Improving Microwave Capacity

1

UNDERSTANDING TECHNIQUES TO IMPROVE THROUGHPUT

AVIAT ADVANCED MICROWAVE TECHNOLOGY SEMINAR IMPROVING MICROWAVE CAPACITY

is just a big pipe

you get out what you put in

microwave

“I canna change the laws o’ physics captain”

How to Understand Vendor Capacity Claims?

• It is getting increasingly harder to compare capacity claims from various vendors

• Multiple techniques are being employed to boost throughput figures

• We will attempt to explain the various techniques and how they impact capacity

APRIL 2012 4 AVIAT NETWORKS |

How can you get more data through the pipe?

NOVEMBER 2011 5 AVIAT NETWORKS |

through the pipe? how do you get more data

Strategies for Increasing Microwave Capacities

More Spectral Efficiency

(More Bits per Hz)

More Spectrum (More Hz)

More “Effec5ve” Throughput

(More Data per Bit)

Technique

Higher Modula6on Levels

Adap6ve Modula6on

Reduced FEC Redundancy

Technique

Header Op6miza6on/ Suppression/Compression

Payload Compression

Asymmetric Opera6on

APRIL 2012 AVIAT NETWORKS | 6

Technique

Wider Channels

Mul6ple channels with link aggrega6on (incl. CCDP)

Get a Bigger Pipe!


How can you get more data through the pipe? get a bigger pipe!

Use Wider Channels

6 GHz

30 MHz

60 GHz

250 MHz

70-90 GHz

5 GHz

11 GHz

40 MHz

18 GHz

80 MHz 23 GHz

50 MHz

APRIL 2012 AVIAT NETWORKS | 8


Get a Bigger Pipe! How can you get more data through the pipe? use more efficient schemes to pack more data into the pipe

Increasing Modulation Level

þ  Improves bits/Hz efficiency within the same channel size

☒  Diminishing capacity improvement with every higher modulation step

☒  Much lower system gain - shorter hops, larger antennas

☒  Much higher sensitivity to interference – difficult link coordination, reduced link density

☒  Increased phase noise and linearity – increased design complexity cost

þ  Should be deployed with ACM to offset lower system gain


Modula6on Level (QAM)

Bits/Symbol Bits/s/Hz

Incremental Capacity Gain

4 (QPSK) 2 -‐

8 3 50%

16 4 33%

32 5 25%

64 6 20%

128 7 17%

256 8 14%

512 9 13%

1024 10 11%

2048 11 10%

Higher Modulation = More Capacity, but…


8QA

M

16Q

AM

32Q

AM

64Q

AM

128Q

AM

256Q

AM

512Q

AM

1024

QA

M

2048

QA

M

10%

15%

20%

25%

30%

35%

40%

45%

50%

55%

Cap

acity

Incr

ease

45

40

35

30

25

20

15

10

5

0 Car

rier t

o In

terf

eren

ce R

atio

(C/I)

, dB

110

105

100

95

90

85

80

75

70

65

Syst

em G

ain,

dB

Applying Adaptive Modulation

• AM/ACM allows higher order modulations to be employed, but mitigate the adverse effects

• Modulation rate/capacity adapts to increase system gain when needed

• Fixed modulation links can be upgraded to ACM to: 1.  Increase link capacity 2.  Decrease antenna size, and so tower rental costs 3.  Increase link availability 4.  Or, a combination of 1+2+3


Forward Error Correction (FEC)


PAYLOAD FEC

Typical Radio Frame NMS

Bytes reserved for radio link and network

management informa6on

FEC bytes enable radio to correct a limited number of

bit errors, increasing receiver performance

Forward Error Correction


PAYLOAD FEC


PAYLOAD FEC NMS

‘Light’ FEC

Increased Payload = Higher Throughput

Less FEC = Decreased System Gain

‘Strong’ Forward Error Correction


PAYLOAD FEC


PAYLOAD FEC NMS

PAYLOAD FEC NMS

‘Light’ FEC

‘Strong’ FEC

Decreased Payload = Lower Throughput

More FEC = Beaer System

Gain

Use more than one pipe


use more than one pipe

Link Aggregation using IEEE 802.1AX

•  The most common legacy link aggregation approach (originally defined in IEEE 802.3ad)

•  802.1AX cannot dynamically redistribute traffic load for optimal utilization of available links


Switch/Router

Mod

ule

Mod

ule

Eclipse INU/INUe

DAC GE3

P3 DPP1

DPP2 P5

DAC GE3

DPP1

DPP2

RAC 60

P4

P3

P5

P4

RAC 60

RAC 60

RAC 60

P1

P2

P3

P4

P5

P6

Eclipse INU/INUe

DAC GE3

P3 DPP1

DPP2 P5

DAC GE3

DPP1

DPP2

RAC 60

P4

P3

P5

P4

RAC 60

RAC 60

RAC 60

Switch/Router

Mod

ule P1

P2

P3

Mod

ule P4

P5

P6

4+0 Link

CCDP/XPIC or

ACAP

LAG

Designed for this

Supports this

Layer 1 Link Aggregation (L1 LA)

•  Unique and Aviat patented radio link aggregation scheme designed to address limitations of the traditional 802.1AX approach

