A robust asynchronous multiuser STBC-OFDM transmission scheme for frequency-selective channels

In this paper, we propose a robust STBC transmission scheme to combat the timing synchronization errors over frequency-selective multiple-access channels. First, the equivalent channel model in the presence of timing synchronization errors is derived and we find that the synchronization errors result in an equivalent channel model with larger number of correlated channel taps. Based on this correlated equivalent channel model, the statistical power profile is analyzed and a robust statistical bit loading algorithm is proposed. At the receiver, by exploiting the algebraic structure of the Alamouti STBC, a closed-form expression of the QR receiver is derived which further simplifies computational complexity. Simulation results show that our proposed scheme is robust to timing synchronization errors.

This paper propose a flexible and robust unbalanced multiple description coding and transmission scheme,which is capable of quickly recovering from packet losses and ensuring continuous playback,and further adaptive to both multiple path and single path transmission.Furthermore,this paper discusses the problem of rate allocation between different descriptions when only single path transmission is available and proposes an approximate while efficient rate allocation scheme with the help of two-state Markov link model and a representative rate-distortion model.The experimental results demonstrate the effectiveness of the proposed scheme.

This paper investigates an unmanned aerial vehicle (UAV)-base station (BS) integrated network, where a UAV transmits downlink secrecy data to multiple ground cognitive users while a ground BS utilizes jamming beamforming to help the UAV counter the eavesdropping attack of a ground eavesdropper. In particular, we consider the imperfect eavesdropping and jamming channel state information (CSI) related to the eavesdropper. To maximize the minimum sum secrecy rate of the cognitive users, a robust secure transmission scheme is proposed. The UAV trajectory, UAV transmit power, BS beamforming, and user scheduling are jointly optimized with the constraints of the communication quality of the primary users served by the BS and the UAV available propulsion energy. We formulate a non-convex optimization problem which is challenging to be solved mathematically, and we utilize an alternating optimization technique to divide the original problem into three sub-problems, i.e., UAV trajectory sub-problem, transmit power sub-problem, and user scheduling sub-problem. Besides, they can be solved by the successive convex approximation, semi-definite relaxation and S-procedure, and bivariate relaxation methods, respectively. Moreover, we explore the impact of different parameters of the proposed transmission scheme on the minimum sum secrecy rate of the cognitive users, and verify the superiority of the proposed robust secure transmission scheme design.

A robust image transmission scheme deploying distributed-Alamouti space-time code (STC) over wireless relay networks is proposed. Specifically, we propose a cross-layer design combining application, networking, and physical layer to enhance the quality of multimedia data over error-prone wireless channels. At the application layer, a coded image sequence based on the wavelet transform is divided into two priorities. The higher priority contains the most significant information of image and the lower priority conveys less important information. At the physical layer, two pre-assigned relays cooperate to form a distributed-Alamouti code which help the source to transmit the low priority sequence of the image over error-prone wireless channels. At the networking layer, among the whole relay nodes in the networks we select two relay nodes which provides the maximum signal-to-noise ratio to convey the higher priority. With this strategy, we implicitly achieve unequal error protection for image transmission without controlling power or varying modulation and coding at the transmitter at the expense of increasing network's overhead (i.e. feedback information). The selection of relays needs limited feedback, hence, enabling our proposed scheme feasible in practical applications. Analytical and simulation results are provided to verify our proposal. It has been shown that the image quality is remarkably enhanced in terms of objective quality using the proposed scheme compared to the conventional transmission schemes.

This paper presents a new scheme for robust video transmission over packet erasure wireless channels based on Wyner-Ziv coding of motion regions. The multipath fading and shading of the wireless channels usually lead to loss or erroneous video packets which on occasions result in some spontaneous drop in video quality. Existing approaches with forward error correction (FEC) and error concealment have not been able to provide the desired robustness in video transmission. We develop a new scheme with a motion-based Wyner-Ziv coding (MWZC) by leveraging distributed source coding (DSC) ideas for error robustness. This new scheme is based on the fact that motion regions of a given video frame are particularly important in both objective and perceptual video quality and hence should be given preferential Wyner-Ziv coding based embedded protection. To achieve high coding efficiency, we determine the underlining motion regions based on a rate-distortion model. Within the framework of H.264/AVC specification, motion region determination can be efficiently implemented using flexible macroblock ordering (FMO) and data partitioning (DP). The bit stream generated by the proposed scheme consists two parts: the systematic portion generated from conventional H.264/AVC bit stream and the supplementary bit stream for error robust video transmission generated by the Wyner-Ziv coding of motion regions. Experimental results demonstrate that the proposed scheme significantly outperforms both decoder-based error concealment (DBEC) and conventional FEC with DBEC approaches.

In this paper, the edge caching optimization problem in fog radio access networks (F-RANs) is investigated. Considering that fog access points (F-APs) can offer cooperation gain by jointly transmitting the same file or content diversity gain by concurrently transmitting the coded subfiles, we propose to use both joint transmission (JT) strategy and parallel transmission (PT) strategy to serve users. Using tools from stochastic geometry, we first derive the expressions of successful transmission probability (STP) under different transmission strategies, and then derive the expressions of fractional offloaded traffic (FOT) and delay. We further formulate the corresponding edge caching optimization problem to maximize the STP, FOT or minimize the delay. Considering the NP-hard property of the above optimization problem, we propose an improved fruit fly optimization (FFO) based edge caching scheme, which utilizes the dynamic search step to avoid pre-mature convergence. Furthermore, we theoretically analyze the convergence and global optimality of our proposed scheme. Numerical results show that a significant performance gain is achieved by using our proposed edge caching scheme compared with the baseline schemes.

