Patent Publication Number: US-2009221324-A1

Title: Switching Between the Wireless Communication System Mode and the Satellite Positioning System Mode, Based on the Detected Voice Activity of the Transmitter

Description:
FIELD OF THE INVENTION 
     Embodiments of the invention relate to a combined global navigation satellite system (GNSS) receiver and cellular system receiver. More specifically embodiments of the invention relate to a receiver in which the radio path between GNSS and cellular system signals can be shared. Embodiments of the invention also relate to a corresponding method, system, module and computer program product. 
     BACKGROUND OF THE INVENTION 
     In cellular systems, different multiple access techniques can be applied depending on the cellular system standard. In the global system for mobile communications (GSM), combined time and frequency division multiple access techniques are applied (TDMA/FDMA). The FDMA technique involves the division of the 25 MHz bandwidth into 124 carrier frequencies spaced 200 kHz apart. Several carrier frequencies can be assigned to each base station (BS). According to the TDMA technique, these carrier frequencies are then divided in the time domain. The fundamental time unit in this TDMA technique is called a burst period (or time slot) and it lasts 15/26 ms (or approximately 0.577 ms). Eight burst periods or time slots are grouped into a TDMA frame ( 120/26 ms, or approximately 4.615 ms), which forms the basic unit for the definition of logical channels. One physical channel is defined to be one burst period per TDMA frame. 
     Minimising interference in the network is a goal in any cellular system, since it allows better service for a given cell size, or the use of smaller cells, thus increasing the overall capacity of the system. Discontinuous transmission (DTX) aims at increasing the system efficiency through a decrease of the interference level by inhibiting the transmission of the radio signal when not required from an information point of view. DTX takes advantage of the fact that a person speaks less than 40 percent of the time in normal conversation. An added benefit of DTX is that power is conserved at the mobile unit. DTX is also called variable bit rate since in the DTX mode the transmitted bit rate is less than in a situation in which a person is speaking. 
     The most important component of DTX is voice activity detector (VAD). It must distinguish between noise and voice inputs. When the transmitter is turned off, there is total silence heard at the receiver. To assure the receiving end that the connection is not dead, comfort noise is created at the receiver to match the transmitting end&#39;s background noise characteristics. For instance in GSM, the noise characteristics are transported to the receiving end by specific frames called silence descriptor (SID) frames. A SID frame is sent at the beginning of every inactivity period, and more are then sent regularly, at least twice a second, as long as the inactivity lasts. Therefore, the receiving end can generate comfort noise based on the received SID frame. DTX can be used also in systems employing code division multiple access (CDMA) technique. An example of such a cellular system is for instance universal mobile telecommunication system (UMTS), which employs wideband CDMA. 
     Currently GNSS receivers are being integrated into cellular system terminals.  FIG. 1  presents a prior art solution in which two separate radio frequency (RF) sections are used; one for cellular signals and one for satellite signals. It is also possible to use a common shared RF section for both GNSS and cellular system receivers.  FIG. 2  presents this solution in which a common RF section is shared between GNSS and cellular system reception. If there is a need for GNSS and cellular system receivers to operate simultaneously, the RF section must be time shared between these two receivers. This degrades the performance of both receivers. 
     U.S. Pat. No. 6,831,911 by Ashvattha Semiconductor Inc relates generally to a system and method for receiving and processing global positioning system (GPS) and wireless phone signals using a combination receiver, more particularly, receiving and processing GPS signals and wireless signals during alternate time segments by suspending reception of GPS signals during times when wireless signal is received. In the event that the user desires to place or receive a wireless phone call, using a time division technology wireless phone, the receiver will suspend reception of GPS signal to receive or transmit the wireless phone signal. Therefore, it becomes possible to combine a GPS receiver and a wireless phone using a single integrated circuit because either the GPS receiver or the wireless phone is operating, but not both at the same time. A TDMA wireless phone signal can be received and processed in time segments alternating with a GPS signal. The TDMA data is sent in signal bursts that last a predetermined length of time in accordance with the particular time division standard. Therefore, the GPS receiver can be turned on to receive a GPS signal, then turned off to receive a TDMA signal. When the TDMA signal has been received, the receiver can be switched to the GPS operational mode again. 
