Ubiquitous Network. Hotspot Network. ad-hoc & RF-ID

Transcription

1 Ubiquitous Network Suguru Kameda, Seong-Kweon Kim, Hiroyuki Nakase, Kazuo Tsubouchi Research Institute of Electrical Communication Tohoku University Katahira 2-1-1, Aoba-ku, Sendai , Japan {kameda, skkim, nakase, Abstract Ubiquitous means every present in all places. To connect central processing units (CPUs) in all places, wireless network systems are indispensable. We call next generation wireless network Ubiquitous Network. Using the Ubiquitous Network, we can get a perfect communication environment of anytime, to anywhere, to anybody, and with every information. In this paper, we report our recent two progresses toward the Ubiquitous Network: all digital one-chip wireless modem for ad-hoc & radio frequency identification (RF-ID) and seamless handover method for hotspot network. Furthermore, we describe the novel device and system, which are applicable to the Ubiquitous Network. Communication distance [m] (Mobility) 1k 100 PDC cdma One Cellular: Voice PHS W-CDMA cdma2000 IEEE Wireless LAN: Broadband (LAN) 4G (100 Mbit/s?) b a/g 100 Mbit/s Hotspot Network 1 Gbit/s I. INTRODUCTION In 1988, Mark Weiser, who joined in the Palo Alto Research Center (PARC) of Xerox Corporation, named the third wave in computing Ubiquitous Computing [1]. First wave in computing was mainframes. One central processing unit (CPU) was shared by a lot of people. Second wave in computing was personal computers (PCs). One CPU on PC was shared by a man. In the third wave, which was named Ubiquitous Computing, many CPUs in all places were shared by a man. Ubiquitous means every present in all places. To connect CPUs in all places, wireless network systems are indispensable. In this paper, we call next generation wireless network Ubiquitous Network. Using the Ubiquitous Network, we can get a complete communication environment with anytime, anywhere and anybody. The Ubiquitous Network includes following three applications: 1) communication among human beings 2) searching, reading and watching of base contents 3) sensing and control Example of the first application, communication among human beings, is voice communication using a cellular phone system. At the present time, wireless cellular infrastructures provided by major common carriers have led the brilliant technical progress and services. A major voice rate of wideband code-division multiple-access (W-CDMA) in Japan is 64 kbit/s [2]. Example of the second application, searching, reading and watching of base contents, is world wide web (WWW). Recently, hotspot services using wireless local area network (LAN) modems such as Institute of Electrical and Electronics Engineers (IEEE) a/b/g [3 5] are used widely [6]. A 10 Short range: Data (serial) ad-hoc & RF-ID Fig k RF tag 100k Bluetooth 1M 10M 100M UWB? 1G Data rate [bit/s] Classification of wireless systems for Ubiquitous Network. maximum rate of the hotspot in Japan is 54 Mbit/s using the IEEE a. Example of the third application, sensing and control, is radio frequency identification (RF-ID). The research and development of RF-ID has been brilliantly carried out such as the µ-chip [7], in-vivo communication of NORIKA3 [8] and a contact-less integrated circuit (IC) of Suica by East Japan Railway Company (JR East) [9]. The features of RF- ID are ultra-small size, low-power operation and low cost implementation. Figure 1 shows a classification of wireless systems for the Ubiquitous Network. The horizontal axis is rate. The vertical axis is communication distance. In Fig. 1, the wireless systems can be classified into three kinds of systems, cellular for voice communication, wireless LAN for broadband communication and short range communication for ad-hoc & RF-ID. Three kinds of systems correspond to the three applications of the Ubiquitous Network, respectively. In Fig. 1, there are two keywords, ad-hoc & RF-ID and hotspot network. In this paper, we report our recent two progresses toward the Ubiquitous Network: all digital one-chip wireless modem for ad-hoc & RF-ID and seamless handover method for hotspot network. Furthermore, we describe novel

