Division Duplex Research Articles

Adversarial training-aided time-varying channel prediction for TDD/FDD systems

In this paper, a time-varying channel prediction method based on conditional generative adversarial network (CPcGAN) is proposed for time division duplexing/frequency division duplexing (TDD/FDD) systems. CPcGAN utilizes a discriminator to calculate the divergence between the predicted downlink channel state information (CSI) and the real sample distributions under a conditional constraint that is previous uplink CSI. The generator of CPcGAN learns the function relationship between the conditional constraint and the predicted downlink CSI and reduces the divergence between predicted CSI and real CSI. The capability of CPcGAN fitting data distribution can capture the time-varying and multipath characteristics of the channel well. Considering the propagation characteristics of real channel, we further develop a channel prediction error indicator to determine whether the generator reaches the best state. Simulations show that the CPcGAN can obtain higher prediction accuracy and lower system bit error rate than the existing methods under the same user speeds.

Capacity Region and Scheduling for Non-Orthogonal Duplex

Existing wireless mobile networks configure the uplink (UL) and downlink (DL) resources based on the orthogonal duplex principle, which has significantly evolved from the static frequency/time division duplex (FDD/TDD) to the semi-dynamic TDD in 4G and the fully-dynamic TDD in 5G. Fueled by the successful realizations of full duplex (FD) transmission, non-orthogonal duplex (NOD) emerges as an attractive candidate technique for future networks to improve the bidirectional throughput. In this paper, we investigate the performance limit of the NOD scheme, which imports the FD mode on the basis of fully-dynamic TDD. We first focus on a single-cell scenario by assuming no cooperation among cells, and strive to characterize the bidirectional capacity region by finding the capacity-optimal transmission mode scheduling policy. We obtain the optimal policies for the systems with and without modulation and coding scheme (MCS), respectively, where the policies are based on the instantaneous channel gains and the distribution of channels. We proceed to develop a scheduling policy that only relies on the instantaneous channel and queue information, and extend it to the multicell multiuser scenario with coordinated scheduling. Numerical and simulation results demonstrate the great potential of the NOD scheme in increasing bidirectional capacity and reducing the queuing delay.

Exploiting Multiple-Antenna Techniques for Non-Orthogonal Multiple Access

This paper aims to provide a comprehensive solution for the design, analysis, and optimization of a multiple-antenna non-orthogonal multiple access (NOMA) system for multiuser downlink communication with both time duplex division and frequency duplex division modes. First, we design a new framework for multiple-antenna NOMA, including user clustering, channel state information (CSI) acquisition, superposition coding, transmit beamforming, and successive interference cancellation. Then, we analyze the performance of the considered system, and derive exact closed-form expressions for average transmission rates in terms of transmit power, CSI accuracy, transmission mode, and channel conditions. For further enhancing the system performance, we optimize three key parameters, i.e., transmit power, feedback bits, and transmission mode. Especially, we propose a low-complexity joint optimization scheme, so as to fully exploit the potential of multiple-antenna techniques in NOMA. Moreover, through asymptotic analysis, we reveal the impact of system parameters on average transmission rates, and hence present some guidelines on the design of multiple-antenna NOMA. Finally, simulation results validate our theoretical analysis, and show that a substantial performance gain can be obtained over traditional orthogonal multiple access technology under practical conditions.

Angle Domain Signal Processing-Aided Channel Estimation for Indoor 60-GHz TDD/FDD Massive MIMO Systems

This paper proposes a practical channel estimation for 60-GHz indoor systems with the massive uniform rectangular array at base station. Through antenna array theory, the parameters of each channel path can be decomposed into the angular information and the channel gain information. We first prove that the true direction of arrivals of each uplink path can be extracted via an efficient array signal processing method. Then, the channel gain information could be obtained linearly with small amount of training resources, which significantly reduces the training overhead and the feedback cost. More importantly, the proposed scheme unifies the uplink/downlink channel estimations for both the time duplex division and frequency duplex division systems, making itself particularly suitable for protocol design. Compared with the existing channel estimation algorithms, the newly proposed one does not require any knowledge of channel statistics and can be efficiently deployed by the 2-D fast Fourier transform. Meanwhile, the number of user terminals simultaneously served can be increased from a sophisticatedly designed angle division multiple access scheme. Simulation results are provided to corroborate the proposed studies.

