Patent Publication Number: US-2005118957-A1

Title: Testing mobile telephone terminals

Description:
TECHNICAL FIELD  
      This invention relates to a method and apparatus for testing a mobile telephone terminal.  
      Known mobile terminal testers implement most of the communications protocol that a base station would use to communicate with the terminal, and interact with the terminal so as to measure its performance, for example, in terms of bit error rate and modulation quality. These testers are therefore relatively complicated both in terms of their hardware and software.  
      An object of the invention therefore is to provide a simplified method and apparatus for testing mobile telephone terminals.  
     DISCLOSURE OF THE INVENTION  
      This is achieved according to the present invention by using a predetermined transmitted data pattern to trigger a response, preferably, an access request, from the terminal, and analysing the response to assess the performance of the terminal without responding to the terminal. The test apparatus does not therefore need to incorporate the associated hardware or software.  
      The invention will now be described by way of example with reference to the accompanying drawings, in which: 
    
    
     DESCRIPTION OF THE DRAWINGS  
       FIG. 1  illustrates a conventional mobile ratio test set;  
       FIG. 2  illustrates a test set according to the invention; and  
       FIG. 3  illustrates an alternative embodiment of the invention.  
    
    
     EMBODIMENTS OF THE INVENTION  
      The architecture required for a conventional mobile radio test set, as illustrated in  FIG. 1 , comprises the following:  
      1. The MMI at the top of the tree: This usually includes some form of display to inform the user of the current instrument and test status. Keys allow the user to implement the chosen test.  
      2. Layer 3 protocol: This layer forms messages for the mobile and interprets messages from the mobile.  
      3. Layer 2 protocol: This layer&#39;s job is to ensure reliable transmission and reception of messages from/to Layer 3. For example, when sending a message to the mobile a response is usually made. If Layer 2 does not hear this response it will retransmit the message, on the assumption that the original transmission was not successful.  
      4. Layer 1b protocol: A subset of Layer 1. On the downlink this layer takes the Layer 2 blocks and applies channel encoding to aid successful transmission on the air interface. On the uplink the reverse happens and channel decoding is used to reveal the Layer 2 message from the mobile.  
      5. Layer 1a protocol (a subset of Layer 1): On the downlink this layer takes the binary information from Layer 1b and modulates it to give baseband I and Q samples. For the uplink this layer receives IQ samples and demodulates them back to binary values.  
      6. IQ modulator: On the downlink this takes the baseband IQ generated by Layer 1 and forms a signal at the correct carrier frequency using a local oscillator L 01 .  
      7. IQ demodulator: The reverse of the IQ modulator—it takes the modulated carrier and derives IQ at baseband using a local oscillator L 02 .  
      8. RF combiner where RF transmit/receive paths are combined into a single connection  9  of the antenna of the mobile telephone.  
      When a mobile  10  is first connected to the test set, there needs to be a signal that it can recognise. For GSM this takes the form of the Broadcast Control Channel (BCCH) in the downlink  11 . There are a number of constituent elements to this channel: 
      (a) Frequency Control Channel (FCCH)     (b) Synchronisation Channel (SCH)     (c) System Information Messages    

      The mobile  10  uses the FCCH and SCH to synchronise to the test set emulation of a basestation, allowing it to demodulate and interpret the System Information Messages. Once it has done this, it may attempt to register with the test set. This registration process is initiated by the mobile  10  when it sends an Access burst on the Random Access Channel on the uplink  12 . The test set demodulates the Access burst and responds. A brief series of messages pass between the test set and mobile as they exchange and verify system information.  
      Once a mobile  10  is registered, it is then possible to initiate a call to/from the mobile which will allow parametric tests of the mobile&#39;s transmitter and receiver.  
      The need to interact in real-time with the mobile leads to a complicated software/hardware architecture.  
      The invention simplifies the test set architecture by appreciating that a considerable amount of testing can be done by simply getting the mobile  10  to send an Access burst on the Random Access Channel. The invention achieves this with the architecture as illustrated in  FIG. 2 .  
      The IQ modulator  6  remains with its associated Local Oscillator (LO 1 ), but the IQ data applied to it is no longer coming from a conventional Layer 1, 2, 3 architecture. Instead, a fixed Broadcast Control Channel is stored in a memory  13  as IQ samples. These are clocked out by an address generator  14  and applied to the IQ modulator  6 .  
      Alternatively, the predetermined pattern may be generated using a subset of the protocol stack  2  to  5 , for example, stored data symbols may be processed by a baseband modulator, which is a subset of Layer 1a, before being applied to the IQ modulator  6 .  
      The mobile  10  responds to the fixed BCCH by sending an Access burst but it does not get a reply. The test set uses a power detector  15  to determine whether the mobile makes a transmission and this may be indicated to the user on a display  16 . The power detector  15  may simply determine whether or not the transmission power is above a threshold level or may determine the actual transmission power level and report this to the display  16 .  
      Alternatively, the access burst may be captured by a radio frequency receiver and analysed. The analysis may determine modulation quality, such as vector value, and report this or a comparison with allowable limits; or the analysis may determine spectral characteristics, such as adjacent channel power, occupied bandwidth and spurious signals, and report this or the comparison with allowable limits; or the analysis may determine the power envelope against time and compare this with a mask defining upper and lower allowable limits.  
      When the mobile  10  fails to get a reply to its Access burst it will try again a number of times, before searching for another signal.  
      The information in the stored BCCH tells the mobile the power level at which to transmit its Access burst, and the number of burst retries to perform So, a number of different BCCH can be stored and selected to test the mobile&#39;s power level control.  
      Placing an attenuator in the downlink would vary the output level from the test set to the mobile. This allows measure of sensitivity—slowly lowering the output power until the mobile no longer transmits Access bursts.  
      The test set may be connected directly to an antenna connector on the mobile phone  10  using a cable  9 , as in the prior art of  FIG. 1 .  
      An alternative option, rather than cable connection  9  between the test set and the mobile, is to use a coupler  17 , as illustrated in  FIG. 3 .  
      The coupler  17  makes a connection to the mobile  10  over the air interface rather than through a piece of cable. As such, the coupler  17  and mobile  10  may need to be screened from other signals as shown by screening  18  in  FIG. 3 . This makes sure that the mobile can only hear the test set signal. This approach then allows the test set to verify that the mobile&#39;s antenna is functioning correctly.  
      Thus, comparing the invention with the conventional test sets, the use of a stored downlink data pattern (BCCH) instead of a complete protocol stack, requires a lot less software development and does not require the complex signal processing hardware of conventional test sets.  
      The test set according to the invention is simpler, cheaper and more robust which makes it suitable for widespread use, for example, in retail outlets which sell mobile telephones. The retail outlets can then check a mobile to see if it is faulty before returning it to a more expensive repair centre.  
      The invention has been described above with reference GSM, but there are no reasons why the invention is not applicable to other systems such as Wideband CDMA.