Abstract:
A geo-location technique for use in mobile communications networks employs both FDD and Time Division Duplex (TDD) modes of operation, and is applicable when both FDD and TDD systems are jointly deployed or both FDD and TDD modes of a wireless system such as UMTS are jointly activated. It has been determined that the near-far interference can be much easier controlled on purpose in the TDD mode than in the FDD mode thanks to the slotted data transmission nature of a TDD system that permits adjustment of the interference level at the time slot level instead of the frame level. Indeed, in a TDD system, loading and interference levels can be gracefully decreased in a single time slot without harming the ongoing traffic or complicating the power control operations, as would be the situation in a UMTS FDD system via IPDL or similar solutions that require to mute the pilot transmission. The invention applies to both situations whether or not the terminals are equipped with a dual receiver. This is realized by detecting the level of interference in the FDD system and comparing it with a first threshold. If the interference level is greater than the first threshold, operation is switched to the TDD system to perform the geo-location process. Otherwise, the geo-location process is performed in the FDD system. However, when in the FDD system, if the accuracy of the geo-location measurement is not determined to be satisfactory because, e.g., an insufficient number of pilot signals can be measured in a predetermined time interval, the operation is also switched to the TDD system to perform the geo-location process. Then, when in the TDD system, a time slot is selected that has low interference for the purpose of signal measurements. Once the time slot is selected the interference level is reduced by employing a prescribed technique until the interference level is less than a second threshold. Thereafter, the geo-location process is effected in the TDD system.

Description:
TECHNICAL FIELD 
     This invention relates to obtaining geo-location estimates and, more particularly, for improving accuracy in obtaining such estimates in mobile communications networks. The invention also relates to combating near-far interference in wireless communication environments. 
     BACKGROUND OF THE INVENTION 
     In mobile communications networks, for example, Universal Mobile Telecommunications Systems (UMTS) employing Frequency Division Duplex (FDD), base stations continually broadcast pilot signals that are spread using a known (standardized) pseudo-random sequence. All base stations in a UMTS network use the same pilot signal sequence. However, pilot signal sequences used by base stations are offset from one another in time. UMTS mobile wireless terminals (and wireless terminals in other multiple access systems that may employ Code Division Multiple Access (CDMA) based technologies or other spread spectrum technologies) are capable of measuring the relative phase differences between any two detected pilot signal sequences. This measurement capability provides a mechanism that can be used to help determine the location of a mobile wireless terminal. 
     Mobile wireless terminal estimates of the relative phase difference of detectable pilot signals are used by the Observed Time Difference of Arrival (OTDOA) geo-location technique outlined in the UMTS system specification (see for example, 3PP TS 25.305 v5.4.0, “Stage  2  functional specification of User Equipment (UE) positioning in UTRAN”). One such prior art system is shown in FIG.  1 . 
     It is noted without further comment that circle  105  is based on the round trip time estimate of a transmission from mobile wireless terminal  101  to serving base station  102  and back; that hyperbola  106  is the OTDOA hyperbola along which a pilot signal phase measurement is constant between serving base station  102  and neighboring base station  104 ; and that hyperbola  107  is the OTDOA hyperbola along which a pilot signal phase measurement is constant between serving base station  102  and neighboring base station  103 . 
     Pilot signals from at least three different base stations  102 ,  103  and  104  are required to accurately estimate the position of a mobile wireless terminal  101  using the OTDOA method, or any other geo-location method employing triangulation of pilot signal measurements of the serving base station  102  and neighboring base stations  103  and  104 . Because of the interference-limited nature of mobile communications systems and, in particular, CDMA based systems such as UMTS, detecting pilot signals from two or more neighboring base stations is often not possible over a large portion of the coverage area of a cell. It is well known, for example, that due to the near-far effect, when all base stations are transmitting at maximum power, only the pilot signal from the serving base station  102  can be detectable by the mobile wireless terminal  101  over as much as 40% of the cell&#39;s coverage area (the region nearest the base station). When only a single base station is detectable in these prior known systems, the error of the geo-location estimate is unacceptably high. This error can cause OTDOA-based algorithms to fail to satisfy the stringent position error requirements outlined by the United States Federal Communications Commission (FCC) in the Phase II of the Enhanced 911 (E911) Mandate for emergency calls (see for example, FCC E911 Calls, www.fcc.gov/911/enhanced): 
     for network-based solutions: within 100 m for 67% of calls and within 300 m for 95% of calls; 
     for handset-based solutions: within 50 m for 67% of calls, and within 150 m for 95% of calls. 
     Visibility of more than one pilot signal is a serious issue, especially in the FDD system of UMTS, from a geo-location perspective. This is because the transmission from the strongest pilot signal, the one creating the near-far interference, the phenomena that does not allow to measure other pilots, is continuous. 
