HK1240448B - Methods, network node and wireless device for handling access information - Google Patents

Description

Method, network node and wireless device for processing access information

Technical Field

The present disclosure generally relates to a network node of a radio network, a wireless device and methods therein for processing access information broadcast over a radio coverage area served by the network node.

Background Art

Over the years, different types of radio networks have been developed to provide radio communications for various wireless devices in different areas, typically divided into cells. Radio networks (also commonly referred to as wireless, cellular, or mobile networks) are constantly being improved to provide better capacity, quality, and coverage to meet the demands of users using the services and the needs of increasingly advanced communication terminals (such as smartphones and tablets), which typically require large amounts of bandwidth and resources for data transmission within the network. Therefore, achieving high capacity and good performance (e.g., in terms of high data throughput, low latency, and low data discard or loss rates) in radio communications between network nodes in the radio network and the various wireless devices communicating with the network nodes is often a challenge.

In the field of mobile or wireless communications, the term "wireless device" is often used and is used in this disclosure to refer to any communication entity that can communicate with a radio network by sending and receiving radio signals, such as mobile phones, tablets and laptops. Another common term in this field is "user equipment, UE". In this context, a wireless device can also be an automatically operated machine-to-machine type device, such as a sensor, a counter or a measurement entity that is configured to send reports on the radio network, for example at certain time intervals or based on certain events. In addition, the term "network node" is used here to refer to any node of a radio network that is arranged to communicate radio signals with a wireless device. A network node in this context is also commonly referred to as a base station, radio node, e-NodeB, eNB, NB, base transceiver station, access point, etc.

To improve the capacity and performance of radio networks, various features designed to make radio communications more efficient in terms of resource usage can be employed. In particular, it is desirable to reduce energy consumption in the network and the amount of interference generated by transmissions from network nodes and wireless devices, which in turn can improve capacity and performance. For example, it is desirable to limit the broadcast of system information from network nodes (sometimes commonly referred to as the "broadcast layer").

Figure 1 illustrates a communication scenario within a hierarchical network structure, including a macro node 100 providing radio coverage over a relatively large area C1, and multiple network nodes 102 providing radio coverage over smaller areas C2 substantially within area C1. Macro node 100 broadcasts system information over large area C1 that can be read by any wireless device D present in area C1, enabling data communication with network node 102 when present in any area C2. Broadcasting system information typically requires a higher power than that required to transmit data to a specific wireless device. This is because the broadcasted system information must be correctly received by any wireless device within the large radio coverage area C1, including those located on the outskirts of area C1, while the transmitted data only needs to reach a specific device, for example, within one of the smaller areas C2, using a transmit power and direction that can be adjusted for correct reception by the device. It is estimated that approximately 99% of the total energy consumed for downlink transmissions in a radio network is typically used to broadcast system information.

One specific topic that has been addressed in this context is the broadcasting of access information containing parameter settings regarding how wireless devices in idle mode should transmit random access messages on the physical random access channel (PRACH). Thus, such access information relates to various parameters to be used by wireless devices when accessing the network, such as frequency, synchronization, time window, preamble sequence in PRACH messages, power level, etc.

In addition, in the event of a risk of collision due to two or more wireless devices transmitting at the same time, contention-based access can be employed, in which case any wireless device can send a message to the serving network node on the PRACH without pre-reserving radio resources. Further access-related parameter settings that may be broadcast for contention-based access may relate to backoff timers, power increase step sizes, a maximum number of PRACH attempts before backoff, access restrictions related to, for example, closed user groups (including, for example, family members or employees who are allowed to access a certain network node such as a home base station), and service class or user type priority information, so that when there is congestion on the PRACH, only certain devices or devices with certain service requests are allowed to perform PRACH transmission attempts.

It has been proposed that the same access information should be broadcast at regular intervals in a synchronized manner over a relatively large area, for example by macro nodes providing large radio coverage, and/or broadcast simultaneously by several network nodes, each providing smaller radio coverage, in order to reduce and minimize the total broadcast duration and avoid interference. The goal is to transmit as little as possible to each device other than data transmission. If there is no data transmission in progress, the network node can turn off its transmitter and enter a discontinuous transmission mode, commonly referred to as DTX, to save power. Thus, any idle wireless device in the area can derive relevant access information from the broadcast access information based on a specific system signature index sequence (referred to as SSI) received from the network node, as a reference to a specific set of access parameters, or as an entry in the broadcast access information to be used when making random access to the network node.

However, different network nodes may need to apply different sets of access-related parameters locally in different areas, depending on the current traffic situation in terms of ongoing data communications, the number of wireless devices present in a particular area, the number of random access messages currently being sent, etc. In addition, network nodes may need to dynamically and quickly switch between different sets of access-related parameters to adapt the random access procedure to changes in traffic conditions. Currently, there is no solution to achieve such flexible use of different access-related parameters.

Summary of the Invention

It is an object of the embodiments described herein to address at least some of the problems and circumstances outlined above.This object and other objects may be achieved by using a network node, a wireless device and a method therein as defined in the appended independent claims.

