WO2008077629A1

WO2008077629A1 - Power-efficient multi-branch reception

Info

Publication number: WO2008077629A1
Application number: PCT/EP2007/011385
Authority: WO
Inventors: Ülo PARTS; Juha Heiskala; Mikko Kokkonen
Original assignee: Nokia Corporation
Priority date: 2006-12-22
Filing date: 2007-12-21
Publication date: 2008-07-03

Abstract

The present invention relates to a method, system, apparatus, receiver module and computer program product for providing a power-efficient reception, wherein a transmission signal is initially received via at least one selected or default receiving branch. Then, it is checked whether the transmission signal has been received successfully, and at least one additional receiving branch is added to the at least one selected receiving branch for retransmission, if the transmission signal has not been received successfully. Thereby, a trade-off between savings in power consumption and reduction in network capacity can be achieved.

Description

Power-Efficient Multi-Branch Reception

FIELD OF THE INVENTION

The present invention relates to a method, system, apparatus, receiver module, and computer program product for providing power-efficient reception in system with at least two receiving branches or chains.

BACKGROUND OF THE INVENTION

Rising importance of wireless services has led to corresponding increased de- mand for higher network capacity and performance. Conventional options include higher bandwidth, optimized modulation or code-multiplex systems, but offer practically only limited potential to increase spectral efficiency.

In so-called SIMO (Single Input Multiple Output) or MIMO (Multiple Input Multiple Output) systems antenna arrays are used to enhance bandwidth efficiency. MIMO systems provide multiple inputs and multiple outputs for a single channel and are thus able to exploit spatial diversity and spatial multiplexing. Further information about MIMO systems can be gathered from the IEEE specifications 802.11 n,

802.16-2004 and 802.16e, as well as 802.20 and 802.22 which relate to other standards. Specifically, MIMO systems have been introduced to radio systems like e.g. WiMAX (Worldwide Interoperability for Microwave Access) and are currently standardized in 3GPP for WCDMA (Wideband Code Division Multiple Access) as well as 3GPP E-UTRAN (Enhanced Universal Mobile Telecommunications System

(UMTS) Terrestrial Radio Access Network), such as LTE (Long Term Evolution) or 3.9G.

Different MIMO transmission modes in downlink require different information in order to allow appropriate link adaptation. A mobile station (MS, also referred to us "user equipment" (UE) in 3D terminology) may have a linear or non-linear recep- tion unit and Mr reception antennas, while the node B has Mt transmission antennas. Based on partial or full channel state information (CS!) fed back from the MS, the BS may perform appropriate space-time processing such as multiuser sched- uling, power and modulation adaptation, beamforming, and space-time coding. The CSI may include a channel direction information (CDI) and a channel quality information (CQI), which can be used for determining beamforming direction and power allocation.

In cellular systems, frequencies allocated to a service are re-used in a regular pattern of areas, called 'cells', each covered e.g. by one base station. To ensure that the mutual interference between users remains below a harmful level, adjacent cells use different frequencies. In fact, a set of C different frequencies {fi, ..., fc) can be used for each cluster of C adjacent cells. Cluster patterns and the corresponding frequencies are re-used in a regular pattern over the entire service area. A frequency reuse factor of C=3 indicates a utilization of 1/3 of the available frequency spectrum.where most operational systems need to apply even higher frequency reuse factors in order to achieve full coverage. Preferably, the frequency reuse factor should be C=1 while still maintaining acceptable signal-to-interference (SIR) conditions even at cell borders. As an example, modem applications for 3.9G (3.9th Generation) communicaton systems will be deployed with frequency reuse factor C=1. One of the goals is to support high data rates and high spectral efficiency. The latter goal is achievable by applying MIMO techniques which re- quire at least two receiver chains or branches in the user terminal.

Different radio algorithms (decoding, channel estimation, frequency synchronization and timing synchronization) are typically performed concurrently in each receiver branch or chain of multi-antenna or multi-branch receiver system, such as MIMO. The more critical the channel properties are the more sophisticated baseband algorithms need to be used for channel estimation and channel decoding. This leads to high processing loads and corresponding high power consumption, which is undesirable - especially for mobile applications such as mobile terminals or the like. However, not all possible applications demand high data rates which demand MIMO transmission schemes. An example of such an application is voice over Internet protocol (VoIP), i.e., a voice service. Additionally, various other applications are known which demand data rates lower than the maximum system data rates. An important user experience and differentiation factor is the available talk time for such voice services or other low data rate applications. It is thus important to consider means to decrease the power consumption of mobile devices. SUMMARY

It is therefore an object of the present invention to provide an enhanced method, apparatus and/or system, by means of which power consumption can be reduced in multi-branch receiver applications for wireless or wired communications.

