EP1310133A1

EP1310133A1 - Adaptation of the timing advance in synchronous handover

Info

Publication number: EP1310133A1
Application number: EP01964898A
Authority: EP
Inventors: Stefan Oestreich
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2000-08-16
Filing date: 2001-08-10
Publication date: 2003-05-14
Also published as: JP2004506392A; US20040128095A1; CN1470146A; DE10039967B4; CA2419615A1; WO2002015624A1; DE10039967A1

Abstract

The aim of the invention is to adapt the timing advance of a mobile terminal (MS) during synchronous handover from a first (BS1) to a second base station (BS2) of a radio communications system. To this end a time delay (Δt, Δta, Δtd) between time standard (N1, 2, N2a, N2d) received by the terminal from the two base stations are measured. A timing advance value (TA1) that is used by the terminal (MS) prior to handover for transmission to the first base station (BS1) is corrected using the time delay measured. The corrected timing advance value is reduced by a value (2Gsync) derived from the accuracy (Gsync) of the synchronicity of the two base stations (BS1, BS2) and is used as the timing advance value (TA2) for transmission to the second base station (BS2).

Description

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The invention is based on the insight that, although the tatsäch ^¬ Liche synchronism error between two base stations in the individual case a specific handover can not be specified, but that it is generally possible to specify the accuracy of the Synchronitat the two base stations, that is, an upper limit for estimate the amount of the synchronism error, which it will not exceed with a predetermined probability.

By reducing the from the terminal using a

Time difference between the time standards of the two base stations determined timing advance value, i.e. a delay in transmission by the subscriber station, depending on the known accuracy of the synchronicity, is achieved that the radio signal of the terminal device transmitted with reduced timing advance may be at the second base station does not arrive immediately at the beginning of the allocated time slot, but in no case before the beginning of the time slot. On the other hand, reaching the radio signal into the guard period following the time slot can be tolerated.

The reduction in the timing advance value is preferably twice the accuracy of the synchronicity specified in time units.

If the accuracy of the synchronicity is too poor, a reduction in the timing advance value corrected on the basis of the measured time shift could result in essential parts of the radio signal falling into the guard period or even into the subsequent time slot of another station on the base station. In such a case, it is more appropriate to completely refrain from correcting the timing advance value and to use a timing advance value of 0 for transmission to the second base station. In this case, a new measurement of the timing advance by the second base station is essential. The accuracy of the synchronicity of the two base stations involved in the handover is preferably signaled to the terminal in the course of the handover process. This allows the network operator, for each pair of base stations that may be involved in ei ^¬ nem handover, the accuracy of the Syn ^¬ chronitat in individual cases to calculate or measure, and provide a level of accuracy obtained all devices available to that one Have to perform handover between said two base stations.

Alternatively, heuristic estimates of the accuracy of the synchronicity are also conceivable. For example, Assume that the accuracy of the synchronicity is proportional to the distance between two base stations. The distance to the first base station is known to the terminal from its timing advance used before the handover. If one assumes that the distance to the second base station will be of the same order of magnitude as that to the first, the terminal can derive an estimate of the accuracy of the synchronicity directly from the timing advance value.

For technical handling, it is useful if the pairs of base stations of the radio communication system are classified into one of several classes depending on the accuracy of their synchronicity, and the terminal is signaled in each case to the class to which the pair of stations belongs between which the Handover takes place. In this way, the signaling of the accuracy of the synchronicity can be limited to the transmission of a small number of bits. If the terminal takes the upper limit of such a class as the value for the accuracy of the synchronicity, a premature arrival of the signal at the base station is reliably avoided, regardless of the actual value of the accuracy.

The number of classes is preferably at least three. These classes preferably include one where the accuracy the synchronicity is so good that a reduction in the timing advance value corrected on the basis of the measured time shift can be completely dispensed with. Such a class expediently comprises pairs of stations at which the accuracy of the synchronicity does not exceed a limit in the range 100-500 ns.

A further division of the classes expediently distinguishes those pairs of stations where a reduction in the timing advance value by a value derived from the accuracy of the synchronicity makes sense from those pairs where the accuracy of the synchronicity is so bad that a complete redefinition timing advance by the second base station is more advantageous. The limit for this subdivision is expediently between 500 ns and 2.5 μs in the calculation.

