WO2010114442A1

WO2010114442A1 - Method and arrangement for base station synchronisation

Info

Publication number: WO2010114442A1
Application number: PCT/SE2009/050346
Authority: WO
Inventors: Youping Su; Chunhui Zhang
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2009-04-01
Filing date: 2009-04-01
Publication date: 2010-10-07
Also published as: WO2010114442A9; CN102369771A

Abstract

Method, arrangement and computer program product in an indoor base station for synchronization of phase and frequency with an outdoor base station. The indoor base station and the outdoor base station are comprised within a wireless communication network and are adapted to send and receive data in radio frames. The indoor base station is adapted to alternatively operate in a first synchronization mode and in a second operative mode. The method comprises the steps of entering the first synchronization mode, sending a request for random access to the outdoor base station, receiving FPACH adjustment information from the outdoor base station, synchronizing the phase and frequency according to the received FPACH adjustment information and changing mode into the second operative mode.

Description

Method and arrangement for base station synchronisation

TECHNICAL FIELD

The present invention relates to a method and arrangement in a wireless communication network and, more in particular, to a mechanism to achieve synchronization for an indoor Time Division Duplex Base Station.

BACKGROUND

In technologies such as e.g. Time Division Duplex (TDD) in Wideband Code Division Multiple Access (WCDMA), Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) and TDD in Long Term Evolution (LTE) within the 3rd Generation Partnership Project (3GPP), the base stations, or NodeB:s as they also may be referred to, need to be synchronized with each other both in predefined frequency accuracy and phase accuracy.

For TDD, uplink and downlink use the same frequency and cannot transmit simultaneously. Uplink and downlink can however share the time in a flexible way, and by allocating different amounts of time, such as the number of time slots of a radio frame, to uplink and downlink, it is possible to adapt to asymmetric traffic and resource needs in uplink and downlink.

The expression uplink is here used to denominate the transmission path from a terminal, e.g. a Mobile Phone, to a base station; downlink is used to denominate the transmission path from the base station to the terminal.

Frequency synchronization relates to the alignment of clocks in frequency, a process that is referred to as synchronization. Phase synchronization implies that the two clocks are aligned in phase, a process that also referred to as relative-time synchronization. Phase synchronization is also referred to as time-of-day synchronization or wall-clock synchronization where the clocks in question are traceable to a common, universal, time- base such as e.g. Coordinated Universal Time (UTC). Note that if two clocks are synchronized in phase then they are also synchronized in frequency. For technologies like e.g. Global System for Mobile Telecommunications (GSM) and Frequency-Division Duplex (FDD) WCDMA, frequency synchronization may be adequate; for TDD WCDMA, TD-SCDMA and TDD LTE a combination of frequency and phase synchronization may be required.

in TD-SCDMA, TDD WCDMA, Code Division Multiple Access (CDMA), CDMA2000 and Mobile Worldwide Interoperability for Microwave Access (WiMAX), these 3G TDD systems all require phase and frequency accuracy within a predefined range. For TD- SCDMA for example, the time alignment accuracy is +/- 1.5 micro seconds and frequency accuracy is within 50 ppb.

Current synchronization reference for TDD WCMDA, CDMA2000 and TD SCDMA is the GPS PP1 S. Though the GPS can deliver the frequency and time with up to 50 ns accuracy, and at the GPS hold over period, an expensive oscillator will be needed to hold the frequency and phase.

The E1/T1 transmission only provides the frequency accuracy but no phase info for TD accuracy can be derived.

Wired synchronization methods like e.g. IEEE 1588v2 provides less than 1 us phase accuracy to the end user. However, products implementing this standard have not been largely deployed by Telecom operators.

An indoor Pico/Femto base station may be installed in a user's house in the coverage area of the outdoor base station. The indoor user will use the indoor Pico/Femto base station connection to make e.g. a call.

According to the statistic data, the 90% 3G data service is estimated to come from indoor base stations within a close future. For indoor coverage, there are basically three scenarios:

In a first scenario, the received signal level from outdoor TDD base station is less than A dBm where "A" may be e.g. 95dBm. However this number may be different with the different vendors and different standards. Thus there is no indoor coverage for the outdoor TDD base station and with this level, the basic R4 service cannot be accessed from the outdoor TDD base station. According to a second scenario, the received signal level from the outdoor TDD base station may be between B dBm and A dBm, where "B" may be e.g. 85dBm. However this number may be different with the different vendors and different standards. The low data rate R4 and voice service can be accessed from outdoor TDD base station.

