Time Division Duplex Research Articles

Dynamic-TDD interference tractability approaches and performance analysis in macro-cell and small-cell deployments

Meeting the continued growth in data traffic volume, Dynamic Time Division Duplex (D-TDD) has been introduced as a solution to deal with the uplink (UL) and downlink (DL) traffic asymmetry, mainly observed for dense heterogeneous network deployments, since it is based on instantaneous traffic estimation and provide more flexibility in resource assignment. However, the use of this feature requires new interference mitigation schemes capable of handling two additional types of interference between cells in opposite transmission direction: DL to UL and UL to DL interference. The aim of this work is to provide a complete analytical approach to model inter-cell interference in macro-cell and dense small-cell networks. We derive the explicit expressions of Interference to Signal Ratio (ISR) at each position of the network, in both DL and UL, to quantify the impact of each type of interference on the system performance. Also, we provide the explicit expressions of the coverage probability as functions of different system parameters by covering different scenarios. Finally, through system-level simulations, we analyze the feasibility of D-TDD implementation in both deployments and we compare its performance to the static-TDD (S-TDD) configuration.

Energy Efficiency of Two-Way Communications Under Various Duplex Modes

This article studies the energy efficiency (EE) of the two-way wireless communication system operating in the full-duplex (FD) and half-duplex (HD) modes, respectively. Particularly, both the residual self-interference (RSI) and power consumption for the self-interference cancellation (SIC) in the FD mode are modeled as linear functions over the transmit power. The EE maximization problems for FD, time-division duplex (TDD), and frequency-division duplex (FDD) modes with the sum and individual spectral efficiency (SE) constraints are studied, respectively. With the sum SE constraint, closed-form expressions for the maximum EE of these three modes are derived, and the maximum EE among them are compared. Based on the comparison results, a duplex selection scheme to achieve the highest EE among the three duplex modes is proposed. With the individual SE constraint, the optimal and suboptimal resource allocation are obtained by utilizing fractional programming for the three duplex modes. Somehow surprisingly, numerical results reveal that the FD mode achieves the best EE performance when the target sum SE or the distance between the two transceivers is relatively large.

Detecting active eavesdropper in large-scale antenna systems over Rician fading channels

Physical layer security is efficient in improving the security of transmission in wireless communications. It is effective in relaxing the complexity of the required cryptographic technologies. In this paper, we propose two detection schemes of an active eavesdropper in the physical layer of wireless communications. The system consists of a multi-antenna base station, a single-antenna legitimate user, and a single-antenna active eavesdropper. The large number of antennas at the base station is arranged as a planar array. It is assumed that the system is time division duplex (TDD) and the channels are of Rician distribution. The proposed two detection schemes are used to detect the eavesdropper by the base station and legitimate user, respectively. In both methods, the statistical characteristics of the received signals are analyzed and two test-statistics are constructed to detect the eavesdropper. The performances of the two methods are also analyzed. Simulation results show that both approaches are effective in detecting the active eavesdropper.

Analisa Kinerja Pada Perencanaan TD-LTE ADVANCED Studi Kasus Kota Bandung

In LTE Advanced technology there are two methods used in the duplexing process, there are frequency division duplex (FDD) wherein this duplexing concept communication is divided based on the frequency and the other is time division duplex (TDD) where communication is divided based on the time. Duplexing using the TDD method has advantages of handling data-based services that the majority have Non-Guarantee Bit Rate (N-GBR) characteristics because most of these services do not require a minimum bit rate to be able to work and this is an advantages because nowadays people like to use data-based services. So in this LTE Advanced network planning using the TDD method, frequency 2300 MHz for TD-LTE advanced, and parameters that to be the main focus are throughputs, reference signal received power (RSRP), reference signal strength indicator (RSSI), carrier to interference noise ratio (CINR), and block error rate (BLER). And the result of the simulations from TD-LTE Advanced planning are the mean of throughput value is 3,5 Mbps, mean of RSRP value is -110,8 dBm, mean of RSSI value is -72,36 dBm, mean of CINR value is 4,81 dB, and mean of BLER value is 0,07%.

