Long Term Evolution-Advanced Downlink Research Articles

Exhaustive Appraisal of Adaptive Hybrid LTE-A Downlink Scheduling Algorithm

Long Term Evolution- Advanced (LTE-A) networks have been introduced in Third Generation Partnership Project (3GPP) release – 10 specifications, with an objective of obtaining a high data rate for the cell edge users, higher spectral efficiency and high Quality of service for multimedia services at the cell edge/Indoor areas. A Heterogeneous network (HetNet) in a LTE-A is a network consisting of high power macro-nodes and low power micro-nodes of different cell coverage capabilities. Due to this, non-desired signals acting as interference exist between the micro and macro nodes and their users. Interference is broadly classified as cross-tier and co-tier interference. The cross tier interference can be reduced by controlling the base station transmit power while the co-tier interference can be reduced by proper resource allocation among the users. Scheduling is the process of optimal allocation of resources to the users. For proper resource allocation, scheduling is done at the Main Base station (enodeB). Some LTE-A downlink scheduling algorithms are based on transmission channel quality feedback given by user equipment in uplink transmission. Various scheduling algorithms are being developed and evaluated using a network simulator. This paper presents the performance evaluation of the Adaptive Hybrid LTE-A Downlink scheduling algorithm. The evaluation is done in terms of parameters like user’s throughput (Peak, Average, and Edge), Average User’s spectral efficiency and Fairness Index. The evaluated results of the proposed algorithm is compared with the existing downlink scheduling algorithms such as Round Robin, Proportional Fair, Best Channel Quality Indicator (CQI) using a network simulator. The comparison results show the effectiveness of the proposed adaptive Hybrid Algorithm in improving the cell Edge user’s throughput as well the Fairness Index.

A Machine Learning Approach to Achieving Energy Efficiency in Relay-Assisted LTE-A Downlink System.

In recent years, Energy Efficiency (EE) has become a critical design metric for cellular systems. In order to achieve EE, a fine balance between throughput and fairness must also be ensured. To this end, in this paper we have presented various resource block (RB) allocation schemes in relay-assisted Long Term Evolution-Advanced (LTE-A) networks. Driven by equal power and Bisection-based Power Allocation (BOPA) algorithm, the Maximum Throughput (MT) and an alternating MT and proportional fairness (PF)-based SAMM (abbreviated with Authors’ names) RB allocation scheme is presented for a single relay. In the case of multiple relays, the dependency of RB and power allocation on relay deployment and users’ association is first addressed through a k-mean clustering approach. Secondly, to reduce the computational cost of RB and power allocation, a two-step neural network (NN) process (SAMM NN) is presented that uses SAMM-based unsupervised learning for RB allocation and BOPA-based supervised learning for power allocation. The results for all the schemes are compared in terms of EE and user throughput. For a single relay, SAMM BOPA offers the best EE, whereas SAMM equal power provides the best fairness. In the case of multiple relays, the results indicate SAMM NN achieves better EE compared to SAMM equal power and BOPA, and it also achieves better throughput fairness compared to MT equal power and MT BOPA.

Software implementation of LTE-advanced using Matlab Simulink

Long Term Evolution Advanced (LTE-A) is the evolution of the LTE that developed by 3rd Generation Partnership Project (3GPP).LTE-A exceeded International Telecommunication Union (ITU) requirements for 4th Generation (4G) known as International Mobile Telecommunications (IMT-Advanced). It is formally introduced in October 2009. This paper presents a study and an implementation of the LTE-A downlink physical layer based on 3GPP release 10 standards using Matlab simulink. In addition, it provides the LTE-A performance in terms of Bit Error Rate (BER) against Signal to Noise Ratio (SNR) for different modulation and channel coding schemes. Moreover, different scenarios of Carrier Aggregation (CA) are modeled and implemented. The Simulink model developed for the LTE-A transceiver can be translated into digital signal processor DSP code or VHDL on FPGA code.

