In CDMA systems, outer loop power control (OLPC) determines the target value of SNR at the receiver, mostly by using look-up tables to map bit error rates (BERs) to SNRtargets. In this contribution, transmission delay and packet loss rate constraints in the data link layer (DLL) are invoked in order to determine the optimum outer loop SNR-target setpoint analytically, according to the number of active users in cell. Optimality is, in this sense, the maximization of system throughput. Using the optimum SNR-target, the optimal spreading factor is determined. Subsequently, the joint optimization of outer loop SNR-target and variable spreading factor (VSF), at the physical(PHY)-layer, with truncated automatic repeat request (ARQ) error control mechanism at the data link layer are proposed. Our scheme is compared with ‘constant SNR-target’ and ‘PHY-layer based variable SNR-target’ cases under continuous power and rate variation to show (analytically and by simulations) the achievable gain through the coupling of physical and data link layers parameters.
Published in: 2011 IEEE Global Telecommunications Conference – GLOBECOM 2011
Date of Conference: 05-09 December 2011
Date Added to IEEE Xplore: 19 January 2012
Conference Location: Houston, TX, USA
Introduction
Effective and efficient resource allocation strategies are vital in achieving desirable performance in direct-sequence code division multiple access (DS-CDMA) systems. In particular, QoS provisioning in 3rd generation networks with Femtocell layers requires more efficient techniques for allocation of limited resources [1]. Adaptive resource allocation methods have been widely considered in the last decade. These schemes exploit the time-varying nature of a channel in order to manage resources optimally, yielding better throughput. Typical adaptive techniques include adaptation of transmitter power [2], adaptive modulation [3], adaptive coding [4], adaptive spreading factor [5], [6], or any combination of these methods [5], [7].
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