Manli Qian

Inter-cell interference coordination through adaptive soft frequency reuse in LTE networks

In 3GPP Long Term Evolution (LTE) networks, the frequency reuse schemes such as fractional frequency reuse (FFR) and soft frequency reuse (SFR) are used to improve system capacity. The allocation of transmit power and subcarriers to each cell in these schemes are fixed prior to network deployment. This limits the potential performance of these frequency reuse schemes. In this paper, we propose to improve the capacity of SFR scheme by jointly optimizing subcarrier and power allocation in multi-cell LTE networks. An iterative algorithm that can adaptively vary the number of major subcarriers and adjust the transmit power for each cell according to wireless traffic loads is proposed. Simulation results show that the proposed algorithm outperforms the existing Reuse 1, FFR and static SFR schemes in both system throughput and cell edge user performance.

A Novel Radio Admission Control Scheme for Multiclass Services in LTE Systems

In this paper, a novel radio admission control (RAC) scheme is proposed for handling multiclass services in Long Term Evolution (LTE) systems. An objective function of maximizing the number of admitted users is proposed to evaluate the system capacity. To solve the optimization problem, we present a combined complete sharing (CS) and virtual partitioning (VP) resource allocation model and develop a service degradation scheme in case of resource limitations in the proposed RAC scheme. Call blocking probability, system resource utilization and system capacity are used as performance metrics and are evaluated by using a K-dimensional Markov Chain model. Numerical results show that an optimal proportion of resource deployment for different service groups can be identified to maximize system capacity while at the same time maintaining quality of service (QoS) constraints of all admitted users.

Baseband Processing Units Virtualization for Cloud Radio Access Networks

In cloud radio access networks (C-RANs), the baseband processing units (BBUs) from traditional base stations (BSs) are virtualized and moved into a single centralized location. By virtualization, the computing resources of BBUs can be dynamically shared among all cells, enabling a significant improvement in computing resource utilization and power efficiency. In this letter, we propose a BBUs virtualization scheme that minimizes the power consumption with a linear computational complexity order. The scheme is based on a heuristic simulated annealing (HSA) algorithm, which combines a bin packing algorithm with SA. Simulation results show that the HSA effectively decreases system power consumption when compared to standard approaches.

Adaptive Soft Frequency Reuse Scheme for Wireless Cellular Networks

Spectrum scarcity and intercell interference (ICI) are two fundamental limiting factors in wireless cellular systems. Soft frequency reuse (SFR) has been proposed as an effective way to manage the spectrum and reduce ICI in cellular systems. In a static SFR scheme, the allocations of transmit power or subcarriers in each cell are fixed prior to system deployment. This limits the potential performance of the SFR scheme. In this paper, we propose an intercell resource-allocation algorithm, which is referred to as the adaptive SFR algorithm (ASFR), that dynamically optimizes subcarrier and power allocations for multicell wireless networks to improve system capacity. The ASFR first finds the subcarrier and power allocations in each cell by using exhaustive search and greedy descend methods and then iteratively repeats among cells until a predefined convergence criterion is satisfied. The theoretical analysis proves the convergence of the ASFR algorithm. Simulation results show that the ASFR achieves a higher system throughput and better cell edge user performance than existing frequency reuse schemes.

Distributed coverage optimization for small cell clusters using game theory

Small cell cluster is a new paradigm to extend the usage of small cells from residential environment to large indoor or outdoor areas. However, coverage optimization is a challenge due to the ad-hoc deployment and plug-and-play feature of small cells. This paper considers decentralized self-optimization network (SON) architecture of small cell cluster and proposes distributed coverage optimization algorithm using game theory (DGT). A non-cooperate game is modeled to tune the Tx power of each small cell with a net utility function considering both gain of throughput and punishment of interference. Nash Equilibrium (NE) is proved to be existed in the game and a power update scheme is proposed which converges to the NE. Simulation results show that DGT can significantly improve throughput as well as coverage ratio with only several iterations. Compared with centralized algorithm such as modified particle swarm optimization (MPSO) and simulated annealing (SA), DGT algorithm reaches higher network throughput, uses less iteration and keeps considerable coverage ratio.

