SAFNAQ, An Algorithm for Transmission Power Allocation in MC- CDMA Muhammad Safdar Shabbir 1 and Muhammad Aqueel Ashraf Department of Electronics, Quaid-i-Azam University, 45320 Islamabad, Pakistan. Abstract. A power allocation algorithm for MC-CDMA communication systems is proposed. There are many algorithms of power allocation in MC-CDMA, e.g., frequency domain power allocation algorithm (FDPA), time domain power allocation algorithm (TDPA) and eigenvector based power allocationalgorithm (EBPA) etc., available in literature. The FDPA algorithm uniformly allocates power to some adaptively chosen strongest sub-carriers and all other deeply faded sub-carriers are shut off. In TDPA, the power adaptation is considered so that the desired signal strength at MRC receiver maintains at a fixed level. The EBPA algorithm allocates power in accordance with a power balance vector. This power balance vector is an eigenvector corresponding to the maximum eigenvalue of the modified projection matrix orthogonal to the interference signal subspace. The proposed algorithm, named SAFNAQ algorithm, is cohesion of FDPA and EBPA algorithms. It allocates transmission power to some adaptively chosen strongest sub-carriers not uniformly but in accordance with the power balance vector computed as in EBPA algorithm. Simulation results show that SAFNAQ algorithm outperforms both FDPA and EBPA algorithms as well as the no allocation algorithm. Keywords: SAFNAQ, Multi-Carrier, CDMA, Power Allocation, Adaptive Systems, Rayleigh Fading. 1. Introduction Multi-carrier code division multiple access (MC-CDMA) inherits the characteristics of both orthogonal frequency division multiplexing (OFDM) and code division multiple access (CDMA). It appears most suitable for future 4G mobile wireless communications with high data rate. Its main advantages include multiple access capability, frequency diversity, robustness against fading, and ability to mitigate the inter symbol interference (ISI) [1]. Power allocation is the most important issue among many research issues of MC-CDMA that ensures the efficient use of power to maximize performance gain of the system. In multi-carrier communications, the channel fading for each user and at different sub-carriers is different. The multi-user water filling power allocation was derived on the idea of Cheng and Verdue [2]. They proposed that a user should use a sub-channel at which his sub-channel is best among all users. Many authors have proposed different schemes for resource allocation on the basis of channel state information (CSI) [3–5]. Zhu and Gunawan [5] proposed that the sub-carriers having channel gains higher than a given threshold should only be used and turn off the deeply faded sub-carriers and apply maximal ratio combining (MRC) at the receiver. This approach results in no transmission, when all sub-channel gains remain below the threshold level. However, it is acceptable for delay tolerable traffics only. Zhu and Bar- Ness [4] proposed an eigenvector based power allocation (EBPA) algorithm for MC-CDMA systems with projection matrix based receiver. Lee and Bar-Ness [3] proposed frequency domain power allocation (FDPA) and time domain power allocation (TDPA) schemes and combination of these both for uplink MC- CDMA transmissions with MRC receiver. However, cohesion of frequency domain power adaptation scheme [3] with optimum EBPA algorithm described in [4] has not yet been discussed for uplink MC- CDMA systems. This idea is implemented in form of SAFNAQ algorithm. 1 + Corresponding author. Tel.: + (923365043042); fax: + (92-42-637.0580) . E-mail address: (msafdar87@gmail.com). 2011 International Conference on Computer and Software Modeling IPCSIT vol.14 (2011) © (2011) IACSIT Press, Singapore 232