TY - JOUR
T1 - Optimization of amplify-and-forward multicarrier two-hop transmission
AU - Zhang, Wenyi
AU - Mitra, Urbashi
AU - Chiang, Mung
N1 - Funding Information:
The work of W. Zhang and U. Mitra was supported in part by NSF OCE-0520324. Preliminary results in this paper have appeared, in part, in [1].
PY - 2011/5
Y1 - 2011/5
N2 - In this paper, frequency-domain relay processing in a two-hop transmission system is investigated. The relay is constrained to be "non- regenerative"; that is, the relay is only allowed to perform a symbol-by-symbol memoryless transformation of its received signals. Multicarrier modulation, e.g., orthogonal frequency division multiplexing (OFDM), is utilized to convert each hop into a collection of non-interfering parallel subcarriers. In contrast to conventional scalar amplify-and-forward (AF) relays that scale all the subcarriers uniformly, it is possible to suppress relay noise and to exploit frequency-domain diversity by optimizing the relay scaling coefficients of different subcarriers jointly with subcarrier power allocation at the source transmitter. This type of scheme is denoted by multicarrier amplify-and-forward (MCAF). Although the end-to-end achievable rate of MCAF is a non-concave function of the power allocation vectors, its optimization is accomplished with an algorithm (O-MCAF) whose computational complexity grows only quadratically with the number of subcarriers, by utilizing a structural property of the problem. Further motivated by the problem structure, a suboptimal algorithm (WF-MCAF) with a linear complexity is also proposed, in which each hop performs waterfilling separately over a selected subset of subcarriers. For hops with a frequency-flat channel response, the maximum achievable rate is explicitly derived from the associated optimization. For hops with Rayleigh fading frequency-domain channel responses, numerical results are presented and it is illustrated that the proposed low-complexity WF-MCAF algorithm usually achieves near-optimal performance.
AB - In this paper, frequency-domain relay processing in a two-hop transmission system is investigated. The relay is constrained to be "non- regenerative"; that is, the relay is only allowed to perform a symbol-by-symbol memoryless transformation of its received signals. Multicarrier modulation, e.g., orthogonal frequency division multiplexing (OFDM), is utilized to convert each hop into a collection of non-interfering parallel subcarriers. In contrast to conventional scalar amplify-and-forward (AF) relays that scale all the subcarriers uniformly, it is possible to suppress relay noise and to exploit frequency-domain diversity by optimizing the relay scaling coefficients of different subcarriers jointly with subcarrier power allocation at the source transmitter. This type of scheme is denoted by multicarrier amplify-and-forward (MCAF). Although the end-to-end achievable rate of MCAF is a non-concave function of the power allocation vectors, its optimization is accomplished with an algorithm (O-MCAF) whose computational complexity grows only quadratically with the number of subcarriers, by utilizing a structural property of the problem. Further motivated by the problem structure, a suboptimal algorithm (WF-MCAF) with a linear complexity is also proposed, in which each hop performs waterfilling separately over a selected subset of subcarriers. For hops with a frequency-flat channel response, the maximum achievable rate is explicitly derived from the associated optimization. For hops with Rayleigh fading frequency-domain channel responses, numerical results are presented and it is illustrated that the proposed low-complexity WF-MCAF algorithm usually achieves near-optimal performance.
KW - Amplify-and-forward
KW - multicarrier
KW - nonconvex optimization
KW - relay
KW - two-hop transmission
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U2 - 10.1109/TCOMM.2011.022811.100017
DO - 10.1109/TCOMM.2011.022811.100017
M3 - Article
AN - SCOPUS:79956258449
SN - 0090-6778
VL - 59
SP - 1434
EP - 1445
JO - IEEE Transactions on Communications
JF - IEEE Transactions on Communications
IS - 5
M1 - 5723048
ER -