WO2010057331A1

WO2010057331A1 - Method of and user equipment for optimizing hysteresis value for handover

Info

Publication number: WO2010057331A1
Application number: PCT/CN2008/001887
Authority: WO
Inventors: Jie Mao; Jiuhui Du; Bin Xu
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2008-11-20
Filing date: 2008-11-20
Publication date: 2010-05-27
Also published as: WO2010057331A8

Abstract

A method of optimizing a hysteresis value in a User Equipment (UE) utilized for a handover of the UE in a cellular radio telecommunications network is provided. The method comprises receiving a hysteresis value for the UE configured by a controller in the cellular radio telecommunications network (302, 502), determining a movement speed of the UE (304, 504), modifying the hysteresis value based on the determined movement speed (306, 506), and using the modified hysteresis value for the handover of the UE (308, 508). A UE (206) configured to carry out the above method and a cellular radio telecommunications network comprising at least the UE are also provided.

Description

METHOD OF AND USER EQUIPMENT FOR OPTIMIZING HYSTERESIS VALUE FOR HANDOVER

TECHNICAL FIELD The present invention generally relates to a cellular radio telecommunications network and, more particularly, to the optimization of a hysteresis value in a User Equipment (UE) utilized for a handover of the UE based on movement speed of the UE.

BACKGROUND

In a cellular radio telecommunications network, as a UE moves from a source cell to a neighbor cell, a handover will be triggered by the UE measurement of the neighbor cell. For example, if the UE measurement indicates that the signal level of the neighbor cell is above a handover threshold, a handover from the source cell to the neighbor cell can be performed.

However, since the signal level of the neighbor cell is always fluctuating, as shown in Fig. IA, the signal level of the neighbor cell may be above the handover threshold for a short while and then may be below the handover threshold for a short while, and then may be above the handover threshold for a short while again, and so on. In this case, the UE will handover back and forth in a fairly rapid manner between two or more cells. Fig. IA shows six unnecessary handovers before the UE finally handovers to the neighbor cell. The phenomenon is known as a handover oscillation or a ping-pong effect, and has many adverse effects in the cellular network. On one hand, temporary muting is experienced by the subscriber during each handover, and this adversely affects voice quality when it is repeatedly experienced in a short period of time. On the other hand, the ping-pong effect increases system overhead and often results in a call to the UE being dropped.

The existing cellular radio telecommunications networks address the handover oscillation problem by introducing hysteresis into a handover decision. In particular, the network can configure a value for "hysteresis" time which is a parameter of a UE.

In the case of use of the "hysteresis" time in the example shown in Fig. IA₅ a handover is not performed immediately the signal level of the neighbor cell becomes above the handover threshold. Only when the signal level of the neighbor cell is above the handover threshold for the "hysteresis" time is a handover performed. In this way, as shown in Fig. IB, only one handover happens by means of the "hysteresis" time.

However, the above solution still has a number of limitations and can be problematic in the context of particular cases. Specifically, all UEs in the same cell use the same hysteresis value in the existing solutions, but one hysteresis value generally works best for a UE moving at a particular speed. For a UE moving at a speed much higher than the particular speed, a handover should be triggered with a much shorter delay after the signal quality of the neighbor cell reaches some handover threshold. Otherwise, the connection may be lost due to the fact that the channel quality of the source cell becomes bad rapidly. As shown in Fig. 1C, if a UE moves at a speed much higher than the particular speed, the "hysteresis" time is so long that the call will be dropped. Therefore, for a UE moving at a speed higher than the particular speed, a shorter hysteresis value is needed, whereas for a UE moving at a speed lower than the particular speed, a longer hysteresis value is needed to prevent unnecessary handovers.

Further, even if a network could configure different hysteresis values for different UEs in a cell, because some of the UEs are changing their movement speeds from time to time, it is impossible for the network to reconfigure the hysteresis value for each UE after the UE movement speed changes.

For example, for a cell covering a railway station, some UEs in the cell may move very fast due to the fact that they are in a train that doesn't stop. But other UEs may be stationary. It will be impossible for a network to reconfigure the hysteresis values to guarantee all the UEs in the cell trigger handover properly. Accordingly, it would be desirable to provide a method of and a

UE for improving a handover of the UE based on movement speed of the UE in a cellular radio telecommunications network.

