4.9Ghz in Public Safety

The use of 4.9GHz in Public Safety Settings

Police, fire, and emergency medical services agencies are currently using Strix Access/One wireless mesh network products to improve the speed and accuracy with which information can be communicated. With video surveillance cameras becoming increasingly pervasive, and with a cities installation of IP-based cameras on lamp-posts, buildings, and patrol cars, police can use their PDAs or laptops to watch what's going on a manage an event from clear across town. Secure broadband access enables the transmission of databases, fingerprints, and photo images from anywhere in the community. Secure, high-speed capabilities are necessary to upload and download field reports and images that require fast data throughput. Fire trucks in-route to a building on fire can request detailed information about fire hydrant water supply and gain access to additional structural building details. Doctors and emergency room technicians can assist in the live remote diagnoses and monitoring of patient conditions while in route to the hospital. With Strix Access/One nodes deployed along streets and roadways, ambulances can be equipped as mobile networks and video cameras to provide two-way video image and voice communications between the ambulance and emergency medical centers. Strix Access/One wireless mesh network products provide the scalability and performance to assist in the management of resources and the quality and flow of information.

In 2004, the FCC finalized the regulatory details of the newly opened 4.9 GHz Public Safety frequency band. The rules make available 50 MHz of spectrum, from 4.940 GHz to 4.990 GHz, for the use of broadband wireless data, voice and video communications in public safety applications. All state, local and federal governmental agencies working with state and local public safety systems are eligible for 4.9 GHz licensing.

Licenses granted by the FCC allow for operation across the 50 MHz spectrum and within the legal jurisdiction of the licensee or government entity sponsoring the non-government organization. These licenses apply to (a) base and mobile networks or (b) temporary fixed stations operating for less than 12 months. For permanent, fixed point-to-point stations, the FCC will issue licenses for individual sites issued on a secondary, non-interference basis to the primary uses.

There are no specific limitations regarding licensed use of the 4.9GHz band as long as it's use is for the purpose of public safety. Some common examples include:

    * small, medium and large-scale wireless mesh networks
    * Data, Voice and Video
    * Emergency mobile communications
    * In-the-field Mobile ad-hoc command communications
    * Emergency Medical
    * Mobile networks for off-site workers
    * Video security, monitoring, or surveillance systems
    * Voice communication utilizing VoIP
    * Intranet or Internet applications
    * Fixed line (T1) replacement

Additional Background

The 4.9 GHz band was transferred from Federal Government to non- Federal Government use in 1999, in accordance with the provisions of the Omnibus Budget Reconciliation Act. In 2000, the Commission released a Notice of Proposed Rulemaking (65 FR 14230, March 16, 2000) proposing to allocate the 4.9 GHz band to non-Government fixed and mobile services, and to allow flexible use of this band. In 2002, the Commission adopted the fixed and mobile allocation, designated the band for use in support of public safety, and sought comment on the establishment of licensing and service rules for the 4.9 GHz band. In the Third Report and Order, the Commission adopted service rules for use of this band and addressed petitions for reconsideration of its decision to prohibit aeronautical mobile operations in this band.

NPSTC petitions urged the adoption of two different emission masks, one mask for low power operations, the other for high power operations. NPSTC proposes a technology standard for general and interoperability use in the 4.9 GHz band, and sought mandatory regional planning and the inclusion of a conflict resolution process in regional plans.

In the proposed Rulemaking (67 FR 17038 April 9, 2002), the Commission sought comment on whether technical standards should be adopted for the 4.9 GHz band for which standards would be appropriate. The Commission adopted a flexible band plan suited to emerging broadband technologies that could enhance public safety operations. It also adopted an emission mask to minimize out-of-band emissions that could result in interference between 4.9 GHz devices. This mask, currently incorporated into Sec. 90.210 of the rules, is referred to herein as the Section 90.210 Mask.

NPSTC submitted that the Section 94.210 Mask was unnecessarily restrictive and would added significantly to the cost of 4.9 GHz equipment, thereby potentially delaying public safety's use of the band. It argued that public safety must leverage currently available (i.e., ``commercial-off-the-shelf'' (COTS)) technologies used in adjacent bands, such as the 5.4. GHz Unlicensed National Information Infrastructure (U-NII) unlicensed band and the intelligent Transportation System (ITS) band, NPSTC indicated that the current mask would prohibit any significant transfer of technology from the equipment used in these bands. For example, NPSTC contended that the more restrictive mask would hamper the ability of 4.9 GHz equipment to use chipsets employed in equipment designed for the U-NII or ITS bands.

