Yafei Tian

Joint Scalable Coding and Routing for 60 GHz Real-Time Live HD Video Streaming Applications

Transmission of high-definition (HD) video is a promising application for 60 GHz wireless links, since very high transmission rates (up to several Gbit/s) are possible. In particular we consider a sports stadium broadcasting system where signals from multiple cameras are transmitted to a central location. Due to the high pathloss of 60 GHz radiation over the large distances encountered in this scenario, the use of relays might be required. The current paper analyzes the joint selection of the routes (relays) and the compression rates from the various sources for maximization of the overall video quality. We consider three different scenarios: (i) each source transmits only to one relay and the relay can receive only one data stream, and (ii) each source can transmit only to a single relay, but relays can aggregate streams from different sources and forward to the destination, and (iii) the source can split its data stream into parallel streams, which can be transmitted via different relays to the destination. For each scenario, we derive the mathematical formulations of the optimization problem and re-formulate them as convex mixed-integer programming, which can guarantee optimal solutions. Extensive simulations demonstrate that high-quality transmission is possible for at least ten cameras over distances of 300 m. Furthermore, optimization of the video quality gives results that can significantly outperform algorithms that maximize data rates.

Quality-aware coding and relaying for 60 GHz real-time wireless video broadcasting

Wireless streaming of high-definition video is a promising application for 60GHz links, since multi-Gigabit/s data rates are possible. In particular we consider a sports stadium broadcasting system where video signals from multiple cameras are transmitted to a central location. Due to the high pathloss of 60GHz radiation over the large distances encountered in this setting, the use of relays is required. This paper designs a quality-aware coding and relaying algorithm for maximization of the overall video quality. We consider the setting that the source can split its data stream into parallel streams, which can be transmitted via different relays to the destination. For this, we derive the related formulation and re-formulate it as convex programming, which can guarantee optimal solutions.

Joint optimization of HD video coding rates and unicast flow control for IEEE 802.11ad relaying

This paper proposes a joint optimization framework for minimizing high-definition (HD) video coding rates and selecting optimal relay nodes in 60 GHz millimeter-wave (mmWave) IEEE 802.11ad very high throughput (VHT) wireless systems. While IEEE 802.11ad VHT aims to support uncompressed HD video wireless transmission, its major limitation is the extremely high attenuation even in line-of-sight situations, which leads to a short admissible distance between transmitter and receivers and/or the necessity to compress video. To deal with this problem, the IEEE 802.11ad VHT draft standard defines efficient relaying protocols to extend the network coverage. When multiple source-destination pairs and multiple relays are present, a key question is which relay should help in the forwarding of which source flow. This selection should be done in such a way that the average video quality of the streams, which is related to the throughput in a nonlinear way, is maximized. We solve this problem by an integer programming framework that selects optimal relay nodes, their cooperation modes (i.e., amplify-and-forward, decode-and-forward, or non-cooperation), and the video coding (compression) rates which can maximize transmission quality.

Asymmetric Two-Way Relay with Doubly Nested Lattice Codes

Two-way relaying can significantly improve the spectrum efficiency of bi-directional information transmission between two nodes with the help of half-duplex relays. However, in the general case of asymmetric channel gains, the achievable rates of both directions are restricted by the link with the worse channel quality. In this paper, we propose a new three-phase cooperative transmission protocol, which exploits the direct link and the time resource of a two-way relay system more efficiently. We derive the rate region outer bound of this protocol, and propose a practical transmission scheme based on doubly nested lattice codes, which can achieve this outer bound within 0.5 bit. Numerical results show the superiority of this protocol over two other classical protocols in asymmetric channels.

Energy-Efficient Coordinated Beamforming Under Minimal Data Rate Constraint of Each User

Coordinated beamforming has been optimized to maximize the sum rate under the transmit power constraints or to minimize the transmit power under the data rate constraints. In this paper, we design a precoder that maximizes the energy efficiency (EE) of multicell multiantenna downlink network with coordination and, in the meantime, ensures the minimal data rate requirement of each user. To find a solution of such a nonconvex optimization problem, we construct a convex subset of the original constraint set and a quasi-concave lower bound of the EE. Then, we propose an iterative algorithm to maximize the lower bound of the EE within the convex subset, which is shown to rapidly converge to a local optimum of the original problem. We evaluate the EE of the proposed algorithm through simulations under different user locations, data rate requirements, and numbers of antennas. The results demonstrate that the proposed precoder performs closely to an upper bound derived from interference-free assumption. When the circuit power consumption is dominant, the proposed precoder is much more energy efficient than the transmit power minimization precoder, as well as a precoder, including an interference alignment (IA) beamformer and the optimized transmit power maximizing the EE.

