CN101091332B - Method and apparatus for fast downlink notification of uplink out-of-sync - Google Patents

Abstract

An information system, detector and method for a communication link, such as the downlink of a cellular telephone system, reduces the problem of uplink transmit power peaks when the uplink is out of synchronization (OoS). A method of indicating that a first link to a communication node is OoS includes the step of including an OoS signal in signals transmitted by the node on a second link. The OoS signal includes at least one data bit transmitted by the node indicating whether the first link is synchronous or OoS. A method of determining that a first link to a communication node is OoS includes the step of detecting an OoS signal in signals transmitted by the node on a second link. The OoS signal includes at least one data bit indicating whether the first link is synchronous or OoS, including a sign change of a symbol, a power level offset between information elements, or different scaling factors for pilot symbols. When the first link is OoS, transmit power control commands from the second link are not included in determining transmit power on the first link.

Description

Method and apparatus for fast downlink notification of uplink out-of-sync

background

This invention relates to communication systems having synchronized transmitters and receivers, and more particularly to indicating to a transmitter that it is out of synchronization with a receiver, and even more particularly to transmitters and receivers in a wireless telephone system .

Digital communication systems include time division multiple access (TDMA) systems, such as cellular radiotelephone systems conforming to the GSM telecommunications standard and its enhancements like GSM/EDGE, and include code division multiple access (CDMA) systems, such as conforming to IS-95, cdma2000 and Wideband CDMA (WCDMA) telecommunications standards for cellular radiotelephone systems. Digital communication systems also include "hybrid" TDMA and CDMA systems, such as cellular radiotelephone systems that comply with the Universal Mobile Telecommunications System (UMTS) standard, which specifies A third generation (3G) mobile system developed within the framework of IMT-2000. The 3rd Generation Partnership Project (3GPP) has published the UMTS standard. For the sake of brevity, this application focuses on WCDMA systems, but it will be understood that the principles described in this application can be implemented in other digital communication systems.

WCDMA is based on direct-sequence spread spectrum technology. In the downlink (base station to terminal) direction, the base station and the physical channel (terminal or user) are separated by pseudo-noise scrambling code and orthogonal channelization code. Since in a CDMA system all users share the same radio resources, it is important that each physical channel does not use more power than it needs. This is achieved through a transmit power control (TPC) mechanism in which, among other things, the base station sends TPC commands to the user. The TPC command causes the user to increase or decrease its transmit power level in increments, thereby maintaining the target signal-to-interference ratio (SIR) of the dedicated physical channel (DPCH) between the base station and the user. WCDMA terminology is used here, but it will be understood that other systems have corresponding terminology. Scrambling and channelization codes and transmit power control are well known in the art.

Figure 1 shows a mobile radio cellular telecommunication system 10, which may be, for example, a CDMA or WCDMA communication system. Radio Network Controllers (RNCs) 12, 14 control different radio network functions, including radio access bearer setup, diversity handover, etc., for example. More generally, each RNC directs mobile station (MS) or remote terminal calls via the appropriate base station (BS) through the downlink (i.e., base station to mobile station or forward) and uplink (i.e., Mobile to base station or reverse) channel to communicate with each other. RNC 12 is shown coupled to BSs 16, 18, 20 and RNC 14 is shown coupled to BSs 22, 24, 26. Each BS serves a geographic area, which can be divided into one or more cells. BS 26 is shown with 5 antenna sectors S1-S5, which may be said to form the cell of BS 26. The BS is coupled to its corresponding RNC through a dedicated telephone line, optical fiber link, microwave link, etc. The RNCs 12, 14 are connected to external networks such as the Public Switched Telephone Network (PSTN), the Internet, etc. through one or more core network nodes like a Mobile Switching Center (not shown) and/or a Packet Radio Service Node (not shown) .

As the user terminal moves relative to the base station, and possibly vice versa, the connection is maintained through the handover process. For example, in a cellular telephone system, a user's connection is handed over from one base station to another as the user moves from one cell to another. Early communication systems used hard handover, in which the base station of the first cell (covering the cell the user was leaving) would stop communicating with the user exactly when the second base station (covering the cell the user was entering) started communicating. Modern systems typically use soft handover, in which a user is connected to two or more base stations simultaneously. In FIG. 1, MSs 28, 30 are shown communicating with multiple base stations in a diversity handover situation. The MS 28 communicates with the BSs 16, 18, 20 and the MS 30 communicates with the BSs 20, 22. The control link between the RNCs 12, 14 allows diversity communication with the MS 30 via the BSs 20, 22.

