No abstract

We provide a comprehensive performance comparison of soft-output and hard-output demodulators in the context of non-iterative multiple-input multiple-output bit-interleaved coded modulation (MIMO-BICM). Coded bit error rate (BER), widely used in literature for demodulator comparison, has the drawback of depending strongly on the error correcting code being used. This motivates us to propose the mutual information of the equivalent modulation channel (comprising modulator, wireless channel, and demodulator) as a code-independent performance measure. We present extensive numerical results for spatially independent identically distributed (i.i.d.) ergodic and quasi-static fading channels under perfect and imperfect channel state information. These results reveal that the performance ranking of MIMO demodulators is rate-dependent and provide new insights regarding MIMO-BICM system design, i.e., the choice of antenna configuration, symbol constellation, and demodulator for a given target rate.Index Terms-Bit-interleaved coded modulation (BICM), loglikelihood ratio, multiple-input-multiple-output (MIMO), mutual information, performance limits, soft demodulation.

Due to its flexibility, cost-efficiency, and the ability to support mobility, wireless connectivity is seen today as a key enabler for a wide range of applications beyond classical mobile communications. A significant part of these applications depends on the capability of the wireless communication system to provide reliable connectivity. However, due to the randomness of the wireless propagation channel, reliability is still a critical issue in these systems. Some applications, such as vehicular and industrial applications, demand a level of reliability that wireless communication systems typically are not able to guarantee. This paper provides a framework that enables these applications to make use of wireless connectivity only if the transmission conditions are favorable enough. The concept is based on the idea that -despite the fact that it is practically impossible to ensure error-free wireless communication -it is feasible to derive boundary conditions for the transmission success. To this end, the paper introduces a novel metric for UltraReliable Communication (URC) referred to as "Availability", that determines the expected presence or absence of link reliability at the time of transmission. The availability is signaled by means of an Availability Indicator (AI) to the applications. Moreover, we develop the system model for computing the AI and illustrate the potential benefits of the new reliability metric by means of a possible implementation for automotive scenarios.