Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
2002-03-04
2004-09-21
Chin, Wellington (Department: 2664)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S310000, C370S441000, C375S130000
Reexamination Certificate
active
06795417
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to wireless time division duplex using code division multiple access (TDD/CDMA) communication systems. In particular, the invention relates to determining channelization codes for use in multiuser detection in the downlink for TDD/CDMA systems.
A TDD/CDMA communication system is illustrated in FIG.
1
. The system
10
has multiple base stations
12
1
to
12
5
. Each base station
12
1
has an associated operating area. User equipments (UEs)
14
1
to
14
3
in a base station's operating area communicate with that base station
12
1
. Communications transmitted from a base station
12
1
to a UE
14
1
are referred to as downlink communications and communications transmitted from a UE
14
1
to a base station
12
1
are referred to as uplink communications.
In a wireless TDD/CDMA communication system, multiple communications are sent in a shared frequency spectrum. One such system is proposed in a third generation wideband-CDMA (W-CDMA) standard. In CDMA systems, multiple communications are sent in the shared spectrum and are distinguished by channelization codes. In TDD/CDMA systems, the shared spectrum is also time divided using repeating frames having a fixed number of time slots, such as fifteen (15) time slots. Each time slot is used to transmit either only uplink or downlink communications.
As a result, the communications are distinguished by both channelization codes and time slots. A single channelization code used in a single time slot is referred to as a resource unit. Based on a communications bandwidth, the communication may require one or multiple resource units. Typical data modulation schemes used in TDD/CDMA systems are quadrature phase shift keying (QPSK), binary phase shift keying (BPSK) and N Quadrature Amplitude Modulation (QAM), such as N=8, 16 or 64.
Data is transmitted in such systems using communication bursts
16
. A communication burst
16
carries data in a single time slot using a single channelization code (a single resource unit). A typical communication burst
16
has a midamble
20
, a guard period
18
and two data bursts
22
,
24
, as shown in FIG.
2
. The midamble
20
separates the two data bursts
22
,
24
. The guard period
18
separates the communication bursts
16
to allow for the difference in arrival times of bursts
16
transmitted from different transmitters. The two data bursts
22
,
24
contain the communication burst's data. The midamble
20
contains a midamble code for use in estimating the channel response between the receiver and transmitter.
Since multiple communication bursts may be transmitted in a single time slot, a receiver must be able to distinguish data from the multiple bursts. One approach to recover the received data is multiuser detection (MUD).
In MUD, a receiver recovers all communication bursts' data in a time slot, including bursts transmitted to other UEs. To recover all the bursts' data, the MUD receiver needs to know all of the channelization codes used to transmit the bursts. In the proposed TDD mode of W-CDMA, each UE
14
1
to
14
3
only knows which channelization and midamble codes are used for carrying information intended for it. To determine all the channelization and midamble codes, a bank of matched filters is used to detect all possible channelization/midamble combinations. The output power from each matched filter is compared to a threshold to determine whether a particular channelization/midamble combination was used. Due to the number of required matched filters, this approach has a high complexity. Additionally, if there is a high correlation between channelization codes, this approach may have poor performance. Accordingly, it is desirable to have alternate approaches for UEs
14
1
to
14
3
to be able to determine the active channelization codes.
SUMMARY OF THE INVENTION
A wireless time division duplex communication system using code division multiple access has a base station and user equipments. The system communicates using communication bursts. Each communication burst has a unique channelization code and a midamble code. Each midamble code is mapped to a set of at least one channelization code. For each communication burst to be transmitted in a time slot from the base station, the midamble code mapped to that burst's channelization code is determined. Communication bursts are generated and transmitted in the time slot. Each burst has the determined midamble code for its channelization code. The user equipment receives the bursts and determines each received midamble code. The user equipment determines the channelization codes of the transmitted communication bursts based on in part a result of the determining of each received midamble code.
The invention provides a user equipment (UE) for a wireless time division duplex communication system which uses code division multiple access. The system communicates using communication bursts, each communication burst having a unique channelization code and a midamble code which is uniquely related to the channelization code. Each such midamble code being uniquely related to one or more channelization code. The UE has an antenna for receiving communication bursts and a midamble detector which detects each midamble code in a received communication burst. A logic block determines the channelization codes related to each detected midamble based on a mapping of midamble codes to related channelization codes. A channelization code detector detects channelization codes in the received communication burst from among channelization codes determined by said logic block. A multiuser detection device recovers data from the received communication burst based on in part the channelization codes detected by said channelization code detector. Where all midamble codes are uniquely related to one channelization code, the multiuser detection device recovers data from the received communication burst based on in part the determined channelization codes without the need for the channelization code detector.
REFERENCES:
patent: 6078607 (2000-06-01), Monroe et al.
patent: 6339612 (2002-01-01), Stewart et al.
patent: 6567461 (2003-05-01), Moon et al.
patent: 6611513 (2003-08-01), ten Brink
patent: 2351422 (2000-12-01), None
patent: WO9940698 (1999-08-01), None
patent: WO9952249 (1999-10-01), None
Reznik Alexander
Terry Stephen E.
Zeira Ariela
Zeira Eldad
Chin Wellington
InterDigital Technology Corporation
Jain Ray
Volpe and Koenig P.C.
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