High-speed multimedia radio

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High-speed multimedia radio (HSMM), colloquially referred to as the hinternet, is the implementation of wireless data networks over amateur radio frequencies using commercial off-the-shelf (COTS) hardware such as 802.11 access points and D-Star equipment. Licensed amateur radio operators may use amplifiers and specialized antennas to increase the power and coverage of the 802.11 signal.

The name hinternet comes from a combination of the words ham and Internet and can be used to refer to any high speed data network over amateur radio, not just 802.11 networks.

A typical piece of equipment used for HSMM (Linksys WRT54G)
A typical piece of equipment used for HSMM (Linksys WRT54G)

Contents

[edit] Basics

The idea behind this implementation is to use the 900 MHz (33 cm), 2.4 GHz (13 cm), 3.4 GHz (9 cm), and 5.8 GHz (5 cm) amateur radio bands under the FCC Part 97 rules (amateur radio service) instead of the Part 15 rules (unlicensed). This enables amateur operators to legally use higher output power for wireless devices and allows for longer-range communications. Such communications can be used to assist in emergency communications and disaster relief operations and in everyday amateur radio communications.

[edit] What can it do?

The "hinternet" can support most of the traffic that the Internet currently does, including video chat, voice, instant messaging, the Web (HTTP), file transfer (FTP), and forums. The only differences being that on the hinternet such services are community instead of commercially implemented and the "hinternet" is mostly wireless. The hinternet can even be connected to the Internet and used for "Web surfing", although because of the FCC regulations on permitted content, this is rarely done. Using high gain antennas and amplifiers, reliable long-distance wireless links over many miles are possible and only limited by the radio horizon.

[edit] Frequencies and channels

The following is a list of the 802.11 channels that overlap into an amateur radio band under the FCC in the United States. Note that the 5 cm amateur band extends from 5650 to 5925 MHz, so that there are many frequencies outside the Part 15 ISM/UNII block used for 802.11a. Some equipment can be programmed to operate on these “extra” channels, and some cannot. Many commercial grade 802.11a access points can also operate in between the normal channels by using 5 MHz channel spacing instead of the standard 20 MHz channel spacing. 802.11a channels 132, 136 and 140 are only available for unlicensed use in ETSI regions.

802.11b/g (13 cm)
Channel Center Frequency FCC Rules
−1 2.402 GHz Part 97
0 2.407 GHz Part 97
1 2.412 GHz Part 97 & Part 15
2 2.417 GHz Part 97 & Part 15
3 2.422 GHz Part 97 & Part 15
4 2.427 GHz Part 97 & Part 15
5 2.432 GHz Part 97 & Part 15
6 2.437 GHz Part 97 & Part 15
  
802.11a (5 cm)
Channel Center Frequency FCC Rules
132 5.660 GHz Part 97
136 5.680 GHz Part 97
140 5.700 GHz Part 97
149 5.745 GHz Part 97 & Part 15
153 5.765 GHz Part 97 & Part 15
157 5.785 GHz Part 97 & Part 15
161 5.805 GHz Part 97 & Part 15
165 5.825 GHz Part 97 & Part 15
169 5.845 GHz Part 97
173 5.865 GHz Part 97
177 5.885 GHz Part 97
180 5.905 GHz Part 97

The following images show the overlapping relationship of the Part 15 unlicensed bands and the Part 97 licensed bands. The images are not to scale.

2.4 GHz 802.11b/g

5.8 GHz 802.11a

[edit] Channels and power

[edit] 802.11a

The 802.11a amateur radio band consists of twelve non-overlapping channels in the 5.650–5.925 GHz (5 cm) band. The 802.11a standard uses OFDM or "Orthogonal Frequency Division Multiplexing" to transmit data and therefore is not classified as spread-spectrum. Because of this 802.11a hardware is not subject to the power rules in FCC Part 97 § 97.311 and the maximum allowable output power is 1500 watts (W) PEP.

[edit] 802.11b

The 802.11b amateur radio band consists of eight overlapping channels in the 2.390–2.450 GHz (13 cm) band. The 802.11b specification uses Direct Sequence Spread Spectrum (DSSS) to transmit data and is subject to the rules of FCC Part 97 § 97.311. Therefore the maximum allowable power output is 100 W PEP. If the transmitter power exceeds 1 W, the station must use automatic power control.

[edit] 802.11g

The 802.11g amateur radio band consists of eight overlapping channels in the 2.4 GHz (13 cm) band. The 802.11g standard uses OFDM or "Orthogonal Frequency Division Multiplexing" to transmit data and therefore is not classified as spread-spectrum. Because of this 802.11g hardware is not subject to the power rules in FCC Part 97 § 97.311 and the maximum allowable output power is 1500 W PEP.

