Sc Swales

The performance enhancement of multibeam adaptive base-station antennas for cellular land mobile radio systems

The problem of meeting the proliferating demands for mobile telephony within the confinement of the limited radio spectrum allocated to these services is addressed. A multiple-beam adaptive base-station antenna is proposed as a major system component in an attempt to solve this problem. The approach is demonstrated by employing an antenna array capable of resolving the angular distribution of the mobile users as seen at the base-station site, and then using this information to direct beams toward either lone mobiles, or groupings of mobiles, for both transmit and receive modes of operation. The energy associated with each mobile is thus confined within the addressed volume, greatly reducing the amount of cochannel interference experienced from and by neighboring cochannel cells. To ascertain the benefits of such an antenna, the conventional and proposed antenna systems are modeled in a typical mobile radio environment. For a given performance criterion, the theoretical results indicate that a significant increase in the spectral efficiency, or capacity, of the network is obtainable with the proposed antenna. >

Multi-beam adaptive base-station antennas for cellular land mobile radio systems

The authors address the problem of meeting the proliferating demands for mobile telephony within the confinements of the limited radio spectrum allocated to these services. A multiple-beam adaptive base-station antenna is proposed as a major system component in an attempt to solve this problem. The approach is demonstrated by employing an antenna array to resolve the angular distribution of the mobile users as seen at the base-station site, and then using this information to direct beams towards the mobiles in both transmit and receive modes. The energy associated with each mobile is thus confined within the addressed volume, greatly reducing the number of co-channel cells. For a given performance criterion, this results in an increase in the spectral efficiency or capacity of the network. The concept is demonstrated using results generated by a computer simulation of a simplified mobile scenario. The realization of a fully adaptive base-station antenna test rig is discussed.<<ETX>>

A comparison of CDMA techniques for third generation mobile radio systems

A comparison is made between both direct sequence (DS) and frequency hopping (FH) spreading techniques in code division multiple access (CDMA) based upon the stringent requirements of proposed third generation mobile radio systems in Europe. Given the many criteria against which this comparison is made, the outcome is slightly in favour of DS-CDMA.

Performance enhancement of DS-CDMA microcellular networks with adaptive antennas

This paper considers the performance of a DS-CDMA system which employs adaptive antenna technology at the base station site of a microcell. By utilising the capability of ray-tracing to provide the complex channel impulse response, a new ray-based simulation methodology for an adaptive antenna in a DS-CDMA system is presented. Results for a typical microcellular environment highlight the behaviour of the adaptive antenna. Finally, with the help of a Monte-Carlo type DS-CDMA capacity analysis, the potential performance enhancement and the sensitivity of the system upon the misspointing of the main beam, are evaluated.

On the sensitivity of the capacity enhancement of a TDMA system with adaptive multibeam antennas

The paper presents results for the likely capacity improvement when an adaptive multibeam antenna is used in conjunction with air interface parameters akin to the DCS1800 system. The analysis investigates the possible capacity enhancement whilst taking into account parameters such as power control, number of available handover channels, radiation pattern, radio channel characteristics and different frequency reuse patterns. The results show that a substantial capacity improvement can be achieved with adaptive antennas and also underline the sensitivity of the capacity upon several operational parameters. Finally, based on observations made from the simulation results, a more efficient architecture which fully supports onward beamforming on the handover process, is proposed.

Performance enhancement of DS-CDMA PCS cellular networks with smart antennas

This paper considers the performance of a DS-CDMA system which employs adaptive antenna technology at the basestation site. By utilising the capability of ray-tracing to provide the complex channel impulse response, a new ray-based simulation methodology for an adaptive antenna in a DS-CDMA system is presented. Results for a typical microcellular environment highlight the behaviour of the adaptive antenna. Finally, with the help of a DS-CDMA capacity analysis, the potential spectrum efficiency enhancement is evaluated.

Adaptive Antennas for Microcellular and Mixed Cell Environments withDS-CDMA

Adaptive antenna technology is now regarded as one of the key system components in future generation cellular networks. This paper considers the performance of a DS-CDMA system which employs adaptive antennas at the base station sites of both microcell and mixed micro/umbrella cell operational environments. A microcellular ray tracing propagation tool has been employed in order to ascertain site specific propagation data. Results for a typical small cell environment highlight both the propagation characteristics and the behaviour of the adaptive antenna, as well as the sensitivity of the system upon parameters such as the mutual coupling effect. This work does not assume idealised propagation conditions or antenna radiation patterns for the small cell analysis.In summary, the results indicate that microcellular base stations employing adaptive antenna signal processing can offer a significant capacity enhancement and improved channel characteristics when compared with their omnidirectional counterparts. In addition, it is shown that umbrella cells overlaying microcells within the same RF bandwidth allocation, do not impact upon system capacity providing that adaptive antenna technology is employed at the umbrella cell site.

Frequency hopped CDMA for third generation mobile radio systems

Third generation mobile radio systems will provide unified mobile access to a wide range of services for the mass user market. Code division multiple access (CDMA) is one of the most viable access techniques to provide the flexible air interface required. Frequency hopped (FH) CDMA is investigated, and a system architecture is proposed to rival the more widely researched direct sequence (DS) approach. The results presented concur with other recent work in finding that the claimed advantages of DS can also apply to frequency hopping.

A diversity combining antenna array for land mobile satellite communications

A unified approach to adaptive antenna array design and transceiver signal processing architectures is proposed for the user segment of the land mobile satellite communication service. This technique is described in its conceptual form, and compared with steered antenna array configurations currently favored for this class communication system. The proposed system uses established diversity combining techniques previously developed for mobile terrestrial radio. It is suggested that a diversity-based receiver architecture would allow the coherent recombination of the multipath signal energy present at the mobile terminal site, and thereby enhance system performance for a given link budget. The cophasing of the multipath signals can be implemented using a FFSR (feedforward signal regeneration) signal-processing architecture, which uses the presence of a pilot-tone within the communications channel. On transmit, a retrodirective beam is formed towards the active satellite. The economic viability of such a transceiver is also considered.<<ETX>>

Downlink Design for a Wideband DS-CDMA Demonstrator

DS-CDMA is recognised as one of the foremost mobile radio access techniques today. However, to date, there has been scant information on the system implementation and the many problems facing radio engineers. In this contribution, the design of the downlink (base to mobile) for a wideband (8.192Mchips/sec) DS-CDMA air interface is described along with practical results gained from its successful implementation in a full DS-CDMA system demonstrator developed under the U.K. DTI/EPSRC LINK programme. The aim is to provide a practical insight into CDMA and its application as a candidate for future personal communication systems. Synchronisation was one of the major challenges with the downlink and the techniques developed as part of this work are described fully.