Zhiliang Qiu

A Novel Doppler Frequency Offset Estimation Method for DVB-T System in HST Environment

A novel Doppler frequency offset estimation method is proposed for the digital video broadcasting-terrestrial (DVB-T) system in the high-speed-train (HST) environment. Based on the analysis of the effect of the scattered components of the wireless channel on the accuracy of the Doppler frequency offset estimation, we separate the path with the Line-of-Sight(LOS) component from the multipath channel, and only use it to estimate the frequency offset caused by Doppler shift. Simulation results show that the mean square error (MSE) of the proposed scheme is far better than those of the available schemes.

Fast Time-Varying Channel Estimation Technique for LTE Uplink in HST Environment

A novel channel estimation technique is proposed for the time-division-duplex long-term evolution (TDD-LTE) single-carrier frequency-division multiple-access (SC-FDMA) system in the high-speed-train (HST) environment. In the new defined transform domain, the channel parameters of the two block pilots in the SC-FDMA subframe are first estimated, then the polynomial basis expansion model (P-BEM) is employed to estimate the channel parameters of the data symbols, and an autoregressive (AR) model is used to improve the estimation accuracy of the channel parameters of the data symbols out of the two block pilots. The symbol-by-symbol changes of the channel parameters can be effectively estimated by the proposed method. Simulation results show that the proposed method is robust to the fast time-varying channel in the HST scenario, and that the frame error rate (FER) performance of the system by using the proposed method can obtain a gain in the signal-to-noise ratio (SNR) of more than 10 dB compared with those of the available methods.

Beamforming Based Receiver Scheme for DVB-T2 System in High Speed Train Environment

In this paper, the received signal from the different base stations (BSs) of the second generation of Terrestrial Digital Video Broadcasting (DVB-T2) in the high-speed-train (HST) scenario is modeled as a fast time-varying signal with the multiple Doppler frequency offsets. The interference caused by the multiple Doppler frequency offsets and the channel variations, and the signal to interference plus noise ratio of the received signal, are derived for the DVB-T2 receiver. The results of the theoretical analysis show that the interference greatly degraded the performance of the DVB-T2 system. To suppress the interference, we proposed a beamforming based receiver scheme for DVB-T2 system. By using the new signal processing scheme for the received signal vector from the antenna array, one can separate the received signal with the multiple Doppler frequency offsets into the multiple signals, each of which is with a single Doppler frequency offset. The separated signals are compensated by the corresponding Doppler frequency offsets and equalized by the estimated channel responses respectively, then combined into a signal to be demodulated. The results of the simulation show that the proposed scheme can effectively suppress the interference and greatly improve the performance of the DVB-T2 system in the HST environment.

Bidirectional shuffle-exchange network and tag-based routing algorithm

We enhance the general shuffle-exchange network (GSEN) with bidirectional links. For bidirectional links, the bidirectional GSEN can be divided into two dependent networks, forward network and backward network. Based on the idea of inversely using the forward tag, we propose a tag-based routing algorithm for the backward network, so as to reduce the computation of the shuffle-exchange operation.

Evolution properties of Bessel-Gaussian Schell-model beams in non-Kolmogorov turbulence.

The analytical expressions for the spectral degree of coherence, the effective radius of curvature and the propagation factor of the Bessel-Gaussian Schell-model (BGSM) beam in turbulent atmosphere are derived based on the extended Huygens-Fresnel principle and the second-order moments of the Wigner distribution function (WDF). The evolution properties of BGSM beams propagating in non-Kolmogorov turbulence are investigated by a set of numerical examples. It is demonstrated that the spectral degree of coherence of the BGSM beam evolves into Gaussian profile twice with the increasing of the propagation distance. The turbulence-induced degradation can be remarkably reduced by using the BGSM beam with the proper source parameters. The effects that the generalized refractive-index structure constant, outer and inner scales, and the spectral index of spatial power spectrum of atmospheric turbulence have on the evolution properties of BGSM beams are also discussed in detail.

