KR20020091282A - Improving the performance of a CDMA system - Google Patents

Abstract

A method of utilizing resources of a CDMA telecommunication system comprising a plurality of base stations and one or more mobile stations, the method comprising: causing the base station to indicate whether they have unused capacity, and causing one or more of the mobile terminals to A method of utilizing resources in a CDMA telecommunications system comprising changing or keeping a constant data rate or power output in accordance with an indication of unused capacity received from a system. A contention resolution phase may be used so that only enough terminals to accommodate unused capacity increase their data rate.

Description

Improving the performance of a CDMA system

The present invention relates to improving the performance of a code division multiple access (CDMA) system, preferably a system comprising a mixture of voice and data services.

CDMA systems are known and examples of such systems known or proposed are UMTS, cdmaOne, W-CDMA, multi-point CDMA WiLL technologies, and some other DS Direct Sequence-CDMA (CDMA) systems. The invention is also applicable to frequency hopping CDMA systems.

CDMA systems are now well established, but efforts to improve these systems have focused primarily on voice transmission and circuit switch services, in particular using power control and soft hand-off techniques. Still, there is a need for simple and optimal methods in transmitting burst data services where delay variations in DS-CDMA systems can be tolerated. Examples of such services are email, file transfer, still image transfer, non real time voice, non real time video images, and the like. All these services will be provided by third generation systems, such as UMTS and can be supported by packet data transmission mechanisms capable of burst data transmission and independent of delay variation.

There remains an urgent need to provide an efficient way to optimize uplink throughput and capacity for DS-CDMA systems that mix voice and data traffic.

A typical cell phone system is shown in FIG. The system comprises a plurality of base stations B ₁ to B _n and a second plurality of mobile terminals MT ₁ to MT _n (for example mobile phones or radios) using a cellular system.

Although only a few cells and mobile stations are shown in FIG. 1, of course there will usually be a large number of cells and mobile stations.

Each of the base stations receives and decodes transmissions from several mobile stations MT in a given frequency band. This is schematically illustrated in FIG. 2. In addition, as shown in FIG. 1, a signal transmitted from each mobile terminal such as MT ₁ will typically be received by a plurality of base stations. In this case, the signal from the mobile terminal MT ₁ is received by the base stations B ₁ , B ₂ , B ₃ , B ₄ , but is received by each base station because the mobile terminal is at different distances from them. The signal strength that will be different will vary. Similarly, mobile terminal MT ₁ may also receive transmissions from each of these base stations.

Any given base station receives and decodes transmissions from multiple mobile terminals. However, any particular base station has only some uplink capacity. This can be seen as the maximum useful receive power that the base station can handle while maintaining a satisfactory level of interference from other transmitters. The amount of useful received power received by this base station at any point in time obviously depends on the number of mobile terminals communicating with this base station and the signal power received from each mobile terminal (the terminal can change its transmit power). . 3 shows the power received by the base station with respect to time. At the first time, only the first mobile terminal MT _a is communicating and therefore the base station has received the average power P _a . Later at time T ₁ , the second terminal starts communication at power P ₂ in addition to the first terminal. Therefore, the power received by the base station is averaged, to be P ₁ + P ₂ . Subsequently, the third mobile terminal MT _c is added to the power P ₃ so that the received power is P ₁ + P ₂ + P ₃ , and so on. The transmission from each terminal can be seen as an interference source for the received signal of other terminals when detected at the base station.

The base station has a maximum capacity P _MAX and is currently approaching it.

At any time, a given base station receives and decodes transmissions from many mobile terminals as described above. However, the uplink capacity of this base station is not yet saturated. In this case, whenever this unused uplink capacity is available, it would be desirable to use it, for example, by increasing the data rate of one or more mobile terminals transmitting packet data. Thus, in the example of FIG. 3, the maximum capacity of the base station has not yet been reached. Since it is most efficient for the base station to be fully utilized, any of the mobile stations MT _a to MT _d will be able to increase their power output, which will increase the total power received so that P _MAX will be reached. .

However, simply instructing one or more mobiles to increase their data rate causes more energy to be released by that particular mobile. As shown in FIG. 1, the signal from the mobile terminal MT ₁ is received not only by the base station B ₁ but also by the base stations B ₂ , B ₃ and B ₄ . Thus, if the mobile terminal MT ₁ increases its data rate, more energy will be emitted by this mobile terminal, thus adding interference to adjacent cells. If any of these neighboring cells is already operating at its maximum uplink capacity, by this added interference, all other transmissions of that neighboring cell to the base station will be blocked by excessive interference. Thus, increasing capacity utilization in the first cell can have an undesirable effect on adjacent cells that were previously heavily loaded.