     SUMMARY OF THE INVENTION 
     The applicant has recognised that there is a need to share the RF section part of the receiver between the cellular and GNSS signals based on the detected voice activity of the transmitter. 
     According to a first aspect of the invention, there is provided a method for a first wireless communication device to operate in wireless communication system mode and satellite positioning system mode, wherein in the satellite positioning system mode the first wireless communication device receives signals from the satellite positioning system and in the communication system mode it receives signals from the communication system, the method comprising the first wireless communication device: communicating with a second communication device; determining voice activity of at least one of the communication devices; based on the determined voice activity, switching between the wireless communication system mode and the satellite positioning system mode. 
     The invention has in accordance with one embodiment the advantage that it provides a way to optimise the performance of the communication device with minimal speech quality degradation. The invention makes it possible to switch between satellite system signal reception and communication system signal reception. 
     Further, according to a first aspect of the invention the wireless communication device is a mobile phone handset. 
     Other aspects of the invention are in the claims appended hereto. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       These and other features of the present invention will by way of example become apparent from the following detailed description when considered in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates a block diagram of a prior art solution for receiving cellular and satellite positioning system signals; 
         FIG. 2  illustrates a block diagram of another prior art solution for receiving cellular and satellite positioning system signals; 
         FIG. 3  illustrates an environment in which embodiments of the invention can be applied; 
         FIG. 4  is a block diagram illustrating a wireless terminal in accordance with an embodiment of the invention; 
         FIG. 5  is a simplified flow diagram in accordance with an embodiment of the invention; 
         FIG. 6  is a block diagram of the signal reception and RF parts of the receiver in accordance with an embodiment of the invention; 
         FIG. 7  is a flow diagram in accordance with an embodiment of the invention; 
         FIG. 8  illustrates one operation mode of the receiver as a function of time in accordance with an embodiment of the invention; 
         FIG. 9  illustrates another operation mode of the receiver as a function of time in accordance with an embodiment of the invention; 
         FIG. 10  is a flow diagram in accordance with another embodiment of the invention; 
         FIG. 11  illustrates another operation mode of the receiver as a function of time in accordance with an embodiment of the invention; 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Operational Environment 
       FIG. 3  illustrates an operational environment in which embodiments of the present invention may exist. Specifically, in  FIG. 3 , there are shown portable electronic devices  310 ,  350 , in this case mobile phone handsets. 
       FIG. 3  also shows two communication network elements. First network element is an access point  320 , in this case a base station (BS). The first network element could also be any other access point capable of communicating with the communication device  310 . The base station  320  can work according to any existing standard, for instance GSM, GPRS, EDGE, HSCSD, UMTS, CDMA 2000, IS95, etc., or future cellular network standards. Alternatively, base station  320  could act as an access point of a wireless local area network, such as Bluetooth, WiMAX, or any variation of 802.11 standard. Furthermore, base station  320  could be connected to the mobile phone handset with any other suitable wireless connectivity method. The second network element is a mobile switching centre (MSC)  330 . MSC  330  controls the operation of a cellular network. Furthermore, the environment of  FIG. 3  includes four GNSS satellites  340 . The communication network may also comprise other network elements not shown in the figure, for instance a base station controller (BSC). 
     The mobile phone handsets  310 ,  350  communicate with each other via the communication network comprising the BS  320  and the MSC  330 . The BS  320  communicates with the mobile phone handsets  310 ,  350  using RF transmissions or any other suitable communication means in order to transmit signals to the mobile phone handsets  310 ,  350 . Accordingly, the mobile phone handsets  310 ,  350  receive transmissions sent by the BS  320 . The mobile phone handsets  310 ,  350  also send signals to the BS  320 . Thus, the communication is two directional. BSs and MSCs form part of the cellular communications network, such as a GSM network. In this particular exemplary embodiment the mobile phone handsets  310 ,  350  are communicating with each other and the handset  310  is also able to receive signals from at least one of the satellites  340 . The satellites  340  transmit signals to the mobile phone handsets  310 ,  350  either directly, without intervention of the communication network or via the cellular communication network so that the communication network can send assistance data to the mobile phone handsets  310 ,  350 . Wireless communication link is used for signal transmissions from the satellites  340  to the handsets  310 ,  350  and to the BS  320 . In the communication network, the satellite signals are received by a location measurement unit (LMU), which may be physically located in the same place as the BS  320 . If however, the LMU is located in the different place than the BS  320 , the signal needs to be conveyed to the BS  320  so that the BS  320  can then send it to the mobile phone handsets  310 ,  350 . The signals received from the satellites  340  can also be processed before they are sent to the mobile phone handsets  310 ,  350  as assistance data. 
