Technology Overview
As GSM900MHz rapid expansion of digital mobile communications network capacity in many areas, frequency resources become increasingly strained, to some extent It has restricted the development of the mobile communications business. In order to meet the needs of the business development of mobile communications, some provinces, the city has GSM frequencies used to expand the bandwidth of 12.2MHz, even so, the frequency resources are still tight. In the case of an analog network temporarily can not be returned frequency, how to improve the frequency utilization, improve the capacity of the GSM network as much as possible, it has become a hot issue mobile communications operations and many manufacturers of common concern. For this reason many new technologies developed frequency reuse.
technical requirements
former Ministry of Posts issued "900MHz TDMA digital public terrestrial cellular mobile communication network technology system" requirements, the use of directional antennas, is recommended 4 × 3 multiplexed manner, a large-traffic areas, according to the capabilities of the device may also use other multiplexing methods, such as multiplexing mode 3 × 3, 2 × 6 multiplexing methods. Either reuse mode, the basic principle is to consider different propagation conditions, the different factors multiplexing mode and a plurality of interference, interference protection ratio requirements must be met, namely:
cochannel interference protection ratio: C / I (carrier / interference) ≥9dB
adjacent channel interference protection ratio: when C / I (carrier / interference) ≥9dB
400KHz offset from the carrier interference protection ratio: C / I (carrier / interference) ≥-41dB
Note: for an engineering design of the above C / I margin plus 3dB.
System Specification
on the recommendation GSM system specification, typically are used in radio network planning 4 × 3 frequency reuse mode, i.e., four base stations areas (each base station is divided into 3 120 ° 60 ° sector cell or cell trefoil), 12 sectors of a cluster of cells. This way due to the frequency reuse with the same frequency reuse distance, can more reliably meet the indicator for the same GSM system frequency interference protection ratio and adjacent channel interference protection ratio, the GSM network to run good quality, good security.
However, the use of low frequency multiplexed manner, not meet the requirements of large service areas to expand network capacity. my country's urban population density great, GSM network after several large-scale expansion, large cities and some major cities of the urban macrocell base station away from the average of less than 1000m, the cell coverage radius is about a few hundred meters, some "hot spots" area away from the station is only about 300m. Visible, and then rely on large-scale cell splitting technology to increase network capacity has been unrealistic.
prospects
Thus, for many economically developed cities, in order to meet the rapid growth of mobile users demand, a measure DCS1800 is to develop, build dual-band network. Another measure is the frequency at 900MHZ existing resources, frequency multiplexing using densified.
all manufacturers and software functions according to the capabilities of its own equipment using different multiplexing densified, but the same is to reduce the frequency reuse distance, reducing the cost of interference protection ratio. Since in the GSM system, it has taken many anti-jamming technology, such as frequency hopping, power control, discontinuous transmission of voice (the DTX), the diversity reception and the like, the effective application of these techniques would further increase the carrier to interference ratio C / I, so C / I have a certain margin, thus, may increase the network capacity by multiplexing further densified using the frequency, and the network to meet quality of service requirements. Typical densified frequency multiplexing mainly 3 × 3,2 × 6,2 × 3,1 × 3 technology.
we are actually of a conventional 4 × 3 Frequency Reuse and densified 3 × 3,2 × 3,1 × 3 mixed using frequency multiplexing. Due to the different ways of mixing employed, also there are several different multiplexing modes.
frequency reuse formula:
Application Examples
C Intelsat Used band forward circularly polarized waves, i.e., a-pol (L upstream, downstream dextrose), and anti-circularly polarized waves, i.e., B-pol (right-upward, left downward) dual circular polarization are formed, together with the isolation region is achieved using a frequency four repeats (e.g. 5th generation satellite --IS-V), i.e. East and West a-pol hemispheric beams and East, West B-pol region of the beam. Achieve frequency on the first generation satellite IS-VI 6 and 7 generation satellite IS-VI six repeated with the B-pol into north, east, south east, northwest, southwest four beams, see Fig. The use of spot beams, the frequency reuse also increases with frequency and may also increase the downlink effective isotropic radiated power (EIRP), but smaller coverage area.
in the domestic satellite communication system, C-band multi-lane achieved using linearly polarized wave polarized, 24 can be arranged in the transponder bandwidth 36MHz 500MHz bandwidth. Double up both vertically polarized polarization is horizontal polarization have the same frequency band, the downlink as well. The satellite transponder is not more than 12, only a single line of polarization, that is to say, the use of vertically polarized wave upward, downward and horizontal polarization waves. In addition to the big countries do not need to band division manner by a region C to achieve frequency reuse. Higher Ku-band frequencies, a region division method facilitates to achieve frequency reuse.