paper review - yonsei universitytera.yonsei.ac.kr/class/2015_1_2/presentation/radio-over... ·...

Special Topics in Optical Engineering II (15/1) 유병민

Paper review


Content

1. Background

2. Introduction

3. Physical layer performance

① Wireless PANs

② Wireless LANs

③ Wireless MANs/WANs

4. External modulated link modeling (OFDM over fiber)

5. Higher-layer protocol issue

6. Complete sensor network

7. Broadband 60GHz RoF systems

8. Conclusion


Background (Computer Network)

• PAN (Personal Area Network): Area about one person (<10m)

Wireline: USB, FireWire

Wireless: Bluetooth, UWB, ZigBee

• LAN (Local Area Network): Area about building

Wireline: Ethernet (TCP/IP)

Wireless: wireless LAN (IEEE 802.11)

• MAN (Metropolitan Area Network): area about a few city

ATM, FDDI, SMDS

• WAN (Wide Area Network): Network between countries/continents


Background (802.11 standard)

• 802.11: Standard specification of Wireless Local Area Network (LAN)

to compensate wireline LAN(Ethernet)

801.11a: 5 GHz band, 54 Mb/s maximum (OFDM)

801.11b: 2.4 GHz band, 11 Mb/s maximum

801.11g: same data rate with 801.11a, 2.4 GHz band

• 802.11n (2009.10): to improve 802.11a, 802.11g (600 Mb/s)

4 MIMO stream

Physical layer, MAC layer, Frame aggregation


Background (RoF)

- RoF: radio signals are carried over fiber-optic cable

- A single antenna can receive any and all signals

Advantage of RoF

Low attenuation

Low complexity

Lower cost


RoF Link Experiment: PANs

• Ultrawideband (UWB): interest in PANs (1 Gb/s)

Coexistence with other wireless service

Low radiate power

Low probability of interception

• Experiment types

Impulse-radio (IR): High definition audio, video content in FTTH network.

A. IR-UWB: External modulator, SSMF is used

B. IR-UWB: VCSEL (upconversion (8.5 GHz 62, 66 GHz))

C. MB-OFDM UWB: MMF, VCSEL(850 nm operation)



A. IR-UWB over fiber

1.25 Gb/s Gated optical pulse

Optical pulse train Monopulse shaped

6.6 GHz

IR-UWB transmission in FTTH demonstration setup




• −10 dB bandwidth: 3.2 GHz (5~8.2 GHz)

• Stringent equivalent isotropic radiated power (EIRP) limits



A. IR-UWB over fiber 20 GHz MZM

IR-UWB transmission in FTTH demonstration setup




• 10-9 BER: to 50 km of SSMF (RoF of 1.25 Gb/s IR-UWB)


Monocycle spectrum at baseband

after fiber transmission

8.5 GHz upconverted spectrum

after fiber transmission


B. IR-UWB over SSMF and upconversion

• 3dB bandwidth: 1.7 GHz (800 MHz – 2.5 GHz)

• LPF (5.2 GHz): reduce spurious power

• Upconversion: USB (9.3 – 11 GHz with 8.5 GHz LO)



C. MB-UWB over fiber

• ECMA 368 standard based: Ultra wide band PHY and MAC standard

• VCSEL: modulation



C. MB-OFDM UWB over fiber

MB-OFDM UWB EVM results for different MMF lengths

• ECMA-368 standard requirements: 18.84% EVM


Typical implementation of RoF system

RoF Link Experiment: LANs

A. 802.11a and upconversion

• IR−UWB signal (PAN-a) is used

• 5.1 GHz band 802.11a signal, 2m of SSMF

• fLO = 2 GHz, fRF = 1.1 GHz

• VCSEL: modulation (E/O conversion)

• Target: Minimum EVM

EVM depending on Ibias, PLO and PRF



B. MMF links for 802.11g

• Low-cost MMF RoF for 802.11g standard

(2.4 GHz, 64 QAM OFDM, 54 Mb/s over 100 m)

• Low-cost approach: IM-DD (intensity modulation – direct detection) technique

Radio over MMF using IM-DD for WLANs



B. MMF links for 802.11g

• EVM requirement (IEEE 802.11g): 5.4 %

• 50 nm MMF: 2.5 % EVM up to 600 m fiber length

• RF power ⬆ : distortion, EVM ⬆

EVM as function of RF power level

for 2.4 GHz & 300 m RoF link

EVM as function of fiber length


RoF Link Experiment: MANs and 3G

• High data rate, many users: reduction cell size

802.16 WiMAX, 3G mobile communications,

(with picocellular system design)

