the benefits of dynamic adaptive modulation

8/12/2019 The Benefits of Dynamic Adaptive Modulation

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White Paper

The Benefits of Dynamic Adaptive Modulation

for High Capacity Wireless Backhaul Solutions

Rony Kowalski

Product Line Manager - Ceragon Networks

Ceragon Networks, CeraView, FibeAir and the FibeAir design mark are registered trademarks of CeragonNetworks Ltd., and Ceragon, PolyView, ConfigAir, CeraMon, EtherAir, QuickAir, QuickAir PartnerProgram, QuickAir Partner Certification Program, QuickAir Partner Zone, EncryptAir and Microwave Fiber aretrademarks of Ceragon Networks Ltd. All rights reserved.


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The Benefits of Dynamic Adaptive Modulation in High Capacity WirelessBackhaul Solutions

Ceragon Networks October 20072

The Benefits of Dynamic Adaptive Modulation in High Capacity Wireless Backhaul

Solutions

Wireless backhaul enjoys a growing popularity with both fixed and mobile carriers who

wish to speed their network deployments and cut back on both CAPEX and OPEX. But

going wireless sometimes comes at a cost. Wireless communication systems are

affected by changing weather conditions. If not handled correctly, such systems may not

be able to cope with issues such as signal degradation thereby seriously endangering a

carriers quality of service obligations. Dynamic Adaptive Modulation which ensures

maximum bandwidth most of the time with guaranteed critical services all the time, can

bring carriers piece of mind, fueling further adoption of wireless backhaul solutions.

Background

Adaptive Modulation refers to the automatic modulation adjustment that a wireless system can

make to prevent weather-related fading from causing communication on the link to be

disrupted. When heavy weather conditions, such as a storm, affect the transmission and

receipt of data and voice over the wireless network, the radio system automatically changes

modulation so that non-real-time data-based applications may be affected by signal

degradation, but real-time applications will continue to run uninterrupted.

Since communication signals are modulated, varying the modulation also varies the amount of

bits that are transferred per signal - thereby enabling higher throughputs and better spectral

efficiencies. For example, 256 QAM modulation can deliver approximately four times the

throughput of 4 QAM (QPSK). It should be noted, however as a higher modulation technique is

used, a better Signal-to-Noise Ratio (SNRs) is needed to overcome interference and maintaina tolerable BER (Bit Error Ratio) level.

Full Range Adaptive Modulation

A Dynamic Adaptive Modulation algorithm, such as the one incorporated in the Ceragon

FibeAir IP-MAX2, ensures an increase in capacity by using the highest possible modulation in

accordance with link quality degradation. The assumption is that while high revenue real-time


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applications such as video and voice require constant high performance transport, lower

revenue non-real-time applications, such as email or web browsing, require less stringent

transport performance.

The example in figure 1 shows that on a clear day, an IP-MAX2 system transmits and receives

data and voice at 400 Mbps, using a modulation of 256 QAM. When the weather becomes

overcast and stormy, the Dynamic Adaptive Modulation algorithm changes the modulation to

32 QAM and the system transmits at 250 Mbps. This switchover guarantees that the real-time

voice applications will not experience signal degradation, while at the same time reducing the

amount of bandwidth required for the non-real-time data applications.

Figure 1: Typical throughputs over 56 MHz radio channel

Unlike existing solutions that need several seconds to adjust themselves thereby killing the

signal for the period of time it takes for the system to adjust to the new modulation - theswitchover offered by the Ceragon FibeAir IP-MAX2 is implemented using a Hitless algorithm

with zero down time. Spectrum usage is maximized while enabling increased capacity over a

given bandwidth.

The illustration is figure 2 shows that as weather conditions change, the system dynamically

alters the modulation so that the highest availability of capacity is ensured at any given time.

Real-time services remain unaffected throughout the process ensuring constant, uninterrupted

service.


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Throughput

Ceragon's Adaptive Modulation is extremely quick so switchovers can be performed even tens

of times per second. When a switchover is performed it will step up or down through the six

modulation schemes covered from 256QAM down to QPSK. This enables the system to

handle 100dB/sec fading fluctuations and ensures that the link operates at the highest possible

modulation in any given moment.

In order to optimise radio performance and prevent modulation flapping, Adaptive Modulationthresholds are pre-configured by Ceragons FibeAir IP-MAX2. This is done in the following

manner: The modem decreases the modulation when the MSE (mean-squared error) crosses

2dB above the 10-6 BER threshold in order to change the constellation pre-emptively before

any errors are detected. When the MSE reaches 4dB above the 10-6 BER upper threshold, the

modem increases the modulation to the next constellation point.

Figure 2: Dynamic Adaptive Allocation i n changing weather conditions example

Adaptive Modulation and Built-in Quality of Service

Ceragon's Adaptive Modulation has a remarkable synergy with the equipment's built-in Layer 2

Quality of Service (QoS) mechanism. Since QoS provides priority support for different classes

of service, according to a wide range of criteria it is possible to configure the system to discard

only low priority packets as conditions deteriorate. FibeAir IP-MAX2 can classify packets

according to the most external header, VLAN 802.1p, TOS / TC - IP precedence , MPLS

experimental field, VLAN ID, and UDP packets. All classes use 4 levels of prioritization with


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streaming of critical services becomes a true differentiator. Providing high bandwidths at

hundreds of Mbps and higher is simply not enough since extreme weather conditions can

severely degrade signals rendering the maximum capacity potential irrelevant.

Dynamic Adaptive Modulation, now offered for the first time with Ceragons FibeAir IP-MAX2,

ensures maximum bandwidth most of the time with guaranteed critical services all the time.

The solutions hitless algorithm ensures zero down time to enable a constant flow of voice and

real-time services allowing carriers to meet their service commitments for enhanced user

experience.

For more information about Ceragons FibeAir solutions family please visit our website at:

www.ceragon.com

the benefits of dynamic adaptive modulation

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