Showing papers by "Beijing University of Posts and Telecommunications published in 2004"
17 May 2004
TL;DR: Numerical results indicate that with the proposed PA scheme, the system performance not only outperforms that of the direct transmission system, but also obtains the maximum channel capacity or SNR of the relaying system.
Abstract: Cooperative relaying is considered as an effective way to combat Rayleigh fading, to offer better quality of communication link or channel capacity. From the perspective of information theory, channel capacity depends on the SNR of the received signal, therefore, how to allocate transmit power between transmitter and relay to achieve maximum SNR at the receiver or maximum channel capacity is an important issue. In general, there are two types of relaying system, i.e. non-regenerative and regenerative systems. This paper puts emphasis on the power allocation (PA) of regenerative systems. Based on a 2-hop relaying channel suffering from Rayleigh fading, with and without diversity, an adaptive PA scheme is proposed, under transmit power constraints, to keep the system running at the optimum level. Numerical results indicate that with the proposed PA scheme, the system performance not only outperforms that of the direct transmission system, but also obtains the maximum channel capacity or SNR of the relaying system.
130 citations
17 May 2004
TL;DR: The paper analyzes the two-hop non-regenerative relaying channel with and without diversity, and investigates the optimal PA scheme between the source terminal (Tx) and the relaying terminal (RS) under power constraints.
Abstract: In order to combat fading in wireless networks and increase the capacity of a system, cooperation is allowed among the terminals in a network. The adaptive optimal power allocation (PA) scheme, based on a certain system performance, is an important issue for relaying routing and network operation. The paper analyzes the two-hop non-regenerative (NR) relaying channel with and without diversity, and investigates the optimal PA scheme between the source terminal (Tx) and the relaying terminal (RS) under power constraints. Since, in real relaying environments, the transmitter usually knows the instantaneous channel state information (ICSI) of the 1st hop and the statistical channel state information (SCSI) of the 2nd hop, the proposed PA schemes are based on two-hop ICSI and two-hop mixed channel state information (MCSI) respectively. With the adaptive scheme, the system performance not only outperforms that of the direct transmission system, but also obtains the maximum channel capacity or SNR of the relaying system.
129 citations
TL;DR: In this paper, a general theoretical model using the coupling effect between the torsion and bending is presented, which characterizes the static properties of the electrostatic torsional micromirror, especially its pull-in effect.
Abstract: A general theoretical model using the coupling effect between the torsion and bending is presented in this paper, which characterizes the static properties of the electrostatic torsional micromirror, especially its pull-in effect. A set of normalized equations governing the static actuation properties of the torsional micromirror based on the parallel plate capacitor model is derived to demonstrate the relationships between the parameters of static characteristics, such as torsion angle, vertical displacement, and applied voltage. Thereafter, the pull-in effect is investigated specifically to predict pull-in voltage, pull-in angle, and pull-in displacement, which highly depend on the electrode size and position, and ratio of the bending and torsion effect of the torsion beam. The ratio of the bending and torsion effect plays a key role in the pull-in phenomena. It also determines the instability mode of torsional micromirrors dominated by either the torsion or bending effect. Then, a group of torsional micromirrors is fabricated using three-layer-polysilicon micromachining process and measured using an optical projection method to verify the static actuation relation and pull-in effect respectively. The experimental data are processed and analyzed, and the theoretical analysis is in good agreement with the experimental results.
98 citations
TL;DR: Empirical power law relations of the period and transient iterations with the computation precisions and the sizes of coupled systems are obtained, useful for possible applications of chaos, e.g., chaotic cryptography in secure communication.
Abstract: Fundamental problems of periodicity and transient process to periodicity of chaotic trajectories in computer realization with finite computation precision is investigated by taking single and coupled Logistic maps as examples. Empirical power law relations of the period and transient iterations with the computation precisions and the sizes of coupled systems are obtained. For each computation we always find, by randomly choosing initial conditions, a single dominant periodic trajectory which is realized with major portion of probability. These understandings are useful for possible applications of chaos, e.g., chaotic cryptography in secure communication.
82 citations
TL;DR: From the simulation results, it is verified that the ICI self-cancellation scheme obviously decreases the amount of ICI caused by phase noise and the improvement of C/I could reach 10 dB when the normalized 3 dB bandwidth of phase noise is 0.4.
