Multiplex communications – Diagnostic testing – Determination of communication parameters
Reexamination Certificate
1998-09-02
2001-09-25
Kizou, Hassan (Department: 2662)
Multiplex communications
Diagnostic testing
Determination of communication parameters
C370S337000, C370S332000, C370S347000, C455S067150, C455S115200, C455S423000
Reexamination Certificate
active
06295279
ABSTRACT:
BACKGROUND OF THE PRESENT INVENTION
1. Field of the Invention
The present invention relates generally to telecommunications systems and methods for measuring the carrier to interference ratio in a time division multiple access cellular network, and specifically to providing an accurate field measurement of the carrier to interference ratio on the reverse-link.
2. Background and Objects of the Present Invention
Mobile communications, especially cellular radio, is one of the fastest growing and most demanding telecommunications applications ever. Today it accommodates a large and continuously increasing percentage of all new telephone subscriptions around the world with the increasing service requirements. Cellular networks have evolved into two different networks within Time Division Multiple Access (TDMA) technology. The European cellular network uses the Global System for Mobile Communication (GSM) standard as the digital cellular system. In the United States, cellular networks have traditionally been primarily analog, but recent advances have been incorporating digital systems within the analog networks. One such North American cellular network is the D-AMPS network, which is described hereinbelow.
With reference now to
FIG. 1
of the drawings, there is illustrated a D-AMPS Public Land Mobile Network (PLMN), such as cellular network
10
, which in turn is composed of a plurality of areas
12
, each with a Mobile Services Center (MSC)
14
and an integrated Visitor Location Register (VLR)
16
therein. The MSC/VLR areas
12
, in turn, include a plurality of Location Areas (LA)
18
, which are defined as that part of a given MSC/VLR area
12
in which a mobile station (MS)
20
may move freely without having to send update location information to the MSC/VLR area
12
that controls the LA
18
.
Each Location Area
12
is divided into a number of cells
22
. Mobile Station (MS)
20
is the physical equipment, e.g., a car phone or other portable phone, used by mobile subscribers to communicate with the cellular network
10
, each other, and users outside the subscribed network, both wireline and wireless. The MSC
14
is in communication with a Base Station (BS)
24
. The BS
24
is the physical equipment, illustrated for simplicity as a radio tower, that provides radio coverage to the geographical part of the cell
22
for which it is responsible.
With further reference to
FIG. 1
, the PLMN Service Area or cellular network
10
includes a Home Location Register (HLR)
26
, which is a database maintaining all subscriber information, e.g., user profiles, current location information, and other administrative information. The HLR
26
may be co-located with a given MSC
14
, integrated with the MSC
14
, or alternatively can service multiple MSCs
14
, the latter of which is illustrated in FIG.
1
.
The VLR
16
is a database containing information about all of the Mobile Stations
20
currently located within the MSC/VLR area
12
. If a MS
20
roams into a new MSC/VLR area
12
, the VLR
16
connected to that MSC
14
will request data about that Mobile Station
20
from the HLR database
26
(simultaneously informing the HLR
26
about the current location of the MS
20
). Accordingly, if the user of the MS
20
then wants to make a call, the local VLR
16
will have the requisite identification information without having to reinterrogate the HLR
26
. In the aforedescribed manner, the VLR and HLR databases
16
and
26
, respectively, contain various subscriber information associated with a given MS
20
.
The radio interface between the BS
24
and the MS
20
utilizes Time Division Multiple Access (TDMA) to transmit information between the BS
24
and the MS
20
, with one TDMA frame per carrier frequency. Each frame consists of six timeslots or physical channels. Depending upon the kind of information sent, different types of logical channels can be mapped onto the physical channels. For example, speech is sent on the logical channel, “Traffic Channel” (TCH), and signaling information is sent on the logical channel, “Control Channel” (CCH).
Currently, speech and data are transmitted from the BS
24
to the MS
20
on a forward-link channel
30
and from the MS
20
to the BS
24
on a reverse-link channel
32
. Interference on either the forward-link or reverse-link channel can significantly reduce the quality of the signal transmitted on these channels. At present, there are two types of interference: co-channel interference and adjacent channel interference. Co-channel interference is the interference caused by the usage of the same frequency within two different clusters (not shown) of cells
22
. Adjacent channel interference is caused by the usage of adjacent frequencies between adjacent cells
22
within the same cluster or within two different clusters.
The carrier-to-interference (co-channel or adjacent-channel) (C/I) ratio is one of the most important radio network performance criteria in evaluating a wireless communication system, including, but not limited to the GSM network, the new Personal Communications System (PCS) network, the D-AMPS network, and the AMPS network. In order to reduce interference within the cellular system
10
, both co-channel and adjacent channel interference must be minimized. Therefore, by increasing the ratio, e.g., by reducing the interference with respect to the carrier (level) of the desired signal, the co-channel or adjacent channel interference can be reduced and the signal quality received by MSs
20
within the cell
22
can be improved.
The EIA/TIA IS-136 standards specify the minimum performance requirements of the carrier-to-co-channel interference and the carrier-to-adjacent channel interference for a BS
24
. In order for vendors to ensure that their products meet C/I minimum performance requirements, the reverse-link C/I performance must be measured. These C/I field performance measurements are used by many operators as one of the criteria in comparing different vendors' products and evaluating the quality of purchased products. Furthermore, an accurate field knowledge of the C/I performance for the system is important for designing a cellular network and optimizing an existing network. However, at present, there is no accurate technique of C/I field measurement available.
It is, therefore, an object of the present invention to provide a system and method for obtaining an accurate Carrier-to-Interference field measurement.
SUMMARY OF THE INVENTION
The present invention is directed to telecommunications systems and methods for obtaining an accurate reverse-link C/I measurement for a Time Division Multiple Access (TDMA)-based system in a field environment. The field measurement is performed by using one time slot (voice channel) of one TDMA carrier for recording the carrier signal strength while two other time slots (two idle voice channels) are used in recording the co-channel or adjacent channel interference in a pseudo real time basis. Either the maximum interference or the average interference on the two additional time slots can be used to determine the C/I performance. Alternatively, one additional time slot can be used to measure the interference if the other additional time slot is in conversation. Advantageously, the system and method of the present invention can be applied to any TDMA-based system deployed for outdoor or indoor applications without any major modifications. In addition, this system and method can also be applied to reverse-link C/I lab measurement without major modifications. Furthermore, the system and method of the present invention provides a performance C/I measurement for the cellular network at a system level instead of at a component level (Base Station).
REFERENCES:
patent: 5533055 (1996-07-01), Matzek
patent: 5799243 (1998-08-01), Ojaniemi
patent: 5898928 (1999-04-01), Karlsson et al.
patent: 6006092 (1999-12-01), Ward
Ericsson Inc.
Jenkens & Gilchrist P.C.
Kizou Hassan
Tran Thien
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