TY - JOUR
T1 - The capacity of downlink fading channels with variable rate and power
AU - Goldsmith, Andrea J.
N1 - Funding Information:
Manuscript received December 10, 1995; revised June 4, 1996. This work was supported in part by Pacific Bell and in part by NSF under Career Development Award NCR-9501452. The author is with the Department of Electrical Engineering, California Institute of Technology, Pasadena, CA 91125 USA. Publisher Item Identifier S 0018-9545(97)04635-5.
PY - 1997
Y1 - 1997
N2 - We obtain the Shannon capacity region of the downlink (broadcast) channel in fading and additive white Gaussian noise (AWGN) for time-division, frequency-division, and codedivision. For all of these techniques, the maximum capacity is achieved when the transmitter varies the data rate sent to each user as their channels vary. This optimal scheme requires channel estimates at the transmitter; dynamic allocation of timeslots, bandwidth, or codes; and variable-rate and power transmission. For both AWGN and fading channels, nonorthogonal code-division with successive decoding has the largest capacity region, while time-division, frequency-division, and orthogonal code-division have the same smaller region. However, when all users have the same average received power, the capacity region for all these techniques is the same. In addition, the optimal nonorthogonal code is a multiresolution code which does not increase the signal bandwidth. Spread-spectrum code-division with successive interference cancellation has a similar rate region as this optimal technique, however, the region is reduced due to bandwidth expansion. We also examine the capacity region of nonorthogonal code-division without interference cancellation and of orthogonal code-division when multipath corrupts the code orthogonality. Our results can be used to bound the spectral efficiency of the downlink channel using time-division, frequencydivision, and code-division, both with and without multiuser detection.
AB - We obtain the Shannon capacity region of the downlink (broadcast) channel in fading and additive white Gaussian noise (AWGN) for time-division, frequency-division, and codedivision. For all of these techniques, the maximum capacity is achieved when the transmitter varies the data rate sent to each user as their channels vary. This optimal scheme requires channel estimates at the transmitter; dynamic allocation of timeslots, bandwidth, or codes; and variable-rate and power transmission. For both AWGN and fading channels, nonorthogonal code-division with successive decoding has the largest capacity region, while time-division, frequency-division, and orthogonal code-division have the same smaller region. However, when all users have the same average received power, the capacity region for all these techniques is the same. In addition, the optimal nonorthogonal code is a multiresolution code which does not increase the signal bandwidth. Spread-spectrum code-division with successive interference cancellation has a similar rate region as this optimal technique, however, the region is reduced due to bandwidth expansion. We also examine the capacity region of nonorthogonal code-division without interference cancellation and of orthogonal code-division when multipath corrupts the code orthogonality. Our results can be used to bound the spectral efficiency of the downlink channel using time-division, frequencydivision, and code-division, both with and without multiuser detection.
KW - Capacity region
KW - Code-division
KW - Downlink
KW - Fading
KW - Variable power
KW - Variable rate
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U2 - 10.1109/25.618181
DO - 10.1109/25.618181
M3 - Article
AN - SCOPUS:0031208431
SN - 0018-9545
VL - 46
SP - 569
EP - 580
JO - IEEE Transactions on Vehicular Technology
JF - IEEE Transactions on Vehicular Technology
IS - 3
ER -