Further, in a third scenario, the received signal level is greater than B dBm which means high data rate can be accessed from outdoor base station.

To improve the indoor data service, usually the Pico/Femto TDD base station will be deployed. For the first scenario, the same frequency can be deployed. For the second and third scenarios, the different frequency for indoor base station should be deployed to avoid the interference from the outdoor base station.

A problem with the existing solution is that the indoor TDD base station needs a Global Positioning System (GPS) reference which in turn requires that one antenna is installed outside the building. Also a high stable Oven-Controlled Crystal Oscillator (OCXO) to lock the output radio frequency generated by a Voltage Controlled Temperature Compensated Crystal Oscillator (VCTCXO) when the GPS signal is not available may be comprised within the indoor base station.

The installation of the GPS antenna and GPS receiver for the indoor base station and the expensive OCXO will render additional cost to the TDD base station.

SUMMARY It is an object to obviate at least some of the above disadvantages and provide an improved mechanism within a wireless communication network.

According to a first aspect, the object is achieved by a method in an indoor base station for synchronization of phase and frequency with an outdoor base station. The indoor base station and the outdoor base station are comprised within a wireless communication network and are adapted to send and receive data in radio frames. The indoor base station is adapted to alternatively operate in a first synchronization mode and in a second operative mode. The method comprises entering the first synchronization mode including receiving DwPTS and TSO from outdoor base station. Also, the method comprises sending a request for random access to the outdoor base station. Further, the method comprises receiving Fast Physical Access Channel (FPACH) adjustment information from the outdoor base station. Additionally, the method comprises synchronizing the phase and frequency according to the received FPACH adjustment information. Furthermore, the method comprises changing mode into the second operative mode.

According to a second aspect, the object is also achieved by an arrangement in an indoor base station for synchronization of phase and frequency with an outdoor base station. The indoor base station and the outdoor base station are comprised within a wireless communication network and are adapted to send and receive data in radio frames. The indoor base station is adapted to alternatively operate in a first synchronization mode and periodically in a second operative mode. The arrangement comprises a switching unit, adapted to switch between the first synchronization mode and the second operative mode. Also, the arrangement comprises a sending unit. The sending unit is adapted to send a request for random access to the outdoor base station. Further, the arrangement comprises a receiving unit. The receiving unit is adapted to receive time adjustment information from the outdoor base station. In addition, the arrangement comprises a synchronization unit. The synchronization unit is adapted to synchronize the phase and frequency according to the received adjustment information.

Thanks to the present methods and arrangements, it is possible to synchronize the indoor base station with an outdoor base station, without being dependent upon an Oven- Controlled Crystal Oscillator (OCXO), and/or a GPS antenna/receiver comprised within the indoor base station. This is accomplished by receiving FPACH adjustment information from the outdoor base station and synchronizing the phase and frequency according to the received FPACH adjustment information and the midamble from Time slot 0. Thereby expensive hardware components are saved for indoor radio base station. Thus an improved mechanism for synchronization within a wireless communication network is provided.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention.

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 illustrating a user scenario in a wireless communication network.

Figure 2 is a block diagram illustrating a radio frame structure.

Figure 3 is a block diagram illustrating TDD base station switch points.

Figure 4 is a block diagram illustrating indoor TDD base station working in different modes, according to some embodiments.

Figure 5 is a schematic flow chart illustrating embodiments of a method in an indoor base station.

Figure 6 is a block diagram illustrating embodiments of an arrangement in an indoor base station.

DETAILED DESCRIPTION

The present solution is defined as a method, and an arrangement in an indoor base station which may be put into practice in the embodiments described below. The present solution 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 present solution. It should be understood that there is no intent to limit the present methods, and arrangements to any of the particular forms disclosed, but on the contrary, the present methods and arrangements are to cover all modifications, equivalents, and alternatives falling within the scope of the present solution as defined by the claims.

The present solution may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the solution. The present embodiments are to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein. Figure 1 is a schematic illustration over a wireless communication network 100. The wireless communication network 100 comprises an indoor base station 110 and is arranged to comprise a mobile terminal 120. The indoor base station 110 may send and receive wireless signals to and from the terminal 120 situated within the coverage area of the indoor base station 110. The wireless communication network 100 further comprises an outdoor base station 130. The indoor base station 1 10 and the terminal 120 may be situated inside a structure 140, while the outdoor base station 130 may be situated outside the structure 140 but with the indoor base station 110 within the coverage area.

Although only two base stations 110, 130 are shown in Figure 1 , it is to be understood that another configuration of base station transceivers may be connected through, for example, a mobile switching centre and other network nodes, to define the wireless communication network 100.

