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Adaptive Scheduling for Beyond 3G Cellular Networks
Published in Mohamed Ibnkahla, Adaptation and Cross Layer Design in Wireless Networks, 2018
OFDMA has greatly attracted attention as an efficient multiple-access and modulation technique for wireless communications since it is based on orthogonal frequency division multiplexing (OFDM) and inherits its very high immunity to ISI and frequency selective fading, the conventional problems ofwireless transmission. Moreover, OFDMA is very flexible as a multiple-access scheme since it has the ability to schedule resources in two dimensions: frequency and time. This property makes it more suitable for the exploitation of multiuser diversity through scheduling in the frequency dimension, as well as adaptable to the time-varying nature of wireless mobile channels through scheduling in the time dimension.
WLAN Technology Basics
Published in Rihai Wu, Xun Yang, Xia Zhou, Yibo Wang, Enterprise Wireless Local Area Network Architectures and Technologies, 2021
Rihai Wu, Xun Yang, Xia Zhou, Yibo Wang
OFDMA is an orthogonal frequency division multiple access technology that distinguishes different users by frequency. In FDMA, each frequency represents a user, with GIs required between frequencies to reduce interference, as illustrated in Figure 2.30. By contrast, OFDMA uses orthogonal frequencies whose orthogonality, as described in Section 2.2.2, eliminates mutual interference as well as the need for GIs. Such frequencies can even overlap with each other, as illustrated in Figure 2.31. Therefore, OFDMA offers significantly improved spectrum utilization when compared with FDMA.
5G Concepts
Published in Saad Z. Asif, 5G Mobile Communications Concepts and Technologies, 2018
OFDM capitalizes on the use of cyclic prefixes to reduce intersymbol interference (ISI) and IFFT/FFT operations. IFFT/FFT (Inverse/Fast Fourier transform) allow combining multiple carriers at the baseband leading to OFDMA. OFDMA offers bandwidth scalability, robustness to multipaths, and effective integration with MIMO. However, aside from the benefits, OFDM suffers from high PAPR (Peak-to-Average Power Ratio) and inferior frequency localization due to the use of pulse shape filters. Details on OFDM/OFDMA can be found in [7].
Outage Trade-Offs Between Full/Half-Duplex Relaying for NOMA Aided Multicarrier Cooperative D2D Communications System
Published in IETE Technical Review, 2022
Motivated by existing literature, this paper proposes a NOMA-aided C-D2D communications system where DT operates either as an HD or FD relay for cellular downlink signal utilizing DF relaying protocol. The system model consists of P D2D pairs along with M CUs and a BS. Using OFDMA, available cellular bandwidth is split into N independent and orthogonal subcarriers, wherein every subcarrier acquires the same subchannel bandwidth. In the proposed model, we have assumed that the D2D communication is operator-controlled [31], i.e. the BS assigns resources between CU and D2D users. According to the proposed scheme, BS broadcasts N subcarriers to CU and D2D pair. Out of N received subcarriers, D (where D<N) subcarriers are assigned to DT for relaying the downlink cellular transmission signal, and the remaining subcarriers are assigned to the D2D user for its own transmission. BS utilizes NOMA for simultaneously transmitting cellular downlink and D2D signals. Precisely, the D2D and cellular downlink signals are superimposed by the BS employing power domain multiplexing. Further, this superimposed signal is broadcasted by the BS to CU as well as the D2D user. SIC is utilized at DT, wherein cellular downlink signal is decoded first assuming D2D signal as interference, and subsequently, it is subtracted from the superimposed signal for decoding the D2D signal.
Hardware chip performance analysis of different FFT architecture
Published in International Journal of Electronics, 2021
Amit Kumar, Adesh Kumar, Aakanksha Devrari
The work is carried on the Xilinx ISE software with different FPGA supporting synthesis environment. The limitation of the work is that the hardware utilisation summary, timing report will change on different software platforms such as Modelsim, Quartus-2, which are also popular tools and their FPGA hardware support is different. The novelty of the work is that the suggested FFT architectures can be configured on any Xilinx supporting FPGAs and the FFT length is variable. The FFT architecture varies from 8-point to 65,536-point, which more enough for high-speed applications. The FFT is widely used transformation in several applications of digital signal processing and communication system. FFT is the integral part of 4 G, 5 G communication techniques such as OFDM, OFDMA, 5 G new radio and software defined radio, spectrum analyser and many more. It is always challenging to choose the specific FFT architecture for a particular application, and analyse its behaviour on FPGA. The research work will help the hardware designers to pre-estimate the required FFT architecture and its performance on FPGA. The overhead in the work is that the performance of the FFT designs can be compared based on other FPGA parameters, such as slices, LUTs, flip-flops, memory, delay, throughput and frequency support. We have considered only DSP slices, block RAM and transform cycles. The machine learning algorithm can help to predict the massive configurability to FFT architectures and FPGA synthesis in case of multiple processors and blocks are configured together.
What is in store in the January-February 2020 issue of IETE Technical Review?
Published in IETE Technical Review, 2020
Orthogonal Frequency Division Multiple Access (OFDMA) has several disadvantages such as tight synchronization, orthogonality constraints, and significant bandwidth wastage. One way to overcome this problem is to use a combination of Non Orthogonal Multiple Access (NOMA) and Universal Filtered Multi-Carrier (UFMC). Ajit Singh, K. Krishna Naik and C.R.S. Kumar, in their paper entitled “NOMURA: A Spectrally Efficient Non-orthogonal 5G Multiple Access Downlink Scheme for Cognitive Radio” propose NOMA-UFMC-based Radio Access (NOMURA) scheme which is asynchronous, bandwidth efficient and provides higher throughput. By benchmarking their simulation results against OFDMA and Filter Bank Multi-Carrier-Filtered Multi-Tone, they show that NOMURA is more apt for flexible bandwidth allocations, active cancellation, higher throughput and provides equivalent Bit Error Rate performance under AWGN and Rayleigh fading conditions.