sábado, 20 de marzo de 2010

RADIO-FREQUENCY CHANNEL ARRANGEMENTS FOR MEDIUM AND HIGH CAPACITY ANALOGUE OR DIGITAL RADIO-RELAY SYSTEMS OPERATING IN THE UPPER 6 GHZ BAND

RADIO-FREQUENCY  CHANNEL  ARRANGEMENTS  FOR  MEDIUM  AND
HIGH  CAPACITY  ANALOGUE  OR  DIGITAL  RADIO-RELAY  SYSTEMS
OPERATING  IN  THE  UPPER  6  GHz  BAND
Introduction
Developments in fixed wireless equipment technology has emnabled the use of higher order modulation schemes that reduce the radio channel bandwidth requirements. Specific to the upper 6 GHz band, the use of higher order modulation techniques has enable the deployment of SDH STM-1 systems in 30MHz channles instead of currently specified 40 MHz channels.  The UK therefore proposes the addition of an RF arrangement permitting the use of 30 MHz channels in the upper 6 GHz band.
The ITU Radiocommunication Assembly,
considering

a) that radio-relay systems with a capacity of 2 700 telephone channels should prove to be feasible in the 6 GHz band, if due care is exercised in the planning of radio paths to reduce multipath effects;
b) that it is sometimes desirable to be able to interconnect, at radio frequencies, radio-relay systems on international circuits in the 6 GHz band;
c) that it may be desirable to interconnect up to eight go and eight return channels in a frequency band 680 MHz wide;
d) that economy may be achieved if at least four go and four return channels can be interconnected between systems, each of which uses common transmit-receive antennas;
e) that a common radio-frequency (RF) channel arrangement for both up to 1 260 and 2 700 telephone channel radio relay systems offers considerable advantages;
f) that the use of certain types of digital modulation (see Recommendation ITU-R F.1101) permits the use of the RF channel arrangement defined for 2 700 telephone channel systems for the transmission of digital channels with a bit rate of the order of 140 Mbit/s or synchronous digital hierarchy bit rates;
g) that for these digital 140 Mbit/s radio systems, further economies are possible by accommodating up to eight go and return channels on a single antenna with suitable performance characteristics;
h) that many interfering effects can be reduced substantially by a carefully planned arrangement of the radio frequencies in radio-relay systems employing several RF channels;
j) that RF channels should be so arranged that for analogue radio-relay systems an intermediate frequency of 70 MHz may be used for up to 1 260 telephone channels;
k) that RF channels should be so arranged that for analogue radio-relay systems an intermediate frequency of 140 MHz may be employed for 2 700 telephone channels;
l) that single- and multi-carrier digital radio-relay systems are both useful concepts to achieve the best technical and economic trade-off in system design,
m) that digital radio-relay systems can deliver SDH STM-1 capacities using high order modulation techniques that reduce the necessary bandwidth
recommends
1 that the preferred radio-frequency channel arrangement for up to eight go and eight return channels, each accommodating 2 700 telephone channels, or a bit rate of the order of 140 Mbit/s, or synchronous digital hierarchy bit rates (Note 3), and operating at frequencies in the upper 6 GHz band, should be derived as follows:
Let f0 be the frequency of the centre of the band of frequencies occupied (MHz),
 fn be the centre frequency of one RF channel in the lower half of the band (MHz),
 f ¢n be the centre frequency of one RF channel in the upper half of the band (MHz),

then the frequencies of individual channels are expressed by the following relationships:
 lower half of the band: fn = f0–350+40 n MHz
 upper half of the band: f ¢n = f0–10+40 n MHz
where:
 n = 1, 2, 3, 4, 5, 6, 7 or 8;
2 that, in the section over which the international connection is arranged, all the go channels should be in one half of the band, and all the return channels should be in the other half of the band;
3 that different polarizations should be used alternately for adjacent radio-frequency channels in the same half of the band;
4 that, when common transmit-receive antennas are used, and not more than four channels are accommodated on a single antenna, it is preferred that the channel frequencies be selected by making either:
 n = 1, 3, 5 and 7 in both halves of the band
or
 n = 2, 4, 6 and 8 in both halves of the band (Note 4);
5 that the preferred arrangement of RF polarization
6  that a co-channel arrangement may also be used for digital radio-relay systems which can be derived from the arrangements

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