Abstract:
A code power measurement device for measuring an interference level with respect to a desired code potentially used in a code division multiple access communication system includes an input, a correlating device, and a power measurement device. The input is configured to receive a signal corresponding to a received radio frequency spectrum potentially used by the desired code. The correlating device correlates the received signal with the desired code. The power measurement device measures a power level of the correlated signal.

Description:
[0001]     This application claims priority of U.S. patent application Ser. No. 09/901,289 filed Jul. 9, 2001, which in turn claims benefit of Provisional Application No. 60/217,093, filed Jul. 10, 2000 which are incorporated by reference as if fully set forth herein. 
     
    
     BACKGROUND  
       [0002]     The invention relates generally to resource allocation in wireless spread spectrum time division duplex communication systems using code division multiple access. More specifically, the invention relates to assigning time slots and codes in such systems.  
         [0003]      FIG. 1  depicts a wireless spread spectrum time division duplex (TDD) communication system using code division multiple access (CDMA). The system has a plurality of base stations  20   1 - 20   7 . Each base station  20   1  communicates with user equipments (UEs)  22   1 - 22   3  in its operating area or cell. Communications transmitted from the base station  201  to the UE  22   1  are referred to as downlink communications and communications transmitted from the UE  22   1  to the base station  20   1  are referred to as uplink communications. In addition to communicating over different frequency spectrums, spread spectrum TDD/CDMA systems carry multiple communications over the same spectrum. The multiple signals are distinguished by their respective codes.  
         [0004]     Since a signal sent using a particular code is distinguishable from other signals in the same spectrum, each code creates a virtual communication channel within the spectrum. For use in distinguishing signals originating from different cells, each base station  20   1 - 20   7  has an assigned scrambling code, c* scramb . To transmit a specific data signal in such a system, the data signal is mixed with its base station&#39;s scrambling code, c* scramb , and spread using its assigned channel code.  
         [0005]     Also, to more efficiently use the spread spectrum, TDD/CDMA systems use repeating frames  26  divided into a number of time slots  24   1 - 24   n , such as fifteen time slots, as illustrated in  FIG. 2 . In such systems, a communication is sent in selected time slots  24   1 - 24   n  using selected codes. Accordingly, one frame  26  is capable of carrying multiple communications distinguished by both time slot  24   1 - 24   n  and code. The use of a single code in a single time slot at a single frequency spectrum with a spreading factor of sixteen is referred to as a resource unit. If a lower spreading factor is used, the use of a single code in a time slot is considered more than a single resource unit. To illustrate, using a spreading factor of one for a code in a time slot is sixteen resource units.  
         [0006]     A system using N time slots, S 1 -SN, M channel codes, Code  1 -Code M, and O frequency spectrums, Frequency  1 -Frequency O, is illustrated in the Matrix  28  of  FIG. 3 . Each empty box in the Matrix  28  represents a single resource unit (if a spreading factor of sixteen is used). This Matrix  28  has a total of M×N×O resource units. A typical TDD system uses 15 time slots, 16 channel codes and one or multiple frequency spectrums. Based on the bandwidth required to support a communication, one or multiple resource units are assigned to that communication.  
         [0007]     One problem in such systems is assigning resource units in the presence of radio interference. Radio interference has multiple causes, such as nearby radio frequency sources and cross interference by signals transmitted in neighboring cells. Sending a communication over a resource unit with a high interference level may result in a loss of signal data.  
         [0008]     One technique for dealing with this problem is to measure the interference level in each time slot immediately prior to assigning resource units to a communication. Only resource units in time slots having acceptable interference levels will be assigned to the communication. Although this technique reduces the possibility of signal data loss, it does not eliminate all resource units suffering unacceptable interference levels. Additionally, measuring the interference levels immediately prior to assignment requires extensive monitoring using valuable system resources. Accordingly, there exists a need for an alternative approach for assigning resource units.  
