The Journal of China Universities of Posts and Telecommunications, 2012, 19 (5). doi： 10.1016/S1005-8885(11)60293-8
Abstract ( 1887 ) PDF (0 KB)( 328 )
In this paper, firstly presented a geometrically based statistical channel model with scatterers that are with inverted parabolic spatial distribution around mobile station (MS) within a circle wherein the base station (BS) and MS are included. This paper presented a technique to simply derive PDFs of AOA, TOA and Doppler spectra to characterize the outdoor macrocell and microcell wireless environments by employing various distances between BS and MS, or different size of circular region. Employing this channel model, we analyze the impacts of a directional antenna with the main-lobe width at BS on the fading and the Doppler spectra.
The Journal of China Universities of Posts and Telecommunications, 2012, 19 (5). doi： 10.1016/S1005-8885(11)60294-X
Abstract ( 1396 ) PDF (0 KB)( 273 )
In multi-cell cooperative MIMO systems, base station (BS) can exchange and utilize channel state informations (CSI) of adjacent cell users to manage co-channel interference. Users quantize the CSIs of desired channel and interference channels using finite-rate feedback links, then BS can generate cooperative block diagonalization (BD) precoding matrices using the obtained quantized CSI at transmitter to supress co-channel interference. In this paper, a novel adaptive bit allocation scheme is proposed to minimize the rate loss due to imperfect CSI. We derive the closed-form expression of rate loss caused by both channel delay and limited feedback. Based on the derived rate loss expression, the proposed scheme can adaptively allocate more bits to quantize the better channels with smaller delays and fewer bits to worse channels with larger delays. Simulation results show that the proposed scheme yields higher performance than other allocation schemes.
The Journal of China Universities of Posts and Telecommunications, 2012, 19 (5). doi： 10.1016/S1005-8885(11)60295-1
Abstract ( 1495 ) PDF (0 KB)( 292 )
Coordinated Multi-Point (CoMP) transmission is a promising technique to improve both cell average and cell edge throughput for Long Term Evolution-Advanced (LTE-A). For CoMP-JT (Joint Transmission) in heterogeneous scenario, if JT users are firstly scheduled, other non-JT users will not be allocated sufficient resources, i.e., scheduling relevancy exists in the users under different cells in the same coordination cluster. However, the CoMP system throughput will decline remarkably, if the impact of scheduling relevancy is not considered. To address this issue, this paper proposes a novel scheduling scheme for CoMP in heterogeneous scenario. The principles of the proposed scheme include two aspects. Firstly, this scheme gives priority to user fairness, based on an extended proportional fairness (PF) scheduling algorithm. Secondly, the throughput of the coordination cluster should be maintained at a high level. By taking the non-CoMP system as a baseline, the proposed scheme is evaluated by comparing to random PF (RPF) and orthogonal PF (OPF) scheme. System-level simulation results indicate that, the proposed scheme can achieve considerable performance gain in both cell average and cell edge throughput.
The Journal of China Universities of Posts and Telecommunications, 2012, 19 (5). doi： 10.1016/S1005-8885(11)60296-3
Abstract ( 1571 ) PDF (0 KB)( 294 )
Coordinated multiple point transmission/reception (CoMP) has been investigated recently as a promising technology to increase the cell-edge user performance of LTE-Advanced, and channel estimation is a crucial technology for CoMP systems. In this paper, we consider a reduced-complexity Minimum Mean Square Error (MMSE) channel estimator for CoMP systems. The estimator uses Space Alternating Generalized-EM (SAGE) algorithm to avoid the inverse operation of the joint MMSE estimator. In the proposed scheme, the Base Stations (BSs) in the CoMP system estimate the channels of all the coordinated users serially and iteratively. We derive the SAGE-based estimators and analyze complexity. Simulation results verify that the performance of the proposed algorithm is close to the joint MMSE estimation algorithm while reducing the complexity greatly.