Scheduling and Dynamic Pilot Allocation for Massive MIMO With Varying Traffic

In this letter, we consider the problem of joint user scheduling and dynamic pilot allocation in a Time-Division Duplex (TDD) based Massive MIMO network under varying traffic condition. One of the main problems with Massive MIMO systems is that the number of available orthogonal pilot signals is limited, and the dynamic allocation of these signals to different users is crucially needed to utilize the full benefit of these systems. In addition, pilot signals are radio resource control (RRC) configured in practice, and hence the frequent reconfiguration causes high signaling overhead and is costly. Using Lyapunov optimization framework, we develop an optimal algorithm that first assigns pilots dynamically based on queue sizes and the channel conditions of users as well as the reconfiguration cost at large time-scale. Then, it schedules users on a small-time scale. Numerical results show the efficacy of our algorithm and demonstrate that pilots do not need to be configured frequently at the expense of increased queue delay.

Relaying Systems With Reciprocity Mismatch: Impact Analysis and Calibration

Cooperative beamforming can provide significant performance improvement for relaying systems with the help of the channel state information (CSI). In time-division duplexing (TDD) mode, the estimated CSI will deteriorate due to the reciprocity mismatch. In this work, we examine the impact and the calibration of the reciprocity mismatch in relaying systems. To evaluate the impact of the reciprocity mismatch for all devices, the closed-form expression of the achievable rate is first derived. Then, we analyze the performance loss caused by the reciprocity mismatch at sources, relays, and destinations respectively to show that the mismatch at relays dominates the impact. To compensate the performance loss, a two-stage calibration scheme is proposed for relays. Specifically, relays perform the intra-calibration based on circuits independently. Further, the inter-calibration based on the discrete Fourier transform (DFT) codebook is operated to improve the calibration performance by cooperation transmission, which has never been considered in previous work. Finally, we derive the achievable rate after relays perform the proposed reciprocity calibration scheme and investigate the impact of estimation errors on the system performance. Simulation results are presented to verify the analytical results and to show the performance of the proposed calibration approach.

Joint Sparse Beamforming and Power Control for a Large-Scale DAS With Network-Assisted Full Duplex

In this paper, we studied the joint sparse beamforming and power control for network-assisted full duplex (NAFD) in large-scale distributed antenna system (L-DAS), where the remote antenna units either be operating in half-duplex mode or full-duplex mode are all connected to the central processing unit (CPU) via high-speed backhaul links. With joint processing at CPU, NAFD could achieve truly flexible duplex, including flexible half-duplex and full-duplex. Cross-link interference and the finite-capacity backhaul are the main problems of NAFD in L-DAS. To solve these problems, we aim to maximize the aggregated rate of uplink and downlink subject to quality of service constraints and backhaul constraints. Two approaches have been proposed to solve the optimization problem, where the first approach converts the object function to the difference of two convex functions with semi-definite relax (SDR) and then an iterative SDR-block coordinate descent method is applied to solve the problem. The second method is based on sequential parametric convex approximation. Simulation results have shown that the proposed algorithms yield a higher rate gain compared to the traditional time-division duplex scheme.

Deep Reinforcement Learning for Dynamic Uplink/Downlink Resource Allocation in High Mobility 5G HetNet

Recently, the 5G is widely deployed for supporting communications of high mobility nodes including train, vehicular and unmanned aerial vehicles (UAVs) largely emerged as the main components for constructing the wireless heterogeneous network (HetNet). To further improve the radio utilization, the Time Division Duplex (TDD) is considered to be the potential full-duplex communication technology in the high mobility 5G network. However, the high mobility of users leads to the high dynamic network traffic and unpredicted link state change. A new method to predict the dynamic traffic and channel condition and schedule the TDD configuration in real-time is essential for the high mobility environment. In this paper, we investigate the channel model in the high mobility and heterogeneous network and proposed a novel deep reinforcement learning based intelligent TDD configuration algorithm to dynamically allocate radio resources in an online manner. In the proposal, the deep neural network is employed to extract the features of the complex network information, and the dynamic Q-value iteration based reinforcement learning with experience replay memory mechanism is proposed to adaptively change TDD Up/Down-link ratio by evaluated rewards. The simulation results show that the proposal achieves significant network performance improvement in terms of both network throughput and packet loss rate, comparing with conventional TDD resource allocation algorithms.

