Pulse shaping for direct-sequence offset quadrature-spread UWB communication signals

1.1 Impulse Radio (IR) Ultra Wideband (UWB) Communications Ultra wideband (UWB) communication is a fast emerging technology that offers new opportunities such as high data rates, low equipment cost, low power, precise positioning capability and extremely low interference Ghawami (2005). A wide range of possible UWB communication system applications includes radars due to UWB ultra high precision ranging at the centimeter level, wireless personal area networks (WPAN), sensor networks, imaging systems, UWB positioning systems, etc. Yang (2004), Kshetrimayum (2009). From a commercial point of view, the high data rates are the most attractive feature of UWB systems for which speeds of over 100Mb/s have been demonstrated Ghawami (2005). There exist three main types of UWB technologies: impulse radio (IR UWB), direct sequence (DS UWB), and multi-band orthogonal frequency division multiplexing (MB OFDM) Ran (2009). IR UWB communication technique is essentially different from all other communication techniques because it is carrier free and uses for communication between transmitters and receivers very narrow radio frequency (RF) pulses generated from the UWB pulse generator, while traditional transmission systems transmit information by varying the power, frequency, and/or phase of a sinusoidal wave in a modulation process Kshetrimayum (2009), Yao (2007). Consequently, complicated frequency mixers and local oscillators for carrier frequency up and down conversion are not necessary Yao (2007). IR UWB modulation techniques are especially important because the UWB spectrum has been made available by the Federal Communication Commission (FCC) and it can be used with IRs developed to date Lin (2005). Waveforms for IR UWB are designed to obtain a flat frequency response over the bandwidth of the pulse and to avoid a DC component. The large spectrum of a UWB signal may interfere with existing users. In order to keep this interference to the minimum, FCC specifies spectral masks for different applications, i.e. the allowed power output for specific frequencies Ghawami (2005). A contiguous bandwidth of 7.5GHz is available in the frequency interval of (3.1− 10.6)GHz at a maximum power output of −41.3dBm/MHz which is considered as extremely low Ghawami (2005). The power spectral density (PSD) of UWB systems defined as a ratio of the transmitted power P in watts and a signal bandwidth B in hertz is extremely low as compared to other communication systems due to the very wide bandwidth B of short pulses that are typically of nanosecond or picosecond order Ghawami (2005). The selection of the impulse signal type for IR UWB communication system is essential since it determines

This work presents an M-ary multiple access code-selected direct sequence (DS) ultra wideband (UWB) communication system. A high data rate multiple access UWB system can be obtained by a code selection mechanism. In the proposed system, each user is assigned a DS code set with M/2 DS code sequence and a particular DS code sequence can be selected by the log2 (M/2) bits from the DS code set. More importantly for this M-ary UWB communication system, with the increase of the modulation level M, it allows to reduce the required transmitter power maintaining the number of users, the data transmission rate and the multiple access performance. In this paper, we also introduce the detailed algorithm to compute the bit error rate (BER) over the AWGN channel and correlation receivers.

In the ultra-wideband (UWB) communication systems, a critical spectral mask is released to restrict the allowable interference to other wireless devices by the Federal Communications Commission (FCC), and then some pulse shaping methods have been presented to fulfil the mask. However, most pulse shaping methods do not consider the antenna distortion which cannot be neglected in the UWB communication systems compared with the conventional systems. To this end, an orthogonal wavelet based pulse shaping method is proposed in this paper to integrate compensation of antenna distortion into pulse shaping. Simulation results show that the novel pulse shaping method can be used to achieve compensation for antenna distortion, optimization of transmission power spectrum, and simplification of the algorithm, as well as simple implementation of the pulse generator.

In this paper, a closed form expression for the bit error rate performance of the multi-band orthogonal frequency division multiplexing (MB-OFDM) ultra wideband (UWB) communication system in the presence of interference is analytically analysed. The considered channel is the Saleh-Valenzuela multipath fading channel model. The interference is modelled as the OFDM-based IEEE802.11n wireless local area networks (WLANs). The dependence of the bit error rate performance of the MB-OFDM UWB communication system on the transmission range along with the impact of interference is also analytically investigated. Numerical results are validated with the aid of simulations. It is shown that the range performance of the MB-OFDM UWB communication system is severely deteriorated due to the presence of such interference.

