KR19990015298A - Hard Handoff Method Between Frequency Assignments (FA) - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

The present invention relates to a hard handoff method between frequency assignments (FAs).

2. The technical problem to be solved by the invention

The present invention performs hard handoff between frequency allocation (FA) by software processing without using a pilot beacon base station, but improves the accuracy of the hard handoff decision between FAs and maintains the accuracy of the frequency of the hard handoff target. It is intended to provide a hard handoff method between FAs that sets forward coverage.

3. Summary of Solution to Invention

According to the present invention, the forward coverage of a frequency requiring hard handoff between frequency allocations (FA) is set to an area where the fundamental frequency attempts a soft handoff, so that the forward frame error rate, the pilot signal strength of the active group, and the gain value of the forward traffic channel are set. When six pieces of information such as the forward traffic channel information, the power control reference value of the reverse traffic channel, the distance between the base station and the terminal, and the base station / cell number reach a threshold, the hard handoff between frequency allocations (FA) is determined.

4. Important uses of the invention

The present invention is used for hard handoff between frequency allocations (FAs).

Description

Hard Handoff Method Between Frequency Assignments (FA)

In the present invention, a code division multiple access (CDMA) digital mobile communication system does not use a separate pilot beacon base station in a boundary area between base stations having different numbers of allocated frequency channels. The present invention relates to a hard handoff method between FAs that enables hard handoff between frequency assignment (hereinafter simply referred to as FA).

Based on the IS-95 (International Standard-95) standard, the handoff service provided in the DS-CDMA (Direct Sequence-CDMA) cellular system includes a soft handoff method and a hard handoff service. There is a hard handoff method.

The soft handoff method refers to a mobile station that is allocated a call channel from two base stations simultaneously while the mobile station is in service between the serving base station and the neighboring base station. The hard handoff method is adjacent to the serving base station. When the frequencies used by the base stations are different, the current frequency is disconnected and replaced by a new frequency supported by the adjacent base station to continue the call.

The terms used in the present invention are defined as follows.

The Power Measurement Report Message (PMRM) is a message for forward power control that the base station / base station controller receives periodically or aperiodically from the mobile station through the reverse call channel.

A pilot strength measurement message (PSMM) is a pilot strength measurement message received by a base station / base station controller from a mobile station.

The pilot beacon is a frequency that provides only a pilot channel without a traffic channel.

Ec / Io is the ratio of the pilot energy Ec accumulated over one pseudonoise (PN) chip period to the total power spectral density (Io) in the reception bandwidth.

A pilot measurement request order (PMRO) is a forward traffic channel message that requires a terminal to send a pilot strength measurement message (PSMM).

Eb / No is the ratio of traffic channel signal-to-noise power density per bit.

The erasure bit is the first bit of the reverse traffic channel message and is set (1) to notify the base station when an error is detected in the information received from the forward traffic channel or the transmission speed is unknown.

The fundamental frequency is a frequency being serviced all over the region, and it is assumed that a busy frequency generally hands off to a fixed frequency when a hard handoff between FAs is required. Therefore, the newly allocated frequency due to the hard handoff between FAs is the fundamental frequency.

In general, the code division multiple access (CDMA) digital mobile communication system has a high frequency utilization because the same frequency can be reused for each cell. That is, since the subscriber capacity can be increased with a limited frequency resource and the same frequency can be used, the call disconnection rate can be reduced by performing a soft handoff when moving subscribers between cells.

Currently, since different numbers of CDMA frequency channels are allocated and operated according to subscriber capacity, the number of frequency channels is not the same for each cell. Therefore, in the related art, a pilot beacon base station is installed in a boundary area of a base station having a different number of frequency channels, and is used as a buffer area for hard handoff between FAs. However, a base station having a pilot beacon installed for hard handoff between FAs between base stations having a different number of frequency channels has a problem in that an additional radio frequency (RF) module and digital hardware are additionally installed.

