WO2010090556A1

WO2010090556A1 - Method and arrangement for scheduling transmissions

Info

Publication number: WO2010090556A1
Application number: PCT/SE2009/050109
Authority: WO
Inventors: Mats Blomgren
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2009-02-04
Filing date: 2009-02-04
Publication date: 2010-08-12

Abstract

The present invention relates to a method and a communication network node for scheduling transmissions in a communication network system. The communication network system comprises communication network nodes communicating with several user equipments on uplink and downlink channels over a radio interface. Each transmission is sent within a time transmission interval. And, the transmissions from each user equipment are scheduled in a pre-determined offset order.

Description

METHOD AND ARRANGEMENT FOR SCHEDULING TRANSMISSIONS

TECHNICAL FIELD

The present invention relates to a method and a communication network node in a communication network system and, more particular, to a communication network node allowing for scheduling transmissions as well as a method for such scheduling

BACKGROUND

Dividing a common channel according to Time Division Multiple Access (TDMA) is a well known method for communication systems to keep transmissions from different nodes orthogonal This access method is a strong candidate to further improve the data traffic capacity of the enhanced uplink in Wideband Code Division Multiple Access (WCDMA)

Typically in a TDMA system, all nodes in a cell have a common time alignment enabling an efficient switch between active nodes, i e transmissions should neither overlap nor have an unnecessary time gap between them This common alignment could for instance mark when transmissions should start and end

The introduction of time aligned UE transmissions will not be without problems in the WCDMA uplink Currently, the user equipments (UEs) follow a procedure to maintain a rough time alignment towards their serving NodeB (± 256 chips) Since the NodeBs do not have a common time alignment there is naturally a timing problem for users coming from other cells The handover problem is further aggravated by the fact that as a UE enters soft handover (SHO) there is no control over which NodeB it will try to align to All this results in that there is little control over the UEs' perception when Transmission Time Intervals (TTIs) start and/or end, even for users with the same serving cell Ultimately, the poor time alignment makes it difficult to use TDMA in the WCDMA uplink (UL)

In order to facilitate a capacity increase by introducing TDMA in the WCDMA UL the time alignment should be dealt with in some way, the UEs (and possibly the NodeBs) could be aligned in time by additional signaling, alternatively, algorithms that take the lack of time alignment into consideration could be developed The latter alternative provides opportunities to go forward in this area without standard changes; furthermore, there are other parts of the system relying on that users are not aligned in time.

SUMMARY Accordingly, one object of embodiments of the present invention is to provide an improved method and communication network node for scheduling transmissions in a communication network system comprising communication network nodes communicating with several user equipments on uplink and downlink channels over a radio interface, whereby each transmission is sent within a time transmission interval.

According to a first aspect of embodiments of the present invention this objective is achieved through a method as defined in the characterizing portion of claim 1 , which specifies that transmissions are scheduled by a method which performs the step of scheduling said transmissions from each user equipment in a pre-determined offset order

According to a second aspect of embodiments of the present invention this objective is achieved through a communication network node as defined in the characterizing portion of claim 4, which specifies that transmissions are scheduled by a communication network node comprising a scheduler arranged to schedule said transmissions from each user equipment in a pre-determined offset order.

Further embodiments are listed in the dependent claims.

Thanks to the provision of a method and a communication network node, in which users are scheduled in an ascending offset order, a fully orthogonal TDMA operation in a non aligned system, such as the WCDMA uplink, is enabled.

Still other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein. BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, wherein like reference characters denote similar elements throughout the several views:

Figure 1 shows an example of a WCDMA communication network architecture;

Figure 2 illustrates two nodes with different offset in relation to a reference;

Figure 3a shows a TDMA schedule according to prior art;

Figure 3b shows a TDMA schedule according to embodiments of the present invention;

Figure 4 is a flowchart illustrating the inventive procedure according to a preferred embodiment;

Figure 5 is a simplified block diagram of a user equipment and an inventive communication network node.

DETAILED DESCRIPTION Figure 1 depicts a communication system including a Radio Access Network (RAN), such as the UTRAN architecture, comprising at least one Radio Base Station (RBS) 15 (two are shown in figure 1 ) connected to a controller unit, such as a radio network controller node (RNC) 10. The RAN is connected to a Core network (CN) 12. The RAN and the CN 12 provide communication and control for a plurality of user equipments (UE) 18 that each uses downlink (DL) channels 16 and uplink (UL) channels 17. For the reason of clarity, only one uplink channel is denoted 17 and one downlink channel denoted 16. On the downlink channel 16, the RBS 15 transmits data blocks to each user equipment 18. On the uplink channel 17, the user equipments 18 transmit data blocks to the RBS 15.

According to a preferred embodiment of the present invention, the communication system is herein described as a WCDMA communication system. The skilled person, however, realizes that the inventive method and arrangement works very well on other packet based communications systems as well, such as cdma2000. The user equipments 18 may be mobile stations such as mobile telephones ("cellular" telephones) and laptops with mobile termination and thus may be, for example, portable, pocket, hand-held, computer- included or car-mounted mobile devices which communicate voice and/or data with the RAN

In the enhanced uplink (EUL) of WCDMA, a number of nodes share the same channel The channel may be shared in many different ways but in embodiments of the present invention TDMA is used, where the signal is divided into different time slots Thus, one node at a time is supposed to transmit, each using its own time slot

TDMA is mainly considered for UEs capable of 2ms transmission time intervals (TTIs), but in principle there is nothing that prevents the following to be expanded to include 10 ms TTIs

As stated above, the time in WCDMA is divided into TTIs The UEs make a rough time alignment with the help of the downlink This results in that the UEs will have different offset values to a common reference as shown in figure 2

