Closed-loop Spatial Multiplexing Research Articles

Performance Evaluation of Channel Equalizer Techniques in LTE-Advanced under Vehicular Environments

The 3GPP LTE standard has developed into the most innovative wireless technology for future generations, capable of data transmission data at rates exceeding 1 Gbps. Improving total user communication performance highly depends on selecting the detection technique correctly, however, by choosing the proper mode of transmission. We analyzed channel equalization techniques Minimum Mean Square Error (MMSE) and Soft-Sphere Decoder (SSD), at the downlink of physical-layer of LTE‑A system under MIMO technology, besides studying the characteristics of utilizing various transmission schemes such-as Transmit Diversity (TxD) and Spatial Multiplexing (SM) (Open-Loop SM (OLSM) and Closed-Loop SM (CLSM)). For MIMO technology, the 4x2 configuration of transmitter-receiver antennas is preferred. To simulate and evaluate the system’s performance in throughput and Bit Error Rate (BER) used the LTE-A link level simulation program developed by “The Vienna University of Technology” which used in MATLAB, across various channel type including Vehicular-A (VehA) at a speed of 30km/s and Vehicular-B (VehB) at a speed of 120km/s.

Downlink Performance of Beamforming for High Mobility Users in 5G Cellular Network

5G cellular infrastructures are supposed to provide higher data rate and lower latency along with the prospects of other various novel applications. But the signal strength seems to fluctuate unexpectedly due to doppler shift resulting in negative impacts on downlink performance parameters over the network for high-speed users. One potential solution to overcome this problem can be the concentration of energy to a particular location using multiple antennas at the base station so that receiving power can be increased for the intended user while suppressing interferences from others. So, this paper has investigated the performance of beamforming with closed loop spatial multiplexing over a specific range of velocity of users. However, the simulation results also demonstrate that by scaling the number of transmitting antennas, beamforming can elevate average throughput, improve quality of service for cell edge users and ensure better spectral efficiency under any existing scheduler with no complexities involved in system designing. Moreover, through the estimations of the channel conditions obtained from the precoding matrix of closed loop spatial multiplexing, the strength of the transmitted signal can be amplified accordingly to improve mean throughput and minimize the bit error rate. Therefore, the proposed scheme of scaling transmitting antennas through CLSM along with beamforming seems to circumvent the repercussions of doppler shift on downlink (DL) performance of high velocity cellular users.

Performance Evaluation of Different Scheduling Schemes for Marcocell with MIMO Closed Loop Spatial Multiplexing (CLSM) 2×2 Antenna Configuration

Performance Evaluation of Different Scheduling Schemes for Marcocell with MIMO Closed Loop Spatial Multiplexing (CLSM) 2×2 Antenna Configuration

Design of Simulation System for LTE-U Using 5 GHz Band in MATLAB

Unused spectrum is being a limited commodity for the telecom industry. However, up to 500 MHz of unlicensed spectrum in 5 GHz band is in use for several applications and services, particularly in WiFi around the world. Unlicensed spectrum has foreseen to play a vital role in 5G. It is already under discussion at different forums that how the unlicensed band advantage can promote 4G Long Term Evolution (LTE) networks. Long Term Evolution Unlicensed (LTE-U) is an extension of existing LTE mobile networks, and allow LTE technology to use unlicensed bands as an adjunct to the licensed band. It will not only deliver a better user experience to end users but also boost capacity for network operators. In this paper, a Simulink based LTE PDSCH (Physical Downlink Shared Channel) model is introduced which uses the 5 GHz band according to the specifications prescribed by LTE-U Forum and 3GPP (Third Generation Partnership Project). It demonstrates multi-codeword transmission within a small cell from an eNodeB to a User Equipment (UE). LTE enabling technologies like OFDMA, closed-loop spatial multiplexing, turbo channel coding and link adaptations are used to design this model. Minimum mean square error (MMSE) technique as a linear detection method is used for spatially multiplexed Multiple Input Multiple Output (MIMO). Bit error rate is analyzed for QPSK, 16-QAM, and 64-QAM and compared for hard and soft decisions MMSE based MIMO detection. Fairly improved throughputs are obtained for multi-antenna configurations considering the low mobility scenarios and low correlation settings between links.

