GB2410861A

GB2410861A - An apparatus for network communications in a multi-radio access technology system.

Info

Publication number: GB2410861A
Application number: GB0402501A
Authority: GB
Inventors: Hamid Reza Falaki
Original assignee: NEC Technologies UK Ltd
Current assignee: NEC Technologies UK Ltd
Priority date: 2004-02-04
Filing date: 2004-02-04
Publication date: 2005-08-10
Anticipated expiration: 2024-02-04
Also published as: GB0402501D0; GB2410861B

Abstract

An apparatus for network communication on at least one standby radio access technology (RAT) in a multi-RAT communication system comprising a means for communicating with a network on a communication RAT, a means for determining that communication is required between the network and at least one Standby RAT, a means for identifying future breaks in the communication between the communication RAT and the network and a means for providing data to the at least one Standby RAT to define the timing and duration of the break in communication.

Description

An Apparatus for Network Communication in a Multi-Radio Access Technology

System The present invention relates an apparatus for network communication in a multi-radio access technology system.

Many modern communication devices include multi-radio access technology systems (RATs), for example Global System for Mobile Communications (GSM) and Wideband Code Division Multiple Access (WCDMA). In use, these devices select a communication RAT on which they communicate preferably and one or more Standby RAT s which are held in idle mode. During operation, the signal quality of the communication RAT may be reduced due to signal blockages or other reasons. When the signal strength of the communication RAT is reduced below a predefined limit, the device can switch RATs and communicate on one of the Standby RATs which provides a stronger signal in order to maintain communication. For the device to switch to a Standby RAT quickly and efficiently, as required by the user, the device must maintain synchronization with the networks of the Standby RATs. Devices maintain synchronization with the networks by periodically monitoring the networks of the Standby RATs.

Radio networks transmit information in regular, periodic, cycles. During communication, the device does not require all information transmitted by the network.

Therefore, there are regular periods during the communication cycle in which the communication RAT is not active, ie not communicating with the network. Since these breaks in communication occur at regular or welldefined positions in the cycle, the communication RAT can - 2 - accurately predict the time and duration of any approaching gaps in the air interface.

Devices can only monitor one RAT at any one time, ie send or receive one communication signal. These breaks in communication of the communication RAT provide opportunities within which the Standby RAT s can communicate with their network by making network measurements. During the communication gaps, the physical media, eg the RF resources, of the device are not used by the communication RAT. Therefore, the RF resources may be used by Standby RAT during these intervals. Network measurements enable the Standby RATs to remain synchronized with their networks and the network or handset to make a decision on a cell change or hangover.

Typically, the gaps in the air interface of the communication RAT are of short duration. Therefore, the Standby RAT must know the exact timing and duration of the opportunity in order that it can complete its required measurements within this allocated period. In order to take a measurement, or communicate with its network, the Standby RAT must be activated and synchronized to its network. Any required hardware must also be enabled.

Therefore, the Standby RAT requires prior warning of when it will have an opportunity to communicate with its network in order that it can complete its measurements within the allocated time frame or multiples of time frame opportunities if the measurement can not be made in one attempt. Inter-frequency and Inter-RAT type of measurements require the radio frequency (RF) sub-system to change the synthesiser's frequency and hence in these cases we need to use these measurement opportunities. - 3 -

The measurement types are defined in standards as: Intra-frequency measurements (downlink physical channels at the same frequency as the active set), Inter-frequency measurements (downlink physical channels at frequencies that differ from the frequency of the active set and on downlink physical channels in the active set), Inter-RAT measurements (downlink physical channels belonging to another radio access technology than UTRAN, e.g. GSM when active in FDD), Traffic volume measurements (uplink traffic volume), Quality measurements (downlink quality parameters, e.g. downlink transport block error rate) and, UE-internal measurements (UK transmission power and UE received signal level). Not all these measurement types require the use of the transmission gap. For example Quality, traffic volume, and US internal measurements can be done without the use of these gaps.

Each RAT system is organised in the form of layers.

