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### 不同类型收发器的IR-UWB系统中的到达时间（TOA）估计 #### 摘要与背景介绍本文献主要探讨了在脉冲辐射超宽带（Impulse-Radio Ultra-WideBand, IR-UWB）系统中，采用不同类型的接收机进行到达时间（Time of Arrival, TOA）估计的技术性能分析。文中着重分析了存储参考（Stored-Reference, SR）、传输参考（Transmitted-Reference, TR）和能量检测（Energy Detection, ED）三种基于到达时间估计的技术，并讨论了它们在亚奈奎斯特采样率下的表现。 #### 主要知识点详解 **1. 超宽带技术（Ultra-WideBand, UWB）概述** - **定义**: UWB是一种利用极宽频谱进行数据传输的无线通信技术。 - **特点**: UWB技术具有极高的带宽（通常大于500MHz），这使得其具备高精度的时间分辨率，能够精确地识别信号的第一个到达成分。 - **挑战**: 大带宽对硬件提出了较高的要求，尤其是在奈奎斯特采样率下运行接收器的成本较高。 **2. 到达时间估计（TOA Estimation）的重要性** - **概念**: TOA是指信号从发射端到接收端的时间差。 - **应用**: TOA估计是实现精确定位、测距等应用的关键技术之一，在无线通信领域尤为重要。 - **挑战**: 在低采样率条件下准确估计TOA存在一定的难度。 **3. 不同类型的接收机及其特性** - **存储参考（SR）接收机** - **原理**: 存储参考接收机通过预先存储的参考信号与接收到的信号进行比较来估计TOA。 - **优势**: 可以有效减少噪声的影响。 - **局限性**: 对于多径环境下的信号分离较为困难。 - **传输参考（TR）接收机** - **原理**: 传输参考接收机通过在信号中嵌入一个已知的参考信号，然后在接收端提取该信号来估计TOA。 - **优势**: 能够更好地适应多径传播环境。 - **局限性**: 需要在信号中插入额外的参考信号，可能会影响传输效率。 - **能量检测（ED）接收机** - **原理**: 能量检测接收机通过检测信号的能量来估计TOA。 - **优势**: 实现简单，适用于低功耗应用。 - **局限性**: 在复杂环境中可能会受到干扰的影响。 **4. TOA估计技术分析** - **基础理论**: 文章首先在加性高斯白噪声（AWGN）信道模型下进行了理论分析，强调了不同接收机之间的基本差异。 - **统计特性**: 分析了不同接收机的能量收集特性和决策统计量，包括准确峰值检测的概率以及接收机操作特征。 - **影响因素**: 探讨了每符号的脉冲数量和平均符号的数量对TOA估计的影响。 - **多径信道分析**: 在考虑实际多径信道的情况下，研究了各种最大似然估计方法，并提出了一种新的联合估计器，它同时利用了噪声统计特性和信道功率延迟剖面。 - **仿真结果**: 仿真结果显示，尽管ED和TR接收机在低采样率下具有更好的能量收集能力，但它们在时间上分布能量的方式导致了一些问题。 #### 结论通过对存储参考（SR）、传输参考（TR）和能量检测（ED）三种接收机类型的分析，可以看出不同的接收机在TOA估计方面有着各自的优势和局限性。在实际应用中，选择合适的接收机类型需要综合考虑系统的具体需求和技术限制。未来的研究方向可以进一步优化现有的接收机设计，提高TOA估计的准确性，特别是在复杂的多径环境下。

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1876 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 54, NO. 4, APRIL 2006

TOA Estimation for IR-UWB Systems

With Different Transceiver Types

Ismail Guvenc, Student Member, IEEE, Zafer Sahinoglu, Member, IEEE

, and

Philip V. Orlik, Member, IEEE

Abstract—In this paper, performances of stored-reference,

transmitted-reference (TR), and energy-detection (ED)-based

time-of-arrival estimation techniques are analyzed for im-

pulse-radio ultra-wideband (IR-UWB) systems at sub-Nyquist

sampling rates. First, an additive white Gaussian noise channel

is considered to emphasize certain fundamental issues related

to these different transceivers. In particular, energy collection

characteristics and decision statistics are presented. Probability

of accurate peak detection is analyzed for each transceiver, and

receiver operating characteristics for the leading edge are derived.

