Improving Microwave Capacity

33
1 UNDERSTANDING TECHNIQUES TO IMPROVE THROUGHPUT AVIAT ADVANCED MICROWAVE TECHNOLOGY SEMINAR IMPROVING MICROWAVE CAPACITY

description

We explain how to improve microwave radio capacity by understanding techniques that improve throughput.

Transcript of Improving Microwave Capacity

Page 1: Improving Microwave Capacity

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UNDERSTANDING TECHNIQUES TO IMPROVE THROUGHPUT

AVIAT ADVANCED MICROWAVE TECHNOLOGY SEMINAR IMPROVING MICROWAVE CAPACITY

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is just a big pipe

you get out what you put in

microwave

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“I canna change the laws o’ physics captain”

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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

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How can you get more data through the pipe?

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through the pipe? how do you get more data

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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  

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Technique  

Wider  Channels  

Mul6ple  channels  with  link  aggrega6on  (incl.  CCDP)  

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Get a Bigger Pipe!

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

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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

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

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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

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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%  

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Higher Modulation = More Capacity, but…

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8QA

M

16Q

AM

32Q

AM

64Q

AM

128Q

AM

256Q

AM

512Q

AM

1024

QA

M

2048

QA

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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

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ce R

atio

(C/I)

, dB

110

105

100

95

90

85

80

75

70

65

Syst

em G

ain,

dB

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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

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Forward Error Correction (FEC)

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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  

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Forward Error Correction

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PAYLOAD   FEC  

Typical Radio Frame NMS  

PAYLOAD   FEC  NMS  

‘Light’ FEC

Increased  Payload  =  Higher  Throughput  

Less  FEC  =  Decreased  System  Gain  

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‘Strong’ Forward Error Correction

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PAYLOAD   FEC  

Typical Radio Frame NMS  

PAYLOAD   FEC  NMS  

PAYLOAD   FEC  NMS  

‘Light’ FEC

‘Strong’ FEC

Decreased  Payload  =  Lower  Throughput  

More  FEC  =  Beaer  System  

Gain  

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Use more than one pipe

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use more than one pipe

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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

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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

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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)

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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

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Comparing Link Aggregation Options

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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

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Only send the data that you need through the pipe

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only send the data that you need

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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

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Ethernet Frame Header Optimization

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!

•  Inter-frame Gap and Preamble Removal

•  MAC Header Compression

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Throughput Improvement

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Header Suppression Throughput Improvement

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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%  

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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

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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

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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)

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IN CONCLUSION

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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

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When it comes to Microwave Capacity

Test, using an industry standard benchmark - RFC 2544

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Best Case Throughput – 80 MHz channel

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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

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Realistic Throughput – 30 MHz channel

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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%

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Capacity Improvements – Hype and Availability

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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   ??  

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