This object is achieved by a method comprising:

• receiving a transmission signal via at least one selected receiving branch;

• checking whether said transmission signal has been received successfully; and

• adding to said at least one selected receiving branch at least one additional receiving branch for retransmission, if said transmission signal has not been received successfully.

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

• a receiver for receiving information via at least one selected receiving branch;

• a checking unit for checking whether said information has been received successfully; and

• a switching unit for adding to said at least one selected receiving branch at least one additional receiving branch for retransmission, if said information has not been received successfully.

The apparatus may be configured as a receiver apparatus, a transceiver apparatus which comprises an additional transmitting functionality or unit, or as a receiver module provided as a part or integrated circuit of a more complex apparatus or system. - A -

Moreover, the above object is achieved by a communication system comprising at least one of the above apparatus and at least one transmitter for communicating with said apparatus.

In addition, the above object is achieved by a computer program product comprising code means for producing the steps of the above methods when run on a computer device.

Accordingly, a reduced number of receiving branches or chains can be selectively used, so that a trade-off can be achieved between savings in power consumption and reduction in the network capacity. This trade-off can optionally be controlled to favour either a low power consumption or a small reduction in the network capacity e.g. by selecting a suitable threshold value so as to switch off a weaker antenna or branch only if the received signal level (or power) difference exceeds the pre- selected threshold value. Thereby, decreased power consumption can be achieved for low data rate services (e.g. VoIP services or the like). This is especially useful and advantageous for mobile devices, such as mobile user terminal or the like. In an example, branch selection may be based on the difference between signal strengths received via available receiving branches. More specifically, an available receiving branch could be switched off, if the difference between a signal strength received via this available receiving branch and a signal strength received via another available receiving branch exceeds a predetermined threshold. As an additional or alternative option, an available receiving branch could be switched off, if signal strengths received via this available receiving branch and at least one other available receiving branch exceed a predetermined minimum strength.

As another additional or alternative option, a network load may be determined and the at least one selected receiving branch may be selected based on the result of the load measuring. In a first example, selection may be based on load information received from the network. In a second example, the network load may be estimated, wherein the selection is based on the estimated load.

As a default setting, the at least one selected receiving branch may be switched on and the at least one additional receiving branch may be switched off. Thereby, power consumption can be kept low initially and can be increased based on the actual environmental conditions and resulting reception quality. This default setting may be controlled e.g. by the above mentioned switching unit. The checking functionality may be based on or may comprise a determination as to whether a retransmission is initiated by a retransmission function. Thus, branch selection or receiver diversity control can be tied to retransmission decisions, so that implementation of the control is facilitated. In a specific example, the proposed retransmission function may be a hybrid automatic repeat request (H-ARQ) function.

Furthermore, the receipt of the transmission signal may be based on a predeter- mined transmission timing. That is, to get knowledge of a signal transmission and resulting possibility of receiving a signal even in cases where reception conditions via the reduced number of branches (e.g., only one branch) are so weak that de- tecetion would not be possible at all, the predetermined timing can be used to assume non-successful receipt and thus switch to the enhanced number of branches (e.g., all branches).

In a specific implementation example, the transmission signal may be a voice signal transmitted over a packet-switched network, such as a VoIP signal.

Reception via the at least one selected receiving branch may be continued, if the checking, e.g., by the above checking unit, reveals that the transmission signal has been received successfully, so that power consumption can be kept low.

As an additional option, the at least one selected receiving branch may be se- lected - e.g. as a default setting - based on the result of a signal quality measuring. This selection may be based on a predetermined threshold value.

The proposed power-efficient branch selection, i.e., the above mentioned receiving, checking and adding, may be performed or activated only for at least one pre- determined transmission service. Optionally, an information may be signaled and received, which indicates the at least one predetermined transmission service.

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

The present invention will now be described on the basis of an embodiment with reference to the accompanying drawings in which:

Fig. 1 shows a schematic block diagram of a multi-branch radio receiver apparatus according to the embodiment;

Fig. 2 shows a schematic flow diagram of a branch selection operation according to the embodiment; and

Fig. 3 shows a schematic block diagram of a computer-implemented embodiment.