The present invention is intended to avoid this situation.

Summary of the Invention

In a first aspect according to the present invention, a method of utilizing resources of a CDMA telecommunications system comprising a plurality of base stations and one or more mobile terminals, wherein the base station provides an indication of unused capacity to the one or more mobile terminals. And causing one or more of the mobile terminals to change or maintain a constant data rate or power output in accordance with the unused capacity indication received from the base station.

According to the present invention, in a CDMA telecommunications network comprising a first plurality of base stations and one or more mobile terminals, each base station is adapted to indicate some unused capacity to the corresponding mobile terminal or each mobile terminal communicating with the base station. Also provided is a CDMA telecommunications network in which the mobile terminals are adapted to change or maintain data rate or power output in accordance with an unused capacity indication received from base stations.

In another aspect, the present invention provides a base station comprising means for indicating, at a base station for a mobile communication network, any unused uplink to mobile terminals in wireless communication with the base station.

In another aspect, the present invention provides a mobile terminal having a variable data rate for a CDMA telecommunications system, the means for receiving indications of unused uplink capacity from any base station with which the mobile terminal communicates, and from the base stations. And a means for maintaining or changing the data rate or power output of the mobile terminal in accordance with the used unused capacity indications.

1 is a diagram schematically illustrating a cellular network.

2 illustrates a plurality of mobile terminals for transmitting and receiving information with a base station.

3 schematically illustrates a power load on a base station.

4 schematically illustrates another power load on a base station.

5 schematically illustrates a base station and a mobile terminal.

Again in the situation of FIG. 1, each of the base stations B ₁ through B ₇ has a specific capacity. In an embodiment of the invention, each base station is configured to broadcast a number or value called an unused uplink capacity broadcast number (UUCBN). This represents the amount of unused uplink capacity available at that time at that base station. Thus, in FIG. 4, the amount of power used by the base station at time T ₁ is PT ₁ . Therefore, the unused capacity at time T ₁ is fn (P _MAX -PT ₁ ). Therefore, the base station can indicate to the UUCBN the amount fn (P _MAX -PT ₁ ) of available uplink capacity. The unused capacity indication in this broadcast may be artificially reduced if there is a base station with the highest load nearby, such as B ₆ , which may not be decoded by one or more mobile stations nearby but may still experience interference. Can be.

Each mobile terminal that transmits packet data decodes UUCBN broadcasts from each base station to which the mobile terminal is connected. This does not require any hardware additions to the mobile terminal and simply needs to slightly modify the software so that the UUCBN data can be decoded among the many different types of data the terminal receives from the base station.

Of course, each mobile terminal receives signals from several base stations as shown in FIG. Therefore, the mobile terminal in the position of transmitting packet data or other data to which delay variation is tolerated continuously determines which of the following three states to apply.

State 1: All UUCBN broadcasts indicate that unused uplink capacity is available at the respective base stations.

State 2: One or more UUCBN broadcasts indicate that the uplink capacity of each base station is fully utilized (ie, the maximum value for self-cell interference).

State 3: One or more UUCBN broadcasts indicate that the uplink capacity of each base station is adversely affected by excessive interference.

If state 2 or state 3 is present, then apparently the mobile terminal cannot increase its data rate or transmit power since it may adversely or overload one or more base stations.

If state 1 exists , at least one mobile terminal may increase its data rate. However, it should be recalled that there may be a plurality of mobile terminals transmitting packet data, and all may simultaneously detect the presence of state 1 for each mobile terminal. Therefore, in FIG. 1, if the base station B ₁ has unused uplink capacity, the mobile terminals MT ₁ and MT ₂ will know. However, if these mobile terminals try to increase their data rate, the uplink capacity can be overloaded. The number of mobiles that detected the presence of state 1 is unknown to the mobiles themselves.

Thus, in some embodiments of the present invention, some form of uplink bandwidth contention solution is needed so that at least one mobile terminal can utilize unused uplink capacity in order to avoid wasting unused uplink capacity. That is, some form of contention between mobile terminals is needed so that only some of the mobile terminals can increase their data rate so that the uplink capacity of the base station can be used.

The preferred way to solve this dilemma is as follows.

Each base station with unused uplink capacity will know at any time how many mobile terminals Mp are transmitting at that base station transmitting packet data. The base station transmits the number of mobile terminals as a number called unused capacity access control number (CCACN). UCACN is derived directly from the number of mobile terminals using a priori-defined algorithm. This may be any one of many suitable algorithms. An example of the generation algorithm of UCACN may be as follows.

