Showing papers on "Pulse-position modulation published in 2007"

A 47pJ/pulse 3.1-to-5GHz All-Digital UWB Transmitter in 90nm CMOS

Abstract: An all-digital UWB TX is presented that generates PPM pulses with a center frequency tunable to 3 channels in the 3.1-to-5GHz band without the use of an RF oscillator. A delay-based spectral scrambling technique is proposed that exploits the digital architecture. The circuit achieves 47pJ/b at a data rate of 10Mb/s.

Channel Capacity of IM/DD Optical Communication Systems and of ACO-OFDM

Abstract: In this paper we investigate the channel capacity of intensity modulated direct detection (IM/DD) wireless optical communication systems for an AWGN channel with a limit on the average transmitted optical power. It has recently been shown that asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) is more efficient in terms of optical power than conventional optical modulation techniques such as pulse position modulation (PPM). When ACO-OFDM is used, the transmitted signal has a clipped Gaussian probability distribution. We calculate the channel capacity for systems using transmitted signals with exponential and clipped Gaussian distributions, and for an ACO-OFDM system. For practical signal to noise ratios, ACO-OFDM has a slightly lower capacity than the other distributions, due to the correlation between samples caused by the ACO-OFDM modulation process. ACO-OFDM has many practical advantages including its tolerance to multipath distortion. This paper shows that it also makes efficient use of the available power and bandwidth.

An Introduction to Adaptive QAM Modulation Schemes for Known and Predicted Channels Relatively simple Quadrature Amplitude Modulation (QAM) systems illustrate the advantages, in error performance and spectral efficiency, of adaptive modulation over fixed modulation.

Abstract: A major disadvantage with fixed modulation (nonadaptive) on channels with varying signal-to-noise ratio (SNR) is that the bit-error-rate (BER) probability performance is changing with the channel quality. Most applications require a certain maximum BER and there is normally no reason for providing a smaller BER than required. An adaptive modulation scheme, on the contrary, can be designed to have a BER which is constant for all channel SNRs. The spectral efficiency of the fixed modulation is constant, while it, in general, will increase with increasing channel SNRs for the adaptive scheme. This in effect means that the average spectral efficiency of the adaptive scheme is improved, while at the same time the BER is better suited to the requirement of the application. Thus, the adaptive link becomes much more efficient for data transmis- sion. The major disadvantage is that the transmitter needs to know the channel SNR such that the best suitable modulation is chosen and the receiver must be informed on the used modulation in order to decode the information. This leads to an increased overhead in the system as compared with a fixed modulation system. In this paper, we introduce adaptive modulation systems by presenting some of the simpler adaptive quadrature amplitude modulation schemes and their performance for both perfectly known and predicted channels.

Energy-Detection UWB Receivers with Multiple Energy Measurements

Abstract: This paper deals with a novel energy-detection receiver for ultra-wideband systems operating in dense multi-path environments. For binary PPM modulation we propose a detection scheme that operates on signal energy measurements taken on small fractions (bins) of the symbol period. Assuming that the fractional energies of the channel response over those bins can be estimated in some way, we look for the decision strategy that minimizes the error probability. This leads us to a receiver structure that generalizes the conventional energy- detection scheme. The new strategy turns out to be superior to the conventional strategy and its performance is found to improve as the bin size decreases. A simple method is proposed to estimate the fractional energies of the channel response exploiting a training sequence. The impact of the estimation errors on the receiver performance is shown to be marginal.

Using LDPC-Coded Modulation and Coherent Detection for Ultra Highspeed Optical Transmission

Abstract: We propose the coded modulation schemes for ultrahigh-speed transmission (100 Gb/s and above) by using commercially available components operating at 40 gigasymbols/s. The bit-interleaved coded modulation in combination with the low-density parity-check codes that are used as component codes has been applied. The modulation is based on either M-ary quadrature-amplitude modulation or M-ary phase-shift keying. bits are mapped into the corresponding signal constellation point using either Gray or natural mapping. The coherent detection scheme has been found to outperform the direct detection one and to provide an additional margin much needed for longer transmission distances or for application in an all-optical network scenario.

