超宽带技术：UWB无线通信的新纪元
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收藏 3.21MB PDF 举报 "本文是关于超宽带（UWB）技术的综述性文章，作者为Liuqing Yang和Georgios B. Giannakis，发表在2004年的IEEE SIGNAL PROCESSING MAGAZINE上。文章详述了UWB在无线通信、网络、雷达、成像和定位系统中的独特优势，并探讨了美国联邦通信委员会（FCC）于2002年制定的规则对UWB技术的推动作用，以及全球各地类似监管进程的影响。"
超宽带（UWB）技术是一种快速发展的无线通信技术，以其独特的特性在多个领域展现出巨大潜力。UWB的主要特点是利用极低功率的超短信息承载脉冲，在3.6至10.1 GHz的频段（噪声地板）进行操作，这在不干扰现存射频系统的同时，提供了大量的“新带宽”。这种技术的引入，为无线通信和网络带来了革命性的变革。
FCC在2002年的规定，实质上释放了这个低功率、高带宽的通信空间，引发了行业、政府机构和学术界对UWB技术的广泛研究兴趣。这些研究主要集中在以下几个方面：
1. **高速宽带接入**：UWB技术可以提供短距离内的极高数据传输速度，使用户能够快速地接入互联网，尤其适用于家庭和办公室环境中的无线连接。
2. **隐蔽通信链接**：由于其低功率和窄脉冲特性，UWB系统可以用于创建不易被探测到的通信链路，适合军事或安全应用。
3. **厘米级定位精度**：UWB在定位系统中的应用，可实现高精度室内定位，如导航、物流追踪或紧急救援等场景。
4. **高分辨率地面穿透雷达**：在雷达系统中，UWB技术能提供精细的地下结构成像，可用于地质勘探、考古挖掘以及基础设施检测。
5. **无线传感器网络**：UWB技术在无线传感器网络中的应用，可以支持大量设备间的低功耗通信，用于环境监控、智能建筑和物联网等场景。
随着全球范围内的监管政策逐步放开，UWB技术的发展和应用将不断扩展，未来有望在无线通信、物联网、智能城市等领域发挥关键作用。同时，UWB技术也面临着与现有无线系统的共存问题，需要解决干扰问题和优化资源分配，以确保其高效、稳定运行。因此，UWB的研究不仅包括技术本身，还包括与现有技术的融合和协同，以实现更广泛的应用。
development of UWB radios because negating ultra-
short pulses were difficult to implement. Another mod-
ulation scheme that does not require pulse negation is
the so termed on-off keying (OOK), where symbol “1”
is represented by transmitting a pulse, and “0” by
transmitting nothing.
As pulse negation became easier to implement, pulse
amplitude modulation (PAM) attracted more attention.
In particular, when
M = 2
, antipodal pulses are used to
represent binary symbols, as in binary phase shift key-
ing (BPSK) or bipolar signaling. Biorthogonal signal-
ing by combining orthogonal PPM with binary PAM as
well as orthogonal waveform and block orthogonal
modulation schemes have also been reported [43].
To allow for multi-user access (MA) to the UWB
channel, time hopping (TH) was introduced early in
[52]. With TH, each pulse is positioned within each
frame duration
T
f
according to a user-specific TH
sequence
c
TH
u
(n)
. Specifically, dividing each frame into
N
c
chips each of duration
T
c
, the
u
th user’s TH code
c
TH
u
(n) ∈ [0,N
c
− 1]
corresponds to a time shift of
c
TH
u
(n)T
c
during the
n
th frame [72]. Consequently,
the
u
th user’s transmitted waveform is given by
v
u
(t ) =
E
u
+∞
n=0
a
u
n/N
f
· p
t − nT
f
− c
TH
u
(n)T
c
− b
u
n/N
f
,
(2)
where
E
u
is the
u
th user’s energy per pulse at the trans-
mitter end. With
s
u
(k) ∈ [0, M − 1]
denoting the
M
-
ary information symbol transmitted by the
u
th user
during the
k
th symbol duration, (2) subsumes several
modulation schemes. When
b
u
(k) = s
u
(k)
, and
a
u
(k) = 1
, (2) describes UWB transmissions with
M
-
ary PPM; when
a
u
(k) = 2s
u
(k) + 1 − M
, and
b
u
(k) = 0
, (2) models
M
-ary PAM. With binary sym-
bols, and
b
u
(k) = 0
,
a
u
(k) = 2s
u
(k) − 1
corresponds to
BPSK, and
a
u
(k) = s
u
(k)
corresponds to OOK [32],
[43], [69].
With TH codes, MA is achieved by altering the
pulse position from frame to frame, according to the
sequence
c
TH
u
(n)
. MA can also be enabled by modify-
ing the pulse amplitude from frame to frame. The latter
allows for many other choices of alternative spreading
codes which, individually or in combination with TH
codes, give rise to the following transmitted waveform
[c.f.
(2)
]:
v
u
(t ) =
E
u
+∞
n=0
a
u
n/N
f
c
u
(n)
· p
t − nT
f
− c
TH
u
(n)T
c
− b
u
n/N
f
,
(3)
where
c
u
(n)
is the user-specific “amplitude code” dur-
ing the
n
th frame. Depending on the spreading codes
employed, the UWB systems are termed TH-UWB
[52], direct-sequence (DS)-UWB [15], or baseband
single-carrier/multicarrier (SC/MC)-UWB [66], [77],
just to name a few.
In addition to facilitating multiple access, spreading
codes also shape the transmit spectrum. Analytical
expressions and simulated power spectral density
(PSD) for UWB transmissions are pursued in [44]
and [70]. A PSD expression for TH-UWB allowing
for both short and long spreading codes is derived
in [44]. The effects of timing jitter on PSD of UWB
transmissions utilizing random TH codes and/or
M
-ary modulation can be found in [70]. In particu-
lar, let us consider “short” spreading codes that are
symbol-periodic with period
N
f
. Let us now define
the symbol level transmitted waveform for user
u
as
IEEE SIGNAL PROCESSING MAGAZINE
NOVEMBER 2004 31
▲ 4. (a) Generally adopted pulse shapes in UWB communications; (b) Fourier transform of several pulse shapes. Pulse width:
0.7
ns.
0 0.1
0.2
0.3 0.4
0.5
0.6 0.7 0.8 0.9
−1
−0.8
−0.6
−0.4
−0.2
0
0.2
0.4
0.6
0.8
1
Time (ns)
(a)
Amplitude (dB)
Gaussian Pulse
Gaussian Monocycle
Scholtz Monocycle
10
0
10
1
−70
−60
−50
−40
−30
−20
−10
0
10
Frequency (GHz)
(b)
Power (dB)
Gaussian Pulse
Gaussian Monocycle
Scholtz Monocycle
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