3GPP Long Term Evolution System Research Articles

Precoding Matrix Selection for LTE System

In the current 4G Long Term Evolution (LTE) system, it adopts the orthogonal frequency division multiplexing (OFDM) and multiple input multiple output (MIMO) schemes to improve the spectral efficiency and increase the data rate for the system. Besides, precoding is an effective technique in MIMO transmission for the transmitter (Tx) to use a suitable precoding matrix in accordance with the change of the channel. With the proper selected precoding matrix, MIMO system can reduce the multiple access interference and increase the received signal to noise ratio (SNR) at the receiver (Rx). In this paper, two precoding matrix selection methods are proposed via using the features of the beam patterns of the adopted precoding matrices for 3GPP LTE system. With a little performance degradation, the first proposed method has the advantage of low computational complexity and the second method can have the zero latency property compared with the conventional full search methods.

Enhanced Signal Detection in 3GPP LTE System with Successive Interference Cancellation

In this paper we introduced interference cancellation (IC) in the cell search and the detection of physical downlink shared channel (PDSCH) in long term evolution (LTE) of 3rd generation partnership project (3GPP). After user equipment (UE) is turned on, it has to first search the target cell using synchronization channel (SCH). After UE gets timing and cell identification (Cell ID) by cell search process, it can start to transmit and receive data through the traffic channel. In most cases, UE experiences the interference from surrounding neighbor cells, which may result in the degradation of the receiver performance. Not only in time division duplex (TDD) but also frequency division duplex network (FDD), the cells must be deployed with the time aligned to support better successful handover and also provide multemedia broadcast and multicast service (MBMS) efficiently in the network. In synchronous network system, since every cell sends his SCH using shared resource allocation, it is inevitable that two or more neighboring cells can interfere each other in some situation. The cell specific reference signal (CRS) is used for channel estimation in downlink reception. The CRS from neighbor cells may overlap with the resource of PDSCH of the target cell. Hence, the collision of SCH and CRS from the neighbor cells can degrade both the performance of cell search and PDSCH reception at the same time. In this paper, we analyzed the improved performance of the cell search and PDSCH reception by using successive interference cancellation. Simulation results show that the proposed scheme can effectively reduce the mutual interference and improve the performance of the signal detection in view of the cell search and PDSCH reception, respectively.

Performance Analysis of FLS, EXP, LOG and M-LWDF Packet Scheduling Algorithms in Downlink 3GPP LTE System

Long-Term Evolution (LTE), an emerging and promising fourth generation mobile technology, is expected to offer ubiquitous broadband access to the mobile subscribers. In this paper, the performance of Frame Level Scheduler (FLS), Exponential (EXP) rule, Logarithmic (LOG) rule and Maximum-Largest Weighted Delay First (M-LWDF) packet scheduling algorithms has been studied in the downlink 3GPP LTE cellular network. To this aim, a single cell with interference scenario has been considered. The performance evaluation is made by varying the number of UEs ranging from 10 to 50 (Case 1) and user speed in the range of [3, 120] km/h (Case 2). Results show that while the number of UEs and user speed increases, the performance of the considered scheduling schemes degrades and in both case FLS outperforms other three schemes in terms of several performance indexes such as average throughput, packet loss ratio (PLR), packet delay and fairness index.

Traffic-based queue-aware scheduling for 3GPP LTE system

Although the medium access control (MAC) signaling has been well-defined in the 3rd generation partnership project (3GPP) long term evolution (LTE) specifications, the scheduling algorithm crucial to guarantee QoS performance, still remains as open issues. In this article, a traffic-based queue-aware scheduling (TQS) algorithm is proposed for evolved nodeB's (eNB's) MAC scheduler in 3GPP LTE broadband wireless networks. The proposed TQS is divided into three sub-algorithms: firstly, the authors propose a traffic model construction (TMC) algorithm which can construct a discrete-time Markov-modulated Poisson process (dMMPP) to represent each flow. Secondly, a newly traffic state estimation (TSE) algorithm is designed to obtain the queue's analytical statistics. Thirdly, based on the derived results of TSE and the channel states, a scheduling action decision (SAD) algorithm is presented that can adaptively allocate bandwidth to flows by considering both queue states and spectrum efficiency. Simulation shows that the TMC and TSE algorithm can capture the fluctuation of traffic and queue accurately. Moreover, compared with a widely accepted traffic-based scheduling algorithm, the proposed TQS has better average queue length and overflow probability performance.

Handover algorithm combined with location prediction in 3GPP LTE systems

Concerning the problem of the decline of 3GPP Long Term Evolution(LTE) system throughput caused by the frequent handover,a location prediction model based on user movement mechanism and changing probability of direction was proposed.The proposed model was combined with the standard handover algorithm of LTE.The model calculated the weight of each possible location using the changing probability of direction,then got the predicted received signal strength through summing.The simulation results show that the number of handover does not change obviously,but the system throughput is improved after using the combined algorithm.In addition,the proposed model is better than the traditional data mining prediction model.

