Evolution of Cellular Systems. Challenges for Broadband Wireless Systems. Convergence of Wireless, Computing and Internet is on the Way

Transcription

1 International Technology Conference, 14~15 Jan. 2003, Hong Kong Technology Drivers for Tomorrow Challenges for Broadband Systems Fumiyuki Adachi Dept. of Electrical and Communications Engineering, Tohoku University, Japan OUTLINE Evolution of Cellular Systems Global System Challenges for Giga- Technology 2003/1/15 FA/Tohoku Univ. 1 Evolution of Cellular Systems New systems appeared every decade according to advancements in wireless technology and changes in user demands. Service type Voice Muldia Narrowband Era 1G 2G ~2.4kbps~64kbps Analog AMPS TACS NTT Digital IS95 IS136 GSM PDC Wideband Era 3G ~2Mbps IMT-2000 Broadband Era 4G ~1Gbps Broadband wireless Year 2003/1/15 FA/Tohoku Univ. 2 Convergence of, Computing and Internet is on the Way 3G Services Started in Japan Introduction of IMT2000 services took place in Japan in 2001 The shift to 3G systems is on going Internet Convergence 2GHz bands IMT2000 Network i-mode type cellular Sept Cellular users: 72,081,000 Users connected to Internet: 57,112,700 (79.2%) i-mode: 34,883,000 Ezweb: 11,150,400 J-sky: 11,079, /1/15 FA/Tohoku Univ. 3 Indoors ~2Mbps Mobile ~144kbps Pedestrian ~384kbps 2003/1/15 FA/Tohoku Univ. 4

2 LAN Trial in Japan Terminal PDA PC LAN access point Spot services HiSWANa (36Mbps) IEEE802.11b (11Mbps) Authentication: MAC address(11b) MT- ID(HiSWANa) Wicket area, platform Hotel lobby, etc Network 2003/1/15 FA/Tohoku Univ. 5 WLAN standards: HiSWANa and IEEE802.11b Significantly higher data rates of 36~54Mbps A shorter-range coverage (100~150m but 500m~1km in LOS condition) than 3G cellular systems HiSWANa IEEE802.11b Frequency band 5.2GHz 2.4GHz Modulation Coded OFDM Spectrum spreading Data rate 36Mbps 11Mbps Multi-access Coverage Network interface TDMA-TDD/DSA (centralized control) ~100m Ethernet/IP/ATM/ IMT2000 CSMA/CA (de-centralized control) ~100m Ethernet Authentication MT-ID MAC address 2003/1/15 FA/Tohoku Univ. 6 Global System Next generation wireless systems may not be based on a single standard, but a global wireless system that consists of many dedicated wireless systems interconnected by broadband Internet technology CRL has initiated the new generation mobile network project (2002~2005) headed by Prof. F. Adachi Future Present Cellular Growth Global wireless system connected by internet technology Growth LAN 2G/3G Cellular Broadcasting Growth 4G cellular Broadcasting LAN 2003/1/15 FA/Tohoku Univ. 7 Global wireless system to provide nationwide coverage by using different wireless systems Hot spot areas with high muldia traffic can be covered by 4G hot spot access of 100Mbps~1Gbps or wireless LAN Relatively wide hot spot areas are covered by 4G cellular of ~100Mbps Other places can be covered by present 2G/3G cellular systems Giga-wireless technology Common wireless technology for cellular and wireless LAN applications Data rates of ~1Gbps Very high spectrum efficiency of 5~10 bps/hz; multiple-input multiple-output (MIMO) antenna systems will play an important role 2003/1/15 FA/Tohoku Univ. 8

3 Challenges for Giga- Technology Data rate Giga-wireless is one of the core technologies for realization of global wireless system 1G 100M 10M 1M 100K 10K LAN Giga- IMT-2000 (3G) 2G cellular (PDC, GSM, IS95) Quasistationarstationary Pedestrian Vehicular Quasi- Stationary Indoor Outdoor Mobility 2003/1/15 FA/Tohoku Univ. 9 Propagation Channel Model Understanding of propagation mechanism is important for system development Transmitted signal is reflected and diffracted by buildings, resulting in a multipath channel Transmitter Distance dependent path loss Blocking Shadowing Reflector Random process receiver Scatterers Multipath fading 2003/1/15 FA/Tohoku Univ. 10 Frequency-Spatial Distribution of Multipath Fading 2GHz 200ns Two Approaches for Giga- DS-CDMA: Time domain spreading Spreading Code sequence Data symbol DS-CDMA signal Gain (db) Frequency (MHz) 2003/1/15 FA/Tohoku Univ Position (cm) MC-CDMA:Frequency domain spreading Data symbol Spreading Code sequence 2003/1/15 FA/Tohoku Univ. 12 S/P I F F T P/S MC-CDMA signal

