Generalized Tamed Frequency Modulation and Its Application for Mobile Radio Communications

Continued investigation of tamed FM (TFM) has led to an extension called generalized tamed FM (GTFM). The very narrow spectral property of a GTFM signal meets the stringent requirements on bandwidth utilization in modern mobile radio applications. The principle of GTFM is first described. It is then shown that the generation of GTFM signals can be made very simple by the use of an ROM table-lookup technique. By an appropriate choice of parameters in GTFM signal generation at the transmitter, a joint optimization for coherent and noncoherent detection with regard to BER performance in the presence of additive white Gaussian noise can be achieved. For mobile radio applications, the robustness of the detection scheme to fast fading is important. A low-complexity noncoherent receiver is presented, Comprising a frequency discriminator and a simple maximum-likelihood sequence estimator. This receiver performs well in a fast fading environment. Computer simulated results of BER performance of this scheme are given. These results are confirmed by experimental measurements.     

Generalized tamed frequency modulation and its application for mobile radio communications

Continued investigation of tamed FM (TFM) has led to an extension called generalized tamed FM (GTFM). The very narrow spectral property of a GTFM signal meets the stringent requirements on bandwidth utilization in modern mobile radio applications. The principle of GTFM is first described. It is then shown that the generation of GTFM signals can be made very simple by the use of an ROM table-lookup technique. By an appropriate choice of parameters in GTFM signal generation at the transmitter, a joint optimization for coherent and noncoherent detection with regard to BER performance in the presence of additive white Gaussian noise can be achieved. For mobile radio applications, the robustness of the detection scheme to fast fading is important. A low-complexity noncoherent receiver is presented, comprising a frequency discriminator and a simple maximum-likelihood sequence estimator. This receiver performs well in a fast fading environment. Computer simulated results of BER performance of this scheme are given. These results are confirmed by experimental measurements.     

An interference suppression scheme for UWB Signals using multiple receive antennas

In this letter a simple narrow band interference (NBI) mitigation scheme for ultra-wide bandwidth (UWB) signals using multiple receive antennas is examined. The low spatial fading characteristic of UWB signals is exploited to provide "interference diversity" by selecting the signal with the lowest received power among multiple antennas. The resulting distribution of the signal-to-interference ratio (SIR) at the receiver is derived and compared with results based on measurement data. The performance improvement of the scheme in mitigating NBI is also examined through BER simulations.     

Grey-based power control for DS-CDMA cellular mobile systems

The propagation channel of a mobile radio system exhibits severe signal shadowing and multipath fading, which results in wide variation of signal-to-interference ratio (SIR) at the receiver. To tackle this problem, power control is used to maintain the desired link quality and thus achieve higher capacity. In order to mitigate the channel variation effect precisely, a new application of grey theory to the power control strategy in the direct-sequence code-division multiple-access cellular mobile systems is introduced. This scheme aims to predict the SIR affected by the channel variation at the receiver and issue an appropriate control signal to the transmitter. The simulation results indicate that the grey-based scheme can offer less outage probability than the previous mechanisms     

A UWB-IR Transmitter With Digitally Controlled Pulse Generator

A novel transmitter for ultra-wideband (UWB) impulse radio has been developed. The proposed architecture enables low-power operation, simple design, and accurate pulse-shape generation. The phase and amplitude of the pulse are controlled separately and digitally to generate a desired pulse shape. This digital control method also contributes to the low-power transmission and eliminates the need for a filter. The transmitter is fabricated using a 0.18-mum CMOS process. The core chip size is only 0.40 mm². From experimental measurements, it was found that the generated signal satisfied the FCC spectrum mask, and the average power dissipation was only 29.7 mW at A 2.2-V supply voltage. Therefore, the developed UWB transmitter generates accurate pulses with low power consumption and simple design architecture     

Method for superimposing data on amplitude-modulated signals

The principles of a new modulation scheme are described which permit an additional data channel to be superimposed on conventional DSBAM signals without increasing band-width or envelope distortion. This scheme, named zero synchronous frequency modulation (ZSFM), requires additional signal processing and provision for combined AM/FM at the transmitter. At the receiver, the data signal is detected by a simple frequency demodulator, while envelope detection of the AM signal is performed in the usual way.     

