IEEE C802.16m-09/1842 Project IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16> Title Proposed changes to MIMO midamble (15.3.5.4.2) Date Submitted 2009-08-31 Source(s) Seunghyun Kang, Jinyoung Chun, Bin-Chul Ihm and Wookbong Lee sh_kang@lge.com LG Electronics Re: IEEE 802.16 Working Group Letter Ballot #30 P802.16m/D1 : MIMO midamble (15.3.5.4.2) Abstract This contribution provides the proposed text for MIMO Midamble. Purpose To be discussed and adopted by TGm for the 802.16m amendment. Notice Release Patent Policy 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. 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Further information is located at <http://standards.ieee.org/board/pat/pat-material.html> and <http://standards.ieee.org/board/pat>. 1 2 1 IEEE C802.16m-09/1842 1 Proposed changes to MIMO midamble (15.3.5.4.2) 2 3 4 Seunghyun Kang, Jinyoung Chun, Bin-Chul Ihm and Wookbong Lee LG Electronics 5 6 7 8 9 10 1. Introduction In session #62, the details of MIMO midamble such as MIMO midamble sequence, subcarrier mapping rule and MIMO midamble symbol location in the DL frame has been proposed and adopted in [1]. In this contribution, we provide analysis of the current MIMO midamble and propose modified MIMO midamble design. 11 12 2. Analysis of the current AWD MIMO midamble 13 14 15 According to the equation (197) in [1], the current MIMO midamble subcarrier mapping rule has its periodicity depending on a number of ABS transmit antennas Nt. Furthermore, the midamble subcarriers are shifted by considering frequency reuse of 3 in order to avoid midamble collision between neighboring cells. 16 Therefore, the period of the midamble subcarriers is 3×Nt and a midamble subcarrier for each antenna is 17 regularly mapped every 3×Nt subcarriers. 18 19 20 21 22 23 24 When there exist ABSs having different cell deployment or exist both Femtocell BS and Macro BS simultaneously, the neighboring cells may be assumed to have different number of transmit antennas. In these cases, there is no way to avoid midamble collision even though the current MIMO midamble subcarrier mapping rule has considered frequency reuse of 3. Figure 1 shows an example of midamble collision between two cells assuming two transmit antennas and four transmit antennas for each. In the figure, there exist midamble collisions in the subcarrier index 6 and 7. Moreover, there exist midamble collisions every 12 subcarriers because of their periodicity. 25 26 Figure 1. Midamble collision between neighboring cells 2 IEEE C802.16m-09/1842 1 2 In the figure 2, the average Mean Square Error (MSE) of channel estimation are derived for MIMO midamble employing 4 cases of transmit antenna configurations. The transmit antenna configurations are as follows. 3 Transmit antenna configurations: 4 Case-1: # transmit antennas of Serving cell = 2 & # transmit antennas of two neighboring cells = 2 5 Case-2: # transmit antennas of Serving cell = 2 & # transmit antennas of two neighboring cells = 4 6 Case-3: # transmit antennas of Serving cell = 4 & # transmit antennas of two neighboring cells = 4 7 Case-4: # transmit antennas of Serving cell = 4 & # transmit antennas of two neighboring cells = 2 8 9 10 11 12 13 14 15 Also, the average MSE has been performed by considering SIR of 0, 3 and 6 dB where SIR is a term for midamble power ratio between a serving cell midamble power and a sum of two neighboring cells midamble powers which are interference to the serving cell. In the figure, the average MSE of Case-1 and Case-3 configurations is getting smaller while increasing SNR. Also, there is no impact of the interference from the neighboring cells since there is no midamble collision. However, for Case-2 and Case-4 configurations, the average MSE are converging to some values depending on SIR. Also, for all the SNR ranges, their average MSE is always larger than that of Case-1 and Case-3 configurations due to the midamble collision. 