WO2011044932A1

WO2011044932A1 - Speed dependent component carrier load balance

Info

Publication number: WO2011044932A1
Application number: PCT/EP2009/063399
Authority: WO
Inventors: Klaus Ingemann Pedersen; Wang Yuanye
Original assignee: Nokia Siemens Networks Oy
Priority date: 2009-10-14
Filing date: 2009-10-14
Publication date: 2011-04-21

Abstract

User equipments connected to a base station are assigned to component carriers of a plurality of component carriers with different carrier frequencies for transmission, in accordance with an estimated speed of the user equipments.

Description

DESCRIPTION

TITLE

SPEED DEPENDENT COMPONENT CARRIER LOAD BALANCE

The present invention relates to component carrier (CC) load balancing. In particular, the invention relates to load bal^¬ ancing between CCs in terms of assignment of users (User Equipments (UEs) ) to CCs for optimizing system and user per- formance.

For example, LTE (Long Term Evolution) -Advanced is a system in which multiple component carriers (CCs) are used for transmission. According to current 3GPP (Third Generation Partnership Project) decisions, Release 8 users can be as^¬ signed only to one CC, while LTE-Advanced users can be as^¬ signed to multiple CCs depending on their capability.

The present invention aims at improving system and user per- formance in communication systems with multiple CCs. In par^¬ ticular, the invention aims at improving scheduling gains, such as e.g. FDPS (Frequency Domain Packet Scheduling) gains, in systems with multiple CCs. According to an embodiment of the invention, user equipments connected to a base station are assigned to component carri^¬ ers of a plurality of component carriers with different car^¬ rier frequencies for transmission, in accordance with an es^¬ timated speed of the user equipments.

In the following the invention will be described by way of embodiments thereof, referring to the accompanying drawings, in which: Fig. 1 shows a simplified block diagram of RRM (Radio Re^¬ source Management) functionalities for an LTE-Advanced system with multiple CCs, assuming independent link adaptation and HARQ (Hybrid Automatic Repeat Request) per CC;

Fig. 2 shows a schematic block diagram illustrating a base station according to an embodiment of the invention; and

Fig. 3 shows a flow chart illustrating a method of assigning user equipments to CCs according to an embodiment of the in^¬ vention .

Fig. 1 shows a simplified conceptual block diagram of main RRM functionalities for an LTE-Advanced system with multiple component carriers #1, #2, .., #N. Layer-1 functionalities are PDCCH (Physical Downlink Control Channel) , a CQI (Channel Quality Indicator) and CSI (Channel State Information) man^¬ ager, and UL (Uplink) / DL (Downlink) PC (Power Control) . Layer-2 functionalities are HARQ, OLLA (Outer Loop Link Adap^¬ tation) , LA (Link Adaptation) and L2 PS (Layer 2 Packet

Scheduling) . Layer-3 functionalities are QoS (Quality of Ser- vice) control, admission control and SpS (Semi Persistent Scheduling) .

Compared to previous Release 8 LTE systems, the LTE-Advanced system shown in Fig. 1 comprises a further functionality at Layer-3 called CC selection. The CC selection functionality is responsible for assigning UEs to CCs, where they after^¬ wards can be scheduled. The Layer-2 PS subsequently schedules the UEs on a set of CCs as decided by the Layer-3 CC selec^¬ tion functionality.

In order to balance the load between CCs in cases where CCs are contiguous and of the same bandwidth, the best perform^¬ ance is obtained by having the same number of active users (UEs) per CC, which is also known as simple round robin CC load balancing. However, the latter is not the case for see- narios with non-contiguous CCs of same or different band^¬ width .

For example, cases with non-contiguous CCs may include sce- narios with some CCs at 800 MHz and CCs at 2.6 GHz. The CCs at the different bands may furthermore be of different band^¬ width, e.g. some CCs may have 10 MHz bandwidth, and some may have 20 MHz bandwidth. One of the differences when considering non-contiguous CCs

(as opposed to contiguous CCs) is that the Doppler frequency is different for each CC, and also the path loss. When con^¬ sidering the example with CCs at 800 MHz and 2.6 GHz, there is more than a factor of 3 in difference in terms of Doppler frequency. The Doppler frequency as compared to CQI feedback delay is of importance for LTE-Advanced systems, as this ba^¬ sically determines if the promising multi-user radio channel aware scheduling gains can be achieved, such as e.g. fre^¬ quency domain packet scheduling (FDPS) gains. As an example, the following has been found from LTE (-Advanced) performance investigations .

High FDPS gains of about 40% are achievable for UE speeds lower than 10 km/h and a CC carrier frequency of 2 GHz. For UE speeds of 30 km/h, the FDPS gain reduces to maximum 10%.

