Because the data-modulated channel es- timator can cope with the time-varying Rayleigh fading effect and the data modulation effect on the error signals, in addition [r]

5 閱讀更多

Published online: 3 February 2010
© Springer Science+Business Media, LLC. 2010
Abstract This paper presents the root-mean-squared **tracking** error performance analysis of **a** class of coherent digital delay-locked loops **for** multicode **direct** **sequence** **spread** spec- trum signals in bandlimited correlated Rayleigh **fading** **channels**. In the transmit side, multiple independent PSK-modulated data streams in the in-phase and qudrature phase branches are **spread** by short mutually orthogonal codes before being further complex **spread** by **a** long complex PN **code**. We assume that the system employs **a** pilot **code** channel to assist the receiver’s synchronization and channel estimation. The proposed **code** **tracking** **loop** incorpo- rates the pilot-aided channel estimator and derives the timing error from all short-**code**-**spread** subchannels. Our analysis takes into account the effects of imperfect channel estimate, corre- lated **frequency** **selective** Rayleigh **fading** and band-limiting. Numerical results are presented to quantify the impact of the resulting multipath interference within the same **code** channel and amongst different **code** **channels**.

顯示更多
18 閱讀更多

Digital **code** **tracking** becomes very popular because of the evolution toward all digital modem implementation of DSSS **systems**.
In this paper, accurate nonlinear analysis **for** the noncoherent second-order digital **code** **tracking** loops is investigated over AWGN **channels** with the presence of Doppler shift. This modeling of channel finds applications in GPS [17] and other civilian or military satellite-based DSSS **systems**, where Doppler shift is due to the relative movement between the satellite and the receiver. In the analysis, based **on** **a** regenerative Markov chain modeling of the **code** **tracking** process, the lock-in range, transient response, MSE, and MTLL are evaluated more accurately than the traditional analysis. Furthermore, in **a** digital DLL, the adaptation of **code** **tracking** can only be done in discrete steps, i.e., quantized adaptation and that will result in significant changes in the **loop** performance. In this analysis, the effect of quantized adaptation is evaluated as well.

顯示更多
11 閱讀更多

B. Acquisition Process
As in nearly all literature, the **code** phase uncertainty 2 of an acquisition system is divided into cells, with **a** cell size to within the lock-in range of the **code** **tracking** **loop** used **for** fine **code** alignment. The acquisition system then searches through the **code** phases and determines which cells are the correct cells, according to some type of **code** phase correlators, search strate- gies, and test methods. As usual, the correct cells will be de- noted as the cells (hypothesis ) and the incorrect cells as the cells (hypothesis ), respectively. In practice, there may be more than one correct cell. **For** simplicity of presen- tation, however, only the case of one correct cell will be used as an example, although the method applies equally well to the more general case with more than one correct cell. Two types of decision errors may occur when detecting **a** cell, namely false dismissal of the cell and false alarm of the cells. When **a** false alarm occurs, the synchronization will be turned to **code** **tracking** **for** fine alignment. In this case, it is assumed that the false alarm can always be detected after some fixed or random time, and the synchronization will be turned back to the **code**

顯示更多
8 閱讀更多

Index Terms— Correlator, delay-locked **loop**, **direct** **sequence** **spread** **spectrum**, **tracking** error variance.
I. S YSTEM D ESCRIPTION AND S IGNAL M ODEL
I N THIS letter, we present **a** **code** **tracking** receiver with less complexity, by employing **a** differentially coherent tech- nique originally proposed **for** pseudonoise (PN) acquisition receiver [3]. The proposed differentially coherent delay-locked **loop** (DCDLL) scheme is shown in Fig. 1. The received signal is first filtered by front-end band-pass filter (BPF) and the bandwidth of BPF is . is set to be chip rate ( , where is the chip duration). Then this proposed DCDLL scheme processes the received signal using **a** differential decoder with **a** delay of -chip duration in the delay path. The decoder output is then correlated with the difference of the advanced (early) and retarded (late) versions of the local PN **code** to produce an error signal. After the error signal is filtered by **a** low-pass filter (LPF), then it drives the voltage-controlled clock (VCC) through the **loop** filter and corrects the **code** phase error of the local PN **code** generator. In this proposed system, the bandwidth of LPF, denoted as , is set to be the system data rate ( , where is the data bit duration). The processing gain of this **direct**-**sequence** **spread**-**spectrum** (DS/SS) system is thus given by or . Usually, if the system is applied in ranging, and

