1. Scattered MIMO Pilot Allocation using cyclic shift IEEE 802.16 Presentation Submission Template (Rev. 9) Document Number: IEEE S802.16m-08/068, Scattered MIMO Pilot Allocation using cyclic shift Date Submitted: 2008-1-16 Source: Hidenori KAYAMA*, Isamu YOSHII**, Katsuhiko HIRAMATSU**Voice: +81-50-3687-6588 *Panasonic Mobile Communications R&D Lab. (Panasonic)E-mail:kayama.hidenori@jp.panasonic.comkayama.hidenori@jp.panasonic.com **Matsushita Electric (Panasonic) Venue: IEEE 802.16 Session #53, Levi, Finland Base Contribution: C802.16m-08/068 Purpose: For discussion of MIMO Pilot Allocation in MIMO case 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: and.http://standards.ieee.org/guides/bylaws/sect6-7.html#6http://standards.ieee.org/guides/opman/sect6.html#6.3 Further information is located at and.http://standards.ieee.org/board/pat/pat-material.htmlhttp://standards.ieee.org/board/pat

2. Introduction We proposed in a contribution for previous meeting a TDM based MIMO pilot allocation using the cyclic shift (TDM CS pilot). In this contribution, a scattered MIMO pilot allocation using the CS (Scattered CS pilot) is presented. By using scattered allocation, it has better channel estimation accuracy in high mobility case than a legacy pilot allocation (Legacy pilot) and the TDM CS pilot, while keeping less total pilot density than the Legacy pilot. This pilot allocation technique in MIMO case can be applied in zones such as AMC in the frame structure for 16m system.

3. Scattered CS pilot After pilot symbols are allocated on M spaced subcarriers in M pilot OFDM symbols per pilot allocation unit in frequency domain, pilot OFDM symbols of each Tx antenna are transmitted with K samples cyclic shift. This pilot signal is formed of N impulses with K sample transmission interval(TI)s, and its N*K sample signals are repeated M times in time domain. After propagating, total multipath channels can be observed like time shifted impulse responses. When the TI is longer than the multipath channel delay, the receiver can extract the multipath channel from each Tx antenna using time windows based on the TI. When K samples is same as the CP length, 8/M antennas pilots can be allocated in one OFDM symbol in case of Reference system. Figure 1 Scattered CS Pilot ( in case of M=2)

4. Pilot Density Comparison in 4 antennas case Figure 2 illustrates allocations of the Legacy pilot, the TDM CS pilot, and the Scattered CS pilot in 4 Tx antennas case and Table 1 shows the pilot densities of them. The Scattered and the TDM CS pilot have approximately 30 percent less total pilot density and 3 times more pilot density per antenna than the Legacy pilot. This is caused by the characteristic that CS pilot can reduce the total pilot density in time-frequency resource keeping the pilot density per antenna in case of large number of Tx antennas. Figure 2 Pilot Allocations in 4 Tx antennas case (a) Legacy pilot (b) TDM CS pilot (c) Scattered CS pilot Total Pilot Density 12/54 = 0.2222 1/6 = 0.1667 1/6 = 0.1667 Pilot Density per Antenna 0.2222/4 = 0.0556 0.1667 Table 1 Pilot density comparison in 4 antennas case

5. NMSE (Normalized Mean Square Error) performance of Channel Estimation Figure 3 shows the NMSE of each pilot allocation in high mobility case that velocity of mobile station equals to 120km/h. Simulation assumption is shown in Table 2. The Scattered CS pilot has better NMSE than the Legacy pilot, while the TDM CS pilot has worse NMSE than the Legacy pilot due to bad channel tracking ability caused by less pilot density in time axis. Figure 3 NMSE comparison Antenna configurationTx:4, Rx:4 Propagation modelPedestrian-B model (v=120km/h) Pilot allocation(1), (2),(3) of Figure 2 Frame structure5MHz DL parameters of [1, table3] Channel estimation Legacy pilot: zero forcing with linear interpolation TDM and Scattered CS pilot: After peak search, complex amplitudes of each antenna’s peak and sinc funcntion replica are matched in time domain. After transforming into frequency domain, linear interpolation between pilot OFDM symbols is applied. Table 2 Simulation assumption [1] WiMAX FORUM, “Mobile WiMAX – Part I: A Technical Overview and Performance Evaluation”, August, 2006

6. Conclusion This contribution proposed the Scattered CS pilot allocation in MIMO case. The Scattered CS pilot has good channel estimation accuracy in high mobility case compared with the Legacy pilot and the TDM CS pilot while having the less total pilot density than the Legacy pilot. This pilot allocation technique in MIMO case can be applied in zones such as AMC in the frame structure for 16m system. It would be worth introducing the CS pilot concept in SDD as a new main function.