       SUMMARY  
       [0009]     Resource units are assigned within a cell of a wireless time division duplex communication system using code division multiple access. Each resource unit is associated with a time slot and a code. For selected ones of the cell&#39;s resource units, the code interference level is measured during that unit&#39;s time slot and using that unit&#39;s code. The code interference level is compared to a threshold to determine whether that unit has an acceptable code interference level. Resource units are assigned to communications out of the unit&#39;s having acceptable interference levels.  
         [0010]     A code power measurement device for measuring an interference level with respect to a desired code potentially used in a code division multiple access communication system includes an input, a correlating device, and a power measurement device. The input is configured to receive a signal corresponding to a received radio frequency spectrum potentially used by the desired code. The correlating device correlates the received signal with the desired code. The power measurement device measures a power level of the correlated signal.  
         [0011]     A code power measurement device for measuring an interference level with respect to a desired code potentially used in a code division multiple access communication system includes receiving means, correlating means, and measuring means. The receiving means receives a signal corresponding to a received radio frequency spectrum potentially used by the desired code. The correlating means correlates the received signal with the desired code. The measuring means measures a power level of the correlated signal.  
         [0012]     A method for measuring an interference level with respect to a desired code potentially used in a code division multiple access communication system begins by receiving a signal corresponding to a received radio frequency spectrum potentially used by the desired code. The received signal is correlated with the desired code and the power level of the correlated signal is measured. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a wireless spread spectrum TDD/CDMA system.  
         [0014]      FIG. 2  is an illustration of time slots in repeating frames.  
         [0015]      FIG. 3  is an illustration of resource units distinguished by channel code, time slot and frequency.  
         [0016]      FIG. 4  is a simplified base station and user equipment.  
         [0017]      FIG. 5  is a flow chart of slow dynamic channel assignment.  
         [0018]      FIG. 6  is an example of a preference matrix.  
         [0019]      FIG. 7  is a code power interference level measurement device.  
         [0020]      FIG. 8  is a flow chart of fast dynamic channel assignment.  
         [0021]      FIG. 9  is an illustration of two threshold code assignment.  
         [0022]      FIG. 10  is an illustration of multiple threshold code assignment.  
         [0023]      FIG. 11  is a flow chart of multiple threshold code assignment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]      FIG. 4  is a simplified base station  20   1  and UE  22   1  used to implement slow and fast dynamic channel allocation (DCA).  FIG. 5  is a flow chart of slow DCA. The flow chart of  FIG. 5  will be described in conjunction with the preference matrix  92  of  FIG. 6 .  FIG. 6  is an illustration of a preference matrix  92  created as a result of slow DCA in a TDD/CDMA system having 16 channel codes, 15 time slots and one frequency. Each box in the matrix  92  represents one out of 240 possible resource units.  
         [0025]     Initially, the radio frequency power interference level in each time slot is measured, such as by interference signal code power (ISCP) or determining inter-cell interference, by link gain, step  80 . The ISCP may be measured using the midambles of received communication bursts, although other ISCP measurement techniques may be used. Each time slot&#39;s interference is measured at either the base station  20   1 , UEs  22   1 - 22   n  or both. For time slots interference measurements taken at the base station  20   1 , the base station&#39;s antenna  30  receives various radio frequency signals. The received signals are passed through an isolator  32  to a demodulator  36  to produce a baseband signal. A time slot interference measurement device  52  processes the baseband signal to measure the interference level, such as by ISCP, within each time slot  24   1 - 24   n  of the frame  26 .  
         [0026]     For time slot interference measurements taken at the UEs  22   1 - 22   n , the UE&#39;s antenna  60  receives various radio frequency signals. The received signals are passed through an isolator or switch  62  to a demodulator  64  to produce a baseband signal. A time slot interference measurement device  78  processes the baseband signal to measure the interference level, such as by ISCP, within each time slot  24   1 - 24   n . The time slot measurements taken at each UE  22   1-22   n  are typically signaled to the base station  20   1 . Alternately, the measurements may be multiplexed with the uplink data sent to the base station  20   1  produced by the data generator  78 .  
