CA2072373C

CA2072373C - Shared-carrier frequency hopping

Info

Publication number: CA2072373C
Application number: CA002072373A
Authority: CA
Inventors: Michael D. Kotzin; Stephen L. Spear
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 1990-02-27
Filing date: 1991-02-20
Publication date: 1998-10-06
Anticipated expiration: 2011-02-20
Also published as: EP0573417A1; KR920704472A; JPH05505082A; MY106999A; EP0573417B1; EP0573417A4; IE910577A1; DE69125949D1; CN1054875A; DE69125949T2; DK0573417T3; US5301188A; IL97284A0; IE78845B1; ES2100950T3; KR960008609B1; WO1991013502A1; IL97284A; PT96905A; CA2072373A1

Abstract

In a TDMA cellular network, there is provided a mechanism for shared-carrier frequency-hopping. It comprises: allocating on a frame basis within a reuse diameter to one coverage area (A-I) during certain timeslot(s) at least one from a pool of TDM frame-hopped carriers and allocating on a frame basis within that carrier reuse diameter to another coverage area (A-I) during certain other, substantially non-overlapping timeslot(s) that frame-hopped carrier, all in substantially non-interfering time-synchronism with any proximal reuse of that carrier, whereby the advantages of frequency hopping are obtained. Stated differently, it comprises: at one instant in time, allocating within a reuse diameter to one coverage area (A-I) at least one of a plurality of hopped carriers and at that same instant in time, allocating within that carrier reuse diameter to another coverage area (A-I) another of that plurality of hopped carriers, all in time-synchronism with any proximal reuse of that carrier. The control and access carriers may also be included in the hopping pool, causing certain timeslots to be hopped on a sequence different from the others. The pool of hopped carriers is further apportioned among co-located sites into hopping groups, thereby reducing intra-system synchronization requirements. To solve the near/far problem, TDM timeslots bordering hopping boundaries are preferentially allocated to less distant mobile users.

Description

2 . PCr/US91/01133 2 0 7 2 ~

SHARED CARRIER FREQUENCY-HOPPING
5, THR FIF.I.D OF TNVENTION
This invention is conc~ lcd with frequency hopping.
10 More particularly, in a cellularradiotelephone system, this invention is conc~ ,ed with mcreasing carrier availability for hopping thsough the employment of various carAer sharing t~,clllu~u~,s.
RAC~C~ROUND OF TH~. ~NV~.NTION
Ce~,~..phie reuse of carrier f~u~,.lc;es has proliferated as a viable solution to the 15 problemofl~itedradio 5~1~111 incellularr~ 1~h~ - systems. T. ~ ;OI~11Y~
a served area is subdivided into clusters of cellular coverage areas which have al~ ed to them groups of c~riers. These clusters are repeated such that calTiersreused from cluster to cluster are s. ,rr., ;~ nrly ~ o~,dphically ~dldted from one another to perrnit siTnl1lt~nçouc reuse of carriers without undo h,~ ; nce.
20 r~u~,nc~ hopping rnight be ernployed to provide sensitivity improvement against slow fading and to improve callier-to nlt~,.r~ lc:e (C/l) margin in cellukls te,l ph~ e systems. Tr~ncmic~;nnc w~thin a given coverage area would be hopped from one caTrier within the group :Ill~slted to that coverage area to cmother within the group, hopping from one to another. However, lhere must be a 25 s~r~ number of caniers in each coverage area over which to hop or the - advantages of ~ ,.. c~ hopping are ~1iminiche~1 In other words, both less dense cellular reuse and greater Ç~ ency hopping improve the ~.ru~lllance in a given WO 91/13502 PCl/US9~/01133 ~72373 coverage area, but both usually draw from the very same (and scarce) s~ ,L. Ul~l.
So, whatever is gained by one technique is gained at ~he expense of the other.
Ln currently-p,o~osed Time-Division, Multiple Access (II)MA) cellular systems, particularly when utilized as an adjunct to p~ .g analog cellular systems or 5 where more than one operator coexist, fewer ca~iers are available to be employed, or are ~qui~ or that matter, because up to eight convel~Liolls talce place in eight repea~ng tim~lotc on a single carrier. hcc~lingly, up to seven-eighths fewer carriers are required to caITy the same channel capacity. I'his reduction in carriers available to each coverage area reduces the o~ u-~ly for employing ~equency 10 hopping as an effective system enhi~nre~nt.
This invention takes as its object to OVi,l-;OIl~ these shol l rr,.~ g~ and to realize certain advantages ~..bsented below.
S~JMMARY OF THF, INVRNTION
In a TDMA cellular network, there is provided a ..-f~ n~ for shared-ca~Tier IS ~ u~,ncy-h~ppin~ It colnpl;se~ oc~tine on a frame basis within areuse di&l~,t~ tO one coverage area duIing certain tirneslot(s) at least one from a pool of TDM-frame-hopped ca~Tiers and ~ ;ng on a frame basis within tha~ carrier reuse r1;~n~tP- to another coverage area during certain other, ~ at~~ lly non-o~ timeslot(s) that frame-hopped ca~ier, all in a~ ulii~tly non-20 i.lt~,.~.ng time-s~.~ u..ism with any prox~nal reuse of that calTier, whereby the advantages of rl~uc~ hopping are obtained. Stated dirr,..,.1tly, it comprises: at one mstartt in time, ~ ing within a reuse ~ e~ to one coverage area at least one of a pl~ality of hopped carriers and at that same instant in time"tnoc~hng within that carrier reuse L~lh,t~- to another coverage area another of that plurality 25 of hopped carriers, all in time-a~llcl.lonisnl with any proximal reuse of that carrier.
The control and access carriers may also be int~htd~d in the hopping pool, causing cenain I ;" ,~ cl~ to be hopped on a s~uen.,e different from the others. The pool of hopped caniers is further a~,~o. ~,oned among c~lccated sites into hopping groups, thereby reducing intra-system ~ hlu~ n ~~uilGmenb. To solve the near/far 30 1~lut1~ , TDM ~;"~ t~ bordering hopping bUL~ S are ple~ ally ~llocat~d to less distant mobile users.

