BEM - 6/7/01 - sc2001 VGs 060601.ppt - 1. OFDM for High Data Rate, ... Future of
Wireless Technology Panel ... Fourth Generation (4G) Wireless Access.
OFDM for High Data Rate, High-Mobility, Wide-Area Wireless Communications LAN data rates with cellular-like coverage SUPERCOMM2001 June 6, 2001 Future of Wireless Technology Panel
AT&T Labs - Research Bruce McNair Wireless Systems Research
[email protected] BEM - 6/7/01 - sc2001 VGs 060601.ppt - 1
Fourth Generation (4G) Wireless Access Cable Cablenetworks networks
POTS POTS
Home HomeLANs LANs
intranets intranets The The Internet Internet 1G/2G 1G/2G 3G
4G
voice/analog sophisticated wired data networking demand ↑ demand for mobility ↑ reliance on mobile computing/PDAs ↑ BEM - 6/7/01 - sc2001 VGs 060601.ppt - 2
data
Þ
Need for sophisticated, high-speed wireless data
Fourth Generation Wireless: High Speed Data Networking in a High Mobility, Wide Area, Cellular-like Environment
The Challenge:
ion g, dispers in d fa th a multip
nce ere erf int
fadin w o shad
g
path loss
Doppler frequency shift
“kTB” noise
Additional challenges for portable terminals: power cost complexity BEM - 6/7/01 - sc2001 VGs 060601.ppt - 3
size
OFDM Basics Nt tones
tone spacing ft Total bandwidth
Tone spacing vs active block time
f Operating bandwidth, fB
f B = Nt ft
ft =
N B = 2 N R + NC + NG + N F
NF FFT samples
tC/2
tF OFDM block, NB sample time t block length tB
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Cyclic Ramp Guard suffix down NG NC/2 NR
NF NF = N B N F + NC + 2 N R + NG
Block efficiency
η=
Tolerance to delay spread
≈ tC ∝ N C
t Ramp Cyclic up prefix NR NC/2
1 tF
tC/2 Raw capacity for M-ary tone modulation
Nt M
OFDM Transmitter
data intf
coder/ intlvr signal/ ctrl
transmitter
mod
IFFT
cyclic ext
pilots controller
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window
PAPR
filter
D/A
filter
RF RF RF
OFDM Receiver
∆f est RF RF RF
filter
A/D
filter
rotate
receiver
FFT
∆t est controller
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ch est
demod
decode/ deintlv
data intf
OFDM tradeoffs 802.11a
4G
DVB-T 2k mode
Data rate
6, 9, 12, 18, 24, 36, 48, 54 Mb/s
2.56-8.96 Mb/s
4.98-31.67 Mb/s
Tone modulation Coding rate
BPSK, QPSK, 16QAM, 64QAM
QPSK,16QAM
QPSK, “16QAM,” “64QAM”
1/2, 2/3, 3/4
1/2, 2/3, 3/4, 7/8
[1/2, 2/3, 3/4, 5/6, 7/8] + RS(204,88)
Nt
52
640
1705
tB
4 µs
200 µs
231-280 µs
tB-tF
800 ns
40 µs
7-56 µs
ft
312.5 kHz
6.25 kHz
4.464 kHz
fB
16.56 MHz
4 MHz
7.6 MHz
fop
~5 GHz
~2 GHz
~500 MHz
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OFDM/TDMA Options r ou s f o e t slot n o Hz 1M D
D/P
D
f
D/P
D
bur s t=1 WO F msec DM f rame = 20 msec
• Full peak data rates are achievable • Dynamic Packet Assignment to base stations, mobiles is an option • Portable terminals can process only relevant traffic for power savings
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t
4G Wireless Research φ1 Prototype
Base station
Channel simulator
• prototype designed with general purpose DSPs for flexibility • two-branch receiver diversity implemented at 1900 MHz • performance measured on typical mobile outdoor channels • robust performance demonstrated BEM - 6/7/01 - sc2001 VGs 060601.ppt - 9
Mobile station
Conclusions • Real-time φ1 DSP prototype demonstrated: • performance within 1-2 dB of theory in AWGN • performance within .25 dB of idealized simulation for two-ray fading • robustness of OFDM against delay spread • OFDM can offer good performance even with straightforward receiver (e.g., simple combining, differential detection, (63,31) RS coder) • Two-branch receiver diversity provides 4 - 8+ dB performance gain for variety of channel conditions. Combined with coding across OFDM tones provides very effective diversity • Signal processing requirements for high speed OFDM is feasible today (i.e. DVB-T) and becoming more feasible for future terminals • Wideband OFDM with improved modulation, coding, channel estimation can achieve excellent performance, even in low delay spread environments • In combination with MIMO smart antennas, peak rates of 20-40 Mb/s in 5 MHz are feasible • OFDM/TDMA offers advantages for portable terminals, dynamic resource assignment • Distinction between wide area and local area wireless data networking is blurring
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