CN101631346A - Region switching method based on signal intensity and load estimation - Google Patents

Abstract

The invention discloses a region switching method based on signal intensity and load estimation, mainly solving problem of switch failure caused by excessive load intensity in a candidate cell. The switching method comprises the following steps: (1) a base station sends measuring control information to a mobile terminal periodically, meanwhile measures load information and resource information in the cell; (2) the base station decides whether a switching process is triggered according to the signal intensity in a measuring report of the mobile terminal, if the signal intensity in the cell is smaller than the signal intensity in other cells, connections are established between the base stations to exchange measured information; if not, step (1) goes on; and (3) the base station normalizes by unit and weighs the signal intensity and the load in each candidate target cell, and selects an optimal cell as a target switching cell. The invention has the advantages of high success rate of switching and low total time lag of switching, and mobile nodes can be switched from a service cell to another service cell in wireless network.

Description

Region switching method based on signal strength signal intensity and load estimation

Technical field

The present invention relates to wireless communication technology field, particularly related to the 3G (Third Generation) Moblie long evolving system, the changing method that a kind of specifically load is estimated.Be used for moving to from a Serving cell switching of another Serving cell at the wireless network mobile node.

Background technology

Be accompanied by the increasing of carrier frequency of future mobile communication system, the number of mobile users purpose constantly increases and variation has taken place in the requirement of new telecommunication service, the coverage of wireless area will further be dwindled, switch and also can become more frequent accordingly, macrocell, Microcell, picocell, and the different districts of different system will carry out overlapping covering to a physical region, and their loading condition separately, resource and service speed etc. all may be inequality, particularly under the environment that merges at the networking, this load, factors such as resource and service speed are more obvious to the influence of switching.

In advanced person's long evolving system LTE-Advanced, mobility comprises mobility under the connection status and the mobility under the idle condition, the speech quality and the service quality QoS requirements that guarantee the mobile subscriber are the emphasis of research, and the mobility under the connection status mainly refers to switching, the success or not of switching directly affects important parameters such as user's switching time and loss of data, particularly real time business is even more important.

Handover decisions depends primarily on the signal strength signal intensity that pilot channel receives in second generation mobile communication system, decides the Target cell that will switch to the size of received signal intensity.But continuous growth along with the more and more and user's request of class of business, when handover decisions is only considered signal strength signal intensity in some cases, can cause a kind of potential handoff failure, such as the signal strength signal intensity optimum of selected Target cell, but situation that load has been transshipped or load may be with the situations of overload.Like this will be when access be blocked by Target cell and the failure that causes switching, thereby bring bigger handover delay even produce the call drop phenomenon to the user.

Summary of the invention

The present invention mainly be at top mention owing to only consider the handoff failure problem that the signal strength signal intensity of Target cell is brought when the handover decisions, a kind of changing method based on signal strength signal intensity and load estimation has been proposed, to improve the probability of handover success, reduce handover delay, and then reduce the call drop phenomenon that causes because of handoff failure.

The technical scheme that realizes the object of the invention is: take all factors into consideration the signal strength signal intensity of Target cell, and total resources, service speed is estimated the switching arrival rate, and new rate of arriving calls and present load wait makes handover decisions.Consider from signal strength signal intensity and surplus resources, select a signal strength signal intensity and resource optimal target sub-district.When predicting the Target cell resource shortage, make the user be directly switch to the sub-district of another signal strength signal intensity suboptimum, reduce the handoff failure probability with this.Make the load of neighbor cell obtain equilibrium simultaneously, improve utilization ratio of wireless resources.Concrete steps comprise as follows:

(1) base station is periodically to portable terminal strength of transmitted signals measuring control information, and portable terminal sends measurement report to the base station according to measuring control information, and load information and the resource information in this sub-district a period of time periodically measured in the base station simultaneously;

(2) after the measurement report of portable terminal arrives the base station, the base station is according to the current area of reporting and the signal strength signal intensity size of peripheral cell, whether decision triggers changeover program, if the current area signal strength signal intensity that terminal receives is less than the peripheral cell signal strength signal intensity, base station and adjacent base station are determined the candidate cell number by the measured information in mutual each sub-district that connects; Otherwise, proceed step (1);

(3) after linking between base station and the adjacent base station set up, unit normalization and weighting are carried out to the signal strength signal intensity of each candidate Target cell with by the information that interface obtained between the base station in the base station, according to gained result's size to candidate cell tabulation rank, first-selected optimum sub-district is as the target switching cell.

Described load information comprises new rate of arriving calls, call failure probability, handoff failure probability and this sub-district present load of sub-district;

Described resource information comprises the service speed and the sub-district total resources information of sub-district.

