Conventional Transmitted Reference Research Articles

A Transmitted Reference Pulse Cluster Averaging UWB Receiver

The transmitted reference pulse cluster (TRPC) structure for ultrawideband communications enables a more robust autocorrelation receiver (AcR) than a conventional transmitted reference (TR) scheme. In this paper, to further improve the performance of TRPC AcR, we propose a TRPC averaging (TRPC-A) AcR by using a TRPC-A method, which is similar but different from the pulse averaging method used in a conventional TR scheme. The proposed receiver structure is designed in both analog and digital methods, and their implementation complexities are explored. Our analytical and simulation results show that the proposed receiver can greatly improve the performance over the original TRPC receiver. What is more, the required additional implementation complexity of the proposed TRPC-A receiver added to the original TRPC AcR is much less than that of the averaging TR AcR added to conventional TR AcR due to the TRPC signaling characteristics. Therefore, from a practical point of view, the designed TRPC-A AcR is considered as a highly recommended practice, particularly in multiuser access environments.

Method for Bandwidth Efficiency Increasing of M-ary PPM Transmitted-Reference UWB Communication Systems

One of the main drawbacks of conventional transmitted reference (TR) ultra-wideband systems is the fact that time delay between the reference and the data pulse has to be at least equal to channel delay spread, in order to avoid inter-pulse interference (IPI). This requirement drastically limits the achievable data rate of conventional TR systems based on M-ary pulse position modulation (PPM). In this paper, the new method for M-ary TR PPM scheme bandwidth efficiency increasing is proposed. In the proposed method the orthogonal codes are used such that only the pulses which can cause IPI are coded. Usage of such type of coding allows the reduction of time delay between the reference and the data pulse, whereas IPI is avoided. The proposed method achieves higher bandwidth efficiency than the conventional TR PPM method for the similar BEP performance level. Furthermore, the results show that an additional increase in bandwidth efficiency can be achieved by using higher modulation levels. Additionally, the analysis on tradeoffs between the BEP performance, bandwidth reduction and system costs is given in this paper.

Performance of transmitted reference pulse cluster ultra‐wideband systems with forward error correction

SUMMARYRecently, an improved transmitted reference (TR) signaling scheme, referred to as transmitted reference pulse cluster (TRPC), was proposed for low‐rate ultra‐wideband (UWB) communications. Compared with conventional TR, TRPC has a more compact and uniform spacing for the reference and data pulses and therefore addresses the implementation problems posed by the long delay line requirement, as well as provides better bit error rate (BER) performance. In this paper, a TRPC‐UWB system, which includes practical forward error correction (FEC) coding such as that specified in the IEEE 802.15.4a standard, as well as more powerful convolutional codes, is developed. A performance analysis, which highlights the importance of selecting appropriate FEC codes, is presented. Results show that with a suitable FEC code, the TRPC‐UWB system is a promising candidate for low‐rate wireless personal area networks. Copyright © 2012 John Wiley & Sons, Ltd.

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 analysis of high rate weighted-TR UWB system in the presence of inter-block and multiuser interferences

Abstract Recently, a novel single-user weighted transmitted-reference (WTR) system has been proposed for high rate ultra-wideband (UWB) communications. The WTR system can achieve a superior performance in high data rates and is also robust to variations of both weight coefficient and integration interval. In this paper, a multi-access (MA) scheme is proposed for the WTR system and its performance assuming perfect power control at the receiver is evaluated over dense multipath channels at 114 Mbps in the presence of inter-block interference (IBI) for the first time. Closed-form representation of both synchronous and asynchronous MA scenarios are derived and validated by simulations, in the presence of noise and all interfering terms for the first time. Interfering terms are inter-path/pulse interference (IPaI/IPI), inter-symbol interference (ISI), and IBI. It is shown that the proposed MA scheme can significantly improve the system performance in multi-user scenario. Moreover, the single user performance of the WTR system is compared to those of a full-Rake receiver, conventional transmitted-reference (CTR), and differential transmitted-reference (DTR) through theoretical analysis and computer simulations by averaging over 100 realizations of IEEE 802.15.3a Channel Model 1 (CM1) including slow fading in the presence of noise and all aforementioned interfering terms.