Another method for the conventional inter-FA hard handoff is that the active group pilot signal strength and frame error rate (FER) are derived from the PMRM message sent by the terminal in the call processing module (CCP) of the base station controller (BSC). If it falls below the threshold, it is a method by the algorithm for determining the hard handoff between FAs in the cell. However, this method has a problem that the success rate of hard handoff between FAs in a real service environment is very low, and in this case, most of the conventional methods use a pilot beacon. Looking at this in detail.

1A to 1C are diagrams illustrating a cell configuration for explaining a conventional hard handoff between frequency allocations (FA), in which a dotted line represents M frequency coverage, a solid line represents N frequency coverage, and A represents M + N frequencies. A cell with, B denotes a cell having M frequencies and N pilots, and C denotes a cell having M frequencies, respectively.

As shown in FIG. 1A, a pilot beacon is a frequency that provides only a pilot channel without a traffic channel, in which M frequency channels are used equally throughout the region, and N frequency channels have a special number of subscribers. In addition, for example, between base stations 1 using M + N frequency channels and base station 2 and base station 4 having M frequency channels, M stations commonly used by neighboring base stations 1, 2 and 4 as buffer zones are used. Base station 3 having a frequency and N pilot beacons is provided.

A terminal moving from base station 1 and base station 2 having M + N frequencies to base station 4 having M frequencies moves in a call on any one frequency channel among N frequency channels that are not serviced equally throughout the region. When passing through a pilot beacon base station, the busy frequency does not support a traffic channel other than the pilot signal, and thus the hard handoff is performed between FAs with a channel resource among the M frequencies.

Therefore, the pilot beacon base station 3 emits only the pilot signal without subscriber service by the number of frequency channels (N) which are not commonly provided for the FA hand-off between terminals moving between base stations having different numbers of frequency channels. Additional radio frequency modules and digital hardware must be installed.

The cell configuration of frequencies to be hard handoff between frequency allocations (FA), as shown in FIG. When the forward coverage becomes larger than the fundamental frequency and attempts to handoff to the fundamental frequency, it fails because the coverage of the fundamental frequency is already out of control and out of control of the cell that detects the handoff.

The cell configuration of the frequency to be hard handoff between frequency allocations (FA) as shown in FIG. 1C is such that if the frequency to be hard handoff between FAs is set to maintain the same coverage as the fundamental frequency, the soft handoff attempt point at the coverage boundary is set. Pass the hard handoff, but the signal strength of the fundamental frequency is also weak at the boundary, so the handoff will fail.

Conventionally, a method of performing hard handoff between FAs from a busy frequency to a fundamental frequency by searching for a pilot signal strength and a frame error rate (FER) of active groups in a PMRM coming from a terminal has been used. Therefore, the basic frequency requires a hard handoff between FAs on a busy frequency. When allocating a new frequency, the base frequency generally needs to be handed off by selecting one of the frequencies serviced throughout the region.

Since the frequency that requires hard handoff is not used in the neighboring base station, the interference is less and the service area is wider than the frequency used in the same manner as the neighboring base station. When attempting to handoff, the mobile station cannot handoff from the cell beyond the coverage of the fundamental frequency and fails because the cell where the terminal is located is unknown.

Therefore, when using the algorithm that induces hard handoff between FAs only by FER and pilot signal strength, there is a high probability of error, so that the appropriate coverage for each frequency can be applied to ensure that the hard handoff is performed accurately with the adoption of a more precise algorithm. Must be set. That is, the reverse frame error rate is often increased compared to the forward frame error rate, and even if Ec / Io is good, the forward and reverse pathlosss are very large, so that a call is not possible.

The present invention devised to solve the conventional problems as described above, while performing the hard hand-off between FA by software processing without using a pilot beacon base station, to increase the accuracy of the hard hand-off decision between FA, An object of the present invention is to provide a hard handoff method between FAs that sets forward coverage of a target frequency of hard handoff to maintain accuracy.

1A to 1C are exemplary cell configurations for explaining hard handoff between conventional frequency allocations (FAs).

2 is a diagram illustrating a configuration of a code division multiple access (CDMA) digital mobile communication system to which the present invention is applied.