Described base station and adjacent base station comprise the base station of neighbor cell and the base station of overlapping coverage cell, and the base station of sub-district under the adjacent heterogeneous network.

The present invention compared with prior art has following advantage:

1) the present invention is owing to measured load information and the resource information in the sub-district in measure signal intensity, these may cause the factor of handoff failure to have added the load information of Target cell and resource information during decision-making, predict the access control situation of each candidate cell with this, thereby reduce after handover decisions, may be because of the load overfill of Target cell, no available resources and the handoff failure that causes have improved the probability of handover success greatly;

2) the present invention has improved the handover success probability owing to added the load information and the resource information of sub-district when decision-making, reduces the handover delay that brings because of handoff failure, effectively avoids the least patient accent words of user phenomenon;

3) the present invention avoids making terminal to switch to the heavier sub-district of load owing to considered the load information and the resource information of Target cell when decision-making, makes the load of neighbor cell obtain equilibrium, has improved utilization ratio of wireless resources.

Simulation result shows that handover decisions method of the present invention has more performance than existing handover decisions method.Particularly the continuous change along with sub-district internal burden intensity is big, and the performance of existing changing method can sharply reduce, and the present invention is having reasonable performance aspect handover success rate and the minimizing time delay.

Description of drawings

Fig. 1 is the interval flow chart that switches of the present invention;

Fig. 2 is that the sub-district under the model environment of Manhattan distributes and UE moves figure;

Fig. 3 is an average load intensity when accounting for sub-district total resources 2/3, adopts the analogous diagram as a result of the handover success rate of two kinds of changing methods;

Fig. 4 is an average load intensity when accounting for sub-district total resources 2/3, the time delay simulation figure that new changing method can reduce;

Fig. 5 adopts the present invention and the handover success probability graph of existing changing method under different average load intensity;

Embodiment

With reference to Fig. 1, concrete implementation step of the present invention is as follows:

Step 1, the base station sends measuring control information to portable terminal, and measures this sub-district relevant information.

1a) base station is periodically to portable terminal strength of transmitted signals measuring control information, portable terminal is according to measuring control information, go to measure from the signal strength signal intensity of current service cell reception and the signal strength signal intensity that receives from neighbor cell, and pairing cell list, send measurement report then to the base station;

1b) information such as rate of arriving calls, probability of call blocking, handoff failure probability, present load, service speed and sub-district total resources in this sub-district a period of time are periodically measured in the base station.

Step 2 determines whether triggering changeover program according to measured signal strengths in the step 1, and the metrical information between the mutual base station.

2a) after the measurement report of portable terminal arrives the base station, the base station is according to the signal strength signal intensity size of current area in the measurement report and peripheral cell, whether decision triggers changeover program, if the current area signal strength signal intensity that terminal receives is less than the peripheral cell signal strength signal intensity or be lower than minimum receive threshold, start changeover program;

2b) simultaneously the base station of this sub-district and it the base station of adjacent all sub-districts, comprise the base station of the neighbor cell under the same network or the base station under the overlapping coverage cell, or the base station under the adjacent heterogeneous network sub-district, set up the connection between the base station, the measured information in mutual each sub-district, make each sub-district all have the load information and the resource information of neighbor cell, determine the candidate cell number; Otherwise, proceed step (1).

Step 3 will be converted into estimating of sub-district by following formula from mutual resulting new rate of arriving calls, the blocking probability that makes a call, handoff failure probability between the base station and switch arrival rate λ _{Pre_i} ^k:

${\mathrm{\λ}}_{\mathrm{pre}\_i}^k=\mathrm{\α}{\mathrm{\λ}}_{H\_i}+(1-\mathrm{\α}){\mathrm{\λ}}_{\mathrm{pre}\_i}^{k-1}$

λ _{H_i}＝P _h(1-B _o)λ _o

Wherein, λ _{Pre_i} ^kBe i sub-district k constantly estimate switching arrival rate, λ _{H_i}Arrival rate, λ are switched in the measurement that is i sub-district _{Pre_i} ^K-1Be i sub-district k-1 constantly estimate the switching arrival rate, α is a weighted factor, λ _oBe new arrival rate of calling out in this sub-district, B _oBlocking probability for making a call in this sub-district, P _hFor initiating the probability of handoff request in this sub-district;

Step 4 is separately converted to load with estimating the new rate of arriving calls of switching arrival rate and sub-district.