SUMMARY Therefore, it is the object of the present invention to obviate or mitigate at least some of the above limitations by providing a method of and a UE for improving a handover of the UE based on movement speed of the UE in a cellular radio telecommunications network.

In one aspect of the invention, a method of optimizing a hysteresis value in a UE utilized for a handover of the UE in a cellular radio telecommunications network is provided. The method comprises receiving a hysteresis value for the UE configured by a controller in the cellular radio telecommunications network, determining a movement speed of the UE, modifying the hysteresis value based on the determined movement speed, and using the modified hysteresis value for the handover of the UE.

In an embodiment, the method comprises modifying the hysteresis value based on the determined movement speed by adding an offset to the hysteresis value based on the determined movement speed. Preferably, the offset will be negative if the determined movement speed is above a particular movement speed, and the offset will be positive if the determined movement speed is below the particular movement speed, and the offset will be zero if the determined movement speed is equal to the particular movement speed.

Preferably, the offset, before being added to the hysteresis value, is further configured by a mapping strategy to map the determined movement speed to the offset provided by the controller in the cellular radio telecommunications network. Preferably, the mapping strategy is to weight the offset by a weight factor provided by the controller in the cellular radio telecommunications network. More preferably, different offsets correspond to different weight factors provided by the controller in the cellular radio telecommunications network.

In an embodiment of the method, the cellular radio telecommunications network is a cellular radio telecommunications network where a Synchronisation Shift (SS) command is available. Preferably, determining a movement speed of the UE is by means of the SS command. More preferably, the movement speed of the UE is directly related to an absolute value of accumulation of the SS commands in a time period. The cellular radio telecommunications network where the SS command is available is one of a Global System for Mobile communications (GSM) network, a Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) network, and a Long Term Evolution (LTE) network.

In an embodiment of the method, determining a movement speed of the UE is by means of a received signal strength of the UE in an environment including a vast flat area. Preferably, the environment is one of sea, prairie, and desert. More preferably, the movement speed of the UE is directly related to an absolute value of a rate of change of the received signal strength of the UE in a time period. The cellular radio telecommunications network is one of a GSM network, a TD-SCDMA network, an LTE network, a Wideband Code Division Multiple Access (WCDMA) network, and a Code Division Multiple Access 2000 (CDMA2000) network. Preferably, the maximum among the absolute values of the rates of change of the UE's received signal strengths is selected as the absolute value of a rate of change of the received signal strength of the UE in the time period for the WCDMA network or the CDMA2000 network. In an embodiment of the method, determining a movement speed of the UE is by means of a Doppler effect of a carrier of a received signal of the UE. Preferably, the movement speed of the UE is directly related to an absolute value of a shift ratio of the carrier frequency of the received signal of the UE. The cellular radio telecommunications network is one of a GSM network, a TD-SCDMA network, an LTE network, a WCDMA network, and a CDMA2000 network.

In another aspect of the invention, a UE configured to optimize a hysteresis value utilized for a handover of the UE in a cellular radio telecommunications network is provided. The UE comprises one or more processing circuits configured to receive a hysteresis value for the UE configured by a controller in the cellular radio telecommunications network, determine a movement speed of the UE, modify the hysteresis value based on the determined movement speed, and use the modified hysteresis value for the handover of the UE.

In an embodiment, the one or more processing circuits are configured to modify the hysteresis value based on the determined movement speed by adding an offset to the hysteresis value based on the determined movement speed. Preferably, the offset will be negative if the determined movement speed is above a particular movement speed, and the offset will be positive if the determined movement speed is below the particular movement speed, and the offset will be zero if the determined movement speed is equal to the particular movement speed.

In an embodiment of the UE, the cellular radio telecommunications network is a cellular radio telecommunications network where an SS command is available. Preferably, the one or more processing circuits are configured to determine a movement speed of the UE by means of the SS command. More preferably, the movement speed of the UE is directly related to an absolute value of accumulation of the SS commands in a time period. The cellular radio telecommunications network where the SS command is available is one of a GSM network, a TD-SCDMA network, and an LTE network.

