doc.: IEEE Submission April 2007 Chang-Joo Kim, ETRISlide 1 [Comparisons of Symbol Structure for Upstream: 7x1 vs. 5x1] IEEE P Wireless RANs Date: Authors: Notice: This document has been prepared to assist IEEE It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chairhttp://standards.ieee.org/guides/bylaws/sb-bylaws.pdf Carl R. StevensonCarl R. Stevenson as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE Working Group. If you have questions, contact the IEEE Patent Committee Administrator at

doc.: IEEE Submission April 2007 Chang-Joo Kim, ETRISlide 2 Abstract When we design the pilot pattern for up stream, we have to consider the trade-off relationships among channel estimation performances, pilot density (i.e. throughput), granularity, and latency for channel estimation, etc. Each pilot pattern may have some advantages and some disadvantages. So the goal of this presentation is to find out which is the most suitable pilot pattern for up stream in WRAN system by considering the trade-off relationships.

doc.: IEEE Submission April 2007 Chang-Joo Kim, ETRISlide 3 7x1 vs. 5x1 Because pilots visit every subcarriers during 7 or 5 OFDMA symbols, the channel information is available in every subcarriers. So the channel estimation performance is same The points are pilot density and granularity Pilot density (Overall efficiency for 1/8 GI mode [1]) –7x1: 1/7=14.2 % (64.80 %) –5x1: 1/5=20 % (62.72 % Granularity [1] –7x1 with 60 subchannel: 16.8 kbps –7x1 with 120 subchannel: 8.4 kbps –5x1 with 84 subchannel: 8 kbps

doc.: IEEE Submission April 2007 Chang-Joo Kim, ETRISlide 4 7x1 vs. 5x1 (Cont’d) In the case of G.729 codec, the required bit rates for VoIP service is as follows [2] –For MP or FRF.12 transmission: 26.8 kbps –For cRTP MP or FRF.12 transmission: 11.6 kbps –For Ethernet: 31.2 kbps The granularity of current 7x1 structure, 16.8 kbps, is still reasonable to support the VoIP service. If we still need to decrease the granularity for upstream, we can obtain the granularity of 8.4 kbps by increasing the number of subchannels to 120 with same pilot density. The 5x1 symbol structure has the granularity of 8 kbps with pilot density of 1/5 (5.8 % increase of pilot density, 2 % loss of overall efficiency)

doc.: IEEE Submission April 2007 Chang-Joo Kim, ETRISlide 5 Uncoded BER for 7x1 (or 5x1) Structure 7x1

doc.: IEEE Submission April 2007 Chang-Joo Kim, ETRISlide 6 Modified 5x1 Symbol Structure If we need to adopt 5x1 symbol structure, it is desirable to use the modified 5x1 symbol structure (refer to next slide). In the adjacent subcarrier permutation for up stream, the staggered pattern is more flexible than regular pattern in the point of channel estimation. Latency for best channel estimation is 5 OFDMA symbols, instead of 7 OFDMA symbols.

doc.: IEEE Submission April 2007 Chang-Joo Kim, ETRISlide 7 Modified 5x1 Symbol Structure (Cont’d) frequency time Repetition Unit OFDMA Symbol

doc.: IEEE Submission April 2007 Chang-Joo Kim, ETRISlide 8 OFDMA Parameters for US (2K FFT) Parameter 1 TV bands 678 Inter-carrier spacing,  F (Hz) (*) FFT period, T FFT (  s) (*) Total no. of sub-carriers, N FFT 2048 No. of guard sub-carriers, N G (L, DC, R)368 (184,1,183) No. of used sub-carriers, N T = N D + N P 1680 No. of data sub-carriers, N D 1344 No. of pilot sub-carriers, N P 336 No. of sub-carriers per BIN (***) 5 (4 datas + 1 pilots) No. of subchannel per OFDMA symbol84 No. of BIN per subchannel4 No. of sub-carriers per subchannel (***) 20 (16 datas + 4 pilots) Occupied bandwidth (MHz) (*) Bandwidth Efficiency (%) (**) 93.8 (*) Italics indicate an approximated value. (**) Bandwidth Efficiency = Subcarrier Spacing * (Number of Used Subcarriers + 1)/BW (***) It is defined over 1 OFDMA symbols

doc.: IEEE Submission April 2007 Chang-Joo Kim, ETRISlide 9 Effective Symbol Structure For All Code Rates Code rate: 1/2, 2/3, 3/4, and 5/6 Least common multiple (LCM) of denominator for all code rate is 12. To support the all code rate effectively, the number of bit after encoding (before mapper) should be a multiple of 12. Among the two symbol structure(7x1 and 5x1, and if possible 10x1), the number of bit after encoding for 5x1 scheme is not a multiple of 12.

