UWB Integration into Heterogeneous Access Networks

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UWB Integration into Heterogeneous Access Networks Ana SIERRA1, Juan CHOLIZ2, Pierre CLUZEAUD3, Emil SLUSANSCHI4 1 Telefónica I+D, Don Ramón de la Cruz 82-84, Madrid, 28006, Spain Tel: +34 913128806, Email: [email protected] 2 Institute of Engineering Research in Aragón, I3A, University of Zaragoza María de Luna 3, Zaragoza, 50018, Spain, Email: [email protected] 3 Thales Communications, 146 boulevard de Valmy, Colombes, 92704, France Email: [email protected] 4 University Politehnica of Bucharest, Department of Computer Science and Engineering Splaiul Independentei 313, Sector 6, 060042 Bucharest, Romania Tel: +40 726104006, Email: [email protected] Abstract: The purpose of this paper is to provide the reader with a vision of the current status of the integration of the Ultra-Wideband (UWB) technology into the heterogeneous access networks. Three different fields have been considered to perform this integration process: user devices, access network equipment and location-aware services. Nowadays user terminals and network devices are equipped with multiple radio interfaces, such as Wi-Fi, UMTS, WiMAX, Bluetooth, but other technologies are expected to be also integrated in the short-term with the objective to offer novel and attractive services. UWB with its lower cost, lower power consumption, higher data rates and better localisation features in relation to present short-range wireless technologies, and LTE as the next radio access interface to be deployed by mobile operators, will play a key role in the development of future multi-radio user devices and network equipment. With the aim of guaranteeing the optimum performance of all these technologies working in close proximity integrated into small-sized multi-interface devices, in this paper, a UWB/UMTSHSPA collaborative mechanism implemented in a smartphone is described. Moreover, the coexistence between UWB and LTE as well as the interworking between UWB and WiMAX is analysed. The results of the evaluation of WiMedia as a network access technology in picocells are also presented. Finally, the inclusion of UWB in novel location-based services is studied in this document. Keywords: Coexistence, Heterogeneous, HSPA, LBS, LTE, UWB, WiMAX.

1. Introduction Next-generation wireless systems (4G) are envisioned to have an IP-based infrastructure with the support of heterogeneous access technologies. Different access technologies such as cellular, cordless, WLAN, short-range connectivity, and wired systems will be combined on a common platform to complement each other optimally for different service requirements and radio environments. Mobile hosts are being increasingly equipped with multiple interfaces capacitating access to different wireless networks. Peaceful coexistence among the different interfaces working in close proximity must be guaranteed, and collaboration mechanisms come up as a solution to avoid any degradation. In this context, High Data Rate (HDR) Ultra-Wideband (UWB) arises as a potential access technology providing very high data rate access in short-range picocells. Data rates up to 480 Mbps provided by WiMedia are unmatched as only IEEE 802.11n is theoretically able to reach higher data rates, but with a much higher level of complexity, and no solutions

reaching the claimed 600 Mbps have been implemented so far. Moreover, in January 2010, the WiMedia Alliance announced the availability of Version 1.5 of its UWB Specification, which increases data rate to 1024 Mbps. Furthermore, UWB has lower power consumption, which is a key requirement for use on portable, battery-operated devices [1]. On the other hand, LDR-LT (Low Data Rate with Location and Tracking) UWB combines remarkable features concerning size and power consumption, providing high precision on distance estimation and allowing simultaneous location and data transmission. With centimetre-level ranging resolution and unmatched performance on multipath environments [2], LDR-LT UWB is a good candidate to provide mobile users with indoor localisation, thus enabling the provision of novel location-based services (LBS).

2. UWB integration into user devices and future coexistence issues 2.1 – UWB/UMTS-HSPA collaborative mechanism in a multi-radio user device In recent times, the smartphones with multiple radio interfaces integrated have hit the market massively. Currently, GSM, UMTS-HSPA, Wi-Fi and Bluetooth are included in this kind of user devices, but in the short-term, it is very likely that other technologies will be enabled in the mobile phones with the aim of providing users with novel and attractive services. One of these technologies could be UWB, a point of reference within the shortrange wireless communications field. The UWB regulation [3] defines a protection distance of 36 cm among UWB devices and incumbent radio access technologies present in a heterogeneous scenario in order to guarantee a peaceful coexistence. For distances shorter than 36 cm, it is the manufacturer’s responsibility to assure this coexistence. This fact, together with the design and interference issues that could arise when implementing several radio interfaces in the same smartphone (distances among radios shorter than 5 cm), and in spite of not sharing spectrum among them, have led to the development of a HDR UWB/UMTS-HSPA collaborative mechanism in a multi-radio user terminal, being this theme of critical interest for the operator. The global architecture of the collaborative mechanism is depicted in Figure 1 (a).