The indoor base station 1 10 may be e.g. a Pico base station or a Femto base station.

Further, the outdoor base station 130 may be referred to as e.g. a macro base station, a Remote Radio Unit, an access point, a Node B, an evolved Node B (eNode B), a Radio Base Station (RBS), a base transceiver station, an Access Point Base Station and/or a base station router, etc depending e.g. of the radio access technology and terminology used.

In some embodiments, the terminal 120 may be represented by a wireless communication device, a wireless communication terminal, a mobile cellular telephone, a Personal Communications Systems terminal, a Mobile Station (MS), a Personal Digital Assistant (PDA), a laptop, a User Equipment (UE), computer (PC) or any other kind of device capable of managing radio resources.

The wireless communication network 100 may be based on technologies such as e.g. Global System for Mobile Telecommunications (GSM), Enhanced Data rates for GSM Evolution (EDGE), General Packet Radio Service (GPRS), Code Division Multiple Access (CDMA), Wideband Code Division Multiple Access (WCDMA), CDMA 2000, High Speed Downlink Packet Data Access (HSDPA), High Speed Uplink Packet Data Access (HSUPA), High Data Rate (HDR) High Speed Packet Data Access (HSPA), Universal Mobile Telecommunications System (UMTS) etc, just to mention some few arbitrary and none limiting examples.

Further, as used herein, the wireless communication network 100 may in addition, according to some embodiments, refer to Wireless Local Area Networks (WLAN), such as Wireless Fidelity (WiFi) and Worldwide Interoperability for Microwave Access (WiMAX), Bluetooth or according to any other wireless communication technology.

However, according to some embodiments, the outdoor base station 130 may be a TDD base station.

It is to be noted however, that the present solution is not in any way limited to be performed exclusively over a radio interface within the wireless communication network 100, but may be performed within a wireless communication network 100 where some nodes are wirelessly connected and some nodes have a wired connection.

The terminal 120 may further communicate with other terminals such as e.g. other terminals not shown in Figure 1 , via the base station 110 comprised within the wireless communication network 100.

The present method and arrangement may cover any of the previously discussed three indoor installation scenarios. In the first scenario, the received signal level from the outdoor base station 130 is less than A dBm, where "A" may be e.g. 95 dBm, depending on the used technology, different hardware producers, different standards, etc. In a second scenario, the received signal level from the outdoor base station 130 may be between B dBm and A dBm (95 dBm), where "B" may be e.g. 85 dBm, depending on the used technology, different hardware producers, different standards, etc. In a third scenario, the received signal level is greater than B dBm (85 dBm).

Further, the present method and arrangement may according to some embodiments use the Time Slot 0 (TSO) and Downlink Pilot Timeslot (DwPTS) of the outdoor base station 130 instead of the GPS, in order to achieve the phase and frequency accuracy.

When acquiring the phase and frequency from the outdoor base station 130, the indoor base station 1 10 may work in a first synchronization mode, or Mobile Station (MS) mode for a period of time (TSO plus DWPTS) in one radio subframe. The period of acquiring the frequency and phase may depend on the stability of the VCTCXO according to some embodiments.

In the herein described exemplary embodiment, 1.28 Mcps TDD Low Chip Rate (LCR) is used as a non-limiting example. However, for e.g. TDD LTE and/or TDD HCR, the procedure may be similar.

There are two working modes in the indoor Pico/Femto base station 1 10, according to the present method: one first synchronization mode, or Mobile Station (MS) mode and one second operative mode, the normal RBS mode. In the RBS mode, the indoor base station 110 may work as a normal base station to provide services to terminals 120 within the cell. In the MS mode, the indoor base station 110 may listen to the DwPTS and TSO of the outdoor base station 130 for frequency and phase correction.

When the indoor Pico/Femto base station 1 10 power on, the indoor base station 1 10 first enters to the cell searching which works as the TDD mobile, i.e. the indoor base station 1 10 operates in MS mode. It is the basic of downlink synchronization between indoor base station 110 and outdoor base station 130.

The detailed cell search procedure may be referred to 3GPP 25.224 Annex C for 3.84Mcps HCR and Annex CA for LCR. During the initial outdoor base station cell search, the indoor Pico/Femto base station 1 10 may determine the DwPTS synchronization, scrambling and basic midamble code identification. Frequency synchronization may be implemented in two steps: rough frequency offset adjustment and precise frequency offset adjustment. The received downlink synchronization SYNC-DL may be used to estimate the frequency offset between the indoor base station 1 10 and the outdoor base station 130 roughly, and the demodulated scrambling and basic midamble code to acquire precise frequency synchronization. The frequency adjustment is via the Automatic Frequency Control (AFC) signal to tune the VCTCXO.

