High Speed Multimedia Radio.Pdf
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By Kris I. Mraz, N5KM High Speed Multimedia Radio Data, voice and video––simultaneously! Experiments are demonstrating the feasibility of low cost, low power technology for the new ham radio “Hinternet.” High Speed Multimedia (HSMM) consists of a low power microwave trans- A small built-in antenna is used on the Radio ceiver that uses a form of spread spectrum desktop PC or laptop so it can communi- HSMM radio is based on what is com- (SS) modulation. Spread spectrum modu- cate with the AP node. Devices using the mercially known as Radio Local Area Net- lation is a way to spread modulation fre- IEEE 802.11b standard (known as WiFi work (RLAN) Technology.1 Take a look at quencies over a very wide signal bandwidth commercially) use frequencies in the 2.4 Figure 1. Each PC (desktop or laptop or while at the same time reducing the power GHz range. That standard must be robust palmtop) has an inexpensive (less than transmitted at any specific frequency. The enough to handle the uncertainties of the $100) radio transceiver/antenna unit at- SS transceivers most studied are manu- radio medium as well as deal with prob- tached to it. Radio repeaters, called nodes factured under a standard called IEEE lems that a wired LAN has never heard of. and known commercially as Access Points 802.11b and the signal occupies a band- Therefore, we’re looking at the marriage (APs), are scattered around the home or width of 22 MHz (11 MHz either side of of radio and software technologies in a office to receive their radio signals. the channel’s center frequency). leading-edge advancement of networking. Now those PCs are no longer tied down. They are free to roam the local area, untethered by an access cable. And, Wired Local Area Network like your cell phone, as you roam around Wired Link the city, your signal can be lost by one Access Point Access Point node but picked up by the next––you’re always connected. Just don’t roam too far. Radio Link These RLAN radios, with their little an- tennas and QRP transceivers, aren’t made for weak-signal work, though. Their in- door range is typically less than 200 feet! The Technologies What are the technologies that allow PC Laptop Palmtop RLANs to work? The radio component Figure 1––Radio Local Area Network. Devices such as PCs, laptop and palmtop 1Notes appear on page 34. computers are connected to a LAN via microwave. Access Point Access Point Radio Link Ham 1 Ham 2 Ham 3 Figure 2––Part 15 microwave radios can be adapted to establish communications among many hams over a large area. From April 2003 QST © ARRL What Does all this Have to do with Amateur Radio? Table 1 IEEE 802.11b Spread Spectrum Channel Assignments for the IEEE 802.11b transceivers, sometimes 2400-2483.5 MHz Band called WiFi devices, actually operate through the range of the 13 cm amateur Channel Center Freq, MHz Comments band and beyond. How can they operate 1 2412 Channels 1-6 are used in the US and other countries by 802.11b devices. Their emissions fall in the ham bands? All of these wireless within the 2400-2450 MHz amateur band. devices operate under FCC Part 15 rules. 2 2417 This means they are unlicensed users of 3 2422 the band and, as such, they must not cause 4 2427 interference to licensed users (hams) and 5 2432 must accept any interference caused 6 2437 them. That is the way the FCC handles 7 2442 Channels 7-11 are used in the US and other Part 15 band sharing among the various countries by 802.11b devices, but cannot be services. Hams can take advantage of the used in the Amateur Service. availability of low-cost Part 15 IEEE 8 2447 802.11b hardware by applying it to our 9 2452 Part 97 service. Imagine your own Part 10 2457 97 wireless network running high (rela- 11 2462 tive) power with high gain antennas tied 12 2467 For use in Europe only. together in a nationwide network. 13 2472 For use in Europe only. Figure 2 takes the same technology 14 2484 For use in Japan only. illustrated in Figure 1 and shows how many amateurs over a wide area are able to communicate via data, voice and video. Since the 9/11 tragedy, Amateur cell phones work––and we generally pre- Veteran hams will recall that the adapta- Radio has taken on a heightened role in fer it. RLAN technology allows for full- tion of commercial FM equipment to the national, regional and local area emer- duplex operation in voice, video and data 2 meter band enabled FM repeaters to gency communications. Emergency com- communication modes. proliferate in the 1970s. munication organizations like RACES and ARES are establishing emergency Voice