This paper proposes a new antenna remoting system for ultra-high frequency (UHF) radio frequency identification (RFID). The system consists of a central baseband controller and a remote antenna subsystem, which are connected using twisted-pair cable. During the inventory session, only baseband signals are transmitted over the twisted-pair cable, whilst the transmitted radio frequency (RF) signals are up and down converted in the antenna subsystem. This new RFID system provides -94.5 dBm of reader sensitivity, and can fulfill long-distance detection tasks with very low performance degradation over up to 150 m of Cat5et cable. Compared with conventional RFID systems using coaxial cables between reader and antenna, the presented RFID system is more flexible and cost-efficient due to its low deployment cost and ease of cable routing

Crisp, MJ

Fu, Z

Penty, RV

White, IH

Yang, S

English

Apollo (Cambridge)

Long Distance Passive UHF RFID Systemover Ethernet CableZhe Fu, Michael J. Crisp, Shuai Yang, Richard V. Penty and Ian H. WhiteCentre for Photonic Systems, Electrical Division, Department of EngineeringUniversity of Cambridge,9 JJ Thomson Avenue, Cambridge, CB3 0FA, U.K.Abstract—This paper proposes a new antenna remoting system for ultra-high frequency (UHF) radio frequency identification (RFID). The system consists of a central baseband controller and a remote antenna subsystem, which are connected using twisted-pair cable. During the inventory session, only baseband signals are transmitted over the twisted-pair cable, whilst the transmitted radio frequency (RF) signals are up and down converted in the antenna subsystem. This new RFID system provides - 94.5 dBm of reader sensitivity, and can fulfill long-distance detection tasks with very low performance degradation over up to 150 m of Cat5et cable. Compared with conventional RFID systems using coaxial cables between reader and antenna, the presented RFID system is more flexible and cost-efficient due to its low deployment cost and ease of cable routing. Keywords—RFID; twisted-pair cable; cat5e; long distance; deployment; flexibility; low cost;I.	 IntroductionRadio Frequency Identification (RFID) is a rapidly growing technology, which allows the identification of real-world objects, animals or persons by associated individual serial numbers encoded onto tags. Targets are automatically identified using electromagnetic waves in accordance with specific communication standards and regulations. Over the last two decades, society has increasingly reaped the benefits of RFID technology. Examples include its use in supply chain management; product or patient tracking and localization; flora and fauna identification; security and surveillance systems; and motorway toll collection [1].As a widely adopted but not yet mature technology, RFID still has a long way to go to achieve its full potential. The use of handheld readers is effective, but it requires intensive manual work. The high cost of fixed RFID hardware and deployment difficulty presents a considerable barrier to many potential clients. In a conventional RFID system, multiple reader antennas have to be deployed to cover the required area due to the detection range limitation of a single reader. Multi-antenna RFID systems significantly improve the coverage and diversity of a single RFID reader [2-5]. Buendia et al. [2] has introduced a smart cable for a single reader RFID system, and this allows the system to cover an area of 16 m × 2.5 m along a corridor. In this smart cable, single pole double throw (SPDT) switches and Wilkinson power combiners are applied to feed 5 rectangular patch antennas in a time division multiplexed approach. A similar solution is proposed by Rodas et al. [3]. They have designed a Power-over-Ethernet (PoE) supported reader-plus-switch to extend a 2-port RFID reader to 8 ports or a 4-port RFID reader to 16 ports. The extended antenna ports are automatically switched based on the pre-programmed software so that the system can detect over a wide area without tag-to-reader and reader-to-reader interferences. In order to further reduce the cost of extra antenna control units, multiport RFID readers have been designed [4]. By adding frequency and phase hopping techniques, along with the antenna diversity the RFID system performance can be enhanced [5]. The demonstrated system is able to achieve near 100% tag detection rate over a 20 m × 15 m area, a substantial increase over conventional switched multi-antenna RFID systems. In [6] it was shown that the use of well separated antennas in a MIMO type system can provide the ability to control wireless power at various locations with a dynamic range of 20 dB. For the above RFID systems (Fig. 1), many coaxial cables are required for connecting the antennas to the RFID reader and other elements. Since coaxial cable is expensive and suffers high attenuation at around 900 MHz, the RFID systems discussed above are limited in the cable lengths they can support. This configuration is sufficient for experimental, some small range, and indoor applications, but for commercial wide area applications, new connection approaches are required for multi-antenna systems. In this paper, a novel long-range passive UHF RFID system over twisted-pair Ethernet cable is proposed. This new system consists of a central controller and a remote antenna subsystem, and is connected by a commonly-used Ethernet cable such as Category 5e (Cat5e). It allows long cable lengths which enable high deployment flexibility and cost benefits, as well as the possibility of new architectures whereby multiple distributed antennas might be cascaded off a single cable.  