Digital multicarrier‐transmission of audio signals over mobile radio channels

Abstract

This paper presents a systematic overview over different concepts of multicarrier‐trans‐mission under the specific aspect of mobile radio transmission. It will be shown that under realistic multipath channel conditions the postulation of ideal bandwidth efficiency has to be given up. As a consequence sub‐optimum multicarrier concepts are regarded and mutually compared under the aspects of intersymbol interference and adjacent channel interference. A specific impuls shaping concept based on time and frequency concentrated impulses (Gaussian shaping) turns out as an appropriate solution since hereby the adjacent channel interference can be largely suppressed at the expense of a small increase in intersymbol inference. The performance of the different multicarrier concepts is illustrated by various simulation results under mobile radio channel conditions.

Asynchronous multicarrier multiple access: Optimal and sub-optimal detection and decoding

“…That is, some degree of ISI and ICI is always present. In this respect, the Gaussian filters turn out to be an interesting choice that allows controlling the interference components [22,35,42].…”

“…In turn, the state transition probability is obtained as the product of the conditional channel pdf with the a priori transition probability between state and S m . In general, the transition metric (22) can be used in the BCJR algorithm [5,18] to calculate the a posteriori probability of the data symbols, the a posteriori probability of the data bits, and the a posteriori probability of a data/bit sequence (see following sections). A block diagram of the baseband processing is depicted in Figure 5.…”

“…The factorization in (23) implies that the evolution of the state defined in (21) observed at the subchannel matched filter outputs can be represented with a Markov chain with transition probabilities defined in (22). It is interesting to note that, when we move on the underlying trellis structure by one step, we increase either the user index, or the subcarrier index, or the time index.…”

Synchronisationsprobleme in digitalen Multiträgersystemen

“…Zur praktischen Mobilfunkübertragung ist also stets ein günstiger Kompromiß zwischen Frequenz-und Zeitselektivität zu wählen [5]. Am Sender wird die zu übertragende Bitfolge zunächst in N Folgen von m-bit-Gruppen zerlegt und in anschließenden Codierern in die komplexen Symbole d,(i) der gewünschten Modulationsform umgesetzt (v = 0,..., N-l; i Zeitindex der Daten).…”