over IP (VoIP) Applications response plans with government organi- VoIP applications such as eQSO, What if you had the ability to build zations such as the National Commu- iLink, EchoLink, IRLP and WIRES are networks like these? What would you do nication System (NCS) and the Federal all practical operations using the HSMM with them? Well, one of the exciting char- Emergency Management Agency mode.2 Explore and let your imagination acteristics these networks share is their (FEMA). Along with traditional commu- go to work in these areas! high throughput capacity. This means nication channels, such as HF/VHF nets, they have the ability to move lots of data packet radio and APRS, wireless LANs Digital Voice from one point to another with high reli- need to become an integral part of the Digital voice lets us use RLAN tech- ability. RLAN technology also allows a Amateur Radio response. nology to add exciting new capabilities single data source to send to a single re- to the old DX PacketCluster operation. ceiver or to many receivers using multi- Two-Way Streaming Video (ATV) Formerly, we just used a terminal pro- cast technologies. Imagine a local Amateur Radio gram to enter DX information and re- Aside from expected Internet-type videophone network that can be operated trieve WWV reports or we chatted by usage—e-mail, Web browsing, FTP, IRC from a PC, but with an RLAN communi- keyboard with other amateurs on the net- (chat) and Instant Messaging—many po- cations medium. Each station can use a work. Now we can take advantage of a tential applications could be built with simple webcam attached to a PC and that widespread, high-speed network with this technology. PC can be connected to the network via a wireless connectivity and enhance these simple wireless access device. Such a capabilities to make them more interest- Emergency Communications network would support both point-to- ing and effective. Instead of just seeing a Emergency communications offer the point and multipoint video calls. DX item, we could click on that spot and greatest opportunity for RLAN technol- hear the actual sound of the DX signal at ogy to excel and for amateurs to push the Full Duplex Streaming Audio the spotter’s location. We could also turn envelope in the public service sector, Imagine never having to say “over” to that “talk” function into a real two-way using the technology. Low power require- transfer transmission. One of the great voice communication tool. ments, low cost, portability, point- barriers to truly conversational contacts to-point, point-to-multipoint and multicast has always been the simplex communi- Remote Control capabilities, coupled with high bandwidth, cation modes we traditionally use. Ever think about putting your station make RLANs an excellent technology for Whether it’s SSB, CW, AM, FM, RTTY in a perfect, uncompromised location “on-the-spot” emergency communica- or advanced digital, other than talking and operating from the comfort of your tions. An emergency volunteer can be over the OSCAR satellites, we typically home? Well, an RLAN approach could equipped with a laptop or a wireless PDA wait for the other operator to finish a be the solution, with the right capa- (Personal Digital Assistant) with a micro- transmission and then commence send- bilities at the right price. With a single phone and a small video camera. He or ing. Full-duplex operation is the ability link from your home to a remote site, she now has the tools needed to act as a for all parties in a contact to be able to you could run full-duplex audio and mobile set of eyes and ears in the midst talk to and hear all other parties simulta- integrated control of your distant of a communications emergency. neously. That is how our telephones and station. From April 2003 QST © ARRL Table 2 Antennas for the Hinternet ARRL 13 cm Band Plan (2400-2450 MHz) By Neil Sablatzky, K8IT Band, MHz Amateur Usage In order to minimize 2400-2403 Satellite interference to FCC Part 2403-2408 Satellite high-rate data 15 users, the ARRL HSMM 2408-2410 Satellite Working Group recom- 2410-2413 FM repeaters (25 kHz mends the strict use of spacing) output horizontal polarization. 2413-2418 High-rate data This is because the major- 2418-2430 Fast-scan TV ity of Part 15 users are 2430-2438 Satellite vertically polarized. It is 2433-2438 Satellite high-rate data important to note, how- Figure A—The design of the slot antenna allows it 2438-2450 Wideband FM, FSTV, ever, that the wireless to be easily reproduced with a milling machine. FMTV, SS, experimental industry uses diversity antennas to achieve both space and polarization diversity.