In an embodiment of the UE, the one or more processing circuits are configured to determine a movement speed of the UE by means of a received signal strength of the UE in an environment including a vast flat area. Preferably, the environment is one of sea, prairie, and desert. More preferably, the movement speed of the UE is directly related to an absolute value of a rate of change of the received signal strength of the UE in a time period. The cellular radio telecommunications network is one of a GSM network, a TD-SCDMA network, an LTE network, a WCDMA network, and a CDMA2000 network. Preferably, the maximum among the absolute values of the rates of change of the UE' s received signal strengths is selected as the absolute value of a rate of change of the received signal strength of the UE in the time period for the WCDMA network or the CDMA2000 network.

In an embodiment of the UE, the one or more processing circuits are configured to determine a movement speed of the UE by means of a Doppler effect of a carrier of a received signal of the UE. Preferably, the movement speed of the UE is directly related to an absolute value of a shift ratio of the carrier frequency of the received signal of the UE. The cellular radio telecommunications network is one of a GSM network, a TD-SCDMA network, an LTE network, a WCDMA network, and a CDMA2000 network.

In yet another aspect of the invention, a cellular radio telecommunications network comprising at least a UE as stated above is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the accompanying drawings, in which:

Fig. I A schematically illustrates a ping-pong effect in a cellular radio telecommunications network; Fig. I B schematically illustrates the elimination of the ping-pong effect shown in Fig. IA by introducing "hysteresis" time;

Fig. 1 C schematically illustrates a case where the "hysteresis" time is so long for a UE moving at a very high speed that the call will be dropped; Fig. 2 is a schematic block diagram of a portion of a

TD-SCDMA network in which one embodiment of the present invention is implemented;

Fig. 3 is a flow chart illustrating a method of optimizing a hysteresis value of a UE for its handover in the TD-SCDMA network in accordance with an embodiment of the present invention;

Fig. 4A schematically illustrates SS commands sent to a UE every sub-frame in a TD-SCDMA network;

Figs. 4B and 4C schematically illustrate a relationship between the movement speed of a UE and an absolute value of accumulation of SS commands in a time period;

Fig. 5 is a flow chart illustrating a method of optimizing a hysteresis value of a UE for its handover in the TD-SCDMA network without utilizing an SS command, in accordance with an alternate embodiment of the present invention; and

Fig 6 is a flow chart illustrating a method of optimizing the hysteresis value of a UE for its handover in the TD-SCDMA network by means of the Doppler effect, in accordance with a further embodiment of the present invention.

Corresponding reference characters indicate corresponding components throughout the several views of the drawings.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the invention and illustrate the best mode of the practicing the invention. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the invention and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims. Throughout the description and claims of this specification, the terminology "UE" includes but is not limited to a mobile station, a mobile subscriber unit, a mobile TV client, a pager, a cellular telephone, a Personal Digital Assistant (PDA), a smart phone, a text messaging device, a network interface card, a notebook computer, or any other type of user device capable of operating in a wireless environment.

Fig. 2 is a schematic block diagram of a portion 200 of a TD-SCDMA network in which one embodiment of the present invention is implemented. The portion 200 comprises a Radio Network Controller (RNC) 202, a Node-B 204, and a UE 206 including one or more processing circuits 208. The one or more processing circuits 208 are configured to optimize a hysteresis value of the UE 206 for its handover in the TD-SCDMA network.

It should be understood that the one or more processing circuits 208 may comprise hardware, software, or any combination thereof. In at least one embodiment, the one or more processing circuits 208 include one or more general or special purpose microprocessor and/or digital signal processor that are programmed to carry out operations corresponding to the method steps as discussed below. Such instructions may be embodied as one or more computer programs comprising stored program instructions in a storage element (e. g. , memory).

The optimization process will be described below in conjunction with Fig. 3. Referring to Fig. 3, there is shown a flow chart 300 illustrating a method of optimizing the hysteresis value of the UE 206 for its handover in the TD-SCDMA network in accordance with an embodiment of the present invention. It should be understood that the method is not necessarily limited to the illustrated sequence, and some steps may be performed together or otherwise in an interrelated fashion.

