Note: Descriptions are shown in the official language in which they were submitted.
21~6071
WO 95/17048 ~ PCT/US94/14562
RAI)IO TELEPHONE SYSTEM FOR MINIMIZING CO-CH~NEL
INTERFERENCE UTILIZING GEOGRAPHIC SEPARATION OF SIGNALS AND
TRANSMISSION POWER CONTROL
Field of the Invention
This invention relates generally to a system for ll.i.. i.. l;~;"g co-rh~nnel
inte. rercl~ce and more particularly, to a system for IlI;llill~ co-channel interference
ili~in~ geographic separation of signals and tr~n~mi~sion power control.
B~l~n~und of the Invention
In general, the purpose of a radio telephone commllnication system is to
~ information-bearing signals from a source, located at one point to a user
tle~ ;on, located at a point some distance away. A radio telephone communicationsystem generally in~ les three basic components: tr~n~mitter, radio commlmil~tion
ch~nn~l, and receiver.
In a Frequency Hopping multiple access communications system such as
1~ disclosed in co-pending U.S. Patent Application Serial No. 08/080,075 filed June 1,
1993 and Israeli Patent Application Serial No. 103,620 filed November 3, 1992, a set
of N carrier frequencies are reused in adjacent colll,llunications sites to provide
~cater than N rninim~lly cross correlated frequency hopping radio comrnunicationch~nnels.
In Time Division Multiplexing ("TDM"), a wideband channel is subdivided into
several narrowband channels by allocating the use of the wideband channel to thedifferent narrowband channels during different time slots. Each of these narrowband
channels is assigned to different users to allow for contemporaneous utilization of the
wideband channel resources by many users.
Time Division Multiple Access ("TDMA") is a technique by which a large
SUBSII~UI~ SIIE~ (RUIE 2G)
PCTIUS94114562 0
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population of subscribers with a low individual probability of becoming active get
access to the channel resources. This technique relies on a dynamic TDM slot
allocation. Similarly, Frequency Division Multiple Access ("FDMA") is an access
meçh~ni~m for which the underlying multiplex~ng technique is Frequency Division
5 Multiplexing ("FDM").
It has been proposed that each of the above minim~lly cross correlated
frequency hopping radio colllllllll~ir~tion channels be further divided by time division
multiplexing. When high usage of this system occurs substantial co-channel
interference is experienced.
PCr patent application, International Publication No. WO 93/10601, published
May 27, 1993, discloses a multiple access co~ unications system in which a measure
of co-channel interference in a first radio commnni~tion channel being used in a first
geographic area is determined. The system reacts to the measure exceeding a
predetermined level to switch the user to a second radio collllllullication channel in
the same geographic area. This system does not address the problem of co-channel
interference by ~ ing such interference but reacts to the problem after the
interference is detected.
It is accordingly an object of the invention to Illillillli~e co-channel interference
in a multiple access co~ ications system.
It is another object of the invention to minimi~e co-channel interference in a
time division multiple access communications system.
It is still another object of the invention to provide a method of minimi7ing co-
channel interference in such a system by lltili7ing geographic separation of signals.
It is a further object of the invention to provide a method of l..il.i"~ g co-
WO95/170~8 ~ 6 0~1 PCT/US94/14562
ch~nnel interference in such a system by ~ltili7in~ geographic separation of signals andL,;~ ...iccion power control.
It is a still further object of the invention to Illill;llli7e co-channel interference
in a time division multiple access communications system which is also frequency
5 hopped.
Summary of the Invention
The foregoing objects are attained by the invention, which provides a method
of and a~aLus for ..~il.illli~;l-g co-ch~nnel interference by geographic separation of
signals and tr~ncmi.Ccion power control in a combined Frequency Hopping/TDMA
10 radio telephone system. The invention includes a first sector divided into geographic
zones, and an adjoining second sector divided into the same number of geographic
zones. Time slots are selectively allocated to each of the different geographic zones
in the first sector and the same time slots are allocated to the geographic zones in the
second sector but in a different order. Thus, every user located within a particular
15 geographic zone within a sector is assigned the same time slot. In addition, each time
zone has an up-link and down-link tr~ncmiccion power associated with it.
The invention will next be described in connection with certain illustrated
embodiments; however, it should be clear to those skilled in the art that various
modifications, additions and subtractions can be made without departing from the
20 spirit or scope of the claims.
