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Telecom operators are under pressure to provide more spectrum resources to meet the increasing demand for high-throughput mobile communications. To achieve this, they have focused on unlicensed frequency bands, but the coexistence of 5G signals with other communication systems on these bands poses a challenge. To address this, beamforming technology has been introduced to reduce interference in space and enable independent demodulation of 5G and Wi-Fi signals. This paper implements a 5G base station (BS) prototype with an eight-antenna beamforming hardware transmitter, which concentrates the transmitted energy on individual 5G receivers while reducing the signal’s impact on Wi-Fi receivers. Angle of arrival estimation and power control mechanisms are also integrated to enhance the efficiency of the solution. To verify the system coexistence, software-defined radio is used to realize 5G and Wi-Fi receivers. The proposed solution is demonstrated via over-the-air experiments to perform reliable transmission to multiple 5G receivers without interrupting Wi-Fi traffic on the same frequency band. The beamformer can also adjust its spatial profile and power level through environment-sensing functions built into the BS prototype. The proposed power control method delivers improved 5G transmitter and Wi-Fi transmitter energy performance by 50% and 51%, respectively.

Massive Machine-type Communications (mMTCs) is a major use case for the 5G standard. The grant-free (GF) sparse-coded multiple access (SCMA) transmission is particularly spectrum efficient in the sporadic uplink traffic, which is characteristic of the mMTC networks. In this paper, an uplink GF-SCMA receiver with a user activity detection (UAD) function was designed and implemented. In particular, several new techniques were proposed to enhance the SCMA decoder performance; they include delayed serial update, early stopping, message passing algorithm equation reformulation, distance approximation, and sum circuit sharing. To meet the real-time operation requirements, we implemented key inner receiver function circuits, such as carrier frequency synchronization, user signature detection, channel estimation and compensation, soft SCMA detection, etc. on a Xilinx KCU1500 FPGA chip. Finally, an over-the-air (OTA) prototype has been constructed, demonstrating the efficient and reliable multi-user GF-SCMA uplink transmission of the proposed system.

Abstract Latest simultaneous multi-slice (SMS) methods greatly benefit MR efficiency for recent studies using parallel imaging technique. However, these methods are limited by the requirement of array coils. The proposed Coherent Wideband method, which employs an extended field of view to separate multiple excited slices, can be applied to any existing MRI instrument, even those without array coils. In this study, the Coherent Wideband echo-planar imaging method was implemented on 7 T animal MRI to exhibit comprehensive enhancements in neuro-architecture, including diffusion tensor imaging (DTI) and functional MR studies (fMRI). Under the same scan time, the time-saving effect can be manipulated to increase the number of averages for DTI SNR improvement, reducing fractional anisotropy difference by 56.9% (from 0.072 to 0.041) and the deviation angle by 64% (from 25.3° to 16.2°). In summary, Coherent Wideband Echo Planar Imaging (EPI) will provide faster, higher resolution, thinner slice, or higher SNR imaging for precision neuro-architecture studies.

Massive machine type communications (mMTC) is one of the three major scenarios in 5G wireless networks. mMTC is an uplink-dominant scenario that supports massive connectivity of small-size packets and sporadic traffic. To meet the requirement of mMTC, non-orthogonal multiple access (NOMA) with grant-free transmission is considered a promising technology because of its higher spectrum efficiency and lower signaling overhead. Request-and-grant-based scheduling process is eliminated in grant-free transmission and thus the base stations need to identify active users first before data detection. Previously, several user activity detection (UAD) algorithms were proposed and they can obtain good performance in flat-fading channels. However, the performance of these works degrades significantly in doubly selective fading channels. In this work, we propose an effective solution for uplink grant-free NOMA with a new user sequence scheme and a novel UAD algorithm suitable for practical channel scenarios. Simulation results validated that the proposed sequences can mitigate the inter-user interference at the base stations, and the proposed UAD algorithm can achieve better detection accuracy. Moreover, detailed complexity analysis showed that the proposed UAD algorithm has relatively low complexity and good scalability.

Mobile devices nowadays have penetrated our daily life and they play a big role in our social, professional, and recreational activities. In order to satisfy the booming demands for mobile communications from their customers, the telecommunication service providers work very hard to secure more spectrum and construct more base-stations. As such, they have looked into unlicensed spectrum for possible deployment of their mobile services. Toward this end, this paper presents a time-domain interference cancellation (TDIC) receiver technique that can enhance the efficiency of mobile communication networks coexisting with Wi-Fi traffic in the unlicensed bands. Moreover, transmitter power control and novel channel estimation are proposed to optimize the overall throughput of the fourth-generation mobile communication networks operating in the unlicensed bands (LTE-U). We further show by simulation and by over-the-air (OTA) real-time demonstration that the proposed solution indeed can achieve reliable reception of LTE-U signals under Wi-Fi interferences with different power levels.

In this paper, we analyzed the error rate of the sphere decoders with reduced search space (SD-RSS) and proposed a formula for estimating their error rate. With the instantaneous error rate information, an adaptive SD-RSSwas designed that could adjust the search space on-the-fly to minimize the complexity while meeting the error rate requirement specified by the standard. We focused on the ultradense network with severe inter-cell interference, which increases the detection complexity and complicates the error rate analysis. The accuracy of the error rate performance estimation was demonstrated by several simulations, and one numerical example was presented to show that the proposed adaptive SD-RSS can significantly reduce its average computational complexity while meeting the LTE block error rate requirement.

Abstract This paper presents an energy-efficient wireless ad hoc communication system and baseband transceiver for sensor networks that gather vital sign information of patients. The design of the proposed system is aimed to facilitate an energy-efficient and low-latency vital sign data transmission service. Based on this aim, the proposed system adopts multi-hop transmission and joint transmitter-receiver beamforming technique to efficiently transmit data at significantly reduced transmission power. Furthermore, to shorten the transmission latency and reduce channel contention, we proposed a novel Medium Access Control (MAC) mechanism which includes neighborhood discovery, packet collision detection and prioritized transmission scheme based on an Orthogonal Frequency Division Multiple Access (OFDMA) physical layer. Simulation of transmission power, transmission latency, and data rate, together with proposed hardware architecture, were all carried out to verify the effectiveness and feasibility of the proposed system.