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In this paper we analyze the performance of Trellis Coded Modulation (TCM) for high capacity digital radio. Some error correcting code is needed to comply with the low background bit error rates prescribed for this application, despite practical imperfections unavoidable in modems and nonlinear distortion of high power amplifiers. The redundancy that can be accepted is very limited, however, due to the strict bandwidth constraints. TCM schemes are very effective in conserving bandwidth. Therefore, they look very promising for digital radio applications. We analyze many aspects of TCM, including multidimensional schemes. We consider the performance of TCM in the AWGN channel and in multipath fading channels, and we evaluate the effect of nonlinear amplification. Finally, we consider decoder complexity. Significant coding gains can be obtained from codes of acceptable complexity. A good compromise between performance and complexity turn out to be 8‐state codes. The complete Viterbi decoder for these codes can be fully integrated on just one chip. As a typical application, a system transporting the first level of the Synchronous Digital Hierarchy (STM ‐ 1; 155.52 Mbit/s) operating on 30 MHz interleaved crosspolarized frequency arrangements is analyzed in detail.

An experimental 800 Mbit/s trans-receiver for circular waveguide application has been designed and realized at GTE-Telecomunicazioni Transmission Laboratory as a part of an Italian research program on high capacity mm-wave communication systems. The whole program [1] [2]is sponsored by the Italian Post and Telecommunication Office (ISPT).The equipment consists of a 41 GHz four-phase transmitter operating at 800 Mbit/s and of a corresponding receiver featuring coherent demodulation at 3.6 GHz IF frequency and regeneration of the received digital signal. The equipment is described in some detail and the measured system performances are also given and briefly discussed. SYSTEM DESCRIPTION. Both the plug-in type units assembled Fig.'1 -External view of the equipment.transmitter and the receiver are realized with in two separate self powered slir-type racks 120 mm wide, 220 mm deep and 1700 mm high as shown by fig.1 (from left to right: transmitter,receiver and a 2nd transmitter for adjacent channel interference tests).The RF sections are located in the upper part of the racks, the IF mo-demodulation sections in the center, while the digital signal processing units as well as the power supply units are placed in the lower part.The mo-demodulation process is performed at the IF frequency of 3.6 GHz and up -and downconverters are, employed to reach the RF operating frequency of 41 GHz.The RF frequency has been chosen in the lower end of the waveguide frequency band for two major reasons: a) because these frequencies will be the first to be used in an operational system and b) because the group-delay equalization problems are much more severe close to the waveguide cut-off frequency.The 3.6 GHz frequency has been selected with the purpose of reducing the fractional bandwidth of all IF processing circuits, while maintaining a good control of their electrical performances.In addition,bit rates moderately higher than 800 Mbit/s could easily be adopted in the future using such an IF frequency.(o) Authors are with GTE-Telecomunicazioni SpA, Milano, Italy. 629