     For clarity of this invention, the global interference level at a mobile wireless terminal in a wireless communication environment is generated by all non-desired signals that generate activity, voluntarily or involuntarily, on the same bandwidth with the signal coming from the desired communication unit. Referring to the scenario addressed by this invention, the desired signal to the mobile wireless terminal is (are) the one (those) coming from the serving base station(s). Note than in CDMA, the soft handover feature allows the mobile wireless terminal to communicate with more than one base station simultaneously, thus mobile wireless terminal has multiple serving base stations in soft handover scenarios. The non-desired signals are those signals coming from other base stations that are not serving the mobile wireless terminal. Due to the reuse factor of one (1) often employed by the systems based on spread spectrum technologies such as CDMA, such systems are inherently characterized by both intra-cell interference and inter-cell interference. The intra-cell interference comes from concurrent communications that are active on the cell area covered by the serving base station(s). The inter-cell interference comes from concurrent communications that are active on neighboring cells. The effect of intra-cell and inter-cell interference is cumulative, and it is what ultimately the mobile wireless terminal measures in order to monitor the system conditions for quality link control for example. The applicant has observed that there is a link between the global level of interference that is present at the mobile wireless terminal location and the visibility of pilot signals from different base stations at the same mobile wireless terminal location, thus the expected accuracy of the geo-location process. This aspect will be further exploited in this invention 
     It can be shown that the global interference has the highest values when close to the serving base station  102 , and not in the region of borders of adjacent cells. Actually, the global interference level decreases when the mobile wireless terminal  101  is moving away from the serving base station(s), e.g., for example base station  102  shown in FIG.  1 . The individual contribution of both intra and inter-cell interference to the global interference is that the level of intra-cell interference decreases with the distance from the base station and the behavior of the inter-cell interference is exactly opposite (see for example, D. Calin, “Geo-location Issues and Accuracy Performance in Wireless Networks”, invited paper to the ASWN02 (Applications and Services in Wireless Networks) workshop, July 2002, France). 
     The high level of global interference in the region close to the serving base station makes possible reception from only one pilot signal, the one from the serving base station. The unavailability of other reference, i.e., pilot, signals may affect dramatically the geo-location accuracy. For all the situations where only one pilot signal is available, the mobile wireless terminal can be located anywhere in the serving sector of a cell at a distance given by the round trip delay. This is a problem in any system based on the FDD system of CDMA or any other wireless technology where the transmission of pilot signals is continuous. 
     The pilot signal visibility depends dramatically on the system loading, and if the system is operated at heavy loading, there is a very high probability to measure only one pilot signal. The near-far interference region is very large in these scenarios and this affects dramatically the mobile positioning accuracy. 
     One approach to increasing the possibility of mobile terminals detecting two or more pilot signals from neighboring base stations is the introduction of the Idle Period in DownLink (IPDL) feature in the UMTS system specification. IPDL is currently an optional feature of UMTS networks (see the “Stage  2  functional specification of User Equipment (UE) positioning in UTRAN” noted above). The IPDL solution decreases system-wide interference by temporarily switching off the serving pilot signal for a period of time. This solution has significant drawbacks, however. Temporary muting of pilot signals adversely affects the performance of the downlink channel for on-going calls, increasing frame error rates, thus risking to degrade calls quality, which may lead to undesirable call interruptions. Furthermore, implementing IPDL requires architectural changes to the UMTS network and complicates critical functions such as downlink power control. 
     SUMMARY OF THE INVENTION 
     Problems and limitations of prior known geo-location arrangements for use in mobile communications networks are overcome, in accordance with the instant invention, by employing both FDD and Time Division Duplex (TDD) modes of operation, and is applicable when both FDD and TDD systems are jointly deployed or both FDD and TDD modes of a wireless system such as UMTS are jointly activated. 
     Applicant has determined that the near-far interference can be much easier controlled on purpose in the TDD mode than in the FDD mode thanks to the slotted data transmission nature of a TDD system that permits adjustment of the interference level at the time slot level instead of the frame level. Indeed, in a TDD system, loading and interference levels can be gracefully decreased in a single time slot without harming the ongoing traffic or complicating the power control operations, as would be the situation in a UMTS FDD system via IPDL or similar solutions that require to mute the pilot transmission. Applicant&#39;s invention applies to both situations whether or not the terminals are equipped with a dual receiver. 
