E-Band Backhaul

 

SaberTek IP offering

SaberTek has designed optimum radio architectures and has developed a collection of IP’s to enable implementation of cost-effective highly-integrated E-band radios with outstanding performance. SaberTek IP’s enable both wideband US E-band systems and channelized EU systems.

E-band Spectrum

E-Band (71-76 GHz, 81-86 GHz) is a worldwide band allocated for multi-Gbps point-to-point communications, capable of offering full-duplex Ethernet connectivity over a long range with relatively simple radio architectures.

The two allocated bands, each boasting a 5-GHz bandwidth, are much wider than most cellular and microwave bands, making them suitable for high data-rate (~10Gbps) wireless communications, while utilizing low-complexity modulation schemes and cost-effective system architectures.

Benefits of E-Band

The unique features of E band have enabled the possibility of achieving a fiber-like data rate, the highest among all commercial wireless technologies. Furthermore, unlike WiFi and WiMax, data rate for E-band links is guaranteed. The narrow pencil-beam pattern of these line-of-sight links results in minimal interference and data collision. E-band communication links with 99.99% availability can be established with lower cost per mile than links using either the 60-GHz band or free-space optics (FSO). Low atmospheric attenuation in the E band further boosts the resilience of E-band links in severe weather conditions such as dust and fog. Due to simple frequency planning and low probability of interference for E-band links, light-licensing schemes have been introduced in several countries, including US, in order to promote adoption of E-band technology by reducing total cost of ownership.

  • Fiber-like data-rate
  • Long-distance communication links
  • Rapid and Cost effective deployment
  • 99.99% all-weather availability

Technology Comparison

With increasing demand for high bandwidths by an increasing number of mobile users, telecom companies need to deploy multi-giga-bit backhaul links. Traditionally, fiber-optic links have been used to provide telecommunication backhaul soluitons. However, the high cost of installing fiber over long distances has been an obstacle in scaling existing networks to meet the requirements of emerging applications, such as 3G/4G and LTE.

A cost-effective wireless technology capable of hosting multi-Gbps long-distance data communication can provide a highly-scalable backhaul solution for 3G/4G carriers, enterprise internet access providers, and other applications.

A Cost-Effective Solution for Backhaul Applications

This wide bandwidth (71-76 GHz, 81-86GHz) enables high data-rate communication (several-Gbps) even with simple modulation schemes such as OOK, BPSK and FSK. The use of simple modulation schemes alleviates the linearity requirements for power amplifiers (PAs); hence the PAs can operate closer to their rated power, while providing higher power efficiency due to non-linear operation. This translates into the feasibility of efficient power transmission at considerably high output powers, resulting in longer communication range.

Use of low-complexity modems, efficient power amplifiers, low-cost diplexers and simpler direct-conversion system architectures, in addition to inexpensive licensing, has made E-band communication links an attractive solution for gigabit backhaul applications.

Very high datarates (>20Gpbs) is also possible by using more complex modulation schemes (like 16-QAM and 64-QAM) with the expense of more complicated transceiver modem and significantly higher power consumption.

Historical Impetus

The 70/80 GHz range was first defined by International Telecommunication Union (ITU) at World Radiocommunication conference (WRC), in 1979. Since 1990’s, FCC has been encouraging designers to use mm-wave frequencies for radio applications 1.

The use of E-band and, to some extent, 60-GHz links for wireless backhaul has gained momentum in recent years, mainly because of following factors:

  • Advances in semiconductor device technology, resulting in commercially-available E-band cost-effective MMICs.
  • Increased congestion in the  microwave bands (6-38GHz)
  • Unprecedented need for high capacity in mobile networks

In order to facilitate migration from microwave frequencies to millimeter-wave range for backhaul applications, a light-licensing scheme was introduced in the US in 2005. As a result, companies were encouraged to design their high-speed point-to-point communication systems within the E-Band frequency range. The European Telecommunications Standards Institute (ETSI) also released technical rules for equipment operating in the 71-76 and 81-86 GHz bands, in 2006.

