Shweta Sagari

Coordinated dynamic spectrum management of LTE-U and Wi-Fi networks

This paper investigates the co-existence of Wi-Fi and LTE networks in emerging unlicensed frequency bands which are intended to accommodate multiple radio access technologies. Wi-Fi and LTE are the two most prominent wireless 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 co-existing Wi-Fi and LTE networks 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, inter-network 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.

Modeling the coexistence of LTE and WiFi heterogeneous networks in dense deployment scenarios

Rapid increases in mobile data demand and inherently limited RF spectrum motivate the use of dynamic spectrum sharing between different radio technologies such as WiFi and LTE, most notably in small cell (HetNet) scenarios. This paper provides a analytical framework for interference characterization of WiFi and LTE for dense deployment scenarios with spatially overlapping coverage. The first model developed is for single LTE and single WiFi access points separated by a specified distance. Results obtained for that model demonstrate the fact that WiFi is significantly degraded by a nearby LTE system, while LTE degradation is minimal as long as the WiFi system is within carrier sense range. A second model for multiple WiFi and multiple LTE systems further demonstrates the fact that LTE causes significant degradation to WiFi and that overall system throughput first increases and then decreases with growing density. Intra- and inter- system channel coordination schemes are considered as a means of improving system performance, and results are presented showing 4-5x gains in system capacity over comparable no coordination cases.

Performance evaluation of mobile hotspots in densely deployed WLAN environments

This paper presents a study of mobile wireless LAN (WLAN) hotspots which are used to provide cellular-WiFi tethering service to personal devices. A dense deployment scenario for fixed and mobile WLAN is described and potential performance problems due to interference are identified. An analytical model for coexisting fixed and mobile WLAN hotspots with heterogeneous traffic is presented. The model is used to evaluate the performance of a mobile WLAN as it transits through a set of densely deployed fixed access points (APs), and performance problems due to lack of frequency coordination are identified. An adaptive channel assignment (ACA) scheme for improving mobile AP performance is proposed and evaluated. It is shown that significant performance gains can be achieved with ACA with maximum absolute and percentage throughput gains up to 1.24 Mbps and 42.8% respectively. We also show that setting the scanning interval in ACA requires consideration of the speed at which the mobile WLAN is moving in order to compensate for the throughput losses during channel scanning.

Fair Channel Sharing by Wi-Fi and LTE-U Networks with Equal Priority

The paper is concerned with the problem Wi-Fi and LTE-U networks sharing access to a band of communication channels, while also considering the issue of fairness in how the channel is being shared. As a criteria of fairness for such joint access, \(\alpha \)-fairness and maxmin fairness with regards to expected throughput are explored as fairness metrics. Optimal solutions are found in closed form, and it is shown that these solutions can be either: (a) a channel on/off strategy in which access to the channels is performed sequentially, or (b) a channel sharing strategy, i.e., where simultaneous joint access to the channels is applied. A criteria for switching between these two type of optimal strategies is found, and its robustness on the fairness coefficient is established, as well as the effectiveness of the fairness coefficient to control the underlying protocol of the joint access to the shared resource is managed. Finally, we note that the approach that is explored is general, and it might be adapted to different problems for accessing a sharing resource, like joint sharing of voice and data traffic by cellular carriers.

Coexistence of LTE and WiFi heterogeneous networks via inter network coordination

Fast increases in mobile data demand and inherently limited RF spectrum motivate the use of dynamic spectrum sharing between different radio technologies such as WiFi and LTE, most notably in small cell (HetNet) scenarios. In our project, we propose an inter-network coordination architecture which facilitates dynamic spectrum management in the HetNets for interference mitigation and efficient spectrum utilization. We aim to model interference between LTE and WiFi networks through experimental evaluation using the ORBIT testbed and the USRP/GNU radio platform. We further propose to study the performance of cooperative algorithms between LTE and WiFi network involving logically centralized system level optimization for maximizing throughput subject to certain constraints.