Implementation of Pilot Channel Estimation Techniques for OFDM System with Low Mean Square Error

Abstract: Orthogonal Frequency Division Multiplexing(OFDM) has grown to be the most popular multi carriercommunication system in high speed data communications.The available bandwidth is utilized efficiently, and more datarates can be achieved because of orthogonal carriers in OFDMsystem. OFDM system requires precise channel estimation andsynchronization to reduce Mean Square Error (MSE). In thiswork, various Pilot Channel Estimation (PCE) techniques areused to compute CSI (Channel State Information). Pilots aretransmitted along with the data and channel response iscomputed with various interpolation techniques such as linear,spline, cubic Interpolation techniques by extracting the pilotsat the receiver. The performance metrics like Mean SquareError (MSE) and computation time are computed andcompared for different PCE techniques. Discrete FourierTransform (DFT) based channel Estimation is combined withinterpolation techniques and channel response is computed andcompared with Least Squares (LS) and Minimum MeanSquare Error (MMSE) approaches. LS, MMSE, LMMSE(Linear MMSE) methods are combined with TimeDivision(TD) and Time Division Duplexing(TDD) techniquesto compute MSE. TD-LMMSE approach achieves least MSEwith more computation time. Index Terms: OFDM, channel estimation, interpolation, CSI,MSE, computation time.

Simulation of LTE-TDD in the HAPS channel

LTE stands for Long Term Evolution. This technology enhances the data rate and capacity using a new radio interface and an optimized core network. This progress was done to satisfy standards defined for the fourth generation of cellular communications in ITU. LTE has two types of transmission: Frequency Division Duplex (FDD) and Time Division Duplex (TDD). Nowadays, LTE-TDD rapidly Grows and takes place of old fixed cellular communications, like WiMAX. Another upcoming technology in the communication industry is High Amplitude Platform Stations (HAPS). Studying the capability of HAPS as a base station for LTE-TDD is the main purpose of this paper. Simulations have done using HAPS channel and compared to Stanford University Interim (SUI) standard channels for different scenarios. Results were compared to achieve a conclusion on HAPS implementation for LTE-TDD based on BER and data throughput.

Increasing LTE-Advanced Network Capacity Using The Inter-band Carrier Aggregation (Downlink Side) Method

According to the identification of the Operating Support System (OSS) by the Smartfren cellular operator in the Central Bandung area, six sites are found to have high traffic capacity with the physical resource block (PRb) percentage of 82.6 %. The use of PRb > 80 % is included in the warning indicator 2 based on the operator’s standards. It is also strengthened by the condition of the existing sites with the average Reference Signal Receive Power (RSRP) of -103.3 dBm, Signal to Interference Noise Ratio (SINR) of 6.28 dB, and throughput of 27.78 Mbps, thus resulting in non-optimal network performance in the area. Therefore, in this study, the inter-band Carrier Aggregation (CA) was applied by combining the 40 Time Division Duplex (TDD) band (2300 MHz) and band 5 Frequency Division Duplex (FDD) (850 MHz). One of the advantages of applying this method is that it can increase the user network capacity by maximizing the resources owned by the operator. The predetermined scenario taking into account the initial network condition indicated a decrease in the PRb percentage by 44.50 % and an increase in the average RSRP value by 12.8 dBm, SINR by 5.14 dB, and throughput by 34.59 Mbps.

Beyond 5G: Leveraging Cell Free TDD Massive MIMO Using Cascaded Deep Learning

This letter deals with the calibration of Time Division Duplexing (TDD) reciprocity in an Orthogonal Frequency Division Multiplexing (OFDM) based Cell Free Massive MIMO system where the responses of the (Radio Frequency) RF chains render the end to end channel non-reciprocal, even though the physical wireless channel is reciprocal. We further address the non-availability of the uplink channel estimates at locations other than pilot subcarriers and propose a single-shot solution to estimate the downlink channel at all subcarriers from the uplink channel at selected pilot subcarriers. We propose a cascade of two Deep Neural Networks (DNN) to achieve the objective. The proposed method is easily scalable and removes the need for relative reciprocity calibration based on the cooperation of antennas, which usually introduces dependency in Cell Free Massive MIMO systems.