E-Band Applications

E-band technology is well-suited for a variety of applications: Mobile backhaul

  • WiMAX/LTE/4G backhaul
  • Ethernet connectivity
  • Remote Storage Access
  • Redundant Access/Network Diversity
  • Local Area Network Extension
  • Wide Area Networks
  • Metropolitan Area Networks (MAN)

A Long-Range Communication Solution

FCC allows considerably high transmitted powers at E band  (3W), which in conjunction with the availability of high-gain, highly-directional antennas, has made this band suitable for long-range communication. These features mitigate the issue of rain fading in link budget design.

The pencil-beam radiation pattern in E-band links minimizes the probability of interference from other sources in the band, to the point that two sources can be located extremely close to each other without much concern about interference. As a result, sophisticated channelization techniques are not necessary and the entire 5-GHz bandwidth can be allocated for a single wide-band signal. However, it is possible (and in some regions, e.g. EU, mandatory) to channelize the bandwidth for implementing more complex data transmission schemes based on the requirements of the application.

E-Band Wireless Communication: Challenges

Although the use of simple modulation schemes is not spectrally-efficient, cost and complexity of the system architecture and technology limitations on commercially available E-band hardware have restricted the complexity level of modulation techniques. Recently, E-band solutions employing 16QAM have been reportedand attempts to employ higher-order modulations such as 64QAM are in progress.

In United States, the entire bandwidth is available for a single wide-band signal and channelization is not mandated by regulations. Therefore, use of simple modulation techniques is feasible, but this is not true for several other regions such as the European Union. Therefore efforts have been made to achieve required data rate while occupying less than 1GHz of bandwidth. This can be obtained by sacrificing system performance or accepting the price of design complexity and overhead. As a result cost will increase. Secondly, the system sensitivity will be reduced due to the higher signal to noise ratio requirements of a more complex system.

E-band links operate at data rates  beyond or at the edge of digital modem technology, which may become the ultimate bottleneck in the system performance. Instead, in the case of simpler modulation schemes (e.g. OOK and BPSK) modulation-demodulation procedure may be performed in the analog domain, reducing the power consumption and complexity of the digital section.

For modulation schemes higher than QPSK, the power amplifier must  operate in the linear region, backed off from its rated operating point, resulting in degraded efficiency and reduced output power. Therefore, the system architecture and link budget must be carefully designed to optimize data rate and link range.

E-band communication links are invariably outdoor units; long cables are required to deliver supply power and data from the peripheral equipment to the units. Furthermore, these radios are exposed to harsher weather conditions (such as high humidity, dust, snow, ice, and rain) and much wider temperature variations than indoor radio systems. Thus, reliability is an important specification for these systems. In most of the applications, these links are expected to operate at distances up to 2km with 99.999% weather availability (i.e., maximum down-time of 5 minutes a year) and up to 7km for 99.99% weather availability (i.e., maximum down-time of 8 hours a year).

E-Band Communication System Architectures

The 71-76GHz and 81-86GHz bands were collectively defined as E-band by ITU in WARC-79. In 2003, the FCC allocated 13GHz of unused spectrum at 70, 80 and 90GHz for high-density fixed-wireless services, which are the highestfrequency bands among the commercially licensed spectrum and form 20% of the licensed spectrum.

The E-band bandwidth is available in both channelized and non-channelized fashion, depending on the regulatory rules of different geographical regions. For example, in the US, there is no sub-channels defined and the entire bandwidth is available for high data-rate communication.

This wide bandwidth (71-76 GHz, 81-86GHz) enables high data-rate communication (~10Gbps) even with simple modulation schemes such as OOK, BPSK and FSK. This suggests the possibility of using simple transceiver architectures such as direct conversion . In turn, the local oscillators should run at frequencies close to the RF signal with wide tuning range and high spectral purity, both non-trivial to achieve at millimeter-wave frequencies. A common solution is to employ a high-performance phase-locked signal source operating at lower frequencies, followed by one or more frequency multipliers to generate the desired frequency. The use of simple modulation schemes, in some regions, alleviates the linearity requirements on the power amplifiers; hence PAs can operate close to their rated power, while providing improved power efficiency due to nonlinear operation. This translates into the feasibility of efficient power transmission at considerably high output powers, resulting in longer communication range.