E~rief Description of the Drawings
For a fuller understanding of the nalure and objects of the invention, reference
should be made to the following detailed description and accompanying drawings, in
which:
W095/17048 5 ~ PCT/US94114562
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FIG. 1 depicts a diagram of three adjoining sectors in a combined Frequency
Hopping/TDMA radio telephone system, in which a system for minimi7ing co-channel
interference operates in accordance with the invention; showing each sector divided
into different geographic zones;
FIG. 2 depicts the sectors of FIG. 1, showing time slot allocations and
tr~n~mi~ion overlap between the different sectors;
FIG. 3 depicts a base station and mobile receivers; showing a tr~n~mitter, a
receiver in a base st~tion, a tr~n~mitter in the mobile receivers and showing the up-
link and down-link l,;~ "~ ions.
10 Detailed Description of the Invention
FIG. 1 is a diagram of three sectors in a combined Frequency Hopping /
TDMA radio telephone system in which an embodiment of the invention operates,
showing three sectors S1, S2 and S3 each adjoining the other two, wherein each sector
is divided into three geographic zones Z11, Z12 Z13, Z21, Z22 Z23, Z31, Z32 and
15 Z33.
Fig. 2 is a diagram of the three sectors of FIG. 1 showing the different
geographic zones Z11, Z12 Z13, Z21, Z22 Z23, Z31, Z32 and Z33 having
col,esl)ollding TDM time frame time slot allocations T1, T2 and T3, tr~n~mi~ion
fields 1-1, 2-2 and 3-3 of the different antennas A1, A2 and A3 and the areas of
20 tr~n~mi~ion overlap F1 2, Fl 3 and F2 3 between tr~n~mi~ion fields 1-1, 2-2 and 3-3.
As will be obvious to one skilled in the art, it is possible to have more than three time-
slots and thus more than three geographic zones in each sector, but for ease of
explanation the three zone per sector system will be described.
F~G. 3 is a diagram of the relationship between base station 10 and a mobile
~ WO95117048 215 6 0 ~1 PCT/US94/14562
receiver 12 during down-link tr~ncmiC~ion and during up-link tr~ncmiccion. During
down-link l~ c~ion~ tr~n~mitter 16 can generate a signal to transmit to a particular
sector. During up-link ~ "~iCcion, tr~ncmitter 14 can generate a signal to L~
from mobile receiver 12. Base station 10 is also capable of ~ccigning time slots to
5 users located in the various geographic zones.
Fig. 2 illustrates what may occur with a three time slot repeat pattern in each
sector, and roughly the same frequency capacity in each sector. Sector Sl is split into
three geographic zones Zll, Z12 and Z13, each zone Z11, Z12 and Z13 being
determined by a corresponding time slot T1, T2 and T3. Sectors S2 and S3 are each
10 divided into an equal number of geographic zones as sector S1 (in this configuration
three), Z21, zæ, Z23, Z31, Z32 and Z33 such that each zone Z21, Z22, Z23, Z31,
Z32 and Z33is determined based upon a corresponding time slot T1, T2 and T3
associated with it. In the three time slot example, the sequences of the time slots T1,
T2 and T3 in sectors S2 and S3 are dictated from the order of the time slots Tl, T2
15 and T3 in sector Sl.
I'he geographic zones Z21 and Z31 located along the fringes Fl2, and Fl3
respectively, of sectors S2 and S3 should be allocated the same time slot as the central
time zone in sector Sl (in this case T1). The central geographic zones Z22, and Z33
in sectors S2 and S3 respectively, should be allocated the same time slots as the
20 geographic zones in sector S1 located adjacent to the respective sectors S2 and S3 (i.e.
geographic zone Z22 should be allocated time slot T2 as is zone Z12 and zone Z33
should be allocated time slot T3 as is zone Z13).
Tr~n~miccions during each time slot T1, T2 and T3 have tr~ncmiccion power
stipulations associated with them for tr:~n.cmiCcion during up-link and down-link. In
WO 95/17048 PCTIUS94/14562
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this illustration a L~ ...icciQn in time slot T1 in sector S1 has a down-link tr~ncmiccion
power associated with it that is lower than the tr~n~miccion power associated with time
slots T1 in sectors S2 and S3, but the tr~n.cmi.c.cion power during up-link is normal.
