Many users consider upgrading existing Wireless Links such as Dragonwave to add greater capacity, or network coverage. When considering a wireless vendor, factors generally include:
Vendor Track Record
Vendor Corporate Stability
Product Performance & Reliability
Product Support and Service
Attractive Vendor Roadmap
Product Pricing including all required options
Generally, Microwave links are required to operate unattended for many years in challenging outdoor environments, and therefore reliable and stable products and vendors are paramount in the selection process.
Turbulence in Wireless Vendor Market Space
Amongst many ongoing changes in the market for Microwave Backhaul and Microwave Transmission vendors, there is ongoing consolidation, M&A, and other activities. Recently, Packet Microwave Vendor Dragonwave recently underwent receivership and buy-out by Transform-X.
Once a significant player in the microwave backhaul space, Ottawa, Canada-based company DragonWave has effectively shutdown, with the Ontario Superior Court of Justice placing a financial receiver in charge of the firm’s “property, assets and undertakings.”
With assets sold by the Receiver to Transform-X, and the Dragonwave business is no doubt being reshaped by the new owners of the business.
Upgrade to Latest Microwave Technology for Higher Capacities
Some vendors are fully shipping products today with 1024QAM, XPIC, and upgrades to 2048QAM, XPIC, 10Gbps MMW (Millimeter Wave), which are features above and beyond those achieved by many in the market today. Customers can upgrade today and achieve higher capacity, longer range, reach and availability, at low Total Cost of Ownership compared to competing options.
Future Roadmap for Microwave Upgrades
In addition to today’s products, an impressive roadmap ensures access to higher speed links and features in future products also. Consideration is worthwhile into:
Vendor roadmaps to higher capacity links with microwave up to 4Gbps or more per link existing today.
Upgrading to E-Band MMW for shorter links especially in congested city environments
Using E-band Millimeter Wave for short links to free-up existing microwave spectrum, relief of spectral congestion and re-using valuable microwave spectrum for longer links where required
1024QAM Microwave Links for High Capacity Wireless Transmission
High Capacity Microwave Links from leading vendors use 1024QAM modulation to achieve high capacity, spectral density and efficiency without sacrificing reliability. This technology sets a new benchmark for microwave transmission capacity for operators including 4G / LTE Backhaul links for mobile operators as well as last-mile links, backbone and other applications.
High Capacity Links require High Order QAM modulation
Leading long-haul microwave equipment vendors are now using dependable long-distance transmissions using 1024 QAM. Relative to the industry-standard 256 QAM, this represents a 25% increase in capacity (and up to double the capacity of legacy SDH links), with all other factors the same. Compared to older 4QAM modulation the increase to 1024QAM is five-fold. Operators of long-haul microwave links will certainly enjoy the boost to their capacity with 1024 QAM, especially when these upgrades are relatively painless and generally require only a minor and quick swap of equipment.
Adaptive Coding and Modulation (ACM)
Leading microwave equipment vendors are able to keep their long-haul transmission links operational even in transient fade and noisy conditions. The enabling technology is ACM: Adaptive Coding and Modulation. Microwave links with ACM technology automatically sense the quality of the transmission link and can automatically decrease the modulation technique in case of degraded signal quality due to interference or other microwave propagation problems such as weather. So, if a microwave transmission is operating at maximum capacity using 1024QAM and suddenly encounters interference or high rainfall, a system such as the CableFree microwave system automatically steps down the modulation to lower levels until the transmission network, although at lower capacity now, maintains the ultra high level of link reliability and availability. As the temporary weather effects disappear, the microwave system automatically re-applies more efficient higher-order modulation techniques to regain full capacity.
Overcoming Tradeoffs due to High Order QAM Modulation
With increasing modulation the receiver sensitivity is greatly reduced, and generally transmit power has to be reduced due to linearity constraints in the transmitter. For fixed modulation speeds the result is either increase of antenna size or reduced distances, which may prevent an operator upgrading to higher capacity. The use of ACM allows use of 1024QAM whilst avoiding sacrifice of distance or antenna sizes, by graceful step-down of modulation to lower rates during rare periods of high rainfall.
Use along with other bandwidth-enhancing technologies such as XPIC
1024QAM modulation is fully compatible with other methods to increase capacity such as XPIC (Cross Polar Interference Cancellation). An advanced microwave modem featuring 1024QAM and XPIC can greatly increase capacity. XPIC alone offers double the capacity compared to a single polarised non-XPIC solution.
