Pulse or digital communications – Receivers – Interference or noise reduction
Reexamination Certificate
1999-08-18
2003-10-28
Chin, Stephen (Department: 2634)
Pulse or digital communications
Receivers
Interference or noise reduction
Reexamination Certificate
active
06639955
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to generating signals in a telecommunication system, and, more particularly, to generating complex Rayleigh fading signals.
2. Description of the Related Art
Fading of a transmitted signal is a characteristic of an over-air channel of, for example, wireless, cellular, and radio telecommunication systems. Fading causes distortion of the transmitted signal with variations in signal amplitude and phase. Distortion of the transmitted signal degrades the operation of a receiver that reconstructs the data contained in the transmitted signal, affecting the reliability and quality of the communication link. Design of robust wireless or similar systems may focus on methods to reduce the effects of fading. Generating fading signals allows for simulation of the transmission channel and allows for development, performance testing, and verification of designs without extensive testing of the design in the actual field environment. Such testing is both expensive and time consuming, especially when many different design aspects are considered.
Complex Rayleigh fading signals are commonly employed for simulation and may be generated in accordance with the Jakes fading model. The in-phase (I) and quadrature-phase (Q) (fading signal) components r
I
(t) and r
Q
(t) in accordance with the Jakes fading model of the prior art are as given in equations (1) and (2). The gain parameters of equations (1) and (2) are defined in equation (3):
r
I
(
t
)
=
2
cos
αcos
ω
m
t
+
2
∑
n
=
1
M
cos
β
n
cos
ω
n
t
(
1
)
r
Q
(
t
)
=
2
sin
α
cos
ω
m
t
+
2
∑
n
=
1
M
sin
β
n
cos
ω
n
t
(
2
)
ω
n
=
ω
m
cos
n
π
2
M
+
1
,
β
n
=
n
π
M
+
1
,
1
≤
n
≤
M
(
3
)
where &ohgr;
m
is the fading bandwidth and &agr; is a constant generally set to zero, but may take on other values for particular implementations to adjust for system and/or transmission channel characteristics.
A system of the prior art for generating complex Rayleigh fading signal components r
I
(t) and r
Q
(t) according to the Jakes fading model is shown in FIG.
1
. The system
100
includes M pairs of in-phase (I) and quadrature-phase (Q) paths
110
(
1
)-
100
(M) and
111
(
1
)-
111
(M), respectively (M an integer and 1≦n≦M). The nth pair of I and Q paths
110
(n) and
111
(n) includes a corresponding signal generator
101
(n) generating a signal with frequency &ohgr;
n
. Each of the I and Q paths
110
(n) and
111
(n) for the nth path pair has gain adjustment of the corresponding signal by amplifiers
102
(n) and
103
(n), respectively. The gain parameters for the adjustment are determined as given in equation (3). An additional path pair
106
and
114
of I and Q paths includes a corresponding signal generator
107
generating a signal with frequency &ohgr;
m
, and this frequency is either based on or equivalent to the fading bandwidth. Each of the I and Q paths
106
and
114
for the additional path pair has gain adjustment by amplifiers
108
and
109
, respectively, with gain parameters determined as given in equation (3).
The output signals of the amplifiers
102
and
108
for all I paths are summed in adder
113
to provide the I component r
I
(t) of fading signal r(t). The output signals of the amplifiers
103
and
109
for all Q paths are summed in adder
112
to provide the Q component r
Q
(t). Adders
112
and
113
may not necessarily be employed if the addition of signals is within the transmission channel.
The advantages of generators that employ the Jakes fading model are (i) the implementation of the generator is relatively simple; (ii) some of the statistical quantities of the model generally agree with or closely approximate the characteristics of ideal channel fading; and (iii) implementations may simultaneously generate multiple fading signals uncorrelated with one another. The Jakes fading model, however, deviates from the ideal fading significantly in that the Jakes model autocorrelation values for the in-phase and quadrature components are different from one another, while the two autocorrelation values for the in-phase and quadrature components for ideal fading signals are generally equivalent.
The autocorrelation values &phgr;
rI
(t) and &phgr;
rQ
(t) for the I and Q components r
I
(t) and r
Q
(t), respectively, are given in equations (4) and (5).
φ
rI
(
t
)
=
lim
T
→
∞
∫
0
T
r
I
(
τ
+
t
)
r
I
(
τ
)
ⅆ
τ
=
cos
2
αcos
ω
m
t
+
2
∑
n
=
1
M
cos
2
β
n
cos
ω
n
t
(
4
)
φ
rQ
(
t
)
=
lim
T
→
∞
∫
0
T
r
Q
(
τ
+
t
)
r
Q
(
τ
)
ⅆ
τ
=
sin
2
αcos
ω
m
t
+
2
∑
n
=
1
M
sin
2
β
n
cos
ω
n
t
(
5
)
As given by equations (4) and (5), &phgr;
rI
(t) is not equivalent to &phgr;
rQ
(t) unless sin
2
&bgr;
n
=cos
2
&bgr;
n
for n=1, . . . , M and sin
2
&agr;=cos
2
&agr;. However, for the condition that &phgr;
rI
(t) is equivalent to &phgr;
rQ
(t), r
I
(t) must be equivalent to r
Q
(t), (i.e., the fading signal has identical real and imaginary parts). For the ideal fading model, the real and imaginary components of the fading signal are desirably independent, and so these conditions are not desirable for a complex fading signal generator.
SUMMARY OF THE INVENTION
The present invention relates to generating one or more complex fading signals. A fading signal may be generated by generating in-phase (I) and quadrature phase (Q) signals for each of a plurality of complex carriers, each complex carrier having a frequency related to a fading bandwidth of the complex fading signal; and providing i) one or more of the I signals corresponding to an I component of the complex fading signal, and ii) one or more of the Q signals corresponding to a Q component of the complex fading signal. For each fading signal, the I and Q components of the complex fading signal have substantially equivalent autocorrelation values.
REFERENCES:
Dent et al., Jakes Fading Model Revisited, Jun. 24, 1993, Electronics Letters, vol. 29, No. 13, pp. 1162-1163.*
Banister et al., Tracking Algorithm of the RLS Algorithm Applied to an Antenna Array in a Realistic Fading Environment, May 2002, IEEE Transactions On Signal Processing, vol. 50, pp.: 1037-1050.*
Patzold et al., Statistical Properties of Jakes' Fading Channel Simulator, May 18-21, 1998, Vehicular Technology Conference, 1998. VTC 98. 48th IEEE, vol.: 2, pp.: 712-718.*
Li et al.,Modified Jakes' Model for Simulating Multiple Uncorrelated Fading Waveforms, VTC 2000-Spring Tokyo. 2000, Vehicular Technology Conference Proceedings, 2000, pp.: 1819-1822.*
“Jakes Fading Model Revisited” by P. Dent, G. F. Bottomley and T. Croft; Electronics Letters 24thJun. 1993, vol. 29; No. 13.
Agere Systems Inc.
Chin Stephen
Hughes Ian M.
Mendelsohn Steve
Williams Lawrence
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