Comparison of SPS and FA methods for Blind Carrier Frequency Offset Estimation in OFDM systems

In orthogonal frequency-division multiplexing (OFDM) systems, synchronization issues are of great importance since synchronization errors might destroy the orthogonality among all subcarriers and, therefore, introduce intercarrier interference (ICI) and intersymbol interference (ISI). Several schemes of frequency offset estimation in OFDM systems have been investigated. This paper compares performance and computational complexity of Smoothing Power Spectrum (SPS) and Frequency Analysis (FA) methods for blind carrier frequency offset (CFO) estimation in OFDM systems.

Pilot-Assisted OFDM for Underwater Acoustic Communication

Multicarrier techniques have made it possible to wirelessly transmit data at higher rates for underwater acoustic (UWA) communication. Several multicarrier techniques have been explored in the past for wireless data transmission. OFDM is known to fight off inter-symbol interference due to the orthogonality of its subcarriers. However, due to time variations, OFDM suffers from intercarrier interference. As the UWA channel is both a time and frequency variant, channel estimation becomes complex. We propose a pilot-based channel estimation technique and explore two equalizers for improving the error performance of an OFDM-based UWA system. Both the equalizers employ pilot subcarriers to estimate the UWA channel. One equalizer is a least squares (LS) equalizer and the other is a zero forcing (ZF) equalizer. Using computer simulations, it is observed that, for an acceptable error performance, the number of pilots should be one-fourth the number of subcarriers. Moreover, if the energy of the pilots is increased without changing the overall symbol energy, the error performance degrades. It is also noted that both the LS and ZF equalizers give an acceptable error performance with the ZF performing marginally better than the LS. Furthermore, the error performance of the proposed system is evaluated as a function of the transmitter-receiver distance and an acceptable error performance is observed even at 1250 m.

Partial Fractional Fourier Transform (PFrFT)-MIMO-OFDM for Known Underwater Acoustic Communication Channels

Communication over doubly selective channels (both time and frequency selective) suffers from significant intercarrier interference (ICI). This problem is severe in underwater acoustic communications. In this paper, a novel partial fractional (PFrFT)-MIMO-OFDM system is proposed and implemented to further mitigate ICI. A new iterative band minimum mean square error (BMMSE) weight combining based on LDLH factorization is used in a scenario of perfect knowledge of channel information. The proposed method is extended from SISO-OFDM configuration to MIMO-OFDM. Simulation results demonstrate that the proposed PFrFT-LDLH outperforms the other methods in the SISO-OFDM scenario and that its performance can be improved in MIMO-OFDM scenarios.

Flexible Numerology in 5G NR: Interference Quantification and Proper Selection Depending on the Scenario

The 3rd Generation Partnership Project (3GPP) adopted cyclic prefix OFDM (CP-OFDM) for both uplink and downlink communications (although DFT-s-OFDM is also allowed in the uplink) in 5G New Radio (NR) Release 15. However, due to the variety of proposed deployment options and scenarios, a single numerology will not be enough to fulfil all performance requirements. A scalable OFDM numerology was required to enable diverse services on a wide range of frequencies and deployments, and finding the right numerology for each scenario is of special relevance for the proper functioning of 5G NR. Using a simulator calibrated according to the parameters established for NR performance by the 3GPP, this paper presents the performance evaluation of NR for the main 5G scenarios and different CP-OFDM numerologies and device speeds. Results show that increasing subcarrier spacing boosts the strength of the system against intercarrier interference (ICI) caused my Doppler spread; however, to increase subcarrier spacing, the CP must be reduced proportionally, which makes intersymbol interference (ISI) and ICI caused by insufficient CP have a more predominant effect. Therefore, it is necessary to quantify the total interference of the system, in order to determine the proper numerology for each scenario, which will depend on all the factors mentioned above, and not only on the operation band, as suggested in the standardization process. All this allows concluding that the choice of the appropriate numerology for a particular system depends not only on the band of operation but also on the deployment scenario and the speed of the user equipment (UE). Likewise, it is concluded that it is even possible to use more than one numerology for the same scenario.

