Performance of the 7T/4-DQPSK, OMSK, and QAM Modulation Schemes in Mobile Radio with Multipath Fading and Nonlinearities

As mobile communications have become so indispensable, every possible effort should be spent to achieve the optimum operating conditions. In addition to the normal impairments associated with wireless communications, in general, the mobile channel suffers from particular limitations that confine the performance of a mobile radio system. Among those impairments are the bandwidth limitation, interference, and multipath fading. With the strong motivation toward portable radio and personal communication systems, power limitation has manifest itself in the picture, and, consequently, nonlinear operation of the amplifiers involved (hence, the channel) will have to be dealt with. Constant envelope modulation schemes have been used in digital mobile radio systems recently installed. The Gaussian minimum shift keying (GMSK) is employed in the global system for mobile (GSM) communications installed in Europe, while in the North American IS-54 system, the used modulation scheme is the 7T/4-DQPSK. As the quest for higher data rates has kept on increasing, multilevel modulation schemes have been proposed with their performance over nonlinear channels having been overlooked. The intent of this paper is to provide a comparative study, based on simulation, and test the performance of various modulation schemes operating over a wide variety of mobile radio channel conditions described above. The effective throughput of all systems is also considered.