定义效率谱使用

WORKINGGROUP1 DEFINITIONS OFEFFICIENCY INSPECTRUMUSE OCTOBER1,2008 DEFINITIONS OFEFFICIENCY INSPECTRUMUSE When Marconi conducted the first radio transmissions in 1895, the energy from his sparkgaptransmitter occupied the entire usable radio spectrum.The first transatlantictransmission in 1901, which blanketed an area of over a hundred million square miles, wascapableof sending as little as one bit every 6 seconds.In fact,only a single suchtransmission could be accommodated on the surface of the earth using that technology. It isnow possible to conduct a million voice conversations, or equivalent data exchanges, in theusable radio spectrum in one location. Furthermore, cellular systems today allow the radiospectrum to be reused 50 times or more within the boundaries of a single large city.Ofcourse, the demand for access to spectrum and the types of applications has also explodedand it has become a critical resource to be effectively managed by governments worldwide. Thereis a strong need for the U.S.government to manage spectrum in as effective amanner as possible so as to optimize the overall utility of this important resource, while atthe same time meeting important and increasing U.S. Government mission requirementsthat can only be accomplished through the use of spectrum resources.One critical aspectof spectrum management is the efficiency of its assignment and use.Unfortunately, it isnot possible to establish a uniform metric for spectrum use efficiency that encompasses thewide range of services and uses for which spectrum is needed.As an extreme example,comparing cellular voice systems with military radar systems is unlikely to produce a usefulmutual comparison.Spectrum efficiency determinations for federal operations require ananalysisthat involves both technical and subjective considerations.Thus,to addressefficiency a taxonomy of spectrum uses is identified and efficiency within each class of useisconsidered separately.Beyondsimple efficiency metrics,the actual optimal use ofspectrum also relates to the effectiveness with which the spectrum meets the actual user ormission requirements.In some cases efficiency may become subservient to usage-basedconsiderations.For example, when safety or mission assurance requirements are involved,usersmay well choose to sacrifice some level of efficiency in exchange for increasedreliability or access. DEFININGSPECTRALEFFICIENCY Before one can discuss possible metrics for spectral efficiency it is important actually specifywhat one is interested in attempting to measure based on the intended purpose of themeasurement.For example, one could be interested in Technical Spectral Efficiency whichwould consider the theoretical capacity of the wireless components to carry traffic using theleast amount of spectrum.This would be somewhat different from a notion of OperationalSpectralEfficiency which would measure the practical efficiency of a system underoperational conditions.The difference between technical and operation SE can be seen byconsidering an LMR system designed to provide coverage for a given area.A very dense,multi-site,trunked LMR system would provide maximum technical SE.However,theoperational SE would include planned or measured traffic loading, and it might show thatthe system capacity greatly exceeded the expected needs of the coverage area.Thus for a given operational situation, the “improvements” in technical efficiency of one system overanother might not be significant.One could also define a notion of Allocational SpectralEfficiency that measures traffic over the actually allocated spectrum.This was described inarecent Korean paper,”Frequency Use Status Investigation and Spectrum UtilizationMetric” from ISART 2008.This notion would handle the problem of how well the bandallocationsmatch the demand for the respective services.Itmakes no sense to buildsystems with higher SE, if that change merely means that more frequencies in the allocatedband remain completely unused.This factor is intended especially to motivate the spectrummanager to make better use of all frequencies, instead of only requiring efficient practicesfrom the users. Beyond understanding the purpose of measuring the system efficiency we should also notethat there are somewhat different modes of wireless communications which may demanddifferentefficiency considerations.Thesewill factor into the taxonomy that we use inanalyzing spectral efficiency.Wireless systems can be used in a transport mode wheredata is moved across a region without providing any local services.This mode of use puts apremium on point to point communication.Wireless access systems on the other handprovide local serviceswithout net transport of data across a region.Insuch systems,access capacity to the served users is paramount.Systems may also becoverageorientedsystems in which a minimal amount of access service is provided across a defined coveragearea.This corresponds, for example, to many public safety syste