FILTER BANK MULTICARRIER (FBMC) UNTUK 5G

Saat ini, teknologi pada bidang telekomunikasi berkembang dengan pesat. Pengguna telekomunikasi membutuhkan teknologi komunikasi yang cepat dengan bandwidth yang lebih lebar. Oleh karena itu dikembangkanlah Filter Bank Multi Carrier/Offset Quadrature Amplitude Modulation yang merupakan teknologi kandidat modulasi yang akan digunakan pada 5G. Filter Bank Multi Carrier/Offset Quadrature Amplitude Modulation (FMBC/OQAM) merupakan perkembangan dari Orthogonal Frequency Division Multiplexing (OFDM) yang dimodifikasi dengan menggunakan filter untuk mengurangi noise. OFDM menggunakan teknik multiplexing yang membagi bandwith menjadi beberapa frekuensi sub-carrier. Tetapi OFDM memiliki kelemahan yaitu memerlukan Cyclic Prefix (CP) untuk mengatasi Intersymbol Interference (ISI) serta Intercarrier Interference (ICI). Dengan menggunakan Filter berdasarkan Lembaga Physical layer for dynamic spectrum access and cognitive radio (PHYDYAS) ,lebar bandwith yang bertambah akibat Cyclic prefix akan dapat dikurangi Hasil yang dicapai dalam penelitian ini adalah FBMC berhasil diterapkan dan data yang dikirim sama dengan data yang diterima.

PAPR Reduction of OFDM System with Biorthoganoal Wavelet Transforms

Orthogonal Frequency Division Multiplexing (OFDM) and Multiple Input and Multiple Output (MIMO) are two main techniques employed in 4th Generation Long Term Evolution (LTE). In OFDM multiple carriers are used and it provides higher level of spectral efficiency as compared to Frequency Division Multiplexing (FDM). In OFDM because of loss of orthogonality between the subcarriers there is intercarrier interference (ICI) and intersymbol interference (ISI) and to overcome this problem use of cyclic prefixing (CP) is required, which uses 20% of available bandwidth. Wavelet based OFDM provides good orthogonality and with its use Bit Error Rate (BER) is improved. Wavelet based system does not require cyclic prefix, so spectrum efficiency is increased. It is proposed to use wavelet transform including biorthoganoal wavelet transform with OFDM systems. This approach will reduce PAPR in the OFDM system effectively. We will design this model with different modulation Techniques like QPSK and QAM and compare the BER results.

Enhancing Throughput of Optimum Channel in of Dm Based Full Duplex Communication

The efficient use of radio facilities in cellular networks is essential and being widely studied. This letter sees a cellular relay system where various user couples perform trans-directional interaction via various relays relying on Orthogonal Frequency-Division Multiplexing (OFDM) communication.. Joint implementation of route and transmit allocation, along with subcarrier coupling, subcarrier distribution as well as relay choice, for complete output redistribution is identified as a combination estimation issue.. Using a graph conceptual strategy, we can efficiently fix the problem in exponential time by converting it into a Optimum Adjusted Bipartite Tracking (MWBM) issue. Simulation experiments are conducted to assess the complete throughput of the network versus transmitting energy per node and the number of relay nodes. Carrier frequency offset causes a number of impairments including attenuation and rotation of each of the subcarriers and intercarrier interference (ICI) between carrier frequency offset causes a number of impairments including attenuation and rotation of each of the subcarriers and intercarrier interference (ICI) between subcarriers. In the mobile radio environment, the relative movement between transmitter and receiver causes doppler frequency shifts, in addition, the carriers can never be perfectly synchronized. These random frequency errors in OFDM system distort orthogonality between subcarriers and thus intercarrier interference (ICI) occurs. A Number of methods have been developed to reduce this sensitivity to frequency offset

Partial ML Detection for Frequency-Asynchronous Distributed Alamouti-Coded (FADAC) OFDM

To further enhance frequency-asynchronous distributed Alamouti-coded (FADAC) orthogonal frequency division multiplexing (OFDM), we propose a new scheme which combines the partial maximum likelihood detection (PMLD) to the residual intercarrier interference cancellation (RIC). In order to decrease the performance gap from intercarrier interference- (ICI-) free level after single time iteration of the RIC, the final stage of the proposed scheme performs the PMLD limited to the symbols of less-reliable decision variables. We show that with the practically acceptable candidate symbol set size, a single iteration for RIC is enough to achieve the ICI-free performance. Moreover, the proposed scheme substantially expands the allowable ranges of the three undesirable terms, i.e., the timing and frequency offsets between the transmit antennas and the multipath delay spreads.