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Fast Acquisition for Transmitted Reference Ultra-Wideband Systems with Channelized Receiver
Abstract
The acquisition performance of the channel-ized receiver for ultra-wideband (UWB) transmitted reference (TR) system is presented. Instead of sampling the received UWB signal with a single ADC as in a conventional fullband receiver, the channelized receiver digitizes with multiple slow ADCs, each of which samples a partial band of the UWB sig-nal. In this paper, we show that the frequency channelized receiver naturally leads to fast acquisition. In the channelized receiver, the reduced bandwidth in each subband widens the correlation peak, allowing the search increment to be corre-spondingly increased. Consequently, the search space in the channelized receiver is reduced, resulting in significantly faster acquisition time than in a fullband receiver.
... IR suffers from long synchronization times since the starting instant of the received pulse has to be estimated with high precision. Considerable effort is required to generate the pulses, and make them fit the spectral mask (the legal power spectral density as defined by the FCC) [13]. IR is appropriate in combination with a rake receiver, since the short duration of the pulses makes them highly resolvable in time, which also makes IR suitable for applications that require localization. ...
... We do not consider the factors that determine K in a real system, but model it as a constant. Example values for K are 4 [15] or 5 [13]. After the system has returned to coarse code acquisition, it may find the true alignment quickly, cycle through the entire code several times (in case of a low detection probability), or generate a new false alarm. ...
... If P d is close to 1, P fa much smaller than 1, and K 4 or 5, as in [13,15], we can see than the bit-normalized mean acquisition time is close to one-half the size of the search space q, a somewhat intuitive result. From Figure 3.4, we can see this is realistic when γ DSSS is higher than 10. ...
The aim of this thesis is to investigate whether noise-based frequency offset modulation (FODMA) is a viable candidate for a wideband radio link in an ultra-low-power wireless sensor network (WSN). Ultra-low-power wireless sensor networks are characterized by low duty-cycles and short data packets. Wideband radio transmission has many advantages such as robustness against narrowband fading and interference, and no requirement for a radio frequency license. It is therefore attractive to use a wideband transmission scheme in a WSN. There are different ways to achieve wideband transmission, and we will be looking at Direct Sequence Spread Spectrum (DSSS) and FODMA
In this thesis, a code division multiple access (CDMA) communication system for the low frequency (LF) channel is proposed, discussed and analyzed. This LF/CDMA scheme is similar to classical CDMA schemes in that K users share a channel by phase modulating their transmissions with signature sequences. Our LF/CDMA scheme is different in that each user's signature sequence set consists of M orthogonal sequences and thus log (2)M bits of information are transmitted by choosing among the signature sequences. Additionally, the users use r-phase modulation and our model includes an impulsive (non-Gaussian) noise source to model LF atmospheric noise. We derive a locally optimum (small signal) receiver structure for our LF/CDMA scheme. This receiver consists of a bandpass correlator followed by a sampler, a zero memory nonlinearity and M discrete time matched filter/correlators. We analyze the performance of this structure in combined multiple access, impulsive and Gaussian noise. When the noise is dominated by either its multiple access or Gaussian component, the receiver predominantly operates in the linear region of the nonlinearity and performance is similar to that of a linear receiver.
An oversampled frequency channelized receiver for UWB radio in a transmitted reference (TR) system is presented. Unlike previous work that assumes a white input noise, this paper includes the effects of the automatic gain controller (AGC) and the analog-to-digital converter (ADC) when large narrowband interference (NBI) is present. A detection method for the frequency channelized receiver when input noise is colored in the TR UWB system is proposed. The proposed receiver significantly outperforms the full band receiver.
To digitize the ultra-wideband (UWB) signal at its Nyquist rate, a frequency channelized receiver for UWB radio based on hybrid filter banks (HFB) is presented. Among the challenges of such receivers are the uncertainties of the analog analysis filters and the slow convergence speed. To overcome these problems, the channelized receiver operates slightly above the critical sampling rate. The proposed receiver, which is designed for use in transmitted reference (TR) systems, combines the synthesis filters and the matched-filter so that only the estimation of the combined response of the analysis filter and the propagation channel is necessary. The resulting convergence speed is comparable to an ideal full band receiver. In addition, all of the receiver functions are performed at the reduced subband sampling rate, relaxing the requirements on the digital circuitry.