1024QAM Microwave Summary
These latest advancements in advanced microwave modulation offer network operators an easy and inexpensive upgrade path to higher capacities to meet demand. Advanced modulation technology of 1024QAM is fully shipping and available today and offers a very cost-effective way to boost capacity in long-haul microwave applications.
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The term ODU is used in Split-Mount Microwave systems where an Indoor Unit (IDU) is typically mounted in an indoor location (or weatherproof shelter) connected via a coaxial cable to the ODU which is mounted on a rooftop or tower top location.
Often the ODU is direct mounted to a microwave antenna using “Slip fit” waveguide connection. In some cases, a Flexible Waveguide jumper is used to connect from the ODU to the antenna.
The ODU converts data from the IDU into an RF signal for transmission. It also converts the RF signal from the far end to suitable data to transmit to the IDU. ODUs are weatherproofed units that are mounted on top of a tower either directly connected to a microwave antenna or connected to it through a wave guide.
Generally, Microwave ODUs designed for full duplex operation, with separate signals for transmit and receive. On the airside interface this corresponds to a “pair” of frequencies, one for transmit, the other for receive. This is known as “FDD” (Frequency Division Duplexing)
ODU Power and data signals
The ODU receives its power and the data signals from the IDU through a single coaxial cable. ODU parameters are configured and monitored through the IDU. The DC power, transmit signal, receive signal and some command/control telemetry signals are all combined onto the single coaxial cable. This use of a single cable is designed to reduce cost and time of installation.
ODu Frequency bands and sub-bands
Each ODU is designed to operate over a predefined frequency sub-band. For example 21.2 – 23.6GHz for a 23GHz system, 17.7 – 19.7GHz for a 18GHz system and 24.5 – 26.5GHz for a 26GHz system as for ODUs. The sub-band is set in hardware (filters, diplexer) at time of manufacture and cannot be changed in the field.
1+0, 1+1, 2+0 Deployments
Microwave ODUs can be deployed in various configurations.
The most common is 1+0 which has a single ODU, generally connected directly to the microwave antenna. 1+0 means “unprotected” in that there is no resilience or backup equipment or path.
For resilient networks there are several different configurations. 1+1 in “Hot Standby” is common and typically has a pair of ODUs (one active, one standby) connected via a Microwave Coupler to the antenna. There is typically a 3dB or 6dB loss in the coupler which splits the power either equally or unequally between the main and standby path.
Other resilient configurations are 1+1 SD (Space Diversity, using separate antennas, one ODU on each) and 1+1 FD (Frequency Diversity)
The other non-resilient configuration is 2+0 which has two ODUs connected to a single antenna via a coupler. The hardware configuration is identical to 1+1 FD, but the ODUs carry separate signals to increase the overall capacity.
Grounding & Surge Protection
Suitable ground wire should be connected to the ODU ground lug to an appropriate ground point on the antenna mounting or tower for lightning protection. This grounding is essential to avoid damage due to electrical storms.
In-line Surge Suppressors are used to protect the ODU and IDU from surges that could travel down the cable in the case of extreme surges caused by lightning
The specification of a typical Microwave ODU is shown below.
Typical ODU Features and Specifications:
4-42GHz frequency bands available
Fully synthesized design
3.5-56MHz RF channel bandwidths
Supports QPSK and 16 to 1024 QAM. Some ODUs may support 2048QAM
Standard and high power options
High MTBF, greater than 92.000 hours
Software controlled ODU functions
Designed to meet FCC, ETSI and CE safety and emission standards
Supports popular ITU-R standards and frequency recommendations
Software configurable microcontroller for ODU monitor and control settings
Low noise figure, low phase noise and high linearity
Compact and lightweight design
Very high frequency stability +/-2.5 ppm
Wide operating temperature range: -40°C to +65°C
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5G Mobile networks, Microwave Backhaul and future trends in Mobile Networks
With 5G mobile communication becoming available around 2020, the industry has already started to develop a fairly clear view of the main challenges, opportunities and key technology components it involves. 5G will extend the performance and capabilities of wireless access networks in many dimensions, for example enhancing mobile broadband services to provide data rates beyond 10 Gbps with latencies of 1 ms.
Microwave is a key element of current backhaul networks and will continue to evolve as part of the future 5G ecosystem. An option in 5G is to use the same radio access technology for both the access and the backhaul links, with dynamic sharing of the spectrum resources. This can provide a complement to microwave backhaul especially in very dense deployments with a larger number of small radio nodes.
