The diverse transmit powers of the base stations (BSs) in a multi-tier cellular network, on one hand, lead to uneven distribution of the traffic loads among different BSs when received signal power (RSP)-based user association is used. This causes under utilization of the resources at low-power BSs. On the other hand, strong interference from high-power BSs affects the downlink transmissions to the users associated with low-power BSs. In this context, this paper proposes a channel access-aware (CAA) user association scheme that can simultaneously enhance the spectral efficiency (SE) of downlink transmission and achieve traffic load balancing among different BSs. The CAA scheme is a network-assisted user association scheme that requires traffic load information from different BSs in addition to the channel quality indicators. We develop a tractable analytical framework to derive the SE of downlink transmission to a user who associates with a BS using the proposed CAA scheme. To mitigate the strong interference, the almost blank subframe (ABS)-based interference coordination is exploited first in macrocell-tier and then in smallcell-tier. The performance of the proposed CAA scheme is analyzed in presence of these two interference coordination methods. The derived expressions provide approximate solutions of reasonable accuracy compared to the results obtained from Monte-Carlo simulations. Numerical results comparatively analyze the gains of CAA scheme over conventional RSP-based association and biased RSP-based association with and without the interference coordination method. Also, the results reveal insights regarding the selection of the proportion of ABS in macrocell/smallcell-tiers for various network scenarios.
Comments: 14 Pages. Submitted to the IEEE Transactions of Communications
[v1] 2015-02-11 08:41:01
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