Power control
Encyclopedia
Power control, broadly speaking, is the intelligent selection of transmit power in a communication system to achieve good performance within the system. The notion of "good performance" can depend on context and may include optimizing metrics such as link data rate
, network capacity, geographic coverage
and range, and life of the network and network devices. Power control algorithms are used in many contexts, including cellular networks, sensor networks, wireless LAN
s, and DSL
modems.
Using a higher transmit power, however, has the following drawbacks:
Typically, there is no simple answer to the problem of power control, and a good algorithm must strike a balance between the benefits and drawbacks associated with targeting a particular transmit power based on the performance criteria of most importance to the designer.
The network devices supporting this feature are IEEE 802.11h
Wireless LAN
devices in the 5 GHz band compliant to the IEEE 802.11a. The idea of the mechanism is to automatically reduce the used transmission output power when other networks are within range. Reduced power means reduced interference problems and increased battery capacity. The power level of a single device can be reduced by 6 dB which should result in an accumulated power level reduction (the sum of radiated power of all devices currently transmitting) of at least 3 dB (which is half of the power).
Bit rate
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....
, network capacity, geographic coverage
Coverage (telecommunication)
In telecommunications, the coverage of a radio station is the geographic area where the station can communicate. Broadcasters and telecommunications companies frequently produce coverage maps to indicate to users the station's intended service area. Coverage depends on several factors, such as...
and range, and life of the network and network devices. Power control algorithms are used in many contexts, including cellular networks, sensor networks, wireless LAN
Wireless LAN
A wireless local area network links two or more devices using some wireless distribution method , and usually providing a connection through an access point to the wider internet. This gives users the mobility to move around within a local coverage area and still be connected to the network...
s, and DSL
Digital Subscriber Line
Digital subscriber line is a family of technologies that provides digital data transmission over the wires of a local telephone network. DSL originally stood for digital subscriber loop. In telecommunications marketing, the term DSL is widely understood to mean Asymmetric Digital Subscriber Line ,...
modems.
Benefits
Increasing transmit power on a communication link has numerous benefits:- In general, for any particular set of channel conditions, a higher transmit power translates into a higher signal power at the receiver. Having a higher signal-to-noise ratioSignal-to-noise ratioSignal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
(SNR) at the receiver reduces the bit error rate of a digital communication link.
- A higher SNR can also allow a system that uses link adaptationLink adaptationLink adaptation, or adaptive coding and modulation , is a term used in wireless communications to denote the matching of the modulation, coding and other signal and protocol parameters to the conditions on the radio link Link adaptation, or adaptive coding and modulation (ACM), is a term used in...
to transmit at a higher data rate, resulting in a system with greater spectral efficiencySpectral efficiencySpectral efficiency, spectrum efficiency or bandwidth efficiency refers to the information rate that can be transmitted over a given bandwidth in a specific communication system...
.
- In a wireless fading channel, using higher transmit power provides more protection against a signal fade. In a cellular network, for example, this results in a lower dropped call probability.
Using a higher transmit power, however, has the following drawbacks:
- Overall power consumption in the transmitting device is higher. This is of particular concern in mobile devices, where battery life is reduced correspondingly.
- Interference to other users in the same frequency band is increased. In cellularCellular networkA cellular network is a radio network distributed over land areas called cells, each served by at least one fixed-location transceiver known as a cell site or base station. When joined together these cells provide radio coverage over a wide geographic area...
spread-spectrum systems such as CDMA, where users share a single frequency and are only separated by different spreading codes, the number of users that a cell can support as well as the size of the cell are typically limited by the amount of interference present in the cell; increased interference therefore results in decreased cell capacity and size. Even in FDMA systems such as GSM where each user in a cell uses a different frequency, interference is still present between different cells and reduces the amount of frequency reuse the network can support. In wireline networks such as DSLDigital Subscriber LineDigital subscriber line is a family of technologies that provides digital data transmission over the wires of a local telephone network. DSL originally stood for digital subscriber loop. In telecommunications marketing, the term DSL is widely understood to mean Asymmetric Digital Subscriber Line ,...
, lines from many subscriber homes are often bundled together, and interference between signals on different lines manifests itself as crosstalk and reduces the achievable data rate to each home.
Typically, there is no simple answer to the problem of power control, and a good algorithm must strike a balance between the benefits and drawbacks associated with targeting a particular transmit power based on the performance criteria of most importance to the designer.
Transmit Power Control
Transmit Power Control is a technical mechanism used within some networking devices in order to prevent too much unwanted interference between different wireless networks (e.g. the owner's network and the neighbour's network).The network devices supporting this feature are IEEE 802.11h
IEEE 802.11h
IEEE 802.11h-2003, or just 802.11h, refers to the amendment added to the IEEE 802.11 standard for Spectrum and Transmit Power Management Extensions. It solves problems like interference with satellites and radar using the same 5 GHz frequency band. It was originally designed to address European...
Wireless LAN
Wireless LAN
A wireless local area network links two or more devices using some wireless distribution method , and usually providing a connection through an access point to the wider internet. This gives users the mobility to move around within a local coverage area and still be connected to the network...
devices in the 5 GHz band compliant to the IEEE 802.11a. The idea of the mechanism is to automatically reduce the used transmission output power when other networks are within range. Reduced power means reduced interference problems and increased battery capacity. The power level of a single device can be reduced by 6 dB which should result in an accumulated power level reduction (the sum of radiated power of all devices currently transmitting) of at least 3 dB (which is half of the power).
See also
- Cellular networkCellular networkA cellular network is a radio network distributed over land areas called cells, each served by at least one fixed-location transceiver known as a cell site or base station. When joined together these cells provide radio coverage over a wide geographic area...
- Cellular trafficCellular trafficThis article discusses the mobile cellular network aspect of teletraffic measurements. Mobile radio networks have traffic issues that do not arise in connection with the fixed line PSTN...
- IEEE 802.11hIEEE 802.11hIEEE 802.11h-2003, or just 802.11h, refers to the amendment added to the IEEE 802.11 standard for Spectrum and Transmit Power Management Extensions. It solves problems like interference with satellites and radar using the same 5 GHz frequency band. It was originally designed to address European...
- Radio resource managementRadio resource managementRadio resource management is the system level control of co-channel interference and other radio transmission characteristics in wireless communication systems, for example cellular networks, wireless networks and broadcasting systems...
- Spectral efficiencySpectral efficiencySpectral efficiency, spectrum efficiency or bandwidth efficiency refers to the information rate that can be transmitted over a given bandwidth in a specific communication system...
- Wireless LANWireless LANA wireless local area network links two or more devices using some wireless distribution method , and usually providing a connection through an access point to the wider internet. This gives users the mobility to move around within a local coverage area and still be connected to the network...