     This is realized by detecting the level of interference in the FDD system and comparing it with a first threshold. If the interference level is greater than the first threshold, operation is switched to the TDD system to perform the geo-location process. Otherwise, the geo-location process is performed in the FDD system. However, when in the FDD system, if the accuracy of the geo-location measurement is not determined to be satisfactory because, e.g., an insufficient number of pilot signals can be measured in a predetermined time interval, the operation is also switched to the TDD system to perform the geo-location process. Then, when in the TDD system, a time slot is selected that has low interference for the purpose of signal measurements. Once the time slot is selected the interference level is reduced by employing a prescribed technique until the interference level is less than a second threshold. Thereafter, the geo-location process is effected in the TDD system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows, in simplified form, details of a prior known mobile communications network in which the invention may be employed; 
     FIG. 2 depicts, in simplified form, details of a mobile communication network in which embodiments of the invention may be employed; 
     FIG. 3 shows, in simplified form, details of a portion of a mobile communications network including a network configuration in which embodiments of the invention may be employed; 
     FIG. 4 depicts, in simplified block diagram form, details of a mobile communication network in which embodiments of the invention may be employed; 
     FIG. 5 shows, in simplified block diagram form, details of a transceiver that is employed in mobile wireless terminals  101 , and may be employed to support operations in FDD and TDD systems. A similar transceiver may be employed by base station  102 . 
     FIG. 6 is a flow chart illustrating steps in performing the geo-location process, in accordance with one embodiment of the invention; 
     FIGS. 7A and 7B when joined A-A′, B-B′ C-C′ and D—D form a flow chart illustrating steps in a specific embodiment of the invention; and 
     FIG. 8 is a timing diagram showing the normal FDD transmission and a compressed FDD transmission. 
    
    
     DETAILED DESCRIPTION 
     FIG. 2 depicts, in simplified form, details of a mobile communication network  200  in which embodiments of the invention may be employed. The network is a general simplified 3G/UMTS architecture of a type known in the art. 
     Specifically, shown is external network domain  201 , which may be, for example, a Packet Switched Transmission Network (PSTN), the Internet or the like. A first UMTS core network  202 , for example, a circuit switched network, is connected to the external network domain  201  by bi-directional transmission path  203 . Similarly, a second UMTS core network  204 , for example, a packet switched network, is connected to the external network domain  201  by bi-directional transmission path  205 . UMTS core network  202  is connected to radio access network (RAN)  206  and therein to radio network controller (RNC)  207  via standard interface (Iu cs)  208 . Similarly, UMTS core network  204  is connected to radio access network (RAN)  209  and therein to radio network controller (RNC)  210  via standard interface (Iu ps)  211 . UMTS core network  202  is connected to radio network controller (RNC)  210  via standard interface (Iu es)  213 . Similarly, UMTS core network  204  is connected to radio network controller (RNC)  207  via standard interface (Iu ps)  212 . RNC  207  is connected to RNC  210  via standard interface (Iur)  214 . RNC  207  interfaces in a first macro-cell system, i.e., a FDD system, with, for example, base stations  215 ,  216 , and  217 , which service cells  219 ,  220  and  221 , respectively, to communicate with mobile wireless stations (MS) like MS  218 , in well known fashion. Like wise, RNC  210  interfaces in a second macro-cell system, i.e., FDD system, with, for example, base stations  222 ,  223 , and  224 , which service cells  226 ,  227  and  228 , respectively, to communicate with mobile wireless stations (MS) like MS  225 , also in well known fashion. Finally, Operations and Management Center (OMC)  229  is interfaced with RNC  207  and a base station such as  215  via transmission paths  230  and  231 , respectively. Similarly, OMC  229  is interfaced with RNC  210  and a base stations such as  224  via transmission paths  232  and  233 , respectively. Only an OMC control connection with a base station per RAN was shown for illustration purposes, however the OMC has similar control connections with all the other base stations under its supervision. OMC  229  may directly control RNCs  207  and  210 , and base stations  215 ,  216  and  217 , and  222 ,  223  and  224 , respectively. 
     FIG. 3 shows, in simplified form, details of a portion of a mobile communications network  300  including an example network configuration in which embodiments of the invention may be advantageously employed. The RNC  301  and RNC  302  would be included in anetwork similar to that shown in FIG.  2  and described above. It is noted that in another embodiment the RNC  301  and RNC  302  may be completely separated for the macro-cell system, i.e., FDD system and the Micro-cell system, i.e., TDD system for the FDD base stations and the TDD base stations respectively. In this embodiment of the invention, the RNCs may each cover a mixture of the FDD base stations and TDD base stations, which the more likely and is described below. 
     Thus, shown in FIG. 3 are RNC  301  and RNC  302 , interfaced via standard interface  303 . RNC  301  and RNC  302  each interface with a mixture of macro-cell base stations and a mixture of micro-cell base stations to communicate with mobile wireless terminal  318 . In this example, the macro-cell system operates in FDD and the micro-cell system operates in TDD. For simplicity and clarity of exposition FDD system and TDD system will be used to represent the macro-cell system and the micro-cell system, respectively. 