3GPP LTE Downlink PHY Transceiver using Closed-loop Spatial Multiplexing in Frequency Selective Fading Environment

LTE (Long Term Evolution) is a 3GPP (Third Generation Partnership Project) wireless standards that gives us wideband CDMA (Code Division Multiple Access) and HSPA (High Speed Packet Access) a third generation connectivity. LTE is the fourth generation (4G) of wireless communication technologies that brings the standard OFDMA (Orthogonal Frequency Division Multiple Access) modulation , MUMIMO (Multiuser Multiple Input Multiple Output) technology and different multipath fading model EVA (Extended Vehicular a), ETU (Extended Typical Urban) and EPA (Extended Pedestrian A) which allows the operator to use spectrum more efficiently to deliver high speed data. This paper characterizes the downlink performance of LTE. There are many metric to characterize the performance, but one of the most convenient and informative metric is the BER (Bit Error Rate). So the performance is characterized in terms of BER. In this paper the LTE system is modeled and simulated using MATLAB and the BER for 2×2 and 4×4 MIMO using QPSK and 16QAM modulation is obtained against different SNR values. General Terms Mobile Communication

Energy-Efficient Dynamic Point Selection and Scheduling Method for Intra-cell CoMP in LTE-A

In this paper, we propose a novel dynamic point selection (DPS) and user scheduling method for improving the energy efficiency in distributed antenna systems without cell edge spectral efficiency degradation. When DPS is used, each user is served by a single transmission point that can be dynamically switched. The proposed method decreases the power consumption by switching off inactive radio frequency (RF) chains and additionally reduces the interference by a static inter-cell agreement on which transmission points are simultaneously active. The performance of the method is evaluated by computer simulations in a system that accurately models the LTE-Advanced (LTE-A) intra-cell coordinated multi-point scenario 4. Based on the performance simulations, the proposed method achieves a significant energy efficiency gain over closed-loop spatial multiplexing applied on localized or distributed transmitting antennas. In general, the proposed method performs well when the load-independent RF power consumption is high in the active mode and low in the sleep mode. When the proportion of the load-independent RF power consumption to the total load-independent power consumption exceeds a certain limit, which is 22 % in the case of ten users in the 3-sector layout, the proposed method brings always energy efficiency gain even when RF chain micro sleeping cannot be implemented. The usability of the method is not dependent on the traffic load. The same approach can be applied to any distributed antenna system.

SCHEDULING SCHEMES FOR CARRIER AGGREGATION IN LTE-ADVANCED SYSTEMS

Considering the needs of higher data rates and hence wider bandwidths for advanced mobile communication systems, 3GPP standardized carrier aggregation (CA) as one of the important technological components for fourth generation (4G) Long term evolution (LTE) advanced systems. Here the user equipments are assigned carrier component (CC) belonging to different (Interband contiguous/noncontiguous) or same spectrum bands (Intra-band contiguous/non-contiguous). The users share the radio resources as per different scheduling schemes like round robin(RR), proportional fair (PF), best channel quality indicator (CQI), max-min, edge prioritized, channel traffic aware etc. Every scheduler has its own characteristic and provides improvement in terms of throughput or fairness. This paper discusses the simulations carried out to study the performance of RR, PF and best CQI schedulers in an urban, CLSM (closed loop spatial multiplexing) environment using an LTE system level simulator.