As a substitute for the Section 90.210 Mask, NPSTC recommended that the Commission adopt the DSRC-A and DSRC-C masks applicable to ITS equipment. It proposes the DSRC-A mask for low power 4.9 GHz devices with transmitter output power of 20 dBm or less, and recommends the DSRC-C mask for higher power 4.9 GHz devices with transmitter power output greater than 20 dBm.

This power level strikes a reasonable balance between interference avoidance and 4.9 GHz equipment affordability. It also contended that adoption of these emission masks could enable manufacture of devices that could operate in the 4.9 GHz band, the ITS band and the U-NII band, thus providing the public safety community access to these bands using a more economical device.

Consensus was reached with NPSTC that the DSRC-A and DSRC-C masks were a reasonable regulatory substitute for the Section 90.210 Mask, and that the DSRC-A mask should be used for low power devices while the more restrictive DSRC-C mask should be used for high power devices.

On September 10, 2004, NPSTC filed an exparte document that included a set of recommended rules that put the ``high power'' breakpoint at 20 dBm and NPTSC indicated a recognition of the benefits that would accrue to public safety agencies if they could use 4.9 GHz devices adapted from COTS technologies in nearby bands. In particular, leveraging such technologies could result in savings for state and local governments and provide the potential for deployment of dual-band devices that make Internet access available via the U-NII band adjacent to the 4.9 GHz band.

DSRC-A and DSRC-C masks were adopted by the NPTSC in lieu of the Section 90.210 Mask with the intention of that there will not be undue burden on public safety agencies with unnecessary costs for 4.9 GHz devices.

The adoption of a 20 dBm breakpoint is grounded with respect that even consumer equipment in this frequency range is relatively tolerant of interference. The DSRC-A mask is identical to the mask defined in the widely-used 802.11 ``WiFi'' standard for equipment used for in-home wireless LANs and found in consumer ``hotspots'' in businesses ranging from coffee shops to airports. The adjacent channel rejection (ACR) of an 802.11 receiver, using Orthogonal Frequency Division Multiplexing (OFDM), is defined by data throughput as a function of the level of adjacent channel interference. For example, an 802.11 receiver can sustain data throughput of 48Mbits/s in the presence of an equal-power adjacent channel signal and a throughput of 6 Mbits/s when the adjacent channel signal is 16 dB higher. Thus, adjacent channel interference in these systems is a ``graceful degradation'' of data throughput, although loss of service can eventually result at higher levels of adjacent channel interference. Moreover, the potential for interference can be anticipated and taken into account in the placement of 4.9 GHz devices at the scene of an incident.

In assessing the proper breakpoint for requiring the more restrictive emission mask, although 4.9 GHz equipment operating at power levels of 8 dBm or less may be adequate for consumer applications, the reliability requirements of public safety communications favor higher power levels, especially given propagation characteristics at these frequencies. If the NPTSC were to preclude use of higher power on affordable units using the DSRC-A mask, such devices could have so few applications that they might be unattractive to public safety agencies, which then would have to resort to specialized higher power units employing the DSRC-C mask--if they could afford such units. By comparison, allowing the DSRC-A mask to be used for low-cost 4.9 GHz devices at power levels up to 20 dBm would provide enhanced reliability--notably when obstructions are present between devices--albeit with the possibility of some degradation in throughput if multiple systems are operated on adjacent channels in close proximity to one another.

In sum, technical, economic and operational considerations have helped to determine that the DSRC-A mask should be permitted for power levels of 20 dBm and less, and that the DSRC-C mask should apply to all power levels in excess of 20 dBm.

In support of the municipalities, public safety and related federal governmental agencies Strix Systems implemented the DSRC-A to support initial developments in the 4.9Ghz frequency. While deployments for municipalities have not taken full advantage of 4.9Ghz, the added support for the higher power DSRC-C mask will enable greater coverage. While Strix DMA is radio technology agnostic, the high-performance of Strix Access/One architecture lends itself to enabling greater coverage and resilience for public safety deployments regardless of the whether the DSRC-A and DSRC-C mask.

Municipalities continue to deploy 802.11a for backhaul and 802.11b/g for user access. Due to the flexibility of the architecture it doesn't matter which technology is used for backhaul or access other than preference based on engineering and design. In any case, node-to-node backhaul connections are automatically encrypted. Due to the advantages of performance and coverage utilizing 2.4Ghz and 5.8Ghz, 802.11a and 802.11b/g are commonly deployed while 4.9GHz has been considered a future integration and because Strix Access/One is an in-field upgradeable modular product, adding new technologies is seamless through upgrades made available from Strix Systems.

With the addition of the higher-powered DSRC-C mask, there will be increased momentum in the deployment of 4.9GHz as an access technology with 802.11a as a primary method for backhaul. As more devices are developed in support of 4.9GHz, so will the applications and usefulness of technology.