Further features and advantages of the invention result from the following description of an exemplary embodiment with reference to the attached figures. Show it:

1 is a schematic block diagram of a radio communication system in which the present invention is applicable;

2 shows a time diagram to explain the determination of the timing advance value by a terminal in the event of a handover;

3 + 4 the effects of synchronism errors on the determination of the timing advance value;

5 the consideration of the accuracy of the synchronicity when determining a timing advance value by the terminal. 00 00 ro ro P ¹

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03 0 rt ^• »0 P ¹ 0 0 Φ tr P- z Z tr 0 tp P- Φ> u X: 0 KHH o LP 0 tu P- 03 Z Φ rt cx rt tu 3 rt o 03 0 P- t er rt φ ι-i 0 H rt Φ CΛ H er 3 03 03 0 03 X

CΛ Φ 01 0 CX rt "> P- 0 0 rt 0 l-i φ 0 P- v Φ Φ P- P- 3 0 P- rt P- rt

P> H Φ 0 φ o 03 ffi P-. CΛ 0 cx - rt H o φ <0 Ω 0 0 03 0 rt Φ 0 S φ 0 rt 0 cx E CX 0 li 0 P- 0 P- 03 rt rt p rt 0 H φ 0 rt tr Φ 03 φ P- P ¹ CX o 3 left x φ 0 0 0: 03 0 φ * P- Φ Φ Φ 03 O: H P- Φ z rt P- φ ι_ι. P ¹ er pj:

N P- φ 0 α ι-J rt cx 03 X 03 O P- Hi H cn 03 ZO 0 p- • u 0 0 0 Φ φ P- P Φ z 03 0 P- iP cx φ rt o rt 0 CΛ 0 Hl * rt φ P- 0 CX Φ 0 rt φ • s: 0 er Φ P-

• rt tu Φ Φ φ 01 li 0 <& Φ Φ • es 03 0 3 CΛ Φ 0 P- Φ • Φ <J 0 φ 03 0 P- rt φ X 3 0 03 w 5 Φ rt s: cx Φ 0 φ o <j P- tS! Φ <! Φ tu zi N rt φ 0 N P- H 0 Φ rt φ tu P ¹ Φ P- φ Hi P- rt CΛ 0 φ φ t- ¹ S3 P- H Φ 03

CΛ P. 0 P- z Φ 0 CX z O 03 er Φ P- 0 P "3 ι-i rt O 0 es Z Ω φ H cx CΛ Φ φ 3 H ro P- 03 0 φ φ 0 <i 03 Φ Φ 3 0 03 φ Φ CX • P ¹ tr φ 0 tr 0 er φ P- tr P- Hl * U φ 0 P- P ¹ 0 P- P- o 0 P- Φ φ P- 0 0 i Φ P- ¹ 0 P- HN rt 0 rt 0 0

0 P- rt 0 0 tu 0 0 0 P- H 03 σ Φ P- P ¹ P. P- tu 0 0 Φ rt tr 0

0 CJ. 0 φ tu tu CΛ i • Φ 03 3 i P- 0 0 rt φ φ rt CΛ cx tu 3 ι-i P "H X

03 Φ P- 0 03 P- • u 0 to φ er Φ S3 rt p- Φ 03 03 P- φ 3 rt P ¹ 0 0 P- tr 03 0 Φ 1 0 ZP, 0 03 P- tr P- 03 P - cx P- H φ 0 rt 3 rt φ 0 es 03 0 cn 0 p- Z 0 0 «

Φ Φ φ φ P- 0 0 * P- P- 0 φ iP 03 P- rt Φ Φ 3 0 tu rt ιp P- φ io tr P- H CΛ 03 cx φ 03 0 Φ 03 Φ rt 03 P- P- P- CJ. H cx 0 Φ tu 03 φ P- i 0 s

Φ P- 03 0 03 H H 0 φ O 0 0 φ O cx Φ er X CΛ N 03 03 03 CΛ 01 0 3

0 03 ^ i JΛ rt tO rt cx Pd 0 0 0 03 cx er P- cn N LP P ¹ IV) 0 rt rt p- φ rt ≤; 0

• P- 0 0 πj 0 0 Φ Φ P- 0 0 ^ 0 0 O φ z φ Φ • 0 0 Φ Φ 0

N tr rt Φ er P- rt 3 li 3 0 φ 3 Ω Φ ^f ι- <z rt Φ CX P- α 0 • 3 P- 0 P- 03 P- cx 0 01 φ tr 3 <! 0 0 = Φ Cl φ P- P- Φ X

0 3 φ o H) 0 H O H rt 0 φ 01 i-i O 0 INI rt P- φ 0 o 0 0 Φ & 0

03 cx 0 0 Φ 0 Ω 0 cx Φ ⁽ P 1-1 s: Φ 0 P- 0 3 to 0 cx p- 0 Φ p- 0 0 rt

INI 0 φ y Hi tr Φ φ 0 φ Φ P- 01 0 cx 1 S Φ φ LQ CΛ 3 φ es H P-

CNJ Φ H N 0 rt Φ 0 0> l-i p, 0 Z * P- 0 cn «0 CΛ 03 1 03 0 S o

Φ P- O 0 φ 0 es • P "Cd X X φ P- 0 cx Φ 03 CΛ o 0 ≥: 03 rt o tu φ 10 CΛ P- 0

P- rt tt P- φ Hl 0 <INI φ φ Ω Φ 0 S 3 Hi 0 0 o φ o 0 0 O 03 03 rt X) Φ CΛ CΛ Φ P- Cl 0 03 0 φ 0 Cd tr 0 α 1 tr 0 Ω P ¹ 0 0 03 g 0 rt 03

