Download presentation

Presentation is loading. Please wait.

Published byNoah Goble Modified over 2 years ago

1
doc.: IEEE 802.11-03/825r0 Submission November 2003 Ravi Mahadevappa, Stephan ten Brink, Realtek Slide 1 Comparison of 128QAM mappings/labelings for 802.11n Ravi Mahadevappa, ravi@realtek-us.com Stephan ten Brink, stenbrink@realtek-us.com Realtek Semiconductors, Irvine, CA

2
doc.: IEEE 802.11-03/825r0 Submission November 2003 Ravi Mahadevappa, Stephan ten Brink, Realtek Slide 2 Overview 128QAM for increasing data rate of 802.11n –MIMO 2xN: can achieve 2x54Mbps = 108Mbps in 20MHz –108Mbps peak too small to get 100Mbps MAC throughput –MIMO 2xN, 128QAM, R=7/8 code, 20MHz: 147Mbps achievable Consider four 128QAM constellations/labelings –Determine the one which is most suitable Performance comparison using mutual information in bit-interleaved coded modulation (BICM) [1], [2] BER chart in AWGN and Rayleigh channel PER chart in an 802.11a-like setting (2x2, 2x3 MIMO)

3
doc.: IEEE 802.11-03/825r0 Submission November 2003 Ravi Mahadevappa, Stephan ten Brink, Realtek Slide 3 Introduction Bit Interleaved Coded Modulation (BICM) –Gray-labeling of the constellation points is best to achieve a low bit error rate (BER), if no iterative decoding is applied [2] For QPSK, 16QAM, 64QAM, 256QAM –True Gray-labeling possible, using a square constellation –Gray-labeling per I-/Q-channel –I-/Q-channel independent, can be demapped separately For 128QAM –no true Gray-labeling possible –e.g. 128QAM: 7 bits; one bit has to be “distributed” over I/Q

4
doc.: IEEE 802.11-03/825r0 Submission November 2003 Ravi Mahadevappa, Stephan ten Brink, Realtek Slide 4 802.11a Transmitter Bit interleaved coded modulation –Channel encoder (error correcting coding) and QAM symbol mapper are connected through a bit interleaver –The 802.11a WLAN system [3] exhibits this structure

5
doc.: IEEE 802.11-03/825r0 Submission November 2003 Ravi Mahadevappa, Stephan ten Brink, Realtek Slide 5 802.11a Receiver

6
doc.: IEEE 802.11-03/825r0 Submission November 2003 Ravi Mahadevappa, Stephan ten Brink, Realtek Slide 6 64QAM Example: Gray-labeling 64QAM with Gray- labeling: bit labels of neighboring signal points differ by one binary digit Most systems with QAM modulation use Gray-labeling, e.g. 802.11a WLAN [3] Allows low-complexity bit detection (I/Q can be dealt with separately)

7
doc.: IEEE 802.11-03/825r0 Submission November 2003 Ravi Mahadevappa, Stephan ten Brink, Realtek Slide 7 128QAM Constellations: Shifted I Based on two shifted 64QAM constellations Proposed for different systems, e.g. [4] Motivation: I&Q can be demapped separately Bit labels of neighboring signal points differ by two binary digits See later: Good for iterative BICM (demapper/decoder iterations), but not good for BICM

8
doc.: IEEE 802.11-03/825r0 Submission November 2003 Ravi Mahadevappa, Stephan ten Brink, Realtek Slide 8 128QAM: Shifted II, 64QAM/Gray Based on two 64QAM constellations, shifted Gray-labeling per 64QAM constellation Bit labels of neighboring signal points differ by more than one binary digit at several places

9
doc.: IEEE 802.11-03/825r0 Submission November 2003 Ravi Mahadevappa, Stephan ten Brink, Realtek Slide 9 128QAM: Cross I, DVB-C DVB-C(able) [5] uses cross constellation and this bit labeling The two MSB’s are differentially encoded, to be rotationally invariant against 90degree flips “Almost” Gray-labeling within one quadrant, but bit labels differ by many bits along the zero I- and Q-axis Not designed for BICM

10
doc.: IEEE 802.11-03/825r0 Submission November 2003 Ravi Mahadevappa, Stephan ten Brink, Realtek Slide 10 128QAM: Cross II, Gray-like Center: 64QAM with Gray-labeling as 802.11a; the 7th bit (most significant bit, MSB) is set to zero Borders: mirrored 64QAM; horizontally, vertically flipped from center, MSB set to one Labels of neighboring signal points differ by 3 digits at few places All other bit labels of neighboring signal points differ by only one binary digit

11
doc.: IEEE 802.11-03/825r0 Submission November 2003 Ravi Mahadevappa, Stephan ten Brink, Realtek Slide 11 128QAM: Cross II, Gray-like Generation by mirroring, flipping center 64QAM Gray constellation to outside and setting MSB from 0 to 1

