CA2198458A1 - System and method for time slot and frequency allocation in a radio communications system - Google Patents
System and method for time slot and frequency allocation in a radio communications systemInfo
- Publication number
- CA2198458A1 CA2198458A1 CA002198458A CA2198458A CA2198458A1 CA 2198458 A1 CA2198458 A1 CA 2198458A1 CA 002198458 A CA002198458 A CA 002198458A CA 2198458 A CA2198458 A CA 2198458A CA 2198458 A1 CA2198458 A1 CA 2198458A1
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- station
- frequency
- power
- time slots
- stations
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- 238000000034 method Methods 0.000 title claims description 24
- 230000005540 biological transmission Effects 0.000 claims 8
- 230000003466 anti-cipated effect Effects 0.000 claims 1
- 230000008901 benefit Effects 0.000 description 3
- 238000012856 packing Methods 0.000 description 3
- 238000001228 spectrum Methods 0.000 description 3
- 230000001413 cellular effect Effects 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 230000009897 systematic effect Effects 0.000 description 2
- IRLPACMLTUPBCL-KQYNXXCUSA-N 5'-adenylyl sulfate Chemical compound C1=NC=2C(N)=NC=NC=2N1[C@@H]1O[C@H](COP(O)(=O)OS(O)(=O)=O)[C@@H](O)[C@H]1O IRLPACMLTUPBCL-KQYNXXCUSA-N 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 230000001186 cumulative effect Effects 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W72/00—Local resource management
- H04W72/04—Wireless resource allocation
- H04W72/044—Wireless resource allocation based on the type of the allocated resource
- H04W72/0473—Wireless resource allocation based on the type of the allocated resource the resource being transmission power
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- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Mobile Radio Communication Systems (AREA)
Abstract
Radio communication systems employing time division multiple access (TDMA) on several frequency channels are disclosed. The base station transmitting powers can be reduced when communicating with nearby mobile stations while still permitting the base station to employ a constant transmitting power in all time slots of a frequency channel.
Description
~ W 096~(~7287 2~'9~ PCTiUSg5J10~10 SYSTEM AND METHOD FOR TIME SLOT AND FREOUENCY ALLOCATION
IN A RADIO COMMUNICATIONS SYSTEM
~AC K G RO UND
The user capacity of mobile radio ~ systems is limited by the width of the frequency spectrum available for signal l, .,., i~ In order to maximize a system's capacity, therefore, it is desirable to utilize the available frequency band in the most efficient manner possible.
Cellular telephone systems in operation today commonly use an access technique known as Frequency Division Multiple Access (FDMA) to permit a base station to ~ ' with a plurality of mobile stltions. In FDMiA systems, each c"l~ i. ui~ link is allocated a unique frequency slot or channel in the radio spectrum.
Newer systems use Time Division Multiple Access (TDMA), in which a base station .u" n ,: ~ with a plurality of mobiles on the same frequency channel by dividing up a time cycle into time slots. The European GSM standard is an example of a system using FDMA and TDMA to allocate both frequency and time slots to mobile calls. The system uses 200KHz wide frequency slots in each of which a 4.6mS ~ :nll cycle is divided into eight, 560uS time slots, with short guard ~eriods between each.
l'he guard periods in GSMI are provided because base station 1,,.,~.";~ ~"
during a time cycle is not held at a constant power for all time slots, but instead changes the power level for each time slot based on the distance of the mobile station using that time slot from the base station. Moreover, for ~ s which employ frequency hopping, wherein the frequency channel employed for each 4.6mS time cycle changes, a guard period of zero 1"- ~ "~:.,n power is provided whenever power or frequency is changed .1:~ to avoid spectral splatter into other frequency channels.
Another example of a system employing both TDMA and FDMA is the US
T~ """"~ Industry Association standard IS54. The IS54 standard describes a system having 30KHz wide time slots, in each of which a base station employs a wo96107287 ~ 9 ~ 4 ~ 0~
20mS lla~ d~ n cycle divided into three, 6.6mS time slots with no guard period between. The base staLion l~ .. ;n this system is actually just a conLinuous n, ~ of time-.""li;~ 7 data to three mobile stations. There is no guard period provided in TIA lS54 because frequency hopping is not employed, on the 5 contrary, the systenn anticipates that the power level will be the same in all time slots.
~ I S. Patent No. 4,866,710 to Schaeffer describes a method of alloCaLing f~c~lu~ ,lcies and time slots to mobile stations such that all the time slots on a giva frequency are filled first before allocating time slots on another frequency. Bypack;ng mobile stations preferentially in this way, the tl~.~"-itt. l~ and frequencie.s that 10 have not as yet allocated time slots can be swiLched off complelely~ reducingintert'erence. This ~ ould reduce wasted capacity in the lS54 system arising from the le~lu;lClll~l~t Lhat base stations continually Lransmit on all three time slots even when only one is needed. However, it will be noted that the base station still transmits at one maximum power level for each frequency in use, irrespective of the power needs 15 of each particular mobile, resulting in a higher net level of intc~rclcll~c Lhan if the power needs of each mobile were Laken into account.
SUI~IMARY
Accordingly, it is an object of the present invention to achieve reduction of 20 interference by a more effective sLrategy that works even when all time slots are iilled. Exemplary methods according to the present invention allocate mobile stations to time slots on the same frequency as other mobile stations requiring similar base station transmitter power levels. In this way, mobiles which are allocated time sloLs on a given frequency channel w;ll likely lie at similar distances from the base station.
25 The base station transmitter power can then be chosen to be just sufficient for the mob;le station on that frequency that needs the greatest power level. This provides a greater power margin than needed for the other mobiles on that fre4uency, but n~.tl.el.~, allows a lower base station power than if mobiles had been allocated time slots amd frequencies v~ithout regard to power needs. Thus1 each frequency channel 30 will sen~e a group of mobiles with similar base power 11~ l needs, and the base power can be cul-c~ Jh~,ly reduced on each frequency channel so as to be just ~ Wo 961~7287 2 1 !~ 8 ~ ~ ~ PCTlUSgS110810 sufficient for good signal 1~ ... for the group. The cumulative reductions in power on every channel, therefore, will significMtly reduce hILI~If~ ;IICe in the system.
According to an exemplary ~ 1;ll ,1 of the present invention, when the S first mobile linl~ with a given base is set up, the base chooses a frequency Md time slot containing minimum interference. Commands are then issued to the mobile station to adjust its power level to a level sufficient for good received signal quality at the base. The mobile station in turn reports signal strength or qu;llity received from the base station and the base stat;on chooses a power level suflicient to provide good signal quality at the mobile.
