Transmitted Reference Ultra-wideband Systems Research Articles

A Solution to the Non-Ideal Delay Line Problem in Transmitted Reference Pulse Cluster Schemes for UWB Communications

The conventional transmitted reference (TR) technique in ultra wide-band (UWB) communications has provided a springboard for a lot of studies, and a TR pulse cluster (TRPC) structure was proved to have robust performance. Most of TR and TRPC related studies hitherto are based on the assumption that the delay lines (DLs) in their schemes are ideal. However, the group delay ripple (GDR) of nonideal DLs triggered by practical imperfect factors at implementation causes an unexpected distortion in both TR and TRPC UWB systems, and there are few studies so far. In this article, we first analyze the impact of the GDR of nonideal DLs on the performance of TR and TRPC UWB systems. Then a new design solution for both TR and TRPC transceivers is proposed, where the GDR information of the nonideal DL at the receiver side is introduced into transmitter side. The performance of the new design solution is analyzed and simulation results prove the robustness and efficiency of this new design method in reducing the impaction caused by nonideal DLs. Moreover, the proposed design solution can also greatly relieve the high design requirement of DLs in both the transmitter and receiver side and therefore offer valuable insight for the practical transceiver design in both TR and TRPC related UWB systems.

Optimal Receiver Scheme for Transmitted-Reference Ultra-Wideband System in Coal Mine

An average Transmitted-Reference (TR) receiver scheme based on orthogonal codes is proposed for improving the bit error rate (BER) performance and the transmitting rate of Ultra-wideband (UWB) TR receiver systems in coal mine. Orthogonal codes are used for modulating the reference pulses and the data pulses in each frame of every bit. Since the orthogonality of the two codes, the inter-pulse interference (IPI) is greatly reduced. Then the decoding reference pulses and the data pulses are averaged in a frame, which decreases the noise in the reference pulses and the data pulses. Finally, I demonstrate this optimal receiver scheme by the simulation in the coal mine roadway ultra-wideband channel model. Detailed simulation experiments are presented to validate the effectiveness of this proposed method. The experimental results show that this method can not only efficiently reduce the noise interference in receiving signals, but also can provide higher transmission rate, which make UWB signal receiving in coal mines more accurately. Index Terms—Coal mine, Ultra-wideband, Transmitted- Reference receiver, bit error rate

CLOSED-FORM PDF FOR MULTIUSER TR-UWB SYSTEMS UNDER GAUSSIAN NOISE AND IMPULSIVE INTERFERENCE

In most existing transmitted-reference ultra-wideband (TR-UWB) communication systems, receivers use the standard Gaussian approximation (SGA) for multiuser interference (MUI). It is an assumption used in most conventional multiuser systems, where the MUI tends to a Gaussian process by the central limit theorem, and convergence is relatively fast with respect to the number of users. However, for TR-UWB systems which are developed for short-range applications, we have a small number of active users. In this case, significant performance degradation is found in TR-UWB receivers due to the impreciseness of SGA. In this paper, we show that the Middleton class-A model is a more appropriate statistical model for MUI modeling in TR-UWB systems than the often used SGA. A closed-form expression for the probability density function (PDF) of the TR-UWB system under MUI, Gaussian noise and impulsive alpha-stable interference is developed. All these analytical results are confirmed by numerical simulations. (17 References).

Designing delay lines based on group delay ripple range for transmitted-reference ultra-wideband systems

Designing a non-ideal delay line (DL) with phase distortion in a transmitted-reference ultra-wideband system with an autocorrelation receiver is a great technical challenge. Differing from the currently empirical design method of DL, a semi-analytic approach is proposed through Gaussian approximation of the expression for conditional bit error rate (BER), based on investigation on the degradation of average BER caused by a group delay ripple range (GDRR) over independent Nakagami-m fading channels. This GDRR-based design method can directly evaluate its effects on the system performance and determine the acceptable phase distortion level to trade-off the BER performance and system complexity.

Novel signaling and detection schemes for ultra-wideband transmitted-reference systems

Ultra-Wideband (UWB) impulse radio systems apply sub-nanosecond pulses and are able to resolve multipath due to their fine time-resolution capability. To take full advantage of the available signal energy, a Rake receiver with high hardware complexity is required. To remedy this difficulty, an improved scheme called the transmitted reference (TR) systems is proposed. TR systems do not require the complex task of channel estimation and render a simple receiver structure. However, the low-complexity detection in the conventional TR scheme is achieved at the cost of 50% energy/bandwidth disadvantage. This disadvantage has become the popular research focus of UWB TR systems. In this paper a performance-enhanced signal and detection scheme, namely the dual averaging N-bit differential transmitted reference/balanced transmitted reference (A2NDTR/BTR) system, is proposed to increase the data rate while still maintain the overall system performance. Numerical results suggest that this proposed scheme is able to achieve superior data rate while maintain the same or better bit error performance as compared with others.

