Cross-frequency network load balancing

A base station that supports different sectors and co-located different frequencies across the different sectors in a CDMA network having an Access Terminal includes a processing unit which determines a load imbalance on a connection in a first sector at a first frequency. The base station includes a network interface unit through which the processing unit offloads traffic from the connection in the first sector at the first frequency to a first or second sector at a second frequency. A method for sending traffic with a base station that supports different sectors and co-located different frequencies across the different sectors in a CDMA network having an Access Terminal including the steps of determining with a processing unit a load imbalance on a connection in a first sector at a first frequency. There is the step of offloading with the processing unit through network interface unit traffic from the connection in the first sector at the first frequency to a first or second sector at a second frequency.

TECHNICAL FIELD

The present invention is related to a base station which offloads traffic from a connection in a first sector at a first frequency to a first or second sector at a second frequency. (As used herein, references to the “present invention” or “invention” relate to exemplary embodiments and not necessarily to every embodiment encompassed by the appended claims.) More specifically, the present invention is related to a base station which offloads traffic from a connection in a first sector at a first frequency to a first or second sector at a second frequency utilizing a load matrix that contains load information for at least a plurality of co-located frequencies as a basis to offload the traffic.

BACKGROUND

This section is intended to introduce the reader to various aspects of the art that may be related to various aspects of the present invention. The following discussion is intended to provide information to facilitate a better understanding of the present invention. Accordingly, it should be understood that statements in the following discussion are to be read in this light, and not as admissions of prior art.

Network Load Balancing (NLB) Algorithm is existing 1x-EV-DO Advanced concept that provides methods of off-loading traffic from the more loaded radio cells to the less loaded cell, by manipulating allowed forward link cells for every active connection but only on (one) connected frequency.

Current implementation of NLB considers traffic load on every sector in the terminal's active set (A_SET) and intelligently offloads a sector that is more loaded by moving active/connected users' serving Down-Leg (DL) to the other sectors in the A_SET that are less loaded. This improves user's forward link throughput as it is moved to the sector with less contention for the forward link scheduler-resources.

The CDMA radio network can be viewed as a two dimensional space consisting of sectors in the horizontal plane and frequencies in the vertical plane. A CDMA radio-connection must be on the same frequency, as a terminal has only one transmitter, so connection A_SET is managed across the sector/horizontal plane.

Hence, loading imbalances are possible not only across the different sector of a base station (BTS), but also across the frequencies collocated on the same BTS.

Today, there are solutions that manageload across sectors in connected state (NLB) ANDaccess to a collocated carrier (MCTA).

However with data connections expected to last longer as new real-time applications are constantly emerging, a solution is needed to extend offload decisions of the connected users into vertical/frequency plane as well (i.e. not just across the sector of the A_SET on the connected frequency, but also across other frequencies collocated in the area).

The proposed solution extends load balance to the frequency plane, while terminals are in the connected state.

In the current implementation offload for connected users is done only to the cells in the active set that are on the same frequency.

There is no solution for offload to a different frequency, for already connected users.

BRIEF SUMMARY OF THE INVENTION

The present invention pertains to a base station that supports different sectors and co-located different frequencies across the different sectors in a CDMA network having an Access Terminal. The base station comprises a processing unit which determines a load imbalance on a connection in a first sector at a first frequency. The base station comprises a network interface unit through which the processing unit offloads traffic from the connection in the first sector at the first frequency to a first or second sector at a second frequency.

The present invention pertains to a method for sending traffic with a base station that supports different sectors and co-located different frequencies across the different sectors in a CDMA network having an Access Terminal. The method comprises the steps of determining with a processing unit a load imbalance on a connection in a first sector at a first frequency. There is the step of offloading with the processing unit through network interface unit traffic from the connection in the first sector at the first frequency to a first or second sector at a second frequency.

DETAILED DESCRIPTION

Referring now to the drawings wherein like reference numerals refer to similar or identical parts throughout the several views, and more specifically toFIG. 5thereof, there is shown a base station10that supports different sectors and co-located different frequencies across the different sectors in a COMA network20having an Access terminal22. The base station10comprises a processing unit12which determines a load imbalance on a connection in a first sector at a first frequency. The base station10comprises a network interface unit14through which the processing unit12offloads traffic from the connection in the first sector at the first frequency to a first or second sector at a second frequency.