A 400MHz Single‐Chip CMOS Transceiver for Long Range High Definition Video Transmission in UAV Application

A fully-integrated 400MHz transceiver for high definition video transmission in Unmanned aerial vehicle (UAV) is presented. The transceiver integrates a Receiver (RX), a Transmitter (TX), a tunable multi-mode complex filter, two sigma-delta fractional-N PLL frequency synthesizers and some baseband calibration circuits, which is applicable for both Time division duplex (TDD) and Frequency division duplex (FDD) systems. In order to meet different data rate and sensitivity requirements for control signal and video signal transmission, the transceiver supports BPSK/QPSK/QAM modulation. The receiver sensitivity is -75dBm and the transmitter provides emission power up to 12dBm. Besides, the Error vector magnitude (EVM) of -35dB is measured under 64QAM modulation with 54Mbps data rate. Fabricated in a standard 130nm CMOS process and operated at 1.2V supply for most circuits excluding PA, 3.3V supply for PA, the receiver and the transmitter consume 68.2mW and 164.3mW, including the frequency synthesizer, respectively. The total chip area with pads is 6.25mm2.

Reciprocity Calibration of TDD MIMO Channel for Interference Alignment

Interference alignment (IA) is a promising technique to boost the Multiple-input Multiple-output (MIMO) network throughput. Concurrent data transmission links between multiple pairs of transmitters (TX) and receivers (RX) can be established in the same spectrum via cooperation. To make the channel state information (CSI) available on the transmitter side, channel reciprocity in time division duplex (TDD) networks is assumed by a large number of distributed IA algorithms. The physical channel is reciprocal, but nevertheless the channel considered by IA is not, because it also involves the radio frequency (RF) front ends of the transceiver, which are different circuits for transmit and receive modes individually. The difference between the two circuits yields mismatch between the forward and backward channels. Given the mutual coupling effect of the antenna array, the channel's non-symmetry is further complicated. In this paper, we provide the modeling of the non-reciprocity for the TDD MIMO channels and propose a corresponding calibration method to minimize the mismatch. Experimental validation has been conducted with classic distributed IA algorithms. The results highlight the indispensability of the reciprocity calibration for approaching the network capacity gain promised by IA.

Superimposed Pilot for Multi-Cell Multi-User Massive FD-MIMO Systems

In this paper, superimposed pilot based communication strategies are investigated for a time-division duplex (TDD)-based massive Full-Dimension MIMO (FD-MIMO) network jointly considering both uplink (UL) and downlink (DL) performance. To be specific, the DL multi-cell multi-user MIMO operation is connected to UL channel estimation through the superimposed pilot. The performance of UL channel estimation is analytically characterized and the estimated UL channel is linked to the DL MIMO operation for the massive MIMO network. In this way, the corresponding feedback for DL channel state information (CSI) can be eliminated while the UL pilot overhead can be minimized. Results suggest that superimposed pilot could significantly improve the overall network performance of a massive FD-MIMO network.

Machine Learning-Based Channel Prediction in Massive MIMO With Channel Aging

To support the ever increasing number of devices in massive multiple-input multiple-output (mMIMO) systems, an excessive amount of overhead is required for conventional orthogonal pilot-based channel estimation schemes. To circumvent this fundamental constraint, we design a machine learning (ML)-based time-division duplex scheme in which channel state information (CSI) can be obtained by leveraging the temporal channel correlation. The presence of the temporal channel correlation is due to the stationarity of the propagation environment across time. The proposed ML-based predictors involve a pattern extraction implemented via a convolutional neural network, and a CSI predictor realized by an autoregressive (AR) predictor or an autoregressive network with exogenous inputs recurrent neural network. Closed-form expressions for the user uplink and downlink achievable spectral efficiency and average per-user throughput are provided for the ML-based time division duplex schemes. Our numerical results demonstrate that the proposed ML-based predictors can remarkably improve the prediction quality for both low and high mobility scenarios, and offer great performance gains on the per-user achievable throughput.