Performance of Non-Polarized Noise Modulated Communications System in the Presence of Interference

The noise modulated non-polarized communication system, developed by us recently, is an ultra-wideband transmitted-reference system designed for secure interferencefree communications. By using ultra-wideband random noise to spread the signal and by using polarization diversity for transmitting the spread message and the reference signal, we make the transmitted signal appear totally featureless and noise-like. However, the system may encounter intentional and non-intentional interference since its operating bandwidth is very large. This paper derives analytical models to characterize system performance in partial-band jamming channels and channels containing narrowband interference. Models compare very well with simulations and results validate successful system operation under low signal-to-interference ratio conditions. Research also reveals that the center frequency of transmitted signal must be suitably protected to prevent link outage due to the presence of cross-interference terms. Since multipath acts as self-interference for communication systems, a new method which can improve system performance in multipath environments is also introduced in this paper.

IR-UWB Transmitted-Reference Systems With Partial Channel Knowledge: A Receiver Design Based on the Statistical Invariance Principle

This paper deals with detection algorithms for impulse-radio ultrawideband transmitted-reference systems. For binary modulation schemes, we propose a novel detector that operates on the partial autocorrelations of the received signal as computed over time intervals (bins) of size less than the symbol period. Assuming that the receiver has knowledge of the partial autocorrelations of the channel response over those bins, we derive the minimum error probability detector (MEPD). In doing so, we exploit some invariance properties of the detection problem under consideration. It turns out that the receiver adopting such a strategy is superior to a conventional TR system, the more so the smaller the bin size is. Also, we address the problem of estimating the partial autocorrelations of the channel response and propose a simple solution by exploiting a training sequence. The impact of the estimation errors on the receiver performance is shown to be marginal.

Data-Aided Timing Synchronization for FM-DCSK UWB Communication Systems

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Frequency-modulated differential chaos shift keying (FM-DCSK) ultrawideband (UWB) communication systems convey information by transmitting ultrashort chaotic pulses (in the nanosecond scale). Since such pulses are ultrashort, timing offset may severely degrade the bit error rate (BER) performance. In this paper, a fast data-aided timing synchronization algorithm with low complexity is proposed for FM-DCSK UWB systems, which capitalizes on the excellent correlation characteristic of chaotic signals. Simulation results show that the BER performance of such systems is fairly close to that of perfect timing thanks to the proposed new algorithm. Moreover, the new algorithm requires less synchronization searching time and lower computational complexity than the conventional one for transmitted reference UWB systems existing in the current literature. </para>

Transmit-reference UWB system based on m-sequence codes

In this article, a novel transmit-reference (TR) signaling scheme is proposed for ultra-wideband (UWB) system, where by invoking m-sequence codes the reference and data pulses can be transmitted side by side to increase the data rate. This structure enables demodulation with a simple and practical autocorrelation receiver despite existence of severe inter-pulse interference (IPI). To evaluate detection performance of the new designs, closed-form expression for bit error probability (BRP) is theoretically derived and simulation results confirm the analytical results. In addition, the proposed scheme can be extended to M-ary systems to further improve the data rate and power efficiency.

An Improved Recursive Transmitted Reference UWB System

TR-UWB (Transmitted Reference-Ultra Wide Band) systems have low system complexity since they transmit data with the corresponding reference signals and demodulate the data through correlation using these received signals. However, the BER (Bit Error Rate) performance in the conventional TR-UWB systems is sensitive to the SNR (Signal-to-Noise Ratio) of the reference templates used in the correlator. We propose an improved recursive transceiver structure that effectively minimizes the BER for TR-UWB systems by increasing the SNR of reference templates.

Multiuser performance of M-ary orthogonal coded/balanced UWB transmitted-reference systems

A tractable and compact closed-form expression on the channel-averaged signal-to-interference-plus-noise ratio (SINR) is derived for M-ary orthogonal coded/balanced transmitted-reference (BTR) systems, taking into consideration both inter-pulse interference (IPI) and multiple-access interference (MAI) in dense multipath ultra-wideband (UWB) channels. The UWB channel here is a realistic and standard one with lognormal channel gain distribution and double independent Poisson arrival distribution of cluster and ray. Hence, the analytical framework developed here can be applied to typical UWB channel models, especially considering the channel sparseness and cluster overlapping observed in realistic UWB channels. Based on the channel-averaged SINR, the effect of inter-pulse distance (between the reference and data pulses in BTR) on the multiuser performance is fully investigated. A proper selection of user-specific inter-pulse distances in multiuser scenario is then determined to maximize the user capacity for a given UWB channel.

