A. Bateman

The combined analogue locked loop universal modulator (CALLUM)

The CALLUM modulator is proposed. By embodying the LINC component separation concept within a closed-loop feedback structure, it permits the realization of a highly efficient linear transmitter using practical components and requiring minimal calibration. The CALLUM modulator is unique in that it achieves frequency translation and component separation simultaneously using a pair of voltage controlled oscillators within the feedback loop. Several prototype linear transmitters have been built using this approach which have demonstrated the robustness of the technique.<<ETX>>

A LINC transmitter

The LINC (linear amplification using nonlinear components) transmitter shows considerable potential for use in future mobile radio systems employing spectrally efficient linear modulation formats. An experimental LINC transmitter that utilizes modern digital signal processing techniques to perform accurately the necessary signal component separation within the transmitter is described. A technique for significantly reducing the bandwidth required for this digital signal processing is outlined, and practical results which demonstrate that the linearity of the transmitter compares favorably with established linearizing techniques such as Cartesian feedback are presented.<<ETX>>

An evaluation of direct sequence CDMA for future mobile communication networks

The performance and some of the implementation aspects of a practical mobile radio communications network employing direct-sequence code-division multiple access (DS-CDMA) are examined. The use of spread-spectrum techniques results in a wideband system, thus permitting the potential exploitation of multipath signal energy and permitting a means of reducing interference arising from other users of the spectrum. An analytical performance model is developed in order to assess the spectral efficiency of a DS-CDMA communications network. The computer model permits the performance evaluation of various path diversity schemes alongside numerous digital-modulation and error-correction coding techniques while operating in a mobile radio channel. In order to substantiate the results presented, novel power control and handoff protocols are also proposed in light of the assumptions made.<<ETX>>

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>>

Decision feedback channel estimation-a precursor for adaptive data transmission management

Two concepts are introduced: first, the notion of adaptive data transmission management to optimize modulation format and coding to channel conditions and, second, as a consequence of this strategy, the proposal of a reverse modulation channel sounding technique for elimination of the irreducible error rate floor, which otherwise limits modem performance under good signal conditions. The adaptive data transmission concept can potentially increase transmission throughput on a practical data network considerably, provided that a suitable protocol can be established for handling the adaptation process. Reverse modulation, a means for obtaining channel fading information from a data signal without recourse to a separate reference transmission, is shown to be highly effective for a specific DPSK (differential phase shift keying) example. Its performance is slightly inferior to that of a reference-based approach but with greatly reduced transmitter complexity and without the requirement for reference location, which is a nonnegligible overhead in reference tone or reference symbol insertion techniques.<<ETX>>

Voice scrambling for radio, cellular and telephone systems

An overview of the requirements of a scrambler for use with mobile radio equipment is presented. Details of the implementation of a scrambler are given satisfying these requirements. The scrambler is realized using general-purpose DSP technology giving the benefits of low-cost, high-volume production with the flexibility of customization and enhancement though software configuration.<<ETX>>

Transmission strategies for integrated multichannel packet radio networks

The design of robust random access communication protocols and packet multiplexing schemes that can withstand the dynamics of the mobile radio channel and utilize traffic distribution statistics is essential for the provision of service integration and the high transmission efficiency required of the coming generation of packet radio networks. It is shown that appropriate flow control mechanisms can appreciably improve packet traffic performance. In addition, an integrated system allows for effective adaptation to the variations in voice and data traffic load that occur in practice.<<ETX>>

Theoretical performance comparison between reference-based coherent BPSK and BCH coded differential BPSK

Both channel sounding and channel coding are well-known techniques for improving bit error rate (BER) performance of data transmission over a narrowband mobile radio channel. The two techniques share a common ground with regard to the fact that both of them use redundancy signals, (reference signals for channel sounding and parity check bits for channel coding) to achieve the improved performance. A comparison of theoretical phase-shift keying, (PSK) performance in terms of BER is made between the reference-based coherent binary phase shift keying detection and the BCH coded differential detection under different fading conditions. Comparisons are also made between reference-based coherent detection and BCH coded decision-feedback differential phase shift keying (DPSK).<<ETX>>

Practical results for a generic modem using linear mobile radio channels

To date, the majority of work on reference-based sounding techniques, whether targeted towards reference tone insertion or reference symbol insertion, has been based on simulations. In the present work, however, measured performance data are presented for one of the techniques-a reference tone based 16-QAM (quadrature amplitude modulation) system. It is shown that the claims made based on simulation results are indeed borne out in practice, with the reference approach overcoming the irreducible error rate phenomenon in fading and permitting coherent detection and simple symbol timing for complex multilevel modulation systems. A reference-based 16-QAM system is shown to have approximately 2-dB-2.5-dB implementation loss over the theoretically optimum 16-QAM performance, based on real hardware implementation, which, viewed in conjunction with the low complexity of implementation. presents a realistic and viable solution to, high-rate data transmission in a hostile mobile environment.<<ETX>>