3 is an embodiment cell diagram for explaining hard handoff between frequency allocations (FA) in accordance with the present invention;

4 is a graph showing time points for determining hard handoff between frequency allocations (FAs).

5 is a flow diagram of an embodiment of a hard handoff determination procedure between frequency assignments (FA) in accordance with the present invention.

* Explanation of symbols for the main parts of the drawings

201: terminal (PS) 202: base station (BTS)

203: control station (BSC) 204: base station management system (BSM)

205: switching center (MSC) 206: operation maintenance system (OMD)

207: Home Location Register (HLR) 208: Authentication Center (AC)

209: Voice Mailbox System (VMS) 210: Fax Mailbox System (FMS)

211: Short Message Center (SMC) 212: Visitor Location Register (VLR)

In order to achieve the above object, the present invention provides a method for hard handoff between frequency allocation (FA), wherein the forward coverage of a frequency requiring hard handoff is set so as not to exceed the point where the fundamental frequency attempts soft handoff. First step; A second step of setting a threshold of a parameter for determining whether to perform hard handoff between frequency assignments based on a measured value at a predetermined point within the coverage of the first step; And determining whether to perform hard handoff between frequency allocation FAs using the set threshold.

A hard handoff method between frequency allocations (FAs), comprising: a first step of setting forward coverage of a frequency requiring hard handoff so as not to exceed a point at which the fundamental frequency attempts a soft handoff; A second step of setting a threshold of a parameter for determining whether to perform hard handoff between frequency assignments based on a measured value at a predetermined point within the coverage of the first step; A third step of determining whether the calculated frame error rate exceeds a threshold of the forward frame error rate by collecting erasure bits, each of which transmits an error of a forward traffic channel, per unit time; A fourth step of determining whether the current terminal is located in a boundary area with a base station having a different number of frequency channels; A fifth step of determining whether a signal strength of active group pilots maintained by the terminal is between a predetermined value of a pilot signal strength threshold from a pilot strength measurement message sent by the terminal; A sixth step of determining whether the gain of the forward traffic channel exceeds the threshold of the forward traffic channel gain; A seventh step of determining whether the power control reference value of the reverse traffic channel calculated by the vocoder every frame exceeds the threshold value of the reverse traffic channel power control reference value; And an eighth step of determining whether the distance between the base station and the terminal exceeds a threshold of the distance between the base station and the terminal.

Hereinafter, with reference to the accompanying drawings will be described an embodiment according to the present invention;

2 is a diagram illustrating a configuration of a code division multiple access digital mobile communication system to which the present invention is applied.

Terminal (PS) 201 is within the range of any base station (BTS) 202, and information of terminal 201 is passed through base station 202 and control station (BSC) 203 controlling them. Information transmitted from the switching center 205 is transmitted to the terminal 201 via the base station 202 and the control station 203 controlling the same, and is provided with a wireless mobile communication service. .

A base station (BTS) 202 serves to connect a mobile station (MS) to the control station 203, and includes a digital channel unit (DCU) and a timing / frequency control unit (TCU). It is composed of Radio Frequency Unit (RFU), Global Position System (GPS), etc. to perform various functions for mobile subscribers.

The control station (BSC) 203 connects the base station 202 to the switching center 205 to coordinate the connection between the base stations 202, handles softeners and soft handoffs, supports hard handoffs, And a signal processing function for communication with the base station 202 and the switching center 205.

The exchange station 205 includes a visitor location register (VLR) 212, and a plurality of control stations 203 for controlling the base station 202, and a base station management system (BSM) 204 for managing the base station and the control station; Sends and receives signals and is connected to the home location register (HLR) 207, voice mailbox system 209, fax mailbox system 210, and short message center (SMC) 211 to handle mobile subscriber calls. Do it.

Visitor location register (VLR) 212 is a database that temporarily stores subscriber information associated with the mobile station while the mobile station (MS) is in an area controlled by visitor location register 212.