The Journal of China Universities of Posts and Telecommunications, 2012, 19 (5). doi： 10.1016/S1005-8885(11)60297-5
Abstract ( 1433 ) PDF (0 KB)( 265 )
A jointly optimal sensing-transmission time duration and power allocation scheme for a cooperative relay network is developed by maximizing the network energy efficiency. In particular, observing that the spectrum sensing and data transmission duration lies within a strict interval, the jointly optimal solutions of sensing-transmission duration and power allocation are obtained by sequential optimization. The superiority of the proposed scheme in relay-assisted transmission mode over non-relay transmission mode in terms of energy-efficiency has been verified by quantitative simulation results.
The Journal of China Universities of Posts and Telecommunications, 2012, 19 (5). doi： 10.1016/S1005-8885(11)60298-7
Abstract ( 2162 ) PDF (0 KB)( 291 )
In this paper, a new l1-graph regularized semi-supervised manifold learning (LRSML) method is proposed for indoor localization. Due to noise corruption and non-linearity of received signal strength (RSS), traditional approaches always fail to deliver accurate positioning results. The l1-graph is constructed by sparse representation of each sample with respect to remaining samples. Noise factor is considered in the construction process of l1-graph, leading to more robustness compared to traditional k-nearest-neighbor graph (KNN-graph). The KNN-graph construction is supervised, while the l1-graph is assumed to be unsupervised without harnessing any data label information and uncovers the underlying sparse relationship of each data. Combining KNN-graph and l1-graph, both labeled and unlabeled information are utilized, so the LRSML method has the potential to convey more discriminative information compared to conventional methods. To overcome the non-linearity of RSS, kernel-based manifold learning method (K-LRSML) is employed through mapping the original signal data to a higher dimension Hilbert space. The efficiency and superiority of LRSML over current state of art methods are verified with extensive experiments on real data.
The Journal of China Universities of Posts and Telecommunications, 2012, 19 (5). doi： 10.1016/S1005-8885(11)60299-9
Abstract ( 1388 ) PDF (0 KB)( 265 )
In this paper, the characteristics of clusters induced by a variety of propagation mechanisms in the link from the relay station (RS) to the mobile station (MS) are presented. Based on the results of high resolution channel parameter estimation, an automatic framework integrated with the manual intervention is utilized to perform the cluster identification and tracking. The power proportion and angular spread of clusters are investigated in both the line-of-sight and non-line-of-sight (NLOS) scenarios. The measurement results indicate that the channel characteristics of clusters are different from the link from the base station to the MS due to the lower height of the RS antennas.
The Journal of China Universities of Posts and Telecommunications, 2012, 19 (5). doi： 10.1016/S1005-8885(11)60300-2
Abstract ( 1444 ) PDF (0 KB)( 246 )
The resource allocation scheme for the multiple description coding multicast (MDCM) in OFDM-based cognitive radio network (CRN) is studied, aiming at maximizing the total throughput of the CR users, with constraints on sum transmit power, maximal receiving rate of each CR user and the interference introduced to individual primary user. With the analysis of the model, an algorithm consisting of two parts: the subcarrier assignment and the power allocation using the sub-gradient updating method, is proposed. Meanwhile, to reduce the complexity, a suboptimal algorithm is also proposed which divides the total power into small slices and allocates them one by one. Then the suboptimal algorithm is modified by adding the advanced water-filling process to improve the performance. The simulation results show that the throughput using the MDCM scheme is much higher than that using the conventional multicast (CVM) scheme and the performance of the proposed suboptimal algorithms approximates the above MDCM scheme using sub-gradient updating method very well.
The Journal of China Universities of Posts and Telecommunications, 2012, 19 (5). doi： 10.1016/S1005-8885(11)60301-4
Abstract ( 1437 ) PDF (0 KB)( 242 )
In this paper, we analyze performance of cooperative spectrum sensing under counting rules when exponential model is utilized to characterize the burst nature of primary user (PU) link. Our objective is to minimize the average error probability (AEP) so that the link utilization in the considered link achieves its maximum. We derive a closed-form expression of AEP as well as the probability of interference (PoI) by classifying cognitive transmission into six events. Then, we consider the minimization of AEP over counting rules under the constraint of interference. As the solution, we develop an efficient algorithm to evaluate the optimal fusion rule. Finally, we verify our analysis in numerical results.