High FDPS gains of about 40% are achievable for UE speeds lower than 25 km/h and a CC carrier frequency of 800 MHz. For UE speeds of 60 km/h, the FDPS gain reduces to maximum 10%.

The reported FDPS gains are conditioned on having multiple simultaneous active (schedulable) users within each CC .

According to an embodiment of the invention for assigning us- ers (UEs) to different CCs in a communication system with multiple CCs, the UEs are sorted according to their estimated UE speed, and the UEs with high UE speed are assigned to the CCs with low carrier frequencies, while the UEs with low UE speed are assigned to the CCs with high carrier frequencies. The above assignment of UEs to CCs may be implemented in an eNB (LTE (-A) base station), e.g. as part of the Layer-3 CC selection functionality shown in Fig. 1.

For example, it is assumed that an eNB is configured to have two CCs at fairly different carrier frequencies, e.g. at 800 MHz and 2.6 GHz. A group of UEs is connected to the eNB, where one set of the group of UEs is moving at high speed, while the rest is moving at a considerably lower speed. Ac^¬ cording to the above-described approach, the eNB assigns the UEs moving at the considerably lower speed to the CC with the higher carrier frequency, and the UEs moving at the high speed to the CC with the lower carrier frequency.

Assigning UEs to CCs having different carrier frequencies in accordance with the estimated speed of the UEs as described above improves the performance of a communication system with multiple CCs comprising non-contiguous CCs. The performance is improved both with respect to an average cell spectral ef^¬ ficiency and user experienced data rates.

According to an embodiment of the invention, UEs are assigned to CCs in order to have the same number of UEs per bandwidth unit. That is, if CCs have the same bandwidth, then assign^¬ ment is performed in order to have the same number of active UEs per CC . If e.g. some CCs have double bandwidth compared to others, then those should have assigned twice as much UEs than the other CCs. With this approach, load balancing be^¬ tween CCs can be improved further. Fig. 2 shows a schematic block diagram illustrating a base station 10 according to an embodiment of the invention. The base station 10 may be an eNB of an LTE-Advanced system. The base station 10 comprises a transceiver 11 and a CC selection device 20. The base station 10 may comprise further entities e.g. for performing base station functionality which are not shown in Fig. 2. For example, the base station 10 may com^¬ prise means for estimating a speed of UEs connected to the base station 10.

The CC selection device 20 comprises a processor 21 and a memory 22 which are connected by a bus 23. The transceiver 11 and the CC selection device 20 are connected by a link 12.

The memory 22 may store a program, and the transceiver 11 may be a suitable radio frequency (RF) transceiver coupled to one or more antennas (not shown) for bidirectional wireless com^¬ munications over one or more wireless links with UEs.

The term "connected" or any variant thereof, means any con^¬ nection, either direct or indirect, between two or more ele- ments, and may encompass the presence of one or more interme^¬ diate elements between two elements that are "connected" to^¬ gether. The connection between the elements can be physical, logical, or a combination thereof. As employed herein two elements may be considered to be "connected" together by the use of one or more wires, cables and printed electrical con^¬ nections, as well as by the use of electromagnetic energy, such as electromagnetic energy having wavelengths in the ra^¬ dio frequency region, the microwave region and the optical (both visible and invisible) region, as non-limiting exam- pies.

The memory 22 may include program instructions that, when executed by the processor 21, enable the CC selection device 20 to operate in accordance with the exemplary embodiments of this invention. Inherent in the base station 10 is a clock to enable synchronism among the various apparatus for transmis- sions and receptions within the appropriate time intervals and slots required, as the scheduling grants and the granted resources/subframes are time dependent. The transceiver 11 includes both transmitter and receiver, and inherent in each is a modulator/demodulator commonly known as a modem.

The exemplary embodiments of this invention may be imple^¬ mented by computer software stored in the memory 22 and ex^¬ ecutable by the processor 21, or by hardware, or by a combi- nation of software and/or firmware and hardware in the base station 10.

The memory 22 may be of any type suitable to the local tech^¬ nical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The processor 21 may be of any type suitable to the local techni^¬ cal environment, and may include one or more of general pur- pose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on a multi-core processor architecture, as non-limiting examples.

Embodiments of the invention may be practiced in various com- ponents such as integrated circuit modules. The design of in^¬ tegrated circuits is by and large a highly automated process. Complex and powerful software tools are available for con^¬ verting a logic level design into a semiconductor circuit de^¬ sign ready to be etched and formed on a semiconductor sub- strate. Programs, such as those provided by Synopsys, Inc. of Mountain View, California and Cadence Design, of San Jose, California automatically route conductors and locate compo^¬ nents on a semiconductor chip using well established rules of design as well as libraries of pre-stored design modules. Once the design for a semiconductor circuit has been com^¬ pleted, the resultant design, in a standardized electronic format (e.g., Opus, GDSII, or the like) may be transmitted to a semiconductor fabrication facility or "fab" for fabrica^¬ tion. The processor 21 obtains an estimated speed of user equip^¬ ments (UEs) connected to the base station 10. The speed of the user equipments may be estimated by the processor 21 or by other means e.g. of the base station 10. The processor 21 assigns the user equipments to component carriers of a plurality of component carriers with different carrier frequencies for transmission (i.e. the plurality of component carriers include non-contiguous component carri^¬ ers) , in accordance with the estimated speed of the user equipments.

