Pole Sway and Small Cell Deployments for Wireless Backhaul

The two main vibration types for light poles are shown in figure 1.

The two main vibration types for light poles are shown in this figure. Both of these two vibration types will create sway that might affect the link performance for small cell microwave backhaul.

There is real concern from operators that utility, streetlight and traffic poles are not designed to meet the minimum twist and sway standards for deploying microwave solutions for small cell backhaul. Our research suggests that not all poles are created equal, however. Under certain circumstances these structures can be an option for deploying microwave backhaul for small cells.

Twist and sway requirements for towers and poles that support microwave backhaul hops are more stringent than for other RF equipment. This is especially true for deployments in frequency bands above 18 GHz where the antenna beamwidth is narrower than below 18 GHz. Standards such as the TIA-222-G set a minimum twist and sway that a structure should be able to endure for hosting a microwave installation. This creates concerns for operators interested in deploying microwave for small cell backhaul on structures including utility, streetlight and traffic poles that are not designed to meet this standard. Although the use of a sturdy structure is always recommended a close look at utility, streetlight and traffic poles suggests that under certain circumstances these structures can be an option for deploying microwave backhaul for small cell.

The installation of any equipment on existing poles—including small cell and backhaul radios and antennas—will necessarily change the weight and wind loading characteristics of the deployment pole. This will require a structural analysis to verify if the existing pole still meets the standards or the commercial criteria set by the pole manufacturer. For more information on Aviat’s analysis of pole sway for small cell backhaul see our PDF.

Eduardo Sanchez
Marketing Engineering Specialist
Aviat Networks

It’s a Whole New World at 4G World

4G World October 29, 2012, ChicagoThe 4G World show is in 10 days in Chicago, Ill. Speaking of 4G, those of us at Aviat Networks are excited to see what LTE technology will be on display and its promise of 4G speeds for our mobile networks. Confusion will mount as vendors address the myriad capabilities of LTE and the challenges of implementing such an amazing network. Small cell access will be a key topic. Mobile operators need these outdoor-mounted, street-level smaller versions of their LTE basestations to offload some of the overwhelming demand for capacity in metro areas.

One of the critical small cell challenges is backhaul. Imagine the complexity of aggregating traffic from the numerous small cells deployed at key intersections in a big city. Fiber cannot be everywhere and is not economical to operate in most metro locations. There is a lot of buzz around unlicensed Non-Line-of-Sight (NLOS) Point-to-Multipoint (PMP) radios that take advantage of fewer installations than traditional Point-to-Point (PTP) microwave. But be careful of comparisons between PMP and PTP microwave…we hear a lot of hype, promulgated by confusion and relying on fear!

Unlicensed spectrum sounds good but suffers from serious interference issues. NLOS radio capacity drops significantly when trying to transmit around a building. You have to ask: Is the resultant capacity sufficient to serve this specific small cell backhaul need? There are also concerns over latency because LTE has strict delay requirements, and Voice over LTE (VoLTE) will really struggle if latency is not within specification. What about spectrum…is it actually available? Is there only 20 MHz of spectrum available when 40 MHz of capacity is needed?

What about good ol’ reliable and proven Line of Sight (LOS) PTP microwave? With the emergence of millimeter wave PTP radios, capacities up to 1Gbps can be achieved easily over 1-2 kilometers—certainly sufficient for metro small cell distances!

If you have a chance to attend the show, please take the time to ask some of these questions…or else you may be victimized by hype, confusion or fear.

If you would like to hear straight talk on this topic, tune into Aviat’s Small Cell Backhaul webinar. Stay tuned for future blog posts to read about spectrum, capacity, latency, FCC rule changes and technology evolution as the search for viable solutions to the small cell backhaul challenge continues!

Randy Jenkins
Director Business Development
Aviat Networks

Developments in Fixed Link Spectrum Access in Ireland

spectrum

Spectrum (Photo credit: Free Press Pics)

In response to the ever-growing demand for spectrum to satisfy the increase in usage of data hungry mobile applications and in line with recently published ECC recommendations, ComReg (i.e., Ireland’s telecom regulator) issued a consultation document looking at the future demands on spectrum for point-to-point fixed links. September saw the publication of the conclusions and subsequent decisions arising from that consultation, to which Aviat Networks was the only manufacturer to respond. This blog highlights some of those decisions:

New Spectrum
One of the major topics was the requirement for more spectrum allocated for point-to-point usage. Consequently, ComReg has made the following announcements:

  • ComReg intends to open the frequency bands below, as there is a significant demand for fixed links services in the 28 GHz, 31 GHz and 40 GHz band:ComReg microwave spectrum rules change September 2012
  • The 32 GHz band may be made available for fixed links services at a later stage subject to its potential for future PP/PMP use and the demand on spectrum for PP use in the 31 GHz (31.0 – 31.3 GHz paired with 31.5 – 31.8 GHz) band
  • Within the 28 GHz band, as per REC T/R 13-02 Annex C, the following frequency ranges will be made available for fixed links services: 27.9405 – 28.4445 GHz and 28.9485 – 29.4525 GHz
  • Frequency bands 28 (27.5 – 29.5) GHz, 31 (31.0 – 31.3 paired with 31.5 – 31.8) GHz, 32 (31.8 – 33.4) GHz and 40 (40.5 – 43.5) GHz will not be opened for PMP use in the current spectrum strategy period 2011 – 2013

Aviat Networks supported this initiative during the consultation process and is pleased to see ComReg make these announcements as a move to satisfy the increasing demand for microwave spectrum. Specifically, frequencies in the range of 28 to 42 GHz are ideal for short-haul urban links, and we expect the decision by ComReg to stimulate further growth of microwave for fixed line and mobile network applications.

Technical Changes

  • High-Low search radii for the 23 GHz and 26 GHz bands will be reduced from 200 meters to 100 meters. The consensus of current licensees operating within the 23 GHz and 26 GHz bands is that the reduced radius will improve spectrum planning and reuse, which will improve spectral efficiency
  • There will be no distinction between rural and urban areas concerning the High-Low search radius
  • Antenna size will be limited to 0.6 meters in the 23 GHz and 26 GHz bands
  • ComReg will allow use of 56 MHz channels in the 26 GHz band only where the licensee has a National Block license containing contiguous blocks of spectrum
  • ComReg will permit the use of higher bandwidths, as shown in the table below, to facilitate the increase in mobile data demand:ComReg microwave spectrum rules changes September 2012

Block Licensing
ComReg signalled its intention to potentially reopen the 26 GHz block license scheme for a further round of National Block assignments, subject to market demand. In the past, Aviat Networks commented that it believes block licensing is not the most appropriate method of licensing in the microwave bands. However, ComReg disagrees with that view.

Summary
The combined expansion in spectrum use—new bands and larger channel allocations—underlines the popularity and ongoing viability of microwave as an alternative to fiber in urban networks experiencing rapid traffic growth and geographic expansion.

Aviat Networks welcomes the ComReg announcement. We already address all the band/channel assignments made by ComReg.

Ian Marshall
Regulatory Manager
Aviat Networks

Evolution of Trunking Microwave Radios

Aviat WTM 6000 trunking microwave radio

Aviat WTM 6000 trunking microwave radio

Back in the day, trunking microwave radios were huge power-hungry beasts that consumed vast quantities of power and space at equal rates. They were complex “animals” that took days to install and hours to configure. Then they had to be looked after like well-loved but aged members of the family—with care, all due respect and consideration. Over time, components went out of adjustment and had to be brought back into line through various tuning routines, but overall they did their job as the super-reliable backbone of the POTS (i.e., Plain Old Telephone Service).

Jump forward a few decades and the latest trunking microwave solutions are elegant and graceful—almost svelte. With their current high levels of electronic integration, a complete repeater system can stand in a single rack space—unheard of until the most recent products. Furthermore, these new systems consume dramatically less power—a typical 3+1 system (i.e., four transceivers) consumes less than 400 watts. So now, backbone operators can save significantly on operating expenditure because of decreased space and power requirements at their microwave radio shelters.

Evolving microwave systems from analog to digital microwave systems carrying digital payloads was a rocky and dangerous path. The next migration from TDM payloads to IP payloads appears to be just as treacherous. How can a traditional TDM backbone radio, typically configured with N+1 radio protection switching, be reconfigured to transport a non-TDM payload that does not suit N+1 switching? IP transport is a completely different environment altogether! Luckily, trunking radio system designers have not ignored the Internet revolution and are perfectly aware of these challenges. In fact, well-appointed trunking microwave radio systems allow a graceful evolution from TDM to IP, with capability to transport both types of traffic simultaneously—and with their own ultra-reliable protection schemes!

Today, trunking microwave radios can support both TDM and IP seamlessly, offer robust radio performance and highly reliable switching and really do make it easy for operators to design mission-critical backbone networks. They offer mean time between failure (MTBF) reliability figures into the hundreds-of-years and highly integrated yet modular designs, which make expansion very straightforward. Before deciding on a trunking microwave radio, consider if the system:

  • Allows easy migration from TDM to IP with a minimal amount of replacement materials
  • Can expand to an expected maximum channel capacity (for example, six channels) without needing additional racks, etc.
  • Enables repeater configurations within one rack
  • Has a field-proven heritage of reliability and performance

Terry Ross
Senior Product Manager
Aviat Networks