WO2009140985A1

WO2009140985A1 - Random access in flexible spectrum usage systems

Info

Publication number: WO2009140985A1
Application number: PCT/EP2008/004141
Authority: WO
Inventors: Frank Frederiksen; Preben Mogensen
Original assignee: Nokia Siemens Networks Oy
Priority date: 2008-05-23
Filing date: 2008-05-23
Publication date: 2009-11-26

Abstract

The present invention relates to methods, apparatuses, a system, and a computer program product for providing access to a wireless access network. Desired network access resources are selected based on at least one of channel estimation, measurement and sensing at an access device (20, 30) of a wireless access network, and the desired network access resources are advertised from the access device (20, 30) to a wireless terminal device (10), wherein the desired network access resources define a set of random access channels to select from for accessing the access device (20, 30).

Description

Random Access in Flexible Spectrum Usage Systems

FIELD OF THE INVENTION

The present invention relates to methods, apparatuses, computer program prod- ucts, and a system for providing random access to a wireless network environment.

BACKGROUND OF THE INVENTION

The performance of digital handsets generally has been improving over the years with respect to functionality, performance, and battery life. Handset performance is being addressed by the introduction of 3^rd generation (3G) technology, with higher data rates and better provision for new services. One key consideration is the need for the 3G networks to more than just coexist but handover active calls/data sessions with the current 2/2.5G networks. Where 3G coverage is absent, the user will need to utilize the 2/2.5G network, bringing with it the requirement for the phone to support both radio access technologies (RATs). For this reason, 3G phones often support at least two RATs.

Spectral resources in wireless communications systems are assigned to operators in a fixed manner. The scarce spectral resources could be used more efficiently if the assignment to the operators could be made with some flexibility.

Flexible Spectrum Use (FSU) aims at adapting the available spectrum to a network to reflect the changes on the number of subscribers as well as on daily traffic patterns. FSU should enable more versatile operation of the networks, for example, with varying traffic loads in the networks or with some operators providing more focused coverage than others. FSU should provide enough system flexibility towards geographical differences in regulatory spectrum assignments. FSU also aims at easing the deployment of multiple RATs at the launch of the system, even when spectrum is made available gradually according to increasing traffic demands. Such flexibility may turn out to be of particular importance for the systems requiring wide spectrum bands on frequencies suitable for efficient vehicular communications, e.g., below 6 GHz. Some approaches for flexible spectrum use (FSU) are presented in IST-2003-507581 WINNER D6.3 WINNER Spectrum As- pects: Assessment report, 2005, and in IST-2001-35125 OverDRiVE D13 Specification and Performance of Dynamic Spectrum Allocation.

The FSU concept allows multiple operators to share the same frequency spectrum in a decentralized manner using policy based radio resource optimization. It is expected to be implemented in decentralized and uncoordinated manner, where there will be a lot of independent base stations (BS) or other access devices, potentially belonging to different operators, which are not connected to each other, but on the other hand they are targeting at sharing the same physical spectrum resources according to certain policies. The problem of having such a flexible sharing of spectrum among several operators is that the users need to be informed on the current radio parameter configuration of the BS. Further, each user will need to know when and how to access the control channel whenever communication is needed between the BS and a mobile station (MS) or other terminal device. This requires transmission of some broadcast information, which will typically be sent on a broadcast channel (BCH). Normally, the BCH is seen as a static entity, which is sent on a constant and periodical time-frequency resource and which will contain semi-static information - at least in typical cellular network configurations like for instance GSM (Global system for Mobile communication), UMTS (Universal Mobile Telecommunication System), and LTE (Long Term Evolution). However, when the cell configuration varies in a more frequent manner, mechanisms are needed to handle time variability of the used cell system information. This applies to the BCH as well as to the communication channel for initial access seen from a mobile stations (MS) side

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a mechanism for handling time variability of used cell system information during network access.

This object is achieved by a method comprising:

• selecting desired network access resources based on at least one of channel estimation, measurement and sensing at an access device of a wireless access network; and • advertising said desired network access resources from said access device to a wireless terminal device;

• wherein said desired network access resources define a set of random access channels to select from for accessing said access device.

Furthermore, at the other transmission end the above object is achieved by a method comprising:

• receiving network access resources advertised from a wireless access network; and

• selecting a random access channel from said received network access re- sources based on an interference or quality measurement; and

• using said selected random access channel for accessing said wireless access network.

