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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 1 HNS Proposal for 802.11n Physical Layer Mustafa Eroz, Feng-Wen Sun, & Lin-Nan Lee meroz@hns.com fsun@hns.com llee@hns.com Hughes Network Systems 11717 Exploration Lane Germantown, MD 20876

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 2 Proposal Topics PHY and Air Interface Description Supported Rate Set (mandatory/optional) Proposed Scheme Preamble Design Approach Spectral Mask with non-linear model Short Block Length LDPC Performance Curves

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 3 PHY and Air Interface The air interface is built upon IEEE 802.11a (1999) PHY specifications and associated overhead –OFDM Modulation with PSK and QAM –(20/64) MHz subcarrier spacing, 52 Sub-carrier set 48 data carriers and 4 pilots (center location not used) –Preamble modified for MIMO Compatible with 802.11a air-interface –1, 2, 3 and 4 TX antenna for high throughput modes –One TX Antenna mode for legacy STA support –PHY-MAC maximum efficiency of 60% assumed In AP-STA test, 100Mbps at MSDU 167 Mbps at PHY

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 4 802.11n Rate Set Supported No. of TX Antennas Modulation TypeTransmit bits per channel use Code RateInfo. Bytes per channel. use PHY Info Rate (Mbps) MAC Info Rate (Mbps) @60% of PHY Rate 4BPSK1921/2122414.4 2/3183621.6 QPSK3841/2244828.8 8-PSK5761/2367243.2 16-QAM7681/2489657.6 32-QAM9601/26012072 64-QAM11521/27214486.4 2/396192115.2 3QPSK2881/2183621.6 2/3244828.8 16-QAM5761/2367243.2 2/3489657.6 64-QAM8641/25611267.2 2/37214486.4 2BPSK961/26127.2 QPSK1921/2122414.4 8-PSK2881/2183621.6 16-QAM3841/2244828.8 32-QAM4801/2306036 64-QAM5761/2367243.2 2/3489657.6

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 5 Proposed PHY Layer Block Diagram (Tx) IFFT Prefix Digital-RF-PA OFDM Symbol Generator (frequency domain) Preamble Attachment & 1:n OFDM Symbol Demux Insert Pilots PSK/QAM Modulator LDPC Encoder MIMO LDPC Block Formatter Information bits Prefix Digital-RF-PA MIMO Preambles PA = Rapp’s model, p=3 In x = [ x1 x2… xn ] T x1x1 xnxn

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 6 Proposed PHY Layer Block Diagram (Rx) FFT Remove P/fix FFT Remove P/fix RF-Digital Prefix Timing/Channel Estimation/Symbol Timing / Frequency/Phase Acquisition/Tracking OFDM Demod MAP Detector LDPC DECODER y1 ymym y = [ y 1 … y m ] T Reconstruct PSDU Information bits out Channel Estimates

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 7 Key Elements of the Physical Layer Proposal A family of high-performance FEC codes optimized for the application –Capable of decoding at information rate close to 200 Mbps with modest implementation complexity –Exceptional performance in fading channel at near 10 -2 packet error rate –Flexibility to support short as well as long packets without compromise in throughput at MAC layer An 802.11a/b/g compatible preamble design supports up to 4 Tx antennas

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 8 Considerations for FEC Code Selection With their inherent parallel architecture, Low-Density Parity Check (LDPC) decoders are more suitable for high-speed operation than turbo decoders LDPC codes with block length equal to integer number of OFDM channel uses maximize efficiency by eliminating unnecessary padding or shortening of a code block At one (1) percent or higher block error rates, the performance gap between short and long block codes diminishes Longer codes are extremely inefficient for the transmission of short bursts or the last block of a long burst due to need of padding or shortening Short burst traffic cannot be ignored, as applications such as VoIP and video games are important Decoders for short LDPC codes are much simpler to implement than long LDPC codes

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 9 Our FEC Choice A base LDPC code of block length 192 bits (4 x number of data carriers in an OFDM symbol) A simple means to extend block length with minimal performance compromises to any length in increment of 192 bits.

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 10 LDPC Details Code rates of 1/2 and 2/3 are sufficient to cover a broad range of throughput due to various choice of modulation schemes such as QPSK, 8-PSK, 16-QAM, 32-QAM and 64-QAM. Base LDPC codes have a coded block length of 192 bits with the following parity check matrix format which ensures simple encoding 1 1 1 1 1 1 1 1 1 1 1 B 0 0 where

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 11 LDPC Details The A sub-matrix has a constant column weight of 3. The small column weight ensures simpler decoding while performance is not sacrificed on the fading channel. Larger block sizes are supported by simply concatenating base LDPC codes and adding one extra base block of parity check on select LDPC bits. x x x x x x x x x x x x x : : : : : : : : : : : : LDPC Block 1 LDPC Block 2 LDPC Block 3 LDPC Block m Parity Check Block Parity check on k bits k < or = m

