Abstract:

This paper deals with the combination of advanced multi carrier modulation OFDM/OQAM with CDMA technique in the presence of MIMO channel. This combination takes advantages from multicarrier modulation and spread spectrum. Indeed, the use of OFDM has proved its ability to fight against frequency selective channels but the insertion of guard interval yields spectral efficiency loss and sensitivity to frequency dispersion due to the use of rectangular pulse shape. Thus, cyclic prefix OFDM is replaced by an advanced filter bank-based multicarrier system OFDM/OQAM that operates without guard interval. However, OFDM/OQAM provides orthogonality only on the real domain, so transmitted symbols must be real valued. In the other hand, the CDMA component has two advantages: multiple access interference cancellation and providing orthogonality in the complex domain. From the orthogonality property provided, the Alamouti ST code can be combined with MC-CDMA-OQAM system in order to exploit space and time diversity and to overcome drawbacks of classic cyclic prefix OFDM…

Abstract:

Multiple-input multiple-output (MIMO) technology and orthogonal frequency-division multiplexing (OFDM) can be combined to design a robust communications scheme with increased spectral efficiency and system capacity. To reach high power efficiency, MIMO-OFDM systems are equipped with high power amplifiers (HPA). When it operates near its saturation region, the HPA causes nonlinear distortions. Unfortunately, the nonlinearity of HPA has a crucial impact on the global system performance. In this paper, we focus on the effect of the HPA nonlinearity on the space-time block coded (STBC) MIMO-OFDM systems. Analytic expression of the average Bit error rate (BER) is delivered running under frequency selective channel. We also note an excellent agreement between analytic expressions and Monte Carlo simulation curves. In addition, this work introduces a new iterative cancelation technique for the nonlinearly detected by the receiver. The new proposed approach is based on the Bussgang theorem and consists in iterative estimation and annulation of the nonlinear distortion caused by the high power amplifier of the transmitter.

Abstract:

Multiple-input multiple-output (MIMO) systems are important elements in the recent wireless communication. Space Time Codes (STCs) and Space Multiplexing (SM) are mandatory for the WIMAX systems. The Alamouti’s scheme has played an important role for the growth and development of these systems. But, the Alamouti’s scheme remains with limited data rate (half rate). For this reasons, some research activities aimed to increase the data rate have been made. In particular, this paper deals with combining Alamouti’s system with the orthogonal codes in order to benefit from the full diversity, to increase the data rate and to keep the system simple as possible.