W O 91/13502 PC~r/US91/01133 -3- 2~2~73 DR~SCR7PTION OF THF DRAWINGS
itionAl objects, feanlres and advantages of the invention will be more clearly understood and the best mode cont~mplAt~ for F~ctic~ng it in its ~
lomk)~ t will be appreciated (by way of ~ d example) from the S following detailed de~ , taken together with the acco.,~ ying drawings in which:
Figure 1 is a diagrarn of the network in which the ~lef~ d emho-1im~nt of the invention operates.
Figure 2 illustrates the near/far problem solved by the instant invention.
10 Figure 3 illl~5t~tes timeslot A~ tinn according to the ~ ~fe.l~d embodiment of the instant invention.

nF,TA~ .n nR~CRlPTlON
The y~eR.l~d C-~ "~t of the instant i~ on lI;iC(I~;I' 'es, and then carit~li7es upon the inherent divisibility of TDMA carriers and ~ es them as shared c ,arriers 15 capable of providing a hopping pool far larger than would be the case according to Figure 1 is a diagram of the network in which the l,lefe.l~;d emhoflim~n~ of the on operates.
Figare 1 i ctT~t~S nine coverage areas (A-I) making up a repe~t~hle cluster in the 20 ~ ly-~ os~ GSM, Pan-European Digital Cellular (GSM/PEDC) system.
Each coverage area is served by a 120 degrec sectored antenna. In regions where the full 25 MHz bandwidth is not available (i.e., where moqe than one operator coexist or where there are },l~ E analog cellular systems) a 5 MHz band tof 24 car,riers) would be apportioned among the 9 coverage areas, as follows:

WO 91tl3502 PCI'/US91/01}33 r~

Sector CalTier Allocation A 1, 10 & 19 B 2,11&20 C 3,12 D 4, 13&21 E 5, 14 F 6,15&22 G 7, 16 H 8,17&23 9, 18&24 15 (Ca~rier fi~u.,"cies although nul-l~l~ s~t~uent~ yt are not adjacent).
It is recognized that with tr~ litinn~l t~ ni~lues~ hopping would be possible over only the small number of carriers avaulable in each sector (two, or three at most), providing only ~mited ~,rùllllance improvement over non-hopped systems.