A Home Location Register (HLR) 207 is connected to an exchange office 205, an Operational Maintenance System (OMD) 206, and an Authentication Center (AC) 208 to function as a database management system to manage various information of mobile subscribers. It is in charge of, and in conjunction with several exchanges 205 performs a function such as registration of the subscriber.

3 is a cell configuration diagram for hard handoff between frequency allocations according to the present invention, in which A is a cell having M + N frequencies, C is a cell having M frequencies, and a solid line is a base frequency. Coverage, dashed lines indicate coverage of frequencies to be hard handed off between frequency allocations (FA), respectively. Also, in the drawing, d1 is a soft handoff overlap region from another sector of base station 2 with respect to a frequency to be hard handoff between frequency allocations (FA), d is a time point for determining hard handoff between frequency allocations (FA), and d2 is a frequency. At the time of attempting soft handoff from base station 2 to base station 4 at base frequency as an appropriate coverage of frequencies to be hard handed off between allocations, d3 represents coverage of the base frequency.

Forward frame error rate through erasure bit processing, pilot signal strength of active groups obtained from PSMM message, forward traffic channel gain, reverse power control Eb / No reference value, distance between base station and terminal, base station / cell number, etc. In order to determine hard handoff between frequency allocations based on six pieces of information, forward coverage should be set so that the values of six pieces of information are properly maintained at the boundary area of the frequency where hard handoff between FAs is required.

Forward coverage of frequencies requiring hard handoff between FAs should be set smaller than that of the fundamental frequency. If the forward coverage of the frequency is set smaller than the coverage of the fundamental frequency, the channel state of the fundamental frequency is better, thereby increasing the success rate of the hard handoff between FAs, but the load of the fundamental frequency increases as the handoff to the fundamental frequency is performed too early. Therefore, the traffic channel state of the fundamental frequency should be set to be smaller than the coverage of the fundamental frequency by extending as much as possible to good coverage. That is, as shown in FIG. 3, the forward coverage of frequencies requiring hard handoff between FAs is preferably set to the point where the fundamental frequency attempts soft handoff.

4 is an explanatory diagram showing a state in which Ec / Io changes with distance for each frequency to be hard handoff between FAs, in which a represents a fundamental frequency and b represents a frequency to hard handoff between FAs. Also, d1, d, d2, and d3 indicated on the graph abscissa indicate each point shown in FIG. 3, T_ADD is a base station pilot strength value that a neighbor base station must satisfy to enter a candidate base station, and T_DROP is an active set of base stations. The minimum signal level to remain at.

As shown in the graph of FIG. 4, since the output of the hard handoff target frequency between frequency allocations (FA) is adjusted to have a smaller coverage than the fundamental frequency, the Ec / Io in the graph is also small.

As the terminal moves from the center of the base station 2 to the base station 4, the fundamental frequency (a) decreases at a constant rate of Ec / Io in all sections according to adjacent cell interference. However, the hard handoff target frequency (b) decreases at a constant rate from the center of base station 2 to d1 due to interference from other sectors of the same base station. However, since there is no interference in the interval between d1 and d2, Ec / Io It gradually decreases, and after d2, there is no output, so the Ec / Io decreases rapidly.

Since the Ec / Io of the hard handoff target frequency (b) between the fundamental frequency (a) and the FA moves away from the center of the base station, as shown in the graph, it is busy on the hard handoff target frequency (b) between the FAs. The determination of the inter-FA hard handoff should begin at point d before the terminal reaches the coverage boundary d2.

Therefore, in order for the base station to detect that the terminal that is in the call at the frequency of the inter-FA hard handoff target is at the point d and to start the determination of the hard handoff between the FAs, the terminal is placed in the point d in advance and the next parameter It is required to set the threshold of the inter-FA hard handoff decision algorithm by measuring the value of. On the premise of such threshold setting, it is determined whether or not to perform handoff between FAs.

5 is a flowchart illustrating a hard handoff determination procedure between FAs according to the present invention.

The threshold parameters of the inter-FA hard handoff decision algorithm used herein are as follows.