Additionally, at the network side the above object is achieved by an apparatus comprising:

• selection means for selecting desired network access resources based on at least one of channel estimation, measurement and sensing; and

• transmitting means for advertising said desired network access resources;

• wherein said desired network access resources define a set of random access channels to select from for accessing said apparatus.

Moreover, at the terminal side the above object is achieved by an apparatus comprising:

• receiving means for receiving network access resources advertised from a wireless access network; and

• selection means for selecting a random access channel from said received network access resources based on an interference or quality measurement; and - A -

• access control means for using said selected random access channel for accessing said wireless access network.

The above methods may be implemented as a computer program product comprising code means for producing the respective above steps when run on a com- puter device.

The above apparatuses may be implemented as network elements or nodes, access devices, fixed or mobile terminal devices, or as modules, chips or chip sets provided in these nodes, elements or devices.

Accordingly, desired network access resources for reception are individually selected by access devices. These resources or channels can then be used as proposal for network access. When receiving the proposed desired network access resources, a terminal device can choose a desired access resource which makes the smallest interference into the rest of the network. Thus, additional flexibility can be provided to the system, whereby the terminal device is enabled to take a more active role in selecting resources that are seen better or best fit for transmission of information for network access, rather than just using a predetermined access channel. This potentially improves network performance, e.g. in cases where network deployment is less coordinated.

Additionally, desired transmission resources may be selected as well based on the at least one of channel estimation, measurement and sensing, and may be used by the access device for signaling the desired network access resources. As an example, these transmission resources may comprise at least one broadcast channel for broadcasting the desired network access resources.

Furthermore, the selection of desired resources may be performed based on an estimated interference level.

According to an example, the desired network access resources may comprise a list of random access channels.

Further advantageous modifications are defined in dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described based on embodiments with reference to the accompanying drawings in which:

Fig. 1 shows a schematic diagram indicating a network architecture in which the present invention can be implemented;

Fig. 2 shows schematic block diagrams of a terminal device and an access device according to embodiments of the present invention;

Fig. 3 shows a flow diagram of a terminal-side processing according to an em- bodiment of the present invention;

Fig. 4 shows a flow diagram of a network-side processing according to an embodiment of the present invention;

Fig. 5 shows a schematic representation of physical resources for a random access channel;

Fig. 6 shows a two-dimensional frequency vs. time diagram which illustrates a network resource selection; and

Fig. 7 shows a schematic block diagram of a software-based implementation according to an embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENT

In the following, embodiments of the present invention will be described based on an FSU system with broadcast control channel in a wireless communication network.

Fig. 1 shows a schematic diagram of a general network architecture in which the present invention can be implemented. A radio access network 300, e.g., a cellular Universal Mobile Telecommunications System (UMTS) Terrestrial Access Network (UTRAN) according to the Long Term Evolution (LTE) or 3^rd Generation Partnership Project (3GPP) Release 8 standard, provides access to a user equipment (UE) or - more generally - a MS 10 via a first access device 20, such as a GSM and/or UMTS base station device (e.g. Node B) of a first operator, and a second access device 30, such as an enhanced Node B (eNB) according to LTE of a second operator. It is noted that other access devices can be provided, which are not shown here.

Fig. 5 shows a physical channel structure indicating physical resources for a random access channel (RACH). In Fig. 5, the horizontal dimension corresponds to the time domain, while the vertical dimension corresponds to the frequency domain. As an example, six access slot densities may be provided, e.g. 1/20ms, 1/10ms, 2/1 Oms, 3/10ms, 5/10ms or 10/10ms. Depending on the selected access slot density, one to four time offsets are defined such that the same receiver can cope with more than one cell in a site (except with slot density 10/10ms).

The upper diagram of Fig. 5 shows a frequency division duplex (FDD) case, where uplink and downlink channels are separated in the frequency domain. In FDD, two different RACH frequencies are provided at different timings next to a continuous physical uplink control channel (PUCCH).

The lower diagram of Fig. 5 shows a time division duplex (TDD) case, where up- link and downlink channels are separated in the time domain. In TDD, simultaneous RACHs are needed at different frequencies, because there are less access slots in time.