Spectrally Efficient UWB Pulse Shaping With Application in Orthogonal PSM

Abstract: In this paper, we present a method to obtain a set of orthogonal pulses to be used in pulse-shape modulation (PSM) for ultra-wideband communications. The pulses are built as linear combinations of Hermite functions, which are shown to have unique advantageous features. Mathematical restrictions of orthogonality and spectral efficiency are introduced as guidelines to a fully explained search procedure to find the best set of pulses. Additionally, this procedure is adapted and used to find a single FCC-compliant pulse shape. A quaternary PSM scheme is implemented with orthogonal pulses obtained by the proposed method, and the results of a simulation are shown

Receiver Optimization in Turbulent Free-Space Optical MIMO Channels With APDs and $Q$ -ary PPM

Abstract: We propose an accurate, robust avalanche photodiode (APD) receiver optimization scheme for multiple-input/multiple-output (MIMO) free-space optical links with Q-ary pulse position modulation in the presence of atmospheric turbulence. Through extensive error probability (Pe ) analysis, we show that selecting the APD gain such that the nonfading receiver-array signal-to-noise ratio is maximized essentially minimizes Pe in turbulent MIMO channels with M=2 transmitters and N=2 receivers, for several turbulence and background-radiation levels of interest

LDPC-coded MIMO optical communication over the atmospheric turbulence channel using Q-ary pulse-position modulation

Abstract: We describe a coded power-efficient transmission scheme based on repetition MIMO principle suitable for communication over the atmospheric turbulence channel, and determine its channel capacity. The proposed scheme employs the Q-ary pulse-position modulation. We further study how to approach the channel capacity limits using low-density parity-check (LDPC) codes. Component LDPC codes are designed using the concept of pairwise-balanced designs. Contrary to the several recent publications, bit-error rates and channel capacities are reported assuming that p.i.n. photodetectors are used instead of ideal photon-counting receivers. The atmospheric turbulence channel is modeled using the Gamma-Gamma distribution function due to Al-Habash et al. Excellent bit-error rate performance improvement, over uncoded case, is found.

Energy Efficient Pulsed-UWB CMOS Circuits and Systems

Abstract: A custom UWB transceiver chipset is presented that communicates in three 550 MHz-wide channels in the 3.1 to 5 GHz band by using pulse position modulation (PPM). The transmitter uses an all-digital architecture and calibration technique to synthesize pulses with programmable width and center frequency. No analog bias currents or RF oscillators are required in the transmitter. The receiver performs channel-selection filtering, energy detection, and bit-slicing. The receiver circuits operate at 0.65 V and 0.5 V, and can turn on in 2 ns for duty-cycled operation. The two chips are fabricated in a 90 nm CMOS process, and achieve a combined 2.5 nJ/bit at a data rate of 16.7 Mb/s.

Channel Uncertainty in Ultra-Wideband Communication Systems

Abstract: Channel uncertainty limits the achievable data rates of certain ultra-wideband systems due to the need to estimate the channel. The use of bursty duty-cycled transmission reduces the channel uncertainty because the receiver has to estimate the channel only when transmission takes place, but the maximum amount of burstiness and hence the possible reduction of channel uncertainty both depend on the spectral efficiency of the modulation scheme used. This general principle is demonstrated by comparing the channel conditions that allow duty-cycled direct-sequence spread spectrum (DSSS) and pulse position modulation (PPM) to achieve the additive white Gaussian noise (AWGN) channel capacity in the wideband limit. We show that duty-cycled DSSS systems achieve the wideband capacity as long as the number of independently faded resolvable paths increases sublinearly with the bandwidth, while duty-cycled PPM systems can achieve the wideband capacity only if the number of paths increases sublogarithmically. The difference is due to the fact that DSSS is spectrally more efficient than PPM and hence allows more bursty transmission

Effect of Group Delay in RF BPF on Impulse Radio Systems

Abstract: This paper presents an analysis of the effects of RF filter characteristics on the system performance of an impulse radio. The impulse radio system transmits modulated pulses having very short time duration. Information can be extracted in the receiver side based on the cross-correlation between received and reference pulses. Accordingly, the pulse distortion due to in-band group delay variation can cause serious degradation in system performance. In general, RF band pass filters inevitably cause non-uniform group delays to the signal passing through the filter that are proportional to its skirt characteristic due to its resonance phenomenon. In this work, a small signal scattering parameter, S 21 , which is a frequency domain parameter, and its Fourier transform are utilized to characterize the output pulse waveform under the condition that the input and output ports are matched. The output pulse waveform of the filter is predicted based on the convolution integral between the input pulse and filter transfer function, and the analysis result is compared with previously reported experimental result. The resulting bit error rate performances in a bi-phase modulation and a pulse position modulation based impulse radio system are also calculated. Moreover, improvement of system performance by the pulse shaping method, a potential solution for pulse waveform distortion, is analyzed.

