Implementations of Sorted-QR Decomposition for MIMO Receivers: Complexity,Reusability and Efficiency Analysis

Matrix decomposition of the channel matrix in the form of QR decomposition (QRD) is needed for advanced multiple input and multiple output (MIMO) demapping algorithms like sphere decoder. Due to the computation-intensive nature of the QRD, its implementation has to be highly efficient. Flexibility in several forms, e.g. support for different algorithms, reusability of wireless implementations, portability, etc. is highly sought in wireless devices. The contradictory nature of flexibility and efficiency requires tradeoffs to be made between them in system development. In this paper, we have analyzed such tradeoffs by implementing two minimum mean squared error-sorted QRD algorithms. The algorithms have been implemented in four different methods with varying degree of reusability and in five different forms of portability. The performance of the implementations is evaluated by using the real-time constraints from the LTE standard. For all the implementations, modular equations for accurately estimating the execution time are derived.     

On considering hierarchical modulation in the porting process of legacy waveforms to software defined radio

The novel software defined radio (SDR) technology allows taking the next step in the evolution of military tactical communications. SDRs allow military radio operators to change waveforms on-the-fly according to the mission needs. On the one hand, new wideband networking waveforms will offer new services like high data throughputs and mobile ad-hoc networking capabilities. On the other hand, legacy waveforms will ensure interoperability to legacy equipment in missions where both types of radios are deployed at the same time. In this article, we analyze if an added value can be provided to the operators at SDRs hosting an ‘enhanced’ legacy waveform. This enhancement shall be introduced such that interoperability to the legacy equipment is still guaranteed. The modern concept of hierarchical modulation allows fulfilling this side constraint. While the legacy waveform acts as base-layer, some enhancement-layers offer extra bit budget to transmit additional information. This spare bit budget can be exploited to increase the data rate (i.e. throughput), the error robustness (and with this communication range), or both.     

The EXIT-characteristic of softbit-source decoders

We outline a new technique to compute the EXIT-characteristic of softbit-source decoders analytically without extensive histogram measurements. Based on the analytic considerations it is straightforward to derive a compact determination rule for the maximum value of attainable extrinsic information. We also show that the area under the EXIT-characteristic grows almost logarithmically with the prediction gain which is utilizable due to the residual redundancy in the source data.     

Analysis of BICM-ID Receivers Exploiting Transformations of Extrinsic Information

One of the key problems in the field of Computer Vision is recovering the geometry from multiple views of the same scene. Once the homography of two images is known, the motion of a stereo camera system can be determined, images can be rectified or image registration can be performed. A feature-based approach to determine the homography between two images bases on the extraction and matching of SIFT features (SIFT, Scale-Invariant Feature Transform). By extracting image features from varying images of one scene and finding corresponding image features in both images, the homography of the scene can be determined. The extraction of image features, which provide sufficient quality for computation of the homography of a scene, leads to an algorithm complexity, that prevents real-time applications on conventional CPUs. Therefore, we present and discuss an application-specific instruction-set extensions for a Tensilica Xtensa LX5 ASIP to accelerate a SIFT feature extraction (ASIP, Application-Specific Instruction-set Processor). In total, the complete SIFT feature extraction, executed on an extended processor is accelerated by a factor of x125 compared to the baseline processor. At the same time, the accuracy of the SIFT features is preserved. In addition, the proposed processor extensions maintain the full flexibility of an ASIP for a fast integration of further feature extractors.     

Turbo decodulation: iterative combined demodulation and source-channel decoding

We propose the combination of iterative demodulation and iterative source-channel decoding as a multiple turbo process. The receiver structures of bit-interleaved coded modulation with iterative decoding (BICM-ID), iterative source-channel decoding (ISCD), and iterative source coded modulation (ISCM) are merged to one novel turbo system, in which in two iterative loops reliability information is exchanged between the three single components, demodulator, channel decoder and (softbit) source decoder. Simulations show quality improvements compared to the different previously known systems, which use iterative processing only for two components of the receiver.     

A Technical Review of SCA Based Software Defined Radios: Vision,Reality and Current Status

The SCA 2.2.2 architecture has achieved widespread adoption in the military communications market. Hundreds of thousands of SCA enabled software defined radios (SDRs) have been deployed to date, and world-wide dozens of programs are working to field more of these types of radios. The reasons for this success are the benefits enabled through adoption of the SCA: proven cost and delivery time advantages, lower logistical overhead through enhanced inter-component interoperability, simplified insertion of new communications capabilities in deployed radios, enhanced coalition interoperability through portability of waveforms and reduced development risk. As a result of this success, new countries and new organizations have begun to explore the use of the SCA, driving a second generation of SDR market adoption. Successful deployment of SCA 2.2.2 based SDRs has identified improvements to be made to advance the technology further. The Wireless Innovation Forum is working in close collaboration with the U.S. Department of Defense Joint Tactical Networking Center (JTNC) to evolve the SCA. The resulting SCA 4.1 specification represents the future of defense SDR technology.     

Design and Analysis of Hierarchically Modulated BICM-ID Receivers With Low Inter-Layer Interferences

In this article, we present a novel methodology to optimize Hierarchically Modulated Bit-Interleaved Coded Modulation with Iterative Decoding (HM-BICM-ID). This methodology allows designing a receiver which supports several configurations. Each configuration is able to decode the same transmitted signal over the air with different fidelity. This concept permits using radios with varying processing capabilities, e.g. handheld radios, vehicular based radios etc. However, earlier simulation results have shown that HM-BICM-ID loses, if compared to non-hierarchical schemes, in Bit Error Rate (BER) performance due to Inter-Layer Interferences and design restrictions. Our proposed iterative tunable procedure optimizes hierarchical modulation schemes considering two criteria, the Harmonic Mean of the minimum squared Euclidean Distance and the bit error probability. The optimization is done by moving critical constellation points towards the optimal direction. A novel modulation scheme has been found and simulation results show an improved asymptotic BER performance in a wide range of channel conditions for an exemplary two-layered HM-BICM-ID. Finally, we present an analysis of HM-BICM-ID in context of Extrinsic Information Transfer Charts.     

Minimum Terms of Residual Redundancy for Successful Iterative Source-Channel Decoding

Iterative source-channel decoding (ISCD) improves the error robustness of a digital communication system by iteratively evaluating natural residual source redundancy and artificial channel coding redundancy in a TURBO-like process. Based on recent results to extrinsic information transfer (EXIT) charts we present a novel (experimental) approach to quantify the minimum terms of residual redundancy which are needed for (almost) successful ISCD. Moreover, we clarify why in certain situations the decoding trajectory exceeds the EXIT-characteristic of soft decision source decoding (SDSD) in an ISCD scheme