WO2009041881A2 - Transmission of reference signal between uplink and downlink timeslots - Google Patents

Abstract

The present invention concerns a method and an arrangement in a first node in a wireless communication system. The first node is using a frame structure of a Time Division Duplex mode (TDD mode) physical layer protocol for transmitting a signal from the first node to a second node in a wireless communication network. The method is characterised by the step of Transmitting a Sounding Reference Signal (SRS) in an Uplink Pilot Timeslot comprised within the TDD mode frame structure. Further, the present invention concerns a method and an arrangement in a second node in a wireless communication system.

Description

METHOD AND ARRANGEMENT IN A COMMUNICATION SYSTEM

TECHNICAL FIELD

The present invention relates to a method and an arrangement in a first node and to a method and an arrangement in a second node in a wireless communication system. More particularly the present invention relates to a mechanism in Time Division Duplexing communication where a reference signal is transmitted from the first node to the second node.

BACKGROUND

The currently evolving Long Term 3^rd generation Evolution (LTE) telecommunication standard has bandwidth flexibility and flexibility of spectrum allocation as two of its key features. In order to utilize also unpaired frequency bands it has been decided that at least one Time Division Duplexing (TDD) mode should be supported.

Two-way radio communications commonly use either Frequency Division Duplexing (FDD) or Time Division Duplexing (TDD). The Frequency Division Duplexing approach is used over well separated frequency bands in order to avoid interference between uplink and downlink transmissions, and the Time Division Duplexing approach, Time Division Duplexing, is used where uplink and downlink traffic are transmitted in the same frequency band, but in different time intervals. The uplink and downlink traffic is thus transmitted separated from each other, in the time dimension in a Time Division Duplexing transmission. In order to avoid interference between uplink and downlink, such as interference between base stations and interference between user terminals in the same area, uplink and downlink transmissions between base stations and user terminals in different cells are aligned by means of synchronization to a common time reference and use of the same allocation of resources to uplink and downlink.

A benefit of the Time Division Duplexing mode of operation, as compared to frequency division duplexing, is that paired frequency bands are not required. However time based duplexing also imposes challenges that do not emerge in frequency based duplexing, such as interference between uplink and downlink. In the current 3GPP long-term evolution, also named as Evolved Universal Terrestrial Radio Access (EUTRA), a Time Division Duplex mode is proposed for the physical layer. Time Division Duplex mode may use the same frequency band for both the uplink and the downlink by allocating distinct time slots for uplink traffic and downlink traffic, respectively. Time may be divided in frames which are divided in slots of short duration. Each time slot may be allocated either to the uplink or to the downlink.

For TDD operation with frame structure 2, each 5 ms half-frame may consist of a number of slots, or sub frames and three special fields: Downlink Pilot Time Slot, Guard Period, and Uplink Pilot Timeslot. The three special fields Downlink Piloting Time Slot, Guard Period, and Uplink Pilot Timeslot are situated between the downlink time slots and the uplink time slots. It is also possible that a 10 ms radio frame consists of a first 5 ms half frame as described above and a second half frame with a number of slots, or sub frames, allocated to downlink only. The Guard Period between uplink and downlink is used to separate uplink and downlink also in the presence of propagation delays, and may be chosen for example to cover the maximum round trip propagation delay in the cell.

In LTE, so-called Sounding Reference Signals (SRS) can also be transmitted on the uplink. The purpose of the Sounding Reference Signals is for the network to be able to estimate the uplink channel for different user equipments. Furthermore, from the channel estimates, the uplink channel quality may be estimated in order to apply uplink channel-dependent scheduling and link adaptation, in the sense that the network can determine which users to assign resources in which part of the frequency band and also select the appropriate transmission parameters such as coding, modulation and so on. The channel estimates, or channel equality estimates can also be used to estimate the timing of user equipment transmissions and to derive timing-control commands for uplink time alignment. Another application is uplink power control.

In a TDD operation, the uplink and downlink use the same frequency, and since the radio channel is reciprocal, uplink measurements may also provide information about the downlink channel and hence channel sounding can be used also to adapt downlink transmission for TDD operation. One example of this is to estimate parameters for downlink beamforming from the uplink channel sounding. The terminal then transmits a Sounding Reference Signal which is received by the antennas at the base station and based on these channel estimate it can determine how to transmit data signals in the downlink. Sounding Reference Signals are transmitted independently of the transmission of any uplink data or control, i.e. a user equipment may transmit a Sounding Reference Signal also in sub frames where the user equipment does not have any data transmission. Furthermore, if a sounding is to be received in an uplink sub frame, then there will be fewer resources available for uplink data transmission on the Physical Uplink Shared Data CHannel (PUSCH). When it comes to control signalling, such as acknowledgements to downlink data transmissions and channel quality reports, which is transmitted on a Physical Uplink Control CHannel (PUCCH), at the band edges, it is further not possible for a terminal to transmit both sounding in one symbol in the sub frame and at the same transmit the all the contents on the PUCCH. It may be noted that the sounding-reference-signal bandwidth may be. and typically is, different from that of any simultaneous data transmission from the same user equipment. The consequence of this is that uplink data and control signalling is punctured when uplink channel sounding is employed in the same sub frame. This has a negative impact on uplink data and control, performance such as coverage.