Today, microwave transmission dominates mobile backhaul, where it connects some 60 percent of all macro base stations. Even as the total number of connections grows, microwave’s share of the market will remain fairly constant. By 2019, it will still account for around 50 percent of all base stations (macro and outdoor small cells (see Figure 3). It will play a key role in last mile access and a complementary role the aggregation part of the network. At the same time, fibre transmission will continue to increase its share of the mobile backhaul market, and by 2019 will connect around 40 percent of all sites. Fibre will be widely used in the aggregation/metro parts of the networks and increasingly for last-mile access. There will also be geographical differences, with densely populated urban areas having higher fibre penetration than less populated suburban and rural areas, where microwave will prevail for both short-haul and long-haul links.
Spectrum efficiency (that is, getting more bits per Hz) can be achieved through techniques like higher-order modulation and adaptive modulation, the superior system gain of a well-designed solution, and Multiple Input, Multiple Output (MIMO).
The maximum number of symbols per second transmitted on a microwave carrier is limited by the channel bandwidth. Quadrature Amplitude Modulation (QAM) increases the potential capacity by coding bits on to each symbol. Moving from two bits per symbol (4 QAM) to 10 bits per symbol (1024 QAM) delivers a more than five-fold capacity increase.
Higher-order modulation levels have been made possible through advances in component technologies that have reduced equipment-generated noise and signal distortion. In the future there will be support for up to 4096 QAM (12 bits per symbol), but we are approaching the theoretical and practical limits. Higher-order modulation means increased sensitivity to noise and signal distortion. The receiver sensitivity is reduced by 3 dB for every increased step in modulation, while the related capacity gain gets smaller (in percentage terms). As an example, the capacity gain is 11 percent when moving from 512 QAM (9 bits per symbol) to 1024 QAM (10 bits per symbol).
Increasing modulation makes the radio more sensitive to propagation anomalies such as rain and multi-path fading. To maintain microwave hop length, the increased sensitivity can be compensated for by higher output power and larger antennas. Adaptive modulation is a very cost-effective solution to maximize throughput in all propagation conditions. In practice, adaptive modulation is a prerequisite for deployment with extreme high-order modulation.
Adaptive modulation enables an existing microwave hop to be upgraded from, for example, 114 Mbps to as much as 500 Mbps. The higher capacity comes with lower availability. For example, availability is reduced from 99.999 percent (5 minutes’ yearly outage) at 114 Mbps to 99.99 percent of the time (50 minutes’ yearly outage) at 238 Mbps. System gain Superior system gain is a key parameter for microwave. A 6 dB higher system gain can be used, for example, to increase two modulation steps with the same availability, which provides up to 30 percent more capacity. Alternatively it could be used to increase the hop length or decrease the antenna size, or a combination of all. Contributors to superior system gain include efficient error correction coding, low receiver noise levels, digital predistortion for higher output power operation, and power-efficient amplifiers, among others.
MIMO Multiple Input, Multiple Output (MIMO)
MIMO is a mature technology that is widely used to increase spectral efficiency in 3GPP and Wi-Fi radio access, where it offers a cost-effective way to boost capacity and throughput where available spectrum is limited. Historically, the spectrum situation for microwave applications has been more relaxed; new frequency bands have been made available and the technology has been continuously developed to meet the capacity requirements. However in many countries the remaining spectrum resources for microwave applications are starting to become depleted and additional technologies are needed to meet future requirements. For 5G Mobile Backhaul, MIMO at microwave frequencies is an emerging technology that offers an effective way to further increase spectrum efficiency and so the available transport capacity.
Unlike ‘conventional’ MIMO systems, which are based on reflections in the environment, for 5G Mobile Backhaul, channels are ‘engineered’ in point-to-point microwave MIMO systems for optimum performance. This is achieved by installing the antennas with a spatial separation that is hop distance-and frequency-dependent. In principle, throughput and capacity increase linearly with the number of antennas (at the expense of additional hardware cost, of course). An NxM MIMO system is constructed using N transmitters and M receivers. Theoretically there is no limit for the N and M values, but since the antennas must be spatially separated there is a practical limitation depending on tower height and surroundings. For this reason 2×2 antennas is the most feasible type of MIMO system. These antennas could either be single polarized (two carrier system) or dual polarized (four carrier system). MIMO will be a useful tool for scaling microwave capacity further, but is still at an early phase where, for example, its regulatory status still needs to be clarified in most countries, and its propagation and planning models still need to be established. The antenna separation can also be challenging especially for lower frequencies and longer hop lengths.
