Journal of Communications and Information Networks
Print ISSN 2096-1081 CN 10-1375/TN
Editor-in-Chief: Wei Zhang
The wide spectrum and propagation characteristics over the air give mmWave communication unique advantages as well as design challenges for 5G applications. To increase the system speed, capacity, and coverage, there is a need for innovation in the RF system architecture, circuit, antenna, and package in terms of implementation opportunities and constraints. The discuss mmWave spectrum characteristics, circuits, RF system architecture, and their implementation issues are discussed. Moreover, the transmitter key components, i. e. , the receiver, antenna, and packaging are reviewed.
Recent rapid developments in 4G wireless communication have been motivated by breakthroughs in air interface technology, exemplified by the replacement of WCDMA (Wideband Code Division Multiple Access) with OFDM (Orthogonal Frequency-division Multiplexing). Although the protocol to adopt for 5G HF (High-Frequency) wireless communication—including such matters as waveform, network deployment, and frequency range—has been a controversial issue for a number of years, a common view is that there is a large gap between the rapidly increasing requirements pertaining to traffic capacity and the capabilities of current LTE (Long Term Evolution) networks in terms of spectral and power efficiency. A number of technical challenges need to be overcome in order to bridge this gap. In this paper, by briefly reviewing progress in HF technology, we summarize technical challenges ranging from propagation attenuation and the implementation of circuit devices, to signal processing and the Ka-band to offer feasible reflection on the forthcoming technological revolution.
Although large-scale MIMO can offer a high spectral efficie ncy, there are a number of difficulties in its implementation. Among those, the computational complexity of MIMO detection is crucial and may limit its use at devices of limited computing power such as users’ mobile devices. Random sampling for large-scale MIMO detection of low complexity were studied. In particular, a MMSE approach for random sampling, was formulated from which an iterative detector can be derived for better performances.
The large bandwidth available with mmWave (millimeter Wave) makes it a promising candidate for 5th generation cellular networks. Proper channel estimation algorithms must be developed to enable beamforming in mmWave systems. In this paper, we propose an adaptive channel estimation algorithm that exploits the poor scattering nature of the mmWave channel and adjusts the training overhead adaptively with the change of channel quality for mmWave cellular systems. First, we use a short training sequence to estimate the channel parameters based on the two-dimensional discrete Fourier transform method. Then, we design a feedback scheme to adjust the length of the training sequence under the premise of ensuring the accuracy of the channel estimation. The key threshold in the feedback scheme is derived and its influence on the accuracy of the estimation results is analyzed. Simulation results confirm that the proposed algorithm can adjust the length of the training sequence adaptively according to the current channel condition maintaining a stable estimation accuracy.
A fully integrated 60-GHz transceiver for 802. 11ad applications with superior performance in a 90-nm CMOS process versus prior arts is proposed and real based on a field-circuit co-design methodology. The reported transceiver monolithically integrates a receiver, transmitter, PLL(Phase-Locked Loop) synthesizer, and LO (Local Oscillator) path based on a sliding-IF architecture. The transceiver supports up to a 16QAM modulation scheme and a data rate of 6 Gbit/s per channel, with an EVM (Error Vector Magnitude) of lower than ?20 dB. The receiver path achieves a configurable conversion gain of 36~64 dB and a noise figure of 7. 1 dB over 57~64 GHz, while consuming only 177 mW of power. The transmitter achieves a conversion gain of roughly 26 dB, with an output P1dBof 8 dBm and a saturated output power of over 10 dBm, consuming 252 mW of power from a 1. 2-V supply. The LO path is composed of a 24-GHz PLL, doubler, and a divider chain, as well as an LO distribution network. In closed-loop operation mode, the PLL exhibits an integrated phase error of 3. 3o rms (from 100 kHz to 100 MHz) over prescribed frequency bands, and a total power dissipation of only 26 mW. All measured results are rigorously loyal to the simulation.
To meet the ever growing traffic in mobile communication, mmWave (millimeter-Wave) frequency bands have gained considerable attention for having a greater amount of bandwidth available than the current cellular spectrum below 3 GHz. Several test systems have been reported on recently to validate the possibility of mmWave links in mobile scenarios. However, there still exist practical issues to enable the application of mmWave in mobile communication, including reliability and cost. In this article, we present some new designs that address these issues, where system architecture, transceiver architecture, and related issues such as circuits and antenna arrays are considered. Hypercellular architecture is applied in mmWave mobile networks to overcome blockage problems, and a Butler-matrix-based HBF (Hybrid Beamforming) architecture is considered in an mmWave link. Simulations and experimental results are presented to validate the effectiveness of the Butler-matrix-based system.