To avoid or minimize the interference between the Physical Random Access CHannel (PRACH) and the Sounding Reference Signal, the Sounding Reference Signal may be located in the last or first symbol of the uplink sub-frame. It may also be possible to have multiple Sounding Reference Signal positions in order to co-ordinate the Sounding Reference Signal location among neighbouring cells in synchronous systems.

The uplink interference varies from time to time, thus the Sounding Reference Signal may only provide some reference for the power control, Uplink scheduling and link adaptation. It may then be desirable to provide more reference signals concerning the uplink signal but without puncturing the uplink data transmission.

SUMMARY

It is therefore an object of the present invention to provide an improved mechanism in a node in a wireless communication system for transmitting a reference signal.

According to a first aspect, the object is achieved by a method for transmitting a reference signal. The method is performed in a first node in a cell. The first node and the cell are comprised within a wireless communication network. The wireless communication network is using Time Division Duplexing. The first node is arranged to communicate over a communication channel with a second node. The communication is made by using a frame structure physical layer protocol comprising uplink sub frames and downlink sub frames. A switching zone is situated in the time dimension between the downlink sub frames and the uplink sub frames. The method comprises the step of transmitting the reference signal in the switching zone between the downlink sub frames and the uplink sub frames.

According to a second aspect, the object is achieved by an arrangement in a first node for transmitting a reference signal. The first node is comprised in a cell within a wireless communication network using Time Division Duplexing. The first node is arranged to communicate over a communication channel with a second node. The communication is made by using a frame structure physical layer protocol. The frame structure physical layer protocol comprises uplink sub frames and downlink sub frames. A switching zone is situated in the time dimension between the downlink sub frames and the uplink sub frames. The arrangement comprises a transmitter. The transmitter is adapted to transmit the reference signal in the switching zone between the downlink sub frames and the uplink sub frames.

According to a third aspect, the object is achieved by a method for receiving a reference signal. The method is performed in a second node in a cell. The second node and the cell are comprised within a wireless communication network using Time Division Duplexing. The second node is arranged to communicate over a communication channel with a first node. The communication is made by using a frame structure physical layer protocol. The frame structure physical layer protocol comprises uplink sub frames and downlink sub frames. A switching zone is situated in the time dimension between the downlink sub frames and the uplink sub frames. The method comprises the step of receiving the reference signal in the switching zone between the downlink sub frames and the uplink sub frames.

According to a fourth aspect, the object is achieved by an arrangement in a second node for receiving a reference signal. The second node is comprised in a cell. The second node and the cell are comprised within a wireless communication network. The wireless communication network is using Time Division Duplexing. The second node is arranged to communicate over a communication channel with a first node. The communication is made by using a frame structure physical layer protocol. The frame structure physical layer protocol comprises uplink sub frames and downlink sub frames. A switching zone is situated in the time dimension between the downlink sub frames and the uplink sub frames. The arrangement comprises a receiver. The receiver is adapted to receive the reference signal in the switching zone between the downlink sub frames and the uplink sub frames.

An advantage of transmitting a reference signal in the switching zone between the downlink sub frames and the uplink sub frames in a Time Division Duplex frame structure may be lower overhead in the uplink.

Furthermore, resource for sounding may be taken from the Guard Period rather than from the uplink data and control signalling. Thus the overall performance of the telecommunication system is significantly increased since it can be avoided to take resources from the uplink sub frames used for data transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described more in detail in relation to the enclosed drawings, in which:

Figure 1 is a schematic block diagram over a wireless communication system according to the present method and arrangement.

Figure 2A is a schematic block diagram depicting a physical layer model arrangement according to some embodiments.

Figure 2B is a schematic block diagram depicting a physical layer model arrangement according to some embodiments.

Figure 3 is a flow chart depicting a method step in a user equipment according to some embodiments.

Figure 4 is a schematic block diagram depicting an arrangement in a user equipment. Figure 5 is a flow chart depicting a method step in a base station according to some embodiments.

Figure 6 is a schematic block diagram depicting an arrangement in a base station.