According to one aspect, a method performed by a radio network including at least one network node is provided for processing access information related to how at least one wireless device (residing in a radio coverage area served by the radio network) can access the radio network. In the method, the radio network (i.e., at least one network node therein) broadcasts access information using a demodulation reference signal from a predefined set of demodulation reference signals, the access information including a series of access parameters. The radio network (i.e., at least one network node therein) also transmits a synchronization signal associated with a predefined mapping for at least two candidate demodulation reference signals (including the demodulation reference signal used to broadcast the access information). This enables the at least one wireless device to demodulate the broadcast access information and derive valid access-related parameters from the broadcast access information based on the transmitted synchronization signal.

According to another aspect, a radio network comprising at least one network node is arranged to process access information relating to how at least one wireless device (residing in a radio coverage area served by the radio network) can access the radio network. Each network node comprises a processor and a memory, the memory comprising instructions executable by the processor to cause the radio network (i.e., at least one network node therein) to:

- using a demodulation reference signal from a predefined demodulation reference signal set to broadcast access information including a series of access parameters, and

-Sending a synchronization signal associated with a predefined mapping for at least two candidate demodulation reference signals (including a demodulation reference signal for broadcast access information), thereby enabling at least one wireless device to demodulate the broadcast access information and derive valid access-related parameters from the broadcast access information based on the sent synchronization signal.

According to another aspect, a method performed by a wireless device in a radio network processes access information related to how the radio network can be accessed within a radio coverage area served by the radio network. In the method, the wireless device receives a synchronization signal from the radio network that is associated with a predetermined mapping of at least two candidate demodulation reference signals. The wireless device also receives broadcast access information that includes a set of access parameters. The wireless device then demodulates the broadcast access information using one of the at least two candidate demodulation reference signals and derives valid access parameters from the broadcast access information based on the synchronization signal.

According to another aspect, a wireless device is arranged to process access information relating to how a radio network can be accessed in a radio coverage area served by the radio network. The wireless device comprises a processor and a memory, the memory comprising instructions executable by the processor for causing the wireless device to:

- receiving from the radio network a synchronization signal associated with a predefined mapping for at least two candidate demodulation reference signals,

- receiving broadcast access information including a set of access parameters, and

- deriving valid access parameters from the broadcast access information based on the synchronization signal by demodulating the broadcast access information using one of the at least two candidate demodulation reference signals.

The above-described radio network, network node, wireless device and method may be configured and executed according to different optional embodiments to achieve further features and benefits to be described below.

A computer program is also provided, comprising instructions that, when executed on at least one processor in a scoring management node, cause the at least one processor to perform the aforementioned method for a scoring management node. A carrier embodying the computer program is also provided, wherein the carrier is one of an electrical signal, an optical signal, a radio signal, or a non-tangible computer-readable storage medium.

BRIEF DESCRIPTION OF THE DRAWINGS

The solution will now be described in more detail by means of exemplary embodiments and with reference to the accompanying drawings, in which:

FIG1 is a communication scenario according to the prior art, in which system information is broadcast from a macro node providing large radio coverage, and a wireless device communicates data with a network node providing smaller radio coverage.

FIG2 is a diagram illustrating how access information may be provided from a network node of a radio network to a wireless device according to some possible embodiments.

FIG3 is a flow chart illustrating a process performed by at least one network node of a radio network according to other possible embodiments.

FIG4 is a flow chart illustrating a process performed by a wireless device according to other possible embodiments.

FIG5 is a diagram showing an example of how the synchronization signal SSI may be mapped to different candidate demodulation reference signals AIT RS according to other possible embodiments.

FIG6 illustrates a communication scenario in which a network node transmits different synchronization signals SSI mapped to the same reference signal AIT RS through different sectors or antenna beams according to another possible embodiment.

FIG7 illustrates another communication scenario in which three network nodes transmit different synchronization signals SSI mapped to the same reference signal AIT RS in different areas according to another possible embodiment.

FIG8 is a flow chart illustrating a more detailed example of a process in a wireless device according to other possible embodiments.

FIG9 is a block diagram illustrating at least one network node in a radio network and a wireless device in more detail according to other possible embodiments.

DETAILED DESCRIPTION

By using any of the embodiments described herein, it is possible to achieve, for example, more flexible use of different access parameters depending on the current business situation, so that the access parameters can be used "optimally" or near-optimally, thereby achieving high performance and reducing interference while minimizing energy consumption for broadcasting access information.

The solution described herein relates to processing access information related to how a radio network can be accessed. First, the solution relates to processes and apparatus implemented in a radio network comprising at least one network node, which can be used to obtain appropriate access parameters for at least one wireless device. Second, the solution also relates to processes and apparatus implemented in a wireless device present in a radio coverage area served by the radio network, which can be used to obtain and apply appropriate access parameters. In short, the radio network broadcasts access information using a predefined demodulation reference signal and also transmits a synchronization signal associated with a predefined mapping for at least two candidate demodulation reference signals (including the demodulation reference signal used to broadcast the access information). As a result, a wireless device receiving the synchronization signal is able to correctly demodulate the broadcasted access information and derive valid access-related parameters therefrom based on the synchronization signal.

In this manner, the radio network can broadcast the same access information, for example in the form of an access information table (AIT), using different demodulation reference signals in different regions, for example, defined by one or more cells, sectors, or antenna beams. By transmitting different synchronization signals in different regions, for example in the form of a system signature index sequence (SSI), any wireless device can use the received synchronization signal to demodulate the broadcasted access information and derive relevant access parameters based on the region in which the wireless device is located.

