Orthogonal Frequency Division Multiplexing In Presence Research Articles

Joint MAP channel estimation and data detection for OFDM in presence of phase noise from free running and phase locked loop oscillator

This paper addresses a computationally compact and statistically optimal joint Maximum a Posteriori (MAP) algorithm for channel estimation and data detection in the presence of Phase Noise (PHN) in iterative Orthogonal Frequency Division Multiplexing (OFDM) receivers used for high speed and high spectral efficient wireless communication systems. The MAP cost function for joint estimation and detection is derived and optimized further with the proposed cyclic gradient descent optimization algorithm. The proposed joint estimation and detection algorithm relaxes the restriction of small PHN assumptions and utilizes the prior statistical knowledge of PHN spectral components to produce a statistically optimal solution. The frequency-domain estimation of Channel Transfer Function (CTF) in frequency selective fading makes the method simpler, compared with the estimation of Channel Impulse Response (CIR) in the time domain. Two different time-varying PHN models, produced by Free Running Oscillator (FRO) and Phase-Locked Loop (PLL) oscillator, are presented and compared for performance difference with proposed OFDM receiver. Simulation results for joint MAP channel estimation are compared with Cramer-Rao Lower Bound (CRLB), and the simulation results for joint MAP data detection are compared with “NO PHN” performance to demonstrate that the proposed joint MAP estimation and detection algorithm achieve near-optimum performance even under multipath channel fading.

Performance of Filtered OFDM Over Different Fading Channels

Orthogonal frequency division multiplexing (OFDM) schemes are used extensively nowadays in large number of practical systems, but OFDM may not be the ideal solution for 5G scenarios because OFDM has high Out of band emission (OOBE) due to high spectral leakage and high peak to average power ratio (PAPR). Therefore Filtered OFDM (F-OFDM), which uses sub band filtering, is proposed as the most flexible waveform for 5G. However there is no work listed in the literature so far that compares the bit error rate (BER) performance of F-OFDM and conventional OFDM in AWGN, Rayleigh and Rician channel. This paper presents the simulation results on the BER performance of F-OFDM and OFDM in presence of AWGN, Rayleigh and Rician channel. The comparison is also done in terms of OOBE and PAPR factor. Results indicate that F-OFDM shows significantly less spectral leakage with same performance in terms of BER compared to conventional OFDM. However for the cases considered, OFDM performance is slightly better than F-OFDM in terms of PAPR factor.

Joint MAP Detection for OFDM in Presence of Phase Noise from Free Running and Phase Locked Loop Oscillator

This paper addresses a statistically optimal joint maximum a posteriori (MAP) data detection and phase noise (PHN) estimation algorithm for iterative orthogonal frequency division multiplexing (OFDM) receivers, used for high speed and high spectral efficient wireless communication systems. First the cost function for data detection in presence of PHN is formulated with MAP criterion and is optimized further. The optimization is performed in frequency domain with proposed multidimensional circulatory gradient descent algorithm. With reduced computational complexity, the proposed optimization incorporates the statistics of PHN spectral components in prior. The condition of small PHN is relaxed in the proposed algorithm to achieve near optimal performance. Two different models for time varying PHN: produced by free running oscillator and phase locked loop (PLL) oscillator, are presented and implemented for proposed OFDM receiver. Simulation results demonstrate that the proposed optimization achieves “NO PHN” performance for both the PHN models even under multipath channel fading.

Performance analysis of FFT based OFDM and DWT based OFDM for Underwater Acoustic Communication

The underwater acoustic communication demands high data rate with low power. One of the very important techniques for the requirement is Orthogonal Frequency Division Multiplexing (OFDM). The OFDM systems implemented is a conventional OFDM which has Fast Fourier Transform (FFT) blocks in their receivers and Inverse FFT (IFFT) blocks in their transmitters. Now the research shows the use of Discrete Wavelet Transform (DWT) in place of FFT and Inverse DWT (IDWT) in place of IFFT renders the increased system performance. The major reasons for the performance degradation in the conventional FFT OFDM compared to The DWT OFDM are Carrier Frequency Offset (CFO), Multipath effect and Doppler Effect which need to be tested. The paper discusses about the BER (Bit Error Rate) performance of the DWT OFDM in presence of Channel and without channel individually and the results are compared with that of the conventional OFDM. For this, The Channel estimation is carried over in both DWT OFDM and FFT OFDM using same procedure and their BER performance are simulated using MATLAB and Simulink. In both, for the given channel condition the DWT OFDM fairly outperforms the FFT OFDM. Keywords: Carrier Frequency Offset (CFO), Discrete Wavelet Transform (DWT), Fast Fourier Transform (FFT), Multipath Effect, Underwater Acoustic Communication

Performance Assessment of OFDM Utilizing FFT/DWT over Rician Channel Effected by CFO

Orthogonal Frequency Division Multiplexing (OFDM) is a popular kind of multi-carrier based transmission technique that has found its applications in some wireless and wireline systems. But this system suffers from several facts that degrade its performance resulting in the interference of sub-carriers. Carrier Frequency Offset (CFO) is considered as one of the factor that causes interference in the system, leading to an Inter-Carrier Interference (ICI) between the carriers that results in a degradation in the performance factor of the system. In this research work, a comparative estimation is done on the Bit Error Rate (BER) performance of Discrete Wavelet Transform (DWT) OFDM and Fourier Transform (FFT) OFDM in the presence of CFO in both of the given systems. The research focuses mainly on the improvement of the BER in the system. The complete analysis is done by considering the channel to be Rician and the systems performance is estimated for some practical values of CFO. The complete simulation is done in the MATLAB. As the CFO increases the error in the system also increases, but still in that situation, DWT shows better improvement than the conventional system. The BER performance of OFDM systems shows improvement for all the diverse PSK modulation.