11-10-2012, 10:48 AM
A MODIFIED DIRECTIONAL FREQUENCY REUSE PLAN BASED ON CHANNEL ALTERNATION AND ROTATION
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ABSTRACT
In previous work, we presented a novel Channel
Alternation and Rotation (CAR) scheme that coordinates
channel assignment with antenna directivities. In CAR,
each cell type is allocated an extra channel set that
provides network designer the flexibility to alternate and
rotate channels according to nearest front lobe
interference avoidant strategy to enhance co-channel
interference ratio (C/I). CAR relaxes the constraints
assumed in conventional reuse plans to allow deployment
of smaller, unconventional reuse cluster sizes based on C/I
requirements, thus increases frequency reuse efficiency.
In this paper, we present a new reuse plan in which 2 extra
channel sets are allocated to each cell type and assigned
according to CAR strategy. This reuse plan, referred to as
2x(3+2), increases channel capacity by 20% in
comparison with conventional 4x3 reuse plan while still
provides signals above the minimum acceptable C/I
margin. 2x(3+2) reuse plan is simple and can be
implemented without costs.
INTRODUCTION
Unlike Omni-directional antenna which power radiates
equally in all directions, directional antennas project main
beams power onto front lobe regions, thus side and back
lobes interference is reduced. To take advantages of the
antenna directivities to enhance C/I, most cellular systems
employ three 1000 to 1200 directional antennas at each base
station (BS) [2][3]. Fig. 1 depicts a typical 3dB beamwidth,
1200 antenna’s radiation pattern obtained at [7].
With in which, front lobe region is generally within
± 600 from the bore-sight (at azimuth angle 00).
In a conventional cellular network, the entire radio
frequency is assigned to each reuse cluster of N adjacent
cells. To provide equidistant separation among co-channel
cells, N must be a rhombic number determined by the two
shift parameters i and j , and expressed as,
CONCLUSION
Since interference from antenna back lobe is negligible
and interference from the side lobe is significantly
reduced, CAR scheme was proposed to take full advantage
of antenna directivities to enhance C/I and increase
channel capacity. In CAR, each cell type is allocated an
ex an extra channel set, which provides network designer
the flexibility to is used to strategically rotate and
alternate channels to minimize the effects of and to avoid
front lobe interference to and from the nearest co-channels.
Since reducing the separation between co-channel cells
hence reduces C/I protection level, conventional reuse plan
tighter than 4x3 is not practical for TDMA systems that
require C/I of 14 dB [2][6]. In this paper, we presented a
high capacity directional reuse plan referred to as 2x(3+2)
in which 2 alternate channels are used for channel rotation
and alternation