The method begins with step 302 in which the UE 206 receives a hysteresis value via the Node-B 204 from the RNC 202. In this way, the RNC 202 can configure a hysteresis value for the UE 206. In step 304, the UE 206 determines its movement speed by means of an SS command sent by the Node-B 204.

Turning to Fig. 4A, in a TD-SCDMA network, an SS command from a Node-B will be sent to a UE every sub-frame. If the UE is moving away from the Node-B, the Node-B will send "positive" SS commands continuously to order the UE to start to send uplink transmission earlier. If the UE is moving toward the Node-B, the Node-B will send "negative" SS commands continuously. As shown in Figs. 4B and 4C, the higher an absolute value of accumulation of SS commands in a time period is, the higher the movement speed of the UE is. It can be seen from above that the movement speed of the UE is directly related to the absolute value of accumulation of SS commands in a time period. Therefore, the movement speed of the UE can be given by:

vug = /XII(SS commands)|) Eq. (1)

where v_UE is the movement speed of the UE, I represents the summation of all the SS commands in a time period, and /X) is a function which is directly related to the absolute value of accumulation of SS commands in the time period. As an embodiment of Eq. (1) in practice, the function /X) can be taken as a positive constant. Then, Eq. (1) reduces to the following equation:

vuE = KiH(SS commands)! Eq. (2)

where Ki is a positive constant.

Referring back to Fig. 3, in the same manner as above, the UE

206 can determine its movement speed vu_{E 20ό} by means of Eq. (2). In step 306, the UE 206 modifies the hysteresis value configured by the RNC 202 by adding an offset to the hysteresis value based on its movement speed VUE 206 as follows:

Hmodified ⁼ H_oonf_lgured+H₀ff_Set Eq. (3)

where H_modified is the modified hysteresis value for the UE 206, Hconfigured is a hysteresis value configured by the RNC 202, and H_Off_Set is a hysteresis offset added by the UE 206.

Since H_conf_lgured usually works best for a particular movement speed Vo, H offset can be taken as zero for the particular movement speed Vo. Further, for a UE moving at a speed higher than Vo, a negative value of H_Off_Set should be added to H_0Onfigured so that a handover can be triggered with a shorter delay after the signal quality of the neighbor cell reaches some handover threshold, thus reducing the probability of dropping the call. The higher the movement speed of the UE, the bigger the absolute value of H_off_Set should be. On the other hand, for a UE moving at a speed lower than Vo, a positive value of H₀ff_set should be added to H_config_Ured so that a handover can be triggered with a longer delay after the signal quality of the neighbor cell reaches some handover threshold, thus prevent a ping-pong effect. The lower the movement speed of the UE, the bigger the absolute value of H_0ffset should be. Thus, H_Offset can be represented by:

Hoffsβt = g(Vo-vrø) Eq. (4)

where g() is a function which is directly related to the deference between Vo and V_UE- Also, as an embodiment of Eq. (4) in practice, the function g() can be taken as a positive constant. Then, Eq. (4) reduces to the following equation:

Hoffsβt = L(VO-VUE) Eq. (5)

where L is a positive constant.

Substituting Eq. (2) into Eq. (5) and then substituting the resulting Eq. (5) into Eq. (3) yield:

H_mOdi_fied ⁼ ( H_configu_red+LVo ) -LKiIX(SS commands)| Eq. (6)

Since H_oonfig_Ured, L, Ki, and Vo can be configured by the RNC

202, Hmodi_fied can be calculated by means of Eq. (6) upon knowing the absolute value of accumulation of SS commands in a time period.

Furthermore, the RNC 202 doesn't configure V₀ for the UE 206 if

V₀=O. In addition, H_offset can also be weighted by a weight factor provided by the RNC 202. Further, different values for H_Off_set can be weighted by different factors provided by the RNC 202. More generally speaking, the RNC 202 can configure a mapping strategy as desired for the UE 206 to map the current movement speed to the hysteresis offset value. The weight factor(s) or the mapping strategy from the RNC 202 may be sent to the UE 206 alone or along with the configured hysteresis value. This can realize the control of the hysteresis offset value by the TD-SCDMA network, thus enhancing control flexibility.