Parallel transmission of vehicle mirror control signals by a singleoptical fiber

Describes a vehicle mirror control signal transmission system consisting of a transmitter, a single optical fiber, and a receiver terminal. The transmitter in the mirror controller to be operated by the driver controls the mirror functions, and the receiver terminal consists of a multifrequency receiver, a data processor, mirror control circuits to control an inner rearview mirror, and a pair of outside door mirrors. Multifrequency signals at 135, 235, 335, and 435 kHz are encoded to obtain 4-bit binary data that specifies the instructions to control these mirrors. The 4-bit multifrequency signal identified as 4-bit binary data is formed in accordance with the frequency division multiplexing (FDM) scheme, fed to the voltage-controlled oscillator (VCO) to obtain the square-wave frequency modulation (SWFM) signal in accordance with the SWFM scheme, and then transmitted from the transmitter to the receiver terminal through a single optical fiber. After the 4-bit binary data is reproduced from the 4-bit multifrequency signal, the mirrors are controlled by the data processor to accomplish their operating functions satisfactorily     

An Effective Timing Synchronization Scheme for DHTR UWB Receivers

In performing short-distance, high-data-rate wireless communications using ultra-wideband (UWB) systems, it is necessary to reduce the average transmission power and ensure a fixed synchronization error between the transmitter and receiver ends. Furthermore, to reduce multipath interference, the UWB system should be sometimes implemented using a rake receiver. However, for such receivers, the delay time and attenuation loss over each transmitted route must be known in advance. In the present study, the complexity of rake receivers with a large number of “fingers” is reduced by means of a delay-hopped transmitted-reference (DHTR) scheme, in which the delayed signal is correlated with the original signal; thereby avoiding the need for a separate template signal. The synchronization performance of the proposed DHTR receiver is analyzed both theoretically and numerically. An effective timing synchronization scheme, designated as “parallel signal acquisition with shared looped delay-line” (PS-SLD), is then proposed. The simulation results show that for multipath environments with a single user, the proposed synchronization scheme achieves a higher detection probability and a lower normalized mean square error (MSE) than the traditional timing dirty templates (TDT) algorithm.     

Additive mixing modulation for public key encryption based on distributed dynamics

We introduce a public key encryption scheme that is based on additive mixing of a message with chaotic nonlinear dynamics. A high-dimensional dissipative nonlinear dynamical system is distributed between transmitter and receiver. The transmitter dynamics is public (known to all) and the receiver dynamics is private (known only to the authorized receiver). Bidirectional signals that couple transmitter and receiver are transmitted over a public channel. Once the chaotic dynamics which is initialized with a random state converges to the attractor, a message is mixed with the chaotic dynamics at the transmitter. The authorized receiver who knows the entire dynamics can use a simple algorithm to decode the message. An unauthorized receiver does not know the receiver dynamics and needs to use computationally unfeasible algorithms in order to decode the message. Security is maintained by altering the private receiver dynamics during transmission. We show that using additive mixing modulation is more efficient than the attractor position modulation distributed dynamics encryption scheme. We demonstrate the concept of this new scheme by simulating a simple coupled map lattice.     

Energy Detector in Ultra Wideband Systems Using Phase Compensation Technique

Energy detectors have the advantage of simple structure and inexpensive price. Due to the low signal to noise ratio (SNR) of the received signal in ultra-wideBand (UWB) system, these desirable advantages can be achieved at the expense of non-trivial performance degradation. This paper presents a phase compensation (PC) technique to improve the performance of energy detector in UWB systems. In PC-UWB, the frequency dependent phase of the system response at the transmitter is extracted and its opposite spectral phase is used as prefilter. Because of Low complexity, cost and energy consumption of energy detectors, PC techniques has extensive potential for future of UWB communication systems. Measurement results show that the use of PC-UWB leads to signal power concentration at the receiver, which reduces the number of RAKE fingers required in coherent detection as well as achieves a higher data rate with less intersymbol interference. However time reversal UWB can achieve secure data transmission, but its performance is worse than PC-UWB. Simulation results show that phase compensation reduces the inter symbol interference impacts. Therefore it is possible to use a simple receiver with insignificant performance degradation. It is also shown that PC-UWB considerably outperforms TR-UWB and has satisfying performance in SNR greater than 13 dB.     