doc.: IEEE Submission April 2007 Chang-Joo Kim, ETRISlide 10 Four Symbol Structure Options Note: From Gerald’s spread sheet by the name of “Pilot Carrier Density-2.xls”

doc.: IEEE Submission April 2007 Chang-Joo Kim, ETRISlide 11 Relation b/w Bit and Symbol for Code Rate Code RateNumber of data subcarrier per subchannelNumber of bit per subchannel after encoding 1/224 (7x1)48 (QPSK), 96 (16QAM), 144 (64QAM)24 (QPSK), 48 (16QAM), 72 (64QAM) 16 (5x1)32 (QPSK), 64 (16QAM), 96 (64QAM)16 (QPSK), 32 (16QAM), 48 (64QAM) 18 (10x1)36 (QPSK), 72 (16QAM), 108 (64QAM)18 (QPSK), 36 (16QAM), 54 (64QAM) 2/324 (7x1)48 (QPSK), 96 (16QAM), 144 (64QAM)32 (QPSK), 64 (16QAM), 96 (64QAM) 16 (5x1)32 (QPSK), 64 (16QAM), 96 (64QAM) (QPSK), (16QAM), 64 (64QAM) 18 (10x1)36 (QPSK), 72 (16QAM), 108 (64QAM)24 (QPSK), 48 (16QAM), 72 (64QAM) 3/424 (7x1)48 (QPSK), 96 (16QAM), 144 (64QAM)36 (QPSK), 72 (16QAM), 108 (64QAM) 16 (5x1)32 (QPSK), 64 (16QAM), 96 (64QAM)24 (QPSK), 48 (16QAM), 72 (64QAM) 18 (10x1)36 (QPSK), 72 (16QAM), 108 (64QAM)27 (QPSK), 54 (16QAM), 81 (64QAM) 5/624 (7x1)48 (QPSK), 96 (16QAM), 144 (64QAM)40 (QPSK), 80 (16QAM), 120 (64QAM) 16 (5x1)32 (QPSK), 64 (16QAM), 96 (64QAM) (QPSK), (16QAM), 80 (64QAM) 18 (10x1)36 (QPSK), 72 (16QAM), 108 (64QAM)30 (QPSK), 60 (16QAM), 90 (64QAM)

doc.: IEEE Submission April 2007 Chang-Joo Kim, ETRISlide 12 Summary: Comparison Table Items Structure Granularity (kbps) Pilot density Overall efficiency (%) Latency for best channel estimation (OFDMA symbols) 1) Performance of channel estimation 2) Flexible channel estimation in AMC subchannel Ratio of DS to US for data field3) Effective- ness to support all code rates 7x1 with 60 subchannels /7 (14.2%) Same Available 2.4 (17/7) Effective 7x1 with 120 subchannels 8.4 1/7 (14.2%) 64.87Available 2.4 (17/7) Effective Modified 5x1 with 84 subchannels 8.0 1/5 (20.0%) 62.75Available 3.8 (19/5) Not effective 5x1 with 84 subchannels 8.0 1/5 (20.0%) Not Available 3.8 (19/5) Not effective 1)It is related to the AMC subchannel. In diversity subchannel, we should always wait 7 or 5 OFDMA symbols. 2)The best performance of channel estimation using 7 or 5 OFDMA symbols is always same. 3)We assume 2K FFT and 1/8 GI mode. In this case, the number of data OFDMA symbols per frame is 24 excluding 1 frame preamble and 1 FCH/MAP symbol.

doc.: IEEE Submission April 2007 Chang-Joo Kim, ETRISlide 13 Conclusions On the whole, considering the important characteristics for upstream symbol structure, such as granularity, pilot density, latency, performances, flexibility for channel estimation, ratio of DS data to US data, effectiveness to support all code rates, etc. The 7x1 scheme with 120 subchannels can be most suitable for symbol structure in the upstream.

doc.: IEEE Submission April 2007 Chang-Joo Kim, ETRISlide 14 References [1] Gerald Chouinard, “ _OFDMA_Parameters”, IEEE , January [2] Voice Over IP – Per Call Bandwidth Consumption, Cisco Systems,