16 AWD Midamble, SIR=6[dB] AWD Midamble, SIR=3[dB] 1.000 Average MSE Average MSE 1.000 0.100 0.010 0.100 0.010 0.001 0 4 8 12 16 0.001 0 SNR [dB] 4 8 12 16 SNR [dB] AWD,Case-1 AWD,Case-2 AWD,Case-3 AWD,Case-4 AWD,Case-1 17 AWD,Case-2 AWD,Case-3 AWD,Case-4 18 AWD Midamble, SIR= 0[dB] Average MSE 1.000 0.100 0.010 0.001 0 4 8 12 16 SNR [dB] 19 20 AWD,Case-1 AWD,Case-2 AWD,Case-3 AWD,Case-4 Figure 2. Average MSE performance of the current AWD midamble design (SIR=0, 3 and 6[dB]) 21 3 IEEE C802.16m-09/1842 1 3. Modified MIMO midamble 2 3 4 The subcarrier mapping rule of the current MIMO midamble design causes midamble collisions when the neighboring cells are assumed to have different number of transmit antennas. In order to avoid midamble collision with minimal change, we have modified the current MIMO midamble equation as follows. 5 6 24 10 0.2 k s N 1 1 2 G ([ k u offsetD ( fft)] mod fft), k used , k mod 24 g mod N t 8 * ( BSID mod 3) bk Nt 2 N1 * N sc 0, otherwise 7 8 9 10 11 12 13 14 First of all, the period of the subcarrier mapping rule is fixed to the period of the eight transmit antennas regardless a number of transmit antennas. By using this modification on the subcarrier mapping rule, a midamble subcarrier for each antenna is regularly mapped every 24 subcarriers. Also, the shift values for frequency reuse of 3 is fixed to the period of the eight transmit antennas. As a result of this modification, the number of midamble subcarriers is proportionally reduced. In order to compensate the midamble subcarrier density, we have increased the midamble signal power depending on Nt. Since the period of the subcarrier mapping rule and the shift values for frequency reuse have been fixed, there is no midamble collision between neighboring cells having a different number of transmit antennas. 15 16 17 18 In the figure 3, the average MSE performance of the modified midamble design has been evaluated and compared with that of the current AWD midamble design. The modified midamble design shows almost same performance for the Case-1 and Case-3 configurations and shows good enhancement for the Case-2 and Case-4 configurations. 19 Midamble comparison Case-1, SIR= 0[dB] Midamble comparison Case-2, SIR= 0[dB] 1.000 Average MSE Average MSE 1.000 0.100 0.010 0.001 0.100 0.010 0.001 0 4 8 12 16 0 4 8 SNR [dB] AWD 12 16 SNR [dB] Modified AWD Modified 20 21 Midamble comparison Case-3, SIR= 0[dB] Midamble comparison Case-4, SIR= 0[dB] 1.000 Average MSE Average MSE 1.000 0.100 0.010 0.100 0.010 0 4 8 12 16 0 4 8 SNR [dB] AWD Modified AWD 22 23 12 SNR [dB] Figure 3. Average MSE comparison (SIR= 0[dB]) 4 Modified 16 IEEE C802.16m-09/1842 1 2 3 4. References 4 5 [1] IEEE P802.16m/D1, “Draft Amendment to IEEE Standard for Local and Metropolitan Area Networks- Part 16: Air Interface for Broadband Wireless Access Systems” 6 [2] IEEE 80216m-09/0037, “Call for Contributions on Project 802.16m Amendment Content” 7 [3] IEEE C802.16m-09/1313r3, “MIMO midamble sequence proposal” 8 [4] IEEE C802.16m-09/1700, “Proposed Changes to MIMO Midamble (15.3.5.4.2) for the IEEE 802.16m/D1” 9 10 5. Text proposal for inclusion in the 802.16m AWD 11 12 13 Proposed text has been underlined in blue and deleted text has been struck through in red. Existing AWD text is shown in black. 