Control technique for a communication system
View Patent ↗A control technique for a communication system in which a microcell base station is co-located with a macrocell base station. The microcell base station tracks hot spots as they move within the macrocell. The microcell base station may utilize a two-dimensional (2-D) antenna array, which is co-located with the macro cell antenna. The two-dimensional antenna is steerable in both the horizontal and vertical directions. The size of the microcell coverage area depends upon the distance from the cell site antenna as well as the dimensionality of the array, which determines the angular spread of the beam. Filter tap weights may be adjusted to point the beam to any desired location in the macrocell. The orthogonality between the macrocell and the microcell may be obtained either in the frequency domain or in the code domain, depending upon the system in which it is implemented.
1. A base station, servicing a macrocell and at least one microcell, comprising:
at least one steerable N-dimensional (N≧2) antenna array within the macrocell for serving the microcell and co-located with a macrocell antenna of said base station, the steerable N-dimensional antenna array including at least two antenna elements and an N-dimensional digital filter for receiving inputs from said at least two antenna elements and processing the inputs to produce a resultant output beam,
wherein at least one of the inputs and outputs are weighted using filter tap weighting coefficients of a plurality of filter taps to steer the resultant output beam, and
wherein the weighting coefficients of a given filter tap are determined as a function of an antenna element spacing value between antenna elements, a look direction of the resultant output beam and a wavelength of an incident signal.
2. The base station of claim 1 , wherein said at least one steerable N-dimensional array serving the microcell is co-located on an antenna tower with the antenna serving the macrocell.
3. The base station of claim 1 , wherein the microcell includes a hot spot.
4. The base station of claim 1 , wherein said base station includes a steerable N-dimensional (N≧2) array for each microcell within the macrocell.
5. The base station of claim 1 , wherein said at least one steerable N-dimensional (N≧2) array serves a hot spot.
6. The base station of claim 1 , wherein an angular spread and the look direction of the resultant output beam are varied by varying a number of the plurality of filter taps.
7. The base station of claim 1 , wherein said at least two antenna elements are arranged in a two-dimensional plane or on a surface of a cylinder.
8. The base station of claim 6 , wherein the weighting coefficients for a given filter tap are complex coefficients, w j , determined by:
w
j
=
cos
[
2
π
K
d
λ
sin
θ
]
-
i
·
sin
[
2
π
K
d
λ
sin
θ
]
where
k=the filter tap,
d=antenna element spacing,
θ=look direction of the resultant output beam, and
λ=wavelength of an incident signal.
9. The base station of claim 1 , wherein said base station is part of a TDMA system and the macrocell and the microcell are separated in the frequency domain.
10. The base station of claim 1 , wherein said base station is part of a CDMA system and the macrocell and the microcell are separated in one of the frequency and the code domains.
11. A method of servicing at least one microcell in a macrocell, the at least one microcell and the macrocell supported by a base station, comprising:
co-locating, with a macrocell antenna at the base station, at least one steerable N-dimensional (N≧2) antenna array within the microcell, the N-dimensional antenna array having at least two antenna elements and an N-dimensional digital filter;
receiving inputs from said at least two antenna elements at said N-dimensional digital filter;
processing the inputs at said N-dimensional digital filter to produce a resultant output beam for serving the microcell; and
steering the resultant output beam toward the at least one microcell,
wherein steering further includes using filter tap weighting coefficients to weight at least one of the inputs and outputs to steer the resultant output beam, and
wherein the weighting coefficients of a given filter tap determined as a function of an antenna element spacing value between antenna elements, a look direction of the resultant output beam and a wavelength of an incident signal.
12. The method of claim 11 , wherein said at least one steerable N-dimensional array serving the microcell is co-located on an antenna tower with the antenna serving the macrocell.
13. The method of claim 11 , wherein the microcell includes a hot spot.
14. The method of claim 11 , wherein said co-locating step includes co-locating a steerable N-dimensional (N≧2) array with the base station for each microcell within the macrocell.
15. The method of claim 11 , wherein the at least one steerable N-dimensional array serves a hot spot.
16. The method of claim 11 , further comprising varying a number of said plurality of filter taps of the resultant output beam to vary an angular spread and the look direction of the resultant output beam.
17. The method of claim 11 , further comprising arranging the at least two antenna elements in a two-dimensional plane or on a surface of a cylinder.
18. The method of claim 16 , the weighting coefficients for a given filter tap are complex coefficients, w j , determined by
w
j
=
cos
[
2
π
K
d
λ
sin
θ
]
-
i
·
sin
[
2
π
K
d
λ
sin
θ
]
where
k=the filter tap,
d=antenna element spacing,
θ=look direction of the resultant output beam, and
λ=wavelength of an incident signal.
19. The method of claim 11 , wherein the base station is part of a TDMA system and the macrocell and the microcell are separated in the frequency domain.
20. The method of claim 11 , wherein the base station is part of a CDMA system and the macrocell and the microcell are separated in one of the frequency and the code domains.