According to an embodiment, a joint BCH and RACH structure provides several candidates for the MS to choose from when requesting initial access to the BS. To achieve this, a BS, e.g. the BSs 20, 30 of Fig. 1 , transmits a cell specific configuration on a set of broadcast channels, so that a listening MS, e.g. the MS 10 of Fig. 1 , is provided with a set of BCHs to listen to in case of other interfering transmitting units on the same resources. The transmitted BCHs are adapted to advertise a set of candidate resources (e.g. RACH candidates) that the MS is allowed to use for transmitting its random access data. Based on this information, the MS can select a physical resource for RACH transmission according to the estimated interference situation at the MS, e.g., the MS can in principle estimate or sense interference levels at the suggested resources.

Fig. 2 shows schematic block diagrams of a terminal device or terminal (e.g. the MS 10) and a network node or network device (e.g. first or second access devices 20, 30) according to the embodiment of the present invention. At the MS 10, a received broadcast information is checked by a resource detection (RD) functionality or unit 15 for provision of a list or set of RACH resources coded in or added to a received data stream. The resource detection functionality or unit 15 may be provided as a part of an RRC functionality which controls reception operation of a receiver part of a radio frequency (RF) front-end unit 16 which enables wireless transmission and reception via an antenna. Based on interference or quality measurements or estimations performed e.g. at the resource detection functionality or unit 15, a suitable RACH resource is selected and a corresponding information or control signaling is forwarded to an access controller or control unit 14 which uses the selected RACH resource to initiate a network access operation.

At the first and second access devices 20, 30, suitable BCH and RACH resources are determined at a resource indication (Rl) functionality or unit 22, e.g., based on channel measurements, estimations and/or sensing performed e.g. at the re- source indication functionality or unit 22. The selected suitable RACH resources are incorporated in or added to a control message in a message control information (MCI) functionality or unit 23 and broadcast via an RF front-end unit 24 and an antenna, by using at least one of the selected BCH resources.

Fig. 3 shows a flow diagram of a terminal-side processing according to an embodiment of the present invention, which could be implemented based on a processing routine executed in the MS 10.

In step S101 , a list of RACH resources is received via a BCH resource. Then, in step S102, interference or reception quality levels are estimated, and at least one desired RACH resource is selected in step 103 from the received list, based on the estimation results. Finally, in step S104, a network access is initiated by using at least one of the selected RACH resources.

Fig. 4 shows a flow diagram of a network-side processing according to an em- bodiment of the present invention, which could be implemented based on a processing routine in the access devices 20, 30.

In step S201 , a channel measurement, sensing or estimation is performed as a basis for selection of suitable TX channels (e.g. BCH resources) and RX channels

(e.g. RACH resources) in step S202. Then, in step S203, a list or set of selected RACH resources is generated. Finally, in step S204, the obtained set or list of RACH resources is broadcast by using at least one of the selected TX channels (e.g. BCH resources).

Fig. 6 shows a two-dimensional frequency vs. time diagram which illustrates the suggested principle in a TDD case, where the access device (e.g. BS) transmits in a downlink time period through a set of selected broadcast channels (BCH) to advertise a set of random access channels to a terminal device (e.g. MS). The terminal device can choose from the received set of random access channels for transmission during an uplink period (indicated by the bolt frame in Fig. 6).

Now, considering the system setup as shown in Fig. 6, it can be seen that the uplink and downlink directions are separated in time (TDD system)c- while the same frequency resources are used for both link directions. When employing FSU, multiple access devices (e.g. BSs) try to access the same frequency resources in or- der to increase the throughput for themselves (and for the system in general). By measuring and/or estimating and/or sensing at the access device, it can be estimated which channels are better for the access device (e.g. from an interference point of view) to use for transmission of the BCH, as well as which channels (resources) are better to receive upon. These channels or resources will then be used for transmission of the BCH, which in turn should indicate which frequency resources are to be used for the random access channel (RACH). When receiving the list of possible RACH resources, the terminal device will estimate the interference levels seen from its side and choose the RACH resource which makes the smallest interference into the rest of the network. As the terminal device might also have information on other access devices, it might be able to choose the resources that are not in use at other access devices.

Hence, it is suggested having the RACH physical resources defined through the BCH, such that the set of potential RACH resources can be advertised based on the estimated interference level at the access device.