When a second mobile link with the same base is set up, the base estimates the pouer level to be transmitted to that mobile and allocates to the second mobile Mother time slot on the same frequency if the power level to be tMnsmitted is close to that used for the first mobile. If the required power level is slightly higher thM
that for the first mobile, the base smoothly increases the power transmitted to the h;gher level. If the second mobile requires a power sufficiently lower than the first mobile, it is allocated a time slot on a second frequency. The base then adapts its power and commands the mobile power to ."""~",. Ievels to maintain ade~uate signal quality in both directions.
According to exemplary; ',.:,.1;". .,1~, when a new mobile link is to be established with a base slation already having a plurality of ongoing ~ ,- "...;~ ,~I;..I~C, the base station first estimates the power level that is appropriate for II. I~.I II;I.L to that mobile. This is compared to the power level of all ongoing i ~nc on r~u..~C;., that lave at least one empty time slot. The mobile is then allocated a 25 time slot on that frequency where the 1,~ ;- ." power is greater than but closest to the estimated power. If 110 existing transmitter is of h;gh enough power, the highest power 1"",~ ;, - is smoothly increased to the estimated ~~uh~ "~ l for the new mobile, Md the new mobile allocated an umlsed time slot on that frequency.
21g8~
Wo 961072~7 ~ ~ PCTlltS95/1081 Bl~lh'.F D~,~CRIPIION OF Tl-IE DRAWINGS
The foregoing, and other, objects. features and advantages of the present invention will he more readily understood upon reading the following detailed description in conjunction with the drauings in which:
Figure l(a) shows an exemplary pattern of base station power ~c~ui~ r~,uL~ for each time siot vn four r~ u~"~
Figure l(b) illustrates actual ~IAII'- I '' On power used by a conventional basestalion for each of the fime slots of Figure l(a~;
Figure 2(a) shows a pattern of base station power ~c,u.,i,~"ic;."~ for a scheme in which all time slots on a given fre~uenc.y are filled before allocating time slots on anothe.r frequency;
Figure 2(b) illustrates actual ~ power used by a u~nvelltiollal base station for lhe thlle slDts of Figure 2(a);
Figure 3(a) shows an exemplary pattern of base station power profiles for nnobiles which are allocated to time slots and frequencies according to the present ;nvention;
Figure 3(b) illustrates base IIA~ II pouer according to an exemplary embodiment of the present invention for the time slots illustrated in Figure 3(a); and Figure 4 shows an exemplary network block diagram according to the present invention.
DETAILEID DE~SCRIPI~IO~
In order tD fully appreciate syste.ms and methods according to the present inven~ion, a more detailed description of cv,,~...livnal systems will first be provided.
Figure.s I and 2 ;llustrate conventional allocation schemes whereby the base station transmits at maximum power to the mobiles, irrespective of their power Uilem.,l~. In Figure l(a), mobiles are assigned fre~uencies (Fl-F4) and time slots CTsl-Ts3) essentially at random. Regardless of the power level required for eachmobile, the base station transmits at the same maximum power level on all time slots as seen in Figure l(bj. Figure 2(a) illustrates allocating frequency and time slots to new mob;les so as to ccmr~ntrPtP the mobiles on as few frequencies as possible in ~ Wog6/07287 ~ 5~ Pcr/usss/losln order to eliminate ~ f~n on other l;~u~"c;~". Note that all of the time slots on f~ucn~icb Fl and F2 and t~vo of the three time slots on F3 have been filled. It can be seen in Figure 2(b), however, that all base stations having at least one active time slot transmit at the same maximum power level according to this conventional S scheme while those that have no active time slot are switched off. Moreover, neither conventional allocation scheme adjusts the pouer level transmitted by the base to be nl""" ~ uith that required by tile mobiles.
Figure 3(a) shows mobiles having the same power IcuuhclllcllL~ as used in Figures l(a) and 2(a) being allocated to time slots (Ts) and ll~u~a~ ;~,, (F) according 10 to an exemplary ~I"I,o.lh~ L o f the present invention. Note that the three mobiles (1, 7 and 4) requiring the most power are allocated time slots on frequency Fl, the next highest three mobiles (8, 2 and 5) are allocated on frequellcy F2 and the mobiles requiring the lowest base transmit power (6 and 3) are allocated to frequency F3, illustrating that many i ~ transmit at lower than maximum power while those~5 that have no aclive time slots do not transmit at all. Although the number of dlt~l~ which have been switched off (one) is the same as in Figure 2(b), an additional benefit is obtained by operating those ll~ lll;lt~l~ that are active at reduced pouer levels.
According to an exemplary r~ ". m of the present invention, when the 20 first mobile link with a given base is ~et up, the base either chooses a frequency and time slot at random, or chooses the rri~quency and time slot containing minimum i,l,.~f.l~;llce. Commands are issued to the mobile station over the air to adjust its power level to a level suffcient for good received signal quality at the base.
According to one ~ ",i o~ ..;, this power level can be that which is just high enough 25 to provide good received signal quality at the base. The mobile station reports signal strength or quality received from the base sLation and the base station chooses a power level sufficient to provide good signal quality at the mobile. Again, this power level may be that which is only just sufficient for this purpose.
When the second mobile link with the same base is set up, the base estimates 30 the power level to be transmitted to that mobile and, if, for example, within the range ~dB higher to lOdB lower than that used for the first mobile~ the base allocates to the Wo 961072~ 5- 8 P~r~llsg~l081~--second mobile another time slot on the same frequency as the first mobile, preferably the time slot conhining the lowest level of hlt~ c. Note in this regard the similarity in power ~ Ui~ ts for each mobile on each fre~iuency chaulnel Fl, F2 and F3 in Figure 3~a). If the reciuired power for the second mobile link level is, for example, 0 to 6dB higher than that for the first mobile, the base smoothly increases the power transmitted to the higher level. If the second mobile reciuires a power more than, for example, 10dB lower, or 6dB higher, than the first mobile, it is aliocated a time slot on a second frequency, preferably the time slot which a3ntains the minimum level uf blt~ llce. The base then adapts its power and commands the mobile power lo appropriate levels to just maintain adequate signal quality in both directions, as before.
When the third mobile link with the same base is set up, the base estimates the power it will need to transmit to the third mobile. Assuming the first two nnobiles are aiready using the same freciuency, if the third mobiie lc~uh~ ,-L is within the range of, for example, 12dB greater than the weaker of the first two mobiles to 12dB lower than the stronger of the first two mobiles, the third mobile is allocated another time slot on the same freguency and power level$ are adapted ~IJ ul~ ly as berore.
Otherwise, the third mobile is allocated a time slot on another frequency. preferably that having the lowest level of h~b lr~-",. e.