Ultra-wideband (UWB) communication systems provide very high data rates by transmitting extremely short duration pulses. The impulse waveform is one of the key factors that influence the performance of these systems. While fulfilling the FCC spectral emission requirements, the pulse shape must offer high detection capabilities with suitable levels of accuracy. In this paper, we evaluate the effect of pulse shapes on the performance of an UWB computationally-efficient acquisition scheme in the presence of multiple user interference (MUI) and Gaussian noise. In the comparisons, different pulses with same duration were used in extensive Monte-Carlo simulations. Results show that the pulse shape has a noticeable impact on the performance of our UWB computationally-efficient acquisition scheme. Moreover, it is concluded that the 6th or the 8th order Gaussian derivative is the most suitable pulse shape to choose, depending on spectral bandwidth requirements.

Ultrawideband (UWB) is a promising technology for getting high data rate communications. UWB communications refer to the utilization of signals with a frequency range (3.1 to 10.6 GHz) on the condition of having a fractional bandwidth of 20% or absolute bandwidth of 500 MHz or higher. The limited power spectral density of − 41.3 dBm/MHz allows UWB communications to be safely deployed with existing wireless communication systems without causing any interference. Consequently, UWB communication systems have been proposed for different outdoor and indoor scenarios. A variety of applications are suitable for UWB communications ranging from infostations, wireless sensor networks (WSNs), on-body communications, in addition to consumer, medical and military applications. Recently, this technology shows a promising step for indoor positioning accuracy where the functioning of navigation systems such as Global Positioning System (GPS) or GLObal NAvigation Satellite System (GLONASS) might be degraded. In this paper, the fundamental properties of UWB communications are presented with an illustration on the present and future direction of this technology.

In this paper we consider a FDMA (frequency division multiple access) system employing OQPSK modulations (offset quaternary phase shift keying) with quasi-constant envelope. To increase the overall spectral efficiency we consider spectral overlapping between different frequency channels. We present an iterative frequency-domain receiver with parallel multiuser detection. Our performance results show that our receiver is able to cope with the strong ACI levels (adjacent channel interference) inherent to spectral overlapping, as well as with the interference between the in-phase (I) and quadrature (Q) components of the OQPSK signals, even for severely time-dispersive channels.

The paper addresses the signal design and performance analysis of direct-sequence ultra-wideband (DS-UWB) multiuser communication employing offset quadrature-spread phase shit keying (OQPSK) modulation with novel chip waveforms. Analytical bit error rate (BER) performance analysis is derived for different receiver structures, emphasizing the impact of the chip mean-squared auto-correlation function (MS-ACF) on BER performance in multiuser and multipath environments. A low-complexity flexible algorithm for designing chip pulses that maximize multiuser system capacity by minimizing the chip MS-ACF is proposed. The optimized waveforms are based on the use of prolate spheroidal wave function (PSWF) expansions. The proposed schemes also provide increased spectrum placement flexibility and minimized phase jumps compared to carrier-less pulse amplitude modulation (PAM) UWB schemes. Several design examples and numerical results are presented to illustrate the relative performance of the novel pulses compared to UWB schemes employing Gaussian monocycle derivatives and modified Hermite polynomials, and it is shown that a clear improvement in multiple access capacity can be achieved by the proposed PSWF-based pulses, particularly with maximum ratio combining receivers.

Phase shift keying modulation approaches are widely used in the communication industry. Differential phase shift keying (DPSK) and Offset Quadrature phase shift keying (OQPSK) schemes are chosen to be investigated is multi environment channels, where both systems are designed using MATLAB Simulink and tested. Cross talk and unity of signals generated from DPSK and OQPSK are examined using Cross-correlation and auto-correlation, respectively. In this research a proposed system included improvement in bit error rate (BER) of both systems in the additive white Gaussian Noise (AWGN) channel, by using the convolutional and block codes, by increasing the ratio of energy in the specular component to the energy in the diffuse component (k) and the diversity order BER in the fading channels will be improved in both systems.

Radio over fiber is becoming an increasingly important technology for the wireless market since it introduces a higher data transmission rate and large bandwidth. In this paper, we have compared OQPSK and DPSK bidirectional radio over fiber ROF systems, where an offset quadrature phase shift keying (OQPSK) or differential phase shift keying (DPSK) signals are used for down-link and an on-off keying (OOK) signal re-modulated for up-link. Several measurements were performed including Bit Error Rate (BER) curves for uplink and downlink, RSOA gain curve and noise figure with the variation of input power and temperature for each system.