2 TABLE I SELECTION OF PHASE. (tx) modulator (rx) phase 0 π/2 π 3π/2 system clock one-chip digital circuit Measurement Fig. 2. System block diagram of all digital one-chip wireless modem. (a) BPSK Modulator CMOS amplifier (b) QPSK Fig. 3. divider Block diagram of transmitter. Output (c) π/4- QPSK consteration eye pattern consteration eye pattern Serial to Parallel Selector 0 π π/2 3π/2 QPSK (1) Before BPF (2) After BPF BPF: band pass filter Fig. 5. Measurement results of transmitted. divider D-FF D-FF Received CMOS amplifier Differential Data Fig. 4. Block diagram of QPSK modulator. Fig. 6. Block diagram of receiver. device and system, which are applicable to the Ubiquitous Network. II. ALL DIGITAL ONE-CHIP WIRELESS MODEM FOR AD-HOC & RF-ID A. Concept Ad-hoc & RF-ID are significant wireless technologies for Ubiquitous Network. Requirements of ad-hoc & RF-ID are ultra-small package, low power operation and low cost implementation. µ-chip [7], which has been proposed and fabricated by Hitachi Ltd., is ultra-small RF-ID chip. The µ- chip was designed using analog/digital mixed process. However, the µ-chip does not have a function of interactive communication for ad-hoc. We have proposed a new design method for the digital wireless modem using digital large scale integration (LSI) [10 18]. Figure 2 is a block diagram of all digital one-chip wireless modem. The design method has been achieved with a programmability of modulation type by simple logic design. B. Design method of the proposed modem The feature of proposed design method is that a clock has been used as carrier of modulation. Figure 3 shows a block diagram of transmitter of wireless modem using proposed design method. In transmitter, carrier has generated from divided clock. The carrier frequency and symbol rate is decided from the number of divide. In the proposed design method, modulated can be simply obtained. Figure 4 shows the quadrature phase shift keying (QPSK) modulator using delay flip-flop (D-FF) and inverter. The input is the divided clock. Delayed means π/2- shifted carrier. Inverted means π-shifted. QPSK modulation is carried out by selecting 4-type depending on baseband digital as listed in Table I. Other PSK modulation, such as binary PSK (BPSK), π/4-shift QPSK, et al., can be obtained by changing the number of D-FF. Differential coding in transmitter has been employed for simple demodulation. Figure 5 shows measurement results of modulated using proposed modulation method, (a) BPSK, (b) QPSK and (c) π/4-shift QPSK. A field-programmable gate-array (FPGA, Xilinx Vertex V300PQ) was used for implementation. HP89410A vector analyzer was used for measurement. In the measurement, clock frequency of LSI was 48 MHz and carrier frequency is 12 MHz. Data rate was 1.5 Mbit/s. Figure 6 shows a block diagram of receiver of wireless modem using the proposed method. In frontend of the modem, complementary metal-oxide semiconductor (CMOS) amplifiers using CMOS inverter have been used as shown in Fig. 7. A received is converted to a digital due to saturated operation of the CMOS inverter. In the, differential detection has been employed. Figure 8 shows the differential detector using delay

3 RF/IF input output ( input) pad QPSK Fig. 7. Delay line D-FF Delay line CMOS amplifier. Ex-OR Ex-OR Parallel to Serial Fig µm core 150 µm 150 µm 1330 µm Photograph of designed BPSK modem LSI using 0.25µm process. Fig. 8. Block diagram of differential. modulator CLK (TX) 4-divider modulator LSI ATT TSG-106 LSI D differential encoder D D D TX RX Fig. 11. white Gaussian noise generator Block diagram of measurement system. TABLE II MEASUREMENT PARAMETERS. T symbol one-chip digital circuit System clock f clock Carrier frequency f c Symbol rate R s Detection Technique 84 MHz 21 MHz MHz Differential detection Fig. 9. Block diagram of designed BPSK modem. lines and exclusive-or (Ex-OR) gates. Baseband without carrier synchronization can be obtained using these structures. Delay time of the delay line is equal to the symbol duration. After differential detection, decision of symbol is carried out. C. Implementation of the proposed modem LSI A BPSK modem using the proposed design method has been designed and implemented using 0.25 µm CMOS process. We used Circuit Multi-Projets (CMP, France) as a broker and STMicroelectronics as a foundry. Figure 9 shows a block diagram of the designed BPSK modem. Figure 10 shows a photograph of the designed modem LSI. Verilog hardware description language (Verilog-HDL) has been used for circuit design. Carrier frequency to be 1/4 of clock frequency and symbol rate to be 1/8 of carrier frequency have been designed. The clock frequency of 160 MHz leads to 40 MHz carrier frequency and 5 Mbit/s rate. Figure 11 shows the measurement block diagram. The system parameter is listed in Table II. Additive white Gaussian noise (AWGN) channel was assumed. In the measurement, clock synchronization between transmitter and receiver was ideal. Figure 12 shows the measurement result of bit error rate (BER) performance of the proposed modem. Since degradation at BER of 10 3 is less than 1.0 db from theoretical limit of differential BPSK (DBPSK), it is confirmed that the designed LSI has sufficient performance for practical use. III. SEAMLESS HANDOVER METHOD FOR HOTSPOT NETWORK A. Concept Cellular systems with internet protocol (IP) oriented network have been discussed. However, a lot of time for standardization of the cellular systems is required. On the other hand, public hotspot services using wireless LAN [3 5] have been realized such as JR East and Japan Telecom Co., Ltd. [6]. Mobile IP phone, which applied voice over IP

