On the Selection of Training Sequence Code Pair for MIMO Technology in 3GPP GERAN System Jae-Hyuk Lee, Jun-Ho Baek, Seung-Hoon Hwang*, Byoung-Jo Choi**
* Dept. ofElectronics Engineering, Dongguk University, Seoul, Korea ** University ofIncheon, Incheon , Korea Tel: +82 (0)222603994, Fax: +82 (0)222793994 E-mail:
[email protected]
Abstract- In this paper, we investigate to relationship between TSCs (training sequence codes) and find optimal pair to decrease the channel estimation error in GSM/EDGE evolution system. For the proposed pair, the cross-correlation between the TSCs is employed. Such TSC codes as in normal symbol rate, high symbol rate , and MUROS (Multi User Reusing One Slot) scheme are considered. To decrease the channel error variance may result in improving the performance of channel estimation.
performance due to channel estimation error will occur if we select unsuitable TSC pairs. Considering SM-MIMO transmission scheme for GSMIEDGE, in this paper, we investigate how to fmd suitable TSC pairs for MIMO (using 2 transmit and 2 receive antennas) in 3GPP GERAN Evolution.
II. Training Sequence Code
TSC, TSC pair, Cross-correlation, Channel estimation, MUROS
Keywords -
High-order modulation schemes such as 16QAM or 32QAM were employed in the GERAN Evolution system with a single antenna in order to increase data rate. The receiver uses the I. Introduction MLSE (Maximum Likelihood Sequences Estimation) which is Beyond dispute, GSM (Global System for Mobile optimized equalizer to estimate transmitted symbol, under communications) network is the most successful commercial multi-path fading channel. In case of MLSE, the number of cellular mobile communication system hitherto. It is reported state is Mkwhere, M is modulation order. Generally on the that the number of GSM users all over the world had reached 4 urban channel environment TU (Typical Urban) and billion by 2009.[1] The increase in the number of users and considering Tx Rx's filter, k is 3-4. Therefore, the number of voice traffic puts a huge pressure on operators especially in states is in the range of 16 3-164 in case of the high-order populous countries. GSM launched GPRS (General Packet modulation MLSE makes it impossible to implement the Radio Service) to support high speed packet data. As a result of mobile handsets. Thus in order to increase data rate in GERAN the transition from voice communications to multimedia Evolution system, we use the high-order modulation scheme applications, EDGE (Enhanced Data for GSM Evolution) has along with to SM-MIMO scheme. been involved in GSM [2]. Since 2000, 3GPP TSG (Technical Ta ble I. TSCs for Normal Symbol Rat e Specification Group) GSMIEDGE Radio Access Network (GERAN) had been enhanced performance toward 4G. I ~T SC_(No.) Training Seq uence for Norm al Sym bo l Rat e (26 sy m bols) According to the latest standard, GERAN Evolution was 0010010 11 10000100010010 111 0 introduced high order modulation order, Turbo coding high 001011011 10111100010110111 1 symbol rate [3] to support higher symbol rate (325k symbol/s), 010000 1 110 1110100 100001 110 which is 1.2 times faster than normal symbol rate (271k 2 symbol/s). GSM/EDGE standard specifies a set of eight 01000111101101000100011110 3 training sequences code (TSC) for channel estimation that have 000 1101011100 1000001 101011 4 26 symbols for normal burst (L-TSC) and 31 symbols for high 0 10011 10101100000100111010 symbol burst (H-TSC)[3]. The 4G candidate technologies, such 5 as HSPA-Evolution, LTE-advance and WiMAX phase-2, etc., 1 0 1 0 0 111 11 0 1 1 0 0 01 0 1 0 0 1 11 1 1 6 were commonly adapted the SM (Spatial Multiplexing)-MIMO 1110 111 1000100101110 111 100 7 scheme [4]-[6]. Theoretically, SM-MIMO can increase throughput as number of min (Tx, Rx) antennas increases. From this trend, it is not impossible to adapt SM-MIMO Table 1 shows the regular structures of training sequences for antennas technique for the GERAN Evolution [7]. For 2 by 2 normal symbol-rate in L-TSC case. L-TSC scheme is case, two different TSC should be sent simultaneously from considered to be used in GSMIEDGE, but H-TSC shown by both transmitter antennas. In generally, the TSC has good table 2, is not. Moreover, for H-TSC, auto-correlation is the auto-correlation property but its cross-correlation properties are only condition to be taken into account when choosing H-TSC good only for certain combination of sequence. Lower for antennas. In this paper, we assume that GSM/EDGE
ISBN 978-89-5519-146-2
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Feb. 7-10, 2010 ICACT 2010
Evolution systems use H-TSCs with both auto-correlation and cross-correlation properties. And we consider to cross-correlation between the L-TSC and N-TSC under the MUROS scheme. Ta ble 2. TSCs for Higb Symbol Rate n .rSC_(No.)
