Pulse position amplitude modulation for time-hopping multiple access UWB communications

Modulation techniques have attracted increasing attention in optical wireless communications. Basic schemes such as on off keying (OOK), pulse amplitude modulation (PAM) and pulse position modulation (PPM) have been validated as suitable for the optical wireless channel. This paper starts from the analysis of these three modulation schemes in terms of their power and bandwidth requirements. As a result, a new tunable hybrid modulation technique is proposed. The proposed modulation scheme takes the real time channel conditions into account, which is different from other schemes. By employing amplitude and position modulation selectively, a guaranteed system performance can be secured, without compromising power and bandwidth efficiency. This is also a new approach to realize reliable optical wireless links.

ABSTRACTA timing correction approach is proposed in this article to improve the performance of high-speed serial data link involving pulse position modulation (PPM) and pulse amplitude modulation (PAM) techniques. The proposed technique corrects the timing error that arises from combining the PAM approach with the PPM approach, which allows transmitting more bits and hence achieving higher data rate for the designed serial link. The proposed technique uses the recovered AM bits to adapt the reference voltage of the comparator circuit at the receiver side in order to correct the jitter results from combining the time modulation with the amplitude modulation. A 5-bit 4-Gb/s serial data link that involves PAM and PPM has been designed and simulated using the proposed technique in 130 nm CMOS technology using 800 MHz as an input clock signal. The simulation results indicate that when combining AM and PPM techniques, the total number of the transmitted bits can be increased using the proposed technique. The total power consumption of the proposed link is less than 84 mW. A performance comparison between the proposed link and other serial links has been carried out that indicates an improved performance for serial links involving the proposed technique.

In this paper we test and compare different modulation strategies to be used in ultra-wide band (IR-UWB) communications. In the UWB systems of interest in this work the information is conveyed by short-duration pulses; the modulation scheme determine how the data stream is to be transmitted over those pulses. Here we test and compare several schemes based on three types of modulation. The first type is the pulse position modulation (PPM), which includes a pulse delay according to the data to be transmitted. The second is the recently proposed pulse shape modulation (PSM), that uses a different pulse shape to each data. The third one, proposed in this paper, is an M-ary modulation scheme that combines the shape and amplitude of the pulse to transmit the data, which we call pulse amplitude and shape modulation (PASM). Other M-ary schemes are tested, including the recent orthogonal M-ary PSM, based on orthogonal Hermite functions, and a new quaternary PPM scheme, also proposed here. All schemes are tested over an AWG channel.

This paper investigates the parameters of time-hopping impulse radio ultra wide band (TH-IR-UWB). At a given spreading factor and a given system load, a trade-off has to be done in the choice of the frame length and the repetition factor. This trade-off lays on the condition of validity of the standard Gaussian approximation for multi user interferences (MUI). This study concerns both pulse amplitude modulation and pulse position modulation and may be applied to UWB networks with high density of users and low data rates like ad-hoc sensor networks, as well as networks with higher data rate and small number of users

