Igor Dotlic

Low Complexity Chirp Pulsed Ultra-Wideband System with Near-Optimum Multipath Performance

This paper describes the Impulse Radio Ultra-Wideband (IR-UWB) system using linear chirp UWB pulses as symbols. The novel method of coherent or differentially coherent detection of chirp pulses in multipath channels is introduced. The method divides detection in the receiver between its analog and digital part; in the analog part of the receiver, received signal is compressed in frequency by mixing with locally generated chirp pulse and low-pass filtering. In this way, the time-bandwidth (TB) product of the resulting signal is reduced compared to the received signal and made approximately independent of duration of the transmitted signal. This results in relatively low complexity digital back-end of the receiver that is able to capture a large portion of the multipath energy, regardless of duration of the transmitted waveform. The work includes derivation of analytical properties of the system, including derivation of loss parameters that quantify system multipath performance. Numerical results include discussion on the system multipath loss performance with varying chirp duration. As well, a comparison is made with error performance of sampling receivers featuring the same computational complexity. Analysis of the robustness of the systems performance to different chirp pulse implementation errors is also provided.

Performance analysis of Impulse Radio Ultra-Wideband differential detection schemes for Body Area Networks

In this work differentially coherent communication schemes for Impulse Radio Ultra-Wideband (IR-UWB) that transmit single uninterrupted package of energy per symbol, expected to be included in the IR-UWB IEEE 802.15.6 wireless Body Area Networks (BAN) standard are considered. Models for two receiver architectures, suitable for such communication schemes and feasible to implement in current CMOS technology — duty-cycled sampling receiver and chirp receiver are derived. After that, two differential detection techniques for employed receiver architectures — ordinary DPSK and Sample-wise DPSK (S-DPSK) are described. Theoretical analysis of probability of error for S-DPSK is also provided. Performances of the sampling and the chirp receiver architectures with DPSK and S-DPSK detection methods employed are analyzed under narrowband and Frequency-Modulated UWB (FM-UWB) types of interference.

Preamble structure and synchronization for IEEE 802.15.6 Impulse-Radio Ultra-Wideband physical layer

The paper develops a method of synchronization for synchronization header (SHR) structure described in the draft of IEEE 802.15.6 standard for body area network (BAN) and its Impulse-Radio Ultra-Wideband (IR-UWB) physical layer (PHY) with differential phase modulation. Uniqueness of this PHY is that transmitted waveform shape is not known to the receiver at the time of synchronization and therefore classic synchronization methods based on correlation cannot be employed. Based on the developed synchronization method, synchronization performances with the different SHR structures are evaluated and solutions are suggested for the SHR structure described in the standard.

Interference performance of IEEE 802.15.6 Impulse-Radio Ultra-Wideband physical layer

The paper analyses performances of the mandatory mode of Body Area Network IEEE 802.15.6 Impulse-Radio Ultra-Wideband DPSK physical layer in different types of interference; namely Frequency Modulated Ultra-Wideband, WiMax and other co-located IEEE 802.15.6 Impulse-Radio Ultra-Wideband devices. Interference performance of two receiver architectures suitable for the specification of this physical layer: duty-cycled sampling receiver and chirp receiver are analyzed through probabilities of error in different phases of packet reception.

Novel Trellis Coded Modulation for coherent IEEE 802.15.4a Impulse-Radio Ultra-Wideband communications

The paper proposes a novel Trellis Coded Modulation (TCM) scheme for coherent Impulse-Radio Ultra-Wideband (IR-UWB) IEEE 802.15.4a communications that, in comparison with the current IEEE 802.15.4a IR-UWB communications scheme, is able to reduce energy per bit consumed in the receiver two times with approximately 2 dB performance loss. Furthermore, changed in the IEEE 802.15.4a coherent IR-UWB radio required to implement proposed TCM are minimal. Downside is that the proposed TCM scheme cannot be detected by non-coherent receivers. Discussion starts by looking at the current IEEE 802.15.4a IR-UWB coding and modulation scheme as a rudimentary TCM. After that, a transition is made through the TCM framework from the current IEEE 802.15.4a IR-UWB coding and modulation scheme to the proposed one.