During soft handover (SHO), a terminal receives TPC commands from more than one base station, and methods for handling collisions between TPC commands from different base stations have been developed. Since when a user terminal or equipment (UE) leaves a cell, the base station of that cell receives a gradually weaker signal, the TPC command of the base station requires an increase in power, while at the same time the user terminal may enter a new cell, and the base station of the new cell Gradually stronger signals are received, so the new base station's TPC commands require power reduction, so collisions are expected. In 3GPP compliant systems, the UE combines TPC commands from the reliable downlink with a logical OR function, which results in a UE transmit power reduction when any reliable command indicates a "down". This is described in the Physical layer procedures (FDD) of Section 5.1.2.2.2.3 of 3GPP TS 25.214 (V5.6.0) Rel.5 (2003).

Reliable OR combination of TPCs can be implemented in UE in different ways, e.g. by using a reliability threshold, "Power control command combination during WCDMA soft handover" (N. Wiberg, H. Rong, F. Gunnarsson and B. This is described in .Lindoff, "Combining of powercontrol commands during soft handover in WCDMA", Proc. of the 14thlnt'l Symposium on Personal, Indoor and Mobile Radio Communication (PIMRC), 2003). Other aspects of the TPC are described in US Patent 6,594,499 to A. Andersson et al., entitled "Downlink Power Control in Cellular Telecommunications Network".

Soft handover in WCDMA and other 3G communication systems involves the Active Set Update - ADD procedure described eg in the aforementioned 3GPP TS 25.214. The UE reports event 1A (radio link addition) to the network and the RNC notifies the new base station Node B to start uplink (UL) synchronization. When an acknowledgment message from the Node B is received in the RNC, an "Active Set Update - ADD" message is transmitted to the UE and at the same time the new Node B starts transmitting on the downlink (DL). Before achieving UL synchronization, the TPC command transmitted by the Node B on the new DL requires the UE to increase its transmit power; according to section 5.1.2.2.1.2 of TS 25.214, the TPC command sequence is ...11111.... The UE receives the "Active Set Update - ADD" message and decodes it, after which the terminal's physical layer starts combining the DL information from Node B and the "old" base station Node A, including TPC commands.

Depending on channel conditions, UL synchronization when entering or adding a link in soft handover can take 100 milliseconds (ms) or even longer. This delay is mainly due to the fact that the Node B is unaware of the UE, which forces the Node B to search its entire cell, and due to the generally low power of the UL signal received by the Node B and the low number of UL DPCCH pilots, which forces the Node B to obtain a reliable channel and receive a large number of symbols before path estimation.

To reduce this time delay, the physical layer (Layer 1) in Node B obtains Layer 3 information from the RNC to initiate UL synchronization before transmitting a Layer 3 "Active Set Update" message to the UE. It has an impact on the period when TPC on DL is open loop. Although the amount of improvement due to this for Node B is difficult to calculate, there have been indications in at least one RNC log that the delay is only 30-40ms. Compared to DL, UL (Node B) has at least two other timing advantages when establishing synchronization: the Active Set Update message itself is 20ms long, and then the UE needs time to process it. The processing time of the UE depends on the architecture of the UE and the current load on the real-time processing unit in the terminal. A further delay of 30-50 ms may occur in the terminal before it starts to assemble new DL information on layer 1 . The sum of these delays in DL is about 100ms, which means that the start of UL sync can be expected to happen at least about 100ms before DL sync takes place. However, the end of UL synchronization may occur after the UE receives the Active Set Update message and starts combining power control commands from the new base station. In this case, there is the possibility of a control loop problem in the form of UL power peak, ie too much UL power, or UL power dip, ie too small UL power.

Field experiments have shown a phenomenon during soft handover that is clearly not prohibited by the current TPC method. When a terminal or user equipment enters soft handover or adds a communication link in soft handover, if the initial downlink power on the new link is set , after receiving and processing the "Active Set Update" message) within 30-40ms after the new Node B fails to achieve uplink synchronization, a 20-40dB peak can be observed in the uplink (UE to base station) transmit power. It was also observed in the field test that after the communication link established in the SHO is synchronized, there is a certain possibility that the link becomes out of synchronization (OoS). If this happens, the link will typically be resynchronized in a process that is the same as in the initial synchronization case, and therefore there will be the possibility of a large UL transmit power peak.

Since UL synchronization takes time, TPC on UL and DL of a newly or re-synchronized connection in soft handover can operate open loop for 100-200 ms, and such long delays can be considered as the main cause of spikes in transmit power. These power peaks interfere with other users, thus causing problems for users and the system as a whole. UL synchronization detection methods and apparatus are described in US Patent Application 10/839,926, filed May 6, 2004, by B. Lindoff et al., entitled "Synchronization Detection Methods and Apparatus."

overview

Therefore, it would be desirable to have an OoS notification system and detector for DL to reduce the UL peaking problem in such cases.

In one aspect of Applicants' invention, a method of indicating that a first communication link is out of sync includes the step of including an OoS signal in a signal sent over a second communication link. The OoS signal includes at least one data bit transmitted indicating whether the first communication link is synchronous or OoS.

In another aspect, a method of determining that a first communication link is OoS includes the step of detecting an OoS signal in a signal transmitted over a second communication link. The OoS signal includes at least one data bit indicating whether the first communication link is synchronous or OoS.