UCACN = K x 1 / Mp (1) or

UCACN = K x 100 / Mp (2) or

UCACN = K x (a / Mp + b / Mp + c / Mp + ...) (3)

Here, K is a coefficient at which a value is selected to balance the probability that an excessive number of mobile terminals access unused uplink capacity and that no mobile terminal accesses unused uplink capacity. Series a, b, and c represent the subscription priority weighting coefficients. These series may be used, for example, if users can pay a fee to grant them priority access upon subscription. In an embodiment of the present invention, this fee payment does not guarantee preferential access but rather gives a higher probability that the preferred access will be given to the mobile terminal.

Clearly, many other algorithms can be used instead.

Each of the Mp mobile terminals determines whether it can increase its uplink data transmission rate within the usable capacity indicated by the received set of UUCBNs. If possible, the mobile station randomly generates a number of access attempts (AAN) with a probability of 1 / UCACA that meets certain selection criteria (e.g., below a certain threshold). Alternative relationships between AAN and UCACN may be used within the main purpose of the present invention. If a particular criterion is met, the mobile station informs the corresponding base station or each base station with unused capacity that it will increase its data data and increases the data rate. Normally this is done by doubling one preset data rate step, for example, that data rate.

There may be a situation that results from the algorithm indicating that too many mobile terminals want to increase their data rates. This may cause another phase of contention resolution, in which case the base station randomly selects among the mobile stations that wish to increase their data rate and is granted (or not authorized) access to unused uplink capacity. Signal only to selected mobile terminals.

If a Direct Sequence-CDMA (DS-CDMA) system has a spreading factor such as 4, 8, 16, 32, etc., and uses a spreading factor, the algorithm that generates the AAN is more likely to achieve selection criteria for low-rate users. May contain factors that give better opportunities. This means that high rate users will exceed their uplink capacity too quickly by doubling their rate, whereas users who are currently sending data at low bit rates can increase the power level by a small amount so that more users will rate their rate. Because it can increase. In one example,

AAN = random number / legacy data rate (4)

Therefore, the smaller the data rate, the higher the probability of success. The AAN value may be affected by the number of base stations to which the mobile terminal soft-offs.

If the subscription configuration for a given user is enabling high or low priority access to unused uplink capacity, then the AAN generation algorithm in the mobile terminal can be adjusted appropriately to take this into account. For example,

AAN = random number × Priority Waiting (5)

Applying the explanation behind the derivation of equations (4) and (5), the AAN may be based on the following algorithm.

AAN = random number × preferred standby / existing data rate (6)

if

AAN> Threshold

then

Increased data rate

else

No change

endif

If state 2 exists , the mobile station continues to transmit data at the previous data rate without taking new action.

If state 3 exists , the mobile station informs the affected base station that it will reduce its data rate and reduces the data rate by a predetermined rate step. This data rate reduction can be achieved by terminating one of the spreading codes used by the mobile station (if multiple codes are used), or by increasing the spreading rate while keeping the absolute chipping rate the same. have.

Not all mobiles need to reduce their power. If this is the case, some of the mobile terminals connected to the base station may "select themselves at random" using mechanisms equivalent to those described for state 1 above to reduce their power. Most preferably, this includes the option of allowing mobile terminals that consume more capacity, or mobile terminals with lower priorities, to reduce their power first.

Moreover, mobile terminals in state 3 that are in soft handoff but are not actually controlled by a base station exhibiting excessive interference may preferentially maintain their current data rates because their interference contributions will be less. This is because the power received from these mobile terminals will be lower than the mobile terminals whose power is controlled by the base station. One non-limiting example of a threshold detection algorithm may be as follows.

DRRN = random number × priority wait × PC-fac / existing data rate (7)

Where DRRN is " data rate reduction number " and PC-fac is 1.0 if the mobile station received a " power down " power control command from the affected base station and 1.5 otherwise.

if

DRRN <threshold

then

Data rate reduction

else

No change

endif

5 illustrates a base station B ₁₀ and a mobile terminal MT ₁₀ . Each has respective processing means 50, 51 used to generate respective values of the invention, such as UUCBN, UCACN and AAN. The processing means will generally be existing processors that each base station already has, and software can be used in embodiments of the invention to generate various values and the like.