The base station10may include a memory16having a load matrix18that contains load information for at least a plurality of co-located frequencies, the processing unit12using the load information in the load matrix18to offload the traffic. The processing unit12may send a Route Update Request message through the network interface unit14as a basis for measuring radiofrequency conditions for potential cross-frequency targets. The network interface unit14may receive a measurement of pilots on frequency belonging to a sector-carrier having a lowest load in the load matrix18, and the processing unit12checks if any of the pilots has a signal-to-noise ratio greater than a predetermined signal-to-noise ratio.

The processing unit12may check if each pilot having a signal-to-noise radio greater than the threshold signal-to-noise ratio has a suitability metric greater than a predetermined suitability metric which is relative to the suitability metric of a current serving DL. For at least one pilot having a suitability metric greater than the predetermined suitability metric, the processing unit12may set resources on new sector-carriers and sends a Traffic Channel Assignment through the network interface to move the Access terminal22to the new sector-carriers reported in the Route Update Response message.

The processing unit12may check if a number of contending users in a current serving DL sector-frequency is higher than a predetermined level of contending users. The processing unit12may determine if a least loaded frequency in the load matrix18has a load above a predetermined load level, which is relative to the load level of a current serving DL. If the processing unit12determines that the number of contending users is less than the predetermined number of contending users or if the least loaded frequency in the load matrix18has a load above the predetermined load level, the processing unit12may wait a time T before checking again if the number of contending users is less than the predetermined level of contending users or if a least loaded frequency in the load matrix18has a load above the predetermined load level, where T is predetermined.

The present invention pertains to a method for sending traffic with a base station10that supports different sectors and co-located different frequencies across the different sectors in a CDMA network20having an Access terminal22. The method comprises the steps of determining with a processing unit12a load imbalance on a connection in a first sector at a first frequency. There is the step of offloading with the processing unit12through network interface unit14traffic from the connection in the first sector at the first frequency to a first or second sector at a second frequency.

The base station10may include a memory16having a load matrix18that contains load information for at least a plurality of co-located frequencies, and there may be the step of the processing unit12using the load information in the load matrix18to offload the traffic. There may be the step of sending by the processing unit12a Route Update Request message through the network interface unit14as a basis for measuring radiofrequency conditions for potential cross-frequency targets. There may be the step of the network interface unit14receiving a measurement of pilots on frequency belonging to a sector-carrier having a lowest load in the load matrix18, and the processing unit12checks if any of the pilots has a signal-to-noise ratio greater than a predetermined signal-to-noise ratio.

There may be the step of the processing unit12checking if each pilot having a signal-to-noise radio greater than the threshold signal-to-noise ratio has a suitability metric greater than a predetermined suitability metric which is relative to the suitability metric of a current serving DL. For at least one pilot having a suitability metric greater than the predetermined suitability metric, there may be the step of the processing unit12setting resources on new sector-carriers and sends a Traffic Channel Assignment through the network interface to move the Access terminal22to the new sector-carriers reported in the Route Update Response message.

There may be the step of the processing unit12checking if a number of contending users in a current serving DL sector-frequency is higher than a predetermined level of contending users. There may be the step of the processing unit12determining if a least loaded frequency in the load matrix18has a load above a predetermined load level, which is relative to the load level of a current serving DL.

If the processing unit12determines that the number of contending users is less than the predetermined number of contending users or if the least loaded frequency in the load matrix18has a load above the predetermined load level, there may be the step of the processing unit12waiting a time T before checking again if the number of contending users is less than the predetermined level of contending users or if a least loaded frequency in the load matrix18has a load above the predetermined load level, where T is predetermined.

In the operation of the invention, there is provided a technique to extend network load-balancing across all supported frequencies in the network, not just across the sectors that are on the same frequency.

This creates a two-dimensional NLB decision space consisting of sectors and frequencies, unlike one dimensional load balancing across sectors of the same frequency.

The basis of decision making is a Load Matrix18(LM) that BSC/RNC keeps for every connection. That matrix18contains load information for every collocated and potential non collocated frequency for all members of the A_SET.

The algorithm makes intelligent decisions as to when inter-frequency offload is needed and sends a Route Update Request message as a vehicle for measuring RF conditions on potential cross-frequency targets.