Measurment and analysis on QoS of wireless LAN densely deployed with transmission rate control

This paper investigates Quality of Service (QoS) of the personal mobile wireless LANs (m-WLANs). The situations in the m-WLANs differs from the situations in the normal use of WLANs; the access point (AP) and the associated terminals (TEs) are in proximity. In the m-WLANs, the capture effect (CE) significantly affects on the throughput performance. To measure the impact on the QoS by the CE, the experimental study considering the interference from other power sources (APs and TEs) are required. However, since it is difficult to understand the detailed relationships between the QoS factors, the analytical calculations were also performed. With the experimental and analytical results, we demonstrated that the auto rate fallback algorithm of WLAN causes degradation of the QoS performance. We propose two transmission rates controlling schemes to improve the QoS performance.

Bargaining over Fair Channel Sharing Between Wi-Fi and LTE-U Networks

Wireless networks are increasingly moving towards a heterogeneous operating model involving the sharing of spectrum resources by different access technologies. Sharing wireless resources between different wireless technologies requires protocols that share spectrum in an equitable manner. In this paper, we examine the time-sharing of wireless channels by Wi-Fi and LTE-U networks. To design fair access protocol for the networks we use \(\alpha \) fairness criterion. It allows to find a continuum of fair protocols (a protocol per \(\alpha \)). To find the most fair from this continuum of fair protocols we apply Nash bargaining approach. In particular, we show that such a time-sharing bargaining protocol, in spite of the interference between signals, can lead to a gain for both networks under an increase of the transmission power to one of them.

Fair Allocation of Throughput Under Harsh Operational Conditions

Fairness plays an important role in networking as it fundamentally describes how different communication participants access and share network resources. The fair sharing of resources becomes complicated when the network faces harsh operational conditions, which may be associated with mutual interference or adversarial conditions. In this paper, we study the problem of fair allocation of resources in a network facing harsh operational conditions associated with communication transmission. Such a problem is becoming increasingly relevant in wireless system design as multiple wireless technologies are being deployed in shared spectrum, e.g. WiFi and LTE-U, and wireless networks are facing unprecedented levels of malicious activities. To obtain insight into this problem we suggest a simple game theoretical model involving resource allocation. We solve the game explicitly, which allows us to explore the structure of resource allocation strategies, and thereby provide guidance into the integration of fair resource allocation in networks.

Measurement study of adjacent channel interference in mobile WLANs

Over the last few years, mobile wireless LANs (m-WLANs), which are characterized by portable access points (APs) and a small number of connected clients, are becoming popular. When a large number of such personal mobile APs operate close to each other, for example in crowded urban areas and conference venues, the quality of service (QoS) of the connected clients can be severely degraded due to co-channel and adjacent-channel interference. While there exists a large pool of literature on interference management techniques for fixed WLANs, the small form-factor mobile APs present new challenges in terms of high-density deployments and mobility-induced dynamic interference relations. The importance of minimizing interference in m-WLANs is additionally motivated from an energy-efficiency point of view. Since mobile APs rely on limited battery power, packet collisions and retransmissions have a direct impact on the on-time of the APs. In this paper, we present results from a detailed measurement study based on commercially-available m-WLAN devices - two brands of mobile APs and smartphone based clients. While the QoS characteristics of m-WLANs operating on the same channel have been investigated in prior work, we believe this is the first study of adjacent-channel interference using real-world mobile APs. Our experiments reveal the relationship between the distance between m-WLANs and the total throughput of each m-WLAN in various combinations of channels used. Further, we outline how the results can be used for designing optimal channel allocations in dense m-WLAN settings.

Adaptive geolocation based interference control for hierarchical cellular network with femtocells

This paper presents an adaptive interference control method to mitigate undesirable interference from femtocells to macrocell users in hierarchical cellular networks. Such mechanisms usually require over-the-air signalling for estimation of interference resulting significant bandwidth overhead. The proposed ‘Adaptive Interference Scaling’ (AIS) method uses geolocation information for femtocell power control for interference avoidance. In this approach, each femtocell calculates interference contributed to nearby macrocell users and adjusts the power to meet specific target signal-to-interference-plus-noise (SINR) level. Results from simulations show that AIS is able to increase the number of macrocell users achieving target data rates by up to 158% relative to baseline without adaptive control, while resulting in only 12.2% femtocell users receiving rates below the target. AIS achieves improved performance by using location information to calculate and limit the interference power contributed by femtocells to macrocell users, while allowing the network operator to set any desired target rates.