CN1145295C - Method for Soft Handover Cell of Mobile Station in Code Division Multiple Access Communication System - Google Patents

Abstract

The invention discloses a method for soft handover of a mobile station in a code division multiple access communication system. The method mainly increases the influence conditions of reverse link interference, and the performance of the reverse link is judged by forward fading and reverse load. The method It can comprehensively evaluate the interference of the forward link and the interference of the reverse link, and can also comprehensively consider the load and distance fading of the reverse link in front of the cell. When there are many serving cells to be selected, it is convenient to establish the most suitable soft handover branch to ensure that the serving cell that maximizes the system gain is selected.

Description

Method for Soft Handover Cell of Mobile Station in Code Division Multiple Access Communication System

technical field

The invention relates to a broadband mobile communication system, more specifically to a method for soft handover of a mobile station in a code division multiple access communication system in a CDMA2000 system.

Background technique

The ability to perform soft handover is a unique advantage of Code Division Multiple Access (CDMA) systems. It specifically refers to the mobile station switching between different cells (or sectors) on a frequency point, and generally includes three steps, 1) The mobile station periodically searches for all available PNs on the current frequency point (please mark the Chinese meaning) offset Set the pilot signal to find that the pilot frequency of the original serving cell becomes weaker and the adjacent cell becomes stronger; 2) the mobile station reports the frequency strength measurement report (PSMM) to the base station controller (BSC), and the base station controller (BSC) BSC) sends a message through the base transceiver station (BTS) to let the new cell allocate traffic channels for the mobile station and establish a connection. Diversity state of the connection; 3) as the mobile station moves further away from the original cell, after the signal of the original cell drops to a certain threshold for a period of time, the mobile station reports the frequency strength measurement report (PSMM) to the base station controller (BSC), and the base station transmits and receives The BTS sends a message to order the original cell to terminate the connection with the mobile station. The mobile station is solely served by the new cell. So far, the soft handover process ends. For the convenience of expression, the division of sectors in a cell is not considered here.

Soft handover may be caused by the movement of the mobile station, or by other reasons such as changes in the wireless environment. In short, it is caused by changes in the radio reception conditions between the cell and the mobile station. The mobile station continuously measures all available pilots, and as long as it detects a pilot whose strength is greater than a certain threshold and the base station controller (BSC) allows it, it establishes a connection with its corresponding cell. The benefits brought by the soft handover to the system are: 1) The seamless handover is truly realized. The mobile station maintains the service all the time during the soft handover, and there will be no call interruption caused by the hard handover measurement, which reduces the possibility of call drop. 2) When the mobile station maintains connections with multiple base stations at the same time, the base station controller (BSC) improves the frame error rate of the reverse received signal through diversity, reduces the transmit power required by the mobile station, and reduces the interference, increasing the reverse capacity.

In order to obtain the best diversity effect and enter the best cell after soft handover, it is generally required to select a cell with better forward wireless connection during soft handover, so that the mobile station diversity combines the optimal received signal. The transmit power required in the forward direction can be reduced. However, it is incomplete to only consider the forward cell selection, and the reverse impact should also be considered. On the reverse link, when the mobile station is in the soft handover state, it has generally formed strong interference to adjacent cells. At this time, if the accessed cell can minimize the required reverse transmission power, the interference to adjacent cells will be minimized. , the reverse capacity of the system can be maximized.

Therefore, soft handover cell selection should also consider the following three factors: 1) Distance attenuation. 2) Interference on the forward link. 3) Interference on the reverse link. In the traditional method, the handover decision is only based on the measurement of the pilot strength of the forward link, which is the E _c /I _o value of the pilot signal, which reflects the distance between the base station and the interference of the forward link size, without reflecting the effect of reverse load. In a system with symmetrical services (such as IS-95), the forward and reverse link loads are equal, so there is no need to consider the interference of the reverse link. However, in the CDMA2000 system, the services are asymmetrical. If the forward load is greater than the reverse load , that is, when the forward capacity limitation is the bottleneck of service access, for the sake of simplicity, the influence of the reverse load may also be ignored. However, in some areas, if the reverse load is greater than the forward load, the selection of the cell needs to consider the above three factors comprehensively. Otherwise, although the selected cell requires low forward transmit power, the overall performance of the system is limited due to the heavy reverse load, high transmit power of the mobile station, and reduced reverse capacity.