In step 308, the UE 206 uses the modified hysteresis value Hmodified as a new hysteresis value for its handover in the TD-SCDMA network.

In this way, the UE 206 can dynamically modify the hysteresis value for its handover in the TD-SCDMA network based on its movement speed, thus reducing the probability of the call and preventing unnecessary handovers further. As a result, the robustness of the TD-SCDMA network is improved.

The method illustrated in Fig. 3 applies not only to a TD-SCDMA network, but also to a GSM network, an LTE network, or any other cellular radio telecommunications network where an SS command is available. In particular, for a GSM network, the method of Fig. 3 is performed in the same way except that a Base Station

Controller (BSC) is substituted for the RNC 202, a Base Transceiver Station (BTS) for the Node-B 204, and a Mobile Station (MS) for the

UE 206. For an LTE network, the method of Fig. 3 is performed in the same way except that an evolved Node-B (eNode-B) is substituted for the RNC 202 and the Node-B 204.

Moreover, the method illustrated in Fig. 3 is applicable to various environments including indoor, outdoor, countryside, urban, suburb, sea, prairie, desert, stationary, moving, etc.

However, it is possible that the UE 206 determines its movement speed without utilizing an SS command. Fig 5 is a flow chart 500 illustrating a method of optimizing the hysteresis value of the UE 206 for its handover in the TD-SCDMA network without utilizing an SS command, in accordance with an alternate embodiment of the present invention. It should be understood that the method is not necessarily limited to the illustrated sequence, and some steps may be performed together or otherwise in an interrelated fashion.

Referring to Fig. 5, the UE 206 receives a hysteresis value via the Node-B 204 from the RNC 202 in step 502. In this way, the RNC 202 can configure a hysteresis value for the UE 206. In step 504, the UE 206 determines its movement speed by means of its received signal strength rather than an SS command.

The received signal strength of the UE 206 is affected by various factors. Even when the UE 206 is moving at a low speed, its received signal strength may vary much, especially in an urban environment. However, for an environment including a vast flat area, such as sea, prairie, and desert, where there is scarcely an obstacle to signal propagation, a rate of change of the received signal strength of the UE 206 is mainly dependent on its movement speed. In general, the higher an absolute value of the rate of change of the received signal strength of the UE 206 is, the higher the movement speed of the UE 206 is. Thus, the movement speed of the UE 206 is directly related to the absolute value of the rate of change of the received signal strength of the UE 206. This relationship can be formulated as:

vrø =/,(|ΔRSS|) Eq. (7)

where VUE is the movement speed of the UE 206, ΔRSS represents the rate of change of the received signal strength of the UE 206 in a time period, and f₂Q is a function which is directly related to an absolute value of the rate of change of the received signal strength of the UE 206 in the time period. As an embodiment of Eq. (7) in practice, the function /^O can be taken as a positive constant. Then, Eq. (7) reduces to the following equation:

vrø = K₂|ΔRSS| Eq. (8)

where K₂ is a positive constant.

As stated above, the UE 206 can determine its movement speed by means of Eq. (8). In step 506, the UE 206 modifies the hysteresis value configured by the RNC 202 by adding an offset to the hysteresis value based on its movement speed. The deduction process of Step 506 is the same as that of step 306. Finally, Substituting Eq. (8) into Eq. (5) and then substituting the resulting Eq. (5) into Eq. (3) yield:

H_modified = ( H_conflgured+LV₀ ) -LK₂!ΔRSS| Eq. (9)

Since H_0Onfigured, L₅ K₂, and Vo can be configured by the RNC 202, Hmodified can be calculated by means of Eq. (9) upon knowing the absolute value of the rate of change of the received signal strength of the UE 206 in the time period. Furthermore, the RNC 202 doesn't configure V₀ for the UE 206 if V₀=O.

Again, H₀ff_set can also be weighted by a weight factor provided by the RNC 202. Further, different values for H_OffSet can be weighted by different factors provided by the RNC 202. More generally speaking, the RNC 202 can configure a mapping strategy as desired for the UE 206 to map the current movement speed to the hysteresis offset value. The weight factor(s) or the mapping strategy from the RNC 202 may be sent to the UE 206 alone or along with the configured hysteresis value. This can realize the control of the hysteresis offset by the TD-SCDMA network, thus enhancing control flexibility. In step 508, the UE 206 uses the modified hysteresis value H_modi_fi_ed as a new hysteresis value for its handover in the TD-SCDMA network.

