Progressive Linear Precoder Optimization for MIMO Packet Retransmissions

This paper investigates the optimal linear precoder design for packet retransmissions in multi-input-multi-output (MIMO) systems. To fully utilize the time diversity provided by automatic repeat request (ARQ), we derive a sequence of successive optimal linear ARQ precoders for flat fading MIMO channels, which minimize the mean-square error between the transmitted data and the joint receiver output. The optimization is subject to an overall transmit power constraint. This progressive linear ARQ precoder combines the appropriate power loading and the optimal pairing of channel matrix singular values in the current retransmission with previous transmissions. This optimal pairing is a special feature unique to our sequential ARQ precoding approach. Simulation results demonstrate the effectiveness of this optimized ARQ precoding in reducing symbol MSE and detection bit-error rate

On the Performance of MIMO-ARQ Systems with Channel State Information at the Receiver

This paper investigates the performance of multiple-input-multiple-output (MIMO) systems in the presence of automatic repeat request (ARQ) feedback. We show that, for a large range of performance metrics, the data transmission efficiency of the ARQ schemes is determined by a set of parameters which are scheme-dependent and not metric-dependent. Then, the results are used to study different aspects of MIMO-ARQ such as the effect of nonlinear power amplifiers, large-scale MIMO-ARQ, adaptive power allocation and different data communication models. The results, which are valid for various forward and feedback channel models, show the efficiency of the MIMO-ARQ techniques in different conditions

Using Channel Output Feedback to Increase Throughput in Hybrid-ARQ

Hybrid-ARQ protocols have become common in many packet transmission systems due to their incorporation in various standards. Hybrid-ARQ combines the normal automatic repeat request (ARQ) method with error correction codes to increase reliability and throughput. In this paper, we look at improving upon this performance using feedback information from the receiver, in particular, using a powerful forward error correction (FEC) code in conjunction with a proposed linear feedback code for the Rayleigh block fading channels. The new hybrid-ARQ scheme is initially developed for full received packet feedback in a point-to-point link. It is then extended to various different multiple-antenna scenarios (MISO/MIMO) with varying amounts of packet feedback information. Simulations illustrate gains in throughput.Comment: 30 page

Optimized Live 4K Video Multicast

4K videos are becoming increasingly popular. However, despite advances in wireless technology, streaming 4K videos over mmWave to multiple users is facing significant challenges arising from directional communication, unpredictable channel fluctuation and high bandwidth requirements. This paper develops a novel 4K layered video multicast system. We (i) develop a video quality model for layered video coding, (ii) optimize resource allocation, scheduling, and beamforming based on the channel conditions of different users, and (iii) put forward a streaming strategy that uses fountain code to avoid redundancy across multicast groups and a Leaky-Bucket-based congestion control. We realize an end-to-end system on commodity-off-the-shelf (COTS) WiGig devices. We demonstrate the effectiveness of our system with extensive testbed experiments and emulation

Transmission and Combining for Hybrid Automatic Repeat Request in Multiple-Input Multiple-Output Systems

Hybrid automatic repeat request (HARQ) schemes combine packet retransmission with forward error correction to ensure a reliable communications. In multiple-input multiple output (MIMO) systems, interference cancellation (IC) detection is widely used where the detection and cancellation steps of the simultaneously transmitted data streams occur. In principle, the signal stream estimated at one IC stage is utilized to cancel the interference of other signal streams at the next IC stage. Thus, the detection probabilities of the transmitted data streams are mutually dependent. With HARQ, the detection performance of a packet also depends on how many times the packet has been retransmitted. The dissertation consists of three main contributions. Firstly, we develop a HARQ transmission state control algorithm for MIMO systems with IC detection to improve throughput. The HARQ transmission state is defined as the distribution of the initial packets and retransmission packets transmitted during a packet transmission time interval (PTTI). The proposed algorithm generates the transmission state in which initial packets and retransmission packets are sent together. The outcome is that it achieves a lower error probability for initial packets by exploiting the IC process and a significantly higher throughput than the conventional HARQ system, which is verified by simulation results. However, the maximum allowable number of retransmission is limited to one in this algorithm. Secondly, in order to extend the analysis for a more general case, we define the concept of the effective interference level (EIL) as the performance parameter to choose the set of packets during one PTTI and establish a relationship between EIL and the effective signal-to-interference-plus-noise ratio (SINR). We then show that choosing the set of packets that minimize the EIL successively from the lowest to the highest HARQ round leads to a lower packet error and higher throughput than conventional HARQ, which is verified by simulation. Also, the proposed EIL based scheme uses only the acknowledgement feedback messages like a conventional HARQ, because the number of HARQ rounds of each packet is the only required information to calculate the EIL. Simulation results highlight the superiority of the proposed scheme over the conventional scheme in terms of throughput with the signal-to-noise ratio gain of about 4.2 dB at maximum for MIMO systems with four transmit and four receive antennas. Thirdly, a low-complexity symbol-level combining (SLC) scheme is developed for Chase combining based HARQ (CC-HARQ) in MIMO systems, when the linear detection is considered at the receiver. In the proposed scheme, instead of using the entire channel matrix as in the existing SLC schemes, a subset of row vectors in the channel matrix is selected in the proposed scheme, and the selected row vectors are sequentially used during the estimation procedures of the retransmitted symbols, where the sequential utilization is enabled by using the Sherman-Morrison-Woodbury (SMW) lemma. Therefore, according to the number of the selected row vectors, this approach enables the proposed SLC scheme to have an advantage in complexity compared to the existing SLC schemes. In addition, we develop a row vector selection criterion for the proposed scheme to compute the amount of the SINR improvement by using a squared norm of each row vector with a significantly lower computational complexity. Simulation results show that compared to the existing SLC schemes, the proposed SLC scheme achieves similar or better error performance, while its computational complexity is lower or in the worst case similar

Resource Allocation, Scheduling and Feedback Reduction in Multiple Input Multiple Output (MIMO) Orthogonal Frequency-Division Multiplexing (OFDM) Systems

The number of wireless systems, services, and users are constantly increasing and therefore the bandwidth requirements have become higher. One of the most robust modulations is Orthogonal Frequency-Division Multiplexing (OFDM). It has been considered as an attractive solution for future broadband wireless communications. This dissertation investigates bit and power allocation, joint resource allocation, user scheduling, and limited feedback problem in multi-user OFDM systems. The following dissertation contributes to improved OFDM systems in the following manner. (1) A low complexity sub-carrier, power, and bit allocation algorithm is proposed. This algorithm has lower computational complexity and results in performance that is comparable to that of the existing algorithms. (2) Variations of the proportional fair scheduling scheme are proposed and analyzed. The proposed scheme improves system throughput and delay time, and achieves higher throughput without sacrificing fairness which makes it a better scheme in terms of efficiency and fairness. (3) A DCT feedback compression algorithm based on sorting is proposed. This algorithm uses sorting to increase the correlation between feedback channel quality information of frequency selective channels. The feedback overhead of system is successfully reduced