For Phase synchronization, since indoor Pico/Femto base station 110 occasionally operates in MS mode, functioning as a mobile terminal, it may start to initiate an uplink synchronization to the outdoor base station 130 by sending Synch-UL, after power on. After the detection of the SYNC-UL sequence in the searching window, the outdoor base station 130 may evaluate the timing, and reply by sending the adjustment information to the indoor base station 1 10 to modify its timing for next transmission. This may be done with the Fast Physical Access Channel (FPACH) within the following 4 sub-frames. The TAuI advance time contained in FPACH (unit is 1/8 chip) may be calculated from the received SYNCHJJL from the indoor base station 110, by the base station 130 and may be used as adjustment offset to derive the air frame start time to avoid the interference with other base stations 110, 130. Since in TDD RBS, the System Frame Number (SFN) may be calculated using the GPS time, all the base stations 130 may use the same SFN number at the same time. The SFN number for the current radio frame may also be decoded (SFNprime) from BCH and this may be utilized by the indoor base station 110.

Once the phase and frequency of the indoor base station 110 is determined by acquiring timing information from the outdoor base station 130, the indoor base station 1 10 can be switched into the operative RBS mode. The indoor base station 1 10 may be configured to a different/same frequency through e.g. an optional control node such as e.g. a Radio Network Controller (RNC), depending on different scenarios.

Considering the network planning, the frequency of indoor base station 110 can be configured in two categories: one is the same frequency deployed with outdoor base station 130 which is the case of the first scenario previously described. The other is the different frequency which may be the case in the second and third scenario previously described.

Figure 2 shows the general description for the Radio Frequency Hardware of the indoor base station 1 10, e.g. a Multi-carrier TDD base station. The switch S2 is used for the different frequency configuration with outdoor base stations 130. The switch S1 is used to switch from uplink to downlink or vice verse for Time Division Duplex mode. The S1 switch time may be controlled by signal Synchronization derived from air time. The Digital Down Converter (DDC) block may be implemented by a Field-Programmable Gate Array (FPGA). The functionality of the DCC is to down convert IF data to base band data. It is however to be noted that the illustrated embodiment using an DCC for performing this functionality is only an example of embodiment. The same functionality as the DCC may be performed by e.g. a FPGA or a Digital Signal Processor (DSP) instead of the DCC. A FPGA is programmed using a logic circuit diagram or a source code in a hardware description language to specify how the chip will work. The FPGA comprise programmable logic components which may be referred to as logic blocks, and a hierarchy of reconfigurable interconnects that allow the blocks to be interconnected. Logic blocks may be configured to perform complex combinational functions, or logic gates like AND and XOR. The logic blocks may also comprise memory elements.

The external antenna may be used if the same frequency is configured to indoor base station 110 and outdoor base station 130. The switch S2 may be switched to external antenna when it needs to re-synch the outdoor base station 130 for the frequency and phase. Indoor base station 1 10 may work in MS mode during TSO and DwPTS time and UpPTS. In MS mode, the switch S2 may be switched to the external antenna and the switch S1 may be switched to uplink at the guard period of the TS6. The switch time S1 and S2 of the indoor base station 110 relative to the normal radio frame structure will be further discussed in association with the presentation of Figures 3A and 3B.

In the case of the different frequency configured to indoor base station 110 and outdoor base station 130, the switch S2 may be switched to the internal antenna only, according to some embodiments. The outdoor frequency may be configured to the DDC as one receiving carrier. The Synchronization signal to control the uplink and downlink switch point S1 may trigger the switch S1 at the guard period of TS6 to receive the TSO and DWPTS from the outdoor base station 130.

Figure 3 A illustrates a radio frame 300 of 10 ms duration in a TDD environment. Furthermore, each 10 ms radio frame is divided into two subframes 310 of 5 ms duration where each subframe 310 has seven traffic timeslots for uplink and downlink communication.