Downlink multiple access schemes for transmitted reference pulse cluster UWB systems

AbstractTransmitted reference pulse cluster (TRPC) signaling was recently proposed for low data rate ultra‐wideband communications. Compared with the conventional transmitted reference (TR), TRPC has a more compact and uniform spacing for the reference and data pulses and therefore solves the implementation problem posed by the long delay line requirement in the conventional TR. In this paper, downlink multiple access issue is further investigated for TRPC systems. According to the TRPC signaling structure, both code division multiple access (CDMA) and time division multiple access (TDMA) methods are discussed. Theoretical analysis and simulation results show that TDMA outperforms CDMA in both bit error rate performance and throughput. Copyright © 2010 John Wiley & Sons, Ltd.

Hybrid coherent and frequency-shifted-reference ultrawideband radio

Ultrawideband communications often occur in heterogeneous networks where different receivers have different complexity and energy consumption requirements. In this case it is desirable to have a modulation scheme that works well with coherent receivers as well as simpler receivers, namely transmitted-reference (TR) receivers. In particular, we consider a TR scheme that employs slightly frequency-shifted-reference (FSR) signals [D.L. Goeckel, Q. Zhang, Slightly frequency-shifted-reference ultrawideband (UWB) radio, IEEE Trans. Commun. (2007)] and thus avoids one of the main drawbacks of conventional TR schemes, namely the need to implement a delay line. We propose and analyze a modulation scheme that works well with both FSR receivers (where it has at least the same performance as conventional TR modulation), and coherent receivers. Coherent receivers receiving conventional TR modulation suffer a 3 dB penalty, because they cannot make use of the energy invested into the reference pulse. Our proposed scheme avoids this drawback by including a data preprocessor that can be viewed as a nonsystematic rate- 1 / 2 convolutional code. These codes give 1.5 dB gain over our previously proposed constraint-length-two systematic codes at a BER of 1 × 1 0 − 4 in 802.15.3a CM4 multipath fading channels. We also develop a sliding-window based scheme to derive the template waveform that is needed for coherent rake receivers. This scheme exploits the data preprocessor structure and flexibly uses the received signal over a certain window. The distortion to the self-derived template waveform is a decreasing function of the window length; in the extreme but unrealistic case of a very long window length in a slowly fading channel, the self-derived template waveform is noiseless (i.e., the ideal template without distortion).

A New Transmitted Reference Pulse Cluster System for UWB Communications

To meet the implementation constraint posed by ultra- wideband (UWB) delay lines, a new transmitted reference pulse cluster (TRPC) structure is proposed where a group of reference and data pulses with short uniform spacing is used for transmission. This structure enables a simple, robust, and practical autocorrelation detector to be implemented in the receiver. It overcomes the major hurdle to the practical implementation of conventional transmitted reference (TR) systems, i.e., the long-wideband-delay-line requirement. TRPC is also compatible with the signal format proposed within the IEEE 802.15.4a Working Group for coherent and noncoherent systems. The performance of the proposed TRPC receiver and noncoherent pulse-position modulation (NC-PPM) with energy detection are analyzed and compared. Simulation results show that TRPC outperforms the conventional TR, NC-PPM, the recently proposed dual-pulse scheme, and the frequency-shifted reference system. In particular, it achieves power saving over NC-PPM by about 1.3-1.9 dB for IEEE 802.15.4a channel model 1 and 1.3-2.3 dB for channel model 8.