     Handset 
       FIG. 4  is a block diagram of the mobile phone handset  310  or  350  of  FIG. 3 . The handset  310  functions as a cellular telephone according to, for instance, one or many of the following standards: GSM, GPRS, EDGE, HSCSD, UMTS, CDMA 2000, IS95, etc. The handset  310  comprises a memory  405 . The memory may have random access (RAM) and read only memory (ROM) parts. Suitable data can be stored in that memory. Furthermore, handset  310  contains input/output (I/O) means  408 . Input means may be, for instance, a keyboard but it can also be a touch pad or a touch screen. A microphone may also be provided as an input means for receiving voice information. Output means may be provided for instance by a display, such as a liquid crystal display (LCD). A loudspeaker may also be provided as an output means for outputting speech or sound. Other suitable input/output means are also possible. 
     The handset  310  also includes a cellular engine  406  for providing communication capabilities with the cellular communication network, such as GSM network. For receiving and processing the satellite transmissions, the handset comprises a positioning engine (pos engine)  407 . The handset  310  also includes transceiver unit  402  (TRX). For receiving and transmitting signals, the handset  310  includes an antenna  401 . Two or more physically separated antennas could also be used, but in this embodiment the cellular and satellite system antennas are combined into a single physical antenna which can receive and transmit signals of the cellular system and receive signals of the satellite system. 
     The handset  310  also includes a central processing unit  403  (CPU) for centrally controlling the functioning of the handset  310 . The CPU includes one or more processing units depending on the implementation of the handset  310 . For detecting voice activity, the handset  310  comprises a VAD  404  and for detecting the comfort noise received by the antenna  401 , the handset  310  comprises a comfort noise detector (CND)  409 . 
     General Methodology 
       FIG. 5  illustrates a simplified flow chart for depicting a method for the handset  310  to receive signals both from the handset  350  and from any of the satellites  340  in accordance with one embodiment of the invention. For the sake of clarity, in this exemplary embodiment the handset  310  is denoted as a receiving handset  310  and the handset  350  is denoted as a transmitting handset  350  even though both of the handsets  310  and  350  are capable of receiving and transmitting signals. At step  501  it is determined whether dual mode reception of both cellular system and satellite positioning system signals is needed. By dual mode reception it is meant a situation in which the receiver is able to receive signals from the cellular network and from the satellites using an appropriate multiplexing method, such as time division multiplexing. 
     If there is no need for dual mode signal reception, then at step  505  either one of these signals can be received at a time or there may not be a need for any signal reception. If however at step  501  it is determined that there is a need for dual mode signal reception, then at step  502 , voice activity of the transmitting handset  350  is determined. At step  503  signal reception is switched between cellular and satellite system reception depending on the transmitting handset  350  voice activity determined in step  502 . If the transmitting handset  350  is silent, then the RF section of the receiving handset  310  can be predominantly used for reception of satellite signals. If it is determined that the transmitting handset  350  is not silent, then the RF section of the receiver can be predominantly used for reception of cellular system signals. At step  504  it is again determined whether there is a need for dual mode reception of signals from the satellites  340  and from the cellular system. If there is a need for dual mode signal reception then the voice activity is again determined at step  502 . If there is no need for dual mode signal reception then at step  505  either satellite or cellular system signals can be received at a time or there may not be a need for any signal reception. 
