services and applications. 1. Introduction. The subject ... reconfiguration of terminals at all stages of design, production and in the field. This paper ... as is the impact of software downloading on 3G and possible future 4G standards. 2. Software ...
Software Radio and Reconfiguration Paul Bucknell Philips Research Laboratories, UK
Abstract. Dynamic Re-configuration of lower layers of the protocol stacks used in communications terminals is key to the development of future multimode software radios. Together with the use of software downloading, future terminals will become a platform to support the deployment of yet unspecified services and applications. 1. Introduction The subject of software radio emerged as a "hot topic" in mobile communications in the early 1990's, when many people saw the technology as a solution to the problems of complex RF and IF processing required in modern multi-mode/multi-band mobile terminals. Today software radio is viewed more as a technology to enable the reconfiguration of terminals at all stages of design, production and in the field. This paper introduces the concepts of software radio and reconfiguration. The potential use of these concepts to provide a terminal with reconfigurable protocol stacks is examined as is the impact of software downloading on 3G and possible future 4G standards. 2. Software Radio Software radio is best defined as the software implementation of functions inside a radio transceiver more usually implemented with analogue or digital electronic circuits, where software can be defined as a set of instructions running on a programmable processor.
ADC DAC
Digital RF And IF Processing
Radio Control
Baseband Modem Processing
Software Control
User Interface
Figure 1: The Ideal Software Radio Architecture Figure 1 shows an ideal software radio where analogue to digital conversion takes place after the antennae and all subsequent processing is carried out in software. Two antennae are shown, but more conventionally one would be used along with some method for isolating the transmitting and receiver parts of the transceiver. The disadvantage of this architecture is that all the RF spectrum is converted by the ADC (Analogue to Digital Converter) making the specifications of this device (bandwidth, dynamic range and
sampling rate) unrealisable with currently foreseen technologies. All the main functions are carried out in software including the RF and IF processing of the signals, followed by the baseband functions such as modulation and demodulation. The user interface block includes I/O (input/output) functions like audio transducers and display devices. Although the ideal software radio may currently be impracticable, it should be noted that many functions in today’s handsets and basestations are implemented as software code and not as hardware parts. These can be regarded as practical software radios. 3. Software Reconfiguration Software reconfiguration facilitates roaming, lower terminal costs, dynamic spectrum management, bug-fixing, new features, third parties involvement, extra value to network operators (their own customisations), and personalisation (customer’s own customisations). Open software architectures would allow terminals to become programmable transceivers for radio, television, home-networks, and offices i.e. fixed-mobile-broadcast integration. Upgrading software allows future-proofing and shields from ever faster cycles of innovations and obsolescence. The following list shows the key benefits from manufacturing terminals and integrated circuit platforms for terminals that can be reconfigured by downloading new software: •
• • •
Reduction in the number of different models. Reconfiguration of terminals should allow fewer terminal variants to have to be manufactured to support different technical standards. This allows the large-scale manufacture of terminals leading to lower unit costs. Last minute or deferred customisation. The use of downloading means that the final configuration of the terminal can be made even after deployment, so increasing the functionality of a product and reducing the likelihood of any product recalls, or returns. Running applications. End user applications such as games, productivity applications, etc. will be the first of the downloaded applications running on future terminals. Open Platform. If an open platform is introduced then third party developers will be able to develop innovative applications for the terminal, which should increase the appeal of the terminal to the end user.
The disadvantages of downloading software include the difficult task of managing different versions of software in the different terminals deployed in the field, also the problems of ensuring robustness in all user environments. 4. Downloading new air interfaces The ultimate software reconfiguration in terminals is seen by may people as the download of a new air interface. The increasing power and reducing cost of digital signal processing will allow the use of reconfigurable baseband processing in mobile handsets which will in turn permit the use of flexible air interfaces. This would give the consumer a terminal capable of working with any network, whilst not significantly increasing the cost of the terminal. This scenario also benefits the terminal/IC manufacturer as it allows the manufacture of one RF and baseband processor to fit all available standards and markets. One of the main advantages of such a terminal to the end user is the ability to roam between many different air interface standards. There are three key elements required to make an air interface reconfigurable terminal:
• • •
Software Radio. The use of Software Defined Radio (SDR) to implement as much of the radio processing as possible; hardware re-configuration is possible, but is generally more costly than implementation in software. Standards. The reconfiguration of a terminal to operate on a new air interface standard will require standardised protocols for the transfer, verification and testing of the downloaded software. A software architecture in the terminal which can either be completely changed on the fly, or is built in such a way that key parts of the protocol software can be easily changed without this having a great impact on the cost of the terminal.
