CHARACTERISTICS OF ORTHOGONAL SLOW FREQUENCY-HOPPING 16-QUADRATURE AMPLITUDE-MODULATION SYSTEM WITH AN INTERFERENCE IMMUNITY DECODING METHOD FOR DIGITAL LAND MOBILE COMMUNICATIONS

This characteristics of a slow frequency-hopping system using 16-ary q uadrature amplitude modulation (SFH/16-QAM) to provide superior spectr al efficiency and high-quality transmissions in digital land mobile co mmunications is investigated. In this method, highly efficient transmi ssions are realized with 16-QAM through fading distortion compensation based on the injection of pilot symbols; but, since 16-QAM alone prov ides insufficient immunity to interference, several strategies are req uired for applications to cellular systems. Here, a new interference i mmune decoding method is proposed that is based on an improvement in e rror-correction methods. In the orthogonal SFH, since mutually differe nt hopping patterns are used for each cell, the interference waveforms from other cells are randomized with respect to the desired waveform. By using this property, the level of the interference superimposed on the desired waveform is detected and estimated from the gaps of inser ted periodic slots, and the interference immunity of 16-QAM with minim um weighted Euclidean distance decoding is improved. Computer simulati ons of frequency selective fading shows that the proposed method has s trengths relative to the near-far problem and is especially effective for utilization in the cellular system uplink. The introduction of voi ce activated control is shown to be effective in the downlink. Also, a s a result of the frequency diversity realized through SFH, performanc e degradations due to slow fading are slight.