E-band communication links are invariably outdoor units; hence long cables are required to deliver supply power and data from the peripheral equipment to the units. Furthermore, these radios are exposed to harsher weather conditions (such as high humidity, dust, snow, ice, and rain) and much wider temperature variations than indoor radio systems.

One of the key features that E-band links should have is the Gigabit Ethernet (GbE) interface. Depending on the application, an E-band link may need to have the ability to communicate with a fiber link, e.g. a fiber network where E-band serves as the last-mile link.

E-Band Regulatory Requirements

Different geographical regions have different regulations for 71-76GHz and 81-86GHz frequency bands.

In the United States, these bands are available without any sub-channel definition, which allows frequency-division duplexing (FDD). A 3W transmitted power is allowed by the FCC and the maximum out-of-band emission must be less than -13dBm. In contrast with the relaxed transmitted power requirements, the antenna requirements are stricter in order to guarantee a narrow beam radiation pattern for the link, hence simplifying the interference requirements and facilitating a light-licensing scheme.

Parameter

Requirement
Maximum EIRP 55dBW (300 kW)
Maximum Transmitter Power 5dBW (3W)
Maximum Transmitter Power Spectral Density 150mW/100MHz
Minimum Antenna Gain 43dBi
Minimum Spectral Efficiency 0.125bps/Hz

In Europe, the CEPT has allocated 19 channels of 250-MHz bandwidth each and two 125-MHz guard bands, in each of the 5-GHz-wide E bands. Several channel-pairing scenarios are possible, and time-division duplexing (TDD) is also allowed. In several countries in Europe, including UK, all of the 19 channels can be paired together, resulting in a 4.75-GHz-wide band. In some countries, some portions of the bands are not available for commercial use due to prior allocation for other applications such as military communication. For example, in the Czech Republic, only 74-76GHz and 84-86GHz frequency ranges are available for commercial communication.

Regulatory requirements for E-band are more stringent in Europe than in the US. The EMC and safety rules in Europe are very similar to 60-GHz regulations. A maximum EIRP of 55dbW and minimum antenna gain of 38dBi are mandated. Typical maximum allowed transmitted power is 30dBm. Out-of-band emission is limited to -55dBW/MHzat the band edge. Similar to other point-to-point communication links in Europe, spurious emissions should be less than -30dBm.

In Europe, the Earth Exploration Satellite Service band from 86 to 92 GHz is a passive band and necessitates very low out-of-band emission for the adjacent bands. As a result the E-band frequency mask experiences a sharp discontinuity at the 86GHz boundary.

Australia also uses the non-channelized bands of 71.125-75.875GHz and 81.125-85.875GHz. It has adopted the 2007 version of the regulatory rules in United Kingdom, with a minimum antenna gain of 43dBi, maximum EIRP of 45dBW and maximum transmitter output power of 30dBm.

Due to the fact that a huge amount of study and legislative effort is required in order to open a new portion of the spectrum for public use, E-band is not licensed in a vast region across the world such as Canada, China, Japan and India. However, employing this band for data communication has been examined under temporary license schemes and as a result, some E-band wireless links have been installed.

E-Band Licensing

The unique characteristics of E-band narrow-beam highly-focused radiation and non-channelized frequency band suggest easy frequency planning.

The regulatory agencies in different countries have found the above characteristics as enabling factors in the simplification of the licensing process. With a simplified interference analysis and no frequency coordination, conventional link-licensing schemes are not necessary. The application processing time has been reduced to near real-time, with interference analysis and approval realizable in minutes. As a result of these savings in time and expenses, the cost of such licenses has been significantly reduced, promoting adoption of high data-rate link services at the E-band frequencies.

 

  1. www.fcc.gov