DETAILED DESCRIPTION

The invention is defined as a method and an arrangement in a first node and a method and an arrangement in a second node, which may be put into practice in the embodiments described below. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. It should be understood that there is no intent to limit the present method and arrangement in a first node and method and arrangement in a second node to any of the particular forms disclosed, but on the contrary, the present method and arrangement in a first node and method and arrangement in a second node is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the claims.

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

Figure 1 depicts a wireless communication system 100 comprising a first node 110 communicating with a second node 120 in a cell 125. The communication is made over a communication channel 140.

In some embodiments, the first node 110 may be a user equipment such as e.g. a wireless communication terminal, a mobile cellular telephone, a Personal Digital Assistant (PDA), a laptop, a computer or any other kind of device capable of managing radio resources may communicate wirelessly with any other node within range. The second node 120 may in some embodiments be a base station, a wireless Communications station, a fixed station, a control station, a repeater or any similar arrangement for radio communication including the case that the second node 120 is of similar type as the first node 110. However, the second node 120 may also be referred to as e.g. an access point, a Node B, an eNode B and/or a base transceiver station, Access Point Base Station, base station router, etc depending e.g. of the radio access technology used. However, in order to not unnecessarily complicate the understanding of the present methods and arrangements, the expression "base station" will be used consistently in this text for describing the second node 120. It may however not be precluded that both the first node 110 and the second node 120 are of the same type. Thus, according to some embodiments, both the first node 110 and the second node 120 may be a user equipment such as e.g. a wireless communication terminal, a mobile cellular telephone, a Personal Digital Assistant (PDA), a laptop, a computer according to some embodiments. According to some embodiments, both the first node 110 and the second node 120 may be a base station, a wireless communications station, a fixed station, a control station, a repeater or any similar arrangement for radio communication.

However, the situation may as well be different, such as in some other embodiments, wherein the first node 110 may be a base station, a wireless communications station, a fixed station, a control station, a repeater or a similar arrangement for radio communication, and the second node 120 may be e.g. a wireless communication terminal, a mobile cellular telephone, a Personal Digital Assistant (PDA), a laptop, a computer or any other kind of device capable of managing radio resources.

However, in this text the term user equipment 1 10 will be used for the first node 110 and the term base station 120 will be used for the second node 120 in order to somewhat facilitate the comprehension of the present methods and arrangements.

The radio communication can be based on code division multiple access (CDMA), wideband CDMA (WCDMA) and derivatives thereof such as used in WCDMA₁ CDMA 2000, High Speed Downlink Packet Data Access (HSDPA), High Data Rate (HDR). The communication can also be based on OFDM or pre coded OFDM such as SC-FDMA as used in LTE. Figure 2A presents a frame structure of a Time Division Duplex mode (TDD mode) physical layer protocol according to some embodiments of the present method and arrangement. A radio frame 200 may be divided into two half frames 210. The radio frame 200 may be e.g. 10 ms long. A half frame 210 may accordingly be e.g. 5 ms long. The half frame 210 may in turn be divided into seven sub frames 220, 221 , 222, 223, 224, 225, 226, which may be used for transmitting data. Each sub frame 220, 221 , 222, 223, 224, 225, 226 may be e.g. 0.675 ms long or, alternatively, e.g. 1 ms long. In another embodiment, the half frames 210 may contain four sub frames of length 1 ms. In yet another embodiment, the radio frame 200 may not be divided into two half frames, or the two half frames have different configurations.

Radio signals are sent from the user equipment 110 over a radio link 140 and are received by the base station 120. This is called uplink signalling. Also, radio signals are sent from the base station 120 over the radio link 140 and are received by the user equipment 110. The latter is referred to as downlink signalling.

In order to avoid interference between the downlink signalling and uplink signalling, downlink signalling is scheduled in downlink sub frames 220 and uplink signalling is scheduled in zero, one or more consecutive sub frames 221 , 222, 223, 224, 225, 226. The sub frames 221 , 222, 223, 224, 225, 226 not used for uplink signalling are used for downlink signalling. There may then be a switch from uplink to downlink after one of the sub frames 221 , 222, 223, 224, 225 or 226.

According to some embodiments, the sub frames 221 , 222, 223, 224, 225 and 226 may be allocated to either uplink or downlink. In the non limiting, illustrative example depicted in Figure 2A, sub frame 220 is a downlink sub frame and sub frames 221 , 222, 223, 224, 225, 226 are allocated for uplink. This is however just an arbitrary example of resource allocation.

There may thus be one switching zone 250 at the switch from downlink and uplink as well another switch from uplink to downlink after one of the sub frames 221 , 222, 223, 224, 225 or 226. A period of silence may be comprised in the switching zone 250 between the downlink signals and the uplink signals. This period of silence may be referred to as a Guard Period 230, or idle period, during which Guard Period 230, no data is transmitted.

