U.S. patent application number 11/098733 was filed with the patent office on 2005-08-04 for base station midamble selection.
This patent application is currently assigned to InterDigital Technology Corporation. Invention is credited to Reznik, Alexander, Terry, Stephen E., Zeira, Ariela, Zeira, Eldad.
Application Number | 20050169198 11/098733 |
Document ID | / |
Family ID | 22660319 |
Filed Date | 2005-08-04 |
United States Patent
Application |
20050169198 |
Kind Code |
A1 |
Zeira, Ariela ; et
al. |
August 4, 2005 |
Base station midamble selection
Abstract
Midamble codes are selected in a wireless time division duplex
communication system. At least one channelization code is assigned
to a user equipment. A mapping is provided between midamble codes
and channelization codes. At least one midamble code is mapped to a
plurality of channelization codes having a same spreading factor.
The midamble code mapped to the at least one channelization code to
the user equipment is selected. A communication burst is formed
with the assigned at least one channelization code and the selected
midamble code.
Inventors: |
Zeira, Ariela; (Huntington,
NY) ; Zeira, Eldad; (Huntington, NY) ; Reznik,
Alexander; (Titusville, NJ) ; Terry, Stephen E.;
(Northport, NY) |
Correspondence
Address: |
VOLPE AND KOENIG, P.C.
DEPT. ICC
UNITED PLAZA, SUITE 1600
30 SOUTH 17TH STREET
PHILADELPHIA
PA
19103
US
|
Assignee: |
InterDigital Technology
Corporation
Wilmington
DE
19801
|
Family ID: |
22660319 |
Appl. No.: |
11/098733 |
Filed: |
April 4, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11098733 |
Apr 4, 2005 |
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10090498 |
Mar 4, 2002 |
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6885649 |
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10090498 |
Mar 4, 2002 |
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09775969 |
Feb 2, 2001 |
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60180402 |
Feb 4, 2000 |
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Current U.S.
Class: |
370/280 ;
375/E1.024; 375/E1.025 |
Current CPC
Class: |
H04B 1/7105 20130101;
H04B 2201/70701 20130101; H04B 1/70735 20130101; H04B 2201/70709
20130101; H04B 1/707 20130101; H04J 13/00 20130101; H04B 2001/70935
20130101; H04B 1/7103 20130101; H04J 13/16 20130101 |
Class at
Publication: |
370/280 |
International
Class: |
H04B 001/69 |
Claims
What is claimed is:
1. A method for selecting midamble codes in a wireless time
division duplex communication system, the method comprising:
assigning at least one channelization code to a user equipment;
providing mapping between midamble codes and channelization codes,
where at least one midamble code is mapped to a plurality of
channelization codes having a same spreading factor; and selecting
the midamble code mapped to the at least one channelization code to
the user equipment; and forming a communication burst with the
assigned at least one channelization code and the selected midamble
code.
2. A wireless time division duplex base station, the base station
comprising: means for assigning at least one channelization code to
a user equipment; a mapping between midamble codes and
channelization codes, where at least one midamble code is mapped to
a plurality of channelization codes having a same spreading factor;
and means for selecting the midamble code mapped to the at least
one channelization code to the user equipment; and means for
forming a communication burst with the assigned at least one
channelization code and the selected midamble code.
3. A wireless time division duplex base station, the base station
comprising: a spreading and modulation device for forming a
communication burst with an assigned channelization code and a
selected midamble code, the assigned channelization code being
assigned to a user equipment, a mapping between midamble codes and
channelization codes is provided where at least one midamble code
is mapped to a plurality of channelization codes having a same
spreading factor; and the selected midamble code is mapped to the
channelization code.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/090,498, filed Mar. 4, 2002 which is a
continuation of U.S. patent application Ser. No. 09/775,969, filed
Feb. 2, 2001, which claims priority from U.S. Provisional Patent
Application No. 60/180,402, filed Feb. 4, 2000, all of which are
incorporated by reference as if fully set forth.
BACKGROUND OF THE INVENTION
[0002] 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.
[0003] A TDD/CDMA communication system is illustrated in FIG. 1.
The system 10 has multiple base stations 12.sub.1 to 12.sub.5. Each
base station 12.sub.1 has an associated operating area. User
equipments (UEs) 14.sub.1 to 14.sub.3 in a base station's operating
area communicate with that base station 12.sub.1. Communications
transmitted from a base station 12.sub.1 to a UE 14.sub.1 are
referred to as downlink communications and communications
transmitted from a UE 14.sub.1 to a base station 12.sub.1 are
referred to as uplink communications.
[0004] 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.
[0005] 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.
[0006] 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).
[0007] 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.sub.1 to 14.sub.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.sub.1 to 14.sub.3 to be able to determine the
active channelization codes.
SUMMARY OF THE INVENTION
[0008] Midamble codes are selected in a wireless time division
duplex communication system. At least one channelization code is
assigned to a user equipment. A mapping is provided between
midamble codes and channelization codes. At least one midamble code
is mapped to a plurality of channelization codes having a same
spreading factor. The midamble code mapped to the at least one
channelization code to the user equipment is selected. A
communication burst is formed with the assigned at least one
channelization code and the selected midamble code.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is an illustration of a time division duplex/code
division multiple access communication system.