Chirp Impulse Radio Ultra-Wideband antenna array with low sample-rate digital beam steering

In this paper, we propose a novel type of Impulse Radio Ultra-Wideband (IR-UWB) beamforming structure that we named a chirp beamformer. It represents an alternative to the well-known correlation beamforming paradigm. The chirp beamformer uses a chirp pulse as a symbol waveform. In comparison with a correlation beamformer, the chirp beamformer requires considerably lower timing resolution in cases where the IR-UWB symbol consists of a relatively long single uninterrupted waveform, as in the mandatory modes of two of the IEEE 802.15 IR-UWB standards, namely IEEE 802.15.4a-2007 and IEEE 802.15.6-2012. Furthermore, the bandwidth of the signal that the chirp beamformer generates in the baseband is considerably lower than in the case of the correlation beamformer. Hence, in the case of digital baseband signal generation, the chirp beamformer requires a considerably lower sampling rate than the correlation beamformer. A method for shaping the beam pattern of the chirp beamformer is also described. All concepts introduced are illustrated by numerical examples.

Sample-wise differential detection of Impulse-Radio Ultra-Wideband Pulse Position modulated symbols

The paper describes technique for differential detection of Impulse Radio Ultra-Wideband (IR-UWB) Pulse Position Modulated (PPM) symbols. An expression for probability of error in noise is derived. The numerical results show the methods performance enhancement compared to the energy detection in noise and considerable performance enhancement in multiuser interference. The method is applicable to the mandatory mode of the IEEE 802.15.6 Body Area Network (BAN) IR-UWB standard.

Design of the Orthogonal UWB Pulses with the Cognitive Radio Applications

In this paper, a method for the design of non-linear phase, full-band, UWB pulses that satisfy any given spectrum mask is described. The method uses convex programming in each step of the iterative procedure that updates the phase distribution of the goal function. Thanks to its mathematical structure, method performance is much better than the performance of similar methods found in literature. Techniques of adapting pulses waveforms for the cognitive radio applications are described; pulses waveforms are modified in order to achieve low interference to the victim systems.

Impulse radio ultra-wideband antenna array correlation beamforming

The paper presents a method of antenna array pattern shaping, i.e. beamforming, for Impulse Radio Ultra-Wideband (IR-UWB) correlation beamformers. The method is based on Second Cone Programming (SOCP) and allows for several parameters of shaped pattern to be simultaneously optimized; it allows for arbitrary antenna array geometry as well as for arbitrary UWB frequency-dependent radiation pattern to be considered. Before the method is described, the paper introduces time domain model of wideband antenna array along with IR-UWB correlation beamforming structure. Numerical examples using a realistic UWB antenna as an array element are also provided.

IEEE 802.15.4a-based Impulse Radio Ultra-Wideband system with joint channel equalization and decoding

The paper proposes a modification of the hybrid PPM/BPSK modulation described in the IEEE 802.15.4a Impulse Radio Ultra-Wideband (IR-UWB) Physical Layer (PHY) specifications. Proposed modulation is intended for reception by the coherent IEEE 802.15.4a IR-UWB PHY receivers; it considerably reduces the distance between PPM positions compared to the IEEE 802.15.4a IR-UWB PHY specifications. In this way, proposed modulation considerably reduces the time that the receiver needs to be turned on during the symbol period, i.e. it reduces receiver duty-cycle and hence it reduces receiver power consumption. However, due to a large Inter-Position Interference (IPI) that this small PPM distance inflicts, a need for equalization arises. The paper shows how the Viterbi algorithm used for the decoding of the IEEE 802.15.4a IR-UWB PHY systematic convolutional code can be exploited for simultaneous equalization and decoding by changing its metric. As numerical simulations show, this decoding and equalization method results in relatively small performance loss compared with the case when IPI is negligible.