Claims (29)

A method of utilizing resources of a CDMA telecommunication system comprising a plurality of base stations and one or more mobile stations, the method comprising: causing the base station to provide an indication of unused capacity (UUCBN) to the one or more mobile terminals, Causing the terminals to change or maintain a constant data rate or power output in accordance with the unused capacity indication received from the base station. 2. The method of claim 1, comprising causing the mobile station to increase its data rate only if all base stations communicating with the mobile station indicate that they have unused capacity. . 3. The resource utilization of a CDMA telecommunications system of claim 2, comprising a contention resolution step wherein only a portion of the mobile terminals in communication with a group of base stations indicating that all have unused capacity increase their data rate. Way. 4. The base station of claim 3, wherein each base station with unused capacity is configured to transmit a first value relating to the number of mobile terminals that are in data communication with the terminal, and each mobile terminal is to meet selection criteria related to the value. And randomly generate a second value having a probability, and wherein only the mobile terminals whose generated second value meets the criterion are enabled to increase their data rate. 5. The method of claim 4, wherein the first value uses a coefficient of a value that is selected to balance the probability that an excessive number of mobile terminals access unused uplink capacity and the probability that no mobile terminal accesses unused capacity. Resource utilization method of a CDMA telecommunication system. 6. The method of claim 5, wherein the first value UCACN is K × X / Mp and K is a balance between the probability that an excessive number of mobile terminals access unused capacity and the probability that no mobile terminal accesses unused capacity. Wherein X is a number and Mp is the number of mobile terminals in data communication with the base station. 7. The method of claim 6, wherein the first value UCACN is K × (a / Mp + b / Mp + c / Mp ...), where K is the probability that an excessive number of mobile terminals will access unused capacity. A mobile terminal is also selected to balance the probability of not accessing unused capacity, and the series a, b and c represent subscription priority weighting factors. 8. A method according to any one of claims 4 to 7, wherein the second value (AAN) generated by each mobile terminal has a probability 1 / UCACN that satisfies the selection criterion, wherein the UCACN is generated by a base station. The first value, resource utilization method of the CDMA telecommunications system. 10. The method of claim 8, wherein the second value (AAN) is generated by an algorithm that gives lower data rate users better opportunities to achieve selection criteria. 10. The method of claim 8 or 9, wherein the second value (AAN) generated by a mobile terminal is related to the number of base stations to which the mobile terminal is soft handing off. 11. The method of claim 8 to 10, wherein the second value (AAN) is related to a preferred access level according to the mobile terminal user. 12. The resource of a CDMA telecommunications system according to any one of claims 4 to 11, wherein if too many mobile terminals succeed in the contention resolution step, another step in which the base station randomly selects one or more terminals is executed. How to use. 2. The resource of a CDMA telecommunications system according to claim 1, comprising the step of causing one or more mobile stations to reduce their data rate if the base station is indicating that its uplink capacity is being affected by excessive interference. How to use. 14. The method of claim 13, comprising a contention resolution step of selecting which of the mobile terminals affecting the base station will reduce their data rate. 15. The method of claim 14, wherein mobile handsets that are soft handed off and whose power is not controlled by a base station exhibiting excessive interference preferentially maintain their existing data rate. The method of any one of the preceding claims, wherein the unused capacity indication of a base station is reduced when a large load or a full load is placed on an adjacent or nearby base station. A CDMA telecommunications network comprising a first plurality of base stations and one or more mobile terminals, each base station adapted to indicate a certain unused capacity to a corresponding mobile terminal or each mobile terminal communicating with the base station, the mobile terminal Are adapted to change or maintain their data rate or power output in accordance with the unused capacity indication received from the base stations. 18. The CDMA telecommunications network of claim 17 comprising contention resolution means. A base station for a mobile communication network, comprising: means for indicating certain unused uplink capacity to mobile terminals in wireless communication with the base station. 20. The base station of claim 19, further comprising means for generating and transmitting a value related to the number of mobile terminals in data communication with the base station. 21. The base station of claim 19 or 20, wherein the indication of unused uplink capacity is in accordance with information of capacities of adjacent base stations. A mobile terminal having a variable data rate for a CDMA telecommunications system, the means for receiving indications of unused uplink capacity from any base station with which the mobile terminal communicates, and according to the unused capacity indications received from the base stations. And means for maintaining or changing the data rate or power output of the mobile terminal. 23. The mobile terminal of claim 22, adapted to change its data rate only if it indicates that all base stations have unused capacity. The mobile terminal of claim 23 comprising contention resolution means. A method of utilizing the resources of a CDMA system as described with reference to and as shown in the accompanying drawings. A contention resolution method as described with reference to the accompanying drawings and shown in these accompanying drawings. A CDMA telecommunications system as described with reference to the accompanying drawings and shown in these accompanying drawings. A base station as described with reference to the accompanying drawings and shown in these accompanying drawings. A mobile terminal described with reference to the accompanying drawings and shown in these accompanying drawings.