Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2001-11-01
2003-07-08
Vo, Nguyen T. (Department: 2685)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S063300, C370S335000, C370S336000
Reexamination Certificate
active
06591109
ABSTRACT:
BACKGROUND
The invention generally relates to wireless time division duplex (TDD) communication systems using code division multiple access (CDMA). In particular, the invention relates to reducing cross cell user equipment interference in such systems.
FIG. 1
is an illustration of a wireless TDD/CDMA communication system
10
. The communication system
10
has base stations
12
1
to
12
n
(
12
) which communicate with user equipments (UEs)
14
1
to
14
n
(
14
). Each base station
12
has an associated operational area or cell. The base station communicates with UEs
14
in its cell.
In CDMA communication systems, multiple communications are sent over the same frequency spectrum. These communications are distinguished by their channelization codes. To more efficiently use the frequency spectrum, TDD/CDMA communication systems use repeating frames divided into timeslots, such as fifteen timeslots, for communication. In TDD, each cells' timeslots are used solely for either the uplink or downlink at a time. A communication sent in such a system has one or multiple associated code(s) or timeslot(s) assigned to it. The use of one code in one timeslot with spreading factor of sixteen is referred to as a resource unit.
Cross cell interference is a problem in such systems as illustrated in FIG.
2
. If two different cells' UEs
14
are close to each other, their uplink transmissions interfere with the other UE's downlink transmissions in the same timeslot. As shown in
FIG. 2
, UE
14
1
uplink transmission U
1
interferes with UE
14
2
downlink transmission D
2
. Likewise, UE
14
2
uplink transmission U
2
interferes with UE
14
1
downlink transmission D
1
. Although the effective isotropic radiant power (EIRP) of UEs
14
is much less that base stations
12
, the close proximity of the UEs
14
results in the unacceptable interference. This problem is exacerbated when adding new users or user services. Although a cell's base station and UE
14
may make timeslot interference measurements, such as interference signal code power (ISCP), to assure its new transmissions will not see unacceptable interference, other cells' users may end up experiencing unacceptable interference due to the new transmission. As a result, existing calls may be dropped or unacceptable quality of service (QOS) may occur.
Accordingly, it is desirable to reduce cross cell interference.
SUMMARY
Potentially interfering user equipments with respect to a particular UE are identified in a time division duplex communication system using code division multiple access. Timeslots used for uplink transmissions by a plurality of nearby UEs are identified. Each nearby UE is not in a cell of the particular UE and is geographically close to the particular UE. At the particular UE, an interference level is measured in each of the identified timeslots. The identified timeslots are classified using the measured interference level. Non-interfering and interfering UEs are determined using the identified timeslots for each UE and the timeslot classification.
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patent: 5533013 (1996-07-01), Leppanen
patent: 6212384 (2001-04-01), Almgreen et al.
patent: 6360077 (2002-03-01), Mizoguchi
patent: 2002/0015393 (2002-02-01), Pan et al.
patent: 1087630 (2001-03-01), None
patent: 2320648 (1998-06-01), None
Essam Sourour, “Time Slot Assignment Techniques for TDMA Digital Cellular Systems,” IEEE Transactions on Vehicular Technology, vol. 43, No. 1, Feb. 1994, pp. 121-127.
Hitoshi Takanashi, Tomoyoski Oono & Toshiaki Tanaka, “Frequency-Segregated Dynamic Channel Allocation for Asynchronized TDMA/TDD Frame Among Base Stations,” IEEE, 1996, pp. 933-937.
Mihailescu C. et al., Dynamic resource allocation for packet transmission in UMTS TDD-CDMA systems:, Vehicular Technology Conference, 1999 IEEE 49th Houston, TX, USA May 16-20 1999, Piscataway, NJ, USA, IEEE, US, May 16, 1999, pp. 1737-1741, XP010342115, ISBN: 0-7803-5565-2.
Yoshitaka Hara, Toshihisa Nabetani & Shinsuke Hara, “Time Slot Assignment for Cellular SDMA/TDMA Systems with Antenna Arrays,” YRP Mobile Telecommunications Key Technology Research Laboratories Co., Ltd., pp. 1-4.
Thit Minn & Kai-Yeung Siu, “Dynamic Assiegnment of Orthogonal Variable-Spreading-Factor Codes in W-CDMA,” IEEE, 2000, pp. 1429-1439.
InterDigital Technology Corporation
Vo Nguyen T.
Volpe and Koenig P.C.
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