One reason for this is to allow the base station 120 and the user equipment 110 to switch their circuits between transmission mode and receive mode.

Another reason, which may put stronger requirements on the duration of the Guard Period 230 under most circumstances, is that when a base station 120 or user equipment 110 is switched from transmission mode to receive mode, signals from other base stations or user equipments may still be propagating in the air, possibly causing interference between uplink and downlink signalling. Depending on e.g. the size of the cell 125 and inter-base station distance, the duration of the length of the Guard Period 230 may be different for different cells 125. However, according to other embodiments, the duration of the Guard Period 230 may be the same for the whole network 100, which may facilitate the implementation.

It may be mentioned as an illustrating example only, that e.g. elevated base stations 80 km away, corresponding to a propagation delay of about 0.27 ms, may give interference above the noise floor after a downlink to uplink switch. With aggregation of downlink transmissions from several base stations even further away, the interference level may be very significant and may influence reception in a negative way.

Thus, in order to avoid interference in Time Division Duplexing mode communication, a Guard Period 230 may be introduced in the switching zone 250 between downlink and uplink sub frames. As a non limiting example only, the Guard Period 230 may be 50 μs according to some embodiments. In other embodiments, the size of Guard Periods 230 may be set in a flexible manner and may e.g. be set to different values for different cells 125, depending for example on the cell size.

Data transmissions are preferably not scheduled to use any part of the Guard Period 230, as such scheduled transmissions may be lost. Thus data transmissions are preferably scheduled for outside the Guard Period 230. The transmission quality of a communication and/or coherence properties of a communication channel 140 between the base station 120 and the user equipment 110 may differ, depending on a plurality of unwanted influence on the signal and the radio propagation conditions. Some non limiting examples of such unwanted influence may be thermal noise and interference and a non limiting example of phenomena that adversely affect the propagation conditions are path loss, signal multi-path, and Doppler spread. Further the accuracy of channel estimation will affect the transmission quality.

In order to estimate the transmission quality and/or coherence properties of the communication channel 140, a reference signal may be sent from the user equipment 110 to the base station 120. The reference signal, which also may be referred to as a reference symbol, a pilot, or a Sounding Reference Signal, is a signal known by the base station 120. When receiving the reference signal, the base station 120 may estimate the transmission quality of the communication channel 140 by comparing the received reference signal with prestored reference values.

The obtained information concerning the transmission quality may then be used e.g. for sending a command to the user equipment 110 to adjust the signalling power of the user equipment 110, according to some mebodiments.

However, as the signal propagation conditions on the downlink signal is approximately the same as on the uplink signal, the obtained information also may be used for adjusting e.g. the signalling power of the base station 120.

In order to provide the reference signal from the user equipment 110 to the base station 120, without sending the reference signal in any of the uplink sub frames which includes 221 and possibly some of the following sub frames 222, 223, 224, 225 or 226, the reference signal may, according to some embodiments, be sent in the switching zone 250 between the downlink sub frames 220 and the uplink sub frame 221.

According to some embodiments, the reference signal may be sent from the user equipment 110 to the base station 120 within the Guard Period 230, e.g. at the end of the Guard Period 230. An advantage with that is that the reference signal is not as critical for the system 100 if a truncation in order to create sufficient idle Guard Period 230 has to be made. The switching zone 250 between downlink and uplink sub frames may according to some embodiments comprise three fields: a Downlink Part (DwPTS) 231 , the Guard Period 230, and an Uplink Part (UpPTS) 232.

According to some embodiments, the reference signal may be sent from the user equipment 110 to the base station 120 in a dedicated timeslot 232. The dedicated timeslot 232 may be e.g. an Uplink Part. This dedicated time slot 232 may then be special in the sense that no data transmissions are done in this time slot 232. This ensures that there is no impact or collisions between data transmission and transmission of sounding symbols. It may also be so that no control signalling carrying acknowledgements in response to downlink transmissions or channel quality indicators are transmitted in this time slot 232.

According to some embodiments, the reference signal e.g. a Sounding Reference Signal may be transmitted in an Uplink Part in Time Division Duplexing mode. According to some embodiments, the inclusion of the reference signal e.g. a Sounding Reference Signal in an Uplink Part 232 in Time Division Duplexing mode may be mandatory.

According to some embodiments of the invention, the reference signal such as e.g. a Sounding Reference Signal may be transmitted in the Downlink Part 231 in a frame structure in Time Division Duplexing mode, according to some embodiments.