0 0 NXP »* rt φ P ¹ P- 0 P- P- φ ι-i φ ts 0 CΛ 0 0: Hi tr Ω cn rt P- o LP •

O 0 £ 0 0 tu 0 CX 03 Ω rt 0 i-i o 0 Φ H • <0 P "er l-i tr H 03 er cx cn

H ; Φ Ω H Ω φ 01 φ 3 03 CΛ P- Ω 01 P- rt 0 P- φ φ o 03 p- N P- tu rt

3 rt P- rt tu tr Φ tr Φ rt 0 o Ω P- P- cx rt tr rt • 0 Ω p- rt P ¹ 0 φ 03 Φ

0 ω H P- 03 tu P- 0 φ ¹ 0 tr 3 03 P- 3 Φ 0 Φ tr tu 0 0 S

\ -> 3 rt cn, to o P Φ 0 0 rt P- rt P ^, H P- φ 0 cx 3 1 rt 0 φ φ rt φ Φ 0 g CΛ

II Φ Φ 0 1 0 1 Φ P- 0 P- φ 0: Φ H P- _^ Φ 1 H li P- ι-i P- 0

≥; o 1 3 P- H O φ 1 l-i 0 H 1 Φ 0 1 1 1 1 1

P * 1 0 CΛ 0 1 rt 1

reaches the terminal MS at time t = dl / c, where dl is the path length between the base station BS1 and the terminal MS. This delay dl / c is also the value of the timing ad vance ^¬ TA1, which the terminal MS is used for transmitting to the base station BSl.

The subscriber station MS uses a local time scale for the time control of its tasks before the handover, which is based on the time standard transmitted by the base station BS1. You can see the time of arrival

Define time standard Nl at the subscriber station MS as the zero point t ^λ = 0 of its time scale t ^x related to the base station BSl.

The terminal MS is assigned a time interval for sending to the base station BSl, which begins at a time t = tl and is symbolized by a hatched section along the time axis of the base station BSl. In order for the signal emitted by the terminal MS to reach the base station BS1 within this time window, it must begin to transmit at a time t = tl-TAl. Since the local time scale of the terminal device follows that of the base station BS1 by TA1, this corresponds to the time t ^Λ = tl-2xTAl on the time scale t ^{λ of} the terminal device.

The time standard N2 of the base station BS2 arrives later at the terminal MS by Δt = (d2-dl) / c than the time standard N1, where d2 is the distance between the base station BS2 and the terminal MS. The arrival of the time standard N2 defines for the terminal MS a new zero point t ^λ = 0 of its local time scale, from which the time for sending to the base station BS2 is now determined.

The distance .DELTA.t between the arrival times of the two time standards denotes the amount by which the terminal MS must correct its timing advance value in order to be able to communicate correctly with the base station BS: the terminal MS 00 oo ro ro P> P ¹

0π o cπ o Cn o Cπ

CΛ x es> LP 0 * 1 S p. cx 0 OJ. φ 0 P "xt rt cx cs tu LP cx ≥i H tr P- cx • U (XN er P ¹

Φ 0 Φ et Φ 0 P- p- p- φ P- Φ p- P P- 0 0 ^ φ Φ oι φ Φ Φ P ¹ φ tr φ P- φ 0 Φ P-

0 tr P- rt Φ iP X φ 3 Ω cx 0 P "Φ π 03 II H p- ^ li H 0 _^ 0 rt H 0 P li 10 φ

CX Φ rt cx • P- φ • tr o Φ LQ Ω P- rt rt 0 pi: P- N • 03 P-

Φ H P- Φ Ω 0 s is Ω H. rt tr 03 * U 03 Ω rt 0 t ≥! N rs tu tu Φ 0 rt

0 p- Hö tr O Mi> tr 3 ~> tr Φ CΛ 1 P- X LP 0 IV ⁾ N 0 Φ 0 oo 0 0

N Hi 0 ö P ^J 03 X <03 0 Φ rt ro P 0 NS 03 ZH p- 03 03 CX rt 0 er 0 Hi Cd 03 NN Φ Ω Hi 03 cx Φ 3 P- 0 X. P ¹ 0 CΛ 0 P- 0 P- rt P- N P- φ P ¹

Φ Φ P- 0 φ φ tr 0 O P- H tu rt t-3 0 0 03 P- 03 u 0 03 Φ 01 0 0 cn

LP 10 H tu H 0 P- N pj: 0 Hi Φ 03 0 tu Φ P- ro? V er CΛ 03 Ω Ω o o 03 P- CΛ • er

P- li Φ rt 0 _" « LP Φ rt LP Φ X P. 03 O ro cx Φ Hi rt tr tr P "i- rt rt 0

0 o 0 H x tu rt P- N Φ H 0: ιp> <CΛ 0 Φ Φ H: 0 rt φ LP 3 0 rt 0 ö rt φ

0 EP N Φ 0 CX rt 0 0 0 0 rt Φ 0 Ω P ¹ X 03 P- Φ P ¹ rt 0 φ 0 rt rt φ ^ 0 rt Hi φ 01 0 cx P ^J 0 φ 03 0 PS 0 tr tu H - φ 0 Ω P * P- p- P- p- H II φ