Tra ining Sequence for Higher Symbo l Rate (31 symbols)
0
0 1 0010 00 10 1 1 1 1 1 1 1 0 0101 11 1 0 0111 0
1
1 1 1 00 1 1 00 0 1 1 111 0101 1 0 1 00 01 00 100 10011101 1100 1 011 0 11 11 1 00 0 1 0 100 0
" 3
0 0 00 1 1 10 00 0 0 0 100 11 1 0 1 0 110 0 1 01 0 0
4
10 1 0 0 1 110 001 1 011 00101 11 11110 10 0
5
0 0 10 10 0 1 10 10 1 1 100 1 0 00 00 0 1 1 1 0 0 00
6
10 1111 1101 10 1 0 0 01 1101 1 00 0 11 10 10
I
10 1111 1 0 110 10111 00001 10 11 1 0 1 10 0
Tablc 3. TSCs for MUROS ~-T S C_0-io .)
New Training Sequence for MUROS (26 symb ols)
0
0 1 100 0 1 00 0 1 00 1 0 0 1 1 1 1 0 1 0 1 1 1
1
0 10 1 1 1 10 100 1 10 1 1 10 1 1 10000 1
2
0 100000 10 1 1 00 0 1 1 1 0 1 1 1 0 1 1 00
3
0 0 1 0 1 1 0 1 1 1 0 1 1 100 1 1 1 10 10 00 0
4
0 1 1 1 0 1 00 1 1 1 10 100 1 1 10 1 1 1 1 10
5
0 10 0 00 0 1 00 1 10 10 100 1 1 1 100 1 1
6
0 0 0 1 0 0 00 1 10 10000 1 10 1 1 10 10 1
7
0 10 00 1 0 1 1 100 1 1 1 1 1 100 10 100 1
Figure 1 shows a flow chart of the proposed method. In receiver side, if receiver can support MIMO scheme, the receiver classified as a compatible device. Otherwise, the receiver is operates SISO mode. When the receiver operates in MIMO mode, we try to find out best TSC-pairs for each antenna. In GSMIEDGE, GERAN Evolution system, to increase the capacity, we use multiple antennas (with a assigned to the TSC code for each one) to transmit and receive the signal. The next subsection will show the algorithm to choose TSC pairs to reduce interference while using MIMO technology. Using 2 by 2 MIMO antennas for transmitting and receiving in burst high-symbol GERAN Evolution scenario, the received signal from two antennas simultaneously transmit the discrete model as follows (1)
Where, r~ is the TSC symbol matrix received by two antennas, defmed as r~ = [r1.1rl.zf . n~ and q~ are respectively noise and co-channel interference and can be defined in the same way with r~. A~ is the TSC symbol matrix, transmitted by two
A
antennas, defined as A~ = [ 61A~.1 A62 A~.J. A t ,l and A t •z is consist ofTSC symbols and the size ofthe Toeplitz convolution matrix. L is the number of the taps in multi-path channel. All 4-channel stream matrix is defined as h, = [hII hII hIz hIzF. Using the Joint-LS(Least Square) channel estimation techniques to obtained following channel estimation matrix. hILS can be defined as (2)
Table 3 shows the TSCs for MUROS scheme. [8]
III. Proposed Method
As shown in table 3, there are 4 H-TSC pairs with the smallest values of cross-correlation, make channel estimation error minimized, as a result. Channel estimation, when self-correlation is taken into consideration, is defmed as (3)
Where, (J~ is the dispersion of noise. From this equation, the higher the value of A~H A~ is, the smaller the value of channel estimation error is. In Other words, the smaller value of A~H A~ make channel estimation's performance decrease dramatically. Our proposal method is to use TSC pairs with smallest values base on cross-correlation for transmitting and receiving signal (under the 2 by 2 MIMO system) to increase the performance of channel estimation. HSR BurstforTxAnt 1
HSR Burstfor TI Ant 2
18
0.\1.\
l
69
18
o.m
l
69
End
IIl·YSCJ il.1I.TI;CJ Lll E Itll·TSCJOI.H·TSCj 51:. llf·TSC-, II. H·TM.'J JI:. :1I·YSCJ11. u.rscJ ~I: . 11l·TSCJ t "'lI·TSCJillJ
Figure 1. Flow chart of the proposed method
ISBN 978-89-5519-146-2
Figure 2. HSR burst Structures with two H-TSCs
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Feb. 7-10, 2010 ICACT 2010
Figure 2 show the case that two transmit antennas use the same carrier, but different H-TSCs . Antenna 1 uses H-TSCG), the other uses H-TSC(k) . H-TSCs are chosen so that the cross-correlation is as small as possible by following equation .
Tab le 4. Cross-cor relation values for find optimal H-TSC pair
~
U
0
CCF _HH - TSc(j, k ) =
(4) I
-x" £.., H - TSC _ ( J' ) xH - TSC _ ( k ) ,
J,. k
E
(0 , .. , 7) , } • -r-J,
k
31
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Normal Bu~ forTx Ant 2
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