The Journal of China Universities of Posts and Telecommunications, 2011, 18 (6). doi： 10.1016/S1005-8885(10)60115-X
The long term evolution advanced (LTE-advanced) standards target at high system performance comparable or superior to the requirements of the International mobile telecommunications advanced (IMT-advanced). In order to support backward compatibility with LTE, most of the key technologies have been retained in LTE-advanced, one of which is the discontinuous reception mechanism (DRX). LTE-advanced adopts carrier aggregation technology to extend the system bandwidth, which requires the LTE DRX applied in single-transceiver scenario to be adapted to multi-transceiver scenario with multiple component carriers. Apparently, carrier aggregation will influence the performance of DRX severely, so it’s worth studying the impact brought by the coexistence of LTE DRX and carrier aggregation on the system performance, e.g., the system delay. In this paper, first an overview of DRX in carrier aggregation scenario is given. Then it is modeled as a Markov process based on the queuing theory. Simulation results show that the independent component carrier configuration with a uniform Inactivity Timer achieves a superior service delay performance compared with other reference schemes.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (6). doi： 10.1016/S1005-8885(10)60116-1
This article analyzes the energy-efficiency performances of fixed relaying schemes, selection relaying schemes and incremental relaying schemes in the three-node relay network. The closed-form asymptotic energy per good-bit (EPG) expressions for the state-of-the-art relaying protocols at high signal-to-noise ratio (SNR) regime are derived. In the formulation of the energy consumption model, the transmission, circuit and retransmission energies are all taken into account. To facilitate the comparison of energy-efficiency performances between different relaying protocols, the link reliabilities and retransmission probabilities are determined by the asymptotic outage probabilities at high SNR regime under the Rayleigh fading assumption. Computer simulations are carried out in both symmetric and asymmetric relay networks. The simulation results show the differences of system energy expenditure between these state-of-the-art relaying protocols. Finally some practical implications can be made from the observation.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (6). doi： 10.1016/S1005-8885(10)60117-3
High-speed high-resolution analog-to-digital (A/D) conversion demanded by ultra wideband (UWB) signal processing is a very challenging problem. This paper proposes a parallel random projection method for UWB signal acquisition. The proposed method can achieve high sampling rate, high resolution and technical feasibility of hardware implementation. In the proposed method, an analog UWB signal is projected over a set of random sign functions. Then the low-rate high-resolution analog-to-digital convertors (ADCs) are used to sample the projection coefficients. The signal can be reconstructed by simple linear calculation with the sampling matrix, without complying with optimization algorithm and prior knowledge. In other aspects, unlike other approaches that need to utilize an accurate time-shift at extremely high frequency, or design a hybrid filter bank, or generate specific basis functions or work for signals with prior knowledge, the proposed method is a universal sampling approach and easy to apply. The simulation results of signal to noise ratio (SNR) and spurious-free dynamic range (SFDR) validate the efficiency of the proposed method for UWB signal acquisition.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (6). doi： 10.1016/S1005-8885(10)60118-5
In this paper, the design of linear leakage-based precoders is considered for multiple-input multiple-output (MIMO) downlinks. Our proposed scheme minimizes total transmit power under each user’s signal-to-leakage-plus-noise ratio (SLNR) constraint. When the base station knows perfect channel state information (CSI), suitable reformulation of design problem allows the successful application of semidefinite relaxation (SDR) techniques. When the base station knows imperfect CSI with limited estimation errors, the design problem can be solved using semidefinite program (SDP). At the same time, it can dynamically allocate each user’s SLNR threshold according to each user’s channel state, so it is more feasible than other similar SINR-based precoding methods. Simulation results show that using large SLNR thresholds, the proposed design has better bit error rate (BER) performance than maximal-SLNR precoding method at high signal-to-noise ratio (SNR). Moreover, when the base station knows imperfect channel state information, the proposed precoder is robust to channel estimation errors, and has better BER preformance than other similar SINR-based precoding methods.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (6). doi： 10.1016/S1005-8885(10)60119-7
In cognitive radio (CR) systems, efficient spectrum sensing ensures the secondary user (SU) to successfully access the spectrum hole. Typically, the detection problem has been considered separately from the optimization of transmission strategy. However, in practice, due to non-zero probabilities of miss detection and false alarm, the sensing phase has an impact on the throughput of SUs as well as on the transmission of primary user (PU). In this paper, using energy detection, we maximize the total throughput of SUs by jointly optimizing the detection threshold and transmission strategy in multiband CR systems. A set of iteration based algorithms are proposed to solve this mix-integer programming problem, which show better performance compared with uniform detection threshold selection algorithm suggested by IEEE 802.22 standard.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (6). doi： 10.1016/S1005-8885(10)60120-3
A novel receiver is proposed in this paper that uses the blind adaptive multi-user detection (MUD) technique to deal with the presence of multiple-access interference (MAI) and inter-symbol interference (ISI) in terms of high speed time-hopping ultra-wideband (TH-UWB) system. The receiver firstly adopts constrained recursive least squares constant modulus algorithm (RLS-CMA) to conduct adaptive decorrelation for eliminating MAI and ISI, and then uses projection approximation subspace tracking with deflation (PASTd) algorithm to launch channel estimation, do maximal ratio combining (MRC) and improve signal to interference plus noise ratio (SINR). The simulation results show that the proposed receiver can go to convergence rapidly under all four IEEE’s UWB channel models, the bit error ratio (BER) performance is better than that of the traditional receiver and rake receiver.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (6). doi： 10.1016/S1005-8885(10)60121-5