In yet another aspect, a communication node adapted to transmit and receive electromagnetic signals includes: a detector adapted to determine whether a first receive link is synchronized; and means, responsive to the detector, adapted to transmit on a second link The signals include OoS signals. The OoS signal includes at least one data bit indicating whether the first receive link is synchronous or OoS.

In another aspect, a communication terminal adapted to transmit and receive electromagnetic signals comprises: means adapted to recover information from electromagnetic signals received on a first link, the information including pilot symbols and transmit power control (TPC) a command; a control unit adapted to control a power level of an electromagnetic signal transmitted by the terminal on the second link based on the TPC command; and a detector adapted to monitor the recovered information to observe in the signal received on the first link Whether there is an OoS signal, wherein the OoS signal includes at least one data bit indicating whether the second link is synchronous or OoS.

In yet another aspect, a communication system includes: at least one base station adapted to propagate and receive electromagnetic signals, wherein the electromagnetic signals include at least one common pilot channel (CPICH) and at least one dedicated physical channel (DPCH); and At least one user equipment adapted to propagate electromagnetic signals to and receive electromagnetic signals from at least one base station. The user equipment comprises: means adapted to recover information from the CPICH and DPCH, the information including pilot symbols and TPC commands; and a control unit adapted to control a power level of a transmitter in the user equipment based on the TPC commands. The base station includes a detector adapted to determine whether an uplink (UL) from the user equipment is synchronized; and when the detector determines that the UL is OoS, the base station changes a DPCH pilot symbol propagated to the user equipment.

In yet another aspect, a method of indicating that a first link to a communication node is OoS includes the steps of: checking, by the node, whether the UL is OoS; if the first link is synchronized, transmitting on the second link pilot symbols with a first scaling factor; and transmitting pilot symbols with a second scaling factor on a second link if the first link is OoS.

In yet another aspect, a method of controlling transmit power on a first link to a communication node includes the step of detecting a scaling factor for pilot symbols received on a second link, wherein if the first link is synchronous , then a pilot symbol with the first scaling factor is detected, and if the first link is OoS, then a pilot symbol with the second scaling factor is detected; if a pilot symbol with the second scaling factor is detected, then limiting TPC commands received on the second link in the TPC command combination; and including TPC commands received on the second link in the TPC command combination if a pilot symbol having the first scaling factor is detected.

In yet another aspect, a method of determining in a user equipment that an UL to a communication node is OoS comprises the steps of: comparing an updated TPC command received from the node with an older TPC command; if the generated TPC command from the comparing step if the output signal exceeds a threshold, a DL measurement of a signal-to-interference ratio (SIR) from the node; and based on the measured SIR, determine whether the node is following TPC commands sent to the node in the UL. If the node is not following TPC commands, it is determined to be OoS.

Brief description of the drawings

The various nature, objects and advantages of applicants' invention will be understood by reading this specification in conjunction with the accompanying drawings, in which:

Fig. 1 shows a kind of communication system;

Fig. 2 is a block diagram of a base station and a receiver according to the applicant's invention;

Fig. 3 is a flow chart of the method according to the applicant's invention;

4A, 4B, and 4C are flow charts of other methods according to the applicant's invention; and

Fig. 5 is a flowchart of another method according to applicant's invention.

Detailed description

The present invention describes a method to reduce the likelihood of UL transmit power peaks when a synchronized uplink becomes out of sync. For convenience, this description focuses on WCDMA systems, but it will be understood that the invention is not limited to such systems.

One way for a UE to know that its UL is OoS at a node such as a base station is to introduce the UL OoS signal into the control signals exchanged by at least that node with the UE. Such a control signal may be one or more data bits transmitted by a node (specifically a Node B) that tells the UE whether the UL between the UE and that particular Node B is synchronized or not. Synchronize. For example, data bit = 1 may indicate synchronization, while data bit = 0 may indicate out of synchronization. With such a control signal, the UE detects the transmitted sync/out-of-sync bit, and whenever this bit indicates a sync condition, the UE includes the TPC command stream from that Node-B in its TPC command combination. If OoS is detected by the UE detecting the OoS bit, the UE stops including TPC commands from the Node B, or reduces its reliance on TPC commands from the Node B. Thus, the base station (ie, receiver) indicates the loss of synchronization to the UE (ie, transmitter), and the transmitter operates according to the indication.

Such an indication is only a single bit of information, easily implemented as a sign change of a predetermined sign, and in other ways as described in more detail below. In a communication system such as a WCDMA system, a conveniently available predetermined symbol is a pilot symbol transmitted by a BS on a Dedicated Physical Channel (DPCH) of a UE. The BS also transmits pilot symbols on a Common Pilot Channel (CPICH), and UEs typically use the CPICH pilot symbols in estimating the impulse response to the BS's radio channel. It will be appreciated that due to the generally higher signal-to-noise ratio of the CPICH, the UE uses the CPICH pilots for channel estimation rather than the DPCH pilots, but the UE still uses the DPCH pilots, mainly for SIR estimation, i.e. for DL power control.