The existing soft handover technology is based on the E _c /I _o value of the pilot when selecting a cell. This value can only reflect the fading of the signal on the forward link and the interference of the forward link, but cannot reflect The interference of the reverse link may make it possible for the mobile station to access a forward link better, but the reverse capacity is reduced in a cell with a large reverse transmit power. In fact, since a good forward link means that the forward transmit power is small, this means that the forward transmit power and the reverse transmit power should be considered comprehensively. Obviously it is optimal when both are small. However, there may be such a situation that the mobile station establishes a connection with cell 1 and requires a small forward transmit power but a large reverse transmit power; the mobile station establishes a connection with cell 2 and requires a large forward transmit power but a reverse transmit power Small, which cell should be selected for access needs to comprehensively evaluate the impact of these two factors on the system. Therefore, the existing soft handover method only emphasizes one aspect and is not perfect enough.

Contents of the invention

For this reason, the purpose of the present invention is to propose a kind of code division multiple access communication system mobile station soft handover cell method, this method can comprehensively consider the load and the distance fading of the reverse link before the cell, increase the influence condition of the reverse link interference , when selecting a cell in soft handover, the cell can be evaluated more comprehensively to ensure that the serving cell that maximizes the system gain is selected.

In order to achieve the above object, the present invention adopts the following technical solutions; the soft handover cell method is based on a code division multiple access system, in which a base station controller is included, and several base station transceivers controlled by the base station controller are controlled by mobile The reverse link from the station to the activated base transceiver station and the forward link from the activated base transceiver station to the mobile station, the mobile station and each base transceiver station include a transceiver, characterized in that the method comprises the following steps :

a. Make the mobile station establish a traffic channel with at least one base transceiver station in the system, and the mobile station periodically search for the pilot frequency of each base transceiver station on the frequency point used;

b. The base station controller determines the active set joining threshold or the active set dynamic joining threshold according to the number of pilots in the pilot active set of the mobile station, and sends the active set joining threshold or the active set dynamic joining threshold to the mobile station;

c. The mobile station continuously detects the pilot strength of each base transceiver station and reports it to the base station controller;

d, the base station controller judges the number of pilots in the current active set of the mobile station and sends the judgment result to the mobile station and the relevant base transceiver station through the forward link;

e. The base station controller selects a cell with a low system performance priority value Es to be removed from the active set or not to enter, and then notifies the mobile station of the selected cell through a pilot assignment message, and the mobile station establishes a new cell according to the instruction of the base station controller. After the connection of the cell is completed, return to step a, wherein the system performance priority value Es is negatively correlated with forward link interference, reverse link interference and distance attenuation;

f. The above steps are repeated until the mobile station ends the service state.

Because the mobile station soft handover cell method in the code division multiple access communication system of the present invention has adopted above-mentioned method, increases the influence condition of reverse link interference, reverse link performance judges with forward fading and reverse load, therefore, The method of the present invention can comprehensively evaluate the interference of the forward link and the interference of the reverse link, and can also comprehensively consider the load and distance fading of the front reverse link of the cell, and can evaluate the cell more comprehensively when the cell is selected by soft handover In this situation, when there are many available serving cells, it is convenient to establish the most suitable soft handover branch to ensure that the serving cell that maximizes the system gain is selected.

Description of drawings

Below in conjunction with accompanying drawing and embodiment, method of the present invention is described in detail:

FIG. 1 is a schematic diagram of the principle of a code division multiple access communication system.