The layers of each RAT form a stack, known as the Protocol Stack. The stacks include a number of defined layers in which each layer performs a number of designated functions. The standard structure of the stack is defined by the Open System Interconnection (OSI) reference model.

In the OSI model, the layers are arranged in a hierarchy with each layer performing a different function. The higher layers become increasingly more complex. Each layer within a RAT is connected to the layers above and below to enable commands to be sent from the higher layers to the lower layers and information to be transmitted up and down the stack. The lowest point of this structure is usually known as the physical layer which communicates through the physical media in this case Radio transceiver.

Each RAT has its own stack consisting of the required layers. A first RAT can perform logical communications - 4 with a second RAT by transmitting a communication up and down the layers to the corresponding layer in the second RAT using the defined interlayer interfaces and the primitives known at each layer. Transfer of information in this way is usually within the Software and is not tightly coupled to the air interface timing.

The lowest layer of a stack is the physical layer. In the physical layer the transfer of information is time critical and therefore is closely coupled to the air interface's time base for maintaining time critical actions required by the that particular RAT such as normal communication and measurements. Physical layers of different RATs within a device are used to code and decode the signals over the RF communication channel.

The radio interface in UMTS FDD is layered into three protocol layers: physical layer (Ll), data link layer (L2); network layer (L3). Layer 2 is split into sub layers: Medium Access Control (MAC), Radio Link Control (RLC), Packet Data Convergence Protocol (PDCP) and Broadcast/Multicast Control (BMC). Layer 3 and RLC are divided into Control (C-) and User (U-) planes. PDCP and BMC exist in the U-plane only. In the C-plane, Layer 3 is partitioned into sub-layers where the lowest sub-layer, denoted as Radio Resource Control (RRC), interfaces with layer 2 and terminates in the UTRAN. The next sub-layer provides 'Duplication avoidance' functionality as

specified in 3GPP Technical Specification TS24.007

"Mobile radio interface signalling layer 3". It terminates in the CN but is part of the Access Stratum; it provides the Access Stratum Services to higher layers. The higher layer signalling such as Mobility Management (MM) and Call Control (CC) is assumed to belong to the non-access stratum. On the general level, the protocol architecture - 5 - is similar to the current ITU-R protocol architecture, ITU-R M.lO35.

In known systems, when the signal for the communication RAT becomes weak and the device determines that it requires measurements from a Standby RAT, the Standby RAT is instructed to take measurements via a signal transmitted across the network layer. The communication RAT advises the Standby RAT of the timing and duration of a gap in the air interface during which it is able to take its measurements on its network. Since different RATs operate on different timebases, ie have different clocks, the software of the device must convert the timing of the communication opportunity into the timebase of the Standby RAT in order that the Standby RAT knows when it may take measurements on its network.

A known procedure for advising the Standby RAT of the timing of the forthcoming measurement opportunity involves a number of steps. Firstly, the network layer of the communication RAT determines that network measurements for a Standby RAT are required. The network layer identifies the timing and duration of the forthcoming gaps in the air interface. The network layer sends this information to the physical layer in order to determine the position of these gaps in terms of the timebase of the communication RAT. This information is then sent back up the stack to the network layer.

The higher layers of the stack convert the timing of the communication opportunities into the timebase of the Standby RAT. This information is then transmitted across the network layer to the Standby RAT. The network layer of the Standby RAT receives this information, advises its physical layer, which then enables any required hardware - 6 - and takes the required measurements. Once the measurements are complete, the network layer of the Standby RAT informs the network layer of the communication RAT that it has completed its measurements and that the communication RAT can recommence its communication.

There are a number of problems associated with this known method which may lead to windows of opportunity for communication being missed, particularly, when the gaps in the air interface are short. These problems are associated mainly with a time delay and further with the transmission of data up and down the protocol stacks as it is not closely synchronous with the air interface.

These delays are particularly problematic when several short duration gaps in the communication air interface are required for the measurement and the overhead (ie time period) associated with communication across stack is comparable to the payload time period of the measurement data to be passed up and down the stacks.