     The FDD system base stations include, for example, FDD base stations  304   305  and  306  associated with macro-cells  307 ,  308  and  309 , respectively. The TDD system base stations include among others, for example, TDD base stations  310 ,  311 ,  312  and  313  associated with micro-cells  314 ,  315 ,  316  and  317 , respectively. Mobile wireless terminal  318  is located somewhere in the geographical area shown in FIG.  3  and benefits from both FDD macro-cells coverage and TDD micro-cells coverage. For illustration purposes, FDD base stations  304 ,  305  and  306 , and TDD base stations  310  and  313  are interfaced with RNC  301 . Similarly, FDD base station  304 , and TDD base stations  311  and  312  are interfaced with RNC  302 . 
     It is noted that FDD base stations and TDD base stations are not typically co-located. In some instances they may be co-located but will not necessarily be both operating simultaneously. 
     Additionally, in wireless communications systems such as UMTS FDD and UMTS TDD, the mobile wireless terminal performs usually measurements that are required to execute the geo-location determination process. Therefore, the mobile wireless terminal can locate itself or as an alternative can transmit the information to the system via its serving base station(s) and the system can locate it. In both cases, the position of the mobile wireless terminal is determined by using geo-location algorithms such as those known in the art, for example. It should also be noted that satisfactory geo-location accuracy could be more easily obtained in the TDD system because of its Time Slotted structure that allows it to listen to other pilot signals of the system without requiring the interruption of the data transmission. Thus, although the specific example shown in FIG. 3 has been described in terms of the macro-cell system being a FDD system and the micro-cell system being a TDD system other combinations may equally be employed. For example, an embodiment of the invention may include two macro-cell systems, one being a FDD system and the other being a TDD system. Another embodiment of the invention may include two micro cell systems, one being a FDD system and the other being a TDD system. Still another embodiment of the invention, may also include a macro-cell and a micro-cell system in which the macro-cell system is a TDD system and the micro-ell system is a FDD system. Of course, those skilled in the art may employ other than the FDD and TDD systems in yet other embodiment of the invention. 
     FIG. 4 shows, in simplified block diagram form, details of a mobile communication system in which embodiments of the invention may be employed. Specifically, shown are one or more mobile wireless terminals  101 - 1  through  101 -N. Each of mobile wireless terminals  101 - 1  through  101 -N transmits and receives signals via an associated antenna  401 - 1  through  401 -N, respectively. The signals are transmitted primarily in a FDD system or when needed in a TDD system from mobile wireless terminals  101 - 1  through  101 -N via antennas  401 - 1  through  401 -N, respectively, to serving base station  102  where they are received by antenna  402 . FIG. 4 is a simplified block diagram that captures the fact that the serving base station  102  can be either a FDD base station or a TDD base station, or it can be a common platform that supports the implementation of both FDD and TDD. Signals transmitted from serving base station  102  via antenna  402  are in the FDD system and/or the TDD system, including the required pilot signals that are received at wireless terminals  101 - 1  through  101 -N via associated antennas  401 - 1  through  401 -N, respectively. Again, as will be explained further below, the mobile wireless terminals  101  utilize the received pilot signals from one or more base stations to effect the geo-location process. In one specific example, the signals are UTMS using the CDMA format. 
     FIG. 5 shows, in simplified block diagram form, details of a transceiver  500  that may be employed in mobile wireless terminals  101 . Particularly, this transceiver may be configured to support operations in FDD and TDD systems and is adapted to support the inventive concepts of the present invention. A similar transceiver may be employed by the base station  102 . It is noted that typically the mobile wireless terminal would be equipped with only one such transceiver. In such an instance, the transceiver would have to be switched from the FDD system of operation to the TDD system of operation to make the desired measurements, which would eventually require momentarily interrupting the call, in the absence of data compression capability that is particularly specific to the FDD mode, or in case that temporary muting the serving pilots is not implemented. In the context of this invention, the last may be an option to locate mobile wireless terminals in idle mode (no ongoing calls). The FDD compressed mode and its capability will be discussed in the analysis of FIG.  7 . However, for clarity purposes it is worth to mention at this point that the FDD compressed mode is a standardized feature in the 3GPP standard for UMTS Wideband CDMA (WCDMA), which is the FDD mode of UMTS. The compressed mode allows creating discontinuities in data transmission over a FDD system by employing data compression techniques that do not affect the ordinary data flow. Other, mobile wireless terminal may have dual transceivers that would allow the terminal to simultaneously operate in the FDD system and the TDD system. Also note that the FDD and TDD base stations would use different antennas to transmit in the FDD system and the TDD system. The mobile wireless terminal would have just one antenna. Specifically, shown is a block diagram of a transceiver  500  that is adapted to support the inventive concepts of the preferred embodiments of the present invention. The transceiver  500  contains an antenna  502  preferably coupled to a duplex filter or circulator  504  that provides isolation between receive and transmit paths within the transceiver  500 . The receiver path, as known in the art, includes scanning receiver front-end circuitry  506  (effectively providing reception, filtering and intermediate or base-band frequency conversion). The scanning front-end circuit is serially coupled to a signal processing function  508 . An output from the signal processing function is provided to a suitable output device  510 , such as a screen or flat panel display. The receiver chain also includes