Time-Delay Neural Network for Smart MIMO Channel Estimation in Downlink 4G-LTE-Advance System

Long-Term Evolution (LTE) is the next generation of current mobile telecommunication networks. LTE has a new flat radio-network architecture and significant increase in spectrum efficiency. In this paper, main focus on throughput performance analysis of robust MIMO channel estimators for Downlink Long Term Evolution-Advance (DL LTE-A)-4G system using three Artificial Neural Networks: Feed-forward neural network (FFNN), Cascade-forward neural network (CFNN) and Time-Delay neural network (TDNN) are adopted to train the constructed neural networks‟ models separately using Back-Propagation Algorithm. The methods use the information received by the received reference symbols to estimate the total frequency response of the channel in two important phases. In the first phase, the proposed ANN based method learns to adapt to the channel variations, and in the second phase, it estimates the MIMO channel matrix and try to improve throughput of LTE. The performance of the estimation methods is evaluated by simulations in Vienna LTE-A DL Link Level Simulator. Performance of the proposed channel estimator, Time-Delay neural network (TDNN) is compared with traditional Least Square (LS) algorithm and ANN based other estimators for Closed Loop Spatial Multiplexing (CLSM) Single User Multi-input Multi-output (MIMO-2×2 and 4×4) in terms of throughput. Simulation result shows TDNN gives better performance than other ANN based estimations methods and LS.

Artificial Neural Network trained by Genetic Algorithm for Smart MIMO Channel Estimation for Downlink LTE-Advance System

Long-Term Evolution (LTE) is the next generation of current mobile telecommunication networks. LTE has a flat radio-network architecture and significant increase in spectrum efficiency, throughput and user capacity. In this paper, performance analysis of robust channel estimators for Downlink Long Term Evolution-Advanced (DL LTE-A) system using three Artificial Neural Networks: Feed-forward neural network (FFNN), Cascade-forward neural network (CFNN) and Layered Recurrent Neural Network (LRN) are trained separately using Back-Propagation Algorithm and also ANN is trained by Genetic Algorithm (GA). The methods use the information got by the received reference symbols to estimate the total frequency response of the channel in two important phases. In the first phase, the proposed ANN based method learns to adapt to the channel variations, and in the second phase it estimates the channel matrix to improve performance of LTE. The performance of the estimation methods is evaluated by simulations in Vienna LTE-A DL Link Level Simulator in MATLAB software. Performance of the proposed channel estimator, ANN trained by Genetic Algorithm (ANN- GA) is compared with traditional Least Square (LS) algorithm and ANN based other estimator like Feed- forward neural network, Layered Recurrent Neural Network and Cascade-forward neural network for Closed Loop Spatial Multiplexing (CLSM)-Single User Multi-input Multi-output (MIMO-2×2 and 4×4) in terms of throughput. Simulation result shows proposed ANN- GA gives better performance than other ANN based estimations methods and LS. Index Terms — LTE-A, MIMO, Artificial Neural Network (ANN), Back-Propagation, Layered Recurrent Neural Network (LRN), Feed-forward neural network (FFNN), Cascade-forward neural network (CFNN), Genetic Algorithm (GA).

Statistical Performance Analysis for MIMO Beamforming and STBC when Co-Channel Interferers Use Arbitrary MIMO Modes

In a cellular-like system, the multiple-input multiple-output (MIMO) mode used by a base station (BS) can be adaptively varied among several candidate MIMO modes, including space-time block coding (STBC), open-loop spatial multiplexing (OLSM), closed-loop spatial multiplexing (CLSM), MIMO beamforming (MBF), and maximal ratio transmission (MRT). In practice, during any one given period of time, when the desired BS performs downlink transmission with a specific MIMO mode, each co-channel interfering BS will use a MIMO mode the same as or different from that used in the desired link and any two co-channel interfering BSs may use different MIMO modes, so that the interference scenario becomes quite complicated. In this paper, considering realistic propagation conditions including both path-loss and Rayleigh fading and considering the existence of unequal-power interferers, the statistical distributions of the post-processing signal-to-interference ratios (SIRs) for either MBF or STBC downlink transmissions are analyzed when co-channel interfering BSs employ arbitrary MIMO modes. In particular, closed-form expressions for the probability density function (PDF) of the interference terms in the post-processing SIRs are derived. Further, the statistical distributions of the post-processing SIRs are analyzed. Simulation results verify the validity of the theoretical analyses.