A GRA-BKP (Grey Relational Analysis-Bounded Knapsack Problem) scheme was proposed for the radio resource management of the 5G networks. It consists of two steps, access selection and admission control. The former step was executed via GRA, whereas the latter problem was formulated as a bounded knapsack problem. Accordingly, an optimal solution of the BKP was given for access selection a greedy algorithm, GRA-Greedy, was proposed for admission control. The simulation results show that the GRA-BKP scheme can effectively increase system profit and decrease the drop-ping probability compared with the existing scheme. In addition, GRA-Greedy achieves comparable perform-ance with the optimal solution GRA-DP, but its computational complexity is much lower than that of the latter.
Nowadays, the increase amounts of mobile data has resulted in great demand on existing communication networks. The millimeter-wave band offers large bandwidths to be exploited, which eases the spectrum crunch for bands below 3 GHz. In order to mitigate the path loss from high frequencies, a large antenna array and beamforming technology are adopted to increase the link gain. However, a challenge arises from the new band. Given the order of gigahertz bandwidth and the high sampling rate, the high-resolution ADC (Analog-to-Digital Converter) used in the large array creates a power consumption bottleneck. One solution is to use a low-resolution ADC to replace the full-precision ADC. In this paper, we propose a mixed LMS (Least Mean Square) receiver beamforming method for a millimeter-wave one-bit antenna array. We first use a grid-based approach to roughly estimate the DOA (Direction of Arrival) of the incoming signal. Then, we use the steering vector for the DOA as an initial value for the LMS method. A simulation shows that our proposed mixed LMS receiver beamforming method for the onebit antenna array attains a performance level near the optimal one that obtained with an accurate DOA. The radiation pattern of the mixed LMS method almost overlaps the pattern for the accurate DOA, and the spectral efficiency of the mixed LMS method reach up with that obtained from accurate DOA. Furthermore, owing to the use of initial values from rough DOA estimation, the mixed LMS method has a fast convergence.
The millimeter-wave frequency band (30~300 GHz) has received significant attention. Millimeter-wave frequencies have been used for backhaul, cell communication, and other high speed communication. With the advent of 5G communication, millimeter-wave frequencies such as 60-GHz band have been attracting attention as possible candidate for next-generation wireless networks. The traditional application for 60-GHz band is point-to-point communication. Some typical scenarios have been cited in a recent 5G white paper. There exist some traditional channel models for 3G and 4G communication. However, 5G has a new channel model (the outdoor-to indoor channel model, or O2I) that has not been clearly studied. Some conventional channel measurements have been conducted for this new band. Two measurement systems in the 60-GHz band for penetration loss and small-scale measurement for different scenarios are presented. By analyzing our measurement data, we can prove that the O2I channel does not generate new paths and only add some material penetration loss.
Traditional mobile communication systems mainly work on the licensed frequency band near or below 3 GHz; however, this band is becoming increasingly crowded. On the other hand, there are abundant unlicensed spectrum resources in higher frequency bands, e. g. , 6 GHz, 15 GHz, and 28 GHz, and if those bands are applied, the current spectrum shortage problem could be effectively alleviated. However, the wireless channel characteristics and models are important but still unknown, and thus in this study, extensive measurements and modeling have been conducted to study the characteristics of the high-frequency 15-GHz band. Specifically, a PN(Pseudo Noise) sequence based time-domain measurement system was built and applied to measure the propagation characteristics of the LOS (Line-of-Sight) and NLOS (Non-Line-of-Sight ) scenarios in an indoor corridor at 15 GHz. Then, in-depth analysis and modeling on the large-scale characteristics of wireless channels, the relationship between distance and path loss, the path loss exponent, and the shadow fading standard variance are provided. Moreover, the relationship between received power and different elevation angles was studied. In the measurement, two 25-dBi horn antennas with a 10 half-power beam width are used to change elevation angles in the transmitting terminal and azimuth angles in the receiving terminal for all measurement points. The findings and results in this work will serve as a reference and basis for future theoretical studies of the 15-GHz band.
Test results for a 10-Gbps prototype demonstrator working at 71~76 GHz frequency band with a 2-bit/s/Hz spectral efficiency are reported. To overcome the speed limitation of the commercial DA/ADs, a two-channel analog IF multiplexing and demultiplexing topology is adopted as a trade-off between cost and spectrum efficiency. The same approach is also used to achieve up to 20 Gbps with a full 10-GHz bandwidth of the allocated commercial bands (71~76 GHz and 81~86 GHz).
The rapid boosting in mobile traffic and the scarcity of available radio spectrum have hindered the improvement of capacity in cellular networks. It is necessary to discover an appropriate coexistence between cellular and other radio access technologies (mainly Wi-Fi) to offload the high traffic on to unlicensed bands. Dealing with joint time and power allocation to devices, a non-convex problem is modeled to maximize the throughput as well as guarantee the desired user satisfaction. A two-step traffic balancing scheme is proposed to derive the solution. We also focus on the inner competition among cellular users instead of traditional competition between cellular and Wi-Fi in the unlicensed bands. Finally, simulation results show the effectiveness of the proposed two-step traffic balancing scheme.
