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Openmili: a 60 Ghz Software Radio Platform with a Reconfigurable

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Openmili: a 60 Ghz Software Radio Platform with a Reconfigurable OpenMili: A 60 GHz Software Radio Platform With a Reconfigurable Phased-Array Antenna Jialiang Zhang, Xinyu Zhang, Pushkar Kulkarni and Parameswaran Ramanathan Department of Electrical and Computer Engineering University of Wisconsin-Madison {jialiang.zhang, xyzhang}@ece.wisc.edu, {pkulkarni, parmesh.ramanathan}@wisc.edu ABSTRACT source, spanning 57 GHz to 64 GHz in many countries, en- The 60 GHz wireless technology holds great potential for ables multi-Gpbs data rate. The small wavelength (∼ 5mm) multi-Gbps communications and high-precision radio sens- enables miniature antenna-arrays that can form highly direc- ing. But the lack of an accessible experimental platform has tional \pencil beams" to boost link quality and spatial reuse. been impeding its progress. In this paper, we overcome the mmWave is thus considered as an enabling technology for barrier with OpenMili, a reconfigurable 60 GHz radio archi- 5G wireless broadband [1]. Recent commercialization of 60 tecture. OpenMili builds from off-the-shelf FPGA processor, GHz devices (e.g., by Qualcomm [2] and Intel [3]) also trig- data converters and 60 GHz RF front-end. It employs cus- gers low-cost mmWave sensing applications, which used to tomized clocking, channelization and interfacing modules, to be available only in dedicated environment for medical/se- achieve Gsps sampling bandwidth, Gbps wireless bit-rate, curity inspection. Together, short wavelength and high di- and Gsps sample streaming from/to a PC host. It also in- rectionality translates into high sensitivity, enabling subtle corporates the first programmable, electronically steerable object localization/tracking [4], vital-sign detection and mo- 60 GHz phased-array antenna. OpenMili adopts program- bile mmWave imaging [5]. ming models that ease development, through automatic par- Realizing the vision of mmWave networking and sensing allelization inside signal processing blocks, and modular, necessitates a reconfigurable experimental platform that al- rate-insensitive interfaces across blocks. It provides com- lows prototyping before the protocols/applications are de- mon reference designs to bootstrap the development of new ployed. Ideally, one would need a mmWave software-radio network protocols and sensing applications. We verify the platform that allows reconfiguration from the PHY layer up effectiveness of OpenMili through benchmark communica- to applications, can transmit customized waveforms and ac- tion/sensing experiments, and showcase its usage by proto- quire RSS/phase information for sensing applications [4, 6{ typing a pairwise phased-array localization scheme, and a 8]. On the 2.4 GHz and 5 GHz microwave spectrum, coun- learning-assisted real-time beam adaptation protocol. terpart devices such as USRP [9], WARP [10] and Sora [11] have reshaped the landscape of wireless experimentation in the past decade, speeding up the ratification of next- CCS Concepts generation wireless standards (e.g., 802.11ax [12]) and sens- •Networks ! Network experimentation; Programming in- ing appliances [13]. However, to our knowledge, there exists terfaces; •Hardware ! Digital signal processing; •Computer no reconfigurable platform that can capture the unique fea- systems organization ! Reconfigurable computing; tures of 60 GHz wireless systems, particularly the Gsps sam- pling bandwidth and electronically steerable phased-array antennas. Keywords In this paper, we propose OpenMili, an open-access 60 60 GHz, Millimeter-wave, Software radio, Testbed, Experi- GHz software-radio, which fills the gap and opens up new mental platform directions for mmWave sensing and protocol development. OpenMili has a software-defined mmWave network stack spanning PHY layer signal processing to applications. It 1. INTRODUCTION can also act as a programmable 60 GHz radio sensor with a The unlicensed millimeter-wave (mmWave) spectrum around custom-built phased-array. From the hardware architecture the 60 GHz frequency promises a blueprint of wireless net- perspective, OpenMili integrates off-the-shelf baseband pro- working at wire-speed. The vast amount of spectrum re- cessing unit (BPU), ADC/DAC and 60 GHz RF front-end (frequency up/down-converters), and develops a signal chain Permission to make digital or hard copies of all or part of this work for personal or to enable Gsps of sampling bandwidth. It allows flexible classroom use is granted without fee provided that copies are not made or distributed channelization and reclocks the 60 GHz front-end to over- for profit or commercial advantage and that copies bear this notice and the full cita- tion on the first page. Copyrights for components of this work owned by others than come its inherent phase-noise problem. OpenMili's base- ACM must be honored. Abstracting with credit is permitted. To copy otherwise, or re- band processing unit (BPU) centers around a Kintex Ultra- publish, to post on servers or to redistribute to lists, requires prior specific permission Scale FPGA, and uses a customized PCIe module to realize and/or a fee. Request permissions from [email protected]. 