The processor 21 may sort the user equipments according to their estimated speed, thereby obtaining user equipments with high estimated speed and user equipments with low estimated speed or considerably lower estimated speed. The processor 21 may assign the user equipments with the high estimated speed to the component carriers with low carrier frequencies, and assign the user equipments with the low or considerably lower estimated speed to the component carriers with high carrier frequencies.

For example, the base station 10 is configured to have a plu^¬ rality of component carriers comprising component carriers with low carrier frequencies and comprising component carri- ers with high carrier frequencies. Low carrier frequencies may be in the range of 800 MHz, and high carrier frequencies may be in the range of 2 GHz. User equipments connected to the base station 10 which move with high estimated speed com^¬ pared to the other user equipments connected to the base sta- tion 10 are assigned to the component carriers with low car^¬ rier frequencies, and user equipments connected to the base station 10 which move with low estimated speed compared to the other user equipments connected to the base station 10 are assigned to the component carriers with high carrier fre^¬ quencies .

According to an embodiment of the invention, the processor 21 may assign user equipments with an estimated speed lower than a first predetermined value to the component carriers with high frequency carriers, and assign user equipments with an estimated speed higher than the first predetermined value to the component carriers with low frequency carriers. Moreover, the processor 21 may assign user equipments with an estimated speed higher than the first predetermined value and lower than a second predetermined value to the component carriers with low frequency carriers. The first predetermined value may be set to about 10 km/h, and the second predetermined value may be set to about 25 km/h.

According to an embodiment of the invention, the component carriers may comprise different numbers of units of band^¬ width, and the processor 21 may assign the user equipments within the component carriers, to which the user equipments have been assigned in accordance with their estimated speed, such that there is the same number of user equipments per bandwidth unit.

Fig. 3 shows a flow chart illustrating a method of assigning user equipments connected to a base station to component car^¬ riers configured in the base station according to an embodi- ment of the invention.

In step S31, an estimated speed of user equipments connected to a base station is obtained. In step S32, the user equip^¬ ments may be sorted according to their estimated speed, thereby obtaining user equipments with high estimated speed and user equipments with low estimated speed. In step S33 it is decided whether or not a user equipment in question of the user equipments connected to the base station has a low esti^¬ mated speed. In case it is decided that the user equipment in question has a low estimated speed (Yes in step S33) , the user equipment in question is assigned to at least one compo^¬ nent carrier out of a plurality of component carriers with different carrier frequencies for transmission, which has a high carrier frequency (step S34) . In case it is decided that the user equipment in question has no low estimated speed (No in step S33) , the user equipment in question is assigned to at least one component carrier out of the plurality of compo^¬ nent carriers, which has a low carrier frequency (step S35) . Thus, the user equipments are assigned to component carriers in accordance with the estimated speed of the user equip- ments.

A low carrier frequency may be in the range of 800 MHz, and a high carrier frequency may be in the range of 2 GHz . Alternatively or in addition, user equipments with an esti^¬ mated speed lower than a first predetermined value may be as^¬ signed to component carriers with high frequency carriers, and user equipments with an estimated speed higher than the first predetermined value may be assigned to component carri- ers with low frequency carriers. Moreover, user equipments with an estimated speed higher than the first predetermined value and lower than a second predetermined value may be as^¬ signed to the component carriers with low frequency carriers. The first predetermined value may be set to about 10 km/h, and the second predetermined value may be set to about 25 km/h .

The component carriers may comprise different numbers of units of bandwidth, and the user equipments may be assigned within the component carriers, to which the user equipments have been assigned in accordance with their estimated speed, such that there is the same number of user equipments per bandwidth unit .

In step S36 it is checked whether or not all user equipments connected to the base station have been assigned to at least one of the plurality of component carriers. If all user equipments connected to the base station have been assigned (Yes in step S36) , the process ends, and if not (No in step S36) , the process returns to step S33.

According to an embodiment of the invention, an apparatus which may comprise the CC selection device 20 of Fig. 2 com^¬ prises obtaining means for obtaining an estimated speed of user equipments connected to a base station, and first as- signing means for assigning the user equipments to component carriers of a plurality of component carriers with different carrier frequencies for transmission, in accordance with the estimated speed of the user equipments. The processing means and the first assigning means may comprise the processor 21.