Abstract: Phase noise in orthogonal frequency division multiplexing (OFDM) systems destroys the orthogonality of the subcarriers and inter-carrier interference (ICI) is caused. In this paper, the ICI self-cancellation scheme is adopted to combat the ICI caused by phase noise in OFDM systems. Moreover, the error coefficients are defined and the theoretical expressions of carrier to interference ratio (C/I) with and without the ICI self-cancellation scheme are separately derived. From the simulation results, it is verified that the ICI self-cancellation scheme obviously decreases the amount of the ICI caused by phase noise and the improvement of C/I could reach 10 dB when the normalized 3 dB bandwidth of phase noise is 0.4. However, the convolutional coding OFDM (COFDM) system could supply more performance gain at the expense of increasing decoder complexity compared to OFDM system with the ICI self-cancellation scheme in the frequency-selective channel.
81 citations
07 Mar 2004
TL;DR: The proposed AQM scheme, called loss ratio based RED (LRED), measures the latest packet loss ratio, and uses it as a complement to queue length in order to dynamically adjust packet drop probability, and is responsive even if the number of TCP flows varies significantly.
Abstract: Active queue management (AQM) is an effective method to enhance congestion control, and to achieve tradeoff between link utilization and delay. The de facto standard, random early detection (RED), and most of its variants use queue length as a congestion indicator to trigger packet dropping. The proportional-integral (PI), use both queue length and traffic input rate as congestion indicators; effective stability model and practical design rules built on the TCP control model and abstracted AQM model reveal that such schemes enhance the stability of a system. In this paper, we propose an AQM scheme with fast response time, yet good robustness. The scheme, called loss ratio based RED (LRED), measures the latest packet loss ratio, and uses it as a complement to queue length in order to dynamically adjust packet drop probability. Employing the closed-form relationship between packet loss ratio and the number of TCP flows, this scheme is responsive even if the number of TCP flows varies significantly. We also provide the design rules for this scheme based on the well-known TCP control model. This scheme's performance is examined under various network configurations, and compared to existing AQM schemes, including PI, random exponentially marking (REM), and adaptive virtual queue (AVQ). Our simulation results show that, with comparable complexity', this scheme has short response time, better robustness, and more desirable tradeoff than PI, REM, and AQV, especially under highly dynamic network and heavy traffic load.
72 citations
29 Nov 2004
TL;DR: This method successfully solves the coexistence problem between UWB systems and the existing narrowband systems without the need of reducing UWB pulse power spectral density (PSD) over the whole UWB frequency band.
Abstract: In this paper, we present a new ultra-wideband (UWB) pulse design method for narrowband interference (NBI) suppression. With a short time duration, the obtained UWB pulses not only meet the Federal Communications Commission (FCC) spectral mask, but also dramatically suppress the mutual interference between UWB systems and multiple narrowband communication systems. This method successfully solves the coexistence problem between UWB systems and the existing narrowband systems without the need of reducing UWB pulse power spectral density (PSD) over the whole UWB frequency band. Therefore, the application range of UWB systems can be enlarged by increasing the transmitted UWB pulse power.
52 citations
TL;DR: A new carrier frequency offset estimation scheme in orthogonal frequency-division multiplexing (OFDM) system is proposed, and the proposed tracking estimator is a maximum-likelihood estimator, and in AWGN channel, the Cramer-Rao lower bound is met at high signal-to-noise ratio (SNR).
Abstract: A new carrier frequency offset estimation scheme in orthogonal frequency-division multiplexing (OFDM) system is proposed. The carrier frequency offset estimation includes acquisition and tracking, and the acquisition range is as large as one half of overall signal bandwidth. The proposed tracking estimator is a maximum-likelihood estimator, and in AWGN channel, the Cramer-Rao lower bound is met at high signal-to-noise ratio (SNR); in multipath channel, the tracking algorithm works well at moderate SNR. Timing synchronization can be also performed during the course of acquisition.
48 citations
29 Nov 2004
TL;DR: Simulation and analysis show that this novel design with starvation supervision has better performance over the traditional design and updating the average rate to users with no data to send may not get the overall maximized system utility.