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(a) (b) Figure 1: UWB/UMTS-HSPA collaborative mechanism: architecture (a) and web service structure (b)

Currently smartphones or PDAs with UWB technology embedded are not available in the market to reach a real true integration. Therefore, some first steps have been taken, consisting of a proof-of-concept of the interworking of UWB commercial equipment with user devices. On the basis of the off-the-shelf Wireless USB (WUSB) adapter set from Wisair, the purpose of the application is to demonstrate a collaborative mechanism between the UMTS-

HSPA and UWB interfaces of a user terminal, based on a threshold defined for the UMTSHSPA RSSI (Received Signal Strength Indicator) to guarantee a communication with an acceptable QoS (Quality of Service). When the RSSI of the UMTS-HSPA signal goes lower than the value of the threshold, the collaborative mechanism is applied and the UWB transmission decreases automatically its transmit power. Moreover, the application developed on the user device monitors not only the UMTSHSPA interface, but also the Wi-Fi and UWB radios, being possible to manually modify the transmit power and the channel of the UWB communication. The user terminal selected for the implementation is the HTC Tattoo smartphone with Android Operating System (OS), taking advantage of the benefits provided by an open source OS. The HTC Tattoo is UWB-enabled by means of Wisair’s WUSB device adapter. In addition to the monitoring/reconfiguration application on the smartphone, on the UWB-enabled host-PC a command-based application to implement the requests to modify the UWB communication features has been developed. To establish the communication between the UWB-host and the Android smartphone, a structure of web services has also been implemented, as shown in Figure 1 (b). Interoperability is the main advantage of this solution, since no matter what OS is either behind the web server or the client. There are two communication ways between the HTC Tattoo and the UWB-enabled host-PC: control and data. Control communications are sent through a Wi-Fi link when a UWB change is required. After the UWB-host is updated with this change, the status of the properly associated UWB-device is updated accordingly through the UWB interface. The data communication between the UWB adapters is always transmitted via UWB. In this way, the cooperation and the interworking among UMTS-HSPA, UWB and WiFi in a heterogeneous environment have been demonstrated. 2.2 – UWB/LTE coexistence working in close proximity The integration of multiple radio interfaces into the next generation of wireless devices will allow the users to enjoy anytime the best connection, exploiting the heterogeneity offered by future access networks. In this sense, the cellular technologies HSPA and, over all, LTE will play a decisive role in the access to the broadband services in mobility, since users increasingly demand this kind of services. LTE is now on the market. Release 8 was frozen in 2008 and this has been the basis for the first wave of LTE equipment. In novel multiaccess scenarios, different available technologies will complement each other to provide various data rates as well as coverage ranges, satisfying the requirements of each service. Taking into account the complementary features of UWB and LTE, and the expected integration of both technologies into future small-sized user terminals, the study of the UWB/LTE coexistence is mandatory and of great interest for both users and service providers, although, the same as happened with UMTS, UWB and LTE work at different frequencies. Figure 2 shows the laboratory setup assembled for evaluating the coexistence.

Figure 2: UWB/LTE interference measurement setup

The laptop (UWB_Host) on Figure 2 has been provided with UWB connectivity by means of a Host Wire Adapter (Wisair’s WUSB adapter set) inserted in its USB port, accessing remote content stored in an external hard disk drive (UWB_device_HD), which has been UWB-enabled thanks to a Device Wire Adapter, through a UWB link at one of the three bands of WiMedia BG #1 (3168-3696 MHz for Band #1, 3696-4224 MHz for Band #2, 4224-4752 MHz for Band #3). At the same time, an LTE interfering source generated by the SMBV100A from Rohde & Schwarz is brought closer firstly to the UWB_Host (Dist_B) and secondly to the UWB_device_HD (Dist_C), for a fixed Dist_A of 1.5 m. The LTE signal is transmitted in downlink at 2.68 GHz, with 50 Resource Blocks (RB) assigned, 10 MHz of bandwidth and a power level of +16 dBm. The most significant results have been obtained for UWB_device_HD and are shown in Figure 3. 7

