多窄带干扰下的非相干UWB通信技术

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"Non-Coherent UWB Communication in the Presence of Multiple Narrowband Interferers" 这篇文献主要探讨了在存在多个窄带干扰源环境下的非相干超宽带（UWB）通信技术。超宽带通信是一种利用极短脉冲进行传输的无线通信方式，具有低功率、高时间分辨率和抗多径衰落等优点，广泛应用于室内定位、无线传感器网络和高速数据传输等领域。文章由Alberto Rabbachin、Tony Q. S. Quek、Pedro C. Pinto和Ian Oppermann等人共同撰写，并发表在2010年11月的《IEEE Transactions on Wireless Communications》上。该期刊是电气与电子工程师学会（IEEE）出版的权威无线通信研究期刊，具有很高的学术价值。文中重点研究了在非相干检测的场景下，UWB信号如何在多个窄带干扰的影响下保持有效的通信性能。非相干检测是指不依赖载波相位信息进行解调的方法，它通常比相干检测更简单且对系统要求较低，但对抗干扰能力可能有所牺牲。在存在多个窄带干扰的情况下，这些干扰可能会对UWB信号的接收造成严重影响，降低系统的误码率和通信质量。作者们提出了针对这一问题的解决方案，可能包括采用特定的信号处理技术，如干扰抵消、多径分离或者利用UWB信号的时间分散特性来改善接收端的性能。他们通过理论分析和仿真结果展示了这些方法的有效性，为实际系统设计提供了参考。通过访问链接（http://dx.doi.org/10.1109/twc.2010.091510.080203），读者可以获取到此篇论文的最终发表版本，其内容受到IEEE的版权保护，同时也遵循了MIT教师的开放存取政策，使研究结果能更广泛地传播和应用。这篇论文深入研究了非相干UWB通信在多窄带干扰环境中的挑战与对策，对于理解UWB通信系统的抗干扰性能以及优化设计方案有着重要的指导意义。

RABBACHIN et al.: NON-COHERENT UWB COMMUNICATION IN THE PRESENCE OF MULTIPLE NARROWBAND INTERFERERS 3367

can be written as

𝑏

(𝑘)

(𝑡)=

𝑁

−1



𝑗=0



𝐸

𝑎

(𝑘)

𝑗

𝑝(𝑡 −𝑗2𝑇

− 𝑐

(𝑘)

𝑗

𝑇

𝑏

(𝑘)

(𝑡)=

𝑁

−1



𝑗=0



𝐸

𝑎

(𝑘)

𝑗

𝑝(𝑡 −𝑗2𝑇

− 𝑐

(𝑘)

𝑗

𝑇

− 𝑇

)

(4)

where 𝑏

(𝑘)

(𝑡) is equal to a version of 𝑏

(𝑘)

(𝑡) delayed by 𝑇

In TH signaling, {𝑐

(𝑘)

𝑗

} is the pseudo-random sequence of the

𝑘th user, where 𝑐

(𝑘)

𝑗

is an integer in the range 0 ≤ 𝑐

(𝑘)

𝑗

<𝑁

and 𝑁

is the maximum allowable integer shift. The bipolar

random amplitude sequence {𝑎

(𝑘)

𝑗

} together with the TH

sequence are used to mitigate interference and to support

multiple access. The essential duration of the unit energy

bandpass pulse 𝑝(𝑡) is 𝑇

and its center frequency is 𝑓

.The

energy of the transmitted pulse is 𝐸

= 𝐸

/𝑁

where

𝐸

is the symbol energy associated with TR signaling. Note

that the transmitted energy is equally allocated among 𝑁

reference pulses and 𝑁

/2 modulated pulses. The duration of

the received UWB pulse is 𝑇

= 𝑇

+ 𝑇

,where𝑇

is the

maximum excess delay of the channel. We consider 𝑇

≥ 𝑇

and (𝑁

− 1)𝑇

+ 𝑇

≤ 2𝑇

,where𝑇

is the time

separation between each pair of data and reference pulses

to preclude intra-symbol interference (isi) and inter-symbol

interference (ISI).

3) UWB BPPM Nodes: In this case, the transmitted signal

for user 𝑘 can be expressed as

𝑠

(𝑘)

BPPM

(𝑡)=



𝑖



(1 + 𝑑

(𝑘)

𝑖

)

𝑏

(𝑘)

(𝑡 − 𝑖𝑇

)

(1 − 𝑑

(𝑘)

𝑖

)

𝑏

(𝑘)

(𝑡 − 𝑖𝑇

)



(5)

where 𝑑

(𝑘)

𝑖

∈{−1, 1} is the 𝑖th data symbol and 𝑇

𝑁

𝑇

is the symbol duration with 𝑁

and 𝑇

denoting the number

of pulses per symbol and the average pulse repetition period,

respectively.