Also in this way, the UE 206 can dynamically modify the hysteresis value for its handover in the TD-SCDMA network based on its movement speed, thus reducing the probability of the call and preventing unnecessary handovers further. As a result, the robustness of the TD-SCDMA network is improved.

The method illustrated in Fig. 5 applies to various cellular radio telecommunications networks including both a cellular radio telecommunications networks where an SS command is available, e.g. a GSM network, a TD-SCDMA network and an LTE network, and a cellular radio telecommunications networks where an SS command is not available, e.g. a WCDMA network and a CDMA2000 network. In particular, the method of Fig. 5 is primarily applicable to an environment including a vast flat area, such as sea, prairie, and desert, where there is scarcely an obstacle to signal propagation.

Note that in the case that the method of Fig. 5 is utilized in a WCDMA network or a CDMA2000 network, since a UE may receive multiple signal strengths from neighbor cells for its handover, the maximum among the absolute values of the rates of change of the UE's received signal strengths can be selected as the term |ΔRSS| in Eq. (9) in each calculation. The rest remains the same.

In addition to the preceding, the UE 206 can determine its movement speed by means of a Doppler effect of a carrier of its received signal. Fig 6 is a flow chart 600 illustrating a method of optimizing the hysteresis value of the UE 206 for its handover in the

TD-SCDMA network by means of the Doppler effect, in accordance with a further embodiment of the present invention. It should be understood that the method is not necessarily limited to the illustrated sequence, and some steps may be performed together or otherwise in an interrelated fashion. Referring to Fig. 6, the UE 206 receives a hysteresis value via the Node-B 204 from the RNC 202 in step 602. In this way, the RNC

202 can configure a hysteresis value for the UE 206. In step 604, the

UE 206 determines its movement speed by means of the Doppler effect of a carrier of its received signal.

The carrier of the received signal of the UE 206 moving at a particular speed has a frequency shift due to the Doppler effect. In general, the higher an absolute value of the shift ratio of the carrier frequency of the received signal of the UE 206 is, the higher the movement speed of the UE 206 is. Thus, the movement speed of the UE 206 is directly related to the absolute value of the shift ratio of the carrier frequency of the received signal of the UE 206. This relationship can be formulated as:

f, - f_B

VUE = fs( I) Eq. (10)

where V_UE is the movement speed of the UE 206, fo is a nominal carrier frequency of the signal transmitted by the Node-B 204, fd is a carrier frequency of the received signal of the UE 206, and /X) is a function which is directly related to an absolute value of the shift ratio of the carrier frequency of the received signal of the UE 206. As an embodiment of Eq. (10) in practice, the function /j() can be taken as a positive constant. Then, Eq. (10) reduces to the following equation:

VWT = K₃I ^H Eq. (1 1)

where K₃ is a positive constant.

As stated above, the UE 206 can determine its movement speed by means of Eq. (1 1). In step 606, the UE 206 modifies the hysteresis value configured by the RNC 202 by adding an offset to the hysteresis value based on its movement speed. The deduction process of Step 606 is the same as that of step 306. Finally, Substituting Eq. (1 1) into Eq. (5) and then substituting the resulting Eq. (5) into Eq. (3) yield:

f - f

Hmodified ^~ ( H_COnfigured⁺LVo ) -LK3 Eq. (12)

Since H_configured, L, K3, and Vo can be configured by the RNC 202, and the value of f₀ can be sent to the UE 206 by the Node-B 204, Hmodified can be calculated by means of Eq. (12) upon knowing the absolute value of the shift ratio of the carrier frequency of the received signal of the UE 206. Furthermore, the RNC 202 doesn't configure V₀ for the UE 206 if V₀=O. Again, H₀ff_set can also be weighted by a weight factor provided by the RNC 202. Further, different values for H_OffSet can be weighted by different factors provided by the RNC 202. More generally speaking, the RNC 202 can configure a mapping strategy as desired for the UE 206 to map the current movement speed to the hysteresis offset value. The weight factor(s) or the mapping strategy from the RNC 202 may be sent to the UE 206 alone or along with the configured hysteresis value. This can realize the control of the hysteresis offset by the TD-SCDMA network, thus enhancing control flexibility. In step 608, the UE 206 uses the modified hysteresis value

Hmodified as a new hysteresis value for its handover in the TD-SCDMA network.