Another section of the microwave capacity toolbox for 5G Mobile Backhaul involves getting access to more spectrum. Here the millimeter-wave bands – the unlicensed 60 GHz bands and the licensed 70/80 GHz band – are growing in popularity as a way of getting access to new spectrum in many markets (see Microwave Frequency Options section for more information). These bands also offer much wider frequency channels, which facilitate deployment of cost-efficient, multi-gigabit systems which enable 5G Mobile Backhaul.
Throughput efficiency (that is, more payload data per bit), involves features like multi-layer header compression and radio link aggregation/bonding, which focus on the behaviour of packet streams.
Multi-layer header compression
Multi-layer header compression removes unnecessary information from the headers of the data frames and releases capacity for traffic purposes, as shown in Figure 7. On compression, each unique header is replaced with a unique identity on the transmitting side, a process which is reversed on the receiving side. Header compression provides relatively higher utilization gain for packets of smaller frame size, since their headers comprise a relatively larger part of the total frame size. This means the resulting extra capacity varies with the number of headers and frame size, but is typically a 5–10 percent gain with Ethernet, IPv4 and WCDMA, with an average frame size of 400–600 bytes, and a 15–20 percent gain with Ethernet, MPLS, IPv6 and LTE with the same average frame size.
These figures assume that the implemented compression can support the total number of unique headers that are transmitted. In addition, the header compression should be robust and very simple to use, for example offering self-learning, minimal configuration and comprehensive performance indicators.
Radio Link Aggregation (RLA, Bonding)
Radio link bonding in microwave is akin to carrier aggregation in LTE and is an important tool to support continued traffic growth, as a higher share of microwave hops are deployed with multiple carriers, as illustrated in Figure 8. Both techniques aggregate multiple radio carriers into one virtual one, so both enhancing the peak capacity as well as increasing the effective throughput through statistical multiplexing gain. Nearly 100 percent efficiency is achieved, since each data packet can use the total aggregated peak capacity with only a minor reduction for protocol overhead, independent of traffic patterns. Radio link bonding is tailored to provide superior performance for the particular microwave transport solution concerned. For example, it may support independent behaviour of each radio carrier using adaptive modulation, as well as graceful degradation in the event of failure of one or more carrier (N+0 protection).
Just like carrier aggregation, radio link bonding will continue to be developed to support higher capacities and more flexible carrier combinations, for example through support for aggregation of more carriers, carriers with different bandwidths and carriers in different frequency bands.
The next section of the capacity toolbox is network optimization. This involves densifying networks without the need for extra frequency channels through interference mitigation features like super high performance (SHP) antennas and automatic transmit power control (ATPC). SHP antennas effectively suppress interference through very low sidelobe radiation patterns, fulfilling ETSI class 4. ATPC enables the transmit power to be automatically reduced during favorable propagation conditions (that is, most of the time), effectively reducing the interference in the network. Using these features reduces the number of frequency channels needed in the network and could deliver up to 70 percent more total network capacity per channel. Interference due to misalignment or dense deployment is limiting backhaul build-out in many networks. Careful network planning, advanced antennas, signal processing and the use of ATPC features at a network level will reduce the impact from interference.
Looking to the future, 5G and Beyond
Over the coming years, microwave capacity tools for 5G Mobile Networks will be evolved and enhanced, and used in combination enabling capacities of 10 Gbps and beyond. Total cost of ownership will be optimized for common high-capacity configurations, such as multi-carrier solutions.
Modulation is a data transmission technique that transmits a message signal inside another higher frequency carrier by altering the carrier to look more like the message. Quadrature Amplitude Modulation (QAM) is a form of modulation that uses two carriers—offset in phase by 90 degrees—and varying symbol rates (i.e., transmitted bits per symbol) to increase throughput. The table in this blog post (Figure 1) describes the various common modulation levels, associated bits/symbol and incremental capacity improvement above the next lower modulation step.
2. Must all operators who use microwave backhaul use higher-order QAMs?
Higher-order QAMs are not necessarily a must-have for all network operators. However, higher-order modulations do provide one method of obtaining higher data throughput and are a useful tool for meeting LTE backhaul capacity requirements.
3. What is the main advantage of using higher-order QAMs with microwave radios?
The main advantage is increased capacity, or higher throughput. However, capacity improvement diminishes with every higher modulation step (i.e., moving from 1024QAM to 2048QAM the improvement is only about 10 percent!), so the real capability of higher-order modulations alone to address the objective of increasing capacity is very limited. Other techniques will be needed.
4. What are the tradeoffs of higher-order QAMs on RF performance?
First, with each step increase in QAM the RF performance of the microwave radio is degraded as per the Carrier-to-Interference (C/I) ratio. For example, going from 1024QAM to 2048QAM will produce an increase of 5 dB in C/I (Figure 2). This results in the microwave link having much higher sensitivity to interference, making it more difficult to coordinate links and reducing link density. Along with this increase in phase noise there will be an increase in design complexity cost.
