OFDMA

LTE-Advanced is the combination of downlink and uplink modulation techniques along with the Multiple Input Multiple Output (MIMO) schemes. This enables to achieve the target for the improved performance in terms of spectral efficiency, high throughput, lower latency and higher cell capacity. The key goal of this paper is to implement the cell search and synchronization procedure using primary and secondary signal. Synchronization between the signals using CAZAC sequence has been implemented. The performance of SC-FDMA has been compared with the OFDMA in terms of PAPR for 16-QAM and 64-QAM. Results show that SC-FDMA has low PAPR as compared to OFDMA and best for uplink technique.

The main techniques applied to provide quality of service guarantees in metropolitan area networks are OFDMA and MCS. OFDMA organizes the information within a bidimensional frame considering the time and frequency domains while MCS defines the level of robustness of a transmission. The loca-lization of the data within the frame are defined in map messages transmitted in each frame. Thus, the main contribution this paper is to present a deep analysis of the overhead generated by these map messages. This analysis presents the behavior of the network in several scenarios that consider variations in the amount of data transmitted and in the quantity of mobile stations. Furthermore, we consider the variability of the wireless channel. Resumo. As principais técnicas utilizadas para prover garantias de qualidade de serviço em redes sem fio metropolitanas são OFDMA e MCS. A técnica OFDMA organiza as informações nos domínios tempo e frequência, formando um quadro bidimensional, enquanto a técnica MCS define o nível de robustez da transmissão. Nesse contexto, para os dados serem dispostos no quadro, deve-se utilizar informações de mapas que indicam a localização destes dados. Assim, a principal contribuição deste artigó e apresentar uma profunda análise relativa ao overhead causado pelos mapas no quadro OFDMA. Essa análise apresenta o comportamento da rede em diversos cenários, variando a quantidade de da-dos transmitidos e a quantidade de estações móveis, bem como considerando a diversidade do meio sem fio.

This paper demonstrates the use of some novel cognitive techniques we propose to improve the throughput of a mobile WIMAX network and minimize the packet losses. We propose a novel method called Orthogonal Frequency Division Most Congested Access First (OFDMCAF), to modify the spectrum sharing technique of (Time Division Multiple Access) TDMA and (Orthogonal Frequency Division Multiple Access) OFDMA and to manage the spectrum access. The heavy multimedia traffic is managed by OFDMCAF with novel spectrum sharing and buffer management methods we propose. By use of novel cognitive methods, real time voice and video packet transmissions have been provided with full success and the packet loss rate of data packets has been minimized. The simulation results are confirmed by comparing them with results of other publications and comparing with results of packet loss calculations we made. The results are usable in designing unicast mobile multimedia network with improved system throughput.

Filter bank multicarrier (FBMC) is considered a competitive waveform candidate for 5G that can replace orthogonal frequency division multiplexing (OFDM). However, channel estimation (CE) is a big challenge in FBMC because it suffers from intrinsic interference which is due to the orthogonality of the subcarrier functions in the real field only. In this paper, we investigate a proposed modified interference approximation scheme (M-IAM) by approximating the intrinsic interference from the neighbouring pilots to accommodate the complex channel frequency and thus improving CE performance besides simplifying its processing. The M-IAM scheme has a larger pseudo pilot magnitude than other conventional preamble schemes, namely the interference approximation method (IAM) with its versions (IAM-C) and (E-IAM-C); in addition to the novel preamble design (NPS). In addition, the proposed (M-IAM) scheme is characterized by the lower transmitted power needed. The CE performance of the M-IAM is investigated through 512 and 2048 subcarriers via different types of outdoor and indoor multipath fading channels that are time-invariant such as IEEE 802.22, IEEE 802.11, Rician, and additive white Gaussian noise (AWGN), as well as time-varying channels such as Rayleigh and Vehicular A (Veh-A). Simulation results demonstrate that the proposed M-IAM scheme achieves a lower bit error rate (BER), lower normalized mean square error (NMSE) and lower peak-to-average power ratio (PAPR) over the conventional preamble schemes under the aforementioned channel models. The proposed scheme has the advantage of saving the transmitted power, a requirement that could match 5G low power requirements. KEYWORDS Filter bank multicarrier (FBMC), intrinsic interference, preamble based channel estimation methods