As the demand for network services continues to grow in critical infrastructure and public safety, it will become increasingly important for small cells to provide high-throughput and high-efficiency backhaul. In a recent demonstration, Cambium Networks established a point-to-point network link streaming high-definition (HD) video and voice over Internet Protocol (VoIP) services stretching over 150 miles.
The network link was designed with two parallel links, using a pair of wireless broadband antennas operating in the 5 GHz unlicensed spectrum. The point-to-point link spanned from Pikes Peak, Colo., through the metropolitan area of Denver, Colo., and then ending in Cheyenne, Wyo. The network was managed by dynamic spectrum optimization (DSO), which enabled the network to automatically sample and change communication channels, avoiding interference without affecting service.
The data transmission was based on Orthogonal Frequency Division Multiplexing (OFDM), a technology that splits and encodes data on multiple carrier frequencies. OFDM technology transmits data over several parallel data streams, using a large number of closely spaced modulated carrier signals. This method of splitting data over multiple streams has the advantage of reducing severe channel conditions, such as attenuation of high frequencies, narrowband interference, and frequency-selective fading—without having to resort to complex equalization filters.
The other advantage of the OFDM waveform is that it provides point-to-point communications out of the line of sight. The network link was able to provide coverage across rugged terrain, ignoring tall buildings, foliage, and other obstructions that normally limit wireless broadband access. While Cambium Networks operated the backhaul link with 256-QAM adaptive modulation, the OFDM waveform can support multiple modulation schemes—such as the four used in IEEE 802.11 networks—to adjust data rates based on signal conditions.
These point-to-point communication links are growing more widespread in an attempt to reduce costs and enhance existing services. The technology is taking root among public safety workers, emergency responders, and utilities and energy companies, among others. In a recent example, the Urbalis Fluence train-control system developed by Alstom was upgraded to communications-based signaling to manage high-capacity metro lines.
The parallel links used in the network were established using Cambium’s PTP 650 and PTP 700 backhauls. The former, operating from 4.9 to 6.05 GHz, is capable of pulling 450 Mbits/s of throughput in a 45 MHz channel. The PTP 700, on the other hand, supports up to 450 Mbps of aggregate throughput in a 45 MHz channel, operating from 4.4 GHz to 5.9 GHz.