Fujitsu’s Challenges for WiMAX System-on-a-Chip Solutions V Tamio Saito V Makoto Awaga V Takeshi Takano (Manuscript received March 10, 2008) Worldwide Interoperability for Microwave Access (WiMAX) is a promising candi- date for providing high-data-rate mobile broadband access systems around the world. This paper describes specific features of Mobile WiMAX, such as scalable orthogonal frequency division multiple access (OFDMA), adaptive modulation and coding, and smart antenna technologies, a system configuration, candidate applica- tions, and our challenges for WiMAX system-on-a-chip (SoC) solutions. 1. Introduction (MS: mobile station, SoC: system-on-a-chip, RF: In recent few years, the number of mobile radio frequency). Internet access users has been increasing very This paper summarizes Mobile WiMAX’s rapidly and requirements for high-data-rate specific PHY features, a WiMAX system configu- mobile broadband access systems are also ration, candidate applications for the system, and increasing. Worldwide Interoperability for our challenges for Mobile WiMAX SoC solutions. Microwave Access (WiMAX) is a promising candidate for high-speed mobile broadband 2. Mobile WiMAX specific PHY access. There are two flavors of standards features for WiMAX: IEEE 802.16-20041) a n d Here, we describe some PHY features that IEEE 802.16e-2005.2) IEEE 802.16-2004 is are specific to Mobile WiMAX. mainly focused on fixed wireless access technolo- gies while IEEE 802.16e-2005 is an amended 2.1 Scalable OFDMA version of IEEE 802.16-2004 that adds features Mobile WiMAX uses a scalable orthogonal and attributes to support mobility. In the frequency division multiple access (OFDMA) IEEE 802.16e-2005 standard, there are a lot of technology. A comparison between Fixed WiMAX parameters related to the media access control and Mobile WiMAX is shown in Figure 1. For (MAC) protocol and physical (PHY) layers. Fixed WiMAX, the size of the fast Fourier Therefore, to keep interoperability among devic- transform (FFT) is fixed to 2048 points. If es, an industry consortium called the WiMAX the signal bandwidth changes, the sub-carrier Forum develops guidelines known as system frequency spacing changes too. This means that profiles, which specify the frequency band, if the system changes the service bandwidth from PHY parameters, and MAC parameters to be 20 MHz to 10 MHz in a mobile environment, the used. We have already released commercial Doppler effects will change because there are products such as MS baseband SoC,3) MS RF different Doppler effects for the 20- and 10-MHz module4) and base stations5),6) for Mobile WiMAX bandwidths. To achieve the same performance FUJITSU Sci. Tech. J., 44,3,p.219-226(July 2008) 219 T. Saito et al.: Fujitsu’s Challenges for WiMAX System-on-a-Chip Solutions for the systems, the channel estimation function tions from these modulation schemes and coding should be changed according to the bandwidth, schemes to achieve a high data rate, as shown in but this increases the circuit complexity. The Table 1. scalable OFDMA technology used in Mobile WiMAX avoids this phenomenon. The scalability 2.3 Smart antenna technologies is provided by adjusting the FFT size while fixing To enhance system performance, Mobile the sub-carrier spacing at 10.94 kHz. Since the WiMAX uses smart antenna technologies that sub-carrier spacing is fixed, the impact of the include beamforming, space-time coding (STC), Doppler effect is the same for systems using and spatial multiplexing (SM). For beamforming, different bandwidths. This approach enables the system uses multiple antennas to transmit one particular channel estimation method to be weighted signals to increase the system’s cover- applied to the entire range of environments. age and capacity. This enables a base station (BS) to get a feedback signal from an MS; then, the BS 2.2 Adaptive modulation and coding calculates the weight for each signal. The STC is To enhance the coverage and capac- a transmit diversity technology7) and the scheme ity of mobile applications, Mobile WiMAX uses two transmit antennas and one receive uses an adaptive modulation and coding antenna. The STC provides a spatial diversity (AMC) function in the system. Mobile WiMAX gain in the system and this technique reduces the supports quadrature phase shift keying (QPSK), fading margin. The SM8) achieves higher peak 16 quadrature amplitude modulation (16QAM), rates and increases the data throughput in a and 64QAM as mandatory in the downlink and link. With SM, multiple data streams are trans- supports QPSK and 16QAM as mandatory in mitted from multiple antennas. If two transmit the uplink. In addition, the system supports antennas and two receive antennas are used, the both convolutional coding (CC) and convolutional increase in data transmission rate is twice that turbo coding (CTC) with variable coding rate and in the best condition before. repetition coding. AMC can use various combina- OFDMA: 802.16-2004 Scalable OFDMA: 802.16e-2005 • FFT size is fixed to 2048 for all bandwidths • Allocate the FFT size according to available • Interval of the sub-carriers becomes narrower frequency bandwidth as available bandwidth. • Interval of sub-carriers is fixed. • More difficult to keep performance 2048/20 MHz 2048/20 MHz 2048/10 MHz 1024/10 MHz 512/5 MHz 128/1.25 MHz (a) Fixed WiMAX (b) Mobile WiMAX Figure 1 Comparison between Fixed WiMAX and Mobile WiMAX. 