Single-symbol maximum-likelihood (ML) decodable space-time block codes (SSDCs) can achieve a maximal symbol rate of 6/7 for multiple-input multiple-output (MIMO) communication system with five or six transmit antennas by using rate-efficient generalized coordinate interleaved orthogonal designs (RE-GCIODs). Unfortunately, there are many zero entries in the codeword matrix of RE-GCIODs. The zero entries result in high peak-to-average power ratio (PAPR) and also impose a severe constraint on hardware implementation. In this paper, for MIMO communication systems with five or six transmit antennas and one receive antenna, a new SSDC is proposed. By combining Alamouti code and orthogonal space-time block code (OSTBC), desirable properties like RE-GCIODs can be achieved and are derived, including maximal symbol rate up to 6/7, full diversity and single-symbol ML decodability. Moreover, by reducing the number of zero entries in the codeword matrix, the peak-to-average power ratio (PAPR) of our proposed code is lower than RE-GCIODs. Simulation results show that the proposed codes outperform RE-GCIODs under peak power constraint while performing almost same under average power constraint.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (6). doi： 10.1016/S1005-8885(10)60122-7
Systems are always designed and optimized based on full traffic load in the current literatures. However, practical systems are seldom operating at full load, even at peak traffic hours. Instead of maximizing system rate to achieve the full load, an optimal energy-efficient scheme to minimize the transmit power with required rates is investigated in this article. The considered scenario is a two-way relay channel using amplify-and-forward protocol of physical layer network coding, where two end nodes exchange messages via multiple relay nodes within two timeslots. A joint power allocation and relay selection scheme is designed to achieve the minimum transmit power. Through convex optimization theory, we firstly prove that single relay selection scheme is the most energy-efficient way for physical layer network coding. The closed-form expressions of power allocation are also given. Numerical simulations demonstrate the performance of the designed scheme as well as the comparison among different schemes.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (6). doi： 10.1016/S1005-8885(10)60123-9
In wireless multicast, network coding has recently attracted attentions as a substantial improvement to packet retransmission schemes. However, the problem of finding the optimal network code which minimizes the retransmissions is hard to solve or approximate. This paper presents two schemes to reduce the number of retransmissions for reliable multicast efficiently. One is retransmission using network coding based on improved Vandermonde matrix (VRNC), the other is retransmission using network coding based on adaptive improved Vandermonde matrix (AVRNC). Using VRNC scheme the sender selects the packets all receivers have lost and encodes them with improved Vandermonde matrix; when receivers receive enough encoded retransmission packets, all the lost packets can be recovered. With AVRNC scheme, the sender can obtain the recovery information from all the receivers after sending out per retransmission packet, and then the improved Vandermonde matrix can be updated, thus reducing the complexity of encoding and decoding. Our proposed schemes can achieve the theoretical lower bound assuming retransmission packets lossless, and approach the theoretical lower bound considering retransmission packets loss. Simulation results show that the proposed algorithms can efficiently reduce the number of retransmissions, thus improving transmission efficiency.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (6). doi： 10.1016/S1005-8885(10)60124-0
Heterogeneous network (Het-Net) is part of the long-term evolution advanced (LTE-A) study item and represents cellular deployments with a mixture of cells of different overlapping coverage areas, e.g., a number of relay and pico cells overlaid by a macro cell in the same frequency. Traffic balancing and interference management are required in Het-Net design for LTE-A to maintain system performance. In this paper, we propose an inter-domain cooperative traffic balancing scheme focusing on reducing the effective resource cost and mitigating the co-channel interference in multi-domain Het-Net. We first set up the conception of multi-domain in Het-Net and incorporate the co-channel interference into the proposed traffic balancing scheme. Then we model the traffic balancing issue as a multi-domain traffic resource optimization problem for minimizing the effective resource cost. The detailed implementation for the proposed traffic balancing scheme is designed. In the numerical evaluation, the genetic algorithm (GA) as an optimization method is used to demonstrate that the total effective resource cost is significantly reduced through our proposed inter-domain traffic balancing scheme，comparing with the intra-domain traffic balancing scheme. The 43% of the resource cost is saved. In the system level simulation, the performance results of signal interference noise ratio (SINR) and throughput demonstrate that the proposed scheme has great advantages in interference management in Het-Net.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (6). doi： 10.1016/S1005-8885(10)60125-2
In a peer-to-peer (P2P) live streaming system, each peer uses greedy strategy to download chunks as many as possible so as to assure smooth playback and promote the chunk propagation. However, diversity of video playback rate, heterogeneity of peer downlink bandwidth and no prefetching limitation determine that greedy strategy is not the best strategy for P2P video-on-demand (VoD) system though this strategy performs well in P2P live system. To reasonably assign upload bandwidth among peers, we first present a stochastic model to relate expected downloading speed (EDS) with buffered data amount (BDA, the amount of data has been fetched in buffer, however has not been played yet by the peer), video playback rate and fluency (the probability of no interruption in a viewing process). On the base of this model, we design an equal fluency bandwidth assigning algorithm (EFBAA). In this algorithm, requesting peers compute EDS according to several local parameters (such as BDA, video playback rate and fluency) dynamically and independently and send the EDS to neighbor peers together with buffer map. Then the neighbor peer proportionally partitions and assigns its upload bandwidth to requesting peers according to their EDS. Extensive simulations demonstrate that EFBAA outperforms greedy strategy in terms of server load and startup latency.
