Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
2001-04-11
2004-02-03
Banks-Harold, Marsha D. (Department: 2686)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S069000, C455S070000
Reexamination Certificate
active
06687510
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to mobile radio telephone Systems. More specifically, the present invention relates to systems and methods for controlling the amount of power that will be transmitted from a base station to a remote station in a communication system.
2. Description of the Related Art
It has recently become more common to use spread spectrum techniques, such as code division multiple access (CDMA) techniques, to communicate information over wireless communication systems. For example, CDMA techniques are in wide use for communications between stationary base stations and mobile cellular telephones in a cellular telephone network. In accordance with CDMA techniques, several streams of information, typically from different sources, are each encoded (or “Channelized”) using a different code. These codes allow the information to be transmitted over the same frequency band (commonly referred to as a “CDMA channel”). Each such Channelized information stream is commonly referred to as a “Code Channel.”
It is presently well known that in order to minimize the amount of interference between Code Channels of a CDMA channel, the amount of power that is transmitted on each of the Code Channels must be carefully controlled. Furthermore, it is common for a single amplifier to be responsible for transmitting the entire CDMA channel. When a single amplifier is used to transmit an entire CDMA channel, the more power transmitted in one Code Channel, the less power is available to the other Code Channels. This is because there is typically a limit on the amount of total output power that such an amplifier can provide without undesirably distorting the amplified signals. For at least these reasons, it is important to properly allocate transmit power to each Code Channel in the same CDMA channel.
In one system used primarily for transmitting information at high data rates over a wireless communication link, all of the Code Channels in one direction are used to provide parallel data paths for information from a first end point to a second end point of the communication link. For example, information transmitted from a base station to one particular remote station is transmitted over all of the Code Channels. The transmission path in this direction is commonly referred to as either the “Forward Link” or “Down Link.” In such a high data rate system, each Code Channel on the Forward Link is allocated approximately the same amount of power for transmission from the base station. Furthermore, transmissions to different remote stations are time multiplexed. That is, during a first time slot, all of the Code Channels of the CDMA Channel are allocated to transmitting information to a first remote station. During a second time slot, all of the Code Channels of the CDMA Channel are allocated to transmitting information to a second remote station. Additional time slots provide communication links between the base station and other remote stations.
The data path by which information is transmitted from a particular remote station to the base station is commonly referred to either as the “Reverse Link” or the “Up Link.” In one high data rate system, the Code Channels of a Reverse Link are each allocated to different remote stations. The amount of power that is used to transmit the information on the Reverse Link must be controlled to reduce interference at the receiving base station between Code Channels of the same CDMA channel.
Accordingly, portions of each Code Channel on the Forward Link are reserved for transmitting power control information. The reserved portions of a particular Code Channel within one slot form a “Reverse Link Power Control (RLPC) Channel.” Each such RLPC Channel on the Forward Link is associated with one remote station. The power control information that is transmitted on a particular RLPC Channel is intended to be received and used by one particular remote station to control the reverse link power transmitted by that particular remote station. The power control information assists in maintaining the output power from each remote station at a minimum level required for information to be reliably received from each remote station on the Reverse Link.
FIG. 1
is an illustration of the format of a Forward Link of one particular communication system. In the system shown in
FIG. 1
, a portion of each Code Channel forms a RLPC Channel over which reverse power control information is transmitted.
FIG. 1
shows the Forward Link
100
formatted in Code Channels
102
. Two Code Channels
102
a
and
102
b
are explicitly shown in FIG.
1
. However, in accordance with the format shown in
FIG. 1
, 32 Code Channels are provided on the Forward Link CDMA channel. Each Code Channel is divided into “Slots”
104
. In a typical system, such as the one shown in
FIG. 1
, each Slot
104
in the Forward Link has a predetermined duration. Each Slot is assigned to a particular remote station. In the system shown in
FIG. 1
, each Slot comprises 2048 “Chips.” A Chip is defined as a duration in time that is equal to the duration of one bit of the code used to channelize the Code Channels. Each Slot
104
begins with a first data field
106
that is
464
Chips in length. A pilot field
108
follows the first data field
106
. The pilot field is
96
chips in length. The pilot field
108
, among other uses, allows the receiving device to synchronize to the phase of the incoming Forward Link signals (which include the pilot field
108
itself. A second data field
110
having a length of
464
Chips is then transmitted. A third data field
112
having a length of
400
Chips is transmitted next. Following the third data field
112
, a power control field
114
is transmitted. The first power control field
114
has a length of 64 Chips. Next, a second pilot field
116
having a length of 96 Chips is transmitted, followed by a second power control field
118
having a length of 64 Chips. The last field in the Slot
104
is a fourth data field
120
having a length of 400 Chips.
The power control fields
114
and
118
within one Code Channel
102
form one RLPC Channel. Accordingly, the RLPC Channel is “Embedded” in the Data. Under most conditions, a determination can be made at the base station as to whether more, less, or the same amount of power needs to be transmitted over the Reverse Link transmitted from a remote station. The determination is made based on the strength of the signal received by the base station from a particular remote station.
Typically, when transmitting the Forward Link, the same amount of power is used to transmit each Code Channel in the CDMA channel. It is appropriate to transmit the Code Channels at the same power, since the Data is essentially directed to one remote station. For the purposes of this description, “Data” is defined as information that is provided by the communication system user, and does not include information that is transmitted between components of the system in order to manage and/or support system operations (such as overhead messages). However, since each RLPC Channel is directed to a different remote station, transmitting each RLPC Channel of the CDMA channel at the same power level means that some of the RLPC Channels will be transmitted at power levels that are either greater than or less than is required. This is because the amount of power that is required to transmit to a remote station that is closer is less than the amount of power required to transmit to a remote station that is farther away. Accordingly, it can be seen that transmitting all RLPC Channels at the same power level is undesirable for the following reason. There is an absolute maximum total amount of power that can be transmitted by all of the RLPC Channels taken together. Therefore, using more power than required for some RLPC Channels means that other RLPC Channels will get less power than might otherwise be possible if the power were allocated based on the actual requirements of each RLPC Channel rather than b
Black Peter J.
Esteves Eduardo A. S.
Baker Kent
Banks-Harold Marsha D.
Hsu Lee
Moore James K
Qualcomm Incorporated
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