The transmitted signal for 𝑑

(𝑘)

𝑖

=+1and 𝑑

(𝑘)

𝑖

−1 can be written, respectively, as

𝑏

(𝑘)

(𝑡)=

𝑁

−1



𝑗=0



𝐸

𝑎

(𝑘)

𝑗

𝑝(𝑡 − 𝑗𝑇

− 𝑐

(𝑘)

𝑗

𝑇

𝑏

(𝑘)

(𝑡)=

𝑁

−1



𝑗=0



𝐸

𝑎

(𝑘)

𝑗

𝑝(𝑡 − 𝑗𝑇

− 𝑐

(𝑘)

𝑗

𝑇

− Δ)

(6)

where the parameter Δ is the time shift between two different

data symbols and the rest of the terms in (6) are deﬁned

similarly as in (4). For BPPM with non-coherent receivers, the

bipolar random amplitude sequence {𝑎

(𝑘)

𝑗

} can only serve the

purpose of spectrum smoothing. The energy of the transmitted

pulse is then 𝐸

2𝐸

𝑁

,where𝐸

is the symbol energy

Note that we set 𝑇

𝑇

so that the symbol durations of the two

signaling schemes are the same.

associated with BPPM. Note that the position modulation is

used and the transmitted energy is allocated among 𝑁

modulated pulses. To preclude isi and ISI, we assume Δ ≥ 𝑇

and (𝑁

− 1)𝑇

+Δ+𝑇

≤ 𝑇

C. Wireless Propagation Characteristics

1) NB Propagation: We consider that the impulse response

of the NB channel between the 𝑛-th interferer and the UWB

receiver is given by

ℎ

(𝑛)

(𝑡)=

𝑅

𝜈

𝑛

𝛼

𝑛

𝑒

𝜎

𝐺

𝑛

𝛿(𝑡 − 𝜏

𝑛

). (7)

We consider 𝛼

𝑛

to be Rayleigh distributed with 𝔼{∣𝛼

𝑛

∣

} =1,

which is an appropriate model when the signals are NB [41],

[42]. The term 𝜏

𝑛

accounts for the asynchronism between the

interferers. The shadowing term 𝑒

𝜎

𝐺

𝑛

follows a log-normal

distribution with shadowing parameter 𝜎

and 𝐺

𝑛

∽ 𝒩(0, 1).

According to the far-ﬁeld assumption, the signal power decays

as 1/𝑅

2𝜈

𝑛

,where𝜈 is the amplitude loss exponent and 𝑅

𝑛

the distance between the 𝑛th interferer and the UWB receiver.

2) UWB Propagation: We consider that the impulse re-

sponse of the UWB channel is given by [12], [14]



ℎ

(𝑡)=

𝑅

𝜈

𝑒

𝜎

𝐺

ℎ

(𝑡) (8)

where

ℎ

(𝑡)=

𝐿



𝑙=1

ℎ

𝑙

𝛿(𝑡 − 𝜏

𝑙

) (9)

with ℎ

𝑙

and 𝜏

𝑙

representing the attenuation and the delay of

the 𝑙th path component, respectively. We consider a resolvable

dense multipath channel, i.e., ∣𝜏

𝑙

− 𝜏

𝑗

∣≥𝑇

, ∀𝑙 ∕= 𝑗,where

𝜏

𝑙

= 𝜏

+(𝑙 −1)𝑇

,and{ℎ

𝑙

}

𝐿

𝑙=1

are statistically independent

random variables (r.v.’s). We can express ℎ

𝑙

= ∣ℎ

𝑙

∣exp (𝑗𝜙

𝑙

where 𝜙

𝑙

=0or 𝜋 with equal probability. We consider that

the terms

𝑅

𝜈

and 𝑒

𝜎

𝐺

representing the path-loss and the

shadowing in (8) are quasi-static, and therefore can be treated

as constant gains introduced by the UWB channel. Thus, for

simplicity, we will use ℎ

(𝑡) instead of



ℎ

(𝑡) to represent the

channel impulse response between the UWB transmitter and

the UWB receiver for the rest of the paper.

III. BEP

IN THE ABSENCE OF INTERFERENCE

A. AcR-TR-BPAM

As shown in Fig. 2, the AcR ﬁrst passes the received signal

through an ideal bandpass zonal ﬁlter (BPZF) with center

frequency 𝑓

to eliminate out-of-band noise [27], [31]. If the

bandwidth 𝑊 of the BPZF is large enough, then the signal

spectrum will pass through the ﬁlter undistorted. In the rest

of the paper, we focus on a single UWB user system and

we will suppress the index 𝑘 for notational simplicity. In the

absence of interference, the received signal can be expressed

as 𝑟

(𝑡)=ℎ

(𝑡) ∗ 𝑠

(𝑡)+𝑛(𝑡),where𝑛(𝑡) is zero-mean,

We use 𝒩 (0,𝜎

) to denote a Gaussian distribution with zero-mean and

variance 𝜎

Note that the amplitude loss exponent is 𝜈, while the corresponding power

loss exponent is 2𝜈. The parameter 𝜈 can approximately range from 0.8 (e.g.

hallways inside buildings) to 4 (e.g. dense urban environment), where 𝜈 =1

corresponds to free space propagation [43].

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