The timeslots are numbered from 0 to 6 and will in this context be referred to as TSO - TS6. TSO is always assigned as the downlink direction and conveys control messages such as the Broadcast Channel (BCH) while TS1 is always allocated as uplink. Between TSO and TS1 is a first switching point e.g. transition from downlink to uplink situated. The first switching point is at the Guard Period (GP), situated between the Downlink Pilot Time Slot (DwPTS), and Uplink Pilot Time Slot (UpPTS). The second switching point, from uplink to downlink may occur anywhere between the end of TS1 and the end of TS6. It is this second switching point that determines the traffic nature of a particular subframe 310, that is, symmetric or asymmetric. In asymmetric mode, at least one uplink timeslot and one downlink timeslot must be allocated for traffic, e.g. TSO for downlink and TS1 for uplink. The position of the DwPTS, GP, and UpPTS is always between TSO and TS1 whatever the level of asymmetry may be.

UpPTS is used for uplink transmission and may be used by the base station 130 to determine the received timing from the indoor base station 1 10 operating in a MS mode. In order to reduce interference to outdoor radio base station 130, the air frame transmission from the indoor base station 1 10 operating in base station mode, may be phase aligned with the outdoor base station 130. The timing used for the UpPTS transmission for indoor base station 1 10 may be estimated from the received DwPTS after decoding BCH from the outdoor base station 130. The base station 130 may then detect the SYNC-UL request (128 codes in total) transmitted in the UpPTS and may issue timing commands to the indoor base station 1 10, for adjusting its new transmission time in a resolution of 1/8 chips.

GP is used to create a guard period between DwPTS and UpPTS i.e. periods of downlink and uplink transmission. The guard period may be configured to have different lengths in order to avoid interference between uplink and downlink transmissions and is typically chosen based on the supported cell radius. In the illustrated example in Figure 3A, the

Guard Period is 96 chips long and may support a cell radius of up to about 11 km for the uplink synchronization operation. UpPTS shifting which GP will include TS1 and become 96+864+32=996 chips to have a larger cell.

The guard period insures that a terminal 120 transmitting the UpPTS does not disturb the reception of the DwPTS for other close-by terminals.

DwPTS is used for downlink synchronization. During the cell search procedure, the indoor base station 110, or the terminal 120 may acquire the timing of the DwPTS by correlating with the SYNC-DL code transmitted in the DwPTS. The indoor base station 110, or the terminal 120 may identify which SYNC-DL sequence is used out of 32 SYNC-DL possible sequences. Since each SYNC-DL is mapped to four basic midamble codes, out of 128 basic midamble codes in total, the indoor base station 110, or the terminal 120 can identify which basic midamble code is used at the base station 130. Knowing the basic midamble code may also identify the unique associated scrambling code.

Figure 3B illustrates a radio subframe 310 comprising time slots, wherein the switch points where the switch S1 switch from uplink to downlink transmission, and vice versa are indicated. The switch S1 is used to switch from uplink to downlink or vice verse for Time Division Duplex mode. The S1 switch time may be controlled by signal Synchronization derived from air time, according to some embodiments.

Figure 3C illustrates a radio subframe 310 for an indoor base station 110, working alternatively in a first synchronization mode (MS mode) and in a second operative mode (RBS mode), alternatively. The switch S2 may switch between the two modes such that the indoor base station 1 10 works in the first synchronization mode (MS mode) in TSO and DwPTS periodically, and in the second operative mode (RBS mode) the rest of the time, according to some embodiments. Thus a terminal 120, served by the indoor base station 110 may not be affected. The Figure 3C thus shows the switch points S1 and S2 of the indoor base station 1 10 relative to the normal radio frame structure as illustrated in Figure 3B, i.e. the points in time when the switches S1 and S2 are adapted to switch.

The period for the indoor base station 110 to work in the first synchronization mode may depend on the stability of the VCTCXO. The recommended time may be preset and stored as Synch-timer in the indoor base station 110. When the Synch-timer times out, the indoor base station 110 may be set into the first synchronization mode to re-synch the frequency and frame phase listed in Figure 4.

Figure 4 is a schematic flow chart illustrating the present method according to some embodiments. The switch of functionality for the indoor base station 110 from the first synchronization mode and the second operative mode is illustrated.

The allocated time slot and code for the Paging Channel (PCH) and the Forward Access Channel (FACH) respectively may be broadcasted at the BCH. To prevent the loss of the paging information for the served terminal 120, the Secondary Common Control Physical Channel (S-CCPCH) that has been used to transfer the PCH and FACH may be mapped to a time slot different from TSO such as e.g. TS1-TS6. In a first step, the power of the indoor base station 110 may be switched on. The indoor base station 1 10 enters the first synchronization mode, MS mode. Then downlink synchronization for frequency correction may be initiated and performed.