4 DS-CDMA vs. C-CDMA freq. 1 chip 1 data symbol (a) DS-CDMA user#3 user#2 user#1 user#0 1 data symbol (b)mc-cdma user#3 user#2 user#1 user#0 2003/1/15 FA/Tohoku Univ. 13 freq. 1 chip BER Performance DS- and MC-CDMA provide similar performance Average BER 1.E-01 1.E-02 1.E-03 1.E-04 1.E-05 1.E-06 QPSK C= SF=256, GI=32 8-path Rayleigh Ideal channel estimation DS-CDMA MC-CDMA Average received Eb/N0 (db) 2003/1/15 FA/Tohoku Univ Throughput Hybrid ARQ combined with powerful turbo coding Throughput is almost independent of the spreading 1 factor Total throughput (bps/hz) L =4, α=0, M =1, K =1024, f D T c =1/32000 Ideal channel estimation Average received Ec/N0=8dB Average received Ec/N0=4dB Dow nlink Uplink WMSA channel estimation 0.2 RCPT HARQ using DS-CDMA Spreading Factor 2003/1/15 FA/Tohoku Univ. 15 DS- and MC-CDMA Access systems Either DS- or MC-CDMA can be a common wireless technology for construction of cellular and hot spot systems PN#2 PN#3 PN#1 PN#0 PN#4 PN#6 Random TDMA with scheduling PN#5 LAN type (SF=1) Cellular type (SF>1) 2003/1/15 FA/Tohoku Univ. 16

5 Cellular type(sf>1) Real and non-real services with relatively low data rate per user LAN type (SF=1) Hot spot areas Non-real services with very high data rate per user are provided by random TDMA system with appropriate scheduling. An SF=1 system can be extended to a cellular system with the aid of fast selection of transmit cell and adaptive antenna array. Virtual Cellular System Links for 100Mbps~1Gbps becomes not only interference limited but also severely power limited Propagation loss is in proportion to f 2.6 x transmission rate Peak transmission power for 100Mbps@5GHz is about 135,000 s that of 8kbps@ 2GHz, e.g., 1W --> 135kW. This cannot be allowed Cell size should be reduced by about 29 s (pico-cell, e.g., 1,000m --> 34m cell) Fundamental change in wireless access network architecture is required that allows significant reduction in mobile transmit powers 2003/1/15 FA/Tohoku Univ /1/15 FA/Tohoku Univ. 18 Virtual cell consisting of many distributed wireless ports for non-real IP packet transport Transmit and receive functions are not necessarily installed at all wireless ports Receive-only ports in addition to receive and transmit ports Network control station (a) Virtual cellular Distributed port Central port Base station (b) Conventional cellular 2003/1/15 FA/Tohoku Univ. 19 Total average transmit power per virtual cell can be significantly reduced 1 Reverse link MRC Reverse link SC Forward link MRC Forward link SC Total average transmit power ratio (relative) Number K of wireless ports per virtual cell 2003/1/15 FA/Tohoku Univ. 20

6 Access Network access network may become closer to present wireless LAN but with nationwide mobility management Base station Advanced Antenna Technology Adaptive antenna array (AAA) system Space- Transmit Diversity (STTD) system Multi-input/multi-output (MIMO) antenna system N t antennas N r antennas WNC LR IP-based wireless access network Tx Multipath channel Rx IP-based core network WNC: Network Control LR: Location Register 2003/1/15 FA/Tohoku Univ /1/15 FA/Tohoku Univ. 22 AAA System AAA system confines the transmitting radio energy in a narrow angle width to increase the link capacity in no. users/hz and cellular capacity in no. users/hz/m 2 Interference from other users located at different positions are suppressed by forming narrow beams Desired signal Interference Virtual antenna w 2003/1/15 M-1 FA/Tohoku Univ. 23 w 0 + {w} Demod. MMSE STTD System STTD system exploits independent fading seen on different transmit antennas to improve the transmission quality in BER or FER Simple example is Alamouti s STTD, that can achieve MRC diversity improvement with 3dB power penalty C d d2 (2 2) 2n + 1 = n+ 1 2n d 2n 2 antennas d space d 2n Space- {d 2n,d 2n+1 } coding S/P C (2x2) d 2n /1/15 FA/Tohoku Univ. 24

7 MIMO System MIMO antenna system transmits different data sequences from different antennas to increase achievable data rate within the limited bandwidth, i.e., the channel capacity in bps/hz If 8 antennas are used with QPSK transmission, then 16bps/Hz can be achieved N t antennas N r antennas Multipath channel Coding S/P Channel separation Decod. 2003/1/15 FA/Tohoku Univ. 25 Another Interesting Technology: UWB Ultra wideband (UWB) technology for short range communication (several tens meters) has been attracting a strong attention Possible applications: Personal area network, home area network, computer commun., adhoc network CRL has initiated UWB project (2002~2005) headed by Prof. R. Kohno >100Mbps UWB communications system using 3~30GHz and >30GHz Devices, pulse signal processing, interference suppression techniques, propagation modeling, etc Conventional ns pulse bandpass signal UWB f Several GHz Power density 2003/1/15 FA/Tohoku Univ. 26 Conclusion systems are now becoming an important infrastructure of our society. A global wireless system was suggested to offer broad ranges of Internet services to cellular and nomadic users Many dedicated wireless systems are efficiently interconnected, including 2~4G cellular systems, wireless LANs, broadcasting systems, etc., each optimized to each communications environment Common wireless technology is desirable to be used in 4G cellular and wireless LAN type systems Either DS- or MC-CDMA can be used technology of 100M~1Gbps capability is a challenging research for the coming 10 years 2003/1/15 FA/Tohoku Univ. 27