Synchronized Ranging Structure for IEEE P802 Synchronized Ranging Structure for IEEE P802.16m/D1: Discussion and Simulation Results (15.3.9.1.4.2 and 15.3.9.2.4.2) Document Number: C80216m-09/1994 Date Submitted: 2009-08-30 Source: Pei-Kai Liao, Yih-Shen Chen and Paul Cheng E-mail: pk.liao@mediatek.com, yihshen.chen@mediatek.com MediaTek Inc. Yan-Xiu Zheng E-mail: zhengyanxiu@itri.org.tw ITRI Venue: IEEE Session #63, Jeju, Korea Base Contribution: This is base contribution Re: To be discussed in TGm for IEEE P802.16m/D1 Purpose: For TGm members’ discussion and approval Notice: This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It represents only the views of the participants listed in the “Source(s)” field above. It is offered as a basis for discussion. It is not binding on the contributor(s), who 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 802.16. Patent Policy: The contributor is familiar with the IEEE-SA Patent Policy and Procedures: <http://standards.ieee.org/guides/bylaws/sect6-7.html#6> and <http://standards.ieee.org/guides/opman/sect6.html#6.3>. Further information is located at <http://standards.ieee.org/board/pat/pat-material.html> and <http://standards.ieee.org/board/pat >.

Design Considerations Low overhead Meet the latency requirement with low overhead High timing estimation accuracy Meet the required timing accuracy of WiMAX system High detection rate Support up to P-user transmission simultaneously Able to detect the transmitted code sequences by K users successfully P depends on the system load and user arrival rate Performance requirements Miss detection rate ≦ 1% False alarm rate ≦ 0.1% Timing estimation error ≦ ± (Tb/32)/4 samples (0.7143 us) ≦ ± 4 samples when the channel bandwidth is 5 MHz ≦ ± 8 samples when the channel bandwidth is 10 MHz ≦ ± 16 samples when the channel bandwidth is 20 MHz

Proposed Synchronous Ranging Channel Structure (1/5) Ranging Channel Structure for Synchronized AMSs UL ranging channel for synchronized AMSs is used for periodic ranging in macrocells; initial ranging, handover ranging and periodic ranging in femtocells RCP length is equal to normal CP and RP length is equal to Tb It occupies 72 subcarriers by K OFDM symbol time For femtocells, K = 1 and the rest of subcarriers are used for data transmission (5-symbol LRUs) Ranging Preamble Codes Frequency-domain cyclic padded Zadoff-Chu code is applied Code #1: Adopted by current AWD Code #2: Suggested modification

Proposed Synchronous Ranging Channel Structure (2/5) Suggested code sequence configuration Code #2 is suggested Technical reason is described in the Appendix The number of cyclic shifted codes per ZC root index for code #2 is shown as follows index 1 2 3 M 4 8

Proposed Synchronous Ranging Channel Structure (3/5) Allocation of synchronous ranging channel Idle-to-active latency requirement in SRD: 100 ms Handover interruption time requirement in SRD Intra-frequency: 27.5 ms Inter-frequency: 40 ms (within a spectrum band), 60 ms (between spectrum bands) The requirement applied to initial ranging, handover ranging in femtocells so it has to be allocated much more frequent in femtocells than in macrocells Shorter allocation periodicity; larger overhead Proposed approach can reduce the overhead in femtocells Synchronous ranging channel allocations for macrocell and femtocell can be separate or co-located

Proposed Synchronous Ranging Channel Structure (4/5) 1 bit to signal two formats in SFH Format Multiplexing Mode TDM/CDM among cells: 72 subcarriers × 3 OFDM symbols per ranging channel allocation Cells with mod(Cell_ID, 2)=q utilize (3×q+1)th ~ (3×q+3)th OFDM symbol of the subframe for ranging channel allocation. 1 CDM among cells: two duplicate 72 subcarriers × 3 OFDM symbols per ranging channel allocation All cell utilizes 6 OFDM symbols of the subframe for the ranging channel allocation.

