In this paper, we are proposing a pilot-aided channel estimator for the multiple-input multiple-output (MIMO) directsequence code-division multiple access (DS-CDMA) communication systems based on the minimum mean-square error (MMSE) estimate of the attenuated transmitted signals in the presence of Rayleigh fading channel coupled with the white Gaussian noise. The proposed receiver consists of bank of matched filters matched to the signature waveform of the desired user followed by a nonlinear estimator, resulting from the MMSE estimate of the attenuated transmitted signal. Simulation results carried out for multiple values of signal to noise ratio (SNR) and number of users show that the theoretical predictions are very well substantiated.

Orthogonal Frequency Division Multiplexing (OFDM) is a highly regarded technique used in the 4G mobile communication systems to provide reliable communication and high data rates due to the orthogonality between its sub carriers. However, it cannot be used in the next generation cellular system i.e. 5G. Thus, a new technique Generalized Frequency Division Multiplexing (GFDM) has been proposed to meet the demands of the next generation systems, which are higher data rates than 4G, minimum response time, lower power consumption etc. GFDM is a non-orthogonal, multicarrier scheme, which seems to fulfil the requirements of the new wireless communication system. The aim of this paper is to use the pilot symbols and their optimum placements within the data for the channel estimation of the GFDM system. It is shown that the optimum arrangement of the pilot symbols is to place them uniformly on equal intervals within the data and to cluster them in the middle of the data.