BackFi: High Throughput WiFi Backscatter
17 Aug 2015-Vol. 45, Iss: 4, pp 283-296
TL;DR: It is shown that it is possible to design devices and WiFi APs such that the WiFi AP in the process of transmitting data to normal WiFi clients can decode backscatter signals which the devices generate by modulating information on to the ambient WiFi transmission.
Abstract: We present BackFi, a novel communication system that enables high throughput, long range communication between very low power backscatter devices and WiFi APs using ambient WiFi transmissions as the excitation signal. Specifically, we show that it is possible to design devices and WiFi APs such that the WiFi AP in the process of transmitting data to normal WiFi clients can decode backscatter signals which the devices generate by modulating information on to the ambient WiFi transmission. We show via prototypes and experiments that it is possible to achieve communication rates of up to 5 Mbps at a range of 1 m and 1 Mbps at a range of 5 meters. Such performance is an order to three orders of magnitude better than the best known prior WiFi backscatter system [27,25]. BackFi design is energy efficient, as it relies on backscattering alone and needs insignificant power, hence the energy consumed per bit is small.
Citations
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TL;DR: This paper aims to provide a contemporary and comprehensive literature review on fundamentals, applications, challenges, and research efforts/progress of ambient backscatter communications.
Abstract: Recently, ambient backscatter communication has been introduced as a cutting-edge technology which enables smart devices to communicate by utilizing ambient radio frequency (RF) signals without requiring active RF transmission. This technology is especially effective in addressing communication and energy efficiency problems for low-power communications systems such as sensor networks, and thus it is expected to realize numerous Internet-of-Things applications. Therefore, this paper aims to provide a contemporary and comprehensive literature review on fundamentals, applications, challenges, and research efforts/progress of ambient backscatter communications. In particular, we first present fundamentals of backscatter communications and briefly review bistatic backscatter communications systems. Then, the general architecture, advantages, and solutions to address existing issues and limitations of ambient backscatter communications systems are discussed. Additionally, emerging applications of ambient backscatter communications are highlighted. Finally, we outline some open issues and future research directions.
650 citations
Cites background or methods from "BackFi: High Throughput WiFi Backsc..."
...BackFi is different from RFID systems since it reuses ambient signals from the Wi-Fi AP which is already deployed for standard wireless networks....
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...Architecture of the backscatter receiver used in BackFi [79]....
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...In [73], the authors introduce BackFi which offers high bitrate and long-range communication between backscatter sensor transmitters....
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...Nevertheless, the n-QAM modulation is susceptible to noise, thereby resulting in the normalized power loss [79]....
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...Unlike [12], BackFi uses a Wi-Fi AP as an ambient RF source as well as a backscatter receiver....
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TL;DR: A new transmission model is formulated, the data detection algorithm is designed, and two closed-form detection thresholds are derived to approximately achieve the minimum sum bit error rate (BER).
Abstract: Ambient backscatter technology that utilizes the ambient radio frequency signals to enable the communications of battery-free devices has attracted much attention recently. In this paper, we study the problem of signal detection for an ambient backscatter communication system that adopts the differential encoding to eliminate the necessity of channel estimation. Specifically, we formulate a new transmission model, design the data detection algorithm, and derive two closed-form detection thresholds. One threshold is used to approximately achieve the minimum sum bit error rate (BER), while the other yields balanced error probabilities for “0” bit and “1” bit. The corresponding BER expressions are derived to fully characterize the detection performance. In addition, the lower and the upper bounds of BER at high signal-to-noise ratio regions are also examined to simplify a performance analysis. Simulation results are then provided to corroborate the theoretical studies.
362 citations
Cites methods from "BackFi: High Throughput WiFi Backsc..."
...In 2015, full-duplex technology was introduced with WiFi access point (AP) to cooperate with backscatter to enlarge data throughput [16]....
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Proceedings Article•
16 Mar 2016TL;DR: In this paper, the authors present a network stack design that enables passive Wi-Fi transmitters to coexist with other devices in the ISM band, without incurring the power consumption of carrier sense and medium access control operations.