When a new mobile link is to be established with a base station already having a pluraiity of ongoing . rlnc. the base station first estimates the power level that is appropriate for h~ Lhly to that mobile. This is compared to the power level of ail ongoing n,. . ln;~ "~ on frequencies that have at least one empty time.
slot. The mobile is then ailocated a time slot on that frequency for which the transmit power is greater than but closest to the estimated power. If no existing transmitter is of high enough power, the highest power t~ ;V~ is smoothly increased to the e$timated ~ uh~n~ l for the new mobile, and the new mobile ailocated an unused time slot on tha~ frequency. preferably that containing the least i"tc,-~....ce. The transmit power levels are then adjusteci a~J~Jlu~Jli..~ Iy as before. Similarly, the Ll power can be ramped down for freciuencies in which a highest power ~ wo g.j,0,28, 2 1 9 8 ~ 5 ~ Pf~TlUS9~/10810 time slot becomes ;dle after a connection serviced on that time slot becomes fl;~.. ,. ~ t~l Figure 4 shows an exemplary network block diagram according to the present invention. A mobile switching center (MSC) 40 is connected by landline or other 5 . links to a number oF base station sites referenced by numerals 41,42.
Each base station site contains a number of TD~fA L~ , receivers and antennas. The operating rle4L'~ ;~ of each transmitter and receiver may be fixedaccording to a so-called cell plan or frequency-reuse pattern, but are preierably ,."", -I,le to any channel in the allocated frequency band. The base station site 10 may also contain a base shtion controller 43. The optional base station controller can be provided when it is desired to separate the in~ en~e for h~ h~e the current im~ention from those functions normally performed by the ~fSC. When the MSC 40 is able to perform the functions required, the base station controller 43 may simply be a e~ to funnel ~ u~ between the transceivers and the 15 MSC.
As a further option, an h.t~ "~ e as.sessment receiver 44 can be used to provide i~ru~lllcLiun via the base station controller to assist in the allocation of frequency and time slots to mobiles. The interference assessment receiver can be a scanning receiver, spectrum analyzer or ~lti~-h ~nn~l device adapted to determine the 20 il,Lc:lr,-~n;~ energy levels in each of the presently unused r t;~uc.,cies and time slots at that base station site. This can be .~ 1 by u.~u.clllenLs from the traffic receivers in unused time slots on their own r ~ lu~ .lCic~.
The base station normally also contains a calling channel transmitter and random access receiver. lhe calling channel transmitte~ broadcasts i~lrwlll~Liull about 25 the status of the base station to mobiles that may wish to establish, The random access receiver receives ~ In from mobiles attempting to establish ~ u --- 1--- ;- u ;. .1- before a traffic channel is allocated to the mobile according to this exemplary f~ o~ of the present invention. In the IS54 system, the calling channel is presently a non-TDMA L~ ;u~ employing continuous L~ ;on on 30 a special frequency. The random access re,eiver operates on a ~;u-~ Ju"ding frequency 45MHz lower. Calling channel broadcasts and random access tal;e place 21 984~
wo ~6/072~7 ~ Pcl~msssllo8lo using Mc~ h~t~l code frequency modulated data L~ .,.. as in the US AMPS
cellular system. At a later date it is probable that a TDMA calling channel will be introduced, together with a TDMA random access channel. If the TI)MA calling channel uses, for example, only one out of three time slots while traffic is transmitted S in the other two, then traffic requiring full power should be assigned to the remaining time slots on the calling channel frequency which typically requires full power.It will be appreciated that the functions of the MSC and the base station controller as described above can be hll~ f ,~t.',l cu.,~ licllLI!/ with the aid of one or more l~lil.,lU~JlUCe,!i,5UI~ or computers and appropriate software. The processor or 10 computer receives data messages transmitted by mobile stations requesting call set up or, for already ex;sting l~.nm~ n;l ~ 3 reporting signal strength or quality levels received from the base station. The computer or processor also receives data from the base station receivers which provides i..rO~ iu~ pertaining to the signal strength or quality received from the mobiles, as well as illLclrclc~c levels in unused time 15 slots.
According to th;s exemplary ~."l,udil".,lL of the present inventic~n, the computer processes this data to determine an appropriate frequency and time slot for g with a given mobile station, and send.s control sign~s to the chosen base station transmitter-receiver so that it expects the mobile signal. The computer 20 generates a me.ssage for n.~ .,. to the mobile to command it to operate in the chosen frequency and time slot. Messages are also generated ~for Ll~ : ." to themobile to command it to adjust its power level according tû the received signal strength or quality at the base station receiver. Similar control signals are also sent to the base station transmitter so as to control its power level tû be, for example, the 25 minimum necessary to maintain signal quality as reported by the mobile on that frequency receiving the lowest quality. Alternatively, the power level can be selected to be some margin higher than this minimum necessary power.
When a base station maintains a large number of ongoing ~UIl~ iUlls with a ~~ulLi~ y of mobile stations, there can arise reasons to change the frequency and 30 timeslot allocatiûns between mobile stations even when no old calls are terminating and nû new calls are being initiated. Due to mobile motion, a mobile previously ~ W096/07287 PcrluS95110810 2~4~
requiring high power may now be satisfied by lower base station power or vice versa.
A simple systematic means to reshuffle frequency and timeslot allocations is for the network to maintain a list of ongoing conversations sorted by order of signal strength received from the mobiles, or, more accurately, sorted in order of radio ~,.u~,agalio~
5 loss between the base station and the mobiles. The radio ~lu~ ,aliull loss may be computed from a knowledge of the received signal strength and the power level the mobile was previously cu~nlllauded to adopt. A second check on this value may becomputed from a knowledge of the signal quality reported back by the mobile and the transmitter power the network is Lla~ liLLhlg to it. All such information may be10 utilized and averaged over a period of a fe.w seconds to obtain a smoothed estimate of u,url~;aLiùll loss.
Using the sorted list, the network ensures to the best of i~s ability that the top three mobiles on the list are allocated timeslots on the highest power carrier frequency; the next three mobiles in the list are allocated timeslots on the next 15 strongest carrier frequency and so forth. If a Digital Control Channel is in use and transmitted on the strongest carrier, then the top two mobiles in the list are allocated the same carrier, the next three the second strongest carrier and so-on. The network may, if required, swap two mobiles between two carriers to achieve this. For example, if the highest power mobile X on carrier B due to relative movement now20 has a higher power r~ .h~ ,n..~L than the lowest power mobile Y on a stronger carrier A, then X and Y are caused to change frequency and timeslot allocations ky issuing them with hand-off commands. Such hand-offs within the same base station area are called "internal handovers", and are made purely to achieve a more optimum frequency/timeslot packing that minimizes created int~ ,f~,.w.~,e with neighboring 25 bases.