220 FUJITSU Sci. Tech. J., 44,3,(July 2008) T. Saito et al.: Fujitsu’s Challenges for WiMAX System-on-a-Chip Solutions 3. Mobile WiMAX system convergence, such as fixed-mobile conver- configuration gence (FMC) A next-generation packet-based network To deal with the issues of quality, security, configuration is shown in Figure 2. 3G/3.5G, and robustness LTE and WiFi/WiMAX systems are connected to To achieve autonomic control and an all-IP-based network (IP: Internet protocol). self-organization As described before, WiMAX has very flexible To satisfy these requirements, the Next functions for achieving a variety of services. To Generation Network (NGN) is a promising candi- support these features effectively, the all-IP date for the all-IP core network. core network should be flexible to handle their functions. Thus, the core network should satisfy 4. Candidate applications for the following requirements:9) Mobile WiMAX • Functionality to cope with the demand for This section describes some candidate appli- continuous broadband service cations for Mobile WiMAX. Mobile WiMAX • Ease of use and ease of service provision provides a high-data-rate service in the mobile To achieve new services provided through environment at a low cost. Some service models Table 1 Mobile WiMAX PHY data rates with partial usage of sub-channels. 0ARAMETER $, 5, $, 5, 3YSTEMBANDWIDTH-(Z &&4SIZE .ULLSUB CARRIERS 0ILOTSUB CARRIERS $ATASUB CARRIERS 3UB CHANNELS 3YMBOLPERIOD 4SMICROSECONDS &RAMEDURATIONMILLISECONDS /&$-SYMBOLSFRAME $ATA/&$-SYMBOLS $,5, -OD #ODERATE $,-BS 5,-BS $,-BS 5,-BS #4#X #4#X 103+ #4#X #4#X #4# #4# 1!- #4# #4# n n #4# n n 1!- #4# n n #4# n n $,$OWNLINK 5,5PLINK FUJITSU Sci. Tech. J., 44,3,(July 2008) 221 T. Saito et al.: Fujitsu’s Challenges for WiMAX System-on-a-Chip Solutions for Mobile WiMAX are shown in Figure 3. uses that can be considered: satellite and cable The first model is a fixed application in television (CATV) broadcasting through WiMAX which Mobile WiMAX is used as a fixed broad- and data transmission from a user’s personal band service such as a replacement for digital media assistant. This application is very suitable subscriber line (DSL) access. Of course, there for Mobile WiMAX because it needs a very high is Fixed WiMAX for this area. However, a lot of data transmission rate. For the voice-centric carriers would like to use Mobile WiMAX instead usage, voice-over-IP (VoIP) technology is applied of Fixed WiMAX. This is because Fixed WiMAX to the Mobile WiMAX system. Although the system currently is not so popular and the 2G/3G cellular communication systems already system cost is relatively high. have a legacy voice communication function The second model is a hot zone applica- in the system, WiMAX does not. Therefore, tion. For this purpose, there are three usage this function may be necessary to cover voice categories: data-centric, rich-media-centric, and applications. voice-centric. For data-centric usage, Mobile The third model is a hot zone with cellular WiMAX is used to keep the data transmission system application. This application is a combi- rate high when a notebook personal computer nation of Mobile WiMAX and a cellular system (PC) or personal digital assistant (PDA) is used. such as 2G or 3G. This application requires a This service is almost the same as the current dual-mode mobile phone, and the uncertain feasi- HSDPA/HSUPA (high-speed downlink/uplink bility of dual-mode technology and its high cost packet access) service in the 3G system. However might be a bottleneck. Mobile WiMAX can provide a higher data trans- One idea for a new mobile communica- mission rate at a relatively low cost. For the tion service using Mobile WiMAX is shown in rich-media-centric usage, there are two main Figure 4. This idea is for a user to send and Service Circuit switched IP multimedia service Streaming service emulation service Control/management Resource control/mobility management PSTN Internet Transport/access IP core network AGW xGSN 3G/3.5G xDSL/FTTx RNC AGW AGW 3G-LTE WiFi/WiMAX HGW BTS BTS BTS BTS AP AP BTS: Base station transceiver AGW: Access gateway RNC: Radio network controller LTE: Long term evolution xGSN: Serving/gateway GPRS support node FTTx: Fiber to the home/curb/premises, etc. HGW: Home gateway Figure 2 Next-generation packet-based network configuration.