Abstract-This paper presents an overview of the ORBIT (Open Access Research Testbed for Next-Generation Wireless Networks) radio grid testbed 1 , that is currently being developed for scalable and reproducible evaluation of next-generation wireless network protocols. The ORBIT testbed consists of an indoor radio grid emulator for controlled experimentation and an outdoor field trial network for end-user evaluations in real-world settings. The radio grid system architecture is described in further detail including an identification of key hardware and software components. Software design considerations are discussed for the open-access radio node, and for the system-level controller that handles management and control. The process of specifying and running experiments on the ORBIT testbed is explained using simple examples. Experimental scripts and sample results are also provided.

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This paper investigates the co-existence of Wi-Fi and LTE in emerging unlicensed frequency bands which are intended to accommodate multiple radio access technologies. Wi-Fi and LTE are the two most prominent access technologies being deployed today, motivating further study of the inter-system interference arising in such shared spectrum scenarios as well as possible techniques for enabling improved co-existence. An analytical model for evaluating the baseline performance of coexisting Wi-Fi and LTE is developed and used to obtain baseline performance measures. The results show that both Wi-Fi and LTE networks cause significant interference to each other and that the degradation is dependent on a number of factors such as power levels and physical topology. The model-based results are partially validated via experimental evaluations using USRP based SDR platforms on the ORBIT testbed. Further, internetwork coordination with logically centralized radio resource management across Wi-Fi and LTE systems is proposed as a possible solution for improved co-existence. Numerical results are presented showing significant gains in both Wi-Fi and LTE performance with the proposed inter-network coordination approach.

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Providing air-time guarantees across a group of clients forms a fundamental building block in sharing an access point (AP) across different virtual network providers. Though this problem has a relatively simple solution for downlink group scheduling through traffic engineering at the AP, solving this problem for uplink (UL) traffic presents a challenge for fair sharing of wireless hotspots. Among other issues, the mechanism for uplink traffic control has to scale across a large user base, and provide flexible operation irrespective of the client channel conditions and network loads. In this study, we propose the SplitAP architecture that address the problem of sharing uplink airtime across groups of users by extending the idea of network virtualization. Our architecture allows us to deploy different algorithms for enforcing UL airtime fairness across client groups. In this study, we will highlight the design features of the SplitAP architecture, and present results from evaluation on a prototype deployed with: (1) LPFC and (2) LPFC+, two algorithms for controlling UL group fairness. Performance comparisons on the ORBIT testbed show that the proposed algorithms are capable of providing group air-time fairness across wireless clients irrespective of the network volume, and traffic type. The algorithms show up to 40% improvement with a modified Jain fairness index.

Abstract-This paper presents a spectrum etiquette protocol for efficient coordination of radio communication devices in unlicensed (e.g. 2.4 GHz ISM and 5 GHz U-NII) frequency bands. The proposed etiquette method enables spectrum coordination between multiple wireless devices using different radio technologies such as IEEE 802.11.x, 802.15.x, Bluetooth, Hiperlan, etc. The basic idea is to standardize a simple common protocol for announcement of radio and service parameters, called the "common spectrum coordination channel (CSCC)". The CSCC mechanism is based on the low bit-rate mode of the 802.11b physical layer, along with a periodic broadcast protocol at the MAC layer. The CSCC protocol is "policy neutral" in the sense that it provides a general mechanism which can accommodate a wide range of specific spectrum sharing rules. One possible CSCC protocol implementation is described in terms of the packet formats used and related channel access rules. Proof-of-concept experimental results from a CSCC prototype are presented for an example scenario in which nearby 802.11b and Bluetooth devices contend for 2.4 GHz ISM band access. Results showing file transfer delay with and without CSCC etiquette are given for comparison purposes.