•> Hi H P- EP Φ P- LP 0 CX z 0 0 = H CΛ Φ l-i tu • tr rt O P- cx O Φ O rt 0

3 et N 0: 03 0 Ω P- φ LP rt Hi 0 ro LP 0 0 • 0 φ φ X g 0 0 0 tu P ¹

CΛ P- Φ rt 03 CX tr P. tu φ i-i 03 H Hi rt <ι cx ü Φ Φ 0 0 3 Φ 0 1 Hl

Er rt he P- et P- Φ Φ 0 rt <! 0: Hi Hi O iP φ rt ö 0 rt EP 0 lU tu H to P-

P- Φ et S 0 φ 0 H H tu 0 O S tr 0 0: 0 0 φ H Φ φ 0 t Cd 0 CΛ 03 3

0 cx H X CΛ rt et 0 03 0 0 0 CΛ φ n ι-i 3 l-i l-i N rt P- CX 03 tu H ro rt Pd P-

Φ Φ 0 P- t ι 01 CΛ et 01 P l-i x 0: 0 0 01 0 p- • CΛ P- 0 each

CΛ H Ω 0 3 O 0 Φ N 1 <P- ro rt 0 cx d Φ rt 0 Φ 0 3 pi: rt Φ 0 P ¹ Φ rt to LP

P- t P- 0 03 iP 0 3, 03 cx XH 0 0 0 CΛ 3 03 CΛ 0 0 Ω H Ω Φ p- HP ^| * et E P- Φ li C ¹ Φ 01 φ tu P- P ¹ 03 • <LP Φ tr tu tr Φ <0 P- 0 P-

0 tu 0 0 0 Hi o Hl 0 0 •>

0 o Φ Φ rt tu 01 0 P- O cn rt 03 CΛ Hi 03 cx H) φ cx

0 rt CΛ 03 LP Ω P ¹ 01 0 * <Hi φ CΛ Ω 0 P- 0 S3 0 cx P- Hi 0 H P- Φ Hi P- <

LP φ P- p. P »rt φ tr Φ Φ rt CΛ 0 rt x 1-1 P- Φ φ L Ω N 0: 03 rt 0 0 φ H Φ 0 0 03 rt 0 P- P- Ω 0 L0 03 LP i 01 H φ tr φ x tr tu φ 0 er H tr 3 rt Φ φ cx O <P cx 03 ts 0 X Φ rt X rt H Φ P- φ Φ CΛ CΛ N 0 Ω

Φ s3 Φ P- P- rt φ S 0 0 φ 0 φ 0 0: ii 0 P- 0: rt 3 P> ro ^■ 0 Φ φ ts H rt ON 03 P- 0 P- tr cx P- P ¹ rt 0: c; 0 H φ rt ö X •> 0 H tu 1

P- 0 H Φ 0 rt cx tu 0 Φ φ rt φ rt 3 X CΛ P- 0 tu 0 Ω 0 s!

0 EP rt P- Φ Φ Φ φ 0 CΛ 03 H H 0 cx l-i rt ro Φ 0 Hi 0 0 ö tr i-i φ

0 cr P- P- t 0 3 g ro Ω φ • £ tu H 0 Hi cx 03 P- ι-i Φ 03 H rt P- P. 0 0 0 CΛ X r P- Cd 0 t tr 03 CΛ 03 rt cx P Φ rt iP φ o Z rt rt

0 Φ O Φ Φ ro l Hl 0 0 p- 0 0 03 ö <φ ö P- H Φ φ P. 0: cx 01 03 ι-i ι-i 0 0 Φ OH φ 03 φ t 0 er 0 II 03 P- er Φ 0 ii P- tu P- 0 0 H

0 3 N p- 0 Ω Ω 03 CX P- 0 03 Φ Ω σ Hi rt 0 0: Φ 0 03 03 0> tr t Pd 0 0 <tr> PN tr tr Φ φ CΛ cx cx li Pd Hi N CX rt 03 0 Ω t

Φ 0 P- Φ H Φ 0 i 03 Φ LP tu Φ Hi P- Φ Φ tu P- rt tr CX II

H cx 3 φ L H Φ N 0 P- α <rt H φ 3 Ω l-i φ 3 H 03 P, ι-i S 01 P- rt P-. -.

