Simulation of Models and BER Performances of DWT-OFDM versus FFT-OFDM

Simulation approaches using MATLAB for wavelet based OFDM, particularly in DWT-OFDM as alternative substitutions for Fourier based OFDM are demonstrated. Conventional OFDM systems use IFFT and FFT algorithms at the transmitter and receiver respectively to multiplex the signals and transmit them simultaneously over a number of subcarriers. The system employs guard intervals or cyclic prefixes (CP) so that the delay spread of the channel becomes longer than the channel impulse response. The system must make sure that the cyclic prefix is a small fraction of the per carrier symbol duration. The purpose of employing the CP is to minimize inter-symbol interference (ISI). However a CP reduces the power efficiency and data throughput. The CP also has the disadvantage of reducing the spectral containment of the channels. Due to these issues, an alternative method is to use the wavelet transform to replace the IFFT and FFT blocks. The wavelet transform is referred as Discrete Wavelet Transform OFDM (DWT-OFDM). By using the transform, the spectral containment of the channels is better since they are not using CP. The wavelet based OFDM (DWT-OFDM) is assumed to have ortho-normal bases properties and satisfy the perfect reconstruction property. We use different wavelet families and compare with conventional FFT-OFDM system. BER performances of both OFDM systems are also obtained. It is found that the DWT-OFDM platform is superior as compared to others as it has less error rate, especially using bior5.5 or rbior3.3 wavelet family

Cross-tier interference avoidance technique for LTE-A femtocell networks using fractional frequency reuse

Deploying femtocell overlays over LTE-A macrocellular networks is an effective way to overcome the scarcity of bandwidth, increase the network coverage, enhance the indoor users’ performance, and improve the quality of service. Nevertheless, it will bring the cross-tier interference issue to prominence leading to dramatic degradation of these networks’ performance if no strategy is taken to tackle this problem. Using the Fractional Frequency Reuse (FFR) concept can be one of the good solutions to manage this interference. This paper proposes an FFR scheme for LTE-A femtocell networks to handle the downlink crosstier interference, generated between macro-cells and femtocells, in order to increase the Signal-to-Interference and Noise Ratio (SINR) and improve the overall network performance. The simulation results obtained by MATLAB reveal the superiority of the proposed-FFR scheme over the non-FFR one; as both SINR and user throughput have been enhanced. Outage probability results also prove that the proposed scheme can effectively support more users

QOS downlink schedulers in LTE towards 5G network

LTE is expected to be the dominant system used by operators in these years due to its promising solutions for achieving high capacity and data rate. However, LTE packet scheduling and distributing resources among users is still the main challenge due to unfairness and low performance which occur when allocating resources to users. In this paper, the above mentioned challenges are studied and analysed, focusing on three schedulers; they are Proportional Fair (PF), Maximum Throughput (MT) and Blind equal throughput (BET). These methods do not provide QoS to users that use different types of traffic flows. The proposed algorithm in this paper is to modify the PF scheduler in order to fulfil the QoS criteria maximizing throughput and minimizing the delay for real time service. VoIP and video have been selected as real time traffic and best effort as non-real time. LTE-Sim simulator is used to compare between the mentioned schedulers in terms of throughput, delay, packet loss ratio and spectrum efficiency

QoS downlink schedulers in LTE towards 5G network

LTE is expected to be the dominant system used by operators in these years due to its promising solutions for achieving high capacity and data rate. However, LTE packet scheduling and distributing resources among users is still the main challenge due to unfairness and low performance which occur when allocating resources to users. In this paper, the above mentioned challenges are studied and analysed, focusing on three schedulers; they are Proportional Fair (PF), Maximum Throughput (MT) and Blind equal throughput (BET). These methods do not provide QoS to users that use different types of traffic flows. The proposed algorithm in this paper is to modify the PF scheduler in order to fulfil the QoS criteria maximizing throughput and minimizing the delay for real time service. VoIP and video have been selected as real time traffic and best effort as non-real time. LTE-Sim simulator is used to compare between the mentioned schedulers in terms of throughput, delay, packet loss ratio and spectrum efficiency

Performance of BER with different diversity techniques for millimeter-wave communication system

In a communications system, a diversity technique is used to enhance the reliability of a message signal by using at least two channels with different characteristics. In this paper, all four possible scenarios are considered: Single-input and singleoutput (SISO), single input and multi-output (SIMO), multipleinput and single-output (MISO), Multiple-input and multiple output (MIMO) systems. Antenna arrays will be used to reduce BER and improve the performance of the system using array gain in the line of sight channel for 60 GHz frequency in an indoor scenario. Single input and single output are investigated before analysis of multiple inputs and multiple output channel in the line of sight (LOS) and multipath propagation. MATLAB simulation has been performed using BPSK modulation. The comparative studies show that the performance of the MIMO diversity technique is more reliable in terms of BER to improve the performance and efficiency of the communication system

An efficient modulation technique to mitigate nonlinearities in optical OFDM

The optical OFDM (O-OFDM) system is a growing technology for next generation high-speed optical communication. Two types of O-OFDM; CO-OFDM (Coherent- Optical OFDM) and Direct-current-based optical OFDM (DCOFDM) are discussed. Mach–Zehnder modulators (MZMs) are used in up-converter part of CO-OFDM system to convert the RF signal to optical signal when the light cannot directly modulate for higher speed. The MZM has a cosine behavior with high nonlinear characteristic that affects the system performance. This paper aims to investigate an efficient pulse modulation technique for mitigating nonlinearity effect in the Mach-Zehnder modulator of CO-OFDM system. It also highlights the proposed method, an efficient CO-OFDM system to solve the existing nonlinearity issue. This technique influences positively on OSNR to reduce non linearity over different distances of optical channel and improve the system performance in terms of power consumption and bandwidth efficiency

Frequency diversity improvement factor for rain fade mitigation in Malaysia

Microwave communication systems in tropical region like Malaysia, operating at higher frequency ranges, are degraded its performance severely during rains. Hence, the rain fade must be taken in consideration for the MW link design to track the service outage and quality. This paper aims to develop and propose frequency diversity Improvement Factor prediction model for rain fade mitigation from 5 – 40 GHz. The rain attenuation is predicted based on ITU-R rain attenuation prediction method using measured rain rate in Malaysia. The predicted data are analysed to develop and propose a prediction for the improvement factor. The proposed improvement factor model is investigated according to the fade margin where the frequency separation is set to 5 GHz only