Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-06-27
2003-07-08
Urban, Edward F. (Department: 2685)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S436000, C455S423000, C455S067150, C455S454000, C455S424000, C455S067700, C370S332000, C370S333000, C375S224000, C375S227000
Reexamination Certificate
active
06591110
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is generally related to a method for detecting and calculating the contribution of external jammer signals to total power received in a reverse link of a communication system.
2. Description of the Related Art
Communication systems, and in particular, wireless communication systems comprise a plurality of communication channels through which subscribers of such systems communicate with each other and with the system. Wireless communication systems such as Code Division Multiple Access (CDMA) systems and other communication systems have a certain capacity; that is they are limited by the amount of communication channels that can be made available to subscribers of such systems. The capacity of a communication system is the amount of total information per unit time (i.e., information rate, R
T
) that can be conveyed (within the system) while maintaining an acceptable quality of communications. The acceptable quality of communications is typically defined by the operator (or service provider) of the communication system. Usually, the capacity is directly related to the number of subscribers using the system; the more subscribers using the system the higher the information rate.
Referring to
FIG. 1
there is shown part of a typical topography of a cellular CDMA wireless communication system. The communication system depicted in
FIG. 1
comprises a plurality of cells each of which delineates a particular geographical area or terrain that is covered by the communication system. The cells have borders which form hexagons. The hexagons (
108
,
114
,
110
,
112
) symbolically represent areas of coverage within which subscribers located in the same cell communicate with the cell (i.e., cell system equipment). Each cell has system equipment (owned and controlled by a system operator or service provider) that are used by the system to admit subscribers to the system; that is to allow subscribers of the system to gain access to the communication system for communicating with each other and/or with the system. At least part of the system equipment is typically located at a base station (e.g.,
100
,
102
,
104
,
106
). Some of the system equipment at the base stations are Radio Frequency (RF) transmitters and receivers for conveying (i.e., transmitting and receiving) communication signals.
Other system equipment, which can also be located at a base station, provide the Operations, Administration and Maintenance (OA&M) services typically associated with communications equipment. For example, subscriber billing, allocating communication channels for subscribers, and giving subscribers access to the communication system are some of the services provided by the OA&M equipment. Subscribers given access to the communication system can communicate with other subscribers via the cell's base station.
For a CDMA communication system, such as the one depicted in
FIG. 1
, a subscriber gains access by making a request to system equipment (usually located at a base station). For example, subscriber
124
in cell
112
makes a request to base station
100
to have access to the communication system. System equipment at base station
100
receive the request and decide whether to give subscriber
124
access to the communication system. Subscriber
124
and base station
100
(as well as other base stations and subscribers) communicate via communication channels called forward links and reverse links. A forward link is a communication channel through which base station
100
transmits communication signals to subscriber
124
. A reverse link is a communication channel through which subscriber
124
transmits communication signals to base station
100
. Thus, each subscriber has a forward link and a reverse link that it uses to communicate with system equipment and/or with other subscribers of the communication system.
Typically, the system decides to provide access to a subscriber by performing a power level analysis that attempts to maintain the quality of communications between subscribers at an acceptable level as defined by the system operator. The system could continue to admit subscribers requesting communication services (or continue to respond to a system request or “page” to admit subscribers) and thus continue to increase its information rate. At some point an overload condition will occur causing the quality of communications provided by the communication system to be degraded. An overload condition occurs when the information rate of the communication system causes the quality of communications (e.g., existing voice and/or data calls) to drop below an acceptable level set by the system operator. Usually the acceptable level is set as a threshold below the system's ultimate capacity. One example of an overload condition is when a cell communicates with a relatively large number of subscribers such that the system cannot meet the desired signal to noise ratio (SNR) requirement. The number of subscribers that can be adequately serviced by a cell depends on the SNR usually expressed in terms of a ratio,
E
b
N
0
,
where E
b
represents the total received signal energy per unit of information (e.g., energy per bit) and N
0
represents the total noise power density. The higher the
E
b
N
0
of the signal measured at a receiver, the better the quality of communications.
The following equation defines the reverse-link signal to noise ratio
(
E
b
N
0
)
i
,
k
m
for subscriber i in cell k as measured by cell m:
(
E
b
N
0
)
i
,
k
m
≡
(
W
R
)
i
,
k
×
S
i
,
k
m
N
th
+
J
+
∑
j
=
1
j
≠
i
M
k
υ
j
,
k
S
j
,
k
m
+
∑
l
=
1
l
≠
k
L
∑
j
=
1
M
l
υ
j
,
l
S
j
,
l
m
(
1
)
The indices i and j designate particular subscribers and the indices k, l and m designate particular cells. M
l
is the number of subscribers in cell l, M
k
is the number of subscribers in cell k, L is the total number of cells in the system,
(
W
R
)
i
,
k
is called the processing gain for subscriber i in cell k where W is the bandwidth or a CDMA carrier signal and R is the information rate of subscriber i. The average power of the reverse-link signal is defined as the product of the power level (S) and the voice activity factor (&ngr;) of the reverse-link signal. In equation (1) above, S
j,k
m
is the power level of the communication signal of subscriber j in cell k as measured at cell m, and the voice activity &ngr;
j,k
represents how often subscriber j in cell k speaks during a telephone conversation or how often a data energy burst is transmitted by the subscriber. N
th
represents the power level of thermal noise typically generated by electrical and electronic circuitry. J represents the power level of any external jammer signals, which is a type of interference. Any signal other than a subscriber's communication signal is called interference. Two major sources of interference are thermal noise and external jammer signals. An external jammer signal is any signal not generated by the communication system, but is received by the communication system or received by a subscriber of the communication system. For example, an external jammer interfering with a CDMA communication system is an analog mobile telephone user transmitting signals whose frequency spectrum is partially or entirely the same as the spectral band of the CDMA system; in such a situation the analog mobile signal interferes with CDMA subscriber signals because the subscriber or the communication system or both receive the analog mobile signal.
The aggregate power received by a base station is due to thermal noise (N
th
), external jammers (J), and the CDMA subscriber signals (&ngr;S). Thus, the total received power through a particular reverse link of a base station, which is called the received signal strength indicator (RSSI), has three components and is represented for a particular cell m by the following equation:
RSSI
m
≡
N
th
+
J
+
∑
l
=
1
L
∑
j
=
1
M
l
υ
Kim Kyoung Il
Salvarani Alexandro Federico
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