Received Signal Strength Indicator (RSSI) circuitry  512 , which in turn is coupled to a controller  514  for maintaining overall subscriber unit control. The controller  514  is also coupled to the scanning receiver front-end circuitry  506  and the signal processing function  508  (generally realized by a DSP). The controller  514  may therefore receive Bit Error Rate (BER) or Frame Error Rate (FER) data from recovered information. The controller is also coupled to a memory device  516  that stores operating routines, such as decoding/encoding functions, synchronization patterns, code sequences, pilot signal sequences and the like. The memory device  516  stores data relating to neighboring cell sites or systems. Furthermore, a timer  518  is operably coupled to the controller  514  to control the timing of operations (transmission or reception of time-dependent signals) within the transceiver  500 , particularly in regard to FDD system, including the FDD compressed mode, and TDD system. As regards the transmit path, this essentially includes an input device  520 , such as a keypad, coupled in series through transmitter/modulation circuitry  522  and a power amplifier  524 . The transmitter/modulation circuitry  522  and the power amplifier  524  are operationally responsive to the controller. Of course, the various components within the transceiver  500  can be realized in discrete or integrated component form, as well as code in a digital signal processor (DSP) with an ultimate structure therefore being merely an arbitrary selection. The scanning receiver front-end circuitry  506 , the transmitter/modulation circuitry  522  and power amplifier  524 , under the control and guidance of the signal processing function  508 , memory device  516 , timer function  518  and controller  514  have been adapted to receive and/or transmit to the infrastructure in the compressed mode of the FDD system. This is performed in response to instruction from the infrastructure to enter such a mode, or as a self-initiated function decided by the controller  514  in response to recognition of the transceivers operating conditions. These receiver elements are also adapted to support operations over the slotted structure that is specific to the TDD systems. 
     FIG. 6 is a flow chart illustrating steps in performing the geo-location process in accordance with one embodiment of the invention. This addresses the case of a mobile wireless terminal that operates in the FDD system initially. In this embodiment the mobile wireless terminal is equipped with a transceiver capable of supporting operations in FDD mode as well as in TDD mode (similar to that in FIG.  5 ). The mobile wireless terminal gets instructions to initiate the geo-location process either from the infrastructure via the serving base station(s) or from the controller  514  itself. The role of the infrastructure in initiating the geo-location process may be sought in applications such as mobile wireless terminal location tracking. Alternatively, the mobile wireless terminal may initiate the geo-location process in applications that require to position users equipped with such a terminal, for example in case of emergency calls where user&#39;s position must be determined first. The geo-location process will invoke the specific geo-location algorithms that are implemented within the wireless systems where the mobile wireless terminal is operating, e.g., triangulation based algorithms in the first system (FDD system in the preferred embodiment) and triangulation based algorithms in the second system (TDD system in the preferred embodiment). The process is started in step  601 . Step  602  then tests if a geo-location request has been received in the FDD system. If the test result is NO, step  602  is repeated until it yields a YES result. Then, in step  603 , while in the FDD system, the mobile wireless terminal starts to measurethe FDD interference level that is characteristic to the position of the mobile wireless terminal, in a manner well known in the art. The global interference level implication on the visibility of pilot signals from various cell locations and its ultimate impact on the geo-location accuracy has already been discussed on the introductory part of FIG. 1 in this invention. Step  604  tests to determine whether the measured interference level is greater than a first predetermined threshold value, namely, TH 1 . If the test result in step  604  is NO, the measured interference level is satisfactory. Thereafter, step  605  causes the mobile wireless terminal  101  and therein, an FDD transceiver to perform the geo-location process in the FDD system. Thereafter, step  606  tests to determine whether the resulting location of mobile wireless terminal  101  is accurate. If the test result in step  606  is YES, the geo-location process is successfully completed, causing a transition from step  606  to step  612 , which is the END state of the process. If the test result in step  606  yields a NO result, the control is transferred to step  607 . Similarly, if the test result in step  606  yields a YES result, the control is transferred to step  607 . In step  607 , mobile wireless terminal  101  (FIG. 4) is caused to switch from FDD to TDD. This is realized by the transceiver processor being enabled to control a switching unit (not shown) to switch the duplex path from antenna  401  to a TDD transceiver. Thereafter, step  608 , in the TDD system, causes the TDD transceiver to make a measurement of the interference level that is characteristic to the position of the mobile wireless terminal, in a manner well known in the art. Then, step  609  tests to determine whether the measured interference level is less than a second threshold level value, namely, TH 2 . If the test result in step  609  is NO, step  610  causes the TDD transceiver to reduce the interference level. This is effected, in one example, by either interrupting data transmission of some of those calls carried on elected Time Slots if it does not affect their quality of service and/or reallocating resources by moving some calls (transmissions) from the elected Time Slots to other Time Slots to reduce loading and thus interference on the elected Time Slots. Then, control is passed back to step  608  and appropriate ones of steps  608  through  610  are iterated until step  609  yields a YES result. Thereafter, step  611  causes the mobile wireless terminal  101  (FIG. 4) and therein, the TDD transceiver to perform the geo-location process in TDD. Then, the process is ended in step  612 . 