Effects of number of pulses per symbol and number of averaging

symbols are investigated in detail. Then, realistic multipath chan-

nels are addressed, and various maximum-likelihood estimation

approaches are investigated. A new estimator that jointly exploits

the noise statistics and power delay proﬁle of the channel is pro-

posed, and a Bayesian estimator that (ideally) gives a lower bound

is analyzed. Simulation results show that while ED and TR have

better energy collection capabilities at low-rate sampling, they

suffer from distributing the energy over time.

Index Terms—Energy detector, impulse radio (IR), ranging,

stored-reference (SR), subsampling, time-of-arrival (TOA) esti-

mation, transceivers, transmitted-reference (TR).

I. INTRODUCTION

LTRA-WIDEBAND (UWB) is a technology that has dis-

tinct features characterized by its extremely wide band-

width. Due to high time resolution, it is arduous but possible to

accurately identify the ﬁrst arriving signal component. However,

the large bandwidth, which is typically larger than 500 MHz,

makes it difﬁcult and costly to operate receivers at above the

Nyquist rate. Instead, energy can be captured at lower sampling

rates after certain analog front-end processing.

The energy detection (ED) of the signal is achieved by

passing the signal through a square-law device, followed by an

integrator and sampler. Another option is to correlate the signal

with a stored-reference (SR) before an integrate-and-dump

circuitry. The latter is more robust to noise effects due to

the template being noise-free. In order to avoid timing and

pulse-shape mismatch between the template and received

signal, a transmitted-reference (TR) scheme can also be con-

sidered, where a template is transmitted with and matches the

transmitted data signal with a known delay in between. After en-

ergy capturing in ED, SR, and TR via low-rate digital samples,

Manuscript received August 10, 2005; revised January 14, 2006.

I. Guvenc is with the Department of Electrical Engineering, University of

South Florida, Tampa, FL 33613 USA (e-mail: iguvenc@eng.usf.edu).

Z. Sahinoglu and P. V. Orlik are with the Mitsubishi Electric Research Labo-

ratories, Cambridge, MA 02139 USA (e-mail: zafer@merl.com; porlik@merl.

com).

Digital Object Identiﬁer 10.1109/TMTT.2006.872044

leading edge detection is needed for precision ranging. Apart

from the fact that each receiver type has different captured-en-

ergy statistics, they also have different levels of susceptibilities

to timing mismatches and responses to sub-Nyquist sampling.

Typical approaches for UWB time-of-arrival (TOA) estima-

tion in the literature are based on Nyquist-rate (or near-Nyquist-

rate) sampling of signals [1], [2], using an SR [3], [4], and

an ED [4], [5] receivers. A coarse timing estimate of a signal

can be achieved by maximum energy selection (MES) [3], [5],

[6]–[10]. Some other detection-related work in the literature

includes [11], where detection performances of impulse-radio

UWB (IR-UWB) signals with a square-law device were investi-

gated, and [12], where receiver operating characteristics (ROCs)

for coherent UWB random noise radars have been analyzed. De-

tection performances of weighted square-law and cross-corre-

lation UWB receivers are analyzed in [13]. In [14], an in-depth

analysis of signal acquisition using matched ﬁltering and ED

is carried out. Acquisition is achieved using generalized-likeli-

hood ratio testing (GLRT) and noisy templates in [15] and [16].

On the other hand, a coherent acquisition scheme with low-rate

samples is discussed in [17], which shows that the complexity

can be reduced by subsampling. Once an initial acquisition is

achieved, precise arrival of the leading edge can be estimated

by various thresholding techniques [1], [18], [19]. Tradeoffs be-

tween SR and TR transceiver types for symbol detection are ad-

dressed in [20].

