The Sky is No Longer the Limit - Getting the Most Out of Your Microwave Radio Spectrum

8/6/2019 The Sky is No Longer the Limit - Getting the Most Out of Your Microwave Radio Spectrum

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The Sky is no Longerthe Limit - Getting

the Most Out of Your Microwave Radio

Spectrum


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The Sky is no Longerthe Limit - Getting the Most Out of Your Microwave Radio Spectrum

September, 2010

Copyright by ECI Telecom, 2010. All rights reserved worldwide.

The information contained in the documentation and/or disk is proprietary and is subject to all relevant copyright, patent, and other lawsprotecting intellectual property, as well as any specific agreement protecting ECI Telecom's rights in the aforesaid information. Neitherthis document nor the information contained in the documentation and/or disk may be published, reproduced, copied, modified ordisclosed to third parties, in whole or in part, without the express prior written permission of ECI Telecom. In addition, any use of thisdocument, the documentation and/or the disk, or the information contained therein for any purposes other than those for which it wasdisclosed, is strictly forbidden. ALL RIGHTS NOT EXPRESSLY GRANTED ARE RESERVED BY ECI TELECOM.

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CONTENTS

ECI Telecom Ltd. Proprietary iii

ContentsIntroduction ........................................................................................................................... 5General Optimization Schemes ........................................................................................... 6

Modulation .................................................................................................................... 6Benefits of Modulation .............................................................................. 6BG-Wave Support ...................................................................................... 6

Adaptive Coding and Modulation (ACM) ...................................................................... 7Benefits of ACM......................................................................................... 8BG-Wave Support ...................................................................................... 8

Co-Channel Dual Polarization (CCDP) ........................................................................ 9Benefits of CCDP ....................................................................................... 9BG-Wave Support ...................................................................................... 9

TDM-based Optimization Schemes ................................................................................... 10Super PDH (SPDH) ..................................................................................................... 10

Benefits of SPDH ..................................................................................... 10BG-Wave Support .................................................................................... 10

TDM Grooming ........................................................................................................... 10Benefits of TDM Grooming...................................................................... 10BG-Wave Support .................................................................................... 10

Packet-based Optimization Schemes ............................................................................... 11Multiradio .................................................................................................................... 11

Benefits of Multiradio ............................................................................. 11BG-Wave Support .................................................................................... 11

Service-Aware Diverse Routing ................................................................................ 11Benefits of Service-Aware Diverse Routing ........................................... 12BG-Wave Support .................................................................................... 12

Packet Header Compression .................................................................................... 12Benefits of Packet Header Compression ............................................... 12BG-Wave Support .................................................................................... 13

Statistical Multiplexing .............................................................................................. 13Benefits of Statistical Multiplexing ......................................................... 13BG-Wave Support .................................................................................... 13

Spectrum Optimization in Action ....................................................................................... 14About ECI Telecom ............................................................................................................. 15


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CONTENTS

iv ECI Telecom Ltd. Proprietary

List of FiguresFigure 1: Adaptive coding and modulation........................................................................ 7Figure 2: Single link carrying multiple services with different SLAs ............................... 8Figure 4: Single-polarization transmission ...................................................................... 9Figure 5: Co-channel dual-polarization transmission...................................................... 9Figure 6: Diverse routing for increased bandwidth utilization ....................................... 12Figure 7: Spectrum optimization in action ...................................................................... 15


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INTRODUCTION

ECI Telecom Ltd. Proprietary 5

Introduction

Microwave (MW) transmission may look invisible but it is very real, with the cost

of the necessary licensed spectrum being paid for by operators. In some cases thespectrum is scarce or exhausted. Lower frequencies and wider channels that

provide greater transmission distances and higher payload cost more. While MW

systems have to meet higher bandwidth demand and transport attributes, like QoS,

reliability, and resiliency, the cost per bit has to be reduced. All these factors point

to making MW systems more efficient.

Efficient MW radio network operation can only be achieved through a holistic

design incorporating a tool set of features and capabilities.

This paper describes the mechanisms built into BG-Wave Multiservice Radio Node

(MRAN) platforms to maximize the bandwidth payload and optimize the

utilization of a scarce and costly spectrum.


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GENERAL OPTIMIZATION SCHEMES

6 ECI Telecom Ltd. Proprietary

General Optimization Schemes

Modulation

Modulation is the method by which data is coded within an RF transmission

signal. The coded data, called symbols, is transmitted over the air. Each symbol

represents several bits of data, for example, QPSK carries two bits per symbol

while 256QAM carries eight. Additional bits can be inserted to allow error

correction. A higher number of additional bits (increased coding rate) improves the

quality of the transmission but reduces the percentage of net information bits,

thus lowering efficiency.

