Third Generation Wireless Communication Systems
Design and development of future generation wireless systems is one of the most active and important areas of research and development in wireless communications. Third-generation (3G) wireless systems promise significantly higher data rates (up to 2 Mbits/sec) and a new array of mobile communication services, such as video teleconferencing and web browsing. Full interoperability (global roaming) of 3G mobile systems is now a possibility as a result of the international IMT-2000 standardization effort. In November of 1999, a comprehensive set of radio interface specifications for IMT-2000 was approved. The five required interfaces enabling interoperability are IMT-DS (Direct Spread), IMT-MC (Multi-Carrier), IMT-TC (Time Code), IMT-SC (Single Carrier), and IMT-FT (Frequency Time). 3G field trials are currently underway with plans to begin commercial operation in 2001.
NIST has been involved in 3G systems since 1998. At that time, there were 16 radio technology proposals for IMT-2000. NIST WCTG selected two of the more promising proposals to follow, and began analysis and modeling. Those two proposals, UTRA (W-CDMA) and cdma2000, were selected in Nov. 1999 to make up three of the five IMT-2000 radio interfaces. NIST's role in this work is not going to be limited to 3G wireless systems. It will be an ongoing effort for next generations of wireless technology.
Mike Miller: e-mail: email@example.com; Telephone: (301) 975-3996
Hamid Gharavi: e-mail firstname.lastname@example.org; Telephone: (301) 975-3634
Rosemary Wyatt-Millington: e-mail: email@example.com
Cadence Design Systems, Inc.
NIST and Cadence Design Systems, Inc. have jointly developed simulation models for the cdma2000 system based on Cadence's SPW communication system design/simulation tool. An extension of the IS-95 standard for cellular phone systems based on mostly Qualcomm's technology, cdma2000 is one of the major systems proposed to the International Telecommunication Union (ITU) for the IMT-2000 standard for third-generation wireless systems.
SPW is an object-oriented language for software development and testing of communication systems. SPW includes models for many basic building blocks in a communication system. The joint work by NIST and Cadence combines and extends these building blocks to yield models for the cdma2000 system, based on the proposed standard specifications. These models will allow communication engineers to measure the performance of the physical layer of cdma2000 systems over a range of communication channel conditions, e.g., whether the cellular phone user is mobile or stationary, the type of environment the user is in (urban/ suburban/countryside), and how much interference the user is getting from other cellular users. This makes it possible to characterize the performance of a cdma2000 system prior to hardware prototyping and expensive field tests.
The following cdma2000 models are currently available:
Tommi Makelainen, Nokia Research Center
Maarit Melvasalo, VTT
Two former guest researchers at NIST, Maarit Melvasalo, from VTT, Finland, and Tommi Makelainen from Nokia Research Center, Finland, built a simulation of the 3GPP FDD proposal for 3G wireless. The simulation can run on Simulink or as a stand alone C-coded program. It includes the channel encoding, interleaving, rate matching, modulation, spreading(channelization), a channel model, a RAKE receiver, and the corresponding decoding functions. Both the downlink and uplink have been modelled.
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Dual-Priority W-CDMA Transmission System for Video
Hamid Gharavi: email: firstname.lastname@example.org; Telephone: (301) 975-3634
Siavash Alamouti, Cadence Design Systems, Inc.
The wireless telecommunications industry is now planning the deployment of a third-generation of mobile systems in anticipation of growing demands for voice and multimedia services. In particular, visually based services such as video conferencing, medical emergency consultation, wireless web access, and remote site surveys might dominate future services offered to subscribers in future third-generation mobile systems. Unfortunately, existing video compression standards, developed for relatively benign, nearly error-free environments, cannot be directly applied in the more hostile communication environments experienced by mobile systems. As part of the evaluation of the CDMA-based 3G systems, NIST has been working to assist industry to enable efficient use of radio bandwidth to support audio-visual services. The work has been based on the performance testing and evaluation of the W-CDMA for transmission of ITU-T H.263 compressed video bitstream. In collaboration with Cadence Design Systems, a compatible dual-priority transmission system has been developed. The end-to-end transmission system consists of a robust video partitioning scheme and a flexible 3G W-CDMA model. A demo system has been developed and implemented in the SPW model, which provides a subjective assessment of the transmitted video over IMT-2000 channels. The enclosed images represent two video frames: without dual-priority W-CDMA transmission system (on the left), and with dual-priority W-CDMA transmission system (on the right).
For further information, please refer to:
H. Gharavi and S. M. Alamouti, "Multipriority Video Transmission for Third-Generation Wireless Communication Systems," Proceedings of the IEEE, vol. 87, pp. 1751-1763, October 1999.
Performance Analysis and Dynamic Resource Allocation in Multi-Service DS-CDMA Networks
Vadimir Marbukh: email: email@example.com; Telephone: (301) 975-2235
The main force driving evolution of wired networking technology is the need to handle multimedia traffic with widely varying statistical characteristics and with specific requirements for Quality of Service (QoS). While this trend will continue, future network infrastructures will be a mixture of both wired and wireless networks. In fact, wireless access to the Internet will probably become much more common than wired access. To prevent waste of resources in the wired backbone, the wireless access network must have the same or comparable capabilities to handle multimedia traffic. Today, wireless technology lags far behind wired technology in its ability to serve multimedia traffic. The effectiveness of wireless technology is restricted by wireless channel impairments and by severe limitations on wireless bandwidth and on transmission power by mobiles. To overcome these restrictions, system designers have a finite but complex set of techniques to employ. Such techniques include error-correction and error-detection coding, source coding, medium access protocols, smart antennas, power control algorithms, and retransmissions.
Recently, Direct-Sequence Code Division Multiple Access (DS-CDMA) has emerged as a technology for 3G wireless communication systems. DS-CDMA allocates the wireless bandwidth on demand: all users share the same wireless bandwidth and simultaneous transmissions affect each other through an increase in the random noise. However, in DS-CDMA a user bit-service rate is a complex non-linear function of various intrinsic parameters, such as transmission power and processing gain, as well as various extrinsic parameters, such as interference from other users and conditions on the wireless channel. To provide guaranteed QoS for multimedia traffic DS-CDMA requires fast, closed-loop control of system parameters based on real-time information about the intrinsic and extrinsic parameters, and about the performance of the system. For a closed-loop system to operate successfully, accurate and timely measures of appropriate parameters must be fed into the control algorithm. Our work includes identifying the system parameters, besides transmission power, having the greatest effect on the provision and maintenance of the QoS for multimedia traffic, developing control algorithms based on the parameters identified, and comparison of the performance of the proposed algorithms against the theoretical limits.
This work is supported by NIST ATP.
V. Marbukh, "On Ability of a Communication Channel to accommodate Multimedia Traffic," Proc. Globecom, Rio de Janeiro, Brazil, 1999.
V. Marbukh and N. Moayeri, "A Framework for Throughput and Stability Analysis of a DS-CDMA Network," Proc. IEEE VTC, Houston, US, 1999.
V. Marbukh and N. Moayeri, "A Queueing Model of a Spread Spectrum Multiple Access," Proc. 4th ACTS Mobile Communications Summit, Sorrento, Italy, 1999.