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XZero: Cross-Technology Interference Nulling for Improved LTE-U/WiFi Coexistence

What is XZero?

Smart antennas can unlock the potential of unlicensed spectrum by letting the coexisting networks transmit concurrently without harmful interference. This is possible by strategically allocating the antenna degrees-of-freedom for both beamforming toward the intended receiver and interference nulling toward the victim receiver(s). Our solution, named Xzero, achieves this goal for the particular case of LTE-unlicensed (LTE-U) and WiFi by overcoming the challenges of cross-technology interference nulling by a null search at the LTE-U BS with assistance from the WiFi network.


What is the demo showing?

Our demo shows a running prototype of Xzero implemented using USRP SDR platform running srsLTE and commodity WiFi hardware. We illustrate the change in the airtime of colocated WiFi and LTE-U networks upon activation of Xzero and fast reconfiguration of the null beam upon a change in WiFi node’s location.



Video URL: youtu.be/_njFMqHyrjM or www.youtube.com/watch


The full paper can be found here: dl.acm.org/citation.cfm or www2.informatik.hu-berlin.de/~zubow/mobisys18demos-final11.pdf


LtFi: Cross-technology Communication for RRM between LTE-U and IEEE 802.11

What is LtFi?

Cross-technology communication (CTC) was proposed in recent literature as a way to exploit the opportunities of collaboration between heterogeneous wireless technologies. We present LtFi, a system which enables to set-up a CTC between nodes of co-located LTE-U and WiFi networks. LtFi follows a two-step approach: using the air-interface LTE-U BSs are broadcasting connection and identification data to adjacent WiFi nodes, which is used to create a bi-directional control channel over the wired Internet. This way LtFi enables the development of advanced cross-technology interference and radio resource management schemes between heterogeneous WiFi and LTE-U networks.


LtFi is of low complexity and fully compliant with LTE-U technology and works on WiFi side with COTS hardware. It was prototypically implemented and evaluated. Experimental results reveal that LtFi is able to reliably decoded the data transmitted over the LtFi air-interface in a crowded wireless environment at even very low LTE-U receive power levels of -92dBm. Moreover, results from system-level simulations show that LtFi is able to accurately estimate the set of interfering LTE-U BSs in a typical LTE-U multi-cell environment.

What is the demo showing?

The demo shows a scenario consisting of two cells: 1) LTE-U cell and 2) WiFi cell. At the beginning LtFi is disabled and hence the LTE-U duty cycle is set manually. After enabling LtFi the fair airtime utilization for the two cells based on the actual load, i.e. one LTE-UE and three WiFi STAs, is negotiated over the CTC channel. The LTE-U CSAT duty cycle is set accordingly, i.e. 25%.



Video URL: youtu.be/bHDXs5dgsfM or www.youtube.com/watch


The full paper can be found here: arxiv.org/pdf/1707.06912.pdf


BIGAP - Seamless Handover in High Performance Enterprise IEEE 802.11 Networks

Enterprise IEEE 802.11 networks need to provide high network performance to operate a large number of diverse clients like laptops, smartphones and tablets as well as capacity hungry and delay sensitive novel applications like mobile HD video & cloud storage efficiently. Moreover, such devices and applications require much better mobility support and higher QoS/QoE. Existing solutions can either provide high network performance or seamless mobility but not both.

We present BIGAP, a novel architecture achieving both of the above goals. The former is achieved by assigning different channels to co-located APs in order to fully utilize the available radio spectrum. The latter is achieved by providing a mechanism for below MAC-layer handover through exploiting the Dynamic Frequency Selection capability in 802.11. In essence BIGAP forces clients to change AP whilst they ’believe’ they are simply changing channel. BIGAP is fully compatible with 802.11 and requires no modifications to the wireless clients. Testbed results demonstrate a significant improvement in terms of network outage duration (which is 32x smaller as compared to state-of-the-art solutions) and negligible throughput degradation during handover operation. In this way frequent and seamless handover operations can take place thus supporting both seamless mobility and efficient load balancing.

A presentation of the BigAP solution can be found here: BigAP

A BigAP poster is here: BigAP-Poster



Direct comparison between BIGAP softhandover (smartphone, left) and standard hard-handover scheme (tablet, right)


An Infrastructure for Automated BAN Experimentation

We demonstrate an infrastructure for experimenting with Body Area Network (BAN) communication protocols and applications without the involvement of human test-person. The core of our infrastructure consists of a mobile robot, on which a simplistic human structure equipped with BAN nodes is located. This set-up can emulate human movements within a controlled RF interference in-door environment. Both, the robot movements and the RF environment, can be remotely controlled via standard Internet access. As a representative usage example, we compare different frequency selection schemes for BAN communication.




More can be found in the [demo paper](Link) presented at 10th European Conference on Wireless Sensor Networks (EWSN'13). This demonstration got Best Demo Award at the conference.







Better WLAN with Robots








TWIST Tutorial








Unsere Forschung ist international/Our research is international








Exploiting Context Awareness for Communication Efficiency Improvement









Kooperation mit UC Berkeley zum Thema  "Cognitive Radio" (Interview DW-TV in German)


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