Carrier Ethernet 7 Benchmarking Wireless Ethernet Throughput

White Paper Benchmarking Wireless Data Thro ugh put No. 7 This is White Paper No. 7 in a series produced by Harris Stratex Networks on Carrier Ethernet. Keynote How can you make 340 Mbit/s look like 450 Mbit/s? The throughput of a wireless transport system can be presented in different ways, and can be manipulated to create competitive advantage were there is in fact none. Available radio bandwidth and the modulation level determine the actual throughput that can be achieved over a radio link, with some small variation. However, this does not stop some vendors presenting numbers that include components that are not usable (radio overhead, etc), or that are stripped off before transmission over the radio link (Ethernet pre-amble and inter-frame gaps). The result is that a 340 Mbit/s link can be easily made to look like a 450 or even 466 Mbit/s link. Th is p a pe r attem p t s t o ex p la in t h e tec h n i qu e s i n v ol v ed an d d is p el t h e mar k et in g sp in , so that you can better judge and compare performance between different systems on an ‘apples for apples’ basis. “A 340 Mbit/s link can be easily made to look like a 450 or even 466 Mbit/s link.” Some Background to Wireless Transpor t Point-to-Point Licensed FDD Operation For the purposes of this comparison, only licensed wireless systems are considered. These radio products operate in regulated frequency bands using FDD (frequency division duplex) channel arrangements, and provide full-duplex throughput that is available 100% of the time. Th e al t er n at iv e to Poin t -t o- Poin t Lic en se d FDD Op e r at io n is un li cense d op er at io n, an d a myriad of products are available using cheap OTS (Off The Shelf) chipsets or more expensive proprietary technologies to transport varying amounts of data over the unlicensed bands. “There is no ‘free lunch’, meaning that if someone is claiming dramatically better performance then you should really check the fine print.” Data Preparation and Overhead To tran sp or t Et h er net d ata over a r ad io li n k t h e d ata f ir st nee d s to b e p r ep ar ed b ef ore it can be used to modulate an RF carrier. This includes adding additional information for error correction (FEC), link and network management, and auxiliary data. This overhead information is transmitted over the link on top of the customer payload. For most radio systems the amount of overhead is very similar. For example, for an Eclipse data link providing 150 Mbit/s of usable custom er through put , about 18 Mbit/s of radio overhead is added, giving a total aggregate link speed of 168 Mbit/s. Modulation and Channel Bandwidth Modern digital radios all employ QAM (Quadrature Amplitude Modulation) or similar techniques (TCM, MLCM etc.), to encode data onto a radio frequency (RF) carrier. For highest throughput all vendors use 256 QAM in a 50 MHz (for North America) or 56 MHz (Internat ional) channel. More recently, some vendors have been marketing systems for use in 80 MHz channels in the US, originally designed for the International 56 MHz channel allocation. This channel size is only available in the 18 GHz Common Carrier band for the US. It is unique from other FCC bands where t he m axim um channel bandw idth av ailable is only 30 or 40 MHz. This 1/30/20 08 Benchmarking Wireless Data Throughput Page 1 of 5 Copyright ©2008 Harris Stratex Networks, all rights reserved. www.harrisstratex.com

Carrier Ethernet 7 Benchmarking Wireless Ethernet Throughput

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