Base station for code assignment for a common packet channel

Details Base station for code assignment for a common packet channel Base station for code assignment for a common packet channel

2002-02-14

2004-10-05

Pham, Chi (Department: 2667)

Multiplex communications

Communication over free space

Combining or distributing information via code word channels...

Reexamination Certificate

active

06801517

ABSTRACT:

BACKGROUND
The invention relates generally to resource allocation in a wireless code division multiple access communication system. More specifically, the invention relates to assigning uplink and downlink channels in response to access requests of user equipment.
FIG. 1
depicts a wireless spread spectrum Code Division Multiple Access (CDMA) communication system
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. A base station
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communicates with user equipment (UE)
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in its operating area. In a spread spectrum CDMA system
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, data signals are communicated between UEs
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and the base station
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over the same spread bandwidth. Each data signal in the shared bandwidth 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
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to the UEs
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are sent on downlink channels and signals from the UEs
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to the base station
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are sent on uplink channels. For coherent detection of downlink transmissions by the UEs
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, pilot signals are transmitted to all the UEs
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within the base station's operating range. The UEs
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condition their receivers based on the pilot signals to enable data reception.
In many CDMA systems, a common packet channel (CPCH) is used for uplink transmissions. A CPCH is capable of carrying packets of data from different UEs
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. Each packet is distinguishable by its code. For detection by the base station
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, the packets have a preamble which also distinguishes it from other packets. The CPCH is typically used to carry infrequently communicated data at high rates.
FIG. 2
depicts a CPCH access scheme
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. The CPCH access scheme
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is time divided into intervals having time slots
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, such as 8 time slots proposed for the Third Generation Mobile Telecommunications System (IMT-2000). A group of predetermined signatures
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are assigned to the time slots
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to allow more than one UE
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to use the same time slot
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. A particular signature used within a particular time slot is referred to as an access opportunity
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. For instance, for each of the 8 time slots in the proposal for IMT-2000, one out of 16 signatures is available to be chosen, resulting in 128 access opportunities. Each signature
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is preassigned a virtual channel. A virtual channel uniquely defines operating parameters for both the uplink and downlink, i.e., an uplink spreading factor and a unique code for the downlink.
Broadcast from the base station
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to each UE
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is the availability of each virtual channel over an acknowledge indication channel (AICH). The UE
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monitors the AICH to determine the availability of each virtual channel. Based on the operating parameters required by the UE
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and the availability of the virtual channels, the UE determines the access opportunity to select. Upon identifying a particular access opportunity, the base station
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sends out an acknowledgment message (ACK) if the corresponding downlink channel is still available. In the proposal for IMT-2000, the ACK simply repeats the signatures
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associated with the access attempt. If the downlink channel is not available, a negative acknowledge (NAK) is sent.
After receiving a corresponding acknowledgment, the UEs
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determine the proper code to recover communications on the downlink channel based on the access opportunity
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used to send the UEs' packet. Either stored in the UEs
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or transmitted on a Base Station's Broadcast Channel is a list of the code assigned to each access opportunity
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. This scheme severely increases the packet collision probability and therefore the packet delay which is undesirable.
In some situations, monitoring the AICH is not desirable. At a particular moment, some UEs
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will be operating in a “sleep” mode. In the “sleep” mode, the UE
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only runs when there is a need to send data. Monitoring the AICH during “sleep” mode will both reduce battery life and introduce a delay in the transmission of the first packet. Additionally, when a UE
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borders between two base station's operating areas, monitoring multiple AICHs further exacerbates these drawbacks.
Monitoring creates other problems. It further complicates the UE's receiving circuitry, making the UE
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more expensive.
Monitoring results in a suboptimum use of the CPCH. AICH monitoring provides information when a channel becomes busy. The time at which the channel becomes free is deduced on a worst case maximum packet length. If a packet is not maximum length, the channel will be idle while the UEs
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are waiting to transmit. On the other hand, if monitoring is not performed in such a system, channel availability information is unavailable. The UE
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may randomly choose a busy virtual channel increasing the packet delay by causing a collision. Accordingly, it would be desirable to allow the UEs
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to wait a period shorter than the maximum packet length and provide for some other collision reducing mechanism.
One technique to reduce the possibility of collision is to raise the number of codes, for instance to 128 different codes. In the proposal for IMT-2000 the 128 sequences represent approximately half of the sequences available at the base station
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. Accordingly, this solution is undesirable. Additionally, since monitoring the AICH complicates the UE receiver circuitry increasing its cost, it is undesirable. Accordingly, an alternate approach to assign virtual channels is desirable.
SUMMARY
A base station receives access opportunities and packet data over a common packet channel. The common packet channel is defined by a predetermined set of codes and has a plurality of access opportunities. Each access opportunity is defined by a time slot and a signature. A code selection controller selects a currently unused code based on a code associated with a received access opportunity, such that a code, if available, is selected in response to receiving a signature in one of the time slots. The access opportunity defined by the received signature and the one time slot. A transmitter transmits an identifier of the selected available code. The transmitter sends communications encoded with the selected code.


REFERENCES:
patent: 5339330 (1994-08-01), Mallinckrodt
patent: 5533014 (1996-07-01), Willars et al.
patent: 5883899 (1999-03-01), Dahlman et al.
patent: 6169759 (2001-01-01), Kanterakis et al.
patent: 6389056 (2002-05-01), Kanterakis et al.
patent: 6507601 (2003-01-01), Parsa et al.
patent: 6577618 (2003-06-01), Diachina et al.
patent: 6606313 (2003-08-01), Dahlman et al.
patent: 6643318 (2003-11-01), Parsa et al.
patent: WO9849857 (1998-11-01), None
“Mobile Station-Base Station Compatibility Standard for Wideband Spread Spectrum Cellular Systems”, Telecommunications Industry Association, Mar. 1999.
3rd Generation Partnership Project (3GPP), “UTRA FDD; Physical Layer Procedures,” TS 25.214 V1.0.0 (Apr. 1999), pp. 1-32.
Agenda Item, TSGR1#7(99)A74, Hannover, Germany, Aug. 30-Sep. 3, 1999, TSGR1#6(99)A48, Epsoo, Finland, Jul. 13-18, 1999.
Agenda Item, TSGR1#7(99)A73, Hannover, Germany, Aug. 30-Sep. 3, 1999, TSGR1#6(99)A47, Epsoo, Finland, Jul. 13-18, 1999.

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