Fig. 2 is a schematic diagram of establishing a connection between a mobile station and a cell in a code division multiple access communication system.

FIG. 3 is a schematic diagram of establishing connections between a mobile station and multiple cells in a code division multiple access communication system.

Fig. 4 is a schematic flow chart of the method of the present invention.

Detailed ways

Please refer to shown in Fig. 1, generally, in the code division multiple access communication system, at least comprise a base station controller 11, a plurality of base station transceivers 121～12N (each base station transceiver corresponds to a base station transceiver) controlled by this base station controller 11 Cell), the reverse link from the mobile station 13 to the active base transceiver station (BTS) and the forward link from the active base transceiver station to the mobile station 13. Wherein, the mobile station 13 includes a transceiver, and each base transceiver station also includes a transceiver.

In the non-handover state, the mobile station 13 only detects a pilot whose intensity is greater than the active set joining threshold T_ADD, that is, only one active base transceiver station establishes contact with the mobile station 13 . If there are multiple active sets with large strengths added to the pilot of the threshold T_ADD, it is possible to establish contact with multiple base stations at the same time, that is, to establish multiple soft handover branches, as shown in Figure 2, considering that the establishment of branches will reduce the forward capacity, and Too many branches are of little significance to the reverse gain, and the number of soft branches is generally not more than 3.

Generally speaking, when a mobile station selects a cell, after accessing a cell with a smaller forward transmit power, the forward E _c /I _o value is larger, and the required reverse transmit power is lower when the same demodulation threshold is satisfied. A small cell should have a relatively large signal-to-interference ratio, which requires a corresponding radio link with small fading and low interference. However, the reverse fading cannot be accurately measured at present, and it can only be approximated by the forward fading.

During soft handover cell selection, if a cell with heavy reverse load or large reverse fading is selected, since the signal-to-interference ratio on this link is relatively small, when the reverse transmit power remains unchanged, the signal received by the base station of the cell will be framed incorrectly. The higher the rate, after the reverse diversity combination, the required reverse transmission power under power control is also larger. That is to say, during soft handover, accessing this kind of cell requires more reverse transmission power than accessing other cells with light reverse load or small fading. The greater the mobile station transmit power, the greater the reverse interference to each cell. Therefore, the selection should also be combined with the reverse link conditions, giving preference to cells with light reverse load and small fading.

Based on above-mentioned considerations, soft handover cell method of the present invention comprises the following steps:

a, make the mobile station 13 establish a traffic channel with at least one base station transceiver in the system, the mobile station 13 is in the service state, the frequency point used is f1, and the mobile station 13 periodically searches for each base station transceiver 121 on the frequency point f1 -12N pilot.

b. The base station controller 11 determines the active set addition threshold T_ADD or the active set dynamic addition threshold T_ADD_DYC according to the number of pilots in the mobile station 13 pilot active set, and issues the active set addition threshold T_ADD or the active set dynamic addition threshold T_ADD_DYC to the mobile station Taiwan 13. The significance of adding the threshold T_ADD_DYC dynamically is to limit the establishment of new branches with low gain when there are many soft handoff branches established.

c. The mobile station 13 continuously detects the pilot strength of each base station transceiver 121 - 12N and reports to the base station controller 11 .

d. The base station controller 11 judges the number of pilots in the current active set of the mobile station 13 and sends the judgment result to the mobile station and the relevant base transceiver station through the forward link.

e, the base station controller 11 selects a cell with a low system performance priority value Es to be removed from the active set or not to enter, and then notifies the mobile station 13 of the selected cell through a pilot assignment message, and the mobile station 13 according to the base station controller 11 The command establishes a connection with the new cell, and returns to step a after the execution is completed.

f. The above steps are repeated until the mobile station 13 ends the service state.

