Co-channel interference
Encyclopedia
Co-channel interference or CCI is crosstalk from two different radio transmitters using the same frequency
. There can be several causes of co-channel
radio interference; four examples are listed here.
Co-channel interference may be controlled by various radio resource management
schemes.
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
. There can be several causes of co-channel
Channel (communications)
In telecommunications and computer networking, a communication channel, or channel, refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel...
radio interference; four examples are listed here.
- Cellular Mobile Networks: In cellular mobile communicationCellular 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...
(GSM & LTE3GPP Long Term Evolution3GPP Long Term Evolution, usually referred to as LTE, is a standard for wireless communication of high-speed data for mobile phones and data terminals. It is based on the GSM/EDGE and UMTS/HSPA network technologies, increasing the capacity and speed using new modulation techniques...
Systems, for instance), frequency spectrum is a precious resource which is divided into non-overlapping spectrum bands which are assigned to different cells (In cellular communications, a cell refers to the hexagonal/circular area around the base station antenna). However, after certain geographical distance, the frequency bands are re-used, i.e. the same spectrum bands are re-assigned to other distant cells. The co-channel interference arises in the cellular mobile networks owing to this phenomenon of Frequency reuse. Thus, besides the intended signal from with in the cell, signals at the same frequencies (co-channel signals) arrive at the receiver from the undesired transmitters located (far away) in some other cells and lead to deterioration in receiver performance.
- Adverse weather conditions: During periods of abnormally high-pressureAnticycloneAn anticyclone is a weather phenomenon defined by the United States' National Weather Service's glossary as "[a] large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere"...
weatherWeatherWeather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...
, VHF signals which would normally exit through the atmosphereAtmosphereAn atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
can instead be reflected by the troposphereTroposphereThe troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....
. This tropospheric ducting will cause the signal to travel much further than intended; often causing interference to local transmitters in the areas affected by the increased range of the distant transmitter.
- Poor frequency planning: Poor planning of frequencies by broadcasters can cause CCI, although this is rare. A very localised example is Listowel in the south-west of IrelandIrelandIreland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
. The RTÉNLRTÉ Network LimitedRTÉ Transmission Network Limited is a wholly owned subsidiary of Raidió Teilifís Éireann which runs Ireland's principal terrestrial television and radio broadcast signal transmission networks. They operate 10 main sites, and over 100 smaller relays and transposers, which carry either television,...
UHF television transmitter systems in Listowel and Knockmoyle (near Tralee) are on the same frequencies but with opposite polarisation. However in some outskirts of Listowel town, both transmitters can be picked up causing heavy CCI. This problem forces residents in these areas to use alternative transmitters to receive RTÉ programming.
- Overly-crowded radio spectrum: In many populated areas, there just isn't much room in the radio spectrum. Stations will be jam-packed in, sometimes to the point that one can hear loud and clear two, three, or more stations on the same frequency, at once. In the USA, the FCC propagation models used to space stations on the same frequency are not always accurate in prediction of signals and interference. An example of this situation is in some parts of Fayetteville, Arkansas the local 99.5 FM KAKSKAKSKAKS is a radio station broadcasting a Sports format. Licensed to Huntsville, Arkansas, USA, it serves the Fayetteville area...
is displaced by KXBLKXBLKXBL is a Classic Country station known as "Big Country 99.5.". Located in Henryetta, Oklahoma, it broadcasts to the Tulsa, Oklahoma area on 99.5 FM...
99.5 FM in Tulsa, particularly on the west side of significant hills. Another example would be of ClevelandCleveland, OhioCleveland is a city in the U.S. state of Ohio and is the county seat of Cuyahoga County, the most populous county in the state. The city is located in northeastern Ohio on the southern shore of Lake Erie, approximately west of the Pennsylvania border...
's WKKYWKKYWKKY is a commercial FM radio station in Geneva, Ashtabula County, Ohio, broadcasting at 104.7 MHz with a country music format. The station broadcasts using the HD Radio format.The station was started by Donald E. Martin on April 28, 1982 as WDON...
104.7 having interference from ToledoToledo, OhioToledo is the fourth most populous city in the U.S. state of Ohio and is the county seat of Lucas County. Toledo is in northwest Ohio, on the western end of Lake Erie, and borders the State of Michigan...
's WIOTWIOTWIOT is a FM radio station in Toledo, Ohio. Owned by Clear Channel Communications, the station broadcasts at 104.7 MHz.WIOT was Toledo's first FM rock station when it went on the air December 25, 1972, replacing a beautiful music/classical format. The call letters stood for "In Our Time"...
104.7 FM on the OntarioOntarioOntario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
shore of Lake Erie, as well as WoodstockWoodstock, OntarioWoodstock is a city and the county seat of Oxford County in Southern Ontario, Canada. Woodstock is located 128 km southwest of Toronto, north of Highway 401 along the historic Thames River...
's CIHR-FMCIHR-FMCIHR-FM is an FM radio station located in Woodstock, Ontario, Canada. The station plays an adult contemporary format branded as 104.7 Heart FM and is owned by Byrnes Communications Inc....