     Receiver Architecture 
       FIG. 6  describes a signal reception and RF part for receiving signals from cellular and satellite positioning systems in accordance with an embodiment of the invention. The signal reception part consists of two branches; one branch for cellular system signal reception and one branch for satellite system signal reception. Each branch comprises an antenna  601 ,  602  for receiving RF signals and a band pass filter (BPF)  603  for filtering out low and high frequencies. Each branch further comprises a low noise amplifier (LNA)  604  for amplifying the signal after the BPF. The cellular system reception part also comprises a comfort noise detector (CND)  605  for detecting the SID frames received by the antenna  601 . The CND  605  can also detect comfort noise generated by the handset  310 . After the signal reception part there is a selector or switch  606  for selecting signals either from the cellular system signal reception branch or from the satellite system signal reception branch. Functionally connected to the switch  606 , there is also a voice activity detector  607 . In accordance with this invention, the switch  606  is programmed to switch between the satellite system and cellular system reception parts depending on the information received from the CND  605  and/or VAD  607 . The CND  605  block does not necessary have to be physically located between the LNA  604  and the switch  606 . 
     After the selector  606  the signal is led into the RF section part where the signal is divided into two different branches. These two branches comprise same components and the difference in these two branches is that the signal has in the other branch 90 degrees phase offset due to the phase offset block  608 . After the selector  606  the signal is mixed with the local oscillator  609  signal and for the signal in the other branch a 90 degrees phase offset is introduced. After the mixer  610 , there is a low pass filter (LPF)  611  for filtering out high frequencies. After the LPF  611 , the signal is amplified by variable gain amplifier (VGA)  612  and finally the analogue signal is converted to digital form by the analogue-to-digital (A/D) converter  613 . The signal is then led to digital base band part of the receiver. 
     Detailed Methodology 
     The operation of the handset  310  of  FIGS. 3 and 4  will now be described in more detail with reference to  FIG. 4  and the flow charts of  FIGS. 5 ,  7  and  10 . In  FIG. 5 , at step  501 , the receiving handset  310  determines whether dual mode signal reception is needed from the transmitting handset  350  in the cellular system and from the satellite positioning system satellites  340 . In these exemplary embodiments, the communication system is a cellular system, especially a system working in accordance with the GSM standard, but the communication system could also be other than a cellular system. The satellites  340  may operate according to the following standards: Global Positioning System (GPS), Russian GLONASS or European alternative Galileo, which is not yet in operation, or some other satellite navigation system. If there is no need for dual mode signal reception, then at step  505 , only one signal either from the cellular system or satellite system is received at a time. It is possible also not to receive any signal, for instance when the receiver is switched off. Alternatively merely control channel signals can be received. 
     However, if it is determined at step  501  that there is a need for dual mode signal reception from both the transmitting handset  350  and from the satellites  340 , then at step  502  voice activity of the transmitting handset  350  is determined. This can be done by the receiving handset  310  detecting data frames sent by the transmitting handset  350 . If it is detected that the transmitting handset  350  has sent a specific frame, for instance a SID frame, indicating that the transmitting handset  350  is inactive, then the receiving handset  310  can determine that the transmitting handset  350  is not speaking, i.e. it is inactive. The transmitting handset  350  can also send comfort noise to the receiving handset  310 . In this case, if the VAD  404  of the handset  350  detects that the user of the handset  350  is not active, the comfort noise is sent at a lower bit rate than speech would be sent. This reduces load in the communication network. There can also be a VAD in the receiving handset  310  and when it is detected that the receiving handset  310  is silent then it can be predicted that the transmitting handset  350  is speaking. Or alternatively when it is detected that the receiving handset  310  is speaking then it can be predicted that the transmitting handset  350  is silent. 
     Then at step,  503  the selector  606  of  FIG. 6  is programmed to switch between reception from the transmitting handset  350  and from the satellites  340  depending on the determined voice activity at the transmitting handset  350 . If it is determined, by for instance receiving a SID frame, that the transmitting handset  350  is silent, then the selector  606  can switch to reception from the satellites  340  since there is no significant information sent by the transmitting handset  350 . Then after certain time period the selector  606  can be programmed to switch back to cellular system reception in order to detect whether the transmitting handset  350  is still inactive. If it is detected that the user of the transmitting handset  350  has started to speak then the receiving handset  310  stays in the cellular system reception mode as far as the user of the transmitting handset  350  is again inactive. However, even if the user of the transmitting handset  350  is active, the selector can be programmed to switch for a short time period for satellite system mode. When the receiving handset  310  is operating in satellite system mode, there may be a need to receive for instance control channel signals from the cellular system at certain intervals even if the transmitting handset  350  is silent. So even if the user of the transmitting handset  350  is silent, there may be a need to receive signals from the cellular system at certain bit rate, which is lower than the bit rate used when the user of the transmitting handset  350  is speaking. 