Abstract: The average rate updating mechanism was first promoted for the starvation problem emerging when some user experiences a sudden drop in channel quality or just keeps on moving backward from the base station under the proportional fair scheduler in the HDR system. Although proportional fair scheduling has received much theoretic research attention recently for its attractive capability on the tradeoff between system utility and fairness, the influence of average rate updating mechanism to the performance of scheduler has been neglected. We point out here that the previous rate update mechanism based on fixed time window is insufficient in keeping the users from starvation. Furthermore, updating the average rate to users with no data to send may not get the overall maximized system utility. We also promote a new average update mechanism as the basis of the proportional fair scheduling algorithm. Simulation and analysis show that this novel design with starvation supervision has better performance over the traditional design.
39 citations
TL;DR: In this paper, a new direct extraction method to determine the small-signal and rate-equation model parameters for laser diode is presented, which differs from previous ones by extracting the whole model parameters without global numerical optimization techniques.
Abstract: A new direct extraction method to determine the small-signal and rate-equation model parameters for laser diode is presented in this paper. This method differs from previous ones by extracting the whole model parameters without global numerical optimization techniques. The main advantage of this method is that a unique and physically meaningful set of extrinsic and intrinsic parameters are extracted by using a set of closed-form expressions based on the input reflection coefficients and modulation responses taken from on-wafer measurement. Simulated and measured results for the input reflection coefficients and modulation responses exhibit good agreement over a wide range of bias points.
35 citations
TL;DR: For the first time the particle swarm optimization (PSO) algorithm with local neighborhood structure has been introduced in adaptive PMD compensation and is shown to be effective in this application to optimum searching and adaptive tracking control.
TL;DR: It is shown that with suitable cooperative applications of both chaotic and conventional approaches, the output of the spatiotemporally chaotic system can easily meet the practical requirements of random numbers.
Abstract: A one-way coupled chaotic map lattice is used for generating pseudo-random numbers. It is shown that with suitable cooperative applications of both chaotic and conventional approaches, the output of the spatiotemporally chaotic system can easily meet the practical requirements of random numbers, i.e., excellent random statistical properties, long periodicity of computer realizations, and fast speed of random number generations. This pseudo-random number generator system can be used as ideal synchronous and self-synchronizing stream cipher systems for secure communications.
TL;DR: In this article, a long wavelength resonant cavity photodetector with InP/air-gap Bragg reflectors, fabricated by using selective wet etching, is presented.
Abstract: We demonstrate a long wavelength resonant cavity photodetector with InP/air-gap Bragg reflectors, which is fabricated by using selective wet etching. The peak quantum efficiency is 59% at 1510 nm. A 3-dB bandwidth of 8 GHz has been achieved with the active area of 50/spl times/50 /spl mu/m/sup 2/. Compared with the detector of same absorption depth, a three-fold increase of absorption efficiency is obtained at resonant wavelength.
TL;DR: Based on the cascaded nonlinear interactions of sum-and difference-frequency generation (SFG+DFG), a novel all-optical wavelength conversion scheme is proposed for the first time in periodically poled LiNbO/sub 3/ (PPLN) waveguide, in which a double-pass configuration is introduced as discussed by the authors.
Abstract: Based on the cascaded nonlinear interactions (/spl chi//sup (2)/:/spl chi//sup (2)/) of sum- and difference-frequency generation (SFG+DFG), a novel all-optical wavelength conversion scheme is proposed for the first time in periodically poled LiNbO/sub 3/ (PPLN) waveguide, in which a double-pass configuration is introduced. The performance of this scheme is thus different from the previous single-pass SFG+DFG scheme. The concept of the "balance condition" is presented to optimize the power and frequencies of the two pump sources. Under this condition, the energy is transferred irreversibly from the pump waves to the SF wave during the forward propagation. The equations describing the SFG can be solved analytically under this condition. Subsequently, the DFG equations are solved under the assumption that the SF wave would be constant during the backward propagation. Theoretical expressions are derived and are found to be consistent with numerical calculations. Compared with the conventional converter based on the cascaded /spl chi//sup (2)/:/spl chi//sup (2)/ interactions of second-harmonic generation and difference frequency generation SHG+DFG, the same conversion efficiency can be achieved in our scheme by employing two pump sources with lower power, or conversely higher conversion efficiency can be reached using two pump sources similar to that used in SFG+DFG scheme. The profile of the conversion efficiency can be further improved by adjusting the wavelengths of the two pump sources. In addition, compared with the single-pass SFG+DFG scheme, the main advantage of this new scheme rests on the fact that the conversion efficiency can be enhanced significantly. The advantages of the double-pass SHG+DFG scheme and the single-pass SFG+DFG scheme are combined in this new design to a great extent.