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The best performance of the UWB link corresponds to Band #2 and Band #3, since these frequencies are more separated from the selected LTE band than Band #1. Based on these results, from the point of view of the design of future user devices with UWB and LTE integrated, it is remarkable that to achieve the maximum throughput provided by the UWB equipment (6.4 MBps), UWB and LTE radios should be separated at least 27 cm. On the other hand, no degradation on the LTE transmission is detected in the presence of a UWB communication in close proximity (1 cm). This result was expected because the UWB spectrum mask imposed by current regulation is very restrictive.

3. UWB integration into access network equipment 3.1 – UWB/WiMAX gateway The WiMAX technology is still evolving. Moreover it is used in many different fields such as public safety applications. A HDR UWB/WiMAX platform has been designed in this way: UWB link is used to transmit high data rate video applications. An onboard software makes video treatments in order to adapt the flow to the WiMAX link that has a lower capacity. As there are no mobile user stations which include WiMAX and UWB, it has been decided to integrate radios in a small rugged computer whose architecture is shown in Figure 4.

Figure 4: UWB/WiMAX platform

The platform is composed of the following radio:  A WiMAX dongle based on the 802.16e standard, working in the 3.4-3.6 GHz band with a maximal output power of +23 dBm, provided by Thales  A HDR UWB card based on the ECMA-368 standard, supporting the Band #1, #2 and #3 of the Band Group #1 provided by Sigma Designs The system runs under windows XP as it is for the moment the only OS supporting the WiMAX drivers. Both radios are transparent to Ethernet, which makes the use of an IP remote camera easier. The goal of this platform is to demonstrate the coexistence between UWB and WiMAX in the same band. Tests have been performed by configuring the HDR UWB in the Band #1 (3168-3696 MHz) where the WiMAX emission spectrum is. In this platform WiMAX and UWB antennas are spaced 20 cm. The first step has been testing the UWB and the WiMAX link performances alone. Two cases have been performed:  UWB and WiMAX of the platform are transmitting at the same time  UWB of the platform is receiving while WiMAX is transmitting to the base station (UWB video data remote scenario) and vice versa It has been possible to make the two cases work by acting on the antennas (directivity, gain) and by modifying the WiMAX output power (UWB output power had remained the same in order to keep the performance as high as possible). However that has been done while the units are fixed. In order to get a dynamic system that may work with a different hardware configuration (antennas characteristics and separation) as well as radio parameters (frequency, automatic power control…), it is necessary in a second step to develop a collaborative mechanism between HDR UWB and WiMAX. Different solutions are being studied: based on the output power (as for the UWB/UMTS-HSPA platform) or based on a synchronisation scheme to alternate the UWB/WiMAX transmission. 3.2 – WiMedia UWB as a network access technology in picocells

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UMTS/HSPA, WiMAX and Wi-Fi are among technologies used to provide wireless network access, complementing each other and offering different data rates and coverage ranges that capture the needs of mobile users. HDR UWB systems, such as WiMedia, can provide high-capacity access in short-range picocells. But physical data rate of 480 Mbps specified by WiMedia [4] is effectively reduced due to PHY and MAC overhead. PHY layer overhead is assessed in Figure 5 in terms of effective PHY bit rate in relation to payload data rate and payload length. 420 360 300

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Figure 5: Dependence of PHY effective equivalent bit rate on payload data rate and payload length

As the time needed to transmit the preamble and header does not vary with payload data rate, it constitutes a proportionally larger portion of frames sent at higher data rates. Therefore, overhead increases with the nominal data rate, growing from 2.15% at 53.3 Mbps to 17.27% at 480 Mbps. Burst preambles entail less overhead than standard preambles, thus increasing effective bit rate. Payload length is a key factor in attaining good performance especially for high data rates (480 Mbps) and efficiency is significantly reduced for frames with 512 bytes or less. On the other hand, the precise quantification of MAC layer overhead is very complex, as there are several factors that impact on MAC