     At step  504  it is again checked whether dual mode signal reception from the transmitting handset  350  and from the satellites  340  is still needed. If this is the case then again at step  502  the voice activity of the transmitting handset  350  is determined. If however there is no need for dual mode signal reception, then at step  505  just signals from the satellites  340  or from the transmitting handset  350  can be received at a time. 
     Example 1 
       FIG. 7  shows a more detailed flowchart of the method in accordance with an embodiment of the invention. In this embodiment the VAD  404  is only needed in the transmitting handset  350 . At step  701  it is determined that dual mode reception is needed from the satellites  340  and from the transmitting handset  350 . At step  702  dual mode reception is started. 
     At step  703  the receiving handset  310  functions in transmitting handset active mode. In transmitting handset active mode the GNSS reception part is active, for instance, 100 ms in a second. In this case cellular system signal reception would be active a majority of the time, for instance 900 ms in a second. This is illustrated in  FIG. 8 . When the receiving handset  310  determines that the transmitting end  350  is active the handset can operate in cellular system mode. The handset can remain in this mode 900 ms at a time according to this exemplary embodiment. During this period, no signals from the satellite system are received. 
     Then at step  704  the receiving handset  310  determines whether dual mode reception is needed. If there is no need for dual mode reception, then at step  709  the dual mode reception can be terminated. If however dual mode reception is needed, then at step  705  it is determined whether the transmitting handset  350  is active or not. This can be done by the receiving handset  310  decoding data frames sent by the transmitting handset  350  during cellular system mode. If a SID frame is detected then the receiving handset  310  can determine that the user of the transmitting handset  350  is inactive. If however speech frames are received by the receiving handset  310 , then it can be determined that the user of the transmitting handset  350  is speaking and is therefore active. The VAD  404  is needed in the transmitting handset  350  to detect whether the user of the transmitting handset  350  is active or not. If the user is not active, then data can be sent to the receiving handset  310  at a lower bit rate then speech would be sent. If the user of the transmitting handset  350  is active, then at step  703  transmitting handset active mode is used. 
     If the receiving handset  310  determines that the transmitting handset  350  is not active then at step  706  transmitting handset silent mode is used. In transmitting handset silent mode the GNSS reception part is active, for instance, 900 ms in a second. In this case cellular system signal reception would be active minority of the time, for instance 100 ms in a second. This is illustrated in  FIG. 9 . Some bursts sent by the transmitting handset  350  are missed to optimise the satellite system mode operation. The bursts that are missed may, for instance, contain SID frame information. The time period when the handset operates in satellite system mode cannot be too long so that if the transmitting handset  350  suddenly becomes active that does not degrade the received speech quality too much. Also other suitable active periods for the different reception parts can be used. Because the receiving handset  310  knows when it can expect to receive a SID frame, the moment when the handset is operating in the cellular system mode should preferably coincide with the reception of a SID frame. If during the cellular reception mode the receiving handset  310  detects that the transmitting handset  350  has become active, the receiving handset  310  can stay in cellular reception mode. 
     At step  707  it is again determined whether there is a need for dual mode signal reception. If there is no need for dual mode reception, then at step  709  the dual mode reception can be terminated. If dual mode reception is still needed then the receiving handset  310  determines at step  708  whether the transmitting handset  350  is active or not. If the transmitting handset  350  is not active, then at step  706  transmitting handset silent mode is used. If however the transmitting handset  350  is active, then at step  703  transmitting handset active mode is used. 
     Example 2 
       FIG. 10  presents another embodiment to implement the invention. In this embodiment VAD  404  is needed in both handsets  310  and  350 . At step  1001  it is determined that dual mode reception is needed from the satellites  340  and from the transmitting handset  350 . At step  1002  dual mode reception is started. 