Exploiting Spatial, Frequency, and Multiuser Diversity in 3GPP LTE Cellular Networks

This paper addresses the problem of frequency domain packet scheduling (FDPS) incorporating spatial division multiplexing (SDM) multiple input multiple output (MIMO) techniques on the 3GPP Long-Term Evolution (LTE) downlink. We impose the LTE MIMO constraint of selecting only one MIMO mode (spatial multiplexing or transmit diversity) per user per transmission time interval (TTI). First, we address the optimal MIMO mode selection (multiplexing or diversity) per user in each TTI in order to maximize the proportional fair (PF) criterion adapted to the additional frequency and spatial domains. We prove that both single-user (SU-) and multi-user (MU-) MIMO FDPS problems under the LTE requirement are NP-hard. We therefore develop two types of approximation algorithms (ones with full channel feedback and the others with partial channel feedback), all of which guarantee provable performance bounds for both SU- and MU-MIMO cases. Based on 3GPP LTE system model simulations, our approximation algorithms that take into account both spatial and frequency diversity gains outperform the exact algorithms that do not exploit the potential spatial diversity gain. Moreover, the approximation algorithms with partial channel feedback achieve comparable performance (with only 1-6 percent performance degradation) to the ones with full channel feedback, while significantly reducing the channel feedback overhead by nearly 50 percent.

An Enhanced Observed Time Difference of Arrival Based Positioning Method for 3GPP LTE System

In 3GPP (3-rd Generation Partnership Project) LTE (Long Term Evolution) system, the use of PRS (Positioning Reference Signal) for OTDOA (Observed Time Difference of Arrival) based positioning method has been agreed. However, PRSs can be overlapped at the receiver side in synchronous network because the frequency shift pattern of PRS is decided by cell ID (Identity). Moreover, in asynchronous network, the loss of orthogonality between received PRSs generates continuous interferences. Even though autonomous muting can be applied to solve the interference problems in synchronous and asynchronous networks, the muting scheme degrades the overall positioning efficiency and requires additional network complexity. Therefore, in this paper, we propose novel OTDOA based positioning methods at the receiver side to improve positioning efficiency: cancellation method of serving PRS for synchronous network, TDORS (Time Domain Orthogonal Reference Signal) generation and useful CIR (Channel Impulse Response) selection methods for asynchronous network. We verified that the proposed methods can achieve an accurate estimation and stable operation without PRS muting.

Accelerating the 3GPP LTE System Level Simulation with NVidia CUDA

With the rapid progress of standardization of 3GPP’s LTE (Long Term Evolution) and LTE-Advanced, many research attentions have been focused on the link level evaluations of the 3GPP LTE systems, so as to demonstrate the rationality of novel transmission techniques. Different from theoretical studies, incorporating novel transmission techniques in to the LTE communication systems may affect many parts of the systems, such as signaling process, reference signal design, feedback link design, and compatibility, etc. Link level studies might be too simple to evaluate the benefits of these novel techniques to the entire system. On the other hand, system level simulation concentrates on the performance of the entire network with tens of cells and hundreds to thousands of users. It is possible to illustrate the actual performance of a LTE system by simulations designed from a system standpoint. Since the simulated system is quite large, one can understand the speed of simulation is very important for system level simulation platform. In this paper, we propose a design of Matlab-based 3GPP LTE system level simulator, which makes use of parallel computing techniques supported by NVidia GeForce GTX 260 graphic card. Our simulation experience shows that the simulation time reduces by nearly 1/3 after employing parallel computing techniques.

A Handover Decision Strategy with a Novel Modified Load-Based Adaptive Hysteresis Adjustment in 3GPP LTE System

This paper introduces a hard handover strategy with a novel adaptive hysteresis adjustment that is needed to reduce handover drop rate in 3GPP long term evolution (LTE). First of all, we adopt a Hybrid handover scheme considering both the received signal strength (RSS) and the load information of the adjacent evolved Node Bs (eNBs) as a factor for deciding the target eNB. The Hybrid scheme causes the load status between the adjacent eNBs to be largely similar. Then, we propose a modified load-based adaptive hysteresis scheme to find a suitable handover hysteresis value utilizing the feature of the small load difference between the target and serving eNBs obtained from the result of the Hybrid scheme. As a result, through the proposed modified load-based adaptive hysteresis scheme, the best target cell is very well selected according to the dynamically changing communication environments. The simulation results show that the proposed scheme provides good performance in terms of handover drop rate.

Mobility Management Survey for Home-eNB Based 3GPP LTE Systems

Abstract: The specification of the Home Evolved NodeB (Home-eNB), which is a small base station designed for use in residential or small business environment, is currently ongoing in 3GPP LTE (Long Term Evolution) systems. One of the key requirements for its feasibility in the LTE system is the mobility management in the deployment of the numerous Home-eNBs and other 3GPP network. In this paper, we overview the characteristic of Home-eNB and also describe the mobility management issues and the related approaches in 3GPP LTE based Home-eNB systems. Keywords : Home-eNB, 3GPP LTE (Long Term Evolution), Mobility Management 1. Introduction issues of HeNB in 3GPP LTE systems and related approaches A significant interest within the telecommunications industry has recently focused on the femto-cell which is defined broadly as low-cost, low-power cellular base stations that operate in licensed spectrum to connect conventional, unmodified mobile terminals to a mobile operator’s network [1][2][3]. Femto-cell has been actively discussed in 3