4a) convert the resulting switching arrival rate of estimating to the bandwidth number by following formula:

$W_{\mathrm{pre}}={\stackrel{\‾}{\mathrm{\λ}}}_{\mathrm{pre}}^k*{\mathrm{\ω}}_{\mathrm{pre}}$

${\stackrel{\‾}{\mathrm{\λ}}}_{\mathrm{pre}}^k=\frac{1}{n}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{\mathrm{\λ}}_{\mathrm{pre}\_i}^k$

Wherein, W _PreFor estimating the shared bandwidth of switch call, λ _Pre ^kFor all neighbor cells arrive the average handoff request arrival rate of this sub-district, λ _{Pre_i} ^kBe i sub-district k constantly estimate switching arrival rate, ω _PreFor estimating the bandwidth number that switch call on average takies, n is the number of neighbor cell.

4b) convert direct new rate of arriving calls to the bandwidth number by following formula from the sub-district that interface obtained between the base station:

$W_o={\mathrm{\λ}}_o^n*{\mathrm{\ω}}_o$

Wherein, W _oBe new shared bandwidth, the λ of calling out _o ⁿFor at n new rate of arriving calls constantly, ω _oThe bandwidth number that on average takies for new calling.

Step 5, the signal strength signal intensity of base station to from the measurement report of portable terminal, being obtained, the load that obtains by mutual resource information that obtains between base station and the base station and step 4 is carried out the normalization weighting by following formula and is obtained utility function Y:

Y＝βq _i/Q+(1-β)(1-L _i/S _i)

L _i＝l _i+W _pre+W _o

Wherein, q _iBe the signal strength signal intensity of i sub-district, Q is the maximum signal of whole candidate cell, S _iBe the total resources of i sub-district, β is a weight coefficient, L _iBe the total load intensity of i sub-district, l _iBe the present load intensity of i sub-district.

Effect of the present invention can further specify by following emulation:

1) simulated conditions: make up the simulation model under the environment of Manhattan, this Manhattan model comprises 72 base stations, a sub-district is arranged under each base station, the size of each building block is 200m * 200m, speed with 36km/h moves portable terminal along the street, to the mobile of all directions is equiprobable, during terminal initial at random begin to move from certain crossroad, statistics in a period of time the user this section at random on the mobile alignment the handover success probability in the sub-district of process.

2) simulation result:

2a) will adopt the handover success probability of the inventive method and former changing method to carry out emulation, its result as shown in Figure 2.In Fig. 2, former handover decisions is only considered the signal strength signal intensity size, when the intensity of load in the sub-district is overweight, can be because to the unknown of the loading condition and the idling-resource of Target cell, and cause the failure of switching; And the inventive method has been owing to taken into account the load information and the resource information of Target cell when considering the signal strength signal intensity of Target cell, thereby reduces the phenomenon that causes handoff request to get clogged because of Target cell load overfill, improved the probability of handover success.By among Fig. 2 as can be seen, when the inventive method accounts for sub-district total resources 2/3 in average load intensity, along with the variation of time is keeping the power that changes near 100% substantially.

2b) handover delay that the inventive method is reduced when average load intensity accounts for sub-district total resources 2/3 carries out emulation, and its result as shown in Figure 3.By among Fig. 3 as can be seen, when the inventive method accounted for sub-district total resources 2/3 in average load intensity, more former changing method can reduce the total handover delay near 20%, handoff failure or the call drop phenomenon of having avoided the user to cause because of time delay is excessive.

2c) to the inventive method and former changing method under different loads intensity the handover success probability carry out emulation, its result is as shown in Figure 4.By among Fig. 4 as can be seen, the probability of success and the inventive method of former changing method are approaching when load is light; Along with the change of intensity of load is big, the probability of success of former changing method will lower gradually, and influence becomes big because the load information of Target cell is to the access of handoff request, and at this moment the handover delay that brings because of handoff failure and the phenomenon of conversation loss will become big; And employing the inventive method, signal strength signal intensity, load information and resource information to Target cell when handover decisions are taken all factors into consideration, the probability of success of improve switching greatly, and along with the probability of the enhancing handover success of intensity of load remains at more than 90%.Terminal can be switched to the sub-district that load is low weight and signal strength signal intensity is more excellent, make the load of neighbor cell obtain equilibrium, improve utilization ratio of wireless resources.

2d) handover delay that the inventive method under different loads intensity is reduced carries out emulation, and its result as shown in Figure 5.By among Fig. 5 as can be seen, the handover delay that is reduced along with enhancing the inventive method of intensity of load also becomes big thereupon, because the present invention has considered the load information and the resource information of Target cell, reduced the probability of handoff failure, effectively reduce the time delay of bringing because of handoff failure, reduce the flagrant call drop phenomenon of user.Particularly under high load condition, can significantly reduce the time delay of bringing because of handoff failure.

Simulation result shows, the inventive method is all having more performance than former changing method aspect handover success probability and the time delay, can effectively reduce the time delay that the user brings because of handoff failure, avoid the flagrant call drop phenomenon of user as much as possible, it is microminiaturized day by day to be particularly suitable for present wireless area, switches the situation of increasedization.And along with the increase of intensity of load, the performance of the inventive method will be far superior to former changing method.