It has already been indicated above that an exception to the packing rule may be desirable if there is a large dB difference (e.g., > lOdB) between the carrier povver and that needed by a mobile next on the list. It may be desirable to allocate that mobile to a lower power carrier together with the next two mobiles below it in 30 the list. This results in an apparently l~ y higher power Ll,~ " ûn a timeslot that is not allocated, but this departure from the absolute tightest packing WO 96/07287 21 ~ 8 ~ 5 ~ - PCT/U~9511081--algorithm has the advantage thaL a few unoccupied timeslots are distributed throughout the signal strength range and are thus available for allocating to new calls without having first to disturb a large number of ongoing Wll~ dliUn~. It can even be adopted as a deliberate strategy, to leave a "hole" every 15dB or so of ~Jlu~d~dliun loss range, depending on the loading of the system, in order more rapidly to be able to ~ cul~ t~ r- new calls. If because of this coarse power step between "holes", a mobile has to be allûcated to a ~hole" on a carrier that is unnecessary, this will be corrected by the systematic resorting procedure that takes place on a slower timescale.
Such a continuous resorting procedure also handles the event of a mobile call terminating. In principle all mobiles bek~w it in the power/~,lu~,d~ d(iul, loss list can be moved up, resulting in the highest of three perhaps receiving an hlternal halldover to the next highest power carrier. This does not however take place all at once necessarily but gradually. The rate of handovers can be restricted so that nû mobile receives a handover more often than, for example, say once per ten seconds. If amobile has received an internal handover or handoff within the last ten seconds for example, it is not allowed to he a candidate for a handoff until ten seconds have passed. When the strongest of three mobiles on the three timesloh on a given carrier terminates its call, the power of the carrier may of course be regulated down to the stronger of the two ren aining, thus reducing created h~lclrr_~r_ln,c levels.
The above-described exemplary ' ' are intended to be illustrative in all respects, rather than restrictive, of the present invention. Thus the present invention is capable of many variations in detailed i-.~plf /''~ ;nn that can be derived from the description contained herein by a person skilled in the art. All such variations and n-O-Iiri~ t'l;n~; are considered lo be within the scope and spirit of the ~5 present invention as defined by the following claims.
IN A RADIO COMMUNICATIONS SYSTEM
~AC K G RO UND
The user capacity of mobile radio ~ systems is limited by the width of the frequency spectrum available for signal l, .,., i~ In order to maximize a system's capacity, therefore, it is desirable to utilize the available frequency band in the most efficient manner possible.
Cellular telephone systems in operation today commonly use an access technique known as Frequency Division Multiple Access (FDMA) to permit a base station to ~ ' with a plurality of mobile stltions. In FDMiA systems, each c"l~ i. ui~ link is allocated a unique frequency slot or channel in the radio spectrum.
Newer systems use Time Division Multiple Access (TDMA), in which a base station .u" n ,: ~ with a plurality of mobiles on the same frequency channel by dividing up a time cycle into time slots. The European GSM standard is an example of a system using FDMA and TDMA to allocate both frequency and time slots to mobile calls. The system uses 200KHz wide frequency slots in each of which a 4.6mS ~ :nll cycle is divided into eight, 560uS time slots, with short guard ~eriods between each.
l'he guard periods in GSMI are provided because base station 1,,.,~.";~ ~"
during a time cycle is not held at a constant power for all time slots, but instead changes the power level for each time slot based on the distance of the mobile station using that time slot from the base station. Moreover, for ~ s which employ frequency hopping, wherein the frequency channel employed for each 4.6mS time cycle changes, a guard period of zero 1"- ~ "~:.,n power is provided whenever power or frequency is changed .1:~ to avoid spectral splatter into other frequency channels.
Another example of a system employing both TDMA and FDMA is the US
T~ """"~ Industry Association standard IS54. The IS54 standard describes a system having 30KHz wide time slots, in each of which a base station employs a wo96107287 ~ 9 ~ 4 ~ 0~
20mS lla~ d~ n cycle divided into three, 6.6mS time slots with no guard period between. The base staLion l~ .. ;n this system is actually just a conLinuous n, ~ of time-.""li;~ 7 data to three mobile stations. There is no guard period provided in TIA lS54 because frequency hopping is not employed, on the 5 contrary, the systenn anticipates that the power level will be the same in all time slots.
~ I S. Patent No. 4,866,710 to Schaeffer describes a method of alloCaLing f~c~lu~ ,lcies and time slots to mobile stations such that all the time slots on a giva frequency are filled first before allocating time slots on another frequency. Bypack;ng mobile stations preferentially in this way, the tl~.~"-itt. l~ and frequencie.s that 10 have not as yet allocated time slots can be swiLched off complelely~ reducingintert'erence. This ~ ould reduce wasted capacity in the lS54 system arising from the le~lu;lClll~l~t Lhat base stations continually Lransmit on all three time slots even when only one is needed. However, it will be noted that the base station still transmits at one maximum power level for each frequency in use, irrespective of the power needs 15 of each particular mobile, resulting in a higher net level of intc~rclcll~c Lhan if the power needs of each mobile were Laken into account.
SUI~IMARY
Accordingly, it is an object of the present invention to achieve reduction of 20 interference by a more effective sLrategy that works even when all time slots are iilled. Exemplary methods according to the present invention allocate mobile stations to time slots on the same frequency as other mobile stations requiring similar base station transmitter power levels. In this way, mobiles which are allocated time sloLs on a given frequency channel w;ll likely lie at similar distances from the base station.
25 The base station transmitter power can then be chosen to be just sufficient for the mob;le station on that frequency that needs the greatest power level. This provides a greater power margin than needed for the other mobiles on that fre4uency, but n~.tl.el.~, allows a lower base station power than if mobiles had been allocated time slots amd frequencies v~ithout regard to power needs. Thus1 each frequency channel 30 will sen~e a group of mobiles with similar base power 11~ l needs, and the base power can be cul-c~ Jh~,ly reduced on each frequency channel so as to be just ~ Wo 961~7287 2 1 !~ 8 ~ ~ ~ PCTlUSgS110810 sufficient for good signal 1~ ... for the group. The cumulative reductions in power on every channel, therefore, will significMtly reduce hILI~If~ ;IICe in the system.
According to an exemplary ~ 1;ll ,1 of the present invention, when the S first mobile linl~ with a given base is set up, the base chooses a frequency Md time slot containing minimum interference. Commands are then issued to the mobile station to adjust its power level to a level sufficient for good received signal quality at the base. The mobile station in turn reports signal strength or qu;llity received from the base station and the base stat;on chooses a power level suflicient to provide good signal quality at the mobile.
