Measured Channel State Research Articles

Computer Vision Aided Codebook Design for MIMO Communications Systems

MmWave communications systems usually rely on analog or hybrid analog/digital architectures and thus need a predefined codebook to perform beamforming. Traditional codebooks are designed for universal environments, although in practice a particular BS will only serve a particular environment. In this paper, we propose novel site-specific codebook design methods by utilizing the visual information captured through cameras. Different from other site-specific codebook design methods that require a large amount of measured channel state information (CSI), the proposed ones need only a simple snapshot of the environment followed by efficient computer vision (CV) techniques. Thus the proposed CV-aided codebook design reduces the overhead of communications system, such as the cost of time, human resources, as well as the hardware installation and calibration. Specifically, we propose a CV-based approach that detects the LOS area around the BS and reconstructs the LOS channel vectors set (CVS).With this knowledge, we build a vision-based beam codebook using Lloyd algorithm. Further, we design a FusionNet to generate the codebook that can serve the non-line-of-sight (NLOS) users. The simulation results demonstrate the effectiveness of the proposed CV-aided codebook design methods and their superiority compared to the conventional methods.

Boosting Vehicle-to-Cloud Communication by Machine Learning-Enabled Context Prediction

The exploitation of vehicles as mobile sensors acts as a catalyst for novel crowdsensing-based applications such as intelligent traffic control and distributed weather forecast. However, the massive increases in Machine-type Communication (MTC) highly stress the capacities of the network infrastructure. With the system-immanent limitation of resources in cellular networks and the resource competition between human cell users and MTC, more resource-efficient channel access methods are required in order to improve the coexistence of the different communicating entities. In this paper, we present a machine learning-enabled transmission scheme for client-side opportunistic data transmission. By considering the measured channel state as well as the predicted future channel behavior, delay-tolerant MTC is performed with respect to the anticipated resource-efficiency. The proposed mechanism is evaluated in comprehensive field evaluations in public Long Term Evolution (LTE) networks, where it is able to increase the mean data rate by 194% while simultaneously reducing the average power consumption by up to 54%.

Opportunistic feedback with multiple classes in wireless systems

An opportunistic feedback protocol with multiple access probabilities is proposed, where users are divided into several classes according to their measured channel state. Different random access probabilities are assigned to each class. All users compete to send a feedback message through random access if their scheduling metric exceeds a threshold. An analytical model is developed for evaluating the proposed feedback protocol in terms of the sum-rate capacity and the feedback load. The proposed feedback protocol achieves an asymptotic sum-rate capacity with a minimal amount of feedback information.

Beamforming Degradation of a W-CDMA Smart Antenna Under FDD and MAI Channel Estimation Errors

A smart antenna adopts the beamforming technique to increase the signal-to-(interference plus noise) ratio (SINR) and system capacity. In this paper, the impact of two channel estimation errors - frequency-division duplex (FDD) estimation error and multiple-access interference (MAI) estimation error for the beamforming of a wide-band code-division multiple-access smart antenna - are analyzed by using the measured channel state information. Results show that for a complex conjugate beamforming, FDD estimation error will cause median degradation of less than 1 dB if the desired signal is in a line-of-sight (LOS) channel and 1-3 dB if in a non-LOS (NLOS) channel. In addition, the MAI estimation error will cause 0.3-0.5 dB degradation per interference in the LOS case and 0.5-1 dB degradation in the NLOS case

Evaluation of Asymmetric TDD Systems Employing AMC and HARQ by Considering MCS Selection Errors

In this paper, we evaluate the performance of asymmetric Time Division Duplex (TDD) system that employs Adaptive Modulation and Coding (AMC) and Hybrid ARQ, with consideration of the effect of control delays in TDD. Channel reciprocity characteristic in TDD allows utilization of open loop channel estimation to choose appropriate modulation and coding scheme (MCS) level for AMC. However, control delay in AMC and HARQ depends on TDD time slot allocation formats. Large control delay in AMC will result in false MCS selection due to the poor channel correlation between measured channel state from the received signals and instantaneous channel state of actual transmission with the MCS selected based on the measured channel state. We present an analytical approach to calculate the probability of MCS level selection error in different channel conditions for different asymmetric time slot allocations. From the theoretical and simulation results, it is shown that the instantaneous throughput per slot depends not only on maximum Doppler frequency but also on asymmetric slot allocations. Average delay time that yields error free packet reception in the downlink increases as the number of continuous downlink slots increases.

Performance Comparison of Two SDMA Approaches for OFDM Signals Using Measured Indoor Channel Data

We have proposed two space division multiple access (SDMA) approaches for OFDM signals: Virtual Subcarrier Assignment (VISA) and Preamble Subcamer Assignment (PASA), both of which can enhance the system capacity without significant change of transmitter/receiver structures for already-existing OFDM-based standards such as IEEE802.1 la. In order to investigate the performance of the proposed approaches in real wireless scenarios, we conducted a measurement campaign to obtain real channel state data at 5-GHz band in an indoor environment. Using the measured channel data, we can make the performance evaluation realistic. In this paper, after the brief overview of the two proposed SDMA approaches, we describe our measurement campaign in detail. Furthermore, we evaluate the performance of VISA-based system and PASA-based system by computer simulations using the measured channel state data and present a comparative study on the performance of the two proposed SDMA approaches in the realistic wireless environment.