Abstract: Wi-Fi has traditionally been considered a power-consuming communication system and has not been widely adopting in the sensor network and IoT space. We introduce Passive Wi-Fi that demonstrates for the first time that one can generate 802.11b transmissions using backscatter communication, while consuming 3- 4 orders of magnitude lower power than existing Wi-Fi chipsets. Passive Wi-Fi transmissions can be decoded on any Wi-Fi device including routers, mobile phones and tablets. Building on this, we also present a network stack design that enables passive Wi-Fi transmitters to coexist with other devices in the ISM band, without incurring the power consumption of carrier sense and medium access control operations. We build prototype hardware and implement all four 802.11b bit rates on an FPGA platform. Our experimental evaluation shows that passive Wi-Fi transmissions can be decoded on off-the-shelf smartphones and Wi-Fi chipsets over distances of 30-100 feet in various line-of- sight and through-the-wall scenarios. Finally, we design a passive Wi-Fi IC that shows that 1 and 11 Mbps transmissions consume 14.5 and 59.2 µW respectively. This translates to 10000x lower power than existing Wi-Fi chipsets and 1000x lower power than Bluetooth LTE and ZigBee.
298 citations
11 Sep 2017
TL;DR: The first wide-area backscatter system is presented and it is shown that it costs less than a dime at scale and consumes only 9.25 &mgr;W of power, which is more than 1000x lower power than LoRa radio chipsets.
Abstract: The vision of embedding connectivity into billions of everyday objects runs into the reality of existing communication technologies -- there is no existing wireless technology that can provide reliable and long-range communication at tens of microwatts of power as well as cost less than a dime While backscatter is low-power and low-cost, it is known to be limited to short ranges This paper overturns this conventional wisdom about backscatter and presents the first wide-area backscatter system Our design can successfully backscatter from any location between an RF source and receiver, separated by 475 m, while being compatible with commodity LoRa hardware Further, when our backscatter device is co-located with the RF source, the receiver can be as far as 28 km away We deploy our system in a 4,800 ft2 (446 m2) house spread across three floors, a 13,024 ft2 (1210 m2) office area covering 41 rooms, as well as a one-acre (4046 m2) vegetable farm and show that we can achieve reliable coverage, using only a single RF source and receiver We also build a contact lens prototype as well as a flexible epidermal patch device attached to the human skin We show that these devices can reliably backscatter data across a 3,328 ft2 (309 m2) room Finally, we present a design sketch of a LoRa backscatter IC that shows that it costs less than a dime at scale and consumes only 925 mW of power, which is more than 1000x lower power than LoRa radio chipsets
296 citations
Cites background from "BackFi: High Throughput WiFi Backsc..."
...However, existing backscatter solutions such as RFID and Passive Wi-Fi are limited to tens of meters of operating distance in best-case scenarios....
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...Radios includingWi-Fi, Bluetooth and ZigBee operate up to 100s of meters while wide area LoRa and SigFox deployments extend operation to kilometers....
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...Radios including Wi-Fi, BLE, ZigBee, Lora and SigFox all consume between 10 to 500 mW, which is 3–4 orders of magnitude higher than the power consumption of backscatter systems including RFID, Passive Wi-Fi and the LoRa backscatter system....
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...Given the absence of expensive radio analog components including RF oscillators, decoupling capacitors and crystals, backscatter designs including passive RFID and Wi-Fi backscatter [35, 37] cost only a few cents to manufacture at scale [6]....
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...5 m BackFi [52] 1-5 Mbps N/A 5 m (Full Duplex) LoRea [61] 2....
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22 Aug 2016
TL;DR: Frequency-shifted backscatter is practical in typical mobile and static on-body sensing scenarios while only using commodity radios and antennas and can also leverage multiple radios typically present on mobile and wearable devices to construct multi-carrier or multi-receiver scenarios to improve robustness.
Abstract: In this paper, we look at making backscatter practical for ultra-low power on-body sensors by leveraging radios on existing smartphones and wearables (e.g. WiFi and Bluetooth). The difficulty lies in the fact that in order to extract the weak backscattered signal, the system needs to deal with self-interference from the wireless carrier (WiFi or Bluetooth) without relying on built-in capability to cancel or reject the carrier interference. Frequency-shifted backscatter (or FS-Backscatter) is based on a novel idea --- the backscatter tag shifts the carrier signal to an adjacent non-overlapping frequency band (i.e. adjacent WiFi or Bluetooth band) and isolates the spectrum of the backscattered signal from the spectrum of the primary signal to enable more robust decoding. We show that this enables communication of up to 4.8 meters using commercial WiFi and Bluetooth radios as the carrier generator and receiver. We also show that we can support a range of bitrates using packet-level and bit-level decoding methods. We build on this idea and show that we can also leverage multiple radios typically present on mobile and wearable devices to construct multi-carrier or multi-receiver scenarios to improve robustness. Finally, we also address the problem of designing an ultra-low power tag that can frequency shift by 20MHz while consuming tens of micro-watts. Our results show that FS-Backscatter is practical in typical mobile and static on-body sensing scenarios while only using commodity radios and antennas.
