Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-03-23
2001-03-13
Bost, Dwayne D. (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S447000
Reexamination Certificate
active
06201972
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a frequency carrier allocation method for a cellular system using the FDD (Frequency Division Duplex) scheme of performing two-way communication between a base station and a mobile station by using different frequency carriers in the uplink and downlink directions and, more particularly, to a frequency carrier allocation method in a case wherein traffics in the uplink and downlink directions become asymmetrical to provide multimedia communication services or a cellular system in which the transmission efficiencies based on frequency carriers in the uplink and downlink directions become asymmetrical.
In general, in a cellular system using the FDD scheme, transmission and reception are simultaneously performed between a base station and a mobile station by using different frequency carriers in the uplink direction, in which signals are transmitted from the mobile station to the base station, and in the downlink direction, in which signals are transmitted from the base station to the mobile station.
In each cell (communication area) set for each base station, the allocated frequency carrier is divided with time or codes to virtually set many channels on one frequency carrier, thereby realizing communication between many mobile station and the base station with one frequency carrier.
In addition, each frequency carrier is simultaneously and repeatedly used in a plurality of cells to increase the number of frequency carriers that can be used in one cell.
A cellular system having a hierarchical structure is used. In this system, a plurality of micro-cells, each covering a range having a radius of about several hundred meters or less, are arranged in each macro-cell covering a range having a radius of about one kilometer or more. In a general hierarchical cellular system, macro-cells are set in correspondence with a plurality of macro-cell base stations, and micro-cells are set in correspondence with a plurality of micro-cell base stations in each macro-cell.
Each micro-cell is used to partly increase the traffic accommodation capacity in a place where many mobile stations gather and the entire traffic cannot be accommodated by one macro-cell or to provide high-quality communications to a place where radio waves from a macro-cell do not easily reach. If a frequency carrier having the same band width as that used by a macro-cell is allocated to a micro-cell, in particular, a traffic as large as that can be accommodated by the macro-cell can be accommodated by even the micro-cell having a small area. Therefore, even in an area where the traffic is very high, the traffic can be accommodated by using micro-cells.
In a cellular system having such a hierarchical structure, if the same frequency carrier is allocated to a macro-cell and a micro-cell, since the transmission power of the base station and a mobile station in the macro-cell is higher than that of the base station and a mobile station in the micro-cell, the macro-cell causes strong interference with the micro-cell. For this reason, different frequency carriers are used in the macro-cell and micro-cell.
FIG. 4
shows the schematic arrangement of each of transmission/reception apparatuses in macro-cell base stations and micro-cell base stations.
FIG. 5
shows the schematic arrangement of each of transmission/reception apparatuses in the mobile stations. As shown in
FIG. 4
, a plurality of reception circuits and a plurality of transmission circuits are connected to an antenna through a transmission/reception multiplexer. As shown in
FIG. 5
, in the mobile station, a pair of reception and transmission circuits are connected to an antenna through a transmission/reception multiplexer.
Referring to
FIG. 4
, in the base station, a reception section
440
includes three reception circuits, and a transmission section
450
also includes three transmission circuits. The three reception circuits of the reception section
440
and the three transmission circuits of the transmission section
450
are connected to an antenna
410
through a transmission/reception multiplexer
420
. An interference wave power measuring circuit
430
is connected to the transmission/reception multiplexer
420
to measure the reception power of interference waves coming from neighboring mobile stations.
Referring to
FIG. 5
, in the mobile station, a pair of a reception circuit
540
and a transmission circuit
550
are connected to an antenna
510
through a transmission/reception multiplexer
520
.
As described above, the base and mobile stations respectively use transmission/reception multiplexers
420
and
520
each used to separate transmission and reception signals having different frequencies. Since transmission and reception signals that are simultaneously transmitted/received greatly differ in level, they must be separated sufficiently.
For this reason, the frequency intervals between frequency carriers used in the uplink direction and frequency carriers used in the downlink direction must be sufficiently larger than those between frequency carriers used in the same communication direction. The FDD scheme therefore uses two frequency bands separated from each other by a protective band width which is the frequency interval required to separate transmission and reception signals in the transmission/reception multiplexer
420
. One of these frequency bands is exclusively allocated to communications in the downlink direction, and the other is exclusively allocated to communications in the uplink direction.
As described above, since different frequency carriers are allocated to macro-cells and micro-cells, a frequency carrier arrangement (allocation) like the one shown in
FIG. 6
is used. In this frequency carrier arrangement, the numbers of frequency carriers used in the respective directions are constant.
In general, as described above, two frequency bands FB
1
and FB
2
have the same width, and the numbers of frequency carriers F
11
to F
16
and F
21
to F
26
in the downlink and uplink directions are the same. In the FDD scheme, if, therefore, the traffic ratios in the uplink and downlink directions differ, a frequency carrier shortage occurs in the direction in which the traffic is larger, while the frequency carriers cannot be fully used in the direction in which the traffic is smaller.
Assume that the traffic ratios in the uplink and downlink directions are the same. Even in this case, if the transmission efficiency based on the frequency carriers in one of the uplink and downlink directions is higher than that in the other direction, a frequency carrier shortage occurs in the direction in which the transmission efficiency is lower, while some of the frequency carriers in the opposite direction are left unused, and all the frequency carriers cannot be effectively used.
As a method of solving this problem, a method is disclosed in Japanese Patent Laid-Open No. 8-275230, in which the frequency carrier passband in the downlink direction is set to be larger than that in the uplink direction, and uplink frequency carriers and downlink frequency carriers are alternately arranged in the respective frequency bands.
According to this method, by allocating frequency carriers from the different frequency bands to each mobile station in the uplink and downlink directions, the utilization efficiency of the frequency bands can be increased while the required frequency interval between transmission and reception signals is ensured in each transmission/reception multiplexer even if the traffic in the downlink direction is larger than that in the uplink direction.
In this method, however, frequency carrier passbands in the uplink and downlink directions must be determined in advance by predicting traffic ratios and transmission efficiencies in the uplink and downlink directions. Although transmitters and receivers used in base stations and mobile stations must be designed in accordance with the respective passbands, the arrangements of the transmitter and receiver of each mobile station, in particula
Bost Dwayne D.
NEC Corporation
Scully, Scott, Murray & Presser
Vuong Quochien B.
LandOfFree
Cellular system and frequency carrier allocation method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cellular system and frequency carrier allocation method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cellular system and frequency carrier allocation method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2495028