LP P- »H 03 0 Φ P- 0 P- Φ t 0 H X tr: t-i P- Φ O Φ CΛ 03 01 o Φ Φ CX

3 φ 0 OX 0 cx Φ H rt tu pj: Hl 0 tr 0 0 0 HN P- rt 0 0 P ¹

P- l-i LP Cd EP 0: SO • u φ cx 03 03 P- 0 rt 0 Φ φ 0 LP N X

X P- 0 03 03 0 rt li 0 φ t- ¹ φ z LP 03 0 ω tu \ rt pj: P- Φ rt 0 P- tu 0 Φ tu Φ 03 rt Hi es 0 Ω et> 0 0 0 / iP 0 et li 0 pi: 03 0 P- "• LP Φ Hi JP> li 0 P- 3 rt P- Φ Φ 03 ^• - 'φ cx ES 0 3 • ι-i P- 03 rt 03 ω 03 0> rt 0 0 Φ 0 O tr P- P-

P- +

S <0 Φ LP φ 03 Hi tu P- 0 rt tu Λ CΛ Hi CΛ H t <! Hi t 03 rt 0 P "rt 03>

0 CΛ 0 0 P- 00 rt P- 0 ω 0 CΛ rt ι <Φ φ 01 CΛ 0 N φ cn P- Φ 01 rt φ 0 03 et tu • 03 N LP 01 iP rt P ¹ 0 g 0 0 to 0 o 3 Φ P- φ O t H rt

H N o cx 03 P- P- φ rt p- • rt T 03 cx P- o P- rt 0 CΛ 03 er 0 Hι

0 φ X P- ^ 3 t 0 φ 0 <! O P- O rt φ 3 er φ tu rt 0 Φ ro rt Φ es P- Hi CΛ 0 H P- rt Φ 0 σ O Φ N Φ α 03 Φ O tu N rt P- 03

Φ Hi d Φ Hi Ω <Φ 01 P- t-i 0 P- l-i φ • u N P- Φ * 0 H ü CΛ 01 z II O rt

P- H CΛ Φ Φ Ξ P- 0 rt O tr tu 03 CΛ P- 0 o 03 3 0 3 p- P ¹ φ P- rt 0 • rt 0: to Φ H 03 H P- P- 0 P- CΛ tu P- α rt P ¹ L rt Ω <i 0 Hi • 0 03 P ¹

<i tr H Φ φ 1 ι-i φ 0 ro CΛ CΛ Φ φ X ¹ Φ tu o ^ Hi α Ω tu tu

Φ P- 0 0 CX 03 0 P- tu cx P- ro H ι-i 0 φ 0 P 0 N 0 Φ Φ ö Φ tr 0 CΛ 03 ii 03 N 1 Φ cx 0 CΛ Φ 3 LP • rt 0 Φ 0 1 P- rt Φ 0 t 1 0 rt H ro H P- 1 0 1 φ 0 rt rt rt 03

oo oo ro t P> P ¹

Cπ o Cn o Cπ o Cπ o o cn cx 3 03 cn tu ö 0 Φ α et P- 0 L £> rs t cn Hi P- & CΛ tu Q 0 d s: N CΛ CX ffi 03 Φ cn

0 φ P- φ P- rt Φ 0 Φ P- P- P- Φ φ P- Cπ Φ φ 03 0: 0 rt 0 Φ 0 3 Φ 0 P- 0 P- P- P- Ω

I 03 0 rt 0 0 03 3 Ω> P φ K rt o \ o P- rt ^■ H 01 tr pi: cx 01 H * ö P- LQ -3 φ φ 0 tr tu -3 03 et 0 P- tr Φ 01 pj: rt ii 0 0 0 LQ rt Hi 03 0 cT H li Φ P-

CΛ Φ rt t tu P- 0 03 t et 0 Φ 0 CΛ rt 0 * Ö Ω P. Φ 0 P- Φ O: P- 0 Φ O 0 P ¹ rt φ ro li 0 P- Φ O P- 03 0 rt 0 ^ P- 0 LP 0 H cx φ li li φ 0 g P ¹ φ P- Φ CΛ er rt rt 0 N 0 LP rt cx ιp Cd cx 0 cn Ω 0 cx 01 Hl 0 pi: rt H LP Φ 3 03 0 Ω 0

0 P- rt 0 Φ 0 L Φ P- ι-i Ω ω tr CX φ P- <rt 03 P- φ 0 rt tr 0

0 Pd O ι-i L 0 Φ rt φ N Ω 3 P- tr << et rt Φ l-i> τ) 0 o <! Φ P- Cd N 0 0 P- o INI i-i LQ

Ω> 0 Φ P- P- H Φ tr P- tr H 0 01 0 cx 0 Φ 01 ω 3 Φ φ Ω n cx Φ 0 tr k> Φ Hi 0 03 rt O pi: P- Φ rt H o Ω 0 : 3 CΛ 0 H • rt X P- 3 tr 1-1 P- P- Hl <!