Macro-Pico Amplitude-Space Sharing with Optimized Han-Kobayashi Coding

Heterogeneous network is a new paradigm in next generation cellular systems, which is promised to significantly improve the spatial spectrum efficiency through overlapped coverage. This however calls for efficient interference management techniques. In this paper, we propose an amplitude-space sharing strategy among the macro-cell user and pico-cell users, where different users occupy different levels in the signal amplitude-space. By optimizing the space sharing scheme, different layers of signal and interference are separable at each receiver and the network sum-rate can be maximized. We start from the single pico-cell scenario, where we employ Han-Kobayashi coding and derive the optimal transmit powers allocated to the private and common information of the users. With a unified framework, we derive the achievable sum-rates for various interference scenarios ranging from very strong to very weak cases. We then illustrate how the amplitude-space sharing strategy can be applied to the multiple pico-cell scenarios by developing a simple transmission scheme. Simulation results show the superiority of the proposed scheme over other interference management schemes.

Noncoherent Multiple-Symbol Detection in Coded Ultra-wideband Communications

Recently, ultra wideband (UWB) impulse radio systems based on noncoherent detection, such as transmitted reference and differential modulation systems, have drawn a lot of attention for their potential applications in low-rate and low-cost communications. In this paper, a unified approach is presented to develop and analyze a noncoherent multiple-symbol detection (MSD) algorithm for various UWB signaling formats in multi- path environments. Pair-wise error probabilities of coherent and noncoherent MSD algorithms are derived and compared. The intrinsic connection between the coherent and noncoherent MSD algorithms is revealed, tradeoff curves between their performance and complexity are obtained, and optimal transmission signal design rules for noncoherent detection are provided. The bit error rates are shown through simulations to verify the analysis and to evaluate the performance of the developed algorithms in realistic environments.

Energy-efficient coordinated beamforming with individual data rate constraints

Coordinated beamforming has been optimized to maximize the sum rate under the transmit power constraints, or to minimize the transmit power under the data rate constraints. In this paper, we study coordinated beamforming to maximize the energy efficiency (EE) of multi-cell multi-antenna systems meanwhile ensuring the individual data rate requirement of each user. To find a solution of the non-convex optimization problem for the precoding design, we construct a convex subset of the original constraint set and a quasi-concave lower bound of the EE. Then, we propose an iterative algorithm to maximize the lower bound of the EE within the convex subset. We evaluate the EE of the proposed algorithm through simulations under different data rate requirements, user locations, and cell-edge signal-to-noise ratios. The results demonstrate that the proposed precoder is much more energy-efficient than the transmit power minimization precoder when the circuit power consumption dominates, and always outperforms two interference-free transmission schemes with the optimized transmit power toward maximizing the EE.

A preprocessing algorithm of ultra-wideband signal for space-time focusing transmission

Ultra-wideband (UWB) signal has fine time resolution and can resolve a large amount of multipath in densely scattered environments. Exploiting these features, UWB systems can accomplish space-time focusing transmission. At the focused spot there will exhibit an energy peak, while in other places very weak interference will be induced. The space-time focusing transmission can not only enable the use of simple receiver structure, but also enhance the coexistence capability of UWB systems with the legacy narrowband systems. In this paper, a novel preprocessing method is proposed for multiuser UWB systems. By filtering the transmitted signal, the received signal at the focused time can be sampled without intersymbol interference and multiuser interference. Moreover, the interference to narrowband users can also be avoided.

Reduced-order Multiuser Detection in Multi-rate DS-UWB Communications

In ultra-wideband (UWB) systems, the ultra-wide bandwidth and abundant multipath components can provide great spreading gain and diversity gain, but will also induce complicated interference suppression algorithm because of the requirements of very high sampling rate and large number of filter taps. A reduced-order multi-user detector (R-MUD) is proposed in this paper which can significantly reduce the sampling rate thus the computational burden by down-sampling the received multipath signal at appropriate locations, where the energy of the desired user can be effectively captured and the interferences from other users can be dramatically suppressed. The superior performance of the R-MUD is justified by computer simulations.