It is clear that the higher the modulation, the higher the bandwidth. The tradeoff is

that higher modulation requires higher Signal to Noise Ratio (SNR) to decode the

modulated signal. Higher SNR is usually achieved by using larger antennas. On the

other hand, a higher coding rate enables a lower SNR and smaller antennas.

Benefits of Modulation

Operators can choose between:

1. Lower modulations:

a. Larger distance reducing the number of relays or hops

b. Smaller antennas resulting in lower equipment costs and rental fees andreducing the load on the tower

2. Higher modulations:

a. Higher bandwidth without using additional spectrum

This flexibility leads to optimal CAPEX and OPEX for a specific scenario.

BG-Wave Support

BG-Wave platforms support modulation options from QPSK to 256 QAM for all

frequency bands, 6 GHz to 38 GHz, and for all channel bandwidths, 7 MHz to 56

MHz, providing the maximum bandwidth capacity with the greatest possible

distance. Supporting high modulation for 7 MHz and 14 MHz narrow channels

provides much higher bandwidth without paying additional license fees for wider

channels, which in some cases may not be available.


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Adaptive Coding and Modulation (ACM)

ACM is an automatic mechanism which dynamically changes the code rate and

modulation according to the current radio propagation conditions in the link. Based

on preset performance monitoring (PM) criteria, ACM changes modulation in both

directions (increase and decrease) to cope with changing environmental conditions,

like rain, snow, and so on.

Figure 1: Adaptive coding and modulation

ACM selects the highest possible modulation that meets QoS requirements. ACM

is used together with Automatic Transmit Power Control (ATPC) to provide the

highest availability possible at any given time.

Combined with Class of Service (CoS) schemes, ACM enables high and low

availability services without additional investments (for example, in large

antennas).

The concept is best explained by an example. Assume that we need to support three

applications, one voice and two data, with different Service Level Agreements

(SLAs).

Application Bit rate [Mbps] Availability [%]

Voice 20 99.999

Data 1 120 99.99

Data 2 60 99.9


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In total we need to deliver 200 Mbps. Without ACM, the link design would be

based on the higher availability requirements of the voice service, a 200 Mbps link

with 99.999% availability that requires the use of high modulation and largeantennas. With ACM, we can design a link that guarantees 20 Mbps at 99.999%

availability (with smaller antennas and lower modulation) but still has the 200

Mbps support with lower availability (using higher modulation). The linkage to the

CoS mechanism allows tagging of services according to their SLA. This

information determines if a service is kept or discarded when the ACM mechanism

reduces the amount of bandwidth delivered at a particular moment.

Figure 2: Single link carrying multiple services with different SLAs

Benefits of ACM

ACM provides the maximum bandwidth capacity possible at any given time, while

meeting the availability requirements of the various services carried over the

microwave link by dynamically utilizing the merits of different modulation levels.

It allows the design of a link based on high availability for a predefined bandwidth

while enjoying much higher bandwidth whenever environmental conditions allow.

The result is smaller antennas, increased distance, and fewer relays, and support of

high bandwidth without using additional spectrum.

BG-Wave Support

Dynamic hitless and errorless switchover between modulation schemes and

Forward Error Correction (FEC) code rate according to link conditions.

Multiple CoS levels where bandwidth is guaranteed for higher classes and

bandwidth adaptation is applied for the middle/lower classes. CoS levels apply

to both TDM and packet traffic in hybrid mode.


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Co-Channel Dual Polarization (CCDP)

Standard radio signals are transmitted in one polarity, either vertical or horizontal.

CCDP technology simultaneously utilizes two orthogonal polarities over a single

radio channel, thus transmitting separate and independent signals over the same

wireless channel with a single antenna.

However, due to imperfect antenna isolation and channel degradation, some

interference between signals may occur. To counteract this, the receiver can

include a Cross Polarized Interference Cancellation (XPIC) which processes and

combines signals from two receiving paths to recover the original independent

signals.

Figure 3: Single-polarization transmission

Figure 4: Co-channel dual-polarization transmission

Benefits of CCDP

Using two polarities over the same wireless link doubles the capacity of the

frequency channel, providing better utilization of the spectrum and the license fee.

Many mobile operators have exhausted their frequency channel allocations and

CCDP increases their bandwidth use on the same channels.