Song MAO Zhao Cheng-Lin
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (6). doi： 10.1016/S1005-8885(10)60126-4
This paper proposes a novel energy efficient unequal clustering algorithm for large scale wireless sensor network (WSN) which aims to balance the node power consumption and prolong the network lifetime as long as possible. Our approach focuses on energy efficient unequal clustering scheme and inter-cluster routing protocol. On the one hand, considering each node’s local information such as energy level, distance to base station and local density, we use fuzzy logic system to determine one node’s chance of becoming cluster head and estimate the corresponding competence radius. On the other hand, adaptive max-min ant colony optimization is used to construct energy-aware inter-cluster routing between cluster heads and base station (BS), which balances the energy consumption of cluster heads and alleviates the hot spots problem that occurs in multi-hop WSN routing protocol to a large extent. The confirmation experiment results have indicated the proposed clustering algorithm has more superior performance than other methods such as low energy adaptive clustering hierarchy (LEACH) and energy efficient unequal clustering (EEUC).
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (6). doi： 10.1016/S1005-8885(10)60127-6
In this paper, a scalable connection-based flow control scheme is proposed for application-specific network-on-chip (NoC). The proposed scheme exploits two distinctive characteristics of NoC, namely traffic predictability and abundant wire resource, to achieve significant performance enhancements. First, the burst injection data are regulated into constant data streams and a connection-based method is used to ensure that all links are not overloaded at any time. Consequently, the number of packets in the network is decreased, leading to a reduced congestion probability and improved communication performance. Second, a simple architecture of the central controller is proposed to guarantee that the proposed scheme has small area overhead and is scalable. Simulation results show that compared with traditional switch-to-switch (STS) flow control scheme and pre-allocation based flow control schemes, the proposed scheme greatly increases the throughput and cuts down the average latency with reasonable area and energy overhead.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (6). doi： 10.1016/S1005-8885(10)60128-8
In anomaly detection, a challenge is how to model a user’s dynamic behavior. Many previous works represent the user behavior based on fixed-length models. To overcome their shortcoming, we propose a novel method based on discrete-time Markov chains (DTMC) with states of variable-length sequences. The method firstly generates multiple shell command streams of different lengths and combines them into the library of general sequences. Then the states are defined according to variable-length behavioral patterns of a valid user, which improves the precision and adaptability of user profiling. Subsequently the transition probability matrix is created. In order to reduce computational complexity, the classification values are determined only by the transition probabilities, then smoothed with sliding windows, and finally used to discriminate between normal and abnormal behavior. Two empirical evaluations on datasets from Purdue University and AT&T Shannon Lab show that the proposed method can achieve higher detection accuracy and require less memory than the other traditional methods.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (6). doi： 10.1016/S1005-8885(10)60129-X
Polarization controllers (PCs) are indispensable passive components for state of polarization (SOP) control in optical fiber communication systems. In order to overcome the disadvantages of existing polarization controller (PC), a novel PC based on the artificial birefringence is designed in this paper. The PC results from the concatenation of 3 phase retardation control units each of which consists of two polarization beam splitters, two prisms and one piezoz-lectric transducer (PZT) piezoelectric ceramic. The experimental results show that the proposed PC can convert an arbitrary input SOP to any expected output one with high accuracy under low control voltage.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (6). doi： 10.1016/S1005-8885(10)60130-6
Jitter analysis and a linear model is proposed in this paper which predicts the characteristics of serial-deserial (SerDes) clock and data recovery circuit, and the characteristics include jitter transfer, jitter tolerance and jitter generation are particularly analyzed. The simulation results of the clock data recovery (CDR) model show that the jitter specifications exceed the mask of ITU-T optical transport network (OTN) G.8251 recommendations. The whole systems are validated by 9.95–11.5 Gbit/s CDR and the jitter attenuation phase locked loops (PLL) circuits using TSMC 65 nm CMOS technology.