Thus, depending on the demodulation reference signal used, different sets of access-related parameters can be applied in different areas of the network in a flexible manner. This flexibility is achieved by mapping the synchronization signal to two or more demodulation reference signals, one of which is used to broadcast access information, so that the radio network can easily switch between these demodulation reference signals in a specific area, thereby implementing the corresponding set of access-related parameters in that area, without having to change the content of the broadcast information and the synchronization signal sent.

Figure 2 schematically illustrates how the access information and synchronization signal described above can be broadcast and transmitted, respectively, over a radio network. In this example, the access information is broadcast in the AIT at a certain time period, while the synchronization signal is transmitted in the SSI at another period that may be shorter than the AIT period. Technically, temporal separation of the AIT and SSI is not required, and they can also be separated in frequency or by a combination of time/frequency/code. In some cases, the AIT period can be the same as the SSI period, for example when the network contains only one transmitting network node, in which case it may be desirable to transmit the AIT and SSI together simultaneously.

The AIT may be broadcast over a large area, for example, by the macro node 100 shown in FIG1 , and different SSIs may be sent in different smaller areas within the large area, for example, by different “smaller” network nodes (such as the network node 102 shown in FIG1 ). Alternatively, the same network node may send different SSIs in different directions, such as sectors or antenna beams.

Once a wireless device has received SSI in a specific area, it will identify at least two candidate demodulation reference signals based on the predefined mapping described above (assuming the device knows the mapping). The wireless device will then attempt to demodulate the broadcast AIT using each of the at least two candidate demodulation reference signals until demodulation is successful because one of the demodulation reference signals is used for the broadcast AIT. The term "candidate" means that the device does not know which demodulation reference signal is correct before attempting to demodulate the AIT.

Figure 2 further illustrates that the broadcast of the AIT and the transmission of the SSI are separated in time, and that the SSI is transmitted at a much shorter period than the broadcast AIT to ensure that the device has received the SSI before receiving the AIT. It also illustrates that the SSI can be transmitted by both macro nodes and "small" nodes. The AIT can also be transmitted by both macro nodes and smaller nodes. The SSI, or generally the synchronization signal, is actually "critical" to the correct and valid access parameters (e.g., AIT) in the broadcast access information.

For example, it may be desirable to broadcast any system information and access information, such as on the physical broadcast channel (PBCH) in a so-called "single frequency network" (SFN) transmission format, meaning that the same information is broadcast over a large area. However, this is not possible in networks that use a one-to-one mapping between synchronization signals and demodulation reference signals for broadcast information. The one-to-one mapping discussed above is not optimized for exploiting, for example, beamforming gain or macrodiversity gain.

An example of how the solution can be used on the network side will now be described with reference to the flowchart in Figure 3, which shows a process in which actions are performed by a radio network comprising at least one network node to implement the above-mentioned functionality. Figure 3 can also be seen as a process in which actions are performed by one or more network nodes of the radio network. The radio network operates to process access information relating to how at least one wireless device present in a radio coverage area served by the radio network accesses the radio network. A "network node" in this context can be a base station or equivalent for sending and receiving radio signals, but can also be a control node such as a network management node, a radio network controller RNC or an operation & maintenance (O&M) node, which is used to control and instruct one or more base stations to transmit radio signals. In addition, the following actions can be performed by the same network node or two or more different network nodes in the radio network.

The first action 300 shows that the radio network broadcasts access information comprising a series of access parameters using a demodulation reference signal from a predefined set of demodulation reference signals.In a possible embodiment, the radio network may broadcast the access information in an Access Information Table (AIT) as described above.

The broadcast access information may relate to various access parameters used by wireless devices when accessing the network. Typical, but non-limiting, examples of such access parameters that devices need to know include transmission frequency, synchronization, the time window for random access, the preamble sequence used in PRACH messages, power level, backoff timer, power increase step size, the maximum number of transmission attempts allowed before backoff, access restrictions associated with certain user groups or types, and service class or user type priority information, which indicates that only certain devices or certain service requests are allowed to make random access transmissions when the access channel is congested.

In the next illustrated action 302, the radio network transmits a synchronization signal associated with a predefined mapping for at least two candidate demodulation reference signals, including the demodulation reference signal used for broadcast access information. The mapping is thus "predefined" in the sense that both the network and the at least one wireless device have knowledge of the mapping. Thus, the at least one wireless device is able to demodulate the broadcast access information and derive valid access-related parameters from the broadcast access information based on the transmitted synchronization signal.

In another possible embodiment, the radio network may transmit the synchronization signal using the system signature index sequence SSI as described above. In another possible embodiment, the radio network may broadcast access information at a first period and transmit the synchronization signal at a second period that is shorter than the first period, as shown in FIG2 , for example. It should be noted that actions 300 and 302 may be repeated any number of times and in any order. For example, action 302 may be performed multiple times before and/or after action 302 is performed, as shown in FIG2 , for example.