Further, the System Frame Number for the current radio frame may also be decoded (SFNprime) from the Broadcast Channel and this may be utilized by the indoor base station 1 10. Then, while the indoor base station 110 is still in the first synchronization mode, MS mode, uplink synchronization may be performed, to get TAuI advance time and store for air time offset adjustment. The TAuI advance time contained in FPACH may be calculated from the received SYNCHJJL time from indoor base station 1 10, by the base station 130 and may be used as adjustment offset by the indoor base station 1 10 to derive the air frame start time to avoid the interference with other base stations 130. Then, the switch S2 may switch into the second operative RBS mode. At that moment, a count down timer Synch-timer is initiated and starts to count down. When the Synch-timer times out, the indoor base station 1 10 again may be set into the first synchronization mode, MS mode. The switch may be made at the guard period TS6, to start receiving outdoor base station 130 TSO and DwPTS signal. Also, adjustment of the AFC to correct the frequency drift may be performed. Then the indoor base station 1 10 again may enter the second operative mode, RBS mode. The switch may be made at the guard period between the DwPTS and the UpPTS.

The indoor base station 110 implemented using the described solution does not need to have an OCXO which is expensive and the indoor base station 110 may work in a normal condition.

As the indoor base station 110 according to the present solution may not need the GPS antenna/receiver to be installed, the production cost may be reduced.

Figure 5 is a flow chart illustrating embodiments of method steps 501-511 performed in an indoor base station 130. The method aims at synchronizing phase and frequency with an outdoor base station 130. The indoor base station 110 and the outdoor base station 130 are comprised within a wireless communication network 100 and are adapted to send and receive data in radio frames 300. Further, the indoor base station 110 is adapted to alternatively operate in a first synchronization mode and in a second operative mode. The indoor base station 110 may further according to some embodiments comprise an internal antenna 210 and an external antenna 220 and a switching unit S2 adapted to change from sending/ receiving over the internal antenna 210 to the external antenna 220 and vice versa and wherein the change of mode from the first synchronization mode into the second operative mode is performed by changing the switching unit S2 from sending/ receiving over the external antenna 220 to the internal antenna 210 and wherein the change of mode from the second operative mode to the first synchronization mode is performed by changing the switching unit S2 from sending/ receiving over the internal antenna 210 to the external antenna 220.

To appropriately synchronizing phase and frequency of the indoor base station 110 with the outdoor base station 130, the method may comprise a number of method steps 501- 511.

It is however to be noted that some of the described method steps 501-511 are optional and only comprised within some embodiments. Further, it is to be noted that the method steps 501-511 may be performed in any arbitrary chronological order and that some of them, e.g. step 502 and step 503, or even all steps 501-511 may be performed simultaneously or in an altered, arbitrarily rearranged, decomposed or even completely reversed chronological order, according to different embodiments. The method may comprise the following steps:

Step 501

The indoor base station 110 enters the first synchronization mode.

Step 502

This step is optional and may only be performed within some embodiments.

A broadcast may be received from the outdoor base station 130, which broadcast comprises a System Frame Number. This step may optionally be performed before the step of sending a request for random access to the outdoor base station 130 from the indoor base station 110 to the outdoor base station 130, according to some embodiments.

Step 503 This step is optional and may only be performed within some embodiments. The received System Frame Number is used for adjusting the frame number of the radio frames 300 to be sent by the indoor base station 110. This step may optionally be performed before the step of sending a request for random access to the outdoor base station 130 from the indoor base station 110 to the outdoor base station 130, according to some embodiments.

Step 504

A request for random access to the outdoor base station 130 is sent from the indoor base station 110 to the outdoor base station 130.

Step 505

Fast Physical Access Channel (FPACH) adjustment information is received from the outdoor base station 130.

Step 506

The phase and frequency are synchronized according to the received FPACH adjustment information.

Step 507

This step is optional and may only be performed within some embodiments.

The received air time offset may be used for adjusting the air time offset of radio frames 300 to be sent by the indoor base station 110.

Step 508

The mode is changed into the second operative mode.

The change of mode from the first synchronization mode into the second operative mode may be performed in a Guard Period between the Time Slot 0 and Downlink Pilot Timeslot in a radio frame 300.

Step 509

This step is optional and may only be performed within some embodiments. A synchronization timer 610 may be initiated at the moment of changing mode from the first synchronizing mode into the second operative mode.

Step 510 This step is optional and may only be performed within some embodiments.

The indoor base station 110 may enter the first synchronization mode when the synchronization timer 610 times out.

The change of mode from the second operative mode into the first synchronization mode may be performed in a Guard Period between the Time Slot 6 and Time Slot 0 in a radio frame 300.