When a second mobile link with the same base is set up, the base estimates the pouer level to be transmitted to that mobile and allocates to the second mobile Mother time slot on the same frequency if the power level to be tMnsmitted is close to that used for the first mobile. If the required power level is slightly higher thM
that for the first mobile, the base smoothly increases the power transmitted to the h;gher level. If the second mobile requires a power sufficiently lower than the first mobile, it is allocated a time slot on a second frequency. The base then adapts its power and commands the mobile power to ."""~",. Ievels to maintain ade~uate signal quality in both directions.
According to exemplary; ',.:,.1;". .,1~, when a new mobile link is to be established with a base slation already having a plurality of ongoing ~ ,- "...;~ ,~I;..I~C, the base station first estimates the power level that is appropriate for II. I~.I II;I.L to that mobile. This is compared to the power level of all ongoing i ~nc on r~u..~C;., that lave at least one empty time slot. The mobile is then allocated a 25 time slot on that frequency where the 1,~ ;- ." power is greater than but closest to the estimated power. If 110 existing transmitter is of h;gh enough power, the highest power 1"",~ ;, - is smoothly increased to the estimated ~~uh~ "~ l for the new mobile, Md the new mobile allocated an umlsed time slot on that frequency.
21g8~
Wo 961072~7 ~ ~ PCTlltS95/1081 Bl~lh'.F D~,~CRIPIION OF Tl-IE DRAWINGS
The foregoing, and other, objects. features and advantages of the present invention will he more readily understood upon reading the following detailed description in conjunction with the drauings in which:
Figure l(a) shows an exemplary pattern of base station power ~c~ui~ r~,uL~ for each time siot vn four r~ u~"~
Figure l(b) illustrates actual ~IAII'- I '' On power used by a conventional basestalion for each of the fime slots of Figure l(a~;
Figure 2(a) shows a pattern of base station power ~c,u.,i,~"ic;."~ for a scheme in which all time slots on a given fre~uenc.y are filled before allocating time slots on anothe.r frequency;
Figure 2(b) illustrates actual ~ power used by a u~nvelltiollal base station for lhe thlle slDts of Figure 2(a);
Figure 3(a) shows an exemplary pattern of base station power profiles for nnobiles which are allocated to time slots and frequencies according to the present ;nvention;
Figure 3(b) illustrates base IIA~ II pouer according to an exemplary embodiment of the present invention for the time slots illustrated in Figure 3(a); and Figure 4 shows an exemplary network block diagram according to the present invention.
DETAILEID DE~SCRIPI~IO~
In order tD fully appreciate syste.ms and methods according to the present inven~ion, a more detailed description of cv,,~...livnal systems will first be provided.
Figure.s I and 2 ;llustrate conventional allocation schemes whereby the base station transmits at maximum power to the mobiles, irrespective of their power Uilem.,l~. In Figure l(a), mobiles are assigned fre~uencies (Fl-F4) and time slots CTsl-Ts3) essentially at random. Regardless of the power level required for eachmobile, the base station transmits at the same maximum power level on all time slots as seen in Figure l(bj. Figure 2(a) illustrates allocating frequency and time slots to new mob;les so as to ccmr~ntrPtP the mobiles on as few frequencies as possible in ~ Wog6/07287 ~ 5~ Pcr/usss/losln order to eliminate ~ f~n on other l;~u~"c;~". Note that all of the time slots on f~ucn~icb Fl and F2 and t~vo of the three time slots on F3 have been filled. It can be seen in Figure 2(b), however, that all base stations having at least one active time slot transmit at the same maximum power level according to this conventional S scheme while those that have no active time slot are switched off. Moreover, neither conventional allocation scheme adjusts the pouer level transmitted by the base to be nl""" ~ uith that required by tile mobiles.
Figure 3(a) shows mobiles having the same power IcuuhclllcllL~ as used in Figures l(a) and 2(a) being allocated to time slots (Ts) and ll~u~a~ ;~,, (F) according 10 to an exemplary ~I"I,o.lh~ L o f the present invention. Note that the three mobiles (1, 7 and 4) requiring the most power are allocated time slots on frequency Fl, the next highest three mobiles (8, 2 and 5) are allocated on frequellcy F2 and the mobiles requiring the lowest base transmit power (6 and 3) are allocated to frequency F3, illustrating that many i ~ transmit at lower than maximum power while those~5 that have no aclive time slots do not transmit at all. Although the number of dlt~l~ which have been switched off (one) is the same as in Figure 2(b), an additional benefit is obtained by operating those ll~ lll;lt~l~ that are active at reduced pouer levels.
According to an exemplary r~ ". m of the present invention, when the 20 first mobile link with a given base is ~et up, the base either chooses a frequency and time slot at random, or chooses the rri~quency and time slot containing minimum i,l,.~f.l~;llce. Commands are issued to the mobile station over the air to adjust its power level to a level suffcient for good received signal quality at the base.
According to one ~ ",i o~ ..;, this power level can be that which is just high enough 25 to provide good received signal quality at the base. The mobile station reports signal strength or quality received from the base sLation and the base station chooses a power level sufficient to provide good signal quality at the mobile. Again, this power level may be that which is only just sufficient for this purpose.
When the second mobile link with the same base is set up, the base estimates 30 the power level to be transmitted to that mobile and, if, for example, within the range ~dB higher to lOdB lower than that used for the first mobile~ the base allocates to the Wo 961072~ 5- 8 P~r~llsg~l081~--second mobile another time slot on the same frequency as the first mobile, preferably the time slot conhining the lowest level of hlt~ c. Note in this regard the similarity in power ~ Ui~ ts for each mobile on each fre~iuency chaulnel Fl, F2 and F3 in Figure 3~a). If the reciuired power for the second mobile link level is, for example, 0 to 6dB higher than that for the first mobile, the base smoothly increases the power transmitted to the higher level. If the second mobile reciuires a power more than, for example, 10dB lower, or 6dB higher, than the first mobile, it is aliocated a time slot on a second frequency, preferably the time slot which a3ntains the minimum level uf blt~ llce. The base then adapts its power and commands the mobile power lo appropriate levels to just maintain adequate signal quality in both directions, as before.
When the third mobile link with the same base is set up, the base estimates the power it will need to transmit to the third mobile. Assuming the first two nnobiles are aiready using the same freciuency, if the third mobiie lc~uh~ ,-L is within the range of, for example, 12dB greater than the weaker of the first two mobiles to 12dB lower than the stronger of the first two mobiles, the third mobile is allocated another time slot on the same freguency and power level$ are adapted ~IJ ul~ ly as berore.
Otherwise, the third mobile is allocated a time slot on another frequency. preferably that having the lowest level of h~b lr~-",. e.