There may also be errors associated with the conversion between timebases. Again this can lead to measurement windows being missed or not optimized. This known method also requires complicated software to deal with the timebase conversions. These operations do not lead to efficient or optimised power consumption.

We have appreciated that it is important for Standby RAT s to communicate with their network in order that they can maintain synchronization with their network. Gaps in the air interface of the communication RAT provide opportunities for Standby RAT s to perform these communications. However, these opportunities may be short in duration and it is essential that the Standby RAT has prior notice of the timing of these gaps in order that it - 7 - can enable the required hardware to communicate at the commencement of the opportunity. We have also appreciated that it is critical to advise the Standby RAT of measurement opportunities quickly. Therefore, it is inefficient to transmit information regarding the timing of communication opportunities following multiple commands up and down the protocol stacks and conversion of timebases which require complicated software and often experience unacceptable delays.

The present invention addresses these problems by advising a Standby RAT of forthcoming gaps in the air interface which represent communication opportunities via an interrupt which is transmitted across the hardware connection between the physical layers of the RATs. The interrupt advises the Standby RAT that an opportunity for communication is approaching and of the start time and duration of the communication window. The time period between the transmission of the interrupt and the start of the measurement window is a predetermined time period, thus removing the requirements for conversion of timebases. Embodiments of the invention remove the requirement of transmitting data up and down the protocol stack and hence reduce any delays in the transmission of the information. Furthermore, the complexity of the software that would otherwise be required for converting the timebases is also reduced.

The invention is defined more precisely in its various aspects in the appended claims to which reference should now be made.

Embodiments of the present invention will now be described in detail by way of example with reference to the accompanying drawings, in which: \ 8 - Figure l shows the communication links between different RATs in a communication device.

Figure 2 is a flow diagram showing the steps taken by embodiments of the invention in order to take measurements on non-serving networks.

Figure 3 shows the flow of information between RATs in a multi-RAT device.

Figure 4 is an example of the interrupt transmitted from the physical layer of the communication RAT.

Figure l shows the communication paths between the protocol stacks of two RAT s in a mobile communication device. The radio access technology systems may be any suitable system including GSM and WCDMA. Further embodiments of the invention may incorporate more than two RATs in the same device. Figure l shows three protocol layers associated with each RAT. In practice, the stacks may include a number of higher layers. The lowest layer of each stack is the physical layer lA and 2A. The physical layers of each stack are joined by a hardware link lo. The physical layers control the timebase of each RAT and the timing of execution of actions and measurements.

Each RAT includes a data link layer lB and 2B. The data link layers are positioned higher than the physical layers and are linked to the physical layer to enable data associated with the RAT to be passed between the layers.

The highest of the indicated layers are the network layers lC and 2C. The network layers may communicate with each other via a software interface defined as link 20 since 9 - they are in the same physical device. Each network layer can also communicate with a base station via radio links and 40.

In Figure 2 the network layer of the communication RAT determines that measurements are required to be taken on one or more of the Standby RAT s at 210. Typically, this determination may be made in dependence on the strength of the signal from the base station for the communication RAT. Once the network layer has determined that measurements should be taken on the Standby RAT, the network layer identifies forthcoming gaps in the air interface at 220. The network layer then sends the timing and duration of the gaps down to the physical layer along with a command for the physical layer to transmit this information across the hardware connection to the Standby RAT. This sets the interrupt active and the physical layer commences transmission of the interrupt. In a system having multiple Standby RAT s the network layer may also specify the Standby RAT to which it wishes the information to be sent.

At 230 the network layer of the communication RAT transmits a signal to the network layer of the Standby RAT to inform the Standby RAT that the Standby RAT is required to take measurements and that it will transmit details of the timing at which the Standby RAT may take measurements.