TL;DR: In this paper, the induced birefringence effects on uniform fiber Bragg grating (FBG) and linearly chirped FBG under lateral compression are experimentally investigated, respectively.
05 Sep 2004
TL;DR: A distributed MIMO channel model which comprises relative path loss, correlated shadow fading and correlated small scale fading is proposed, and the impact of two kinds of fading correlation on capacity of distributed M IMO channel is investigated and compared carefully by Monte Carlo simulations.
Abstract: Distributed multiple-input multiple-output (MIMO) system combines the advantages of point-to-point MIMO systems and distributed antenna systems, and improves link quality and coverage. A distributed MIMO channel model which comprises relative path loss, correlated shadow fading and correlated small scale fading is proposed. The impact of two kinds of fading correlation on capacity of distributed MIMO channel is investigated and compared carefully by Monte Carlo simulations, and the characteristics of capacity space distribution of distributed MIMO channel with spatial shadowing correlation are also obtained.
TL;DR: In this article, two papers of chaotic synchronization, namely, [Phys. Rev. Lett. 76 (1996) 1232] and [P.Lett. A 321 (2004) 50], were analyzed by numerical simulations.
TL;DR: This paper presents neighborhood-following algorithms for linear programming that are wide neighborhood primal-dual interior point algorithms and proves that the algorithms are quadratic convergence if the optimal vertex is nondegenerate.
Abstract: In this paper, we present neighborhood-following algorithms for linear programming. When the neighborhood is a wide neighborhood, our algorithms are wide neighborhood primal-dual interior point algorithms. If the neighborhood degenerates into the central path, our algorithms also degenerate into path-following algorithms. We prove that our algorithms maintain the O9√nL) -iteration complexity still, while the classical wide neighborhood primal-dual interior point algorithms have only the O(nL-iteration complexity. We also proved that the algorithms are quadratic convergence if the optimal vertex is nondegenerate. Finally, we show some computational results of our algorithms.
TL;DR: A new carrier frequency offset estimation scheme in the orthogonal frequency division multiplexing (OFDM) system is proposed, which can utilize the correlativity among all small blocks of a training symbol more sufficiently than the M&M algorithm, and thus it is more accurate and robust.
Abstract: A new carrier frequency offset estimation scheme in the orthogonal frequency division multiplexing (OFDM) system is proposed. The proposed algorithm is an extension of the Michele Morelli (M&M) algorithm. By dividing one training symbol into L>1 identical small blocks, the carrier frequency offset estimation range up to /spl plusmn/L/2 times subcarrier spacing can be obtained. The proposed algorithm can utilize the correlativity among all small blocks of a training symbol more sufficiently than the M&M algorithm, and thus it is more accurate and robust. Without increasing the estimation errors, the computational complexity of the proposed algorithm can be further reduced by increasing parameters H/sub l/ and H/sub h/ with a positive value simultaneously.
TL;DR: Simulations results show that the proposed resilience scheme based on recovery at the lowest layer can efficiently improve network utilization and be even more capacity-efficient than resilience schemes based on Recovery at the highest layer.
Abstract: The survivability of IP over WDM networks gains importance as network traffic keeps growing. Recovery at the lowest layer is fast and scalable. However, it is usually considered to provide poor network utilization. In this article we propose a resilience scheme based on recovery at the lowest layer in which intralayer and interlayer backup resource sharing is utilized to improve the network utilization. By applying interlayer backup resource sharing, we can totally depend on the reserved backup resources for fiber link failures to guarantee 100 percent recovery of IP router failures. In addition, by applying intralayer backup resource sharing, the network utilization improvement of recovery at the lowest layer is much more significant than at the highest layer. Simulations results show that the proposed scheme can efficiently improve network utilization and be even more capacity-efficient than resilience schemes based on recovery at the highest layer.
21 Mar 2004
TL;DR: The stream control transport protocol (SCTP) is put forward as a transport layer approach for multi-access, and an efficient SCTP load-sharing enhancement is proposed to provide better robustness and connectivity than other solutions in the wireless multi- access scenarios.
Abstract: Future communication systems might be characterized by an integration of multiple access systems, and people are expecting excellent multi-access solutions for better services. However, currently proposed solutions in different layers are unable to completely fulfill the requirements. In this paper, we put forward the stream control transport protocol (SCTP) as a transport layer approach for multi-access, and propose an efficient SCTP load-sharing enhancement. The evaluation of performance has been investigated in the key multi-access scenarios with theoretical analyses, simulations in NS and some Linux-kernel experiments. Since SCTP supplies an effective multi-homing mechanism and the transport layer solutions for multi-access can quickly adapt to the fluctuating network conditions, our SCTP approach is able to bring more throughput for the simultaneous multi-access perform seamless behavior during the vertical handover between heterogeneous access networks, and provide better robustness and connectivity than other solutions in the wireless multi-access scenarios.
Journal Article•
TL;DR: In this article, the performance of type III HARQ with code combing in wireless channel environments is lucubrated through both theoretical research and simulation analysis, and is compared with those of the other two HARQ schemes, viz. type I HARQ and type II HARQ, with chase combining.
Abstract: The performance of type III HARQ with code combing in wireless channel environments is lucubrated through both theoretical research and simulation analysis, and is compared with those of the other two HARQ schemes, viz. type I HARQ and type II HARQ with chase combining. All the research in this paper is carried out on both the AWGN channel and Rayleigh fading channel, respectively. By applying renewal theory and channel coding theorem, we obtained the closed-form solutions to the typeⅠHARQ and type II HARQ. For the type III HARQ, although the closed-form solution is not obtained, we did get the integral solution. Furthermore, using Turbo codes as forward error correction, the throughput and the residual FER of the three HARQ schemes are simulated. It shows that for arbitrary block fading channel, comprising AWGN channel, the performance of type III HARQ is always better than that of type II HARQ, whereas type II HARQ is always better than that of type I HARQ. Especially, the advantage of type III HARQ will be more prominent on Rayleigh fading channel.
TL;DR: The authors consider that this kind of charging contrast arises from the different redistribution rates of secondary electrons returning to the surface under the surface local field of the charged specimen.
Abstract: The charging effect of an insulating specimen from electron beam (e-beam) irradiation may be utilized to facilitate imaging in the scanning electron microscope (SEM). This has been confirmed by a g...
TL;DR: A novel integrated multistage optical MEMS-mirror switch architecture design with Shuffle Benes Inter-stage Connecting principle is proposed, which is very suitable for building large 2D MEMS switches and achieves better performance in terms of beam divergence loss, mirror size, wafer size, port-to-port repeatability and power consumption.
Journal Article•
TL;DR: The "Comprehensive Information Based Methodology for Natural Language Understanding" presented in the paper is an application of the Comprehensive Information(CI) Theory, which was established by the author of the paper years ago for meeting the needs in artificial intelligence research.
Abstract: The "Comprehensive Information Based Methodology for Natural Language Understanding" presented in the paper is an application of the Comprehensive Information(CI) Theory, which was established by the author of the paper years ago for meeting the needs in artificial intelligence research Different from other works in the field of natural language processing, the major features of the methodology presented in the paper include two folds Firstly, instead of the syntactic or/and semantic information is used, all components of the comprehensive information are fully utilized for natural language understanding Secondly, instead of using one or another approach preferably, both the rule-based approach and the statistics-based approach have been complementarily integrated The successes of the research projects guided by the methodology and completed last few years prove the methodology promising
14 Sep 2004
TL;DR: This work proposes an extension QoS routing algorithm based on dynamic source routing (DSR) protocol while adopting fuzzy logic to select the appropriateQoS routing in multiple paths which are searched in parallel.
Abstract: Since the nodes in mobile ad hoc network act as a router and host, the routing protocol is the primary issue and has to be supported before any applications can be deployed for ad hoc wireless network. In recent years much work has been done on routing in ad hoc networks. But most of them couldn't provide the quality-of-service (QoS). Considering the characters of dynamic topology and the imprecise state information in mobile ad hoc network, we propose an extension QoS routing algorithm based on dynamic source routing (DSR) protocol while adopting fuzzy logic to select the appropriate QoS routing in multiple paths which are searched in parallel. The algorithm can tolerate a high degree of information imprecision by adding the fuzzy logic module which integrates the QoS requirements of application and the routing QoS parameters to determine the most qualified one in every node. This scheme considers not only the bandwidth and end-to-end delay of routing, but also the cost of the path. So it also may improve the network performance. On the other hand the merit of using fuzzy logic is that it can be implemented by hardware. This makes the realization of the scheme easier and faster. However our algorithm is based on DSR, the maximal hop count should be less than 10, i.e., the scale of mobile ad hoc network should not be very large.
02 May 2004
TL;DR: This paper proposes a strategy proof trust management system fitting to wireless ad hoc networks that is incentive compatible in which nodes can honestly report trust evidence and truthfully compute and broadcast trust value of themselves and other nodes.
Abstract: Trust management is a basic component for wireless ad hoc networks. Some existing trust management mainly aims at. Internet application and generally depends on a centralized trusted third party. The inherent characteristics of a wireless ad hoc network mounts more of a challenge to the design and deployment of trust management in wireless ad hoc networks. This paper proposes a strategy proof trust management system fitting to wireless ad hoc networks. This system is incentive compatible in which nodes can honestly report trust evidence and truthfully compute and broadcast trust value of themselves and other nodes.
26 Sep 2004
TL;DR: In this paper, a two-hop cellular system, based on time division multiple access (TDMA), incorporated with a non-regenerative relaying station (NRRS), or a regenerative relay station (RRS), where the RS works in time division duplex (TDD) mode, is described.
Abstract: In future wireless communication systems, an architecture introducing wireless relaying technologies into the cellular infrastructure seems a promising approach to enlarge the coverage area and enhance the system capacity. The paper describes a two-hop cellular system, based on time division multiple access (TDMA), incorporated with a nonregenerative relaying station (NRRS), or a regenerative relaying station (RRS), where the RS works in time division duplex (TDD) mode. A general analysis of the system performance is provided in a multi-cell environment, where two power allocation schemes, optimal power allocation (OPA) and uniform power allocation (UPA), between the base station (BS) and the RS, are compared. Simulation results show that, compared with the single-hop system, the relaying system not only can obtain diversity gain and improve the performance, but also, with the OPA scheme and the proper arrangement of RSs, the performance gains can be further improved.
26 Sep 2004
TL;DR: In this paper, a two-dimensional adaptive channel estimation based on a 2D-LMS algorithm was proposed to make full use of the time and frequency-domain correlations of the frequency response of time-varying dispersive fading channels.
Abstract: In orthogonal frequency division multiplexing (OFDM) systems, two-dimensional (both time and frequency) minimum mean square error (2D-MMSE) channel estimation is optimum. However, accurate channel statistics are required to realize it, which are often unavailable in practice. In contrast, two-dimensional adaptive channel estimation based on a two-dimensional least mean square (2D-LMS) algorithm does not require any channel statistics, and at the same time can make full use of the time and frequency-domain correlations of the frequency response of time-varying dispersive fading channels. In this paper, we further study two-dimensional adaptive channel estimation in OFDM systems. We derive two-dimensional normalized least mean square (2D-NLMS) algorithm and find that the 2D-LMS algorithm with the optimum step-size parameter is just its special case. Furthermore, a parallel 2D-(N)LMS channel estimation scheme is proposed to solve the realtime realization problem due to high computational complexity encountered by two-dimensional adaptive channel estimation. Finally, we apply two-dimensional adaptive channel estimation to multiple-input multiple-output (MIMO) OFDM systems.
26 Sep 2004
TL;DR: A cooperative relaying system model based on MIMO technology, where the RSs are utilized to emulate the multi-antenna environment is proposed, where an OPA scheme, through singular value decomposition (SVD) of the channel matrix, is developed among theRSs under a certain power constraint to achieve the maximum channel capacity.
Abstract: In a cooperative relaying system, multiple-input-multiple-output (MIMO) capacity enhancement techniques are applied to mobile terminals (MT) with a limited number of antenna elements. The adaptive optimal power allocation (OPA) scheme among the relay stations (RSs) is an important issue to achieve power efficiency and maximum performance improvement. The paper proposes a cooperative relaying system model based on MIMO technology, where the RSs are utilized to emulate the multi-antenna environment. In addition, an OPA scheme, through singular value decomposition (SVD) of the channel matrix, is developed among the RSs under a certain power constraint to achieve the maximum channel capacity. Numerical results indicate that, compared with the uniform power allocation (UPA) scheme, the OPA scheme improves the capacity significantly when the RSs are close to the transmitter (TX). However, if the RSs are close to the receiver (RX), there is almost no difference between these two schemes, which is similar to the case in the traditional MIMO system.