In said step b, if there is only one pilot in the active set of pilots of the mobile station 13, the base station controller 11 issues the active set adding threshold T_ADD to the mobile station; if there is more than one pilot in the active set of the mobile station 13 pilots frequency, the base station controller 11 sends the active set dynamic threshold T_ADD_DYC to the mobile station 13.

Described active set joins threshold T ADD value is set by system, generally gets-13db; Described active set adds threshold T_ADD_DYC value dynamically according to formula (1)

Find out.

In said step c, the mobile station 13 continuously detects the pilot strength of each base transceiver station and reports to the base station controller 11, which means when it is found that the pilot strength is greater than the active set joining threshold T_ADD or the active set dynamically joining threshold T_ADD_DYC When conducting a pilot, the pilot is reported to the base station controller 11 through a pilot strength measurement report message.

In said step d, when the base station controller 11 judges the number of pilots in the current active set of the mobile station, if the number of pilots is less than 3, then directly add the new pilot to the active set; if the number of pilots is greater than or equal to 3 , since the front and back transmit powers are relatively independent, the comprehensive evaluation of the impact on the system can use weighted summation, then according to the formula (2)

$\mathrm{<span\; class="notranslate">\; Es</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; max</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Calculate the system performance priority value Es of the pilots in the current active set and the new pilot, select the pilot with the lowest priority value, if the pilot is in the current active set, delete it from the active set, if the pilot is a new pilot frequency, refuse to join the active set.

In the formula (2), Es is the obtained system performance priority value, which is used to judge the cell selection during soft handover, and the cell with the higher value is preferred to establish a soft handover branch. Pf is the forward initial transmission power, that is, the initial transmission power required by the base station. Pr is the reverse initial transmit power, that is, the transmit power required by the mobile station. P _{f_max} is the maximum transmission power allocated to a single user in the forward direction, α is a positive weight, reflecting the impact of forward transmission power on system performance, and β is also a positive weight, reflecting the impact of reverse transmission power on system performance Influence. These two values are set in the background database and can be adjusted by the system. In the case of needing to simplify the operation or the reverse load is not heavier than the forward load, β=0 can be taken.

The formula (2) $\mathrm{Es}=\frac{\mathrm{\&alpha;}}{P_f/P_{f\_\max }}+\frac{\mathrm{\&beta;}}{P_r/P_r\_\max }$ Among them, the forward initial transmission power Pf specified by the mobile station is according to the formula (3)

$P_f=\min [P_{\mathrm{pilot}\_\mathrm{send}}\&Center\; Dot;10\frac{\mathrm{D.}+0.5m}{10}\&Center\; Dot;\frac{R}{W,}{P}_{\max }]............\left(3\right)$ Calculation. In the formula (3), P _f is the forward initial transmission power specified by the mobile station;

P _{pilot_send} is the forward pilot intensity transmitted by the base station;

D is the ratio of the information bit energy to the interference spectral density that the base station must satisfy as required by the demodulation at the mobile station side, that is, (mobile station side);

M is the content of the forward pilot strength item obtained above, M=-2·10·logPS;

P _max is the maximum power that the mobile station can use.

And the reverse initial transmission power Pr according to the formula (4)

$P_r=\frac{{\left(\frac{{\mathrm{E.}}_b}{I_0}\right)}_{\mathrm{BS}}\&CenterDot;R\&Center\; Dot;\mathrm{RSSI}}{P_{r\_\mathrm{loss}}\&CenterDot;W}............\left(4\right)$ Calculation.