The network layer also indicates which measurements are required to be made. On receipt of the signal from the network layer of Communication RAT, the network layer of Standby RAT sends a command to the physical layer of Standby RAT to receive the incoming interrupt at 240 and to take the required measurements in the identified opportunities. The Standby RAT may then activate suitable software to receive the incoming interrupt if required. - 10

At 250 the physical layer of the communication RAT transmits the interrupt to the physical layer of the standby RAT. The interrupt is received at 260. On receipt of the interrupt, the physical layer of the standby RAT creates a measurement schedule at 270 in which it determines which of the required measurements it will make in each of the available measurement opportunities.

In certain situations, the measurement opportunity will not be sufficiently long for the standby RAT to make all of its required measurements. In this case, the physical layer will make some of the required measurements in the first measurement opportunity and wait for further opportunities to complete the required measurements.

Once the standby RAT has completed all required measurements it sends the measurement report to the network layer of the standby RAT at 280. The measurement report includes details of all measurements. The network layer of the standby RAT then transmits the measurement report to the network layer of the communication RAT.

At 290, the communication RAT determines whether further measurements are required to be taken on standby RATs. If not, then the network layer of the communication RAT instructs the physical layer of the communication RAT to stop transmitting the interrupt at 300. However, if further measurements are required, the network layer of the communication RAT instructs the physical layer to transmit the interrupt to a designated standby RAT.

This process may be used for many different RATs.

Figure 3 shows the flow of information between radio access technologies as a function of time. It also shows - 11 - the period for which the interrupt is transmitted from the communication RAT. Figure 3 depicts the network (N) and physical(P) layers of the communication RAT and the Standby RATs. At 310, the network layer of the communication RAT instructs the physical layer to transmit an interrupt identifying the measurement opportunities to Standby RAT 1. The physical layer then commences transmission of the interrupt. At 320 the network layer of the communication RAT advises the network layer of Standby RAT 1 that it is transmitting an interrupt across the physical layer and that the Standby RAT must take required measurements when the interrupt indicates.

Details of the required measurements are included in the advice at 320. The network layer of Standby RAT 1 instructs its physical layer to receive the interrupt at 330.

Once physical layer has executed all required measurements in one or several opportunity gaps, it sends the measurement report to network layer at 340. The network layer of the Standby RAT 1 then transmits the measurement report to the network layer of communication RAT at 350.

If the communication RAT requires further measurements from standby RAT's, it may advise other Standby RATs that it is transmitting an interrupt by repeating these steps to the other Standby RAT s as represented by steps 360 - 390. Once the network layer of the communication RAT has received confirmation that the last Standby RAT has completed its measurement report, it instructs its physical layer to stop transmitting the interrupt at 400. - 12

Figure A shows an example of an interrupt transmitted from the physical layer of the communication RAT to the physical layer of the Standby RAT to advise of the forthcoming schedule of measurement opportunities. The interrupt includes a burst of predefined duration and timing advance characterizes hereafter referred to as preamble P which is followed by optional bursts of binary signals to indicate the period of the interrupt. The preamble is transmitted at a predetermined time interval before the start of the measurement opportunity.

Furthermore, the bursts a-e are positioned at known time intervals after the preamble, ie before the start of the measurement opportunity S. This known positioning of the bursts enables the Standby RAT to know exactly when to start the measurements without having to convert the time periods between time bases, since it knows the predefined time periods in terms of its own timebase. The binary signals indicate the duration of the burst as shown in

Table 1.

Burst State description

Indicates units for measurement interval 0 = milliseconds l = multiples of lO microseconds B Binary x l6 C Binary x 8 D Binary x 4 E Binary x 2 Table l: Duration of the communication opportunities indicated by the interrupt. - 13

In this example the period of time between P and a is the constant value of 50 microseconds and the period between P and S is the constant value of 150 microseconds.

These values are arbitrary and the timers of specific embodiments should be fine tuned to the specific time periods of the embodiment.

The purpose of the preamble is to wake up the Standby RAT hardware before the start of the measurement opportunity, which is identified as point S in Figure 4.