DESCRIPTION OF EMBODIMENTS

The embodiment will now be described based on a multi-antenna radio apparatus which may be any type of device, component, circuit, module etc., such as - but not limited to - a wireless access device, a cellular base station device, a cellular telephone, a handheld computer, a multimedia device, or an integrated chip. The apparatus according to the embodiment can be employed in any wireless communication network which allows receipt of transmission signals via different receiving branches or chains. However, it is to be noted that the present invention is by no means intended to be limited to wireless multi-antenna apparatuses. Rather, it can be used in any receiver or transceiver apparatus which comprises at least two receiving branches or chains for receiving a signal tranmitted over a wired or wireless medium.

More specifically, the multi-antenna radio apparatus according to the embodiment may be a SIMO- or MIMO-based apparatus including different multi-antenna operating modes, e.g., SU-MIMO as well as MU-MIMO, for an exemplary case of two available receiving (Rx) antennas. It may be provided in an evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (EUTRAN) environment. However, it will be apparent from the following description and is therefore explicitly stressed that the present invention can be applied to any other network architecture with different radio access technologies involving multi-antenna transmitter devices, e.g., user terminals (such as user equipments (UEs), mobile stations or mobile phones), base station devices, access points or other access devices.

Fig. 1 shows a schematic block diagram of an exemplary multi-antenna radio apparatus 10, such as a mobile station (or UE in 3G terminology), which can be radio-connected to a base station device (not shown) or Node B (in 3G terminology) or other type of wireless access device. The radio apparatus 10 may as well be any other wireless transmit/receive unit which comprises a multi-branch receiver functionality or module.

In the present example of Fig. 1 , two antennas are connected to a receiver with respective receiver units Rx1 12 and Rx2 14. Of course, both antennas could as well be connected to a single receiver unit having separate receiving branches or chains. The receiver units 12 and 14 are further connected to a signal processing stage 20 which is responsible for receiver-related processing, such as demodulating, descrambling, decoding etc. for a received transmission signal, in order to output received data 50. The signal processing stage 20 is controlled by a branch selection functionality or unit 30 which generates a branch selection control signal 40 based on a reception quality information 60 issued by or derived from the signal processing stage 20, to thereby control the number of receiving branches or chains to be used for reception. In the present exemple of Fig. 1 , one or both receiver units 12, 14 can be selected. It is noted that the branch selection control unit 30 not necessarily has to be provided as a physically separated unit. It may be implemented as a discrete circuit part or additional software routine provided in the the signal processing stage 20 or any other control function or processing device of the radio apparatus 10.

In MIMO mode transmission, if a packet at receiver decoding is in error, then a re- transmission is requested, wherein the MIMO transmitter can use the same format to re-transmit the packet. In this case, the packet can be re-transmitted using the same error-encoded packet or can be re-transmitted using different error coding redundancy. The re-transmitted packet and erroneous packet can be combined in soft symbol form or can be decoded with the re-transmitted packet and erroneous packet as a code coming. This procedure is called hybrid automatic repeat request

(H-ARQ) and can be used to derive the reception quality information 60 used by the branch selection unit 30 to decide on selection of the used receiving branch(es). If H-ARQ retransmission is initiated, this indicates that reception was not successful. However, of course, other reception quality indicators could be used for triggering branch selection.

According to the embodiment, the radio apparatus 10 can be set to an single- branch operation mode where only one receiver branch or chain is activated or selected, although network deployment may demand usage of at least two Rx antennas. This single-branch operation mode can be selected fors specific low data rate services (such as VoIP or the like) which require less network capacity. Thereby, power consumption can be reduced.

The single-branch operation mode may be selected as a default setting or in dependence on a indication of a corresponding service which allows reduced network capacity. The one receiving branch or chain may be selected based on initial or continuous signal quality measurements of both receiving branches or chains, i.e., kind of selection diversity.

Fig. 2 shows a schematic flow diagram of a branch selection operation according to an embodiment.

Initially, in step S101 , a low data rate packet (e.g. VoIP packet) is received with one receiver branch or chain, e.g. the signal processing stage 20 is controlled by the branch selection unit 30 to select only one of the receiver units 12, 14 for reception. This may achieved based on a quality measurement and involve a corre- sponding control signaling between the signal processing stage 20 and/or the branch selection unit 30 on one hand, and the receiver units 12, 14 on the other hand, so as to deactivate or deselect one of the receiver units 12, 14.

