Yuanye Wang

Carrier aggregation for LTE-advanced: functionality and performance aspects

Carrier aggregation is one of the key features for LTE-Advanced. By means of CA, users gain access to a total bandwidth of up to 100 MHz in order to meet the IMT-Advanced requirements. The system bandwidth may be contiguous, or composed of several non-contiguous bandwidth chunks that are aggregated. This article presents a summary of the supported CA scenarios as well as an overview of the CA functionality for LTE-Advanced with special emphasis on the basic concept, control mechanisms, and performance aspects. The discussion includes definitions of the new terms primary cell (PCell) and secondary cell (SCell), mechanisms for activation and deactivation of CCs, and the new cross-CC scheduling functionality for improved control channel optimizations. We also demonstrate how CA can be used as an enabler for simple yet effective frequency domain interference management schemes. In particular, interference management is anticipated to provide significant gains in heterogeneous networks, envisioning intrinsically uncoordinated deployments of home base stations.

Carrier load balancing and packet scheduling for multi-carrier systems

Abstract-In this paper we focus on resource allocation for next generation wireless communication systems with aggregation of multiple Component Carriers (CCs), i.e., how to assign the CCs to each user, and how to multiplex multiple users in each CC. We first investigate two carrier load balancing methods for allocating the CCs to the users- Round Robin (RR) and Mobile Hashing (MH) balancing by means of a simple theoretical formulation, as well as system level simulations. At Layer-2 we propose a simple cross-CC packet scheduling algorithm that improves the coverage performance and the resource allocation fairness among users, as compared to independent scheduling per CC. The Long Term Evolution (LTE)-Advanced is selected for the case study of a multi-carrier system. In such a system, RR provides better performance than MH balancing, and the proposed simple scheduling algorithm is shown to be effective in providing up to 90% coverage gain with no loss of the overall cell throughput, as compared to independent scheduling per CC.

Performance Analysis of Enhanced Inter-Cell Interference Coordination in LTE-Advanced Heterogeneous Networks

The performance of enhanced Inter-Cell Interference Coordination (eICIC) for Long Term Evolution (LTE)- Advanced with co-channel deployment of both macro and pico is analyzed. The use of pico-cell Range Extension (RE) and time domain eICIC (TDM muting) is combined. The performance is evaluated in the downlink by means of extensive system level simulations that follow the 3GPP guidelines. The overall network performance is analyzed for different number of pico-eNBs, transmit power levels, User Equipment (UE) distributions, and packet schedulers. Recommended settings of the RE offset and TDM muting ratio in different scenarios are identified. The presented performance results and findings can serve as input to guidelines for co-channel deployment of macro and pico-eNBs with eICIC.

Enhanced inter-cell interference coordination in co-channel multi-layer LTE-advanced networks

Different technical solutions and innovations are enabling the move from macro-only scenarios towards heterogeneous networks with a mixture of different base station types. In this article we focus on multi-layer LTE-Advanced networks, and especially address aspects related to interference management. The network controlled time-domain enhanced inter-cell interference coordination (eICIC) concept is outlined by explaining the benefits and characteristics of this solution. The benefits of using advanced terminal device receiver architectures with interference suppression capabilities are motivated. Extensive system level performance results are presented with bursty traffic to demonstrate the eICIC concepts ability to dynamically adapt according to the traffic conditions.

eICIC Functionality and Performance for LTE HetNet Co-Channel Deployments

Different technical solutions are enabling the move from macro-only scenarios towards heterogeneous networks with a mixture of different base station types. In this paper we focus on multi-layer LTE-Advanced networks, and especially address aspects related to co-channel interference management. The network controlled time-domain enhanced inter-cell interference coordination (eICIC) concept is outlined by explaining the benefits and characteristics of this solution. Extensive system level performance results are presented with bursty and non-bursty traffic to demonstrate the eICIC concepts ability to dynamically adapt according to the traffic conditions.

