CDMA POWER CONTROL USING FIREFLY ALGORITHM

Abstract

Power control is an essential radio resource management method in CDMA cellular communication systems because the users transmit their signals simultaneously in the same frequency band. Each user is given a dedicated spreading code, which is used to identify the users in the receivers by correlating the received signal with a replica of the desired user’s code. The cross-correlation of different spreading codes is ideally zero, but due to multipath propagation and non-ideal spreading codes this is not the case in practice. The receiver therefore sees the other users’ signals as interference and the more users in the system the more interference are generated. CDMA is interference-limited, which means that it is the interference from other users that limits the capacity of the system. To increase capacity, some methods are needed for interference management. Power control aims to control the transmission power levels in such a way that acceptable quality of service for the users is guaranteed with lowest possible transmission powers. All users benefit from the minimized interference and the preserved signal qualities. For CDMA system Power control is the most important system requirement. If power control is not implemented many problems such as the near-far effect will start to dominate and consequently will lower the capacity of the CDMA system. However, when the power control in CDMA systems is applied, it allows multiple users to share resources of the system equally between themselves, leading to increased capacity. With appropriate power control, capacity of CDMA system is high in comparison to frequency division multiple access (FDMA) and time division multiple access (TDMA).For power control in CDMA system optimization algorithms i.e. genetic algorithm, particle swarm algorithm and firefly algorithm can be used which determines a suitable power vector [1], [2]. These power vector or power levels are determined at the base station and told to mobile units to adjust their transmitting power in accordance to these levels. So our aim here was to find out the suitable power vector using firefly algorithm that can be used by different mobile units so that no blocking occurs. In this thesis a new closed loop power control method for CDMA cellular communication systems is proposed