FFT-Based Channel Estimation Scheme in LTE-A Downlink System

In this paper, we propose a channel estimation scheme for a long term evolution-advanced (LTE-A) downlink system. The proposed scheme uses the fast Fourier transform (FFT) interpolation scheme for the user moving at a high speed. The FFT interpolation scheme converts the channel frequency response obtained from the least square or minimum mean square error channel estimation scheme to a time-domain channel impulse response by using the inverse FFT (IFFT). After windowing the channel response in the time domain, the channel frequency response can be obtained using the FFT. We performed a system-level simulation based on the 20 MHz bandwidth of the 3rd Generation Partnership Project LTE-A downlink system. Simulation results show that the proposed channel estimation scheme can improve the signal-to-noise-plus-interference ratio, as well as the throughput and spectral efficiency, of a conventional system.

MIMO AF RSs Based OSTBCs for LTE-A Downlink Physical Layer Network

The link performance between base station (BS) and user equipment (UE) in long term evolution-advanced (LTE-A) system is already quite close to the Shannon limits and from a pure link-budget perspective, the highest data rates supported by LTE-A require a relatively high signal-to-noise ratio. In later releases of LTE-A, various tools such as relaying, enhancing the support for low-power BSs and improving the link budget are included. This paper studies the relay stations (RSs) for LTE-A downlink physical layer. Multi-input multi-output amplify-and-forward RS is used to enhance the received signal of UEs at cell edge. This paper proposes RSs with orthogonal space–time block codes (OSTBC) transmission for LTE-A system. The received signals for different UEs scenarios are mathematically derived and analyzed. The symbol error rate performance of proposed LTE-A system is illustrated for the scenarios of UEs. Results show that the proposed LTE-A system based RSs with OSTBC transmission improve link performance and achieve higher diversity gains.

MIMO Transmission With Vertical Sectorization for LTE-A Downlink

Recently, vertical sectorization (VS) has been proposed for multiple-input multiple-output (MIMO) transmission in long term evolution advanced (LTE-A) downlink systems. In this paper, we will investigate MIMO transmission with VS for LTE-A systems. We first divide each cell into two sectors in vertical direction so that more users can be co-scheduled and more refined beams can be formed in each sector. We then address how to jointly optimize two tilt angles, user scheduling, and resource block allocation for a practical LTE-A system, and provide an efficient VS-based MIMO scheduling algorithm with low-complexity. The performance improvement of the proposed algorithm is demonstrated by system level simulation.

Selective Interference Rejection based Antenna Selection for MIMO over LTE Advanced Networks

An important goal for long term evolution advanced (LTE-A) network is to enhance the cell edge user throughput while achieving the link reliability and high data rate communication. However, the cell edge users’ throughput is limited by inter-cell interference. To suppress the interference signal, interference rejection combining (IRC) receiver is an effective solution for Release 10/11. In Multiple-Input Multiple-Output (MIMO) technique, the IRC receiver utilizes multiple antennas, larger the number of antennas, the more interfering signals can be suppressed. Due to practical constraints of increase in radio-frequency units impose a limit in the number of antennas. In this paper, a new selective interference rejection based antenna selection (SIR-AS) scheme is proposed to perform the better selection of transmitting antenna for cell edge MIMO user and enhance the system throughput. The selective interference rejection is performed by incorporating the IRC receiver, where the covariance matrix (CM) of the received interference signals is estimated and the minimum of CM is selected. The corresponding antenna set with minimum of CM is selected for transmission. Simulation results show that the proposed algorithm can effectively detect intercellular interference at cell boundaries and select the optimal antenna to reduce block error rate (BLER) and improve throughput performance compared to ideal IRC and maximum ratio combining algorithm, making it suitable for LTE-A downlink receiver in multi-cell MIMO systems.