0 Hi 0 P- 0 rt LP et Φ er P- CΛ> H 0 ^» u 3 Hl rt cx et φ Φ rt Hi o cx Hl • N Hi ιP CX rt H p-? V Φ rt"<0 L P- P- Cd 0 03 0 0 X Hi 0 0 φ: φ 0 Φ tu S • K 0 03 0 H 0 Ω tu 03 LP φ P- 03 0 Ω EP CX rt t Φ H

HHM P- ^l 0 ι-i CΛ CΛ 0 0 πj P- 0 03 Φ Ω tr CΛ LP • x 0 O iP tr P_ Φ 0 0 ro

P- rt P- P ¹ P> ii Φ 0 Ω P- tr ι-i P ¹ φ φ Φ 0 φ CX 3 N 03 01 0 X ^f - Φ X LP P- CΛ P- pj: 1-1 tr 0 P, o • 3 Cπ 0 cx cx P- li p- 0 P- rt 0 to P- H 0 • 03 • <N cx o? N 0 cx ii Φ o 0 pj: 01 φ φ rt Φ φ tu 03 Φ 01 ι-i φ 0 0 P- 0 0 0 <0 P- 0 0 Φ ι-i P- tu E zzo H 01 N 0 P - 03 H P-><

3 0 X to φ Ω H 03 Φ 0 01 LP li P- P- rt CΛ Φ P- φ H 0 tu cx cx rt 03 Φ 0 φ «03 rt M tr H 0 P- Ω et <i rt pi: to ι-i lJ Ω CX N tu 0 L φ 0 - 1-1 Ω - ^> o Φ er rt H tu P- O P- tr Φ o: rt <x cx tr 0 Φ 0 0 03 φ 0 rt y er 0 Φ • O 0 3 03 N 0 φ 0 left <! Φ Φ Φ 0 0 LP α P- ii rt p- 0 es <

5 Φ cn 0 03 et 0 H K LP oi Φ o l-i er Ω Φ LP 03 0: P- O 0 Φ o

0 H CX Ω ö P- P- tu 0 l Φ z φ Hi i 0 Hi Φ • CΛ tr K rt φ 03 rt Hi 0 p- l-i

0 Φ Φ tr 0 rt 03 φ et Φ Φ N 03 P- iP Φ 3 0 03 P- Φ H rt P- cx rt p- Ω H ι-i 03 pj: 03 10 rt P- LP Z 03 ι-i Φ tr P- tu tr Ω rt p. 0 P- 0: 0 SN 0 φ 0 tu ir tr P- et rt 1-1 Hi 0 Φ Φ 0 cx er P ¹ rt 0 H tr 0 φ cx rt rt CΛ P- P- li Ω φ

0 0 t Φ t 0 P- P- Φ er P- 0 Φ Φ rt 03 Φ ii 0 ι- (o rt p- Φ Ω tr er ^ rt Φ Φ 0 cn et Hi 0 3 Φ LP 0 H Φ P- 0 P- et <NONH tr tu 03

P- et P- Φ cx CΛ P- Hi CX 0 t φ σ Φ 01 (- ^■ 03 Φ P- φ Φ P- 0 0 0 Φ et 0 Φ t 0 o rt 0 LP * O Φ er Φ 0 0 P - 0 rt 03 <i er O P- l 03 OO 0 03 0

0 Φ 0 φ 0 0 P- 0 Φ 0 03 Φ tu rt Φ Φ 0 rt H tu H 3 P- CX

CΛ O l-i Ω 03 P "H P- φ 03 s; 03 0 l-i 0 Φ cx X CΛ, φ 03 Φ cx

3 ü cx pi: tu rt P- 0 01 ι-i φ 0><CX rt 3 3 01 0 0 to 0 03 tr 03 li φ p- Φ 3 P- rt <! CΛ 03 φ P ^J 03 3 tr 0 • P- p- 0 H 3 Φ Φ O lf rt oi rt P- 0 φ O IV ⁾ P- er P ¹ rt P- Q li 0 tr o Φ ZE 0 Ω P- rt> α 0 0 tu

0 S 0 φ Φ P- 03 0 rt Φ 01 • 0 cx P- 0 tr rt 0 CX P- rt 0 P-

P- φ Φ ü CΛ 0 P- ιp et rt 0 o N Φ φ φ P-, Hi CΛ X 0 0 P- 03 tr

Φ 0 P- Φ 0 0 P- Φ 0 P- Φ 0 tr 0 Φ 0 0 0 Φ 0: CX CX 0 EP O P- n

H ≥! Hi 3 P- 03 φ 03 0 0 O} - • 0 Φ P- cx tr H tr φ Φ CΛ 0 cx 0 03

0 P ¹ Hi P- 0 N 0 rt Ω 0 et P- P- Φ 0 Φ z P- Φ Φ HH 3 P- 0 03 φ 01 N

N φ Φ EP φ 0 INI tr Φ ιp 0 P- P- P- Φ li 0 φ LQ • p- li tu rt 0 s: 0 H et li Hi ffi, Φ 0 OXP ¹ 0 cn 0 H CΛ 0 ιu Φ 0 φ CΛ L φ ≥! Φ 0: 0 P- er CX Φ P- Φ li φ CX Φ 0 O P- 0 t t- ¹ IV) rt Φ