The apparatus may comprise sorting means for sorting the user equipments according to their estimated speed, thereby ob^¬ taining user equipments with high estimated speed and user equipments with low estimated speed, and second assigning means for assigning the user equipments with the high esti^¬ mated speed to the component carriers with low carrier fre^¬ quencies, and assigning the user equipments with the low es^¬ timated speed to the component carriers with high carrier frequencies. The sorting means and the second assigning means may comprise the processor 21.

The apparatus may comprise third assigning means for assign^¬ ing user equipments with an estimated speed lower than a first predetermined value to the component carriers with high frequency carriers, and assigning user equipments with an es^¬ timated speed higher than the first predetermined value to the component carriers with low frequency carriers. The third assigning means may comprise the processor 21.

The apparatus may comprise fourth assigning means for assign^¬ ing user equipments with an estimated speed higher than the first predetermined value and lower than a second predeter^¬ mined value to the component carriers with low frequency car^¬ riers. The fourth assigning means may comprise the processor 21.

The component carriers may comprise different numbers of units of bandwidth, and the apparatus may comprise fifth as^¬ signing means for assigning the user equipments within the component carriers, to which the user equipments have been assigned in accordance with their estimated speed, such that there is the same number of user equipments per bandwidth unit. The fifth assigning means may comprise the processor 21.

It is to be understood that the above description is illus^¬ trative of the invention and is not to be construed as limit^¬ ing the invention. Various modifications and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined by the ap^¬ pended claims.

Claims

CLAIMS :

1. An apparatus comprising:

a processor configured to obtain an estimated speed of user equipments connected to a base station,

wherein the processor is configured to assign the user equipments to component carriers of a plurality of component carriers with different carrier frequencies for transmission, in accordance with the estimated speed of the user equip- ments.

2. The apparatus of claim 1, wherein the processor is config^¬ ured to sort the user equipments according to their estimated speed, thereby obtaining user equipments with high estimated speed and user equipments with low estimated speed, and as^¬ sign the user equipments with the high estimated speed to the component carriers with low carrier frequencies, and assign the user equipments with the low estimated speed to the com^¬ ponent carriers with high carrier frequencies.

3. The apparatus of claim 1 or 2, wherein the processor is configured to assign user equipments with an estimated speed lower than a first predetermined value to the component car^¬ riers with high frequency carriers, and assign user equip- ments with an estimated speed higher than the first predeter^¬ mined value to the component carriers with low frequency car^¬ riers .

4. The apparatus of claim 3, wherein the processor is config- ured to assign user equipments with an estimated speed higher than the first predetermined value and lower than a second predetermined value to the component carriers with low fre^¬ quency carriers .

5. The apparatus of any one of claims 1 to 4, wherein the component carriers comprise different numbers of units of bandwidth, and the processor is configured to assign the user equipments within the component carriers, to which the user equipments have been assigned in accordance with their esti^¬ mated speed, such that there is the same number of user equipments per bandwidth unit.

6. A method comprising:

obtaining an estimated speed of user equipments con^¬ nected to a base station; and

assigning the user equipments to component carriers of a plurality of component carriers with different carrier fre^¬ quencies for transmission, in accordance with the estimated speed of the user equipments.

7. The method of claim 6, comprising:

sorting the user equipments according to their estimated speed, thereby obtaining user equipments with high estimated speed and user equipments with low estimated speed; and

assigning the user equipments with the high estimated speed to the component carriers with low carrier frequencies, and assigning the user equipments with the low estimated speed to the component carriers with high carrier frequen^¬ cies .

8. The method of claim 6 or 7, comprising:

assigning user equipments with an estimated speed lower than a first predetermined value to the component carriers with high frequency carriers, and assigning user equipments with an estimated speed higher than the first predetermined value to the component carriers with low frequency carriers.

9. The method of claim 8, comprising:

assigning user equipments with an estimated speed higher than the first predetermined value and lower than a second predetermined value to the component carriers with low fre^¬ quency carriers .

10. The method of any one of claims 6 to 9, wherein the com^¬ ponent carriers comprise different numbers of units of band^¬ width, the method comprising:

assigning the user equipments within the component car^¬ riers, to which the user equipments have been assigned in ac cordance with their estimated speed, such that there is the same number of user equipments per bandwidth unit.

11. A computer program product including a program for a processing device, comprising software code portions for per forming the steps of any one of claims 6 to 10 when the pro^¬ gram is run on the processing device.

12. The computer program product according to claim 11, wherein the computer program product comprises a computer- readable medium on which the software code portions are stored .

13. The computer program product according to claim 11, wherein the program is directly loadable into an internal memory of the processing device.