顯示更多
3 閱讀更多

The channel transfer function of pilot tones are estimated by using low-rank MMSE estimator, and the channel transfer function of data tones are in- terpolated by piecewise l[r]

9 閱讀更多

II. **A** SSUMPTIONS AND S IGNAL M ODELS
**A**. Assumptions
We consider **a** scenario where one OFDM desired signal with **a** single input/single output channel and one cyclo- stationary interference with period MT 0 share **a** common **frequency** band, where M is **a** positive integer known to the receiver and T 0 is the OFDM symbol duration. The receiver is assumed to precisely acquire synchronization information of the desired signal including symbol timing, carrier **frequency**, carrier phase and channel impulse response, which implies the received waveforms of OFDM sub-carriers are precisely known to the receiver. The channel impulse response of the desired signal is assumed **frequency**-**selective** **fading** and time- invariant in our observation interval of interest. The maximum delay **spread** of the channel is assumed smaller than the length of CP such that ISI and ICI can be avoided by removing CP.

顯示更多
5 閱讀更多

Here we consider a spread spectrum cellular radio architec- ture in which the whole service area is divided into cells and each cell is served by a base. A mobile [r]

7 閱讀更多

1 Introduction
Channel modeling simulation tools that enable researchers and designers to accurately predict the performance of wire- less **systems** become increasingly important as personal com- munications and wireless data services evolve. **A** basic under- standing of the channel is important not only **for** designing modulation and coding schemes **for** robust communication over such channel, but also **for** investigating the channel fad- ing impact **on** existing networking algorithms, such as rout- ing and power adjustment which critically depend **on** channel attenuation. At present, most network protocol simulations and even power control algorithms are using the free space (distance) channel propagation model which is basically only function of transmitter-receiver distance. Typically, **for** the indoor environment, the channel characteristics are much too complex to be modeled by simple distance functions. Yet, **a** realistic channel model is essential **for** network protocol eval- uation, especially in the presence of mobility. Therefore, **a** more realistic channel **fading** model which accounts **for** chan- nel quality variations with movement is needed **for** network protocol simulation.

顯示更多
6 閱讀更多

Abstract—This brief presents **a** **frequency** **tracking** **loop** (FTL) to realize **a** crystalless wireless sensor node (WSN) **for** wireless body area network (WBAN). By **tracking** **a** remote wireless RF reference **for** system clock calibration, the proposed FTL allows WSNs to tolerate **a** large-**frequency** error from **on**-chip CMOS oscillators. Moreover, to achieve energy-efficient transmissions in crystalless, **a** sufficiently accurate convergence clock is required to enable burst overmegabits-per-second system throughput with minimized operation duty cycle. **For** the dedicated purpose, **a** comparison-based binary-search **tracking** scheme, which ensures accurate and robust convergence against noisy wireless channel, is further developed to manage the operation of FTL. The in- termediate **frequency** back-end part of FTL is implemented in 90-nm CMOS process. Measurement results show that the FTL extends an initial tolerance of system clock error to ±3% and achieves **a** final quartz-crystal comparable ±50-ppm accuracy.

顯示更多
5 閱讀更多

TABLE III
B ANDWIDTH C OMPARISON R ESULTS B ETWEEN PSPN C ODES AND PN C ODES
Fig. 4. Plot of bandwidth versus toggle rate of the spreading codes.
The block of “**frequency** divider” generates the clock with data rate. PN **code** generator generates the PN **code**. Despreader is used **for** despreading procedure and the decision circuit detects the signal. The transistor netlist of the blocks in Fig. 6 is implemented. The circuit level simulator Hspice simulates the power consumption of the transistor netlist. All the blocks shown in Fig. 6 are included in this power consumption simulation. The circuit schematics described in Fig. 6 could be operated by different spreading codes with different **code** lengths. That is to say, this is **a** soft-coded **spread** **spectrum** system. The simulation results of the power consumption are listed in Table IV. From Table IV, we find the percentages of reduction **for** power consumption range from 8% to 14% with PSPN codes compared to PN codes. The concept of low toggle rate means low-power consumption has been verified by the simulation results.