是基站侧解调所要求的，上述移动台为了满足服务质量要求而必须满足的信息位比特能量与干扰谱密度的比值；In formula (4),

It is required by the base station side demodulation, the ratio of the information bit energy to the interference spectral density that the mobile station must satisfy in order to meet the quality of service requirements;

R is the information rate of the service;

RSSI is the total strength of the reverse link signal, measured by the base station;

P _{r_loss} is the reverse path fading, similar to the reverse open-loop power control, it can be estimated by the forward path fading P _{f_loss} , that is, P _{r_loss} ≈ P _{f_loss} , and

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; loss</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; pilot</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; rec</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; pilot</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; send</span>}}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; 1.2288</span>}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; 10</span>}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; chip</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; pilot</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; send</span>}}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; W</span>}}$

So formula (4) has:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; =</span>\frac{{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; BS</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; RSSI</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; loss</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; W</span>}}<span\; class="notranslate">\; \&ap;</span>\frac{{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; BS</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; pilot</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; send</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; R</span>}}}{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; 1.2288</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; 10</span>}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; chip</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; RSSI</span>}}{\mathrm{<span\; class="notranslate">\; W</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; W</span>}}<span\; class="notranslate">\; .</span>$

During the soft handover process, the mobile station can detect multiple pilots whose intensity is greater than the active set joining threshold T_ADD. The judgment process is shown in Table 1 and Table 2 below:

Table 1 E _c /I _o (dB) -18 -16 -14 -12 -10 -8 36 32 28 twenty four 20 16 P _send 2.63 1.66 1.05 0.66 0.42 0.26

Table 2

Table 1 is a set of values corresponding to the forward initial transmission power and the pilot strength received by the mobile station, where,

Take P _pilot = 3 watts,

${<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; mobile</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; dB</span>}<span\; class="notranslate">\; ,</span>$

$\mathrm{<span\; class="notranslate">\; D.</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; 10</span>}}^{{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; mobiie</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 10</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2.5</span>}$

$\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 20</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; log</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; dB</span>}<span\; class="notranslate">\; ,</span>\frac{\mathrm{<span\; class="notranslate">\; W</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 128</span>}$

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; send</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; pilot</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; 10</span>}\frac{\mathrm{<span\; class="notranslate">\; D.</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 0.5</span>}\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; 10</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; W</span>}}$

Table 2 is a set of corresponding values of the reverse transmit power and the total reverse link signal strength RSSI measured by the base station, where,

Take P _{pilot_semd} = 3 watts, $\left(\frac{{\mathrm{E.}}_b}{I_o}\right)\mathrm{BS}=7\mathrm{dB},$ $\frac{{\mathrm{E.}}_c}{I_o}=-13\mathrm{dB},$ R＝9.6kbits/s

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; =</span>\frac{{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; BS</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; RSSI</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; loss</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; W</span>}}<span\; class="notranslate">\; \&ap;</span>\frac{{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; BS</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; Piot</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; send</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; R</span>}}{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; 1.2288</span>}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; 10</span>}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; chip</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&CenterDot;</span>\frac{\mathrm{<span\; class="notranslate">\; RSSI</span>}}{\mathrm{<span\; class="notranslate">\; W</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; W</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1.23</span>}\mathrm{<span\; class="notranslate">\; Mbits</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; ,</span>$

Table 1 and Table 2 respectively correspond to the required forward and reverse initial transmission power numerical tables under each value of E _c /I _o and reverse load (assuming that the service is a data service with a fixed rate). It can be seen from Table 2 that when the pilot strength is the same, the transmit power of the mobile station under different reverse loads reflects the degree of influence of poor pilot strength and heavy reverse load on system performance respectively.

It can be seen from Table 1 that corresponding to different receiving pilot strengths, the forward initial transmission power is different. In order to reduce the increase of forward load, the cell with higher receiving pilot strength should be selected.

It can be seen from Table 2 that corresponding to different total reverse signal strengths, the reverse transmit power is different. In order to reduce the increase of the reverse load, the cell with the lower total reverse signal strength should be selected when the reverse fading is the same.