Accordingly, the UE advantageously compares the sign of the CPICH pilot symbol with the sign of the DPCH pilot. If the UE determines that the signs are different, the UE determines that its UL is OoS (and vice versa, of course), and then the UE may not include the TPC commands sent by this node in combination with TPC commands from other BSs. When the base station determines that the UL is synchronous, the base station makes the sign of the DPCH pilot symbol the same as that of the CPICH symbol (of course, it can also be different). The UE detects a change (eg, the UE determines that the DPCH and CPICH pilot symbols have the same sign), and starts listening for TPC commands from the base station.

Indicating OoS in this way should be easy to implement in many current networks, and since no more advanced signaling is required during OoS, OoS detection and response can be fast. To ensure compatibility with UEs that do not utilize these indications, the UE should inform the base station in its layer 3 control signaling that the UE has the fast OoS notification capability described in this application. For example, the UE may indicate that it has this capability by including an appropriate flag, information element or message in the connection establishment messaging.

2 is a block diagram of a communication system including a base station 200 and a user equipment UE 250 according to Applicants' invention. The communication system will generally comprise a plurality of base stations that can simultaneously communicate with the UE, eg during soft handover, and each of these base stations can be identified by a suitable index i.

A base station generally includes a transmit antenna 202 for propagating electromagnetic signals to UE 250 and other remote terminals and a receive antenna 204 for receiving electromagnetic signals transmitted by UE 250 and other remote terminals. It will be appreciated that while the antennas 202, 204 are shown as distinct antennas, they need not be. As mentioned above, in a system like a WCDMA system the signal transmitted by the base station 200 includes a plurality of common channels, such as CPICH, which the encoder 206 combines with the channel code of the base station in use. The number N of dedicated channels transmitted by the base station at any particular moment can be generated by corresponding multiplexers/channel encoders 208-1,...,208-N, each multiplexer/channel encoder combining the number of dedicated channels The data stream is combined with known pilot symbols. The outputs of the encoders 206, 208-1, ..., 208-N are combined, for example by a suitable adder 210, and the result is compared with a predetermined combination of scrambling codes. This result is then provided to transmit antenna 202, preceded by appropriate up-conversion and amplification if necessary.

A UE 250, such as a mobile terminal in a WCDMA communication system, generally transmits and receives radio signals through an antenna 252. These signals are generated by a suitable transmitter 254, which takes the baseband information and upconverts it to radio frequency, and a receiver section which downconverts and samples the received signal. As shown schematically in Figure 2, the signal received by the antenna is provided to the channel estimator 256, which despreads the common pilot channel and the dedicated physical channel of the UE, and recovers the pilot symbols included on the CPICH and DPCH, When required, the received signal level is determined and the impulse response of the radio channel is estimated. Based on some content of this information, Rake combiner 258 combines the echoes of the received data and provides an output signal to symbol detector 260 which produces information that is further processed for the particular communication system. It will be appreciated that while antenna 252 is shown as a single antenna, it may be implemented as different transmit and receive antennas.

Rake combining and channel estimation are well known in the art. Different aspects of Rake receivers are described in the following document: "Introduction to Spread-Spectrum Antimultipath Techniques and Their Application to Urban Digital Radio" by G. Turin, Proc .IEEE, vol.68, pp.328-353 (March 1980); US Patent 5305349 entitled "Quantized Coherent Rake Receiver" (Quantized Coherent Rake Receiver) to Dent; US Patent 6,363,104 for "Method and Apparatus for Interference Cancellation in a Rake Receiver" (Method and Apparatus for Interference Cancellation in a Rake Receiver); and to Wang et al. entitled "Multi-Stage Rake Combining Method and Apparatus" Methods and Apparatus) U.S. Patent 6,801,565; and U.S. Patent Application Publication 2001 entitled "Apparatus and Methods for Finger Delay Selection in Rake Receivers" by Wang et al. / 0028677. Channel estimation is described, for example, in U.S. Provisional Patent Application 60/519,261 by L. Wilhelmsson, entitled "Channel Estimation by Adaptive Interpolation".

In addition to the CPICH and DPCH pilot symbols, the estimator 256 also recovers control symbols, including TPC commands from each node to which the terminal is connected, such as the base station 200, and combines the stream of TPC commands from each link in the UE's active set. Based on the detected commands, control unit 262 generates combined TPC commands that are provided to transmitter 254, which responds by increasing or decreasing the transmit power of the terminal. If there is only one link in the active set, then the combined TPC command is exactly one detected stream of TPC commands for that particular link.

