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Millimeter-Wave Links and Wireless Fiber

Mobile data traffic is going through a period of exponential growth, nearly doubling between 2013 and 2014 and expected to increase 13x by 2019. This is largely fueled by a rapid rate of new subscriptions of smartphones and tablet PCs, as well as by new mobile applications in gaming, entertainment and video transfer. To accommodate the increase in data traffic, projections show that network capacity must grow by at least 1000x in the next 10 years. In this context, we are investigating high-capacity wireless mm-wave links.

Our wireless mm-wave efforts are focused on designing the next generation of extremely-high-throughput wireless links, termed “fiber over wireless”, which can be employed in dense small cell networks. To exploit spectral and spatial degrees of freedom in a line of sight channel, we are revisiting the stack, initially focusing on the design of technologies in the >100GHz bands for large and scalable arrays, and next, through collaborations, moving to system design and architecture solutions.

We have examined the capabilities of transmitter chips, antennas, and RF packages operating at >100GHz [1]. On the system‐level design front, we are focusing on architectural and system solutions using silicon-based hardware that allow a combination of beamforming, diversity, spatial multiplexing, and space division multiple access gains tailored to the unique characteristics of the mm-wave outdoor channel.

In particular, we have designed and implemented point-to-point links based on energy efficient simple modulation schemes and narrow radiation beams for spatial multiplexing for short range applications [2]. To further increase the capacity for even longer ranges (100s of meters), we have investigated the design of a Line-of-Sight (LoS) MIMO link operating at mm-wave frequencies beyond 100 GHz, with four-fold spatial multiplexing and a bandwidth of 10-20 GHz, which holds the potential for data rates from 80-160 Gbps. In addition to the spatial processing required for demultiplexing at the receiver, even small misalignments lead to frequency selectivity. We therefore have examined the performance of a conventional all-digital space-time equalizer (STE) architecture for overcoming misalignments in the channel. Moreover, we have looked into hardware-signal processing co-design in this setting, bearing in mind the difficulty of analog-to-digital conversion at high sampling rates [3-4].

(a) "Wireless fiber," outdoor mesh & backhaul; (b) mm-wave transmitter realized by array of high-EIRP antenna-in-package elements.

Analog channel separation network allowing efficient MIMO processing.

[1] N. Saiz, N. Dolatsha, and A. Arbabian, "A 135GHz SiGe Transmitter and Dielectric Rod Antenna-in-Package for High EIRP/Channel Arrays", Proc. 2014 IEEE Cust. Int. Circuits Conf., San Jose, CA, 2014.

[2] N. Dolatsha, B. Grave, M. Sawaby, C. Chen, A. Babveyh, S. Kananian, A. Bisognin, C. Luxey, F. Gianesello, J. Costa, C. Fernandes, and A. Arbabian, "A Compact 130 GHz Fully-Packaged Point-to-Point Wireless System with 3D-Printed 26dBi Lens Antenna Achieving 12.5Gbps at 1.55 pJ/bit/meter," Proc. 2017 IEEE Int. Solid-State Circuits Conf., San Francisco, CA, 2017, pp. 306-307.

[3] B. Mamandipoor, M. Sawaby, A. Arbabian, and U. Madhow, "Hardware-Constrained Signal Processing for mm-Wave LoS MIMO," Proc. 49th Asilomar Conf. Sig. Syst. Comp., Pacific Grove, CA, 2015, pp. 1427-1431. (Invited Paper)

[4] M. Sawaby, B. Mamandipoor, U. Madhow, and A. Arbabian, "Analog Processing to Enable Scalable High-Throughput mm-Wave Wireless Fiber Systems," Proc. 50th Asilomar Conf. Sig. Syst. Comp., Pacific Grove, CA, 2016, pp. 1658-1662. (Invited Paper)