47 CFR § 90.377 - Frequencies available; maximum EIRP and antenna height, and priority communications.
(a) Licensees shall transmit only the power (EIRP) needed to communicate with an On-Board Unit (OBU) within the communications zone and must take steps to limit the Roadside Unit (RSU) signal within the zone to the maximum extent practicable.
(b) Frequencies available for assignment to eligible applicants within the 5850–5925 MHz band for RSUs and the maximum EIRP permitted for an RSU with an antenna height not exceeding 8 meters above the roadway bed surface are specified in the table below. Where two EIRP limits are given, the higher limit is permitted only for state or local governmental entities.
| Channel No. | Frequency range
(MHz) |
Max. EIRP
1 (dBm) |
Channel use |
|---|---|---|---|
| 170 | 5850–5855 | Reserved. | |
| 172 | 5855–5865 | 33 | Service Channel. 2 |
| 174 | 5865–5875 | 33 | Service Channel. |
| 175 | 5865–5885 | 23 | Service Channel. 3 |
| 176 | 5875–5885 | 33 | Service Channel. |
| 178 | 5885–5895 | 33/44.8 | Control Channel. |
| 180 | 5895–5905 | 23 | Service Channel. |
| 181 | 5895–5915 | 23 | Service Channel. 3 |
| 182 | 5905–5915 | 23 | Service Channel. |
| 184 | 5915–5925 | 33/40 | Service Channel. 4 |
1 An RSU may employ an antenna with a height exceeding 8 meters but not exceeding 15 meters provided the EIRP specified in the table above is reduced by a factor of 20 log(Ht/8) in dB where Ht is the height of the radiation center of the antenna in meters above the roadway bed surface. The EIRP is measured as the maximum EIRP toward the horizon or horizontal, whichever is greater, of the gain associated with the main or center of the transmission beam. The RSU antenna height shall not exceed 15 meters above the roadway bed surface.
2 Channel 172 is designated for public safety applications involving safety of life and property.
3 Channel Nos. 174/176 may be combined to create a twenty megahertz channel, designated Channel No. 175. Channels 180/182 may be combined to create a twenty-megahertz channel, designated Channel No. 181.
4 Channel 184 is designated for public safety applications involving safety of life and property. Only those entities meeting the requirements of § 90.373(a) are eligible to hold an authorization to operate on this channel.
(c) Except as provided in paragraphs (d) and (e) of this section, non-reserve DSRCS channels are available on a shared basis only for use in accordance with the Commission's rules. All licensees shall cooperate in the selection and use of channels in order to reduce interference. This includes monitoring for communications in progress and any other measures as may be necessary to minimize interference. Licensees of RSUs suffering or causing harmful interference within a communications zone are expected to cooperate and resolve this problem by mutually satisfactory arrangements. If the licensees are unable to do so, the Commission may impose restrictions including specifying the transmitter power, antenna height and direction, additional filtering, or area or hours of operation of the stations concerned. Further the use of any channel at a given geographical location may be denied when, in the judgment of the Commission, its use at that location is not in the public interest; use of any such channel may be restricted as to specified geographical areas, maximum power, or such other operating conditions, contained in this part or in the station authorization.
(d) Safety/public safety priority. The following access priority governs all DSRCS operations:
(1) Communications involving the safety of life have access priority over all other DSRCS communications;
(2) Subject to a control channel priority system management strategy (see ASTM E2213–03 DSRC Standard at § 4.1.1.2(4)), DSRCS communications involving public safety have access priority over all other DSRC communications not listed in paragraph (d)(1) of this section. Roadside Units (RSUs) operated by state or local governmental entities are presumptively engaged in public safety priority communications.
(e) Non-priority communications. DSRCS communications not listed in paragraph (d) of this section, are non-priority communications. If a dispute arises concerning non-priority communications, the licensee of the later-registered RSU must accommodate the operation of the early registered RSU, i.e., interference protection rights are date-sensitive, based on the date that the RSU is first registered (see § 90.375) and the later-registered RSU must modify its operations to resolve the dispute in accordance with paragraph (f) of this section.
(f) Except as otherwise provided in the ASTM–DSRC Standard (see § 90.379) for the purposes of paragraph (e) of this section, objectionable interference will be considered to exist when the Commission receives a complaint and the difference in signal strength between the earlier-registered RSU and the later-registered RSU (anywhere within the earlier-registered RSU's communication zone) is 18 dB or less (co-channel). Later-registered RSUs causing objectionable interference must correct the interference immediately unless written consent is obtained from the licensee of the earlier-registered RSU.