Ultra-WideBand (UWB) communication systems are usually classified as any communication system whose instantaneous bandwidth is many times greater than the minimum bandwidth required to deliver information. UWB communication is fundamentally different from all other communication techniques because it employs extremely narrow Radio Frequency (RF) pulses to communicate between transmitters and receivers. Utilizing short-duration pulses as the building blocks for communications directly generates a very wide bandwidth and offers several advantages, such as large throughput, covertness, robustness to jamming, and coexistence with current radio services. UWB technology offers a promising solution to the RF spectrum drought by allowing new services to coexist with current radio systems with minimal or no interference. This coexistence brings the advantage of avoiding the expensive spectrum licensing fees that providers of all other radio services must pay. In this chapter, the application of UWB technology in military areas has been summarized. Its wider applications has been evaluated over several leading technology including military technology systems, government sectors, communication systems, surveillance systems, rescuing, logistics entertainment, public transport, and others.

The impact of electromagnetic noises from a PC on the bit error rate (BER) performance of a multiband orthogonal frequency division multiplexing (MB-OFDM) ultra wideband (UWB) communication system equipped on the PC is analyzed. The results of numerical simulation indicate that the PC noise consisting of the harmonic components of the PC clock causes considerable bit error rate (BER) degradation in the UWB system particularly those systems operated in high data-rate communication modes. It is also found that the frequency modulation of a PC clock signal, the so-called spread spectrum clocking (SSC), has no effect on mitigating BER degradation, although SSC techniques are commonly used in PCs for reducing the power spectral density of radiated noise. An interference mitigation scheme using Viterbi decoding with channel state information (CSI) is proposed on the basis of a novel receiver structure in which a reference PC clock signal is fed into the UWB receiver by the PC in order to accurately estimate the instantaneous frequency of interfering clock harmonics.

Recently, ultra wideband (UWB) communications have received increasing interest due to the high data rate achievable in a short distance. UWB communications can have strong interference mitigation capability. A multicarrier ultra wideband (MC-UWB) system has been introduced in (A.H. Tewfik, et al., (2002)) and (E. Saberinia, et al., (2002)). In the MC-UWB communication systems, multiple symbols are transmitted over different carriers simultaneously. The same symbol is retransmitted over different frequency bands by utilizing frequency hopping (FH) techniques. Frequency hopping and multicarrier technologies smooth the average power spectrum density of the system. In this paper, the expression of the power spectrum density of the MC-UWB system is derived. The radiated emission power for UWB communication systems is limited by the spectrum mask specified by wireless communication authorities, such as the federal communications commission (FCC) in United States. Different parameters in the MC-UWB system will have different effects on the power spectrum density and the maximal achievable data rate. The analysis of impact of parameters in the system on the power spectrum density will help the system designer select proper parameter set to fit in emission power regulation and the required data rate in practical UWB systems. Some examples of parameter selection are also given to illustrate the impact of different parameters in the system on the power spectrum density.

The fast and accurate timing acquisition of short ultra-wideband (UWB) pulse shapes and, implicitly, the required high sampling rates play a significant role in UWB receiver-structure design and create challenges for signal acquisition under non-ideal conditions. Furthermore, the pulse shape is seen as one of the key factors influencing the performance of UWB systems. While fulfilling the power-spectral-density emission requirements, the pulse shape must offer the highest detection capabilities with suitable levels of accuracy. In this paper, a fast acquisition system for UWB wireless multiple-access communications is presented. The proposed acquisition system has explicit design characteristics that offer greatly improved acquisition time, accuracy, and implementation cost, while also yielding very satisfactory performance at high noise and multi-user interference levels. In addition, the impact of pulse shapes on the performance of this fast acquisition system is evaluated to determine the most suitable pulse shape for its implementation.

In this paper, we consider SC-FDE schemes (Single Carrier with Frequency-Domain Equalization) employing OQPSK (Offset Quaternary Phase Shift Keying) signals with quasi-constant envelope. To allow high spectral efficiency, different frequency channels are separated by the symbol rate, regardless of their bandwidth (which is much higher than the symbol rate for quasi-constant envelope OQPSK signals), and we consider a multi-channel frequency-domain receiver with ACI (Adjacent Channel Interference) suppression. Our performance results show that it is possible to have high spectral efficiency with quasi-constant envelope OQPSK signals. This technique is especially interesting for the uplink of future broadband wireless systems since we can employ low-cost, grossly nonlinear power amplifiers at the mobile terminals and almost all signal processing is shifted to the base station.