When a new mobile link is to be established with a base station already having a pluraiity of ongoing . rlnc. the base station first estimates the power level that is appropriate for h~ Lhly to that mobile. This is compared to the power level of ail ongoing n,. . ln;~ "~ on frequencies that have at least one empty time.
slot. The mobile is then ailocated a time slot on that frequency for which the transmit power is greater than but closest to the estimated power. If no existing transmitter is of high enough power, the highest power t~ ;V~ is smoothly increased to the e$timated ~ uh~n~ l for the new mobile, and the new mobile ailocated an unused time slot on tha~ frequency. preferably that containing the least i"tc,-~....ce. The transmit power levels are then adjusteci a~J~Jlu~Jli..~ Iy as before. Similarly, the Ll power can be ramped down for freciuencies in which a highest power ~ wo g.j,0,28, 2 1 9 8 ~ 5 ~ Pf~TlUS9~/10810 time slot becomes ;dle after a connection serviced on that time slot becomes fl;~.. ,. ~ t~l Figure 4 shows an exemplary network block diagram according to the present invention. A mobile switching center (MSC) 40 is connected by landline or other 5 . links to a number oF base station sites referenced by numerals 41,42.
Each base station site contains a number of TD~fA L~ , receivers and antennas. The operating rle4L'~ ;~ of each transmitter and receiver may be fixedaccording to a so-called cell plan or frequency-reuse pattern, but are preierably ,."", -I,le to any channel in the allocated frequency band. The base station site 10 may also contain a base shtion controller 43. The optional base station controller can be provided when it is desired to separate the in~ en~e for h~ h~e the current im~ention from those functions normally performed by the ~fSC. When the MSC 40 is able to perform the functions required, the base station controller 43 may simply be a e~ to funnel ~ u~ between the transceivers and the 15 MSC.
As a further option, an h.t~ "~ e as.sessment receiver 44 can be used to provide i~ru~lllcLiun via the base station controller to assist in the allocation of frequency and time slots to mobiles. The interference assessment receiver can be a scanning receiver, spectrum analyzer or ~lti~-h ~nn~l device adapted to determine the 20 il,Lc:lr,-~n;~ energy levels in each of the presently unused r t;~uc.,cies and time slots at that base station site. This can be .~ 1 by u.~u.clllenLs from the traffic receivers in unused time slots on their own r ~ lu~ .lCic~.
The base station normally also contains a calling channel transmitter and random access receiver. lhe calling channel transmitte~ broadcasts i~lrwlll~Liull about 25 the status of the base station to mobiles that may wish to establish, The random access receiver receives ~ In from mobiles attempting to establish ~ u --- 1--- ;- u ;. .1- before a traffic channel is allocated to the mobile according to this exemplary f~ o~ of the present invention. In the IS54 system, the calling channel is presently a non-TDMA L~ ;u~ employing continuous L~ ;on on 30 a special frequency. The random access re,eiver operates on a ~;u-~ Ju"ding frequency 45MHz lower. Calling channel broadcasts and random access tal;e place 21 984~
wo ~6/072~7 ~ Pcl~msssllo8lo using Mc~ h~t~l code frequency modulated data L~ .,.. as in the US AMPS
cellular system. At a later date it is probable that a TDMA calling channel will be introduced, together with a TDMA random access channel. If the TI)MA calling channel uses, for example, only one out of three time slots while traffic is transmitted S in the other two, then traffic requiring full power should be assigned to the remaining time slots on the calling channel frequency which typically requires full power.It will be appreciated that the functions of the MSC and the base station controller as described above can be hll~ f ,~t.',l cu.,~ licllLI!/ with the aid of one or more l~lil.,lU~JlUCe,!i,5UI~ or computers and appropriate software. The processor or 10 computer receives data messages transmitted by mobile stations requesting call set up or, for already ex;sting l~.nm~ n;l ~ 3 reporting signal strength or quality levels received from the base station. The computer or processor also receives data from the base station receivers which provides i..rO~ iu~ pertaining to the signal strength or quality received from the mobiles, as well as illLclrclc~c levels in unused time 15 slots.
According to th;s exemplary ~."l,udil".,lL of the present inventic~n, the computer processes this data to determine an appropriate frequency and time slot for g with a given mobile station, and send.s control sign~s to the chosen base station transmitter-receiver so that it expects the mobile signal. The computer 20 generates a me.ssage for n.~ .,. to the mobile to command it to operate in the chosen frequency and time slot. Messages are also generated ~for Ll~ : ." to themobile to command it to adjust its power level according tû the received signal strength or quality at the base station receiver. Similar control signals are also sent to the base station transmitter so as to control its power level tû be, for example, the 25 minimum necessary to maintain signal quality as reported by the mobile on that frequency receiving the lowest quality. Alternatively, the power level can be selected to be some margin higher than this minimum necessary power.
When a base station maintains a large number of ongoing ~UIl~ iUlls with a ~~ulLi~ y of mobile stations, there can arise reasons to change the frequency and 30 timeslot allocatiûns between mobile stations even when no old calls are terminating and nû new calls are being initiated. Due to mobile motion, a mobile previously ~ W096/07287 PcrluS95110810 2~4~
requiring high power may now be satisfied by lower base station power or vice versa.
A simple systematic means to reshuffle frequency and timeslot allocations is for the network to maintain a list of ongoing conversations sorted by order of signal strength received from the mobiles, or, more accurately, sorted in order of radio ~,.u~,agalio~
5 loss between the base station and the mobiles. The radio ~lu~ ,aliull loss may be computed from a knowledge of the received signal strength and the power level the mobile was previously cu~nlllauded to adopt. A second check on this value may becomputed from a knowledge of the signal quality reported back by the mobile and the transmitter power the network is Lla~ liLLhlg to it. All such information may be10 utilized and averaged over a period of a fe.w seconds to obtain a smoothed estimate of u,url~;aLiùll loss.
Using the sorted list, the network ensures to the best of i~s ability that the top three mobiles on the list are allocated timeslots on the highest power carrier frequency; the next three mobiles in the list are allocated timeslots on the next 15 strongest carrier frequency and so forth. If a Digital Control Channel is in use and transmitted on the strongest carrier, then the top two mobiles in the list are allocated the same carrier, the next three the second strongest carrier and so-on. The network may, if required, swap two mobiles between two carriers to achieve this. For example, if the highest power mobile X on carrier B due to relative movement now20 has a higher power r~ .h~ ,n..~L than the lowest power mobile Y on a stronger carrier A, then X and Y are caused to change frequency and timeslot allocations ky issuing them with hand-off commands. Such hand-offs within the same base station area are called "internal handovers", and are made purely to achieve a more optimum frequency/timeslot packing that minimizes created int~ ,f~,.w.~,e with neighboring 25 bases.