In fig 2 the reference, denoted r, is chosen to be the downlink, but it is noted that any 2ms period may be selected as reference e g one of the UEs Since the TTIs start every 2ms, it is not necessary to consider any offset values greater than 2ms and less than Oms T is the duration of a TTI and T₁ is the offset value of user equipment i wherein 0 ≤1_t <T Thus, it is seen that UE 1 has an offset τ-i in relation to the reference r and UE 2 has an offset T2 in relation to the reference r

When scheduling is performed according to TDMA the time is divided and each UE receives an integer number of TTIs to transmit in If the TTIs in the different UEs are not aligned this will lead to, either unnecessary gaps between transmissions, or overlaps where two UEs transmit at the same time (or both) Both these situations lead to lower performance in the communication system, and most TDMA systems have methods to align the time slots for the nodes in the system, but as stated above this is not the case in WCDMA

According to embodiments of the present invention, to circumvent the problem of overlapping transmissions is to schedule the user equipments in increasing offset order, i.e. the user equipment with the lowest offset T_\ will be scheduled first and the user equipment with the second lowest offset will follow. When the user equipment with the highest offset has finished its transmission, one TTI will be skipped in order to prevent overlap with the user equipment with lowest offset.

In Figure 3 two examples of TDMA schedules are shown. In the first example, shown in fig. 3a, the offsets are not taken into account resulting in uncontrolled overlaps. In the second example of scheduling, shown in fig. 3b, the proposed method has been applied to the same situation and it is seen that by switching the transmission order of UE 2 and 3 and reduce the number of TTIs for UE 2 from three to two TTIs, a schedule without overlaps is produced. It may be noted that this holds for any number of users and regardless of their offsets.

Another observation is that the time gaps between the UEs will always sum up to exactly one TTI due to the skipped TTI in the end of the schedule.

Since the loss due to uncontrolled overlaps might be substantial, the controlled loss of one TTI per scheduling cycle could be a much better option.

According to a preferred embodiment of the present invention, the procedure for scheduling transmissions in a communication network system comprising communication network nodes communicating with several user equipments on uplink and downlink channels over a radio interface, whereby each transmission is sent within a time transmission interval, as shown in figure 4, is as follows: • If the number of users to schedule is equal to one, perform normal scheduling

(step 41 );

• Otherwise, scheduling said transmissions from each user equipment in a predetermined offset order (step 42);

• Omitting one time transmission interval when a last user equipment has ended its transmission in order to prevent overlap with the next transmission of a first user equipment (step 43).

According to some embodiments, the procedure further comprises the step of scheduling a user equipment having a lowest offset value first and scheduling a user equipment having a highest offset value last. Figure 5 is a block diagram showing a user equipment 18 and a radio base station (RBS) 15, such as eNode B, for scheduling transmissions from a user equipment to a communication network node in a communication network system comprising communication network nodes 15 communicating with several user equipments 18 on uplink 17 and downlink 16 channels over a radio interface, whereby each transmission is sent within a time transmission interval.

The RBS 15 comprises a radio transmitter 52 and a receiver 51. The transmitter 52 is transmitting data to a receiver 57 of the user equipment 18 over a radio interface on the downlink channel 16. The receiver 51 is receiving data from the user equipment 18 on the uplink channel 17. The RBS 15 further comprises a scheduler 54 configured to schedule said transmissions from each user equipment in a pre-determined offset order.

The user equipment 18 comprises a radio transmitter 56 arranged to transmit data packets to the receiver 51 of the RBS 15 over the radio interface on the uplink channel 17 and a receiver 57 arranged to receive data packets transmitted from the transmitter 52 of the RBS 15 on the downlink channel 16.

According to some embodiments, the scheduler 54 is further arranged to omit one time transmission interval when a last user equipment has ended its transmission in order to prevent overlap with the next transmission of a first user equipment.

According to some embodiments, the scheduler 54 is further arranged to schedule a user equipment having a lowest offset value first and to schedule a user equipment having a highest offset value last.

Thus, while there have been shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

Expressions such as "including", "comprising", "incorporating", "consisting of", "have", "is" used to describe and claim the present invention are intended to be construed in a nonexclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural and vice versa.

Numerals included within parentheses in the accompanying claims are intended to assist understanding of the claims and should not be construed in any way to limit subject matter claimed by these claims.

Claims

1. A method of scheduling transmissions in a communication network system comprising communication network nodes (15) communicating with several user equipments (18) on uplink (17) and downlink (16) channels over a radio interface, whereby each transmission is sent with an offset value in relation to a reference within a time transmission interval, characterized in that, the method comprises the step of scheduling said transmissions from each user equipment (18) in a predetermined offset order,

2. A method according to claim 1 , characterized in that, the method further comprises the step of omitting one time transmission interval when a user equipment (18) scheduled last has ended its transmission in order to prevent overlap with the next transmission of a user equipment (18) scheduled first.

3. A method according to claims 1 or 2, characterized in that, the method further comprises the step of scheduling a user equipment (18) having a lowest offset value first and scheduling a user equipment (18) having a highest offset value last.

4. A communication network node for scheduling transmissions in a communication network system comprising communication network nodes (15) communicating with several user equipments (18) on uplink (17) and downlink (16) channels over a radio interface, whereby each transmission is sent within a time transmission interval, characterized in that, the communication network node (15) comprises a scheduler (54) arranged to schedule said transmissions from each user equipment (18) in a pre-determined offset order.

5. A communication network node according to claim 4, characterized in that, the scheduler (54) further is arranged to omit one time transmission interval when a last user equipment (18) has ended its transmission in order to prevent overlap with the next transmission of a first user equipment (18).

6. A communication network node according to claims 4 or 5, characterized in that, the scheduler (54) is further arranged to schedule a user equipment (18) having a lowest offset value first and to schedule a user equipment (18) having a highest offset value last.