CN1689347A - Method and system for providing a hard handoff in communications in a CDMA system - Google Patents

Abstract

The present invention is a method and system for providing hard handover in a CDMA communication system, which includes increasing the signal power of the source cell before the handover; increasing the power of the code channel in the target cell during the handover, and reducing the signal power in the source cell The power of the code channel; readjust the power of the new code channel according to E _b /I _o ; after switching, if E _b /I _o is poor for the new code channel, then pass n·T _c to the new code channel code to convert. The present invention substantially improves the traditional mobile communication system in terms of communication reliability and quality by providing an additional system.

Description

A method and system for providing hard handover in a CDMA communication system

technical field

The present invention relates to mobile telephone systems. It relates to a new mobile unit handover control system in the communication of the mobile station in the Code Division Multiple Access (CDMA) system. More specifically, the present invention is a method and system for providing hard handover in a CDMA communication system.

Background technique

So far, all CDMA systems use soft handover. This is because the Walsh codes used in the existing CDMA system cannot overcome the inter-adjacent cell interference (ACI), especially at the boundary of the cell, where the inter-adjacent cell interference is very high. Soft handover is a means of adopting a diversity scheme to enhance and protect signals within the scope of soft handover by acquiring signals from two cells, the source cell and the target cell. These two signals from the two cells are called two pointers. Usually, since many surrounding cells contain more than two pointers, seven pointers will meet during the soft handover process of the 3G system. Therefore, the soft handover process is very complicated. In addition, the system capacity is reduced since two signal channels serve one user within the handover range. Sometimes, one third of the capacity is lost due to the soft handover system.

Contents of the invention

The invention relates to a method and system for providing hard handover in a CDMA communication system. Hard handover can occur in a system, such as a frequency division or time division system, when all transmitted signals (channels) are orthogonal. In FDMA systems (such as AMPS), all transmitted signals are different frequencies except for the multiplexing of the same frequency within an appropriate distance. Therefore, there is no ACI problem in principle, so hard switching can be realized. The GSM system is a TDMA system. Therefore, it can employ hard handover. In a CDMA system, if a set of clever codes {C _i } can be found satisfying the following properties

Autocorrelation Rc _i (τ)=o where: τ≠o, -t ₁ τ≤t ₁ ;

Cross-correlation Rc _i c _j (τ)=o For all τ, there is: -t ₂ τ≤t ₂ .

Here the window properties -t ₁ τ ≤ t ₁ and -t ₂ τ ≤ t ₂ must eliminate ACI, so hard handover can be achieved.

Now, several ingenious codes have been found. However, it consists of only 32 codes with a window -3t _c τ ≤ 3t _c , where t _c is the chip interval. In order to identify the same 32 code groups in different cells, different means for identifying cells are added. Most of them will cause a white noise effect, ie destroy the zero correlation windows of the two code groups assigned to two adjacent cells. Due to the prevalence of ACI, hard switching cannot be implemented. Now, there is a new class of clever codes called Distinctive Orthogonal Codes (DOC), which have the clever code properties mentioned above. In addition, the code c _i assigned to cell x and the code c _j assigned to cell y have the following characteristics:

Rx _ci y _cj (τ)=o where τ≠o, and -t ₂ τ≤t ₂

In the range of window -t ₂ τ≤t ₂ , except for τ≠o, there is no ACI at the cell boundary in principle.

Despite the fact that ACI is always present, it can be reduced and controlled by the present invention. The present invention provides a method for substantially improving the reliability and quality of communications in conventional mobile telephone systems by providing an add-on system. Technical scheme of the present invention is:

A method of providing hard handover in communication of a CDMA system, comprising the steps of:

Increase the signal power of the source cell before handover;

During the handover process, the power of the code channel in the target cell is increased, and the power of the code channel in the source cell is reduced;

Readjust the power of the new code channel according to E _b /I _o ;

After switching, if E _b /I _o is impoverished for the new code channel, the new code is converted by n·T _c .

Said switching is soft switching or hard switching.

The sizes of the source cell and the target cell are not necessarily equal.

Said handover can be applied to sector-to-sector handover in a cell.

The codes described can be converted to any value, positive or negative.

The power boost can be boosted individually, or with code switching.

Code switching can be switched individually, or as power is boosted.

The present invention also provides a system for providing hard handover in a CDMA communication system. In a cellular telephone system, information signals communicated between one mobile user and another mobile user need to pass through at least a plurality of geographical divisions Each cell is defined as a respective geographic service area, and when a mobile user changes the cell of its service area, the system directly communicating with the mobile user needs to pass through at least one of the cells; The system includes: switching device; power increasing device; code conversion device.

The present invention substantially changes the communication reliability and communication quality of the traditional mobile phone system by providing the additional system.

Description of drawings

The characteristics and advantages of the present invention will be more clear after combining the detailed description of the following four drawings.

FIG. 1A is a schematic diagram of hard handover when there is no ACI in FDMA/TDMA;

FIG. 1B is a schematic diagram of soft handover when there is ACI in FDMA/TDMA;

Figure 2A is a schematic diagram of a hard handover in a CDMA system with a special set of clever codes and energy gains (before handover);

Figure 2B is a schematic diagram of a hard handover in a CDMA system with a special set of clever codes and energy gain (after handover);

Fig. 3A is DOC (characteristic orthogonal code) without energy gain;

Figure 3B is a DOC with energy gain (before hard handover);

Fig. 3C is a DOC with energy gain (hard switching second half);

Fig. 4 is a schematic diagram of a code conversion method according to the present invention.

