Florian Troesch

Noncoherent ultra-wideband systems

The need for low-complexity devices with low-power consumption motivates the application of suboptimal noncoherent ultra-wideband (UWB) receivers. This article provides an overview of the state of the art of recent research activities in this field. It introduces energy detection and autocorrelation receiver front ends with a focus on architectures that perform the initial signal processing tasks in the analog domain, such that the receiver does not need to sample the UWB received signals at Nyquist rate. Common signaling and multiple access schemes are reviewed for both front ends. An elaborate section illustrates various performance tradeoffs to highlight preferred system choices. Practical issues are discussed, including, for low-data-rate schemes, the allowed power allocation per pulse according to the regulators ruling and the estimated power consumption of a receiver chip. A large part is devoted to signal processing steps needed in a digital receiver. It starts with synchronization and time-of-arrival estimation schemes, introduces studies about the narrowband interference problem, and describes solutions for high-data-rate and multiple access communications. Drastic advantages concerning complexity and robustness justify the application of noncoherent UWB systems, particularly for low-data-rate systems.

Hardware Aware Optimization of an Ultra Low Power UWB Communication System

A wireless body area network with an average throughput of 500 kbps based on ultra-wideband pulse position modulation is considered. For a long battery autonomy a hardware aware system optimization with respect to the specific applications at hand is essential. A key feature to achieve power savings is low duty cycle signaling, and its effectiveness when combined with burst-wise transmission at high peak data rate. Exploiting this observation, an ultra-low power system is presented, jointly optimized with respect to application and hardware specific aspects. Based on an exhaustive survey of the state of the art literature, its power consumption is estimated significantly below 1 mW.

UWB geo-regioning in rich multipath environment

We introduce geo-regioning as a method to achieve rough localization in asynchronous UWB networks. The ap- proach is to localize the transmitter position by means of the multipath components in the received channel impulse response (signature). To show the principle feasibility of this approach a first regioning algorithm is introduced and tested with measured data. Therefore, a measurement campaign in a rich multipath environment has been performed. A high number of signatures originating from different regions in a room have been collected. The regioning algorithm presented here is based on the a priori knowledge of the average power delay profiles of the different regions. The performance results show that almost all regions can be localized at reasonable SNR and error probability. We conclude that the geo-regioning approach is a promising alternative or supplement to classical time of arrival based approaches in UWB networks.

Partial Channel State Information and Intersymbol Interference in Low Complexity UWB PPM Detection

We consider an UWB PPM based wireless body area network with an average throughput of about 1 Mbps. For a long battery autonomy a low duty cycle operation of the nodes and thus a high peak data rate is essential. Due to the moderate path loss a peak data rate in excess of 50 Mbps would be feasible within the FCC transmit power constraints. With current low complexity PPM detectors, such as the energy detector, the peak data rate is constrained to much lower values, because they are very sensitive to intersymbol interference (ISI). In this paper we constrain our attention to low complexity detectors for UWB PPM, which utilize an observation window of one symbol duration to generate the decision variables for the subsequent symbol decoder. The key contribution is a family of detectors, which utilize partial channel state information (CSI) to improve the robustness to ISI. Specifically we treat the following cases of partial CSI: (i) no CSI, (ii) average power delay profile (APDP), (iii) instantaneous power delay profile (IPDP). To further improve the performance in presence of ISI, a simple post-detection maximum-likelihood sequence estimator (MLSE) is introduced. Finally performance results are given, that highlight the tradeoff between complexity and performance covered by the proposed detection schemes

Ultra-wideband geo-regioning: a novel clustering and localization technique

Ultra-wideband (UWB) technology enables a high temporal resolution of the propagation channel. Consequently, a channel impulse response between transmitter and receiver can be interpreted as signature for their relative positions. If the position of the receiver is known, the channel impulse response indicates the position of the transmitter and vice versa. This work introduces UWB geo-regioning as a clustering and localization method based on channel impulse response fingerprinting, develops a theoretical framework for performance analysis, and evaluates this approach by means of performance results based on measured channel impulse responses. Complexity issues are discussed and performance dependencies on signal-to-noise ratio, a priori knowledge, observation window, and system bandwidth are investigated.