Wo~se yet, one ~e~;e~ carrier r~u~ne~ in each coverage area is comnu~nly 20 ~ ted to system ~ ling, access and control; and is con~ ly ~ g and 1}.. .~r,"~ fixedly ~ , further ~ .;..;cl.:..g the carriers available forhopping to one ~ two per coverage area (or, in the case of TDMA, certain tim~slotc of the control and access ca~rier are not available for hopping).
Ilv..~ , if all but the nine d~ 1;r~rbd access con~ol eh~nnplc (1-9) are returned to 25 form a hopping pool, rather than being fixedly ~lloc~ted to individual coverage areas, the hopping pool il~ ,aS:eS from one or two per coverage area to fifteen (1~
24) per coverage a~a, provided the hopping sequenr~ is time-sy-l- hroni~.~ d arnong the individual coverage areas. In other words, instead of ~llr~c~tin~ a small group of hopping carriers to an individual coverage area within which all hopping must be 30 done, each of the nine cu.~,~c, areas is ~llr d a unique tirne or index offset for lly in~- Ying into a ci~cular queue (or c,th~ ;c ~lo~
having all fifteen, pooled hopping calTiers. The hopping is ~-r~lu~ in at least TOUgh time-syll~,luul i~ ~om sector to sector and from cluster to cluster to avoid same channel (co-chaMel reuse) in~.r~ "~,nce and adjacent channel ir,~.r~nce 35 within the reuse sli~l~e~n The following table illustrates two different schernes for ~lloc~ting the f~een ca~iers in three hopping groups of five each. Note ~at in XIY/Z hopping, all fi~een ca~Tiers (1~24) are utilized at ever~ co-located sector site (say, A, B, C).
This rec~ es greater site-t~site synch}r)ni7~hon than U/V/W hoppLng, where the 5 hopping group (say, U) is cc". .l,. ;ce~ of carriers from co-located sectors (i.e., A, B
~c C) alone, which, in t~t, requires less s~ u~ tion with non-c~located sites (I)/E/F o~ G/HJl) and lessens the effect of any s~-,cluo.~i7~hon failu~e.
Sector Carrier I U, V, W I X, Y, Z
Allocation I Ho~in~ I Hoppin~
A 1, 10& 19 1 U:10-12, 19&20 I X:10, 13, 16, 19 &21 B 2, 11 & 20 1 U I Y:ll, 14,17, 20 & 23 C 3, 12 1 U I Z:12, 15, 18, 22 & 24 D 4, 13 & 21 I V:13-15, 21 & 22 I X
E 5, 14 I V I Y
F 6, 15 & 22 I V I Z
G 7, 16 I W:16-18,23&24 I X
H 8,17~c23 I W I Y
9,18&24 I W I Z
The foregoing provides a snbst~ irnprovement in noise~ r~ nc~
. r~ e. it is notable that the it occurs only in a fraction (10-24), albeit si~eable fraction, of the total s~,u.,. (1-24). This is due to the t7eAir~tinn of one canier 25 per coverage area (1-9) which cannot be r~used in any othes coverage area that is S~1J~~ ,.t- ~ by less ~han the reuse .1;~ .. (A and A'). N~ I,eless, for illl~lU.
system ~ fo. ~ ~ rc, hopp~ng carAers 1~24 (rather than fixed carners 1-9) could ~e p.ef~,~enlially ~11oc~ted to t-h-ose subs~ih~ having the greatest need Portable, h~...lh~ltl r~ l;ol-lc~ho-~e users, due to their slower movement and lower transmit power, would benefit most from irnproved se.,silivily against slow fading and o~h~ ~ c~ oti~ ,ss against in~.r~ncc provided by rl~u~.lcy hopp~ng. Hopping carners (1~24) rnight also be ~l~,f~ ially ~llrJC~t~A to those e~ cing deu~ ting signal quality (inc.~ing bit error rate), since that is more indicative of slow fading and il.t~,.r~ ,ncc than signal streng~h. Although these t~ 5 attempt to c,~ ~ the utili7~tion o~ fixed (1-9) and hopping (10-24) carriers, itwould be more ~esira~- to include all calTiers ~1-24) in the hopping pool.

