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On the Design of Hierarchically Modulated BICM-ID Receivers with Low Inter-Layer Interferences
- Authors:
- Matthias Tschauner, Farhan Tasnim Oshim, Marc Adrat, Markus Antweiler, Benedikt Eschbach, and Peter Vary
- Book Title:
- Wireless Innovation Forum European Conference on Communications Technologies and Software Defined Radio (WInnComm)
- Venue:
- Erlangen, Germany
- Event Date:
- 5.-9.10.2015
- Organization:
- Wireless Innovation Forum
- Date:
- Oct. 2015
- Page:
- 10
- Language:
- English
Abstract
In this paper, we present a novel methodology to optimize hierarchically modulated Bit Interleaved Coded Modulation with Iterative Decoding (BICM-ID). As shown in our previous work [1], hierarchically modulated BICM-ID allows designing receiver with different configurations of code rate and modulation order. Even though the configurations are different, all realizations are able to decode the same transmit signal on the air, but with different fidelity. The set of configurations supports a wide range of receivers with varying processing capabilities, ranging from low for handhelds up to high for vehicular mounted radios. In the hierarchical design, the base layer carries the elementary information which will be exploited by all receivers for the fundamental reconstruction of the originally transmitted source signal. The enhancement layer carries additional error protection information which can be utilized by the receivers with high processing capabilities for e.g. coverage / range extensions. However, the first simulation results shown in [1] revealed that, if compared to non-hierarchical receivers, hierarchical receivers loose performance in terms of bit error rate because of the inter layer interferences. These result from the additional constraints in a hierarchical receiver design. To overcome / minimize these negative influences, we developed a novel algorithm to optimize the signal constellation in hierarchical modulation schemes. The novel algorithm jointly optimizes a set of critical parameters, e.g. bit error probability Pb,layer and the harmonic mean distance d2h,layer, for each layer. The harmonic mean distance d2h,layer is an important measure in BICM-ID scheme which allows predicting the theoretically achievable performance gains. Due to the contrary nature of these critical parameters, the algorithm typically converges after several iterations to a specific modulation scheme. This scheme considers all critical parameters and can be interpreted as the best possible trade-off among them. The system designer is able to tune the optimization process by a convergence weight for each critical parameter. The adverse effects of the inter layer interferences can be reduced. Finally, we used our novel algorithm to design a new modulation scheme (based on an initial 64-QAM) for a hierarchically modulated BICM-ID system. Simulation results show that the optimized modulation schemes outperform the traditional schemes [1] in terms of bit error rates for different layers and in a wide range for a given channel condition Es/N0.
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