         [0027]     A comparator  56  at the base station  20   1  compares each time slot&#39;s interference level to a threshold, step  82 . If only the base station  20   1  took time slot interference measurements, each of these measurements is compared to the threshold. If only the UEs measurements are used, the comparator  56  compares the average for each time slots interference level to the threshold. If measurements from the base station  20   1  and UEs  22   1 - 22   n  are used, a weighted average of each time slot&#39;s measurement is used with the base station&#39;s given higher weight. If UE measurements or UE and base station measurements differ significantly, each will use its own measurements to determine time slot availability. Alternately, averaging may still be applied. If a time slot&#39;s interference level is above the threshold, all the resource units associated with that time slot are eliminated for potential assignment to communications, step  84 . The resource unit assignment device  58  eliminates all the eliminated time slots&#39; resource units in the stored preference matrix  92 . To illustrate using  FIG. 6 , time slot  4  has an unacceptable interference level. All of the resource units in the column under time slot  4  are marked with an “X” indicating that they are eliminated from potential assignment. Additionally, other time slots are eliminated because they are reserved for other purposes, such as for a broadcast channel, and are likewise marked with an “X”.  
         [0028]     For each resource unit in time slots having acceptable interference levels, the code power interference level is measured, step  86 . The code power measurements may be taken at the base station  20   1  with code power interference measurement device  50 , UE&#39;s code power interference measurement devices  68  or both. Code power measurements taken at the UE  20   1  are either signaled or multiplexed with uplink data.  
         [0029]      FIG. 7  depicts one possible code power interference measuring device  50 ,  68 . The code power measurement  50 ,  68  is taken on a frequency spectrum where the codes of interest are to be transmitted. A signal  94  representing the received frequency spectrum is input into the code power measurement device. The input signal  94  may be a radio frequency, an intermediate frequency or a baseband signal. A code correlation device  96  correlates the input signal with the code of interest. The code correlation device  96  may be a despreader, a correlator or a matched filter. If the code of interest is a complex code, the correlator may perform a complex multiplication for the correlation. The power measurement device  98  sums the power of the correlated chips. If a complex code is used, the sum is the sum of the magnitude of the complex chips. The resulting sum is the code power  100  for the code of interest. The code power measurement is taken during each time slot to be measured. The measured power may be indexed into a short hand value, such as “1” to “10” in  FIG. 6 .  
         [0030]     Each non-eliminated resource unit&#39;s code interference level is compared to a threshold at comparator  54 . If only the base station  201  took code interference measurements, these measurements are compared to the threshold. If only the UE&#39;s measurements are used, the comparator  54  compares the average of these measurements to the threshold. If measurements from the base station  20   1  and UEs  22   1 - 22   n  are used, a weighted average is used. Typically, the base station&#39;s measurement is given a higher weight. Alternately, the interference measurements may be UE  22   1 - 22   n  specific. Furthermore, if UE measurements or UE and base station measurements differ significantly, each will use its own measurements. Each UE&#39;s measurement is compared to a threshold for use in resource assignments for that UE  22   1 - 22   n . Each UE  22   1 - 22   n  has its own preference matrix  92 , if UE specific.  
         [0031]     If a resource unit&#39;s code interference level is above the threshold, the resource unit is eliminated from being assigned, step  88 . The resource unit assignment device  58  eliminates the resource unit in the preference matrix  92 . To illustrate using  FIG. 6 , the resource unit associated with time slot  2  and channel code  1  has an unacceptable interference level and is marked in the matrix  92  with an “x”. The resource unit assignment device  58  also stores in preference matrix  92  an indicator of the code interference level of the acceptable resource units, step  90 . As shown in the preference matrix  92 , the interference levels are indicated with a value of “1” to “10” with a “1” having a high marginally acceptable code interference level and a “10” having an extremely low code interference level.  
