Fig 1. White space radios use the UHF frequencies in the 470- to 700-MHz range because of their ability to communicate without a direct line-of-sight path. Maximum range is typically 10 km.
Fig 2. The Carlson RuralConnect IP Version II basestation consists of a SDR/CR basestation and the CPEs (a). The CPE device (b) mounts on or near the antenna and connects via an Ethernet cable to the customer’s PC or other equipment.
Fig 3. The Neul basestation (bottom) and customer terminal (top) use the license-free white space spectrum for high-speed data transmission in applications like M2M, smart meter communications, and rural broadband. Speeds to 16 Mbits/s are possible depending on the link.
You’ve been hearing a great deal about white spaces over the past few years, yet little has occurred in adoption and application because of the lack of suitable equipment. But that’s changing, as Neul and Carlson Wireless have developed and announced products to serve white space applications. These companies also have announced a joint venture to develop enhanced radios that should start the flow of white space usage.
With the continuing spectrum shortage and the growing desire to implement broadband services across the U.S., including remote and rural areas, white space appears to be an ideal low-cost solution. And with the new commercial radios available from Neul and Carlson Wireless, white space becomes practical and affordable not only for home broadband connections but also for machine-to-machine (M2M) applications.
White Space Spectrum
White space refers to the unused spectrum assigned to TV broadcast stations. Also called TV white spaces (TVWS), the spectrum comprises open 6-MHz VHF and UHF channels 2 to 51 in the 54- to 698-MHz range. The available channels vary from location to location depending upon which channels local stations are using.
Many new channels were freed up in 2009 when the television broadcast industry switched from analog to digital TV and many stations were assigned new channels. Several years ago, the Federal Communications Commission (FCC) said this unlicensed spectrum could be used if certain conditions were met. This spectrum recycling is a real benefit in these times when spectrum is so limited or expensive.
With each channel being 6 MHz wide, about 200 MHz of spectrum is available for broadband connections and other applications in the U.S. Only the UHF channels in the 450- to 700-MHz range are expected to be used. White space is also fully approved in the U.K. by Ofcom. These channels are 8 MHz wide and the bands extend up to about 800 MHz. With plenty of space and bandwidth, relatively high speeds will be available depending on the standard or protocols used.
The target application for white space radios is wireless broadband in rural areas. There are still many rural areas and small towns where good high-speed Internet connections are not available. White space spectrum is ideal for these areas because the lower frequency and non-line-of-sight (NLOS) characteristics make long-range links of several miles not only possible but very reliable. With white space, wireless Internet service providers (WISPs) can help fulfill the federal National Broadband Initiative. The costs should be relatively low for such systems (Fig. 1).
Remote monitoring and control is another great possibility. White spaces should find a niche in M2M applications, supervisory control and data acquisition (SCADA), Smart Grid connections, video surveillance cameras, medical patient monitoring, and sensor networks.
White space communications are better than most other such technologies like Wi-Fi and ZigBee because of the longer range capability. TVWS could also help bring about the predicted “Internet of Things” where we connect 50 billion items to the Internet. Then there are the backhaul possibilities. TVWS could work well in WiMAX and Wi-Fi hotspot backhaul.
White spaces are a good example of an application for cognitive radio (CR) too. CR is an extension of the software-defined radio (SDR) techniques that give radios more intelligence and decision-making capability (see “SDR And CR Boost Wireless Communications” at www.electronicdesign.com).
The FCC’s guidelines for the use of white spaces call for knowledge of the available local channels. The FCC and a number of other organizations like Spectrum Bridge and Telcordia have developed comprehensive databases logging TV stations and other wireless devices such as wireless microphones and services using these channels. To use a channel, a white space radio must access the database to see if it is being used. If the channel is being used, another is selected, preventing interference.
White space radios fall into two categories: basestations and customer premise equipment (CPE) terminals. The CPE terminals may be mobile. If a radio wants to transmit, it sends its location based on GPS coordinates to the basestation that accesses the database to see if the desired channel is open. If it is, the CPE is notified that it can transmit. In some systems, the CPE actually listens to the desired channel to assess the presence of other signals. In any case, both the basestation and CPE radios use forms of CR to make intelligent decisions on what channel to use and when.
Addressing The Market
Carlson Wireless and Neul both target rural broadband access, but their radios also can be used in IP video surveillance, well and pipeline monitoring, smart metering, traffic signal communications, and a variety of M2M applications.
Carlson’s RuralConnect IP Version II (RCIP VII) consists of a SDR/CR basestation and the CPE (Fig. 2). It’s designed to create point-to-point and point-to-multipoint networks with priority routing for voice, data, and video. Operating in the 470- to 786-MHz range, it can achieve data rates of 4, 6, 8, 12, or 16 Mbits/s in a 6-MHz channel using quadrature phase-shift keying (QPSK) or 16-state quadrature amplitude modulation (16QAM). Time division duplexing (TDD) is used as well.
A 6-MHz channel can accommodate from 40 to 60 concurrent users with a typical stream of 3 Mbits/s downstream and 1 Mbit/s upstream. Transmit power is +30 dBm and receive sensitivity is in the –86- to –89-dBm range. Security is by AES-128 with a shared secret key. The units are designed to use the Telcordia and other databases and operate under the FCC’s Part 15 rules as well as Ofcom’s regulations.
The Neul NeulNET system consists of a NeulNET 1 basestation and a NeulNET user terminal (Fig. 3). A fixed CPE terminal is available as well as a portable battery-powered terminal (see “First Commercial White Space Radios Target M2M And Broadband Applications” at www.electronicdesign.com). The basestation uses two antennas for diversity reception, boosting link reliability. Up to 16-Mbit/s data throughput is available per channel. The total range is up to 10 km depending on location, antenna placement, and other factors.
The NeulNET basestation is connected by Ethernet backhaul to the Internet to access the Neul Spectrum Management database, which holds the information for each locality describing available frequency channels and potential interference sources. The basestation adjusts its frequency accordingly. The Neul radios use a single carrier signal with a downlink of 16QAM and an uplink of binary phase-shift keying (BPSK) or QPSK depending on link conditions.
After selecting the Carlson and Neul products, both companies announced plans to offer a new system based on their previous work with Carlson supplying the RuralConnect IP Version II hardware working with Neul’s software. The combined product offering should be available later in December.