     FIGS. 7A,  7 A continued and FIG. 7B when connected A-A′, B-B′, C-C′ and D—D form a flow chart illustrating steps in a specific embodiment of the invention. Note that when using the terms “FDD transceiver” or “TDD transceiver” they are not necessarily different transceivers but can be the same transceiver that is operating in the different FDD and TDD systems. In some applications the terminals may be equipped with dual transceivers, or dual receivers at least though. The geo-location process is started by step  701  in response to a geo-location request in the FDD system. Thus, step  702 , in the FDD system, causes the FDD transceiver to measure the interference level, at the mobile wireless terminal position in a manner well known in the art. Step  703  tests to determine whether the measured interference level is greater than a first predetermined threshold value, namely, TH 1 . If the test result in step  703  is YES, the measured interference level is satisfactory to continue the geo-location procedure over the FDD system. We will return to step  703  below. Then, step  704  causes the mobile wireless terminal  101  and therein, the FDD transceiver under control of the processor to perform the geo-location process in the FDD system. At this point one estimates the geo-location accuracy by available methods such as referring to the size of the location area where it is known the mobile wireless terminal is located. The larger this area, the higher the uncertainty of the positioning and thus the poorer the accuracy of the geo-location estimate. Step  705  tests to determine whether the accuracy detected during the geo-location process performed in step  704  is satisfactory. If the test result in step  705  is NO, step  706  tests to determine whether a predetermined time-out interval has expired. If the test result in step  706  is NO, control is returned to step  705  and appropriate ones of steps  705  and  706  are iterated until either step  705  yields a YES result, indicating satisfactory accuracy or step  706  yields a YES result, indicating that the predetermined timing interval has expired, but that the accuracy of the geo-location estimates was not satisfactory. We will return to step  706  below. When step  705  yields the YES result indicating that the geo-location measurement is sufficiently accurate, control is passed to step  707 . Step  707  causes the geo-location request to be deleted. Thus, the test has been completed in the FDD system for the mobile wireless terminal  101 . 
     Thereafter, step  708  tests to determine whether the ongoing call has been interrupted or postponed. If the test result in step  708  is NO, step  709  stops the process. If the test result in step  708  is YES, the ongoing call has been interrupted or postponed. Then, step  710  determines via a joint resource allocation policy for the FDD and TTD systems operation whether the ongoing call should be resumed in the FDD system (always if switched to the TDD system was not made), or if possible carried on in the TDD system (may happen if switching to the TDD system had occurred). Then, control is returned to step  709  that stops the process, as indicated above. 
     Returning now to step  703 , if the test result indicates that the interference level is greater than TH 1  the test result is NO and control is transferred to step  711 . Similarly, returning to step  706  and the predetermined time-out interval has expired the test result is YES, thereby indicating that there was not satisfactory geo-location accuracy detected during the geo-location process performed over the FDD system, and control is also transferred to step  711 . Step  711  tests to determine whether the geo-location request is from an ongoing call. If the test result is NO, control is transferred to step  712 . Then, step  712  causes the mobile wireless terminal to switch from the FDD system to the TDD system, and to determine the interference level in all Time Slots (TSs) or only some specific Time Slots of the TDD frame, depending on the particular embodiment of the invention being used. Note that since the mobile wireless terminal did not carry on an ongoing call, the mobile wireless terminal was in idle mode. If the test result in step  711  is YES, step  713  tests to determine if the mobile wireless terminal has a dual receiver. If the test result in step  713  is YES, control is transferred to step  712 . Then, one transceiver can continue to carry on the ongoing call over the FDD system while the second transceiver is making measurements and covers all the geo-location process over the TDD system in parallel. If the test result in step  713  is NO, step  714  tests to determine whether transmission over the FDD system can be temporarily discontinued without affecting call data flow, e.g., by activating a so-called compression mode of FDD system operation, to allow measurements to be made of TDD systems. Note that the test result in step  713  being NO, indicates that the mobile wireless terminal is equipped with a single receiver, so there is no way to carry on the call and do inter-system measurements (measure TDD signals) at the same time while maintaining the continuous transmission over the FDD system (see  801 , FIG.  8 ), or any frequency duplex system where the data transmission is continued during the active call (because one needs some idle periods (see  803 , FIG. 8) on the transmission to be able to get measurements from other systems). If the test result in step  714  is YES, step  715  determines the measurement pattern, and the idle periods positioning within the FDD frame transmissions (see  803 , FIG. 8) that are needed to capture the Time Slots (TSs) loading in the TDD system. Note that prior to effecting step  715  synchronization must be acquired first. In addition, step  715  represents the instance when data transmission over the FDD system can be temporarily discontinued without affecting the overall call data flow. This means that the same quantity of information is sent over a frame while idle periods  803  (FIG. 8) within the frame are created—this is possible