The above actions 300 and 302 can be implemented in different ways in practice. For example, a control node (such as an RNC or an O&M node) can select a demodulation reference signal to be used from a predefined set of demodulation reference signals, for example, based on the current traffic situation (such as ongoing data communications, the number of wireless devices present in the radio coverage area, the number of random access transmissions, the amount of interference generated, etc.) in order to implement corresponding access parameters that are suitable or even best suited to the traffic situation. The control node can then instruct one or more base stations, etc. to use the selected demodulation reference signal in action 300 and send a synchronization signal mapped to the selected demodulation reference signal in action 302. In addition, access information can be broadcast and synchronization signals can be sent from the same base station or from different base stations, which has been described above with respect to Figure 2. All of the above activities can also be performed by the same base station or generally by a network node.

The radio network may also employ various other embodiments as follows. In one possible embodiment, the radio network may use a demodulation reference signal to broadcast access information over a specific area, and may transmit a synchronization signal only in the specific area, so that any wireless device present in the specific area can perform random access using the corresponding access-related parameters. Thus, the corresponding access-related parameters will be implemented in the specific area, while other access-related parameters can be implemented in a similar manner in other areas, thereby locally adapting the access process to different areas. This adaptation may also be performed dynamically by switching between different demodulation reference signals and corresponding access-related parameter sets, thereby adapting the random access process to changes in traffic conditions as described above. Thus, performance in the radio network can be improved by dynamically and locally adopting appropriate or even optimal access-related parameters based on the typically fluctuating traffic conditions in each area.

In another possible embodiment, the radio network may further broadcast different synchronization signals in different sectors or antenna beams, so that different access-related parameters are effective in different sectors or antenna beams. In this case, according to another possible embodiment, the radio network may also monitor the random access message in each sector or antenna beam based on the corresponding access-related parameters applied in the sector or antenna beam.

In another possible embodiment, different synchronization signals, such as SSI, may be associated with different antenna ports. In another possible embodiment, a predefined set of demodulation reference signals may be arranged in a predefined tree structure comprising multiple groups of demodulation reference signals. In this case, the synchronization signal may be mapped to at least one set of candidate demodulation reference signals in the tree structure. An example of such a tree structure will be summarized below with reference to FIG5 .

In another possible embodiment, the synchronization signal may be further associated with a predefined mapping of various attributes of the physical channel used to broadcast access information, which wireless devices may need to know and use to demodulate and decode the broadcast access information. These physical channel attributes may include at least one of the following: physical channel format, scrambling code, and cyclic redundancy check (CRC) code. Thus, the synchronization signal can be used to inform devices of the physical channel used to broadcast access information.

An example of how this solution can be employed on the device side will now be described with reference to the flowchart in Figure 4, which illustrates a process by which a wireless device performs actions to implement the above functionality. The wireless device operates to process access information relating to how a radio network can be accessed within a radio coverage area served by the radio network.

Action 400 shows that the wireless device receives a synchronization signal associated with a predefined mapping for at least two candidate demodulation reference signals from a radio network.In a possible embodiment, the wireless device may receive the synchronization signal in a system signature index sequence SSI as already described above.

In the next illustrated action 402, the wireless device also receives broadcast access information including a set of access parameters. Some examples of such access parameters have been described above. In another possible embodiment, the wireless device may receive the access information in a received access information table (AIT) as described above. Then, in action 404, the wireless device derives valid access parameters from the broadcast access information based on the synchronization signal by demodulating the broadcast access information using one of the at least two candidate demodulation reference signals.

The radio network may also employ various other embodiments as follows. In one possible embodiment, the wireless device may respectively use the at least two candidate demodulation reference signals to attempt to demodulate the broadcasted access information until demodulation is successful. An example of the process when employing this embodiment will be described below with reference to FIG8 .

In a possible embodiment, the synchronization signal may be further associated with a predefined mapping of properties of a physical channel used to broadcast the access information, wherein the physical channel properties include at least one of the following: a physical channel format, a scrambling code, and a cyclic redundancy check (CRC) code. In this case, the wireless device may attempt to demodulate the broadcasted access information based on the properties of the physical channel.

In another possible embodiment, the wireless device may continue to perform random access to the radio network based on the derived valid access parameters (ie, by sending one or more access requests on a radio channel such as the aforementioned physical random access channel PRACH using the derived access parameters).

An example of how a predetermined mapping of synchronization signals to two or more demodulation reference signals can be associated is shown in Figure 5, which schematically illustrates a portion of a mapping table. In this example, multiple synchronization signals in the form of SSIs are mapped to different predefined demodulation reference signals RS, denoted as "AIT RS" in the figure. Specifically, as indicated by the arrows, synchronization signal SSI 17 is mapped to three demodulation reference signals, namely AIT RS 0, AIT RS 16, and AIT RS 17. This mapping is predefined, i.e., known to the network and any wireless device, as described above.

Therefore, when the wireless device receives the synchronization signal SSI 17 from the radio network, the wireless device can identify AIT RS 0, AIT RS 16, and AIT RS 17 as three candidate demodulation reference signals based on the predefined mapping. Therefore, the wireless device can also derive valid access parameters from the broadcast access information by demodulating the broadcast access information using one of AIT RS 0, AIT RS 16, and AIT RS 17. The radio network can also broadcast access information using any one of the demodulation reference signals AIT RS 0, AIT RS 16, and AIT RS 17, so that the corresponding access parameters are implemented while the device has received the synchronization signal SSI 17.