Claims (6)

1. the region switching method based on signal strength signal intensity and load estimation comprises the steps:

(1) base station is periodically to portable terminal strength of transmitted signals measuring control information, and portable terminal sends measurement report to the base station according to measuring control information, and load information and the resource information in this sub-district a period of time periodically measured in the base station simultaneously;

(2) after the measurement report of portable terminal arrives the base station, the base station is according to the current area of reporting and the signal strength signal intensity size of peripheral cell, whether decision triggers changeover program, if the current area signal strength signal intensity that terminal receives is less than the peripheral cell signal strength signal intensity, base station and adjacent base station are determined the candidate cell number by the measured information in mutual each sub-district that connects; Otherwise, proceed step (1);

(3) after linking between base station and the adjacent base station set up, unit normalization and weighting are carried out to the signal strength signal intensity of each candidate Target cell with by the information that interface obtained between the base station in the base station, according to gained result's size to candidate cell tabulation rank, select optimum sub-district as the target switching cell.

2. according to the described region switching method of claim 1, wherein the described load information of step (1) comprises the new rate of arriving calls of sub-district, the blocking probability that makes a call, handoff failure probability and this sub-district present load; Described resource information comprises the service speed and the sub-district total resources information of sub-district.

3. according to the described region switching method of claim 1, wherein described base station of step (2) and adjacent base station comprise the base station of neighbor cell and the base station of overlapping coverage cell, and the base station of sub-district under the adjacent heterogeneous network.

4. according to the described region switching method of claim 1, wherein unit normalization and weighting are carried out to the signal strength signal intensity of each candidate Target cell with by the information that interface obtained between the base station in the described base station of step (3), carry out as follows:

(4a) obtain i sub-district and switch arrival rate λ estimating of the k moment by following formula _{Pre_i} ^k:

${\mathrm{\λ}}_{\mathrm{pre}\_i}^k={\mathrm{\α\λ}}_{H\_i}+(1-\mathrm{\α}){\mathrm{\λ}}_{\mathrm{pre}\_i}^{k-1}$

λ _{H_i}＝P _h(1-B _o)λ _o

Wherein, λ _{H_i}Arrival rate, λ are switched in the measurement that is i sub-district _{Pre_i} ^K-1Be i sub-district k-1 constantly estimate the switching arrival rate, α is a weighted factor, λ _oBe new arrival rate of calling out in this sub-district, B _oBlocking probability for making a call in this sub-district, P _hFor initiating the probability of handoff request in this sub-district;

(4b) will estimate and switch arrival rate and all be converted into load from the new rate of arriving calls of the sub-district that interface obtained between the base station;

(4c) the normalization weighting is carried out in signal strength signal intensity and load and is obtained utility function Y by following formula:

Y＝βq _i/Q+(1-β)(1-L _i/S _i)

L _i＝l _i+W _pre+W _o

Wherein, q _iBe the signal strength signal intensity of i sub-district, Q is the maximum signal of whole candidate cell, S _iBe the total resources of i sub-district, β is a weight coefficient, L _iBe the total load intensity of i sub-district, l _iBe the present load intensity of i sub-district, W _PreEstimate the shared bandwidth of switch call, W _oBe the shared bandwidth of new calling.

5. according to the described region switching method of claim 4, wherein the described switching arrival rate of will estimating of step (4b) is converted into load, is to convert the bandwidth number to by following formula:

$W_{\mathrm{pre}}={\stackrel{\‾}{\mathrm{\λ}}}_{\mathrm{pre}}^k*{\mathrm{\ω}}_{\mathrm{pre}}$

${\stackrel{\‾}{\mathrm{\λ}}}_{\mathrm{pre}}^k=\frac{1}{n}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{\mathrm{\λ}}_{\mathrm{pre}\_i}^k$

Wherein, W _PreFor estimating the shared bandwidth of switch call, λ _Pre ^kFor all neighbor cells arrive the average handoff request arrival rate of this sub-district, λ _{Pre_i} ^kBe i sub-district k constantly estimate switching arrival rate, ω _PreFor estimating the bandwidth number that switch call on average takies, n is the number of neighbor cell.

6. according to the described region switching method of claim 4, wherein the described new rate of arriving calls with the sub-district of step (4b) is converted into load, is to convert the bandwidth number to by following formula:

$W_o={\mathrm{\λ}}_o^n*{\mathrm{\ω}}_o$

Wherein, W _oBe new shared bandwidth, the λ of calling out _o ⁿFor at n new rate of arriving calls constantly, ω _oThe bandwidth number that on average takies for new calling.

Images