Efficient design and implementation of LTE UE link-layer protocol stack

3GPP Long Term Evolution (LTE) and its enhancement has become the main candidate of 4G standards. Due to the requirements on high data rate and low latency for broadband wireless communication systems, LTE air-interface protocol stack must be designed and implemented with high data processing efficiency. Following a general description of the LTE user equipment (TIE), this paper analyzes the main challenges in the link-layer protocol stack design and implementation, including the data processing efficiency, synchronization, flexibility and portability. A reference design of LTE TIE link-layer protocol stack software is then presented with several design methodologies. A memory access optimization and light-weighted thread model are proposed to improve the data processing efficiency, while a hardware triggered synchronization mechanism is exploited to maintain synchronous between the link-layer protocol stack and the physical layer. Finally, the platform flexibility and portability is achieved by employing interface abstraction and adapters. Extensive system level testing shows that the proposed LTE TIE protocol stack software achieves high data rate and low data processing latency in a hardware resource restricted platform, which can be further extended to commercial LTE TIE products.

Research and application on LTE technology in smart grids

The development of smart grid requires higher data rate and wider coverage for current communication networks. Whats more, the communication network should be rapidly and flexibly deployed in emergency situation. In this paper, we first investigate the requirements of communication network in smart grid. Then application of LTE in normal and emergency situations in smart grid is proposed. Finally, the network architecture and the optimize strategies of LTE system in smart grid are discussed.

Efficient Time Synchronization Approach for Wireless Communication Systems on GPP-Based Software-Defined Radio Platform

General purpose processer (GPP) based software-defined radio (SDR) platforms provide wireless communication system engineers with maximal architecture flexibility and versatility to construct a wideband wireless communication system. Nevertheless, the lack of hardware real-time timing control makes it difficult to achieve time synchronization between the base station and the terminals. In this paper, a software-based time synchronization (STS) method is proposed to realize the time synchronization of time division multiple access (TDMA) based wireless communication systems. A high precision software clock source is firstly constructed to measure the elapse of processing time. The Round-Trip Delay (RTD) algorithm is then presented to calculate timing advance values and achieve time synchronization. An example TDMA system is implemented on Microsoft Sora platforms to evaluate the performance. Experiments show that the proposed mechanism is effective to enable time synchronization for wideband wireless communication systems on GPP-based SDR platforms.

FFT Traffic Classification-Based Dynamic Selected IP Traffic Offload Mechanism for LTE HeNB Networks

Traffic offloading is a promising technique to alleviate the traffic load in LTE core networks. Based on 3GPP “SIPTO” (Selected IP Traffic Offload) architecture, this paper proposes dynamic SIPTO mechanism (D-SIPTO) for traffic offloading in LTE HeNB networks, which combines fast fourier transform (FFT) based IP traffic classification scheme (FFTTCS) with the dynamic traffic offload path selection algorithm (DTOPSA). Simulation results show that FFTTCS can realize on-line traffic classification with similar precisions but only using less than 10 % of the time needed by existing methods. Combined with DTOPSA, the proposed D-SIPTO can reduce the core network traffic by 60 % while selecting the optimal offload path according to the type of traffic to be offloaded.

Game-Theoretic Power Control for Interference Mitigation in Two-Tier Small Cell Networks

Interference mitigation is a major challenge in deploying a two-tier small cell network, where small cells are deployed underlaying a central macrocell and share the same spectrum with the macrocell. In this paper, we develop a new decentralized power control solution for interference mitigation in a two-tier small cell network, from a game theoretic perspective. We aim to maximize the number of small cell user (SU) transmissions that can be admitted in the network while satisfying the signal-to- interference-noise ratio (SINR) constraints of both transmitting SUs and the macrocell user (MU). We formulate the problem of power control for SUs as a game with common utility. The Nash equilibria of the game are investigated. We then propose a learning automata based distributed discrete power control algorithm with which the SUs can learn from their action-reward histories and adjust their transmit powers towards a NE point. Simulation results show the proposed algorithm achieves higher number of SU transmissions that can be admitted compared with existing schemes in the literature.