Replacing Cryptography with Ultra Wideband (UWB) Modulation in Secure RFID

Abstract: Existing secure RFID tags rely on digital cryptographic primitives in the form of hashes and block ciphers, which lead to large system latencies, high tag power-consumption and large tag silicon area. In addition, existing passive RFID systems rely on simple coding and modulation schemes using narrowband radio frequencies, which can easily be eavesdropped or jammed. To address the above problems, we propose a new approach for secure passive RFIDs based on ultra wideband (UWB) communications. We adopt time-hopped pulse-position modulation (TH-PPM), in which the hopping sequence is known only to the reader and the tag. By adopting the hopping sequence as a secret parameter for the UWB communication link, eavesdropping of the communication is extremely difficult. Thus, we can avoid digital cryptography and support privacy directly at the physical-communication layer.

UWB Energy Detection in the Presence of Multiple Narrowband Interferers

Abstract: There has been an emerging interest in non-coherent ultra wideband (UWB) communications, particularly as a technology for low-data rate UWB applications, due to its low-complexity and low-power consumption. In this paper, we evaluate the performance of the energy detector (ED) receiver in terms of bit error probability (BEP). We consider an ED receiver based on a conventional square-law detector and binary pulse position modulation (BPPM). We analyze the BEP in a multipath fading channel, both in the absence and presence of narrowband interference (NBI). We consider two cases: (1) single NBI, where the interfering node is located at a fixed distance from the receiver, and (2) multiple NBI, where the interfering nodes are scattered according to a spatial Poisson process. Our framework is simple enough to allow a tractable analysis and provide insights that can be of value in the design of practical UWB systems subject to interference.

Fresh Prime Codes Evaluation for Synchronous PPM and OPPM Signaling for Optical CDMA Networks

Abstract: In this paper, we have proposed a novel prime spreading sequence family hereby referred to as ldquodouble-padded modified prime code (DPMPC)rdquo for direct-detection synchronous optical code-division multiple-access (OCDMA) networks. The new code is applied to both pulse-position and overlapping pulse-position modulation CDMA networks, and their performances were evaluated and compared with existing prime codes family. In addition, we have analyzed the system throughput and also introduced a new interference cancellation technique which significantly improves the bit error probability of OCDMA networks.

A synopsis of modulation techniques for wireless infrared communication

Abstract: A number of modulation techniques have been proposed and thoroughly analysed in literature for optical wireless communication systems. Each modulation technique has its unique attractive features as well as its challenges. Some are very simple to implement and bandwidth efficient like the on-off keying (OOK). Pulse interval modulation (PIM) techniques are reputed for their inherent synchronisation pulse, subcarrier modulation offers increased throughput, resilience to the inter-symbol interference (ISI) and immunity against the fluorescent-light noise near DC, while pulse position modulation (PPM) provides the unparalleled power efficiency in line of sight (LOS) links but the performance degrades severely in dispersed communication channel. There has been an enormous work on the analysis of these and many more modulation techniques under different channel and environmental conditions; we however present here a concise synopsis of the mostly reported wireless infrared modulation techniques.

Performance analysis of b-bit digital receivers for TR-UWB systems with inter-pulse interference

Abstract: An ultra-wideband (UWB) transmitted reference (TR) system transmits an un-modulated pulse and a delayed modulated pulse pair. Then, a correlation receiver uses the former to demodulate the latter. Because of the long spread of a typical UWB channel, time delay between the two pulses is preferable to be larger than the channel delay spread for reduced noise at the receiver. However, for bandwidth efficiency, that delay should be made small, resulting in inter-pulse interference at the receiver. In this paper, digital receivers are constructed for TR-UWB systems including inter-pulse interference. A typical mean matching technique, appropriate for both PPM and PAM schemes, is implemented digitally to obtain a good template for symbol detection. Joint estimation and detection performance of this family of digital receivers, using finite number of bits in analog-to-digital conversion and finite noisy observations, is analyzed. Closed form results are derived and verified by computer simulations. In addition, the effect of time offset between the reference pulse and information carrying pulse is studied. Overlap of the two pulses does not incur noticeable performance degradation. The proposed analytical framework can be applied to study detection performance of other related digital receivers not covered in this paper

Spatial modulation method and transmitting and receiving apparatuses using the same in a multiple input multiple output system

Abstract: A spatial modulation method and transmitting and receiving apparatuses using the spatial modulation method in a MIMO system are provided. The spatial modulation method uses an index of an activated antenna and a signal modulation constellation as an information source. The spatial modulation method is applied to the transmitting apparatus. The receiving apparatus uses a spatial modulation detection method in which a channel path gain is repeatedly multiplied to detect the spatially modulated signal efficiently.

