Future Mobile Communications beyond 3G Systems

1. Future Mobile Communications beyond 3G Systems A Multicarrier CDMA Architecture Based on Orthogonal Complementary Codes George Wai Wong Prepared for EECE565 – Wireless Communication Systems

2. Maturity of 3G Systems • Extensive evaluation of W-CDMA has been carried out in both simulations and field trials. • In May 2001, Japan initiated the world’s first testing commercial services for 3G mobile communications based on W-CDMA. George Wai Wong

3. Maturity of 3G Systems (cont.) • The first 3G networks based on CDMA2000 technology were launched in Korea in October 2000. George Wai Wong

4. Maturity of 3G systems (cont.) • CDMA2000 terminal products are already available in the market. George Wai Wong

5. 4G mobile communications • At the time of this presentation, nobody is very sure what 4G will look like. • Systems beyond 3G ought to deliver a much higher data rate which should be roughly in range of 10 to 100Mbps George Wai Wong

6. High data rate in mobile channel • Mobile communication channels are highly unpredictable. (This is why EECE563 final exam is so unpredictable) • Questions are: • how to guarantee such a high data rate in mobile communication channel • what types of air link architecture are qualified to deliver high-data-rate services George Wai Wong

7. New CDMA architecture • The new CDMA architecture ought to be technically feasible and should not introduce too much multiple access interference (MAI). • The multicarrier CDMA architecture based on orthogonal complete complementary code (CC) code can satisfy the above-mentioned requirements. George Wai Wong

8. Complete Complementary Code • CC code is based on a “flock” of elements codes instead of a single code as in traditional CDMA codes. • In other words, every user in the proposed CDMA system will be assigned a flock of elements codes as its signature code which must be transmitted possibly via different channels George Wai Wong

9. CC Code (cont.) George Wai Wong

10. MAI-free operation means ‘+’ means ‘-’ Signature for user 1: A0 = + + + - and A1: + - + + Signature for user 1: B0 = + + - + and B1: + - - - A0: A1:  0  0  0  8  0  0  0 Spreading modulated signal for user 1 (assume the information bits are all +) f1 f2 George Wai Wong

11. MAI-free operation (cont.) means ‘+’ means ‘-’ Signature for user 1: A0 = + + + - and A1: + - + + Signature for user 1: B0 = + + - + and B1: + - - - A0: A1:  0  0  0  0  0  0  0 Spreading modulated signal for user 2 (assume the information bits are all +) f1 f2 George Wai Wong

12. Bit error rate in AWGN channel • Downlink BER comparison (synchronized channel) • Length of Gold code, M-sequence code, and CC code are 63, 63, 4 x 16 respectively • Note that the new CDMA system has almost identical BER performance regardless of the number of users George Wai Wong

13. Bit error rate in AWGN channel (cont.) • Uplink BER comparison (approximately synchronized channel) • Lengths of Gold code, M-sequence code, and CC code are 63, 63, 4 x 16, respectively. • At least 2dB is obtainable from the proposed CDMA system George Wai Wong

14. Bandwidth efficiency • In traditional DS-CDMA techniques, the spreading efficiencies (SEs) are equal to 1/N, where N is denoted as the length of a spreading code • In the proposed CDMA system, the SEs are much higher compare to the traditional DS-CDMA systems. George Wai Wong

15. Bandwidth efficiency (cont.) George Wai Wong

16. Technical limitations • Given the element code length L of the CC code, it is necessary to choose a digital modem capable of transmitting L+1 different levels • If a long CC code is employed in the proposed CDMA system, the number of different levels generated from a baseband spreading modulator can be a problem!!! • One possible solution to this problem is to use (L+1)-QAM digital modem George Wai Wong

17. Technical limitations (cont.) • A relatively small number of users can be supported by a family of CC codes. One possible solution to this problem is to introduce frequency divisions on top of the code division to create more transmission channel. George Wai Wong

18. Conclusions • The proposed CDMA system offers much higher bandwidth efficiency than traditional CDMA systems. • It also offers MAI-free operation in both up- and downlink channels. • The BER of the proposed CDMA system under MAI and AWGN channel is relatively lower than traditional CDMA systems. George Wai Wong

19. Conclusions (cont.) • The technical limitations of the proposed CDMA system are a relatively small family of CC codes and the need for complex multilevel digital modem. • Nevertheless, the proposed CDMA architecture based on complete complementary codes offers a new option to implement future wideband mobile communications beyond 3G. George Wai Wong

20. References • H. H. Chen; J. F. Yeh; N. Suehiro, “A multicarrier CDMA architecture based on orthogonal complementary codes for new generations of wideband wireless communications,”IEEE Commun. Mag., vol 39, no. 10, Oct. 2001, pp. 126 –135 • N. Suehiro, “Complementary Code Composed of N-Multiple-Shift Orthogonal Sequences,” Trans IECE, vol. J65-A, Dec. 1982, pp. 1247-53. • T. Imoto, N. Suehiro, N. Kuroyanag, R. Fan, “Avoidance of inter-cell interference on approximately synchronized CDMA without co-channel interference nor multipath fading using complete complementary code,” Spread Spectrum Techniques and Applications, 2000 IEEE Sixth International Symposium on, vol. 1, 2000, pp. 102 –106. • E. H. Dinan and B. Jabbari, “Spreading Codes for Direct Sequence CDMA and Wideband CDMA Cellular Networks,” IEEE Commun. Mag., vol 36, no. 9, Sept. 1998, pp. 55-81 George Wai Wong

21. Questions? George Wai Wong