[0010] FIG. 2 is an illustration of a communication burst.
[0011] FIG. 3 is an illustration of a simplified base station
transmitter and a user equipment receiver.
[0012] FIG. 4 is a flow chart of downlink channelization code
identification.
[0013] FIG. 5 is an illustration of midamble sequence to
channelization code mapping.
[0014] FIG. 6 is a channelization code detection device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0015] FIG. 3 illustrates a simplified base station transmitter 26
and a UE receiver 28 using multiuser detection (MUD). Data to be
communicated to the active UEs 14.sub.1 to 14.sub.3 is produced by
data generators 32.sub.1 to 32.sub.K. Each generator 32.sub.1 to
32.sub.K produces data to be sent in a particular communication
burst. Each communication burst's generated data is subsequently
formatted into a communication burst by a spreading and modulation
device 34.sub.1 to 34.sub.K. The spreading and modulation device
34.sub.1 to 34.sub.K adds the midamble and spreads the generated
data with a channelization code associated with that communication
burst. Additionally, the spread data is time multiplexed into the
appropriate time slot. All of the communication bursts are combined
by a combiner 52. The combined communication bursts are modulated
up to radio frequency, such as by a mixer 36, and the radio
frequency signal is radiated by an antenna 38 through a wireless
radio channel 30. If transmit diversity is utilized by the base
station 14.sub.1, the radio frequency signal will be transmitted by
multiple antennas.
[0016] At a UE receiver 28, radio frequency signals are received by
an antenna 40. The received signals are demodulated to a baseband
signal, such as by a mixer 42. A channel estimation device 44 is
used to estimate the channel that the communication bursts were
transmitted in using the transmitted midamble codes. A multiuser
detection (MUD) device 46 processes the baseband signal using the
estimated channel information and the active channelization codes
to produce hard symbols.
[0017] Identifying active channelization codes is shown in the flow
chart of FIG. 4. One approach to aid in identifying active
channelization codes at the UE 14.sub.1 is to provide a mapping
between midamble codes (midamble sequences) 54.sub.1 to 54.sub.N
and channelization codes 56.sub.11 to 56.sub.NM, 58. Each midamble
sequence 54.sub.1 to 54.sub.N is associated with a set of
channelization codes 56.sub.11 to 56.sub.NM, as illustrated in FIG.
5. The sets may contain only a single channelization code, which is
a one to one mapping of midambles to channelization codes. A burst
transmitted by the base station 12.sub.1 with a channelization code
of a midamble's set is formatted with that midamble sequence, 60,
62. To illustrate, if a burst with channelization code 21 was sent,
midamble sequence 2 is used for that burst.
[0018] At the UE receiver 28, after channel estimation, the
transmitted midamble sequences are detected by a midamble sequence
detection device 48, 64. Based on the detected midambles, a logic
block 45, utilizing the midamble to channelization code mapping 49,
determines the set of possible channelization codes. A
channelization code detection device 50 determines the received
channelization codes based on the determination, 66. If a one
midamble code to one channelization code mapping is used, the logic
block 45 determines the channelization codes. As a result, for a
one to one mapping, the channelization code detection device 50 is
not used. The MUD device 46 uses the determined channelization
codes and the channel response for the midamble sequences
associated with the channelization codes to detect the data from
all the bursts, 68.
[0019] One channelization code detection device 50 is shown in FIG.
6. Matched filters 82.sub.1 to 82.sub.M are matched to the possible
channelization codes and associated channel responses as determined
by the logic block 45. Since only the possible channelization codes
need to be checked, the number of matched filters 82.sub.1 to
82.sub.M is greatly reduced, reducing the complexity and improving
the performance of the receiver 28. The power of the soft symbols
produced by each matched filter 82.sub.1 to 82.sub.M is measured by
corresponding power measurement devices 84.sub.1 to 84.sub.M. The
comparator 80 determines the received channelization codes based on
the power measurement for each channel. If the number of
transmitted channelization codes is known, the comparator 80
selects that number of channels with the highest measured power.
Otherwise, the comparator 80 compares each channel's power level to
a threshold to determine the transmitted channelization codes.
[0020] To aid in identifying channelization codes, channelization
code information, such as transmitted channelization codes or a
number of transmitted channelization codes, may be signaled to the
UE 14.sub.1. The signaled information can be used in conjunction
with channelization/midamble code mapping or when mapping is not
used. The additional channelization code information will increase
the accuracy in determining the active channelization codes at the
UE receiver 28. One such signal would be a layer one signal, where
the midamble code or midamble code shift is associated with the
information. The midamble detection device 48 determines the
received midamble code(s) and the logic block 45 recovers the
channelization code information using the determined midamble
codes. Using the recovered information, the channelization code
detection device 50 uses the recovered information to aid in the
channelization code determination. Another approach signals
channelization code information using a layer 2/3 signal. The
signal is generated by the network circuitry. The layer 2/3 signal
can be used in conjunction with layer one signals or with the
midamble/channelization code mapping.
* * * * *