HK1082634A - Method and system for performing call admission control in the uplink for third generation wireless communication systems - Google Patents

Description

Method and system for performing call admission control in the uplink of a third generation wireless communication system

Technical Field

The present invention relates to the field of communications, and more particularly, to wireless communications. More particularly, the present invention relates to call admission control in third generation wireless systems.

Background

Third generation wireless communications, such as wideband code division multiple access (WCDMA-TDD) systems, support not only voice services, but also various broadband services, such as video and internet traffic. In such a system, the purpose of call admission control is to ensure that the quality of service (QoS) of all users admitted to the system is met. Call admission control directly affects the quality of service (QoS) of mobile users and affects the stability and capacity of the system. Therefore, call admission control is of paramount importance for WCDMA-TDD system design.

In recent years, call admission control has progressed in WCDMA-FDD systems, but WCDMA-TDD systems have little progress in call admission control. One approach to the problem of such systems is to allocate resources according to a fixed required signal-to-interference ratio (SIR). However, in WCDMA-TDD systems, the necessary SIR for a user is not fixed, but rather varies over time due to imperfect power control. In a WCDMA-FDD system there are no time slots, whereas in a WCDMA-TDD system a user may use more than one time slot.

Therefore, it is desirable to provide call admission control for TDD systems.

Disclosure of Invention

A method and system for performing call admission control is disclosed in which admission decisions are based on a dynamic SIR requirement and it is assumed that a user may use multiple timeslots. The invention is implemented without using on-line measures, thereby avoiding increasing the implementation cost of software and hardware.

Drawings

Fig. 1 shows a method for performing call admission control in the uplink of a third generation wireless communication system, according to a preferred embodiment of the present invention.

FIG. 2 shows a call admission control system according to a preferred embodiment of the present invention.

Detailed Description

According to the present invention, call admission control (in which a user can use a plurality of slots) is performed in a WCDMA-TDD system while taking into consideration the fact that a necessary signal-to-interference ratio (SIR) of each user is a random variable. The resource allocation is optimized to produce a minimum total outage probability (P) for a new user_out-total) And ensure P_out-totalBelow a predetermined value.

Preferably, the invention is implemented using the following assumptions. First, each frame is divided into 15 slots according to the Third Generation Partnership Project (3 GPP) standard. Second, the chip rate of the WCDMA-TDD system is 3.84Mcps, making the chip rate of 256kcps for one slot the same (i.e., 3.84Mcps/15 ═ 256 kcps). Third, a multi-user detection (MUD) receiver is used at the Base Station (BS).

In each slot, the channelization code is encoded using an Orthogonal Variable Spreading Factor (OVSF). In the uplink, the spreading factor of the channelization code may take on values of 2, 4, 8, and 16. For the purposes of describing the present invention, a Resource Unit (RU) corresponds to a particular physical channel and is defined as a channelization code having a spreading factor of 16 in a particular time slot. Thus, a Resource Unit (RU) corresponds to a physical channel in a particular time slot.

For new users that are requesting permission to talk, the talk admission control is primarily targeted at appropriately configuring Resource Units (RUs) (i.e., physical channels), thereby guaranteeing quality of service (QoS) requirements for the new users and the users in the talk. The number of Resource Units (RUs) required for a new user depends on the type of call the user has dialed in. For example, a new user that is dialling up a voice call requires two Resource Units (RU), while a new user that is dialling up a 64k data call requires five Resource Units (RU).

The call admission control system makes a decision depending on whether a Resource Unit (RU) can be successfully configured to a new user. Whether a Resource Unit (RU) can be successfully configured to a new user depends on the individual outage probability (P) of all time slots for which a Resource Unit (RU) has been assigned_out). Thus, P_outIs the likelihood that the required SIR of a user in a particular slot will be below a predetermined value. However, in the WCDMA-TDD system, the necessary SIR of the user is not fixed but varies from distribution to distribution, making it difficult to calculate P_out. That is, even if the distribution of SIR is known, P is calculated_outStill very complex and cannot be done in real time.

In contrast, Gaussian (Gaussian) approximation provides a sufficiently approximate result and is relatively low in computational complexity. Thus, the Gaussian-probability algorithm is used to allow the RNC (Radio Network Controller) to calculate P for each slot_outAnd resource allocation is performed in real time.

P of all time slots that can be assigned to new user_outCombined together to calculate P for new user_out-total. Assuming Resource Units (RUs) in a certain number of time slots are allocated to a new user, P for the new user_out-totalIs defined asThe likelihood of an interruption in at least one of the time slots. Can be used as required

Calculating P_out-total. For example, can be as followsTo calculate P_out-totalWhere Ω is the set of slots for which a Resource Unit (RU) has been configured to a new user.

Referring now to fig. 1, a method 10 is shown for performing call admission control on an uplink in a third generation wireless communication system. Assuming, purely for purposes of illustrating the present invention, that a new user requires two Resource Units (RUs) (i.e., the new user has placed a voice call), the method 10 begins at step 12 by calculating the current P for each uplink timeslot_out. Thirdly, P_outIs the likelihood that the SIR of a new user in a particular slot is below a predetermined value and is calculated for each uplink slot. Thus, in step 12, the likelihood that the new user's SIR is below the predetermined value is calculated for each slot. As illustrated, P_outConsider that the SIR of a user actually varies over time and is calculated by the RNC using a gaussian profile algorithm to reduce computational complexity.