The length of the Uplink Part 232 may as a non limiting example be e.g. 0.141 ms. The length of the Guard Period 230 may be 0.05 ms, and the length of the Downlink Part 231 may be 0.084 ms, in accordance with some embodiments of the present methods and arrangements. However, these figures are mentioned as non limiting examples only. In another embodiment the length of the Uplink Part 232 may be configured in terms of a number of OFDM symbols and have length 1 or 2 symbols. The length of the Uplink Part 232, the Downlink Part 231 and/or the Guard Period 230 may vary considerably without limiting the scope of protection of the invention. Hence in one embodiment the total length of the switching zone may be 1 ms and the length of the Uplink Part 231 may be set to e.g. 1/12, 2/12, 1/14 or 2/14 ms.

For some embodiments of frame structures, a Sounding Reference Signal may be transmitted in one long single carrier FDMA (SC-FDMA) symbol. The length of the symbol depends on the cyclic prefix length used in the cell 125 which in turn can be chosen in accordance to the time dispersion in the cell 125. The length of a SC-FDMA symbol may then be 1/12 or 1/14 ms. According to some embodiments of the present methods and arrangements, 1/12 or 1/14 ms is kept in the end of Uplink Part 232 of the frame structure type 2, for Sounding Reference Signal. According to some embodiments of the method and arrangement, the first e.g. 0.141-0.075 ms are reserved for an extended Guard Period 230, thus the Guard Period 230 may be up to 0.116 ms. If the Downlink Part 231 is also permitted to be reserved for the longer Guard Period 230, 0.2 ms may be kept, according to some embodiments of the present methods and arrangements.

It may also be possible that the Uplink Part 232, is only used for reception of random access preambles in some parts the bandwidth. According to some embodiments of the method and arrangement, the non used frequency bands may be used for some form of narrowband sounding if a number of frequency slots are used for RACH in the Uplink Part 232.

Figure 2B presents a frame structure of a Time Division Duplex mode (TDD mode) physical layer protocol according to some embodiments of the present methods and arrangements.

A radio frame 200 may be e.g. 10 ms long. The radio frame 200 may be divided into ten sub frames 220, 250, 221 , 222, 223, 224, 250, 225, 226, 227, 1 ms long each. Eight of the sub frames 220, 221 , 222, 223, 224, 225, 226, 227 may be used for transmitting data.

Two sub frames 220, 224 in each radio frame 200 are always dedicated for downlink transmission, according to some embodiments. The other sub frames 221 , 222, 223, 225, 226, 227 may be allocated for uplink and/or downlink transmission.

A special sub frame 250 may be referred to as a switching zone, situated in between the downlink sub frames 220, 224 and the uplink sub frames 221 , 225.

Two special sub frames 250 may be split into three fields: a Downlink Part 231 , which may be referred to as DwPTS. An idle part 230, which may be referred to as Guard Period and an Uplink Part 232, which may be referred to as UpPTS. The Guard Period 230 is a period during which no data is transmitted, e.g. to cover cell round trip propagation delay and/or allow the user equipment 110 to switch from transmission mode to receiving mode, as previously discussed.

5 The Uplink Part 232 may be used e.g. for transmitting Sounding Reference Signals. Thus it is possible to sound band edges. Also, no puncturing of control or data has to be made. According to some embodiments, the Uplink Part 232 may be used for RACH preamble. According to some embodiments, the Uplink Part 232 may be used as a prolongation of the Guard Period 230. However, the Uplink Part 232 may not be used for transmitting 10 data, according to some embodiments.

Figure 3 is a schematic flow chart illustrating a method in a first node 110 for transmitting a reference signal. The first node 110 is comprised in a cell 125 comprised within a wireless communication network 100 using Time Division Duplexing. The first node 110 is

15 arranged to communicate over a communication channel 140 with a second node 120. The communication is made by using a frame structure physical layer protocol. The frame structure physical layer protocol comprises uplink sub frames 221 and downlink sub frames 220 with a switching zone 250 in the time dimension between the downlink sub frames 220 and the uplink sub frames 221.

20

To appropriately transmit the reference signal, the method may comprise a method step 310.

Step 310

25 The reference signal is transmitted in the switching zone 250 between the downlink sub frames 220 and the uplink sub frames 221. According to some embodiments, the reference signal is transmitted in a timeslot situated in the switching zone 250.

The switching zone 250 may, according to some embodiments, comprise a Guard Period 30 230 and the reference signal may be transmitted in a timeslot situated at the end of the Guard Period 230, in the time dimension.

The switching zone 250 may further comprise a Guard Period 230 and the reference signal may be transmitted in a timeslot situated after the Guard Period 230, in the time 35 dimension, according to some embodiments. The switching zone 250 may further comprise a dedicated timeslot 232 situated after the Guard Period 230 in the time dimension. The reference signal may be transmitted in the dedicated timeslot 232. The dedicated timeslot 232 may be an Uplink Pilot Timeslot (UpPTS).

