Mingju Li

Energy Source Aware Target Cell Selection and Coverage Optimization for Power Saving in Cellular Networks

The spread of mobile connectivity is generating major social and economic benefits around the world, while along with the rapid growth of new telecommunication technologies like mobile broadband communication and M2M (Machine-to-Machine) networks, larger number of various base stations will be employed into the network, which will greatly increase the power expense and CO2 emission. In order to degrade the system power expense, variety of researches on new energy and novel transmission technology are put in agenda. In this paper, instead of reducing the absolute power expense, the research focuses on guiding more power consumption into green source energy, which implying that the UEs (User Equipment), especially the cell edge UEs, will have preferential access to the BSs (Base Station) with natural energy supply. To realize the tendentious connection, two detailed approaches are proposed, the HO (Hand Over) parameter tuning for target cell selection and power control for coverage optimization. The system evaluation shows that, by proper setting of parameters in HO and power control, both of the two approaches can achieve good balance between energy saving effect and system throughput impact.

Component Carrier Management for Carrier Aggregation in LTE-Advanced System

This paper focuses on investigating appropriate management of Component Carriers(CCs) in carrier aggregation( CA) system, which is identified as one of the most distinct features of 4G systems including Long Term Evolution- Advanced (LTE-A). An LTE-A user equipment (UE) is allowed to concurrently utilize multiple carriers, which leads to scalable increase in user throughput. However, in certain circumstances, aggregating entire available carriers for a UE is not meaningful due to probably low channel quality or high traffic load in some of the CCs. Therefore, how to make good use of multiple carriers in real deployment scenarios is an important issue. Based on the analysis of resource allocation across multiple carriers in Layer-2, two CC management methods in Layer- 3 are proposed. The proposed method is shown by simulation results to be effective in providing comparable user throughput with lower implementation complexity, as compared to solely ingenious resource allocation.

Uplink Control for Low Latency HARQ in TDD Carrier Aggregation

A higher data rate and lower latency are two main features of Long Term Evolution Advanced (LTE-A). In order to support a higher peak data rate, carrier aggregation (CA) is implemented into LTE-A systems to provide sufficient bandwidth for data transmission. However, there is a problem in achieving lower latency. Time Division Duplexing (TDD) systems may not have a sufficient number of uplink subframes to transmit downlink hybrid automatic repeat request (HARQ) feedback, which results in additional latency compared with Frequency Division Duplexing (FDD) systems. In TDD CA systems, the downlink HARQ round trip time (RTT) of a component carrier (CC) is related to its TDD configuration. In this paper, a low latency downlink HARQ feedback method for TDD CA systems is proposed to shorten the transmission delay. The serving eNB determines whether to allocate the physical uplink control channel (PUCCH) to a new CC by comparing the downlink HARQ RTT of that CC to that of the primary cell. If the downlink HARQ RTT can be reduced, the eNB will allocate the PUCCH to this new CC. By using this method, the downlink HARQ RTT of TDD CA systems can be significantly reduced.

A novel resource reservation scheme for fast and successful handover

In order to reduce handover delay caused by handover failure, radio resource is reserved for handover users not only at target cell, but also at prepared cells. This has been agreed in 3GPP LTE. However, these reserved resources cannot be assigned for other users until the finishing of the handover, which results in inefficiency of radio resource utilization. This paper presents a new resource reservation scheme for handover users to achieve fast handover failure recovery and efficient radio resource utilization. By proposed scheme, a resource pool at prepared cells is shared among multiple users, and the number of prepared cells is dynamically set according to the service type of users. Numerical analysis and simulation results show that the proposed scheme can improve successful handover probability and reduce handover delay.

Access probability aware cell reselection for load balancing

In LTE, AC barring check is performed by UEs before initiating an RRC connection. In some cells with a low access probability, the UEs may have to keep retrying access in the serving cell which results in higher connection failure and longer access delay. We therefore propose balancing the UEs by adjusting the cell reselection criteria based on the access probability in the serving cell and neighboring cells, so that the UEs in a serving cell with a lower access probability shall be more encouraged to reselect a cell with a higher access probability. The proposed methods are analyzed in a simplified model and further validated using computer simulation. They both show the significant advantage over existing criteria in LTE.

Downlink Power Control for Dense Small Cell Deployment in LTE-Advanced

This paper proposes a power control scheme that reduces the small cell interference for sets of user equipment (UE) at the cell edge. 3GPP LTE-Advanced adopted small cell enhancement to improve both the cell average and cell edge throughput. However, since the number of small cells in one cluster is increasing, the interference between small cells will increase significantly. As is well known, if the power level is reduced in a serving cell, the UEs in the same cell will experience throughput loss and UEs in neighboring cells will experience throughput improvement. In order to tradeoff the throughput loss and improvement, this paper presents a method to estimate accurately the loss and improvement. Then a transmission power decision method depending on loss and improvement is described. Performance evaluation results show that the proposed scheme improves the cell edge throughput by a maximum of 33%.

A new PUCCH resource mapping method in interband TDD carrier aggregation systems

In order to support a higher peak data rate, carrier aggregation (CA) is implemented into Long Term Evolution Advanced (LTE-A) systems to provide sufficient bandwidth for data transmission. In Time Division Duplexing (TDD) CA systems, aggregation of Component Carriers (CCs) with different TDD configurations is necessary due to the coexistence with legacy TDD systems. To achieve the peak data rate of Secondary Cell (SCell) in case of cross-carrier scheduling, the Physical Downlink Shared CHannel (PDSCH) hybrid automatic repeat request (HARQ) timing of SCell should follow its own PDSCH HARQ timing. Meanwhile, Primary Cell (PCell) still uses its own PDSCH HARQ timing. However, using different PDSCH HARQ timing between PCell and SCell may lead to Physical Uplink Control CHannel (PUCCH) resource mapping collision, which sacrifices downlink (DL) peak data rate and increases transmission latency for the reason of PDSCH HARQ feedback failure. In this paper, a new implicit PUCCH resource mapping method is proposed to avoid PUCCH collision in inter-band TDD CA systems. ENB and user equipment (UE) re-allocate PUCCH resources for each DL subframe on SCell. By using this proposal, PUCCH collision for cross-carrier scheduling in TDD CA systems can be completely eliminated without introducing significant PUCCH overhead increase.

Handover Methods Considering Channel Conditions of Multiple Aggregated Carriers

Carrier aggregation was introduced to Long Term Evolution Advanced in order to improve the performance especially in terms of a higher peak data rate. When employed, sets of user equipment will have a set of serving cells, which includes a Primary cell (PCell) and Secondary cells (SCells). For inter evolved Node B (eNB) handover, target eNB is selected only consider the channel condition of the PCell. Thus, a suitable set of serving cells cannot be selected. In order to address this problem, this paper proposes three handover methods considering channel conditions for multiple cells. Methods 1 and 2 adjust the handover margin according to the difference in channel conditions between the PCell and SCells for the serving eNB. Method 3 decides handover based on equivalent channel conditions for the PCell and SCells in both the serving eNB and neighboring eNBs. Simulation results show that the proposed methods provide higher cell-edge throughput and a much smoother handover at the cost of a slightly increased number of handovers.