First, the threshold fwd_ferl of the forward frame is a threshold for the forward frame error rate calculated through the erasure bit every unit time.

The threshold pilot1 of the active group pilot signal strength is a threshold value for the active group pilot signal strength obtained from the PSMM sent by the terminal requested by the PMRO.

The threshold max_gain1 of the forward traffic channel gain is a threshold for the forward traffic channel gain (digital gain).

The threshold rvs_eb_no1 of the reverse traffic channel power control reference value is a threshold for the reverse traffic channel power control reference value (Eb / No set point).

The threshold dist1 of the distance between the base station and the terminal is a threshold for the distance between the base station and the terminal calculated as a round trip delay.

The boundary area between frequency allocations (FAs) is a threshold expressed by a base station / cell number.

The conventional algorithm described above determines hard handoff between FAs only with forward FER and pilot signal strength. However, the algorithm according to the present invention adds information such as the gain value of the forward traffic channel, the reverse traffic channel power control reference value, the distance between the base station and the terminal, and increases the accuracy for determining the hard handoff between FAs. In addition, since this algorithm is in the base station controller (BSC) call processing module (CCP), the number of cells requiring inter-FA hard handoff is unnecessarily avoided in cells that can only be soft handoff unnecessarily. Stored and executed only in these cells to minimize the load on the algorithm.

These six parameters may have priority, and by appropriately adjusting the coverage of the threshold, one can determine the inter-FA hard handoff based on importance.

One embodiment algorithm for determining the inter-FA hard handoff is shown in FIG. 5 and added to the block for determining the handoff type such as softer, hard, etc. in the call processing module (CCP) in the base station controller (BSC). Should be.

When the terminal moves from the base station 2 to the base station 4 and makes a call with a frequency between the FA's hard handoff targets, the frame is calculated by collecting the erasure bits sent by the terminal every unit time. It is determined whether the error rate has exceeded the threshold of the forward frame error rate (501).

As a result of the determination, if the frame error rate exceeds the threshold of the forward frame error rate, it is determined whether the current terminal is located in a boundary area with a base station having a different number of frequency channels (502), and the frame error rate does not exceed the threshold of the forward frame error rate. If not, it recognizes that the call is available and terminates the inter-FA hard handoff determination procedure (508).

If the current terminal is located in the boundary area with the base station having a different frequency channel number, the terminal requests the PSMM to be sent as a forward traffic channel message, so that the signal strength of the active group pilots maintained by the terminal from the PSMM sent by the terminal is set. Threshold If the terminal is not located in the boundary area between base stations with different frequency allocation (FA) numbers, the determination procedure is terminated (508).

And, the signal strength of the active group pilots of the active group pilot signal strength threshold value If so, it is determined whether the gain of the forward traffic channel exceeds the set threshold (504), and the signal strength of the active group pilots is equal to that of the active group pilot signal strength threshold. If not, the determination procedure is terminated (508).

As a result of the determination, if the gain of the forward traffic channel exceeds the set threshold, it is determined whether the power control reference value (Eb / No set point) of the reverse traffic channel calculated by the vocoder every frame exceeds the set threshold (505). If the gain of the channel does not exceed the set threshold, the determination procedure is terminated (508).

In addition, when the power control reference value of the reverse traffic channel exceeds the set threshold, it is determined whether the distance between the base station and the terminal calculated as a round trip delay exceeds the set threshold (506), and the power of the reverse traffic channel is determined. If the control reference value does not exceed the set threshold, the mobile station recognizes that the call is available and terminates the determination procedure (508).

Finally, when the distance between the base station and the terminal exceeds the set threshold, the hard handoff between FAs is determined to allocate resources such as a new frequency, frame offset, and channel (507), and the distance between the base station and the terminal exceeds the set threshold. If not, the mobile station recognizes that the call is available and terminates the execution (508).

The present invention described above is capable of various substitutions, modifications, and changes without departing from the spirit of the present invention for those skilled in the art to which the present invention pertains, and the above-described embodiments and accompanying It is not limited to the drawing.