2 ~ 7 ~ 3 rl ~

The f~regoing rliccuc~;r)n relies filnr~ ont~lly upon sharing a camer among various coverage areas s~l.c}l.vllously in time, but does not requ~re a slotted TOMA
channel ~Il u.;~ ;. But, in fact, GSM/P~DC is a TDMA system; each ca~ier is subdividod into eight separate ch~n~-lc in a repeating eight- timeslot fiame (Slot 0 -Slot 7). Slot 0 (and perhaps others) on a Aecigrl~ted calTier in each coverage area is rese~ved and ~ for ascess to the system and is, llr~ ,fol~, not available for hopping5 but Slots 1-7 are available for other traffic. A f~er c~mrlirltion is that the r3~cign~t~ calTier in each coverage area must c~ y be ~ . "; l ~ g its L~u.,~ y such that its signal strength can be ~l~tol~,d by users in 10 adjacent coverage area for pul~ses of evaluating handover c~n~ y, ~ efo-~this frequency cannot be reused within the reuse di~llc~.. Ullfol lunalely, reserving Slot 0 of every carner would result in an ~n-A~cel,lab'e loss of one-eighth of the available capacity. Resen~ing one carrier per coverage area that is not part of the hopping pool was the solution ~c pGs~,d in the foregoing rliccuCcionl but there 15 is another sollltion There could be a different hopping s~ue.lce for Slots 1-7 than that of Slot 0. Time Slot 0 could be hopping: ... abcde abcde ..., while slots 1-7 would b_ hopping: ... abcdef abcdef ..., where carr~er f (and its Slot 0) would be ~e~ pA for access and contsol. Thus, Slot 0 of calTies f would always b_ available for ciEy~ ling, access and control.
20 An ~ ."pl~ eight-slot TDMA system, for one sectored coverage area (say, A), ha~ing five hopping carriers (a~) and one carrier (f) u,l~t~;..;ng Slot 0 for access control and slots l-7 that must c~ y be ll ~n~ l a slotlcamer ~ titm for A might be:
Slr~tq ...1101?~45671101?345671tol01?1456711017~45671101?1456711 ...
25 A: . . . Ilaaaaaaaallbbb~bbbllccccccccltOlddddddddllceeeeeeellafffffffllbaaaaaaall~..
Af: ...llffffffffllffffffffllffffffffltolffffffffllffffffffllf-------llffffffffll---Within the reuse sep~~ion ~ mpt~ caslier f would not be available for hopping,but a-e would. If carrier g were deAi~-~tçd ~o, say, coverage area B, an ~ccept~hle sluL/~ )n for B would be:
30 3: ...llbbbbbbbbllccccccccllddddddddltOleeeeeeeellagggggggllbaaaaaaallcbbbbbbbll~-.
Bg: ...IlgggggggglIggggggggllggggggggltOlggggggggllg-------l~gggggggglIggggggggll---, . , .

WO 91/13~02 P~/llS91/01133 ' 7 2i~ ~37 3 One should note that extra ~ .c.~ . . C~ui~ ught be n~ces~ tO ensure that the f callier is always tr~nsmitting for the subscri~s evaluating handover c~nAiA~y even when there is no user traffic to pu/ there. In GSMIPEDC, durnrny bursts are defined for this puIpose. F~ llUl~, it should be noted that ~
S e~ lh -1~ must ~e capable of ch~nging f~equency on a slot-t~slot basis as opposed to the f~ ,g~ g ~:cr..c!:on which did not include the d~~ calTier and the implied irnpact upon ~ame-to-f~me hopping capability.
Using this scheme, there are certain inct~n~ç5 where a distant cellular subsrr~h~
could c~ t~,~r~,..,nce due to differential tr~n~mic~ n delays. Assume that 10 both cell sites are S~llC}Il~ ni~l (to) and share the sarne hopping pool, as abow.
Figure 2 illus~rates the near/far problem solved by the instant invention. When a s~lhs~ibe.r is reladvely far f~om cell sites in his area, but svu~ . l.a~ closer to one (A) than the other (B), at frame k~und~ies (when the ~queneies change), with limited guard time between slots, he might tA~.ience ~.lt-,.r~ ince from the tail of 15 one (B) ov ,I~ ing with the the be~ g of the other (A). The farther out the subsc~iber, the more likely (and sev~xe) the overlap~ Figure 3 illust~t~f s timeslot n a~CJIding to ~e p~-,f~ d c~bJ~li~nt of the instant il.~vnlion~ The solu~on to this F ,,: --t cf""l)ljr_l;,.n of L~"ency hopping is not to allocate those time slots nearest the fiame bow~ to distant s~lhs~ih~s, but allocate them 20 instead to tho~se c-~ - s nearer the site ~as ~.l,~d by timing advance, for example). If L~u~ hopping takes place on a frame basis, such that rl~4..cn-;y changes occur only from Slot 7 to Slot 0 (and Sl~ 0 to Slot 1 in the case of thede li~ cont~l calTier), previous Slot 7 and subs~u~n~ Slot 0 on ei~her side of the frame b~uJ~ (and Slot 1 of carrier f/g) would b_ aU~x?t~ ~ nearer sl1hs~ib~s while Slots 2-6 would be ~l1oc~tf~1 to more distant s~lks~hers. With this ~llfY~if n of time slots, the near/farproblem is subst~nti~lly reduced. A
u~l near/farproblem in the ~u~s.~ to-cell-site di~n is solved with the very same strategy.
The c~ular queue means tor ~1f t ~ . . .;~ ;c ~ rithm means) for time-30 a~llclonously ~ hng ca~iers pointers in ~he fashion descnbed is well wi~in the c~h;lity of one ordinarily sl~lled with cellular base station con~ol n~r doloEif s employed within the ~l1oc~tion Control P~ces~l of Figure 2.