According to some embodiments, no data transmission may be done in the dedicated timeslot 232. The reason for this is e.g. to not interfere with and/or disturb the reference signalling.

The reference signal may be a Sounding Reference Signal. The Sounding Reference Signal is sometimes referred to as Sounding Reference Sequence.

The first node 110 may, according to some embodiments be represented by a user equipment such as a portable communication device e.g. a mobile cellular telephone.

Figure 4 is a schematic block diagram illustrating an arrangement 400 in a first node 110. The arrangement 400 is adapted to perform the above described method step 310, for transmitting a reference signal. The first node 110 is comprised in a cell 125 comprised within a wireless communication network 100 using Time Division Duplexing. The first node 110 is arranged to communicate over a communication channel 140 with a second node 120. The communication is made by using a frame structure physical layer protocol comprising uplink sub frames 221 and downlink sub frames 220. A switching zone 250 is situated in the time dimension between the downlink sub frames 220 and the uplink sub frames 221.

The arrangement 400 comprises a transmitter 410. The transmitter 410 is adapted to transmit the reference signal in the switching zone 250 between the downlink sub frames 220 and the uplink sub frames 221.

For the sake of clarity and in order not to render unnecessary aggravating circumstances for the uninitiated reader to comprehend the present first node 110, any internal electronics of the first node 110, not completely necessary for performing the present method according to step 310 has been omitted from Figure 4. Figure 5 is a flow chart illustrating a method in a second node 120 for receiving a reference signal. The second node 120 is comprised in a cell 125 within a wireless communication network 100 using Time Division Duplexing. The second node 120 is arranged to communicate over a communication channel 140 with a first node 110. The communication is made by using a frame structure physical layer protocol comprising uplink sub frames 221 and downlink sub frames 220. A switching zone 250 is situated in the time dimension between the downlink sub frames 220 and the uplink sub frames 221.

To appropriately receive a reference signal in the second node 120, the method may comprise a method step 510.

Step 510

The reference signal is received in the switching zone 250 between the downlink sub frames 220 and the uplink sub frames 221. According to some embodiments, the reference signal is received in a timeslot situated in the switching zone 250.

The switching zone 250 may, according to some embodiments, comprise a Guard Period 230 and the reference signal may be transmitted in a timeslot situated at the end of the Guard Period 230, in the time dimension.

The switching zone 250 may further comprise a Guard Period 230 and the reference signal may be transmitted in a timeslot situated after the Guard Period 230, in the time dimension, according to some embodiments.

The switching zone 250 may further comprise a dedicated timeslot 232 situated after the Guard Period 230 in the time dimension. The reference signal may be transmitted in the dedicated timeslot 232. The dedicated timeslot 232 may be an Uplink Pilot Timeslot.

According to some embodiments, no data transmission may be done in the dedicated timeslot 232. The reason for this is e.g. to not interfere with and/or disturb the reference signalling.

The reference signal may be a Sounding Reference Signal. The Sounding Reference Signal is sometimes referred to as Sounding Reference Sequence. The second node 120 may, according to some embodiments be represented by a base station.

Figure 6 is a schematic block diagram illustrating an arrangement 600 in a second node

5 120. The arrangement 600 is adapted to perform the above described method step 510, for receiving a reference signal. The second node 120 is comprised in a cell 125 within a wireless communication network 100. The wireless communication network 100 is using

Time Division Duplexing. The second node 120 is arranged to communicate over a communication channel 140 with a first node 110. The communication is made by using a0 frame structure physical layer protocol comprising uplink sub frames 221 and downlink sub frames 220. A switching zone 250 is situated in the time dimension between the downlink sub frames 220 and the uplink sub frames 221.

The arrangement 600 comprises a receiver 610. The receiver 610 is adapted to receive5 the reference signal in the switching zone 250 between the downlink sub frames 220 and the uplink sub frames 221.

The methods in the first node 110 for sending the reference signal and the methods in the second node 120 for receiving the reference signal may be implemented through one or0 more processors, together with computer program code for performing the functions of the methods. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the method according to the present invention when being loaded into the first node 110 and/or the second node 120. The data carrier may be a CD ROM disc,5 a memory stick, or any other medium such as a disk or tape that can hold machine readable data. The computer program code can furthermore be provided as pure program code on a server and downloaded to the first node 110 and/or the second node 120 remotely. 0 Thus a computer readable medium encoded with a computer program for sending a reference signal may perform the method step according to step 310.

Thus also a computer readable medium encoded with a computer program for receiving a reference signal may perform the method step according to step 510. 5 As will be appreciated by one of skill in the art the present invention may be embodied as a method in the first node 110, an arrangement 400 in the first node 110, a method in the second node 120, an arrangement 600 in the second node 120, or computer program products.

