Given end users often spend fourty percent of their time indoors, the cellular operators are considering femto cells deployed in indoor environments such as homes and enterprise buildings as a complement to macro cells for the purposes of enhancing capacity and coverage indoors. As the wireless data services proliferate, high capacity femtos and their scalable deployment will be very crucial.
Our research efforts on Ultra-broadband Femto cells focus on following:
Design and demonstration of ultra-broadband femtos
Standards such as LTE, and WiMAX are designing air interfaces that use increasingly wider bands of spectrum (e.g., up to 20 MHz per channel) to increase access rates. However, given the restricted size of operator licenses, the number of wide-band channels is limited. As broadband wireless access gains adoption and media-rich end user devices (e.g., iPhones) proliferate, the next frontier will be ultra-broadband wireless access which inevitably needs more spectrum. The femto cells may be the first user equipment to offer such ultra-broadband access. In this work, we are exploring novel ways to enable such ultra-broadband femtocells by opportunistically accessing wider swaths of spectrum. Check publications, presentations and patents.
Scalable deployment of first generation co-channel femtos
A large-scale femto cell underlay network will increase an operatorís total number of cells by two to three orders of magnitude and presents significant scaling problems in spectrum reuse. We argue that to achieve this scale and interoperability with the existing macro-cell network and handsets, the femto cell must use novel yet simple cognitive techniques: sensing, smart handover and idle mode cell camping.
The Bell Labs Ireland team has recently investigated in detail design and evaluation of a novel passive RF fingerprinting technique in the context of UMTS femtocells to address the problem of signaling storms caused by increased core network-signaling load due to idle mode cell camping. These techniques can be extended to OFDM-based air interfaces (such as LTE, WIMAX). Check publications, presentations and patents.
TDD-FDD interference issues
Issue of co-existence of TDD-TDD and TDD-FDD systems is gaining widespread importance as mix of TDD (e.g.: WiMAX, LTE)) and FDD (e.g.: LTE, HSPA) technologies continue to be deployed. Introduction of femto cells adds another dimension to this co-existence issue. We are exploring novel, cognitive solutions to allow scalable deployment of TDD/FDD femto cells. Check presentations .
Dynamic spectrum allocation to femtocells based on parameters such as location, macro-cell network spectrum use and available spectrum white spaces
Milind M. Buddhikot