by transmitting at twice the rate for half the time of a frame and by creating a half-a frame idle period, for example. Moreover, these  803  (FIG. 8) idle periods can be created both at the end and at the beginning of a frame; hence by concatenating two consecutive frames (see FIG. 8) one can obtain up to a frame, i.e., 10 ms of idle frame to take measurements from the TDD system. This guarantees that the synchronization channels of the TDD system will be captured, as the TDD frame is also 10 ms—thus it works also in case the two systems, FDD and TDD are not synchronized. In the TDD system the mobile wireless terminal is in charge of performing measurements and reporting back to the base stations. According to the 3GPP standard specifications, the interference level in the Time Slots is determined by measuring the Interference Signal Code Power (ISCP) of codes that are specified by the network through the broadcast channel (BCH). Note that in TDD systems, radio channels are created using codes that have orthogonal property and that are transmitted in a Time Slot.15 Time Slots are available in a TDD radio frame, the same as in the FDD system, but the data transmission per Time Slot is limited in time to the Time Slot, e.g. {fraction (1/15)} of a 10 ms frame only. High data rate calls may have assigned multiple slots and/or multiple codes during a frame. Up to 16 codes may be mapped on a single Time Slot and they may belong to different calls/connections. Thus, when step  714  yields a YES result, as indicated above, the process must determine the measurement pattern and how the idle periods  803  (FIG. 8) are created within the FDD frame to measure the interference level of the TSs of the TDD system. In an embodiment of the invention, all the Time Slots should be monitored, in another embodiment of the invention only a portion of all the 15 Time Slots may need to be monitored. The specific embodiment of the invention must be known in order to calibrate the duration of the idle period  803  (and its pattern). The pattern refers to if and when the idle periods must be repeated (again see  803 , FIG. 8 for idle periods in the compression mode). Thereafter, control is transferred to step  712 . If the test result in step  714  is NO, which may imply that the data compression is either not supported or does not work properly for the calls associated with the geo-location request, step  516  tests to determine whether the geo-location request has a high priority, i.e., a high level of urgency. If the test result in step  716  is YES, step  717  tests to determine whether the current call has “strong” real time transmission constraints, e.g., voice, real time video or the like. If the test result in step  717  is YES, step  718  causes interruption of the ongoing call transmissions over FDD. Thereafter, control is passed to step  712 . If the test result in step  717  is NO, the action is to postpone the ongoing call over the: FDD system until the geo-location process is successfully completed. Then, control is passed to step  712  to continue the geo-location process over the TDD system. For clarification purposes, the invention makes a clear distinction between call interruption and call postponing. Call interruption means that the call needs to be completely stopped, essentially because its constraints such as real time constraints for example cannot be fulfilled. Call postponing may be equivalent to putting the call on hold, which may be typical for data transmission that does not have stringent time delivery requirements. If the test result in step  716  is NO, step  720  causes the geo-location process to wait until the current call has been completed, i.e., terminated. Call completion is tested at step  721 . If the test result in step  721  is NO, control is returned to step  720  and steps  720  and  721  are iterated until step  721  yields a YES result. Then, control is passed to step  712 . As indicated above, step  712  causes the switching from the FDD system to the TDD system, and to determine the interference level in the particular TSs that have been selected. As indicated above, when in the TDD system, in a particular embodiment of the invention, all the Time Slots (15 in UMTS TDD) may be scanned. In another embodiment of the invention, only a part of these Time Slots may be scanned for geo-location purposes. The tradeoff is the time required to process these measurements versus the efficiency of the procedure, though enough accuracy may be obtained in TDD with a small number of Time Slots, even one Time Slot would suffice if the interference level can be kept low enough to allow good quality measurements. 
     Returning now to step  706 , if the test result is YES, control is passed to step  711  (FIG. 7B) and appropriate ones of steps  711  through step  721  are executed, as described above. After step  712  has been executed, control is passed to step  722  (FIG.  7 A). The mobile wireless terminal is taking signal measurements from the TDD system, tests to determine whether any Time Slot (TS) has an interference level less than a predetermined second threshold level, namely, TH 2 . Typically, interference level threshold value TH 2  is set to a value such as to guarantee a high probability of geo-location accuracy in the TDD system. However, if the Time Slots interference level is estimated too high, the interference level can be further decreased to guarantee better geo-location accuracy, as described below, in accordance with an aspect of the invention. If the test result in step  722  is YES, the selected Time Slots interference levels are considered satisfactory and step  723  selects one of these Time Slots to perform the geo-location process in. For accuracy purposes, the selected Time Slot should be the one that has the least interference, for example, the Time Slot having the lowest loading level. Then, step  724  performs the geo-location process in the TDD system by making the appropriate measurements is the selected Time Slot, in a manner well known in the art, e.g., by applying triangulation or other known geo-location techniques. 