Once P has been calculated for each slot_outAt step 14, the lowest P is selected_outI.e., slot i). Since the time slot i is the lowest P_outSo P in slot i_outIs marked as P_out(i) In that respect In step 16, a Resource Unit (RU) is assigned to time slot i and P is updated accordingly_out(i) In that respect Once the first Resource Unit (RU) has been assigned, the method proceeds to step 18. In step 18, the methodA determination is made whether additional Resource Units (RUs) need to be assigned. As described, for the purpose of illustrating the present invention, it is assumed that a new user requires two Resource Units (RUs). The decision at step 18 is therefore positive and the method proceeds to step 20.

In step 20, the method determines P_out(i) Whether or not it is still the lowest P_out(i.e., despite being assigned a Resource Unit (RU), the method determines whether slot i still has the lowest P_out). If P is_out(i) Is still the lowest P_outThe method returns to step 16 and assigns a second Resource Unit (RU) to slot i and proceeds as indicated. On the contrary, if P_out(i) Is no longer the lowest P_outThe method proceeds to step 22. At step 22, P 'is calculated'_contribution. Suppose though in reality P_out(i) Is no longer the lowest P_outSlot i still accepts the next Resource Unit (RU), i.e. the second Resource Unit (RU) in accordance with the assumptions as described above, thus P'_contributionWill make P_out-totalAnd (4) increasing. P'_contributionNew P equal to time slot i_out. Namely, P'_contributionIs equal to P_out(i)′。

In step 24, P is calculated_contribution. Assuming the lowest P_outReceives the next Resource Unit (RU) (i.e., the second Resource Unit (RU) in accordance with the assumptions as described above), and thus P_contributionWill make P_out-totalAnd (4) increasing. P_contributionIs according to P_contribution＝1-(1-P_out(i))·(1-P_out(j) Obtained by (1). Once P 'has been calculated'_contributionAnd P_contributionThe method proceeds to step 26 where P is determined_contributionWhether or not is greater than or equal to P'_contribution(i.e., P)_out(i) '). If P is_contributionIs greater than or equal to P'_contributionThe method proceeds to step 16, where the next Resource Unit (RU) is assigned to time slot i, regardless of whether time slot i actually has no lowest P any more_out. I.e. albeit at the timeGap i no longer has the lowest P_outAssignment of the next Resource Unit (RU) to slot i still results in P_out-totalLower than the next Resource Unit (RU) assigned to slot j (slot j actually has the lowest P)_out). On the contrary, if P_contributionIs less than P'_contributionI is set equal to j at step 28 and the method proceeds to step 16. The method sets i equal to j, step 16, since assigning the next Resource Unit (RU) to slot j results in the lowest P_out-totalSo the next Resource Unit (RU) is assigned to slot j.

From step 16, the method again proceeds to step 18. Note that if the new user only needs one Resource Unit (RU), steps 20 to 28 are not required. However, since the user requires two Resource Units (RUs) in the assumed example, steps 20 to 28 need to be performed once in order to decide the optimal configuration of the second Resource Unit (RU). Steps 20 to 28 are performed for each Resource Unit (RU) required by the user. Once all Resource Units (RUs) have been assigned, the method proceeds to step 30. In step 30, P is calculated_out-totalThe outage probability of the new user is determined according to the allocated Resource Unit (RU), as configured in steps 12 to 28.

In step 32, the method determines P_out-totalWhether less than or equal to a predetermined value (i.e., theta). The predetermined value θ is an operand dependent parameter (operand dependent parameter) and may be any value depending on the desired level of network stability. If P is_out-totalLess than theta, the new user is allowed (step 34). Otherwise, the new user is rejected (step 36).

According to the invention, P_out-totalIncreases with the number of users and is about the predetermined value theta, thereby significantly improving the system stability (i.e., the number of dropped calls). The present invention also results in a significantly increased likelihood of congestion (also increasing as the number of users increases) compared to static continuous and random call admission control methods due to strict admission criteria. Incremental stability and likelihood of occlusionUser quality of service (QoS) is significantly improved since from a user perspective, call blocking is much better than call interruption.

Referring now to fig. 2, a system 100 for implementing call admission control in accordance with the present invention is shown. The system 100 includes a Radio Network Controller (RNC)102, a Base Station (BS) or node B104 and User Equipment (UE)106, wherein the Base Station (BS) and the User Equipment (UE) have a multi-user detection (MUD) receiver 103, 108, respectively.

When a user places a call with the User Equipment (UE)106, the Radio Network Controller (RNC)102 will perform call admission control and allocate appropriate timeslots in Resource Units (RUs) required for the new call to ensure the lowest probability P_out-totalAnd ensure P_out-totalRemain below the predetermined threshold.

