Abstract: Exact expressions for bit-error probability (BEP) for
coherent square detection of uncoded and coded M-ary quadrature
amplitude modulation (MQAM) using an array of antennas with
maximal ratio combining (MRC) in a flat fading channel interference
limited system in a Nakagami-m fading environment is derived. The
analysis assumes an arbitrary number of independent and identically
distributed Nakagami interferers. The results for coded MQAM are
computed numerically for the case of (24,12) extended Golay code
and compared with uncoded MQAM by plotting error probabilities
versus average signal-to-interference ratio (SIR) for various values of
order of diversity N, number of distinct symbols M, in order to
examine the effect of cochannel interferers on the performance of the
digital communication system. The diversity gains and net gains are
also presented in tabular form in order to examine the performance of
digital communication system in the presence of interferers, as the
order of diversity increases. The analytical results presented in this
paper are expected to provide useful information needed for design
and analysis of digital communication systems with space diversity
in wireless fading channels.
Abstract: High-frequency (HF) communications have been used by military organizations for more than 90 years. The opportunity of very long range communications without the need for advanced equipment makes HF a convenient and inexpensive alternative of satellite communications. Besides the advantages, voice and data transmission over HF is a challenging task, because the HF channel generally suffers from Doppler shift and spread, multi-path, cochannel interference, and many other sources of noise. In constructing an HF data modem, all these effects must be taken into account. STANAG 4539 is a NATO standard for high-speed data transmission over HF. It allows data rates up to 12800 bps over an HF channel of 3 kHz. In this work, an efficient implementation of STANAG 4539 on a single Texas Instruments- TMS320C6747 DSP chip is described. The state-of-the-art algorithms used in the receiver and the efficiency of the implementation enables real-time high-speed data / digitized voice transmission over poor HF channels.