An Efficient ICI Self-cancellation Scheme for High order Constellations

Because of its great spectral efficiency and resistance to multipath interference, OFDM is a well-established modulation method in today’s broadband wireless mobile communication systems. The vulnerability of the OFDM system to frequency offset induced by oscillator imperfections and the Doppler shift in the channel is well-known. The loss of orthogonality is caused by the carrier frequency offset (CFO), in which case the signals sent on each carrier are not independent of one another, resulting in Inter Carrier Interference (ICI).

To lessen the effect of frequency offset, several approaches have been devised. These methods may be classified into two types. The frequency offset estimate and correction category is the first one. The frequency-offset reduction category is the second group. Duplicate items fall under this second group. To accomplish a trade-off between frequency offset sensitivity and bandwidth economy, modulation is required.

A novel strategy for ICI self-cancellation is presented in this chapter. This scheme’s core notion is first demonstrated using a simple single carrier system, and then it is adapted to multicarrier modulation systems. Each symbol is conjugated and repeated in the proposed system to create a data pattern in the transmitted stream. This data pattern will be used to negate CFO mistakes at the receiver. As a result, the sent stream has the following format: X1X1*X2X2*X3X3*…. Each symbol has a CFO phase error at the receiver. The phases of received symbols R1A and R1B* corresponding to broadcast signals X1 and X1* may be calculated by averaging these two phases. It is estimated the rectified received signal. Conjugate Phase Additive (CPA) is the name given to our proposed ICI self-cancellation technique. The suggested single carrier modulation strategy is applied to the OFDM system, and two novel conjugate approaches, Adjacent Conjugate Phase Additive OFDM (ACPA) and Symmetric Conjugate Phase Additive OFDM (SCPA), are developed (SCPA). In the MATLAB environment, the recommended strategies are implemented and simulated. Their findings are compared to existing ICI self-cancellation programmes. These two techniques, in contrast to prior ICI cancellation strategies, show a more gentle deterioration of Bit Error Rate (BER) as the normalised frequency offset increases. The SCPA method outperforms the SCSR by 7 dB in BER when compared to the best documented ICI self-cancellation system (ASR, SCSR). For 256-QAM modulation, the normalised frequency offset is 0.1.

 

In terms of hardware resource usage and frequency offset analysis, the proposed 256-QAM ACPA OFDM ICI self-cancellation system is implemented using the Xilinx System Generator tool for DSP design, co-simulated on Spartan3A DSP 3400 device FPGA, and compared with the widely used CFO Error estimation and Correction technique (CFO-EC), using cyclic prefix. The ACPA scheme requires less than half the CFO correction hardware that the traditional CFO-EC technique requires. The 256-QAM ACAP method delivers equivalent immunity against frequency offset errors across the realistic frequency offset range when compared to the standard 128-QAM OFDM system with CFO-EC correction.

Author(S) Details

S. E. D. Habib
Department of Electronics and Electrical Communications Engineering, Cairo University, Cairo, Egypt.

Reem I. Sayed
Electronics Factory, AOI, Egypt.

Hisham M. Hamed
Wasiela Company, Egypt.

Magdi Fikri
Department of Electronics and Electrical Communications Engineering, Cairo University, Cairo, Egypt.

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