Ultra wideband (UWB) radio is a promising technology for short range wireless communications. It can be used for both high rate and low rate transmissions. High data rate can be achieved by using multiband (MB)-UWB approach whereas low data rate with robust system performance can be obtained by employing time hopping (TH)-UWB radio systems Majhi et al. (2006); Win & Scholtz (1998a). Nowadays, applications of UWB are spreading to various fields such as vehicle communications, wireless sensor networks, ad hoc wireless networks, and controller area networks. The most of the systems require low to moderate (1 kbs-100 mbs) data rates with an acceptable implementation cost. However, due to the presence of fast Fourier transform (FFT) and inverse FFT (IFFT), MB-UWB may not be a cost effective procedure for low data rate systems. Therefore, one needs an efficient system which adaptively changes the data rate from low to moderate with robust system performance. TH-UWB with OOK-PSM modulation provides low data rate with robust system performance Majhi, Madhukumar, Premkumar & Richardson (2008). However, it is possible to scale the TH-UWB radio system for low to moderate data rates by incorporating higher level modulation schemes with an adaptive method. For TH-UWB systems, various M-ary modulation schemes such as pulse positionmodulation (PPM), pulse amplitude modulation (PAM), pulse shape modulation (PSM), and their combined forms have been proposed to improve data rates and system performance with low complexities Bin et al. (2003); Durisi & Benedetto (2003); Ghavami et al. (2002); Michell et al. (2003); Usuda et al. (2004). However, due to the increase of inter symbol interference (ISI) in the presence of multipath channel, M-ary PPM or M-ary orthogonal PPM (OPPM) are not effective for TH-UWB systems with RAKE reception when M is high Foerster (2003); Win & Scholtz (1998b). High-level M-ary PAM is rarely used in short range and low power consumption communications systems Guvenc & Arslan (2003). This is because that the Euclidian distances between constellations become small with increase in M. Due to its robustness against ISI and multiple access interference (MAI), pulse-based modulation such as PSM has become an interesting research topic in TH-UWB, direct sequence UWB (DS-UWB) and transmitted referenceUWB (TR-UWB) radio systemsChu M de Abrue et al. (2003); Gezici et al. (2006); Hwang et al. (2007); Kim & Womack (2007); Parr et al. (2003). However, high-level M-ary PSM cannot be used due to the limited auto correlation properties 2

The PPM (Pulse Position Modulation) is commonly used in Free Space Optic (FSO) systems owing to its power efficiency, but it shows a rapid decline in spectral efficiency with increase in the power efficiency and moderate data rate. In order to improve these two parameters, we present a modified modulation scheme of the existing PPM, on the basis of PPM, PAM (Pulse Amplitude Modulation) and PWM (Pulse Width Modulation). This modified version called DAWPPM (Dual Amplitude-Width PPM). The average power requirements, bandwidth efficiency and normalized data rate are studied after introducing symbol structure. The proposed scheme shows an improvement in terms of data rate and bandwidth efficiency, and when in come to power efficiency it shows lower efficiency compared to PPM. We present theoretical expressions of data rate, spectral efficiency, and normalized power requirements, and we present comparison results to PPM modulation scheme. Index Terms—PPM, PAM, PWM, DAWPPM, data rate, power requirements and bandwidth efficiency.

To increase the transmission data rate, we propose to use M-ary pulse position modulation (PPM) for transmitted reference (TR) ultra-wideband (UWB) systems. The performance of TR UWB systems employing M-ary PPM is investigated in multipath, multiuser environments without centralized power control. The interference from high-power users is shown to significantly degrade the performance of TR UWB systems using M-ary PPM. Chip discrimination is used to mitigate the detrimental effect of high-power users. Theoretical analysis on the performance of M-ary PPM applied to TR UWB systems is derived. A tight upper bound for the symbol error probability is obtained. Analysis and numerical results show that TR UWB systems with M-ary PPM using chip discrimination is robust against high-power interfering users in wireless networks where centralized power control is infeasible, such as ad-hoc networks.

In this paper, a coded M-ary pulse position modulation (PPM) scheme for transmitted reference ultra-wideband (TR-UWB) systems is proposed. In conventional M-ary PPM TR-UWB scheme, modulation level M is defined only with a number of possible pulse positions Z. So, Z radio frequency (RF) wideband delay lines are required in order to map data bits into the proper pulse position, which makes such system very impractical to implement when the current CMOS technology is used. In the proposed scheme the number of required delay lines is reduced by mapping data bits in both, pulse position and K different orthogonal codes on frame level of the signal, producing a modulation level of M = KZ. To evaluate the performances of the proposed coded M-ary PPM scheme, the analytical model for realistic IEEE standard UWB channel models is developed. The performances of the proposed scheme are compared with these of the conventional M-ary PPM scheme for the same modulation level M. The results show that the proposed coded M-ary PPM scheme achieves approximately the same bit error probability (BEP), higher data rate and higher bandwidth efficiency, while the hardware complexity is lower in terms of number of required RF delay lines. However, by increasing the number of used orthogonal codes the minimum number of frames per one information symbol rises and consequently the maximum achievable data rate is limited. Thus the trade-off between the number of orthogonal codes and target data rate should be made. DOI: http://dx.doi.org/10.5755/j01.eee.20.10.6797