An Efficient Scheduling Scheme for OFDMA Resource Blocks with Joint User Scheduling based on Earliest Deadline First with Carrier Aggregation (CA) in LTE-A System

This paper focuses on the resource planning within the downlink of Long Term Evolution Advanced (LTE-A) in addition to Carrier Aggregation (CA) technology. Every time CA is being put to use, it is very vital to complement the LTE-A system with a robust and suitable resource scheduling plan. The two basic resource scheduling schemes are Separate Random User Scheduling and Joint User Scheduling (JUS). The former scheme is simpler, but less efficient, while the latter performs optimally at the expense of higher computation complexity. As a matter of fact, LTE-Advanced networks are designed to render minimal latency and additional broadcast rates, coupled with increased spectral operational performance beyond the benchmark of 3G networks. Nevertheless, concerning the insufficient radio resources, the efficient application and management of these scarce resources are most desirable. Hence, the best approach for profitable resource allocation must be of central focus to meet the Quality of Service (QoS) standard. For the purpose of enhancing the system equity and refraining from high complexity of the system, it is recommended that the JUS is based on Earliest Deadline First (EDF), to offer QoS guarantees and equitable distribution of radio resources. From the simulation results, the following improvements were made: The proposed JUS based on EDF, improved the throughput of the users by adjusting the deadline for the allocated resource blocks of the users. The JUS-EDF has improved the users throughput by 10 % as compared to simple JUS. It also enhanced the system fairness by adjusting the priority of each user according to Earliest Deadline compared to JUS, by 8.88 %. Also JUS-EDF reduced packet delays by 1 s, as compared to the conventional JUS. This paper has introduced a sub-optimized packet scheduling algorithm to fully utilize the new feature in LTE-A downlink system.

Open-field emulation of cooperative relaying in LTE-A downlink using the GNU radio platform

Long Term Evolution-Advanced (LTE-A) plans the adoption of cooperative relaying in order to extend coverage and improve Quality-of-Service of future-generation mobile wireless networks. In the present paper, we propose the usage of open-source GNU radio tools to build a full-Software-Defined Radio (SDR) implementation of cooperative relaying for an LTE-A downlink connection. Experimental results demonstrate the effectiveness, tested in open-field, of the cooperative relaying in terms of augmented coverage and improved throughput, with a substantial added value provided by the SDR implementation in terms both of algorithmic flexibility and network reconfigurability.

Novel Receiver Architecture for LTE-A Downlink Physical Control Format Indicator Channel with Diversity

Physical control format indicator channel (PCFICH) carries the control information about the number of orthogonal frequency division multiplexing (OFDM) symbols used for transmission of control information in long term evolution-advanced (LTE-A) downlink system. In this paper, two novel low complexity receiver architectures are proposed to implement the maximum likelihood- (ML-) based algorithm which decodes the CFI value in field programmable gate array (FPGA) at user equipment (UE). The performance of the proposed architectures is analyzed in terms of the timing cycles, operational resource requirement, and resource complexity. In LTE-A, base station and UE have multiple antenna ports to provide transmit and receive diversities. The proposed architectures are implemented in Virtex-6 xc6vlx240tff1156-1 FPGA device for various antenna configurations at base station and UE. When multiple antenna ports are used at base station, transmit diversity is obtained by applying the concept of space frequency block code (SFBC). It is shown that the proposed architectures use minimum number of operational units in FPGA compared to the traditional direct method of implementation.

Analysis of Macro-Diversity in LTE-Advanced

Coordinated Multi-Point (CoMP) transmission / reception is being studied in Long Term Evolution-Advanced (LTE-A) for future evolution of the 3 rd Generation Partnership Project (3GPP) LTE. Support of soft handover is essential for improving the performance of cell edge users. CoMP provides a natural framework for enabling soft handover in the LTE system. This paper evaluates the soft handover gain in LTE-A downlink. Mathematical analysis of signal to interference plus noise ratio (SINR) gain and the handover margins for soft handover and hard handover are derived. CoMP system model is developed and an inter-cell and intra-cell interference model is derived, taking into account the pathloss, shadowing, cell loading, and traffic activity. Reference signal received power (RSRP) is used to define the triggers and the measurements for soft handover. Our results indicate that parameter choices such as handover margin and the CoMP set size impact CoMP performance gain.