The method illustrated in Fig. 6 applies to various cellular radio telecommunications networks including a GSM network, a TD-SCDMA network, an LTE network, a WCDMA network, a CDMA2000 network, etc.

Moreover, the method illustrated in Fig. 6 is applicable to various environments including indoor, outdoor, countryside, urban, suburb, sea, prairie, desert, stationary, moving, etc.

Throughout the description and claims of this specification, the words "comprise", "include" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

It will be understood that the foregoing description of the embodiments of the invention has been presented for purposes of illustration and description. This description is not exhaustive and does not limit the claimed invention to the precise forms disclosed.

Modifications and variations are possible in light of the above description or may be acquired from practicing the invention. The claims and their equivalents define the scope of the invention.

Claims

1. A method of optimizing a hysteresis value in a User Equipment (UE) utilized for a handover of the UE in a cellular radio telecommunications network, said method comprising the steps of: receiving a hysteresis value for the UE configured by a controller in the cellular radio telecommunications network (302, 502); determining a movement speed of the UE (304, 504); modifying the hysteresis value based on the determined movement speed (306, 506); and using the modified hysteresis value for the handover of the UE (308, 508).

2. The method of claim 1 , wherein modifying the hysteresis value based on the determined movement speed comprises adding an offset to the hysteresis value based on the determined movement speed.

3. The method of claim 2, wherein the offset will be negative if the determined movement speed is above a particular movement speed, and the offset will be positive if the determined movement speed is below the particular movement speed, and the offset will be zero if the determined movement speed is equal to the movement particular speed.

4. The method of any of claims 2 to 3, wherein the offset, before being added to the hysteresis value, is further configured by a mapping strategy to map the determined movement speed to the offset provided by the controller in the cellular radio telecommunications network.

5. The method of claim 4, wherein the mapping strategy is to weight the offset by a weight factor provided by the controller in the cellular radio telecommunications network.

6. The method of claim 5, wherein different offsets correspond to different weight factors provided by the controller in the cellular radio telecommunications network,

7. The method of any of claims 1 to 6, wherein the cellular radio telecommunications network is a cellular radio telecommunications network where a Synchronisation Shift (SS) command is available.

8. The method of claim 7, wherein determining a movement speed of the UE is by means of the SS command.

9. The method of claim 8, wherein the movement speed of the UE is directly related to an absolute value of accumulation of the SS commands in a time period.

10. The method of any of claims 7 to 9, wherein the cellular radio telecommunications network where the SS command is available is one of a Global System for Mobile communications (GSM) network, a Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) network, and a Long Term Evolution (LTE) network.

1 1. The method of any of claims 1 to 6, wherein determining a movement speed of the UE is by means of a received signal strength of the UE in an environment including a vast flat area.

12. The method of claim 1 1 , wherein the environment is one of sea, prairie, and desert.

13. The method of any of claims 1 1 to 12, wherein the movement speed of the UE is directly related to an absolute value of a rate of change of the received signal strength of the UE in a time period.

14. The method of any of claims 1 1 to 13, wherein the cellular radio telecommunications network is one of a Global System for Mobile communications (GSM) network, a Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) network, a Long Term Evolution (LTE) network, a Wideband Code Division Multiple Access (WCDMA) network, and a Code Division Multiple Access 2000 (CDMA2000) network.

15. The method of claim 14, wherein the maximum among the absolute values of the rates of change of the UE' s received signal strengths is selected as the absolute value of a rate of change of the received signal strength of the UE in the time period for the WCDMA network or the CDMA2000 network.

16. The method of any of claims 1 to 6, wherein determining a movement speed of the UE is by means of a Doppler effect of a carrier of a received signal of the UE.