Therefore, the preamble must be uniquely recognizable to the physical layer of the receiving RAT in order that the Standby RAT identifies that a measurement opportunity is forthcoming. For example, the signal may be initiated prior to the measurement duration to give just enough time for the Standby RAT to calculate and schedule an optimised use of the upcoming opportunity measurement gap. The type of preamble signal used is specific to the hardware design implementation. An example of a preamble signal could be a pulse of 1.8V for 1 ms duration. In practice, any signal could be used as long as the device is programmed to identify the signal to be the preamble signal.

The software component responsible for the Standby RAT receiving the interrupt must be active by the time that the interrupt is started. To ensure that the physical layer is ready to receive the interrupt, a signal is transmitted across the network layer to inform the Standby RAT that it will shortly receive an interrupt and to activate any required software.

Once the physical layer of the Standby RAT receives the preamble it knows exactly when the measurement opportunity will start, is 150 microseconds later. It also knows when to expect to receive bursts a-e, which confirm the duration of the burst. After the time for receiving burst e has passed, the Standby RAT knows the start time and duration of the measurement opportunity. The time delay between the preamble and the start of the measurement opportunity must be sufficiently long in order that the Standby RAT has sufficient time to enable the hardware which is required to take the measurements.

Since the time between the reception of the preamble and the start of the window is predetermined, this time period will be programmed into the Standby RAT in terms of its timebase and, therefore, there is no need for the device to include software to convert between the timebases.

The preamble P indicates to the Standby RAT to become ready and to schedule its measurements within the communication opportunity period which starts at point S. ie 150 microseconds later. During this period the Standby RAT can read the bursts a-e and become aware of the measurement opportunity period. The Standby RAT can then perform the measurement in one or several opportunities and can compile the measurement report for the higher layers.

In embodiments including more than one Standby RAT, the routing of the hardware interrupt across the RATs may be achieved in different ways. In one embodiment including n RATs, the interrupt can be achieved by directly routing the interrupt for each of the n RATs to a dedicated receive port on the receiving RAT. In such an embodiment, each RAT must be provided with (n-l) interrupt transmission output ports and (n-l) interrupt receive ports. Each individual port will be hardwired to the physical layer of a different RAT. - 15

Alternative embodiments may provide the physical layer of each RAT with a multiplex switch for transmission and a multiplex switch for reception. Such embodiments only require the physical layer of each RAT to have a single transmission and reception port. In this case, the communication RAT can only transmit an interrupt to a single Standby RAT at a time due to the single output transmission port.

Further embodiments of the present invention may utilise the registers of the device to indicate the state of each RAT at a given time. An example of the registers for a typical embodiment are shown in table 2.

RAT select mode RAT mode indicator A B C D RAT 1 idle O O O O RAT l in communication O O O l RAT 2 idle 0 0 l 0 RAT 2 in communication O 0 1 1 RAT n idle l l l O RAT n in communication l l l l Table 2: Use of the registers to indicate the state of the RATs in a device.

The registers are shared between all the Digital Signal Processors (DSPs) in the RATs to indicate which RAT - 16 is the communication RAT and the status of its communication at a given time. For example, during sleep periods the communication RAT monitors less information from the network than during periods in which the device is engaged on a call. Therefore, during the sleep periods, the communication RAT will have longer intervals between communications with the network and consequently the opportunity for measurements by Standby RATs will be greater. This hardware information element allows the measuring, ie standby, RAT to schedule its measurements in small opportunity sessions during communication periods or longer opportunity periods during sleep periods. In preferred embodiments the registers may only become active when there is a need for measurement and, at other times, remain in a low power state. The information from the register may be transmitted via the network layers or can be incorporated into the interrupt.