•  Uniform load balancing even for ACM links and carriers of different capacities •  High utilization and low added overhead •  Carrier-grade convergence and recovery from individual link failures (<50 msec)


Switch/Router

Mod

ule

Mod

ule

Eclipse INU/INUe

DAC GE3

P3 DPP1

DPP2 P5

DAC GE3

DPP1

DPP2

RAC 60

P4

P3

P5

P4

RAC 60

RAC 60

RAC 60

P1

P2

P3

P4

P5

P6

Eclipse INU/INUe

DAC GE3

P3 DPP1

DPP2 P5

DAC GE3

DPP1

DPP2

RAC 60

P4

P3

P5

P4

RAC 60

RAC 60

RAC 60

Switch/Router

Mod

ule P1

P2

P3

Mod

ule P4

P5

P6

4+0 Link

L1LA Domain Layer 2 (802.1AX) Domain

LAG

LAG

Sta

ckin

g

Comparing Link Aggregation Options


LAG 802.1AX L1 LA

Load balancing Effec6veness Medium High

Easy capacity expansion Yes Yes

Latency High Low

Adap6ve to RF No Yes

L1LA is the ideal solution for N+0 links

Only send the data that you need through the pipe

NOVEMBER 2011 20 AVIAT NETWORKS | through the pipe

only send the data that you need

Using Ethernet Optimization

• Using common Ethernet optimization and compression techniques: • Ethernet Frame Suppression • MAC Header Compression • Multi-Layer Header Compression • Payload Compression

• Send only needed data over the radio link. Suppress or compress everything else

• Asymmetric link operation


Ethernet Frame Header Optimization


!

•  Inter-frame Gap and Preamble Removal

•  MAC Header Compression

Throughput Improvement


Header Suppression Throughput Improvement


Frame Size

Standard Frame IFG & Preamble IFG & Preamble & MAC header

Frame Space Mbps Frame

Space Mbps Increase Frame Space Mbps Increase

64 84 76.2 68 94.1 24% 58 110.3 45%

128 148 86.5 132 97.0 12% 122 104.9 21%

260 280 92.9 264 98.5 6% 254 102.4 10%

512 522 96.2 516 99.2 3% 506 101.2 5%

1518 1538 98.7 1522 99.7 1% 1512 100.4 2%

Multi-Layer Header Compression

• AKA ‘Packet Throughput Boost’, ‘Enhanced Packet Compression’ ‘Layer 1/2/3/4 Header Compression’ or ‘Deep Ethernet header compression’

• Adds compression of IPv4/v6 header address bytes • Still highly dependent upon payload traffic type and frame size


Payload Compression

•  Some microwave vendors are employing common compression techniques

•  Pros •  Replaces strings of repeated patterns of data

•  Promises dramatic throughput improvement (2.5x), with no additional spectrum requirement

•  Cons •  Improvement is not guaranteed nor predictable, since it is highly

dependent on the traffic mix

•  Increased link latency

•  Most data traffic is already compressed

•  Typical real-world improvement is minimal (~4%)

•  Payload compression has not been generally adopted in the industry


Asymmetric Link Operation

• Proposal to configure links with lower capacity upstream than downstream

• Assumes downstream traffic is much higher volume than upstream, and that backhaul links can be similarly dimensioned

• Claimed benefits are higher downstream speeds and frequency savings (upstream)


IN CONCLUSION

Beware common tactics to inflate throughput

•  Present throughput figures based upon 64 byte frame sizes only

•  Assume that up to 100% (or a large proportion) of traffic is compressible

•  Assume availability of very wide channels (80 MHz) •  Assume 2+0 co-channel operation on the same frequency

assignment (using XPIC) •  Present half-duplex throughput figures •  Include non-payload overhead (NMS, FEC) •  Assume gains from other unproven techniques


When it comes to Microwave Capacity

Test, using an industry standard benchmark - RFC 2544

Best Case Throughput – 80 MHz channel


340

Airlink Strong FEC

360

IFG+PA Suppression

450

MAC HC

520

2+0 XPIC

1040

Payload Compression

2000

1024QAM

2500

360 360

720 720* 900

‘Guaranteed’ throughput

Maximum ‘Best Efforts’ throughput 64 byte frame size, ideal traffic profile

Throughput figures are stated in Mbit/s and are approximate for a single 80MHz RF channel and 256QAM (unless otherwise stated)

* + Latency

Realistic Throughput – 30 MHz channel


180

Airlink Strong FEC

190

IFG+PA Suppression

201

MAC HC

209

2+0 XPIC

418

Payload Compression

435

1024QAM

544

190 190 380 380*

475

‘Guaranteed’ throughput

Maximum throughput For 260 bytes average frame sizes, and typical traffic profile

Throughput figures are stated in Mbit/s and are approximate for a single 30MHz RF channel and 256QAM (unless otherwise stated)

* + Latency

+4%

+6% +4%

+25%

Capacity Improvements – Hype and Availability


Hype Factor Availability Higher Modula6on Medium 6-‐12 months

Strong FEC Low Now

ACM Low Now

Aggregated Mul6-‐Channel Low Now

Traffic Op6miza6on High Now

Payload Compression High Now

Asymmetrical Opera6on High ??

AVIATNETWORKS.COM

Improving Microwave Capacity

Technology

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