CDMA communication system and method using priority-based...

Details CDMA communication system and method using priority-based... CDMA communication system and method using priority-based...

1998-10-26

2002-07-16

Olms, Douglas (Department: 2661)

Multiplex communications

Communication over free space

Combining or distributing information via code word channels...

C370S328000

Reexamination Certificate

active

06421335

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to Code Division Multiple Access (CDMA) communication systems, and more particularly, to a system and method for integrating a priority-based quality of service in CDMA communication systems that implement data packet transmission, in order to effectively allocate radio resources.
BACKGROUND OF THE INVENTION
Future mobile cellular networks must be able to support data communication, particularly packet data communications. One question that is raised is how the radio resources are to be allocated in a system that transports data packets over the radio interface in an asynchronous manner. For example, where a mobile terminal transmits and receives internet protocol (IP) data packets, the radio resource may be used without any predictable pattern. Therefore, it would be beneficial to have a system and method that effectively allocates radio resources among different connections. One radio communications scheme that could provide such a radio interface for data communications is CDMA. The present invention describes various manners in which data packets can be communicated via a CDMA communications system, such that congestion problems can be effectively managed.
In order to fully appreciate the concept, purpose, and advantages of the present invention, a general understanding of Code Division Multiple Access (CDMA) radio technology is necessary. CDMA technology is fundamentally based on spread spectrum modulation. Generally, spread spectrum modulation is a type of modulation that scatters data transmissions across an available frequency band in a pseudorandom pattern. Spreading the data across the frequency spectrum causes the signal to be more resistant to noise, and has a high tolerance to jamming and signal interception.
A spread spectrum signal is one that is transformed with a function e(c) using a code c. The code, typically a pseudo-random code, is a sequence that is combined with the data signal to transform the initial narrowband signal into a wideband signal that can have the appearance of a noise signal. The effect of this transformation is illustrated in
FIG. 1
, which includes
FIGS. 1A
,
1
B and
1
C.
Referring first to
FIG. 1A
, a narrowband signal S
n
10
a
is shown in the frequency domain having a bandwidth B
n
. The signal S
n
10
a
is transformed by the function e(c) using a code c to produce the wideband signal S
w
10
b
having bandwidth B
w
as shown in FIG.
1
B. To create the wideband signal S
w
, the narrowband signal S
n
is “spread out” using the function e(c) over the increased bandwidth B
w
, typically using a spreading technique such as direct sequence (DS) or frequency hopping (FH). These spreading techniques are well-known in the art. The wideband signal S
w
10
b
is then transmitted, and the targeted receiver applies the same function e(c) based on code c to the transmitted wideband signal S
w
10
b
to reproduce the initial narrowband signal S
n
10
c
, as shown in FIG.
1
C.
The term Code Division Multiple Access indicates that there can be several signals carried within the same frequency band or “channel” using different codes. This is possible because only the signal with the correct code c
i
can be reproduced into the narrowband signal at the targeted receiver. Signals transmitted with other codes c
k
are not decoded at that particular receiver, and these other transmitted signals will have a noise-like appearance at the receiver.
FIG. 2
illustrates this concept.
FIG. 2A
represents two independent narrowband signals S
n
1
20
a
and S
n
2
22
a
. These two signals could represent two independent data transmissions, voice transmissions, or the like. Narrowband signal S
n
1
20
a
is transformed using code c
1
of the spreading function e(c
1
), and narrowband signal S
n
2
22
a
is transformed using code c
2
of the spreading function e(c
2
), to respectively produce wideband signals S
1
20
b
and S
w
2
22
b
shown in FIG.
2
B. The targeted receiver for original narrowband signal S
n
1
20
a
decodes the signal using the same code c
1
to reproduce the narrowband signal S
n
1
20
c
as shown in FIG.
2
C. However, because that particular targeted receiver does not include the code c
2
, signal S
w
2
22
c
is not decoded, and remains a wideband signal S
n
2
22
c
as illustrated in FIG.
2
C. The overlapping signal area represented by block
24
represents the noise imparted to the signal S
n
1
22
c
due to the wideband signal S
w
2
22
c.
As the number of signal transmissions over the common wideband channel increases (e.g., the number of concurrent users increases), it appears to the reproduced narrowband signal as an increase in background noise. This is illustrated in
FIG. 3
, which represents the signals seen at a particular signal receiver. As was described in connection with
FIG. 2C
, the overlapping area
24
is seen by the receiver as noise, so additional signals that are not decoded by that receiver are seen as cumulative noise. For example,
FIG. 3
depicts a reproduced narrowband signal S
n
1
30
, and four other undecoded wideband signals S
w
2
32
, S
w
3
34
, S
w
4
36
, and S
w
5
38
. Each of the undecoded wideband signals cumulatively increases the noise on the decoded narrowband signal S
n
1
32
, as illustrated by overlapping noise blocks
40
,
42
,
44
and
46
. Thus, the signal
oise ratio (SNR) of a single user decreases with the increasing number of users or transmitted signals in the common wideband channel. At some limit N
max
, the number of users cannot be increased any more or the individual resulting narrowband signals become too weak. In practice, the users with the weakest signal due to distance and radio conditions are first to lose their radio connection.
In order to guarantee an adequate signal-to-noise ratio (SNR) for existing connections, a control system is required. This would allow a new user to utilize the communication interface only where an adequate SNR would still be available after the new signal has been included in the common wideband frequency channel.
One prior art method of appropriating an acceptable number of users is to count the number of users, and allow new users to be included on the communication interface only if the number of users remains below a predetermined maximum number. In such a case, there is no distinction between users, and all users are treated equally. It is essentially a first-come, first-served system. However, this type of system does not take into account the various needs of different users, and particularly their willingness to pay for a higher degree of certainty that their connection will be made available. Thus, a future third generation network cellular system must be able to differentiate the user desires and needs.
Such a fixed differentiation system may pose complexity problems however. This rigid differentiation scheme does not take into account the magnitude of short term connections that transport relatively short data packets. This type of system would lack efficiency by disallowing many short term transfers, and would inevitably waste available bandwidth capacity.
Therefore, there is a need in the communications industry for a communications control system that allocates radio resources using a dynamically variable priority-based system. Such a system would account for individual users' willingness to pay more for a higher degree of transmission certainty, or to pay less for noncritical applications. The present invention provides such a system while avoiding the potential complexities and inefficiencies of more rigid schemes. The present invention therefore overcomes the aforementioned and other shortcomings of the prior art, and provides these and additional advantages over the prior art.
SUMMARY OF THE INVENTION
The present invention is directed to a system and method for integrating a priority-based quality of service in CDMA communication systems that implement data packet transmission, in order to effectively allocate radio resources.
In accordance with one

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