Step 511 This step is optional and may only be performed within some embodiments.

The received Time Slot 0 and Downlink Pilot Timeslot signal may be used for adjusting the phase and frequency of the indoor base station 110.

Figure 6 is a block diagram illustrating embodiments of an arrangement 600 situated in an indoor base station 110. The arrangement 600 is configured to perform the method steps 501-510 for synchronization of phase and frequency with an outdoor base station 130. The indoor base station 110 and the outdoor base station 130 are comprised within a wireless communication network 100. The indoor base station 110 and the outdoor base station 130 are also adapted to send and receive data in radio frames 300. The indoor base station 110 is adapted to alternatively operate in a first synchronization mode and in a second operative mode.

For the sake of clarity, any internal electronics of the arrangement 600, not completely necessary for performing the present method has been omitted from Figure 6.

The arrangement 600 comprises a switching unit S2. The switching unit S2 is adapted to switch between the first synchronization mode and the second operative mode. However, it may be noted that such a switch may only be performed in the previously described first scenario. For the second and third scenario above, only the internal antenna is needed. So, S2 statue may not necessarily need to actually change. Further, the arrangement 600 comprises a sending unit 604. The sending unit 604 is adapted to send a request for adjustment information to the outdoor base station 130. Also, the arrangement 600 comprises a receiving unit 605. The receiving unit 605 is adapted to receive adjustment 5 information from the outdoor base station 130. Additionally, the arrangement 600 comprises a synchronization unit 606. The synchronization unit 606 is adapted to synchronize the phase and frequency according to the received adjustment information.

The arrangement 600 may according to some embodiments comprise a processing unit 10 620. The processing unit 620 may be represented by e.g. a Central Processing Unit (CPU), a processor, a microprocessor, or other processing logic that may interpret and execute instructions. The processing unit 620 may perform all data processing functions for inputting, outputting, and processing of data including data buffering and device control functions, such as call processing control, user interface control, or the like. 15

Also, the arrangement 600 optionally may comprise a synchronization timer 610. The synchronization timer 610 may be adapted to start counting down from a preset time value to zero. When the timer is zero, the indoor radio base station 110 may change mode from the second operative mode to MS mode. Further yet, the arrangement 600 may 0 according to some embodiments comprise an obtaining unit 607. The obtaining unit 607 may be adapted to obtain a System Frame Number, which may be used for adjusting the frame number of the radio frames 300 to be sent by the indoor base station 110.

Further, according to some embodiments, the arrangement 600 optionally may comprise, 5 or at least be attached to, an internal antenna 210 and an external antenna 220. The switching unit S2 is adapted to alternatively switch between transmission over the internal antenna 210 and over the external antenna 220.

It is to be noted that the described units S2-620 comprised within the arrangement 600 0 may be regarded as separate logical entities, but not with necessity as separate physical entities. Any, some or all of the units S2-620 may be comprised or co-arranged within the same physical unit. However, in order to facilitate the understanding of the functionality of the arrangement 600, the comprised units S2-620 are illustrated as separate physical units in Figure 6. 5 Thus the transmitting unit 604 and e.g. the receiving unit 605 may, according to some embodiments, be comprised within one physical unit, a transceiver, which may comprise a transmitter circuit and a receiver circuit, which respectively transmits outgoing radio frequency signals and receives incoming radio frequency signals via any of the optional 5 antennas 210, 220, depending on the mode. The antennas 210, 220 may be an embedded antenna, a retractable antenna or any other arbitrary antenna without departing from the scope of the present arrangements.

Some embodiments

10 The method steps 501-51 1 in the indoor base station 110 may be implemented through one or more processing units 620 in the indoor base station 110, together with computer program code for performing the functions of the present steps 501-511. Thus a computer program product, comprising instructions for performing the method steps 501-511 in the indoor base station 110 may perform a method for synchronization of phase and

15 frequency with an outdoor base station 130 when the computer program product is run on a processing unit 620 comprised within the indoor base station 110.

The computer program product mentioned above may be provided for instance in the form of a data carrier carrying computer program code for performing the method steps 501-

20 511 according to the present solution when being loaded into the processing unit 620. The data carrier may be e.g. a hard disk, a CD ROM disc, a memory stick, an optical storage device, a magnetic storage device or any other appropriate medium such as a disc or tape that can hold machine readable data. The computer program product may furthermore be provided as computer program code on a server and downloaded to the

25 indoor base station 110 remotely, e.g. over an Internet or an intranet connection.

