Kerstin Johnsson

M2M: From mobile to embedded internet

Is M2M hype or the future of our information society? What does it take to turn the M2M vision into reality? In this article we discuss the business motivations and technology challenges for machine-to-machine communications. We highlight key M2M application requirements and major technology gaps. We analyze the future directions of air interface technology improvements and network architectures evolution to enable the mass deployment of M2M services. In particular, we consider the salient features of M2M traffic that may not be supported efficiently by present standards, and provide an overview of potential enhancements. Finally, we discuss standards development for M2M.

Capacity and coverage enhancement in heterogeneous networks

Disruptive innovations in mobile broadband system design are required to help network providers meet the exponential growth in mobile traffic demand with relatively flat revenues per bit. Heterogeneous network architecture is one of the most promising low-cost approaches to provide significant areal capacity gain and indoor coverage improvement. In this introductory article, we provide a brief overview of heterogeneous network architectures comprising hierarchical multitier multiple radio access technologies (RAT) deployments based on newer infrastructure elements. We begin with presenting possible deployment scenarios of heterogeneous networks to better illustrate the concepts of multitier and multi-RAT. We then focus on multitier deployments with single RAT and investigate the challenges associated with enabling single frequency reuse across tiers. Based on the spectrum usage, heterogeneous networks can be categorized into single carrier usage, where all devices within the network share the same spectrum, and distinct carrier usage, where different types of devices are allocated separate spectra. For single carrier usage, we show that interference management schemes are critical for reducing the resulting cross-tier interference, and present several techniques that provide significant capacity and coverage improvements. The article also describes industry trends, standardization efforts, and future research directions in this rich area of investigation.

Cellular traffic offloading onto network-assisted device-to-device connections

While operators have finally started to deploy fourth generation broadband technology, many believe it will still be insufficient to meet the anticipated demand in mobile traffic over the coming years. Generally, the natural way to cope with traffic acceleration is to reduce cell size, and this can be done in many ways. The most obvious method is via picocells, but this requires additional CAPEX and OPEX investment to install and manage these new base stations. Another approach, which avoids this additional CAPEX/OPEX, involves offloading cellular traffic onto direct D2D connections whenever the users involved are in proximity. Given that most client devices are capable of establishing concurrent cellular and WiFi connections today, we expect the majority of immediate gains from this approach to come from the use of the unlicensed bands.

3GPP LTE traffic offloading onto WiFi Direct

Mobile network operators are struggling to handle the rapidly increasing amounts of data traffic on their networks. As a result, 3GPP is currently investigating possible scenarios for device-to-device (D2D) offloading in LTE networks. However, it remains unclear what kinds of gains can be expected from in-band D2D solutions. By comparison, the already available WiFi Direct D2D technology enables offloading onto unlicensed bands at data rates generally higher than infrastructure cellular links. In this paper1, we study the performance of WiFi Direct as a prominent technology for D2D communications in urban environments. We also discuss some of the potential performance gains for WiFi Direct communications in the presence of 3GPP LTE network-level management. Our extensive simulation study of LTE traffic offloading onto WiFi Direct covers a range of D2D loads and interference levels. We focus on the case where the D2D overlay network is assisted by the cellular infrastructure network; or more specifically, where the cellular network supplies its clients with service discovery information to facilitate the establishment of D2D sessions.

Analyzing Assisted Offloading of Cellular User Sessions onto D2D Links in Unlicensed Bands

For the past years, the analysts have been predicting a tremendous and continuous increase in mobile traffic, causing much of industry and academia to seek out any and all methods to increase wireless network capacity. In this paper, we investigate one such method, cellular data offloading onto direct connections between proximate user devices, which has been shown to provide significant wireless capacity gains. To do so, we formulate a new system model that couples a cellular network in licensed bands and a device-to-device (D2D) network in unlicensed bands. We propose that devices be continually associated with the cellular base station and use this connectivity to help manage their direct connections in unlicensed spectrum. In particular, we demonstrate that assisted offloading of cellular user sessions onto the D2D links improves the degree of spatial reuse and reduces the impact of interference. In this study, a session is a real-time flow of data from one user to another, which adheres to a Poisson point process (PPP). By contrast to a throughput- or capacity-centric system view, the application of PPP enables formulations where entire user sessions, rather than singular data packets, are arriving at random and leaving the system after being served. The proposed methodology is flexible enough to accommodate practical offloading scenarios, network selection algorithms, quality of service measures, and advanced wireless technologies. In this study, we are primarily interested in evaluating the data session blocking probability in dynamically loaded cellular and D2D networks, but given the importance of energy efficiency for mobile devices, we are also interested in characterizing the energy expenditure of a typical data session in these different networks. First with our advanced analytical methodology and then with our detailed system-level simulator, we evaluate the performance of network-assisted data session offloading from cellular to D2D connections under a variety of conditions. This analysis represents a useful tool in the development of practical offloading schemes and ongoing standardization efforts.