The remainder of the paper is organized as follows. In Section II, we introduce the new reader architecture with a full explanation of each operational block. Following that, the testing results and related discussion are included in Section III, and finally conclusions are presented in Section IV.II.	System DesignIn a conventional RFID system, both the baseband block and radio frequency (RF) block (consisting of the RF front end and a frequency synthesizer) are integrated on a single PCB (or even IC) to form an RFID reader, and a short coaxial cable is applied to connect the reader to its antenna (Fig. 2 (top)). Since the cable loss is directly proportional to the cable length and is normally of the order of dB’s per meter at frequencies around 900 MHz, the maximum reader output power and antenna gain limit the maximum allowable cable length if the maximum effective isotropic radiated power (EIRP) allowed by the local regulations is to be reached. For a typical 1 W conducted power and 6 dBi gain antenna, this is often only a few metres. While the maximum cable length in the downlink can be increased by increasing the conducted output power (at the expense of electrical power consumption), in the uplink the cable loss eventually results in a noise limited link and reduced sensitivity. Twisted-pair cable such as Category 5e (Cat5e) is an attractive option to form a new configuration of RFID system to extend antenna deployment distance. However, Cat5e cable suffers very high attenuation in the carrier frequency band (860-960 MHz). Nonetheless, this problem can be solved by moving some RF blocks to the antenna side and so only baseband signals need to be communicated over the Ethernet cable. The structure of this new system is shown in Fig. 2(bottom). It is composed of a central controller and antenna subsystem. In the forward link, the baseband transmit signals are generated in the digital block based on local regulations and standards. After digital to analog conversion, the resulting analog baseband signals are transmitted to the remote antenna subsystem over a twisted-pair cable. Up-conversion is performed in the RF front end. A short coaxial cable can be applied between the antenna and the antenna subsystem depending on requirements of the installation. The backscattered signals, in the reverse link, experience similar processes but in a reverse order. They are received as RF at the antenna, and mixed back to I and Q baseband components in the antenna subsystem before transmission over the two pairs of the Cat5e to the central controller where digitization and protocol operations are executed. The local oscillator for up and down conversion is generated in the antenna subsystem, and a reference tone is carried from the central controller, so multiple antenna subsystems can be potentially phase locked in the future for the coherent systems described in Section I.A.	Central Controller The high-level block diagram of the central controller is given in Fig. 3. This design is based around the Impinj Indy R2000 chip [7] which provides all the baseband and RF functions required to implement a reader based on the EPC global Gen 2/ISO 18000-6C standard (although in this implementation some of the functionality is unused). An Atmel AT91SAM7S256-MU [8], microcontroller implements the EPC Class 1 Gen 2 protocol and provides an interface for external control. The baseband transmit signal can be accessed from the analog test pins of the R2000 as a differential signal. However, since these baseband signals are directly connected to the internal analog bus, they have little current driving capability. A line driver is therefore designed to amplify these analog signals without loading down the signal bus. Due to the ASK modulation in the downlink, the data on the I channel is null (0) and signals only exist on the Q channel. In this way, only a single twisted pair is required to transmit the downlink signals. In respect of the uplink, an analog buffer block in the central controller is employed to buffer the received baseband signals and provide noise filtering. After this block, the analog tag signals are fed into the R2000 chip for additional filtering and processing via the inputs designed for the external dense reader mode (DRM) filters, thus allowing bypassing of the RF to IF conversion stages on the IC. The reference signal block allows for future frequency and phase hopping of the local oscillator in the antenna subsystem by varying the phase and frequency of the reference signal. Thus, a 10 MHz signal is generated as an external reference source in this block for the frequency synthesizer in the antenna subsystem.B.	