Pulse or digital communications – Spread spectrum
Reexamination Certificate
2000-05-19
2004-01-06
Ghayour, Mohammad H. (Department: 2634)
Pulse or digital communications
Spread spectrum
C455S522000, C375S135000
Reexamination Certificate
active
06674787
ABSTRACT:
BACKGROUND
The invention relates generally to random access channels in a wireless code division multiple access communication system. More specifically, the invention relates to raising the packet data payload of packets transferred over a random access channel.
FIG. 1
depicts a wireless spread spectrum Code Division Multiple Access (CDMA) communication system
20
. A base station
22
communicates with user equipment units (UEs)
24
1
-
24
n
in its operating area. In a spread spectrum CDMA system
18
, data signals are communicated between UEs
24
1
-
24
n
and the base station
22
over the same spectrum. Each data signal in the shared spectrum is spread with a unique chip code sequence. Upon reception, using a replica of the chip code sequence, a particular data signal is recovered.
Since signals are distinguished by their chip code sequences (code), separate dedicated communication channels are created using different codes. Signals from the base station
22
to the UEs
24
1
-
24
n
, are sent on downlink channels and signals from the UEs
24
1
-
24
n
, to the base station
22
are sent on uplink channels. For coherent detection of downlink transmissions by the UEs
24
1
-
24
n
, pilot signals are transmitted to all the UEs
24
1
-
24
n
within the base station's operating range. The UEs
24
1
-
24
n
condition their receivers based on the pilot signals to enable data reception.
In many CDMA systems
20
, random access channels are used by multiple users. One random access channel is a common packet channel (CPCH) which is used for uplink transmissions. A CPCH is capable of carrying packets of data from different UEs
24
1
-
24
n
. Each UE's packets have an associated uplink scrambling code which distinguishes it from other UE's packets. The CPCH is typically used to carry infrequently communicated data at high rates.
The CPCH as shown in
FIG. 2
is time divided into frames
30
1
-
30
m
having time slots
24
1
-
28
n
, such as eight time slots proposed for the Third Generation Mobile Telecommunications System (IMT-2000)-UMTS. The UE
24
1
transmits a data packet over the CPCH using an assigned uplink scrambling code starting in a specific time slot. The packet typically lasts for multiple frames
30
1
-
30
m
. The uplink packets are used to carry data and control signals. The base station
22
receives and recovers data from the uplink data packet. Typically, a dedicated downlink control channel is established for use in sending control signals from the base station
22
to the UE
24
1
as well as other data.
FIG. 3
is a simplified UE
24
1
and base station
22
for transmitting and receiving packet data over a random access channel
42
in a CDMA system
20
. A data packet is generated by a data packet generator
32
at the UE
24
1
. The data is subsequently encoded for error protection, such as by convolutional encoding, by an encoder
34
. The encoded data is spread by a spreading device
36
, such as by mixing the encoded data with a spreading code. The spread data is modulated to radio frequency by a modulator
38
and radiated by the UE's antenna
40
.
The radio frequency signal is sent through a random access channel
42
, such as the CPCH, to the base station
22
. An antenna
44
at the base station
22
receives radio signals. The radio signals are demodulated by a demodulator
46
to produce a baseband signal. The baseband signal is despread by a despreading device
48
, such as by mixing the baseband signal with a replica of the original spreading code. The de-spread signal is passed through a decoder
50
to recover the original data packet.
CDMA systems
20
typically use some form of adaptive power control. In a CDMA system
20
, many signals share the same spectrum. When a UE
24
1
or base station
22
receives a specific signal, all the other signals within the same spectrum are noise-like in relation to the specific signal. Increasing the power level of one signal degrades all the other signals within the same spectrum. However, reducing transmission power levels too far results in undesirable received signal quality at the receivers. To maintain a desired signal quality at the minimum transmission power level, transmission power control is used.
Along with other data, both the UE
24
1
and base station
22
send transmission power control (TPC) signals. The TPC signals tell the receiving UE
24
1
or base station
22
to increase or decrease its transmission power level based on the quality of the received signals. Once the UE
24
1
or base station
22
receives the TPC signals, it adjusts its transmission power level accordingly. For signals sent from the UE
24
1
to the base station
22
on the CPCH, typically, a closed loop power control preamble (CLPC-Preamble) is used to carry the TPC signals. The CLPC-Preamble precedes other data being carried in the packet.
To assure that the initial power level of uplink communications is not set too high, the UE
24
initially sets its transmission power level at a sufficiently low power level. The initial power level is set such that it is highly unlikely that the transmitted data will cause a degradation to reception of other UEs. Both the UE
24
1
and base station
22
have their transmission power levels adjusted to a desired transmission power level by the corresponding uplink and downlink TPC signals.
Until either the UE
24
1
or base station
22
reaches a sufficient transmission power level, no data is being transferred. This lack of data transfer is an inefficient use of the systems resources and is undesirable. Accordingly, it is desirable to increase data transfer in such systems.
SUMMARY
A data packet is provided for transmission having a first processing gain for reception at a first power level or higher. The data packet is modified prior to transmission such that the data packet has a preamble wherein data in the preamble has a second processing gain higher than the first processing gain for reception at a second power level lower than the first power level or higher. The user equipment unit transmits the modified data packet over the random access channel at a power level such that the modified data packet is initially received at the base station at least the second power level. The transmission power level is adaptively controlled while the preamble data is transmitted such that the base station receives the data of the data packet having the first processing gain at least the first power level.
REFERENCES:
patent: 5224120 (1993-06-01), Schilling
patent: 6160803 (2000-12-01), Yuen et al.
patent: 6262971 (2001-07-01), Schilling
3rd Generation Partnership Project (3GPP), “Technical Specification Group Radio Access Network; Physical Channels and Mapping of Transport Channels Onto Physical Channels (FDD),” 3G TS 25.211, V3.3.0 (2000-06) (Release 1999), pp. 1-42.
Dick Stephen G.
Zeira Eldad
Ghayour Mohammad H.
InterDigital Technology Corporation
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