Then, in step S102, data is received via the selected receiving branch or chain, and it is checked in step S103 whether reception of a packet or signal portion was successful, e.g., based on a decision on H-ARQ retransmission as signaled by the reception quality information 60. If the reception was determined to be successful, i.e. no retransmission required, predetermined quality or signal-to-interference

(SIR) threshold met, etc., the procedure jumps back to step S102 and waits for the receipt of the next packet or signal portion. If reception is determined in step S103 to be not successfully, retransmission of the same packet will be requested to the transmitting end (due to H-ARQ) and the branch selection unit 30 issues a branch selection control information 40 so as to switch-on the available second receiver branch or chain in step S104, so that the retransmitted packet will be received via both receiver branches or chains. During this period also signal quality measurements of both or all branches can be performed in step S105.

It is noted that more then two receiver branches or chains may be provided, so that switching or selection may be performed for more than one branch or chain. Any number of receiving branches or chains can be selected and combined based on a desired quality and amount of power saving.

There are several ways to implement the switching to the two-branch or full-branch operation mode which may be a continuous mode for the remainder of the transmission or which may be re-evaluated based on quality measurements so as to selectively return to the single-branch or partial-branch operation mode.

The embodiment thus provides a trade-off between savings in the power con- sumption and reduction in the network capacity. The trade-off can be controlled to favour either a low power consumption or a small reduction in the network capacity by selecting a suitable threshold value and by switching off the weaker antenna or branch only if the received signal level (or power) difference exceeds the preselected threshold value. Thereby, power consumption in the apparatus can be reduced in case of predetermined low data rate services, e.g., VoIP service. More specifically, the number of Rx antennas that are used may be determined by thresholding a feature or parameter related to signal quality. This feature or parameter could be for example the difference between respective signal strengths. In this example, the idea is that if the difference is large enough, the other branch can be switched off without substantially affecting detection performance. Another example is that if either of the antenna signals is strong enough, then the reception will be successful even without the other antenna.

Of course, other suitable selection criteria an be used, which are apparent to the skilled person. For example, information about the load of the network could be taken into account. That is, if the network is very loaded, there will be less single

Rx branch usage. The information about the network load could be obtained in various ways. It could be signaled to the radio apparatus 10 by the network, or the load could be estimated by the radio apparatus 10. In the latter case, one possibility could be to analyze control channel information, such as allocation of time- frequency resources to radio apparatuses (e.g. UEs, mobile terminals, mobile sta- tions, etc.) or indirect methods like total power measurements of a symbol, where only dedicated data is transmitted, etc.

The initial single-branch or partial-branch operation mode may be activated based on an information received from the transmitting side (e.g. base station device such as a base transceiver station (BTS) or node B) or network side, which informs the radio apparatus 10 (e.g. user terminal) that for some time interval only a low data rate service is scheduled to the radio apparatus 10.

The radio apparatus 10 may be enabled to detect that a first non-successful transmission has occurred based on a predetermined or known transmission timing of the data packets or signal portions, so that the radion transmitter 10 knows straight away if it has failed to receive one, and the signal processing stage

20 can generate a corresponding reception quality information 60 to trigger selection of all or more receiving branches or chains. Hence, the H-ARQ process or any other reception quality determination process can be used to drive receiving branch selection control.

Fig. 3 shows a schematic block diagram of a software-based implementation of the proposed functionalities for achieving channel-sensitive complexity adjustment. These functionalities can be implemented with a processing unit 210, which may be any processor or computer device with a control unit which performs control based on software routines of a control program stored in a memory 212. Program code instructions are fetched from the memory 212 and are loaded to the control unit of the processing unit 210 in order to perform the processing steps of the above functionalities described in connection with the respective branch selection and signal processing blocks 20, 30 of Fig. 1 and the flow diagram of Fig. 2. These processing steps may be performed on the basis of input data Dl and may generate output data DO, wherein the input data Dl may correspond to output of a retransmission function and/or other quality indicator information, and the output data DO may correspond to control information used for selecting a corresponding number of receiving branches or chains. To summarize, a method, system, apparatus, receiver module and computer program product for providing a power-efficient reception have been described, wherein a transmission signal is initially received via at least one selected or default receiving branch. Then, it is checked whether the transmission signal has been received successfully, and at least one additional receiving branch is added to the at least one selected receiving branch for retransmission, if the transmission signal has not been received successfully. Thereby, a trade-off between savings in power consumption and reduction in network capacity can be achieved.

It is to be noted that the present invention is not restricted to the embodiments described above, but can be implemented in any communication apparatus with a multi-branch or multi-chain receiver functionality for any type of wired or wireless application. As an example, the transmission signal may be received from a cable, optical fibre, or other type of electrical, magnetic, electro-magnetic or optical waveguide. The processing steps of Fig. 2 may be implemented as discrete digital circuits, modules or logical signal processing structures. The embodiment may thus vary within the scope of the attached claims.