17. The method of claim 16, wherein the movement speed of the

UE is directly related to an absolute value of a shift ratio of the carrier frequency of the received signal of the UE.

18. The method of any of claims 16 to 17, wherein the cellular radio telecommunications network is one of a Global System for Mobile communications (GSM) network, a Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) network, a Long Term Evolution (LTE) network, a Wideband Code Division Multiple Access (WCDMA) network, and a Code Division Multiple Access 2000 (CDMA2000) network.

19. A User Equipment (UE) configured to optimize a hysteresis value utilized for a handover of the UE in a cellular radio telecommunications network, said UE comprising one or more processing circuits (208) configured to : receive a hysteresis value for the UE configured by a controller in the cellular radio telecommunications network (302, 502); determine a movement speed of the UE (304, 504); modify the hysteresis value based on the determined movement speed (306, 506); and use the modified hysteresis value for the handover of the UE (308, 508).

20. The UE of claim 19, wherein the one or more processing circuits (208) are configured to modify the hysteresis value based on the determined movement speed by adding an offset to the hysteresis value based on the determined movement speed.

21 . The UE of claim 20, wherein the offset will be negative if the determined movement speed is above a particular movement speed, and the offset will be positive if the determined movement speed is below the particular movement speed, and the offset will be zero if the determined movement speed is equal to the movement particular speed.

22. The UE of any of claims 20 to 21 , wherein the offset, before being added to the hysteresis value, is further configured by a mapping strategy to map the determined movement speed to the offset provided by the controller in the cellular radio telecommunications network.

23. The UE of claim 22, wherein the mapping strategy is to weight the offset by a weight factor provided by the controller in the cellular radio telecommunications network.

24. The UE of claim 23, wherein different offsets correspond to different weight factors provided by the controller in the cellular radio telecommunications network.

25. The UE of any of claims 19 to 24, wherein the cellular radio telecommunications network is a cellular radio telecommunications network where a Synchronisation Shift (SS) command is available.

26. The UE of claim 25, wherein the one or more processing circuits (208) are configured to determine a movement speed of the UE by means of the SS command.

27. The UE of claim 26, wherein the movement speed of the UE is directly related to an absolute value of accumulation of the SS commands in a time period.

28. The UE of any of claims 25 to 27, wherein the cellular radio telecommunications network where the SS command is available is one of a Global System for Mobile communications (GSM) network, a Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) network, and a Long Term Evolution (LTE) network.

29. The UE of any of claims 19 to 24, wherein the one or more processing circuits (208) are configured to determine a movement speed of the UE by means of a received signal strength of the UE in an environment including a vast flat area.

30. The UE of claim 29, wherein the environment is one of sea, prairie, and desert.

31. The UE of any of claims 29 to 30, wherein the movement speed of the UE is directly related to an absolute value of a rate of change of the received signal strength of the UE in a time period.

32. The UE of any of claims 29 to 3 1 , wherein the cellular radio telecommunications network is one of a Global System for Mobile communications (GSM) network, a Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) network, a Long Term Evolution (LTE) network, a Wideband Code Division Multiple Access (WCDMA) network, and a Code Division Multiple Access 2000 (CDMA2000) network.

33. The UE of claim 32, wherein the maximum among the absolute values of the rates of change of the UE's received signal strengths is selected as the absolute value of a rate of change of the received signal strength of the UE in the time period for the WCDMA network or the CDMA2000 network.

34. The UE of any of claims 19 to 24, wherein the one or more processing circuits (208) are configured to determine a movement speed of the UE by means of a Doppler effect of a carrier of a received signal of the UE.

35. The UE of claim 34, wherein the movement speed of the UE is directly related to an absolute value of a shift ratio of the carrier frequency of the received signal of the UE.

36. The UE of any of claims 34 to 35, wherein the cellular radio telecommunications network is one of a Global System for Mobile communications (GSM) network, a Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) network, a Long Term Evolution (LTE) network, a Wideband Code Division Multiple Access (WCDMA) network, and a Code Division Multiple Access 2000 (CDMA2000) network.

37. A cellular radio telecommunications network comprising at least a User Equipment (UE) of any of claims 19 to 36.