Multicode based communications in Impulse Radio UWB systems

Ultra wideband-impulse radio (UWB-IR) systems transmit data by ultra short pulses. The UWB-IR systems can achieve a time diversity gain by transmitting some pulses for each information symbol. In L. Yang et al. (2002) the space time (ST)-UWB-IR system was proposed to achieve a space-time diversity gain by transmitting space-time block coded symbols with some antennas. In the ST-UWB-IR system, the transmit antennas transmit the same symbol over an ST code block simultaneously. If all the transmit antennas can transmit different symbols independently, that is, if it separates the symbols from each antenna, we can expect a higher transmission rate than the ST-UWB-IR system. Moreover, at the same transmission rate, we can expect a larger diversity gain by sending more pulses for each symbol. This paper proposes a space hopping (SH)-UWB-IR system. In the SH-UWB-IR system, to allow each user to transmit different symbols from different antennas, a unique time hopping sequence is assigned to each antenna, which is known to the receiver. In addition, to get the larger diversity gain in the SH-UWB-IR system, the transmitted symbols are interleaved over the transmit antennas. From the results of our computer simulation, we show that when the number of users is small, the bit error rate (BER) of the SH-UWB-IR system is superior to that of the ST-UWB-IR system at the same data rate.

In an ultra-wideband (UWB) impulse radio (IR) system, a number of pulses, each transmitted in an interval called a "frame," is employed to represent one information symbol. Conventionally, a single type of UWB pulse is used in all frames of all users. In this paper, IR systems with multiple types of UWB pulses are considered, where different types of pulses can be used in different frames by different users. Both stored-reference (SR) and transmitted-reference (TR) systems are considered. First, the spectral properties of a multipulse IR system with polarity randomization is investigated. It is shown that the average power spectral density is the average of the spectral contents of different pulse shapes. Then, approximate closed-form expressions for the bit-error probability of a multipulse SR-IR system are derived for Rake receivers in asynchronous multiuser environments. The effects of both interframe interference (IFI) and multiple-access interference (MAI) are analyzed. The theoretical and simulation results indicate that SR-IR systems that are more robust against IFI and MAI than a "conventional" SR-IR system can be designed with multiple types of ultra-wideband pulses. Finally, extensions to multipulse TR-IR systems are briefly described.

Pulse-based communication systems are a promising candidate in the deployment of future wireless networks, thanks to the potential robustness and capacity guaranteed by the transmission of pulses of very short duration. In the framework of pulse-based communication systems, the Impulse Radio-Ultra Wide Band (IR-UWB) technique recently received particular attention. In the past, most of the UWB research focused on hardware and physical layer aspects in order to solve the technological challenges posed by IR-UWB. UWB peculiar characteristics may, however, also stimulate innovative higher layers' design. This work addresses Medium Access Control (MAC) issues for IR-UWB communication systems and extends the discussion to wireless optical communication systems. Typical characteristics of an IR-UWB system are presented, and solutions proposed for such systems at the MAC layer are reviewed. The applicability of such solutions to an optical wireless communications system is then discussed, highlighting analogies and differences between IR-UWB and wireless optical systems.

Multiuser detection of time-hopping PPM UWB system in the presence of multipath fading

Low-complex and low-power non-coherent energy detectors (EDs) are interesting for low data rate impulse radio (IR) ultra wideband (UWB) systems, but suffer from a loss in performance compared to coherent receivers. The performance of an ED also strongly depends on the integration interval (window size) of the integrator and the window position. This paper presents a non-coherent fourth-order detector (FD) which can discriminate between Gaussian noise signals and non-Gaussian IR-UWB signals by directly estimating the fourth-order moment of the received signal. The performance of the detectors is evaluated using realistic channels measured in a corridor, an office and a laboratory environment. The results show that bit-error-rate (BER) performance of the proposed FD receiver is slightly better than the ED in low signal-to-noise ratio (SNR) region and its performance improves as the SNR increases. In addition, BER of the FD receiver is less sensitive to overestimation of the integration interval making it relatively robust to variations of the channel delay spread. Finally, a criteria for the selection of integration time of the proposed detector is suggested.

The link budget of the transmission gain is usually evaluated by using the Friis' transmission formula. However, it is not directly applicable to ultra wideband impulse radio (UWB-IR) transmission systems. This paper presents the link budget evaluation formula in the term of transmission gain for the UWB-IR systems that takes into account the transmitted waveform, its distortion due to the antennas, the channel and the correlation receiver. Since the antennas are significant pulse-shaping filters in UWB-IR, the various kinds of the antennas are experimentally examined, especially focused on the effect of the received signal and the isotropic template waveforms.

Power efficient ultra-wideband based wireless communication for wireless body area network applications

The possibility to accurately localize tags by using wireless techniques is of great importance for several emerging applications in the Internet of Things. Precise ranging can be obtained with ultra wideband (UWB) impulse radio (IR) systems, where short impulses are transmitted, and their time-of-arrival (ToA) is estimated at the receiver. Due to the presence of noise and multipath, the estimator has the difficult task of discriminating the time intervals where the received waveform is due to noise only, by those where there are also signal components. Common low-complexity methods use an energy detector (ED), whose output is compared with a threshold, to discriminate the time intervals containing noise only from those containing signal plus noise. Optimal threshold design for these methods requires knowl- edge of the channel impulse response and of the receiver noise power. We propose a different approach, where ToA estimation is based on model selection by information theoretic criteria (ITC). The resulting ToA algorithms do not use thresholds, and do not require any information about the channel or the noise power level. These blind, universal ToA estimators show, for completely unknown multipath channels and in the presence of noise with unknown power, excellent performance when compared with ideal genie-aided schemes.

