Wireless Network Virtualization (with Prof. David Tipper)
Virtualization refers to the creation of a set of logical architectures using a given set of physical entities, but in a manner that is transparent to the user. For example, a physical server comprised of processors, memory, network interface cards, and storage may be used to create a set of ``virtual" servers that all employ the physical hardware, but the users see these virtual servers as separate entities by themselves. The challenge is to allocate the physical entities to the virtual entities in a way that maximizes utilization of the physical entities while providing the required performance to the user. Ideally, such an allocation should be dynamic depending on the needs of users. Further, the allocation process should not be cumbersome or resource intensive by itself. The reasons for virtualization are increased hardware efficiencies, easier migration to newer products or technologies while supporting legacy products, and overall reduced cost of equipment and management. Virtualization of end systems such as servers and cloud computing systems is now widespread and commonplace. Currently virtualization of computing systems is characterized by three properties: isolation, customization and resource efficiency. That is isolation of users, customization of services and greater utilization of systems.
The motivations for virtualizing wireless networks follow from the observed benefits in a wired network. First, it becomes a natural extension of wired network/end systems virtualization and can potentially enable segregation of traffic (e.g., in terms of QoS, Security) and provide a mechanism to support the popular idea of bring your own device (BYOD) to organizations. Second, spectrum is a scarce resource and virtualization of spectrum has the potential to provide better utilization, making it more efficient for operators. Third, it allows decoupling operators from the cost of infrastructure ownership (capital and operation expenditures) and to also decouple service providers from operators. In such cases, users will simply subscribe to services or applications. The operators just deliver the access service. In other words, this may even decouple users from operators! Lastly, it will likely support the emergence of new services.
When virtualization is applied to wireless networks, things quickly become complicated and large differences with virtualized wired networks occur. Wireless network virtualization includes both infrastructure sharing and spectrum sharing. Furthermore, there are many different topologies for wireless networks (infrastructure and ad hoc, and within ad hoc, single and multi-hop), different spectrum bands ranging from several hundred MHz to several GHz, unlicensed versus licensed spectrum bands, different geographic coverage (wide, metro, local, and personal area) and finally, different mobility requirements. When wireless networks are deployed, the interference that is caused within an administrative unit (e.g., one service provider's network) and across administrative units becomes important. Physical entities in wireless networks can be as diverse as the complex mobility management entity in 4G cellular networks to inexpensive access points in Wi-Fi networks. Furthermore, the air-interface and bandwidth slices employed by different technologies can be very different. The protocols on the air (access) and in the backbone (core) networks can be very different across technologies. Also, unlike wired networks, users and services can be mobile in wireless networks. Lastly, it is worth noting that governments heavily regulate the basic resource of spectrum and how it can be used.
We are investigating several research challenges in wireless network virtualization.