On the Impact of Ultra-Wideband (UWB) on Macrocell Downlink of UMTS and CDMA-450 Systems

Results of the analytical analysis to assess the effect of the ultra-wideband (UWB) emissions on the [universal mobile telecommunication system (UMTS) and code division multiple access systems (CDMA-450)] are presented. The (UMTS and CDMA- 450 systems) normalized range and normalized capacity degradation are evaluated. A free-space propagation model is used to calculate the UWB signal power that interferes with both mobile systems. It is shown that, for the case of a single UWB transmitter, the UMTS can easily tolerate UWB interference when the UWB equivalent isotropically radiated power (EIRP) is -92.5 dBm/MHz or less for a distance between the UWB transmitter and the UMTS mobile of 1 m or higher. Also, it is shown that, for the case of multi-UWB transmitters, the UMTS can easily tolerate the UWB interference when the UWB EIRP is -94.5 dBm/MHz. For the single UWB transmitter case, the CDMA-450 downlink can tolerate UWB interference when the UWB power density is in the order of -106 dBm/MHz. For the case of multi-UWB transmitters, the power density that can be tolerated by the downlink of the CDMA- 450 system is in the order of -108 dBm/MHz.     

Frequency-Division Bidirectional Communication Over Chip-to-Chip Channels

Frequency division multiple access is applied to bidirectional communication over chip-to-chip links. Frequency division is implemented by dividing the spectrum into low-frequency (dc) and high-frequency (ac) bands using a simple LC filter. The nonidealities that this filter introduces are compensated for with a transmitter/receiver pair that can recover signals in both bands. The receiver uses a dual-path topology that includes hysteresis to recover data from a signal with no dc content. The transmitter is a 6-tap (FIR) pre-emphasis equalizer with variable tap spacing. In simulation, the transmitter and receiver simultaneously communicate error-free at 8 Gb/s over the ac channel and at 500 Mb/s over the dc channel. Measurements shows that the ac and dc signals can be individually recovered and that the two signals occupy distinct frequency bands.      

Performance analysis of non-coherent UWB receivers at different synchronization levels

Non-coherent ultra-wideband (UWB) receivers require no channel state information for demodulating the received signal. The primary non-coherent receiver in the UWB literature is the autocorrelation receiver, which autocorrelates the received signal at specific time lags, circumventing problems of template signal design and multipath energy combining. A unique advantage of the UWB autocorrelation receiver is its robustness to synchronization errors, which has not been explored yet to date. This paper investigates two major UWB schemes employing autocorrelation receivers: the transmitted reference (TR) scheme (R. Hoctor and H. Tomlinson, 2002) and the differential (DF) scheme (M. Ho et al., 2002). Performance is analyzed for TR and DF receivers at different synchronization accuracy levels, their robustness to synchronization errors is shown, and the existence of a tradeoff between performance and synchronization complexity for non-coherent UWB receivers is revealed. As a result of our analysis, comparisons of TR and DF schemes are also made in the presence of synchronization errors, which have not been addressed before. Simulations corroborate our findings.     