[edit] Frequency sharing

[edit] 802.11a

The 5 cm band is shared with the fixed-satellite service in ITU Region 1, and the radiolocation service. In ITU Region 2 (US) the primary user is military radiolocation, specifically naval radar. Amateur radio operators have secondary privileges to the Federal radiolocation service in the entire band and may not cause interference to these users. Amateur operators are allocated this band are in a co-secondary basis with ISM devices and space research. Amateur, space research, and ISM operators each have the "right to operate". Due to the lack of a high number of Part 15 users (compared to 2.4 GHz), the noise level tends to be lower in many parts of the US but can be quite congested in urban centers and on mountaintops.

[edit] 802.11b/g

The 13 cm band is shared with Part 15 users as well as the Federal radiolocation service, and ISM (industrial, scientific, medical) devices. Amateur radio operators have secondary privileges to the Federal radiolocation service in the entire band and may not cause interference to these users. Amateur radio operators have primary privileges to ISM devices from 2.390–2.417 GHz and secondary privileges from 2.417–2.450 GHz. Because of the high number of Part 15 users, the noise level in this band tends to be rather high.


[edit] Identification

As with any amateur radio mode stations must identify at least once every 10 minutes. One acceptable method for doing so is to transmit one’s call sign inside an ICMP echo request (commonly know as a ping). If the access point is set to "master" then the user’s call sign may be set as the "SSID" and therefore will be transmitted at regular intervals. Another method is to change the MAC address of the transmitting node so the operators call sign will be broadcasted along with every packet sent or received.
802.11 hardware may transmit and receive the entire time it is powered on even if the user is not sending data.

[edit] Security

Because amateur transmissions may not be encoded or encrypted in any way, security measures that are implemented must be published. This makes it very difficult to keep unauthorized users from accessing HSMM networks, although casual eavesdroppers can effectively be deterred. Current schemes include using MAC address filtering, WEP and WPA/WPA2. MAC address filtering and WEP are all hackable by using freely available software from the Internet, making them the less secure options. Per FCC rules the encryption keys themselves must be published in a publicly accessible place if using WEP, WPA/WPA2 or any other encryption, thereby undermining the security of their implementation.
Using professional or modified hardware it is possible to operate on 802.11a channels that are outside the FCC authorized Part 15 bands but still inside the 5.8 GHz (5 cm) amateur radio band. Transverters or "frequency converters" can also be used to move HSMM 802.11b/g operations from the 2.4 GHz (13 cm) band to the 3.4 GHz (9 cm) amateur radio band.

[edit] Custom frequencies

Using professional grade commercial hardware or modified consumer grade hardware it is possible to operate 802.11 on channels that are outside of the normal FCC allocated frequencies for unlicensed users but still inside an amateur radio band. Some of these frequencies are inside the 2.4 GHz (13 cm), 3.4 GHz (9 cm) and the 5.8 GHz (5 cm) amateur radio bands, thereby providing better security and interference characteristics to amateur radio operators. While using amateur-only frequencies all but alleviates the security concerns of using 802.11, the relative high cost of such devices is a large deterrent to their widespread deployment.

[edit] 2.4 GHz custom frequencies

Using professional grade hardware or modified consumer grade hardware it is possible to operate on 802.11b/g hardware on channels that are effectively "0" at 2.407 GHz and "−1" at 2.402 GHz. Using these channels allows amateur operators to move away from unlicensed Part 15 operators but may interfere with AMSAT satellite downlinks near 2.400 GHz and 2.401 GHz.

[edit] 3.4 GHz transverters

Frequency conversion involves the use of transverters that convert the operating frequency of the 802.11b/g device from 2.4 GHz to another band entirely. Transverter is a technical term and is rarely used to describe these products which are more commonly known as frequency converters, up/down converters, and just converters. Commercially-available converters can convert a 2.4 GHz 802.11b/g signal to the 3.4 GHz (9 cm) band which is not authorized for unlicensed Part 15 users.

[edit] 5.8 GHz custom frequencies

Using professional grade hardware or modified consumer grade hardware it is possible to operate on 802.11a channels 116–140 (5.57–5.71 GHz) and channels above 165 (> 5.835 GHz). These frequencies are outside of the FCC allocated Part 15 unlicensed band, but still inside of the 5.8 GHz (5 cm) amateur radio band. Modifying consumer hardware to operate on these expanded channels often involves installing after-market firmware and changing the "country code" setting of the wireless card. When buying professional grade hardware, many companies will authorize the use of these expanded frequencies for a small additional fee.

[edit] Custom firmware

One popular way to access amateur only frequencies is to modify an off-the-shelf access point with custom firmware. This custom firmware is freely available on the Internet from projects such as DD-WRT and Openwrt. The most popular piece of hardware that is modified is the Linksys WRT54GL because of the widespread availability both the hardware and third party firmware.

[edit] See also

[edit] External links

[edit] Sources