Joint scheduling and mapping in support of downlink fairness and spectral efficiency in ieee 802.16e OFDMA system

SummaryThe next generation broadband wireless networks deploy orthogonal frequency division multiple access (OFDMA) as the enabling technologies for broadband data transmission with QoS capabilities. In such broadband wireless systems, one major issue is how to utilize radio resource efficiently while maintaining fairness between sessions as well as providing adequate QoS. In this work, we propose an approach for OFDMA/time division duplex (TDD) downlink suitable for IEEE802.16e WiMAX systems that combines scheduling and burst mapping algorithms for a trade‐off between session fairness, QoS, and spectral efficiency. While optimizing radio resources under QoS and fairness constraints is an NP‐hard problem, we follow a heuristic approach that simplifies the complexity of the algorithm. Performance results show that while the new scheme outperforms the Proportional Fair algorithm in terms of fairness, it also improves the overall system spectral efficiency. Copyright © 2016 John Wiley & Sons, Ltd.

Software defined radio platform with wideband tunable front end

The paper presents a Software Defined Radio (SDR) development platform with wideband tunable RF (Radio Frequency) front end. The platform is based on the SB3500 Multicore Multithreaded Vector Processor and it is intended to be used for a wide variety of communication protocols as: Time Division Duplexing/Frequency Division Duplexing Long Term Evolution (TDD/FDD LTE), Global Positioning System (GPS), Global System for Mobile/General Packet Radio Service (GSM/GPRS), Wireless Local Area Network (WLAN), Legacy Worldwide Interoperability for Microwave Access (WiMAX). As an example, we describe briefly the implementation of the LTE TDD/FDD communication protocol. As far as we know, this is the only LTE category 1 communication protocol entirely developed and executed in software (SW), without any hardware (HW) accelerators.

A new MAC protocol for broadband wireless communications and its performance evaluation

This paper presents a new Time Division Multiple Access/Frequency Division Duplexing (TDMA/FDD) based Medium Access Control (MAC) protocol for broadband wireless networks, supporting Quality of Service (QoS) for real-time multimedia applications. It also gives the Call Blocking Probability (CBP), packet end-to-end delay and utilization analysis of different service classes, as they are most essential performance criterions in broadband wireless network assessment. The Connection Admission Control (CAC) mechanism in the proposed MAC efficiently organizes the bandwidth allocation for different service classes by means of a fairness based scheduling algorithm. In addition, the simulation model of the proposed MAC scheme is realized by using OPNET Modeler network simulator. The results of the analytical calculations for the CBPs are compared to those of the simulation of the proposed MAC, thus validity of the MAC protocol is proved.

Cross‐layer optimization for CDMA/TDD wireless mesh networks

AbstractThis paper proposes a new cross‐layer optimization algorithm for wireless mesh networks (WMNs). CDMA/TDD (code division multiple access/time division duplex) is utilized and a couple of TDD timeslot scheduling schemes are proposed for the mesh network backbone. Cross‐layer optimization involves simultaneous consideration of the signal to interference‐plus‐noise ratio (SINR) at the physical layer, traffic load estimation and allocation at medium access control (MAC) layer, and routing decision at the network layer. Adaptive antennas are utilized by the wireless mesh routers to take advantage of directional beamforming. The optimization formulation is subject to routing constraints and can be solved by general nonlinear optimization techniques. Comparisons are made with respect to the classic shortest‐path routing algorithm in the network layer. The results reveal that the average end‐to‐end successful packet rate (SPR) can be significantly improved by the cross‐layer approach. The corresponding optimized routing decisions are able to reduce the traffic congestion. Copyright © 2010 John Wiley & Sons, Ltd.

Dynamic slot assignment protocol for QoS support on TDMA-based mobile networks

An efficient bandwidth allocation scheme in wireless networks should not only guarantee successful data transmission without collisions but also enhance the channel spatial reuse to maximize the system throughput. The design of high-performance wireless Local Area Network (LAN) technologies making use of TDMA/FDD MAC (Time Division Multiple Access/Frequency Division Duplex – Medium Access Control) is a very active area of research and development. Several protocols have been proposed in the literature as TDMA-based bandwidth allocation schemes. However, they do not have a convenient generic parameters or suitable frame repartition for dynamic adjustment. In this work, we undertake the design and performance evaluation of a QoS (Quality of Service)-aware scheme built on top of the underlying signaling and bandwidth allocation mechanisms provided by most wireless LANs standards. The main contribution of this study is the new guarantee-based dynamic adjustment algorithm used in MAC level to provide the required QoS for all traffic types in wireless medium especially Wireless ATM (Asynchronous Transfer Mode). Performance evaluation of this approach consists of improving the bandwidth utilization, supporting different QoS requirements and reducing call reject probability and packet latency.