CCDP can be combined with ACM. As CCDP doubles the capacity over the same

channel and ACM can increase it by a factor of 4:1, in total an overall

improvement of 8:1 can be achieved.

BG-Wave Support

CCDP and XPIC are supported by all BG-Wave platforms. Typical configurations

include 2+0 with two unprotected carriers transmitting over the same channel, or

2+2 with two protected carriers transmitting over the same channel.


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TDM-BASED OPTIMIZATION SCHEMES


TDM-based Optimization Schemes

Super PDH (SPDH)

By eliminating the SDH overhead, SPDH allows transporting 84 x E1s/T1s over a

155 Mbps link instead of 63 x E1s supported by a typical SDH STM-1.

Benefits of SPDH

Increase of approximately 30% in capacity (84 x E1s/T1s) compared to traditional

SDH. Combining SPDH and XPIC doubles that value to 168 x E1/T1 per carrier.

BG-Wave Support

All-native Hybrid BG-Wave platforms support SPDH. SPDH combined with

packet traffic in a hybrid radio frame enables flexible bandwidth allocation forSPDH and Ethernet traffic. SPDH working in conjunction with ACM and XPIC for

maximum spectral efficiency also supports SNCP for high availability, matching

the SDH/SONET standard.

TDM Grooming

TDM grooming is the ability to groom together the used time slots from partially

populated E1/T1 links into fewer fully populated links. A 64 Kbps (time slot)

switching granularity is required in order to do this.

Benefits of TDM GroomingFewer links are used to support the required traffic. For example, consider a hub

site serving three 2G/2.5G BTS through E1 connections using an STM-1 MW to

connect to the metro ring. As each BTS requires at least one to two E1 connections,

the maximum number of cell sites that the STM-1 ring can handle is about 30. The

E1s arriving at the hub site are often not fully populated, thus simple 64 Kbps

grooming can decrease the total number of E1s used within the STM-1 ring by

30% and more. The number of cell sites served by the hub site can therefore be

doubled without increasing the ring capacity.

BG-Wave Support

The hybrid BG-Wave product line supports an optional 1/0 matrix enabling TDMgrooming.


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PACKET-BASED OPTIMIZATION SCHEMES


Packet-based Optimization Schemes

Multiradio

Multiradio is the simultaneous transmission of packet data over multiple radio

carriers. This configuration requires a separate Outdoor Unit (ODU) for each

carrier link, all transmitted through a single antenna. Transmissions may be over

multiple channels or over a single channel using XPIC technology. Load balancing

is accomplished on the physical radio layer, independent of the packet flows or

data traffic paths defined at a higher level. Since modulation for each radio carrier

varies independently, multiradio service can be combined with ACM technology

for optimal bandwidth utilization

Benefits of Multiradio

Delivering higher bandwidth than can be supported over a single carrier

Increased transmission distance by using lower modulation per carrier

Better resilience to interference using multiple carriers

BG-Wave Support

Supported by the entire BG-Wave product line and transparent to the application,

which is aware only of a single high-capacity link.

Service-Aware Diverse Routing

Diverse routing is a method of reserving bandwidth to secure an alternative route in

case of a failure.

Service-aware diverse routing allows the use of the extra radio link bandwidth set

aside for protection purposes as long as it is not active. QoS priority schemes are

added, enabling the delivery of high priority traffic over the main link and lower

priority best effort traffic over the protection path. If the main traffic link goes

down or if capacity is reduced due to ACM downshifting, the high priority

protected traffic takes precedence and is immediately rerouted to the backup link.

The best effort traffic is buffered or discarded until lower priority bandwidth is

available again.


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Figure 5: Diverse routing for increased bandwidth utilization

Benefits of Service-Aware Diverse Routing

Doubling the effective usable capacity of the microwave link Providing improved spectrum utilization

BG-Wave Support

Supported by the entire BG-Wave product line. Service-aware functions of QoS

and priority schemes are provided through MPLS-TP and Provider Bridge (PB)

support.

Packet Header Compression

A packet header is information added on top of the payload by different protocols,

including Ethernet protocol, the IP protocol, transport protocols like TCP or UDP,and application protocols like RTP. This information helps to maintain reliable

communication across large distances and multiple hops, and carries source and

destination addresses, protocol identifiers, error checks, sequence numbers, etc.

Header compression is achieved by observing the fields remaining constant or

changing in a specific pattern. Headers are either not sent with every packet or

represented in a smaller number of bits.

Benefits of Packet Header Compression

Less bandwidth used for the header translates into more bandwidth available for

the application. This leads to better utilization of the spectrum.