Antenna SubsystemAs shown in Fig. 4 the antenna subsystem is mainly composed of quadrature modulator and demodulator, RF power amplifiers, and a PLL-based frequency synthesizer. The AD8349 [9] quadrature modulator and the ADL5380 [10] quadrature demodulator are used to fulfil up- and down-conversion tasks. The carrier frequency is generated by a fractional-N/integer-N PLL-based frequency synthesizer ADF4350 [11], which can work with either its internal oscillator or an external reference signals. In this implementation, an external 10 MHz reference signal from the central controller is applied. Two RF amplifiers (RF5110G [12]) are adopted for provide sufficient gain for the signals both in the downlink and uplink. The output power of this amplifier can be controlled from -10 dBm to +35 dBm by changing the voltage level of power control (Vapc). C.	Twisted-pair CableCategory-5e cable is selected for building this new system, since it has sufficient bandwidth (100 MHz) and its price is relatively cheap compared to other higher-bandwidth twisted-pair cables. Typically, there are four pairs of wires in one Cat5e cable (Fig. 5), and all pairs are used in this new system; one for transmitting the baseband reader signals, one for the synthesizer reference frequency from reader controller and two for receiving in-phase and quadrature down-converted tag signals from the antenna subsystem. Although not implemented for this proof of concept demonstration, it would be possible to transmit the DC power required for the antenna subsystem over the pairs in a manner similar to power over Ethernet (PoE). Since these Ethernet cables have same wiring scheme, other types of twisted-pair cable such as Cat6 can also be applied for the controller-subsystem connection.In addition to the attenuation benefits of the Cat5e scheme it is also worth noting that it is lower cost, and easier to install than LMR-400 and LMR-1700 co-axial cables commonly used for RFID applications, owing to the narrower diameter and smaller minimum bend radius. More details of comparison in terms of weight and price are shown in Table I.TABLE I. 	Comparisons of Cat5e Cable and Coaxial cables Cable Type	Cat5eCable	LMR-400Coaxial Cable [13]	LMR-1700Coaxial Cable [14]Weight (kg)	30m	0.93	3	33	150m	4.65	15	165Approximate Price (£)	30m	24	90.9	1,306	150m	120	454.5	6,530III.	Results and DiscussionIn order to fully and reliably evaluate this new RFID system performance, a RFID Tester TC-2600A [15] is applied. This tester can emulate a reference tag for measuring reader performance. Regarding the sensitivity measurement, the RFID Tester can calculate the reader’s bit error rate (BER) and frame error rate (FER) by comparing its sent RN16 signal while emulating a tag with the RN16 included in ACK signal from the reader. The sensitivity of the system can then be captured by determining the minimum backscattered power of remaining the desired BER or FER.  A series of tests have been conducted to measure the system sensitivity with various lengths of Cat5e cable. In these tests, the Miller-2 PR-ASK modulation is used and a 10 MHz reference signal with a power of 10 dBm is transmitted from the central controller over the Cat5e cable. Due to the maximum input power limits of the RFID Tester, the output power of the antenna subsystem is set to +16.4 dBm at a carrier frequency of 867.4 MHz. The threshold of FER for determining the sensitivity is set at 45%. The system sensitivity for each cable length has been measured 10 times, and the average sensitivity value is shown in Fig. 6. It is shown that the best sensitivity result of this system is - 94.5 dBm when 30 m Cat5e cable is used to connect the controller and antenna subsystem. After increasing the length of Cat5e cable to 150 m, the sensitivity reduces slightly to - 94.2 dBm. As a result, the system sensitivity is initially independent of cable length up to 150 m. Cable Type	Cat5eCable	LMR-400Coaxial Cable [13]	LMR-1700Coaxial Cable [14]Testing Frequency	350kHz	900MHz	900MHzCable Loss (dB)	30m	0.32	3.84	0.93	90m	0.96	11.52	2.79	150m	1.60	19.2	4.65TABLE II. 	Cabel loss of Cat5e Cable and Coaxial cables In order to investigate the dependence of sensitivity on the cable attenuation, the attenuation of backscattered signal in the Ethernet cable has been measured (although for experimental reasons, this has been emulated using a function generator at 350 kHz). The results are summarized in Table II alongside the losses of common coax cables derived from their specifications. It can be seen that the tag signal suffers from 0.3 dB attenuation over 30 m and 1.6 dB over 150m Cat5e cable respectively. The attenuation difference between these two lengths is around 1.3 dB, which is significantly larger than the sensitivity reduction. Additionally, a practical demonstration of the detection range of a 300 m Cat5e connected RFID system has been carried out. Two 8.5 dBic circularly polarized antennas are deployed in height of 1.5 m connected to antenna subsystem in a bistatic configuration as shown in Fig. 7 using two 2 m coaxial cables. An UPM Raflatac DogBone tag [16] can be successfully detected at same height 6 m away from the antennas with a downlink transmission power of 31.9 dBm EIRP. Here the transmission distance is limited by the space available and is not an upper limit, but shows the potential for long range tag reading over a Cat5e cable equal in length to over 3 times the limit for standard Ethernet.IV.	