The present invention as described above, by performing the hard hand-off between FA by software processing in the code division multiple access digital mobile communication system, not only can reduce the investment cost of the facility for pilot beacon use, but also hand off There is a very good effect of remarkably improving the success rate of FA hand-to-FA through proper coverage of frequency and determination of reliable hard handoff.

Claims (7)

In the hard handoff method between frequency allocation (FA), Setting a forward coverage of the frequency requiring hard handoff so that the base frequency does not exceed the point at which the soft handoff attempts; A second step of setting a threshold of a parameter for determining whether to perform hard handoff between frequency assignments based on a measured value at a predetermined point within the coverage of the first step; And A third step of determining whether to perform hard handoff between frequency allocation FAs using the set threshold; Hard handoff method between the frequency allocation (FA) made, including. The method of claim 1, The third step, A fourth step of judging whether the frame error rate calculated for each unit time of the erasure bit, which transmits an error of the forward traffic channel, exceeds a threshold of the forward frame error rate; A fifth step of determining whether the active group pilot signal strength is between a predetermined value of the active group pilot signal strength threshold; And A sixth step of determining whether the current terminal is located in a boundary area with a base station having a different number of frequency channels Hard handoff method between the frequency allocation (FA) made, including. The method of claim 1, The third step, A fourth step of judging whether the frame error rate calculated for each unit time of the erasure bit, which transmits an error of the forward traffic channel, exceeds a threshold of the forward frame error rate; A fifth step of determining whether the active group pilot signal strength is between a predetermined value of the active group pilot signal strength threshold; And Sixth step of determining whether the gain of the forward traffic channel exceeds the threshold of the forward traffic channel gain; Hard handoff method between the frequency allocation (FA) made, including. The method of claim 1, The third step, A fourth step of judging whether the frame error rate calculated for each unit time of the erasure bit, which transmits an error of the forward traffic channel, exceeds a threshold of the forward frame error rate; A fifth step of determining whether the active group pilot signal strength is between a predetermined value of the active group pilot signal strength threshold; And A sixth step of determining whether the power control reference value of the reverse traffic channel calculated by the vocoder every frame exceeds the threshold value of the reverse traffic channel power control reference value Hard handoff method between frequency assignments made, including. The method of claim 1, The third step, A fourth step of judging whether the frame error rate calculated for each unit time of the erasure bit, which transmits an error of the forward traffic channel, exceeds a threshold of the forward frame error rate; A fifth step of determining whether the active group pilot signal strength is between a predetermined value of the active group pilot signal strength threshold; And A sixth step of determining whether the distance between the base station and the terminal exceeds a threshold of the distance between the base station and the terminal; Hard handoff method between frequency assignments made, including. The method of claim 1, The forward coverage set in the first step is Hard handoff method between frequency allocations, characterized in that it is set smaller than the coverage of the fundamental frequency. In the hard handoff method between frequency allocation (FA), Setting a forward coverage of the frequency requiring hard handoff so that the base frequency does not exceed the point at which the soft handoff attempts; A second step of setting a threshold of a parameter for determining whether to perform hard handoff between frequency assignments based on a measured value at a predetermined point within the coverage of the first step; A third step of determining whether the calculated frame error rate exceeds a threshold of the forward frame error rate by collecting erasure bits, each of which transmits an error of a forward traffic channel, per unit time; A fourth step of determining whether the current terminal is located in a boundary area with a base station having a different number of frequency channels; A fifth step of determining whether a signal strength of active group pilots maintained by the terminal is between a predetermined value of a pilot signal strength threshold from a pilot strength measurement message sent by the terminal; A sixth step of determining whether the gain of the forward traffic channel exceeds the threshold of the forward traffic channel gain; A seventh step of determining whether the power control reference value of the reverse traffic channel calculated by the vocoder every frame exceeds the threshold value of the reverse traffic channel power control reference value; And Eighth step of determining whether the distance between the base station and the terminal exceeds the threshold of the distance between the base station and the terminal Hard handoff method between the frequency allocation (FA) made, including.