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Planar Pattern Reconfigurable Integrated With a WiFi System for Multipath Mitigation and Sustained High Definition Video Networking in a Complex EM Environment

Amit Mehta1, Shivam Gautam1, Hasanga Goonesinghe1, Arpan Pal1, Rob Lewis2 and Nathan Clow3 1College of Engineering, Swansea University, Swansea, U.K. [email protected] 2BAE Systems, Chelmsford, UK 3DSTL, Fort Halstead, UK

Abstract—A planer pattern reconfigurable square integrated in a complete system is presented. II. ANTENNA CONFIGURATION The antenna is designed to operate at 5 GHz WiFi band of Fig. 1 shows the top and side view of the SLA designed IEEE 802.11 ac. The antenna under electronic switching for 5 GHz WiFi band. The Antenna structure is inspired generates four tilted beams in the four space quadrants. These four beams are moved intelligently and automatically in space from [4]. The SLA has four conducting arms, each of length using a C# program for achieving and sustaining maximum 32 mm and a track width of 1.5 mm. The square loop is possible throughput. This auto beam steering is advantageous etched on top of a Rogers 4350B (ɛr=3.66, tanδ=0.009) for scenarios where a mobile user suffers from multipath substrate having a thickness of 9.6 mm and an area of 60 fading in a complex electromagnetic environment. mm × 60 mm. The entire structure is backed by a metal . The SLA is excited at the center point of each I. INTRODUCTION arm (A, B, C and D) by four vertical probes of diameter 1.3 Indoor wireless communication in 5 the GHz WiFi band of mm which are connected to the four SMA ports (A0, B0, C0 IEEE 802.11 ac is becoming popular today due to the and D0) at the bottom of the antenna. affordability of mobile computing devices. Delivering live High Definition (HD) video using a WiFi link poses y possible quality issues because of multipath fading in the 60 mm reflective indoor wireless channel. Previous studies have shown that multipath fading and channel interference led to a significant increase in the packet loss [1]. In order to avoid multipath in a wireless channel, one has to receive a signal D C from a narrow window while rejecting signals from all other directions. Such spatial isolation of the signal of interest x effectively reduces reflective multipath which causes mm w=1.5 mm throughput reduction. 60 In order to steer the beam in a particular direction and A create a null in all other direction use of smart antennas have B been discussed [2]. Currently these smart antenna systems use multi-element antennas for pattern reconfigurability. However, these antennas are not suitable Top view for modern portable handheld devices due to restricted available space. In addition, such antennas are expensive, 32 mm have a complex feeding network and require a lot of Ɛ =3.48 9.6mm overhead processing. Therefore, contemporary and future r wireless transceivers require a single element pattern (A , D ) (B , C ) with a simple feeding mechanism 0 0 0 0 Side view [3]. In this paper the design and development of a pattern reconfigurable Square Loop Antenna (SLA) integrated with Fig. 1. Top and side view of SLA designed for 5 GHz band a wireless communication device are presented for multipath mitigation. III. REFLECTION COEFFICIENT AND Furthermore, a HD video networking setup is established OF THE ANTENNA to demonstrate the effectiveness of the pattern Fig. 2 shows the simulated and measured reflection reconfigurability using the SLA in a complex EM coefficient of the SLA when only port A is excited and environment. 0 remaining ports are left open circuited. There is a good agreement between simulation and measurement. The antenna has a reflection coefficient bandwidth (≤ -10dB) of was sustained by the user on the move in a multipath 630 MHz and operates over the 5 GHz WiFi band of IEEE environment. However, this was not the case when the 802.11 ac standard. Since all other feeding ports are intelligent switching algorithm was switched off. symmetric with respect to the antenna structure, the Pattern reconfigurable frequency responses of reflection coefficient for these ports Square Loop Antenna are similar to that of port A 0. y φ=90 When any of the ports A0, B0, C0 and D0 is excited and the remaining ports are kept open circuited the antenna D C WiFi access point generates a tilted beam of θmax=58° directed away from the -x φ=0 x excited port. The antenna offers a of 7.5 dBi in φ=180 A B the direction of maximum radiation. Hence, by exciting one port at a time employing a SP4T RF switch [5] the SLA can φ=270 -y steer its beam in four different quadrants, i.e. ɸmax=45°,

