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The CORAL is a cognitive radio platform for research and commercial applications. The radio is based on the IEEE 802.11 standard (WiFi) and operates in the License-Exempt (ISM) 2.4 and 5.8 Ghz, bands where it is becoming difficult to use congested radio spectrum. If concepts for cognitive radio can be proven in the ISM bands, they will likely be effective in other bands. As the development of the CORAL evolves we expect to see the radio operate in other lightly licensed/license exempt bands that are being planned for sub-700 MHz, 3.65 GHz, and even 60 GHz. Currently developed for fixed operation, it is expected that later versions of the CORAL will be used for mobile applications.

The relationship between the architecture of a cognitive radio network and the applications that it can be programmed for was central to the design of the CORAL. Our approach was to design a network radio module that allows configuration of its spatial, temporal, and spectral emission characteristics. We did this by building a cognitive radio ‘shell’ around a IEEE 802.11 standard RLAN terminal, thus creating CORAL's WiFi_CR. In doing so we created a flexible wireless building block that could be used to implement wireless architectures such as point to point, point to multipoint, mesh, relays, and backhaul/picocell grids. Management and control of the WIFI_CR terminals is undertaken using a Network Management System (NMS) that can be remote or co-located with the terminals. Details of the NMS are shown in Figure 1. It is within the NMS that the intelligence of the created network resides. Within the NMS the cognitive control algorithms (cognitive engines) manage the WIFI_CR terminals that form a coexistence community of access points and client radios.

Key Features:

1.   A scheduled TDD multiple access architecture in which client radios and access points are assigned slots in time within which the IEEE 802.11g/a CSMA protocol is executed without contention from the other WIFI_CR radios of the network. The coexistence community must still deal with (and coordinate responses to) the interference and bandwidth demands created by other (non-WIFI_CR) users operating in the same band.
2. The WIFI_CR terminals have position location and timing derived using GPS. Accurate timing is provided to control TDD scheduling, especially over wide areas. The position location and timing resolutions are to within +/- 0.2 meters and +/- 100 ns respectively. Position location is important for many lightly-licensed band applications and facilitates interference characterization and radio emission direction control.
3. Non-GPS synchronization of CORAL networks is possible, allowing in-building use or support of certain kinds of wireless data distribution networks.
4. The WIFI_CR has the ability to support beamforming that can be scheduled and synchronized with the TDD slot assignments. Antenna systems to undertake this are a separate CRC development, but are being considered in the context of our program. Beamforming on TDD slot and on a per-packet basis can be implemented.
5. WIFI_CR devices are IP addressable and can be configured as Access Points or Clients under the direct control of the Network Management System (NMS). Channel number, EIRP, antenna directivity, data rate, scheduling of emissions and their direction, interference monitoring requests, and some IEEE 802.11 MAC/PHY functions are controllable by the NMS.
6. Radio spectrum monitoring is undertaken using a secondary receiver that scans prospective channels and quantifies the incidence level, identity, geographical origin, and time of occurrence of IEEE 802.11 interference. The radio is equipped with a narrow band spectrum scanning system having a noise floor sensitivity of approximately -100 dBm/MHz. Spectrum monitoring can be improved or augmented by using radio signal sensors specifically designed to detect radars, TV signals, microphone beacons, etc., as required under some regulations.
7. A FPGA/Ethernet interface is provided with the radio that allows IP packet examination and implementation of data throttling, coordination of RLAN beacon and IP data bursts, and scheduling. This interface can be enlarged to undertake more sophisticated scheduling.

The CORAL is an experimental radio platform that allows new network concepts and topologies to be realized as real physical wireless systems. It offers an approach to ISM band spectrum usage that is different but not too far removed from the prevalent CSMA/CA protocol inherent to the IEEE 802.11 (WiFi) standard. Having a hybrid of WiFi and cognitive radio features, the radio can be used to test new concepts for RLAN deployment in an interference dominated radio environment. Designed with consideration to radio resource and spectrum management issues, this technology will allow investigation of such topical cognitive radio wireless concepts such as radio environment awareness, white space selection, and co-channel interference scheduling; issues that are important to future cellular and wireless access systems including MIMO systems.

For more details, see our CRC-CORAL brochure.