Pulse or digital communications – Receivers – Interference or noise reduction
Reexamination Certificate
2000-08-21
2004-06-15
Chin, Stephen (Department: 2634)
Pulse or digital communications
Receivers
Interference or noise reduction
C375S134000, C375S334000, C375S340000
Reexamination Certificate
active
06751273
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a Bluetooth system; and more particularly, to an apparatus for compensating a channel distortion for use in a Bluetooth system.
BACKGROUND OF THE INVENTION
Recently, with the rapid advent of information age accompanied with fast development of various communication technologies, industries have taken strong interests in wireless personal area networks (WPAN) such as the so-called Bluetooth and shared wireless access protocol (SWAP). In particular, the Bluetooth system is focused on a low cost, simple hardware and robustness facilitating protected ad-hoc connections for stationary and mobile communication environments.
The Bluetooth system has three main application areas: a wire replacement, a local area network (LAN) access point and a personal area network. In the so-called Bluetooth ad-hoc network or piconet, data is conveyed in a packet having access codes, a header and a payload. There are two link types: a synchronous connection-oriented (SCO) link and an asynchronous connection-less (ACL) link. The SCO link is a point-to-point link between a master and a single slave. The ACL link is a point-to-multipoint link between a master and slaves in a piconet.
The Bluetooth system usually adopts a slotted time division duplex (TDD) scheme for full duplex transmission, wherein in this case, a length of each slot is 625 &mgr;s and two slots form one frame. A fast frequency hopping scheme of 1600 hops/s and a short data packet format are used for robustness in a noisy and interference environment. Also, a forward error correction (FEC) and an automatic repeat request (ARQ) are used as error correction schemes. The purpose of a FEC scheme on a data payload is to reduce the number of retransmission for improving throughput thereof. The data transmitted has a gross bit rate of 1 Mbit/sec.
A Gaussian-shaped frequency shift keying (GFSK) modulation is applied to minimize a transceiver complexity thereof. The nominal and supported range of the Bluetooth system is from 10 cm to 10 m; but the range can be extended to 100 m with an external power amplifier. A binary GFSK with modulation index between 0.28 and 0.35 is employed for a simple and small transceiver implementation.
FIG. 1
shows a block diagram of a GFSK transmitter for use in a conventional Bluetooth system. The GFSK transmitter includes a Bluetooth link controller
11
, a packet generator
13
, a Gaussian low pass filter (LPF)
15
, an integrator
17
and a modulator
19
. The packet generator
13
generates a packet signal under the control of the Bluetooth link controller
11
. The Gaussian LPF
15
filters the packet signal to thereby provide a filtered signal g(t). Then, the integrator
17
performs integration on the filtered signal g(t) to thereby feed an integrated signal. The modulator
19
modulates the integrated signal to thereby generate a GFSK signal p(k). A binary. GFSK with modulation index between 0.23 and 0.35 is employed for a simple and small transceiver implementation.
In the above, the p(t) can be written as:
p
(
t
)
=
Re
{
2
E
T
ⅇ
j2π
{
f
c
t
+
h
∫
-
∝
t
g
(
τ
)
ⅆ
τ
}
}
wherein E is an energy per a symbol; T is a symbol period; f
c
is a carrier frequency; h is a modulation index; and g(t) is the output of the Gaussian LPF
15
. The g(t) can be expressed as:
g
(
t
)
=
∑
k
=
-
∝
∞
a
k
v
(
t
-
kT
)
wherein a
k
=±1; and
v
(
t
)
=
1
2
{
erf
(
-
λ
B
b
T
)
+
erf
(
λ
B
b
(
t
+
T
)
)
}
,
λ
=
2
ln
2
π
,
B
b
T=0.5, B
b
being a 3 dB bandwidth of GLPF and
erf
(
t
)
=
∫
0
t
2
π
ⅇ
-
t
2
ⅆ
t
.