顯示更多
8 閱讀更多

Abstract-Inheriting the properties of the frequeucy-domaiu approach 111 to avoid MA1 in the asynchronous multiuser com- munications and sharing the rationale behind OFDM sys[r]

5 閱讀更多

The residual inter-chip interference (ICI) after the modified KMA proposed here, the timing er- ror signals, mean square timing error and mean time to lose lock (MTLL) fo[r]

4 閱讀更多

Efficient channel estimation is important **for** multiple-antenna sys- tems especially when the number of antennas increases. To avoid the degradation of estimation accuracy due to interference, an intuitive way is to transmit training sequences **for** each transmitting antenna in turn [1]. **For** **a** system with M antennas, this scheme requires M times band- width compared with **a** single antenna transmitter system. However, orthogonal training sequences can be simultaneously applied **for** each transmitter antenna to estimate the channel efficiently [2], [3]. **For** **a** single tap coefficient discrete channel model, it is well known that or- thogonal sequences are the optimal training sequences that minimize the estimation errors if the additive noises are identical independent Gaussian random processes. In this case, **a** Hadamard matrix can be ap- plied. However, in the case of multipath channel, the channel **for** each pair of transmitting and receiving antennas should be modeled by sev- eral taps. It can be proven that the training sequences should have both good autocorrelation and cross correlation. Existence of such training **sequence** sets is still an open problem. In this paper, we discuss the existence of such optimal binary training **sequence** sets and propose **a** search algorithm.

顯示更多
6 閱讀更多

Fig. 6. Probability distributions of P and P as functions of S with several SNR values.
**For** the power management module, the functional blocks of noise estimator, sampling rate generator, and threshold gener- ator are included in this module. The operating frequencies of sampling rate generator and threshold generator are exactly the refresh rate of the noise estimator, which is denoted by . is the rate at which the noise estimator update the estimated channel noise level. The refresh **frequency** depends **on** the co- herent time of the channel. **For** example, the refresh **frequency** of the system with fast-**fading** channel will be larger than that with slow-**fading** channel. According to this reason, we assume that the channel is slow-**fading** channel. There are several prac- tical considerations when designing the refresh rate. The data rate is usually several times of refresh rate. And the sampling rate is also several times of data rate. Because the switch fre- quency of the power management module is much less than that of the PN acquisition structure, the power consumption of this module can be ignored. Therefore, the power consumption of this proposed architecture is dominated by the **code** acquisition structure, which is mainly depends **on** the sampling rate.

顯示更多
13 閱讀更多

these subbands at the same time in the same channel, the SS-CDMA multiplexing scheme is particularly well suited to subband coding that divides the image informa[r]

15 閱讀更多

The difficulties of design BER-minimized STF block codes **for** the MIMO highly **frequency**-**selective** block-**fading** chan- nels can be discussed in three aspects. Note that we take the IEEE 802.15.3**a** UWB channel model as an example in this paper. 1) First, the IEEE 802.15.3**a** channel model has four different sets of parameters, named CM1, CM2, CM3, and CM4. **For** different **channels**, we have to design different codes to reflect the channel characteristics. One challenging issue arises: Is there **a** universal **code** which is optimal **for** all the four channel models CM 1–4 **for** given numbers of subcarriers and transmit antennas? 2) As the numbers of subcarriers and transmit antennas increase, the number of all possible codes becomes astronomical. Thus, the second challenge is how to search the optimal codes efficiently. 3) Because traditional STF coding methods focus **on** linear codes, it will be challenging to examine if there exist nonlinear optimal STF block codes.

顯示更多
5 閱讀更多

14 閱讀更多

ABSTRACT
The OFDM (orthogonal **frequency** division multiplexing) signaling is one kind of "Multi-Carrier" technology, which can slow down delayed transmission especially **for** operating at **frequency** non-**selective** **fading** **channels**. Therefore, it gains quite large profit making **a** study of executing efficiency at different **frequency** non-**selective** **fading** **channels**. The OFDM system has become the most popular choice of transmission modulation in the new wireless communication field. Hence, in this article utilize **a** method of OFDM modulation to explore the statistical characteristic of distributions of Rayleigh、Ricean、Weibull while working in **fading** channel.

顯示更多
2 閱讀更多

Chieh-Ho Lee, Student Member, IEEE, and Chung-Ju Chang, Senior Member, IEEE
Abstract— This letter proposes an approximation method by characteristic function (AM-CF) method to approximate the distribution of interference in DS/CDMA cellular **systems**. This method considers the effects of **frequency**-**selective** multipath fad- ing; it also assumes perfect power control and **a** rectangular/sinc chip waveform. The AM-CF method can yield results that fit the Monte Carlo simulation results more accurately than the conventional standard Gaussian approximation method.

3 閱讀更多