P- 0 IV) 0 0 X tr 0 tr rt Φ <! Φ P- Ω 3 Φ 0 0 φ i- ¹ 0 P ¹ 03 CX 0 P- rt rt N 0 Φ H cx Φ X li φ H rt tr 0 cn cn rt 0 0 LP 0 LP Φ 0 Φ

Φ Pd cx 0 H Φ o ι- (0 Φ l-i x LQ N Φ es Φ Φ er φ <l Hl T cn φ P- 0 P-

0 P- φ> 0 <0 Ω z P- CX Φ φ z 0 0 Hi ι-i Φ Cd O pj: 0 0 P ¹

3 H et N φ P- e tr φ 0 Φ P- LQ φ 0 0 0 et 0 HP ¹ 0 φ N t rt tu P- Z ≤: li et 0 0 H rt φ li 0 0: tr 0 φ cx cx tr 01 0 3 ex 0 CΛ Φ

0 0 NN P- Φ Z Φ. tϊ er et P- Ω li P ¹ P- LP 0 Φ Ω X P- rt t 0

01 LP z Z φ P- P- <! ^I U <rt φ Φ CΛ <Φ ** ιp tr P ¹ φ EP ι- (tr 03 Hi Φ ι-i

P- φ P- H o P- O rt 0 * <o X 01 cx Φ P- H P O 0 Φ 01

01> P- 03 er t CX 0 LQ l-i z Φ 0 0 0 Φ CX φ rt 0 0 Q 0: 0 Φ P- 10 0 S Hi CX

01 x Ω Φ • φ 0 rt ^

Ω 0 Φ P- 1-1 rt rt P- tr Ω 0 P- Hi 3 0 rt <tu tr H 03 CX CX CX H 0 tr N 0 rt Z Ω Φ 03 Ω φ tr H Φ 1 Φ ¹ H

0 0 0 Φ Φ P- P- φ Cn Φ cx S P- H • P- tr 3 0 tr 0 Φ 0 0 0 Ω rt 0 1 0 P- CΛ Φ ι-i 3 φ p- 03 o tu cx ii 1 g rt cx H CX φ • tr

P- 1 rr 1 0 rt 1 • φ P- CΛ φ 1 0 P- 1 03 1 ι-i ι-i 1 1

TA2 = TAl + Δt-2Gsync In the event that the two base stations BS1, BS2 are perfectly synchronized, this means that the signal from the terminal MS arrives at the base station BS2 in a time interval F _o which is counter to the hatched reception ^{¬ the} time window is delayed by 2xGsync.

If one assumes that the base station BS2 is sending Gsync prematurely compared to the base station BS1, which corresponds to the dash-dotted time normal line N2a in the figure, the terminal MS measures a time difference Δt _a = ((d2-dl) / c) -Gsync; there is a timing advance value TA2 _a = TAl + Δt _a -2Gsync = TA1 + ((d2-dl) / c) -3Gsync.

The timing advance value is thus 3Gsync smaller than in the case of FIG. 2; At the same time, the reception window for the signal of the terminal MS at the base station BS2 is premature by Gsync, so that the signal of the terminal MS arrives at the base station BS2 with a delay of 4Gsync against its reception window in the time interval F _a .

On the other hand, if one assumes that the base station BS2 has a delay of Gsync compared to the base station BS1, which corresponds to the dash-dotted time normal line N2d in FIG. 5, there is a difference between the time standards Δt _d = ((d2-dl) / c) + Gsync.

The timing advance value is thus calculated as TA2 _d = TAl + Δt _d -2Gsync = TA1 + ((d2-dl) / c) -Gsync. The timing advance value is therefore smaller by Gsync than with perfect synchronization. On the other hand, the reception window of the base station BS2 is also delayed by Gsync compared to that of the base station BS1, so that the signal of the terminal MS at the base station BS2 coincides exactly with the reception window F _{d assigned} to it. The risk that the signal of the terminal MS at the Basissta ^¬ tion BS2 arrives too early to be evaluated to correct, is thus eliminated regardless of the amount and direction of the actual synchronization error Esync.

If the synchronization of the base stations BS1, BS2 is bad, Gsync thus large values of e.g. Assuming 2.5 μs, the use of the method described above can lead to very considerable reductions in the timing advance value and could even result in the timing advance value becoming negative. Such a value would correspond to a negative distance between the terminal MS and the second base station BS2, which is obviously not physically meaningful. If the calculation described above returns a value TA2 <0, TA2 = 0 is therefore always set. In order to avoid excessive reductions in the timing advance value, it is furthermore expedient to define an upper limit for the accuracy of the synchronicity, and to limit the application of the method described above to only those pairs of base stations within a radio communication system, whose synchronicity is better than this limit. When handover between base stations where the synchronicity is worse than this limit value, the terminal MS uses a timing advance value TA2 = 0 for the communication with the second base station until the base station BS2 issues a command to set a value measured by it transmitted.