         [0032]     The base station&#39;s resource unit assignment device  58  sends signals to the base station&#39;s data estimation device  48 , channel estimation device  46  and spreading and training sequence insertion devices  42   1 - 42   n  to control which codes and time slots are used by each device. The channel estimation device  46  and data estimation device  48  process the baseband signal in the time slots and appropriate codes assigned to the uplink communication&#39;s burst and the base station&#39;s scrambling code, c* scramb . The assigned time slots and codes are sent to the channel estimation device  46  and data estimation device  48  from the resource unit assignment device  58 . The channel estimation device  46  commonly uses the training sequence component in the baseband signal to provide channel information, such as impulse responses. The channel information is used by the data estimation device  48  to estimate the data in the received burst.  
         [0033]     Data to be sent to the UEs  20   1 - 20   n , such as over a traffic channel, is generated by data generators  44   1 - 44   n . The data is assigned one or multiple resource units based on the communications&#39; bandwidth requirements by the resource unit assignment device  58 . Each spreading and training sequence insertion device  42   1 - 42   n  mixes the data with the base station&#39;s scrambling code, c* scramb , spreads the data and makes the spread reference data time-multiplexed with a training sequence in the appropriate time slots and codes of the assigned resource units. The output of the spreading and training sequence insertion devices are referred to as a communication burst. Each communication burst is subsequently amplified by a corresponding amplifier  40   1 - 40   n . Each amplified communication burst is summed by a sum device  38  with any other communication burst created through other devices. The summed communication bursts are modulated by a modulator  34 . The modulated signal is passed through an isolator  32  and radiated by an antenna  30 , as shown, or, alternately, through an antenna array. The radiated signal is passed through a wireless radio interface  80  to the UEs  22   1 - 22   n .  
         [0034]     The base station&#39;s resource unit assignment device also sends the resource unit assignments to the UEs  22   1 - 22   n . The assignments may be signaled to the UEs  22   1 - 22   n  or multiplexed with traffic data. The sent assignments are used by the UE&#39;s resource unit assignment device  76  to determine which resource units are assigned to the UE&#39;s downlink and uplink channels.  
         [0035]     For the received downlink data, the channel estimation device  68  and data estimation device  70  processes the received baseband signal in the time slots and appropriate codes assigned to the downlink communication burst and the base station&#39;s scrambling code, c* scramb . The assigned time slots and codes are sent to the channel estimation device  68  and data estimation device  70  from the resource unit assignment device  58 . The channel estimation device  68  commonly uses the training sequence component in the baseband signal to provide channel information. The channel information is used by the data estimation device  70  to estimate the data in the received burst. Uplink data is generated by a data generator  78 . The uplink data is assigned one or multiple resource units based on the communication&#39;s bandwidth requirements. Spreading and training sequence insertion device  74  mixes the data with the base station&#39;s scrambling code, c* scramb , spreads the data and makes the spread reference data time-multiplexed with a training sequence in the appropriate time slots and codes of the assigned resource units. The assigned resource units are sent to the spreading and training sequence insertion device  74  by the resource unit assignment device  76 . The resulting sequence from the spreading and training sequence insertion device  74  is referred to as a communication burst. The communication burst is subsequently amplified by an amplifier  72 . The amplified communication burst is modulated to radio frequency by the modulator  66 , passed through an isolator  62  and radiated by an antenna  60  or, alternately, by an antennal array. The radiated signal passes through the wireless radio interface  80  to the base station  20   1 .  
         [0036]     The preference matrix  92  used by the resource unit assignment device  58  may be updated on a per frame basis or on a more periodic basis. Using a statistical analysis, the preference matrix  92  may be updated from a period of minutes to a daily basis. In one approach, the user equipments  22   1 - 22   n  measure the time slot interference level and the code interference level during the idle time between successive reception and transmission bursts. These measurements are sent to the base station  20   1 . In another approach, the measurements are taken on a periodic basis. In a different approach, the base station  201  signals the UE  22   1 - 22   n  to take measurements. Accordingly, the measurements are taken on-demand. The base station  20   1  updates the preference matrix  92  based on these measurements. The updated resource unit assignments are subsequently sent from the base station  20   1  to the UEs  22   1 - 22   n .  