Comparison of pulse position modulation and pulse width modulation for application in optical communications

Abstract: Different modulation methods for optical wireless have different power and bandwidth efficiencies. Each approach has a direct bearing on the quality and effectiveness of wireless optical communications. As two prime examples, pulse position modulation (PPM) and pulse width modulation (PWM) are compared. The comparison includes the power and bandwidth efficiencies, the power spectrum distribution, and the ability to resist intersymbol interference. Compact system models of multilevel digital PPM (L-PPM), and multilevel digital PWM (L-PWM) are also introduced. The results show that L-PPM has advantages in power efficiency and an approximately uniform spectral distribution, whereas L-PWM has a greater ability to resist intersymbol interference.

A Radio-Over-Fiber Downstream Link Employing Carrier-Suppressed Modulation Scheme to Regenerate and Transmit Vector Signals

Abstract: In this letter, the optical carrier-suppressed (OCS) modulation scheme is employed to transmit vector signals in radio-over-fiber systems. The proposed architecture employing the OCS modulation scheme needs only a balanced single driven Mach-Zehnder optical modulator, and has advantages of dispersion immunity and doubled frequency. Both detailed theoretical analysis and experiments are presented to demonstrate the feasibility of the proposed architecture.

Method and apparatus for characterizing modulation schemes in a hfc network

Abstract: The available modulation schemes of a network are analyzed to determine which ones contain excessive phase noise or narrowband interference. A network element is selected and assigned to a test channel at a first modulation scheme at a predetermined power level to achieve a predetermined PER. The network element transmits a test signal and the network controller measures the signal to noise ratio (SNR) in the received test signal. If the SNR is not within a predetermined tolerance range of an estimated SNR for the modulation scheme at the predetermined PER, the modulation scheme is determined to have excessive phase noise or narrowband interference. Each available modulation scheme is tested by instructing the network element to transmit the test signal using each modulation scheme and assigning the power level of each modulation scheme. The suitable modulation schemes may be determined.

SNR Estimation Methods for UWB Systems

Abstract: The problem of estimating the signal-to-noise ratio for time-hopping binary pulse position modulated signals, time- hopping binary phase shift keying signals, and direct-sequence binary phase shift keying signals in an ultra-wide bandwidth (UWB) system is studied. Both an additive white Gaussian noise channel and a multipath fading channel are considered. Several new estimators are derived by making use of different properties of the UWB signals. The performances of the estimators are examined and compared in terms of their root-mean-squared errors. Numerical results show that they have excellent performances when operating in an ultra-wide bandwidth system.

System and method for adaptive modulation and power control in a wireless communication system

Abstract: A system for adaptive modulation and power control in a wireless communication system includes a downlink from a base station to a remote unit and an uplink from the remote unit to the base station. The base station incorporates adaptive modulation on the downlink while power control is not utilized. In contrast, the remote unit utilizes a fixed modulation level and power control to control transmit power levels. In an exemplary embodiment, the remote unit uses QPSK modulation. The header of uplink messages include data from the remote unit to instruct the base station which modulation level to utilize on downlink transmissions. This provides closed-loop, non-iterative modulation control. In an exemplary embodiment, the modulation selection data is included in all uplink messages so that adaptive modulation can be communicated on a frame-by-frame basis.

Optimum Adaptive Modulation and Channel Coding Scheme for Frequency Domain Channel-Dependent Scheduling in OFDM Based Evolved UTRA Downlink

Abstract: In the evolved UTRA (UMTS terrestrial radio access) downlink, orthogonal frequency division multiplexing (OFDM) based radio access was adopted because of its inherent immunity to multipath interference and flexible accommodation of different spectrum arrangements. This paper presents the optimum adaptive modulation and channel coding (AMC) scheme for simultaneously assigned resource blocks (RBs) for the same user when frequency and time domain channel-dependent scheduling is used in the downlink OFDMA radio access with single-antenna transmission. Theoretical analyses and simulation results show that, irrespective of the application of power adaptation to RB-dependent modulation, the improvement in the achievable throughput of the RB-dependent modulation scheme compared to that for the RB-common modulation scheme is slight, i.e., 4 to 5%. In addition, the number of required control signaling bits in the RB-dependent modulation scheme becomes greater than that for the RB-common modulation scheme. Therefore, the authors conclude that the RB-common modulation and channel coding rate scheme is preferred, when multiple RBs of the same coded stream are assigned to one user in the case of single-antenna transmission.