Several methods of determining and combining TPC commands are known, such as Nilsson et al., entitled "Methods, Receivers, and Computer Program Product for Determining Transmission Power Control Commands Using Bias Interpretation" (Methods, Receivers, and Computer Program Product for Determining Transmission Those methods described in US patent application publication US 2004/0058700 of Power Control Commands Using Biased Interpretation). The DL TPC pattern sent by a node such as a Node B to a UE to control UL power may be different in different networks. For example, even though the 3GPP specification indicates that the all-up TPC mode should be used, the network may instead send a toggling pattern, ie a sequence of (up and down) pairs that may occasionally include "extra" up commands. The iterative mode is discussed in section 5.1.2.2.1.2 of 3GPP TS 25.214.

Signals transmitted by remote terminals, such as UE 250, are received by the receiving antenna 204 of the base station, which includes N detectors 214-1, ..., 214-N, which process the signals from the corresponding remote terminals and recover the transmitted information. These detectors synchronize themselves to their corresponding signals, which is typical in digital communication systems. For different reasons, the detectors 214 may lose synchronization, ie the detectors become out of sync. Corresponding OoS detectors 216-1, . . . , 216-N advantageously detect out-of-sync conditions, but it will be appreciated that one or more OoS detectors may be shared between receive channels. OoS detectors 216-1, . . . , 216-N generate corresponding output signals, which are provided to combiners 218-1, . Combination of streams of symbols. Each OoS detector 216 may be implemented as a comparator that determines whether the estimate of the UL SIR is above a certain threshold; if it is above the threshold, the UL is in-sync, otherwise, the UL is OoS. SIR estimates for UL channels 1-N are determined by a suitable processor 220, and various methods of estimating SIR are known in the art. The signal power S and the interference power I of a channel are generally estimated using pilot symbols, ie known symbols transmitted on one or more channels. SIR estimation is described, for example, in US Patent Application 10/700855 by J. Nilsson et al., entitled "Interference Estimation in CDMA Systems Using Alternative Scrambling Codes".

As described above, when the OoS detector 216 detects an out-of-sync condition, its output signal is altered in such a way that the DPCH pilot symbols are altered accordingly. For example, the OoS output signal may be +1 for in-sync conditions and -1 for out-of-sync conditions, and combiner 218 may be a binary multiplier. The result is that the DPCH pilot symbols are multiplied by the scaling factor +1 when the base station's receiver is synchronized with the UE's transmitter, and by the scaling factor -1 when not. Of course, it will be appreciated that the opposite could happen, ie multiply by -1 when in sync and +1 when not in sync.

At the UE, the polarity of the DPCH pilot symbols is detected by a channel estimator 256, which recovers the pilot symbols included on the CPICH and DPCH from the base station. If the polarity is as expected for synchronization conditions, eg +1, a suitable indication is passed to the control unit 262, which may arrange to use TPC commands from the base station in the UE's determination of its proper transmit power level. If the polarity is different than expected, eg contrary to expectations, a suitable indication is passed to the control unit 262, which may arrange to not include the TPC command from the base station in the UE's determination of its appropriate transmit power level.

Figure 3 is a flowchart of a method according to applicant's invention. In step 302, the UE notifies the network of its fast OoS detection capability, eg by including appropriate information elements in messages exchanged during connection establishment. This preliminary step is not required if all UEs have the applicant's fast OoS detection capability, or if the network does not care that the UE lacks this capability.

For example, when the UE is in SHO, the base station in the active set checks whether its corresponding UL from the UE is OoS (step 304). If the UL is synchronous, then the scaling factor +1 is applied (multiplied) to the DL DPCH pilot p transmitted to the UE, and the flow returns to step 304. If UL is OoS, then a scaling factor of -1 is applied (multiplied) to the DL DPCH pilot p and a re-synchronization procedure is initiated (step 306). According to a resynchronization procedure, the DL transmit power level is fixed at a specific level, and in the downlink transmits such as ..., up, up, up, ... or ..., up, down, up, down , l... A special sequence of TPC commands.

As mentioned above, the UE detects the UL OoS condition, eg by checking pilot symbols p or channel estimates obtained from CPICH and DPCH (step 308). If OoS is detected, the UE does not use DL TPC commands from the BS with OoS UL in its TPC combining algorithm. In step 310, the BS checks if the UL of the BS is synchronized, and if not, the flow returns to step 306 and transmits the DPCH pilot p with a -1 scaling factor. When UL re-syncs, the BS changes the scaling factor of its DPCH pilot to +1 (step 312). The UE detects a scaling factor change, which indicates its UL is in-sync, and starts using TPC commands from the BS again in its TPC command combining algorithm (step 314).

Applicant's method of changing the scaling factor of DL DPCH pilot symbols when UE's UL becomes OoS in SHO can be implemented in all system operation modes where channel estimation can be based on CPICH (primary or secondary CPICH) pilot frequency symbol. Such approaches include, for example, the normal approach (ie, no beamforming, where only DPCH pilots are used for channel estimation) and open-loop transmit diversity. Although the method is described above for the case where the uplink becomes out of sync, it can also be used when the UE enters SHO or adds a link in SHO. In such cases, the DPCH pilot symbols eg have a negative sign until the UL is in sync.

