Rolf Kraemer

Overview of MAC layer enhancements for IEEE 802.15.4a

Ultra wideband impulse radio (IR-UWB) based on the IEEE 802.15.4a PHY standard offers unique features which are exploitable in MAC designs for wireless personal area networks (WPANs) and wireless sensor networks (WSNs) to improve performance and robustness. To achieve this, different strategies of cross-layer optimizations to the IEEE 802.15.4 MAC using features of UWB have been proposed. This paper compares current approaches and exposes individual advantages and disadvantages regarding energy efficiency and positioning.

Synchronisation performance of wireless sensor networks

Ultra Wideband (UWB) has been gaining growing research and industry interests in many different areas of wireless communications. Among them using UWB as a radio interface for wireless sensor network is of high interest due to its precise localisation and low power consuming capabilities. In this paper we carry out quantitative analysis into the synchronisation performance of UWB when it operates under usual wireless channel environments. Simulation results confirm that coherent receiver needs around 10 dB less signal to noise ratio to achieve synchronisation compared to the noncoherent detection. Higher spreading factors lead to noticeable improvement for both coherent and noncoherent detection.

Performance and design of IR-UWB transceiver baseband for wireless sensors

Using UWB for wireless short range, low rate communication has been attracting growing interest due to its low power consumption and very high bandwidth. Moreover, it is able to offer accurate localization in the range of few centimeters. Recognising these qualities, it is desirable to design IR-UWB transceiver which can draw minimum possible power when it is applied for battery driven wireless sensors. For this reason, in this paper, baseband design and performance of IR-UWB transceiver based on the standard IEEE.802.15.4a was investigated with particular emphasis on reducing power consumption. Synchronization algorithm that achieves 16 ns is presented and its performance is very promising offering nearly 100% synchronization for as low SNR as 8 dB. Different resolutions of analogue to digital converter (ADC) are investigated to find out the optimum with respect to power consumption and performance. 4 bit ADC was found to be the most optimal for the sample rate of 62.4 MHz. BER performance of pulse position modulation was evaluated under realistic channel conditions with multipath components.

Evaluation and optimization of robustness in the IEEE 802.15.4a standard

In this paper, we introduce ways to improve the robustness by lowering the packet loss rates of transmissions using ultra-wideband impulse radio (UWB-IR). It has been shown that the packet loss rate caused by erroneous synchronization can be tremendously decreased compared to the preamble specified in the standard IEEE 802.15.4a by our approach. These improvements are particularly intended for low-power, low-complexity transceivers operating in environments with harsh multi path propagation and high noise levels, such as industrial control. These improvements include novel ways for receiver implementation to reduce detection errors for low-power energy detection receivers with slow sampling rates. We also introduce a modified preamble that significantly reduces packet loss caused by failed preamble synchronizations We evaluate our improvements by simulation. Our approach to receiver implementation enables receiver to achieve the same packet loss rate at a signal-to-noise ratio (SNR) 10 dB lower than traditional receiver designs.

IR-UWB single-chip transceiver for high-band operation compliant to IEEE 802.15.4a

This paper describes a monolithic integrated single-chip transceiver intended for impulse radio (IR) - Ultra-wide Band (UWB) applications compliant to the IEEE 802.15.4a standard. The transceiver operates in the higher UWB band on the mandatory channel #9 (7.9872 GHz). The implemented nominal data rate is 850 kb/sec. The presented chip consists of the entire RF-front-end, 6-bit-resolution successive approximation register (SAR) analogue-to-digital converter (ADC), and the baseband processor running with a clock of 31.2 MHz. The analogue frontend can be further segmented into a pulse generation and transmit part and a quadrature direct down conversion receiver part, whereas both parts share a frequency synthesizer based on an integer-N phase-locked loop (PLL). The impulse generation is based on the gated oscillator principle allowing required on-off keying (OOK) as well as binary phase shift keying (BPSK). While the receiver supports both, coherent and non-coherent impulse detection, here only non-coherent operation will be presented. The baseband processor part contains a separated 499.2 MHz clocked block for transmitter control and provides a serial peripheral interface (SPI) for data exchange with an external micro controller. The presented chip was fabricated in a 0.25 μm SiGe:C BiCMOS technology occupying a Si area of 3.25 - 3.25 mm2.

Performance and implementation of a multi-rate IR-UWB baseband transceiver for IEEE802.15.4a

Design, simulation, implementation and performance of IR-UWB baseband conforming to IEEE802.15.4a are discussed. The baseband can support various data rates such as 850 Kb/s, 6.81 Mb/s and 27.24 Mb/s. The design and parameter selection were considered carefully taking into account all possible imperfections that IR-UWB high frequency signal can experience. Energy detection receiver employing a comparator clocked at 499.2 MHz was adopted for the digitisation. Using I and Q path both positive and negative pulses were detected with a high reliability leading to a very good synchronisation performance. Simulation results confirm that the synchronisation is very robust being always correct for office NLOS environment and a large clock deviation between transmitter and receiver. The algorithm presented in this paper was implemented with discrete components, FPGA and signal generators. Experimental results show a good agreement with the simulation for all the data rates and the implemented baseband offers around six meter communication range tested along with a high frequency frontend from discrete components.

Extension of IEEE 802.15.4a to improve resilience for wireless automation using soft-bit combination

Ultra-Wideband Impulse Radio is a promising technology for industrial automation applications because of its inherent multipath robustness and coexistence features. In our efforts to deploy UWB-IR for industrial automation, we use an adapted version of the IEEE 802.15.4a PHY. In this paper, we present a way to improve robustness for low-latency sensor-actor networks with short cyclic packets of process data, as found in industrial control applications. Due to the low cycle times of the wireless network, which can be shorter than the application cycle, soft-bit combinations across multiple repetitions of a packet can be used to collect enough information to recover packets that would not be decodable by a single transmission. To determine if a packet is a repetition or contains different data than the last transmission, a change indicator is inserted into the packet by the sender. The findings are proven by simulation against IEEE industrial channel models and show a significant improvement.

Performance of UWB and its suitability for wireless sensors

Ultra-wideband (UWB) has become one of the key technologies in wireless communication industries. In this paper we discuss and evaluate the performance of UWB under different channel conditions when it is applied for wireless sensors. The simulation was carried out for various detection and modulation schemes. Simulation results confirm that UWB with coherent detection outperforms the noncoherent detection the difference being 10dB in SNR to achieve the same performance. Coded UWB improves the performance by another 2dB. Low rate UWB performs better than the high rate one.

FPGA and ASIC implementation and testing of IR-UWB baseband transceiver for IEEE802.15.4a

A digital baseband was designed and implemented according to the standard IEEE802.15.4a both in FPGA and as well as ASIC. The baseband supports data rates 850 Kb/s, 6.81 Mb/s and 27.24 Mb/s running at the clock speed of 31.2 MHz. The transmitter and receiver were tested by introducing various distortions to the signal being received. The baseband was shown to be fully functional being able to receive even under heavy distortion. Both the synchronization and data detection performance are robust. The baseband tested with a FPGA was further made as an ASIC in the 250 nm BiCMOS technology from IHP, Germany.

A packet-level adaptive forward error correction scheme for wireless networks

Especially for synchronization-critical wireless networks like ultrawideband impulse radio (UWB-IR), data packets are lost not only due to single bit errors in the payload but also to a large degree because of synchronization errors or preamble failures. Current FEC codes only address bit errors inside a packet. Packets that are lost because of errors in preambles or headers can only be recovered on packet level. In this Paper we propose a low-complexity adaptive packet-level FEC and prove by simulation that it can reduce packet loss with very small overhead.