According to a preferred embodiment of the method, the handover between two base stations does not necessarily signal the accuracy of the synchronicity to the terminal that has been determined for the two base stations, but rather only an indication of the affiliation of the relevant pair of base stations to one transferred from several accuracy classes. In this way, the number of bits required for signaling the accuracy is reduced to the two-logarithm of the number of classes. In practice there are four or even three classes sufficient: a first class, to which strictly coupled ^pairs of stations with an accuracy of synchronicity of typically approx. ± 100 ns belong. When handover between two such stations, taking into account the accuracy Gsync described above when determining the new timing advance value TA2 can in the worst case lead to a delay of the signal by 400 ns, which is the case, for example, in a UMTS radio communication system with a Spreading factor of 16 is less than the duration of two chips (1 chip = approx. 250 ns). When handovering between pairs of base stations that belong to this accuracy class, the accuracy of the synchronicity when determining the new timing advance value can therefore be completely dispensed with, since the resulting time shifts result in the detection of the - midamble and thus the symbol estimate at the base station Can not affect BS2.

A second class comprises pairs of base stations with an average accuracy of the synchronicity Gsync of typically ± 500 ns. With such a value of Gsync, taking it into account when determining TA2 in the worst case can lead to a delayed arrival of the signal at the base station BS2 by 2 μs.

A third accuracy class contains those pairs of base stations already mentioned above in which the accuracy of the synchronicity is so poor that taking them into account when determining TA2 can lead to unusually large delays in the signal at the base station BS2.

If the terminal MS has been signaled that the base stations BS1 and BS2 belong to the second class, it uses the upper accuracy limit of this class as Gsync to determine TA2.

If three classes are used, for example, all pairs of base stations with Gsync <200 ns can enter the first Class, those with 200 ns <Gsync <1 μs in the second and all with Gsync> 1 μs in the third class. In order to keep the signal delays resulting from Gsync as small as possible in individual cases, it may be desirable to subdivide the second class. For example, a subdivision is also conceivable where a class 2a contains all pairs of stations with 200 ns <Gsync <500 ns and in class 2b the pairs with 500 ns <Gsync <1.5 μs. In such a case, the terminal MS would base the determination of TA2 on the handover between stations of class 2a, an accuracy = 500 ns, in the case of stations of class 2b, an accuracy Gsync = 1.5 μs.

Claims

claims

1. Method for adapting the timing advance (TA1, TA2) of a mobile terminal (MS) during synchronous handover from a first to a second base station (BSl; BS2) of a radio communication system, in which a time shift (Δt) between time standards (Nl , N2, N2a, N2d), which the terminal (MS) receives from the two base stations (BSl, BS2), is measured and a timing used by the terminal (MS) before the handover for transmission to the first base station (BSl) Advance value (TA1) is corrected on the basis of the measured time shift (Δt, Δt _a , Δtd), characterized in that the corrected timing advance value by one of the accuracy (Gsync) of the synchronicity of the two base stations (BS1, BS2) derived value is reduced and used as timing advance value (TA2) for transmission to the second base station (BS2).

2. The method according to claim 1, characterized in that the derived value is twice the accuracy (Gsync) of synchronicity specified in time units.

3. The method according to any one of the preceding claims, characterized in that when the accuracy (Gsync) of the synchronicity exceeds a predetermined limit value, the timing advance value (TA2) used for transmission to the second base station is set to zero.

4. The method according to any one of the preceding claims, characterized in that the accuracy (Gsync) of the synchronicity is signaled to the terminal (MS).

5. The method according to claim 4, characterized in that the pair of the two base stations (BS1, BS2) is classified into one of several classes depending on the accuracy of their synchronicity, and that the terminal (MS) is signaled to the class to which the couple heard.

6. The method according to claim 5, characterized in that the number of classes is at least three.

7. The method according to claim 5 or 6, characterized in that a first limit value of accuracy, which separates a first and a second class from each other, is between 100 and 500 ns, and that if the accuracy of the synchronicity is better than the first limit value , the value derived from the accuracy of the synchronicity is set to 0.

8. The method according to any one of claims 5 to 7, characterized in that a second limit of accuracy, which separates a second from a third class, is between 500 ns and 2.5 μs, and that if the accuracy of the synchronicity in the second Class falls below the second limit, the value derived from the accuracy of the synchronicity is set equal to twice the second limit.

9. Radio communication system with a plurality of cells synchronized with one another with a known accuracy

(ZI, Z2), characterized in that when a handover of a terminal (MS) between two of its cells (ZI, Z2) signals an indication of the synchronicity of these two cells (ZI, Z2) to the terminal (MS).