Multiple Access Performance of Balanced UWB Transmitted-Reference Systems in Multipath

Recently, a novel balanced transmitted-reference (TR) system has been proposed for UWB communications. This TR system is capable of properly eliminating the inter-pulse interference (IPI) between the reference and data pulses in a single user multipath environment. In this paper, we investigate its multiple access (MA) performance by evaluating the second- order moments of noise and interference terms. The analytical framework developed here can also be used to accurately evaluate the MA performance of conventional TR system. It is shown that the proposed balanced TR system can achieve comparable MA capacity as conventional TR, while operating at higher information rate. On the other hand, given a target information rate, the balanced TR system in conjunction with <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -ary signaling offers higher MA capacity than conventional TR system. The performance results suggest there exists a trade-off between the inter-pulse distance, thus the achievable information rate, and the MA capacity.

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.

A Novel Modulation Diversity Assisted Ultrawideband Communication System

In this paper, a novel modulation diversity assisted (MDA) ultrawideband (UWB) communication system is proposed. Pulse position modulation and pulse amplitude modulation are applied to successive transmitted pulses alternately. The resulting modulation diversity helps to overcome channel estimation difficulties in typical UWB channels and permits low complexity receiver design. If every two consecutive pulses are grouped together, some connections with a transmitted reference (TR) system are demonstrated. But significant advantages of the proposed system are observed in smooth spectrum and increased data rate. Utilizing statistical properties of the modulated signals and inherent diversity, different receivers are designed for such a system. A conceptual receiver performs symbol detection using neighboring received signal to construct the template, while an advanced receiver uses a block of received signals to obtain a better template. The advanced receiver may continue to improve the template as ongoing detected symbols are available. A maximum likelihood estimator is also derived as a performance benchmark. The conceptual receiver shows slightly better performance than a conventional TR receiver while the advanced receiver shows comparable performance of the receiver using a maximum likelihood template estimator. Performance of the advanced receiver is studied both analytically and numerically. In a case of severe multipath channel distortion that results in interference between received signals from consecutive transmitted pulses, a corresponding template estimator and different receivers are also presented with detection performance numerically studied.

Ultra-Wideband Communications using Hybrid Matched Filter Correlation Receivers

Transmitted-reference (TR) schemes for time-hopping impulse radio (TH-IR) ultra-wideband (UWB) communications allow the use of simple receiver structures that are able to combine energy from different multipath components without channel estimation. A conventional TR receiver consists of a simple delay-and-multiply operation combined with an integrator. On the downside, it shows a performance loss due to non-linear operations on noise terms (generation of noise-noise cross-terms) when forming the decision variable. This paper describes a hybrid receiver structure for UWB communications that reduces these noise-noise cross-terms by first performing a "matched filtering" operation matched to the time-hopping sequence of pulses. The receiver retains most of the simplicity of the conventional TR receiver, but requires an analog correlator for the time-hopping sequence of pulses. The performance the proposed receiver is analyzed in both AWGN and multipath channels. For the AWGN case, the exact expression for the bit error probability is obtained, which takes into account the nonGaussian nature of the noise-noise cross-terms arising in the correlators. For the multipath case, both inter-frame interference and multipath interference from the reference pulse to the data pulse are considered, and approximate closed-form expressions are derived based on the assumption of a large integration interval. Also approximate criteria for optimal integration interval are obtained for the best receiver performance. Simulation studies are presented to analyze the performance of the proposed receiver structure and to confirm the theoretical analysis

Multiuser transmitted reference ultra-wideband communication systems

A conventional transmitted reference (TR) modulation scheme is an effective means to combat severe multipath distortion in an ultra-wideband (UWB) system, significantly relaxing the equalization requirements. However, it suffers from multiple-access interference and a data rate loss. In this paper, we propose a multiuser TR scheme to extend TR modulation to the multiuser case, while almost doubling the data rate by allowing arbitrarily small spacing of pulse pairs. The proposed scheme assigns a pair of pseudorandom sequences to each user to enable multiple access, modulating the amplitude of data and reference pulses, respectively. A waveform template is first estimated, followed by data demodulation. A time-hopping code can be employed to further minimize the effect of signal collisions. The method is appropriate for both pulse amplitude modulation and pulse position modulation. Waveform estimation and bit-error rate analysis are provided, and confirmed with simulations. Substantial detection improvements over conventional TR detectors are observed.