46(4), July 2000,
pp. 1384-1400.

This work is supported by the National Science Foundation under
grant #NCR-9734090.