Claims

1. A method comprising:

a. receiving a transmission signal via at least one selected receiving branch;

b. checking whether said transmission signal has been received successfully; and

c. adding to said at least one selected receiving branch at least one additional receiving branch for retransmission, if said transmission signal has not been received successfully.

2. The method according to claim 1 , further comprising providing a default setting where said at least one selected receiving branch is switched on and said at least one additional receiving branch is switched off.

3. The method according to claim 1 or 2, wherein said checking comprises de- termining whether a retransmission is initiated by a retransmission function.

4. The method according to claim 3, wherein said retransmission function is a hybrid automatic repeat request function.

5. The method according to any one of the preceding claims, further comprising determining a receipt of said transmission signal based on a predetermined transmission timing.

6. The method according to any one of the preceding claims, wherein said transmission signal is a voice signal transmitted over a packet-switched network.

7. The method according to any one of the preceding claims, further comprising continuing receiving via said at least one selected receiving branch, if said checking reveals that said transmission signal has been received successfully.

8. The method according to any one of the preceding claims, further comprising measuring signal quality and selecting said at least one selected receiving branch based on the result of said signal quality measuring.

9. The method according to claim 8, further comprising performing said selection based on a predetermined threshold value.

10. The method according to claim 9, wherein said selection is based on the difference between signal strengths received via available receiving branches.

11. The method according to claim 10, wherein an available receiving branch is switched off, if the difference between a signal strength received via said available receiving branch and a signal strength received via another available receiving branch exceeds said predetermined threshold.

12. The method according to claim 10 or 11 , wherein an available receiving branch is switched off, if signal strengths received via said available receiving branch and at least one other available receiving branch exceed a predetermined minimum strength.

13. The method according to any one of the preceding claims, further comprising determining network load and selecting said at least one selected receiving branch based on the result of said load measuring.

14. The method according to claim 13, wherein said selection is based on load information received from a network.

15. The method according to claim 13 or 14, further comprising estimating said network load, wherein said selection is based on said estimated load.

16. The method according to any one of the preceding claims, further comprising performing said receiving, checking and adding only for at least one predetermined transmission service.

17. The method according to claim 16, further comprising receiving an information which indicates said at least one predetermined transmission service.

18. An apparatus comprising:

a. a receiver for receiving information via at least one selected receiving branch;

b. a checking unit for checking whether said information has been received successfully; and

c. a switching unit for adding to said at least one selected receiving branch at least one additional receiving branch for retransmission, if said information has not been received successfully.

19. The apparatus according to claim 18, wherein said switching unit is configured to provide a default setting where said at least one selected receiving branch is switched on and said at least one additional receiving branch is switched off.

20. The apparatus according to claim 18 or 19, wherein said checking unit is configured to perform said checking by determining whether a retransmission has been initiated by a retransmission function.

21. The apparatus according to claim 20, wherein said retransmission function is a hybrid automatic repeat request function.

22. The apparatus according to any one of claims 18 to 21 , wherein said checking unit is configured to determine a receipt of said transmission signal based on a predetermined transmission timing.

23. The apparatus according to any one of claims 18 to 22, wherein said transmission signal is a voice signal transmitted over a packet-switched network.

24. The apparatus according to any one of claims 18 to 23, wherein said switching unit is configured to control said receiver so as to continue receiving via said at least one selected receiving branch, if said checking of said checking unit reveals that said transmission signal has been received successfully.

25. The apparatus according to any one of claims 18 to 24, wherein said switching unit is configured to select said at least one selected receiving branch based on the result of a signal quality measurement.

26. The apparatus according to claim 25, wherein said switching unit is configured to perform said selection based on a predetermined threshold value.

27. The apparatus according to any one of claims 18 to 26, wherein said apparatus is configured to perform said branch selection only for at least one prede- termined transmission service.

28. The apparatus according to claim 27, wherein said apparatus is configured to receive an information which indicates said at least one predetermined transmission service.

29. A communication system comprising the apparatus according claim 15 and a transmitter for communication with said apparatus.

30. A transceiver apparatus comprising the apparatus according to claim 18 and a transmitter apparatus.

31. A receiver module comprising:

32. A wireless terminal device comprising a receiver module according to claim 31.

33. The wireless terminal device according to claim 32, wherein said wireless terminal device is a mobile station.

34. A wireless access device comprising a receiver module according to claim 31.

35. The wireless access device according to claim 34, wherein said wireless access device is a base station.

36. A computer program product comprising code means for producing the steps of method claim 1 when run on a computer device.