Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-12-28
2003-10-28
Trost, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S452100, C455S562100, C455S422100, C455S452200, C455S063400
Reexamination Certificate
active
06640104
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to wireless communication systems and, in particular, to channel assignment schemes.
BACKGROUND OF THE RELATED ART
Call quality and capacity are important concerns in wireless communication systems. Carrier signal to interference (C/I) ratio is a primary factor in determining call quality and capacity. Specifically, the higher the C/I ratio, the better the call quality and the higher the capacity. By contrast, the lower the C/I ratio, the poorer the call quality while potentially adversely affecting capacity. Several schemes exist for improving the C/I ratio. Two such schemes involve dynamic channel assignment (DCA) techniques and fixed multi-beam intelligent antenna (FMBIA) systems.
The first scheme, i e., DCA, is a flexible channel allocation technique for dynamically assigning communication channels to mobile-stations based on interference level measurements. Generally, communication channels having low or lower associated interference level measurements are assigned to mobile-stations before communication channels having high or higher associated interference level measurements. This scheme improves the chances that communication channel assigned to mobile-stations will have a high or acceptable C/I ratio.
A DCA technique in accordance with the prior art utilizes long term interference level measurements and short term or near real-time interference level measurements to dynamically assign communication channels. The DCA technique includes a channel segregation procedure and a dynamic channel assignment procedure, wherein the dynamic channel assignment procedure is based on the results of the channel segregation procedure. The channel segregation procedure involves measuring interference levels for each communication channel not currently active (i.e., idle communication channels) in a given cell or sector. The interference levels are measured using two different processes referred to herein as a long term process and a short term process.
The long term process is used to create a “long list”, which is then used by the short term process to create a “short list.” The long term process involves measuring interference levels for all idle communication channels over a long term (i.e., every few minutes to few hours). These interference level measurements (also referred to herein as “long term interference level measurements”) are used to create the long list, which is a list of the idle communication channels ranked in ascending order from lowest to highest average long term interference level measurements. The top portion of the long list includes the idle communication channels with the lowest average long term interference level measurements, and is referred to herein as “candidate channels” for channel assignment.
The short term process involves measuring interference levels for the candidate channels over a short term or near real-time (i.e., every few seconds to few minutes). These interference level measurements (also referred to herein as “short term interference level measurements”) are used to create the short list, which is a list of the candidate channels ranked in ascending order from lowest to highest average short term interference level measurements. Since the short list is updated more frequently than the long list, the interference level measurements of the candidate channels in the short list are more up-to-date than the interference level measurements in the long list resulting in perhaps a different order for the candidate channels (compared to the long list). Accordingly, the short list is used by the dynamic channel assignment procedure to assign candidate channels to mobile-stations.
The dynamic channel assignment procedure involves using short term C
est
/I
short
ratios to determine whether a candidate channel is acceptable for assignment, where C
est
is an estimate of a carrier signal strength based on the mobile-station's uplink signal transmitted during call setup and I
short
is the measured average short term interference level. Several algorithms may be used to assign candidate channels to a mobile-station. For example, the candidate channel at the top of the short list (i.e., candidate channel with the smallest average interference level) may be the first channel assigned to a mobile-station if it has an acceptable C
est
/I
short
ratio, or any candidate channel with an acceptable C
est
/I
short
ratio may be assigned to the mobile-station. Therefore, DCA improves the chances that idle communication channels assigned to mobile-stations will have a high or acceptable C/I ratio.
The second scheme for improving the C/I ratio, i.e., FMBIA systems, involves using multiple narrow beam coverage in order to reduce co-channel interference to active communication channels.
FIG. 5
depicts a geographical area or cell
10
associated with base station
14
for providing wireless communication services to mobile-stations within cell
10
, wherein base station
14
has incorporated a FMBIA system in accordance with the prior art. Cell
10
is divided into a plurality of 120° sectors
12
-j, wherein each sector is further divided into four 30° sub-sectors.
FIG. 6
depicts a schematic of a generic fixed multi-beam intelligent antenna system
20
for a time division multiple access (TDMA) based wireless communication system in accordance with the prior art, wherein communication channels are defined by a frequency and a time slot. FMBIA system
20
comprises an antenna array
22
, low noise amplifiers
24
, RF switch matrix
26
, radios
28
and intelligent antenna controller (IAC)
29
(implementable in a digital signal processor). Antenna array
22
produces twelve 30° beams for providing wireless communication coverage to the sub-sectors of cell
10
. The 30° beams are channeled to radios
28
via low noise amplifiers
24
and RF switch matrix
26
. Radios
28
are assigned to process (e.g., modulate and demodulate) signals on active communication channels, and are equipped with beam scan receivers for sequentially sampling and measuring received-signal strengths (RSS) of the twelve beams for each time slot in each frequency channel. Each RSS is mapped to a RSS indicator (RSSI) value using a RSS-RSSI conversion or look-up table, wherein higher RSSI indicates higher signal levels for active communication channels. The RSSI are provided to IAC
29
, which uses the RSSI to select an optimal beam or beams (i.e., beam with highest RSSI moving average) for each active communication channel. Upon selecting the optimal beam or beams, IAC
29
directs RF switch matrix
26
to channel the optimal beam or beams to the appropriate radios
28
assigned to process signals for the corresponding active communication channels. Thus, FMBIA systems improve the C/I ratio on active communication channels at mobile-stations by directing optimal beams to the mobile-station.
The C/I ratio in FMBIA systems can be further improved through the use of dynamic channel assignment techniques adapted for FMBIA systems. Accordingly, there exists a need for a dynamic channel assignment scheme adapted for FMBIA systems.
SUMMARY OF THE INVENTION
The present invention is a method for improving call quality and capacity by integrating a dynamic channel allocation technique into intelligent antenna systems. Channels are dynamically assigned to a mobile-station by measuring interference levels on each beam in a set of beams for a plurality of communication channels, and assigning to the mobile-station a communication channel from the plurality of communication channels based on the measured interference levels on each beam in the set of beams.
In one embodiment, the present invention measures long term interference levels on each beam in a set of beams for a plurality of communication channels, measures short term interference levels on each beam in the set of beams for a portion of the plurality of communication channels, and assigns to a mobile-station a communication channel from the portion of the plurality of communicatio
Borst Simon C.
Cheng Terry Si-Fong
Grandhi Sudheer A.
Lubachevsky Boris Dmitrievich
Whiting Philip Alfred
Ferguson Keith
Goo Jimmy
Lucent Technologies - Inc.
Trost William
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