TY - JOUR
T1 - Practical multiuser diversity with outdated channel feedback
AU - Ma, Qian
AU - Tepedelenlioglu, Cihan
N1 - Funding Information:
Manuscript received November 14, 2003; revised September 22, 2004. The work in this paper was supported by the National Science Foundation CAREER Grant No. CCR-0133841; portions of this paper have appeared in [1] and [2]. The review of this paper was coordintaed by Prof. J. Shea.
PY - 2005/7
Y1 - 2005/7
N2 - Inspired by the information theoretic results concerning multiuser diversity, we address practical issues in implementing multiuser diversity in a multiple access wireless setting. Considering a channel-assigning strategy that assigns the channel only to the user with the best instantaneous SNR [3], our emphasis is on the effects of channel feedback delay in downlink transmissions. A finite set of M-ary quadrature amplitude modulation (M-QAM) constellations is adopted and a constant transmit power is assumed in this practical multiuser adaptive modulation scheme. Based on the closed-form expressions for average bit error rate (BER) and average data rate, we illustrate the impact of channel feedback delay on the achievable multiuser diversity gain with the number of users. Simple and accurate asymptotic approximations are also provided in the limit of large numbers of users. Focusing on different applications, we propose two optimization criteria for the switching thresholds, based on either an average BER, or an outage probability constraint. Two novel constant power, variable rate M-QAM schemes that are less sensitive to feedback delay are proposed using the optimal switching thresholds, which are derived to maximize the average data rate subject to these two constraints, respectively. To obtain a certain degree of fairness among the users, we also consider a fair channel-assigning strategy that assigns the channel to only the user with the greatest normalized SNR.
AB - Inspired by the information theoretic results concerning multiuser diversity, we address practical issues in implementing multiuser diversity in a multiple access wireless setting. Considering a channel-assigning strategy that assigns the channel only to the user with the best instantaneous SNR [3], our emphasis is on the effects of channel feedback delay in downlink transmissions. A finite set of M-ary quadrature amplitude modulation (M-QAM) constellations is adopted and a constant transmit power is assumed in this practical multiuser adaptive modulation scheme. Based on the closed-form expressions for average bit error rate (BER) and average data rate, we illustrate the impact of channel feedback delay on the achievable multiuser diversity gain with the number of users. Simple and accurate asymptotic approximations are also provided in the limit of large numbers of users. Focusing on different applications, we propose two optimization criteria for the switching thresholds, based on either an average BER, or an outage probability constraint. Two novel constant power, variable rate M-QAM schemes that are less sensitive to feedback delay are proposed using the optimal switching thresholds, which are derived to maximize the average data rate subject to these two constraints, respectively. To obtain a certain degree of fairness among the users, we also consider a fair channel-assigning strategy that assigns the channel to only the user with the greatest normalized SNR.
KW - Adaptive modulation
KW - Average BER
KW - Fading channels
KW - Fairness
KW - Feedback delay
KW - M-QAM
KW - Multiuser diversity
KW - Multiuser scheduling
KW - Outage probability
KW - Threshold optimization
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U2 - 10.1109/TVT.2005.851325
DO - 10.1109/TVT.2005.851325
M3 - Article
AN - SCOPUS:24644482355
SN - 0018-9545
VL - 54
SP - 1334
EP - 1345
JO - IEEE Transactions on Vehicular Technology
JF - IEEE Transactions on Vehicular Technology
IS - 4
ER -