Utility Maximization in LTE-Advanced Systems with Carrier Aggregation

Long Term Evolution (LTE)-Advanced is expected to aggregate multiple Component Carrier (CC)s to fulfil the high data rate requirement. It may serve users with different capabilities in accessing these CCs, e.g., some can access all CCs, whereas some may operate on only one CC. This gives challenges to the packet scheduler to maximize the system performance over all CCs. In this paper we provide a mathematical model of the log-measure utility in an LTE-Advanced system, and give proof that our previously developed cross-CC Proportional Fair (PF) packet scheduler maximizes this utility. System level simulations are performed, which confirm that cross-CC PF scheduling offers much higher utility than independent PF and channel blind schedulers. This scheduler is then generalized to adjust the resource sharing among users. It can trade off between average cell throughput and cell edge user throughput. However, any adjustment in the resource sharing leads to a loss in utility.

Fixed Frequency Reuse for LTE-Advanced Systems in Local Area Scenarios

LTE-Advanced systems, which aim to provide high data rate wireless services, have received world-wide researching interests nowadays. In this paper, the performance of fixed frequency reuse with different reuse factors is studied in LTE-Advanced systems. Performance is measured in terms of both average cell throughput and cell edge user throughput. It is found that a properly chosen reuse factor with respect to cell size (which leads to different level of inter-cell interference), can offer up to 30% gain in average cell throughput and much higher gain for cell-edge user throughput in Local Area (LA). This high gain from frequency reuse makes it attractive for future LTE-Advanced systems.

Carrier load balancing methods with bursty traffic for LTE-Advanced systems

In this paper we focus on LTE-Advanced performance under bursty traffic conditions, and devote our effort to the different methods for balancing the load across multiple carriers. These carriers are the component carriers (CCs) that belong to the same carrier frequency. They are bonded together in order to fulfill the requirement of wide spectrum in LTE-Advanced. We first derive the analytical model for a bursty birth-death traffic model with fixed payload size for OFDMA with different frequency domain packet schedulers. Applying this model for a multi-carrier system, we compute the performance for different system setups. The obtained analytical results are verified using extensive system level simulations. Based on the analytical and simulation results, it is suggested to assign the users on all CCs if a cell is not heavily loaded. Otherwise, assign each user with only one CC using the load balancing method of Round Robin is preferable, in the sense that it maintains good performance with low uplink overhead.

Time and Power Domain Interference Management for LTE Networks with Macro-Cells and HeNBs

Interference management for co-channel deployment of macro-cells and closed subscriber group (CSG) home-cells (HeNBs) are studied. We especially address the downlink macro-layer coverage-hole problem, where HeNBs may create too high interference to nearby macro-users, unless active interference management is applied. Interference management techniques based on HeNB power setting and partial Time Domain (TDM) muting of HeNBs are studied. Cases with TDM muting require optimization of the macro-cell packet scheduler, including taking into account that the interference level varies significantly at the users as function of the enforced muting pattern for the HeNBs. During subframes where HeNBs are muted, some interference is still generated due to the fact that signals like common reference signals are still to be transmitted. It is therefore studied how much the HeNB interference from muted subframes shall be reduced for TDM muting to perform better than schemes with simple HeNB power reduction.

CRS interference cancellation in heterogeneous networks for LTE-Advanced downlink

Enhanced Inter-Cell Interference Coordination (eICIC) for co-channel deployment of pico-cells throughout a macro-cell layout is a promising solution to increase system capacity and network coverage in Long Term Evolution (LTE)-Advanced systems. The use of both pico-cell Range Extension (RE) and time domain eICIC (TDM muting) in this scenario has been proved to provide high gains compared to the traditional homogeneous network. Nevertheless, performance results in literature assume ideal Common Reference Signals (CRS) interference cancellation in the pico-UEs during Almost Blank Subframes (ABS), i.e., receivers are capable of perfectly suppressing all CRS interference from all neighbour cells. In this paper we investigate the impact of non-ideal CRS Interference Cancellation (IC) in eICIC systems. We propose a simple RSRP-based CRS IC criterion not requiring any extra signaling. The performance is evaluated and compared to the ideal case in the downlink by means of extensive system level simulations that follow the 3GPP guidelines. Results confirm that TDM eICIC can still provide significant gains when realistic CRS IC is considered.