Detailed ways

The present invention provides a kind of method of hard switching in CDMA communication system, and this method comprises the following steps:

Increase the signal power of the source cell before handover;

During the handover process, the energy of the code channel is increased in the target cell, and the energy of the code channel is decreased in the source cell;

Readjust the energy of the new code channel according to the condition E _b /I _o ;

If E _b /I _o is impoverished for the channel of the new code after switching, the new code is converted to n·T _c .

face the real environment;

Rx _ci y _cj (τ)=δ where τ≠o, and -t ₂ τ≤t ₂

Here δ is a small value that ACI hopes to achieve. The ACI of a source cell can come from direct paths or multiple paths of all adjacent cells. ACI has the greatest impact on the cell border, where the characteristics of smart codes can be used to reduce ACI, except for the point where τ=o.

Firstly, Fig. 1A, Fig. 1B , and Fig. 2A, Fig. 2B show the methods for solving the ACI problem in the prior art. Hard handover is used in FDMA or TDMA systems because there is no ACI. While ACI exists due to the non-zero correlation window characteristic, soft handoff is used in CDMA systems. Shown in Fig. 2A, Fig. 2B, Fig. 2C is the special code group formed by the ingenious code DOC. A high cross-correlation is ACI at τ=o, which is unavoidable.

The present invention increases the power of the signal for a short time before hard handoff. The result satisfies the following formula:

$\frac{\mathrm{<span\; class="notranslate">\; C</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; xy</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\frac{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; Y</span>}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; xy</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&ap;</span>\frac{\mathrm{<span\; class="notranslate">\; x</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; xy</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; )</span>}$

Here, ρ _xy (o) is a cross-correlation coefficient (-1≤ρ≤1).

When the power of C increases, C/I increases accordingly. This is exactly what we need.

The second step of the present invention is: during the hard handover period, the power of the code channel is increased in the target cell, and the power of the code channel is decreased in the source cell. After the hard handover is completed, the power of the code channel is reduced according to E _b /I _o .

When the two cells are equal in size, the ACI is in a critical state. If a cell is larger than its neighbor, then at τ=o (which is half the distance between two base stations), the ACI is located in the larger cell, closer to its base station. In this case, the mobile unit is covered by a stronger signal.

After the hard switching is completed, reduce the power of the new code channel. If E _b /I _o is poor for the new code channel, the new code can be converted by n T _c . As shown in Figure 4, the value range of n can be is 1 to 3 or -3 to -1; suppose, C ₁ is the code of cell x and C ₂ is the code of cell y. Shift the _C2 code to the right means so that the ACI zero-time peak is shifted to the base station close to cell y. Shift the _C2 code to the left means so that the ACI zero-time peak is shifted to the base station close to cell x. This step page provides more guarantees that the ACI can be shifted from the received power position, that is, the autocorrelation position is equal to zero, and the hard handover can be successfully performed.

It should be noted that when the solution of the present invention is applied, the sizes of the two cells do not need to be completely equal. Here, it can be any number of codes, and any size of the relevant window. During the switching process, the code conversion can be converted to any value, positive or negative, and the power increase can be increased alone or accompanied by the code conversion. Likewise, code transformations can be transformed alone or with power increases. In addition, in order to reduce various interferences, the code conversion provided by the present invention can be applied to any environment.

A system for providing hard handover in a CDMA communication system of the present invention, in a mobile phone system, information signals communicated between a mobile user and another mobile user need to pass through at least one cell in a plurality of geographical divisions, each A cell is defined as a respective geographic service area. When a mobile subscriber changes cells in its service area, the system communicating directly with said mobile subscriber passes through at least one of said cells. The system includes: a switching device; a power increasing device; a code converting device.

The present invention substantially improves the traditional mobile communication system in terms of communication reliability and quality by providing an additional system.

The above description of the specific embodiments provides a technical solution for making and using the present invention. There are various transformable technical solutions in implementing the present invention, and these transformable solutions can be easily derived. Therefore, the above specific embodiments are only used to illustrate the present invention, rather than limit the present invention.

Claims (8)

1. method that direct-cut operation is provided in cdma communication system is characterized in that may further comprise the steps:

Before switching, promote the signal power of cell-of-origin;

In handoff procedure, promote the power of sign indicating number passage in the Target cell, and reduce the power of the sign indicating number passage in the cell-of-origin;

According to E _b/ I _oReadjust the power of new sign indicating number passage;

After switching, if E _b/ I _oFor described new sign indicating number passage is poor, then passes through nT _cNew sign indicating number is changed.

2. method according to claim 1 is characterized in that, described soft handover or the direct-cut operation of switching to.

3. method according to claim 1 is characterized in that, the phasing not of uniform size of described cell-of-origin and purpose sub-district etc.

4. method according to claim 1 is characterized in that, described switching can be applied to the switching of a sector in the sub-district to the sector.

5. method according to claim 1 is characterized in that, described sign indicating number can be converted into arbitrary value, comprise on the occasion of or negative value.

6. method according to claim 1 is characterized in that, what the lifting of described power can be independent is raised, and perhaps promotes along with the conversion of sign indicating number.

7. method according to claim 2 is characterized in that, the conversion of sign indicating number can be changed separately, perhaps changes along with the lifting of power.

8. system that direct-cut operation is provided in cdma communication system, in mobile telephone system, the information signal of communicating by letter between mobile subscriber and another mobile subscriber at least need be through a sub-district in a plurality of geographical zones, each sub-district all is defined as geographic service area separately, when a mobile subscriber changed the sub-district of its coverage, directly the system that communicates by letter with described mobile subscriber at least need be through in the described sub-district; It is characterized in that described system comprises: switching device shifter; Power improves device; The code conversion device.

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