Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
2000-12-08
2004-07-06
Corsano, Nick (Department: 2684)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S069000, C455S442000
Reexamination Certificate
active
06760597
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is generally related to a method of allocating power to subscriber and system equipment for transmission of information in CDMA communication networks.
2. Description of the Related Art
With the increasing popularity of wireless communication networks among the public, service providers want to provide more resources to their subscribers and be able to efficiently use the resources that are currently being used by their subscribers. The service providers are typically local or national telephone companies that own, operate and control system equipment that constitute a communication network. The resources of a communication network comprise such items as the amount of bandwidth available to the network, the power allocated to communication channels of the network and the transceiver system equipment (e.g., radio transmitters and receivers) used by the network to transmit and receive communication signals. Service providers want to increase the capacity of their network without having to substantially increase their cost of operation through increased power allocations, larger bandwidths and deployment of more system equipment. Moreover, the usage of certain resources (power, bandwidth) is controlled by governmental regulatory entities and standards organizations. Consequently, service providers cannot simply increase their power usage in response to increased capacity demands from their subscribers. Therefore, to achieve efficient use of their limited resources, service providers implement various techniques for controlling such resources as bandwidth and power allocation.
Power allocation is one of the resources that is controlled by service providers through the use of techniques that promote the efficient use of resources. In Code Division Multiple Access (CDMA) wireless communication networks, the power allocated to the communication channels is critical because power allocation is one of the major factors that determine the capacity of the network. The capacity of a communication network is the number of subscribers that is using a communication network to convey (i.e., transmit and/or receive) information at a particular time.
A typical wireless CDMA communication network is configured as a cellular network. The network comprises a plurality of cells where each cell contains at least one base station that conveys subscriber information to subscribers in the cell and signaling information to subscribers and other base stations. The cell is a geographical area being served by a base station where such cell is defined by a particular size and shape. Subscriber equipment (e.g., cell phone, wireless laptop, Personal Digital Assistant (PDA)) physically located in a cell convey information to other subscribers of the wireless network or other networks via the base station serving that cell. The terms ‘subscriber equipment’ and ‘mobile’ will hereinafter be used interchangeably.
Subscriber information are the various types of information (e.g., voice, data, video) conveyed by subscribers. Signaling information are various information conveyed among system equipment and between mobile and system equipment for initiating, maintaining and terminating communications between subscribers of the same or different networks. Each base station comprises various system equipment for processing communication signals. The communication channel through which a subscriber transmits information to a base station is commonly referred to as a reverse link. The communication channel through which a subscriber receives information from a base station is commonly referred to as a forward link.
In CDMA networks (and other networks), often when a mobile transmits information to its base station over the reverse link, the information is received by the intended base station and other base stations. The information is typically transmitted in the form of a block called a frame. Several base stations process the received frames by determining their quality, i.e., whether a frame contains errors; this scenario is called a soft handoff. Thus in a soft handoff the mobile's information is received and processed by more than one base station and the network takes advantage of the combined quality of the reverse links of the base stations to select a received frame from one of the base stations. The use of soft handoff thus tends to improve the Frame Error Rate (FER) of the mobile because if at least one frame has no errors, the frame selected is the one having no errors. A frame which is received with errors is an erroneous frame. The ratio of the number of erroneous frames received to the total number of frame received for a defined period of time is called the Frame Error Rate (FER). Any or all of the transmitted frames may be adversely affected by anomalies (e.g., fading, scattering) in the reverse links that cause errors to occur.
The FER is a parameter which is used by CDMA networks to implement power allocation techniques for controlling the amount of power used by a base station and a mobile in transmitting and/or receiving communication signals. A widely used technique is a power control method commonly referred to as directed power control. The directed power control method for a mobile in soft handoff contains two control loops called the outer loop and the inner loop. There is an outer loop for the reverse and forward links. Also, there is an inner loop for the reverse and forward links.
For a reverse link outer loop, each of the base stations in soft handoff with a mobile receives a frame and processes that frame to determine its quality. Each of the base station then transmits its received frame or information about the quality of the received frame to system equipment at the Message Switching Center (MSC) of the network. Each of the base stations will also determine a setpoint based on the quality of its received frame. The quality is typically quantified in terms of the FER of the received information. The setpoint is a power level at which the mobile should transmit its information in order to meet a target FER set by the communication network. The setpoint is defined in terms of a ratio of signal power (proportional to E
b
) to noise power (proportional to N
1
) at the mobile, i.e., E
b
/N
1
where E
b
is the energy per information unit and N
1
is the noise power spectral density. If one or more of the received frames contains no errors, the MSC will then transmit a message to the base stations advising them that an errorless frame was received and to proceed with receiving the next frame. Each of the base stations, in turn, sends a message over its forward link to the mobile instructing the mobile to transmit its information at a power level that is less than the power level of the last frame. In other words, after receiving the instruction from the MSC, the base stations reduce the computed setpoint by a certain amount and transmit a new setpoint value to the mobile. Note that when all of the frames received contained errors, the MSC sends a message to the base stations advising each base station that its frame was erroneous causing each base station to increase its computed setpoint value. During the transmission of the next frame, the mobile will attempt to reduce (or increase) the power level of its communication signals to meet the new setpoint computed by the base stations; this is done by reverse the inner loop operation.
In the reverse inner loop, each of the base stations sends instructions to the mobile instructing the mobile to decrease (or increase or maintain) its transmission power level while the frame is being transmitted to comply with the new setpoint computed by the base stations. For example, many CDMA networks have 20 ms frames during which each base station transmits 16 inner loop instructions (one instruction every 1.25 ms) causing the mobile to increase, decrease or maintain the power level at which it is transmitting its frame. In particular, after computing a new setpoint, a base stat
Salvarani Alexandro
Weaver Carl Francis
Corsano Nick
Lucent Technologies - Inc.
Milton J.
Teitelbaum Ozer M. N.
Trinh Tan
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