The indoor base station 110 and the outdoor base station 130 are comprised within a wireless communication network 100 and are adapted to send and receive data in radio frames 300. The indoor base station 110 is adapted to alternatively operate in a first 0 synchronization mode and in a second operative mode. The computer program product comprises instructions for entering the first synchronization mode. Further, the computer program product comprises instructions for sending a request for random access to the outdoor base station 130. Further, the computer program product comprises instructions for receiving Fast Physical Access Channel (FPACH) adjustment information from the 5 outdoor base station 130. Additionally, the computer program product comprises instructions for synchronizing the phase and frequency according to the received FPACH adjustment information. Further yet, the computer program product comprises instructions for changing mode into the second operative mode, when the computer program product is run on a processing unit 620 comprised within the indoor base station 110.

The terminology used in the detailed description of the particular exemplary embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention.

As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms "includes," "comprises," "including" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do 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.

Claims

1. Method in an indoor base station (110) for synchronization of phase and frequency with an outdoor base station (130), the indoor base station (110) and the outdoor base station (130) are comprised within a wireless communication network (100) and are adapted to send and receive data in radio frames (300), the indoor base station (110) is adapted to alternatively operate in a first synchronization mode and in a second operative mode, the method comprises the steps of: entering (501 ) the first synchronization mode, sending (504) a request for random access to the outdoor base station (130), receiving (505) Fast Physical Access Channel, FPACH, adjustment information from the outdoor base station (130), synchronizing (506) the phase and frequency according to the received FPACH adjustment information, and changing (508) mode into the second operative mode.

2. Method according to claim 1 , comprising the further steps of: receiving (502) a broadcast from the outdoor base station (130), which broadcast comprises a System Frame Number, and using (503) the received System Frame Number for adjusting the frame number of the radio frames (300) to be sent by the indoor base station (110).

3. Method according to any of claim 1 or claim 2, wherein the received FPACH adjustment information comprises an air time offset and the method comprises the further step of: using (507) the received air time offset for adjusting the air time offset of radio frames (300) to be sent by the indoor base station (110).

4. Method according to any of the claims 1-3, wherein the received FPACH adjustment information comprises a Time Slot 0 and a Downlink Pilot Timeslot signal and the method comprises the further step of: using (511 ) the received Time Slot 0 and a Downlink Pilot Timeslot signal for adjusting the phase and frequency of the indoor base station (110).

5. Method according to any of the claims 1-4, wherein the method comprises the further steps of: initiating (509) a synchronization timer (610) at the moment of changing mode into the second operative mode, and when the synchronization timer (610) times out, entering (510) the first synchronization mode.

6. Method according to any of the claims 1-5, wherein the change of mode from the second operative mode into the first synchronization mode is performed in a Guard Period between the Time Slot 6 and Time Slot 0 in a radio frame (300).

7. Method according to any of the claims 1-6, wherein the change of mode from the first synchronization mode into the second operative mode is performed in a Guard Period between the Time Slot 0 and Downlink Pilot Timeslot in a radio frame (300),

8. Method according to any of the claims 1-7, wherein the indoor base station (110) further comprises an internal antenna (210) and an external antenna (220) and a switching unit (S2) adapted to change from sending/ receiving over the internal antenna (210) to the external antenna (220) and vice versa and wherein the change of mode from the first synchronization mode into the second operative mode is performed by changing the switching unit (S2) from sending/ receiving over the external antenna (220) to the internal antenna (210) and wherein the change of mode from the second operative mode to the first synchronization mode is performed by changing the switching unit (S2) from sending/ receiving over the internal antenna (210) to the external antenna (220).

9. Arrangement (600) in an indoor base station (110) for synchronization of phase and frequency with an outdoor base station (130), the indoor base station (110) and the outdoor base station (130) are comprised within a wireless communication network (100) and are adapted to send and receive data in radio frames (300), the indoor base station (110) is adapted to alternatively operate in a first synchronization mode and in a second operative mode, the arrangement (600) comprises: a switching unit (S2), adapted to switch between the first synchronization mode and the second operative mode, a sending unit (604), adapted to send a request for adjustment information to the outdoor base station (130), a receiving unit (605), adapted to receive adjustment information from the outdoor base station (130), a synchronization unit (606), adapted to synchronize the phase and frequency according to the received adjustment information.

10. Arrangement (600) according to claim 9, wherein the arrangement (600) further comprises: a synchronization timer (610) adapted to start counting down from a preset time value to zero at the moment of changing mode into the second operative mode.