Ayad Atiyah Abdulkafi

Energy efficiency and cell coverage area analysis for macrocell networks

The issues of energy efficiency and environmental protection are becoming critical issues for both fixed and wireless network operators worldwide. For wireless network operators, the challenge generally lies on providing maximum energy efficiency with largest possible coverage area. In this paper we first investigate the parameters affecting energy efficiency and the cell coverage area. We later analyze the relationship between area power consumption and transmission range (cell radius), transmission power, frequency band, shadowing and the path-loss exponent. From the analysis, optimal inter site distance that utilizing minimum area power consumption can be obtained for different percentage requirement of coverage area corresponding to minimum transmit power that achieves this degree of coverage. The optimal inter site distance is determined for macrocell without the impact of shadowing to be equal about 1250 m with minimum area power consumption of 526 W/km2. With the effect of shadowing, the optimal inter site distance and minimum area power consumption are 1050 m and 778.7 W/km2 respectively.

Energy efficiency of LTE macro base station

The growing energy consumption in wireless networks driven by dramatic increases in mobile users and network traffic, are putting mobile operators under immense challenges towards meeting the demands of both cost reduction and environment conservation. The network Energy Efficiency (EE) considers not only energy consumed by the base station (BS), but also the capacity and coverage of the network. In this paper we study the impact of modulation and coding schemes (MCS), bandwidth (BW) size and transmitted power on the energy efficiency of a LTE macro base station. Although it is very much expected that higher transmission power results in lower EE, the difference actually diminishes when cell size increases. At around 1200m it is found that the EE are almost equal for all transmission power considered. On the other hand, EE increases significantly as the BW increases. Similar effect on EE is observed when MCS changes from lower order to higher order scheme. In fact EE becomes more sensitive to MCS change at higher bandwidth.

On performance analysis of LS and MMSE for channel estimation in VLC systems

Channel estimation is a key feature for wireless optical communication systems. This paper presents an evaluation of channel estimation techniques for indoor visible light communication (VLC) systems using a direct current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) scheme. The VLC system can simultaneously provide illumination and wireless communication at a high data rate. However, the coverage area is limited and the distance is about 3 m. In this paper, performance analysis of two channel estimation methods is presented, one using the least squares (LS) algorithm and the other the minimum mean square error (MMSE) algorithm, to estimate channel response by applying them to various M-QAM modulations. The performance of these two methods is compared by mathematical analysis and by simulation by measuring bit error rate (BER) and mean square error (MSE) versus signal-to-noise ratio (SNR). The results shown that, at higher SNR, the MMSE algorithm outperforms the LS for both BER and MSE.

Performance analysis of DCO-OFDM in VLC system

The performance of indoor visible light communication (VLC) systems using a direct current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) scheme is investigated in this paper. The impact of nonlinearity of Light Emitting Diode (LED) and its beam angle on the VLC system performance is studied. We later analyze the effect of modulation order, number of subcarriers, signal scaling and biasing operation on the peak to average power ratio (PAPR) which is a major issue in OFDM based VLC system. Simulation results show that the bit error rate (BER) decreases as the degree of nonlinearity increases and a better BER can be achieved as the LED behavior approaches linear model. In addition, it is shown that reducing the QAM order or increasing the number of subcarriers may reduce the effect of the LED nonlinearity, thus improving the BER performance of the VLC system. Moreover, it is demonstrated that PAPR is higher for a large number of subcarriers and modulation order. Finally, the PAPR of the visible light OFDM system can significantly be reduced by employing the signal scaling combined with biasing operation.

Energy-aware load adaptive framework for LTE heterogeneous network

One of the main approaches for improving the network energy efficiency EE is through the introduction of load adaptive techniques, where the networks components/subsystems are switched off when the network is lightly loaded. Optimising such a dynamic operation in a heterogeneous network HetNet remains an active topic of research. In this paper, a traffic load-adaptive model that aims to evaluate the EE of base stations in Long Term Evolution LTE HetNet is presented. First, a model that simulates the load-adaptive power consumption behaviour of LTE HetNet is developed. In this regard, a load adaptation factor is introduced to assess the networks EE performance. The model also adapts and predicts the achievable data rate of each base station with respect to the traffic load. Our study shows that the fully load-adaptive LTE HetNet can significantly improve networks EE up to 10%, 40%, and 80% for high, medium, and low loads, respectively, as compared to the conventional non load-adaptive HetNet. In addition, we show that the full adaptive network operation can achieve significant EE gains under a realistic daily traffic profile up to 86%. The proposed evaluation model is essential to assess the network EE and can be used in future studies that focus on improving the adaptation level of the already installed network equipments. Copyright ©2014 John Wiley & Sons, Ltd.

QoS-aware joint uplink-downlink scheduling in FDD LTE-Advanced with carrier aggregation

Efficient resource utilization is of a high importance for LTE/LTE-A network performance and provisioning of user quality of experience. The eNodeB (LTE base station) is responsible for controlling the radio resources between the user and LTE /LTE-A network. The resources can be scheduled in two schemes; either independently or jointly by considering both uplink (UL) and downlink (DL) together. Joint scheduling is an attractive approach for resource utilization and for providing better Quality of Service (QoS), but it adds some computational complexity to the system. This paper aims to provide QoS-aware joint UL-DL scheduling for LTE-A utilizing the functionality of carrier aggregation. The scheme presented enforces the fair sharing of the resources between the UL and DL channels while maintaining good QoS. The work is based on simulation using the MATLAB-based IS-Wireless system level simulator. The key contributions of this work lie in addressing both the joint scheduling and the carrier aggregations while considering the QoS and traffic conditions of the users.

On the extension of traditional resource allocation algorithms in LTE-A to joint UL-DL scheduling with FDD carrier aggregation

Through and spectral efficiency maximization are two of the most challenging issues to be addressed by current and future cellular networks. To achieve these goals however, radio resources need to be utilized in a coordinated manner to provide better network performance and ensure adequate user quality of service (QoS). The radio resources are controlled by LTE base station (eNodeB) and can be scheduled either independently or jointly by considering both uplink (UL) and downlink (DL). This paper addresses the joint UL-DL scheduling in a carrier aggregation (CA) supportive LTE-advanced networks. This work provides good insights of the implementation of the traditional scheduling algorithms for joint UL-DL scheduling for LTE-A utilizing the functionality of CA. We present preliminary results from a MATLAB-based IS-Wireless system level simulator that confirm the importance of the fair sharing of the resources between the UL and DL channels while maintaining a good QoS. Furthermore, simulation results show that the resource utilization and spectral efficiency can be significantly improved by dynamically changing the bandwidth portion between the UL and DL. Finally, we also show that there is a significant improvement in both UL and DL data rates using the proposed CA and joint scheduling schemes.