In-car wireless data communications systems require a short-range unlicensed radio communications technology that causes a very low level of interference in the other, already deployed radio links and networks, offers low and medium data rate, can reuse the already occupied radio-frequency (RF) bands, and assures low probability of message collisions. Ultrawide band (UWB) impulse radio employs RF pulses with very short duration to carry the information; consequently, it is an optimal candidate for the in-car wireless communications and intravehicular wireless sensor networks. Data rate and shape of RF carrier pulse determine the performance of a UWB radio link. To limit the interference caused, the maximum power radiated by an UWB device is restricted by the Federal Communications Commission (FCC) in the U.S. Introducing a new mathematical model and starting from the FCC regulations, analytical expressions for the calculation of FCC power limits are derived here. It is shown that the low- and high-rate UWB impulse radio systems are peak and average power limited, respectively. The relationship between the mathematical model and the parameters of an UWB carrier pulse used in a built UWB radio is established. The performances of RF carrier pulses known from the literature are evaluated and compared. All expressions derived are verified by measurements.

Low-complexity low-rate super-orthogonal turbo codes (SOTC) are proposed in this work to replace the implicit repetition code (RC) in an ultra-wide band impulse radio (UWB-IR) system to improve BER, transmission range and system throughput. Various receivers including matched-filter and RAKE receivers are adopted for data detection in the additive white Gaussian noise (AWGN) channel and the indoor IEEE 802.15.3a channel. The performance of SOTC-encoded UWB is analyzed and validated by computer simulation. It is shown that the SOTC-based UWB-IR system can achieve significant performance improvement over the conventional DS- UWB system encoded by RC.

The compressed sensing(CS) theory has provided a new solution for the low-rate sampling design of Impulse Radio Ultra-WideBand (IR-UWB) signal. This paper gives full consideration of the influence of quantization noise in IR-UWB system, and designs an effective quantization and reconstruction mechanism with high performance of resisting noise. Based on the analysis of noise distribution characteristics in compressed sampling value, the signal reconstruction model is revised, and then the performances of Dantzig-Selector (DS) method, Subspace Pursuit(SP) method, and traditional reconstruction algorithms are compared. On this basis, a signal reconstruction method (hybrid DS-SP method) with self-adaptability in DS and SP is proposed. Based on hybrid DS-SP method and consideration of overload uniform quantization, overload hybrid DS-SP mechanism is proposed which considered both the digital rear-end and analog front-end of IR-UWB receiver under compressed sensing framework. Simulation results show that the overload hybrid DS-SP mechanism achieves the exceptional reconstruction performance compared to the traditional reconstruction algorithms under different noise conditions with a compromised complexity between DS and SP.

In a conventional impulse radio (IR) UWB system, the multiuser interference (MUI) and serious multipath interference (MPI) present major challenges in terms of both technological capability and implementation complexity. In this paper, we develop a new multiuser detection method to cancel MUI, especially for the impulse modulation and UWB channel. It makes some perfect algorithms easy to be applied in multiuser detection of the IR-UWB. Those algorithms, such as Kalman, are difficult to be directly used in conventional multipath DS-CDMA system. Furthermore, the receiver employs blinking Rake combining in order to collect more energy output from detection above. This multiuser receiver reduces the computing complexity in high-data-rate communication, and it also improves the speed of adaptive convergence and steady-state performance. With the simulation in different conditions, the receiver achieves a perfect performance

A direct-sequence ultra-wideband impulse radio (DSUWB-IR) system is developed for low-power wireless applications such as wireless sensor networks. This system adopts impulse radio characterized by a low duty cycle, and a direct-sequence 0.7-GHz bandwidth, which enables low-power operation and extremely precise positioning. Simulation results reveal that the system achieves a 250-kbps data rate for 30-mdistance wireless communications using realistic specifications. We also conduct an experiment that confirms the feasibility of our system.

New technologies can help to develop preventive healthcare, thereby leading to significant life quality improvements. Medical Body Area Networks are expected to become a key element in tomorrow's medical IT infrastructure by enabling the long term collection and analysis of health parameters. For this vision to become a reality, several challenges must be addressed. This work focuses on the technological aspects of ultra low power consumption, low latency and packet error rate. We consider and evaluate state of the art technologies currently under evaluation by the IEEE Standard Association 802.15.6 task group on body area networks, using detailed network simulation models, which have been calibrated with hardware measurements whenever possible and with MATLAB communication link simulations otherwise. We observe that the expected power consumption levels are similar for all considered platforms, and that they are determined mainly by the medium access control protocol. Trade-offs between communications latency, throughput and power consumption are identified. The performance of the Ultra Wideband Impulse Radio system is clearly impacted by its lack of carrier sensing capability. We conclude that the existing technologies are mature enough and that the remaing obstacles to widespread adoption are organizational and societal.

The primary characteristic of the ultra-wideband (UWB) indoor radio channel is the large frequency diversity, which translates into a large number of resolvable paths and, consequently, in a low signal energy-per-path. Code acquisition is particularly difficult in such a hostile environment if the available diversity is not exploited. This paper deals with the initial code acquisition for an UWB impulse radio (IR) system in a dense multipath environment. In particular, we propose an approach based upon a non-coherent Rake detector (NCRD), which combines the energy collected from different paths in a non-coherent fashion. System performance of the NCRD is analyzed in multipath fading channels, showing that satisfactory performance is achievable with relatively low complexity.