Accordingly, the present invention may take the form of an entirely hardware embodiment, a software embodiment or an embodiment combining software and hardware aspects all generally referred to herein as a "circuit" or "module." Furthermore, the present invention may take the form of a computer program product on a computer-usable storage medium having computer-usable program code embodied in the medium. Any suitable computer readable medium may be utilized including hard disks, CD-ROMs, optical storage devices, a transmission media such as those supporting the Internet or an intranet, or magnetic storage devices.

Computer program code for carrying out operations of the present methods may be written in any arbitrary programming language such as Java®, Smalltalk or C++. However, the computer program code for carrying out the steps of the present method may also be written in any conventional procedural programming languages such as the "C" programming language and/or a lower level assembler language. The program code may execute entirely on the first node 110, partly on the first node 110, as a stand-alone software package, partly on the first node 110 and partly on a remote computing device or entirely on the remote computing device. In the latter scenario, the remote computing device may be connected to the first node 110 through a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer, for example, through the Internet using an Internet Service Provider.

The program code according to another aspect may execute entirely on the second node 120, partly on the second node 120, as a stand-alone software package, partly on the second node 120 and partly on a remote computing device or entirely on the remote computing device. In the latter scenario, the remote computing device may be connected to the second node 120 through a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer, for example, through the internet using an Internet Service Provider. Furthermore, the present methods were described in part above with reference to flowchart illustrations and/or block diagrams of the first node 110, the second node 120, methods, and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, may be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function/act specified in the flowchart and/or block diagram block or blocks.

The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

Alternative embodiments

According to some embodiments, a method in a first node 110 in a wireless communication system 100 is provided. The first node 110 is using a frame structure of a Time Division Duplex mode (TDD mode) physical layer protocol for transmitting a signal from the first node 110 to a second node 120 in a wireless communication network 100. The method is characterised by the step of Transmitting a Sounding Reference Signal in an Uplink Pilot Timeslot 232 comprised within the TDD mode frame structure.

According to some embodiments, an arrangement in a first node 110 in a wireless communication system 100 is provided. The first node 110 is using a frame structure of a Time Division Duplex mode (TDD mode) physical layer protocol for transmitting a signal from the first node 110 to a second node 120 in a wireless communication network 100. The arrangement is characterised by that an Uplink Pilot Timeslot 232, comprised within the TDD mode frame structure, is being configured to comprise a Sounding Reference Signal.

According to some embodiments of the present method and arrangement, random access could possibly be received in some other uplink sub frame.

According to some embodiments of the present method and arrangement, the random access may not be allocated to the Uplink Part 232 every 5 ms half frame.

According to some embodiments of the present method and arrangement, the reference signal may be transmitted in the switching zone 250 in addition to the reference signalling which is made in the sub frames 220, 221 , 222, 223, 224, 225, 226, 227. Thus the reference signalling may be enhanced, which may lead to an improved control over the signal quality.

However, according to some other embodiments of the present method and arrangement, the reference signal may be transmitted only in the switching zone 250, without sending reference signals in the sub frames 220, 221 , 222, 223, 224, 225, 226, 227. Thus overhead may be reduced and the data transmission capacity may increase.

Yet an advantage is that Uplink channel-dependent scheduling does work well due to interference variation, why a slightly loser sounding period as compared to sounding in every uplink sub frame will not be any problem.

Another advantage is that a Time Division Duplex frame structure according to some embodiments might require sounding for direction of arrival -based beamforming, why a slightly loser sounding period instead of sounding in ordinary uplink sub frames will not cause big difference.

The example of solution supports the same sounding sequence-design in Time Division Duplex frame structure according to some embodiments. Also, the longest Guard Period 230 may become 0.116 ms or 0.2 ms depending on whether Downlink Pilot Time Slot 231 may be reserved for Guard Period 230 or not.

Yet another advantage is that users, which experience bad channel conditions, have their scheduling of transmit resources performed in a more efficient fashion, all in order to reduce the performance loss incurred by introducing necessary Guard Periods 230.

Yet another advantage is that sounding can be performed with no impact on data or control signalling in the uplink time slots. This is beneficial from an uplink performance such as coverage perspective.

Another advantage is that the invented method and arrangement does not leave much impact on the sounding usage.

While the methods and arrangements described in this document are susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and are herein described in detail. It should be understood, however, that there is no intent to limit the present methods and arrangements to the particular forms disclosed, but on the contrary, the present methods and arrangements are to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the methods and arrangements as defined by the claims.

Like reference numbers signify like elements throughout the description of the figures.