Fig. 7 shows a schematic block diagram of an alternative software-based implementation of the above embodiment and its implementation examples for achieving a dynamic control channel structure. The required functionalities can be im- plemented in a processing unit 210, which may be any processor or computer device with a control unit which performs control based on software routines of a control program stored in a memory 212. The control program may also be stored separately on a computer-readable medium. Program code instructions are fetched from the memory 212 and are loaded to the control unit of the processing unit 210 in order to perform the processing steps of the above functionalities of Figs. 2 to 4, which may be implemented as the above mentioned software routines. The processing steps may be performed on the basis of input data Dl and may generate output data DO. At the network side (access device) the input data Dl may correspond to obtained channel interference or quality, and at the terminal side the input data Dl may correspond to the received set or list of RACH resources. Furthermore, at the network side the output data DO may correspond to a message or signalling with the added list or set of offered RACH resources and at the terminal side the output data DO may correspond to the selected RACH resource.

Consequently, the above embodiments may be implemented as a computer program product comprising code means for generating each individual processing step when run on a computer device or data processor of the first and second access devices 20, 30 or terminal device (e.g. MS 10), respectively.

In summary, methods, apparatuses, a system, and a computer program product for providing access to a control channel of a wireless access network have been described, wherein desired network access resources are selected based on at least one of channel estimation, measurement and sensing at an access device of a wireless access network, and the desired network access resources are advertised from the access device to a wireless terminal device, wherein the desired network access resources define a set of random access channels to select from for accessing the access device.

It is apparent that the invention can easily be extended to any transmission link for any kind of wireless network which supports usage of control channels. Specifically, the present invention is not intended to be restricted to cellular networks. The embodiment may thus vary within the scope of the attached claims. Furthermore, while the invention has been described mainly for the case of access devices 20, 30 and the MS 10 is a terminal device, other devices can take the respective role as well.

Claims

1. A method comprising:

a) selecting desired network access resources based on at least one of channel estimation, measurement and sensing at an access device (20, 30) of a wireless access network; and

b) advertising said desired network access resources from said access device to a wireless terminal device (10);

c) wherein said desired network access resources define a set of random access channels to select from for accessing said access de- vice (20, 30).

2. The method according to claim 1 , further comprising selecting desired transmission resources based on said at least one of channel estimation, measurement and sensing, and using said transmission resources for signaling said desired network access resources.

3. The method according to claim 2, wherein said transmission resources comprise at least one broadcast channel for broadcasting said desired network access resources.

4. The method according to any one of the preceding claims, wherein said selecting is performed based on an estimated interference level.

5. A method comprising:

a) receiving network access resources advertised from a wireless access network (300); and

b) selecting a random access channel from said received network access resources based on an interference or quality measurement; and

c) using said selected random access channel for accessing said wireless access network (300).

6. The method according to claim 4, wherein said desired network access resources comprise a list of random access channels.

7. An apparatus comprising:

a) selection means (22) for selecting desired network access resources based on at least one of channel estimation, measurement and sensing; and

b) transmitting means (24) for advertising said desired network access resources;

c) wherein said desired network access resources define a set of ran- dom access channels to select from for accessing said apparatus

(20, 30).

8. The apparatus according to claim 7, wherein said selection means (22) is adapted to select desired transmission resources based on said at least one of channel estimation, measurement and sensing, and to use said transmission resources for signaling said desired network access resources.

9. The apparatus according to claim 8, wherein said transmission resources comprise at least one broadcast channel for broadcasting said desired network access resources.

10. The apparatus according to any one of claims 7 to 9, wherein said selection means (22) is configured to perform selection based on an estimated interference level.

11. An apparatus comprising:

a) receiving means (16) for receiving network access resources adver- tised from a wireless access network (300); and

b) selection means (15) for selecting a random access channel from said received network access resources based on an interference or quality measurement; and c) access control means (14) for using said selected random access channel for accessing said wireless access network (300).

12. The apparatus according to claim 11 , wherein said desired network access resources comprise a list of random access channels.

13. A computer program product comprising code means for generating the steps of method claim 1 or 5 when run on a computer device.

14. A system for providing access to a control channel, said system comprising at least one apparatus according to claim 7 and at least one apparatus according to claim 11.

15. A network access device comprising an apparatus according to claim 7.

16. A mobile terminal device comprising an apparatus according to claim 11.

17. A chip device comprising an apparatus according to claim 7 or 11.