         [0037]      FIG. 8  is a flow chart for fast DCA and will also be explained in conjunction with  FIGS. 4 and 6 . To support communications, a cell is assigned resource units for both the uplink and the downlink. The number of assigned resource units is based on the uplink and downlink bandwidth demand. When the cell requires additional resource units, the resource unit assignment device  58  will select additional resource units to allocate for uplink and downlink communications, step  106 . Using the preference matrix  92 , the resource unit assignment device  58  will assign a corresponding number of resource units from the available resource units, step  94 . When demand decreases, conversely, the resource unit assignment device  58  releases the resource units.  
         [0038]     One approach for selecting resource units is first available. Using this technique, the assignment device  58  searches through the preference matrix  92  until it reaches the first available acceptable time slot. To illustrate using matrix  92 , if two resource units were requested, starting at code  1 , slot  1  and first working left to right, code  1 , slots  5  and  6  would be selected. These slots are the first encountered acceptable slots.  
         [0039]     Another approach is least interfered channel. The assignment device  58  searches through the preference matrix  92  for the resource unit with the lowest code interference level. To illustrate, if one resource unit was selected, code  5 , slot  11  having a value of “10” is selected. Since this approach searches through the entire matrix  92  before selecting a resource unit, it requires more processing time. However, since the selected resource unit has the lowest interference level out of the available resource units, communication interference is reduced.  
         [0040]     In systems using adaptive power control, it is advantageous to assign consecutive time slots. In such systems, a modified approach may be used. Using first available, the first available number of consecutive time slots would be assigned. For instance, if three time slots were to be assigned, code  1 , S 5 -S 7  would be selected. Using least-interfered channel, the consecutive time slots with the least interference are selected. For instance, if three were assigned, code  1 , S 11 -S 13  would be selected.  
         [0041]     Similarly, to minimize the number of time slots used, multiple codes within a time slot are assigned, such as codes  1 -3, S 11 . Additionally, a hybrid approach, such as blocks, may be used—i.e. for four resource units, code  1 , S 11 -S 12  and code  2 , S 11 -S 12 .  
         [0042]     One technique for assigning resource units is to minimize the number of time slots used. By reducing the number of used time slots, interference to neighboring cells is reduced. Using the multiple threshold technique, when resource units need to be allocated initially, the system finds the time slot or slots with the maximum number of codes available as determined by the interference level. As a result, the minimum number of time slots are allocated for a given number of resource units.  
         [0043]     After the initial allocation, resource units are assigned to the time slots which already allocated codes to communications but still have codes available first. This allocation prevents additional time slots from being used. After the previously assigned time slots are used, new time slots are assigned with the time slot having the highest number of available codes being assigned first.  
         [0044]      FIG. 11  illustrates an approach for controlling the maximum number of codes assigned to a time slot. Generally, it is desirable to limit the number of time slots used. By not using time slots, these time slots are left available for use by other cross interfering cells.  
         [0045]     An interference level for each time slot is measured,  124 . To determine the number of codes that should be used in each time slot, a multiple threshold scheme is utilized. The measured interference for each slot is compared to the multiple thresholds  126 , and a maximum number of time slots to assign is determined from the comparison,  128 . One multiple threshold scheme uses two thresholds, I 1  and I 2  as shown in  FIG. 9 . If the measured interference level is below I 1 , multiple codes  110  may be assigned to the time slot. If the measured interference level is between I 1  and I 2 , one code  112  may be assigned in these time slots. If the interference level is above I 2 , no codes  114  may be used in this time slot.  
         [0046]     Another multiple threshold scheme uses more than two interference levels, I 1 , I 2 , . . . ,I n . If the measured interference level is above I n , no codes  122  are available. If between I n  and I n-1 , one code  120  is available. The codes available for the time slot keep increasing by one per each threshold, I n-2 , I n-3 , etc., until the interference level is less than I 1 . When the interference is less than I 1 , n codes  118  are available for the time slot.