ɸmax=135°, ɸmax=225° and ɸmax=315°, in-front of the antenna WiFi USB adaptor Computer (C# codes) as shown of the Fig. 3. This high gain beam steering is the key for sustaining a reliable communication link in a complex multipath WiFi channel. It is this beam steering capability that will enable the antenna to dynamically point the beam in a particular direction while having a low gain SP4T zone in other directions. In the next section the experimental RF switch setup of the SLA integrated with a PC is presented. Switching control 0 circuitry Fig. 3. Experimental setup

-5 V. CONCLUSION

630 MHz A complete communication system for 5 GHz WiFi band -10 consisting of a planar pattern reconfigurable SLA is D C presented. The antenna has four feeding ports and by exciting one port at a time it can steer the radiation beam in -15 the four different spatial quadrants in front of the antenna. A B Simulated

Reflection Reflection Coefficient (dB) These four beams are steered in space using a SP4T switch Prototype Measured which is controlled by a laptop. The laptop has a C# code -20 4 4.6 5 5.6 6 which intelligently scans the beam and automatically locks Frequency (GHz) to the direction which offers maximum S/I for achieving and sustaining the maximum possible throughput. This auto Fig. 2. Simulated and measured reflection coefficient of beam scanning sustains the quality of the HD video link in a SLA. (Inset) Experimental prototype. complex multipath EM environment.

IV. PATTERN RECONFIGURALABLE SLA INTEGRATED ACKNOWLEDGEMENT WITH A WIRELESS COMPUTING DEVICE The computational resources required to obtain the Fig. 3 shows the block diagram of the experimental setup. numerical results discussed in this work were provided by The pattern reconfigurable SLA’s four ports are connected High Performance Computing (HPC) Wales. to the main RF feeding line using a SP4T RF switch. The main feeding line is used for both uplink and downlink of REFERENCES the HD video over the internet. Using a WiFi USB adapter [1] Rehman, S.U.; Turletti, T.; Dabbous, W., "Multicast video the main RF line is connected to the communicating device streaming over WiFi networks: Impact of multipath fading and (Laptop). Using the SLA the laptop is connected to the interference," Computers and Communications (ISCC), 2011 IEEE Symposium on , vol., no., pp.37,42, June 28 2011-July 1 2011 WiFi Access Point. A C# code running on the laptop [2] Nuteson, T.W.; Mitchell, G.S.; Haque, D.S.; Clark, J.S., "A smart decides intelligently when to switch the ports of the SLA. antenna employing digital for WLAN surveillance," To do this it analyzes the Signal to Interference ratio (S/I) Wireless Communication Technology, 2003. IEEE Topical and when the S/I starts to deteriorate it executes the Conference on , vol., no., pp.398,399, 15-17 Oct. 2003. algorithm. This algorithm undertakes a fast scan of the EM [3] A. Mehta and D. Mirshekar-Syahkal, “Spiral antenna with adaptiveradiation pattern under electronic control,” in Proc. IEEE environment and then locks the SLA to the port which offers Antennas Propag. Soc. Int. Symp., Monterey, CA, USA, Jun. 2004, the best possible S/I. The DC control voltages to the RF pp. 843–846. switch from the laptop are provided using an electronic [4] A. Pal, A. Mehta, D. Mirshekar-Syahkal, and P. J. Massey, control circuitry. It is important to note that intelligent “Shortcircuited feed terminations on beam steering square loop algorithm for fast sensing and locking ensures that while antennas,” IEE Electron. Lett., vol. 44, no. 24, pp. 1389–1390, Nov. 2008. scanning, all the communication data is buffered at the end [5] https://www.hittite.com/content/documents/data_sheet/hmc241lp3. devices and hence, is not lost. Using this system, it was pdf. observed that when using beam steering, an HD video call