ConclusionA cost-effective UHF RFID system using Cat5e Ethernet cable to address remote antennas has been demonstrated. It is shown that the reader sensitivity of this new system can achieve - 94.5 dBm over 30 m Cat5e cable, and its sensitivity can still remain at around - 94.2 dBm with 150 m Cat5e. The passive tags can be successfully detected over a 6 m wireless range following 300 m of twisted-pair cable between the central controller and antenna. This new system configuration provides its high performance for long distance passive RFID applications, and also reveals massive benefits for multi-antenna RFID systems. Despite its lower cable cost and high deployment flexibility, the circuit of the conventional RFID reader can also be simplified by sharing the digital and control blocks and communicating with remote subsystems by simply splitting and combining desired baseband signals. However, the synchronization of controller-subsystems communication and cable immunity may be the challenges, which require further investigation. Future work will also involve the study of the application of this method to wide area reader systems, where the cost savings from the lower cost cable and potentially easier installation are expected to be substantial. V.	NOTEAdditional data related to this publication is available at the University of Cambridge data repository https://doi.org/10.17863/CAM.9264References[1]	D.M. Dobkin, RF in RFID: UHF RFID in Practics, 2nd edition, Elsevier Inc. 2013.[2]	V.G. Buendia, S. Kenny, S.K. Podilchak, G. Goussetis, A. Costanzo, and P. Nicole, “Smart cable for Radio Frequency Indentification in aeroautical applications,” in 2016 10th European Conference on Antennas and Propagation, pp.1-3, April 2016.[3]	J. Rodas, V. Barral, C.J. Escudero and R. Langwieser, “A Solution for Optimizing Costs and Improving Diversity of RFID Readers,” in 19th International Conference on Systems, Signals and Image Processing, pp. 84-88, April 2012. [4]	Y. Wang, N. Zhang, and L. Jin, “The Hardware Design and Implementation of Four-Channel UHF RFID Reader Based on Impinj R2000,” in 2015 6th IEEE International Conference on Software Engineering and Service Science, September 2015.[5]	S. Sabesan, M.J. Crisp, R.V. Penty, and I.H. White, “Wide Area Passive UHF RFID System Using Antenna Diversity Combined With Phase and Frequency Hopping,” Antennas and Propagation, IEEE, vol. 62, no. 2, pp. 878-888, 2014.[6]	D. Arnitz and M. S. Reynolds, "MIMO Wireless Power Transfer for Mobile Devices," in IEEE Pervasive Computing, vol. 15, no. 4, pp. 36-44, Oct.-Dec. 2016.[7]	Indy R2000 Datasheet, [Online]. Available from: https://support.impinj.com/hc/en-us/articles/202755828-Indy-R2000[8]	SAM7 Series Summary: AT91SAM7S256 Datasheet, [Online]. Available from: http://www.atmel.com/devices/AT91SAM7S256.aspx[9]	AD8349 Datasheet, Analog Devices, [Online]. Available from: http://www.analog.com/en/products/rf-microwave/iq-modulators-demodulators/iq-modulators/ad8349.html#product-overview[10]	ADL5380 Datasheet, Analog Devices, [Online]. Available from: http://www.analog.com/en/products/rf-microwave/iq-modulators-demodulators/iq-demodulators/adl5380.html#product-overview[11]	ADF4350 Datasheet, Analog Devices, [Online]. Available from:  http://www.analog.com/en/products/rf-microwave/pll-synth/fractional-n-plls/adf4350.html[12]	RF5110G Datasheet, RFDM, [Online]. Available from: http://www.qorvo.com/products/p/RF5110G#parameters[13]	LMR-400 Datasheet, Times Microwave, [Online]. Available from: https://www.timesmicrowave.com/documents/resources/LMR-400.pdf[14]	LMR-1700 Datasheet, Times Microwave, [Online]. Available from: http://www.timesmicrowave.com/documents/resources/LMR-1700.pdf[15]	TC-2600A Datasheet, [Online]. Available from; https://mcs-testequipment.com/product/tescom-tc2600a-rfid-test-system/[16]	UPM Raflatax DogBone  Datasheet, [Online]. Available from: http://www.fastrfid.com/raflatac/UHF/tech_speck_3001572_letter.pdfFig. 1.   Multi-antenna solutions for single RFID readerFig. 3.   Block diagram of the central controllerFig. 2.   A comparison of a conventional RFID system (top) and the proposed RFID system (bottom)Fig. 6.   Sensitivity performance over different cable lengthsFig. 4.   Block diagram of antenna subsystemFig. 5.   Signals in the Ethernet cableFig. 7.	Detection range measurement setup 

Long distance passive UHF RFID system over ethernet cable

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Long distance passive UHF RFID system over ethernet cable

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