• RoF: Proposed for such systems

• MMF: moderate distance transmission (~hundreds of meters)

• Experiment

RoF experiments for WiMAX and 3G systems

Low-cost, 850 nm VCSEL, MMF


Measurement setup for WiMAX over MMF


A. WiMAX over fiber

EVM (left) conformance (right) of WiMAX measurement

• 3.5 MHz 64-QAM 3/4 WiMAX signal with 3.5 GHz band (fiber length < 400 m)

• Standard spectral mask(red line), measurement result (yellow line)



B. 3G and adjacent channel leakage

Experimental setup of multi system transport over a VCSEL multimode fiber link



• EVM requirement: 12.5 %

• Adjacent channel leakage ratio(ACLR)

50 dB at 10 MHz offset, 45 dB at 5 MHZ

Noise floor is dominant until 0 dBm VCSEL input power

EVM (left) results of a VCSEL multimode fiber link ACLR measurement

B. 3G and adjacent channel leakage


External modulated link modeling (OFDM over fiber)

• Key aspect of RoF system: modulation format, OFDM

• Behavior of OFDM signal in RoF for WLAN

• Simulation model: 802.11a WLAN signals

MZM RoF system model



MSE depending on MZM modulation index

• Modulation index (𝛤MZM) < 0.45: MSE < 10-3

• 𝛤MZM > 0.45: MSE Rapidly increased

• SNR: also rapidly increased from 0.45 𝛤MZM

Signal amplitude and output intensity



BER dependence on fiber length Receiver performance with FEC

• BER with/without error correction, fiber length

• Forward error correction (FEC): constraint length of 7

• −16 to −14 dBm input power: 10-3 to 10-4 BER (1 km, without FEC)

• Performance gain: 4 dBm (using FEC)

• 2~3 dBm loss in 1 km length of SSMF

4 dBm


High Layer Protocol Issue

• MAC, TCP, UDP protocol: performance degradation

system performance depending on High layer protocol

Variation of throughput using basic access

Variation of throughput using RTS/CTS

(Request to Send / Clear to Send)

• Throughput < data rate: control overhead (1 Mb/s control bit)

• RTS/CTS: More control data reduce throughput

• Steadily reduce as fiber length increase: waiting times, lost

• 5~7% FER (Frame error rate): 5.5 Mb/s

A. Impact of the 802.11 MAC


High Layer Protocol Issue

B. Impact on TCP/UDP

Signal amplitude and output intensity

• MAC: provide retransmission retransmission at TCP layer (x)

• UDP: alternative transport protocol to TCP (confirm step isn’t it)


Sensor Network

• Wireless indoor communication system: sensor area network

• Low data rate (20~200 kb/s) 802.15.4, extremely low power consumption

• 250 kb/s, 4 bit symbol

Maximum fiber length: 86.4 km(ask time out: 54 symbol)

• 84 km fiber length: about 0 time-out probability

Time-out uncertainty due to clock jitter


Broadband 60 GHz RoF System

• 12.5 Gb/s data with 60

GHz band

• DC bias: Vπ

For DSB-SC signal

• NRZ-OOK data

modulation

• Detection with 70 GHz PD

Schematic of 60 GHz RoF setup



• Error-free broadband wireless communication up to 12.5 Gb/s

• Error-free: at -46 dBm received power, 10.3125 Gb/s at 40 m

BER after 2.5 m data transmission BER levels for multi Gbit data transmission

after 20 and 40 m data transmission



• Extending wireless path length to the ~km (outdoor experiment)

• 60GHz band attenuation in free-space: 15.5 dB/km

• 10-9 BER at 12.5 Gb/s: < 1100 m (99% link availability)

< 800 m (99.99% link availability)

< 500 m (99.999% link availability)

Maximum wireless path lengths


Conclusion

1. Physical layer performance

① Wireless PANs

② Wireless LANs

③ Wireless MANs/WANs

2. External modulated link modeling

3. Higher-layer protocol issue

4. Sensor network

5. Broadband 60GHz RoF systems


Paper review

High-Speed Circuits and Systems Lab, Yonsei Univ.

Byung-Min Yu

[email protected]


Reference

paper review - yonsei universitytera.yonsei.ac.kr/class/2015_1_2/presentation/radio-over... ·...

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