Xinning Zhu

A coloring-based resource allocation for OFDMA femtocell networks

In order to improve the spectrum efficiency in the femtocell network and mitigate the co-tier/cross-tier interference, we propose a novel graph-theoretic scheme based on coloring algorithm for self-adaptive spectrum resource allocation in femtocells. A dynamic orthogonal spectrum sharing between macrocell and femtocell is utilized in the proposed allocation scheme to reduce the cross-tier interference. In order to mitigate the cotier interference, a graph-based clustering resource allocation (GCRA) scheme is presented. The interference graph of the femto-tier is built first based on the measurement reports of femtocell user equipments (FUEs). Then a coloring algorithm is implemented in a distributed way to construct disjoint clusters in which the frequency band can be reused to improve the spectrum efficiency. Finally, a dynamic orthogonal resource allocation is performed to avoid the inter-cluster interference. The simulation results reveal that the GCRA approach enhances the spectrum efficiency of the femtocell network, while mitigating the co-tier/cross-tier interference of the heterogeneous network.

Survey of intercell interference mitigation techniques in LTE downlink networks

This paper presents a survey of intercell interference mitigation techniques in long term evolution (LTE) networks and focuses on algorithms which are more relevance with LTE downlink networks. A total of 20 different algorithms are reviewed and a qualitative comparison is done in terms of cell throughput and cell edge throughput. The comparison provided in this paper can be used to select the most appreciate technique for each particular goal.

On the performance of capacity integrated CoMP handover algorithm in LTE-Advanced

Coordinated multipoint (CoMP) transmission and reception is the key technique in LTE-Advanced to improve the cell-edge throughput and/or system throughput. Joint processing (JP) in CoMP technology provides multiple data transmission points for each user among multiple cooperated radio base stations. Handover is one of the key components in cellular network mobility management. A handover algorithm is needed for making a handover decision. In this paper, a capacity integrated CoMP handover algorithm supporting JP in LTE-A system is proposed. Capacity integrated CoMP handover algorithm aims to ensure the radio resources are efficiently used in the system in both capacity and channel quality domains while reducing unnecessary feedbacks. Simulation results show that capacity integrated CoMP handover algorithm not only can improve the system throughput but also minimize the system delay, packet loss, and less total number of handovers than open literature CoMP handover algorithm.

A distributed non-uniform pricing approach for power optimization in spectrum-sharing femtocell network

This paper presents a power optimization strategy based on pricing for femtocell-deployed networks. Assuming that the central Macrocell Base Station (MBS) considered as a leader sells transmission power quota to femtocells, a Stackelberg game is formulated and constraints to avoid unnecessary high transmission power are designed. The Stackelberg Equilibrium (SE) is studied and a Distributed Non-uniform Pricing (DNP)scheme where femtocells are self-organized is proposed, which needs only a little interactions. The simulation results verify the performances of DNP. It is shown that the proposed scheme performs well in terms of power optimization and interference mitigation. It also guarantees the fairness and Quality of Service (QoS) at the same time.

Limited Comp Handover Algorithm For LTE-Advanced

Coordinated multipoint (CoMP) transmission and reception is the key technique in LTE-Advanced to improve the cell-edge throughput and/or system throughput. Joint processing (JP) in CoMP technology provides multiple data transmission points for each user among multiple cooperated radio base stations. Hard handover mechanism is adopted to be used in LTE-Advanced. Standard hard handover algorithm could not satisfy the concept of JP in CoMP in LTE-A due to the constraint of single connection for each user at any time. While the radio resources in the system are fixed, the more multiple data connections a user has, the more radio resources are used for the extra data connections, thus the lower capacity a system becomes. Therefore a new handover algorithm that not only supports JP in CoMP but also takes system capacity into consideration in LTE-A system is necessary. This paper proposes a new handover algorithm known as Limited CoMP Handover Algorithm to support JP in CoMP and overcome the system capacity issue. System performance of Limited CoMP Handover Algorithm is evaluated and compared with open literature handover algorithm via simulation in this paper. The simulation results show that Limited CoMP Handover Algorithm outperforms open literature handover algorithm by having shorter system delay and less system load whilst maintaining a higher system throughput in a high congested network.

Analysis of joint effect of phase noise, IQ imbalance and amplifier nonlinearity in OFDM system

The Orthogonal Frequency Division Multiplexing (OFDM) based system is highly sensitive to Radio Frequency (RF) impairments including phase noise and IQ imbalance at the receiver and High Power Amplifier (HPA) nonlinearity at the transmitter. In this paper, the theoretical characterization of the joint effects of these RF impairments on the performance of the OFDM system with QPSK and 16QAM modulations are presented. The theoretical models for the three RF impairments are derived individually and jointly. Furthermore, the Bit Error Rate (BER) as a function of the RF impairments parameters is formulated for the OFDM system over AWGN channels. The results indicate that phase noise, IQ imbalance and HPA nonlinearity strengthen each other when they are jointly evaluated. The average BER performance is inversely proportional to the RF impairments, and there exists a BER error floor when RF impairments are high. The close matching of the work presented in this paper with previous works confirm the validity of the proposed theoretical approach.

PAPR reduction for carrier aggregated uplink in LTE-A system

The adoption of Carrier Aggregation (CA) technology enables the LTE-Advanced (LTE-A) system to support very-high-data-rate transmission over wide frequency bandwidths and to keep the backward compatibility of LTE system. Nevertheless, the authors have to deal with the significant increase of peak-to-average power ratio (PAPR) associated with the carrier aggregation, which determines the efficiency of Power Amplifier (PA) and the coverage of the terminal. This paper proposes an improved Selected Mapping (SLM) scheme to reduce PAPR of the LTE-A uplink data and demodulation reference signal (DMRS) symbols by 2 to 3 dB for different component carrier (CC) numbers and modulation modes, in which the signaling overhead of conventional SLM is eliminated by exploiting the features of DMRS. The linear property of Inverse Fast Fourier Transformation (IFFT) is used to reduce the computational complexity of SLM. The proposed scheme with 4 initial phase sequences reduces the complex multiplications by 63.5% and the complex additions by 68.2% compared with the conventional SLM scheme with 16 phase sequences while keeping the similar PAPR reduction performance.

System level simulation to evaluate the interference in macrocell-picocell downlink systems

System level simulations are required to evaluate the influences of cell planning, scheduling, or interference management methods on the performance of the new mobile network technologies. Interference is one of the important challenges when co-channel is used as the frequency deployment for macrocell- picocell scenario. Interference could degrade the system throughput especially for users located in cell edge regions. Therefore, a system level analysis is needed to assess the performance of macrocell-picocell scenario when an interference management technique is deployed. This paper presents a structure for system level simulation based on MATLAB to evaluate the performance of macrocell-picocell heterogeneous networks in the framework of International Mobile Communication (IMT)-Advanced evaluation. Then, the performance of an enhanced intercell interference coordination (eICIC) method is evaluated through the proposed structure.