Since the forward and reverse transmission power is relatively independent, in order to comprehensively evaluate the impact on the system, a weighted summation method is adopted, namely:

$\mathrm{<span\; class="notranslate">\; Es</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; max</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; max</span>}}$

Wherein E _s is the obtained system performance priority value, and the cell selection during soft handover is performed based on this value, and the cell with a relatively high value is preferred to establish a soft handover branch. P _f is the forward initial transmission power, that is, the transmission power required by the base station, which is assumed to be under the condition of ideal power control. Pr is the reverse transmission power, that is, the transmission power required by the mobile station. P _{f_max} is the maximum transmission power allocated to a single user in the forward direction. Here, when the system is fully loaded and is a basic rate service, P _{f_max} can be roughly taken as 1 watt; P _{r_max} is the maximum transmission power in the reverse direction, which is generally taken as 20 mW. α is a positive weight, reflecting the impact of forward transmit power on system performance, and β is also a positive weight, reflecting the impact of reverse transmit power on system performance. Here, α=0.6 and β=0.4 are taken, and these two weights can be adjusted according to the different requirements of the actual service of the system on the forward and reverse capacity.

Table 3 below is a comprehensive consideration of forward and the selection of cells under the influence of reverse RSSI

table 3

district Transmitting power (watts) Degrees (RSSI) (mW) Power (mW) Priority value result A -16 1.66 5× ^10-9 15 0.89 do not choose B -14 1.05 1.59×10 ^-6 18 1.02 choose

Calculate the reverse initial transmission power according to the total strength of the reverse link signal RSSI, and estimate the stable value of the reverse transmission power relatively simply. Since the reverse attenuation cannot be obtained, it is estimated by the forward attenuation, so the estimated value is the same as The actual value has a certain deviation.

The soft handover method of the present invention adopts the existing CDMA2000 air interface protocol and corresponding structure, the method is easy to realize and the time used for calculation does not increase significantly, and the required parameters and hardware can be provided by the existing CDMA2000 system. The corresponding relationship Table 1-Table 3 obtained through numerical calculation proves that the idea based on it is reasonable, and compared with the traditional switching method, it can effectively improve the system performance. Through the above description, it is not difficult for those skilled in the art to realize the soft handover cell selection combined with the reverse load in the CDMA2000 system.

Claims (7)

1. A mobile station soft handover cell method in a code division multiple access communication system, the method is based on a code division multiple access system, in the system, including a base station controller, several base station transceivers controlled by the base station controller, The reverse link from the mobile station to the activated base transceiver station and the forward link from the activated base transceiver station to the mobile station, the mobile station and each base transceiver station comprising a transceiver, characterized in that the method comprises The following steps: a. Make the mobile station establish a traffic channel with at least one base transceiver station in the system, and the mobile station periodically search for the pilot frequency of each base transceiver station on the frequency point used; b. The base station controller determines the active set joining threshold or the active set dynamic joining threshold according to the number of pilots in the pilot active set of the mobile station, and sends the active set joining threshold or the active set dynamic joining threshold to the mobile station; c. The mobile station continuously detects the pilot strength of each base transceiver station and reports it to the base station controller; d, the base station controller judges the number of pilots in the current active set of the mobile station and sends the judgment result to the mobile station and the relevant base transceiver station through the forward link; e. The base station controller selects a cell with a low system performance priority value Es to be removed from the active set or not to enter, and then notifies the mobile station of the selected cell through a pilot assignment message, and the mobile station establishes a new cell according to the instruction of the base station controller. After the connection of the cell is completed, return to step a, wherein the system performance priority value Es is negatively correlated with forward link interference, reverse link interference and distance attenuation; f. The above steps are repeated until the mobile station ends the service state. 2. The cell method for mobile station soft handover in the code division multiple access communication system as claimed in claim 1, wherein in said step b, if there is only one pilot in the active set of mobile station pilots, then the base station controller Send the active set addition threshold T_ADD to the mobile station; if there is more than one pilot in the active set of the pilots of the mobile station, the base station controller sends the active set dynamic threshold T_ADD_DYC to the mobile station. 3. The cell method for mobile station soft handover in the code division multiple access communication system as claimed in claim 2, characterized in that: the threshold T_ADD value added to the active set is set by the system, generally getting -13db; the active set Dynamically add the threshold T_ADD_DYC value according to the formula