VN-APIT: virtual nodes-based range-free APIT localization scheme for WSN

AbstractAs an important supporting technology, the localization technology has become the basis of the practical applications of wireless sensor networks for information acquisition and processing . APIT (approximate Point-In-Triangulation) localization scheme is widely used for localization estimation in wireless sensor networks due to the advantages of the high localization accuracy and easy to deploy. However, there are some inherent defects caused by the uneven distribution of sensor nodes in APIT scheme. To overcome the problem, in this paper a novel virtual nodes-based range-free localization scheme, i.e., VN-APIT, is proposed to improve the APIT scheme. By rationally deploying virtual nodes in sensor network according to the proposed VN-APIT test theory, VN-APIT localization scheme can determine independently that whether a target node is inside or outside the triangle formed by three certain anchor nodes. Therefore, it will not subject to the effect of the density and distribution of sensor nodes and there is no the problem of the In-to-Out error and the Out-to-In error in VN-APIT scheme. Simulation evaluation shows that the proposed VN-APIT scheme is more robust and has a lower average localization error (ALE) than the conventional APIT scheme.

Enhanced Two-Level Frame Aggregation with Optimized Aggregation Level for IEEE 802.11n WLANs

IEEE 802.11n defines a significant two-level frame aggregation scheme aimed at improving the transmission efficiency of MAC layer. However, the performance of the two-level frame aggregation scheme does not meet the user expectation due to the inevitable aggregation and retransmission overheads. To overcome this problem, an enhanced two-level frame aggregation with the optimized aggregation level is proposed in this letter for IEEE 802.11n wireless local area networks (WLANs). In the proposed scheme, in order to maximize the throughput of the two-level frame aggregation, the aggregation level (i.e., sub-MPDUs, the number of the aggregated sub-MAC protocol data units) used for the two-level frame aggregation is optimized and adjusted dynamically according to the subframe size, the maximum aggregation level (MAL) allowed by the current two-level frame aggregation and the real-time channel bit-error-rate (BER). Results from the simulation show the superiority of the proposed enhanced two-level aggregation in respect of throughput performance.

Space-memory-memory Clos-network switches with in-sequence service

Clos-network switches have attracted a lot of attention because of their modularity and scalability. However, out-of-sequence problems weigh heavily against the application of buffered Clos-network switches. A space-memory-memory (SMM) Clos-network switch is proposed in this study which is able to provide in-sequence service. There are two features in the proposed switch which are different from the previously proposed schemes. First, two-stage load-balanced Birkhoff-von Neumann (LB-BvN) switches are adopted for each second-stage module. Second, no inter-stage matching is needed. The key idea to provide in-order cell delivery in the proposed SMM Clos-network switch is that cells belonging to the same flow will experience the identical delay when passing through the LB-BvN switches at the second stage, and arrive at their destined third-stage module in order. Each switching module operates independently, which makes the proposed SMM Clos-network switch practical to implement in hardware. Simulations show that the proposed switch can achieve high performance under both Bernoulli and Bursty arrival traffic.

Channel correlation of transmit diversity FSO systems with partially coherent optical beams

Spatial diversity, including transmit diversity, has been proven to be a promising technique to mitigate turbulence-induced signal fading. However, due to the limitation of size in compact FSO (free-space optical) terminals, the transmit antennas cannot always be separated far enough from each other, resulting in increased channel correlation and deteriorated diversity performance. In this paper, we focus on the channel correlation statistics of transmit diversity FSO systems with two transmit beams. Specifically, we consider partially coherent optical beams, which reduce scintillation over fully coherent optical beams. We perform theoretical analysis and obtain some interesting numerical results, such as the degree of channel correlation which changed mainly with source correlation radius from 0.001 to 0.1 m. These results can be helpful for designing transmit diversity FSO systems with partially coherent beams.

Load balance based network bandwidth allocation for delay sensitive services

Satisfying critical QoS requirements in next generation networks poses major challenges, due to its intrinsic complexity of network resource allocation. This paper considers the problem of load balance based bandwidth allocation for delay sensitive services. For satisfying deterministic end-to-end delay requirement, a simple and efficient algorithm for path level optimal bandwidth allocation, path level equal ratio allocation algorithm (P-ERA), is developed first. Based on P-ERA, another algorithm for network level optimized bandwidth allocation, network level equal ratio allocation algorithm (N-ERA), is also presented for much more complicated network circumstances. N-ERA algorithm features appropriate route selection and balanced bandwidth allocation, and can adaptively avoid, or at least delay, the emergence of network bottleneck when a network is heavily loaded. Extensive simulations indicate that N-ERA algorithm can make full use of network bandwidth and admit more services, even if they are delay critical, than other ones dealing with the same problem. And the less computation complexity of N-ERA algorithm makes it of great application value.