14 15 ----------------------------------------------------------------- Text Start ----------------------------------------------------------------- <Modify subsection 15.3.5.4.2 as follows :> 16 15.3.5.4.2 MIMO midamble 17 18 19 20 21 22 MIMO midamble is used for PMI selection in closed loop MIMO. For OL MIMO, midamble can be used to calculate CQI. MIMO midamble shall be transmitted every frame on the second last DL subframe. The midamble signal occupies the first OFDMA symbol in a DL type-1 or type-2 sub-frame. For the type-1 6 symbol DL subframe case, the remaining 5 consecutive symbols form a type-3 subframe. For the type-2 subframe case, the remaining 6 consecutive symbols form a type-1 subframe. 23 The MIMO midamble signal transmitted by the ABS antenna is defined by Equation (196): 24 N used 1 k N used 1 j 2 ( k ) f t Tg j 2f ct 2 s t Re e bk e k 0 N 1 k used 2 (196) 25 26 27 where bk is a complex coefficients modulating subcarriers in the midamble symbol defined from Equation (197) 28 29 30 31 32 k s N 1 1 2 G ([ k u offsetD ( fft)] mod fft), k used , k mod( 3 * N t ) g mod N t N t * ( BSID mod 3) bk 2 N1 * N sc 0, otherwise 24 10 0.2 k s N 1 1 2 G ([ k u offsetD ( fft)] mod fft), k used , k mod 24 g mod N t 8 * ( BSID mod 3) bk Nt 2 N1 * N sc 0, otherwise where k is the subcarrier index (0 ≤k ≤ Nused -1), Nused is the number of used subcarriers, Nt is a number of transmit antennas, G(x) is the Golay sequence defined in Table 658 (0 ≤ x ≤ 2047), fft is 5 IEEE C802.16m-09/1842 1 2 the FFT size used, u is a shift value (0 ≤ u ≤ 127), where the actual value of u is derived from u = mod(BSID, 128), offsetD(fft) is an FFT size specific offset as defined in Table 659, g is a ABS 3 4 transmit antenna index, Nt is a number of ABS transmit antennas, parameter s = 0, for k≤(Nused - 1)/2 and s = 1, for k>(Nused - 1)/2. 5 6 Example of physical structure of MIMO midamble is shown in Figure 447 423 for 4TX antenna and BSID = 0. 7 1st subband 2nd subband Nth subband 8 9 1st TX antenna 3rd TX antenna 2nd TX antenna 4th TX antenna Null subcarrier 10 11 1st subband 2nd subband Nth subband 12 13 14 15 1st TX antenna 3rd TX antenna 2nd TX antenna 4th TX antenna Null subcarrier Figure 423. MIMO midamble physical structure for 4TX antennas and BSID = 0 MIMO midamble shall be transmitted with boosting of 2dB. 16 Table 658 – Golay sequence of length 2048 bits 0xEDE2 0xED1D 0xEDE2 0x12E2 0xEDE2 0xED1D 0x121D 0xED1D 0xEDE2 0xED1D 0xEDE2 0x12E2 6 IEEE C802.16m-09/1842 0x121D 0x12E2 0xEDE2 0x12E2 0xEDE2 0xED1D 0xEDE2 0x12E2 0xEDE2 0xED1D 0x121D 0xED1D 0x121D 0x12E2 0x121D 0xED1D 0xEDE2 0xED1D 0x121D 0xED1D 0xEDE2 0xED1D 0xEDE2 0x12E2 0xEDE2 0xED1D 0x121D 0xED1D 0xEDE2 0xED1D 0xEDE2 0x12E2 0x121D 0x12E2 0xEDE2 0x12E2 0x121D 0x12E2 0x121D 0xED1D 0x121D 0x12E2 0xEDE2 0x12E2 0xEDE2 0xED1D 0xEDE2 0x12E2 0x121D 0x12E2 0xEDE2 0x12E2 0xEDE2 0xED1D 0xEDE2 0x12E2 0xEDE2 0xED1D 0x121D 0xED1D 0xEDE2 0xED1D 0xEDE2 0x12E2 0x121D 0x12E2 0xEDE2 0x12E2 0xEDE2 0xED1D 0xEDE2 0x12E2 0xEDE2 0xED1D 0x121D 0xED1D 0x121D 0x12E2 0x121D 0xED1D 0xEDE2 0xED1D 0x121D 0xED1D 0x121D 0x12E2 0x121D 0xED1D 0x121D 0x12E2 0xEDE2 0x12E2 0x121D 0x12E2 0x121D 0xED1D 0xEDE2 0xED1D 0x121D 0xED1D 0xEDE2 0xED1D 0xEDE2 0x12E2 0xEDE2 0xED1D 0x121D 0xED1D 0x121D 0x12E2 0x121D 0xED1D 0xEDE2 0xED1D 0x121D 0xED1D 1 Table 659 – Offsets in the Golay sequence FFT size 2048 1024 512 Offset 30 60 40 2 3 4 ------------------------------------------------------------------- Text End ------------------------------------------------------------------- 7