As mentioned above, the predefined demodulation reference signal sets can be arranged in a predefined tree structure comprising multiple groups of demodulation reference signals. An example of such a tree structure is shown in FIG5 , where the tree structure includes first-level groups represented as g _0,0 , g _0,1 , g _0,2 , g _0,3 , and so on. The four groups in the first level are included in another group g _1,0 at a higher second level. Therefore, a synchronization signal can be mapped to at least one candidate demodulation reference signal group in this tree structure.

As mentioned above, the radio network can use a specific demodulation reference signal to broadcast access information in a specific area, such as a sector or antenna beam, and synchronization signals can be sent only in the specific area, so that any wireless device therein can derive corresponding access-related parameters to perform random access in that area. Two examples of this embodiment are shown in Figures 6 and 5. In Figure 6, radio network 600 includes a control node 606 and at least one base station 604. Control node 606 controls base station 604 to broadcast access information and send synchronization signals as follows.

Base station 604 broadcasts access information (AIT) over a relatively wide area using a demodulation reference signal, designated AIT RS 4. As shown, base station 604 also transmits different synchronization signals, namely, SSI 4, SSI 5, SSI 6, and SSI 7, in smaller sectors or antenna beams within this wide area. FIG. 6 also shows a mapping table in which all synchronization signals SSI 4-7 are mapped to AIT RS 4. Therefore, any wireless device receiving any synchronization signal SSI 4-7 can identify the mapped demodulation reference signal AIT RS 4 and use it to demodulate the broadcast access information and derive valid access parameters. For example, wireless device 602 receiving synchronization signal SSI 7 can accordingly identify and use the mapped demodulation reference signal AIT RS 4.

Each synchronization signal SSI 4-7 is also mapped to one or more other demodulation reference signals other than AIT RS 4, as indicated by the dashed arrows, which indicate that according to the predefined mapping for SSI 7, SSI 7 is also mapped to AIT RS 7. As a result, the wireless device 602 can attempt to demodulate the broadcast access information using candidate demodulation reference signals AIT RS 4 and AIT RS 7, respectively, and will therefore successfully demodulate when using AIT RS 4.

The base station may, for example, be equipped with an advanced antenna solution that supports analog beamforming in a set of predetermined directions. In this case, it may be advantageous for base station 604 to know in which beam wireless device 602 will have the best reception for the upcoming downlink transmission, and this can already be achieved from the random access procedure in the scenario of FIG6 . Therefore, base station 604 can send a random access response (RAR) to device 602 only in the downlink beam corresponding to the synchronization signal SSI 7 received and used by device 602. Thus, device 602 can indicate which downlink beam is the best by deriving and using random access parameters based on SSI 7.

The base station may also have limited ability to perform baseband processing simultaneously in all different directions and may therefore need to ensure that wireless devices in different downlink beams accurately transmit their RACH preambles while the base station searches for random access transmissions in the corresponding uplink beams. The base station may then be able to perform sequential processing of the PRACH in each possible direction. Using the embodiment of FIG6 , uplink receive beamforming for the PRACH can be achieved while still ensuring good performance for access information broadcasts.

In FIG7 , a radio network 700 includes a base station 704 such as a macro node covering a wide area, three base stations 708 , 710 and 712 covering smaller areas within the wide area, and a control node 706 that controls the base stations 704 , 708 - 712 to broadcast access information and send synchronization signals as follows.

Base station 704 broadcasts access information (AIT) over a relatively wide area using a demodulation reference signal, designated AIT RS 16. Base stations 708-712 and 704 transmit different synchronization signals, SSI 16, SSI 17, SSI 18, and SSI 19, respectively, as shown. FIG7 also shows a mapping table, in which synchronization signals SSI 6-19 are all mapped to AIT RS 16. Therefore, any wireless device receiving any of synchronization signals SSI 16-19 can identify the mapped demodulation reference signal, AIT RS 19, and use it to demodulate the broadcast access information and derive valid access parameters therefrom.

For example, the wireless device 702 that receives the synchronization signal SSI 18 can accordingly identify and use the mapped demodulation reference signal AIT RS 16. Each synchronization signal SSI 16-19 is also mapped to one or more other demodulation reference signals different from AIT RS 16, as shown by the dashed arrows, which indicates that according to the predefined mapping for SSI 18, SSI 18 is also mapped to AIT RS 16, and the wireless device 702 can accordingly attempt to demodulate the broadcasted access information.

Transmitting the AIT 7 over a large area, as shown in FIG7 , achieves so-called macrodiversity gain. However, if the same SSI is also transmitted over the same large area, additional problems may arise, as this may require, for example, RACH coordination between base station sites. If a wireless device transmits a RACH preamble, any network node within the area will be responsible for ensuring that a RAR message is sent in response to the wireless device. If the network nodes are unable to coordinate RAR transmissions, the wireless device may receive several RAR messages sent from different base stations in the network.

One way to avoid this situation could be to send a single AIT (in this case using AIT RS 16) from base station 704 in Figure 7 over the entire area, and still use a different SSI in each smaller area covered by base stations 708-712. In this case, the RACH-related parameters (e.g., RACH preamble) used by wireless device 702 could depend on which SSI has been received.

A more detailed example of a process for a wireless device operating in a radio network according to some of the above-described embodiments will now be described with reference to the flowchart in FIG8 . A first action 800 illustrates that the wireless device receives a synchronization signal associated with a predefined mapping for a plurality of demodulation reference signals from the radio network, substantially as described with respect to action 400 . In a next action 802 , the wireless device identifies candidate demodulation reference signals (DMRSs) according to the predefined mapping. The wireless device also receives, in action 804 , broadcast access information including a set of access parameters.

