Capacity-based compressed mode control method for inter-system handover in universal mobile telecommunication system

Abstract

The Inter-System handover is one of the key features in the third generation cellular systems. The compressed mode, with variable transmission gaps and power levels, is standardized to support the inter-frequency system handover. To minimize the use of system resources while maintaining the border-cell handover quality, a capacity-based compressed mode control method of the present invention is proposed. Considering the tradeoff between the capacity and the communication quality, the control method can adaptively manage the compressed mode operation based on the potential impacts on the capacity and the effectiveness of the compressed mode measurement. The present invention will improve the effectiveness and performance of the compressed mode operation.

Description

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing the relation of R_RSCP and distance in an embodiment according to the present invention.

FIG. 2 is a flow chart of the capacity-based compressed mode control method in an embodiment according to the present invention, which could be applied to the inter-system handover in UMTS.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The objects, features, advantages and others of the present invention will become more apparent from the following detailed description in which reference is made to some embodiments of the invention and the appended drawings:

The Received Signal Code Power (RSCP) is used for the handover between boundary unit systems and as a tool for triggering measurement. The decay speed of RSCP will approach to be linear, and, with this linear relationship, the RSCP ratio (R_RSCP) represents the distance required by the compressed mode. The definition of R_RSCP could be represented by the formula (1) as follows:

$\begin{array}{cc}{R}_{\mathrm{RSCP}}=\frac{T_{\mathrm{stop}}-\mathrm{RSCP}}{T_{\mathrm{stop}}-T_{\mathrm{ho}}}& \left(1\right)\end{array}$

wherein, T_stop is the threshold value for stopping the compressed mode; T_ho is the threshold value for triggering the handover boundary cell; and, RSCP is the receiving signal encoding power value.

FIG. 1 is a diagram showing the relation of R_RSCP and distance in an embodiment according to the present invention. R_RSCP is used to estimate the partially effective distance operated in the compressed mode. When R_RSCP is zero, the compressed mode will be stopped; and, when R_RSCP is one, it indicates the occurrence of handover to the Global System for Mobile Communication (GSM).

The capacity-based compressed mode control method in an embodiment according to the present invention is used for inter-system handover in UMTS, which employs the compressed mode by suspending the subscriber with lower priority to limit the power level, and when keeping appropriate handover priority, it could assure the capacity. The suspend factor Fi(n) in each frame is defined with the formula (2) as follows:

$\begin{array}{cc}{F}_i\left(n\right)=\frac{N_{\mathrm{meas},i}\left(n-1\right)}{{R_{\mathrm{RSCP},i}\left(n\right)}^k}\times R_{\mathrm{suspend},i}\left(n\right)& \left(2\right)\end{array}$

wherein, R_RSCP is a ratio guiding R_RSCP; N_meas(n−1) is a set of GSM samples after measurement; and, R_suspend is a record for the latest compressed mode, in which R_suspend is defined with the formula (3) as follows:

$R_{\mathrm{suspend},i}\left(n\right)=\{\begin{array}{c}a\left(\mathrm{suspending}\mathrm{record}\mathrm{for}\mathrm{latest}\mathrm{compressed}\mathrm{mode}\right)\\ \mathrm{na}\left(\mathrm{others}\right)\end{array}$

wherein, a is an integer, and n is a positive integer.

Referring to both the formula (2) and formula (3), the control method in an embodiment according to the present invention is preferred to suspend the subscriber near the base station (with smaller R_RSCP) or suspend the one with larger N_meas in GSM carrier wave measurement; in which, the factor k in the formula (2) defines the dominant grade for the distance, and the sorting mechanism will enforce each subscriber having the same N_meas/R_RSCP^k, and try to balance the measured set number with the effective distance operated in the compressed mode. When suspending the compressed mode last time, R_suspend is “a”; otherwise, R_suspend is “na” under other conditions. When the subscriber is just suspended, R_suspend will reduce the priority as 1/n, and is designed to prevent a subscriber from being continuously suspended. As well known in the art, the continuous suspending will delay the measurement performance, especially during handing emergent handover. Furthermore, the number of measurement by the RSSI is measured by arranging all subscribers being executed the compressed mode through one base station.

Next, the method will observe the transmission power of the base station, and configure a suspend threshold power P_thr, and the suspend threshold power P_thr is smaller than the maximum transmission power. If the estimation of the transmission power of the base station P_BSest does not exceed the suspend threshold power P_thr, the system will normally operate the compressed mode to assure the measurement performance. If the estimation of the transmission power of the base station P_BSest exceeds the suspend threshold power P_thr, the system will suspend the compressed mode for each subscriber based on the suspend factor F_i(+) following the priorities until the transmission power of the base station P_BSest is smaller than the suspend threshold power P_thr, and there is no entrance of subscriber with the new compressed mode.

FIG. 2 is a flow chart of the capacity-based compressed mode control method in an embodiment according to the present invention, wherein these steps are represented in numbers: in step S201, establishing a new connection; in step S203, calculating the suspend factor for the compressed mode subscriber; in step S205, indicating if the transmission power of the base station is not larger than the suspend threshold power, in step S207, entering the next frame; if, in step S205, the estimation of the transmission power of the base station is larger than the suspend threshold power, entering the step S209, in which a determination whether to suspend the compressed mode for the subscriber according to the priority for each subscriber is made; next, in step S211, if there is other subscriber entering the compressed mode, returning to the step S205; if there is no subscriber entering the compressed mode, entering the step S207 for the next frame; if entering the step S207, returning to the step S203 for re-calculating the suspend factor for each subscriber.

In summary, because the present invention employs the RF conditions, the receiving strength, and the prevention of continuous suspension to determine the priority, and suspend the structure of the compressed mode based on the priority, it could reduce the power consumption, and improve the system performance.

EXPLANATION OF MAIN COMPONENTS

• S201˜S209 step

Claims

1. A capacity-based compressed mode control method for inter-system handover in an Universal Mobile Telecommunication System (UMTS), which includes the following steps: (1) determining the priority for each subscriber, which is determined by a RF (Radio Frequency) condition, a number measured by the Received Signal Strength Indicator (RSSI), and a continuous-suspend preventing value; and(2) determining if the subscriber is going to execute a compressed mode or suspending the compressed mode, which is determined according to the priority for each subscriber.

2. A control method according to claim 1, wherein, in the step (1), the priority for the subscriber could be decided according to the suspend factor Fi(n) of the subscriber, and the Fi(n) is defined with the formula (2):

3. A control method according to claim 2, wherein the definition of the guide Receiving Signal Code Power RRSCP is defined with the formula (1):

4. A control method according to claim 1, further comprises (3) employing a threshold power value to limit the power level of UMTS, and when the estimation of transmission power exceeds the threshold power, suspending the compressed mode for each subscriber according to the priority of each subscriber.

5. A control method according to claim 1, wherein the number measured by RSSI is measured when a base station arranged all the subscribers executing the compressed mode.