Wireless Network-on-Chip (WNoC) appears as a promising alternative to conventional interconnect fabrics for chip-scale communications. WNoC takes advantage of an overlaid network composed by a set of millimeter-wave antennas to reduce latency and increase throughput in the communication between cores. Similarly, wireless inter-chip communication has been also proposed to improve the information transfer between processors, memory, and accelerators in multi-chip settings. However, the wireless channel remains largely unknown in both scenarios, especially in the presence of realistic chip packages. This work addresses the issue by accurately modeling flip-chip packages and investigating the propagation both its interior and its surroundings. Through parametric studies, package configurations that minimize path loss are obtained and the trade-offs observed when applying such optimizations are discussed. Single-chip and multi-chip architectures are compared in terms of the path loss exponent, confirming that the amount of bulk silicon found in the pathway between transmitter and receiver is the main determinant of losses.
Matolak suggested that the wireless chip-scale communications would act as a micro-reverberation chamber with met allic walls @cite_28 , although they did not discuss the package. Others have explored a similar scenario over a large PCB board, including DRAM modules and other components within a computer case up to 300 GHz @cite_42 @cite_13 @cite_36 @cite_57 . In @cite_53 , the authors explored waveguide-like millimeter-wave channels within a reconfigurable metamaterial that integrates multiple chips on a PCB. Finally, the 60-GHz channel has been also studied in larger enclosed environments such as printers @cite_23 or data center cabinets @cite_15 , which also act as reverberation chambers. Although these structures may capture the enclosed nature of a chip package, they have substantially different dimensions, materials, and antenna placement restrictions.
@cite_28 @cite_36 @cite_53 @cite_42 @cite_57 @cite_23 @cite_15 @cite_13
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This paper presents the channel measurements performed within a closed met al cabinet at 60 GHz covering the frequency range 57–62 GHz. Two different volumes of an empty met al cupboard are considered to emulate the environment of interest (an industrial machine). Furthermore, we have considered a number of scenarios such as line of sight, non line of sight, and placing absorbers. A statistical channel model is provided to aid short-range wireless link design within such a reflective and confined environment. Based on the measurements, the large- and small-scale parameters are extracted and fitted using the standard log-normal and Saleh–Valenzuela models, respectively. The obtained results are characterized by a very small path loss exponent, a single cluster phenomenon, and a significantly large root-mean-square (RMS) delay spread. The results show that covering a wall with absorber material dramatically reduces the RMS delay spread. Finally, the proposed channel model is validated by comparing the measured channel with a simulated channel, where the simulated channel is generated from the extracted parameters. A millimeter wave (mm-wave) communication system provides multi-Gb s data rates in short-distance transmission. Because millimeter waves have short wavelength, transceivers can be composed of large antenna arrays to alleviate severe signal attenuation. Furthermore, the link performance can be improved by adopting precoding technology in multiple data stream transmission. However, the complexity of radio frequency (RF) chains increases when large antenna arrays are used in mm-wave systems. To reduce the hardware cost, the precoding circuit can be jointly designed in both analog and digital domains to reduce the required number of RF chains. This paper proposes a new method of building the joint RF and baseband precoder that reduces the computation complexity of the original precoder reconstruction algorithm and enables highly parallel hardware architecture. Moreover, the proposed precoder reconstruction algorithm was designed and implemented using TSMC 90-nm UTM CMOS technology. The proposed precoder reconstruction processor supports the transmissions of one to four data streams for 8 × 8 mm-wave multiple-input multiple-output systems. The operating frequency of this chip was 167 MHz, and the power consumption was 243.2 mW when the supply voltage was 1 V. The core area of the postlayout result was about 3.94 mm 2 . The proposed processor achieved 4, 4.9, 6.7, and 6.7 M channel matrices per second in four-, three-, two-, and one-stream modes, respectively. Recent propagation measurements conducted for emerging applications such as vehicle-to-vehicle communications and wireless sensor systems have illustrated that present worst-case channel models are not sufficient to characterize the small-scale propagation effects seen. New theoretical models have thus been proposed but existing emulation environments do not create sufficiently severe channel conditions. In this work we present the design of a compact, reconfigurable channel emulator (CRCE) specifically designed to create Ricean, Rayleigh and hyper-Rayleigh fading environments in a repeatable manner. The bench-top sized chamber leverages concepts seen in reverberation chambers but in addition to a mechanical stirrer varies the multipath environment through the use of multiple antennas. Emulated channels illustrating space-, time- and frequency-selective behaviors are presented. This paper demonstrates the fabrication, characterization, and experimental imaging results of a 62+62 element λ 2-pitch row-column-addressed capacitive micromachined ultrasonic transducer (CMUT) array with integrated apodization. A new fabrication process was used to manufacture a 26.3 mm by 26.3 mm array using five lithography steps. The array includes an integrated apodization, presented in detail in Part I of this paper, which is designed to reduce the amplitude of the ghost echoes that are otherwise prominent for row-column-addressed arrays. Custom front-end electronics were produced with the capability of transmitting and receiving on all elements, and the option of disabling the integrated apodization. The center frequency and -6-dB fractional bandwidth of the array elements were 2.77 ± 0.26 MHz and 102 ± 10 , respectively. The surface transmit pressure at 2.5 MHz was 590 ± 73 kPa, and the sensitivity was 0.299 ± 0.090 V Pa. The nearest neighbor crosstalk level was -23.9 ± 3.7 dB, while the transmit-to-receive-elements crosstalk level was -40.2 ± 3.5 dB. Imaging of a 0.3-mm-diameter steel wire using synthetic transmit focusing with 62 single-element emissions demonstrated axial and lateral FWHMs of 0.71 mm and 1.79 mm (f-number: 1.4), respectively, compared with simulated axial and lateral FWHMs of 0.69 mm and 1.76 mm. The dominant ghost echo was reduced by 15.8 dB in measurements using the integrated apodization compared with the disabled configuration. The effect was reproduced in simulations, showing a ghost echo reduction of 18.9 dB.