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Cambium Networks introduced a Point-to-Point (PTP) 650S Small Cell backhaul radio that delivers up to 450 Mbps aggregate throughput at 2km and packaged in a small form factor suitable for mounting on the sides of buildings or poles.

The Cambium PTP 650S is a sub-6 GHz point-to-point (PTP) wireless backhaul solution tailored for small cell networks. Non-line-of-sight (NLOS) installations are made possible by 2x2 multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) and Dynamic Spectrum Optimization (DSOTM) technologies. Bands supported include 4.9, 5.2, 5.4 and 5.8 GHz frequencies, and future support of 2.6 and 3.5 GHz is planned. Timing and synchronization support includes IEEE 1588v2 and Synchronous Ethernet.

Cambium also noted that with a volume of less than 3 liters volume (or less than 0.1 cubic feet), the PTP650S can qualify as “De Minimis” in certain European countries and the UK, and therefore does not require planning permission enable rapid small cell deployments.

"Performance, reliability, scalability and agility are the cornerstones of all of our platforms. In PTP 650S, we have given all of these qualities a boost with built-in technologies: dynamic spectrum optimization (DSO), IEEE 1588v2, Synchronous Ethernet, and dual stack IPv4 and IPv6 support to name a few,” said Scott Imhoff, vice president of product management, Cambium Networks. “With small cell networks continuing to proliferate and require additional support, in addition to the need for flexible platforms to suit global connectivity spanning industries and applications, the timing for PTP 650S’s release couldn’t be better."

by Peter Strong, Chief Architect and Director, Cambium Labs, Cambium Networks (

Peter Strong

MIMO-OFDM has become an important wireless communication technique because it can obtain increasing data throughputs from limited wireless spectrum. It provides high spectral efficiency over a wide range of radio channel conditions. This is important as customers demand high throughput for bandwidth hungry applications.

Orthogonal Frequency Division Multiplexing (OFDM) refers to a communication technique where a data stream is sent over a large number of closely packed subcarriers. All subcarriers are modulated at a baud rate below but close to the subcarrier spacing, typically using Quadrature Amplitude Modulation (QAM). The subcarrier spacing for the two prominent broadband wireless access standards today are 15 kHz for LTE and 312.5 kHz for 802.11ac.

Normally OFDM is supplemented with a guard interval, interleaver and forward error correction. The combination allows the OFDM demodulator to provide tolerance to radio links with multipath. The frequency selective fading caused by multipath may introduce deep nulls into a received signal. With coded OFDM, subcarriers with a good receive Signal to Noise Ratio (SNR) can protect the subcarriers with poor receive SNR in the vicinity of the nulls.

Multiple Input and Multiple Output (MIMO) refers to the RF propagation channel. The multiple inputs are the two or more transmit antennas radiating signals into the RF channel, and the multiple outputs are the two or more receive antennas collecting signals from the RF channel.

MIMO systems offer diversity gain, interference mitigation and spatial multiplexing gain. Diversity gain arises at both the transmitter and the receiver due to  de-correlated fading between different TX and RX antenna pairs, diversity gain reduces the fade margin required to sustain a given link availability in a fading channel.

The challenges in making wireless broadband connectivity work are mostly environmental. For radio channels commonly used for broadband wireless, best link performance is typically obtained from Line Of Sight (LOS) channels having no reflections. In contrast, Non-Line of Sight (NLOS) links are perturbed by obstructions and reflections.

While LOS-only operation relaxes the demands on the radio, it adds cost to the system by restricting antenna placement. The overall cost of a wireless link may be significantly reduced by relaxing the requirements to tolerate some level of NLOS operation while still providing the users required data throughput and availability. This reduces the siting constraints of the antennas, which gives link planners more options.

The development of MIMO-OFDM has greatly assisted in the successful deployment of wireless networks in challenging environments. Interference mitigation may be provided by using MIMO to perform beam forming and beam nulling to avoid the interfering sources. Spatial multiplexing gain results from the channel supporting more than one spatial stream.

The techniques of MIMO and OFDM form a particularly compelling combination for broadband wireless. Together these maximize the throughputs and availability achievable in a wide range of RF channel conditions ranging from deep NLOS with high levels of multi-path to benign radio links capable of supporting high rate modulation modes.

The need for more than one antenna with MIMO does not necessarily result in a significant increase in the antenna profile. With 2×2 MIMO, a popular configuration is to use dual polarization antennas occupying the same aperture. This gives the benefits of dual stream operation for most channel conditions and some diversity gain when the channel only supports single stream modes.