If CPICH can be used for DPCH channel estimation, it should be noted that the relationship between channels is as follows:

${\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; DPCH</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; CPICH</span>}}$

where i=1,...,N _p is the number of the radio path (i.e., the signal fingers used in the Rake part of the receiver) from BS _j in the active set, where j=1,..., N _BS , and γ _j >0 are real-valued scaling factors, the same for all radio paths, but different for different BSs. Therefore, detecting the changed sign on the DPCH pilot is the same as detecting the sign of _γj . Methods for estimating the scaling factor γ are known, at least some of which are described in the aforementioned US Patent Application 10/700855 to J. Nilsson et al. Any suitable method may be performed by the UE, for example in the control unit 262 .

For such cases, FIG. 4A shows an exemplary OoS detection method, and the method includes the step of estimating a scaling factor γ _j for each reception slot and each base station BS _j in the active set (step 402). If the estimated γ _i >0, the UE uses the DL TPC commands from BS _j in forming its TPC command combination (steps 404, 406). If the estimated γ _j <0, the UE does not include the DL TPC command from BS _j in its TPC command combination (steps 404, 408).

It will be appreciated that this method can be varied as shown in Figure 4B, for example, by estimating Hi _,j ^DPCH and _Hi,j ^CPICH (step 412), and comparing the sign of the DPCH and CPICH channel estimates (step 414). If the sign is the same for BS _j , then include the DL TPC command from BS _j in the TPC combination (step 416). If the signs are different, then the DL TPC command from BS _j is not included in the TPC combination (step 418).

In some communication systems such as some WCDMA systems, it may not be possible to use the change sign method of Figures 4A and 4B to send OoS signals to UEs, because some UEs may use DPCH pilots as phase references in their detectors . Such systems may use signaling procedures that recognize that a BS is free to transmit its DPCH pilots and/or TPC commands or other data elements in this regard at higher (or lower) power. For example, current WCDMA standards allow the transmission of DPCH pilots and TPC commands at different power levels, and these power offsets are defined by the two parameters PO3 for pilots and PO2 for commands.

A BS or other node can use these power offsets to transmit UL OoS signals in the DL in the following manner. If the UL is synchronous, the PO2 and PO3 levels may be set equal, for example, to a value equal to 0 dB relative to the data bits transmitted on the DPCH. If the UL is OoS, the PO2 level may be increased, eg, to a value of +3dB or +6dB or another suitable value, while the PO3 level remains unchanged. Of course, it will be understood that the PO3 level could alternatively be increased while the PO2 level remains the same, and that one level could even be decreased relative to the other, but that lowering might bring about other problems.

For the UE, what remains unchanged is the estimated power level offset between the DPCH pilot and the TPC command or other information elements included in the DL signal. Based on received signal amplitude or received signal power, this estimation can be done in several ways. In the example below, the PO2 signal amplitude changes by +3dB, and the detection process is similar to the above description.

The relationship between the DPCH pilot channel and the TPC command channel is as follows:

${\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; TPC</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; TPC</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; TPC</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; DPCH</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; DPCH</span>}}$

where i=1,...,N _p is the number of radio paths from BS _j in the active set (i.e., the number of signal fingers used in the Rake or G-Rake part of the receiver), where j= 1, ..., N _BS , and γ are expressed as follows:

${\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; TPC</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; DPCH</span>}}<span\; class="notranslate">\; =</span>\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}$

and is a real-valued scaling factor, the same for all radio paths from a particular BS, but different for different BSs. Also, _uTPC,J is a TPC command from BS _j .

If the UL to BS _j is synchronous, the scaling factor ${\mathrm{\&gamma;}}_j^{\mathrm{TPC}/\mathrm{DPCH}}=1.$ The UE may estimate γ using, for example, the above-described techniques that may be implemented in the control unit 262, assuming uTPC _,j = 1 in the channel estimation process for TPC channel estimation. In general, the estimated value of γ will be less than 1 when the UL is synchronous, since the TPC commands will be +1 or "up" and -1 or "down" in the synchronous case.

If the UL to BS _j is not synchronized, then ${\mathrm{\&gamma;}}_j^{\mathrm{TPC}/\mathrm{DPCH}}=\sqrt{2}$ The UE estimates the scaling factor γ as before, and the estimated value of γ should be approximately , because the TPC "up" command or +1 is always or almost always transmitted from BS _j when UL is OoS.

The UE then only needs to determine that its γ estimate is approximately Or less than this value to detect whether its UL is synchronous or OoS. It will be appreciated that changing the sign of the "up" and "down" commands in this example does not change the basic principle of operation.

