Harald Kröll

Efficient channel shortening for higher order modulation: Algorithm and architecture

Trellis-based channel equalization for GSM/EDGE with 8PSK modulation requires pre-filtering to achieve high performance at acceptable complexity. Since corresponding implementation complexity grows with modulation order, the introduction of 16/32QAM in the latest 2G standard Evolved EDGE requires new solutions to preserve the low-cost attribute of EDGE-enabled devices. This paper describes a novel efficient pre-filter algorithm based on homomorphic filtering. The corresponding hardware implementation in 130 nm CMOS achieves a 5× improvement of area-timing (AT-)product when compared to prior art.

Maximum-Likelihood Detection for Energy-Efficient Timing Acquisition in NB-IoT

Initial timing acquisition in narrow-band IoT (NB- IoT) devices is done by detecting a periodically transmitted known sequence. The detection has to be done at lowest possible latency, because the RF- transceiver, which dominates downlink power consumption of an NB-IoT modem, has to be turned on throughout this time. Auto-correlation detectors show low computational complexity from a signal processing point of view at the price of a higher detection latency. In contrast a maximum likelihood cross-correlation detector achieves low latency at a higher complexity as shown in this paper. We present a hardware implementation of the maximum likelihood cross-correlation detection. The detector achieves an average detection latency which is a factor of two below that of an auto- correlation method and is able to reduce the required energy per timing acquisition by up to 34%.

A low-complexity channel shortening receiver with diversity support for evolved 2G devices

The second generation (2G) cellular networks are the current workhorse for machine-to-machine (M2M) communications. Diversity in 2G devices can be present both in form of multiple receive branches and blind repetitions. In presence of diversity, intersymbol interference (ISI) equalization and co-channel interference (CCI) suppression are usually very complex. In this paper, we consider the improvements for 2G devices with receive diversity. We derive a low-complexity receiver based on a channel shortening filter, which allows to sum up all diversity branches to a single stream after filtering while keeping the full diversity gain. The summed up stream is subsequently processed by a single stream Max-log-MAP (MLM) equalizer. The channel shortening filter is designed to maximize the mutual information lower bound (MILB) with the Ungerboeck detection model. Its filter coefficients can be obtained mainly by means of discrete-Fourier transforms (DFTs). Compared with the state-of-art homomorphic (HOM) filtering based channel shortener which cooperates with a delayed-decision feedback MLM (DDF-MLM) equalizer, the proposed MILB channel shortener has superior performance. Moreover, the equalization complexity, in terms of real-valued multiplications, is decreased by a factor that equals the number of diversity branches.

An Evolved GSM/EDGE Baseband ASIC Supporting Rx Diversity

In this paper, a baseband ASIC which supports receive diversity and soft-output Viterbi equalization for enhanced 2G networks is presented. It includes a transmitter and receiver with a symbol detector and a decoder with a dedicated incremental redundancy implementation, as well as the necessary control capability to autonomously communicate with the RF-IC. The ASIC is connected to an RF-IC to build a complete Evolved EDGE transceiver system. The transceiver system reaches a measured sensitivity close to -112 dBm for single-antenna GSM voice channels and achieves the reference interference performance for adjacent channels 11.4 dB above 3GPP requirements. It is the first reported solution which fulfills the most demanding 3GPP Downlink Advanced Receive Performance Phase 2 testcases specified for Rx-diversity. The ASIC occupies 6 mm 2 in 130 nm CMOS with a power consumption between 3.9 and 14 mW.

Low-complexity frequency synchronization for GSM systems: Algorithms and implementation

Carrier frequency synchronization of a mobile station (MS) is a crucial task at the beginning of the cell selection procedure and during normal operation. Constant monitoring of the base-stations surrounding the MS requires robust synchronization concepts with low computational complexity. In the GSM standard, periodically transmitted frequency correction bursts (FB) provide the necessary information for synchronization. This paper presents a combined low-complexity approach for FB detection and carrier frequency estimation, which achieves high detection probability and frequency estimation accuracy. A thorough performance assessment on a GSM/EGPRS2 testbed proves the suitability of the corresponding FPGA hardware implementation.

An evolved EDGE PHY ASIC supporting soft-output equalization and Rx diversity

In this paper the first complete Evolved EDGE transceiver physical layer ASIC supporting receive diversity and soft-output Viterbi equalization is presented. It comprises transmitter and receiver with detector and a decoder with an autonomous incremental redundancy implementation. The ASIC reaches a measured sensitivity of -111.8dBm for single antenna GSM voice channels and achieves the reference interference performance for adjacent channels 12 dB above 3GPP requirements. It occupies 6mm2 in 130nm CMOS with a power consumption between 5 and 39mW.

Channel shortening and equalization based on information rate maximization for evolved GSM/EDGE

In this paper, we study Ruseks channel shortening receiver based on the maximization of the lower bound of the information rate for inter-symbol-interference scenarios. We introduce the necessary simplifications which enable the use of the channel shortening algorithm for Evolved GSM/EDGE receivers for 2G cellular networks. We derive the computational complexity, evaluate the performance and compare both to state-of-the art Evolved GSM/EDGE receivers. A performance gain of up to 1 dB is achieved over state-of-the-art channel shortening receivers, while being less complex in terms of multiplications. To further substantiate the concept, a VLSI implementation of the core part of the channel shortener is presented which achieves a three times higher area-throughput product than prior art.

Physical Layer Development Framework for OsmocomBB

The open source GSM protocol stack of the OsmocomBB project offers a versatile development environment regarding the data link and network layer. There is no solution available for developing physical layer baseband algorithms in combination with the data link and network layer. In this paper, a baseband development framework architecture with a suitable interface to the protocol stack of OsmocomBB is presented. With the proposed framework, a complete GSM protocol stack can be run and baseband algorithms can be evaluated in a closed system. It closes the gap between physical layer signal processing implementations in Matlab and the upper layers of the OsmocomBB GSM protocol stack. An embedded version of the system has been realized with FPGA and PowerPC to enable real-time operation. The functionality of the system has been verified with a testbed comprising an OpenBTS base-station emulator, a receiver board with RF transceiver and our developed physical layer signal processing system.

Indoor ultra-wideband location fingerprinting

Location fingerprinting based on ultra-wideband (UWB) radio frequency signals is an attractive alternative to conventional positioning concepts which utilize range, angle, or received signal strength estimates. The large bandwidth enables a fine temporal resolution of the multipath propagation channel, which in turn acts as a unique location fingerprint of the positions of transmitter and receiver. This paper presents a thorough experimental performance analysis of the proposed UWB location fingerprinting scheme in a typical office environment. We are able to show that high position location accuracy is achievable in a dense multipath propagation environment with non-line-of-sight conditions where conventional approaches would fail.

A SAW-less RF-SoC for cellular IoT supporting EC-GSM-IoT −121.7 dBm sensitivity through EGPRS2A 592 kbps throughput

The latest extended-coverage (EC-GSM-IoT) and high-throughput (EGPRS2A) enhancements make GSM competitive to LTE-based cIoT standards such as NB-IoT with the advantage of global coverage today. This work introduces the first fully-integrated RF-SoC supporting the complete GSM standard family ranging from EC-GSM-IoT through EGPRS2A. The RF-SoC achieves −121.7 dBm receiver sensitivity and peak data rates close to 600 kbps enabling a broad range of IoT applications.