LTE Network Area Coverage on FDD and TDD Technology

FDD (Frequency Division Duplexing) and TDD (Time Division Duplexing) Technology I is a duplex technology on the 4G LTE network. FDD technology in Indonesia is deployed in the 900 MHz, 1800 MHz and 2100 MHz frequency bands. Meanwhile, TDD technology uses frequency of 2300 MHz. In order to see the performance from the side of coverage, a measurement of the signal strength is conducted by direct measurements in field so that the appropriate technology and frequency band can be determined for the measurement area. The measurements have been done by two samples of different frequencies, namely 1800 MHz for FDD and 2300 MHz for TDD. Measurement of coverage is conducted on the same existing BTS and different BTS for both FDD and TDD modes. The parameter used in this measurement is the RSRQ value as one of the basic parameters of KPI (Key Performance Indicator). The results of drivetest data obtained the farthest coverage area of 789 m, namely the FDD (Frequency Division Duplexing) technology with frequency of 1800 MHz and TDD with frequency of 2300 MHz for 633 m.

LTE Network Area Coverage on FDD and TDD Technology

FDD (Frequency Division Duplexing) and TDD (Time Division Duplexing) Technology I is a duplex technology on the 4G LTE network. FDD technology in Indonesia is deployed in the 900 MHz, 1800 MHz and 2100 MHz frequency bands. Meanwhile, TDD technology uses frequency of 2300 MHz. In order to see the performance from the side of coverage, a measurement of the signal strength is conducted by direct measurements in field so that the appropriate technology and frequency band can be determined for the measurement area. The measurements have been done by two samples of different frequencies, namely 1800 MHz for FDD and 2300 MHz for TDD. Measurement of coverage is conducted on the same existing BTS and different BTS for both FDD and TDD modes. The parameter used in this measurement is the RSRQ value as one of the basic parameters of KPI (Key Performance Indicator). The results of drivetest data obtained the farthest coverage area of 789 m, namely the FDD (Frequency Division Duplexing) technology with frequency of 1800 MHz and TDD with frequency of 2300 MHz for 633 m.

Impact of Traps on the Adjacent Channel Power Ratios of GaN HEMTs

In this work, the impact of traps on a system level parameter, ACPR (adjacent channel power ratio), of commercial RF AlGaN/GaN HEMTs were studied. ACPR usually depends on the transistor linearity and stability, and in this study it was measured in two different signal duplexing schemes: time division duplexing (TDD) and frequency division duplexing (FDD) after using digital predistortion to minimize static nonlinearities. It is theorized traps lead to time-dependent nonlinearity due to the devices changing operating points, which degrades ACPR. Constant drain current deep level transient spectroscopy (CI $_{D}$ -DLTS) measurements were performed to quantitatively characterize the trap energies and concentration and correlate with the different time sensitivities of the TDD and FDD schemes. Linked by the trap concentration and time constant, the $\text{E}_{C}$ -0.57 eV trap was correlated to the FDD ACPR, and the $\text{E}_{C}$ -0.72 eV trap was correlated to the TDD ACPR. Finally, it is shown that both traps have been widely reported, suggesting that many GaN systems’ ACPR can be potentially improved by reducing the trap concentration.

Effective Indoor Coverage via Radio-Over-Cable Fronthauls: Analog Fronthauls Come of Age

This article considers a radio-over-cable (RoC)based analog link on a local area network (LAN) cable [e.g., category (CAT) 5] as the last hop of the fronthaul for indoor mobile service coverage. We first present state-of-the-art mobile systems with RoC-based fronthauls and then discuss a number of critical issues regarding real implementation. These issues include the function module, called the radio-cable access unit (RCU), that interfaces with the radio frequency (RF) and intermediate frequency (IF) signals along the LAN cable as well as the design of an RF front end (RF-FE) that supports time-division duplex (TDD) and frequency-division duplex (FDD) modes. Then, the proposed nonconfigurable distributed antenna unit (NC-DAU) and corresponding resource-mapping scheme [NC air-tocable (NC-A2C)] are introduced, aiming to achieve lowcost, large-scale indoor deployment. We examine the performance of the NC-A2C and compare it with the optimal case.