FIG. 4C shows an exemplary OoS detection method, which includes the step of estimating the scaling factor γ _j ^TPC/DPCH for each receiving slot and each BS in the active set (step 422). If the estimate of the scaling factor [gamma] is less than threshold A, the UE uses the DL TPC commands from BS _j in forming its TPC command combination (steps 424, 426). If the estimate of the scaling factor γ is greater than threshold A, the UE does not include the DL TPC command from BSj in its TPC command combination (steps 424, 428).

Threshold A can be optimized in advance and varies with the number of TPC commands and DPCH pilots in the slot, etc. The threshold A can also vary with the spreading factor. Additionally, hysteresis may be introduced in the detection process. For example, the UL may detect OoS when the gamma estimate is greater than about 0.7, and then only detect sync when the gamma estimate drops to less than about 0.3.

Applicants have recognized yet another way to let a UE know that its UL is OoS without any modification or additional control signaling. When a Node B in SHO loses UL synchronization, the node generally fixes its DL power at some special level, this is because the node cannot "hear" the TPC commands transmitted from the UE in the UL when the UL is OoS, And the node initiates the resynchronization process, for example, the node sends a TPC command requesting "up, up, . . . ". Thus, and as shown in Figure 5, the control unit 262 or another suitable part of the UE may compare the newer TPC commands received from each Node B participating in the SHO with the older TPC commands, e.g. The ratio between TPC commands during the latest time slot and the previous time slot is calculated (step 502). If the output of any of these comparisons is above a threshold (step 504), the Node B corresponding to that comparison may primarily send an "up" command, and this may be taken as a sign that the UL may be OoS (step 506). In response to the indication, the UE receives a SIR for DL measurements corresponding to the Node-B (step 508). If the UL is OoS, the DL power will be constant, at least compared to the SIR from a Node B with UL synchronization, and the received SIR for that link will be roughly constant, and thus in compliance with the UE's TPC commands. An OoS determination can then be made by determining, for example, the SIR change of the DL, and comparing the change to the transmitted TPC command of the UE (step 510). If the change is below the threshold, indicating that the DL is not operating according to the UE's TPC command, OoS is detected (step 512).

It is also possible to note the difference between the SIRs of consecutive slots and correlate the difference to the TPC commands transmitted in the uplink. If the DL follows the transmitted TPC command, the pattern of SIR changes shall follow the pattern of the TPC command. For example, if the pattern of the TPC command transmitted on the uplink is ..., 1, -1, -1, 1, 1, ..., then theoretically the pattern of SIR change should be ..., SIR+ 1. SIR, SIR-1, SIR, SIR+1, . . . It will be appreciated that the SIR is the value just prior to the first TPC command shown in this example. However, due to the fading channel and different path loss values of the downlink, the variation pattern of SIR may not exactly repeat the TPC command pattern. Therefore, it may be advantageous to pass the SIR variation pattern through a filter and provide the filter output to a correlator which will compare the filtered variation pattern with the expected pattern. A comparator would compare the correlation output to an appropriate threshold, and if the correlation exceeds the threshold, the DL is following the transmitted TPC command; otherwise, an OoS condition is determined. A conventional finite impulse response (FIR) or infinite impulse response (IIR) filter with a time constant of about 20-100 ms (i.e., a few frames) and a suitable threshold, which can be determined empirically, can be easily passed by a processor such as processor 262. Processor implementation suitable for programming.

It will be appreciated that the above-described process is repeated as necessary, for example, in response to time-varying characteristics of the communication channel between the transmitter and receiver. For ease of understanding, many aspects of Applicants' invention have been described in terms of sequences of acts that can be performed, for example, by elements of a programmable computer system. It will be appreciated that the various acts may be performed by special purpose circuitry (eg, discrete logic gates or application specific integrated circuits interconnected to perform the specified functions), by program instructions executed by one or more processors, or by a combination of both.

Additionally, Applicants' invention may otherwise be deemed entirely embodied within any form of computer-readable storage medium having stored therein a suitable set of instructions for use in, for example, a computer-based system, a system containing a processor, or from which instructions can be retrieved. The instruction execution system, equipment or device of other systems that execute the instruction are used or used in conjunction with it. As used herein, a "computer-readable medium" may be any component that can contain, store, communicate, propagate, or deliver a program for use by or in connection with an instruction execution system, apparatus, or device. A computer readable medium can be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, device, apparatus, or propagation medium. More specific examples (non-exhaustive list) of computer readable media include electrical connections having one or more wires, portable computer disks, random access memory (RAM), read only memory (ROM), erasable programmable Read Only Memory (EPROM or Flash) and Optical Fiber.

Accordingly, the present invention may be embodied in many different forms, not all of which are described above, and all such forms are intended to be within the scope of the present invention. As with each of the various aspects of the invention, any such form may be referred to as "logic configured to" perform a described action, or as "logic" that performs a described action.

It is to be emphasized that the term "comprising" when used in this application indicates the presence of stated features, integers, steps or components, but does not exclude the presence or addition of one or more other features, integers, steps, components or combinations thereof.