Meanwhile, in the conventional Bluetooth system employed in an indoor environment such as home, office or airport, it is assumed that a statistical channel modeling for the Bluetooth system is performed as a multi-path channel model; and received signals form groups of clusters. A low-pass equivalent channel impulse response can be given
c
(
t
)
=
∑
l
=
0
∞
∑
k
=
0
∞
γ
kl
ⅇ
j
θ
kl
δ
(
t
-
T
l
-
τ
kl
)
wherein T
1
is an arrival time of an l-th cluster; &tgr;
kl
is an arrival time of a k-th ray measured from the beginning of the l-st cluster; &thgr;
kl
is a phage shift; and &ggr;
kl
is a power gain of the k-th ray in the l-st cluster. It is assumed that the Bluetooth system operates in the indoor environment with an rms delay spread of 50 ns, a maximum delay spread of 300 ns and Doppler spread of 10 Hz. The modulated GFSK signal is transmitted at a 1 Mbit/s rate in 625 &mgr;s slot size, which makes the channel to be fixed within a slot.
FIG. 2
depicts a conventional channel modeling of the Bluetooth system. A received GFSK signal s(t) which has been changed while passing the transmission channel, as shown in
FIG. 2
, can be given by:
s
(
t
)
=
m
(
t
)
c
(
t
)
+
n
(
t
)
=
2
E
T
C
(
t
)
ⅇ
j
(
φ
(
t
,
α
_
)
+
φ
c
(
t
)
)
+
N
(
t
)
ⅇ
j
φ
n
(
t
)
=
A
2
(
t
)
+
B
2
(
t
)
ⅇ
j
tan
-
1
B
(
t
)
A
(
t
)
wherein
c(t)=C(t)e
j&phgr;c(t)
is a component of the channel distortion;
n(t)=N(t)e
j&phgr;m(t)
is an additive white Gaussian noise (AWGN);
&phgr;(t,{overscore (&agr;)})=2&pgr;h∫∞g(&tgr;)d&tgr;;
m
(
t
)
=
2
E
T
ⅇ
j
φ
(
t
,
α
_
)
is an equivalent complex envelope of p(t); and
A
(
t
)
=
{
2
E
T
C
(
t
)
cos
(
φ
(
t
,
α
_
)
+
φ
(
t
)
)
+
N
(
t
)
cos
(
φ
n
(
t
)
)
}
,
B
(
t
)
=
{
2
E
T
C
(
t
)
sin
(
φ
(
t
,
α
_
)
+
φ
(
t
)
)
+
N
(
t
)
sin
(
φ
n
(
t
)
)
}
.
A GFSK modulation system usually uses an FM discriminator.
FIG. 3
represents a structure of a conventional GFSK modulator
300
. The GFSK modulator
300
includes a hard limiter
310
, an FM discriminator
320
and an LPF
330
. The hard discriminator
310
compensates an amplitude of the received signal s(t). The FM discriminator
320
detects a phase of the compensated s(t) to thereby extract desired information. The following terms S
c
(t) and &phgr;(t) are related to the desired information, which can be expressed by the following equations:
S
c
(
t
)
=
s
(
t
)
&LeftBracketingBar;
s
(
t
)
&RightBracketingBar;
ⅇ
j
tan
-
1
B
(
t
)
A
(
t
)
,
ϕ
(
t
)
=
ⅆ
{
tan
-
1
B
(
t
)
A
(
t
)
}
ⅆ
t
=
1
1
+
(
B
(
t
)
A
(
t
)
)
2
B
′
(
t
)
A
(
t
)
-
B
(
t
)
A
′
(
t
)
A
2
(
t
)
.
Referring to the above equations for the S
c
(t) and &phgr;(t), it can be understood that a demodulated GFSK signal may be distorted by the channel. In other words, the distortion of the phase and amplitude of a signal transmitted through a channel deteriorates the performance of the demodulator. Further, in the conventional Bluetooth system employed in an indoor environment such as home, office or airport, the distortion of the phase and amplitude of a transmitted signal through a channel can be severely deteriorated due to the reflection, refraction, diffraction or dispersion therein. Accordingly, it is necessary to prepare a channel distortion compensation apparatus in the Bluetooth system.
In a conventional apparatus for compensating the channel distortion in the Bluetooth system, the information for the channel is needed. A pilot signal or a training signal is employed to offer the information for the cha
Cho Jin-Woong
Ju Min-Chul
Paik Jong Ho
Park Cheol-Hee
You Young Hwan
Katten Muchin Zavis & Rosenman
Korea Electronics Technology Institute
Lugo David B.
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