LoRa networks achieve a remarkably wide coverage as compared to that of the conventional wireless systems by employing the chirp spread spectrum (CSS). However, single-hop LoRa networks have limited penetration in indoor environments and cannot efficiently utilize the multiple-access dimensions arising from different spreading factors (SF) because the star topology is typically used for LoRa. On the other hand, a multi-hop LoRa network has the potential to realize extensive network coverage by utilizing packet relaying and improving the network capacity by utilizing different SFs. We evaluated the LoRa receiver performance under co-technology interference via simulation and experiments to realize these potentials. The results show that LoRa can survive interference from time-synchronized packets transmitted by multiple transmitters with an identical SF. Furthermore, we examined the orthogonality between different SFs by evaluating the required signal-to-interference ratio (SIR). Finally, we demonstrated the possibility of employing different SFs to construct the pipeline in a multi-hop relay network to increase network efficiency.

For industrial robotic applications, conveyor tracking is one of fundamental function in the robot manipulator. While the target is moving on the production line, the task becomes sophisticated problems. Thus, a distinct grasping method under visual control system is definitely one of the essential solutions. In this paper, we propose a tracking strategy on moving objects for a robot arm object fetching system combined with distinct recognition algorithm. In addition, the grasping pose of robot arm is corrected by visual feedback system. The system is separated into two parts and discussed in detail. Each part owns its core algorithm to complete industrial tracking and fetching tasks. Because of limitation from the environment, the working conditions will also be illustrated. Eye to hand and eye in hand both contribute to the visual feedback system. Grasping pose for each type of workpiece is adjusted by tracking and optimization algorithms. The result of object recognition is enhanced by visual system in determined pose and orientation. All experimental results were completed by a 7-DoFs robot arm developed in our lab at NTU.

This paper proposes to adopt concurrent trans- mission in a distributed antenna system to achieve the real- time capability and reliability for wireless automation systems. Our scheme is the simplest way to realize spatial diversity by deploying a large number, e.g. several tens, of transmit antennas and allow all of them to participate in simultaneous packet transmission without any cooperation. We examine the performance, including packet error rate and high- reliability area percentage, in simulation and over-the-air experiments under the IEEE 802.15.4 standard, where the experiments are conducted with up to 32 concurrent transmitters using Tmote Sky sensor nodes. We found that the presence of a timing offset limits the performance. By lowering the timing offset to be below half of a chip period, the reliable performance can be achieved without sacrificing the real-time capability.

Real-time and robust communication is essential for wireless control systems (WCS). Preambles are considered as significant communication overheads in WCS where payloads are typically small. To shorten the overhead in OFDM systems, previous works have considered fixed subcarrier sampling to obtain subcarrier-fixed short preambles (SFSP) and adopted frequency-direction interpolation (FDI) for channel estimation. Despite of advantage in fast fading channel, it results in poor performance in frequency-selective fading channel. In this work, we propose a subcarrier-selectable short preamble (SSSP) which provides full sampling coverage of all subcarriers with several preamble transmissions. By exploiting the periodicity of transmissions in WCS, the SSSP scheme obtains the channel estimation of non-selected subcarriers by not only FDI but also the time-direction extrapolation (TDE), which is robust in frequency-selective fading. In addition, in order to make the channel estimation robust in both fast fading and frequency-selective fading we adopt an adaptive algorithm altering between FDI or TDE mode. The feasibility of the proposed method is validated by evaluating symbol error rate (SER) in fast frequency-selective fading. Simulation results verify that unlike the SFSP the adaptive SSSP scheme shows no error floor in SER curve when the channel is frequency-selective fading, and performs similar to the SFSP scheme when the channel is fast fading.

Many works attributed the successful reception of concurrent transmission (CT) to the constructive interference. However, due to the inevitable carrier frequency offset (CFO) and the resulted beating effect, the claim of constructive interference is actually not valid. To clarify the reason behind the successful receptions under CT, we conduct extensive evaluations and identify the following findings. 1) We show that the IEEE 802.15.4 receivers survive the beating effect mainly because of the direct sequence spread spectrum (DSSS), while systems without the protection of DSSS are not applicable to CT. 2) We identify a counterintuitive phenomenon that the IEEE 802.15.4 receiver could survive only the beating results from large CFO, while performing poorly when CFO is small. 3) We demonstrate that, even if the receivers survive, CT links lead to little performance improvements compared to conventional signal transmission links from the SNR point of view.

Many researches have shown that concurrent transmission (CT) helps to improve the energy efficiency and latency of 2.4GHz IEEE-802.15.4-based multi-hop networks. However, it has been shown that the success of CT in IEEE 802.15.4 is mainly due to the DSSS. In view of the great potential of long range sub-GHz technologies for future smart meter applications, we assess the feasibility of applying CT to non-DSSS sub-GHz receivers. In this work, we evaluate the FSK-based receiver performance in the critical case - the scenario that concurrent transmitted signals are received with the same power such so the mutual interference become worst. Our evaluations are based on the 2-FSK mode of TI CC1120 chips. The results show that the basic 2-FSK mode is vulnerable to CT. On the other hand, if the FEC and the interleaver are adopted, the receiver can survive in the heavy interfering region as long as the timing offset is smaller than 1 μs and the CFO is larger than 5 KHz.

