Department Publications

A new modulation technique, π/4-Controlled Transition PSK (π/4-CTPSK), suitable for non-linearly amplified digital mobile satellite communications systems is introduced. This technique is derived from π/4-QPSK, the modulation scheme adopted as the new U.S. and Japanese digital cellular standard. The π/4-CTPSK modulated carrier is shown to undergo significantly less spectral regeneration after non-linear amplification compared to π/4-QPSK, leading to more efficiant utilization of the available power and spectrum. A principal application of π/4-CTPSK is for systems which may require differential or discriminator detection, such an low bit-rate satellite and land mobile radio communications.

An adaptive Viterbi algorithm, derived from a dynamic estimate of the fading channel, is used for the decoding of a convolutionally coded 16 QAM system in a mobile environment. The new technique achieves a BER (bit error rate) performance improvement of 8 dB at P/sub e/=10/sup -3/ in a fast flat Rayleigh fading environment compared to an uncoded system with pilot symbol aided compensation. The BER performance of the new technique in a cochannel interference (CCI) controlled environment is also presented. Results indicate that the 16 QAM scheme achieves significant improvements in spectral and power efficiency when compared to the emerging US standard, which will use pi /4-DQPSK for digital cellular systems.<>

The performance of Miller coded pilot aided modulation systems is studied by computer-aided design techniques. It is shown that the use of this nonredundant code may improve the bit error rate (BER) performance of pilot aided modulation schemes over similar uncoded coherent and noncoherent systems. Miller coded random data have a spectral density about 12 dB lower than uncoded data at and around the unmodulated carrier frequency. The use of this code reduces the interference between the data spectrum and the pilot tone, and hence improves the BER performance. This improvement is significant, particularly in low bit-rate systems where a relatively wide bandpass filter is required for pilot extraction and successful compensation for fading and Doppler shift caused phase variations. This improved BER performance is obtained with no redundancy, but at the cost of some spectral efficiency.<>

The Cellular Intercom enables users to make voice calls among themselves within a local area, using Bluetooth enabled mobile phones. It is an enterprise solution which enables people to use their mobile phones as a wireless intercom or PABX within their office premises. Conventional PABX or intercom systems provide terminals to the office desks of employees. If a person is not at his/her desk, he/she is unreachable. The Cellular Intercom is an attractive alternative for such environments, providing flexibility, ease of use and mobility within the office premises.