Neffx,yrepresents average number of contending users reported by active set member's “x” combined collocated+non-collocated list entry “y”.

One example of LM is shown onFIG. 2.

The flow-chart of the algorithm is give onFIGS. 3 and 4

At the core of the algorithm is maintenance of the LM matrix18. Every sector carrier reports this to the RNC and hence RNC has this info readily available to use.

Algorithm triggers periodically every “T” seconds, where “T” is system configurable. The reason for this is to reduce required processing at the RNC and also prevent too frequent off frequency measurements.

The first thing that CFNLB checks is if number of contending users “NF_dl” in the current serving DL sector-frequency is too high, as defined by another system configurable “THOLD_CF”. The idea is avoid frequent engagement of the algorithm if load on the current serving DL is low.

If case Neff_dl*<=THOLD_CF then

CFNLB stops and will not be called up for next “T” seconds.

CFNLB sorts all elements of LM matrix18from smallest to largest Neff_ij (where Neff_ij is individual element of the LM matrix18).

Next CFNLB checks if (Neff_dl−Neff_ij>NF_DELTA), where NF_DELTA is another system configurable.

If above condition is not true then CFNLB stops and will not be called up for next “T” seconds.

The idea is to terminate algorithm's execution if least loaded element in the LM matrix18is heavily loaded too, as then benefits of inter-frequency switching of a DL are not worth the trouble of off-frequency measuring and potentially inter-frequency Traffic Channel Assignment.

Else, if above condition is true. CFNLB proceeds to a next step, which is to send the RouteUpdateRequest to AT instructing it to measure pilots on frequency belonging to sector-carrier with smallest Neff_ij.

When AT comes back with the measurement, algorithm needs to check if any of the reported pilots from frequency “j” has SNR_i,j>THOLD_SNR, where THOLD_SNR is another system configurable.

If no pilots for off-channel-frequency “j” have SNR>THOLD_SNR then

CFNLB moves to the next candidate in the sorted LM list that has frequency “k” which is different from previous candidates' (“j”). If another candidate like this can be found then CFNLB moves back to checking (Neff_dl−Neff_ij>NF_DELTA) condition, for this new candidate. Otherwise, if end of the list is reached, CFNLB stops and will not be called up for next “T” seconds.

Else if there is at least one pilot from off-channel-frequency “j” that has SNR>THOLD_SNR then following condition is checked:

For every such pilot, check if (SU_ij>SU_dl+SU_DELTA) for (ij) that passed THOLD_SNR, where SU_DELTA is another system configurable and SU stands for Suitability Metric (Suitability metric is calculated as SU=SINR (dB)−Neff (dB)), then if that's the case.

RNC sets resources on new sector carriers and sends TCA to AT with A_SET composed associated with Su_ij and other same-frequency pilots that AT may have reported in response to RouteUpdateRequest. From that point on connection will be served by new set of sector-frequencies and load matrix gets recomputed, for the new set of entries.

Else, if there is no pilot for which (SU_ij>SU_dl+SU_DELTA) then CFNLB moves to next candidate in sorted LM list and proceeds from that point on as described onFIGS. 3 and 4.

The proposed solution provides better utilization of sector carrier resources and improves user forward link throughput, by directing user into sector-carrier targets with fewer contending users.

The proposed solution extends concept of NLB to frequency domain/space.

Abbreviations1x-EV-DO 1x Evolved—Data Optimized (3g technology based on 3GPP2 specs)A_SET Active Set; which is a list of all cells that AT is in reverse link SHOAT Access TerminalBSC Base Station ControllerCFNLB Cross-Frequency Network Load BalancingDL Down Leg (i.e. RN serving AT in forward/downlink direction)DOM Data Only Module (E/// name for RBS modem card in 1x-EV-DO)DRC Data Rate ControlDRC Lock Data Rate Control Lock [bit]. This is how RN indicates that AT can select it for DL serviceKPI Key Performance IndicatorsMAHO Mobile Assisted HandOffNLB Network Load BalancingRN Radio Node (same as DOM)RNC Radio Network Controller (same as BSC in 1xEV-DO)SHO Soft HandoffTCA Traffic Channel AssignmentTHOLD THreshOLD