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<div class="div">
<h1>Frequency Hopping (FH)</h1>

<p>Frequency Hopping is a feature designed to increase the
quality and capacity in the urban propagation environment. The gain is achieved
by means of frequency diversity and interference diversity properties of frequency
hopping.</p>


<p>Slow Frequency Hopping in the GSM 900/1800 means that the
frequency of radio timeslot (RTSL) is changing burst by burst. The frequency
remains the same during a burst (0,577 ms). All dedicated channel types and
their associated channel types (TCH/SACCH/FACCH, SDCCH/SACCH) may hop. The
exact frequency on a certain moment of time is defined as a function of frequency
hopping parameters of a cell and a ‘logical Air interface channel’ (CA, MA,
MAIO, HSN) and the absolute frame number in Air interface (see the GSM 05
series). The frame number synchronises the MS and BTS operation on a time
basis.</p>


<p>As far as the implementation of frequency hopping is concerned,
there are two main options; Baseband Hopping and Radio Frequency (RF) Hopping.
The Nokia BSS supports both of these hopping methods. However, RF hopping
is not supported by the Nokia 2nd generation BTS.</p>


<p>Whether frequency hopping is in use or not is defined on
a cell basis.</p>


<p>If frequency hopping is applied in an Intelligent Underlay
Overlay cell (option), it can be defined on IUO layer basis.</p>


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<h2>Baseband
Hopping</h2>

<p>When baseband hopping is in use in a cell, all the timeslots
hop, except the BCCH timeslot. The number of frequencies in a hopping sequence
is the same as the number of TRXs in the hopping group.</p>


<a name="apr1541834377" shape="rect"></a>
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<img alt="urn:mars:dn0468912:1:en:global:tiff:data:data" border="0" src="NED?action=retrieve&amp;identifier=dn0468912&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=gif&amp;component=data&amp;item=data" /><p class="figure-caption">Figure: Radio timeslots in baseband hopping when IUO not in use</p>
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<h2>Radio
Frequency Hopping</h2>

<p>When RF hopping is in use in a cell, only the timeslots
on other TRXs than the BCCH TRX hop. The frequencies in the hopping sequence
are defined by attaching the cell to one of the Mobile Allocation Frequency
Lists. The operator may define up to 128 different frequency lists per BSC,
each list containing up to 63 frequencies (possible only if BTS SW is DF3.0).</p>


<a name="apr1541835168" shape="rect"></a>
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<img alt="urn:mars:dn0468866:1:en:global:tiff:data:data" border="0" src="NED?action=retrieve&amp;identifier=dn0468866&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=gif&amp;component=data&amp;item=data" /><p class="figure-caption">Figure: Radio timeslots in radio frequency hopping when IUO not in use</p>
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<h2>Shared
frequencies in sectored site</h2>

<p>It is possible to use the same MA frequency list in sectors
of a BTS site provided that the following conditions are met:</p>


<ul>
<li><p>The sectors are synchronised, that
is, they are controlled by the same BCF</p>
</li>
<li><p>Applicable for RF hopping only</p>
</li>
<li><p>The MA-list contains at least as many
frequencies as there are hopping TRXs in the site</p>
</li>
<li><p>The sectors are configured to use the
same HSN (hopping sequence number).</p>
</li>
</ul>


<p>Frequency sharing makes it possible to utilise RF hopping
in cells having relatively small amount of TRXs, still without any need to
allocate more frequencies for the BTS site.</p>


<p>For example, we have a BTS of three sectors, two TRXs in
each sector. To gain from hopping, we need at least three frequencies to hop
over in each sector plus BCCH frequency. Without frequency sharing, this totals
12 frequencies for only 6 TRXs meaning quite an uneconomical use of frequency
band.</p>


<p>By sharing the same MA frequency list between the three
sectors, we can manage with only 6 frequencies: 3 for BCCH TRXs and 3 for
hopping TRXs. The hopping TRX in each of the three sectors hops over the same
3 frequencies, but synchronised in a way that no collisions occur.</p>


<p>The activation of Frequency Hopping in Nokia Talk-family
base stations can be done on sector level, which will minimise the time of
the BCF reset during the new frequency plan implementation.</p>
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