The wireless device then attempts to demodulate the broadcast access information using the first candidate DMRS from the previously identified candidate demodulation reference signals in action 806. If the wireless device determines in a next action 808 that the demodulation attempt was successful, the wireless device can decode the broadcast access information and derive valid access parameters from the demodulated access information in a next action 810. A final action 812 shows the wireless device performing random access to the radio network using the derived access parameters.

However, if the wireless device determines in action 808 that the demodulation attempt was unsuccessful, the wireless device will return to action 806 and use the next candidate demodulation reference signal (DMRS) to attempt to demodulate the broadcast access information. In this manner, actions 806 and 808 will be repeated until the correct candidate DMRS is used in a successful demodulation attempt, allowing actions 810 and 812 to be performed; or until all identified candidate demodulation reference signals have been tried to no avail. In the latter case, as indicated by the dashed arrow, the wireless device will have to return to action 800 and receive another synchronization signal from the radio network, and the entire process can be repeated in the manner described above.

The block diagram in FIG9 shows a detailed but non-limiting example of how at least one network node 900 and a wireless device 902 in a radio network can be configured to achieve the above-described solutions and embodiments, respectively. In this figure, the at least one network node 900 and the wireless device 902 can be configured to operate as follows, as appropriate, according to any of the examples and embodiments using the above-described solutions. Each of the at least one network node 900 and the wireless device 902 is shown as including a processor "P," a memory "M," and a communication circuit "C," which has suitable devices for sending and receiving radio signals in the manner described herein.

The communication circuit C of each of the at least one network node 900 and the wireless device 902 thus comprises devices configured to communicate with each other over a radio interface using a protocol suitable for radio communication according to an embodiment. However, the solution is not limited to any particular type of data or protocol.

The at least one network node 900 includes means configured or arranged to perform actions 300-302 in the flowchart of Figure 3 in the manner described above. In addition, the wireless device 902 includes means configured or arranged to perform actions 400-404 in the flowchart of Figure 4 in the manner described above. The actions of Figures 3 and 4 can be performed by means of functional modules in the corresponding processors P in the at least one network node 900 and the wireless device 902.

At least one network node 900 is arranged to process access information relating to how at least one wireless device (such as device 902) present in a radio coverage area served by the radio network can access the radio network. Thus, at least one network node 900 comprises a processor P and a memory M, the memory comprising instructions executable by the processor to cause the at least one network node 900 to operate as follows.

At least one network node 900 operates to broadcast access information including a series of access parameters using a demodulation reference signal from a predefined demodulation reference signal set. This broadcasting operation may be performed by a transmitting module 900a in at least one network node 900 in the manner described above for action 300.

The at least one network node 900 is further operable to transmit a synchronization signal associated with a predefined mapping for at least two candidate demodulation reference signals (including a demodulation reference signal for broadcasting access information). Thus, the at least one wireless device is able to demodulate the broadcasted access information and derive valid access-related parameters from the broadcasted access information based on the synchronization signal transmitted by the at least one network node 900. This transmission operation may be performed, for example, by the transmitting module 900a in the manner described above with respect to action 302. The at least one network node 900 may further include a logic module 900b for determining which demodulation reference signal to use when broadcasting the access information, and which synchronization signal to transmit as described above. Alternatively, in this regard, the at least one network node 900 may be instructed by a control node (e.g., any of the control nodes 606 and 706 described above).

The wireless device 902 is arranged to process access information relating to how a radio network can be accessed in a radio coverage area served by the radio network.The wireless device 902 comprises a processor P and a memory M comprising instructions executable by the processor to cause the wireless device 902 to operate as follows.

The wireless device 902 operates to receive a synchronization signal associated with a predefined mapping for at least two candidate demodulation reference signals from a radio network. This receiving operation can be performed by a receiving module 902a in the wireless device 902 in the manner described above for action 400. The wireless device 902 also operates to receive broadcast access information including a series of access parameters. This further receiving operation can be performed by the receiving module 902a in the manner described above for action 402.

The wireless device 902 operates to derive valid access parameters from the broadcast access information based on the synchronization signal by demodulating the broadcast access information using one of the at least two candidate demodulation reference signals. This operation can be performed by a demodulation module 902b in the wireless device 902 in the manner described above with respect to action 400. The wireless device 902 can further include, for example, a logic module 902c for identifying the at least two candidate demodulation reference signals, and a transmission module 902d for performing random access to the radio network based on the derived valid access parameters.

It should be noted that FIG9 shows various functional modules in at least one network node 900 and wireless device 902, respectively, and that those skilled in the art are able to implement these functional modules using appropriate software and hardware in practice. Therefore, the solution is generally not limited to the illustrated structures of at least one network node 900 and wireless device 902, and the functional modules 900a-b and 902a-d therein can be configured to operate appropriately according to any features and embodiments described in this disclosure.