1 Gsps real-time sample streaming from/to a PC host. The MobiCom’16, October 03-07, 2016, New York City, NY, USA PC host can reconfigure/monitor the RF front-end and sig- c 2016 ACM. ISBN 978-1-4503-4226-1/16/10. $15.00 nal processing modules in real-time. OpenMili's most out- DOI: http://dx.doi.org/10.1145/2973750.2973760 standing feature is a reconfigurable phased-array antenna Beam Direction Antenna that can switch between 16 beam patterns at µs granularity, Matlab/C Microblaze JESD Controller MCS under the control of the BPU. We design the phased-array Application CSI 204B User PCI-e PCIE AXI BB RF Phased specifically to fit the WR-15 waveguide (a standard antenna API Gen3 AXI DSP AXI DAC TX Kernel x8 DMA JESD204B Array interface on 60 GHz radios), ensuring it can retrofit both Block Driver Bridge ADC RX Ant. OpenMili's RF front-end and other commercial mmWave Engine radios that are typically equipped with WR-15 horn anten- FMC PEM Linux Host KCU105 FPGA Board DAQ2 003 nas [14]. From the software architecture perspective, OpenMili takes Figure 1: OpenMili's hardware architecture. advantage of the massive parallelization on the FPGA to en- able Gsps sample processing. It eases prototyping by using C++ to define signal processing blocks, and using AXI [15] as inter-block gluing mechanism, which facilitates modular- ity and eliminates the need for inter-block rate matching| a well-known headache in FPGA programming. We choose this programming model also because the complexity of intra- block parallelization can be hidden from application develop- (a) ers, although coarse-grained inter-block parallelization still need to be explicitly expressed. OpenMili provides three reference designs which we be- lieve to capture the unique aspects of mmWave and can be instrumental for a wide range of 60 GHz network pro- tocols and wireless sensing applications [4, 6{8]. (i) Gbps baseband communication module: allowing a wide range of network protocol development on the FPGA or PC host; (b) (c) (d) (ii) Real-time RSS/phase sensing: using an 802.11ad-like Figure 2: Portrait of OpenMili: (a) Overall archi- preamble to sense the channel state information (CSI), with tecture; (b) Baseband processing uint (BPU); (c) around 300K CSI readings per second across 1 GHz band- Receiver with phased array antenna; (d) Transmit- width, enabling many real-time sensing applications [8]. (iii) ter without mounting antenna. Real-time phased-array controller: allowing 16 beamforming patterns based on a discrete codebook. Codebook entry se- ware framework and common interfaces to enable the devel- lection is made in real-time on a Microblaze processor, pro- opment of new mmWave communication and sensing appli- grammable in C. This module can also access the real-time cations. This contribution breaks down into the following CSI statistics, allowing beam adaptation based on channel aspects: conditions. (i) Hardware architecture (Sec. 2 and 4): We develop the To showcase the use of OpenMili in prototyping 60 GHz first 60 GHz reconfigurable radio architecture that achieves systems, we propose and implement two new 60 GHz lo- Gsps sampling bandwidth, Gbps wireless bit-rate, and Gsps cation sensing and beamforming adaptation mechanisms, real-time sample streaming from/to a PC host. The hard- which are of independent interest. (i) Pairwise relative local- ware architecture builds on customized clocking, channeliza- ization of phased-arrays. Many recent systems have used 2.4 tion and interfacing modules. Most remarkably, it incorpo- GHz phased-arrays [16,17] for angle-of-arrival (AoA) estima- rates the first programmable 60 GHz phased-array design. tion, but they need multiple phased-arrays to triangulate a (ii) Software framework (Sec. 3): We explore FPGA pro- target radio, and they assume the phase-shift values are con- gramming models that ease development, through automatic tinuously adjustable, which is not applicable to practical 60 parallelization inside signal processing blocks, and modular, GHz phased-arrays that use hard-wired phase-shifters. We rate-insensitive interfaces across blocks. We also provide propose a simple algorithm that leverages the discrete phase- reference designs to bootstrap the development of protocols shifting to estimate the AoA as well as distance between and sensing applications, featuring the Gbps communica- a pair of phased-arrays, enabling pairwise localization in- tions and beam steering capabilities of 60 GHz radios. stead of triangulation.
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