find out, Wherein T_ADD_DYC is the active set dynamic adding threshold, SOFT_SLOPEs is the dynamic slope of the active set adding threshold, Psi is the forward pilot strength of the I base station, ADD_INTERCEPTs is the dynamic intercept of the active set adding threshold, and T_ADD is the active set adding threshold. 4. The mobile station soft handover cell method in the CDMA communication system as claimed in claim 1, characterized in that: in the step c, the mobile station continuously detects the pilot frequency strength of each base station transceiver and reports it to the base station control The detector refers to reporting the pilot to the base station controller through a pilot strength measurement report message when finding a pilot whose strength is greater than the active set addition threshold T_ADD or the active set dynamic addition threshold T_ADD_DYC. 5. The mobile station soft handover cell method in the code division multiple access communication system as claimed in claim 1, characterized in that: in the described step d, when the base station controller judges the number of pilots in the current active set of the mobile station, If the number of pilots is less than 3, then directly add the new pilot to the active set; if the number of pilots is greater than or equal to 3, then according to the formula $\mathrm{<span\; class="notranslate">\; Es</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; max</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; max</span>}}$ Calculate the system performance priority value Es of the pilots in the current active set and the new pilots, where P _f is the forward initial transmission power, P _r is the reverse initial transmission power, and P _{f_max} is the maximum forward transmission allocated to a single user Power, P _{r_max} is the maximum transmission power allocated to a single user in the reverse direction, α is a positive weight, reflecting the impact of forward transmission power on system performance, and β is also a positive weight, reflecting the impact of reverse transmission power on the system Influenced by performance, the pilot with the lowest priority value is selected. If the pilot is in the current active set, it will be deleted from the active set. If the pilot is a new pilot, it will be refused to join the active set. 6. The mobile station soft handover cell method in the code division multiple access communication system as claimed in claim 5, characterized in that: said formula $\mathrm{Es}=\frac{\mathrm{\&alpha;}}{P_f/P_{f\_\max }}+\frac{\mathrm{\&beta;}}{P_r/P_r\_\max }$ Among them, the forward initial transmission power Pf specified by the mobile station is according to the formula $P_f=\min [P_{\mathrm{pilot}\_\mathrm{send}}\&CenterDot;10\frac{\mathrm{D.}+0.5m}{10}\&Center\; Dot;\frac{R}{W,}{P}_{\max }]$ Calculate, wherein, P _{pilot_send} is the forward pilot intensity transmitted by the base station, D is the ratio of the information bit energy and the interference spectral density that the base station must satisfy for the above-mentioned mobile station side demodulation, and M is the forward pilot obtained above The content of the intensity item, R is the information rate of the service, P _max is the maximum power that the mobile station can use, W=1.23Mbit/s. 7. The mobile station soft handover cell method in the code division multiple access communication system as claimed in claim 5, characterized in that: said formula $\mathrm{Es}=\frac{\mathrm{\&alpha;}}{P_f/P_{f\_\max }}+\frac{\mathrm{\&beta;}}{P_r/P_r\_\max }$ Among them, the reverse initial transmit power Pr according to the formula $P_r=\frac{{\left(\frac{{\mathrm{E.}}_b}{I_0}\right)}_{\mathrm{BS}}\&CenterDot;R\&Center\; Dot;\mathrm{RSSI}}{P_{r\_\mathrm{loss}}\&CenterDot;W}$ Calculate, where,

is the ratio of the information bit energy to the interference spectral density that the mobile station must satisfy in order to meet the quality of service requirements required by the demodulation at the base station side, R is the information rate of the service, RSSI is the total strength of the reverse link signal, P _{r_loss} is the reverse path fading.

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