It has already been indicated above that an exception to the packing rule may be desirable if there is a large dB difference (e.g., > lOdB) between the carrier povver and that needed by a mobile next on the list. It may be desirable to allocate that mobile to a lower power carrier together with the next two mobiles below it in 30 the list. This results in an apparently l~ y higher power Ll,~ " ûn a timeslot that is not allocated, but this departure from the absolute tightest packing WO 96/07287 21 ~ 8 ~ 5 ~ - PCT/U~9511081--algorithm has the advantage thaL a few unoccupied timeslots are distributed throughout the signal strength range and are thus available for allocating to new calls without having first to disturb a large number of ongoing Wll~ dliUn~. It can even be adopted as a deliberate strategy, to leave a "hole" every 15dB or so of ~Jlu~d~dliun loss range, depending on the loading of the system, in order more rapidly to be able to ~ cul~ t~ r- new calls. If because of this coarse power step between "holes", a mobile has to be allûcated to a ~hole" on a carrier that is unnecessary, this will be corrected by the systematic resorting procedure that takes place on a slower timescale.
Such a continuous resorting procedure also handles the event of a mobile call terminating. In principle all mobiles bek~w it in the power/~,lu~,d~ d(iul, loss list can be moved up, resulting in the highest of three perhaps receiving an hlternal halldover to the next highest power carrier. This does not however take place all at once necessarily but gradually. The rate of handovers can be restricted so that nû mobile receives a handover more often than, for example, say once per ten seconds. If amobile has received an internal handover or handoff within the last ten seconds for example, it is not allowed to he a candidate for a handoff until ten seconds have passed. When the strongest of three mobiles on the three timesloh on a given carrier terminates its call, the power of the carrier may of course be regulated down to the stronger of the two ren aining, thus reducing created h~lclrr_~r_ln,c levels.
The above-described exemplary ' ' are intended to be illustrative in all respects, rather than restrictive, of the present invention. Thus the present invention is capable of many variations in detailed i-.~plf /''~ ;nn that can be derived from the description contained herein by a person skilled in the art. All such variations and n-O-Iiri~ t'l;n~; are considered lo be within the scope and spirit of the ~5 present invention as defined by the following claims.
Claims (27)
1. A time division multiple access radio communication system comprising:
a plurality of frequency channels for transmission of communication signals;
a plurality of time slots on each frequency channel;
a plurality of first stations which transmit and receive communication signals on the frequency channels and the time slots; and at lease one second station which assigns time slots on a first frequency channel to first stations using the highest transmitter power levels and which assigns time slots on a second frequency channel to first stations using transmitter power levels which are lower than said highest transmitter power levels.
a plurality of frequency channels for transmission of communication signals;
a plurality of time slots on each frequency channel;
a plurality of first stations which transmit and receive communication signals on the frequency channels and the time slots; and at lease one second station which assigns time slots on a first frequency channel to first stations using the highest transmitter power levels and which assigns time slots on a second frequency channel to first stations using transmitter power levels which are lower than said highest transmitter power levels.
2. A time division multiple access radio communication system according to claim 1, further comprising:
means for adjusting the power transmitted by the at least one second station on each frequency channel to be a minimum power level necessary for communication with every first station on that same frequency channel.
means for adjusting the power transmitted by the at least one second station on each frequency channel to be a minimum power level necessary for communication with every first station on that same frequency channel.
3. A time division multiple access radio communication system according to claim 1, further comprising:
means for turning off frequency channels having all time slots presently unallocated to a first station.
means for turning off frequency channels having all time slots presently unallocated to a first station.
4. A time division multiple access radio communication system comprising:
a plurality of frequency channels available for transmission of communication signals;
a plurality of time slots on each frequency channel;
a plurality of first stations which transmit and receive communication signals on the frequency channels and the time slots; and at least one second station which sorts the first stations into groups requiringsimilar transmitting power and allocates a unique frequency to each group and a unique time slot to each first station in each group.
a plurality of frequency channels available for transmission of communication signals;
a plurality of time slots on each frequency channel;
a plurality of first stations which transmit and receive communication signals on the frequency channels and the time slots; and at least one second station which sorts the first stations into groups requiringsimilar transmitting power and allocates a unique frequency to each group and a unique time slot to each first station in each group.
5. A time division multiple access radio communication system according to claim 4, further comprising:
means for turning off frequency channels having all time slots unallocated to a first station.
means for turning off frequency channels having all time slots unallocated to a first station.
6. A time division multiple access radio communication system a plurality of frequency channels available for transmission of communication signals;
a plurality of time slots on each frequency channel;
a plurality of first stations which transmit and receive communication signals on the frequency channels and the time slots; and at least one second station comprising:
a plurality of transmitters and an antenna system for transmitting communication signals to the first stations;
a plurality of receivers for receiving communication signals from the first stations;
a calling channel transmitter for transmitting a channel assignment message to the first stations;
a random access receiver for receiving a random access message from the first stations and for measuring a quality and a signal strength of the random access message;
a station controller for receiving the random access message, random access message quality, and random access message signal strength from the random access receiver and for estimating a transmitting power necessary to communicatewith the first station based on the random access message, random access messagequality, and random access message signal strength; selecting a frequency channel having an unallocated time slot for a second station based on the estimated transmitting power; composing a channel assignment message; and sending the channel assignment message to the second station via the calling channel transmitter.
a plurality of time slots on each frequency channel;
a plurality of first stations which transmit and receive communication signals on the frequency channels and the time slots; and at least one second station comprising:
a plurality of transmitters and an antenna system for transmitting communication signals to the first stations;
a plurality of receivers for receiving communication signals from the first stations;
a calling channel transmitter for transmitting a channel assignment message to the first stations;
a random access receiver for receiving a random access message from the first stations and for measuring a quality and a signal strength of the random access message;
a station controller for receiving the random access message, random access message quality, and random access message signal strength from the random access receiver and for estimating a transmitting power necessary to communicatewith the first station based on the random access message, random access messagequality, and random access message signal strength; selecting a frequency channel having an unallocated time slot for a second station based on the estimated transmitting power; composing a channel assignment message; and sending the channel assignment message to the second station via the calling channel transmitter.
7. A time division multiple access radio communication system according to claim 6, wherein the station controller further comprises means for adjusting a power level on a frequency channel having all time slots presently unallocated to the estimated required transmitting power level for the first station.
8. A time division multiple access radio communication system according to claim 6, wherein the station controller further comprises means for allocating to the first station a time slot on a frequency channel transmitting at a power greater than, but closest to, the estimated transmitting power for the first station.