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 12 We base our approach on the 802.11a OFDM Specifications –There are 53 frequency bins in 802.11a OFDM Indexed -26, -25, …-1, 0, 1 … 25 and 26. The zero index (frequency location) is not used. –-21, -7, 7 and 21 are used as Pilots during data transmission Modulated by127 bit long PN code (x 7 + x 4 + 1) on the ‘1st’ Antenna Use the same frequency set on each of the TX Antennas Use different phase of the 127 bit PN (quasi-orthogonal) on each of the other Antennas –48 remaining bins are used for data transmission Each TX antenna uses the same 48 sub-carrier set but with different data stream The transmission commences with an 802.11a specified preamble called the PLCP preamble –8 usec ‘short’ preamble with only 12 sub-carriers active –8 usec ‘long’ preamble all sub-carriers active per a specified 52 bit sequence –Short preamble empty bins are used by secondary antennas 4 TX supported –52 bits of the Long preamble are transmitted sequentially over the TX antenna set Preamble/ Pilot Approach to HNS PHY Proposal

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 13 (-26) (26) ΔfΔf 0.3125 MHz 1 1 -1 -1 1 1......... Proposed: Long Preamble Sequence Spread Sequentially over the Four TX Antennas Proposed: Short Training Preamble (First 8 usec) over one ‘First’ and Three ‘Other’ Antennas 1+ j -1- j 1+ j -1- j 1+ j Preamble Duration = 8 usec Preamble duration = 8 usec 1.0 1+ j -1- j 1+ j -1- j 1+ j Preamble Duration = 8 usec IEEE 802.11a Standard Short Training Preamble (i.e. first 8 usec) from one TX Antenna - 26 + 26 First Antena (s0) Other Antennas (s1, s2 and s3) ΔfΔf ΔfΔf...... -1 1 1 1 1 L -26,26 per section 17.3.3 Std 802.11a -1999 Preamble Approach for Multiple TX Antennas

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 14 Simulation Conditions 2,3 and 4 TX antenna cases simulated AWGN with recommended channel matrices simulated NLOS Model for B, D and E used in simulation Florescent light effects included for Model D&E Antenna Spacing of half-wavelength used

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 15 OFDM Signal 16-QAM after Non-linear Amplifier IBO = 3 dBOFDM Signal 16-QAM after Non-linear Amplifier IBO = 8 dB Transmit Spectrum of the OFDM Signal Through PA Model Fully compliant with spectral mask Essentially the same spectral density for 64-QAM

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 16 Simulation Methodology Coding and BB TX module –Information bits encoded into 192 bit LDPC code blocks –LDPC code blocks extended to longer code blocks as described previously –generate PSK/QAM modulation symbols OFDM and Channel Model –Arranges into transmission vector for 2, 3 or 4 TX antennas –Converts modulation symbol stream into OFDM symbols with cyclic prefix, 4 usec/OFDM Symbol –Runs through channel model –Detects OFDM signals on each of the Rx antenna –Delivers demodulated samples from each Rx antenna to MAP detector

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 17 Performance for Channel Model B

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 18 Performance for Channel Model D

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 19 Performance for Channel Model E 1.0E-03 1.0E-02 1.0E-01 1.0E+00 2.06.010.014.018.022.026.0 Es/No (dB) Packet Error Rate 4x4, 64QAM R=2/3 4x4, 8PSK R=1/2 QPSK R=1/2 3x3, 16QAM R=2/3 16QAM R=1/2 3x3, QPSK R=2/3 4x4 2x2 3x3

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 20 AWGN Channel Performance

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 21 Channel Model B 1.0E-03 1.0E-02 1.0E-01 1.0E+00 6.07.08.09.010.011.012.0 Es/No (dB) Packet Error Rate 4x4, QPSK R=1/2 One LDPC Block Append a parity block for every 10 LDPC block

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 22 Channel Model D 1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00 4.05.06.07.08.09.010.0 Es/No (dB) Packet Error Rate 4x4, QPSK R=1/2 One LDPC block Append a parity block for every 10 LDPC block

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 23 Channel Model E 1.0E-03 1.0E-02 1.0E-01 1.0E+00 4.05.06.07.08.09.010.0 Es/No (dB) Packet Error Rate 4x4, QPSK R=1/2 One LDPC block Append a parity block for every 10 LDPC block

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 24 Required E s /N o vs PHY Data Speed

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doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 25 Conclusion All the design requirements of 802.11n met with the PHY partial proposal –FEC and MIMO alone achieve the goal –Compatible with current MAC, expect to be compatible with any MAC proposal. –In the interest of best overall proposal, PHY needs to be evaluated separately and then combined with the best MAC. Capable of supporting both 1x and 2x 20MHz approaches. Extremely simple to implement Highly efficient due to its flexible construction technique

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