     At step  1003  the receiving handset  310  functions in transmitting handset active mode. In transmitting handset active mode the GNSS reception part is active for instance 100 ms in a second. In this case cellular reception would be active majority of the time, for instance 900 ms in every second. Also other suitable active periods for the different reception parts can be used. 
     Then at step  1004  it is determined whether dual mode reception is needed. If there is no need for dual mode reception, then at step  1012  the dual mode reception can be terminated. If however the dual mode reception is needed, then at step  1005  the receiving handset  310  determines whether the transmitting handset  350  is active, i.e. the user of the transmitting handset  350  is speaking. If the transmitting handset  350  is active, then at step  1003  transmitting handset active mode is used. For detecting voice activity, the same methods can be employed as explained previously. Since in this embodiment, the VAD  404  is also in the receiving handset  310 , it can be used for predicting voice activity of the user of the transmitting handset  350 . If it is detected that the user of the receiving handset  310  is silent then it can be predicted that the user of the transmitting handset  350  is speaking. Or alternatively when it is detected that the user of the receiving handset  310  is speaking then it can be predicted that the user of the transmitting handset  350  is silent. If it is determined that the transmitting handset  350  is not active then at step  1006  the receiving handset  310  uses both end silent mode. In both end silent mode the cellular system reception part can be active for instance 500 ms in a second whereas the satellite reception part can be active equal time period. This is illustrated in  FIG. 11 . It is also possible that the other reception part is active longer than the other reception part. Finding the right values is a matter or trade-off between optimal satellite system mode operation and degradation of a received speech quality. Since both ends are silent, it is likely that other end will start speaking soon. Therefore time periods much longer than 500 may degrade the received speech quality too much when the receiver is in satellite system mode and the user of the transmitting handset  350  has just started to speak. In this respect shorter switching periods, such as 300 ms, may be preferred. 
     Then at step  1007  the receiving handset  310  determines whether dual mode reception is still needed. If there is no need for dual mode reception, then at step  1012  the dual mode reception can be terminated. If however the dual mode reception is needed, then at step  1008  it is determined whether the user of the transmitting handset  350  is active. If it is determined that the user of the transmitting handset  350  is active then at step  1003  transmitting handset active mode is used. If the user of the transmitting handset  350  is not active then at step  1009  the receiving handset  310  determines whether the user of the receiving handset  310  is active or not. This can be determined by using the VAD  404  in the receiving handset  310 . If the user of the receiving handset  310  is active, then at step  1010  receiving handset active mode is used. In this mode the GNSS reception could be active for instance 900 ms in a second whereas the cellular reception part could be active the remaining time, i.e. 100 ms in a second. If at step  1009  the receiving handset  310  determines that the user of the receiving handset  310  is not active, then at step  1006  both end silent mode is used. 
     Then at step  1011  the receiving handset  310  again determines whether dual mode signal reception is needed. If there is no need for dual mode reception, then at step  1012  the dual mode reception can be terminated. If however the dual mode reception is needed, then at step  1013  the receiving handset  310  determines whether the user of the transmitting handset  350  is active. If the receiving handset  310  determines that the user of the transmitting handset  350  is active then at step  1003  transmitting handset active mode is used. If the user of the transmitting handset  350  is not active then at step  1014  the receiving handset  310  determines whether the user of the receiving handset  310  is active. If the receiving handset  310  determines that the user of the receiving handset  310  is active then at step  1010  the receiving handset active mode is used. If the user of the receiving handset  310  is not active, then at step  1006  both end silent mode is used. 
     The invention also relates to a corresponding computer program product, which can be used to implement at least some parts of the method according to the embodiments described above. 
     In the receiving handset  310  all inventive features could be incorporated into a single module. The module should at least include the selector switch and in some embodiments also the VAD  404  and/or CND  409 . 
     The invention also relates to the receiving handset  310  and transmitting handset  350 , which comprise means for implementing the methods described above. The receiving handset  310  and transmitting handset  350  may also comprise the module described above. 
     Furthermore the invention relates to a system in which the receiving handset  310  can be used. The system comprises at least the receiving handset  310  and transmitting handset  350  and at least one satellite  340 . 
     It is to be noted that the described embodiments can be varied in many ways and that these are just exemplary embodiments of the invention.