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- 4.8 Signalling, control and broadcast methods
- 4.9 Burst structures
- 4.10 Frame structures
- 4.11 Media access control
- 5 Conclusions
- 6 References
- 1 Introduction
4.7 Modulation methodsIn the design of an air interface that uses smart antennas the modulation methods should be selected to maximize the system throughput when network level interference and the capability of the smart antennas to reject that interference is considered. This design may lead to a variable rate modulation structure that operates efficiently over a range of C/I operating points. 4.8 Signalling, control and broadcast methodsOne point that is often discussed is how smart antennas can handle broadcast channels that are common in many existing air interfaces. This is a prime instance where by designing the air interface with adaptive antennas in mind, the broadcast structures can be designed so that they work well within the a multiple-antenna structure. Certainly, the air interface may contain broadcast information, but careful design of that structure must be done or many of the adaptive antenna benefits in terms of base station costs may not be fully realized. The same applies for “blind” channels such as paging where the information is directed to a single user (as opposed to broadcast information), but where the location of that user is not known. 4.9 Burst structuresThe use of adaptive antennas will also impact the design of burst structures. The structures of the burst may include “training” data to help the adaptive antenna processing. A balance between the spectral efficiency benefits and overhead of that data has to be considered to create optimal throughput. 4.10 Frame structuresIf adaptive antennas are not considered, the major consideration on frame structure is latency and resource sharing. Considering adaptive antennas in the design, one may wish to consider the rate of which the spatial information gets updated. This can impact the spectral efficiency as mobility of the user increases. In general the more rapid the updates to the spatial information the better the spectral efficiency as mobility increases. This tends to lead to frames with shorter durations, typically below 10 ms. 4.11 Media access controlThe use of adaptive antennas can have broad implications on the entire protocol chain. This includes elements of the protocol that are traditionally thought to be design-independent of the RF system. One such area is media access, where it has become increasingly important for air interfaces to support random access packet switched data, as well as guaranteed quality of service, for which acceptable latencies are on the orders of tens of ms. The addition of adaptive antenna technology into the system allows for spatial collision resolution in the MAC, reducing access contention and improving performance over that achievable with traditional non-adaptive antenna systems. 5 ConclusionsIntegrating adaptive antenna systems into the design of future IMT 2000 systems and systems beyond IMT 2000, will significantly improve the spectral efficiency of these new radio systems. Spectral efficiency gains from adaptive antenna systems can be used not only to reduce the number of base stations (cells) needed to deploy an IMT 2000 network, but also to obtain significantly increased data rates within a limited amount of spectrum. 6 References[1] S. Haykin. “Adaptive filter theory”. Prentice Hall. 1991 and 1996. [2] Compton. “Adaptive antennas: Concepts and performance”. Prentice Hall 1988. [3] S. Haykin. “Advances in array processing”. Prentice Hall. 1991. [4] B. Widrow, S.D. Stearus. “Adaptive signal processing”. Prentice Hall. 1985. [5] Mozingo, Miller. “Introduction to adaptive arrays”. Wiley Interscience. 1980. [6] Hudson. “Adaptive arrays principles”. Peter Peregrinus. 1981. [7] S. Haykin, Editor. “Advances in spectrum analysis and array processing”. Vol. II Prentice Hall. 1991. [8] Farina. “Antenna based signal processing techniques for radar systems”. Artech House, Boston 1991. [9] J.C. Liberti, T.S. Rappaport, “Smart Antennas for Wireless Communications: IS-95 and Third Generation CDMA Applications”, Prentice Hall Communications Engineering and Emerging Technologies, 1999. [10] T.S. Rappaport, “Smart Antennas: adaptive arrays, algorithms and wireless position location”, Selected Readings IEEE. [11] J. Litva. “Digital Beam forming in Wireless Communications”, Artech House, 1996. [12] J Laiho et al, “Radio Network Planning and Optimisation for UMTS”, Wiley, 2002. [13] T.S. Rappaport: “Wireless communications”, Wiley, 1996. [14] K Kim et al., “Handbook of CDMA System Design, Engineering and Optimization, Prentice Hall, 2000. [15] ETSI TR 125 942 V4.0.0 (2001-09), Technical Report, “Universal Mobile Telecommunications Systems (UMTS); RF System Scenarios”.
Multiple-input multiple-output techniques 1 IntroductionMIMO techniques utilize multi element antennas at both ends of the link with signal processing algorithms which make positive use of the multipath propagation channels found in terrestrial mobile communications. For propagation within a typical urban environment this has been shown to increase the capacity of the link over that available through conventional beam forming techniques. With the wide range of possible antenna configurations that can be considered it is usual in the literature and standardization bodies to categorize the various multi antenna schemes by two indices, the number of transmit antennas used and the number of receive antennas used. Thus an antenna combination for a link is described as type [MTransmit, NReceive] or more simply a type [M,N] scheme. Current 2G systems have terminals with one antenna and therefore typically use: [1,2] – e.g. receive diversity using maximal ratio combining in the uplink [2,1] – e.g. transmit diversity in the downlink In addition, for some IMT 2000 3G systems, the following are being defined: [1,4] – additional receive diversity in the uplink [4,1] – transmit diversity in the downlink based on adaptive feedback from the mobile terminal The classical active beam forming systems are generally of the form: [N,1] – downlink [1,N] – uplink
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