Proposed Synchronous Ranging Channel Structure (5/5) Suggested configuration of time-domain allocation by SFH For macrocells, configuration 2 and 3 are applied For femtocells, configuration 0 and 1 are applied Configurations The subframe allocating Ranging channel OSFth UL subframe in every frame 1 OSFth UL subframes in the first frame in every superframe 2 OSFth UL subframe in the first frame in every 8 superframe 3 OSFth UL subframe of the first frame in every 16 superframes

Format #0 TDM/CDM among cells: One ranging opportunity occupies Nsc subcarriers by K OFDM symbols Nsc=72, K=3 72 subcarriers × 3 OFDM symbols per ranging channel allocation One subframe time is allocated for synchrounous ranging channel in each allocation One cell utilizes only 1 opportunity for periodic ranging, and the rest of ranging opportunities are utilized by other cells Cells with mod(Cell_ID, 2)=q utilize (3×q+1)th ~ (3×q+3)th OFDM symbol of the subframe for ranging channel allocation

Format #1 CDM among cells: One ranging opportunity occupies Nsc subcarriers by K OFDM symbols Nsc=72, K=6 Two duplicate 72 subcarriers × 3 OFDM symbols per ranging channel allocation One subframe time is allocated for synchrounous ranging channel in each allocation K=6, there is only one ranging opportunity for one macrocell All cell utilizes 6 OFDM symbols of the subframe for the ranging channel allocation

Ranging Channel Allocation Partially collocated allocation for femtocells and macrocells Ranging channel allocations for femtocells are more frequency than those for macrocells Some allocations are shared by macrocells and femtocells and others are for femtocells only The size of allocations for macrocells and femtocells can be the same or different

Conclusion Time-domain cyclic-shift is suggested for ranging preamble Two formats are recommended to mitigate inter-cell interference and increase coverage Format 0: reduced inter-cell interference Format 1: large cell coverage According to the simulation, 72 subcarriers over frequency domain can provide enough timing estimation accuracy to meet the requirement According to the simulation, time-domain spreading over 3 symbols can provide good detection performance to meet the requirements 72x3 structure is suggested for synchronized ranging channel

Appendix

Code Sequence Generation How many codes can be generated by circular-shift per root code to meet the timing estimation requirement? Ncs×(NFFT/NRP) >> 2×(maximal timing error) floor(71/8)×(512/71) = 57.69 >> 2×5 = 10 M = 8 can meet the requirement It is suggested to generate up to 8 code sequences per root code by circular-shift Total up to 70×8=560 code sequences

Size of Synchronous Ranging Channel Three candidate structures 6x6, 18x6, 72x1 Timing estimation performance depends on the time-domain autocorrelation property of the designed code sequence If ZC code is applied, its time-domain autocorrelation property depends on the ratio of the number of occupied subcarriers over total subcarriers NFFT/Nrang 6×6: NFFT/Nrang = 512/6 = 85.33 >> 4 (samples) 18×6: NFFT/Nrang = 512/18 = 28.44 >> 4 (samples) 72×1: NFFT/Nrang = 512/72 = 7.11 ～ 4 (samples) 72×1 structure can provide better timing estimation performance, compared to the other two candidates There is no need to consider 144×K structure since 72×K structure can already meet the requirement It is suggested to adopt 72 subcarriers over frequency-domain for synchronous ranging channel

Auto-correlation Property of Candidate Structures

Simulation Parameters Carrier frequency: 2.5 GHz Total bandwidth: 5 MHz FFT size: 512 Sampling rate: 5.6 MHz CP length: 1/8 Antenna configuration: 1 Tx, 2 Rx Channel model: Wideband ITU-PB 3 km/hr, Wideband ITU-VA 120 km/hr Code selection: random selection for the code set Timing error: random within ±8 samples Frequency error: random within 2% subcarrier spacing Ranging detector: correlation detector (full search)

Timing Estimation Performance

Detection Performance