Conventional video traces (which characterize the video encoding frame sizes in bits and frame quality in PSNR) are limited to evaluating loss-free video transmission. To evaluate robust video transmission schemes for lossy network transport, generally experiments with actual video are required. To circumvent the need for experiments with actual videos, we propose in this paper an advanced video trace framework. The two main components of this framework are (i) advanced video traces which combine the conventional video traces with a parsimonious set of visual content descriptors, and (ii) quality prediction schemes that based on the visual content descriptors provide an accurate prediction of the quality of the reconstructed video after lossy network transport. We conduct extensive evaluations using a perceptual video quality metric as well as the PSNR in which we compare the visual quality predicted based on the advanced video traces with the visual quality determined from experiments with actual video. We find that the advanced video trace methodology accurately predicts the quality of the reconstructed video after frame losses.

Chapter 10 - The IEEE 802.16m Physical Layer (Part II)

The capacity of wireless ad hoc networks is constrained by the interference of concurrent transmissions among nodes. Instead of only trying to avoid the interference, physical-layer network coding (PNC) is a new approach that embraces the interference initiatively. We employ a network form of interference cancellation, with the PNC approach, and propose the multihop, broadcast-relay transmission strategy in linear, rectangular, and hexagonal networks. The theoretical analysis shows that it gains the transmission efficiency by the factors of 2.5 for the rectangular networks and 2 for the hexagonal networks. We also propose a practical signal recovery algorithm in the physical layer to deal with the influence of multipath fading channels and time synchronization errors, as well as to use media access control (MAC) protocols that support the simultaneous receptions. This transmission strategy obtains the same efficiency from one-to-one communication to one-to-many. By our approach, the number of the users/terminals of the network has better scalability, and the overall network throughput is improved.

Video transmission over wireless networks suffers from packet loss due to either temporary packet drop or fading-induced bit errors. To ensure that the quality of the decoded video is not overly affected by the channel unreliability, the video applications have to provide sufficient robustness. In this paper, a novel slice interleaving algorithm is proposed for compressed video packetization. Each packet is constructed by interleaving independently decodable slices of the coded video bit-stream in a group of frames. We group slices into packets according to the maximum minimal distance of these slices. The scattered pattern guarantees that each lost slice has, as many as possible, spatial and temporal neighbors that belong to other correctly received packets. This scheme greatly strengthens the error concealment performance compared with traditional methods. Experimental results demonstrate the superiority of the proposed algorithm.

A new integrated framework for source and channel rate allocation is presented for video coding and transmission over wireless channels without feedback channels available. For a fixed total channel bit rate and a finite number of channel coding rates, the proposed scheme can obtain the near-optimal source and channel coding pair, and corresponding robust video coding scheme such that the expected end-to-end distortion of video signals can be minimized. With the assumption that the encoder has the stochastic information such as average SNR and Doppler frequency of the wireless channel, the proposed scheme takes into account robust video coding, channel coding, packetization, and error concealment techniques altogether. An improved method is proposed to recursively estimate the end-to-end distortion of video coding for transmission over error-prone channels. The proposed estimation is about 1-3 dB more accurate compared to the existing integer-pel based method. Rate-distortion optimized video coding is employed for the trade-off between coding efficiency and robustness to transmission errors.

Ad hoc networks are characterized with frequent link failures and network topology change. These features result in a great challenge to transmit video over ad hoc networks. We propose a novel scheme for robust video transmission over ad hoc networks. Video stream is coded by using multiple description coding strategy and then a clustering-based multiple paths algorithm is applied for routing over ad hoc networks. The paper describes the general issues of multiple description coding and the principle of clustering-based multiple paths algorithm. Simulation results clearly demonstrate the effectiveness of this scheme for supporting error resilient video transmission over ad hoc networks.

This paper proposes an adaptive multi-mode transmission strategy to improve the spectral efficiency achieved in the multiple-input multiple-output (MIMO) broadcast channel with delayed and quantized channel state information. The adaptive strategy adjusts the number of active users, denoted as the transmission mode, to balance transmit array gain, spatial division multiplexing gain, and residual inter-user interference. Accurate closed-form approximations are derived for the achievable rates for different modes, which help identify the active mode that maximizes the average sum throughput for given feedback delay and channel quantization error. The proposed transmission strategy can be easily combined with round-robin scheduling to serve a large number of users. As instantaneous channel information is not exploited, the proposed algorithm cannot provide multiuser diversity gain, but it is still able to provide throughput gain over single-user MIMO at moderate signal-to-noise ratio. In addition, it has a light feedback overhead and only requires feedback of instantaneous channel state information from a small number of users. In the system with a feedback load constraint, it is shown that the proposed algorithm provides performance close to that achieved by opportunistic scheduling with instantaneous feedback from a large number of users.

This work considers a setting in which an encoder wishes to communicate with a decoder through a relay that is connected to the decoder via a finite-capacity link. Motivated by communication on the uplink of a cloud radio access cellular network, it is assumed that the relay compresses and forwards the received signal; moreover, the decoder has side information about the transmitted signal that is subject to fading whose realization is unknown to encoder and relay. A robust transmission and compression strategy is proposed that aims at minimizing the transmitted power under competitive rate optimality constraints. This contrasts with more conventional worst-case or average performance criteria. The transmission strategy is based on a broadcast coding and is parameterized by the maximum tolerable delay in terms of number of fading coherence blocks. Numerical results demonstrate the role of delay and the advantages of broadcast coding over the conventional single-layer transmission.

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