     Returning to step  722 , if the test result is NO, indicating that the interference level is too high to guarantee acceptable geo-location accuracy, i.e., greater than threshold TH 2 , step  725  tests to determine whether there are different priority levels for calls carried in all the Time Slots. If the test result in step  725  is YES, step  726  selects the Time Slot transporting the largest number of applications with, for example, the less stringent delay requirements, and control is passed to step  727 . Returning to step  725 , if the test result is NO, all the calls have the same priority, and step  728  selects the Time Slot transporting the least loaded Time Slot out of a predetermined number, M, of Time Slots, in this example M=15 Time Slots in one TDD frame, and control is also passed to step  727 . Step  727  causes the interference level in the selected Time Slot to be reduced, in accordance with prescribed criteria and an aspect of the invention, below threshold level TH 2 . In this example, the interference level in the Time Slot is reduced by either, temporarily interrupting the ongoing call and/or moving calls from the selected Time Slot, to other Time Slots in the TDD frame. Then, control is passed to step  724 , which as explained above, performs geo-location measurements in the selected Time Slot determined in one of the steps  723 ,  728  or  726 . Thereafter, step  729  tests to determine whether there is good geo-location accuracy in the selected Time Slot. If the test result is YES, control is passed back to step  707  and the process proceeds as described above. If the test result in step  729  is NO, the accuracy is not satisfactory and step  730  tests to determine whether the interference in the Time Slot (TS) is less than a third predetermined threshold level, namely, TH 3 . If the test result in step  730  is NO, step  731  causes the interference level in the selected Time Slot to be further reduced below the threshold level TH 3 . Then, control is passed back to step  724  to perform the geo-location process again to obtain the location of mobile wireless terminal. The reduction in interference in step  731  is achieved in the same manner as that obtained in step  727 , described above. Then, if the test result in step  729  is YES, control is passed to step  707  and the process continues. Returning to step  729 , if the test result is NO, the accuracy is still not good enough and step  730  again tests to determine whether the interference level in the selected Time Slot is less than TH 3 . The test result in step  730  should now be YES, since in the prior iteration step  731  reduced the interference to be less than threshold TH 3  and loading variations that could be generated during the execution of steps  724  and steps  729  are expected to be insignificant. This is because either the execution time to complete these two steps is fast or because in one embodiment of the invention, the loading control algorithm may keep the loading and, consequently, the interference on the selected TS below the threshold that has already been set, TH 3  in this circumstance. Then, control is passed to a next step for testing the level of the interference against another threshold level, and possibly to a step for reducing the interference level below the next threshold level and repeating steps  724 ,  729 ,  730  and the next threshold comparison step until a predetermined number N of threshold interference comparison steps is performed or step  729  yields a YES result at a prior one of the comparison steps. The number of N steps of possible comparison step is left to the implementer. As indicated above, steps  707 ,  708  and eventually  710 —if the ongoing call (supported by the mobile wireless terminal involved in the geo-location) was temporarily interrupted or postponed—will be executed to reach step  709  that stops the process. 
     FIG. 8 is a timing diagram showing the normal FDD system of transmission  801  and a compressed FDD system of transmission  802 . Note that in the normal FDD system of transmission  801 , the transmission is continuous. In the compression mode of FDD transmission  802 , there are idle intervals  803  in the transmission that are usually determined by a predetermined measurement pattern for a FDD system. These idle intervals  803  are advantageously used during the geo-location process, as described above. The idel periods can be of different sizes, depending on the data compression capability and data compression requirements. 
     It should be noted that there are tradeoffs in setting the threshold levels. The lower the threshold level is, the better the accuracy is, but more channel allocations and/or temporary call interruptions are necessary. Since the interference level is highly dependent on the position of the mobile wireless terminal in the cell area serviced by the serving base station, it is desirable to have multiple testing threshold levels so as not to trigger excessive channel reallocations when not necessary. To guarantee an acceptable accuracy performance with, for example, a single threshold level, the threshold level should be set at a level with respect to the worst case expected to be encountered. Unfortunately, such a setting would cause a large number of unnecessary channel reallocations, requiring additional signaling to be transported and further degradation of in spectrum efficiency. 
     It will be appreciated by those skilled in the art that they will be able to devise various arrangements and processes, which although not explicitly shown or described herein, embody the principles of the invention and, thus, are within its spirit and scope. 
     Of course, the various components within the base station and the wireless terminals can be realized in discrete or integrated component form, as well as code in a microcomputer, Digital Signal Processor (DSP) or the like, with an ultimate structure therefore being merely an arbitrary selection.