Iterative Coded Pulse-Position-Modulation for Deep-Space Optical Communications

Abstract: This paper presents and compares two iterative coded modulation techniques for deep-space optical communications using pulse-position modulation (PPM). The first code, denoted by SCPPM, consists of the serial concatenation of an outer convolutional code, an interleaver, a bit accumulator, and PPM. The second code, denoted by LDPC-PPM, consists of the serial concatenation of an LDPC code and PPM. We employ Extrinsic Information Transfer (EXIT) charts for their analysis and design. Under conditions typical of a communications link from Mars to Earth, SCPPM is 1 dB away from capacity, while LDPC-PPM is 1.4 dB away from capacity, at a Bit Error Rate (BER) of approximately 10-5. However, LDPC-PPM lends itself naturally to low latency parallel processing in contrast to SCPPM.

Secure rfid based ultra-wideband time-hopped pulse-position modulation

Abstract: A radio-frequency-identification (RFID) system includes an RFID tag and an RFID reader, where the RFID reader is configured to communicate with the RFID tag using time-hopped pulse-position modulation and ultra-wideband modulation. The time-hopped pulse-position modulation includes sending from the RFID tag to the RFID reader a series of pulses in time slots selected by the RFID tag through a cryptographically secure pseudo-random generator.

Delay-Based BPSK for Pulsed-UWB Communication

Abstract: This paper proposes a practical and effective modulation technique applicable to pulsed-UWB systems that mimics the desirable, continuous spectrum of a BPSK signal without requiring an inversion in the signal path. This technique can be used for scrambling the spectrum of a PPM signal, or as a replacement for BPSK signaling. It has been implemented in an all-digital, delay line based UWB transmitter in 90 nm CMOS. An analysis of the spectral characteristics of the modulation technique is given, as well as simulation and measured results.

Additional modulation information signaling for high speed downlink packet access

Abstract: The modulation indication bit is interpreted as a QPSK/xQAM modulation indication if both the user equipment and the serving cell support 64QAM modulation, such that if QPSK is indicated, the 7 code-set information bits in the HS- SCCH part 1 structure is interpreted as is presently interpreted today as defined in the 3GPP release 5 specification, and if xQAM is indicated, the 7 code-set information bits in the HS-SCCH part 1 structure is interpreted such that only 6 bits are used for code information and one bit is stolen for use for the 16QAM/64QAM selection.

Tunable Pulse Amplitude and Position Modulation Technique for Reliable Optical Wireless Communication Channels

Abstract: 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.

Bit-Interleaved Coded Modulation in the Wideband Regime

Abstract: This paper studies the wideband regime of bit- interleaved coded modulation (BICM) in Gaussian channels. Simple formulas for the minimum energy per bit and the wideband slope, both for coded modulation and for bit-interleaved coded modulation, are given. The wideband slope can be decomposed into the product of two terms, respectively due to the fading characteristics and the modulation and binary labeling rule. BICM is found to be suboptimal in the sense that its minimum energy per bit can be larger than the corresponding value for coded modulation schemes. The minimum energy per bit using standard Gray mapping on M-PAM, or M 2-QAM is given by a simple formula, and shown to approach -0.34 dB as M increases.

A CMOS Ultra-Wideband Impulse Radio Transceiver for Interchip Wireless Communications

Abstract: This paper presents a CMOS Ultra-Wideband impulse radio transceiver used for interchip wireless communications. The transmitter employed time hoping pulse position modulation (TH-PPM) scheme is presented for eight users' access simultaneously with 2.5ns hoping time allocated in a frame time of 20ns. A fifth derivative Gaussian pulse generator is used to regulate the pulse shape as well as the pulse spectrum. The pulse train containing data information can be perfectly recovered at the delay time of 780ps with respect to the transmitted pulse train. The transceiver is designed and implemented with TSMC 1.8V O.lSfrac14ni CMOS mixed signal process. The proposed transmitter and receiver are fabricated individually. The power dissipations for transmitter and receiver are 23mW and 108mW, respectively.