The particular embodiments described above are illustrative only, and should not be considered restrictive in any way. The scope of the present invention is determined by the appended claims and all changes and equivalents within the range of the claims are intended to be embraced therein.

Claims (19)

1. A method of indicating that a first communication link is out of synchronization (OoS), comprising the step of including an OoS signal in a signal transmitted over a second communication link, wherein said OoS signal includes a power level offset between information elements included in said signal sent over said second communication link, Or wherein the OoS signal includes at least one symbol indicating whether the first link is synchronous or OoS, and wherein the OoS signal includes a sign change of the at least one symbol. 2. The method of claim 1, wherein the information elements are pilot symbols and transmit power control commands transmitted on a dedicated physical channel. 3. The method of claim 1, wherein the at least one symbol is a pilot symbol transmitted on a dedicated physical channel (DPCH). 4. The method of claim 3, wherein the DPCH pilot symbols have the same sign as pilot symbols transmitted on a common pilot channel when the first communication link is synchronized. 5. A method of determining that a first communication link is out of sync (OoS), comprising the step of detecting an OoS signal in a signal received on a second communication link, wherein said OoS signal comprises a power level offset between information elements comprised in signals received on said second communication link, Or wherein the OoS signal includes at least one symbol indicating whether the first communication link is synchronous or OoS, and wherein the OoS signal includes a sign change of the at least one symbol. 6. The method of claim 5, wherein the information elements are pilot symbols and transmit power control commands received on a dedicated physical channel. 7. The method of claim 5, wherein the at least one symbol is a pilot symbol received on a dedicated physical channel (DPCH). 8. The method of claim 7, wherein when the first communication link is synchronized, the sign of the DPCH pilot symbols is the same as the sign of the pilot symbols transmitted on the Common Pilot Channel (CPICH) The same, and the method further includes the step of comparing the positive and negative signs of the above-mentioned DPCH pilot symbols with the positive and negative signs of the CPICH pilot symbols. 9. The method of any one of claims 5-8, wherein if it is determined that the first communication link is synchronous, then including in determining the transmit power level on the first communication link from the transmit power control commands for a second communication link, and if it is determined that said first communication link is OoS, excluding commands from said second communication link in determining said transmit power level on said first communication link Transmit power control commands for the communication link. 10. A communication node adapted to transmit and receive electromagnetic signals, comprising: a detector adapted to determine whether the first receive link is synchronized; and means, responsive to said detector, adapted to include an out-of-sync (OoS) signal in a signal transmitted on the second link, wherein said OoS signal comprises a power level offset between information elements transmitted by said node on said second link, Or wherein the OoS signal includes at least one symbol indicating whether the first receive link is synchronous or OoS, and wherein the OoS signal includes a sign change of the at least one symbol. 11. The communication node of claim 10, wherein the information elements are pilot symbols and transmit power control commands transmitted on a dedicated physical channel. 12. The communication node of claim 10, wherein the at least one symbol is a pilot symbol transmitted by the node on a dedicated physical channel (DPCH). 13. The communication node of claim 12, wherein when the first receive link is synchronized, the sign of the DPCH pilot symbols is the same as the sign of the pilot symbols transmitted on the common pilot channel. 14. A communication node according to any of claims 10-13, wherein the communication node is a base station in a telecommunication system. 15. A communication terminal suitable for transmitting and receiving electromagnetic signals, comprising: means adapted to recover information from the electromagnetic signal received on the first link, the information comprising pilot symbols and transmit power control (TPC) commands; a control unit adapted to control the power level of the electromagnetic signal transmitted by the terminal on the second link based on the TPC command; and a detector adapted to monitor the recovered information for out-of-sync (OoS) signals in signals received on said first link, wherein said OoS signal includes a power level offset between information elements included in signals received on said first link, Or wherein the OoS signal includes at least one symbol indicating whether the second link is synchronous or OoS, and wherein the OoS signal includes a sign change of the at least one symbol. 16. The communication terminal of claim 15, wherein the information elements are pilot symbols and transmit power control commands transmitted on a dedicated physical channel. 17. The communication terminal of claim 15, wherein the at least one symbol is a pilot symbol received by the terminal on a dedicated physical channel (DPCH). 18. The communication terminal according to claim 17, wherein when the second link is synchronized, the sign of the DPCH pilot symbol is consistent with the sign of the pilot symbol received on the common pilot channel (CPICH) The same, and the terminal further includes a comparator adapted to compare the sign of the DPCH pilot symbol with the sign of the CPICH pilot symbol. 19. The communication terminal according to any one of claims 15-18, wherein if said at least one data bit indicates that said first link is synchronous, then determining the transmit power level on said second link Including a transmit power control command from said node in said node, and if said at least one data bit indicates that said first link is OoS, not including in determining said transmit power level on said second link A transmit power control command from the node.