Performance Evaluation of Closed-Loop Spatial Multiplexing Codebook Based on Indoor MIMO Channel Measurement

Closed-loop MIMO technique standardized in LTE can support different layer transmissions through precoding operation to match the channel multiplexing capability. However, the performance of the limited size codebook still needs to be evaluated in real channel environment for further insights. Based on the wideband MIMO channel measurement in a typical indoor scenario, capacity loss (CL) of the limited size codebook relative to perfect precoding is studied first in two extreme channel conditions. The results show that current codebook design for single layer transmission is nearly capacity lossless, and the CL will increase with the number of transmitted layers. Furthermore, the capacity improvement of better codebook selection criterions is very limited compared to CL. Then we define the maximum capacity boost achieved by frequency domain layer adaption (FDLA) and investigate its sensitivity to SNR and channel condition. To survey the effect of frequency domain channel variation on MIMO-OFDM system, we define a function to measure the fluctuation levels of the key channel metrics within a subband and reveal the inherent relationship between them. Finally, a capacity floor resulted as the feedback interval increases in frequency domain.

Outage analysis of interference-limited systems using STBC with co-channel MIMO interferers

The performance of Space-Time Block Coding (STBC) with co-channel MIMO interference is investigated. For an interference-limited environment, the closed-formexpressions for the probability density functions of the signalto-interference ratio are derived and applied to analyze the outage probability with three typical types of co-channel MIMO interferers: STBC, open-loop spatial multiplexing and closed-loop spatial multiplexing. Both theoretical analyses and simulation results show that the performance of STBC is independent of the MIMO modes used in the interfering links.

Distributed closed-loop spatial multiplexing for uplink multiuser systems

Focusing on the uplink, where mobile users (each with a single transmit antenna) communicate with a base station with multiple antennas, we treat multiple users as antennas to enable spatial multiplexing across users. Introducing distributed closed-loop spatial multiplexing with threshold-based user selection, we propose two uplink channel-assigning strategies with limited feedback. We prove that the proposed system also outperforms the standard greedy scheme with respect to the degree of fairness, measured by the variance of the time averaged throughput. For uplink multi-antenna systems, we show that the proposed scheduling is a better choice than the greedy scheme in terms of the average BER, feedback complexity, and fairness. The numerical results corroborate our findings.

Threshold-Based Substream Selection for Closed-Loop Spatial Multiplexing

We propose a low-complexity closed-loop spatial multiplexing method with limited feedback over multi-input-multi-output (MIMO) fading channels. The transmit adaptation is simply performed by selecting transmit antennas (or substreams) by comparing their signal-to-noise ratios to a given threshold with a fixed nonadaptive constellation and fixed transmit power per substream. We analyze the performance of the proposed system by deriving closed-form expressions for spectral efficiency, average transmit power, and bit error rate (BER). Depending on practical system design constraints, the threshold is chosen to maximize the spectral efficiency (or minimize the average BER) subject to average transmit power and average BER (or spectral efficiency) constraints, respectively. We present numerical and Monte Carlo simulation results that validate our analysis. Compared to open-loop spatial multiplexing and other approaches that select the best antenna subset in spatial multiplexing, the numerical results illustrate that the proposed technique obtains significant power gains for the same BER and spectral efficiency. We also provide numerical results that show improvement over rate-adaptive orthogonal space-time block coding, which requires highly complex constellation adaptation. We analyze the impact of feedback delay using analytical and Monte Carlo approaches. The proposed approach is arguably the simplest possible adaptive spatial multiplexing system from an implementation point of view. However, our approach and analysis can be extended to other systems using multiple constellations and power levels.