Also, by increasing from 1024QAM to 2048QAM, system gain will decrease from above 80 dB to just above 75 dB (Figure 2). With much lower system gain microwave links will have to be shorter and larger antennas will have to be employed—increasing total cost of ownership and introducing additional link design and path planning problems.
All of the above are the results of linear functions: they degrade in a one-to-one relationship with the move to higher-order QAMs. Meanwhile, the capacity increases derived from higher-order QAMs are the function of a flattening curve: Each step increase in QAM results in a reduced percentage increase in capacity compared to prior increases in QAM. The added capacity benefits are diminished when considering the added costs of higher C/I and lower system gain.
5. Do you need to use Adaptive Coding and Modulation (ACM) while using higher-order QAMs?
ACM should be implemented while employing high-order QAMs to offset lower system gain. However, while ACM does help mitigate the effects of more difficult propagation when using higher-order modulations, it cannot help offset increased C/I.
6. What gives CableFree a “heads-up” here when other big name companies seem to be supporting the technology?
CableFree realizes higher-order modulations are not a panacea—a cure-all. While every minor technology improvement in throughput can help, a focus on technologies that grow capacity in hundreds of percentage points vs. tens of percentage points is most critical now. CableFree believes that these hundreds-of-percentage-points-of-improvement-in-capacity solutions will be the most important moving forward. It is in these technologies that CableFree has a “heads-up.” Such techniques include deploying more spectrum—particularly in the form of multichannel RF bonding (N+0) solutions—to achieve a minimum of 200 percent capacity increase. This technique is subject to frequency availability, but with flexible N+0 implementations (such as being able to use frequency channels in different bands and different channel sizes) many congestion issues can be avoided.
Second, intelligently dimensioning the backhaul network based on proven rules, best practices and L2/L3 quality of service (QoS) capabilities is another technique to provide potentially very large gains in backhaul capacity. Higher-order modulations can be one tool to achieve required capacity increases in the backhaul network. However, their inherent drawbacks should be well understood, while the most attention should be paid to other techniques that deliver more meaningful and quantifiable benefits.
7. Will operators need to “retrofit” microwave radios to be capable of higher-order QAM operation in their existing microwave infrastructure? Or will completely new hardware be required?
This depends on the age and model of the existing radios. Older microwave systems will likely need to be “retrofitted” to support 512QAM and higher modulations. Recently installed microwave systems should be able to support these technologies without new hardware.
8. How will QAM evolve in the future? Is the introduction of higher-order QAMs an indefinite process, with no end in sight?
The introduction of higher-order QAMs is not an endless process. As per Figure 1 above in this blog post, the law of diminishing returns applies: Throughput percentage improvement declines as modulation rates increase. The cost and complexity of implementing higher-order QAMs probably is not worth the capacity increase benefits derived—not past 1024QAM, in any event.
Find out information on technology, deployment and applications for modern Digital Microwave Links
Microwave links are widely used for connectivity in modern digital IP networks. With capacities up to 3Gbps and beyond, a modern Microwave Link network can deliver bandwidth in a reliable, cost-effective and flexible manner – without need for disruption and delay caused by digging up streets and avoiding costly leased-line or leased fibre optic alternatives.
On this website you can find more information about radio link deployment and technology. Also we invite you to contact our experts with any questions by sending a message to us on our contact page.
Microwave links are used extensively in 4G/LTE backhaul networks, 2G (GSM) and 3G (UMTS) mobile operators, wireless metropolitan area networks (Wi-MAN) and corporate networks where high performance, flexibility, speed of deployment and low operating costs are required. Key features of links include high spectral efficiency (256QAM, 1024QAM, 2048QAM and 4096QAM), Automatic Transmit Power Control (ATPC) and Adaptive Coding and Modulation (ACM).
Globally, MW radio links are used for around 60% of all mobile backhaul connections due to the compelling technical and commercial arguments in favour of MW radio compared to leased line and trenched fibre alternatives. Speed of deployment and flexibility – the ability to move sites or provision rapidly – are greatly in favour of MW radio over fibre and cabled alternatives.
A link typically features a radio unit and a parabolic antenna, which may vary in size from 30cm up to 4m diameter depending on required distance and capacity. The radio unit is generally either a “Full Outdoor”, “Split Mount” or “Full Indoor” design depending on operator preference, deployment, features and available indoor space for specific sites and installation.
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