The performance tradeoffs and comparison of different

transceiver types for UWB timing estimation is not available

in the literature to the best of the authors’ knowledge. In this

paper, SR-, TR-, and ED-based receivers and timing estima-

tion schemes operating at sub-Nyquist rates are analyzed and

compared. Our contributions are as follows. First, with the

assumption of additive white Gaussian noise (AWGN) chan-

nels, statistics and energy collection characteristics of the three

transceiver types are addressed. Then, peak selection error,

leading edge detection error (conditioned on the energy capture

characteristics of the transceivers at low-rate sampling), and

effects of pulse compression (increasing the number of pulses

per symbol) and processing gain achievable from replicate

symbol transmissions are discussed. Afterwards, the TOA esti-

mation performance is analyzed under multipath channels via

likelihood-based estimators. A Bayesian estimator algorithm

that ideally gives a lower bound is presented.

II. S

YSTEM MODEL

While the transmitted signal structures are the same for SR

and ED receivers, TR includes a delayed version of the same

GUVENC et al.: TOA ESTIMATION FOR IR-UWB SYSTEMS WITH DIFFERENT TRANSCEIVER TYPES 1877

signal and therefore yields a slightly different transmitted signal

model. Let the received UWB signal in multipath channel for the

former schemes be represented as

(1)

while, for the TR case, the received signal is modeled by

(2)

where frame index and frame duration are denoted by

and ,

respectively,

is the chip duration, is the symbol duration,

and

is the TOA of the received signal. Effective pulse after

channel effects is given by

, where is the received UWB pulse at the th tap with

unit energy,

is the symbol energy (we assume pulses

per symbol),

and are the fading coefﬁcients and delays

of the multipath components, respectively, and

The AWGN with zero-mean and double-sided power spectral

density

and variance is denoted by . The delay

between the data and reference signals

is denoted by

, and

energy is appropriately scaled so that the energy per symbol

is identical for all cases. No modulation is considered for the

ranging process. In order to avoid catastrophic collisions (e.g.,

a large number of hits between the pulses of different users)

and smooth the power spectral density of the transmitted signal,

time-hopping codes

are assigned to

different users, where

is the number of chip po-

sitions per frame. Moreover, random-polarity codes

are used to get additional processing gain for the detection of

desired signal and smooth the signal spectrum (see Fig. 1).

A. Sampling the Received Signal After Different

Energy-Collection Techniques

The signal arriving at the receiver’s antenna is passed through

a low-noise ampliﬁer (LNA) and a bandpass ﬁlter (BPF) of

bandwidth

. Different approaches for collecting the energy are

possible before sampling the signal in (1) or (2). The received

signal can be sampled after correlation with a stored-reference

signal [see Fig. 2(a)], after correlation with a TR signal [see

Fig. 2(b)], or after a square-law device [see Fig. 2(c)]. Block

duration (which corresponds to the sampling interval) is de-

noted by

and is equivalent to for chip-spaced sampling.

In the sequel, we assume that a coarse acquisition on the order

of frame-length is acquired, such that in (1)

where

denotes the (continuous) uniform distribution. The

block index that contains the ﬁrst arriving signal energy corre-

sponds to

, where . The

Even though we refer the pair of signals in TR as reference and data signals,

this is just for the sake of distinction, and we consider no data modulation for

ranging purposes.

Fig. 1. Illustration of IR-UWB pulse transmissions in a symbol,

where

(

N ;N

)=(5

;

, and

(

;

(

;

)

. The pulses with solid lines

correspond to ED and SR. Dashed pulses can be included for TR (after

appropriate energy scaling) with

Fig. 2. Sampling of the received signal after: (a) correlation with a local refer-

ence, (b) correlation with a transmitted reference, and (c) energy detection.

signal within time frame plus half of the next frame is sam-

pled and searched to factor in interframe leakage due to mul-

tipath. Thus, the number of samples (or blocks/chips) within

the TOA search region is given by

, and

denotes the sample index with re-

spect to the starting point of the uncertainty region.

With a sampling interval of

, the SR template signal and the

samples collected after correlating the received signal with this

template are given by

(3)

(4)

respectively, where

denotes the correlator pulse shape.

Since

no channel estimate is available prior to signal acquisition and

TOA estimation, absolute values of SR outputs are used (as

shown in Fig. 2), yielding

Note that, since received pulse shape

can change at different multipath

components due to its large bandwidth,

will not typically match with the re-

ceived pulse shapes. However, we have used

for all

in the simulations

for simplicity.

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dangdang_meme

2013-06-03

系统挺简单的，不过还能用

ustc1023

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