The functional modules 900a-b and 902a-d described above can be implemented in at least one network node 900 and wireless device 902, respectively, by program modules comprising corresponding computer programs including code means. When the code means are executed by a processor P, the at least one network node 900 and wireless device 902 perform the aforementioned actions and processes. Each processor P may include a single central processing unit (CPU) or may include two or more processing units. For example, each processor P may include a general-purpose microprocessor, an instruction set processor, and/or an associated chipset and/or a dedicated microprocessor (e.g., an application-specific integrated circuit (ASIC)). Each processor P may also include memory for cache purposes.

Each computer program may be carried by a computer program product in the form of a memory having a computer-readable medium and connected to the processor P in each of the at least one network node 900 and the wireless device 902. Thus, the computer program product or memory M in each of the at least one network node 900 and the wireless device 902 comprises a computer-readable medium on which a computer program in the form of a computer program module or the like is stored. For example, the memory M in each node may be a flash memory, a random access memory (RAM), a read-only memory (ROM), or an electrically erasable programmable ROM (EEPROM), and in alternative embodiments, the program modules may be distributed across different computer program products in the form of memory within the respective network node 900 and the wireless device 902.

The solution described herein can be implemented in each of the at least one network node 900 and the wireless device 902 by a computer program comprising instructions that, when executed on at least one processor, cause the at least one processor to appropriately perform actions according to any of the above-described embodiments. The solution can also be implemented in a carrier containing the above-described computer program on each of the at least one network node 900 and the wireless device 902, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, or a computer-readable storage medium.

Although the solution is described with reference to specific exemplary embodiments, the description is generally intended only to illustrate the concepts of the present invention and should not be considered to limit the scope of the solution. For example, the terms "network node," "wireless device," "access information," "demodulation reference signal," "synchronization signal," and "access-related parameters" have been used throughout this disclosure, but any other corresponding entities, signals, and/or parameters having the features and characteristics described herein may also be used. The solution is defined by the appended claims.

Claims (33)

