Changchuan Yin

On two-dimensional adaptive channel estimation in OFDM systems

In orthogonal frequency division multiplexing (OFDM) systems, two-dimensional (both time and frequency) minimum mean square error (2D-MMSE) channel estimation is optimum. However, accurate channel statistics are required to realize it, which are often unavailable in practice. In contrast, two-dimensional adaptive channel estimation based on a two-dimensional least mean square (2D-LMS) algorithm does not require any channel statistics, and at the same time can make full use of the time and frequency-domain correlations of the frequency response of time-varying dispersive fading channels. In this paper, we further study two-dimensional adaptive channel estimation in OFDM systems. We derive two-dimensional normalized least mean square (2D-NLMS) algorithm and find that the 2D-LMS algorithm with the optimum step-size parameter is just its special case. Furthermore, a parallel 2D-(N)LMS channel estimation scheme is proposed to solve the realtime realization problem due to high computational complexity encountered by two-dimensional adaptive channel estimation. Finally, we apply two-dimensional adaptive channel estimation to multiple-input multiple-output (MIMO) OFDM systems.

Delay-Bounded Power-Efficient Packet Scheduling for Uplink Systems of LTE

In this paper, we study minimal power transmission for uplink systems of LTE with constraints on mean queuing delay. Power consumption is important concern for multimedia services of mobile station of LTE .The power minimizing scheduler adapts power and rate of transmission based on the queue and channel state. Our extensive simulations show that small increases in average delay can lead to substantial savings in transmission power, thereby providing another avenue for mobile devices to save on battery power. We propose a low-complexity scheduler that has near-optimal performance.

Unified view of channel estimation in MIMO-OFDM systems

This paper provides a unified view of time-domain and frequency-domain least square (LS) channel estimation in multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. Time-domain and frequency-domain LS channel estimation are formulated under the same framework and their average mean square error (MSE) lower bounds for arbitrary number of transmit antennas and arbitrary number of pilot symbols are derived. Moreover, general optimum pilot design rules are developed to achieve average MSE lower bounds for time-domain and frequency-domain LS channel estimation, respectively. Their applicable conditions and computational complexity are also investigated and compared. It can be shown by theory and simulation that time-domain LS channel estimation is equivalent to frequency-domain LS channel estimation with discrete-time Fourier transform (DFT) improvement, but time-domain LS channel estimation has boarder applicable condition.

Relay-Assisted MIMO Multiuser Precoding in Fixed Relay Networks

In this paper, downlink multiple input multiple output (MIMO) multiuser transmission using precoding in fixed relay networks is studied. We propose two relay-assisted MIMO multiuser precoding models. For the first model, multiuser precoding is performed at base station (BS). The fixed relay processes the received signal and forwards it, which is amplify- and-forward. While for the second model, the multiuser precoding is done at relay. Thus, detect-and-forward or decode- and-forward transmission can be used. Based on these models, some multiuser precoding algorithms are investigated. Our simulation results show that fixed relay offers significant gain. And our system architectures give the means on how to utilize fixed relay in MIMO multiuser system.

Pilot Aided LS Channel Estimation in MIMO-OFDM Systems

This paper presents the theoretical and simulation results for least square channel estimation in MlMO-OFDM systems based on two types of pilot structure, the block-type pilot and the comb-type pilot. We derive their estimation equations, average mean square error lower bounds and optimum pilot design rules. Simulation results verify the theoretical analysis and show that the comb-type pilot aided channel estimation has a better performance when the channel is time-variant

Multi-Cell Coordinated Scheduling and Power Allocation in Downlink LTE-A Systems

In this paper, we investigate multi-cell coordinated scheduling and power allocation in downlink long term evolution advanced (LTE-A) systems, where orthogonal frequency division multiple-access (OFDMA) is used. The proposed scheme performs joint scheduling, power allocation, and modulation and coding scheme (MCS) selection to maximize the overall weighted throughput with proportional fairness. Our scheme considers the practical constraints in LTE-A systems. Since the optimization problem is a combinatorial and non- convex one and is with high complexity, low- complexity and suboptimal algorithms are proposed, which separate the scheduling and power allocation into two subproblems. Simulation results show that the proposed scheme can improve the average system throughput by 10% and the 10th percentile throughput by 15% compared with the existing scheme.

Multiuser MIMO-OFDM with Adaptive Antenna and Subcarrier Allocation

Subcarrier allocation schemes for SISO-OFDM systems in multiuser downlink scenario is well-documented. In this paper, with the goal of maximizing channel capacity, we extend it to MIMO-OFDM systems and propose a novel resource scheduling scheme with dynamic antenna and subcarrier allocation. This is done by maximizing the number of equivalent parallel subchannels in space-frequency structure and corresponding channel fading coefficients in frequency domain. The results show that our proposed algorithm outperforms multiuser MIMO-OFDM systems with static time-division multiple access (TDMA) technique which employ fixed and predetermined time-slot allocation scheme

A cross-layer mechanism for TCP connection over wireless uplink in cellular networks

In the next generation cellular radio networks (e.g. 4G), the first hop in the uplink that is from the mobile host (MH) to the fix host (FH) is the wireless link and transport control protocol (TCP) is used for data transfer over the end-to-end connection. However, TCP performs poorly in wireless networks. In the paper, a novel cross-layer mechanism called link layer trigger TCP (LLT-TCP) for TCP over radio uplink is presented. The proposed scheme controls the startup of the retransmission timer in TCP layer at the MH according to the information from the radio link control (RLC) layer, which enables TCP protocol to operate over the uplink without suffering from the packet losses resulting from the fading channel and mobility. In addition, the implementation of proposed mechanism only needs to make modifications on the protocol stack in MH.

Tri-Sectoring and Power Allocation of Macro Base Stations in Heterogeneous Cellular Networks with Matern Hard-Core Processes

In the practical heterogeneous cellular networks, a macro base station (MBS) is usually not located at the center of the macrocell and the distances from the MBS to its edges are also different. For this reason, the tri-sectoring method defined by 3GPP which divides three equal sectors and allocates each sector the same power may severely degrade the communication performance of the edge users. In this paper, we propose a novel tri-sectoring method and a MBS sector power allocation scheme for orthogonal frequency division multiple access based downlink of MBSs under co-channel deployment in heterogeneous cellular networks. We first evaluate the performance of 3GPP tri-sectoring method by using a hexagonal grid model and a Matern hard-core process (MHP) model, respectively, to demonstrate the inapplicability of 3GPP tri-sectoring method to the practical MHP model. Then, we devise a novel tri- sectoring method which considers load balancing and the directional radiation pattern of antennas. At last, a MBS sector power allocation scheme is proposed to control their downlink transmit power according to the downlink outage probability of edge macrocell users. Simulation results show that the proposed methods can improve the throughput of femtocell users and area spectral efficiency.

A parallel receiver combining detection and decoding for turbo-coded multi-antenna system

A novel parallel receiver is proposed for turbo-coded multi-antenna system, which combines detection and decoding, and fully utilizes the original information in terms of Shannon information theory. We modify the conventional maximum a posteriori (MAP) BCJR algorithm to decode multi-antenna interference signal directly. This algorithm is insensitive to multi-antenna structure, not like space-time coding (STC), layered space-time (LST), and also obtains receive diversity by combining extrinsic information or log-likelihood ratio (LLR) information. Simulation results verify the proposed receiver algorithm