While most of the early discussions/papers/press-releases on TV White Spaces (TVWS) described the new available spectrum as being useful for local networking akin to Wi-Fi or for M2M communications, it was only time before the biggest stake holders in all things spectrum - the cellular operators (and others in their ecosystem) took a keen interest in it. An example of their growing interest in the topic is the following stats from the just concluded 3GPP Radio Access Network (RAN) Plenary which had presentations from a variety of stake holders (providers, network equipment suppliers, handset vendors, etc.) about the things they feel are important for LTE Release 12 and beyond:
- More than 15 companies talked about leveraging unlicensed band for use with cellular technologies.
- More than 6 companies specifically discussed possibilities related to TVWS.
Key reasons for the new found interest:
1. Quite obviously the acute spectrum crunch: providers are looking at all means for sending more bits/sec to their customers and TV White Spaces offers high capacity 'beach-front' quality spectrum at little cost of ownership.
2. LTE PHY/MAC design: The time-frequency resource block (RB) based resource allocation in LTE is quite suitable for TVWS band operation. Resources can be assigned to users with fine granularity (1 RB = 180 KHz); an occupied TV band between two unoccupied ones can be easily skipped by just blacklisting the corresponding RBs; and being a scheduler based system, the dynamism in the available spectrum can be handled by gracefully lowering capacity as opposed to a Wi-Fi system where availability of less than 20 MHz (1 channel's worth) of spectrum means no operation at all.
3. Increasing heterogeneity of cellular deployments: With micro/femto deployments gaining momentum, there is a need for new technological solutions on both the access and backhaul side of things. So while replacing licensed spectrum would be far-fetched in traditional macro-cells, it can be considered from the ground-up in these brand-new kinds of deployments.
In this light, TVWS is being talked about in the 3GPP and the SDR Forums with regard to a no. of different use cases such as unlicensed band off-loading, last-mile backhaul links for small cells, for access connections in rural areas, and for device-to-device communication assisted by the cellular operator. Going forward, it will be interesting to see which of the use cases gains more momentum and what new co-existence challenges it brings to other technologies operating on the TV White Space bands.
A few interesting links
Technical paper proposing/simulating the use of TVWS for mixed macro/femto deployments: Using TV White Space for Interference Mitigation in LTE Femtocell Networks
Huawei's announcement of TD-LTE trial over TVWS: Huawei to Launch TV White Space LTE TDD System Trial
Blog post highlighting the alignment of LTE and TVWS: LTE and TV White Space, Related set of slides: link
Technical paper studying the use of LTE femotocells for indoor coverage over TVWS band: Interference Study for Cognitive LTE-Femtocell in TV White Spaces
European Commission sponsored technical paper on the technical challenges required to extend LTE for TVWS operation: Extension of LTE Operational Mode over TV White Spaces
Technical paper on a cognitive TD-LTE framework for operation over TVWS: CR Enabled TD-LTE within TV White Space: System Level Performance Analysis
Detailed technical paper from Ericsson research on the feasibility of license-exempt LTE operation over TVWS: License-exempt LTE systems for secondary spectrum usage: Scenarios and first assessment
CogEu feasibility report on LTE over TVWS (page 53): Cognitive radio systems for efficient sharing of TV white spaces in European context