Tr~ncmiccions in time slots T2 and T3 in sector S1 both have normal down-link
5 ~ ...iccion power associated with them, but they both have up-link tr~ncmi.ccion
power associated with them that is lower than the up-link power associated with the
corresponding time slots in the adjoining sectors. In sector S2, tr~ncmiccions in time
slot T2 have the lower down-link tr~n.cmiccion power associated with them and normal
up-link power, while tr~n.cmiccions in time slot T1 and T3 have normal down-link
10 power associated with them, but lower up-link power. In sector S3, tr~ncmiccions in
time slot T3 have the lower down-link tr~ncmiccinn power associated with them and
normal up-link power, while tr~ncmi~cions in hme slots T1 and T2 have normal down-
link power associated with them, but lower up-link power. In this embodiment, time
slots T1, T2 and T3 in sectors S1, S2 and S3 respectively are allocated to mobile
5 trzlncmitters located in the central geographic zones Z11, Z22 and Z33 respectively.
In the three time slots per sector embodiment, use of the radio channels during
time slots that have tr~ncmiCcions which have lower down-link tr~ncmiccion power
associated with them is allocated to users in the central geographic zones (i.e. in S1
the set of users in Z11 would get T1, in S2 the set of users in Z22 would get T2 and
20 in S3 the set of users in Z33 would get T3), while time slots that have tr~ncmiccions
which have lower up-link tr~ncmiccion power associated with them are allocated to
users located near the fringe of the sector (i.e. in S1 the set of users in Z12 or Z13
would get T2 or T3 respectively, in S2 the set of users in Z21 or Z23 would get T1 or
T3 respectively and in S3 the set of users in Z31 or Z32 would get T1 or T2
~ wo 95/17048 21~ 6 0 7 1 PCT/US94/14562
respectively). This arrangement ",il,i",i~ec the possibility of co-channel interference
by geographically separating the users and by controlling the L~ iccion power.
By lvweling the tr~n.cmiCciQn power to users in the central zone during down-
link, the areas of l,~nc~"iccion overlap Fl 2, Fl 3 and F~3 decrease, and the power of the
5 interfering signal (i.e. the signal from S2 during time T2 in sectors S1 and S3) is very
weak as co"~ared to the signal coming from the proper sector antenna (i.e. the signal
from antenna A1 during time T2 will be much stronger in sector S1 during time T2
than the signal in sector S1 from antenna A2). Thus, because of this disparity in the
strength of the two signals, the overlapping signal will not interfere with the actual signal.
By lowering the tr~ncmiccion power from users in the zones located in the
fringes of the sectors during up-link, there is less of a chance for co-ch~nnel
interference, again because there will be less of a tr~n.cmiccion overlap and more of
a disparity in the strength of the .cign~lc.
The Lr~ ",iccion power from any region is determined by the requirements for
15 the received signal strength. Subscriber units which are located in regions in which the
tr~ncmiccion power needs enhancement, can transmit at higher power levels than that
required for tr~ncmicsionc from subscriber units which are located in locations in which
the tr~ncmiccion.c get no co-channel interference. Co,..~-.lll,ications are not being
degraded for some subscriber units to increase quality for other subscriber units, rather
20 communications are being illlproved for subscriber units located in problem areas.
It will thus be seen that the invention efficiently attains the objects set forth
above, among those made apparent from the preceding description. In particular, the
invention pro-vides a system for l~lillilll;~;llg co-channel interference in a combined
Frequency Hopping/TDMA system. Those skilled in the art will appreciate that the
WO 95/17048 PCT/US94/14562 ~
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configuration depicted in FIG. 1 ,.,i"i",i~es the possibility of co-channel interference
efficiently and effectively.
It will be understood that changes may be made in the above construction and
in the foregoing sequences of operation without departing from the scope of the
5 invention. It is accordingly intended that all matter contained in the above description
or shown in the ~ccomr~nying drawings be interpreted as illustrative rather than in a
limiting sense.
It is also to be understood that the following claims are intended to cover all
of the generic and specific features of the invention as described herein, and all
10 statements of the scope of the invention which, as a matter of 1~3n~l~ge, might be said
to fall therebetween.
Having described the invention, what is claimed as new and secured by Letters
Patent is:
