Yuehong Gao

Performance evaluation of flexible duplex implement based on radio frame selection in LTE heterogeneous network

Performance gain can be obtained by dynamically reconfiguring the uplink and downlink radio frames in TDD systems. FDD systems can also benefit from the flexibility in the allocation of uplink and downlink resources. The paper proposes a specific implement of flexible duplex based on selection between different designs of radio frames to make the FDD network more adaptive to the real time situation of uplink and downlink traffic. The interference generated by flexible duplex is analyzed with a typical mathematic model and several scenarios are discussed to find out the ideal scenario to apply flexible duplex. Some simulation results are given to show the gain obtained by the scheme.

System Spectral Efficiency and Stability of 3G Networks: A Comparative Study

CDMA2000, WCDMA and WiMAX are three widely used 3G technologies. Since they share the same goal, which is to provide broader coverage and higher throughput in 3G networks, an impartial comparison of their performance is indispensable. However, they are based on different design principles and methodologies, which make the comparison challenging. This paper presents a comparative study of these technologies, with focus on system spectral efficiency and stability in 3G networks. Specifically, the paper presents a framework for the comparison based on the common set of configurations adopted by these technologies, which include channel models, system parameters and key algorithms. Through extensive simulations, the system spectral efficiency and stability of CDMA2000 1x EVDO Rev.A, WCDMA HSDPA/HSUPA and Mobile WiMAX are compared. It is found that while WiMAX can provide highest throughput, the two CDMA-based technologies achieve higher system spectral efficiency, especially on the downlink. Regarding system stability, it is observed that CDMA2000 1x EV-DO Rev.A can operate under higher interference levels than WCDMA HSDPA/HSUPA and Mobile WiMAX. In addition, the comparison on system spectral efficiency between CDMA2000, WCDMA and WiMAX is also conducted when relevant enhanced technologies, i.e., MIMO and interference cancelation, are adopted. We believe that our work will serve as a cornerstone for a fair comparison between the various technologies for prospective 3G networks.

Spectrum sharing for LTE and WiFi coexistence using decision tree and game theory

In this paper, a spectrum sharing scheme adapted for the operation of Long Term Evolution (LTE) in unlicensed band (LTE-U) and WiFi system is proposed. This scheme optimizes the resource in unlicensed band based on decision tree learning and repeated game. We consider a flexible architecture decoupling control plane from data plane in the coexistence system. In control plane, strong ability of data processing is provided. Controllers learn the latest data set in the pool to build decision trees. According to the decision tree, controllers deduce the network status of the opponent. Repeated game is played to share spectrum resources for maximizing the resource utilization in the coexistence system. At the beginning of each game stage, controllers use decision tree to make informed decisions quickly. In repeated game, an encouragement mechanism is proposed to stimulate operators to share spectrum resources. Simulation results show that dynamic spectrum sharing is able to improve throughput and spectrum efficiency in unlicensed band. At the same time, this scheme also balances the traffic load and guarantees fairness among multiple systems.

Delay and delay-constrained throughput analysis of a wireless powered communication system

In this paper, we investigate the delay and delay-constrained throughput performance of a point-to-point wireless-powered communication system, where one node, e.g. a user equipment (UE), is powered by the wireless energy transferred from the other node, e.g. an access point (AP), and uses the harvested wireless energy to send data to the other node. Our focus is on the delay performance of sending data over the uplink from the UE node to the AP node, and on its throughput performance when a delay constraint is enforced. Two representative time allocation schemes in using the link for the AP node to transfer energy (maybe together with data) and for the UE node to send data are considered. In particular, a lower bound on the cumulative capacity of the uplink is derived. In addition, an upper bound on the delay distribution is obtained for stochastic traffic arrivals, based on which, the delay-constrained throughput performance is further analyzed. Moreover, the accuracy of the analysis is validated by comparison with extensive simulation results. The analysis and results shed new light on the performance of such a wireless-powered communication system.

Stochastic network calculus analysis of energy harvesting rate in wireless networks with delay and energy storage constraints

Energy evaluation of wireless transmission for data service under different QoS (quality of service) constraints is a hot topic in green communications. In this paper, we employ the theory of the stochastic network calculus to investigate the relationship between the traffic arrival rate and energy harvesting rate under the delay and energy storage constraints. We first construct a wireless system model which works only by consuming the harvested renewable energy. Also, stochastic traffic arrivals, packet size as well as a two-state Markov chain interference on energy harvesting are jointly considered to ensure the accuracy of the analysis. We derive the minimum energy harvesting rate needed to satisfy the delay and energy storage constraints under a given average arrival rate. The efficiency of the harvested energy is also studied and shown to be convex in the numerical simulation. Numerical results illustrate that while the minimum energy harvesting rate is positively correlated with the packet size, it is negatively related to the delay requirement, under a given arrival rate. Additionally, the probabilistic bound of energy insufficiency is shown to be positively correlated with the transition cycle of the interference.

Random network coding in MIMO system

Random network coding (RNC) has emerged as a promising technology. In this paper, we seek to answer the question that how RNC benefits cellular systems. A novel RNC-based space–time code (STC) scheme is proposed for the data transmission in MIMO system. In this scheme, RNC is integrated with the STC design for MIMO system. And then, the improved diversity order and multiplexing gain of the RNC-based STC scheme are analyzed and derived. This RNC-based STC scheme can also have benefit of RNC on some practical applications. After that, a general RNC-based STC protocol which describes the data transmission flow in practical system is designed for MIMO transmission. Finally, the performance of RNC-based STC scheme is evaluated through both link-level and system-level simulations. The simulation results show that RNC can provide extra diversity gain, multiplexing gain, or reduce the decoding complexity, and improve the bandwidth efficiency and user fairness in cellular system with MIMO.

A Pilot Assignment Scheme for Single-Cell Massive MIMO Circumstances

—In Time-Division Duplex (TDD) massive MultipleInput Multiple-Output (MIMO) systems, pilot contamination becomes the performance bottleneck when the number of terminals is larger than that of available pilot sequences. In this paper, we first deduce the general formulas for uplink Signal-toInterference Ratio (SIR) and channel capacity in single-cell massive MIMO circumstances with insufficient pilot sequences. Then, in order to enhance the Quality of Service (QoS) for the terminals who suffer from severe pilot contamination, an optimization problem is formulated to maximize the minimum uplink capacity of all terminals. Next, because the complexity of finding the optimal pilot assignment is too high, a suboptimal two-step assignment approach with low complexity is proposed to solve the optimization problem. Compared with the random pilot assignment scheme in single-cell massive MIMO systems, simulation results prove the effectiveness of this two-step scheme in obtaining better minimum uplink SIR and minimum channel capacity when the number of BS antennas is great but finite. Meanwhile, the average capacity of all terminals can also be improved.

Throughput Analysis of an Energy Harvesting Multichannel System Under Delay and Energy Storage Constraints

High power to guarantee strict performance requirement and low power to avoid energy depletion result in an inevitable conflict for a renewable energy harvesting communication system with finite energy storage. This paper proposes a generic approach to study the per-flow performance in such a multichannel system multiplexed by multiple flows. The queueing delay constraint and energy storage constraint are constructed to express the probabilistic bound of queuing delay and that of energy depletion, respectively. We study these constraints with the statistical information of the processes, including traffic arrivals and service, energy harvesting, and consumption. The lower bound of the long-term maximum per-flow throughput is then derived to meet the constraints under a specific system. The accuracy of the proposed approach is validated by simulation experiments. The analysis reveals how the sustained throughput is affected by various factors, such as the queueing delay and energy storage constraints, the packet size, the energy block size, the traffic scheduling schemes, the bandwidth allocation schemes as well as the interdependence among the channel service processes. Particularly, the analysis also provides valuable insight into traffic admission control from the viewpoint of small queueing delay and finite energy storage.

Uplink signal structure design for multi-cell TDD massive MIMO systems

For multi-cell time-division duplex (TDD) massive multiple-input multiple-output (MIMO) systems, pilot contamination originates from limited pilot resources has been proved to be the ultimate limiting factor when the base station (BS) antennas are increased without bound. In this paper, a modified uplink signal structure is proposed to reduce the negative effects of pilot contamination. Specifically, we add a certain amount of identification information for distinguishing the terminals in different cells at the beginning of uplink signals. With this improved uplink signal structure, the BS obtains better channel estimates. Then uplink signal-to-interference ratio (SIR) and available capacity are obviously increased. Further, we also analyze the performance of actual situation when errors occur during the transmission of identification information. Simulation results prove the effectiveness of this signal structure in obtaining better available capacity when the coherence interval is high.

Packet delay analysis in wireless multi-channel networks: A network calculus perspective

In this work, we propose a stochastic network calculus based approach to study the packet delay in a multichannel network comprising one control channel and multiple parallel data channels. A node should compete with other nodes on the control channel before it is allowed to transmit packets on the data channels. The packet delay is the sum of packet (or node) competition delay, queueing delay and transmission delay. We derive an upper bound of the CCDF (complementary cumulative distribution function) of the packet delay, which is also called the probabilistic delay bound, in a general multi-channel network where not only the stochastic traffic can be any type, but also the above three types of delay can either be independent or correlated. Moreover, for further understanding and applying the proposed approach, we also employed Poisson traffic as a specific case to investigate the impact factors on the packet delay through traffic characteristics and network configurations.