Weighted high data rate ultra wideband transmitted-reference system in dense multipath fading channels

A novel weighted high data rate single-user ultra-wideband transmitted-reference (UWB-TR) system is proposed and its performance in log-normal slow fading channels is investigated, which has not been addressed before. This system employs a novel signalling scheme, which provides a nearly inter-symbol interference (ISI) free-channel response at the receiver and eliminates the need for equalisation. It also enhances the reference pulse quality by employing optimum power allocation. The performance of the proposed system is compared with that of the differential transmitted-reference (DTR) system in IEEE 802.15.3a Channel Model 1 (CM1) both analytically and via simulations by taking into account noise, log-normal slow fading, inter-path/pulse interference (IPI) and ISI. Both analytical and simulation results show that our system significantly outperforms the DTR one. It is shown that the proposed method is robust against small changes in both weighting coefficients and integration interval, whereas the UWB-DTR scheme is too susceptible to such changes in the integration interval.

Multiple-Antenna Receiving and Frequency Domain Equalization in Transmitted-Reference UWB Systems

A multiple-antenna receiving and combining scheme is proposed for high-data-rate transmitted-reference (TR) Ultra-Wideband (UWB) systems. The nonlinearity of the inter-symbol interference (IST) model is alleviated via simple antenna combining. Under the simplified ISI model, frequency domain equalization (FDE) is adopted and greatly reduces the complexity of the equalizer. A simple estimation algorithm for the simplified ISI model is presented. Simulation results demonstrate that compared to the single receive antenna scheme, the proposed method can obtain a significant diversity gain and eliminate the BER floor effect. Moreover, compared to the complex second-order time domain equalizer, FDE showed better performance robustness in the case of imperfect model estimation.

M-ary orthogonal coded/balanced ultra-wideband transmitted-reference systems in multipath

A new M-ary orthogonal coded signaling is introduced to avoid the inter-frame interference that is especially detrimental to realizing high rate ultra-wideband (UWB) transmitted-reference (TR) systems. To further increase the information rate, the inter-pulse interference by an overlap of multipath-delayed pulses is controlled by integrating the signaling and a pair of balanced matched Alters in a joint manner, so as to permit a shorter time delay between the reference and data pulses in TR systems. To evaluate an achievable information rate increase relative to conventional TR, the symbol error probability (SEP) is theoretically derived for the proposed M-ary orthogonal coded/balanced TR system, considering the realistic IEEE standard UWB channel models. In addition, we consider the issue of receiver complexity and present two alternative low- complexity receiver implementations for the proposed TR system.

Analysis of Channel-Averaged SINR for Indoor UWB Rake and Transmitted Reference Systems

In this paper, we derive a closed-form expression for channel-averaged signal-to-interference-plus-noise ratio (SINR) for ultra-wideband (UWB) Rake receiving system in an indoor multiuser communication scenario, given that the interference level is fluctuating due to asynchronous transmissions among users. The indoor wireless channel model adopted here is a standard one, recently released by IEEE 802.15 study group 3a . We propose a theoretical framework to derive the channel-averaged SINR considering the lognormal channel gain distribution and the double independent Poisson arrival distribution of cluster and ray, and show that our analysis is well coincident with the simulation results. With this framework, we demonstrate that our analysis can be applied to theoretically determine the optimum integration interval for a UWB transmitted reference system, even in a multiuser scenario.

Analysis of the Channel Energy Capture in Ultra-Wideband Transmitted Reference Systems

In this letter, we analyze the expected value of the channel energy capture as a function of the integration interval of the correlator in a transmitted reference system. A modified Saleh-Valenzuela channel model is employed. We observe that for the system specifications (such as channel model, data rate, and signal-to-noise ratio) considered here, an integration interval that captures approximately 84%-89% of the expected value of the channel energy provides a bit-error probability close to the minimum one.

Transmitted-reference UWB systems using weighted autocorrelation receivers

The application of a fractionally sampled autocorrelation receiver (AcR) is proposed for the demodulation of transmitted-reference (TR) signals, to simplify synchronization and suppress nonlinear intra-symbol-interference and inter-symbol-interference (ISI) by means of linear weighting. A system model is presented for the TR system and its statistical properties are derived, taking into account both noise and ISI. The weighting coefficients are computed in closed form and a method is presented to compute the bit error probability. Multiple ultra-wideband TR systems are compared, which differ with respect to correlation lag, bandwidth, sampling rate, and bit rate. In the absence of ISI, a 250-MHz bandwidth system outperforms the larger bandwidth systems. On the other hand, the larger bandwidth systems are found to be inherently less sensitive to ISI. Furthermore, increasing the fractional sampling ratio is shown to enable the AcR to equalize more (nonlinear) ISI.