In this paper, we propose a novel cooperation strategy for Impulse-Radio Ultra-Wideband (IR-UWB) communication systems with binary Pulse Position Modulation (PPM). Unlike Decode-and-Forward (DF) strategies where a group of PPM symbols, or at least one PPM symbol, is decoded and forwarded to the receiver, the proposed scheme inspects the PPM slots in a sequential manner. In particular, only the UWB pulses that are received at the relay with a sufficient level of fidelity are retransmitted in subsequent PPM slots. This technique limits cooperation to only one symbol duration while avoiding any form of joint decoding at the relay and destination nodes. The proposed scheme corresponds to a selective-relaying protocol where the relay imposes a certain level of selectivity on the symbols to be retransmitted. The error performance of the proposed scheme is evaluated theoretically. Based on this performance analysis, we derived an optimal pulse selection strategy at the relay.

Following FCC approval of ultra-wide band (UWB) radio rules for commercial applications in 2002, a UWB radio physical layer standard is currently under development. Although the UWB transmitting UWB band are spelled out by the FCC, neither UWB signal forms nor modulation schemes are defined by the regulations, stated in ref. [1]. This paper presents the models of two types of impulse radio UWB modulation systems and their simulation performance. They are direct sequence UWB (DS-UWB) and time hopping UWB (TH-UWB). Unique ways of modulating and positioning the impulses, as in transmitted-reference delay (TRD) modulation and pulse-position modulation (PPM) , can result in the simple UWB radio architectures. Systems of TRD for DS-UWB and PPM for TH-UWB are simulated under the same UWB working data rate and under the same AWGN (additive white Gaussian noise) channel conditions. The simulation shows that DS-TRD system presents superior performance over PPM-TH system, which is shown in the comparison cha...

The performance of asynchronous time-hopping ultra-wideband (TH-UWB) multiple access spread spectrum is analytically investigated in a UWB realistic multipath channel and in the presence of narrowband interference (NBI). In particular, an interference suppression receiver for TH-UWB wireless systems is proposed. It consists of selecting the first strongest multipath components using an appropriate Rake receiver with the path diversity combining being based on the minimum mean square error criterion. Pulse position modulation and pulse amplitude modulation schemes are considered. The expressions of the signal-to-interference and noise ratio at the output of the selective Rake combiner, the system multi-access data rate as well as the conditional bit error rate are also derived. The impact of different parameters, such as the number of selected dominant paths, the NBI power as well as the time hopping sequence code on the system performance are studied. Results reveal that the proposed receiver can almost completely eliminate the effect of NBI.

This paper investigates energy efficient methods of increasing data rate for m-ary pulse position modulation (PPM) of impulse-based ultra wideband (UWB) systems in a multipath environment. The data rate of m-ary PPM can be increased by decreasing the pulse repetition interval (PRI) and/or increasing the number of bits transmitted per symbol. However, increasing the data rate beyond a certain limit degrades energy efficiency in a multipath environment. We investigate the relationship between data rate and energy efficiency and seek suitable bounds on the number of bits per symbol and the PRI.

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.

We have proposed a variable-rate multi-pulse pulse position modulation, for visible light communication system based on white LEDs, to achieve joint brightness control and data transmission. Conventionally either pulse width modulation or pulse amplitude modulation is used for brightness control and some variants of pulse position modulation are employed for data transmission. The need for using two different modulation schemes to meet the objectives make the system design complex. Our proposed approach eliminates the use of either pulse width modulation or pulse amplitude modulation and still achieves brightness control. For the proposed modulation, achievable resolution of the brightness control depends on the number of slots used for one information symbol transfer and the resulting code-rate for data transmission depends on the number of pulsed slots per symbol. Simple iterative algorithms for encoder and decoder implementation are developed. Numerical results for performance evaluation show the effectiveness of our proposed approach. We have also obtained experimental results to analyze the effect of brightness-index on symbol error rate.

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