Frank Schreckenbach

Optimization of symbol mappings for bit-interleaved coded Modulation with iterative decoding

We investigate bit-interleaved coded modulation with iterative decoding (BICM-ID) for bandwidth efficient transmission, where the bit error rate is reduced through iterations between a multilevel demapper and a simple channel decoder. In order to achieve a significant turbo-gain, the assignment strategy of the binary indices to signal points is crucial. We address the problem of finding the most suitable index assignments to arbitrary, high order signal constellations. A new method based on the binary switching algorithm is proposed that finds optimized mappings outperforming previously known ones.

Optimized symbol mappings for bit-interleaved coded modulation with iterative decoding

We investigate bit-interleaved coded modulation with iterative decoding (BICM-ID) for bandwidth efficient transmission, where the bit error rate is reduced through iterations between a multilevel demapper and a simple channel decoder. In order to achieve a significant turbo-gain, the assignment strategy of the binary indices to signal points is crucial. We address the problem of finding the most suitable index assignments to arbitrary, high order signal constellations. A new method based on the binary switching algorithm is proposed that finds optimized mappings outperforming previously known ones.

Bit-interleaved coded irregular modulation†

We consider a simple method to improve the adaptiveness and flexibility of bit-interleaved coded modulation (BICM) with different iterative decoding schemes for bandwidth efficient transmission. The basic idea is to apply different signal constellations and mappings within one code word. The combination of different signal constellations allows a fine adaptation of the data rate to the channel characteristics with the modulation, even if only the average channelstate is known at the transmitter. For a receiver performing iterative demapping and decoding (so called BICM-ID system), the mixture of different mappings enables an optimisation of the iterative decoding process according to the system requirements. We call this approach bit-interleaved coded irregular modulation (BICIM) and analyse it using EXIT charts, capacity, error bounds and error rate simulations.

Adaptive Optimization of an Iterative Multiuser Detector for Turbo-Coded CDMA

Extrinsic information transfer (EXIT) charts are utilized to optimize the iterative multiuser detector receiver in a multiuser turbo-coded CDMA system. The (receive) power levels are optimized for the system load using a constrained nonlinear optimization approach. The optimal decoding schedule is derived dynamically using the power optimized EXIT chart and a Viterbi search algorithm. Dynamic scheduling is shown to be a more flexible approach which results in a more stable QoS for a typical system configuration than one-shot scheduling, and large complexity savings over a receiver without scheduling. We verify through simulations that complexity savings of over 50% and power savings of over 8dB can be achieved. We show that the optimized power levels combined with adaptive scheduling allows for efficient utilization of receiver resources for heavily loaded systems.

How to obtain turbo gains in coherent and non-coherent orthogonal transmit diversity

We consider turbo detection for coherent and non-coherent orthogonal transmit diversity. The turbo iterations are done between a convolutional code and the diversity combiner. We show that due to the orthogonal structure of the space-time block codes, extrinsic information which enables turbo gains can only be obtained for special symbol mappings. Such optimized symbol mappings arc given for 8-PSK, 16-PSK and 16-QAM. Furthermore, we present a simple non-coherent soft-output detector for differential space-time block codes. Extrinsic information transfer ( EXIT) charts are used as a powerful tool for analysis and performance prediction of the turbo detector. We show that a turbo detector benefits from spatial diversity in terms of earlier convergence. For quasistatic fading, we introduce the x%-EXIT chart.

Partially unique mappings for bit-interleaved coded modulation with iterative detection

We consider bit-interleaved coded modulation with iterative (turbo) detection and non-unique mappings of bits to QAM/PSK symbols which allow better performance in the error floor region compared to unique mappings. Ambiguities are resolved in the iterative detection process. Furthermore, we propose partially unique mappings which together with a carefully designed channel coding scheme enable a good trade-off between performance without and with turbo iterations. This makes turbo iterations optional but not mandatory. Moreover, the detection complexity and the peak to average power ratio can be reduced with non-unique mappings compared to unique-mappings with turbo detection.

Turbo Modulation and Coding: Design and Evaluation of Iterative Bit-Interleaved Coded Modulation Methods for Wireless Systems beyond 3G

We give an overview of iterative techniques for bit-interleaved coded modulation. We start with simple methods where a convolutional code is concatenated with a standard QAM modulation scheme. The mapping is carefully chosen different from Gray mapping such that significant gains can be obtained by an iterative (turbo) receiver. The idea can also be applied to transmit antenna diversity as well as spatial multiplexing (MIMO). We then consider various powerful iterative coding schemes which are under discussion in standardisation for wireless systems beyond 3G such as serial or parallel concatenated convolutional codes, repeat accumulate codes and LDPC codes. We give a comparison in terms of complexity and performance.The main intention is to provide an illustrative overview over relevant applications of the turbo principle in demodulation and decoding. It is a summary of results which have been obtained in collaboration between the Institute of Communications Engineering, TUM and DoCoMo Euro-Labs. Copyright