1. A method performed by a radio network including at least one network node for processing access information relating to how at least one wireless device present in a radio coverage area served by the radio network can access the radio network, the method comprising: - Use demodulation reference signals from a predefined set of demodulation reference signals to broadcast access information including a series of access parameters, and - Transmit a synchronization signal associated with a predefined mapping for at least two candidate demodulation reference signals, thereby enabling the at least one wireless device to identify the at least two candidate demodulation reference signals based on the transmitted synchronization signal and the predefined mapping, demodulate broadcast access information using one of the identified candidate demodulation reference signals, and derive valid access-related parameters from the broadcast access information: the at least two candidate demodulation reference signals include a demodulation reference signal for broadcasting the access information. 2. The method of claim 1, wherein the radio network broadcasts the access information in an Access Information Table (AIT). 3. The method of claim 1 or 2, wherein the radio network transmits the synchronization signal in the form of a System Signature Index Sequence (SSI). 4. The method according to claim 1 or 2, wherein the radio network broadcasts the access information in a first period and transmits the synchronization signal in a second period shorter than the first period. 5. The method of claim 1 or 2, wherein the radio network uses the demodulation reference signal to broadcast the access information over a specific area, and transmits the synchronization signal only in the specific area, enabling any wireless device present in the specific area to perform random access using the corresponding access-related parameters. 6. The method of claim 5, wherein the radio network broadcasts different synchronization signals in different sectors or antenna beams, such that different access-related parameters are effective in different sectors or antenna beams. 7. The method of claim 6, wherein the radio network monitors random access messages in the sector or antenna beam based on corresponding access-related parameters applied in each sector or antenna beam. 8. The method according to claim 1 or 2, wherein the predefined set of demodulation reference signals is arranged in a predefined tree structure comprising multiple sets of demodulation reference signals, and the synchronization signal is mapped to at least one set of candidate demodulation reference signals in the tree structure. 9. The method of claim 1 or 2, wherein the synchronization signal is further associated with a predefined mapping for attributes of a physical channel used for broadcasting the access information, the attributes including at least one of the following: physical channel format, scrambling code, and cyclic redundancy check (CRC) code. 10. A radio network including at least one network node, configured to process access information relating to how at least one wireless device present in a radio coverage area served by the radio network can access the radio network, each network node including a processor and a memory, the memory including instructions executable by the processor to cause the radio network to perform the following operations: - Use demodulation reference signals from a predefined set of demodulation reference signals to broadcast access information including a series of access parameters, and - Transmit a synchronization signal associated with a predefined mapping for at least two candidate demodulation reference signals, thereby enabling the at least one wireless device to identify the at least two candidate demodulation reference signals based on the transmitted synchronization signal and the predefined mapping, demodulate broadcast access information using one of the identified candidate demodulation reference signals, and derive valid access-related parameters from the broadcast access information: the at least two candidate demodulation reference signals include a demodulation reference signal for broadcasting access information. 11. The radio network of claim 10, wherein the radio network operates by broadcasting the access information in an Access Information Table (AIT). 12. The radio network of claim 10 or 11, wherein the radio network operates by transmitting the synchronization signal with a System Signature Index Sequence (SSI). 13. The radio network of claim 10 or 11, wherein the radio network operates by broadcasting the access information in a first period and transmitting a synchronization signal in a second period shorter than the first period. 14. The radio network of claim 10 or 11, wherein the radio network operates by using the demodulation reference signal to broadcast the access information over a specific area, and by transmitting the synchronization signal only over the specific area, such that any wireless device present in the specific area can perform random access using the corresponding access-related parameters. 15. The radio network of claim 14, wherein the radio network operates to broadcast different synchronization signals in different sectors or antenna beams, such that different access-related parameters are valid in different sectors or antenna beams. 16. The radio network of claim 15, wherein the radio network operates by monitoring random access messages in the sector or antenna beam based on corresponding access-related parameters applied in each sector or antenna beam. 17. The radio network of claim 10 or 11, wherein the predefined set of demodulation reference signals is arranged in a predefined tree structure comprising multiple sets of demodulation reference signals, and the synchronization signal is mapped to at least one set of candidate demodulation reference signals in the tree structure. 18. The radio network of claim 10 or 11, wherein the synchronization signal is further associated with a predefined mapping for attributes of a physical channel used for broadcasting the access information, the attributes including at least one of: physical channel format, scrambling code, and cyclic redundancy check (CRC) code. 19. A method performed by a wireless device in a radio network for processing access information relating to how the radio network can be accessed in a radio coverage area served by the radio network, the method comprising: - Receive a synchronization signal from the radio network associated with a predefined mapping for at least two candidate demodulation reference signals. - Identify the at least two candidate demodulation reference signals based on the received synchronization signal and the predefined mapping. - Receive access information broadcast, including a series of access parameters, and -Demodulate the broadcast access information using one of the identified candidate demodulation reference signals to derive valid access parameters from the broadcast access information. 20. The method of claim 19, wherein the wireless device uses the at least two candidate demodulation reference signals to attempt to demodulate the broadcast access information until demodulation is successful. 21. The method of claim 19 or 20, wherein the synchronization signal is further associated with a predefined mapping for attributes of a physical channel used for broadcasting the access information, the attributes including at least one of: physical channel format, scrambling code, and cyclic redundancy check (CRC) code, and wherein the wireless device attempts to demodulate the broadcast access information based on the attributes of the physical channel. 22. The method of claim 19 or 20, wherein the wireless device performs random access to the radio network based on the derived valid access parameters. 23. The method of claim 19 or 20, wherein the wireless device receives broadcast access information in the Access Information Table (AIT). 24. The method of claim 19 or 20, wherein the wireless device receives the synchronization signal in a System Signature Index Sequence (SSI). 25. A wireless device configured to process access information relating to how a radio network can be accessed in a radio coverage area served by the radio network, the wireless device including a processor and a memory, the memory including instructions executable by the processor to cause the wireless device to perform the following operations: - Receive a synchronization signal from the radio network associated with a predefined mapping for at least two candidate demodulation reference signals. - Identify the at least two candidate demodulation reference signals based on the received synchronization signal and the predefined mapping. - Receive access information broadcast, including a series of access parameters, and -Demodulate the broadcast access information by using one of the identified candidate demodulation reference signals, and derive valid access parameters from the broadcast access information. 26. The wireless device of claim 25, wherein the wireless device operates by attempting to demodulate broadcast access information using the at least two candidate demodulation reference signals until demodulation is successful. 27. The wireless device of claim 25 or 26, wherein the synchronization signal is further associated with a predefined mapping for attributes of a physical channel used for broadcasting the access information, the attributes including at least one of: physical channel format, scrambling code, and cyclic redundancy check (CRC) code, and wherein the wireless device is used to attempt to demodulate the broadcast access information based on the attributes of the physical channel. 28. The wireless device according to claim 25 or 26, wherein the wireless device operates to perform random access to the radio network based on derived valid access parameters. 29. The wireless device according to claim 25 or 26, wherein the wireless device operates to receive broadcast access information in the Access Information Table (AIT). 30. The wireless device of claim 25 or 26, wherein the wireless device operates to receive the synchronization signal in a system signature index sequence (SSI). 31. A method performed by a network node of a radio network for processing access information relating to how at least one wireless device present in a radio coverage area served by the radio network can access the radio network, the method comprising: - Use demodulation reference signals from a predefined set of demodulation reference signals to broadcast access information including a series of access parameters, and - Transmit a synchronization signal associated with a predefined mapping for at least two candidate demodulation reference signals, thereby enabling the at least one wireless device to identify the at least two candidate demodulation reference signals based on the transmitted synchronization signal and the predefined mapping, demodulate broadcast access information using one of the identified candidate demodulation reference signals, and derive valid access-related parameters from the broadcast access information: the at least two candidate demodulation reference signals include a demodulation reference signal for broadcasting access information. 32. A network node of a radio network, the network node being configured to process access information relating to how at least one wireless device present in a radio coverage area served by the radio network can access the radio network, each network node including a processor and a memory, the memory including instructions executable by the processor to cause the radio network to perform the following operations: - Use demodulation reference signals from a predefined set of demodulation reference signals to broadcast access information including a series of access parameters, and A synchronization signal is transmitted associated with a predefined mapping for at least two candidate demodulation reference signals, thereby enabling the at least one wireless device to identify the at least two candidate demodulation reference signals based on the transmitted synchronization signal and the predefined mapping, demodulate broadcast access information using one of the identified candidate demodulation reference signals, and derive valid access-related parameters from the broadcast access information: the at least two candidate demodulation reference signals include a demodulation reference signal for broadcasting the access information. 33. A computer-readable storage medium having instructions stored thereon, which, when executed by at least one processor, cause the at least one processor to perform the method according to any one of claims 1-9, 19-24 and 31.