This paper investigates capacity of CDMA system employing adaptive transmission technique under multipath fading channel. Three power control schemes with rate adaptive capability are proposed to exploit the time variation of channel fading. In all the three schemes, adaptive transmission employing BPSK is realized through adapting the processing gain (PG) to the channel conditions. A minimum PG constraint is made to ensure multiple access capability. When PG is at this minimum value, the system can have an option to adjust the transmission rate through using higher constellation QAM. For scheme 1, system capacity rather than the lower bound reported in [Kim, S.W., 1999] is obtained. System capacities for scheme 2 and 3 are analyzed and computed using numerical calculations. Our numerical results show that the proposed power control schemes 2 and 3 can obtain higher system capacities than that of ideal constant received power at the base station, for a given constant average transmission power per user.
[1]
Andrea J. Goldsmith,et al.
Variable-rate variable-power MQAM for fading channels
,
1997,
IEEE Trans. Commun..
[2]
Sang Wu Kim.
Adaptive rate and power DS/CDMA communications in fading channels
,
1999,
IEEE Commun. Lett..
[3]
J. Cavers,et al.
Variable-Rate Transmission for Rayleigh Fading Channels
,
1972,
IEEE Trans. Commun..
[4]
Shlomo Shamai,et al.
On the capacity of some channels with channel state information
,
1999,
IEEE Trans. Inf. Theory.
[5]
Sang Wu Kim,et al.
Combined rate and power adaptation in DS/CDMA communications over Nakagami fading channels
,
2000,
IEEE Trans. Commun..
[6]
Pravin Varaiya,et al.
Capacity of fading channels with channel side information
,
1997,
IEEE Trans. Inf. Theory.