To perform call admission control, the Radio Network Controller (RNC)102 calculates P for all uplink timeslots_outAnd a Resource Unit (RU) is assigned to the lowest P_outThe time slot of (2). If additional Resource Units (RUs) needed by a new user must be configured, the Radio Network Controller (RNC)102 assigns subsequent Resource Units (RUs) to the same time slots as the existing assigned previous Resource Units (RUs) as long as the time slots still have the lowest P_out. If the slot no longer has the lowest P_outThe Radio Network Controller (RNC)102 determines whether a subsequent Resource Unit (RU) should still be assigned to the timeslot, or to the timeslot that now has the lowest P_outThe time slot of (2). To make this determination, the Radio Network Controller (RNC)102 determines which time slot will cause P_out-totalThe increase is minimal. The radio network controller repeats this analysis for all Resource Units (RUs) required for the new call.

Once all Resource Units (RUs) needed by a new user have been allocated to a particular timeslot, the Radio Network Controller (RNC)102 determines whether the allocation results in P_out-totalBelow the predetermined value. If P is_out-totalIs lower than the predetermined valueThen the new user is allowed. Otherwise, the new user is rejected.

Although the present invention has been described in detail, it is to be understood that the invention is not limited thereto, but may be modified within the spirit and scope of the invention as defined by the appended claims.

Claims (12)

1. A method for performing call admission control, comprising:

assigning resource units required by a new user according to an outage probability of each respective timeslot;

calculating a total interruption probability of the new user;

determining whether the total outage probability is below a predetermined value; and

if the total outage probability is below the predetermined value, the new user is allowed.

2. The method of claim 1, wherein the step of assigning resource units is performed by:

calculating an interruption probability of each time slot;

assigning a first resource unit to the timeslot having the lowest outage probability; and

subsequent resource units are assigned to the time slot that would result in the lowest outage probability for the new user.

3. The method of claim 2 wherein the time slot that results in the lowest overall outage probability is selected based on the individual outage probability for each time slot that increases the overall outage probability.

4. A method for performing call admission control, comprising:

calculating an outage probability for each uplink timeslot;

assigning a first resource unit required by a new user to the timeslot having the lowest outage probability;

assigning subsequent resource units needed by the new user to the timeslot that would result in the lowest outage probability for the new user;

calculating a time slot with total interrupt possibility according to the time slots of the assigned resource units; and

if the total outage probability is below a predetermined value, the new user is allowed.

5. The method of claim 4 wherein identifying the time slot that would result in the lowest outage probability for the new user is by identifying the time slot that would increase the total outage probability for the new user the least.

6. A method for performing call admission control, comprising:

calculating an interruption probability of each time slot;

identifying a timeslot having a lowest interrupt probability;

assigning a first resource unit required by a new user to the identified timeslot;

assigning subsequent resource units required by the new user to a group of timeslots to minimize the total outage probability for the new user;

calculating a time slot with total interrupt possibility according to the time slots of the assigned resource units; and

if the total outage probability is below a predetermined value, the new user is allowed.

7. The method of claim 6 wherein each timeslot in the group of timeslots is selected based on its individual outage probability for each timeslot that increases the total outage probability.

8. The method of claim 6, wherein the step of assigning subsequent resource units further comprises:

calculating a first value indicative of an increase in the total outage probability if a subsequent resource unit is assigned to the identified timeslot;

calculating a second value indicative of an increase in the total outage probability if a subsequent resource unit is assigned to timeslots other than the identified timeslot;

continuing to assign subsequent resource units to the identified time slot as long as the second value is not greater than or equal to the first value; and

continuing to assign subsequent resource units to time slots other than the identified time slot as long as the second value is greater than or equal to the first value.

9. A call admission control system comprising:

a user equipment;

a base station; and

a radio network controller, wherein the radio network controller is adapted to perform the following actions:

assigning resource units required by a new user to the plurality of timeslots based on the respective outage probability for each timeslot that increases the total outage probability; and

if the total outage probability for the new user is below a predetermined value, the new user is allowed.

10. A call admission control system as in claim 9 wherein the radio network controller is adapted to perform the following actions:

calculating an outage probability for each uplink timeslot whenever a new user requests permission;

assigning a first resource unit required by the new user to the timeslot with the lowest outage probability;

assigning subsequent resource units needed by the new user to a group of timeslots that results in the lowest outage probability for the new user; and

if the total outage probability is below a predetermined value, the new user is allowed.

11. A call admission control system as in claim 10 wherein each timeslot in the group of timeslots is selected based on its individual outage probability for each timeslot that increases the overall outage probability.

12. A call admission control system as in claim 10 wherein the radio network controller is configured to select the group of timeslots by:

calculating a first value indicative of an increase in the total outage probability if a subsequent resource unit is assigned to the identified timeslot;

calculating a second value indicative of an increase in the total outage probability if a subsequent resource unit is assigned to timeslots other than the identified timeslot;

continuing to assign subsequent resource units to the identified time slot as long as the second value is not greater than or equal to the first value; and

continuing to assign subsequent resource units to time slots other than the identified time slot as long as the second value is greater than or equal to the first value.