A Cooperative Transmission and Receiving Scheme for IDMA with Time-Reversal Technique

In this paper, we propose an efficient uplink and downlink cooperative transmission and receiving scheme for interleave-division multiple access (IDMA) systems with time-reversal (TR) technique. We refer this system as TDR-IDMA, since the time- division duplexing (TDD) mode is used in this transceiver system. In TDR-IDMA systems, the time-reversed version of the channel impulse responses obtained from the uplink is used to process the received signal before the elementary signal estimator in the receiver of base station (BS). Due to the weak correlations of multi-path for different users, the signal to interference and noise ratio (SINR) at the beginning of turbo-like detection of TDR-IDMA can be increased significantly. Compared with conventional IDMA system, much less iterations is needed for signal detection in TDR-IDMA systems. Thus, the proposed scheme effectively reduces the multi-user detection (MUD) computation load for the uplink, which is the bottleneck for IDMA system. TR processing is also applied in the transmitter of BS to reduce the complexity of user ends (UEs). Simulation and analysis results show that TDR-IDMA can achieve the same performance of the traditional IDMA system with fast processing speed and simple UEs.

Pilot-Based Channel Quality Reporting for OFDMA/TDD Systems with Cochannel Interference

This paper proposes pilot-based channel quality reporting for orthogonal frequency division multiple access/time division duplex (OFDMA/TDD) systems with cochannel interference. In the proposed method, a terminal reports his channel quality in multiple subbands to base station (BS) using channel reciprocity of TDD systems. The terminal transmits uplink pilot signals in the subbands with different transmit power which is inversely proportional to the subband-based interference power. The BS can obtain knowledge of the terminal's received signal-to-interference-plus-noise power ratio on subband basis, measuring the pilot signal power. In performance evaluation, accuracy of channel quality reporting and amount of uplink signalling are examined. From numerical results, it is found that the proposed method becomes effective as the number of subbands and terminals for channel quality reporting increases.

Downlink performance improvement of TDD CDMA cellular networks with time slot and fixed hopping station allocations

In this paper, downlink capacity of time duplex division (TDD) based cellular wireless networks utilizing fixed hopping stations is investigated. In the network, a number of fixed subscriber stations act as hopping transmission stations between base stations and far away subscribers, forming a cellular and ad hoc mobile net- work model. At the radio layer, TDD code division multiple access (CDMA) is selected as the radio interface due to high efficiency of frequency usage. In order to improve the system performance in terms of downlink capacity, we propose different time slot allocation schemes with the usage of fixed hopping stations, which can be selected by either random or distanced dependent schemes. Performance results obtained by computer simulation demonstrate the effectiveness of the proposed network to improve downlink system capacity.

Packet Scheduling Algorithm Considering a Minimum Bit Rate for Non-realtime Traffic in an OFDMA/FDD-Based Mobile Internet Access System

In this letter, we consider a new packet scheduling algorithm for an orthogonal frequency division multiplexing access/frequency division duplex (OFDMA/FDD)-based system, e.g., mobile broadband wireless access or high-speed portable internet systems, in which the radio resources of both time and frequency slots are dynamically shared by all users under a proper scheduling policy. Our design objective is to increase the number of non-realtime service (e.g., WWW) users that can be supported in the system, especially when the minimum bit rate requirement is imposed on them. The simulation results show that our proposed algorithm can provide a significant improvement in the average outage probability performance for the NRT service, i.e., significantly increasing the number of NRT users without much compromising of the cell throughput.

A fast multispeed comma-free reed-solomon decoder for W-CDMA applications using foldable systolic array architecture

This brief proposes a fast multispeed comma-free Reed-Solomon (CFRS) decoder for the frame synchronization and code-group identification in the cell search of the Third Generation Partnership Project wide-band code-division multiple access/frequency division duplexing (W-CDMA/FDD) system. A foldable systolic array is proposed to achieve fast decoding and provide flexible tradeoffs between power consumption, chip size, and decoding latency. Multispeed decoding, an idea that is useful for cell search in different application scenarios, can also be achieved with the same array architecture. The proposed CFRS decoder is implemented in a 3.3-V 0.35-μm CMOS technology with 2.2 × 2.2 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> core area and power dissipation of 13.3 and 1.23 mW in high- and low-speed decoding modes, respectively.

UTRA/FDD RF Transceiver Requirements

Unified RF requirements are derived for an UMTS Terrestrial Radio Access/Frequency Division Duplex (UTRA/FDD) compliant mobile transceiver. A set of transceiver requirements are proposed with consideration to system issues including duplex aspects. From these design-compatible requirements are proposed for each functional block in the transceiver.

Adaptive Modulation/TDMA/TDD with Convolutionally Coded Type-II HybridARQ for Wireless Communication Systems

This paper proposes a time division multiple access/time division duplex (TDMA/TDD)-based adaptive modulation system (AMS) with a convolutionally coded Type-II Hybrid automatic repeat request (ARQ) protocol to achieve high throughput data transmission in wireless communication systems. First, this paper discusses the cause of throughput limitation of the conventional fixed-rate quaternary phase shift keying (QPSK) with ARQ protocol and suggests that the effective means to improve throughput performance are the reduction of re-transmission probability under bad channel condition and the increase of transmission bit rate per TDMA/TDD slot under good channel condition. Based on these strategies, this paper discusses an AMS with a convolutionally coded type-II hybrid ARQ protocol (type-II hybrid ARQ/AMS) and evaluates its performance by computer simulation. The results confirm that the proposed type-II hybrid ARQ/AMS can drastically improve throughput performances compared to the conventional fixed-rate QPSK with selective repeat ARQ protocol (SR-ARQ/QPSK) or a simple combination of SR-ARQ and AMS (SR-ARQ/AMS) under any channel conditions, especially under severe channel conditions.