The optimal receiver for an ultra-wideband transmitted reference (UWB TR) system in a single user multipath environment is derived, based on knowledge of channel properties. The performances of this optimal receiver and other crosscorrelation receivers are analyzed and compared. The usual crosscorrelation receiver which is often used in UWB TR systems is shown to be suboptimal. In addition, an UWB differential transmitted reference (UWB DTR) system is also proposed and its performance is evaluated.
Ultra wideband (UWB) radio is a new wireless technology that uses sub-nanosecond pulses to transmit information, resulting in a bandwidth greater than 1 GHz. The problem of synchronizing a receiver with the incoming signal grows in complexity as the signal bandwidth increases. This paper addresses coarse synchronization in UWB receivers. It analyzes how the design of the correlation process affects the time to achieve synchronization, highlighting the importance of the probability of false alarm in its performance.
Previously, the authors have invented and experimented with a new radio communications scheme called delay-hopped transmitted-reference (DHTR) radio. This technique can function either as an impulse radio, or can employ a more traditional spread-spectrum carrier such as broadband noise. The DHTR method is well-suited to short-range transmissions in a high multipath environment, and, in contrast to time-modulated impulse radio, is easy to synchronize at the receiver. Finally, DHTR receivers and transmitters are not highly complex, and can be implemented in a cost-effective way.
Efficient serial search strategies are presented and shown to reduce drastically the mean acquisition time for UWB signals in a dense multipath environment. Inherent in traditional serial search problems is the assumption that only a single bin or a small number of consecutive bins can properly terminate the search. This assumption leads to search strategies which tend to be linear in nature, e.g., a linear sweep of the uncertainty region. Because of the dense multipath channel present in most UWB systems, this assumption is invalid as seen by the channel's relatively large delay spread. A generalized analysis of various search algorithms is presented based on a Markov chain model of a simple single-dwell serial search. The results from this analysis reveal that the linear search has a considerably larger mean acquisition time than the more efficient search strategy termed the bit reversal search.
A channelized digital ultrawideband (UWB) receiver that efficiently samples the UWB signal at a fraction of the chip frequency is proposed. The received signal is channelized in the frequency domain by employing a bank of mixers and low-pass filters. After sampling at a much reduced frequency, digital synthesis filters optimally estimate the transmitted signals. The signal-to-noise ratio (SNR) of the proposed receiver has been solved and compared against an ideal conventional receiver, which is defined as a receiver that samples at the signal Nyquist rate. When finite resolution analog-to-digital converters (ADC) are employed in the presence of a large narrowband interferer, the proposed receiver significantly outperforms the ideal conventional receiver. For example, the SNR of the proposed receiver is as much as 20 dB higher than the ideal conventional receiver when a 4-bit ADC is used in the presence of a 50 dB (relative to the noise floor) brickwall narrowband interferer with a bandwidth of 15% of the chip frequency.
An all-digital CMOS ultra-wideband (UWB) pulse generator which complies with FCC regulations is presented. The proposed pulse generator generates a single UWB pulse satisfying FCC regulations without any filtering. The average power consumption of the whole circuit is 15.4 mW and 675 μW at the pulse repetition frequency of 500 and 1 MHz, respectively.
Ultrawideband (UWB) impulse radio is an emerging technology suitable for high-rate tactical wireless communications. One of the crucial challenges for a connecting station remains the initial code acquisition, in a hostile propagation environment (e.g., urban combat). In this paper, we address the coarse acquisition of pseudonoise (PN) codes and propose algorithms for speeding up the acquisition process and/or reducing the complexity of the acquisition algorithm itself. Also, in the case of energy detection, we show that the front-end sampling rate may be reduced. An in-depth analysis, supported by simulations in the presence of multipath is presented, and the results discussed.