This paper presents an RSSI-based packet combining (PC) scheme to improve the packet reception reliability affected by a beat interference in wireless sensor networks (WSN) using concurrent transmission (CT). To overcome the beat problem, our PC scheme exploits multiple receptions to perform simple post-detection selection combining based on RSSI values. An implementation verifies its feasibility in resource-limited sensor nodes with time-sensitive CT. Evaluations using computer simulations and hardware experiments show significant reliability improvement.

Spectrally efficient multiple access technologies, such as Multi-User Multiple-Input-Multiple-Output (MU-MIMO) system and Non-Orthogonal Multiple Access (NOMA), are the key enablers for the next generation communication systems to accommodate tremendous devices. Combining NOMA in MU-MIMO systems (NOMA-MIMO) is expected to boost the spectral efficiency even further. However, in order to solve the Inter-Antenna-Interference (IAI) and the Inter-Cluster-Interference (ICI) resulted from multiple-antenna and non-orthogonal transmissions, computation-intensive interference cancellation schemes are usually required in the receivers, which prohibit the employment of NOMA-MIMO system in systems with simple receivers, such as sensor networks. In this work, we propose a non-linear pre-coding method for two-cluster NOMA-MIMO systems that allows simple receiver implementation with only one antenna. Our main contribution is twofold: first, we adopt IAI-oriented pre-coding to spare the receiver from IAI cancellation; second, we propose to regulate the conventionally unsolvable IAI-corrupted ICI onto lattice points, so that the ICI can be removed by simple modulo operations instead of computational-intensive Successive Interference Cancellation (SIC) schemes. The ergodic sum capacity and whole system bit-error-rate (BER) performance are provided to show the validity of the proposed approach.

Cost down and energy saving are concerned issues in recent years. As a result, cloud computing services for enterprises and persons have been increasing. As for cloud Infrastructure-as-a Service (IaaS), virtual machines (VM) in "cloud" are also starting to replace the original local hosts commonly. Meeting consumers' IaaS requirements with different computing powers, different operating systems, and different quantities in a fast and on-demand fashion has become an important issue for cloud service providers. For Chunghwa Telecom's IaaS service, branded "hicloud", we propose a novel mechanism for rapid provisioning a variety of virtual machines. We illustrate the end-to-end IaaS fulfillment process, kernel VM Pool Management and multi-threading VM activation mechanism for fast VM provisioning in this paper in detail.

This paper introduces a new framework of the multiple-input multiple-output (MIMO) detection in iterative receivers. Unlike the conventional methods processing with symbol lattice, we consider the delta symbol lattice, i.e., the difference between two arbitrary points in the symbol lattice. The inherent flexible, symmetric, and sparse properties of the delta lattice enhance the detection in both complexity and performance aspects. Consequently, we propose a delta-list MIMO (DL-MIMO) detection which separately exploits the channel information and the a priori information so that a soft-input soft-output sphere decoder is dispensable. Simulation results demonstrate this hardware-friendly DL-MIMO detection delivers nearly-optimal performance at affordable cost in a practical scenario.

Using the Schnorr-Euchner (SE) order for soft-input sphere decoders is inefficient for implementation, because it requires exhaustive calculation and sorting of partial metrics of all constellation points. Instead, low-complexity methods can be applied by separating the partial metric into channel information and a priori information and solely enumerating based on one of them. With such an orthogonalization, this paper presents an algorithm that effectively combines these two enumerations to deliver an order close to the SE one. Mathematical analyses and simulation results demonstrate that this is the first algorithm allowing for a low-complexity implementation with optimal error rate performance for any number of iterations.

OFDM systems suffer severe performance degradation in the presence of IQ imbalance and phase noise. This paper provides a new IQ imbalance estimation scheme that works under phase noise effect and multi-path channel with large delay spread. Furthermore, the proposed method can suppress the interference from neighboring subcarriers caused by phase noise. The proposed scheme significantly mitigates analog front-end impairments and eases their specifications, which in turn lowers the cost of OFDM transceivers.

This paper presents the algorithm and hardware implementation of a low hardware complexity Rayleigh faders designed for real-time baseband MIMO channel emulation. This novel Rayleigh fader model achieves extremely low hardware complexity through a new mathematical model and extensive hardware sharing.

This paper presents the implementation of a reconfigurable real-time digital baseband MIMO channel emulator with flexible user interface. The emulator implements several transceiver impairments and a wireless correlated MIMO channel with the help of a novel low-complexity Rayleigh fader design. The rich set of emulated effects and high emulation speed make the proposed system very useful in MIMO baseband transceiver development.