Modified pulse repetition coding boosting energy detector performance in low data rate systems

We consider ultra-wideband impulse radio (UWB-IR) low data rate (LDR) applications where a more complex cluster head (CH) communicates with many basic sensors nodes (SN). At receiver side, noncoherent energy detectors (ED) operating at low sampling clock, i.e., below 300 kHz, are focused. Drawback is that EDs suffer from significant performance losses with respect to coherent receivers. Pulse repetition coding (PRC) is a known solution to increase receiver performance at the expense of more transmit power. But in LDR systems known PRC is very inefficient due to the low receiver sampling clock. Boosting transmit power is not possible due to Federal Communications Commissions (FCC) power constraints. Hence, we present a modified PRC scheme solving this problem. Modified repetition coded binary pulse position modulation (MPRC-BPPM) fully exploits FCC power constraints and for EDs of fixed integration duration is optimal with respect to bit error rate (BER). Furthermore, MPRC-BPPM combined with ED outperforms SRAKE receivers at the expense of more transmit power and makes EDs performance robust against strong channel delay spread variations.

Pulse position precoding exploiting UWB power constraints

Due to dense multipath channels, coherent receivers in ultra-wideband impulse radio (UWB-IR) technology are high in hardware complexity and power consumption. This makes coherent receivers n downlink transmission of low data rate (LDR) applications, where a more complex node communicates with many basic sensors, unreasonable. Precoding schemes are known solutions to transfer receiver complexity to transmitter side, while maintaining receiver performance. We sketch performance and scalability potential of precoding schemes in LDR systems in presence of drastic Federal Communications Commissions (FCC) power constraints. This is done by symbol error rate (SER) analysis of an easily realizable pulse position pre-coding (PPP) scheme, supported by simulation results over measured UWB channels. Under realistic conditions, PPP gains up to 9 dB are demonstrated, and it is shown that already a few PPP pulses are sufficient to significantly reduce receiver complexity, at the expense of more transmit power.

MLSE Post-Detection for ISI Mitigation and Synchronization in UWB Low Complexity Receivers

A wireless body area network with an average throughput of 1 Mbps is considered based on ultra-wideband pulse position modulation. For a long battery autonomy, a low duty cycle operation of the nodes and thus, a high peak data rate is essential. Due to the moderate path loss, a peak data rate in excess of 50 Mbps is feasible within the Federal Communications Commissions transmit power constraints. However, with current low complexity pulse position detectors, such as the energy detector, the peak data rate is constrained to much lower values, because they are very sensitive to intersymbol interference. To overcome this constraint a simple post-detection maximum-likelihood sequence estimator is introduced which significantly reduces the impact of intersymbol interference. The same maximum likelihood sequence estimator is then used to replace cumbersome synchronization algorithms at the expense of slight performance losses.

Location-aware adaptation and precoding for low complexity IR-UWB receivers

An environment is considered with many low complexity wireless mobile stations communicating to higher complexity stationary cluster heads. The cluster heads can determine the rough position of the mobile stations using geo-regioning. The mobile stations are not able to perform a channel estimation due to complexity reasons. We present two approaches to utilize regional channel knowledge available at the cluster head for improvement of the data detection performance at the mobile station. First, by feeding back the average power delay profile of the channel from the cluster head to the mobile station, the mobile station can adapt a filter according to this information. Second, at cluster head side the covariance matrix of the channel impulses response vectors is used for precoding optimization. Based on channel impulse responses measured in a realistic environment the performance of both approaches is evaluated. Performance gains of 1 to 3 dB compared to energy detection can be obtained.

Non-Linear UWB Receivers with MLSE Post-Detection

A wireless body area network with an average throughput of 500 kbps is considered based on ultra-wideband (UWB) pulse position modulation. For a long battery autonomy ultra low power consumption is essential. A FCC compliant ultra low power UWB communication system was presented. By means of a 1% duty cycle at 50 Mbps peak data rate, the power consumption of the system is estimated below 1 mW. To increase inter-symbol interference (ISI) robustness as well as for synchronization, a simple post-detection maximum-likelihood sequence estimator (MLSE) has been presented. In this work, we extend this MLSE approach to over-sampled energy detectors and non-ideal integration windows. Furthermore, we present optimal MLSE metrics based on partial channel state information as a performance benchmark.