It will be clear to those skilled in the art that embodiments of the present invention reduce the complexity of the software in a device including multi-radio access technologies. Furthermore, embodiments provide a system which can synchronise the measurements of Standby RATs within the gaps in the air interface of the communication RAT without requiring information relating to the measurement schedule to be transmitted up and down the protocol stack. This removes many sources of delays in the transfer of information. - 17

Claims

Claims 1. A method for network communication on at least one Standby RAT

in a multi-RAT communication system including the steps of: communicating with a network on a communication RAT; determining that communication is required between the network and at least one Standby RAT; identifying future breaks in the communication between the communication RAT and the network; and, providing data to the at least one Standby RAT defining the timing and duration of the break in communication.
2. A method according to claim 1 including the further step of communicating with a network on the Standby RAT during the break in communication between the communication RAT and the network.
3. A method according to claim 1 or 2 in which the step of providing data to the Standby RAT of the timing and duration of the break in communication includes an interrupt signal.
4. A method according to claim 3 in which the interrupt signal is transmitted across the physical layer of the protocol stack.
5. A method according to claim 3 or 4 in which the interrupt signal is transmitted at a predetermined time before the break in communication between the communication RAT and the network.
6. A method according to claim 3, 4 or 5 wherein the interrupt signal identifies whether the communication RAT is in an active or idle state.
7. A method according to claim 3, 4, 5 or 6 including the step of advising the Standby RAT that an interrupt signal is to be transmitted.
8. A method according to claim 7 wherein the Standby RAT is advised that an interrupt signal is to be transmitted by a signal on the network layer of the protocol stack.
9. A method according to any preceding claim including the further step of advising the communication RAT when the Standby RAT has finished communicating with the network.
10. A method according to claim 9 including the further step of stopping transmission of the interrupt signal when the communication RAT has been advised that the Standby RAT has finished communicating with the network.
11. A method according to any preceding claim wherein the step of determining that communication is required on a Standby RAT is made in dependence on the strength of the signal of the communication RAT.
12. A method for informing standby radio access technology systems (RATs) of opportunities for network communications in a multi-RAT system substantially as herein described with reference to the figures.
13. An apparatus for network communication on at least one standby radio access technology (RAT) in a multi-RAT communication system comprising; a means for communicating with a network on a communication RAT; a means for determining that communication is required between the network and at least one Standby RAT; - 19 a means for identifying future breaks in the communication between the communication RAT and the network; and, a means for providing data to the at least one Standby RAT to define of the timing and duration of the break in communication.
14. An apparatus according to claim 13 including the further step of communicating with a network on the Standby RAT during the break in communication between the communication RAT and the network.
15. An apparatus according to claim 13 or 1-4 further comprising a means for generating an interrupt signal to provide data to the Standby RAT defining the timing and duration of the break in communication includes an interrupt signal.
16. An apparatus according to claim 15 wherein the interrupt signal is transmitted across the physical layer of the protocol stack.
17. An apparatus according to claim 15 or 16 wherein the interrupt signal is transmitted at a predetermined time before the break in communication between the communication RAT and the network.
18. An apparatus according to claim 15, 16 or 17 further comprising a register to define the status of the RATs.
19. An apparatus according to claim 15, 16, 17 or 18 wherein the interrupt signal identifies whether the communication RAT is in an active or idle state. - 20
20. An apparatus according to claim 15, 16, 17, 18 or 19 including a means for providing data to the Standby RATs to confirm that an interrupt signal is to be transmitted.
21. An apparatus according to claim 20 wherein the data is provided by a signal transmitted across the network layer of the protocol stack.
22. An apparatus according to any of claims 13 to 21 further comprising a means to confirm that the Standby RAT has completed communication with the network.
23. An apparatus according to claim 22 further comprising a means to stop transmission of the interrupt signal when the Standby RAT has completed communicating with the network.
24. An apparatus according to any of claims 13 to 23 wherein the step of determining that communication is required on a Standby RAT is made in dependence on the strength of the signal of the communication RAT.
25. An apparatus according to any of claims 13 to 24 wherein the physical layer of at least one RAT includes a multiplexer for transmission and reception to control with which RAT it is communicating.
26. An apparatus for network communication on at least one Standby RAT in a multi-RAT communication system substantially as herein described with reference to the figures.