overhead. Existing studies quantify WiMedia MAC layer overhead in 20% and claim a maximum throughput between 384 and 389 Mbps [5][6]. In order to assess WiMedia UWB capacity with real devices, tests have been performed using both UWB development kits and commercial WUSB adapters. Figure 6 shows the throughput measured at MAC layer using the DV9110M Development Kit from Wisair depending on the payload data rate. Theoretical values of effective PHY bit rate are included as a reference. It must be noted that the maximum throughput is not reached as the DV9110M only supports a payload length up to 1512 bytes. The difference between the throughput measured at MAC level and the effective PHY bit rate is due to MAC layer overhead. Overhead becomes more significant as payload data rates increases. The use of Imm-ACK leads to a loss of efficiency around 45% compared to No-ACK. 400

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Figure 6: DV9110M MAC throughput depending on payload data rate

Finally, off-the-shelf WiMedia WUSB dongles have been tested. A multiple access configuration has been set up with a laptop (host) equipped with a WUSB Host Wire Adapter from Wisair, and two devices, a hard drive (device A) and a flash drive (device B), equipped with WUSB Device Wire Adapters. Table 1 shows throughput measured on each link. It must be noted that WUSB standard limits the maximum bandwidth that an isochronous connection can request to 40 Mbps plus 30% for retries, which makes 52 Mbps [7]. When the host reads information from the devices, the performance of the multiple access configuration is satisfactory. When the host transfers information to both devices at the same time, performance is degraded. In this case transfer rate is limited by the flash memory write speed, which can be orders of magnitude slower than read speed. The slower device B then adversely affects the access to device A. Table 1: Multiple access configuration: file transfer rates Test A Test B Host→device_A Host→device_B device_A→Host device_B→Host 20 Mbps 14.2 Mbps 40.8 Mbps 39.5 Mbps

4. UWB and location-aware services in heterogeneous networks Location-awareness is becoming an essential feature demanded by users as positioning systems are being integrated into the new generation of smartphones and mobile devices. Using mobile devices, LBSs leverage user’s physical location to provide enhanced services and experiences. Nowadays most of the applications are based on the GPS. However, the availability of indoor localisation is not covered by satellite-based systems. At this point LDR-LT UWB arises as a very good alternative to provide positioning information in indoor environments, due to its high accuracy, low cost and power consumption and good performance in multipath environments. Indoor positioning provided by UWB combined with cellular networks such as HSPA or WiMAX enables a wide variety of novel and promising LBSs. Furthermore, location information provided by UWB can also be used by the operators to enhance their networks, for example, to estimate call distribution and user mobility for network planning purposes or to implement intelligent handovers based on localisation prediction.

A demonstrator has been built as a platform for the development and test of LBSs in heterogeneous networks. The main elements of the demonstrator are shown in Figure 7. User’s device has LDR-LT UWB (prototype presented in [8]) and UMTS/HSPA (PCMCIA card) interfaces. A LDR-LT UWB picocell composed of 4 fixed nodes is deployed and a location server computes user’s position according to the estimated distances between the user device and the fixed nodes. On the other hand, the user accesses location-aware services on a remote LBS server through the UMTS/HSPA interface.

Figure 7: Location-aware services demonstrator

The demonstrator scenario is a scaled representation of a shopping centre. As the user moves across the scenario, the position provided by the location system is converted into a position in the real shopping centre. Client and server applications have been developed to provide three location-aware services: indoor navigation, location-based search and proximity marketing. This way the user is tracked on a map, gets distance-sorted results when searching for a certain kind of business and is provided with the route to the selected shop and with special offer advertisements from the closest shops. In order to evaluate the performance of the LDR-LT UWB location system, it was deployed in a room with approximate dimensions of 5 x 3 meters. Figure 8 shows a plan of the measurement scenario. The fixed nodes (green dots) were placed near the corners of the room and the estimated position was measured in 13 different locations (blue dots). Node 2