Communication challenges in high-density deployments of wearable wireless devices

Wearable wireless devices are very likely to soon move into the mainstream of our society, led by the rapidly expanding multibillion dollar health and fitness markets. Should wearable technology sales follow the same pattern as those of smartphones and tablets, these new devices (a.k.a. wearables) will see explosive growth and high adoption rates over the next five years. It also means that wearables will need to become more sophisticated, capturing what the user sees, hears, or even feels. However, with an avalanche of new wearables, we will need to find ways to supply them with low-latency highspeed data connections to enable truly demanding use cases such as augmented reality. This is particularly true for high-density wearable computing scenarios, such as public transportation, where existing wireless technology may have difficulty supporting stringent application requirements. In this article, we summarize our recent progress in this area with a comprehensive review of current and emerging connectivity solutions for high-density wearable deployments, their relative performance, and open communication challenges.

Proximity-Based Data Offloading via Network Assisted Device-to-Device Communications

Analysts predict explosive growth in traffic demand on mobile broadband systems over the coming years due to the popularity of streaming video, gaming, and other social media services. While 4G wireless technologies are making a significant effort to keep up with this demand, the expectation is that cellular deployments will fall short of the required capacity unless there is a dramatic shift towards smaller cells. There is already significant interest in femto- and pico-cell deployments for this reason. However, there is another method of creating small cells that the wireless industry has yet to capitalize on, namely direct connectivity between clients in close proximity. 3GPP is currently working to enable device-to-device (D2D) communications within Release 12 of LTE-Advanced. By comparison, IEEE has already defined a D2D communications protocol, termed WiFi Direct, which is based on the 802.11 standards. WiFi Direct not only serves to offload user data onto direct links, but does so using the unlicensed bands. To benefit users further, WiFi Direct can be enhanced by enabling the LTE network to assist during peer discovery and direct connection establishment. In this paper, we discuss the network/client requirements and performance benefits of network-assisted WiFi Direct. We assume that clients are continuously under management by the LTE network, which assists them with service/peer discovery and direct connection establishment. We show that network-assisted WiFi Direct can significantly improve the performance of proximal applications and reduce the power consumed by the clients involved, while also improving capacity of the LTE network.

Network-assisted D2D communications: Implementing a technology prototype for cellular traffic offloading

Currently, cellular operators are struggling to relieve congestion on their networks in the face of rapidly growing mobile data traffic. While deploying an increasing number of base stations is expected to mitigate the disproportion between user demand and available radio resources, this solution is costly and plagued with many practical challenges. An attractive alternative is to enable cellular traffic offloading onto device-to-device (D2D) connections in the unlicensed bands, as current multi-radio user devices are already capable of establishing concurrent LTE and WiFi links. However, WiFi lacks a fast, efficient method of device/service discovery, and it is not equipped to efficiently manage numerous D2D connections. In our research, we have found that a limited amount of network assistance for D2D communications can overcome these limitations; and in this paper we describe our network-assisted D2D technology prototype. Specifically, we outline a complete standards-compliant solution that provides a seamless D2D connectivity experience to the end user. Our solution utilizes WiFi Direct as the link-layer technology for proximal D2D connections. However, the challenges faced during the design phase are universal to all D2D link-layer protocols, thus the proposed solutions are applicable to other potential D2D technologies.

Power control based interference mitigation in multi-tier networks

Significant areal capacity gains and improved cellular coverage can be achieved by hierarchical deployment of Femto Access Points (FAP) over an existing cellular network. However, the introduction of FAPs, which use the same spectrum as the cellular network, can cause severe interference to network and drive users into outage. In order to resolve this issue, advanced interference mitigation (IM) techniques should be applied in multi-tier networks. In this paper, we design and evaluate power control based IM algorithms in cellular systems with femtocell overlay. Simulation results show that FAP power back-off helps lower macro-user outage probability at the cost of femto-user rate reduction. For control channels with low data rate requirement, FAP power control can be a potential IM solution.

Assessing System-Level Energy Efficiency of mmWave-Based Wearable Networks

The emerging fifth-generation (5G) wireless technology will need to harness the massively unused millimeter-wave (mmWave) spectrum to meet the projected acceleration in mobile traffic demand. Today, the available range of mmWave-based solutions is already represented by IEEE 802.11ad (WiGig), IEEE 802.15.3c, WirelessHD, and ECMA-387 standards, with more to come in the following years. As the key performance-related aspects of these enabling technologies are rapidly taking shape, the primary research challenge shifts to characterizing network energy efficiency, among other system-level parameters. This is particularly important in scenarios that are not handled by current 4G communication networks, including congested public places, homes, and offices. In these dense deployments, wireless wearable devices are increasingly proliferating to assist in diverse user needs. However, mmWave operation in crowded environments, and especially for multiple neighboring personal networks, is not nearly well-understood. Bridging this gap, we conduct a full-fledged energy efficiency assessment of mmWave-based “high-end” wearables that employ advanced antenna beamforming techniques. Our rigorous analytical results shed light on the underlying scaling laws for the interacting mmWave-based networks based on IEEE 802.11ad and quantify the impact of beamforming quality on system energy efficiency under various conditions. Furthermore, we look at the system optimization potential subject to realistic hardware capabilities.