Impact of Optical Transmission on Multiband OFDM Ultra-Wideband Wireless System With Fiber Distribution

Multiband (MB) orthogonal frequency-division multiplexing (OFDM) ultra-wideband (UWB) wireless, which provides high data rate access, is required to be distributed by using optical fiber. The performance of MB-OFDM UWB over fiber transmission system is investigated considering optical modulation and demodulation impact. Theoretical analysis of the effect of fiber dispersion, optical transmitter, and optical receiver response on system performance is carried out considering amplitude and phase distortion. Experiments are conducted and verified by our theoretical analysis and good agreement is obtained. It is found that RF modulation index of $sim {hbox {4}}%$ is optimum for optical transmitter with Mach–Zehnder modulator, and optical receiver with Chebyshev-II response is the best for MB-OFDM UWB over fiber. Compared to back-to-back UWB over fiber, optical transmission is mainly limited by laser phase noise converted relative intensity noise and phase distortion induced by fiber dispersion when optimum modulation index is used. Higher modulation index is limited by amplitude and phase distortion to OFDM signal induced by optical transmitter and receiver response nonlinearities and fiber dispersion and the spectral mask. It is also found that highly received optical power is required for transmission of MB-OFDM UWB signal over fiber.      

一种新的基于特征向量合并的超宽带系统分集方案

针对超宽带系统在室内环境中面临严重的多径衰落问题,通常在接收端需使用RAKE接收机来收集多径能量改善性能。该文提出了一种新的分集方案,在发送端信号进行预处理,在接收端使用RAKE合并收集多径能量,同时给出了基于信道矩阵特征值估计的最佳合并权重和时延参数估计算法。理论分析和仿真结果都表明,该算法得到的输出信噪比总是大于传统的RAKE接收机输出信噪比。     

Optimal pilot waveform assisted modulation for ultrawideband communications

Ultrawideband (UWB) transmissions induce pronounced frequency-selective fading effects in their multipath propagation. Multipath diversity gains can be collected to enhance performance, provided that the underlying channel can be estimated at the receiver. To this end, we develop a novel pilot waveform assisted modulation (PWAM) scheme that is tailored for UWB communications. We select our PWAM parameters by jointly optimizing channel estimation performance and information rate. The resulting transmitter design maximizes the average capacity, which is shown to be equivalent to minimizing the mean-square channel estimation error, and thereby achieves the Crame/spl acute/r-Rao lower bound. Application of PWAM to practical UWB systems is promising because it entails simple integrate-and-dump operations at the frame rate. Equally important, it offers a flexible UWB channel estimator, capable of striking desirable rate-performance tradeoffs depending on the channel coherence time.     

Clock synchronization using a linear process model

In this paper, we present a clock synchronization scheme based on a simple linear process model which describes the behaviors of clocks at a transmitter and a receiver. In the clock synchronization scheme, a transmitter sends explicit time indications or timestamps to a receiver, which uses them to synchronize its local clock to that of the transmitter. Here, it is assumed that there is no common network clock available to the transmitter and the receiver and, instead, the receiver relies on locking its clock to the arrival of the timestamps sent by the transmitter. The clock synchronization algorithm used by the receiver is based on a weighted least‐squares criterion. Using this algorithm, the receiver observes and processes several consecutive clock samples (timestamps) to generate accurate timing signals. This algorithm is very efficient computationally, and requires the storage of only a small number of clock samples in order to generate accurate timing signals. Copyright © 2006 John Wiley & Sons, Ltd.     

On the Degradation of a UWB System Due to a Realistic TX‐RX Antenna System

The ultra‐wideband (UWB) signal radiation process in an antenna is different from that of a narrowband signal. In this paper, we study the degradation of the desired signal component according to the antenna structure and location of a receiver in a bipolar time‐hopping UWB system. And we propose a receiver structure with an adaptive template waveform generator to compensate for the degradation caused by a realistic TX‐RX antenna system.     

Fading-resistant modulation using several transmitter antennas

This paper proposes a bandwidth-efficient fading-resistant transmission scheme which implements transmitter diversity using L antennas at the base station. When the antennas are spaced sufficiently far apart, the transmission from each antenna undergoes a different degree of fading. These transmissions are coordinated to mitigate the effects of Rayleigh fading, and the mobile receiver can recover the entire L-dimensional transmitted vector signal as long as the signal energy of at least one coordinate is large enough. L-dimensional fading-resistant signal constellations are generated by maximizing a figure of merit for the Rayleigh fading channel. This scheme offers a significant performance improvement over a conventional single-antenna binary phase-shift keying (BPSK) scheme when coding is ineffective due to slow fading