Performance of modulation‐level‐controlled adaptive modulation systems

AbstractThe multivalued quadrature amplitude modulation (QAM), such as 16 QAM, is a very useful technique in land mobile communication since a high‐speed transmission can be realized without enlarging the transmission band. The technique has a problem, however, in that it is not robust against the decrease of the received signal level due to fading or the effect of the delayed waves, which easily deteriorates the transmission quality. To solve such a problem, this paper proposes an adaptive modulation system where the number of modulation levels is adjusted according to the condition of the channel. In the proposed system, the instantaneous C/N0 and the delay spread are estimated as the condition of the channel, using a method based on time division multiple access/time division duplex (TDMA/TDD).When the channel is in a good situation, a highspeed transmission is executed using a larger number of modulation levels such as 256 QAM. When the channel is in a bad condition, a modulation method with a small number of modulation levels, such as quadraphase‐shift keying (QPSK), is used, which is robust against the noise or the delayed waves. By this scheme, it is possible to realize a high‐speed transmission without deteriorating the transmission quality, compared to the conventional system with the fixed number of modulation levels. The transmission performance is evaluated by a computer simulation, and it is shown that a high‐speed transmission can be realized without deteriorating the transmission quality, compared to the QPSK system, in the uniform Rayleigh fading condition as well as in the situation containing delayed waves.

An approximate analysis of TDMA out-of-slot random access protocols for microcellular mobile communications

In this paper, out-of-slot random access protocols for voice services that operate in microcellular environment are studied and simulated. The bearer service is assumed to be structured as time division multiple access/frequency division multiple access/frequency division duplex (TDMA/ FDMA/FDD). According to a stratification of information flow ascall, talkspurt, andpacket, the protocols are implemented at the talkspurt level. During a call, talkspurts generate a stream of packets. Each talkspurt has to reserve a voice time slot with a special control packet sent in a dedicate control slot (out of slot signaling). After a successful access, a voice slot is assigned for the duration of the talkspurt. This work concentrates on the out of slot random access method. When a transition from the idle state to the active state occurs, a voice terminal starts generating a talkspurt. Access for a voice slotV is then initiated via a dedicated control slotC. The time spent in gaining aV slot depends on the kind of random access protocol used in theC slots. Once the access reservation phase is successful, the talkspurt starts the second phase of information transmission in a freeV slot. If allV slots are occupied by other talkspurts, the new talkspurt is queued until aV slot becomes free. If the sum of the access and queueing times exceeds a thresh-old, a portion of the talkspurt is clipped. In our work we define an analytical model to evaluate the percentage of clipped voice packets. Simulations validate the analytical model.

A spread spectrum cordless telephone

AbstractThe United States industrial, scientific, and medical (ISM) band has been released for spread spectrum communication, and various applications for it are being proposed. A spread spectrum cordless telephone set has been developed for domestic use as one of its applications.In this paper, the design outline and its characteristics are explained. the direct sequence spread spectrum technique with spreading ratio of 16 in the 902‐ to 928‐ MHz ISM band is used. to solve the near‐far problem in the mobile radio communication channel, the frequency division multiple access‐time division duplex (FDMA TDD) technique is adopted where different frequencies can be assigned to each channel. Compact size and low power consumption is achieved by developing a chip in which spread spectrum processing and transceiver multi plexing can be handled on a single ASIC chip.The voice codec uses ADPCM and provides better voice quality compared to the conventional analog cordless phones. Wider talking range compared to the conventional 46/49 MHz cordless phone is obtained by increasing the amount of transmitted power. Moreover, since the ISM band is used, interference from other sources can be avoided by changing the channel frequencies.

Square-QAM adaptive modulation/TDMA/TDDsystems using modulation level estimationwith Walsh function

The authors propose a square-QAM adaptive modulation/time division multiple access/time division duplex (TDMA/TDD) system for land mobile communications to achieve high quality and high bit rate transmission in both flat and frequency selective fading environments. To further improve performance, a new modulation level estimation scheme using the Walsh function and maximum likelihood (MS) estimation is also proposed. Computer simulation confirms that the proposed system gives 8 dB better performance and four times larger delay spread immunity than that of conventional QPSK systems at BER = 10-3.