As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless expressly stated otherwise. It should be further understood that the terms "comprises" and/or "comprising" when used in this specification is taken to specify the presence of stated features, integers, steps, operations, elements, and/or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present. Furthermore, "connected" or "coupled" as used herein may include wirelessly connected or coupled. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Unless otherwise defined, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which these methods and arrangements belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

For purposes of illustration, embodiments of the present methods and arrangements are described herein in the context of a first node 110 and a second node 120. It will be understood, however, that the present methods and arrangements are not limited to such embodiments and may be embodied generally as any electronic device that includes radio signal propagation means thereon.

Claims

1. Method for transmitting a reference signal, the method is performed in a first node (110) in a cell (125) comprised within a wireless communication network (100) using Time Division Duplexing, wherein the first node (110) is arranged to communicate over a communication channel (140) with a second node (120), by using a frame structure physical layer protocol comprising uplink sub frames (221) and downlink sub frames (220) with a switching zone (250) in the time dimension between the downlink sub frames (220) and the uplink sub frames (221), the method comprises the step of: transmitting (310) the reference signal in the switching zone (250) between the downlink sub frames (220) and the uplink sub frames (221).

2. Method according to claim 1 , wherein the switching zone (250) comprises a Guard Period (230) and the reference signal is transmitted in a timeslot situated at the end of the Guard Period (230) in the time dimension.

3. Method according to claim 1 , wherein the switching zone (250) comprises a Guard Period (230) and the reference signal is transmitted in a timeslot situated after the Guard Period (230) in the time dimension.

4. Method according to any of the claims 1-3, wherein the switching zone (250) further comprises a dedicated timeslot (232) situated after the Guard Period (230) in the time dimension, and; wherein the reference signal is transmitted in the dedicated timeslot (232).

5. Method according to claim 4, wherein the dedicated timeslot (232) is an Uplink Pilot Timeslot.

6. Method according to any of the claims 4 or 5, wherein no data transmission is done in the dedicated timeslot (232).

7. Method according to any of the claims 1-6, wherein the reference signal is a Sounding Reference Signal.

8. Arrangement (400) in a first node (110) for transmitting a reference signal, the first node (110) is comprised in a cell (125) within a wireless communication network (100) using Time Division Duplexing, wherein the first node (110) is arranged to communicate over a communication channel (140) with a second node (120), by using a frame structure physical layer protocol comprising uplink sub frames (221) and downlink sub frames (220) with a switching zone (250) in the time dimension between the downlink sub frames (220) and the uplink sub frames (221), the arrangement (400) comprises: a transmitter (410), adapted to transmit the reference signal in the switching zone (250) between the downlink sub frames (220) and the uplink sub frames (221).

9. Method for receiving a reference signal, the method is performed in a second node (120) in a cell (125) comprised within a wireless communication network (100) using Time

Division Duplexing, wherein the second node (120) is arranged to communicate over a communication channel (140) with a first node (110), by using a frame structure physical layer protocol comprising uplink sub frames (221) and downlink sub frames (220) with a switching zone (250) in the time dimension between the downlink sub frames (220) and the uplink sub frames (221), the method comprises the step of: receiving (510) the reference signal in the switching zone (250) between the downlink sub frames (220) and the uplink sub frames (221).

10. Method according to claim 9, wherein the switching zone (250) comprises a Guard Period (230) and the reference signal is transmitted in a timeslot situated at the end of the

Guard Period (230) in the time dimension.

11. Method according to claim 9, wherein the switching zone (250) comprises a Guard Period (230) and the reference signal is transmitted in a timeslot situated after the Guard Period (230) in the time dimension.

12. Method according to any of the claims 9-11 , wherein the switching zone (250) further comprises a dedicated timeslot (232) situated after the Guard Period (230) in the time dimension, and; wherein the reference signal is received in the dedicated timeslot (232).

13. Method according to claim 12, wherein the dedicated timeslot (232) is an Uplink Pilot Timeslot.

14. Method according to claim 12 or 13, wherein no data transmission is done in the dedicated timeslot (232).

15. Method according to any of the claims 9-14, wherein the reference signal is a Sounding Reference Signal.

16. Arrangement (600) in a second node (120) for receiving a reference signal, the second node (120) is comprised in a cell (125) within a wireless communication network (100) using Time Division Duplexing, wherein the second node (120) is arranged to communicate over a communication channel (140) with a first node (110), by using a frame structure physical layer protocol comprising uplink sub frames (221) and downlink sub frames (220) with a switching zone (250) in the time dimension between the downlink sub frames (220) and the uplink sub frames (221), the arrangement (600) comprises: a receiver (610), adapted to receive the reference signal in the switching zone (250) between the downlink sub frames (220) and the uplink sub frames (221).