12
doc.: IEEE 802.11-03/825r0 Submission November 2003 Ravi Mahadevappa, Stephan ten Brink, Realtek Slide 12 128QAM: Comparison, EXIT Chart Extrinsic information transfer (EXIT) chart [6] to predict performance AWGN, E b /N 0 =9dB, at code rate 3/4 For BICM, start of curve essential (this is the mutual information, that demapper “sees”) Cross II: highest start –best for BICM Cross I has “moderate” slope; Shifted II similar –Mediocre for BICM Shifted I: lowest start –bad for BICM –but would be best for iterative demapping and decoding Only start of curve relevant for good BICM performance (the higher, the better)

13
doc.: IEEE 802.11-03/825r0 Submission November 2003 Ravi Mahadevappa, Stephan ten Brink, Realtek Slide 13 128QAM: BER Chart, AWGN AWGN, rate 3/4 memory 6 convolutional code 64QAM (Gray) as reference Best: Cross II Worst: Shifted I Difference about 2dB

14
doc.: IEEE 802.11-03/825r0 Submission November 2003 Ravi Mahadevappa, Stephan ten Brink, Realtek Slide 14 128QAM: BER Chart, Rayleigh Rayleigh channel (ergodic), rate 3/4 memory 6 convolutional code 64QAM as reference Best: Cross II Worst: Shifted I Difference about 2dB

15
doc.: IEEE 802.11-03/825r0 Submission November 2003 Ravi Mahadevappa, Stephan ten Brink, Realtek Slide 15 PER, 802.11a-like High-Rate System MIMO-OFDM simulation, with 11a parameters for symbol duration, guard time, 64FFT etc. M=2 TX antennas (spatial multiplexing), 128QAM rate 3/4 mem. 6 conv. code; PHY rate of 126Mbps MIMO sub-channels: independent fading, with exp. decay profile, T rms = 60ns MIMO ZF detection with soft post processing Ca. 1dB-advantage of Cross II over Shifted II

16
doc.: IEEE 802.11-03/825r0 Submission November 2003 Ravi Mahadevappa, Stephan ten Brink, Realtek Slide 16 Conclusion To increase spectral efficiency, the use of 128QAM is a possible option 128QAM helps to smoothen the rate table Constellation mapping and labeling important Recommendation: If 128QAM is to be considered for 11n, cross- constellation with Gray-like labeling (Cross II) should be used

17
doc.: IEEE 802.11-03/825r0 Submission November 2003 Ravi Mahadevappa, Stephan ten Brink, Realtek Slide 17 References [1]E. Zehavi, “8-PSK trellis codes for a Rayleigh channel”, IEEE Trans. Commun., vol. 40, pp. 873-884, May 1992 [2]G. Caire, G. Taricco, E. Biglieri, “Bit-interleaved coded modulation”, IEEE Trans. Inf. Theory, vol. 44, no. 3, pp. 927-946, May 1998 [3]IEEE Std 802.11a-1999, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, High-speed Physical Layer in the 5 GHz Band [4]IEEE P802.15-15-03-0311-00-003a, “Reasons to use non-squared QAM constellations with independent I&Q in PAN systems”, July 2003 [5]“Digital Video Broadcasting (DVB): Framing structure, channel coding and modulation for cable systems”, EN 300 429, V. 1.2.1 (1998-04), European Standard (Telecommunications series) [6]S. ten Brink, “Convergence of iterative decoding,”, Electron. Lett., vol. 35, no. 10, pp. 806-808, May 1999

18
doc.: IEEE 802.11-03/825r0 Submission November 2003 Ravi Mahadevappa, Stephan ten Brink, Realtek Slide 18 Backup Slides

19
doc.: IEEE 802.11-03/825r0 Submission November 2003 Ravi Mahadevappa, Stephan ten Brink, Realtek Slide 19 128QAM: Comparison, EXIT Chart For Cross I, one needs to increase E b /N 0 by 1dB to achieve the same starting point as Cross II For Shifted I, one needs to increase E b /N 0 by 2.2dB to achieve the same starting point as the Cross II constellation Shifted II: Increase by 1.4dB required Next step: Verify E b /N 0 - offset predictions by BER simulations using memory 6 convolutional code of rate 3/4

Similar presentations

OK

Forschungszentrum Telekommunikation Wien [Telecommunications Research Center Vienna] Göttfried Lächner, Ingmør Lønd, Jössy Säyir Optimization of LDPC codes.

Forschungszentrum Telekommunikation Wien [Telecommunications Research Center Vienna] Göttfried Lächner, Ingmør Lønd, Jössy Säyir Optimization of LDPC codes.

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on object oriented technologies Ppt on diode Download ppt on nutrition in plants and animals Ppt on foldable screen technology Ppt on game theory youtube Ppt on strings in c language Ppt on different solid figures for kids Convert pdf to ppt online for free Ppt on data handling for class 7th Ppt on money and credit for class 10th