272 citations
Cites background or methods from "BackFi: High Throughput WiFi Backsc..."
...BackFi [9] modifies a WiFi Access Point (AP) by augmenting it with the ability to cancel the OFDM carrier signal....
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...More recently, there have been interesting infrastructure-assisted approaches such as BLEBackscatter [13] and BackFi [9]....
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References
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TL;DR: The design and implementation of the first in-band full duplex WiFi radios that can simultaneously transmit and receive on the same channel using standard WiFi 802.11ac PHYs are presented and achieves close to the theoretical doubling of throughput in all practical deployment scenarios.
Abstract: This paper presents the design and implementation of the first in-band full duplex WiFi radios that can simultaneously transmit and receive on the same channel using standard WiFi 802.11ac PHYs and achieves close to the theoretical doubling of throughput in all practical deployment scenarios. Our design uses a single antenna for simultaneous TX/RX (i.e., the same resources as a standard half duplex system). We also propose novel analog and digital cancellation techniques that cancel the self interference to the receiver noise floor, and therefore ensure that there is no degradation to the received signal. We prototype our design by building our own analog circuit boards and integrating them with a fully WiFi-PHY compatible software radio implementation. We show experimentally that our design works robustly in noisy indoor environments, and provides close to the expected theoretical doubling of throughput in practice.
2,084 citations
TL;DR: In this paper, a review of wearable sensors and systems that are relevant to the field of rehabilitation is presented, focusing on health and wellness, safety, home rehabilitation, assessment of treatment efficacy, and early detection of disorders.
Abstract: The aim of this review paper is to summarize recent developments in the field of wearable sensors and systems that are relevant to the field of rehabilitation. The growing body of work focused on the application of wearable technology to monitor older adults and subjects with chronic conditions in the home and community settings justifies the emphasis of this review paper on summarizing clinical applications of wearable technology currently undergoing assessment rather than describing the development of new wearable sensors and systems. A short description of key enabling technologies (i.e. sensor technology, communication technology, and data analysis techniques) that have allowed researchers to implement wearable systems is followed by a detailed description of major areas of application of wearable technology. Applications described in this review paper include those that focus on health and wellness, safety, home rehabilitation, assessment of treatment efficacy, and early detection of disorders. The integration of wearable and ambient sensors is discussed in the context of achieving home monitoring of older adults and subjects with chronic conditions. Future work required to advance the field toward clinical deployment of wearable sensors and systems is discussed.
1,826 citations
20 Sep 2010
TL;DR: In this paper, a single channel full-duplex wireless transceiver is proposed, which uses a combination of RF and baseband techniques to achieve FD with minimal effect on link reliability.
Abstract: This paper discusses the design of a single channel full-duplex wireless transceiver. The design uses a combination of RF and baseband techniques to achieve full-duplexing with minimal effect on link reliability. Experiments on real nodes show the full-duplex prototype achieves median performance that is within 8% of an ideal full-duplexing system. This paper presents Antenna Cancellation, a novel technique for self-interference cancellation. In conjunction with existing RF interference cancellation and digital baseband interference cancellation, antenna cancellation achieves the amount of self-interference cancellation required for full-duplex operation. The paper also discusses potential MAC and network gains with full-duplexing. It suggests ways in which a full-duplex system can solve some important problems with existing wireless systems including hidden terminals, loss of throughput due to congestion, and large end-to-end delays.
1,623 citations
19 Sep 2011
TL;DR: Experimental results show that a re- design of the wireless network stack to exploit full duplex capability can result in significant improvements in network performance.
Abstract: This paper presents a full duplex radio design using signal inversion and adaptive cancellation. Signal inversion uses a simple design based on a balanced/unbalanced (Balun) transformer. This new design, unlike prior work, supports wideband and high power systems. In theory, this new design has no limitation on bandwidth or power. In practice, we find that the signal inversion technique alone can cancel at least 45dB across a 40MHz bandwidth. Further, combining signal inversion cancellation with cancellation in the digital domain can reduce self-interference by up to 73dB for a 10MHz OFDM signal. This paper also presents a full duplex medium access control (MAC) design and evaluates it using a testbed of 5 prototype full duplex nodes. Full duplex reduces packet losses due to hidden terminals by up to 88%. Full duplex also mitigates unfair channel allocation in AP-based networks, increasing fairness from 0.85 to 0.98 while improving downlink throughput by 110% and uplink throughput by 15%. These experimental results show that a re- design of the wireless network stack to exploit full duplex capability can result in significant improvements in network performance.
1,489 citations