WO 91/13S02 PCr/US91/01133 2 ~ 7 ~ 8 -Thus, in a TDMA cellular network, there has been provided a m~rh~nicrn for shared-carrier frequency-hopping. It co..,l,. ;ces ~ ting on a frame basis vithin a reuse .1;~. ". I~,r to one coverage area du~ing certain time~lot(s) a~ least one from a pool of TDM-frame-hopped carriers and ~llo-~ting on a frame basis within that 5 camer reuse diameter to another coverage area dunng cen~in other, subst~nti~l1y non~.~,.la~ ing timeslot(s) that ~ame-hopped carrier, all in subst~nt~ y non-. r~ me-s~ n with any ~lu~ lal reuse of ~hat calTier, whereby the advantages of rl~ucr~ hopping are obtained. Stated .3ir~ , it ccJI~ iSes. at one instant in time, ~ ting within a reuse diameter to one coverage area at least 10 one of a plurality of hopped carriers and at that same instant in t~me, ~ ting within that carrier reuse diarneter to another coverage area another of that plurality of hopped carriers, all in time-~llcl.lun.~ with any proximal reuse of that carrier.
The control and access carriers may also be included in the hopping pool, causing certain timeslots to be hopped on a SC~u~,nCf, differcnt from the others. The pool of 15 hopped camers is further apportioned among co-located sites into hopping groups, thereby reducing intra-system ~ .lcl~ io(~ s. To solve the nearJfar '-m, TDM ~in~lot~ bor~cr~ng hopping l~ull~;.,s are plef~ n~ially ~ d to less distant mobile users.
The ~ ,n~ ha..la~s of this i~ ion include the l,.u~;,i~n of a far larger 20 hopping pool from a smallér nurnber of carriers, ~ . .n;~l;.lg hopping to be offered as a system enk ~ at all in these ~ n~,,, utili7~tir~n of the access andcon~ol carrier in the hopping s~~ ce; irnproved CII and fading ~ ru....~ e;
reduced ~. .~nrlenr~ on intra-system s~l.clllv..;~lion, and solution of the nearJfar probler~
25 While Ihc ~ ,f.,.l~ - n~ of the invention has been ~ec~ihed and shown, it will be a~lf~iabcd by those skilled in this field that other ~ialions and ..~3in~ c of this invention may be implc ..f ~ A Although the ~ of the ~ f~ d e...1~1;...~...t has been in terms of a sectored reuse, there is no reason that the concept need be so limitedl; it is equally ~pplir~f; to omni~lil~Livnal30 antenna rl~ucrl~;r-Division, Multiple Access (FDMA), for exarnple. Similarly, there is no reason that the ~-~ l~ic,ll be limited to TDMA.

WO 91/13502 PCr/US91/01133 9 2~3 1 3 These and all other variations and ~ rt~hons are expec~d to fall within the ambit of ~e appended cla~ms.