Terminals that offer third generation capabilities using SDR will be available commercially in about 3 years. The key benefit to the terminal manufacturer is that the SDR technology will allow one hardware and software architectural platform to be used to address almost all world markets. An estimate of the size of the market for SDR terminals has been made by the SDR forum [1] as about 9.5 million handheld devices in 2000/1 timeframe rising to about 130 million in 2005. A possible software architecture for a 3G terminal, built using SDR, that can accept downloaded lower layer software is shown in Figure 2. This architecture shows that drivers could be used to provide an interface between lower layers of the protocol stack and the hardware used for the un-configurable physical layer functions. The layers of this stack could be implemented on a virtual machine. Decreasing Programmability Possible
Examples
Software Applications
User application
API Support
Re-configurable Radio Protocol stack
Signal processing modules Real-time modules
Drivers Analogue to digital conversion Hardware
Figure 2: Software Architecture 5. Future Standards The technology of mobile communications continues to evolve to provide more bandwidth and many different services for mobile users. One possible evolution path for GSM mobile networks is shown in Figure 3, which shows how GSM, which started out as primarily a voice service evolves into a 3G (UMTS) standard capable of offering the user many service possibilities with higher bandwidths. The evolution of GSM occurs by the use of extensions to the GSM standard; HSCSD (High Speed Circuit Switched Data) and GPRS (General Packet Radio Service), which both provide higher dates rates and in the case of GPRS, a packet data capability.
A possible evolution path for the downloading of software is also shown in Figure 3. Simple menus using the SIM Application Toolkit, (STK) are downloaded in 1999, then WAP (Wireless Application Protocol) allows more complex downloading, followed by the two MExE (Mobile Station Application Execution Environment) standards for downloading applications. MExE-1, is based on WAP and MExE-2 is based on personal Java. Finally the possibility of full dynamic ReConFiGuration (RCFG) by downloading is foreseen in 2003, new standards to allow this are being developed by 3GPP TSGT2/SWG1 (MExE). As increasing reconfiguration takes place, we will require new forms of standardisation. In the future we will move away from rigid standards towards flexibility, the challenge is to do this while still maintaining multi-vendor choices for operators. This is possible if downloading takes place in well-defined software architectures.
MExE-2
UMTS-99
MExE-1 EDGE
WAP GPRS
STK HSCSD
RCFG UMTS-00 2003
2002
2001
2000
1999
Figure 3: Downloading Staircase As currently envisaged, the role of the 3G or UMTS terminal is to provide an easy to operate mobile terminal capable of offering many different Quality of Service (QoS) data flows for applications. The use of lower layer protocol reconfiguration will increase the ability of the terminal to match the desired QoS to that required for an application. The use of reconfigurable technologies and software downloading will enable development of 4G terminals that will offer many different air interface configurations optimised for particular applications. 4G terminals can be expected to be “future proof” and multi-mode multi-service and multi-standard, because of downloadable software reconfigurability. Full software reconfigurability will also allow new base stations and the network infrastructure to be developed that can dynamically adapt to different traffic conditions, and maximise the efficiency of the limited resources (spectrum and bandwidth) available to an operator. 6. Conclusions In the future, terminals will become "future proof" (within the limitations of the terminal's hardware) by having the capability to download new air interfaces, and operate on new communications standards, using lower layer reconfiguration technology implemented with software radio technology. References [1] The SDR Forum (formally MMITS), see http://www.sdrforum.com for more details