4 Measurement AWGN (DBPSK) ASIC BER Fig. 12. process CNR [db] CNR performance of designed BPSK modem LSI using 0.25µm (a) connected with x: BSx: : GW: mobile terminal base station server gateway Internet GW buffered moved BS5 1 (b) connected with packet packet flow wired or wireless backbone connection wireless access connection Fig. 14. Problem of layer-2-forwarding network. Fig wired backbone connection wireless backbone connection intracell wireless access connection hotspot Structure of hotspot network using layer-2 forwarding. (VoIP) technique using the Internet, have been developed [19 21]. Therefore, using many hotspots, broadband mobile communication system can be realized. In this paper, we call the mobile communication system using many hotspots hotspot network. The channel switching with movement of mobile terminals is one of the important problems in mobile communication systems. Two situations can be considered to channel switching: 1) roaming, which is large-scale movement among provider networks, and 2) handover, which is small-scale movement among neighbor hotspots. The roaming has been realized by Mobile IP technology [22]. In this paper, we discuss the handover technique. Using stream such as VoIP, it is necessary to change a channel seamlessly at handover timing. In conventional IP network, however, wireless LAN access points and backbone network consists without consideration of handover. So, disconnection from the network occurred, when the handover happened. For realizing seamless handover, we have proposed a hotspot network for broadband mobile Internet access using layer-2-forwarding technology [23 27]. In this paper, we propose a seamless handover method using layer-2-forwarding technology with dual receiver switching method. In Sect. III-B, the layer-2-forwarding method is discussed. Decrease of throughput at the time of handover is improved to the throughput without handover. In Sect. III-C, the dual receiver switching method for seamless handover is proposed. Finally, in Sect. III-D, the proposed method using

5 main moved sub ACK main moved main (a) main NIC:connected with sub NIC: suspended (b) main NIC:connected with sub NIC: connected with (c) main NIC: connected with sub NIC: suspended Fig. 15. Concept of dual receiver switching method. IEEE b modems is evaluated. B. Hotspot network using layer-2 forwarding For construction of mobile network, IP routing is need by the using the access point as a router. Using the IP routing method, an IP address of a mobile terminal is changed at handover timing. If the IP address is changed, higher rank layer protocols such as transmission control protocol (TCP) are disconnected. So the IP routing is not suitable for mobile network with handover. In the hotspot network using layer-2 forwarding, in order to give a movement with the connection of higher rank layer protocols, routing with media access control (MAC) address is used. We recognized that the layer-2 forwarding, which is used for bridges and switching hubs, can be realized packet routing without change of IP address. Figure 13 shows structure of the proposed hotspot network using layer-2 forwarding. The proposed network forms tree structure. In the proposed network, base stations are connected point-to-point using high rate wired or wireless channel. Mobile terminals are connected with base stations using wireless channel. The base stations transfer packets under the control of MAC address. The features of the proposed network are as follows: 1) easily implementation using bridge program of Free Berkeley Software Distribution (FreeBSD), 2) independent upper layer protocols such as IP version 4 (IPv4) and IP version 6 (IPv6), and 3) load distribution for packet routing. C. Seamless handover using dual receiver switching method Figure 14 shows packet flow of the layer-2-forwarding network. The packets flow from server () to mobile terminal (). Figures 14(a) and (b) show before and after movement of, respectively. Usually, many packets flow one after another such as Fig. 14(a). In the case of handover such as Fig. 14(b), the unreached packets are buffered by base station. Because ch #1 Fig. 16. BR wired: 100 Mbit/s ch #14 wireless: TCP throughput max 1 Mbit/s BR: bridge (layer-2 switch) Block diagram of measurement system. the unreached packets are not transferred again from at a certain time, throughput of the network decreases. If the and can be connected after the movement to, the can get the buffered packets on without throughput loss. To realize the method, we use the dual receiver on. Figure 15 shows the proposed dual receiver switching method. In this paper, the two receivers on are named main and sub receiver, respectively. The main receiver takes part in function of transmitting. Figure 15(a) shows pre-movement of. Usually, only the main receiver is active. The sub receiver is searching next access points for handover intermittently. Packets reach from to via. Figure 15(b) shows just movement of. The main receiver is connected base station. The main transmitter transmits acknowgement (ACK) packet. The sub receiver is active and receives the buffered packet on. Figure 15(c) shows post-movement of. Since the renewal route is informed by ACK packet, packets flow via. The main receiver is active and connect with. The sub receiver is changing to searching mode again.

6 TCP throughput [Mbit/s] Fig without handover proposed method (with 2 NICs) conventional method (with 1 NIC) Measurement handover frequency [times/100sec] TCP throughput performance using dual receiver switching method. D. Implementation of dual receiver switching method We evaluated the proposed dual receiver switching method. Figure 16 shows a block diagram of measurement system. Two IEEE b network interface cards (NICs) were used for. Since only the main interface was given IP address, all packets were send to and from the main interface. The sub interface was active by promiscuous mode because of receiving all packets, which were send to main interface. Base stations and with bridge function were personal computers with NICs. FreeBSD4.4-Release of operating system was used. Data rate between BS and was 1 Mbit/s. Channel numbers of and were 1 and 14 channel, respectively. Data size is 8 Mbyte. Figure 17 shows TCP throughput performance. The horizontal axis is handover frequency. The vertical axis is TCP throughput. Using the proposed dual receiver switching method, the degradation of the TCP throughput is negligibly small. IV. CONCLUSION In this paper, we report our recent two progresses toward the Ubiquitous Network: all digital one-chip wireless modem for ad-hoc & radio frequency identification (RF-ID) and seamless handover method for hotspot network. The proposed device and system have a potential for promising the realization of the Ubiquitous Network. ACKNOWLEDGMENT This work was supported in part by the IT-program (RR2002) of MEXT. 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