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It must be previously noted that the LDR-LT UWB prototypes provide a resolution of 8 cm in distance estimation. Mean distance estimation error was approximately 5 cm, with a standard deviation of 15 cm. No dependency of the error on the actual distance was detected. Concerning localisation, an algorithm based on least squares minimization with prior distance contraction [9] was used. The mean positioning error was approximately 25 cm, varying from 3 cm when the device was placed in the middle of the scenario to 45 cm when it was placed near the corners. The main limitation detected was the short range of the prototypes, around 5 m, although it is expected to be enhanced in future versions. The demonstrator will be further enhanced with the inclusion of HDR UWB access points and a system-independent monitoring and reconfiguration framework. This way, location-aware services can be improved by enabling enhanced localisation-specific management of UWB resources and devices. Both the monitoring and reconfiguration is done by stand-alone, low resource modules loaded on the UWB devices, which transmit or

receive data to or from a specified repository, to facilitate the monitoring of specific, userdefined information, or the corresponding reconfiguration [10]. The architecture of the framework is based on MonAlisa (MONitoring Agents using a Large Integrated Services Architecture), which is used to collect, store and display the data in a scalable manner. To allow for actuation of UWB resources, the framework will implement multi-hop taskscheduling algorithms in homogeneous wireless sensor networks, as described in [11].

5. Conclusions In the last few decades, the proliferation of fixed and mobile access technologies and networks has provided the network operators with a large choice to offer a variety of services. In this context, HDR UWB arises as a potential access technology providing very high data rate access in short-range picocells (up to 384 Mbps of throughput at MAC layer). Only IEEE 802.11n can provide comparable features in terms of throughput, but with higher complexity and power consumption. On the other hand LDR-LT UWB can provide mobile users with accurate localisation in indoor environments, thus enabling mobile operators to offer novel and ubiquitous LBS. Nevertheless, efforts should be driven to increase the range of UWB devices that is the main limitation of the available hardware. The integration of UWB and other wireless interfaces such as LTE, UMTS-HSPA, WiMAX and Wi-Fi into small-sized user terminals and network access points will allow the provision of novel services. As a consequence, customers’ satisfaction will increase and manufacturers, operators as well as service providers will obtain higher income. Although sometimes these radio interfaces do not share the transmission frequency bands, multiple design challenges arise when all these wireless technologies interwork in very close proximity in the same device. Therefore, coexistence tests must be carried out to guarantee the optimum performance, with the development of collaborative mechanisms among the different wireless interfaces as a very promising solution to coexistence issues.

Acknowledgements The work presented in this paper has been carried out within the European research project EUWB that is partly funded by the Commission of the European Union under the 7th European Framework Programme for Research and Technological Development (FP7) and here under the Information and Communication Technologies (ICT) research programme.

References [1] WiMedia Alliance White Paper, “UWB – Best choice to enable WPANs”, January 2008. [2] S. Gezici, Z. Tian, G. B. Giannakis, H. Kobayashi, A.F. Molisch, H. V. Poor, Z. Sahinoğlu, “Localization via Ultra-Wideband Radios. A look at positioning aspects of future sensor networks”, IEEE Signal Processing Magazine, vol. 22, no. 4, July 2005. [3] ECC REPORT 64: “The protection requirements of radiocommunications systems below 10.6 GHz from generic UWB applications”, Helsinki, February 2005. [4] Standard ECMA-368, “High Rate Ultra Wideband PHY and MAC Standard”, 1st Ed., December 2005. [5] N. Kumar, R.M. Buehrer, “The Ultra Wideband WiMedia Standard”, IEEE Signal Processing Magazine, September 2008, pp. 115-119. [6] WiMedia Alliance, “WiMedia Ultra-Wideband: Efficiency Considerations of the Effects of Protocol Overhead on Data Throughput”, January 2009. [7] Wireless Universal Serial Bus Specification, Revision 1.0, May 12, 2005. [8] M. Pezzin, I. Bucaille, T. Schulze, A.V. Pato, L. De Celis, "An open IR-UWB platform for LDR-LT applications prototyping", in Proc. WPNC’09.March 2009. [9] G. Destino, G. Abreu, “Improving Source Localization in NLOS Conditions via Ranging Contraction”, in Proc. WPNC’10, March 2010. [10] C.Cirstoiu, C.Grigoras, M.Toarta, C. Dobre, R.Voicu, “An Agent based, Dynamic Service System to Monitor, Control and Optimize Grid based Applications,” CHEP 2004, Interlaken, September 2004. [11] Andrei Voinescu, Dan Tudose, Nicolae Tapus, "Task Scheduling in Wireless Sensor Networks," Sixth International Conference on Networking and Services, March 7-13, 2010 - Cancun, Mexico.