9. A time division multiple access radio communication system according to claim 6, wherein the station controller further comprises means for allocating to the first station a time slot on a frequency channel having a highest transmitting power when the estimated transmitting power for the first station is greater than a transmitting power of every frequency channel.
10. A time division multiple access radio communication systems according to claim 9, wherein the station controller further comprises means for smoothly increasing the transmitting power of the frequency channel having the highest transmitting power to the estimated transmitting power for the first station.
11. A time division multiple access radio communication system according to claim 6, further comprising means for turning off transmitters on frequency channels having all time slots presently unallocated to a first station.
12. The time division multiple access radio communication system according to claim 6, further comprising means for determining an interference level in each unallocated time slot on the frequency channel and assigning to the first station the time slot on the frequency channel having a lowest interference level.
13. In a time division multiple access radio communication system, a method comprising the steps of:
assigning time slots on a same frequency channel to remote stations requiring similar transmitting power, and assigning time slots on different frequency channels to remote stations requiring dissimilar transmitting power.
assigning time slots on a same frequency channel to remote stations requiring similar transmitting power, and assigning time slots on different frequency channels to remote stations requiring dissimilar transmitting power.
14. The method for assigning time slots of claim 13, further comprising the step of:
choosing a transmitting power for each frequency channel to be the minimum power needed to communicate with each remote station using that channel.
choosing a transmitting power for each frequency channel to be the minimum power needed to communicate with each remote station using that channel.
15. The method for assigning time slots of claim 14, further comprising the step of:
turning off frequencies having no time slots presently allocated.
turning off frequencies having no time slots presently allocated.
16. The method according to claim 13 further comprising the step of:
turning off frequencies having no time slots presently allocated.
turning off frequencies having no time slots presently allocated.
17. The method according to claim 13 further comprising the step of:
assigning a unique frequency to each group of remote stations with similar power needs.
assigning a unique frequency to each group of remote stations with similar power needs.
18. A method for assigning time slots and frequencies in a radio communication system comprising the steps of:
grouping together a first plurality of remote stations having a highest requiredtransmission power;
grouping together a second plurality of remote stations each of which has a lower required transmission power than any of said first plurality of remote stations;
allocating each of said first plurality of remote stations to a time slot on a first frequency; and allocating each of said second remote stations to a time slot on a second frequency.
grouping together a first plurality of remote stations having a highest requiredtransmission power;
grouping together a second plurality of remote stations each of which has a lower required transmission power than any of said first plurality of remote stations;
allocating each of said first plurality of remote stations to a time slot on a first frequency; and allocating each of said second remote stations to a time slot on a second frequency.
19. The method of claim 18, further comprising the step of:
transmitting on said first frequency at a highest required power level of said first plurality of remote stations.
transmitting on said first frequency at a highest required power level of said first plurality of remote stations.
20. The method of claim 18, further comprising the step of:
transmitting on said second frequency at a highest required power level of said second plurality of remote stations.
transmitting on said second frequency at a highest required power level of said second plurality of remote stations.
21. The method of claim 18, further comprising the step of:
continuing to group additional remote stations based on their relative transmission power requirements.
continuing to group additional remote stations based on their relative transmission power requirements.
22. The method of claim 18, further comprising the step of:
turning off frequencies which have no remote stations allocated thereto.
turning off frequencies which have no remote stations allocated thereto.
23. The method of claim 18, wherein said steps of allocating further comprise the step of:
allocating a time slot in said frequencies based on anticipated interference.
allocating a time slot in said frequencies based on anticipated interference.
24. A method of optimizing the allocation of time slots and frequencies for supporting two-way radio communication between a base station and a plurality ofremote stations comprising:
sending commands from said base station to said remote stations to use a higher or lower transmission power level in order to maintain a desired signal quality at said base station;
continuously estimating path loss between each of said remote stations and said base station based on received signal strength and commanded power level;
sorting said remote stations according to said path loss values into an ordered list; and grouping neighboring remote stations in said list to use time slots on the same frequency.
sending commands from said base station to said remote stations to use a higher or lower transmission power level in order to maintain a desired signal quality at said base station;
continuously estimating path loss between each of said remote stations and said base station based on received signal strength and commanded power level;
sorting said remote stations according to said path loss values into an ordered list; and grouping neighboring remote stations in said list to use time slots on the same frequency.
25. The method according to claim 24 in which said base station uses a transmission power on each frequency that is sufficient for the remote station using that frequency having the highest path loss value.
26. The method according to claim 24 in which dummy remote stations are inserted at intervals in said list in order to create a free timeslot/frequency combination for accepting new calls.
27. The method according to claim 25 in which said transmission power is adjusted downwards upon termination of communication with the remote station having the highest path loss.
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| US08/299,255 | 1994-09-01 | ||
| US08/299,255 US5579306A (en) | 1994-09-01 | 1994-09-01 | Time and frequency slot allocation system and method |
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| CA2198458A1 true CA2198458A1 (en) | 1996-03-07 |
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| CA002198458A Abandoned CA2198458A1 (en) | 1994-09-01 | 1995-08-25 | System and method for time slot and frequency allocation in a radio communications system |
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-
1994
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-
1995
- 1995-08-25 CA CA002198458A patent/CA2198458A1/en not_active Abandoned
- 1995-08-25 AU AU34952/95A patent/AU693938B2/en not_active Ceased
- 1995-08-25 BR BR9508662A patent/BR9508662A/en not_active IP Right Cessation
- 1995-08-25 JP JP8508867A patent/JPH10505206A/en active Pending
- 1995-08-25 WO PCT/US1995/010810 patent/WO1996007287A1/en not_active Application Discontinuation
- 1995-08-25 EP EP95931585A patent/EP0779012A1/en not_active Withdrawn
- 1995-08-25 MX MX9701228A patent/MX9701228A/en unknown
- 1995-08-25 CN CNB951948695A patent/CN1141004C/en not_active Expired - Fee Related
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1997
- 1997-02-28 FI FI970853A patent/FI970853A/en unknown
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| WO1996007287A1 (en) | 1996-03-07 |
| JPH10505206A (en) | 1998-05-19 |
| FI970853A (en) | 1997-03-03 |
| CN1157087A (en) | 1997-08-13 |
| US5579306A (en) | 1996-11-26 |
| FI970853A0 (en) | 1997-02-28 |
| CN1141004C (en) | 2004-03-03 |
| AU693938B2 (en) | 1998-07-09 |
| MX9701228A (en) | 1997-05-31 |
| EP0779012A1 (en) | 1997-06-18 |
| BR9508662A (en) | 1997-11-11 |
| AU3495295A (en) | 1996-03-22 |
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