The Journal of China Universities of Posts and Telecommunications, 2012, 19 (5). doi： 10.1016/S1005-8885(11)60302-6
Abstract ( 1561 ) PDF (0 KB)( 309 )
Internet Service Providers (ISPs) have taken some measures to reduce intolerable inter-ISP peer-to-peer (P2P) traffic costs, so that user experiences of various P2P applications have been affected. The recently emerging Offline downloading service seeks to improve user experience by using dedicate servers to cache requested files and provide high-speed uploading. However, with rapid increase in user population, the server-side bandwidth resource of Offline downloading system is expected to be insufficient in the near future. We propose a novel complementary caching scheme with the goal of mitigating inter-ISP traffic, alleviating the load on servers of Internet applications and enhancing user experience. Both architecture and caching algorithm are presented in this paper. On the one hand, with full knowledge of P2P file sharing system and Offline downloading service, the infrastructure of complementary caching is designed to conveniently be deployed and work together with existing platforms. The co-operational mechanisms among different major components are also included. On the other hand, with in-depth understanding of traffic characteristics that are relevant to caching, we develop complementary caching algorithm with respect to the density of requests, the redundancy of file and file size. Since such relevant information can be real-time captured in our design, the proposed policy can be implemented to guide the storage and replacement of caching unities. Based on real-world traces over 3 months, we demonstrate that the complementary caching scheme is capable to achieve the “three-win” objective. That is, for P2P downloading, over 50% of traffic is redirected to cache; for Offline downloading, the average server-dependence of tasks drops from 0.71 to 0.32; for user experience, the average P2P transfer rate is increased by more than 50KB/s.
The Journal of China Universities of Posts and Telecommunications, 2012, 19 (5). doi： 10.1016/S1005-8885(11)60303-8
Abstract ( 1691 ) PDF (0 KB)( 251 )
In Ad hoc wireless network, connectivity is a fundamental issue which restricts the design of system protocol. Based on the theory of stochastic geometry, a connectivity model focused on signal-to-interference (SIR) ratio is set up in presence of Nakagami-m fading and interference. The paper derives a close formula of connectivity probability with interference and Nakagami-m fading which is never obtained in previous works. Two-dimension shot-noise theory in stochastic geometry for interference is well applied. The formula is verified by simulation. The results show that the connectivity is affected by the scatter of users, wireless propagation environment, interference and so on.
The Journal of China Universities of Posts and Telecommunications, 2012, 19 (5). doi： 10.1016/S1005-8885(11)60304-X
Abstract ( 1502 ) PDF (0 KB)( 258 )
With the rise and world wide deployment of cloud utilities, the principle of the cloud download is proposed to provide high-quality file content distribution by using dedicated servers as cloud cache to guarantee the data availability and enhance the data transfer rate. As the system scales up to a large population, how to design appropriate storage capacity of cloud cache is a key challenge for cloud download. In this paper, primary elements impacting on storage capacity are explored through deliberating in large-scale commercial cloud download system, i.e. general user usage pattern and available period. And based on statistical analysis of real-world traces, we formulate storage capacity related to these two elements, which is the original contribution different from all previous works. This model gives guidance of potential system policy design. Finally, the effectivity of this model is demonstrated by simulation results compared with empirical data of practical system.
The Journal of China Universities of Posts and Telecommunications, 2012, 19 (5). doi： 10.1016/S1005-8885(11)60305-1
Abstract ( 1364 ) PDF (0 KB)( 247 )
One of the key issues for radio resources management is network selection strategy in heterogeneous scenarios. In order to provide ubiquitous service, the paper puts forward a network selection algorithm based on multiple attribute decision making (MADM) and group decision making (GDM). Firstly, the proposed algorithm acquires attribute weights’ vectors of the subjective and objective decision makers based on MADM, and then the two attribute weights’ vectors are synthesized to be a new attribute weights’ vector by using GDM. Considering that the results of GDM should be reasonable and convincible, the criterion of consistency is adopted for judging the compatibility of group judgments. More specifically, the algorithm takes into account not only objective attributes of networks but also the preference of subscribers and traffic class. Hence it guarantees that the subscribers can not select the networks with poor performance depending on their preference. The simulation results show that the proposed algorithm can effectively reduce the handoff number and provide subscribers with satisfactory quality of service (QoS).
The Journal of China Universities of Posts and Telecommunications, 2012, 19 (5). doi： 10.1016/S1005-8885(11)60306-3
Abstract ( 1371 ) PDF (0 KB)( 234 )
This paper presents some further results on the local stability of a recently developed Internet congestion control scheme, namely the LRC-RED algorithm. Necessary and sufficient stability conditions in terms of key tuning parameters are derived, which can provide further guidelines for control gain selection. The numerical simulations are given to illustrate the correctness of the theoretical analysis.
The Journal of China Universities of Posts and Telecommunications, 2012, 19 (5). doi： 10.1016/S1005-8885(11)60307-5
Abstract ( 1388 ) PDF (0 KB)( 273 )
With the broad implementations of the electronic business and government applications, robust system security and strong privacy protection have become essential requirements for remote user authentication schemes. Recently, Chen et al. showed that Wang et al.’s scheme is vulnerable to the user impersonation attack and parallel session attack, and proposed an enhanced version to overcome the identified security flaws. In this paper, however, we show that Chen et al.’s scheme still cannot achieve the claimed security goals and report its following problems: (1) It suffers from the offline password guessing attack, key compromise impersonation attack and known key attack; (2) It fails to provide forward secrecy; (3) It is not easily repairable. As our main contribution, a robust dynamic ID-based scheme based on non-tamper resistance assumption of the smart cards is presented to cope with the aforementioned defects, while preserving the merits of different related schemes. The analysis demonstrates that our scheme meets all the proposed criteria and eliminates several grave security threats that are difficult to be tackled at the same time in previous scholarship.
The Journal of China Universities of Posts and Telecommunications, 2012, 19 (5). doi： 10.1016/S1005-8885(11)60308-7
Abstract ( 1424 ) PDF (0 KB)( 282 )
This paper introduces a new model-based soft decoding technique to restore the widely used JPEG streams. The image is modeled as a 2D piecewise stationary autoregressive process, and the decoding task is formulated as an optimization problem with the constraint given by the quantization intervals which freely available at the decoder. The autoregressive model serves as an important regularization term of the objective function of the optimization. And the autoregressive model parameters are solved on the decoded image locally using a weighted total least square method, where a novel bilateral dualside weighting scheme is proposed to minimize the influence of the blocking artifact on the final estimation. Extensive experimental results suggest that the proposed algorithm systematically improves the quality of JPEG images and also outperforms existing JPEG postprocessing algorithms in a wide bit-rate range both in terms of PSNR and subjective quality
The Journal of China Universities of Posts and Telecommunications, 2012, 19 (5). doi： 10.1016/S1005-8885(11)60309-9
Abstract ( 1343 ) PDF (0 KB)( 279 )
Based on the transmission line theory, characteristic of the buried metallic structures and the concerned harmful effects to the buried oil and natural gas pipeline caused by short-circuit fault is further discussed. A closed –form expression of conductive voltage caused by short-circuit fault of high voltage transmission line is given. The transmission line model is set up and a set of formulas for calculating the parameters of the buried pipeline in actual environment condition data are given. With the conductive energization model, conductive current and voltage waveform equation is presented.. At last, the characteristic of he harmful effects of the buried pipeline from the power line short circuit fault are discussed.