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BG-Wave Support

All BG-Wave products support packet header compression.

Statistical Multiplexing

Data traffic is bursty by nature, resulting in a substantial difference between the

average rate and the peak rate. Statistical multiplexing relies on the statistical

nature of traffic (no correlation between peak points of different services) to

allocate less bandwidth to carry traffic than would normally be required if based on

the maximum possible peak rate of all the services together.

Benefits of Statistical Multiplexing

Several data services with the sum of their peak rates greater than the link capacity

can be supported. A link can be designed for a certain bandwidth but actually

supports multiple services with a much higher combined peak rate. Using QoS and priority schemes, the delivery of specific bandwidth and services is guaranteed,

while other services and extra bandwidth are delivered upon availability.

Statistical multiplexing uses oversubscription, delivering higher bandwidth than

that based on static traffic bandwidth allocation. For example, two Fast Ethernet

(FE) links of 100 Mbps each can be served by a single 100 Mbps link using an

over-subscription ratio of 2. Using an over-subscription of 10, which is fairly

common in data networks, enables allocating only 100 Mbps in order to serve 10 x

100 Mbps FE Ethernet with a total theoretical peak capacity of 1 Gbps.

BG-Wave Support

With a full Ethernet/MPLS switch integrated within the BG-Wave, statistical

multiplexing is fully supported.


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SPECTRUM OPTIMIZATION IN ACTION


Spectrum Optimization in Action

The following example illustrates the optimization schemes previously described.

An operator has a 7 MHz licensed frequency channel which he would like to use to

backhaul traffic from a base station.

Using QPSK modulation, a TDM-based microwave link can carry 10 Mbps or 5

E1s. The operator uses 6 Mbps or 3 E1s to backhaul traffic from a 2G GSM base

station. 4 Mbps is available to support new packet-based services like HSPA.

The operator allocates 2 Mbps for high priority packet-based applications and 2

Mbps for low priority and best effort applications.

Let us examine how the operator can get far more bandwidth out of the licensed

bandwidth he has paid for.

1. The first step is to use ACM and 256QAM modulation with low coding gain.This increases the total link capacity to 55 Mbps with 99.9% availability.However, five 9s availability is still guaranteed for the 8 Mbps high priority

traffic as before.

2. The second step is to apply packet header compression to the 49 Mbps of packettraffic. This increases the available bandwidth to 55 Mbps on top of the 6 Mbps

reserved for TDM traffic, giving a total of 61 Mbps.

3. The third step is to use CCDP and XPIC to again double the link capacity to122 Mbps.

4. The fourth step is to apply statistical multiplexing for the packet bandwidthportion with the lower priority. From the 122 Mbps capacity, extract the 6 Mbps

allocated for TDM and the 2 Mbps allocated for high priority packet traffic. We

can extend the allocation to high priority packet traffic to 4 Mbps and still keep

the same high availability. For the remaining 112 Mbps, apply a moderate 1:2

statistical multiplexing resulting in doubling the data services capacity to 224

Mbps.

Together with the 10 Mbps of high priority traffic, we have ended up with a link

capacity of 234 Mbps for a 7 MHz channel that originally provided only 10 Mbps

a x 23 multiplier!

The above example refers to an unprotected link. Let us now add protection. Half

the bandwidth must be reserved for protected traffic, in this case 117 Mbps (half

the final 234 Mbps link). Using service-aware diverse routing, the protection bandwidth can carry low priority best effort traffic as long as the protection

bandwidth is not needed. We are therefore back again to a 234 Mbps link, with

protection for 117 Mbps, way beyond what is required for the high priority traffic.


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ABOUT ECI TELECOM


Figure 6: Spectrum optimization in action

About ECI Telecom

ECI Telecom is a leading global provider of intelligent infrastructure, offering platforms and solutions tailored to meet the escalating demands of tomorrow's

services. Our comprehensive 1Net approach defines ECIs total focus on optimal

transition to Next-Generation Networks, through the unique combination of

innovative and multi-functional network equipment, fully integrated solutions and

all-around services.

For more information, please visithttp://www.ecitele.com.
http://www.ecitele.com/http://www.ecitele.com/http://www.ecitele.com/http://www.ecitele.com/


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lecomassumesnoresponsibilityforanyerrorsthatmay

appearinthisdocumen

1Net defines ECIs focus on facilitating our customers' optimal transition to

Next-Generation Networks, through the unique combination of innovative and

multi-functional network equipment, fully integrated solutions and all-around services

The Sky is No Longer the Limit - Getting the Most Out of Your Microwave Radio Spectrum

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