(on rare occasions), which is also on 104.7 FM, due to the signals travelling very far across Lake ErieLake ErieLake Erie is the fourth largest lake of the five Great Lakes in North America, and the tenth largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also has the shortest average water residence time. It is bounded on the north by the...
.
- Daytime vs Nighttime: In the Medium frequencyMedium frequencyMedium frequency refers to radio frequencies in the range of 300 kHz to 3 MHz. Part of this band is the medium wave AM broadcast band. The MF band is also known as the hectometer band or hectometer wave as the wavelengths range from ten down to one hectometers...
portion of the radio spectrum where most AM broadcastingAM broadcastingAM broadcasting is the process of radio broadcasting using amplitude modulation. AM was the first method of impressing sound on a radio signal and is still widely used today. Commercial and public AM broadcasting is carried out in the medium wave band world wide, and on long wave and short wave...
is allocated, signals propagate full-time via groundwaveSurface waveIn physics, a surface wave is a mechanical wave that propagates along the interface between differing media, usually two fluids with different densities. A surface wave can also be an electromagnetic wave guided by a refractive index gradient...
and, at nighttime, via skywaveSkywaveSkywave is the propagation of electromagnetic waves bent back to the Earth's surface by the ionosphere. As a result of skywave propagation, a broadcast signal from a distant AM broadcasting station at night, or from a shortwave radio station can sometimes be heard as clearly as local...
as well. This means that during the nighttime hours, co-channel interference exists on many AM radio frequencies due to the medium waves reflecting off the ionosphere and being bounced back down to earth. In the United StatesUnited StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
, CanadaCanadaCanada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, MexicoMexicoThe United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
, and the BahamasThe BahamasThe Bahamas , officially the Commonwealth of the Bahamas, is a nation consisting of 29 islands, 661 cays, and 2,387 islets . It is located in the Atlantic Ocean north of Cuba and Hispaniola , northwest of the Turks and Caicos Islands, and southeast of the United States...
, there are international agreementsNorth American Radio Broadcasting AgreementThe North American Radio Broadcasting Agreement, usually referred to as NARBA, is a treaty that took effect in March 1941 and set out the bandplan and interference rules for mediumwave AM broadcasting in North America. Although mostly replaced by other agreements in the 1980s, the basic bandplan...
on certain frequencies which allocate "clear-channel" broadcasting for certain stations to either have their respective frequencies to themselves at night, or to share their respective frequencies with other stations located over hundreds or even thousands of miles away. On other frequencies, there are "Regional Channels" where most stations on these frequencies either reduce power or change to a directional antennaPhased arrayIn wave theory, a phased array is an array of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions.An antenna array...
system at nighttime to help reduce co-channel interference to each other's signals. In the United StatesUnited StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
, there are six "Local Channel" frequencies, also known as "graveyarders" where nearly every station on those frequencies has the same power and antenna pattern both day and night and, as a result of skywave propagation, there is normally massive co-channel interference in rural areas on these frequencies, often making it difficult, if not impossible, to understand what's being said on the nearest local station on the respective channel, or the other distant stations which are bouncing on the same channel, during the nighttime hours.
- Cancellation of signal: In addition, many AM stations, including but not limited to the clear channel stations, often experience cancellation of their own signals within the inner and outer fringes of their normal groundwave coverage areas at nighttime due to the stations' individual skywave signals reaching the listeners' receivers at or near equal strength to the stations' individual groundwave signals; this phenomenon is very similar to the multipath interferenceMultipath interferenceMultipath interference is a phenomenon in the physics of waves whereby a wave from a source travels to a detector via two or more paths and, under the right condition, the two components of the wave interfere...
experienced on FM RadioFM broadcastingFM broadcasting is a broadcasting technology pioneered by Edwin Howard Armstrong which uses frequency modulation to provide high-fidelity sound over broadcast radio. The term "FM band" describes the "frequency band in which FM is used for broadcasting"...
in the VHFVery high frequencyVery high frequency is the radio frequency range from 30 MHz to 300 MHz. Frequencies immediately below VHF are denoted High frequency , and the next higher frequencies are known as Ultra high frequency...
band within mountainous regions and urban areas due to signals bouncing off of mountains, buildings, and other structures, except that the groundwave-skywave cancellation occurs almost exclusively at nighttime when skywave propagation is present.
Co-channel interference may be controlled by various radio resource management
Radio resource management
Radio 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...
schemes.
See also
- Adjacent-channel interferenceAdjacent-channel interferenceAdjacent-channel interference is interference caused by extraneous power from a signal in an adjacent channel. ACI may be caused by inadequate filtering , improper tuning or poor frequency control .ACI is distinguished from crosstalk.Broadcast...
- Crosstalk (electronics)Crosstalk (electronics)In electronics, crosstalk is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel...
- Signal-to-interference ratioSignal-to-interference ratioThe signal-to-interference ratio , also known as the carrier-to-interference ratio , is the quotient between the average received modulated carrier power S or C and the average received co-channel interference power I, i.e...
(SIR or S/I), also known as Carrier-to-interference ratio (CIR or C/I) - Frequency coordinationFrequency coordinationFrequency Coordination is a technical and regulatory process which is intended to remove or mitigate radio-frequency interference between different radio systems which utilize the same operational frequency....