Claims

1. A method of shared-carrier frequency-hopping comprising:
allocating to a first coverage area within a carrier reuse diameter, during a first time interval, a first carrier of a plurality of hopped carriers; and allocating within said carrier reuse diameter to a second coverage area, during a second time interval, said first carrier.

2. A method of shared-carrier frequency-hopping comprising:
regularly allocating to a first coverage area within a carrier reuse diameter, during a first time interval, one carrier from a pool of hopped carriers; and regularly allocating within said carrier reuse diameter to a second coverage area, during a second time interval, said first carrier, whereby the advantages of frequency hopping are obtained.

3. A method of shared-carrier frequency-hopping comprising:
allocating to a first coverage area on a frame basis within a carrier reuse diameter, during a first TDM timeslot, a first TDM-frame-hopped carrier from a pool of TDM-frame-hopped carriers; and allocating on a frame basis within said carrier reuse diameter to a second coverage area, during a second TDM timeslot, said first TDM-frame-hopped carrier, whereby the advantages of frequency hopping are obtained.

4. A method as claimed in claim 2 above, wherein control and access carriers comprise part of the pool of hopped carriers.

5. A method as claimed in claim 2 above, wherein certain time intervals of control and access carriers are hopped on a sequence different from the others.

6. A method as claimed in claim 2 above, wherein the pool of hopped carriers is apportioned among co-located sites into hopping groups.

7. A method as claimed in claim 2 above, wherein the number of carriers per coverage area made available for hopping through pooling exceeds the number that would be available per coverage area if allocated fixedly to that coverage area.

8. A method as claimed in claim 2 above, wherein hopping carriers over fixed carriers are preferentially allocated to those mobile users experiencing deteriorating signal conditions.

9. A method as claimed in claim 3 above, wherein at least one TDM timeslot not bordering hopping boundaries is preferentially allocated to distant mobile users.

10. A method as claimed in claim 3 above, wherein TDM timeslots bordering hopping boundaries are preferentially allocated to less distant mobile users.

11. A method as claimed in claim 3 above, wherein TDM timeslots bordering TDM frame boundaries are preferentially allocated to less distant mobile users.

12. A method as claimed in claim 3 above, wherein certain timeslots of control and access carriers are hopped on a sequence different from the others.

13. An apparatus for shared-carrier frequency-hopping comprising:
means for allocating to a first coverage area within a carrier reuse diameter, during a first time interval, a first of a plurality of hopped carriers operatively coupled with means for allocating within said carrier reuse diameter to a second coverage area, during a second time interval, said first carrier.

14. An apparatus for shared-carrier frequency-hopping comprising:
means for regularly allocating to a first coverage area within a carrier reuse diameter, during a first time interval, one carrier from a pool of hopped carriers operatively coupled with means for regularly allocating within said carrier reuse diameter to a second coverage area, during a second time interval, said first carrier, whereby the advantages of frequency hopping are obtained.

15. An apparatus for shared-carrier frequency-hopping comprising:
means for allocating to a first coverage area on a frame basis within a reuse diameter, during a first TDM timeslot, a first TDM-frame-hopped carrier from a pool of TDM-frame-hopped carriers operatively coupled with means for allocating on a frame basis within said carrier reuse diameter to a second coverage area, during a second TDM timeslot, said first TDM-frame-hopped carrier, whereby the advantages of frequency hopping are obtained.

16. An apparatus as claimed in claim 14 above, wherein certain time intervals ofcontrol and access carriers comprise part of the pool of hopped carriers.

17. An apparatus as claimed in claim 14 above, wherein pooled control and accesscarriers are hopped on a sequence different from the others.

18. An apparatus as claimed in claim 14 above, wherein the pool of hopped carriers is apportioned among co-located sites into hopping groups.

19. An apparatus as claimed in claim 14 above, wherein the number of carriers per coverage area made available for hopping through pooling exceeds the number thatwould be available per coverage area if allocated fixedly to that coverage area.

20. An apparatus as claimed in claim 15 above, wherein at least one TDM timeslotnot bordering hopping boundaries is preferentially allocated to distant mobile users.

21. An apparatus as claimed in claim 15 above, wherein TDM timeslots bordering hopping boundaries are preferentially allocated to less distant mobile users.

22. An apparatus as claimed in claim 15 above, wherein TDM timeslots bordering TDM frame boundaries are preferentially allocated to less distant mobile users.